Pq and vsg smooth switching control system and method based on power compensation

Abstract

The application provides a PQ and VSG smooth switching control system based on power compensation, belongs to the field of new energy grid-connected inverter mode switching control, and the three-phase voltage and current of the output port of the main circuit of the grid-connected inverter and the power compensation signal of VSG are input into a VSG control unit for calculation to obtain the current reference signal of VSG, the three-phase voltage of the output port of the main circuit of the grid-connected inverter, the given reference power and the power compensation signal of PQ are input into a constant power PQ control unit for calculation to obtain the current reference signal of PQ, the current reference signals of VSG and PQ and the d-axis voltage component of the three-phase voltage of the output port of the main circuit are input into a power compensation unit for calculation to obtain the power compensation signal in VSG and the power compensation signal in PQ in the dual-mode switching, a mode switching switch is used for switching the operation mode, the dq-axis signals of the three-phase modulation waves are calculated and input into a space vector modulation (SVPWM) control unit to obtain the trigger pulse signals of each switch tube, and the smooth switching of VSG and PQ during grid connection is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy grid-connected inverter mode switching control, and particularly relates to a PQ and VSG smooth switching control system and method based on power compensation. BACKGROUND

[0002] Modern power systems are rapidly developing towards high proportions of renewable energy and high proportions of power electronic devices, requiring new energy grid-connected devices to adapt to complex working environment requirements, taking into account the voltage and frequency support of the power system under weak networks, and efficient and stable and accurate power output under strong networks. The virtual synchronous generator (VSG) control mode under weak networks uses network-type VSG to simulate the characteristics of synchronous generators to improve the active support of new energy for power grids, but there is a problem of reduced stability under strong networks. Constant power PQ control compensates for the stability problem of VSG under strong networks and has accurate power output capability. Therefore, new energy devices in complex working environments often have multiple control modes, but direct switching between modes during operation can cause phase and internal control structure mutations, resulting in uncontrolled output current. The current VSG and constant power PQ control mode switching relies on accurate samplers to ensure that the phase of the previous running mode is assigned as the initial value of the phase of the subsequent running mode at the switching moment, and complex control structure logic is required to assign the current amplitude of the previous running mode to the running mode after switching to achieve phase synchronization of VSG and constant power PQ control. This method has high requirements for sampling and controller precision and controller computing resources, which is not conducive to large-scale promotion in new energy grid-connected devices.

[0003] In the prior art, the paper "Energy Storage Inverter Control Strategy and Seamless Switching Technology Based on Virtual Synchronous Generator" uses VSG control and active and reactive power (PQ) control to share the current inner loop, realizes smooth transition of the outer loop reference current, ensures the synchronization of the control strategy switching moment and the common coupling point switching moment, and ensures smooth switching of VSG between the two running modes. In this switching technology, grid-connected (PQ) to island (VSG) is directly switched, and the VSG phase and voltage amplitude are automatically adjusted under the load power. When island (VSG) to grid-connected (PQ) is switched, the VSG phase is synchronized with the grid phase using a pre-synchronization method using a phase-locked loop, and the final value of the VSG current inner loop instruction is directly assigned to the initial value of the PQ current inner loop as the initial value at the grid-connected moment. This method can only be used in island (VSG) to grid-connected (PQ) to island (VSG) switching and is not suitable for mutual switching between VSG and PQ modes during grid connection. SUMMARY

[0004] The technical problem to be solved by the present invention is how to achieve smooth switching between the VSG mode and the PQ mode during grid connection.

[0005] The present invention solves the above technical problems through the following technical solutions: a PQ and VSG smooth switching control system based on power compensation, comprising a grid-connected inverter main circuit, a constant power PQ control unit, a VSG control unit, a power compensation unit, a mode switching switch, a current inner loop control unit, and a space vector modulation SVPWM control unit. The three-phase voltage, three-phase current and power compensation signal of the dual-mode switching in the VSG at the output port of the grid-connected inverter main circuit are input into the VSG control unit for calculation to obtain a current reference signal under the VSG control mode. The three-phase voltage, a given reference power and the power compensation signal of the dual-mode switching in the PQ at the output port of the grid-connected inverter main circuit are input into the constant power PQ control unit for calculation to obtain a current reference signal under the constant power PQ control mode. The current reference signal under the VSG control mode, the current reference signal under the constant power PQ control mode and the d-axis voltage component of the three-phase voltage at the output port of the grid-connected inverter main circuit are input into the power compensation unit for calculation to obtain a dual The power compensation signal of mode switching in VSG and the power compensation signal of dual-mode switching in PQ, the mode switching switch is used to switch the operating mode of the main circuit of the grid-connected inverter. When the constant power PQ control mode is switched to the VSG control mode, the power compensation signal of the dual-mode switching in VSG is input to the VSG control unit, and the input reference current of the current inner loop control unit is equal to the current reference signal in the VSG control mode. When the VSG control mode is switched to the constant power PQ control mode, the power compensation signal of the dual-mode switching in PQ is input to the constant power PQ control unit, and the input reference current of the current inner loop control unit is equal to the current reference signal in the constant power PQ control mode. The input reference current of the current inner loop control unit and the actual dq-axis current of the main circuit of the grid-connected inverter are input to the current inner loop control unit for calculation to obtain the dq-axis signal of the three-phase modulation wave. The dq-axis signal of the three-phase modulation wave is input to the space vector modulation SVPWM control unit to obtain the trigger pulse signal of each switch tube in the main circuit of the grid-connected inverter.

[0006] The present invention adopts a power compensation method during the grid-connected period. The compensation control takes the current reference signal calculated by the virtual synchronous generator VSG and the constant power PQ control and the port voltage d-axis component of the main circuit of the grid-connected inverter as input. The power value generated when the current deviation between the VSG control and the constant power PQ control is calculated in the power compensation unit, and the compensation power is input into the constant power PQ control unit and the VSG control unit respectively to achieve synchronization of the current inner loop reference currents of the two, ensuring that the VSG self-generated phase and the current inner loop amplitude are equal before and after the switching between the VSG control mode and the constant power PQ control mode during the grid-connected period, thereby achieving smooth switching of the mode during the grid-connected period.

