CN118449208A - Control method and system capable of providing frequency support for flexible interconnection power distribution network - Google Patents
Control method and system capable of providing frequency support for flexible interconnection power distribution network Download PDFInfo
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Eletrric Generators (AREA)
Abstract
The invention discloses a control method and a system capable of providing frequency support for a flexible interconnection power distribution network, wherein the control method comprises the following steps: providing frequency support by using a permanent magnet direct-drive wind turbine connected into a flexible interconnection power distribution network, measuring direct-current voltage of a wind turbine network side converter, calculating a per unit value and a phase, modulating a voltage amplitude, and generating a trigger pulse signal; monitoring the rotating speed of the wind wheel and the rotor position angle of the synchronous generator, obtaining an optimal power per unit value, and calculating an active power reference value; and combining active power and current control, and generating a trigger pulse signal through a pulse width modulation link by converting the d-axis component and the q-axis component of the modulating voltage of the output machine side converter into three-phase modulating voltage under a static coordinate system through rotating coordinates. The invention realizes that the wind turbine generator provides quick response for the power distribution network in the frequency supporting stage, prevents the rotating speed from stalling and inhibits the frequency from dropping secondarily in the rotating speed recovering stage, and improves the supporting capacity of the wind turbine generator on the power distribution network.
Description
Technical Field
The invention relates to the technical field of flexible interconnection power distribution networks, in particular to a control method and a control system capable of providing frequency support for a flexible interconnection power distribution network.
Background
The green low-carbon transformation becomes the basic guide of energy development in China. Wind power and photovoltaic power generation equipment based on power electronic interfaces replace a traditional synchronous machine to be integrated into a power distribution network on a large scale, and the safety and stability operation of the power distribution network are greatly affected. Flexible interconnection equipment (such as an intelligent soft switch) can be used for connecting different power distribution networks to construct a flexible interconnection power distribution network, so that power flow control is realized, as shown in fig. 1. However, the new energy power generation equipment is difficult to actively respond to the system frequency change, and has inertia characteristics close to zero, so that the inertia of the flexible interconnection power distribution network is reduced, the protection actions such as low-frequency load shedding and high-frequency switching-out of the flexible interconnection power distribution network are easily induced, large-area power failure is caused, and even the operation of the flexible interconnection power distribution network is unstable when serious; in addition, the wind turbine generator system has poor frequency abnormality resistance, and can easily induce large-area off-grid under extreme conditions to cause linkage accidents.
The frequency response process of the wind turbine can be divided into two phases: a frequency support phase and a rotational speed recovery phase. Wind turbines typically operate in a maximum power tracking mode, with their participation in frequency support providing additional energy support by releasing their own rotor kinetic energy. In the frequency support stage, the wind turbine responds to the system frequency change by changing the active output through various additional frequency response strategies, when the active support is restored to the maximum power tracking after the end, once the switching between the frequency support process and the rotating speed restoration process can not be smoothly transited, the power shortage caused by the reduction of the active output of the fan causes the secondary drop phenomenon of the system frequency. Therefore, how to research a control system capable of providing frequency support and restraining frequency secondary drop for a wind turbine generator connected with a flexible interconnection power distribution network is a problem to be solved.
Disclosure of Invention
The present invention has been made in view of the above-described problems.
Therefore, the technical problems solved by the invention are as follows: how to solve the problem that wind turbine generator system lacks and provides frequency support to flexible interconnection distribution network, propose a control system that can provide frequency support to flexible interconnection distribution network, strengthen the frequency stability of flexible interconnection distribution network, restrain the secondary of wind turbine generator system rotational speed recovery in-process frequency and fall.
In order to solve the technical problems, the invention provides the following technical scheme: a control method for providing frequency support for a flexible interconnect power distribution network, comprising: providing frequency support by using a permanent magnet direct-drive wind turbine connected into a flexible interconnection power distribution network, measuring the direct-current voltage of the permanent magnet direct-drive wind turbine network side converter in a control loop of the network side converter, calculating the per unit value and the phase of the direct-current voltage, and calculating the amplitude of the network side modulation voltage;
combining the phase of the direct current voltage and the amplitude of the network side modulation voltage to generate a trigger pulse signal of the network side converter;
In a control loop of the machine side converter, detecting the rotating speed of the wind wheel and the rotor position angle of the synchronous generator, performing machine side current conversion, and obtaining a per unit value of optimal power;
Calculating an active power reference value through the per unit value of the optimal power;
After combining the active power control link and the current control link, the d-axis component and the q-axis component of the modulating voltage of the output machine side converter are converted into three-phase modulating voltage under a static coordinate system through a rotating coordinate;
The three-phase modulation voltage generates a trigger pulse signal of the side converter through a pulse width modulation link.
