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CN107196344B - Self-synchronizing virtual synchronous inverter grid-connected controller and method with local load based on SPF-PLL - Google Patents

Self-synchronizing virtual synchronous inverter grid-connected controller and method with local load based on SPF-PLL Download PDF

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CN107196344B
CN107196344B CN201710418662.4A CN201710418662A CN107196344B CN 107196344 B CN107196344 B CN 107196344B CN 201710418662 A CN201710418662 A CN 201710418662A CN 107196344 B CN107196344 B CN 107196344B
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grid
voltage
inverter
control unit
virtual synchronous
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CN107196344A (en
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帅智康
黄文�
沈征
尹新
沈霞
彭也伦
沈超
王俊
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Hunan University
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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
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • 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
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0012—Control circuits using digital or numerical techniques

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Abstract

The invention discloses a self-synchronizing virtual synchronous inverter grid-connected controller with local load based on SPF-PLL and a method thereof, which consists of an inverter output voltage and current information acquisition module, a grid side voltage information acquisition module, a virtual synchronous inverter control module, an off/grid connection switching module and a PWM driver; the problem of impulse current and the like generated in the switching process of the virtual synchronous inverter in an island mode and a grid-connected mode is solved, and seamless switching of the virtual synchronous inverter with the load from the island mode to the grid-connected mode is achieved.

Description

Self-synchronizing virtual synchronous inverter grid-connected controller and method with local load based on SPF-PLL
Technical Field
The invention belongs to the technical field of microgrid inverter control, and relates to a self-synchronizing virtual synchronous inverter grid-connected controller with local load based on SPF-PLL and a grid-connected method thereof.
Background
With the increasing exhaustion of traditional fossil energy and the increasing environmental pressure, energy structures are undergoing a transition period from traditional energy being the main source to the full utilization of renewable energy. The method has the advantages of wide range of our country, rich wind energy resources, ocean energy resources and biological energy resources, and provides a basic premise for the adjustment of our country energy structure. The self-dispersed nature of new energy makes it more suitable for use as a distributed power source to power a load in the form of a microgrid.
Typically, the microgrid may be operated in a grid-connected mode or an island mode. In island mode, a Distributed Generator (DG) supplies power to a local load. The microgrid is usually switched to an island mode under grid fault conditions, and the grid-connected mode is recovered after the fault is cleared. However, if the microgrid is reconnected to the grid through the grid-connected inverter without pre-synchronization, a huge inrush current will be generated, posing a serious threat to the grid itself. This limits further expansion of the microgrid to a certain extent. Therefore, it is very important to provide a microgrid control strategy to ensure seamless switching between two operating modes.
At present, typical inverter control methods in a microgrid mainly include: droop control, PQ control, VF control, virtual synchronization control, and the like. The virtual synchronous control is an inverter control strategy which simulates the characteristics of a synchronous generator and is proposed by professor Chongchang. The power electronic inverter without mechanical inertia has the characteristic of being equal to the inertia of the synchronous generator, the dynamic performance of the inverter is greatly improved, and the inverter can generate power like the synchronous generator and simultaneously restrain high-frequency ripples in a power grid. Therefore, compared with other control strategies, the virtual synchronous inverter is more suitable for flexible operation in a grid-connected mode and an island mode. However, as with other inverters, to achieve seamless switching of the grid-tie mode, the frequency and phase of the virtual synchronous inverter output voltage also need to be synchronized with the grid.
The influence of the existing control method on the power grid and the local load during the switching transition process can be reduced remarkably. However, all these methods require not only a separate PLL (phase locked loop) unit but also other compensation controllers and communication units. The system regulation structure is slightly complex and generally not suitable for the virtual synchronous inverter.
At present, the presynchronization control strategy with the phase-locked loop unit is widely applied. Some researchers propose a linear integral method for voltage synchronization and a distributed power supply island-grid-connected mode seamless switching strategy suitable for droop control, and the influence of the two methods on a power grid and a local load in the switching transition process is obviously reduced. However, these methods not only require a separate PLL unit, but also require additional compensation controller and communication link, so that the system regulation structure is complicated, and neither method can be directly applied to the virtual synchronous inverter.
Another self-synchronizing inverter has been proposed by the scholars that uses a dummy impedance instead of adding a phase-locked loop PLL synchronization unit. Seamless switching between island mode and grid-connected mode can be achieved by the synchronizer. However, the concept of the new self-synchronizer is proposed based on a grid-connected inverter without any local load, and cannot be applied to a micro-grid with a local load.
Therefore, on the premise of simplifying a synchronous control system and reducing the cost, a control strategy which is generally applicable to a virtual synchronous inverter with a load and a virtual synchronous inverter without the load is researched, and the control strategy for realizing synchronous grid connection has important significance.