[0007] Preferably, the main circuit of the grid-connected inverter includes: a DC power supply U dc , three-phase inverter, three-phase LC filter, DC power supply U dc Connect to the DC input of the three-phase inverter, and the output of the three-phase inverter is connected to the three-phase filter inductor L in the three-phase LC filter. f One end of the three-phase filter inductor L f The other end is connected to the three-phase filter capacitor C f One end of the large power grid u g , three-phase filter capacitor C f Short-circuit the other end.

[0008] Preferably, the constant power PQ control unit includes: a phase-locked loop, a dq conversion link, a PQ control current reference calculation link, and a three-phase voltage u of the output port of the main circuit of the grid-connected inverter. abc Input into the phase-locked loop to obtain the grid phase θ when connected to the grid g , grid phase θ when connected to the grid g The three-phase voltage u of the main circuit output port of the grid-connected inverter abc Input to the dq conversion link to calculate the three-phase voltage u at the output port of the main circuit of the grid-connected inverter abc The d-axis voltage component u d , grid phase θ when connected to the grid g , d-axis voltage component u d , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to the PQ control current reference calculation link for calculation to obtain the current reference signal under constant power PQ control mode

[0009] Preferably, the VSG control unit includes: VSG power outer loop control link, internal potential reference, virtual impedance control link, three-phase voltage u of the output port of the main circuit of the grid-connected inverter abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsg Input to the VSG power outer loop control link for calculation to obtain the internal potential e of the grid-connected inverter abc The reference phase θ and the potential e in the grid-connected inverter abc The reference amplitude E, the potential e in the grid-connected inverter abc The reference phase θ and the potential e in the grid-connected inverter abcThe reference amplitude E is input into the internal potential reference, and the three-phase sinusoidal internal potential reference signal is calculated. Three-phase sinusoidal internal potential reference signal The three-phase voltage u of the main circuit output port of the grid-connected inverter abc Input into the virtual impedance control link for calculation to obtain the current reference signal under VSG control mode

[0010] The present invention also provides a PQ and VSG smooth switching control method based on power compensation, which is applied to the control system and includes the following steps:

[0011] Step 1: Obtain the operating parameters and working mode of the main circuit of the grid-connected inverter, wherein the operating parameters include the three-phase voltage u of the output port of the main circuit of the grid-connected inverter. abc , three-phase current i abc , the working mode is a constant power PQ control mode or a VSG control mode;

[0012] Step 2: The three-phase voltage u at the output port of the main circuit of the grid-connected inverter abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsg Input to the VSG control unit for calculation to obtain the current reference signal under VSG control mode Three-phase voltage u at the output port of the main circuit of the grid-connected inverter abc , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to the constant power PQ control unit for calculation to obtain the current reference signal under the constant power PQ control mode

[0013] Step 3: Current reference signal in VSG control mode Current reference signal in constant power PQ control mode And the three-phase voltage u of the output port of the main circuit of the grid-connected inverter abc The d-axis voltage component u d Input to the power compensation unit 40 for calculation, and obtain the power compensation signal P of the dual-mode switching in the VSG. c,vsg , Q c,vsg and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq ;

[0014] Step 4: Switch the operation mode of the main circuit of the grid-connected inverter through the mode switch. When the constant power PQ control mode is switched to the VSG control mode, the power compensation signal P in the VSG is switched by the dual mode. c,vsg , Q c,vsg Input to the VSG control unit, the input reference current of the current inner loop control unit Equal to the current reference signal in VSG control mode When the VSG control mode switches to the constant power PQ control mode, the power compensation signal P in the PQ c,pq , Q c,pq Input to the constant power PQ control unit, the input reference current of the current inner loop control unit Equal to the current reference signal in constant power PQ control mode

[0015] Step 5: Input reference current of the current inner loop control unit and the actual dq axis current i of the main circuit of the grid-connected inverter d 、i q Input to the current inner loop control unit for calculation to obtain the dq axis signal of the three-phase modulation wave dq axis signals of three-phase modulated wave The trigger pulse signal of each switch tube in the main circuit of the grid-connected inverter is input into the space vector modulation SVPWM control unit.

[0016] When the PQ (grid-connected) switches to the VSG (grid-connected), the compensation power is calculated using the current difference between the PQ and VSG and superimposed into the active frequency link and reactive voltage loop of the VSG, forming a closed loop in the power loop and virtual impedance link. The VSG automatically adjusts the amplitude and phase to keep the output value of the current inner loop consistent with the PQ during the grid-connected period. Because it is a closed loop, the various variables in the VSG power loop and virtual impedance link will not change suddenly after switching at any time, achieving smooth switching. Similarly, when the VSG (grid-connected) of the present invention switches to the PQ (grid-connected), the output value of the PQ control reference current control link is adjusted with the power compensation, maintaining the reference current value of the PQ control unchanged after the switch, achieving smooth switching.

[0017] Preferably, the current reference signal in the VSG control mode Calculated by the following steps:

[0018] 2.1.1. Three-phase voltage u at the output port of the main circuit of the grid-connected inverter abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsgThe input to the VSG power outer loop control link is calculated to obtain the reference phase θ of the grid-connected inverter internal potential e abc and the reference amplitude E of the grid-connected inverter internal potential e abc , and the calculation equation is:

[0019]

[0020] In the formula, P ref is the reference active power, P e is the actual active power output by the grid-connected inverter, P c,vsg is the active power compensation signal of the dual-mode switching in the VSG, J is the rotational inertia of the active-frequency control, ω n is the rated angular frequency, ω is the actual output frequency of the active-frequency control, D p is the droop coefficient of the active-frequency control;

[0021]

