A method and system for actively supporting transient reactive power of new energy under asymmetric fault

Abstract

The present invention belongs to the technical field of renewable energy power generation, and discloses a method and system for actively supporting transient reactive power of renewable energy under asymmetric faults. The method includes: performing dq coordinate transformation and positive-negative sequence decoupling on the three-phase output current and grid connection point voltage of the renewable energy grid-connected system, and obtaining d-axis positive-negative sequence current components, q-axis positive-negative sequence current components, and grid connection point positive-negative sequence voltage; performing decoupling control on the d-axis and q-axis positive-negative sequence current components, respectively, and using different control targets in different control stages, thereby achieving dynamic support for the grid voltage as a whole, reducing the asymmetry and drop depth of the grid voltage, and thus enhancing the stability of the renewable energy grid-connected system under asymmetric faults. The present invention also provides a system for actively supporting transient reactive power of renewable energy under asymmetric faults. The present invention can achieve stable operation of the renewable energy grid-connected system under asymmetric faults.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy power generation, and more specifically, relates to a method and system for actively supporting transient reactive power of renewable energy under asymmetric faults. Background Art

[0002] Due to the low inertia of new energy, the inability to provide frequency support, and strong random volatility, the large-scale access of new energy such as wind and solar power leads to safety and stability problems in the power grid. One of the common safety problems is that the access of new energy to the power grid leads to asymmetric faults in the power grid, resulting in large-scale power outages. Therefore, the stability and optimization control of the new energy grid-connected system under asymmetric faults are crucial.

[0003] At present, the stability control strategy of the new energy power generation system under asymmetric faults in the power grid generally controls the positive sequence component in the power grid; however, asymmetric faults will introduce negative sequence components in the power grid, which will cause errors in the phase obtained by the phase-locked loop in the control strategy, resulting in all electrical physical quantities (such as stator voltage, rotor current, etc.) appearing as a superposition of DC and double power frequency components in the two-phase rotating coordinate system, which has a great impact on new energy equipment. In addition, the existing control strategy cannot generate inductive reactive power to the power grid under asymmetric faults, and cannot support the power grid voltage, which may cause the power grid voltage to drop further during the fault, increasing the risk of power grid voltage collapse. Therefore, the existing new energy control strategy is difficult to adapt to the complex working conditions under asymmetric faults. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method and system for active support of transient reactive power of new energy under asymmetric faults, which aims to improve the stability of the new energy grid-connected system under asymmetric faults.

[0005] To achieve the above object, according to a first aspect of the present invention, a method for actively supporting transient reactive power of new energy under an asymmetric fault is provided, comprising:

[0006] The three-phase output current and grid connection point voltage of the new energy grid-connected system are transformed into dq coordinates and positive and negative sequence decoupling is performed to obtain the d-axis positive and negative sequence current components Id_p and Id_n, the q-axis positive and negative sequence current components Iq_p and Iq_n, and the grid connection point positive and negative sequence voltage U t_p , U t_n ;

[0007] When an asymmetric fault occurs or continues, Id_p, Id_n, Iq_p, and Iq_n are controlled, including:

[0008] The preset d-axis positive and negative sequence current reference signals are respectively used as actual reference signals, and the d-axis positive and negative sequence current error signals are obtained by making a one-to-one difference with Id_p and Id_n, and the d-axis positive and negative sequence current error signals are fed back and controlled to obtain the d-axis positive and negative sequence voltages Ud_p and Ud_n;

[0009] When an asymmetric fault occurs, the preset q-axis positive and negative sequence current reference signals are used as actual reference signals. During the duration of the asymmetric fault, the positive and negative sequence current reference signals are respectively based on U t_p , U t_n The q-axis positive and negative sequence current reference signals of voltage control are obtained as actual reference signals, and the q-axis positive and negative sequence current error signals are obtained by one-to-one difference with Iq_p and Iq_n. After feedback control, the q-axis positive and negative sequence voltages Uq_p and Uq_n are obtained.

[0010] After the dp coordinate inverse transformation and synthesis of Ud_p, Uq_p, Ud_n and Uq_n, they are converted into PWM signals to control the new energy grid-connected system and complete the transient reactive active support.

[0011] Furthermore, based on U t_p , U t_n Obtain the q-axis positive and negative sequence current reference signals for voltage control, including:

[0012] Will U t_p , U t_n After making a difference with the zero-sequence voltage Ut_0 of the grid-connected point, the positive and negative sequence voltage error signals of the grid-connected point are obtained; after signal conditioning, the positive and negative sequence voltage error signals of the grid-connected point are integrated to obtain the q-axis positive and negative sequence current reference signals of the voltage control.

[0013] Furthermore, when the new energy grid-connected system is in the normal operation stage, Id_p, Id_n, Iq_p, and Iq_n are controlled, including:

[0014] The d and q axis positive sequence current reference signals of active and reactive power control are used as actual reference signals, and the d and q axis positive sequence current error signals are obtained by one-to-one difference with Id_p and Iq_p, and the d and q axis positive sequence voltages Ud_p and Uq_p are obtained after feedback control;

[0015] Among them, the d-axis positive sequence current reference signal for active and reactive control is obtained as follows:

[0016] After subtracting the active and reactive reference signals of the new energy stator side from the active and reactive signals of the stator side one by one, the active and reactive error signals of the stator side are obtained; the active and reactive error signals of the stator side are fed back to control the reference signals of the d and q axis positive sequence currents of the active control;

[0017] Using 0 as the actual reference signal, and subtracting it from Id_n and Iq_n respectively, we get the d and q axis negative sequence current error signals, and after feedback control, we get the d and q axis negative sequence voltages Ud_n and Uq_n.

[0018] Furthermore, the feedback control is PI or PID control.