Disclosure of Invention
In order to achieve the purpose, the invention provides a self-synchronizing virtual synchronous inverter grid-connected controller with a local load based on SPF-PLL and a grid-connected method thereof, which solve the problems of impact current and the like generated in the switching process of a virtual synchronous inverter in an island mode and a grid-connected mode and realize seamless switching of the virtual synchronous inverter with the load from the island mode to the grid-connected mode.
The technical scheme adopted by the invention is that a self-synchronizing virtual synchronous inverter grid-connected controller with local load based on SPF-PLL is composed of an inverter output voltage and current information acquisition module, a grid side voltage information acquisition module, a virtual synchronous inverter control module, an off/grid connection switching module and a PWM driver;
the inverter output voltage and current information acquisition module is used for acquiring voltage signals at the output end of the inverter and current signals at the output end of the inverter;
the grid side voltage information acquisition module is used for acquiring voltage signals of grid-connected points; the inverter output voltage and current information acquisition module acquires a voltage signal at a filter capacitor C at the output side of the inverter and outputs a filter inductor LsThe voltage and current signals are transmitted to the voltage and current signal input end of the virtual synchronous inverter control module, and meanwhile, the network side voltage signal is also transmitted to the voltage signal input end of the virtual synchronous inverter control module;
the off/grid-connected switching module is used for judging whether a circuit breaker CB2 for connecting the output end of the virtual synchronous inverter and the public power grid needs to be immediately switched to complete grid-connected control or not according to a signal that whether the output current of the inverter detected by the preceding stage and the voltage phase of the public power grid finish synchronization or not;
the PWM driver is used for providing a switching-on signal and a switching-off signal for a power electronic switching device in the inverter bridge;
the virtual synchronous inverter control module comprises a virtual synchronous algorithm control unit and a self-synchronizing control unit; the virtual synchronous algorithm control unit is used for realizing the characteristic of a synchronous generator when the inverter operates; and the self-synchronization control unit is used for obtaining the compensation quantity of the phase angle and the frequency reference value of the virtual synchronous inverter and completing the synchronization of the output voltage of the inverter and the voltage phase of the power grid.
Further, the self-synchronizing control unit comprises a phase self-tracking control unit and a PI control unit; the phase self-tracking control unit is used for locking the phase angle of the power grid voltage; the PI control unit is used for improving the adjusting performance.
Further, in the phase self-tracking control unit, the grid voltage of the two-phase αβ in the stationary coordinate system is as follows (1):
Figure GDA0002260363270000031
in the formula uα、uβRepresenting the α, β axis components in a two-phase stationary coordinate system, uga、ugb、ugcRepresenting the three-phase voltage of the power grid; egThe voltage amplitude value of the network side after the transformation of the two-phase static coordinates is obtained; thetagIs the grid voltage phase;
the phase angle theta generated by virtual synchronous control is used as a reference phase angle, and the grid voltage u is obtained through Park conversiongThe dq axis component of (2) below:
Figure GDA0002260363270000032
in the formula (I), the compound is shown in the specification,ugd、ugqrepresenting a dq axis voltage direct-current component under a synchronous rotation coordinate system; and theta is the phase angle generated by the virtual synchronization algorithm control unit.
Further, the transfer function G of the PI control unitPI(s) the following formula (3):
Figure GDA0002260363270000033
in the formula, kpFor proportional control of the PI control unit, kiS represents a complex variable, which is a variable converting a time domain signal to a complex frequency domain signal, as an integration constant;
considering that sin (Δ θ) ≈ Δ θ when Δ θ is close to 0, the open-loop transfer function of the self-synchronization control unit (13) is simplified to the following formula (4):
Figure GDA0002260363270000034
in the formula, Gopen(s) simplified open-loop transfer function, τPI＝kp/ki,ko＝kiE*(Eg＝E*)；τPIFor the ratio of the proportional-adjustment parameter to the integral constant, k, in a PI controlleroIs the product of an integration constant and a reference voltage in a PI controller, tauPI、koThe open-loop transfer function setting is convenient to simplify; e*A given grid voltage reference amplitude value; tau isfIs the time constant of the frequency control loop in the virtual synchronization algorithm control unit;
in order to improve the stability and dynamic response performance of the self-synchronizing control unit, the intermediate frequency width h is equal to tauPI/τfShould not be equal to-2, so τPIShould be greater than τfThe gain of the open loop transfer function conforms to the following equation (5):
Figure GDA0002260363270000041
accordingly, the parameters of the PI control unit are expressed as:
Figure GDA0002260363270000042
in general, considering that the value of h is between 5 and 10, then equation (6) can be derived to equation (7):
Figure GDA0002260363270000043
converting the q-axis component u of the grid voltagegqComparing with zero reference value, and comparing ugqThe difference value of the sum 0 is output to the PI control unit, i.e. the value of delta omega can be obtainedsyc，ΔωsycA synchronization compensation amount of a rated angular frequency is inputted as a virtual synchronization algorithm control means (12).