As a preferred embodiment of the control method for providing frequency support for a flexible interconnection power distribution network according to the present invention, the control method comprises: the calculated per unit value and phase of the DC voltage comprises dividing the DC voltage u dc of the network side converter by the rated value u dcn of the DC voltage to obtain the per unit value of the DC voltageThe phase θ is output after passing through an integrator with gain of ω n, where ω n is the rated angular frequency of the power grid;
The calculation of the amplitude of the network side modulation voltage comprises that the difference between the reference value Q gere and the feedback value Q g of the reactive power output by the network side converter passes through a PI regulator and then the initial amplitude U t0 of the network side modulation voltage is overlapped to obtain the amplitude U t of the network side modulation voltage.
As a preferred embodiment of the control method for providing frequency support for a flexible interconnection power distribution network according to the present invention, the control method comprises: the combination of the phase of the direct current voltage and the amplitude of the network side modulation voltage comprises the integration of the phase theta and the amplitude U t into a modulation signal;
Generating a trigger pulse signal of the network side converter comprises generating a sine waveform reference signal synchronous with the frequency of a power grid based on the integrated modulation signal, and generating a high-frequency triangular wave carrier signal with the frequency higher than that of the reference signal for pulse width modulation;
Comparing the reference signal with the carrier signal, when the amplitude of the reference signal is higher than that of the carrier signal, generating a high level, otherwise, generating a low level, so as to generate a PWM signal;
encoding the amplitude and phase information of the reference signal into the pulse width of the PWM signal, and controlling the shape and the size of the output voltage of the network-side converter;
The switching element of the network-side inverter is directly driven by the generated PWM signal, and a trigger pulse signal Sgabc of the network-side inverter is generated.
As a preferred embodiment of the control method for providing frequency support for a flexible interconnection power distribution network according to the present invention, the control method comprises: the method comprises the steps of obtaining a per unit value of optimal power, wherein the per unit value comprises the step of detecting the rotating speed omega t of a wind wheel and the rotor position angle thetar of a synchronous generator in a control loop of a machine side converter;
three-phase alternating current isabc of the machine side converter is subjected to rotary coordinate transformation to obtain current i sd、isq under a dq coordinate system, and the phase for the rotary coordinate transformation is thetar;
Wind wheel rotation speed Dividing the rated value omega tn of the wind wheel rotating speed to obtain the per unit value of the wind wheel rotating speedObtaining the per unit value of the optimal power through the maximum power tracking control module
The calculating the active power reference value includes,After entering the gating control module, the output is Flag bit Flag;
Flag enters the control port Ctrl of the controlled switch S1, the constant 20 is the input of position 1 of the controlled switch S1, and the control coefficient K P is the input of position 2 of the controlled switch S1;
By means of the number 1 and the per unit value of the DC voltage Difference is multiplied by the output of the controlled switch S1 and then superimposedObtaining a reference value of active power output by the machine side converter
The three-phase modulation voltage transformed from the rotation coordinate to the stationary coordinate system includes,Entering an active power control link, and then entering a current control link to output a d-axis component reference value of a side converter modulation voltageQ-axis component reference valueGenerating three-phase modulation voltage under static coordinate system through rotation coordinate transformation
As a preferred embodiment of the control method for providing frequency support for a flexible interconnection power distribution network according to the present invention, the control method comprises: the gating control module adopts a control structure as follows,
The input of the gating control module is the per unit value of the rotating speed of the wind wheelRated value of rotation speed of wind wheelSubtracting to obtain the deviation of the rotation speed of the wind wheelJudgingWhether or not less than 0.015p.u.;
If it is The flag bit F1 has a value of 1; if it isThe value of flag bit F1 is 0;
Calculating the change rate of per unit value of the rotating speed of the wind wheel JudgingWhether or not less than 0.01p.u.;
If it is The flag bit F2 has a value of 1; if it isThe flag bit F2 has a value of 0;
The Flag bit F1 and the Flag bit F2 generate a Flag bit Flag through Boolean logic operation, and the Flag bit Flag is output by the gating control module;
The boolean logic operation is that when f1=1 and f2=1, flag is 1, and when all other conditions occur, flag is 0;
the following relationships are satisfied between the output and input of the controlled switch S1 and the control port Ctrl:
when the value of the control port Ctrl is 0, the output of the controlled switch S1 is the input of position 1;
When the value of the control port Ctrl is 1, the output of the controlled switch S1 is the input of position 2.
As a preferred embodiment of the control method for providing frequency support for a flexible interconnection power distribution network according to the present invention, the control method comprises: the expression of the control coefficient K P is:
Where K is a frequency modulation factor, b is a rotational speed recovery adjustment factor, t is an actual time, t swc is a time when the controlled switch S1 switches from position 1 to position 2, and t off is a time when the control factor K P decreases.
