Network-formation type energy storage compensation control method for transient impact in power grid black start

Abstract

The application discloses a network-constructing type energy storage compensation control method for transient impact in power grid black start. A virtual synchronous generator is used to generate a virtual rotor angle frequency, a voltage phase and a voltage amplitude, and through coordinate transformation, d and q axis reference voltages are obtained; a module value of an unfiltered current is collected, and in combination with a preset inverter current threshold, a current-limiting virtual impedance is updated; the virtual rotor angle frequency is compensated according to the updated current-limiting virtual impedance; d axis virtual impedance voltage is obtained according to the compensated virtual rotor angle frequency, d and q axis currents and the updated current-limiting virtual impedance; the d axis virtual impedance voltage is used to correct the d axis reference voltage; the q axis reference voltage and the corrected d axis reference voltage are input into a voltage and current double closed loop controller, and finally a pulse signal is generated. The method can effectively suppress the impact overcurrent generated in the black start process, while maintaining the bus voltage deviation, and significantly improves the system stability and equipment safety in the black start process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system restoration control, in particular to a network-forming energy storage compensation control method for transient impact in black start of power grid. BACKGROUND

[0002] When a large-scale power outage occurs in the power grid, the traditional black start relies on diesel or gas generators, which has problems such as high carbon emissions and slow response speed. The network-forming energy storage system relies on renewable energy generation, and due to its fast power response and active voltage / frequency support capability, it has become the core choice of new black start power supply. However, during the initial black start, the transformer air-drop excitation inrush current (inductive impact) and the no-load line capacitance charging (capacitive impact) and other transient impact problems may cause device overcurrent, voltage instability and other risks.

[0003] Most control methods of energy storage systems do not fully consider the limitation of transient current during power grid restoration, especially the adaptability and real-time response capability in transient impact and device protection. Under steady-state conditions, some studies achieve power precision distribution through adaptive droop coefficient control, but need to obtain the given power in real time through the tie line, or use genetic algorithm to optimally adjust the parameters of the virtual impedance controller. However, the above methods ignore the power distribution and coupling phenomenon of micro sources under transient state, leading to power control failure and transient instability. SUMMARY

[0004] In view of the shortcomings of the existing control methods, the present application proposes a network-forming energy storage compensation control method for transient impact in black start of power grid. The method of the present application aims at the inductive impact current generated by transformer air-drop or motor start at the initial stage of black start, and the capacitive impact current caused by no-load line charging, and proposes an adaptive virtual impedance-based d compensation control method, which adaptively adjusts the virtual impedance according to the output current, quickly suppresses the impact current during the black start process, realizes current limiting, and corrects the power angle to solve the problem of reactive oscillation.

[0005] The technical solutions adopted by the present application are as follows:

[0006] One, a network-forming energy storage compensation control method for transient impact in black start of power grid, the network-forming energy storage compensation control method comprises the following steps:

[0007] Step 1: The virtual synchronous generator generates virtual rotor angle frequency, voltage phase and voltage amplitude according to the active power reference value and the reactive power reference value, and obtains the d-axis reference voltage and the q-axis reference voltage through coordinate transformation according to the voltage phase and the voltage amplitude.

[0008] Specifically, the filtered output current and the output voltage of the grid-connected point of the grid-forming inverter are collected in real time, and the actual active power and the actual reactive power are calculated by power calculation, and then the actual active power and the actual reactive power are input as input quantities into the virtual synchronous generator, and the virtual synchronous generator generates a virtual rotor angular frequency, a voltage phase and a voltage amplitude in combination with a preset active power reference value and a reactive power reference value; at the same time, the d-axis current, the d-axis voltage, the q-axis current and the q-axis voltage are obtained by coordinate transformation on the filtered output current and the output voltage.

[0009] Step 2: The module value of the unfiltered current is collected, and the current-limiting virtual impedance is updated in combination with the preset inverter current threshold.

[0010] Specifically, the module value of the unfiltered current is obtained according to the unfiltered current of the grid-connected point of the grid-forming inverter collected in real time.

[0011] Specifically, the total virtual impedance is composed of a nominal virtual impedance and a current-limiting virtual impedance. The nominal virtual impedance includes a nominal virtual resistance and a nominal virtual inductance for suppressing high-frequency current, and the current-limiting virtual impedance includes a current-limiting virtual resistance and a current-limiting virtual inductance.

[0012] Specifically, the updating process of the current-limiting virtual impedance is as follows:

[0013] The module value of the unfiltered current is compared with the inverter current threshold;

[0014] When the module value of the unfiltered current is less than or equal to the inverter current threshold, the current-limiting virtual resistance and the current-limiting virtual inductance are both set to 0;

[0015] When the module value of the unfiltered current is greater than the inverter current threshold, the difference between the module value of the unfiltered current and the inverter current threshold is obtained as an out-of-limit difference value, and the current-limiting virtual resistance and the current-limiting virtual inductance are calculated according to the out-of-limit difference value.