Further, the angular frequency reference value ω of the output driving voltage signal e output by the virtual synchronization algorithm control unit is shown in the following formula (8):
Figure GDA0002260363270000044
in the formula, npFor the active droop coefficient, P represents the electromagnetic power output by the inverter, and P*Given active reference power, ω, for a virtual synchronization algorithm control unit*For a given reference frequency;
at the same time, with E*Subtracting nq(Q-Q*) Integrating the result obtained after subtraction in a reactive inertia link to obtain a voltage amplitude E;
integrating angular velocity omega to obtain an A-phase of a reference wave, calculating an A-phase reference sine wave by knowing a voltage amplitude and an A-phase angle, and respectively rotating 120 degrees anticlockwise and clockwise to obtain B-phase and C-phase reference waves, wherein the reference wave signal is compared with a sawtooth wave signal sent by a sawtooth wave generator in a controller to obtain a control signal of a power electronic switching device in an inverter bridge so as to control the on-off of the control signal;
gradually adjusting the angular frequency of the virtual synchronous inverter according to equation (8) to phaseDifference Δ θ ═ θgWhen theta is normalized to zero, the virtual synchronous inverter is marked to be synchronized with the power grid.
The invention adopts another technical scheme that based on the grid-connected method of the SPF-PLL self-synchronizing virtual synchronous inverter grid-connected controller with local load, when the grid-side fault is removed or the grid connection is needed, the system needs to carry out grid-connected switching, the self-synchronizing control unit in the virtual synchronous inverter control module is started, the phase angle theta generated by the virtual synchronous algorithm control unit in the virtual synchronous inverter control module is used as a reference phase angle to be input into the self-synchronizing control unit, and the detected grid-side voltage u is used as a reference phase angle to be input into the self-synchronizing control unitgAlso input into it; obtaining the power grid voltage u through Clark conversion and Park conversiongQ-axis component u ofgqThe q-axis component ugqComparing with a reference value zero, then taking the difference value as the input of the PI controller, and obtaining the delta omega through regulationsycAs the synchronous compensation quantity of the rated angular frequency in the virtual synchronous algorithm control unit; the angular frequency reference value omega of the output voltage of the virtual synchronous algorithm control unit is gradually increased by delta omegasycAnd at the end of the transition to a steady state value; detecting that delta theta is zero and q-axis component u of the network voltagegqAlso zero, indicating that the virtual synchronous inverter is synchronized with the grid voltage, the virtual synchronous inverter control module outputs a switching signal to the off/on switching module to execute an on command, closes the circuit breaker CB2 and removes the angular frequency compensator compensation delta omegasycDuring this process, the active power output of the virtual synchronous inverter remains unchanged.
The invention has the beneficial effect that the self-synchronizing virtual synchronous inverter grid-connected control method with the local load based on the SPF-PLL is provided for the virtual synchronous inverter. Compared with the traditional control method, the invention can complete seamless switching between the island mode and the grid-connected mode without adding any external special synchronous control unit and communication link, solves the problems of impact current and the like generated in the switching process of the virtual synchronous inverter between the island mode and the grid-connected mode, simplifies a control system and has stronger practical value. The method is generally applicable to the conditions with or without local loads, and is very beneficial to further use and popularization of the virtual synchronous inverter.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a topology structure diagram of a self-synchronizing virtual synchronous inverter grid-connected system with a local load according to an embodiment of the present invention.
Fig. 2 is an internal schematic block diagram of a virtual synchronous inverter control module according to an embodiment of the present invention.
Fig. 3 is a diagram of an internal algorithm structure of a virtual synchronization algorithm control unit according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of a PWM driving module control signal generation according to an embodiment of the present invention.
In the figure, 1, an inverter bridge, 2, a PWM driver, 3, a virtual synchronous inverter control module, 4, a public power grid, 5, a signal conditioning module a, 6, AD1, 7, AD2, 8, an off/on grid switching module, 9, AD3, 10, a signal conditioning module b, 11, a local load, 12, a virtual synchronous algorithm control unit, 13, a self-synchronous control unit,
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A grid-connected control method of a self-synchronizing virtual synchronous inverter with a local load based on SPF-PLL (synchronous reference coordinate system phase-locked loop) is generally suitable for virtual synchronous inverters with and without local loads.
The self-synchronizing virtual synchronous inverter with local load based on SPF-PLL, structure is shown in figure 1,
the system is composed of an inverter output voltage and current information acquisition module, a network side voltage information acquisition module, a virtual synchronous inverter control module 3, an off/grid connection switching module 8 and a PWM driver 2;
the inverter output voltage and current information acquisition module comprises a Hall a, a signal conditioning module a5, an AD 16 and an AD 27 and is used for acquiring an inverter output end voltage signal and an inverter output end current signal;
the network side voltage information acquisition module comprises a Hall b, a signal conditioning module b10 and an AD 39 and is used for acquiring voltage signals of a grid-connected point; the inverter output voltage and current information acquisition module acquires a voltage signal at a filter capacitor C at the output side of the inverter and outputs a filter inductor LsAnd transmits the voltage and current signals to the voltage and current signal input end of the virtual synchronous inverter control module 3, and also transmits the network side voltage signal to the voltage signal input end of the virtual synchronous inverter control module 3.