[0019] According to a second aspect of the present invention, there is provided a new energy transient reactive active support system under an asymmetric fault, comprising:

[0020] The positive and negative sequence decoupling module is used to perform dq coordinate transformation and positive and negative sequence decoupling on the three-phase output current and grid connection point voltage of the new energy grid-connected system, and obtain the d-axis positive and negative sequence current components Id_p and Id_n, the q-axis positive and negative sequence current components Iq_p and Iq_n, and the grid connection point positive and negative sequence voltage U t_p , U t_n ;

[0021] The control module is used to control Id_p, Id_n, Iq_p, and Iq_n when an asymmetric fault occurs or during the duration of the asymmetric fault, including:

[0022] The preset d-axis positive and negative sequence current reference signals are respectively used as actual reference signals, and the d-axis positive and negative sequence current error signals are obtained by making a one-to-one difference with Id_p and Id_n, and the d-axis positive and negative sequence current error signals are fed back and controlled to obtain the d-axis positive and negative sequence voltages Ud_p and Ud_n;

[0023] When an asymmetric fault occurs, the preset q-axis positive and negative sequence current reference signals are used as actual reference signals. During the duration of the asymmetric fault, the positive and negative sequence current reference signals are respectively based on U t_p , U t_n The q-axis positive and negative sequence current reference signals of voltage control are obtained as actual reference signals, and the q-axis positive and negative sequence current error signals are obtained by one-to-one difference with Iq_p and Iq_n. After feedback control, the q-axis positive and negative sequence voltages Uq_p and Uq_n are obtained.

[0024] The dq-abc coordinate transformation module is used to perform dp coordinate inverse transformation and synthesis on Ud_p, Uq_p, Ud_n and Uq_n to obtain the actual command value;

[0025] The PWM signal generation module is used to convert the actual command value into a PWM signal to control the new energy grid-connected system and complete transient reactive active support.

[0026] Furthermore, based on U t_p , U t_n Obtain the q-axis positive and negative sequence current reference signals for voltage control, including:

[0027] Will U t_p , U t_n After making a difference with the zero-sequence voltage Ut_0 at the grid-connected point, the positive and negative sequence voltage error signals of the grid-connected point are obtained; the positive and negative sequence voltage error signals of the grid-connected point are conditioned and integrated to obtain the q-axis positive and negative sequence current reference signals of the voltage control.

[0028] Furthermore, when the new energy grid-connected system is in the normal operation stage, the control module is used to control Id_p, Id_n, Iq_p, and Iq_n, including:

[0029] The d and q axis positive sequence current reference signals of active and reactive power control are used as actual reference signals, and the d and q axis positive sequence current error signals are obtained by one-to-one difference with Id_p and Iq_p, and the d and q axis positive sequence voltages Ud_p and Uq_p are obtained after feedback control;

[0030] Among them, the d-axis positive sequence current reference signal for active and reactive control is obtained as follows:

[0031] After subtracting the active and reactive reference signals of the new energy stator side from the active and reactive signals of the stator side one by one, the active and reactive error signals of the stator side are obtained; the active and reactive error signals of the stator side are fed back to control the reference signals of the d and q axis positive sequence currents of the active control;

[0032] Using 0 as the actual reference signal, and subtracting it from Id_n and Iq_n respectively, we get the d and q axis negative sequence current error signals, and after feedback control, we get the d and q axis negative sequence voltages Ud_n and Uq_n.

[0033] Furthermore, the new energy grid-connected system includes a three-phase full-bridge inverter circuit, a DC capacitor, a filter circuit, a grid equivalent impedance and a transmission network;

[0034] The DC capacitor is connected to the input end of the three-phase full-bridge inverter circuit, and the output end of the three-phase full-bridge inverter circuit is connected to the filter circuit; the filter circuit is connected to the power transmission network through the grid equivalent impedance;

[0035] The PWM signal is used to control the on-off of the switch tube in the three-phase full-bridge inverter circuit to complete transient reactive active support.

[0036] According to a third aspect of the present invention, a controller is provided for executing the method for active support of transient reactive power of new energy under asymmetric faults as described in any one of the first aspects.

[0037] According to a fourth aspect of the present invention, there is provided a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for active support of transient reactive power of new energy under asymmetric faults as described in any one of the first aspects.

[0038] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0039] (1) Different from the power control when the new energy grid-connected system is in normal operation, in the present invention, by introducing a dynamic reactive power control strategy, the positive and negative sequence reactive currents are decoupled and controlled to support the grid voltage, thereby improving the stability of the new energy grid-connected system under asymmetric faults. Specifically, considering that when the new energy grid-connected system is in the fault occurrence stage or the fault continuation stage, there is a negative sequence component, and power control according to the preset power command cannot support the grid voltage. Therefore, in the present invention, the three-phase output current i of the new energy grid-connected system is controlled. abc And the grid voltage U tabc Perform coordinate transformation and positive and negative sequence decoupling calculation to obtain the three-phase output current i abc The corresponding d and q axis positive and negative sequence current components and the positive and negative sequence voltages of the grid points are obtained. Based on this, the d and q axis positive and negative sequence current components are decoupled and controlled respectively: on the one hand, the preset d and q axis positive and negative sequence current reference signals are used as actual reference signals to perform reactive current decoupling control on the corresponding d and q axis positive and negative sequence current components respectively, and reactive power is injected through reactive current to increase the grid voltage; on the other hand, when controlling the q axis positive and negative sequence current components, considering that during the duration of the fault, it can be considered that the system is in a short-term equilibrium state under the fault, therefore, the q axis positive and negative sequence current reference signals of the voltage control obtained based on the positive and negative sequence voltages of the grid connection point are used as actual reference signals to control the grid voltage and reduce the voltage drop during the duration of the fault. In this way, different control targets are used in different fault stages, which realizes dynamic support for the grid voltage as a whole, reduces the asymmetry and drop depth of the grid voltage, and thus enhances the stability of the new energy grid-connected system under asymmetric faults.

[0040] (2) Furthermore, when the new energy grid-connected system is in the normal operation stage, the d-axis positive-sequence current reference signal of active control or the q-axis positive-sequence current reference signal of reactive control is used as the actual reference signal to perform power control on the d-axis positive-sequence current component Id_p or the q-axis positive-sequence current component Iq_p, or 0 is used as the actual reference signal to control the d-axis negative-sequence current component Id_n and the q-axis negative-sequence current component Iq_n. Different control targets are used at different stages to ensure that the new energy grid-connected system can operate normally regardless of whether it is in the normal operation stage or in a fault state.