As a preferred embodiment of the control method for providing frequency support for a flexible interconnection power distribution network according to the present invention, the control method comprises: the frequency modulation coefficient k satisfies the following relationship:
Wherein, The per unit value of the rotating speed of the synchronous generator is the rotating speed of the synchronous generator when the wind turbine generator runs stably,The minimum rotation speed per unit value of the wind turbine generator in the frequency supporting process is set;
The t off is set according to the following relation:
the rotational speed recovery adjustment factor b is set according to the following relation:
Control system that can provide frequency support to flexible interconnection distribution network, its characterized in that: comprising the steps of (a) a step of,
The direct-current voltage monitoring and processing module: in a control loop of the grid-side converter, measuring the direct-current voltage of the permanent-magnet direct-drive wind turbine generator grid-side converter, calculating the per-unit value and the phase of the direct-current voltage, and calculating the amplitude of the grid-side modulation voltage;
The network side PWM trigger signal generation module: combining the phase of the direct current voltage and the amplitude of the network side modulation voltage to generate a trigger pulse signal of the network side converter;
wind wheel dynamic monitoring and optimal power calculation module: in a control loop of the machine side converter, detecting the rotating speed of the wind wheel and the rotor position angle of the synchronous generator, performing machine side current conversion, and obtaining a per unit value of optimal power;
the active power reference value calculation module: calculating an active power reference value through the per unit value of the optimal power;
A machine side modulation voltage output module: after combining the active power control link and the current control link, the d-axis component and the q-axis component of the modulating voltage of the output machine side converter are converted into three-phase modulating voltage under a static coordinate system through a rotating coordinate;
The side PWM trigger signal generation module: the three-phase modulation voltage generates a trigger pulse signal of the side converter through a pulse width modulation link.
The invention has the beneficial effects that: according to the method, the wind turbine generator has the operation characteristic of actively supporting the flexible interconnection power distribution network, droop control on direct-current voltage is introduced into an active reference value of the machine side converter, the droop coefficient is regulated in real time according to the rotating speed of the wind wheel, the wind turbine generator can provide rapid frequency support for the flexible interconnection power distribution network in a frequency support stage, rotating speed stall of the wind turbine generator can be effectively avoided in a rotating speed recovery stage, and secondary dropping of the frequency of the flexible interconnection power distribution network in a rotating speed recovery process of the wind turbine generator is restrained.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art. Wherein:
FIG. 1 is a general flow chart of a control method for providing frequency support for a flexible interconnect power distribution network according to a first embodiment of the present invention;
FIG. 2 is a block diagram of a control system for providing frequency support to a flexible interconnect power distribution network according to a first embodiment of the present invention;
FIG. 3 is a waveform diagram of a wind turbine generator set using maximum power tracking control in a flexible interconnection power distribution network according to a second embodiment of the present invention;
FIG. 4 is a waveform diagram of a wind turbine generator set with a constant droop coefficient in a flexible interconnection power distribution network according to a second embodiment of the present invention;
Fig. 5 is a simulation waveform diagram of a wind turbine generator set adopting the control architecture of the present invention in a flexible interconnection power distribution network according to a second embodiment of the present invention.
Detailed Description
So that the manner in which the above recited objects, features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments, some of which are illustrated in the appended drawings. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
Example 1
Referring to fig. 1-2, for one embodiment of the present invention, a control method for providing frequency support for a flexible interconnection power distribution network is provided, including:
S1: and the permanent magnet direct-drive wind turbine connected into the flexible interconnection power distribution network is utilized to provide frequency support, the direct-current voltage of the permanent magnet direct-drive wind turbine network side converter is measured in a control loop of the network side converter, the per-unit value and the phase of the direct-current voltage are calculated, and the amplitude of the network side modulation voltage is calculated.
The DC voltage u dc of the network-side converter is divided by the rated value u dcn of the DC voltage to obtain the per unit value of the DC voltageThe output is phase θ after passing through an integrator with a gain of ω n, where ω n is the nominal angular frequency of the grid.
Calculating the amplitude of the network side modulation voltage comprises superposing the initial amplitude U t0 of the network side modulation voltage after the difference between the reference value Q gere and the feedback value Q g of the reactive power output by the network side converter passes through a PI regulator to obtain the amplitude U t of the network side modulation voltage.
It should be noted that, in the control loop of the grid-side converter of the permanent magnet direct drive wind turbine, the direct voltage u dc of the converter needs to be measured first. This measurement is the basis of the overall control strategy, since the level of the direct voltage directly influences the level of power that the converter can supply to the grid. Per unit value of dc voltage calculationCalculated by dividing the measured dc voltage u dc by the nominal value of the dc voltage u dcn:
the purpose of this step is to normalize the voltage value for comparison and control with other system parameters or standard values, and calculate the calculated DC voltage per unit value of phase After passing through an integrator with a gain of ω n, the output is the phase θ, where ω n represents the nominal angular frequency of the grid. The purpose of this procedure is to adjust the output phase according to the change of the dc voltage, so as to keep the calculation of the amplitude U t of the grid-side modulation voltage in synchronization with the amplitude of the grid-side modulation voltage, which involves the superposition with the initial amplitude U t0 of the grid-side modulation voltage after the difference between the reference value Q gere and the feedback value Q g of the grid-side converter output reactive power has been processed by a proportional-integral (PI) regulator:
Ut＝PI(Qgere-Qg)+Ut0
Here, the function of the Pl regulator is to adjust the reactive power output to maintain grid stability and efficient operation of the wind turbines. The amplitude U t of the grid-side modulation voltage directly influences the power supply of the converter to the grid.