[0016] The product of the out-of-limit difference value and the preset current-limiting virtual resistance proportional gain is obtained to obtain the current-limiting virtual resistance;

[0017] The product of the current-limiting virtual resistance and the preset current-limiting virtual impedance ratio is obtained to obtain the current-limiting virtual inductance.

[0018] Step 3: The virtual rotor angular frequency is compensated according to the updated current-limiting virtual impedance and the inverter equivalent internal resistance to meet the condition that the reactive power increment is 0, i.e. no reactive oscillation occurs.

[0019] Specifically, the virtual rotor angular frequency compensation value is obtained by the following formula:

[0020] Δw=k p,δ sΔR n

[0021] wherein, Δw represents a virtual rotor angular frequency compensation value, k p,δ represents a preset virtual rotor angular frequency compensation coefficient, s represents in a complex frequency domain, ΔR n represents an equivalent internal resistance of an inverter.

[0022] Step 4: obtaining a d-axis virtual impedance voltage according to the compensated virtual rotor angular frequency, the d-axis current, the q-axis current and the updated current-limiting virtual impedance.

[0023] Specifically, the d-axis virtual impedance voltage is obtained by the following formula:

[0024] V d,VI =R VI I od s / (s+w c,hpf )-(w+Δw)L VI I oq s / (s+w c,hpf )+ΔR VI I od -(w+Δw)ΔL VI I oq

[0025] wherein, V d,VI represents the d-axis virtual impedance voltage, R VI represents a nominal virtual resistance, I od represents the d-axis current, s represents in a complex frequency domain, w c,hpf represents a cut-off frequency of a first-order high-pass filter, w represents a virtual rotor angular frequency of an analog virtual synchronous generator, L VI represents a nominal virtual inductance, I oq represents the q-axis current, ΔR VI represents a current-limiting virtual resistance, Δw represents a virtual rotor angular frequency compensation value, ΔL VI represents a current-limiting virtual inductance.

[0026] Step 5: correcting the d-axis reference voltage using the d-axis virtual impedance voltage to obtain a corrected d-axis reference voltage.

[0027] Specifically, the sum of the d-axis virtual impedance voltage and the d-axis reference voltage is taken as the corrected d-axis reference voltage.

[0028] Step 6: inputting the q-axis reference voltage and the corrected d-axis reference voltage, and the d-axis current, the q-axis current, the d-axis voltage and the q-axis voltage into a voltage-current double closed loop controller to finally generate a pulse signal, wherein the pulse signal is used to control a power switch tube of a grid-connected inverter.

[0029] Further, in a specific implementation, the pulse signal is output to the grid-connected inverter.

[0030] Two, a network type energy storage compensation control system for transient impact in power grid black start, for executing the network type energy storage compensation control method

[0031] The network type energy storage compensation control system comprises:

[0032] A virtual synchronous generator is configured to collect the filtered output current and output voltage of the grid-connected point of the network type inverter in real time, and further generate a virtual rotor angle frequency, a voltage phase and a voltage amplitude, and a d-axis current, a d-axis voltage, a q-axis current and a q-axis voltage.

[0033] An adaptive virtual impedance module is configured to collect the unfiltered current of the grid-connected point of the network type inverter in real time, and update the current-limiting virtual impedance according to the modulus of the unfiltered current and a preset inverter current threshold.

[0034] A power angle correction module is configured to compensate the virtual rotor angle frequency according to the updated current-limiting virtual impedance and the equivalent internal resistance of the inverter.

[0035] A current-limiting control module is configured to obtain a d-axis virtual impedance voltage according to the compensated virtual rotor angle frequency, the d-axis current, the q-axis current and the updated current-limiting virtual impedance, and further correct the d-axis reference voltage.

[0036] A voltage-current double closed-loop controller is configured to generate three-phase PWM modulation waves according to the corrected d-axis reference voltage and q-axis reference voltage, and the d-axis current, the q-axis current, the d-axis voltage and the q-axis voltage.

[0037] A pulse width modulator is configured to generate pulse signals according to the three-phase PWM modulation waves and output the pulse signals to the network type inverter.

[0038] The present application has the following advantages:

[0039] 1. In the control system of the present application, the network type energy storage system is configured with a virtual synchronous generator, the virtual synchronous generator generates a voltage phase through the active-frequency loop to simulate the rotor motion equation, and generates a voltage amplitude through the reactive-voltage loop to simulate the potential characteristic, the voltage phase and the voltage amplitude are connected to the voltage-current double closed-loop controller with virtual impedance after coordinate transformation, and the autonomous frequency regulation and voltage regulation and transient support capability in the black start process are realized.