[0041] In summary, the present invention introduces a dynamic reactive power control strategy to decouple positive and negative sequence reactive currents, support the grid voltage, and reduce the asymmetry of the grid voltage, thereby achieving stable operation of the new energy grid-connected system under asymmetric faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of a method for actively supporting transient reactive power of renewable energy under asymmetric faults in an embodiment of the present invention.

[0043] Figure 2 It is a structural schematic diagram of a new energy transient reactive active support system under an asymmetric fault in an embodiment of the present invention.

[0044] Figure 3 4 is a structural diagram of a dynamic reactive active support module in an embodiment of the present invention.

[0045] Figure 4 4 is a structural diagram of a d-axis positive-sequence current control module in an embodiment of the present invention.

[0046] Figure 5 1 is a structural diagram of a q-axis positive-sequence current control module in an embodiment of the present invention.

[0047] Figure 6 4 is a structural diagram of a d-axis negative-sequence current control module in an embodiment of the present invention.

[0048] Figure 7 1 is a structural diagram of a q-axis negative-sequence current control module in an embodiment of the present invention.

[0049] Figure 8 This is a control effect diagram of a new energy power generation system under an asymmetric fault according to an embodiment of the present invention.

[0050] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0051] 1-three-phase full-bridge inverter circuit, 2-DC capacitor, 3-filter inductor, 4-filter capacitor, 5-grid equivalent impedance, 6-transmission network, 7-positive and negative sequence decoupling module, 8-dynamic reactive active support module;

[0052] 80-PWM signal, 81-d-axis positive sequence current control module, 82-q-axis positive sequence current control module, 83-d-axis negative sequence current control module, 84-q-axis negative sequence current control module;

[0053] 811-a first subtractor, 812-a first PI controller, 813-a first selector, 814-a second subtractor, 815-a second PI controller, 8110-a stator side active error signal, 8120-a d-axis positive sequence current reference signal for active control, 8130-an actual d-axis current positive sequence reference signal, 8140-a d-axis positive sequence current error signal;

[0054] 821-a third subtractor, 822-a third PI controller, 823-a fourth subtractor, 824-a first control gain, 825-a first integrator, 826-a second selector, 827-a fifth subtractor, 828-a fourth PI controller, 8210-a stator side reactive error signal, 8220-a q-axis positive sequence current reference signal of reactive control, 8230-a grid-connected point positive sequence voltage error signal, 8240-a conditioned grid-connected point positive sequence voltage error signal, 8250-a q-axis positive sequence current reference signal of voltage control, 8260-an actual q-axis positive sequence current reference signal, 8270-a q-axis positive sequence current error signal;

[0055] 831 - third selector, 832 - sixth subtractor, 833 - fifth PI controller, 8310 - actual d-axis negative sequence reference signal, 8320 - d-axis negative sequence current error signal;

[0056] 841-the seventh subtractor, 842-the second control gain, 843-the second integrator, 844-the fourth selector, 845-the eighth subtractor, 846-the sixth PI controller, 8410-the negative-sequence voltage error signal of the grid-connected point, 8420-the conditioned negative-sequence voltage error signal of the grid-connected point, 8430-the voltage-controlled q-axis negative-sequence current reference signal, 8440 the actual q-axis negative-sequence current reference signal, 8450-the q-axis negative-sequence current error signal. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0058] In the present invention, the terms "first", "second", etc. in the present invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0059] Example 1

[0060] like Figure 1As shown, in an embodiment of the present invention, a method for actively supporting transient reactive power of new energy under an asymmetric fault is provided, comprising:

[0061] S1, collect the three-phase output current i of the new energy grid-connected system abc And the grid voltage U tabc , by the three-phase output current i abc Perform dq coordinate transformation and positive and negative sequence decoupling calculation to obtain the three-phase output current i abc The corresponding d-axis positive and negative sequence current components Id_p, Id_n, q-axis positive and negative sequence current components Iq_p, Iq_n; by the grid connection point voltage U tabc Perform dq coordinate transformation and positive and negative sequence decoupling calculation to obtain the positive and negative sequence voltage U at the grid connection point t_p , U t_n ;

[0062] S2, based on the d-axis positive and negative sequence current components Id_p, Id_n, q-axis positive and negative sequence current components Iq_p, Iq_n, and the grid-connected point positive and negative sequence voltage U t_p , U t_n , through reactive power calculation and control, a PWM signal 80 is obtained;

[0063] S3. Use the PWM signal 80 to control the three-phase full-bridge inverter circuit 1 in the new energy grid-connected system to achieve normal operation of the system.

[0064] Specifically, S2 includes: when an asymmetric fault occurs or during the duration of an asymmetric fault, Id_p, Id_n, Iq_p, and Iq_n are controlled, specifically including:

[0065] The preset d-axis positive and negative sequence current reference signals are respectively used as actual reference signals, and the d-axis positive and negative sequence current error signals obtained by making a one-to-one difference with Id_p and Id_n are used for feedback control, thereby obtaining the d-axis positive and negative sequence voltages Ud_p and Ud_n;

[0066] When an asymmetric fault occurs, the preset q-axis positive and negative sequence current reference signals are used as actual reference signals. During the duration of the asymmetric fault, the positive and negative sequence current reference signals are respectively based on U t_p , U t_n The q-axis positive and negative sequence current reference signals of voltage control are obtained as actual reference signals, and the q-axis positive and negative sequence current error signals are obtained by one-to-one difference with Iq_p and Iq_n. After feedback control, the q-axis positive and negative sequence voltages Uq_p and Uq_n are obtained.

[0067] When the new energy grid-connected system is in the normal operation stage, Id_p, Id_n, Iq_p, and Iq_n are controlled, including:

[0068] The d and q axis positive sequence current reference signals of active and reactive power control are used as actual reference signals, and the d and q axis positive sequence current error signals are obtained by one-to-one difference with Id_p and Iq_p, and the d and q axis positive sequence voltages Ud_p and Uq_p are obtained after feedback control;

[0069] Among them, the d-axis positive sequence current reference signal for active and reactive control is obtained as follows:

[0070] After subtracting the active and reactive reference signals of the new energy stator side from the active and reactive signals of the stator side one by one, the active and reactive error signals of the stator side are obtained; the active and reactive error signals of the stator side are fed back to control the reference signals of the d and q axis positive sequence currents of the active control;

[0071] Using 0 as the actual reference signal, and subtracting it from Id_n and Iq_n respectively, we get the d and q axis negative sequence current error signals, and after feedback control, we get the d and q axis negative sequence voltages Ud_n and Uq_n.