S2: and generating a trigger pulse signal of the network side converter by combining the phase of the direct current voltage and the amplitude of the network side modulation voltage.
The phase θ and the amplitude U t are integrated into one modulated signal.
Generating the trigger pulse signal of the network side converter comprises generating a sinusoidal waveform reference signal synchronous with the frequency of the power grid based on the integrated modulation signal, and generating a high-frequency triangular wave carrier signal with a frequency higher than the reference signal for pulse width modulation.
By comparing the reference signal with the carrier signal, a high level is generated when the reference signal amplitude is higher than the carrier signal, and a low level is generated otherwise, thereby generating the PWM signal.
Amplitude and phase information of the reference signal are encoded into the pulse width of the PWM signal, controlling the shape and magnitude of the output voltage of the grid-side converter.
The switching element of the network-side inverter is directly driven by the generated PWM signal, and a trigger pulse signal Sgabc of the network-side inverter is generated.
It should be noted that the system integrates the measured dc voltage phase θ and the amplitude U t of the grid-side modulation voltage into one modulation signal. The modulation signal integrates the voltage condition of the direct current side and the reflection of the power output requirement of the power grid, and lays a foundation for generating the modulation signal synchronous with the frequency of the power grid.
Reference signal: based on the integrated modulation signal, the system generates a sinusoidal waveform reference signal synchronized with the grid frequency. The amplitude and phase of this reference signal is determined by the integrated modulation signal to ensure that the output of the grid-side converter is consistent with the requirements of the grid.
Carrier signal: the system generates a high-frequency triangular wave carrier signal with a frequency which is obviously higher than that of the reference signal while generating a sine wave reference signal with synchronous power grid frequency. The high frequency nature of the carrier signal enables the final PWM signal to finely control the switching element over a wide frequency range, thereby accurately regulating the output voltage.
Further, by comparing the reference signal with the carrier signal, a PWM signal is generated: outputting a high level (ON state) when the amplitude of the reference signal is higher than the carrier signal; conversely, when the amplitude of the reference signal is lower than the carrier signal, a low level (OFF state) is output. This process encodes the amplitude and phase information of the reference signal into the pulse width of the PWM signal, allowing the shape and magnitude of the output voltage of the grid-side converter to be controlled by adjusting the duty cycle of the PWM signal.
Further, the switching elements (e.g., IGBTs) of the network-side inverter are directly driven with the generated PWM signal, and the trigger pulse signal Sgabc of the network-side inverter is generated. This step is a key step in actually controlling the converter output to meet the grid requirements. The PWM signal controls the precise switching action of the switching element to produce the desired ac output voltage, thereby achieving effective power support to the grid.
S3: in a control loop of the machine side converter, the rotation speed of the wind wheel and the rotor position angle of the synchronous generator are detected, machine side current conversion is carried out, and a per unit value of optimal power is obtained.
In the control loop of the machine side converter, the rotor speed ω t and the rotor position angle θr of the synchronous generator are detected.
The three-phase ac current isabc of the machine side converter is subjected to rotational coordinate transformation to obtain a current i sd、isq in the dq coordinate system, and the phase for the rotational coordinate transformation is thetar.
Wind wheel rotation speedDividing the rated value omega tn of the wind wheel rotating speed to obtain the per unit value of the wind wheel rotating speedObtaining the per unit value of the optimal power through the maximum power tracking control module
It should be noted that in the control loop of the machine side converter, the real-time monitoring of the rotor speed ω of the wind wheel and the rotor position angle θ r of the synchronous generator is first performed. These two parameters are critical to understanding the current operating state of the wind turbine and to adjusting its output. The wind wheel rotating speed omega directly influences the output power of the generator, so that the wind wheel rotating speed omega is important to optimizing the power generation efficiency. The rotor position angle θ r determines the relationship between the motor flux and current phase, which is necessary to achieve high efficiency energy conversion and control the electromagnetic behaviour of the motor. Rotational coordinate transformation of machine side current the three-phase ac current i sabc of the machine side transformer is transformed into current components i sd and i sq in the dq coordinate system by rotational coordinate transformation (commonly referred to as Park transformation). This step is critical to achieving high-efficiency energy control because it allows the control system to handle direct current (d-axis) and alternating current (q-axis) components, respectively, simplifying the control strategy. The phase θ r of the rotational coordinate transformation provides the angular reference required to convert the three-phase current into two direct current components.
Per unit value of wind wheel rotation speedIs calculated by dividing the actual rotor speed ω by the nominal value of rotor speed ω n. This per unit value is used to quantify the position of the rotor speed relative to its design operating point.
Through an MPPT control module, according to the per unit value of the rotating speed of the wind wheelCalculating per unit value of optimal powerThe MPPT control module aims at adjusting the operating point of the wind turbine generator set to enable the wind turbine generator set to always work at the maximum power output point, and the MPPT control module changes along with the change of wind speed.