And the off/grid-connected switching module 8 is used for judging whether a circuit breaker CB2 (such as a circuit breaker CB2 used for connecting the output end of the virtual synchronous inverter and the public power grid 4 in the figure 1) needs to be switched immediately to complete grid-connected control according to a signal whether the output current of the inverter detected by the preceding stage and the voltage phase of the public power grid are synchronized.
And the PWM driver 2 is used for providing on and off signals for power electronic switching devices in the inverter bridge 1.
The virtual synchronous inverter control module 3 comprises a virtual synchronous algorithm control unit 12 and a self-synchronizing control unit 13. The virtual synchronization algorithm control unit 12 is configured to implement that the inverter has the characteristics of a synchronous generator when operating; and the self-synchronization control unit 13 is used for obtaining the compensation quantity of the phase angle and the frequency reference value of the virtual synchronous inverter and completing the synchronization of the output voltage of the inverter and the voltage phase of the power grid.
Virtual synchronization algorithm control unit 12 in virtual synchronization inverter control module 3 outputs current signal i with invertersMultiplying the input three-phase voltage reference value by a power calculation formula to obtain the active and reactive power input of the virtual synchronous inverter control module 3, subtracting a given active power value from an active inertia droop ring in the virtual synchronous algorithm control unit 12 after receiving the active power input, multiplying the difference by an active droop coefficient, subtracting the product from a new input reference value of the virtual synchronous algorithm control unit 12 and integrating to obtain a reference wave angular velocity omega, and integrating the angular velocity to obtain a phase angle of a reference wave; the reactive inertia droop loop in the virtual synchronization algorithm control unit 12 receives reactive power input and then makes a difference with a given reactive power value, the difference is multiplied by a reactive droop coefficient, and the product is subtracted by a reference voltage amplitude value and then integrated, so that a voltage amplitude value E can be obtained. Finally, the amplitude is multiplied by the sine of the reference wave phase angle as one of the outputs of the virtual synchronous inverter control module 3.
The self-synchronizing control unit 13 in the virtual synchronous inverter control module 3 includes two parts:
1. a phase self-tracking control unit for locking the phase angle theta of the grid voltageg。
Firstly, in the phase self-tracking control unit, the grid voltage of the two-phase αβ under the stationary coordinate system is as the following formula (1):
Figure GDA0002260363270000071
in the formula uα、uβRepresenting the α, β axis components in a two-phase stationary coordinate system, uga、ugb、ugcRepresenting the three-phase voltage of the power grid; egThe voltage amplitude value of the network side after the transformation of the two-phase static coordinates is obtained; thetagFor electricity of the electric networkAnd pressing the phase.
The phase angle θ generated by the virtual synchronization control is employed as a reference phase angle. Obtaining the grid voltage u through Park conversiongThe dq axis component of (2) is as follows:
Figure GDA0002260363270000072
in the formula ugd、ugqRepresenting a dq axis voltage direct-current component under a synchronous rotation coordinate system; theta is the phase angle theta generated by the virtual synchronization algorithm control unit.
2. And the PI control unit is used for improving the regulation performance.
Converting the q-axis component u of the grid voltagegqComparing with zero reference value, and comparing ugqThe difference value of the sum 0 is output to the PI control unit, i.e. the value of delta omega can be obtainedsyc，ΔωsycThe synchronization compensation amount of the rated angular frequency is input as the virtual synchronization algorithm control unit 12.
The design principle of the PI control unit in the self-synchronizing control unit 13 according to the present invention is further described in detail. First of all, the transfer function G of the PI control unitPI(s) the following formula (3):
Figure GDA0002260363270000081
in the formula, kpFor proportional control of the PI control unit, kiFor an integration constant, s denotes a complex variable, which is a variable that converts a time domain signal into a complex frequency domain signal, and is also called "complex frequency".
Considering that sin (Δ θ) ≈ Δ θ when Δ θ is close to 0, the open-loop transfer function block diagram of the self-synchronization control unit 13 can be simplified as the following formula (4):
Figure GDA0002260363270000082
in the formula, Gopen(s) simplified open-loop transfer function, τPI＝kp/ki,ko＝kiE*(Eg＝E*)；τPIFor the ratio of the proportional-adjustment parameter to the integral constant, k, in a PI controlleroIs the product of an integration constant and a reference voltage in a PI controller, tauPI、koThe open-loop transfer function setting is convenient to simplify; e*A given grid voltage reference amplitude value; tau isfThe time constant of the frequency control loop in the virtual synchronization algorithm control unit.