[0072] That is, when the new energy grid-connected system is in the fault occurrence stage or the fault continuation stage, the preset d-axis positive-sequence current reference signal Id_pref is used as the actual reference signal, and the actual reference signal is subtracted from the d-axis positive-sequence current component Id_p to obtain the d-axis positive-sequence current error signal; after the d-axis positive-sequence current error signal is feedback controlled, the d-axis positive-sequence voltage Ud_p is obtained; when the new energy grid-connected system is in the normal operation stage, the d-axis positive-sequence current reference signal of active control is used as the actual reference signal to obtain the d-axis positive-sequence voltage Ud_p; wherein, the d-axis positive-sequence current reference signal of active control is obtained as follows: after subtracting the active reference signal Ps_ref of the new energy stator side from the active signal Ps of the stator side, the active error signal of the stator side is obtained; the active error signal of the stator side is feedback controlled (such as PI control) to obtain the d-axis positive-sequence current reference signal of active control.

[0073] The positive sequence voltage U t_pAfter making a difference with the zero-sequence voltage Ut_0 at the grid connection point and after gain adjustment and integration, the voltage-controlled q-axis positive-sequence current reference signal is obtained; when the new energy grid-connected system is in the fault occurrence stage, the preset q-axis positive-sequence current reference signal Iq_pref is used as the actual reference signal; when the new energy grid-connected system is in the fault continuation stage, the voltage-controlled q-axis positive-sequence current reference signal is used as the actual reference signal; the actual reference signal is made different from the q-axis positive-sequence current component Iq_p to obtain the q-axis positive-sequence current error signal; the q-axis positive-sequence current error signal is reversed After feedback control, the q-axis positive-sequence voltage Uq_p is obtained; when the new energy grid-connected system is in the normal operation stage, the q-axis positive-sequence current reference signal of reactive control is used as the actual reference signal to obtain the q-axis positive-sequence voltage Uq_p; wherein, the q-axis positive-sequence current reference signal of reactive control is obtained as follows: the reactive reference signal Qs_ref on the stator side of the new energy is subtracted from the reactive signal Qs on the stator side to obtain the reactive error signal on the stator side, and the reactive error signal on the stator side is subjected to feedback control (such as PI control) to obtain the q-axis positive-sequence current reference signal of reactive control.

[0074] When the new energy grid-connected system is in the fault occurrence stage or the fault continuation stage, the preset d-axis negative-sequence current reference signal Id_nref is used as the actual reference signal; the d-axis negative-sequence current error signal is obtained by subtracting the actual reference signal from the d-axis negative-sequence current component Id_n; after the d-axis negative-sequence current error signal is feedback controlled, the d-axis negative-sequence voltage Ud_n is obtained; when the new energy grid-connected system is in the normal operation stage, 0 is used as the actual reference signal to obtain the d-axis negative-sequence voltage Ud_n.

[0075] The negative-sequence voltage Ut_n of the grid connection point is subtracted from the zero-sequence voltage Ut_0 of the grid connection point, and after gain adjustment and integration, a voltage-controlled q-axis negative-sequence current reference signal is obtained; when the new energy grid-connected system is in the fault occurrence stage, the preset q-axis negative-sequence current reference signal Iq_nref is used as the actual reference signal; when the new energy grid-connected system is in the fault continuation stage, the voltage-controlled q-axis negative-sequence current reference signal is used as the actual reference signal; the actual reference signal is subtracted from the q-axis negative-sequence current component Iq_n to obtain a q-axis negative-sequence current error signal; after the q-axis negative-sequence current error signal is feedback controlled, the q-axis negative-sequence voltage Uq_n is obtained; when the new energy grid-connected system is in the normal operation stage, 0 is used as the actual reference signal to obtain the q-axis negative-sequence voltage Uq_n; wherein, the above-mentioned fault occurrence stage or fault continuation stage refers to the asymmetric fault occurrence stage or the asymmetric fault continuation stage;

[0076] The d-axis positive-sequence voltage Ud_p, the q-axis positive-sequence voltage Uq_p, the d-axis negative-sequence voltage Ud_n and the q-axis negative-sequence voltage Uq_n are subjected to dq inverse coordinate transformation and synthesized to obtain the actual voltage command value; and the PWM signal 80 is converted into a PWM signal 80, which is used to control the on and off of the switch tube in the three-phase full-bridge inverter circuit 1 in the new energy grid-connected system to achieve normal operation of the system.

[0077] Specifically, by detecting whether there is a negative-sequence component in the new energy grid-connected system, it is determined whether the new energy grid-connected system is in the normal operation stage. If there is no negative-sequence component, the system is in the normal operation stage, otherwise, the system is in the fault occurrence stage or the fault continuation stage; according to the time of voltage drop after the occurrence of an asymmetric fault, it is determined whether the system is in the fault occurrence stage or the fault continuation stage; wherein the time of voltage drop is obtained based on experience.

[0078] In the embodiment of the present invention, the feedback control adopts PI control. In other embodiments, other feedback control methods, such as PID control, may also be adopted.

[0079] After obtaining Ud_p, Uq_p, Ud_n and Uq_n, Ud_p, Uq_p, Ud_n and Uq_n are subjected to dp coordinate inverse transformation and synthesis to obtain the actual command value, which is converted into a PWM signal to control the new energy grid-connected system and complete transient reactive active support.