S4: and calculating an active power reference value through the per unit value of the optimal power.
First of all,The output after entering the gating control module is Flag bit Flag.
Flag enters the control port Ctrl of the controlled switch S1, a constant 20 as input to position 1 of the controlled switch S1 and a control coefficient K P as input to position 2 of the controlled switch S1.
By means of the number 1 and the per unit value of the DC voltageDifference is multiplied by the output of the controlled switch S1 and then superimposedObtaining a reference value of active power output by the machine side converter
The gating control module adopts the following control structure:
the input of the gating control module is the per unit value of the rotating speed of the wind wheel Rated value of rotation speed of wind wheelSubtracting to obtain the deviation of the rotation speed of the wind wheelJudgingWhether or not less than 0.015p.u..
If it isThe flag bit F1 has a value of 1; if it isThe flag bit F1 has a value of 0.
Calculating the change rate of per unit value of the rotating speed of the wind wheelJudgingWhether or not less than 0.01p.u.
If it isThe flag bit F2 has a value of 1; if it isThe flag bit F2 has a value of 0.
The Flag bit F1 and the Flag bit F2 generate a Flag bit Flag through Boolean logic operation, and the Flag bit Flag is output by the gating control module.
The boolean logic operates such that when f1=1 and f2=1, flag is 1, and when all other cases occur, flag is 0.
The following relationships are satisfied between the output, input and control port Ctrl of the controlled switch S1:
when the value of the control port Ctrl is 0, the output of the controlled switch S1 is the input of position 1.
When the value of the control port Ctrl is 1, the output of the controlled switch S1 is the input of position 2.
Further, the expression of the control coefficient K P is:
Where K is a frequency modulation factor, b is a rotational speed recovery adjustment factor, t is an actual variable, t swc is a time when the controlled switch S1 switches from position 1 to position 2, and t off is a time when the control factor K P decreases.
The frequency modulation factor k satisfies the following relationship:
Wherein, The per unit value of the rotating speed of the synchronous generator is the rotating speed of the synchronous generator when the wind turbine generator runs stably,The minimum rotation speed per unit value of the wind turbine generator in the frequency supporting process.
It should be noted that the minimum rotation speed per unit value of the wind turbine generator in the frequency supporting processThe obtaining method comprises the following steps:
detecting the real-time rotating speed of the wind wheel every 1 millisecond, detecting the real-time rotating speed of the wind wheel in the last 1 second, and sending the 1000 obtained data into a memory.
The data fed into the memory is processed to divide 1000 data into 100 groups and the 10 data of each group are averaged.
The minimum average value in the 100 groups of average values is the minimum rotation speed per unit value
T off is set according to the following relation:
The rotational speed recovery adjustment factor b is set according to the following relation:
s5: after combining the active power control link and the current control link, the d-axis component and the q-axis component of the modulating voltage of the output machine side converter are converted into three-phase modulating voltage under a static coordinate system through a rotating coordinate.
Entering an active power control link, and then entering a current control link to output a d-axis component reference value of a side converter modulation voltageQ-axis component reference valueGenerating three-phase modulation voltage under static coordinate system through rotation coordinate transformation
Further, the active power reference valueCalculated from the previous step (S4), represents the active power output target that the side converter needs to achieve.Firstly, an active power control link is entered, wherein the d-axis voltage component to be adjusted is calculated through an adjustment strategy (such as a PI controller) according to the difference between a reference value and actual output powerTo compensate for the differences, precise control of the active power is achieved.
Subsequently, the current control link calculates the q-axis voltage component based on the output of the active power control link and the actual measured value of the currentTo control the reactive power of the side converter to further optimize the system performance. The result of the active power control and current control links is the d-axis component of the modulated voltageAnd q-axis componentThese two components directly affect the voltage output of the machine side converter, thereby regulating the power output of the wind turbine. Three-phase modulation voltage rotation coordinate transformation under rotation coordinate transformation to stationary coordinate system: And Through rotation coordinate transformation (usually inverse Park transformation), three-phase modulation voltage under static coordinate system is generatedThe voltage components on the d axis and the q axis are converted back to the traditional three-phase AC voltage form, so that the wind turbine generator set is driven through the machine side converter, and effective interaction with a power grid is achieved.
S6: the three-phase modulation voltage generates a trigger pulse signal of the side converter through a pulse width modulation link.
The trigger pulse signal S mabc of the side converter is generated through a pulse width modulation link.
It should be noted that the three-phase modulation voltage obtained from the previous step (S5)As input to the PWM modulation section. The three-phase voltage is obtained through rotation coordinate transformation and reflects the voltage waveform and amplitude which need to be output by the machine side converter. In the PWM link,Compared to one or more high frequency carrier signals. The carrier signal is typically a triangular or saw tooth wave of a fixed frequency. Outputting a high level (ON state) when the modulation voltage is higher than the carrier signal; when the modulation voltage is lower than the carrier signal, a low level (OFF state) is output.