It can be seen that the open-loop transfer function is a typical type II second-order system, and in order to improve the stability and dynamic response performance of the self-synchronization control unit, the intermediate frequency width h ═ τ isPI/τfShould not be equal to-2, so τPIShould be greater than τfThe gain of the open loop transfer function must conform to the following equation (5):
Figure GDA0002260363270000083
in the formula, E*A given grid voltage reference amplitude value; tau isfIs the time constant of the frequency control loop in the virtual synchronization algorithm control unit; h is τPI/τfIs of medium bandwidth.
Accordingly, the parameters of the PI control unit may be expressed as:
Figure GDA0002260363270000084
in general, considering that the value of h is between 5 and 10, then equation (6) can be derived to equation (7):
Figure GDA0002260363270000091
in addition, in practical application systems, in order to avoid large fluctuations in the virtual synchronous inverter frequency during presynchronization, the output of the PI control unit should be limited.
Then the phase angle frequency delta omega after PI compensation adjustment is carried outsycIs supplied to the virtual synchronous algorithm control unit 12 in the virtual synchronous inverter control module 3.The angular frequency reference value ω of the driving voltage signal e output by the virtual synchronization algorithm control unit 12 is derived as shown in the following equation (8):
Figure GDA0002260363270000092
in the formula, npFor the active droop coefficient, P represents the electromagnetic power output by the inverter, and P*Given active reference power, ω, for a virtual synchronization algorithm control unit*For a given reference frequency;
the core control idea of the self-synchronizing control unit 13 in the invention is to adjust the angular frequency of the virtual synchronous inverter to return the phase difference delta theta to zero and the q-axis component u of the grid voltagegqAnd zero, the self-synchronization of the grid-connected inverter with the local load and the public power grid is realized.
Further, the off/on-grid switching module 8 performs off/on-grid switching of the virtual synchronous inverter system by using the switching signal output by the virtual synchronous inverter control module 3 as an input signal.
The control method of the invention comprises the following steps: when the system operates in an island mode, the circuit breaker CB2 is disconnected, the self-synchronization control unit 13 in the virtual synchronous inverter control module 3 and the external grid-off/grid-connected switching module 8 do not work, the output voltage and current of the virtual synchronous inverter are sent to the virtual synchronous inverter control module 3 through the inverter output voltage and current information acquisition module and the grid side voltage information acquisition module, and the virtual synchronous inverter with the local load 11 is controlled to operate normally.
When the network side fault is removed or the network is connected, the system needs to carry out network connection switching, starts the self-synchronizing control unit 13 in the virtual synchronous inverter control module 3, inputs the phase angle theta generated by the virtual synchronous algorithm control unit 12 in the virtual synchronous inverter control module 3 into the self-synchronizing control unit 13 as a reference phase angle, and detects the network side voltage ugAnd also input thereto. Obtaining the power grid voltage u through Clark conversion and Park conversiongQ-axis component u ofgq. Q-axis component ugqComparing with zero reference value, and using the difference value as PI controlThe input of the device is adjusted to obtain delta omegasycAnd the synchronous compensation quantity is used as the synchronous compensation quantity of the rated angular frequency in the virtual synchronous algorithm control unit. The angular frequency reference value omega of the output voltage of the virtual synchronous algorithm control unit 12 is gradually increased by delta omegasycAnd at the end of the transition to a steady state value. Detecting that delta theta is zero and q-axis component u of the network voltagegqAlso zero, indicating that the virtual synchronous inverter is synchronized to the grid voltage, the virtual synchronous inverter control module 3 outputs a switching signal to the off/on switching module 8 to execute the on command, close the circuit breaker CB2 and remove the compensation Δ ω of the angular frequency compensatorsyc. During this process, the active power output of the virtual synchronous inverter remains unchanged.
Examples
As shown in fig. 1, is supplied from a dc voltage source UdcThree-phase inverter bridge, PWM driver, local load, inverter side impedance (R)s、Ls) Line equivalent impedance (R)g、Lg) Public power grid, inverter output LC filter (L)sAnd C), an inverter output voltage and current sampling module, a network side voltage information acquisition module, a virtual synchronous inverter control module (comprising a virtual synchronous algorithm control unit and a self-synchronizing control unit) and an off/grid connection switching module.
The connection mode is as follows: collecting three-phase voltage signals at a filter capacitor C at the output side of an inverter bridge and outputting a filter inductor LsThe voltage and current signals of the public power grid at the grid-connected point are transmitted to the input ends (as shown by ports a, b and c in fig. 1) of the voltage and current signals of the virtual synchronous inverter control module 3 as actual voltage and current inputs in a mode including but not limited to wired transmission; the output signals of the virtual synchronous inverter control module 3 (as indicated by ports d and e in fig. 1) are used as input signals of the off/on-grid switching module and the PWM driver, respectively.
