CN115473273B - New energy power generation unit self-synchronizing low voltage ride through control method under extremely weak network - Google Patents
New energy power generation unit self-synchronizing low voltage ride through control method under extremely weak network Download PDFInfo
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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
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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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
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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
- H02J3/381—Dispersed generators
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Abstract
The invention discloses a self-synchronizing low-voltage ride through control method of a new energy power generation unit under an extremely weak network, and belongs to the field of power control. The control method comprises the following steps: under the steady-state operation condition, the device has the capability of actively supporting the voltage and the frequency of the power grid, and has better current control capability; during voltage sag, amplitude synchronous control can reduce a current peak value in an initial stage of voltage sag; during the low-pass stable operation period, the power command switching can enable the system to give out reactive power preferentially, and helps the recovery of the power grid voltage; during the voltage recovery period, the phase angle synchronous control can prevent the phase angle mutation caused by voltage drop and prevent overcurrent and overvoltage. The control method can realize low voltage ride through without switching control modes, is relatively simple to control, is not easy to make mistakes, and improves the stability and the power grid adaptability of the new energy grid-connected system.
Description
Technical Field
The invention relates to a self-synchronous low-voltage ride through control method for a new energy power generation unit, in particular to a temporary steady-state control method for the self-synchronous voltage source of the new energy power generation unit under an extremely weak power grid, and belongs to the field of power control.
Background
With the development of the 'double carbon' target, the country pays more attention to the development of new energy technology, and the construction of a new generation power system mainly comprising clean energy becomes a current research hot spot. However, when a disturbance occurs under a weak grid condition, the voltage and frequency of the new energy system are liable to be unstable. Therefore, the active support technology and the system stable operation control method under the high-proportion permeation of new energy are further researched, and the method has great significance for realizing the 'double carbon' target.
In recent years, expert scholars at home and abroad research the problems of active support and stability of a new energy system from various angles, and self-synchronous voltage source control methods such as a virtual synchronous generator and the like are continuously applied. The virtual synchronous generator control method has certain inertia and damping by simulating a rotor motion equation of a traditional generator, and has the capacity of actively supporting a power grid. However, the conventional virtual synchronous generator control method has no low voltage ride through capability, and system overcurrent, overvoltage and system breakdown are extremely easy to cause during the voltage drop of the power grid. In addition, the interaction problem of the new energy system under the weak network or the extremely weak network is complex, and the system stability is greatly reduced.
In order to solve the problems, expert students at home and abroad propose methods mainly comprising:
the Chinese patent application description (CN 113595147A) entitled "virtual synchronous generator control method based on model predictive control" presents a control method in which an optimal switching sequence is directly applied to an inverter by a model predictive method, and the method can effectively improve the system stability under power fluctuation, has active supporting capability, but lacks current control capability, and is easy to generate an overcurrent phenomenon when the voltage of a power grid drops.
In the technical scheme disclosed in the Chinese patent application description (CN 108092308A) entitled "a low voltage ride through control method of a distributed virtual synchronous generator", a comprehensive control method for accelerating the response speed of a reactive power loop, introducing virtual impedance and changing a power instruction during faults is provided, the control method has certain low voltage ride through capability, improves the stability of a new energy system under faults, but has serious interaction conditions under a weak network or an extremely weak network, and the stability of the method is greatly reduced.
The Chinese patent application specification (CN 108718097A) entitled "seamless switching system suitable for low voltage ride through of virtual synchronous generator" proposes a mode seamless switching control method of VSG control and traditional LVRT control based on amplitude and phase presynchronization, the control method has better low voltage ride through capability, however, the control method is complex and is easy to make mistakes in practical application.
In a word, the existing virtual synchronous generator control method has the problems of overvoltage, overcurrent and system breakdown under the condition of a weak power grid or an extremely weak power grid, and the system power angle instability is easily caused after the power grid voltage drops, so that the low voltage ride through is difficult to realize.
Disclosure of Invention
The invention aims to overcome the limitations of various technical schemes, and provides a self-synchronous low-voltage ride-through control method of a new energy power generation unit under an extremely weak network, aiming at the problems that the traditional virtual synchronous generator control method under the weak network is poor in current control capability, overcurrent, overvoltage, power angle instability, system breakdown and the like are easy to occur under the voltage drop of the network.