The high-low level sequence formed by the comparison result is a PWM signal, which is used to directly drive the switching elements (e.g., IGBTs) of the side converter to generate the trigger pulse signal S mabc. By precisely controlling the pulse width (i.e., the duration of each pulse) of the PWM signal, the shape and magnitude of the inverter output voltage can be finely adjusted to control the operating state of the motor.
Further, the PWM technique minimizes energy loss and improves the energy efficiency of the system by operating the switching element only in a fully on or fully off state. By adjusting the pulse width of the PWM signal, the output voltage and current can be controlled very accurately, the fine control of the motor is realized, and the running performance is optimized. PWM allows the system to flexibly adjust the speed and torque of the motor according to actual requirements, and adapt to different running conditions and load requirements.
In the foregoing, the present invention further provides a control system capable of providing frequency support for a flexible interconnection power distribution network, which specifically comprises:
the direct-current voltage monitoring and processing module: in a control loop of the grid-side converter, measuring the direct-current voltage of the permanent-magnet direct-drive wind turbine generator grid-side converter, calculating the per-unit value and the phase of the direct-current voltage, and calculating the amplitude of the grid-side modulation voltage.
The network side PWM trigger signal generation module: and generating a trigger pulse signal of the network side converter by combining the phase of the direct current voltage and the amplitude of the network side modulation voltage.
Wind wheel dynamic monitoring and optimal power calculation module: in a control loop of the machine side converter, the rotation speed of the wind wheel and the rotor position angle of the synchronous generator are detected, machine side current conversion is carried out, and a per unit value of optimal power is obtained.
The active power reference value calculation module: and calculating an active power reference value through the per unit value of the optimal power.
A machine side modulation voltage output module: after combining the active power control link and the current control link, the d-axis component and the q-axis component of the modulating voltage of the output machine side converter are converted into three-phase modulating voltage under a static coordinate system through a rotating coordinate.
The side PWM trigger signal generation module: the three-phase modulation voltage generates a trigger pulse signal of the side converter through a pulse width modulation link.
The computer device may be a server. The computer device includes a processor, a memory, an Input/Output interface (I/O) and a communication interface. The processor, the memory and the input/output interface are connected through a system bus, and the communication interface is connected to the system bus through the input/output interface. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The database of the computer device is used for storing data cluster data of the power monitoring system. The input/output interface of the computer device is used to exchange information between the processor and the external device. The communication interface of the computer device is used for communicating with an external terminal through a network connection. The computer program, when executed by a processor, implements a control method for providing frequency support for a flexible interconnect power distribution network.
Those skilled in the art will appreciate that implementing all or part of the above described methods may be accomplished by way of a computer program stored on a non-transitory computer readable storage medium, which when executed, may comprise the steps of the embodiments of the methods described above. Any reference to memory, database, or other medium used in embodiments provided herein may include at least one of non-volatile and volatile memory. The nonvolatile memory may include Read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high density embedded nonvolatile memory, resistive random access memory (ReRAM), magnetic random access memory (MagnetoresistiveRandomAccessMemory, MRAM), ferroelectric memory (FerroelectricRandomAccessMemory, FRAM), phase change memory (PhaseChangeMemory, PCM), graphene memory, and the like. Volatile memory can include random access memory (RandomAccessMemory, RAM) or external cache memory, and the like. By way of illustration, and not limitation, RAM can take many forms, such as static random access memory (StaticRandomAccessMemory, SRAM) or dynamic random access memory (DynamicRandomAccessMemory, DRAM), among others. The databases referred to in the embodiments provided herein may include at least one of a relational database and a non-relational database. The non-relational database may include, but is not limited to, a blockchain-based distributed database, and the like. The processor referred to in the embodiments provided in the present application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic unit, a data processing logic unit based on quantum computing, or the like, but is not limited thereto.
Example 2
Referring to fig. 3 to 5, for one embodiment of the present invention, a control method for providing frequency support for a flexible interconnection power distribution network is provided, and in order to verify the beneficial effects of the present invention, scientific demonstration is performed through economic benefit calculation and simulation/comparison experiments.
Referring to fig. 3, a simulation waveform of a wind turbine generator set adopting maximum power tracking control in a flexible interconnection power distribution network is shown, wherein the wind speed is 10 m/s, the frequency of stable operation of the flexible interconnection power distribution network is 50Hz, and the disturbance is 1.5MW. After the flexible interconnection power distribution network is added by 40 seconds of disturbance, the frequency of the flexible interconnection power distribution network drops to 49.79Hz, the rotating speed of the wind wheel of the wind turbine generator is kept unchanged, and the output power of the wind turbine generator slightly fluctuates and then is recovered.