[0040] 2. The present application adjusts the d-axis equivalent output impedance of the network type inverter by using the adaptive virtual impedance to realize current-limiting control in view of the inductive impact current generated by transformer air drop, motor start and the like in the initial stage of power grid black start and the capacitive impact current caused by no-load line charging, and simultaneously performs power angle correction, thereby suppressing the reactive oscillation caused by the increase of virtual impedance.

[0041] In summary, the present application combines adaptive virtual additional impedance and power angle correction to dThe shaft compensation control effectively copes with transient impact such as transformer excitation inrush current and no-load line charging current in the process of power grid black start, and significantly improves the system stability and equipment safety in the process of black start. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is the topology of the grid-forming inverter and its control system in the application;

[0043] Figure 2 is the adaptive virtual impedance and power angle correction in the application dq the shaft control flow chart;

[0044] Figure 3 is the grid-forming simulation curve without adaptive virtual impedance and power angle correction in the no-load line charging scenario in embodiment 1 of the application;

[0045] Figure 4 is the grid-forming simulation curve with adaptive virtual impedance and power angle correction in the no-load line charging scenario in embodiment 1 of the application;

[0046] Figure 5 is the grid-forming simulation curve without adaptive virtual impedance and power angle correction in the transformer no-load closing scenario in embodiment 3 of the application;

[0047] Figure 6 is the grid-forming simulation curve with adaptive virtual impedance and power angle correction in the transformer no-load closing scenario in embodiment 3 of the application;

[0048] Figure 7 is the grid-forming simulation curve without adaptive virtual impedance and power angle correction in the motor starting scenario in embodiment 3 of the application;

[0049] Figure 8 is the grid-forming simulation curve with adaptive virtual impedance and power angle correction in the motor starting scenario in embodiment 3 of the application. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the application.

[0051] The application provides a grid-forming energy storage compensation control method for transient impact in power grid black start. The method comprises the following steps:

[0052] Step 1: generating a virtual rotor angular frequency, a voltage phase and a voltage amplitude according to the active power reference value and the reactive power reference value using the virtual synchronous generator, and obtaining a d-axis reference voltage and a q-axis reference voltage by coordinate transformation according to the voltage phase and the voltage amplitude.

[0053] Specifically, in this step, the filtered output current and the output voltage of the grid-connected inverter grid-connected point are collected in real time, and the actual active power and the actual reactive power are obtained by power calculation, and then the actual active power and the actual reactive power are input into the virtual synchronous generator as input quantities, and the virtual synchronous generator generates a virtual rotor angular frequency, a voltage phase and a voltage amplitude in combination with the preset active power reference value and the reactive power reference value; at the same time, the d-axis current, the d-axis voltage, the q-axis current and the q-axis voltage are obtained by coordinate transformation on the filtered output current and the output voltage.

[0054] Step 2: collecting the modulus of the unfiltered current and updating the current-limiting virtual impedance in combination with the preset inverter current threshold. The unfiltered current is the unfiltered current of the grid-connected inverter grid-connected point collected in real time. The current-limiting virtual impedance includes a current-limiting virtual resistance and a current-limiting virtual inductance.

[0055] In this step, the process of the current-limiting virtual impedance is as follows:

[0056] Comparing the modulus of the unfiltered current with the inverter current threshold;

[0057] When the modulus of the unfiltered current is less than or equal to the inverter current threshold, the current-limiting virtual resistance and the current-limiting virtual inductance are both set to 0;

[0058] When the modulus of the unfiltered current is greater than the inverter current threshold, the difference between the modulus of the unfiltered current and the inverter current threshold is obtained as an out-of-limit difference value, and the current-limiting virtual resistance and the current-limiting virtual inductance are calculated according to the out-of-limit difference value.

[0059] The calculation process of the current-limiting virtual resistance and the current-limiting virtual inductance is as follows:

[0060] The product of the out-of-limit difference value and the preset current-limiting virtual resistance proportional gain is obtained to obtain the current-limiting virtual resistance;

[0061] The product of the current-limiting virtual resistance and the preset current-limiting virtual impedance ratio is obtained to obtain the current-limiting virtual inductance.