[0080] Different from the power control when the new energy grid-connected system is in normal operation, in the present invention, by introducing a dynamic reactive power control strategy, the positive and negative sequence reactive currents are decoupled and controlled to support the grid voltage, thereby improving the stability of the new energy grid-connected system under asymmetric faults. Specifically, considering that when the new energy grid-connected system is in the fault occurrence stage or the fault continuation stage, there is a negative sequence component, and power control according to the preset power command cannot support the grid voltage. Therefore, in the present invention, the three-phase output current i of the new energy grid-connected system is controlled. abc And the grid voltage U tabc Perform coordinate transformation and positive and negative sequence decoupling calculation to obtain the three-phase output current i abcThe corresponding d and q axis positive and negative sequence current components and the positive and negative sequence voltages of the grid points are obtained. Based on this, the d and q axis positive and negative sequence current components are decoupled and controlled respectively: on the one hand, the preset d and q axis positive and negative sequence current reference signals are used as actual reference signals to perform reactive current decoupling control on the corresponding d and q axis positive and negative sequence current components respectively, and reactive power is injected through reactive current to increase the grid voltage; on the other hand, when controlling the q axis positive and negative sequence current components, considering that during the duration of the fault, it can be considered that the system is in a short-term equilibrium state under the fault, therefore, the q axis positive and negative sequence current reference signals of the voltage control obtained based on the positive and negative sequence voltages of the grid connection point are used as actual reference signals to control the grid voltage and reduce the voltage drop during the duration of the fault. In this way, different control targets are used in different fault stages, which realizes dynamic support for the grid voltage as a whole, reduces the asymmetry and drop depth of the grid voltage, and thus enhances the stability of the new energy grid-connected system under asymmetric faults.

[0081] When the new energy grid-connected system is in the normal operation stage, the d-axis positive-sequence current reference signal of active control or the q-axis positive-sequence current reference signal of reactive control is used as the actual reference signal to perform power control on the d-axis positive-sequence current component Id_p or the q-axis positive-sequence current component Iq_p, or 0 is used as the actual reference signal to control the d-axis negative-sequence current component Id_n and the q-axis negative-sequence current component Iq_n. Different control targets are used at different stages to ensure that the new energy grid-connected system can operate normally regardless of whether it is in the normal operation stage or in a fault state.

[0082] Example 2

[0083] like Figure 2 As shown, the embodiment of the present invention provides a new energy transient reactive active support system under asymmetric fault, including: a positive and negative sequence decoupling module 7 and a dynamic reactive active support module 8;

[0084] The positive and negative sequence decoupling module 7 is used to collect the three-phase output current i of the new energy grid-connected system abc And the grid voltage U tabc , by the three-phase output current i abc Perform dq coordinate transformation and positive and negative sequence decoupling calculation to obtain the three-phase output current i abc The corresponding d-axis positive and negative sequence current components Id_p, Id_n, q-axis positive and negative sequence current components Iq_p, Iq_n; by the grid connection point voltage U tabc Perform dq coordinate transformation and positive and negative sequence decoupling calculation to obtain the positive and negative sequence voltage U at the grid connection point t_p , U t_n ;

[0085] The dynamic reactive active support module 8 is used to generate the positive and negative sequence current components Id_p and Id_n of the d-axis, the positive and negative sequence current components Iq_p and Iq_n of the q-axis, and the positive and negative sequence voltage U t_p , U t_n , through reactive power calculation and control, a PWM signal 80 is obtained; the PWM signal 80 is used to control the three-phase full-bridge inverter circuit 1 in the new energy grid-connected system to achieve normal operation of the system.

[0086] In the embodiment of the present invention, the above-mentioned new energy grid-connected system includes a three-phase full-bridge inverter circuit 1, a DC capacitor 2, a filter circuit, a grid equivalent impedance 5 and a transmission network 6;

[0087] The new energy injects electric energy into the DC capacitor 2 to maintain the DC voltage on the DC side of the new energy; the DC capacitor 2 is connected to the input end of the three-phase full-bridge inverter circuit 1, and the three-phase full-bridge inverter circuit 1 is used to invert the DC voltage on the DC side of the new energy to obtain AC power; the output end of the three-phase full-bridge inverter circuit 1 is connected to the filter circuit, and the filter circuit is used to filter the AC power to obtain the filtered AC power, that is, the above-mentioned three-phase output current i abc The filtered AC power is transmitted to the power transmission network 6 through the grid equivalent impedance 5; wherein the asymmetric fault occurs in the power transmission network 6. In the embodiment of the present invention, the filter circuit includes a filter inductor 3 and a filter capacitor 4 connected in series.

[0088] Specifically, the positive and negative sequence decoupling module 7 collects the three-phase output current i abc And the grid voltage U tabc Through dq coordinate transformation and positive and negative sequence decoupling calculation, we can obtain the d-axis positive and negative sequence current components Id_p and Id_n, the q-axis positive and negative sequence current components Iq_p and Iq_n, and the grid-connected point positive and negative sequence voltage U t_p , U t_n .

[0089] The dynamic reactive active support module 8 includes a control module, a dq-abc coordinate transformation module 85 and a PWM signal generation module; wherein the control module is used to control Id_p, Id_n, Iq_p, and Iq_n when an asymmetric fault occurs or during the duration of an asymmetric fault, including: using preset d-axis positive and negative sequence current reference signals as actual reference signals, respectively, and performing feedback control on d-axis positive and negative sequence current error signals obtained by making a one-to-one difference with Id_p and Id_n, thereby obtaining d-axis positive and negative sequence voltages Ud_p and Ud_n;

[0090] When an asymmetric fault occurs, the preset q-axis positive and negative sequence current reference signals are used as actual reference signals. During the duration of the asymmetric fault, the positive and negative sequence current reference signals are respectively based on U t_p , U t_nThe q-axis positive and negative sequence current reference signals of voltage control are obtained as actual reference signals, and the q-axis positive and negative sequence current error signals are obtained by one-to-one difference with Iq_p and Iq_n. After feedback control, the q-axis positive and negative sequence voltages Uq_p and Uq_n are obtained.

[0091] When the new energy grid-connected system is in the normal operation stage, the control module is used to control Id_p, Id_n, Iq_p, and Iq_n, including:

[0092] The d and q axis positive sequence current reference signals of active and reactive power control are used as actual reference signals, and the d and q axis positive sequence current error signals are obtained by one-to-one difference with Id_p and Iq_p, and the d and q axis positive sequence voltages Ud_p and Uq_p are obtained after feedback control;

[0093] Among them, the d-axis positive sequence current reference signal for active and reactive control is obtained as follows:

[0094] After subtracting the active and reactive reference signals of the new energy stator side from the active and reactive signals of the stator side one by one, the active and reactive error signals of the stator side are obtained; the active and reactive error signals of the stator side are fed back to control the reference signals of the d and q axis positive sequence currents of the active control;

[0095] Using 0 as the actual reference signal, and subtracting it from Id_n and Iq_n respectively, we get the d and q axis negative sequence current error signals, and after feedback control, we get the d and q axis negative sequence voltages Ud_n and Uq_n.