Referring to fig. 4, a simulation waveform of a wind turbine generator set with a constant droop coefficient is shown in a flexible interconnection power distribution network, wherein droop control with a constant coefficient is introduced on the basis of maximum power tracking control of a machine side converter, the droop coefficient value is 20, the wind speed is 10 m/s, the frequency of stable operation of the flexible interconnection power distribution network is 50Hz, and the disturbance is 1.5MW. After the 40-second disturbance is added into the flexible interconnection power distribution network, the active output of the wind turbine is increased, and the wind wheel rotating speed of the wind turbine is reduced to 0.776p.u.. Compared with the maximum power tracking control, the minimum point of the frequency of the flexible interconnection power distribution network is increased by 0.03Hz when a constant droop coefficient control strategy is adopted, and the active load shedding amount is 0.12p.u. mutation exists in the rotating speed recovery process, so that the secondary droop phenomenon of the frequency of the flexible interconnection power distribution network is caused.
Referring to fig. 5, a simulation waveform of a wind turbine generator adopting the control architecture of the present invention in a flexible interconnection power distribution network is shown, wherein a wind speed is 10 m/s, a frequency of stable operation of the flexible interconnection power distribution network is 50Hz, a disturbance is 1.5MW, a frequency modulation coefficient k is 0.141, and a rotational speed recovery adjustment factor b is 8.38. After the flexible interconnection power distribution network is added by 40 seconds of disturbance, the active output of the wind turbine generator is increased, the wind wheel rotating speed of the wind turbine generator is reduced to 0.776p.u., compared with the maximum power tracking control, the minimum point of the frequency of the flexible interconnection power distribution network is increased by 0.03Hz, the wind wheel rotating speed of the wind turbine generator is recovered slowly, and the frequency secondary drop phenomenon of the flexible interconnection power distribution network is effectively weakened.
In summary, the control system of the invention can lead the wind turbine to have the operation characteristic of actively supporting the flexible interconnection power distribution network, introduce droop control on direct-current voltage on the active reference value of the machine side converter, and provide a method for adjusting droop coefficient in real time according to the rotating speed of the wind wheel, so that the wind turbine can provide rapid frequency support for the flexible interconnection power distribution network in the frequency support stage, the rotating speed stall of the wind turbine can be effectively avoided in the rotating speed recovery stage, and the secondary drop of the frequency of the flexible interconnection power distribution network in the rotating speed recovery process of the wind turbine is inhibited.
It should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered in the scope of the claims of the present invention.
Claims (10)
1. A control method for providing frequency support for a flexible interconnect power distribution network, comprising:
Providing frequency support by using a permanent magnet direct-drive wind turbine connected into a flexible interconnection power distribution network, measuring the direct-current voltage of the permanent magnet direct-drive wind turbine network side converter in a control loop of the network side converter, calculating the per unit value and the phase of the direct-current voltage, and calculating the amplitude of the network side modulation voltage;
combining the phase of the direct current voltage and the amplitude of the network side modulation voltage to generate a trigger pulse signal of the network side converter;
In a control loop of the machine side converter, detecting the rotating speed of the wind wheel and the rotor position angle of the synchronous generator, performing machine side current conversion, and obtaining a per unit value of optimal power;
Calculating an active power reference value through the per unit value of the optimal power;
After combining the active power control link and the current control link, the d-axis component and the q-axis component of the modulating voltage of the output machine side converter are converted into three-phase modulating voltage under a static coordinate system through a rotating coordinate;
The three-phase modulation voltage generates a trigger pulse signal of the side converter through a pulse width modulation link.
2. The method for controlling a flexible interconnect power distribution network to provide frequency support according to claim 1, wherein: the calculated per unit value and phase of the direct current voltage comprise that the direct current voltage u dc of the grid-side converter is divided by the rated value u dcn of the direct current voltage to obtain the per unit value u dc,udc of the direct current voltage, and the per unit value u dc,udc of the direct current voltage is output as a phase theta after passing through an integrator with the gain of omega n, wherein omega n is the rated angular frequency of the grid;
The calculation of the amplitude of the network side modulation voltage comprises that the difference between the reference value Q gere and the feedback value Q g of the reactive power output by the network side converter passes through a PI regulator and then the initial amplitude U t0 of the network side modulation voltage is overlapped to obtain the amplitude U t of the network side modulation voltage.
3. The control method for providing frequency support for a flexible interconnect power distribution network of claim 2, wherein: the combination of the phase of the direct current voltage and the amplitude of the network side modulation voltage comprises the integration of the phase theta and the amplitude U t into a modulation signal;
Generating a trigger pulse signal of the network side converter comprises generating a sine waveform reference signal synchronous with the frequency of a power grid based on the integrated modulation signal, and generating a high-frequency triangular wave carrier signal with the frequency higher than that of the reference signal for pulse width modulation;
Comparing the reference signal with the carrier signal, when the amplitude of the reference signal is higher than that of the carrier signal, generating a high level, otherwise, generating a low level, so as to generate a PWM signal;
encoding the amplitude and phase information of the reference signal into the pulse width of the PWM signal, and controlling the shape and the size of the output voltage of the network-side converter;
The switching element of the network-side inverter is directly driven by the generated PWM signal, and a trigger pulse signal S gabc of the network-side inverter is generated.