[0062] In summary, the current-limiting virtual resistance and the current-limiting virtual inductance can be obtained by the following equation:

[0063] ΔR VI =MAX(k p,Rvi [(I Ld,ref 2 +I Lq,ref 2) 1 / 2 -I thresh ],0)

[0064] ΔL VI =ΔR VI (X / R)

[0065] In the formula, ΔR VI It is a current-limiting virtual resistor, ΔL VI It is a current-limiting virtual inductor, k p,Rvi It is the current-limiting virtual resistance proportional gain, I Ld,ref It is the rated filter inductor current I Labc The d-axis current reference value obtained by coordinate transformation, I Lq,ref It is the rated filter inductor current I Labc The q-axis current reference value obtained by coordinate transformation, I thresh X is the inverter current threshold, MAX() is the maximum value function, and X / R is the current-limiting virtual impedance ratio.

[0066] Furthermore, the rated current is calculated based on the inverter capacity and rated phase voltage. The inverter current threshold I set in this embodiment of the invention... thresh It is 1.5 times the rated current, serving as the upper limit for short-term overload capacity.

[0067] Step 3: Compensate the virtual rotor angular frequency based on the updated current-limiting virtual impedance and the inverter's equivalent internal resistance. In this step, the virtual rotor angular frequency compensation value is obtained using the following formula:

[0068] Δw=k p,δ sΔR n

[0069] In the formula, Δw represents the virtual rotor angular frequency compensation value, and k p,δ This represents the preset virtual rotor angular frequency compensation coefficient, and s represents ΔR in the complex frequency domain. n This represents the equivalent internal resistance of the inverter.

[0070] Step 4: Based on the compensated virtual rotor angular frequency, d-axis current, q-axis current, and updated current-limiting virtual impedance, obtain the d-axis virtual impedance voltage. In this step, the d-axis virtual impedance voltage is obtained using the following formula:

[0071] V d,VI =R VI I od s / (s+w c,hpf )-(w+Δw)L VI I oq s / (s+w c,hpf )+ΔR VI I od -(w+Δw)ΔL VI Ioq

[0072] wherein, V d,VI represents a d-axis virtual impedance voltage, R VI represents a nominal virtual resistance, I od represents a d-axis current, s represents in a complex frequency domain, w c,hpf represents a cut-off frequency of a first-order high-pass filter, w represents a virtual rotor angular frequency of the analog virtual synchronous generator, L VI represents a nominal virtual inductance, I oq represents a q-axis current, ΔR VI represents a current-limiting virtual resistance, Δw represents a virtual rotor angular frequency compensation value, ΔL VI represents a current-limiting virtual inductance.

[0073] Step 5: correcting the d-axis reference voltage using the d-axis virtual impedance voltage to obtain a corrected d-axis reference voltage.

[0074] Specifically: taking the sum of the d-axis virtual impedance voltage and the d-axis reference voltage as the corrected d-axis reference voltage.

[0075] Step 6: inputting the corrected d-axis reference voltage and the q-axis reference voltage, as well as the d-axis current, the q-axis current, the d-axis voltage and the q-axis voltage into a voltage-current double closed loop controller to finally generate a pulse signal and output to the grid-connected inverter. The pulse signal is used to control the power switch tube of the grid-connected inverter.

[0076] The application also provides a grid-connected energy storage compensation control system for transient impact in black start of a power grid, which is used to execute the grid-connected energy storage compensation control method as described above.

[0077] Specifically, the grid-connected energy storage compensation control system comprises:

[0078] a virtual synchronous generator, which is used to collect a filtered output current and an output voltage of a grid-connected inverter in real time, and further generate a virtual rotor angular frequency, a voltage phase and a voltage amplitude, as well as a d-axis current, a d-axis voltage, a q-axis current and a q-axis voltage;

[0079] an adaptive virtual impedance module, which is used to collect an unfiltered current of the grid-connected inverter in real time, and update a current-limiting virtual impedance according to a modulus value of the unfiltered current and a preset inverter current threshold value;

[0080] a power angle correction module, which is used to compensate the virtual rotor angular frequency according to the updated current-limiting virtual impedance and an inverter equivalent internal resistance;

[0081] a current-limiting control module, which is used to obtain a d-axis virtual impedance voltage according to the compensated virtual rotor angular frequency, the d-axis current, the q-axis current and the updated current-limiting virtual impedance, and further correct a d-axis reference voltage;

[0082] a voltage-current double-loop controller for generating three-phase PWM modulation waves according to the corrected d-axis reference voltage and q-axis reference voltage, and the d-axis current, q-axis current, d-axis voltage and q-axis voltage;

[0083] a pulse width modulator for generating pulse signals according to the three-phase PWM modulation waves and outputting to the grid-connected inverter.

[0084] The principles of the method of the present application will be further described below Figures 1-2 The principles of the method of the present application will be further described below

[0085] In the method of the present application, the transient impact in black start is specifically manifested as inductive impact current represented by excitation inrush current generated by transformer air drop and motor start, and capacitive impact current represented by no-load line charging.

