CN115473273B - Self-synchronized low voltage ride-through control method for new energy power generation units under extremely weak grid - Google Patents

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

Self-synchronized low voltage ride-through control method for new energy power generation units under extremely weak grid

Technical field

The invention relates to a self-synchronized low-voltage ride-through control method for a new energy power generation unit, in particular to a temporary steady-state control method for a self-synchronized voltage source of a new energy power generation unit under an extremely weak power grid, and belongs to the field of power control.

Background technique

With the proposal of the "double carbon" goal, the country attaches particular importance to the development of new energy technologies, and building a new generation power system with clean energy as the main body has become a current research hotspot. However, when disturbances occur under weak grid conditions, the voltage and frequency of new energy systems are prone to instability. Therefore, further research on active support technology and system stable operation control methods under high-proportion penetration of new energy is of great significance to the realization of the "double carbon" goal.

In recent years, experts and scholars at home and abroad have studied the active support and stability issues of new energy systems from various angles, and self-synchronous voltage source control methods such as virtual synchronous generators have been continuously applied. The virtual synchronous generator control method simulates the rotor motion equation of the traditional generator, has certain inertia and damping, and has the ability to actively support the power grid. However, the traditional virtual synchronous generator control method does not have low voltage ride-through capability, and it is easy to cause system overcurrent, overvoltage and system collapse during grid voltage drops. In addition, the interaction problems of new energy systems under weak or extremely weak networks are complex, and system stability is greatly reduced.

In response to the above problems, experts and scholars at home and abroad have proposed some methods, mainly including:

The Chinese invention patent application specification (CN113595147A) entitled "Virtual synchronous generator control method based on model predictive control" provides a control method that directly acts on the optimal switching sequence in the inverter through the model prediction method. This method can effectively improve system stability under power fluctuations and has active support capabilities, but it lacks current control capabilities and is prone to overcurrent when the grid voltage drops.

The technical solution disclosed in the Chinese invention patent application specification (CN108092308A) entitled "A low-voltage ride-through control method for distributed virtual synchronous generators" provides a method to speed up the response speed of the reactive power loop, introduce virtual impedance and fault A comprehensive control method that changes the power command at any time. This control method has a certain low voltage ride-through capability and improves the stability of the new energy system under faults. However, the interaction situation under weak or extremely weak networks is serious, and the stability of this method is Greatly reduced.

The Chinese invention patent application specification (CN108718097A) titled "A Seamless Switching System Suitable for Virtual Synchronous Generator Low Voltage Ride Through" proposes a VSG control based on amplitude and phase pre-synchronization that is independent of traditional LVRT control. The seam switching control method has good low voltage ride-through capability. However, the control method is complex and prone to errors in practical applications.

In short, in the face of grid voltage drops, existing virtual synchronous generator control methods have problems with overvoltage, overcurrent, and system collapse under weak or extremely weak grid conditions, and a drop in grid voltage can easily cause system power angle instability. , it is difficult to achieve low voltage ride through.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the limitations of the various technical solutions mentioned above. The traditional virtual synchronous generator control method under weak network has poor current control capability, and overcurrent, overvoltage and power angle instability are prone to occur when the grid voltage drops. As well as problems such as system collapse, a self-synchronized low-voltage ride-through control method for new energy power generation units under extremely weak networks is proposed.

The purpose of the present invention is achieved in this way. The present invention proposes a self-synchronized low-voltage ride-through control method for new energy power generation units under an extremely weak network. The topology of the new energy power generation unit includes a DC power supply U _dc , a DC side filter capacitor C _dc , and a three-phase full-bridge inverter. Circuit, filter inductor L, filter capacitor C ₁ , passive damping resistor R _C , grid-connected equivalent resistance R _g , grid-connected equivalent inductance L _g and three-phase grid _ea , e _b , _ec , DC side filter capacitor C _dc is connected in parallel between the DC source U _dc and the three-phase full-bridge inverter circuit. The three-phase full-bridge inverter circuit is connected in series between the DC side power supply U _dc and the filter inductor L. The filter capacitor C ₁ is first connected passively in series. The damping resistor R _C is connected in parallel between the filter inductor L and the grid-connected equivalent resistance R _g . The grid-connected equivalent inductance L _g is connected in series between the grid-connected equivalent resistance R _g and the three-phase grid _ea , e _b , between e _c ;

The steps of the control method are as follows:

Step 1, sampling and coordinate transformation;

The sampling includes collecting the following data: the voltage at the grid-connected point of the new energy power generation unit is recorded as grid-connected voltage u _oa , u _ob , u _oc , and the current at the grid-connected point of the new energy power generation unit is recorded as grid-connected current i _oa , i _ob , i _oc , the current at the filter inductor L of the new energy power generation unit is recorded as the bridge arm side inductor current i _La , i _Lb , i _Lc , the grid voltage of the new energy power generation unit is recorded as the grid voltage u _ga , u _gb , u _gc ;

The coordinate transformation includes coordinate transformation of the following data: grid-connected voltage u _oa , u _ob , u _oc , grid-connected current i _oa , i _ob , i _oc , bridge arm side inductor current i _La , i _Lb , i _Lc , grid voltage u _ga , u _gb , u _gc are respectively subjected to single synchronous rotation coordinate transformation to obtain the grid-connected voltage dq component U _od , U _oq , the grid-connected current dq component I _od , I _oq , and the bridge arm side inductor current dq component I _Ld , I _Lq , grid voltage dq component U _gd , U _gq ;

Step 2, use the active power calculation equation and the reactive power calculation equation to obtain the average active power P and the average reactive power Q. The active power calculation equation and the reactive power calculation equation are 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 step 2 and the active power command P ₀ given by the new energy power generation unit, the angular frequency ω of the self-synchronous control is obtained through the power angle control equation. The expression of the power angle control equation is as follows:

Among them, ω ₀ is the rated angular frequency of the new energy power generation unit when the active power command P ₀ is given, m is the power angle control droop coefficient, J is the virtual moment of inertia of the simulated synchronous generator unit, and s is the Laplace operator ;

Phase angle synchronous control is performed at the end of the voltage drop, and the angular frequency ω of the self-synchronous control is integrated to obtain the output phase angle θ of the self-synchronous control; the phase angle synchronous control at the end of the voltage drop is the compensation for the output phase difference Δθ, Δθ=θ _g0 -θ _n , where θ _g0 is the output phase angle of the grid voltage at the end of the voltage drop, θ ₀ is the output phase angle of the self-synchronous control at the end of the voltage drop, then the expression of the output phase angle θ of the self-synchronous control as follows:

Step 4: According to the average reactive power Q obtained in step 2 and the reactive power command Q ₀ given by the new energy generation unit, the terminal voltage amplitude command E ^* of self-synchronous control is obtained through the reactive power control equation, and then according to the step The output phase angle θ and terminal voltage amplitude command E of the self-synchronous control obtained in 3. ^* The three-phase terminal voltage command of the self-synchronous control is obtained through the command synthesis equation.

The expressions of the reactive power control equation and command synthesis equation are as follows:

E ^* =U ₀ +n(Q ₀ -Q)

Among them, U ₀ is the rated voltage of the new energy power generation unit when the reactive power command Q ₀ is given, and n is the reactive power-voltage droop coefficient;

Step 5, according to the three-phase terminal voltage command obtained in step 4 And the grid-connected voltage u _oa , u _ob , u _oc obtained in step 1, the current command signal is obtained through the virtual impedance control equation/> The expression of the virtual impedance control equation is:

Among them, R _v is the virtual resistance, L _v is the virtual inductance;

to current command signal Perform single synchronous rotation coordinate transformation to obtain the dq component of the current command signal/>

Step 6: According to the grid voltage dq components U _{gd and} U _gq obtained in step 1, the grid voltage amplitude U _g is obtained through the grid voltage amplitude calculation equation. According to the obtained grid voltage amplitude U _g and the given grid voltage amplitude The value instruction U _ref determines the voltage drop depth D at the grid connection point through the voltage drop calculation equation;

The expressions of the grid voltage amplitude calculation equation and voltage drop calculation equation are as follows:

Step 7: Obtain the current loop q-axis command when the grid voltage drops based on the reactive power compensation control equation in the low voltage ride through standard. The d-axis command of the current loop when the grid voltage drops is obtained through the limiting control equation of the current stress of the power device/>

The reactive power compensation control equation and the power device current stress limiting control equation are as follows:

Among them, K _m is the reactive power compensation coefficient, _IN is the rated current amplitude of the new energy power generation unit;