4. A control method for providing frequency support for a flexible interconnect power distribution network as defined in claim 3, wherein: the method comprises the steps of obtaining a per unit value of optimal power, wherein the per unit value comprises the step of detecting the rotating speed omega t of a wind wheel and the rotor position angle thetar of a synchronous generator in a control loop of a machine side converter;
three-phase alternating current isabc of the machine side converter is subjected to rotary coordinate transformation to obtain current i sd、isq under a dq coordinate system, and the phase for the rotary coordinate transformation is thetar;
Wind wheel rotation speed Dividing the rated value omega tn of the wind wheel rotating speed to obtain the per unit value of the wind wheel rotating speedObtaining the per unit value of the optimal power through the maximum power tracking control module
The calculating the active power reference value includes,After entering the gating control module, the output is Flag bit Flag;
Flag enters the control port Ctrl of the controlled switch S1, the constant 20 is the input of position 1 of the controlled switch S1, and the control coefficient K P is the input of position 2 of the controlled switch S1;
By means of the number 1 and the per unit value of the DC voltage Difference is multiplied by the output of the controlled switch S1 and then superimposedObtaining a reference value of active power output by the machine side converter
The three-phase modulation voltage transformed from the rotation coordinate to the stationary coordinate system includes,Entering an active power control link, and then entering a current control link to output a d-axis component reference value of a side converter modulation voltageQ-axis component reference valueGenerating three-phase modulation voltage under static coordinate system through rotation coordinate transformation
5. The method for controlling a flexible interconnect power distribution network to provide frequency support according to claim 4, wherein: the gating control module adopts a control structure as follows,
The input of the gating control module is the per unit value of the rotating speed of the wind wheelRated value of rotation speed of wind wheelSubtracting to obtain the deviation of the rotation speed of the wind wheelJudgingWhether or not less than 0.015p.u.;
If it is The flag bit F1 has a value of 1; if it isThe value of flag bit F1 is 0;
Calculating the change rate of per unit value of the rotating speed of the wind wheel JudgingWhether or not less than 0.01p.u.;
If it is The flag bit F2 has a value of 1; if it isThe flag bit F2 has a value of 0;
The Flag bit F1 and the Flag bit F2 generate a Flag bit Flag through Boolean logic operation, and the Flag bit Flag is output by the gating control module;
The boolean logic operation is that when f1=1 and f2=1, flag is 1, and when all other conditions occur, flag is 0;
the following relationships are satisfied between the output and input of the controlled switch S1 and the control port Ctrl:
when the value of the control port Ctrl is 0, the output of the controlled switch S1 is the input of position 1;
When the value of the control port Ctrl is 1, the output of the controlled switch S1 is the input of position 2.
6. The method for controlling a flexible interconnect power distribution network to provide frequency support according to claim 5, wherein: the expression of the control coefficient K P is:
Where K is a frequency modulation factor, b is a rotational speed recovery adjustment factor, t is an actual time, t swc is a time when the controlled switch S1 switches from position 1 to position 2, and t off is a time when the control factor K P decreases.
7. The method for controlling a flexible interconnect power distribution network to provide frequency support according to claim 6, wherein: the frequency modulation coefficient k satisfies the following relationship:
Wherein, The per unit value of the rotating speed of the synchronous generator is the rotating speed of the synchronous generator when the wind turbine generator runs stably,The minimum rotation speed per unit value of the wind turbine generator in the frequency supporting process is set;
The t off is set according to the following relation:
the rotational speed recovery adjustment factor b is set according to the following relation:
8. a control system for providing frequency support to a flexible interconnect power distribution network using the method of any of claims 1-7, comprising:
The direct-current voltage monitoring and processing module: in a control loop of the grid-side converter, measuring the direct-current voltage of the permanent-magnet direct-drive wind turbine generator grid-side converter, calculating the per-unit value and the phase of the direct-current voltage, and calculating the amplitude of the grid-side modulation voltage;
The network side PWM trigger signal generation module: combining the phase of the direct current voltage and the amplitude of the network side modulation voltage to generate a trigger pulse signal of the network side converter;
wind wheel dynamic monitoring and optimal power calculation module: in a control loop of the machine side converter, detecting the rotating speed of the wind wheel and the rotor position angle of the synchronous generator, performing machine side current conversion, and obtaining a per unit value of optimal power;
the active power reference value calculation module: calculating an active power reference value through the per unit value of the optimal power;
A machine side modulation voltage output module: after combining the active power control link and the current control link, the d-axis component and the q-axis component of the modulating voltage of the output machine side converter are converted into three-phase modulating voltage under a static coordinate system through a rotating coordinate;
The side PWM trigger signal generation module: the three-phase modulation voltage generates a trigger pulse signal of the side converter through a pulse width modulation link.
9. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor implements the steps of the method of any of claims 1 to 7 when the computer program is executed.
10. A computer readable storage medium, on which a computer program is stored, characterized in that the computer program, when being executed by a processor, implements the steps of the method of any of claims 1 to 7.
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