DC power supply UdcAnd supplying electric energy to the inverter and maintaining the voltage of the direct current bus stable. DC power supply UdcIncluding but not limited to battery, photovoltaic panel, etc., the DC input is converted into DC power via an inverter bridgeAlternating current at a frequency around 50Hz provides electrical power to the grid.
The output end of the three-phase inverter is connected with the LC filter, so that the aims of filtering out high-frequency harmonic waves and improving the waveform quality are fulfilled.
The local load is used for simulating the actual condition of a typical virtual synchronous inversion system.
FIG. 2 is a schematic block diagram of the internal components of the control module of the virtual synchronous inverter of FIG. 1, with the self-synchronizing control unit on the right side of the control module; fig. 2 identifies the mathematical mechanism of the self-synchronizing virtual synchronous inverter based on SPF-PLL in detail, and the specific mathematical mechanism of the self-synchronizing virtual synchronous inverter is analyzed by taking fig. 2 as an example.
Fig. 2 contains three input signals in fig. 1: inverter output terminal voltage signal us(obtained by Hall a of inverter output voltage and current information acquisition module, signal conditioning module a and AD2 in FIG. 1), and inverter output current signal is(obtained from Hall a, Signal Conditioning Module a, AD1 in FIG. 1) and PCC Point Voltage ug(obtained from hall b, signal conditioning module b, AD3 in fig. 1). In addition, the control target reference voltage e and the given active reference power P of the virtual synchronous algorithm control unit are included*Given reactive reference power Q*Given a voltage reference amplitude E*And a given reference frequency omega*And the like.
The specific mathematical principle of the virtual synchronous inverter control module based on the SPF-PLL in fig. 2 is as follows:
in the right self-synchronizing control unit, the actual value u of the three-phase network voltage is firstly detectedgAfter Clark conversion, u is obtainedα＝Egcosθg，uβ＝Egsinθg. The phase angle θ generated by the algorithm of the virtual synchronous inverter control module in the left half of fig. 2 is used as the reference phase angle. Combined uα、uβObtaining the grid voltage dq axis component u under the synchronous rotating coordinate system through Park conversiongd＝Egcos(θg-θ)，ugq＝Egsin(θg- θ). And oriented with the d-axis, then u gd0. Extracting q-axis component u of grid voltagegqComparing with zero reference value, and comparing ugqAnd the difference value of the sum 0 is output to a PI control unit for regulation, and the output of the PI control unit is limited in order to avoid large fluctuation of the frequency of the virtual synchronous inverter in the presynchronization process. Finally, the synchronous compensation quantity delta omega of the rated angular frequency in the left virtual synchronous algorithm control unit is outputsyc. Reference value omega of angular frequency in control unit of original virtual synchronous algorithm*Adding the new input reference value (omega) of the virtual synchronous algorithm control unit 12*+Δωsyc) (i.e., the left part of equation 8 in brackets). Analyzing the interior of a control unit of a left virtual synchronization algorithm, and firstly detecting a three-phase output current instantaneous value isMultiplying the output power P and the reactive power Q by the potential of the inverter to give the active power P*And reactive Q*Respectively subtracting the active power and the reactive power output by the inverter to respectively obtain P-P*And Q-Q*From P to P*And Q-Q*Respectively corresponding to the active droop coefficient npAnd reactive droop coefficient nqMultiplying to obtain np(P-P*) And nq(Q-Q*) Then using (omega)*+Δωsyc) Subtracting np(P-P*) And integrating the difference in an active inertia link to obtain the angular velocity omega. At the same time, with E*Subtracting nq(Q-Q*) And integrating the result obtained after the subtraction in the front in a reactive inertia link to obtain the voltage amplitude E. And then, integrating the angular velocity omega to obtain an A-phase of a reference wave, calculating an A-phase reference sine wave by knowing the voltage amplitude and the A-phase angle, and respectively rotating 120 degrees anticlockwise and clockwise to obtain B-phase and C-phase reference waves, wherein the reference wave signal is compared with a sawtooth wave signal sent by a sawtooth wave generator in the controller to obtain a control signal of a power electronic switching element in the inverter bridge so as to control the on-off of the control signal. When the internal algorithm formula omega of the unit is controlled to be 1/(1+ tau) according to the virtual synchronous algorithmfs)*[ω*+Δωsyc-np(P-P*)]Gradually adjusting the angular frequency of the virtual synchronous inverter to change the phase difference delta theta to thetagMarking the virtual synchronous inverter and the grid when theta is normalized to zeroSynchronization has been achieved when the q-axis component u of the grid voltagegqAlso zero.
When the virtual synchronous inverter control module detects that the virtual synchronous inverter and the power grid are synchronized, a grid-connected switching signal is output to the off/grid-connected control switching module to indicate that the off/grid-connected control switching module enters a grid-connected switching preparation state. CB2 is then closed and the angular frequency compensator compensation Δ ω is removedsycAnd disconnecting the self-synchronizing control unit to complete the grid connection process of the virtual synchronous inverter.