Step 8: According to the current loop d-axis command when the grid voltage drops obtained in step 7 And the current loop q-axis command when the grid voltage drops/> Obtain the active power command under fault through the fault power command calculation equation/> and reactive power directive/> The fault power command calculation equation is:

Step 9: According to the voltage drop depth D at the grid connection point obtained in step 6, obtain the voltage command under the fault through the fault voltage command calculation equation The fault voltage command calculation equation is:

Step 10: Perform power command switching and amplitude synchronization control based on the voltage drop depth D at the grid connection point obtained in step 6. Specifically, the power switching command is _Pref , the reactive power switching command is _Qref , and the voltage switching command is U _ref :

(1) Stable operation stage, D≥0.9, P _ref =P ₀ , Q _ref =Q ₀ , U _ref =U ₀ ;

(2) Grid voltage drop stage, D＜0.9,

(3) Grid voltage recovery stage, P _ref =P ₀ , Q _ref =Q ₀ ,

Step 11, according to the dq component of the current command signal obtained in step 5 With the bridge arm side inductor current dq components I _Ld and I _Lq obtained in step 1, the control signals U _d and U _q are obtained through the current control equation. The current control equation is:

Among them, K _pi is the current loop proportional control coefficient, and K _ii is the current loop integral control coefficient;

The control signals U _d and U _q are obtained through the inverse transformation of the single synchronous rotation coordinate to obtain the control signals U _a , U _b and U _c of the new energy power generation unit, and then the three-phase control signals are generated based on the control signals U _a , U _b and U _c PWM control signal of full-bridge inverter circuit.

Compared with the existing technology, the present invention has the following advantages for new energy power generation systems:

1. Balanced current control can effectively suppress harmonics under small disturbances and improve current control capabilities.

2. Amplitude synchronous control can effectively reduce current spikes during voltage drops, and phase angle synchronous control can effectively reduce current spikes during voltage recovery, improving the stability and grid adaptability of new energy grid-connected systems.

3. When the grid voltage drops, low voltage ride-through can be achieved without switching the control strategy. The control is relatively simple and less prone to errors.

Description of the drawings

Figure 1 is the topological structure of the grid-connected inverter of the new energy power generation unit of the present invention.

Figure 2 is a control block diagram of the self-synchronized low voltage ride-through control method of the new energy power generation unit of the present invention.

Figure 3 is a grid-connected voltage simulation waveform diagram when the grid voltage drops by 50% in the implementation case of the present invention.

Figure 4 is a grid-connected current simulation waveform diagram when the grid voltage drops by 50% in the implementation case of the present invention.

Figure 5 is a simulation waveform diagram of the d-axis component of the bridge arm side inductor current when the grid voltage drops by 50% in the implementation case of the present invention.

Figure 6 is a simulation waveform diagram of the output active power when the grid voltage drops by 50% in the implementation case of the present invention.

Detailed ways

The preferred modes of the present invention will be described in further detail below with reference to the accompanying drawings.

Figure 1 is a topological structure of a new energy grid-connected inverter in an embodiment of the present invention. As can be seen from the figure, the topology of the new energy power generation unit includes DC power supply U _dc , DC side filter capacitor C _dc , three-phase full-bridge inverter circuit, filter inductor L, filter capacitor C ₁ , passive damping resistor R _C , The grid-connected equivalent resistance R _g , the grid-connected equivalent inductance L _g and the three-phase grid _ea , _eb , _ec , the DC side filter capacitor C _dc are connected in parallel between the DC source U _dc and the three-phase full-bridge inverter circuit , the three-phase full-bridge inverter circuit is connected in series between the DC side power supply U _dc and the filter inductor L. The filter capacitor C ₁ is first connected in series with the passive damping resistor R _C , and then connected in parallel between the filter inductor L and the grid-connected equivalent resistor. R _g , the grid-connected equivalent inductance L _g is connected in series between the grid-connected equivalent resistance R _g and the three-phase grid _ea , _eb , _ec . In addition, the PCC in Figure 1 is the grid connection point.

Specifically, the parameters in this embodiment are as follows: the effective value of the output AC line voltage is 380V/50Hz, the rated capacity is 100kW, the inductance value of the filter inductor L is 0.3mH, the capacitance value of the filter capacitor C ₁ is 200μF, and the new energy power generation The unit sampling frequency f _s is 10 kHz, so the sampling period T _s =100 μs.