[0086] Please refer to Figure 1 In the grid-connected inverter topology and its control system schematic diagram, the energy storage battery uses a bidirectional DC-DC converter to complete the mutual exchange and storage of energy. The system adopts a voltage-current double-loop control strategy. When the system is charging, the BUCK circuit stores the excess electrical energy to the battery in a constant current manner. When the system is discharging, the BOOST circuit structure enables the battery to release electrical energy to the system in a constant voltage manner. The grid-connected energy storage inverter part adopts a VSG control strategy. The power calculation link collects the voltage U abc and current I oabc at the grid connection point to calculate the actual power (actual active power P and actual reactive power Q). Through the active-frequency control loop and the reactive-voltage control loop of the VSG, the voltage vector reference value (voltage phase θ and voltage amplitude E) is obtained. After coordinate transformation, U dref , U qref enter the voltage-current double-loop control to control the output voltage (d, q-axis voltage V d , V q ) and the inductance current (d, q-axis current I od , I oq ) of the grid-connected inverter. Finally, pulse signals are obtained through pulse width modulation (PWM), and the pulse signals drive the switching tubes of the grid-connected energy storage inverter.

[0087] In the active-frequency control loop part, combined with the given output active power reference value P ref , the simplified equation (3) is obtained according to the swing equation (1) containing virtual inertia and damping factor and the related regulator equation (2):

[0088] P in -P out=Jw(dw / dt)+D base [(w-w N ) / w nom ] (1)

[0089] P in =P ref -k p S base [(w-w N ) / w nom ] (2)

[0090] P ref -P=Jw(dw / dt)+(k p +D)(w-w N ) (3)

[0091] In the formula, P in is the virtual input power on the generator shaft, P out is the output power of the grid-connected energy storage inverter, J is the virtual system inertia, D is the virtual damping coefficient, S base is the rated power of the inverter, w is the virtual rotor angular frequency, w N is the angular frequency of the collected grid-connected point voltage, w nom is the nominal angular frequency, dw / dt is the derivative of the rotor angular velocity w with respect to time, i.e., the angular acceleration, k p is the pre-selected droop coefficient of the active frequency loop, P is the actual active power, and P ref is the active power reference value.

[0092] In the reactive-voltage control loop part, combined with the given reactive power reference value Q ref , voltage regulation and reactive power support can be achieved through the voltage-reactive power-based equation (4):

[0093] U=U N -k q (Q-Q ref ) (4)

[0094] In the formula, k q is the pre-selected droop coefficient of the reactive voltage loop, K pe and K ie are the time constants of the Gillie, Q ref is the reactive power reference value, Q is the actual reactive power value collected by the VSG system at the Point of Common Coupling (PCC), U is the actual voltage output by the virtual synchronous machine control, U is an intermediate variable, E is the voltage output to the outside, indicating the same quantity; U N is the rated grid voltage, and U abc is the actually measured inverter output voltage.

[0095] Please refer to Figure 2 , the present application to coordinate transformation generated U dref compensation and generate U dref* , U dref* , U qref input voltage and current double closed loop controller. In the compensation process, if the grid connected point of the grid forming inverter is used as the filtered output current I oabc As the current limiting reference current will result in obvious oscillation phenomenon, so the unfiltered current of the grid connected point of the grid forming inverter I Labc The module value is collected, and I Ldq Is obtained through coordinate transformation, and compared with the inverter current threshold I thresh .

[0096] The compensation process is as follows:

[0097] When the detected current I Ldq Does not exceed the threshold I thresh , only the nominal virtual impedance (R VI , L VI ) exists in the line, dq The output current (I od , I oq ) under the coordinate axis is high-pass filtered and shows high-order inhibition voltage drop on the impedance, that is, after high-pass filtering, the transient current is allowed to pass through, but the steady-state virtual impedance voltage drop caused by the positive sequence fundamental current (direct current in synchronous dq coordinate system) is eliminated;

[0098] When the detected current I Ldq Exceeds the threshold I thresh , the current limiting virtual impedance (ΔR VI , ΔL VI ) is put into, and the total virtual impedance (R VI 0 , L VI 0 ) is composed of the nominal virtual impedance (R VI , L VI ) and the current limiting virtual impedance (ΔR VI , ΔL VI ). The current limiting virtual impedance takes effect on the current in the full frequency domain, that is, it suppresses the normal (non-high-pass) overcurrent of the inverter.