[0022] In the formula, Q ref is the reference reactive power, Q e is the actual reactive power output by the grid-connected inverter, Q c,vsg is the reactive power compensation signal of the dual-mode switching in the VSG, D q is the damping coefficient of the reactive-voltage control, v n is the reference amplitude of the grid-connected inverter port phase voltage, v0 is the actual amplitude of the grid-connected inverter output port phase voltage, and K is the reactive inertia coefficient;

[0023] 2.1.2, the reference phase θ of the grid-connected inverter internal potential e abc and the reference amplitude E of the grid-connected inverter internal potential e abc are input into the internal potential reference to obtain the three-phase sinusoidal internal potential reference signal The calculation equation is:

[0024]

[0025] 2.1.3, the three-phase sinusoidal internal potential reference signal and the three-phase voltage u abc of the grid-connected inverter main circuit output port are input into the virtual impedance control link to obtain the current reference signal in the VSG control mode

[0026] Preferably, the current reference signal in the constant power PQ control mode is calculated by the following steps:

[0027] 2.2.1, the three-phase voltage uabc Input into the phase-locked loop to obtain the grid phase θ when connected to the grid g , the grid phase θ when connected to the grid g The phase reference is used for dq conversion, and the grid phase θ when connected to the grid g The three-phase voltage u of the output port of the main circuit 10 of the grid-connected inverter anc Input to the dq conversion link to calculate the three-phase voltage u at the output port of the main circuit of the grid-connected inverter anc The d-axis voltage component u d ;

[0028] 2.2.2 Grid phase θ during grid connection g , d-axis voltage component u d , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to the PQ control current reference calculation link for calculation to obtain the current reference signal under constant power PQ control mode The calculation equation is:

[0029]

[0030] Preferably, the active power compensation signal P in the VSG of the dual-mode switching c,vsg and reactive power compensation signal Q c,vsg The calculation equation is:

[0031]

[0032] Active power compensation signal P in PQ with dual-mode switching c,pq and reactive power compensation signal Q c,pq The calculation equation is:

[0033]

[0034] Preferably, the mode switching switch is a control switch. When the control switch "1" is turned on, it indicates the input reference current of the current inner loop control unit. Equal to the current reference signal in VSG control mode Right now When the control switch "2" is turned on, the input reference current of the current inner loop control unit Equal to the current reference signal in constant power PQ control mode Right now

[0035] Preferably, the current inner loop control unit is in K piis the ratio, K ii The current inner loop control is performed under the PI regulation of the differential parameter, and the port voltage feedforward of the main circuit of the grid-connected inverter is performed, and the dq axis signal of the three-phase modulation wave is The calculation equation is:

[0036]

[0037] Where, is the d-axis signal of the three-phase modulation wave, is the q-axis signal of the three-phase modulation wave, As the modulation signal of SVPWM drive control, They are the input reference current d-axis signal and q-axis signal of the current inner loop control unit, i d 、i q are the actual d-axis current and q-axis current of the main circuit of the grid-connected inverter, K pi and K ii These are the control parameters of the PI controller in the current inner loop control unit.

[0038] When the inverter needs to switch between VSG and constant power PQ control working modes in a complex working environment, the present invention can achieve smooth switching of the control mode through a simple power compensation control strategy without additional requirements for sampler accuracy. It is suitable for large-scale promotion in new energy grid connection in complex working environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of a PQ and VSG smooth switching control system based on power compensation provided in Example 1 of the present invention;

[0040] Figure 2 A schematic diagram of a VSG power outer loop control link in a PQ and VSG smooth switching control method based on power compensation provided in Example 2 of the present invention;

[0041] Figure 3 A schematic diagram of an internal potential reference in a PQ and VSG smooth switching control method based on power compensation provided in Example 2 of the present invention;

[0042] Figure 4 A schematic diagram of a virtual impedance control link in a PQ and VSG smooth switching control method based on power compensation provided in Example 2 of the present invention;

[0043] Figure 5 A schematic diagram of a PQ control current reference calculation link in a PQ and VSG smooth switching control method based on power compensation provided in Example 2 of the present invention;

[0044] Figure 6A schematic diagram of a power compensation unit in a PQ and VSG smooth switching control method based on power compensation provided in embodiment 2 of the present invention;

[0045] Figure 7 A schematic diagram of a mode switching switch in a PQ and VSG smooth switching control method based on power compensation provided in Example 2 of the present invention;

[0046] Figure 8 A schematic diagram of a current inner loop control unit in a PQ and VSG smooth switching control method based on power compensation provided in Example 2 of the present invention;

[0047] Figure 9 This is a simulation waveform diagram of output voltage and current when the constant power PQ control and VSG control are switched between each other in the present invention;

[0048] Figure 10 This is the simulated waveform diagram of the output voltage and current when the constant power PQ control switches to VSG control in the present invention;

[0049] Figure 11 This is the output voltage and current simulation waveform diagram when the VSG control switches to constant power PQ control in the present invention;

[0050] Figure 12 This is a simulation waveform diagram showing the current reference comparison of the constant power PQ control and VSG control outputs of the present invention;

[0051] Figure 13 It is a simulation waveform diagram of active power and reactive power output of the present invention;

[0052] In the figure: 10 grid-connected inverter main circuit, 11 three-phase inverter, 12 three-phase LC filter, 20 constant power PQ control unit, 21 phase-locked loop, 22 dq conversion link, 23 PQ control current reference calculation link, 30 VSG control unit, 31 VSG power outer loop control link, 32 internal potential reference, 33 virtual impedance control link, 40 power compensation unit, 50 mode switching switch, 60 current inner loop control unit, 70 space vector modulation SVPWM control unit. DETAILED DESCRIPTION

[0053] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the following describes the technical solutions of the present invention clearly and completely with reference to specific embodiments and the accompanying drawings. It is obvious that the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0054] Example 1