Figure 2 is a control block diagram of the control method of the present invention. It can be seen from Figure 2 that the steps of the self-synchronized low voltage ride-through control method of the new energy power generation unit under the extremely weak network of the present invention are as follows:

Step 1, sampling and coordinate transformation.

The sampling includes collecting the following data: the voltage at the grid-connected point of the new energy power generation unit is recorded as grid-connected voltage u _oa , u _ob , u _oc , and the current at the grid-connected point of the new energy power generation unit is recorded as grid-connected current i _oa , i _ob , i _oc , the current at the filter inductor L of the new energy power generation unit is recorded as the bridge arm side inductor current i _La , i _Lb , i _Lc , the grid voltage of the new energy power generation unit is recorded as the grid voltage u _ga , u _gb , u _gc .

The coordinate transformation includes coordinate transformation of the following data: grid-connected voltage u _oa , u _ob , u _oc , grid-connected current i _oa , i _ob , i _oc , bridge arm side inductor current i _La , i _Lb , i _Lc , grid voltage u _ga , u _gb , u _gc are respectively subjected to single synchronous rotation coordinate transformation to obtain the grid-connected voltage dq component U _od , U _oq , the grid-connected current dq component I _od , I _oq , and the bridge arm side inductor current dq component I _Ld , I _Lq , grid voltage dq component U _gd , U _gq .

Step 2, use the active power calculation equation and the reactive power calculation equation to obtain the average active power P and the average reactive power Q. The active power calculation equation and the reactive power calculation equation are 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 step 2 and the active power command P ₀ given by the new energy power generation unit, the angular frequency ω of the self-synchronous control is obtained through the power angle control equation. The expression of the power angle control equation is as follows:

Among them, ω ₀ is the rated angular frequency of the new energy power generation unit when the active power command P ₀ is given, m is the power angle control droop coefficient, J is the virtual moment of inertia of the simulated synchronous generator unit, and s is the Laplace operator .

Phase angle synchronous control is performed at the end of the voltage drop, and the angular frequency ω of the self-synchronous control is integrated to obtain the output phase angle θ of the self-synchronous control; the phase angle synchronous control at the end of the voltage drop is the compensation for the output phase difference Δθ, Δθ=θ _g0 -θ ₀ , where θ _g0 is the output phase angle of the grid voltage at the end of the voltage drop, θ ₀ is the output phase angle of the self-synchronous control at the end of the voltage drop, then the expression of the output phase angle θ of the self-synchronous control as follows:

The power angle control equation shows the active power droop curve relationship and virtual inertia size of the new energy power generation unit. Among them, the virtual inertia indicates the rate of change of the system frequency. In order to ensure that the system frequency changes smoothly, a larger virtual inertia is required; however, the virtual inertia is equivalent to adding a first-order inertia link to the system. Too large a virtual inertia may cause System instability. Therefore, parameter selection requires compromise. In order to ensure the stability of the system, the inertia time constant range is τ _virtual =Jω ₀ m≤2e ^-3 s. The active power droop curve relationship in the power angle control equation includes three coefficients. The power angle control droop coefficient m represents the slope of the droop curve. The value principle is that when 100% of the active power changes, the frequency changes within 0.5Hz; given active power The command P ₀ and the corresponding rated angular frequency ω ₀ represent the positional relationship of the droop curve. The main consideration is the output frequency of the new energy grid-connected inverter when the output active power is P ₀ .

In this embodiment, the value of the power angle control droop coefficient is According to the principle of selecting the value of the inertia time constant, τ _virtual =Jω ₀ m＝1.5e ^-3 s can be obtained. J＝0.154kg·m ² is obtained. The given active power command value is P ₀ ＝100kW. At this time, the corresponding rated angle The frequency value is ω ₀ =314.16rad/s.

Step 4: According to the average reactive power Q obtained in step 2 and the reactive power command Q ₀ given by the new energy generation unit, the terminal voltage amplitude command E ^* of self-synchronous control is obtained through the reactive power control equation, and then according to the step The output phase angle θ and terminal voltage amplitude command E of the self-synchronous control obtained in 3. ^* The three-phase terminal voltage command of the self-synchronous control is obtained through the command synthesis equation.

The expressions of the reactive power control equation and command synthesis equation are as follows:

E ^* =U ₀ +n(Q ₀ -Q)

Among them, U ₀ is the rated voltage of the new energy power generation unit when the reactive power command Q ₀ is given, and n is the reactive power-voltage droop coefficient.