FIG. 3 is a diagram of the internal algorithm structure of the left virtual synchronous algorithm control unit in FIG. 2, including the mechanical equation of the rotor, the electromagnetic torque TeA mathematical model of the three-phase output voltage e of the inverter and the reactive output power Q.
Namely:
Figure GDA0002260363270000121
Figure GDA0002260363270000122
Figure GDA0002260363270000123
Figure GDA0002260363270000124
in the formula, Tm、TdAnd J is the mechanical torque, damping torque and virtual moment of inertia applied to the rotor, respectively; mfIs the maximum mutual inductance between the field winding and the stator winding; i.e. ifIs an excitation current; ω is the imaginary axis angular frequency; θ is the rotor phase angle;
Figure GDA0002260363270000125
is the derivative of the imaginary axis angular frequency, i.e. represents the rate of change of the angular frequency; t iseIs the virtual electromagnetic torque inside the virtual synchronous inverter; i is the three-phase vector current flowing from the virtual motor stator; p is virtualThe synchronous inverter actually outputs active power; and Q is the actual output reactive power of the virtual synchronous inverter.
ω is both the angular frequency of the virtual synchronous generator and the angular frequency reference of the drive voltage signal e. e is the input signal of the drive, output by the virtual synchronous inverter algorithm control unit 12.ω is the angular frequency of the virtual synchronous generator in the above 4 equations, and is the angular frequency reference value of the driving voltage signal e in equation (8). 4 formulas are main components of the virtual synchronous inverter algorithm control unit, and the input angular frequency reference value of the original virtual synchronous algorithm control unit 12 is omega*The phase angle synchronization of the method has the function of synchronizing the original omega*Conversion to (ω) in (8)*+Δωsyc) And the closed-loop feedback compensation adjustment function is realized.
The PWM driver shown in fig. 4 has a specific control manner: PWM driver receives voltage and current double closed loop control output signal refPWMWhen it is used, it is generally 0. ltoreq.refPWMLess than or equal to 1, the signal refPWMWhen compared with a sawtooth wave with 5kHz frequency in the driver, the signal value refPWMWhen the value is less than or equal to the value of the sawtooth wave signal, a driver transmits a high-level turn-on driving signal to the control end of a power electronic switching device in the inverter bridge until the signal value refPWMWhen the value is larger than the value of the sawtooth wave signal, the PWM driver transmits a low level turn-off signal to the control end of the switching device; the frequency of the sawtooth wave signal of the prior model is only 5kHz and is only exemplified by the frequency value, and the frequency is not limited to the value in practical application.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims (2)

1. The self-synchronizing virtual synchronous inverter grid-connected controller with the local load based on the SPF-PLL is characterized by comprising an inverter output voltage and current information acquisition module, a grid side voltage information acquisition module, a virtual synchronous inverter control module (3), an off/grid-connected switching module (8) and a PWM driver (2);
the inverter output voltage and current information acquisition module is used for acquiring voltage signals at the output end of the inverter and current signals at the output end of the inverter;
the grid side voltage information acquisition module is used for acquiring voltage signals of grid-connected points; the inverter output voltage and current information acquisition module acquires a voltage signal at a filter capacitor C at the output side of the inverter and outputs a filter inductor LsThe network side voltage information acquisition module also transmits a network side voltage signal to a voltage signal input end of the virtual synchronous inverter control module (3);
the off/grid-connected switching module (8) is used for judging whether a circuit breaker CB2 used for connecting the output end of the virtual synchronous inverter and the public power grid (4) needs to be switched immediately to complete grid-connected control according to a signal that whether the output current of the inverter detected by the preceding stage and the voltage phase of the public power grid are synchronized;
a PWM driver (2) for providing on and off signals to power electronic switching devices in the inverter bridge (1);
the virtual synchronous inverter control module (3) comprises a virtual synchronous algorithm control unit (12) and a self-synchronizing control unit (13); the virtual synchronous algorithm control unit (12) is used for realizing the characteristic of a synchronous generator when the inverter operates; the self-synchronizing control unit (13) is used for obtaining compensation quantities of a phase angle and a frequency reference value of the virtual synchronous inverter and completing synchronization of the output voltage of the inverter and the voltage phase of a power grid;
the self-synchronization control unit (13) comprises a phase self-tracking control unit and a PI control unit; the phase self-tracking control unit is used for locking the phase angle of the power grid voltage; the PI control unit is used for improving the regulation performance;
in the phase self-tracking control unit, the grid voltage of the two-phase αβ in the stationary coordinate system is as follows (1):
Figure FDA0002411264640000011
in the formula uα、uβRepresenting the α, β axis components in a two-phase stationary coordinate system, uga、ugb、ugcRepresenting the three-phase voltage of the power grid; egThe voltage amplitude value of the network side after the transformation of the two-phase static coordinates is obtained; thetagIs the grid voltage phase;