[0055] like Figure 1 As shown, this embodiment provides a PQ and VSG smooth switching control system based on power compensation, including a grid-connected inverter main circuit 10, a constant power PQ control unit 20, a VSG control unit 30, a power compensation unit 40, a mode switching switch 50, a current inner loop control unit 60, and a space vector modulation SVPWM control unit 70. The three-phase voltage u abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsg Input to the VSG control unit 30 for calculation to obtain the current reference signal under the VSG control mode The three-phase voltage u at the output port of the main circuit 10 of the grid-connected inverter abc , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to the constant power PQ control unit 20 for calculation to obtain the current reference signal under the constant power PQ control mode Current reference signal in VSG control mode Current reference signal in constant power PQ control mode And the three-phase voltage u of the output port of the main circuit of the grid-connected inverter abc The d-axis voltage component u d Input to the power compensation unit 40 for calculation, and obtain the power compensation signal P of the dual-mode switching in the VSG. c,vsg , Q c,vsg and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq The mode switching switch 50 is used to switch the operation mode of the grid-connected inverter main circuit 10. When the constant power PQ control mode is switched to the VSG control mode, the power compensation signal P in the VSG is switched in the dual-mode mode. c,vsg , Q c,vsg Input reference current to VSG control unit 30 and current inner loop control unit 60 Equal to the current reference signal in VSG control mode When the VSG control mode switches to the constant power PQ control mode, the power compensation signal P in the PQ c,pq , Q c,pq Input to the constant power PQ control unit 20, the input reference current of the current inner loop control unit Equal to the current reference signal in constant power PQ control mode The input reference current of the current inner loop control unit 60 and the actual dq axis current i of the grid-connected inverter main circuit 10 d 、i q Input to the current inner loop control unit 60 for calculation to obtain the dq axis signal of the three-phase modulation wave dq axis signals of three-phase modulated wave The trigger pulse signal is input into the space vector modulation SVPWM control unit 70 to obtain the trigger pulse signal of each switch tube in the main circuit of the grid-connected inverter.

[0056] The present invention adopts a power compensation method during the grid connection period. The compensation control uses the d-axis and q-axis currents calculated by the virtual synchronous generator (VSG) and the constant power PQ control and the d-axis component of the port voltage of the main circuit of the grid-connected inverter as inputs. The power value generated when the VSG control and constant power PQ control currents deviate in the power compensation unit is calculated. The compensation power is input into the constant power PQ control unit and the VSG control unit respectively, achieving synchronization of the reference current of the current inner loop of the two. This ensures that the VSG self-generated phase and the current inner loop amplitude are equal before and after the switching between the VSG control mode and the constant power PQ control mode during the grid connection period. This achieves smooth switching of the modes during the grid connection period and ensures smooth transition between the VSG and PQ switching at any time. The various variables of the VSG and PQ are always maintained unchanged before and after the switching, without the need for additional or precise sensors to ensure the variables remain unchanged by assignment before and after the switching. When the inverter needs to switch between the VSG and constant power PQ control modes in complex working environments, the present invention can achieve smooth switching of the control modes through a simple power compensation control strategy without additional requirements for sampler accuracy. This is suitable for large-scale promotion in the grid connection of new energy in complex working environments.

[0057] The grid-connected inverter main circuit 10 includes: a DC power supply U dc , three-phase inverter 11, three-phase LC filter 12, DC power supply U dc The DC input terminal of the three-phase inverter 11 is connected to the DC input terminal of the three-phase inverter 11, and the output terminal of the three-phase inverter 11 is connected to the three-phase filter inductor L in the three-phase LC filter 12. f One end of the three-phase filter inductor L f The other end is connected to the three-phase filter capacitor C f One end of the large power grid u g , three-phase filter capacitor C f Short-circuit the other end.

[0058] The constant power PQ control unit 20 includes: a phase-locked loop 21, a dq conversion link 22, a PQ control current reference calculation link 23, and a three-phase voltage u at the output port of the grid-connected inverter main circuit 10. abc Input to the phase-locked loop 21 to obtain the grid phase θ when connected to the grid g , grid phase θ when connected to the grid gThe three-phase voltage u of the output port of the main circuit 10 of the grid-connected inverter abc Input to the dq conversion link 22 to calculate the three-phase voltage u at the output port of the grid-connected inverter main circuit 10 abc The d-axis voltage component u d , grid phase θ when connected to the grid g , d-axis voltage component u d , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to PQ control current reference calculation link 23 for calculation to obtain the current reference signal under constant power PQ control mode

[0059] The VSG control unit 30 includes: a VSG power outer loop control link 31, an internal potential reference 32, a virtual impedance control link 33, a three-phase voltage u at the output port of the grid-connected inverter main circuit 10 abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsg Input to VSG power outer loop control link 31 for calculation, and obtain the internal potential e of the grid-connected inverter abc The reference phase θ and the potential e in the grid-connected inverter abc The reference amplitude E, the potential e in the grid-connected inverter abc The reference phase θ and the potential e in the grid-connected inverter abc The reference amplitude E is input into the internal potential reference 32, and the three-phase sinusoidal internal potential reference signal is calculated. Three-phase sinusoidal internal potential reference signal The three-phase voltage u of the output port of the main circuit 10 of the grid-connected inverter abc Input into the virtual impedance control link 33 for calculation to obtain the current reference signal under the VSG control mode

[0060] Example 2

[0061] This embodiment provides a control method for the PQ and VSG smooth switching control system based on power compensation used in Embodiment 1, including the following steps:

[0062] Step 1: Obtain the operating parameters and working mode of the grid-connected inverter main circuit 10. The operating parameters of the grid-connected inverter main circuit include: the three-phase voltage u of the output port of the grid-connected inverter main circuit; abc , three-phase current i abc, the working mode of the main circuit of the grid-connected inverter is constant power PQ control mode or VSG control mode.

[0063] Step 2: The three-phase voltage u at the output port of the main circuit 10 of the grid-connected inverter abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsg Input to the VSG control unit 30 for calculation to obtain the current reference signal under the VSG control mode The three-phase voltage u at the output port of the main circuit 10 of the grid-connected inverter abc , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to the constant power PQ control unit 20 for calculation to obtain the current reference signal under the constant power PQ control mode

[0064] The current reference signal in the VSG control mode Calculated by the following steps:

[0065] 2.1.1. Three-phase voltage u at the output port of the main circuit 10 of the grid-connected inverter abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsg Input to VSG power outer loop control link 31 for calculation, and obtain the internal potential e of the grid-connected inverter abc The reference phase θ and the potential e in the grid-connected inverter abc The reference amplitude E.