[0099] The above process can be represented by equations (6), (7) and (8):

[0100] R VI 0 = R VI + ΔR VI , L VI0 = L VI +ΔL VI (6)

[0101] ΔR VI =MAX(k p,Rvi [(I Ld,ref 2 +I Lq,ref 2 ) 1 / 2 -I thresh ],0) (7)

[0102] ΔL VI =ΔR VI (X / R) (8)

[0103] where R VI 0 is the total virtual resistance, L VI 0 is the total virtual inductance, R VI is the nominal virtual resistance, L VI is the nominal virtual inductance, ΔR VI is the current limiting virtual resistance, ΔL VI is the current limiting virtual inductance, k p,Rvi is the current limiting virtual resistance proportional gain, I Ld,ref is the rated filter inductor current I Labc ref is the d-axis current reference obtained by coordinate transformation, I Lq,ref is the rated filter inductor current I Labc qref is the q-axis current reference obtained by coordinate transformation, I thresh is the inverter current threshold, MAX() is the maximum function, and X / R is the current limiting virtual impedance ratio.

[0104] For equations (7) and (8), the appropriate current limiting gain k p,Rvi and X / R are chosen to limit the current magnitude to within the threshold during a short circuit fault. For a three-phase short circuit fault, the virtual impedance voltage drop should be equal to the voltage magnitude command:

[0105] V0=I MAX Z VI =I MAX [R VI 2 +(w0L VI ) 2 ] 1 / 2

[0106] where V0represents the maximum voltage drop produced by the virtual impedance, I MAX represents the maximum current magnitude required, and Z VIEquivalent magnitude of virtual impedance (resultant impedance of nominal virtual resistance and inductance), w0 represents rated angular frequency of system, equivalent to nominal angular frequency w nom , R VI is nominal virtual resistance, L VI is nominal virtual inductance.

[0107] In addition, the virtual resistance increases, which causes reactive power oscillation of the inverter, and for this, real-time power angle is compensated to ensure that the system power can maintain power balance under any transient impact, i.e., the reactive power increment is 0. In the method of the application, the power angle is corrected according to the following equation, and the reference voltage is calculated by using the new power angle, which can offset the reactive oscillation caused by the increase of the virtual impedance.

[0108] Δw=k p,δ sΔR n

[0109] In the equation, Δw represents virtual rotor angular frequency compensation value, k p,δ represents preset virtual rotor angular frequency compensation coefficient, s represents in complex frequency domain, ΔR n represents equivalent internal resistance of the inverter.

[0110] d The shaft virtual impedance current limit works by reducing the voltage reference to prevent the voltage controller from commanding an excessive current reference, which can be represented by the following equation:

[0111] V d,VI =R VI I od s / (s+w c,hpf )-(w+Δw)L VI I oq s / (s+w c,hpf )+ΔR VI I od -(w+Δw)ΔL VI I oq

[0112] In the equation, V d,VI represents d-axis virtual impedance voltage, R VI represents nominal virtual resistance, I od represents d-axis current, s represents in complex frequency domain, w c,hpf represents cut-off frequency of first-order high-pass filter, w represents virtual rotor angular frequency, L VI represents nominal virtual inductance, I oq represents q-axis current, ΔR VI represents current-limiting virtual resistance, Δw represents virtual rotor angular frequency compensation value, ΔL VI represents current-limiting virtual inductance.

[0113] The specific implementation of the present application is as follows:

[0114] Example 1

[0115] This embodiment verifies the control effect of adding adaptive virtual impedance and power angle correction in the no-load line charging scene. This embodiment uses the Simulink simulation platform to build a grid-connected energy storage control model, and the simulation model is shown in Table 1. The simulation time is set to 1s, and the 0.5s is put into the 100km no-load line, and the energy storage system charges the no-load line.

[0116] Table 1 Main simulation parameters

[0117] Parameter Value Parameter Value DC bus voltage / V 700 J / kg-m 2 ]]> 3.36 Rated capacity / MW 3 D / N·m·s·rad -1 ]]> 10.24 Sampling frequency Ts / HZ 200000 Nominal virtual resistance / Ω 5 Filter inductance / mH 4 Nominal virtual inductance / mH 25.61 Filter capacitance / uF 400 Current-limiting virtual impedance ratio X / R 5 Current loop proportional coefficient ki 609.07 Current limiting virtual resistance proportional gain k p,Rvi ]]> 0.098 Voltage loop proportional coefficient ku 17.07 I thresh ]] 10

[0118] See Figure 3 and Figure 4 , the grid-connected inverter without adaptive virtual impedance and power angle correction has an under-damped characteristic at the moment of capacitive impact, and the three-phase voltage drops from 388.2V (line voltage effective value) to about 324V in the transient process. The maximum current is the B-phase overcurrent, which is 816.2A (overrun amount 29.1%). Power characteristic analysis shows that the active power increases from 95.5kW to 130.7kW in 86ms, with a transient overrun of 59.72%, and the reactive power increases from 0kW to 302.5kW, with a dynamic overrun of 9.83%, exposing the inherent defects of traditional grid-connected control method in transient stability.