[0096] In the embodiment of the present invention, Figure 3 As shown, the control module includes a d-axis positive-sequence current control module 81, a q-axis positive-sequence current control module 82, a d-axis negative-sequence current control module 83, a q-axis negative-sequence current control module 84, a dq-abc coordinate transformation module 85 and a PWM signal generation module.

[0097] The d-axis positive-sequence current component Id_p is injected into the d-axis positive-sequence current control module 81, and after processing, the d-axis positive-sequence voltage Ud_p is output; the q-axis positive-sequence current component Iq_p and the grid-connected point positive-sequence voltage Ut_p are injected into the q-axis positive-sequence current control module 82, and after processing, the q-axis positive-sequence voltage Uq_p is output; the d-axis negative-sequence current component Id_n is injected into the d-axis negative-sequence current control module 83, and after processing, the d-axis negative-sequence voltage Ud_n is output; the q-axis negative-sequence voltage component Iq_n and the grid-connected point negative-sequence voltage Ut_n are injected into the q-axis negative-sequence current control module 84, and after processing, the q-axis negative-sequence voltage Uq_n is output.

[0098] like Figure 4, which is a structural diagram of the d-axis positive sequence current control module 81 . In the embodiment of the present invention, the d-axis positive sequence current control module 81 includes: a first subtractor 811 , a first PI controller 812 , a first selector 813 , a second subtractor 814 , and a second PI controller 815 .

[0099] The stator side active reference signal Ps_ref of the new energy source is subtracted from the stator side active signal Ps through the first subtractor 811 to obtain a stator side active error signal 8110; the stator side active error signal 8110 is subjected to PI control by the first PI controller 812 to obtain an active controlled d-axis positive sequence current reference signal 8120; the active controlled d-axis positive sequence current reference signal 8120 and the preset d-axis positive sequence current reference signal Id_pref are selected by the first selector 813 to obtain an actual d-axis current positive sequence reference signal 8130 (i.e., the above-mentioned actual reference signal). If the new energy grid-connected system is in the normal operation stage, the first selector 814 is used to select the actual d-axis current positive sequence reference signal 8130. The selector 813 selects the d-axis positive-sequence current reference signal 8120 of active control as the actual d-axis current positive-sequence reference signal 8130. If the system is in the fault occurrence stage or the fault continuation stage, the first selector 813 selects the preset d-axis positive-sequence current reference signal Id_pref as the actual d-axis current positive-sequence reference signal 8130. The actual d-axis current positive-sequence reference signal 8130 is subtracted from the d-axis positive-sequence current component Id_p by the second subtractor 814 to obtain a d-axis positive-sequence current error signal 8140. The d-axis positive-sequence current error signal 8140 is finally passed through the second PI controller 815 to obtain the d-axis positive-sequence voltage Ud_p.

[0100] Specifically, Figure 5 , which is a structural diagram of the q-axis positive sequence current control module 82. In the embodiment of the present invention, the q-axis positive sequence current control module 82 includes: a third subtractor 821, a third PI controller 822, a fourth subtractor 823, a first control gain 824, a first integrator 825, a second selector 826, a fifth subtractor 827, and a fourth PI controller 828.

[0101] The reactive reference signal Qs_ref of the new energy stator side is subtracted from the reactive signal Qs of the stator side by the third subtractor 821 to obtain the reactive error signal 8210 of the stator side; the reactive error signal 8210 of the stator side is PI-controlled by the third PI controller 822 to obtain the q-axis positive-sequence current reference signal 8220 of reactive control. The positive-sequence voltage Ut_p of the grid connection point is subtracted from the zero-sequence voltage Ut_0 of the grid connection point by the fourth subtractor 823 to obtain the positive-sequence voltage error signal 8230 of the grid connection point, and the positive-sequence voltage error signal 8230 of the grid connection point is amplified or reduced by the first control gain 824 to obtain the conditioned positive-sequence voltage error signal 8240 of the grid connection point, and the conditioned positive-sequence voltage error signal 8240 of the grid connection point is input to the first integrator 825 for integration to obtain the q-axis positive-sequence current reference signal 8250 of voltage control. The reactive-controlled q-axis positive-sequence current reference signal 8220, the preset q-axis positive-sequence current reference signal Iq_pref and the voltage-controlled q-axis positive-sequence current reference signal 8250 are selected by the second selector 826 to obtain the actual q-axis positive-sequence current reference signal 8260 (actual reference signal). If the system is in the normal operation stage, the second selector 826 selects the reactive-controlled q-axis positive-sequence current reference signal 8220 as the actual reference signal; if the system is in the fault occurrence stage, the second selector 826 selects the preset q-axis positive-sequence current reference signal Iq_pref as the actual reference signal; if the system is in the fault continuation stage, the second selector 826 selects the voltage-controlled q-axis positive-sequence current reference signal 8250 as the actual reference signal. The actual q-axis positive-sequence current reference signal 8260 is subtracted from the q-axis positive-sequence current signal Iq_p by the fifth subtractor 827 to obtain a q-axis positive-sequence current error signal 8270 . The q-axis positive-sequence current error signal 8270 is finally passed through the fourth PI controller 828 to obtain a q-axis positive-sequence voltage Uq_p.

[0102] Specifically, Figure 6 , which is a structural diagram of the d-axis negative-sequence current control module 83 . In the embodiment of the present invention, the d-axis negative-sequence current control module 83 includes a third selector 831 , a sixth subtractor 832 and a fifth PI controller 833 .