[0066] like Figure 2 As shown, the VSG power outer loop control link 31 includes active-frequency control and reactive-voltage control. By simulating the rotor motion equation of the synchronous machine, the active-frequency control equation is obtained as follows:

[0067]

[0068] In formula (1), P ref is the reference active power, P e is the active power actually generated by the grid-connected inverter, P c,vsg is the active power compensation signal of dual-mode switching in VSG, J is the moment of inertia of active frequency control, ω n is the rated angular frequency, ω is the actual output frequency of the active-frequency control, and θ is the internal potential e of the grid-connected inverter. abc The reference phase, Dp is the droop coefficient of active power-frequency control.

[0069] The equation for reactive power-voltage control is:

[0070]

[0071] In formula (2), E is the internal potential of the grid-connected inverter e abc Reference amplitude, Q ref is the reference reactive power, Q e is the reactive power actually generated by the grid-connected inverter, Q c,vsg is the reactive power compensation signal in the VSG with dual-mode switching, D q is the damping coefficient of reactive-voltage control, v n is the reference amplitude of the phase voltage at the grid-connected inverter port, v0 is the actual amplitude of the phase voltage at the output port of the grid-connected inverter, and K is the reactive inertia coefficient.

[0072] The active power P actually generated by the grid-connected inverter e The calculation equation is:

[0073] P e =u a i a +u b i b +u c i c (3)

[0074] The reactive power Q actually generated by the grid-connected inverter e The calculation equation is:

[0075]

[0076] In formula (3) and formula (4), u a 、u b 、u c Represents the three-phase voltage u at the output port of the grid-connected inverter abc The voltage of each phase A, B, and C, i a 、i b 、i c Represents the three-phase current i of the output port of the grid-connected inverter abc The A, B, and C phase currents.

[0077] The calculation equation for the actual amplitude v0 of the phase voltage at the output port of the grid-connected inverter is:

[0078]

[0079] In formula (5), u d 、u qThey are the three-phase voltage u at the output port of the grid-connected inverter abc Voltage components in the dq coordinate system.

[0080] 2.1.2. Grid-connected inverter internal potential e abc The reference phase θ and the potential e in the grid-connected inverter abc The reference amplitude E is input into the internal potential reference 32, and the three-phase sinusoidal internal potential reference signal is calculated.

[0081] like Figure 3 As shown, the output phase θ of the grid-connected inverter with active power-frequency control output and the internal potential e of the grid-connected inverter with reactive power-voltage control output are abc The reference amplitude E of the three-phase sinusoidal internal potential reference signal is calculated. The calculation equation is:

[0082]

[0083] 2.1.3 Three-phase sinusoidal internal potential reference signal The three-phase voltage u of the output port of the main circuit 10 of the grid-connected inverter abc Input into the virtual impedance control link 33 for calculation to obtain the current reference signal under the VSG control mode

[0084] like Figure 4 As shown, the three-phase sinusoidal internal potential reference signal The three-phase voltage u of the output port of the main circuit 10 of the grid-connected inverter abc After the difference, through the virtual impedance Then we get the virtual three-phase current i la 、i lb 、i lc :

[0085]

[0086] The virtual impedance L v and R v The filter inductor L is simulated f Its parasitic resistance R f , the virtual three-phase current output after passing through the virtual impedance The current near the power frequency on the filter inductor is similar to the grid phase θ when connected to the grid. g As a reference, the current reference signal in the dq axis coordinate system is obtained after the transformation from the abc coordinate system to the dq coordinate system.

[0087] like Figure 5 As shown, the current reference signal in constant power PQ control mode Calculated by the following steps:

[0088] 2.2.1. Three-phase voltage u at the output port of the main circuit 10 of the grid-connected inverter abc Input to the phase-locked loop 21 to obtain the grid phase θ when connected to the grid g , the grid phase θ when connected to the grid g The phase reference is used for dq conversion, and the grid phase θ when connected to the grid g The three-phase voltage u of the output port of the main circuit 10 of the grid-connected inverter abc Input to the dq conversion link 22 to calculate the three-phase voltage u at the output port of the grid-connected inverter main circuit 10 abc The d-axis voltage component u d .

[0089] 2.2.2 Grid phase θ during grid connection g , d-axis voltage component u d , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to PQ control current reference calculation link 23 for calculation to obtain the current reference signal under constant power PQ control mode

[0090] d-axis voltage component u d is the amplitude of the three-phase voltage at the output port of the grid-connected inverter, so the dq-axis components of the three-phase current can be calculated by formula (7) using a given reference power:

[0091]

[0092] In formula (7), is the d-axis current component of the current reference signal in the constant power PQ control mode, is the q-axis current component of the current reference signal in the constant power PQ control mode, is the actual active reference input, which is equal to the given reference active power P ref Active power compensation signal P in PQ with dual mode switching c,pq The superposition of is the actual reactive reference input, which is equal to the given reference reactive power Q ref Reactive power compensation signal Q in PQ with dual mode switching c,pq The superposition of u d is the three-phase voltage u at the output port of the main circuit 10 of the grid-connected inverter abc The d-axis voltage component of

[0093] Step 3: Current reference signal in VSG control mode Current reference signal in constant power PQ control mode And the three-phase voltage u of the output port of the main circuit of the grid-connected inverter abc The d-axis voltage component u d Input to the power compensation unit 40 for calculation, and obtain the power compensation signal P of the dual-mode switching in the VSG. c,vsg , Q c,vsg and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq .

[0094] like Figure 6 As shown, when the constant power PQ control mode switches to the VSG control mode, in order to maintain a smooth transition of the input reference current of the current inner loop control unit 60, the active current reference signal in the VSG control mode should be maintained. and reactive current reference signal in VSG control mode Respectively with the active current reference signal in constant power PQ control mode and reactive current reference signal in constant power PQ control mode Therefore, the difference between the active current reference signal output by the constant power PQ control mode and the VSG control mode is and reactive current difference Get the active power compensation signal P of VSG active-frequency control c,vsg and reactive power compensation signal Q for reactive-voltage control c,vsg , active power compensation signal P in dual-mode switching in VSG c,vsg and reactive power compensation signal Q c,vsg The calculation equation is:

[0095]

[0096] Similarly, when the VSG control mode switches to the constant power PQ control mode, the active current reference signal in the constant power PQ control mode should be maintained. and reactive current reference signal in constant power PQ control mode Respectively with the active current reference signal in VSG control mode and reactive current reference signal in VSG control mode Therefore, the difference between the active current reference signal output by the VSG control mode and the constant power PQ control mode is and reactive current difference Get the active power compensation signal P of dual-mode switching in PQ c,pq and reactive power compensation signal Q c,pq, the active power compensation signal P in PQ of dual-mode switching c,pq and reactive power compensation signal Q c,pq The calculation equation is:

[0097]

[0098] When the PQ (grid-connected) switches to the VSG (grid-connected), the compensation power is calculated using the current difference between the PQ and VSG and superimposed into the active frequency link and reactive voltage loop of the VSG, forming a closed loop in the power loop and virtual impedance link. The VSG automatically adjusts the amplitude and phase to keep the output value of the current inner loop consistent with the PQ during the grid-connected period. Because it is a closed loop, the various variables in the VSG power loop and virtual impedance link will not change suddenly after switching at any time, achieving smooth switching. Similarly, when the VSG (grid-connected) of the present invention switches to the PQ (grid-connected), the output value of the PQ control reference current control link is adjusted with the power compensation, maintaining the reference current value of the PQ control unchanged after the switch, achieving smooth switching.

[0099] Step 4: Switch the operation mode of the grid-connected inverter main circuit 10 through the mode switching switch 50. When the constant power PQ control mode is switched to the VSG control mode, the power compensation signal P in the VSG is switched in the dual mode. c,vsg , Q c,vsg Input reference current to VSG control unit 30 and current inner loop control unit 60 Equal to the current reference signal in VSG control mode When the VSG control mode switches to the constant power PQ control mode, the power compensation signal P in the PQ c,pq , Q c,pq Input to the constant power PQ control unit 20, the input reference current of the current inner loop control unit Equal to the current reference signal in constant power PQ control mode

[0100] like Figure 7 As shown, the mode switching switch 50 is used to switch the operation mode of the grid-connected inverter main circuit 10. The mode switching switch 50 can be a control switch. When the control switch "1" is turned on, it indicates that the input reference current of the current inner loop control unit 60 is Equal to the current reference signal in VSG control mode Right now When the control switch "2" is turned on, the input reference current of the current inner loop control unit Equal to the current reference signal in constant power PQ control mode Right now

[0101] Step 5: Input reference current of the current inner loop control unit 60 and the actual dq axis current i of the grid-connected inverter main circuit 10 d 、i q Input to the current inner loop control unit 60 for calculation to obtain the dq axis signal of the three-phase modulation wave dq axis signals of three-phase modulated wave The trigger pulse signal is input into the space vector modulation SVPWM control unit 70 to obtain the trigger pulse signal of each switch tube in the main circuit of the grid-connected inverter.

[0102] like Figure 8 As shown, in K pi is the ratio, K ii The current inner loop control is performed under the PI regulation of the differential parameter, and the port voltage feedforward of the main circuit of the grid-connected inverter is performed to obtain the dq axis signal of the three-phase modulation wave in the dq coordinate system. The calculation equation is:

[0103]

[0104] In formula (10), is the d-axis signal of the three-phase modulation wave, is the q-axis signal of the three-phase modulation wave, As the modulation signal of SVPWM drive control, They are the input reference current d-axis signal and q-axis signal of the current inner loop control unit 60, i d 、i q are the actual d-axis current and q-axis current of the main circuit 10 of the grid-connected inverter, K pi and K ii These are all control parameters of the PI controller in the current inner loop control unit 60 .

[0105] Simulation test

[0106] In the simulation, the working condition is set to the reference active power P given by the grid. ref =6kW, reference reactive power Q ref =0var. The parameters and control parameters of the main circuit of the grid-connected inverter are set as follows: DC voltage is 300V, rated phase voltage amplitude reference v n 164V, filter inductor L f is 2000μH, the filter capacitor C f The active power droop coefficient D is 45μF and the rated grid frequency is 50Hz. p and reactive damping coefficient D q They are 1100 and 368 respectively, and the virtual moment of inertia J is 0.013kg*m 2 , the reactive inertia coefficient K is 5.5.

[0107] Under the above simulation parameters, Figure 9 This is a simulation waveform diagram of output voltage and current when the constant power PQ control and VSG control are switched between each other in the present invention; Figure 9 This is the simulation waveform of the overall output voltage and current when the constant power PQ control mode and the VSG control mode are switched between each other. At 1-2s, the grid-connected inverter is in constant power PQ control operation. At the 2nd second, the PQ mode is switched to the VSG control mode. At 2-4s, the inverter is in VSG control operation. At the 4th second, the VSG control mode is switched to constant power PQ control. At 4-5s, the inverter is in constant power PQ control operation.

[0108] Figure 10 This is the simulated waveform of the output voltage and current when constant power PQ control switches to VSG control. After using the PQ and VSG smooth switching control strategy based on power compensation, the output current transitions smoothly when the inverter switches from PQ mode to VSG control mode.

[0109] Figure 11 This is the simulated waveform of the output voltage and current when VSG control switches to PQ control. Similarly, under the power compensation strategy, the output current transitions smoothly when the inverter switches from VSG control mode to PQ mode.