The object of the present invention is thus achieved. The invention provides a self-synchronous low-voltage ride through control method of a new energy power generation unit under an extremely weak network, wherein the topology of the new energy power generation unit comprises a direct-current power supply U dc DC side filter capacitor C dc Three-phase full-bridge inverter circuit, filter inductor L and filter capacitor C 1 Passive damping resistor R C Grid-connected equivalent resistor R g Grid-connected equivalent inductance L g And a three-phase network e a 、e b 、e c DC side filter capacitor C dc And is connected with a direct current source U dc And a three-phase full-bridge inverter circuit connected in series with the DC side power supply U dc And a filter capacitor C between the filter inductor L 1 First series connection passive damping resistor R C Then is connected in parallel with the filter inductance L and the grid-connected equivalent resistance R g Between the grid-connected equivalent inductances L g Series connected in parallel with equivalent resistor R g And a three-phase network e a 、e b 、e c Between them;
the control method comprises the following steps:
step 1, sampling and coordinate transformation;
the sampling includes collecting the following data: the voltage of the grid-connected point of the new energy power generation unit is recorded as grid-connected voltage u oa ，u ob ，u oc The current of the grid-connected point of the new energy power generation unit is recorded as grid-connected current i oa ，i ob ，i oc The new energy power generation unit filters the current at the inductance L and records the current as the inductance current i at the bridge arm side La ，i Lb ，i Lc The power grid voltage of the new energy power generation unit is recorded as power grid voltage u ga ，u gb ，u gc ；
The coordinate transformation includes coordinate transformation of: for grid-connected voltage u oa ，u ob ，u oc Grid-connected current i oa ，i ob ，i oc Inductance current i on bridge arm side La ，i Lb ，i Lc Grid voltage u ga ，u gb ，u gc Respectively carrying out single synchronous rotation coordinate transformation to obtain a grid-connected voltage dq component U od ，U oq Grid-connected current dq component I od ，I oq Inductor current dq component I on bridge arm side Ld ，I Lq Grid voltage dq component U gd ，U gq ；
And 2, obtaining average active power P and average reactive power Q by using an active power calculation equation and a reactive power calculation equation, wherein the active power calculation equation and the reactive power calculation equation are respectively as follows:
P＝1.5(U oq I oq +U od I od )
Q＝1.5(U od I oq -U aq I od )
step 3, according to the average active power P obtained in the step 2 and the active power instruction P given by the new energy power generation unit 0 Warp yarnThe angular frequency omega of the self-synchronous control is obtained by an excess power angle control equation, and the expression of the excess power angle control equation is as follows:
wherein omega 0 Giving an active power instruction P to a new energy power generation unit 0 The rated angular frequency is calculated, m is a power angle control sagging coefficient, J is virtual moment of inertia of the simulated synchronous generator set, and s is a Laplacian operator;
performing phase angle synchronous control at the voltage drop ending moment, and integrating the self-synchronous control angular frequency omega to obtain the self-synchronous control output phase angle theta; the phase angle synchronization control at the voltage drop end time is the compensation of the output phase difference delta theta, delta theta=theta g0 -θ n Wherein θ is g0 For the output phase angle, θ, of the grid voltage at the end of the voltage sag 0 For the output phase angle of the self-synchronous control at the end time of the voltage drop, the expression of the output phase angle θ of the self-synchronous control is as follows:
step 4, according to the average reactive power Q obtained in the step 2 and the reactive power instruction Q given by the new energy power generation unit 0 Obtaining a terminal voltage amplitude command E of self-synchronous control through a reactive control equation * And then according to the self-synchronous control output phase angle theta and terminal voltage amplitude command E obtained in the step 3 * Obtaining a self-synchronous control three-phase terminal voltage instruction through an instruction synthesis equation
The expressions of the reactive control equation and the instruction synthesis equation are respectively as follows:
E * ＝U 0 +n(Q 0 -Q)
wherein U is 0 Giving reactive power instruction Q to new energy power generation unit 0 Rated voltage at time, n is reactive-voltage sag coefficient;
step 5, according to the three-phase terminal voltage command obtained in the step 4And the grid-connected voltage u obtained in the step 1 oa ，u ob ，u oc Obtaining a current command signal +.>The expression of the virtual impedance control equation is:
wherein R is v Is virtual resistance, L v Is a virtual inductance;
for current command signalPerforming single synchronous rotationThe transformation of the rotating coordinates to obtain the dq component of the current command signal>
Step 6, according to the power grid voltage dq component U obtained in step 1 gd ，U gq Obtaining a power grid voltage amplitude U through a power grid voltage amplitude calculation equation g According to the obtained power grid voltage amplitude U g With a given grid voltage amplitude command U ref Determining the voltage drop depth D of the grid-connected point through a voltage drop calculation equation;
the expressions of the grid voltage amplitude calculation equation and the voltage sag calculation equation are respectively as follows:
step 7, obtaining a current loop q-axis instruction when the power grid voltage drops according to a reactive compensation control equation in the low voltage ride through standardObtaining a current loop d-axis instruction +.f. when the power grid voltage drops through a limiting control equation of the current stress of the power device>
The reactive compensation control equation and the limiting control equation of the current stress of the power device are respectively as follows:
wherein K is m Is reactive compensation coefficient I N The rated current amplitude of the new energy power generation unit is set;
step 8, according to the current loop d-axis instruction obtained in the step 7 when the power grid voltage dropsAnd current loop q-axis command in case of grid voltage drop +.>Obtaining an active power command +_under fault by a fault power command calculation equation>And reactive power command->The fault power instruction calculation equation is as follows:
step 9, obtaining a voltage instruction under a fault through a fault voltage instruction calculation equation according to the grid-connected point voltage drop depth D obtained in the step 6The fault voltage instruction calculation equation is as follows:
step 10, switching power instructions according to the grid-connected point voltage drop depth D obtained in the step 6 and having the same amplitudeStep control, specifically, a power switching instruction P is set ref Reactive power switching instruction Q ref The voltage switching instruction is U ref ：
(1) In the stable operation stage, D is more than or equal to 0.9 and P ref ＝P 0 ，Q ref ＝Q 0 ，U ref ＝U 0 ；
(2) In the stage of power grid voltage drop, D is less than 0.9,
(3) Stage of recovery of grid voltage, P ref ＝P 0 ，Q ref ＝Q 0 ，
Step 11, based on the current command signal dq component obtained in step 5And the bridge arm side inductance current dq component I obtained in the step 1 Ld ，I Lq The control signal U is obtained through a current control equation d ，U q The current control equation is:
wherein K is pi K is the current loop proportional control coefficient ii Integrating the control coefficient for the current loop;
the obtained control signal U d ，U q Obtaining a control signal U of the new energy power generation unit through single synchronous rotation coordinate inverse transformation a ，U b ，U c Then according to the control signal U a ，U b ，U c Generating three-phase full-bridge inverter powerPWM control signals of the circuit.
Compared with the prior art, the invention has the following advantages for the new energy power generation system:
1. the balance current control can effectively inhibit harmonic waves under small disturbance, and improves the current control capability.
2. The amplitude synchronous control can effectively reduce the current peak during voltage drop, the phase angle synchronous control can effectively reduce the current peak during voltage recovery, and the stability and the power grid adaptability of the new energy grid-connected system are improved.
3. The low voltage ride through can be realized without switching a control strategy when the power grid voltage drops, the control is relatively simple, and the fault is not easy to occur.
Drawings
Fig. 1 is a grid-connected inverter topology of a new energy power generation unit of the present invention.
Fig. 2 is a control block diagram of the new energy power generation unit self-synchronizing low voltage ride through control method of the present invention.
FIG. 3 is a waveform diagram of grid-connected voltage simulation when the grid voltage drops by 50% in the embodiment of the invention.
FIG. 4 is a waveform diagram of grid-connected current simulation when the grid voltage drops by 50% in the embodiment of the invention.
Fig. 5 is a waveform diagram of a simulation of d-axis component of the bridge arm side inductor current when the grid voltage drops by 50% in the embodiment of the invention.
Fig. 6 is a simulated waveform of output active power when the grid voltage drops by 50% in the embodiment of the invention.
Detailed Description
The preferred mode of the present invention will be described in further detail with reference to the accompanying drawings.