[0103] The third selector 831 selects 0 or a preset d-axis negative-sequence current reference signal Id_nref as the actual d-axis negative-sequence reference signal 8310. If the system is in the normal operation stage, the third selector 831 selects 0 as the actual reference signal; if the system is in the fault occurrence stage or the fault continuation stage, the third selector 831 selects the preset d-axis negative-sequence current reference signal Id_nref as the actual reference signal. The actual d-axis negative-sequence current reference signal 8310 is subtracted from the d-axis negative-sequence current signal Id_n by the sixth subtractor 832 to obtain a d-axis negative-sequence current error signal 8320. The d-axis negative-sequence current error signal 8320 is finally passed through the fifth PI controller 833 to obtain a d-axis negative-sequence voltage Ud_n.

[0104] Specifically, Figure 7 , which is a structural diagram of the q-axis negative sequence current control module 84. In the embodiment of the present invention, the q-axis negative sequence current control module 84 includes: a seventh subtractor 841, a second control gain 842, a second integrator 843, a fourth selector 844, an eighth subtractor 845, and a sixth PI controller 846.

[0105] The grid-connected point negative-sequence voltage Ut_n is subtracted from the grid-connected point zero-sequence voltage Ut_0 through the seventh subtractor 841 to obtain a grid-connected point negative-sequence voltage error signal 8410. The grid-connected point negative-sequence voltage error signal 8410 is amplified or reduced by the second control gain 842 to obtain a conditioned grid-connected point negative-sequence voltage error signal 8420. The conditioned grid-connected point negative-sequence voltage error signal 8420 is input to the second integrator 843 for integration to obtain a voltage-controlled q-axis negative-sequence current reference signal 8430. The fourth selector 844 selects 0, the preset q-axis negative-sequence current reference signal Iq_nref or the voltage-controlled q-axis negative-sequence current reference signal 8430 as the actual q-axis negative-sequence current reference signal 8440. If the system is in the normal operation stage, the fourth selector 844 selects 0 as the actual reference signal; if the system is in the fault occurrence stage, the fourth selector 844 selects the preset q-axis negative-sequence current reference signal Iq_nref as the actual reference signal; if the system is in the fault continuation stage, the fourth selector 844 selects the voltage-controlled q-axis positive-sequence current reference signal 8430 as the actual reference signal. The actual q-axis negative-sequence current reference signal 8440 is subtracted from the q-axis negative-sequence current signal Iq_n by the eighth subtractor 845 to obtain a q-axis negative-sequence current error signal 8450, and the q-axis negative-sequence current error signal 8450 is finally passed through the sixth PI controller 846 to obtain the q-axis negative-sequence voltage Uq_n.

[0106] The dq-abc coordinate transformation module 85 is used to perform dp coordinate inverse transformation on Ud_p, Uq_p, Ud_n and Uq_n to obtain the corresponding voltage in the abc coordinate system, and synthesize them to obtain the actual command value;

[0107] The PWM signal generation module is used to convert the actual command value obtained into a PWM signal to control the new energy grid-connected system and complete transient reactive active support.

[0108] The dynamic reactive active support system for new energy under asymmetric faults in the embodiment of the present invention introduces a d-axis positive-sequence current control module 81, a q-axis positive-sequence current control module 82, a d-axis negative-sequence current control module 83, and a q-axis negative-sequence current control module 84, designs a dynamic reactive power control strategy, decouples the positive and negative sequence reactive currents, and realizes dynamic control of reactive power under asymmetric faults to dynamically support the grid voltage, thereby reducing the asymmetry and drop depth of the grid voltage, so as to enhance the stability of the new energy grid-connected system under asymmetric faults.

[0109] The effect of the method of the present invention is further illustrated by a specific example. A simulation model of a new energy station connected to an AC power grid is built in MATLAB / simulink. A two-phase grounding fault occurs in the power grid at 0.5s, the fault phase drops by 50%, and the fault time is 0.5s~0.7s. The electrical quantities such as AC bus voltage, active and reactive output, and DC voltage of the new energy system are analyzed. Figure 8 As shown. It can be seen that the transient reactive active support method of the present invention reduces the non-fault phase voltage from 1.293pu to 1.28pu; the reactive power support during the fault period increases from 2.464Mvar to 4.113Mvar; the fault steady-state DC capacitor voltage fluctuation is reduced from 1105V~1201V to 1195V~1114V. Therefore, the implementation effect of the present invention is good.

[0110] Example 3

[0111] The embodiment of the present invention provides a controller for executing the method for actively supporting transient reactive power of renewable energy under asymmetric fault in the above embodiment 1. For the relevant technical solutions, please refer to the corresponding description in embodiment 1, which will not be repeated here.

[0112] Example 4

[0113] In an embodiment of the present invention, a computer-readable storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, a method for actively supporting transient reactive power of new energy under asymmetric faults as in the above-mentioned embodiment 1 is implemented. For related technical solutions, please refer to the corresponding description in embodiment 1, which will not be repeated here.

[0114] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for active support of transient reactive power of renewable energy under asymmetric faults. It is characterized in that include: The three-phase output current and grid connection point voltage of the new energy grid-connected system are transformed into dq coordinates and positive and negative sequence decoupling is performed to obtain the d-axis positive and negative sequence current components Id_p and Id_n, the q-axis positive and negative sequence current components Iq_p and Iq_n, and the grid connection point positive and negative sequence voltage U t_p , U t_n ; When an asymmetric fault occurs or during the duration of an asymmetric fault, Id_p, Id_n, Iq_p, and Iq_n are controlled, including: The preset d-axis positive and negative sequence current reference signals are respectively used as actual reference signals, and the d-axis positive and negative sequence current error signals are obtained by making a one-to-one difference with Id_p and Id_n, and the d-axis positive and negative sequence current error signals are fed back and controlled to obtain the d-axis positive and negative sequence voltages Ud_p and Ud_n; When an asymmetric fault occurs, the preset q-axis positive and negative sequence current reference signals are used as actual reference signals. During the duration of the asymmetric fault, the positive and negative sequence current reference signals are respectively based on U t_p , U t_n The q-axis positive and negative sequence current reference signals of voltage control are obtained as actual reference signals, and the q-axis positive and negative sequence current error signals are obtained by one-to-one difference with Iq_p and Iq_n. After feedback control, the q-axis positive and negative sequence voltages Uq_p and Uq_n are obtained. After the dp coordinate inverse transformation and synthesis of Ud_p, Uq_p, Ud_n and Uq_n, they are converted into PWM signals to control the new energy grid-connected system and complete the transient reactive active support.