[0119] Under the method of the present application, the dynamic characteristics of the system are significantly improved, and the instantaneous drop amplitude of the three-phase voltage at the initial stage of disturbance is significantly reduced and quickly recovers to the 324V stable operation interval within 50ms. The maximum transient overcurrent A-phase is 715.2A, with an overrun amount of 12.5%, and the power characteristic analysis shows that the active power and reactive power remain consistent before and after the change of control strategy. Under the same no-load line input working condition, the active power overrun is 49.3%, and the reactive power achieves zero overrun.

[0120] Example 2

[0121] This embodiment verifies the control effect of adding adaptive virtual impedance and power angle correction in the transformer no-load closing scene.

[0122] See Figure 5 and Figure 6, the system presents significant transient instability characteristics in the no-load transformer excitation inrush impact moment: the three-phase voltage drops from the initial value 382.6V (line voltage effective value) to 318.3V (drop amplitude is 16.8%), the maximum overcurrent is C-phase excitation inrush, the peak value is 733.1A, and the overshoot is 14.3%. The power dynamic response analysis shows that the active power appears a dynamic overshoot of 10.27% under the working condition, and the reactive power overshoot is 3.7%, verifying the influence of inductive impact on system energy balance.

[0123] Under the method of the application, the maximum impact current is reduced to 665.8A, and the transient current overshoot phenomenon is completely eliminated, the voltage dynamic recovery process is significantly optimized, and the three-phase voltage quickly rises to 376V in the stable operation interval within 20ms after the disturbance. By comparing the power curve, the addition of adaptive virtual impedance and power angle correction control reduces the power peak at the inductive impact moment, the active power overshoot is 6.08%, the reactive power overshoot is 1.5%, effectively suppresses the power oscillation caused by inductive impact, and improves the load carrying capacity of the inverter. In addition, after the system enters the steady state, the control system gradually exits the current limiting control, and does not affect the original power distribution.

[0124] Embodiment 2

[0125] In this embodiment, the control effect of adding adaptive virtual impedance and power angle correction in the motor starting scene is verified. The simulation duration is set to 1s, and a motor is put into the system at 0.5s.

[0126] Please refer to Figure 7 and Figure 8 , the network type inverter without adaptive virtual impedance and power angle correction presents a three-phase voltage transient overshoot from the rated value 381.5V to 439.1V (overshoot amplitude is 15.09%) under instantaneous impact, and then enters a 350V quasi-steady state operation interval. The impact current peak values of B / C phases are 918.6A / 929.8A, the dynamic overshoot is 35%, the active power overshoot is 57.45%, the reactive power is increased by 243.8kVar, and the overshoot is 11.19%.

[0127] Under the method of the application, the system has good transient robustness, the three-phase voltage presents a temporary drop at the disturbance moment, and is restored to 382.5V within 10ms, the maximum impact current is limited to 780.9A, the overshoot is reduced to 13.4%, and by comparing the power characteristic curve, the active power overshoot is 47.9%, the reactive power is increased by 211.1kVar, and the overshoot is 0.0582%, which shows that there is a significant dynamic overcurrent suppression effect and transient stability.

[0128] In summary, the method can effectively suppress the impact current generated in the black start process to the range of 1.134 p.u. rated current, while maintaining the bus voltage deviation of no more than ±5%, reducing the impact of active and reactive power on the equipment, and significantly improving the system stability and equipment safety in the black start process.

[0129] The above specific embodiments are used to explain and illustrate the present application, rather than limiting the present application, and any modifications and changes made to the present application within the spirit and protection scope of the claims of the present application all fall within the protection scope of the present application.

Claims

1. A network configuration type energy storage compensation control method for transient impact in power grid black start, characterized in that, The method comprises the following steps: Step 1: a virtual synchronous generator generates a virtual rotor angle frequency, a voltage phase and a voltage amplitude, and through coordinate transformation, a d-axis reference voltage and a q-axis reference voltage are obtained; Step 2: the modulus of an unfiltered current is collected, and a preset inverter current threshold is combined to update a current-limiting virtual impedance; Step 3: the virtual rotor angle frequency is compensated according to an equivalent internal resistance of the inverter to meet a reactive power increment of 0; Step 4: a d-axis virtual impedance voltage is obtained according to the compensated virtual rotor angle frequency, a d-axis current, a q-axis current and the updated current-limiting virtual impedance; Step 5: the d-axis virtual impedance voltage is used to correct the d-axis reference voltage to obtain a corrected d-axis reference voltage; Step 6: the q-axis reference voltage and the corrected d-axis reference voltage are input into a voltage-current double closed-loop controller to finally generate a pulse signal.