Fig. 1 is a topology of a new energy grid-connected inverter in an embodiment of the present invention. From the figure, the topology of the new energy power generation unit comprises a direct current power supply U dc DC side filter capacitor C dc Three-phase full-bridge inverter circuit, filter inductor L and filter capacitor C 1 Passive damping resistor R C Grid-connected equivalent resistor R g Grid-connected equivalent inductance L g And a three-phase network e a 、e b 、e c DC side filter capacitor C dc And is connected with a direct current source U dc And a three-phase full-bridge inverter circuit connected in series with the DC side power supply U dc And a filter capacitor C between the filter inductor L 1 First series connection passive damping resistor R C Then is connected in parallel with the filter inductance L and the grid-connected equivalent resistance R g Between the grid-connected equivalent inductances L g Series connected in parallel with equivalent resistor R g And a three-phase network e a 、e b 、e c Between them. In addition, the PCC in fig. 1 is a grid-connected point.
Specifically, the parameters in this embodiment are as follows: the effective value of the output alternating current line voltage is 380V/50Hz, the rated capacity is 100kW, the inductance value of the filter inductance L is 0.3mH, and the filter capacitance C 1 The capacitance value of the new energy power generation unit is 200 mu F, and the sampling frequency F of the new energy power generation unit s Is 10kHz, thus sampling period T s ＝100μs。
Fig. 2 is a control block diagram of the control method of the present invention, and as can be seen from fig. 2, the self-synchronous low voltage ride through control method of the new energy power generation unit under the extremely weak network of the present invention comprises the following steps:
and step 1, sampling and coordinate transformation.
The sampling includes collecting the following data: the voltage of the grid-connected point of the new energy power generation unit is recorded as grid-connected voltage u oa ，u ob ，u oc The current of the grid-connected point of the new energy power generation unit is recorded as grid-connected current i oa ，i ob ，i oc The new energy power generation unit filters the current at the inductance L and records the current as the inductance current i at the bridge arm side La ，i Lb ，i Lc The power grid voltage of the new energy power generation unit is recorded as power grid voltage u ga ，u gb ，u gc 。
The coordinate transformation includes coordinate transformation of: for grid-connected voltage u oa ，u ob ，u oc Grid-connected current i oa ，i ob ，i oc Inductance current i on bridge arm side La ，i Lb ，i Lc Grid voltage u ga ，u gb ，u gc Respectively carrying out single synchronous rotation coordinate transformation to obtain a grid-connected voltage dq component U od ，U oq Grid-connected current dq component I od ，I oq Inductor current dq component I on bridge arm side Ld ，I Lq Grid voltage dq component U gd ，U gq 。
And 2, obtaining average active power P and average reactive power Q by using an active power calculation equation and a reactive power calculation equation, wherein the active power calculation equation and the reactive power calculation equation are respectively as follows:
P＝1.5(U oq I oq +U od I od )
Q＝1.5(U od I oq -U oq I od )
step 3, according to the average active power P obtained in the step 2 and the active power instruction P given by the new energy power generation unit 0 The self-synchronous control angular frequency omega is obtained through a power angle control equation, and the expression of the power angle control equation is as follows:
wherein omega 0 Giving an active power instruction P to a new energy power generation unit 0 And the rated angular frequency is m is a power angle control sagging coefficient, J is virtual rotational inertia of the simulated synchronous generator set, and s is a Laplacian operator.
Performing phase angle synchronous control at the voltage drop ending moment, and integrating the self-synchronous control angular frequency omega to obtain the self-synchronous control output phase angle theta; the phase angle synchronization control at the voltage drop end time is the compensation of the output phase difference delta theta, delta theta=theta g0 -θ 0 Wherein θ is g0 For the output phase angle, θ, of the grid voltage at the end of the voltage sag 0 For the output phase angle of the self-synchronous control at the end time of the voltage drop, the expression of the output phase angle θ of the self-synchronous control is as follows:
the power angle control equation shows the relation of the active power sagging curve and the virtual inertia of the new energy power generation unit. The virtual inertia marks the change rate of the system frequency, and in order to ensure that the system frequency changes stably, the virtual inertia needs to be larger; however, the virtual inertia is equivalent to adding a first-order inertia link in the system, and a large virtual inertia may cause instability of the system. Thus parameter selection requires compromise processing. To ensure system stability, the inertia time constant is within the range of tau virtual ＝Jω 0 m≤2e -3 s. The relation of the active power sagging curve in the power angle control equation comprises three coefficients, wherein the power angle control sagging coefficient m represents the slope of the sagging curve, and when the value principle is 100% of active power change, the frequency change is within 0.5 Hz; given active power instruction P 0 And corresponding nominal angular frequency omega 0 The position relation of the sagging curve is expressed, and the active power output by the new energy grid-connected inverter is mainly considered as P 0 When it is output frequency size.