2. The method for actively supporting transient reactive power of new energy under asymmetric fault according to claim 1, It is characterized in that Based on U t_p , U t_n Obtain the q-axis positive and negative sequence current reference signals for voltage control, including: Will U t_p , U t_n After making a difference with the zero-sequence voltage Ut_0 of the grid-connected point, the positive and negative sequence voltage error signals of the grid-connected point are obtained; after signal conditioning, the positive and negative sequence voltage error signals of the grid-connected point are integrated to obtain the q-axis positive and negative sequence current reference signals of the voltage control.

3. The method for actively supporting transient reactive power of new energy under asymmetric fault according to claim 1 or 2, It is characterized in that When the new energy grid-connected system is in the normal operation stage, Id_p, Id_n, Iq_p, and Iq_n are controlled, including: The d and q axis positive sequence current reference signals of active and reactive power control are used as actual reference signals, and the d and q axis positive sequence current error signals are obtained by one-to-one difference with Id_p and Iq_p, and the d and q axis positive sequence voltages Ud_p and Uq_p are obtained after feedback control; Among them, the d-axis positive sequence current reference signal for active and reactive control is obtained as follows: After subtracting the active and reactive reference signals of the new energy stator side from the active and reactive signals of the stator side one by one, the active and reactive error signals of the stator side are obtained; the active and reactive error signals of the stator side are fed back to control the reference signals of the d and q axis positive sequence currents of the active control; Using 0 as the actual reference signal, and subtracting it from Id_n and Iq_n respectively, we get the d and q axis negative sequence current error signals, and after feedback control, we get the d and q axis negative sequence voltages Ud_n and Uq_n.

4. The method for actively supporting transient reactive power of new energy under asymmetric fault according to claim 1, It is characterized in that The feedback control is PI or PID control.

5. A new energy transient reactive active support system under asymmetric faults, It is characterized in that include: The positive and negative sequence decoupling module is used to perform dq coordinate transformation and positive and negative sequence decoupling on the three-phase output current and grid connection point voltage of the new energy grid-connected system, and obtain the d-axis positive and negative sequence current components Id_p and Id_n, the q-axis positive and negative sequence current components Iq_p and Iq_n, and the grid connection point positive and negative sequence voltage U t_p , U t_n ; The control module is used to control Id_p, Id_n, Iq_p, and Iq_n when an asymmetric fault occurs or during the duration of the asymmetric fault, including: The preset d-axis positive and negative sequence current reference signals are respectively used as actual reference signals, and the d-axis positive and negative sequence current error signals are obtained by making a one-to-one difference with Id_p and Id_n, and the d-axis positive and negative sequence current error signals are fed back and controlled to obtain the d-axis positive and negative sequence voltages Ud_p and Ud_n; When an asymmetric fault occurs, the preset q-axis positive and negative sequence current reference signals are used as actual reference signals. During the duration of the asymmetric fault, the positive and negative sequence current reference signals are respectively based on U t_p , U t_n The q-axis positive and negative sequence current reference signals of voltage control are obtained as actual reference signals, and the q-axis positive and negative sequence current error signals are obtained by one-to-one difference with Iq_p and Iq_n. After feedback control, the q-axis positive and negative sequence voltages Uq_p and Uq_n are obtained. The dq-abc coordinate transformation module is used to perform dp coordinate inverse transformation and synthesis on Ud_p, Uq_p, Ud_n and Uq_n to obtain the actual command value; The PWM signal generation module is used to convert the actual command value into a PWM signal to control the new energy grid-connected system and complete transient reactive active support.

6. The new energy transient reactive active support system under asymmetric fault according to claim 5, It is characterized in that Based on U t_p , U t_n Obtain the q-axis positive and negative sequence current reference signals for voltage control, including: Will U t_p , U t_n After making a difference with the zero-sequence voltage Ut_0 at the grid-connected point, the positive and negative sequence voltage error signals of the grid-connected point are obtained; the positive and negative sequence voltage error signals of the grid-connected point are conditioned and integrated to obtain the q-axis positive and negative sequence current reference signals of the voltage control.

7. The new energy transient reactive active support system under asymmetric fault according to claim 5 or 6, It is characterized in that When the new energy grid-connected system is in the normal operation stage, the control module is used to control Id_p, Id_n, Iq_p, and Iq_n, including: The d and q axis positive sequence current reference signals of active and reactive power control are used as actual reference signals, and the d and q axis positive sequence current error signals are obtained by one-to-one difference with Id_p and Iq_p, and the d and q axis positive sequence voltages Ud_p and Uq_p are obtained after feedback control; Among them, the d-axis positive sequence current reference signal for active and reactive control is obtained as follows: After subtracting the active and reactive reference signals of the new energy stator side from the active and reactive signals of the stator side one by one, the active and reactive error signals of the stator side are obtained; the active and reactive error signals of the stator side are fed back to control the reference signals of the d and q axis positive sequence currents of the active control; Using 0 as the actual reference signal, and subtracting it from Id_n and Iq_n respectively, we get the d and q axis negative sequence current error signals, and after feedback control, we get the d and q axis negative sequence voltages Ud_n and Uq_n.

8. The new energy transient reactive active support system under asymmetric fault according to claim 7, It is characterized in that The new energy grid-connected system includes a three-phase full-bridge inverter circuit, a DC capacitor, a filter circuit, a grid equivalent impedance and a transmission network; The DC capacitor is connected to the input end of the three-phase full-bridge inverter circuit, and the output end of the three-phase full-bridge inverter circuit is connected to the filter circuit; the filter circuit is connected to the power transmission network through the grid equivalent impedance; The PWM signal is used to control the on-off of the switch tube in the three-phase full-bridge inverter circuit to complete transient reactive active support.

9. A controller, It is characterized in that Used to execute the method for active support of transient reactive power of new energy under asymmetric faults as described in any one of claims 1-4.

10. A computer-readable storage medium having a computer program stored thereon, It is characterized in that When the program is executed by the processor, the method for active support of transient reactive power of new energy under asymmetric faults as described in any one of claims 1 to 4 is implemented.

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