[0110] Figure 12 This is a comparison simulation waveform of the current reference output of the constant power PQ control and VSG control of the present invention. At 1-2s, the grid-connected inverter is in constant power PQ control operation. After using the PQ and VSG smooth switching control strategy based on power compensation, the compensation power P c,vsg and Q c,vsg After compensating the VSG active frequency loop and reactive voltage loop, the dq axis current reference output under VSG control is obtained. The current reference of the PQ control output Basically the same, therefore, when switching in the 2nd second, the current reference does not change suddenly, and a smooth transition of the control mode is achieved. Similarly, when the grid-connected inverter is in VSG control operation at 2-4 seconds, the compensation power P x,pq and Q c,pq Compensate into constant power PQ control and obtain the dq axis current reference output under PQ control The current reference of the VSG control output The control is basically the same, achieving a smooth transition from VSG control to constant power PQ control in the 4th second.

[0111] Figure 13This is a simulation waveform diagram of the active power and reactive power output of the present invention. After adopting the PQ and VSG smooth switching control strategy based on power compensation of the present invention, when switching between modes, the active power and reactive power remain basically unchanged, realizing a smooth transition when switching the control mode.

[0112] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. The PQ and VSG smooth switching control system based on power compensation is characterized by: The invention comprises a grid-connected inverter main circuit (10), a constant power PQ control unit (20), a VSG control unit (30), a power compensation unit (40), a mode switching switch (50), a current inner loop control unit (60), and a space vector modulation (SVPWM) control unit (70). The three-phase voltage, three-phase current and power compensation signal of the dual-mode switching in the VSG at the output port of the grid-connected inverter main circuit (10) are input into the VSG control unit (30) for calculation to obtain a current reference signal under the VSG control mode. The three-phase voltage, given reference power and power compensation signal of the dual-mode switching in the PQ at the output port of the grid-connected inverter main circuit (10) are input into the constant power PQ control unit (20) for calculation to obtain a current reference signal under the constant power PQ control mode. The current reference signal under the VSG control mode, the current reference signal under the constant power PQ control mode and the d-axis voltage component of the three-phase voltage at the output port of the grid-connected inverter main circuit are input into the power compensation unit (40) for calculation to obtain a power compensation signal of the dual-mode switching in the VSG and a dual-mode switching power compensation signal. The mode switches the power compensation signal in PQ, and the mode switching switch (50) is used to switch the operation mode of the grid-connected inverter main circuit (10). When the constant power PQ control mode switches to the VSG control mode, the power compensation signal in the dual-mode switching in VSG is input to the VSG control unit (30). The input reference current of the current inner loop control unit (60) is equal to the current reference signal in the VSG control mode. When the VSG control mode switches to the constant power PQ control mode, the power compensation signal in the dual-mode switching in PQ is input to the constant power PQ control unit (20). The input reference current of the current inner loop control unit is equal to the current reference signal in the constant power PQ control mode. The input reference current of the current inner loop control unit (60) and the actual dq axis current of the grid-connected inverter main circuit (10) are input to the current inner loop control unit (60) for calculation to obtain the dq axis signal of the three-phase modulation wave. The dq axis signal of the three-phase modulation wave is input to the space vector modulation SVPWM control unit (70) to obtain the trigger pulse signal of each switch tube in the grid-connected inverter main circuit (10).

2. The PQ and VSG smooth switching control system based on power compensation according to claim 1 is characterized in that: The grid-connected inverter main circuit (10) comprises: a DC power supply U dc , three-phase inverter (11), three-phase LC filter (12), DC power supply U dc The DC input terminal of the three-phase inverter (11) is connected to the output terminal of the three-phase inverter (11), and the output terminal of the three-phase inverter (11) is connected to the three-phase filter inductor L in the three-phase LC filter (12). f One end of the three-phase filter inductor L f The other end is connected to the three-phase filter capacitor C f One end of the large power grid u g , three-phase filter capacitor C f Short-circuit the other end.

3. The PQ and VSG smooth switching control system based on power compensation according to claim 1 is characterized in that: The constant power PQ control unit (20) comprises: a phase-locked loop (21), a dq conversion link (22), a PQ control current reference calculation link (23), and a three-phase voltage u at the output port of the grid-connected inverter main circuit (10). abc Input into the phase-locked loop (21) to obtain the grid phase θ when connected to the grid g , grid phase θ when connected to the grid g The three-phase voltage u of the output port of the main circuit (10) of the grid-connected inverter abc Input to the dq conversion link (22) to calculate the three-phase voltage u at the output port of the grid-connected inverter main circuit (10) abc The d-axis voltage component u d , grid phase θ when connected to the grid g , d-axis voltage component u d , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to the PQ control current reference calculation link (23) for calculation to obtain the current reference signal under the constant power PQ control mode 4. The PQ and VSG smooth switching control system based on power compensation according to claim 1 is characterized in that: The VSG control unit (30) includes: a VSG power outer loop control link (31), an internal potential reference (32), a virtual impedance control link (33), a three-phase voltage u at the output port of the grid-connected inverter main circuit (10), and a abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsg Input to the VSG power outer loop control link (31) for calculation, and obtain the internal potential e of the grid-connected inverter abc The reference phase θ and the potential e in the grid-connected inverter abc The reference amplitude E, the potential e in the grid-connected inverter abc The reference phase θ and the potential e in the grid-connected inverter abc The reference amplitude E is input into the internal potential reference (32) to calculate the three-phase sinusoidal internal potential reference signal Three-phase sinusoidal internal potential reference signal The three-phase voltage u of the output port of the main circuit (10) of the grid-connected inverter abc Input into the virtual impedance control link (33) for calculation to obtain the current reference signal under the VSG control mode 5. A method for controlling smooth switching between PQ and VSG based on power compensation, applied to the control system according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Obtain the operating parameters and working mode of the main circuit of the grid-connected inverter, wherein the operating parameters include the three-phase voltage u of the output port of the main circuit of the grid-connected inverter. abc , three-phase current i abc , the working mode is a constant power PQ control mode or a VSG control mode; Step 2: The three-phase voltage u at the output port of the main circuit of the grid-connected inverter abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsg Input to the VSG control unit for calculation to obtain the current reference signal under VSG control mode Three-phase voltage u at the output port of the main circuit of the grid-connected inverter abc , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to the constant power PQ control unit for calculation to obtain the current reference signal under the constant power PQ control mode Step 3: Current reference signal in VSG control mode Current reference signal in constant power PQ control mode And the three-phase voltage u of the output port of the main circuit of the grid-connected inverter abc The d-axis voltage component u d Input to the power compensation unit 40 for calculation, and obtain the power compensation signal P of the dual-mode switching in the VSG. c,vsg , Q c,vsg and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq ; Step 4: Switch the operation mode of the main circuit of the grid-connected inverter through the mode switch. When the constant power PQ control mode is switched to the VSG control mode, the power compensation signal P in the VSG is switched by the dual mode. c,vsg , Q c,vsg Input to the VSG control unit, the input reference current of the current inner loop control unit Equal to the current reference signal in VSG control mode When the VSG control mode switches to the constant power PQ control mode, the power compensation signal P in the PQ c,pq , Q c,pq Input to the constant power PQ control unit, the input reference current of the current inner loop control unit Equal to the current reference signal in constant power PQ control mode Step 5: Input reference current of the current inner loop control unit and the actual dq axis current i of the main circuit of the grid-connected inverter d 、i q Input to the current inner loop control unit for calculation to obtain the dq axis signal of the three-phase modulation wave dq axis signals of three-phase modulated wave The trigger pulse signal of each switch tube in the main circuit of the grid-connected inverter is input into the space vector modulation SVPWM control unit.