the phase angle theta generated by virtual synchronous control is used as a reference phase angle, and the grid voltage u is obtained through Park conversiongThe dq axis component of (2) below:
Figure FDA0002411264640000021
in the formula ugd、ugqRepresenting a dq axis voltage direct-current component under a synchronous rotation coordinate system; theta is a phase angle generated by the virtual synchronization algorithm control unit;
transfer function G of the PI control unitPI(s) the following formula (3):
Figure FDA0002411264640000022
in the formula, kpFor proportional control of the PI control unit, kiS represents a complex variable, which is a variable converting a time domain signal to a complex frequency domain signal, as an integration constant;
considering that sin (Δ θ) ≈ Δ θ when the phase difference Δ θ is close to 0, the open-loop transfer function of the self-synchronization control unit (13) is simplified to the following formula (4):
Figure FDA0002411264640000023
in the formula, Gopen(s) simplified open-loop transfer function, τPI＝kp/ki,ko＝kiE*，Eg＝E*；τPIFor ratio of proportional-adjustment parameter to integral constant in PI controller，koIs the product of an integration constant and a reference voltage in a PI controller, tauPI、koThe open-loop transfer function setting is convenient to simplify; e*A given grid voltage reference amplitude value; tau isfIs the time constant of the frequency control loop in the virtual synchronization algorithm control unit;
in order to improve the stability and dynamic response performance of the self-synchronizing control unit, the intermediate frequency width h is equal to tauPI/τfShould not be equal to-2, so τPIShould be greater than τfThe gain of the open loop transfer function conforms to the following equation (5):
Figure FDA0002411264640000024
accordingly, the parameters of the PI control unit are expressed as:
Figure FDA0002411264640000025
considering that the value of h is between 5 and 10, then equation (6) can be derived to equation (7):
Figure FDA0002411264640000031
converting the q-axis component u of the grid voltagegqComparing with zero reference value, and comparing ugqThe difference value of the sum 0 is output to the PI control unit, i.e. the value of delta omega can be obtainedsyc，ΔωsycA synchronous compensation quantity of a rated angular frequency is input as a virtual synchronous algorithm control unit (12);
the angular frequency reference value omega of the driving voltage signal e output by the virtual synchronization algorithm control unit (12) is shown as the following formula (8):
Figure FDA0002411264640000032
in the formula, npFor the active droop coefficient, P represents the electromagnetic power output by the inverter, and P*For virtual synchronizationGiven active reference power, ω, of the algorithmic control unit*For a given reference frequency;
at the same time, with E*Subtracting nq(Q-Q*) Integrating the result obtained after subtraction in a reactive inertia link to obtain a voltage amplitude E; n isqRepresenting the reactive droop coefficient, Q representing the reactive power, Q*Representing a given reactive reference power;
integrating the angular frequency reference value omega to obtain an A-phase of a reference wave, calculating an A-phase reference sine wave by knowing a voltage amplitude and the A-phase angle, and respectively rotating 120 degrees anticlockwise and clockwise to obtain B-phase and C-phase reference waves, wherein the reference wave signal is compared with a sawtooth wave signal sent by a sawtooth wave generator in a controller to obtain a control signal of a power electronic switch device in an inverter bridge so as to control the on-off of the control signal;
gradually adjusting the angular frequency of the virtual synchronous inverter according to equation (8) to make the phase difference Δ θ equal to θgWhen theta is normalized to zero, the virtual synchronous inverter is marked to be synchronized with the power grid.
2. The grid-connection method of the grid-connected controller of the self-synchronizing virtual synchronous inverter with the local load based on the SPF-PLL of claim 1, characterized in that when the grid-side fault is removed or the grid-connection is required, the system needs to perform the grid-connection switching, the self-synchronizing control unit (13) in the virtual synchronous inverter control module (3) is started, the phase angle theta generated by the virtual synchronizing algorithm control unit (12) in the virtual synchronous inverter control module (3) is input to the self-synchronizing control unit (13) as the reference phase angle, and the detected grid-side voltage u is detectedgAlso input into it; obtaining the power grid voltage u through Clark conversion and Park conversiongQ-axis component u ofgqThe q-axis component ugqComparing with a reference value zero, then taking the difference value as the input of the PI controller, and obtaining the delta omega through regulationsycAs the synchronous compensation quantity of the rated angular frequency in the virtual synchronous algorithm control unit; the angular frequency reference value omega of the output voltage of the virtual synchronous algorithm control unit (12) is gradually increased by delta omegasycIs largeSmall and at the end transitions to a steady state value; detecting that delta theta is zero and q-axis component u of the network voltagegqAlso zero, indicating that the virtual synchronous inverter is synchronized to the grid voltage, the virtual synchronous inverter control module (3) outputs a switching signal to the off/on-grid switching module (8) to execute a grid-connection command, closes the circuit breaker CB2 and removes the angular frequency compensator compensation Δ ωsycDuring this process, the active power output of the virtual synchronous inverter remains unchanged.
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