In this embodiment, the power angle control droop coefficient takes on the value ofTaking tau according to the principle of taking value of inertia time constant virtual ＝Jω 0 m＝1.5e -3 s, J=0.154 kg.m 2 The given active power instruction takes the value P 0 =100 kW, at which point the corresponding nominal angular frequency takes on the value ω 0 ＝314.16rad/s。
Step 4, according to the average reactive power Q obtained in the step 2 and the reactive power instruction Q given by the new energy power generation unit 0 Obtaining a terminal voltage amplitude command E of self-synchronous control through a reactive control equation * And then according to the self-synchronous control output phase angle theta and terminal voltage amplitude command E obtained in the step 3 * Obtaining a self-synchronous control three-phase terminal voltage instruction through an instruction synthesis equation
The expressions of the reactive control equation and the instruction synthesis equation are respectively as follows:
E * ＝U 0 +n(Q 0 -Q)
wherein U is 0 Giving reactive power instruction Q to new energy power generation unit 0 Rated voltage at time, n is the reactive-voltage sag coefficient.
In the present embodiment of the present invention, in the present embodiment,Q 0 =0, corresponding to U 0 ＝311.13V。
Step 5, according to the three-phase terminal voltage command obtained in the step 4And the grid-connected voltage u obtained in the step 1 oa ，u ob ，u oc Obtaining a current command signal +.>The expression of the virtual impedance control equation is:
wherein R is v Is virtual resistance, L v Is a virtual inductance.
For current command signalSingle synchronous rotation coordinate transformation is carried out to obtain dq component of current command signal
In the present embodiment, R v ＝0.05Ω，L v ＝0.52mH。
Step 6, according to the power grid voltage dq component U obtained in step 1 gd ，U gq Obtaining a power grid voltage amplitude U through a power grid voltage amplitude calculation equation g According to the obtained power grid voltage amplitude U g With a given grid voltage amplitude command U ref And determining the voltage drop depth D of the grid-connected point through a voltage drop calculation equation.
The expressions of the grid voltage amplitude calculation equation and the voltage sag calculation equation are respectively as follows:
in the present embodiment of the present invention, in the present embodiment,
step 7, obtaining a current loop q-axis instruction when the power grid voltage drops according to a reactive compensation control equation in the low voltage ride through standardObtaining a current loop d-axis instruction +.f. when the power grid voltage drops through a limiting control equation of the current stress of the power device>
The reactive compensation control equation and the limiting control equation of the current stress of the power device are respectively as follows:
wherein K is m Is reactive compensation coefficient I N And the rated current amplitude of the new energy power generation unit is used.
In the present embodiment, K m ＝-1.5，
Step 8, according to the current loop d-axis instruction obtained in the step 7 when the power grid voltage dropsAnd current loop q-axis command in case of grid voltage drop +.>Obtaining an active power command +_under fault by a fault power command calculation equation>And reactive power command->The fault power instruction calculation equation is as follows:
step 9, obtaining a voltage instruction under a fault through a fault voltage instruction calculation equation according to the grid-connected point voltage drop depth D obtained in the step 6The fault voltage instruction calculation equation is as follows:
step 10, performing power instruction switching and amplitude synchronous control according to the grid-connected point voltage drop depth D obtained in step 6, wherein the power instruction switching instruction is specifically P ref Reactive power switching instruction Q ref The voltage switching instruction is U ref ：
(1) In the stable operation stage, D is more than or equal to 0.9 and P ref ＝P 0 ，Q ref ＝Q 0 ，U ref ＝U 0 ；
(2) In the stage of power grid voltage drop, D is less than 0.9,
(3) Stage of recovery of grid voltage, P ref ＝P 0 ，Q ref ＝Q 0 ，
As can be seen from step 10, in the steady operation phase, the switching between the active power command and the voltage command is not performed; in the grid voltage recovery phase, only the switching of the voltage command is performed.