In this embodiment, Q ₀ =0, the corresponding U ₀ =311.13V at this time.

Step 5, according to the three-phase terminal voltage command obtained in step 4 And the grid-connected voltage u _oa , u _ob , u _oc obtained in step 1, the current command signal is obtained through the virtual impedance control equation/> The expression of the virtual impedance control equation is:

Among them, R _v is the virtual resistance and L _v is the virtual inductance.

to current command signal Perform single synchronous rotation coordinate transformation to obtain the dq component of the current command signal

In this embodiment, R _v =0.05Ω, L _v =0.52mH.

Step 6: According to the grid voltage dq components U _{gd and} U _gq obtained in step 1, the grid voltage amplitude U _g is obtained through the grid voltage amplitude calculation equation. According to the obtained grid voltage amplitude U _g and the given grid voltage amplitude The value instruction U _ref determines the voltage drop depth D at the grid connection point through the voltage drop calculation equation.

The expressions of the grid voltage amplitude calculation equation and voltage drop calculation equation are as follows:

In this embodiment,

Step 7: Obtain the current loop q-axis command when the grid voltage drops based on the reactive power compensation control equation in the low voltage ride through standard. The d-axis command of the current loop when the grid voltage drops is obtained through the limiting control equation of the current stress of the power device/>

The reactive power compensation control equation and the power device current stress limiting control equation are as follows:

Among them, K _m is the reactive power compensation coefficient, and _IN is the rated current amplitude of the new energy power generation unit.

In this embodiment, K _m =-1.5,

Step 8: According to the current loop d-axis command when the grid voltage drops obtained in step 7 And the current loop q-axis command when the grid voltage drops/> Obtain the active power command under fault through the fault power command calculation equation/> and reactive power directive/> The fault power command calculation equation is:

Step 9: According to the voltage drop depth D at the grid connection point obtained in step 6, obtain the voltage command under the fault through the fault voltage command calculation equation The fault voltage command calculation equation is:

Step 10: Perform power command switching and amplitude synchronization control based on the voltage drop depth D at the grid connection point obtained in step 6. Specifically, the power switching command is _Pref , the reactive power switching command is _Qref , and the voltage switching command is U _ref :

(1) Stable operation stage, D≥0.9, P _ref =P ₀ , Q _ref =Q ₀ , U _ref =U ₀ ;

(2) Grid voltage drop stage, D＜0.9,

(3) Grid voltage recovery stage, P _ref =P ₀ , Q _ref =Q ₀ ,

It can be seen from step 10 that during the stable operation phase, the active power command and the voltage command are not switched; during the grid voltage recovery phase, only the voltage command is switched.

Step 11, according to the dq component of the current command signal obtained in step 5 With the bridge arm side inductor current dq components I _Ld and I _Lq obtained in step 1, the control signals U _d and U _q are obtained through the current control equation. The current control equation is:

Among them, K _pi is the current loop proportional control coefficient, and K _ii is the current loop integral control coefficient.

The control signals U _d and U _q are obtained through the inverse transformation of the single synchronous rotation coordinate to obtain the control signals U _a , U _b and U _c of the new energy power generation unit, and then the three-phase control signals are generated based on the control signals U _a , U _b and U _c PWM control signal of full-bridge inverter circuit.

In this embodiment, K _pi =1.0 and K _ii =15.

In order to prove the technical effect of the invention, the invention was simulated.

Figures 3, 4, 5, and 6 respectively show the grid-connected voltage waveform, grid-connected current waveform, and bridge arm of the new energy power generation unit when the grid voltage drops by 50% under an extremely weak grid (short circuit ratio SCR = 1.2). Side inductor current d-axis component waveform and active power waveform. It can be seen from Figures 3 and 4 that the self-synchronized low voltage ride-through control method for new energy power generation units under extremely weak grids provided by the present invention can ensure the rated operation of the grid-connected voltage and grid-connected current during the normal operation stage. During the drop stage, the grid-connected voltage and grid-connected current can be ensured to operate within the rated range, and the voltage recovery stage returns to a stable operating state after experiencing a brief oscillation. It can be seen from Figures 5 and 6 that the self-synchronized low voltage ride-through control method for new energy power generation units under extremely weak grids provided by the present invention can reduce the active power output of the system when the grid voltage drops to help the grid voltage recover, thereby achieving low voltage ride-through. Voltage ride-through improves system stability.

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.