6. The method for controlling smooth switching between PQ and VSG based on power compensation according to claim 5, characterized in that: The current reference signal in the VSG control mode Calculated by the following steps: 2.1.

1. Three-phase voltage u at the output port of the main circuit of the grid-connected inverter abc , three-phase current i abc and the power compensation signal P in the VSG with dual-mode switching c,vsg , Q c,vsg Input to the VSG power outer loop control link for calculation to obtain the internal potential e of the grid-connected inverter abc The reference phase θ and the potential e in the grid-connected inverter abc The reference amplitude E is calculated as follows: Where, P ref is the reference active power, P e is the active power actually generated by the grid-connected inverter, P c,vsg is the active power compensation signal of dual-mode switching in VSG, J is the moment of inertia of active frequency control, ω n is the rated angular frequency, ω is the actual output frequency of active-frequency control, D p is the droop coefficient of active power-frequency control; Where Q ref is the reference reactive power, Q e is the reactive power actually generated by the grid-connected inverter, Q c,vsg is the reactive power compensation signal in the VSG with dual-mode switching, D q is the damping coefficient of reactive-voltage control, v n is the reference amplitude of the phase voltage at the grid-connected inverter port, v0 is the actual amplitude of the phase voltage at the output port of the grid-connected inverter, and K is the reactive inertia coefficient; 2.1.

2. Grid-connected inverter internal potential e abc The reference phase θ and the potential e in the grid-connected inverter abc The reference amplitude E is input into the internal potential reference, and the three-phase sinusoidal internal potential reference signal is calculated. The calculation equation is: 2.1.3 Three-phase sinusoidal internal potential reference signal The three-phase voltage u of the main circuit output port of the grid-connected inverter abc Input into the virtual impedance control link for calculation to obtain the current reference signal under VSG control mode 7. The method for smooth switching between PQ and VSG based on power compensation according to claim 5, wherein the current reference signal in the constant power PQ control mode is Calculated by the following steps: 2.2.

1. Three-phase voltage u at the output port of the main circuit of the grid-connected inverter abc Input into the phase-locked loop to obtain the grid phase θ when connected to the grid g , the grid phase θ when connected to the grid g The phase reference is used for dq conversion, and the grid phase θ when connected to the grid g The three-phase voltage u at the output port of the main circuit (10) of the grid-connected inverter abc Input to the dq conversion link to calculate the three-phase voltage u at the output port of the main circuit of the grid-connected inverter abc The d-axis voltage component u d ; 2.2.2 Grid phase θ during grid connection g , d-axis voltage component u d , given reference power P ref , Q ref and the power compensation signal P in PQ for dual mode switching c,pq , Q c,pq Input to the PQ control current reference calculation link for calculation to obtain the current reference signal under constant power PQ control mode The calculation equation is:

8. The method for controlling smooth switching between PQ and VSG based on power compensation according to claim 5, characterized in that: The active power compensation signal P in the VSG of the dual-mode switching c,vsg and reactive power compensation signal Q c,vsg The calculation equation is: Active power compensation signal P in PQ with dual-mode switching c,pq and reactive power compensation signal Q c,pq The calculation equation is:

9. The method for controlling smooth switching between PQ and VSG based on power compensation according to claim 5, characterized in that: The mode switch is a control switch. When the control switch "1" is turned on, it indicates the input reference current of the current inner loop control unit. Equal to the current reference signal in VSG control mode Right now When the control switch "2" is turned on, the input reference current of the current inner loop control unit Equal to the current reference signal in constant power PQ control mode Right now 10. The method for controlling smooth switching between PQ and VSG based on power compensation according to claim 5, characterized in that: The current inner loop control unit is based on K pi is the ratio, K ii The current inner loop control is performed under the PI regulation of the differential parameter, and the port voltage feedforward of the main circuit of the grid-connected inverter is performed, and the dq axis signal of the three-phase modulation wave is The calculation equation is: Where, is the d-axis signal of the three-phase modulation wave, is the q-axis signal of the three-phase modulation wave, As the modulation signal of SVPWM drive control, They are the input reference current d-axis signal and q-axis signal of the current inner loop control unit, i d 、i q are the actual d-axis current and q-axis current of the main circuit of the grid-connected inverter, K pi and K ii These are the control parameters of the PI controller in the current inner loop control unit.

Images