Step 11, based on the current command signal dq component obtained in step 5And the bridge arm side inductance current dq component I obtained in the step 1 Ld ，I Lq The control signal U is obtained through a current control equation d ，U q The current control equation is:
wherein K is pi K is the current loop proportional control coefficient ii The control coefficient is integrated for the current loop.
The obtained control signal U d ，U q Obtaining a control signal U of the new energy power generation unit through single synchronous rotation coordinate inverse transformation a ，U b ，U c Then according to the control signal U a ，U b ，U c And generating PWM control signals for the three-phase full-bridge inverter circuit.
In the present embodiment, K pi ＝1.0，K ii ＝15。
In order to prove the technical effect of the invention, the invention is simulated.
Fig. 3, 4, 5, and 6 are respectively a grid-connected voltage waveform, a grid-connected current waveform, a bridge arm side inductance current d-axis component waveform, and an active power waveform when the grid voltage drops by 50% in the case of a very weak grid (short circuit ratio scr=1.2) of the new energy power generation unit. As can be seen from fig. 3 and fig. 4, the self-synchronous low-voltage ride through control method for the new energy power generation unit under the extremely weak network provided by the invention can ensure rated operation of grid-connected voltage and grid-connected current in a normal operation stage, can ensure operation of the grid-connected voltage and the grid-connected current in a rated range in a voltage drop stage, and can recover to a stable operation state after short oscillation in a voltage recovery stage. As can be seen from fig. 5 and fig. 6, the self-synchronous low-voltage ride through control method for the new energy power generation unit under the extremely weak network provided by the invention reduces active output of the system when the voltage of the power grid drops, helps the voltage of the power grid recover, thereby realizing low-voltage ride through and improving the stability of the system.
Claims (1)
1. A self-synchronous low-voltage ride through control method for a new energy power generation unit under an extremely weak network comprises the following steps of dc DC side filter capacitor C dc Three-phase full-bridge inverter circuit, filter inductor L and filter capacitor C 1 Passive damping resistor R C Grid-connected equivalent resistor R g Grid-connected equivalent inductance L g And a three-phase network e a 、e b 、e c DC side filter capacitor C dc And is connected with a direct current source U dc And a three-phase full-bridge inverter circuit connected in series with the DC side power supply U dc And a filter capacitor C between the filter inductor L 1 First series connection passive damping resistor R C Then is connected in parallel with the filter inductance L and the grid-connected equivalent resistance R g Between the grid-connected equivalent inductances L g Series connected in parallel with equivalent resistor R g And a three-phase network e a 、e b 、e c Between them;
the control method is characterized by comprising the following steps of:
step 1, sampling and coordinate transformation;
the sampling includes collecting the following data: the voltage of the grid-connected point of the new energy power generation unit is recorded as grid-connected voltage u oa ，u ob ，u oc The current of the grid-connected point of the new energy power generation unit is recorded as grid-connected current i oa ，i ob ，i oc The new energy power generation unit filters the current at the inductance L and records the current as the inductance current i at the bridge arm side La ，i Lb ，i Lc The power grid voltage of the new energy power generation unit is recorded as power grid voltage u ga ，u gb ，u gc ；
The coordinate transformation includes performing the following dataCoordinate transformation: for grid-connected voltage u oa ，u ob ，u oc Grid-connected current i oa ，i ob ，i oc Inductance current i on bridge arm side La ，i Lb ，i Lc Grid voltage u ga ，u gb ，u gc Respectively carrying out single synchronous rotation coordinate transformation to obtain a grid-connected voltage dq component U od ，U oq Grid-connected current dq component I od ，I oq Inductor current dq component I on bridge arm side Ld ，I Lq Grid voltage dq component U gd ，U gq ；
And 2, obtaining average active power P and average reactive power Q by using an active power calculation equation and a reactive power calculation equation, wherein the active power calculation equation and the reactive power calculation equation are respectively as follows:
P＝1.5(U oq I oq +U od I od )
Q＝1.5(U od I oq -U oq I od )
step 3, according to the average active power P obtained in the step 2 and the active power instruction P given by the new energy power generation unit 0 The self-synchronous control angular frequency omega is obtained through a power angle control equation, and the expression of the power angle control equation is as follows:
wherein omega 0 Giving an active power instruction P to a new energy power generation unit 0 The rated angular frequency is calculated, m is a power angle control sagging coefficient, J is virtual moment of inertia of the simulated synchronous generator set, and s is a Laplacian operator;
performing phase angle synchronous control at the voltage drop ending moment, and integrating the self-synchronous control angular frequency omega to obtain the self-synchronous control output phase angle theta; the phase angle synchronization control at the voltage drop end time is the compensation of the output phase difference delta theta, delta theta=theta g0 -θ 0 Wherein θ is g0 For the network voltage at the end of the voltage dropOutput phase angle, θ 0 For the output phase angle of the self-synchronous control at the end time of the voltage drop, the expression of the output phase angle θ of the self-synchronous control is as follows:
step 4, according to the average reactive power Q obtained in the step 2 and the reactive power instruction Q given by the new energy power generation unit 0 Obtaining a terminal voltage amplitude command E of self-synchronous control through a reactive control equation * And then according to the self-synchronous control output phase angle theta and terminal voltage amplitude command E obtained in the step 3 * Obtaining a self-synchronous control three-phase terminal voltage instruction through an instruction synthesis equation
The expressions of the reactive control equation and the instruction synthesis equation are respectively as follows:
E * ＝U 0 +n(Q 0 -Q)
wherein U is 0 Giving reactive power instruction Q to new energy power generation unit 0 Rated voltage at time, n is reactive-voltage sag coefficient;
step 5, according to the three-phase terminal voltage command obtained in the step 4And the grid-connected voltage u obtained in the step 1 oa ，u ob ，u oc Obtaining a current command signal +.>The expression of the virtual impedance control equation is:
wherein R is v Is virtual resistance, L v Is a virtual inductance;
for current command signalPerforming single synchronous rotation coordinate transformation to obtain dq component of current command signal>
Step 6, according to the power grid voltage dq component U obtained in step 1 gd ，U gq Obtaining a power grid voltage amplitude U through a power grid voltage amplitude calculation equation g According to the obtained power grid voltage amplitude U g With a given grid voltage amplitude command U ref Determining the voltage drop depth D of the grid-connected point through a voltage drop calculation equation;
the expressions of the grid voltage amplitude calculation equation and the voltage sag calculation equation are respectively as follows:
step 7, obtaining a current loop q-axis instruction when the power grid voltage drops according to a reactive compensation control equation in the low voltage ride through standardObtaining a current loop d-axis instruction when the power grid voltage drops through a limiting control equation of the current stress of the power device
The reactive compensation control equation and the limiting control equation of the current stress of the power device are respectively as follows:
wherein K is m Is reactive compensation coefficient I N The rated current amplitude of the new energy power generation unit is set;
step 8, according to the current loop d-axis instruction obtained in the step 7 when the power grid voltage dropsAnd current loop q-axis command in case of grid voltage drop +.>Obtaining the fault through a fault power instruction calculation equationActive power command under barrier +.>And reactive power command->The fault power instruction calculation equation is as follows:
step 9, obtaining a voltage instruction under a fault through a fault voltage instruction calculation equation according to the grid-connected point voltage drop depth D obtained in the step 6The fault voltage instruction calculation equation is as follows:
step 10, performing power instruction switching and amplitude synchronous control according to the grid-connected point voltage drop depth D obtained in step 6, wherein the power instruction switching instruction is specifically P ref Reactive power switching instruction Q ref The voltage switching instruction is U ref ：
(1) In the stable operation stage, D is more than or equal to 0.9 and P ref ＝P 0 ，Q ref ＝Q 0 ，U ref ＝U 0 ；
(2) In the stage of power grid voltage drop, D is less than 0.9,
(3) Stage of recovery of grid voltage, P ref ＝P 0 ，Q ref ＝Q 0 ，
Step 11, based on the current command signal dq component obtained in step 5 And the bridge arm side inductance current dq component I obtained in the step 1 Ld ，I Lq The control signal U is obtained through a current control equation d ，U q The current control equation is:
wherein K is pi K is the current loop proportional control coefficient ii Integrating the control coefficient for the current loop;
the obtained control signal U d ，U q Obtaining a control signal U of the new energy power generation unit through single synchronous rotation coordinate inverse transformation a ，U b ，U c Then according to the control signal U a ，U b ，U c And generating PWM control signals for the three-phase full-bridge inverter circuit.
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