2. The network configuration type energy storage compensation control method for transient impact in power grid black start according to claim 1, characterized in that: The updating process of the current-limiting virtual impedance comprises the following steps: When the modulus of the unfiltered current is less than or equal to the inverter current threshold, the current-limiting virtual resistance and the current-limiting virtual inductance are both set to 0; When the modulus of the unfiltered current is greater than the inverter current threshold, a difference value between the modulus of the unfiltered current and the inverter current threshold is obtained as an out-of-limit difference value, and the current-limiting virtual resistance and the current-limiting virtual inductance are calculated according to the out-of-limit difference value.

3. The network configuration type energy storage compensation control method for transient impact in power grid black start according to claim 2, characterized in that: The product of the out-of-limit difference value and a preset current-limiting virtual resistance proportional gain is obtained as the current-limiting virtual resistance, and the product of the current-limiting virtual resistance and a preset current-limiting virtual impedance ratio is obtained as the current-limiting virtual inductance.

4. The network configuration type energy storage compensation control method for transient impact in power grid black start according to claim 1, characterized in that: In step 3, the virtual rotor angle frequency compensation value is obtained through the following formula: Δw = k p,δ sΔR n In the formula, Δw represents a virtual rotor angular frequency compensation value, k p,δ represents a virtual rotor angular frequency compensation coefficient, s represents in the complex frequency domain, ΔR n represents an equivalent internal resistance of an inverter.

5. The network configuration type energy storage compensation control method for transient impact in power grid black start according to claim 1, characterized in that: In step 4, the d-axis virtual impedance voltage is obtained through the following formula: V d,VI =R VI I od s / (s+w c,hpf )-(w+Δw)L VI I oq s / (s+w c,hpf )+ΔR VI I od -(w+Δw)ΔL VI I oq where V d,VI represents a d-axis virtual impedance voltage, R VI represents a nominal virtual resistance, I od represents a d-axis current, s represents a complex frequency domain, w c,hpf represents a cut-off frequency of a first-order high-pass filter, w represents a virtual rotor angular frequency of the virtual synchronous generator, L VI represents a nominal virtual inductance, I oq represents a q-axis current, ΔR VI represents a current-limiting virtual resistance, Δw represents a virtual rotor angular frequency compensation value, ΔL VI represents a current-limiting virtual inductance.

6. The network configuration type energy storage compensation control method for transient impact in grid black start according to claim 1, characterized in that: In step 5, the sum of the d-axis virtual impedance voltage and the d-axis reference voltage is taken as the corrected d-axis reference voltage.

7. The network configuration type energy storage compensation control method for transient impact in grid black start according to claim 1, characterized in that: In step 1, the filtered output current and output voltage of the grid-connected inverter are collected in real time, and the actual active power and actual reactive power are calculated through power calculation and input into the virtual synchronous generator as input quantities, and the virtual synchronous generator generates the virtual rotor angle frequency, the voltage phase and the voltage amplitude in combination with the preset active power reference value and the reactive power reference value; at the same time, the d-axis current, the d-axis voltage, the q-axis current and the q-axis voltage are obtained through coordinate transformation of the filtered output current and output voltage; In step 2, the unfiltered current of the grid-connected inverter is collected in real time, and the modulus of the unfiltered current is obtained; In step 6, the pulse signal is output to the grid-connected inverter.

8. A grid-forming energy storage compensation control system for black start transient impact of power grid, for performing the grid-forming energy storage compensation control method according to any one of claims 1-7, characterized in that, It comprises: a virtual synchronous generator, which is used to collect the filtered output current and output voltage of the grid-connected inverter in real time, and further generate the virtual rotor angle frequency, the voltage phase and the voltage amplitude, and the d-axis current, the d-axis voltage, the q-axis current and the q-axis voltage; an adaptive virtual impedance module, which is used to collect the unfiltered current of the grid-connected inverter in real time, and update the current-limiting virtual impedance according to the modulus of the unfiltered current and a preset inverter current threshold; a power angle correction module, which is used to compensate the virtual rotor angle frequency according to the equivalent internal resistance of the inverter; The current limiting control module is configured to obtain a d-axis virtual impedance voltage according to the compensated virtual rotor angular frequency, the d-axis current, the q-axis current and the updated current limiting virtual impedance, and correct the d-axis reference voltage; The voltage and current double closed loop controller is configured to generate three-phase PWM modulation waves according to the corrected d-axis reference voltage and q-axis reference voltage, and the d-axis current, the q-axis current, the d-axis voltage and the q-axis voltage. The pulse width modulator is configured to generate a pulse signal according to the three-phase PWM modulation waves and output the pulse signal to the grid-connected inverter.

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