Control method, device and equipment for improving stability of grid-connected inverter

Abstract

The invention relates to the technical field of inverter control, and discloses a control method, device and equipment for improving the stability of a grid-connected inverter, and the method comprises the steps: obtaining a common coupling point voltage and an inversion inductive current of a power grid and the grid-connected inverter; obtaining an initial current closed-loop regulating variable according to the common coupling point voltage and the inversion inductive current; performing phase lead compensation on the initial current closed-loop regulation quantity and the partial power grid voltage feed-forward quantity to obtain a final current closed-loop regulation quantity; adding the final current closed-loop regulating quantity and the full feed-forward quantity of the power grid voltage to obtain a modulated wave signal; the grid-connected inverter is controlled to operate based on the modulated wave signal, the grid-connected inverter can stably operate under the condition of wider-range weak power grid impedance, and the stability of a grid-connected inverter system is improved.

Description

Technical Field

[0001] This invention relates to the field of inverter control technology, and more specifically to a control method, apparatus, and equipment for improving the stability of grid-connected inverters. Background Technology

[0002] As the penetration rate of intermittent new energy sources such as wind power and photovoltaics continues to increase, the number of long transmission and distribution lines and distributed generation equipment continues to increase, making the power grid exhibit weak grid characteristics.

[0003] As the interface unit between distributed generation systems and the power system, the performance of the grid-connected inverter determines the power generation quality and efficient, reliable operation of the grid-connected generation system. To ensure sufficient suppression of grid background harmonics, multiple resonant control is typically introduced into the current loop. However, when the added resonant control gain is too high or the number of resonant controller cycles approaches the current loop cutoff frequency, the system stability margin will decrease significantly. Grid voltage feedforward can suppress various grid background harmonics without affecting the system's stability margin; therefore, multiple resonant control and grid voltage feedforward are generally used together to ensure the quality of the grid-connected current waveform under strong grid conditions. However, under weak grid conditions, the presence of grid impedance can introduce a negative phase shift into the low-frequency band of the control loop through the feedforward channel, thereby causing system resonant instability.

[0004] The proposed solution is to add phase lead compensation to the grid voltage feedforward channel to offset the negative phase shift caused by the high impedance of the grid side and the control delay, thereby improving the stability of the system. This method can achieve good results when the equivalent impedance of the grid side is small, but as the impedance of the grid side increases, the system still has the risk of instability. Summary of the Invention

[0005] In view of this, the present invention provides a control method, apparatus and equipment for improving the stability of grid-connected inverters, so as to solve the technical problem of low stability of grid-connected power generation systems under weak grid conditions.

[0006] In a first aspect, the present invention provides a control method for improving the stability of a grid-connected inverter, comprising:

[0007] Obtain the common coupling point voltage of the power grid and the grid-connected inverter, as well as the inverter inductor current;

[0008] The initial current closed-loop regulation is obtained based on the common coupling point voltage and the inverter inductor current.

[0009] Multiplying the common coupling point voltage by the first coefficient yields the partial grid voltage feedforward, and multiplying the common coupling point voltage by the second coefficient yields the full grid voltage feedforward. The first coefficient is greater than 0 and less than 1, and the second coefficient is greater than or equal to 1.

[0010] The initial current closed-loop regulation and part of the grid voltage feedforward are combined and phase lead compensation is applied to obtain the final current closed-loop regulation.

[0011] The modulated wave signal is obtained by adding the final closed-loop current regulation and the full feedforward of the grid voltage.

[0012] The grid voltage feedforward is used to control the grid-connected inverter based on the modulated wave signal.

[0013] In some optional real-time modes, the initial current closed-loop regulation is obtained based on the common coupling point voltage and the inverter inductor current, including:

[0014] The real-time active current reference value is calculated based on the common coupling point voltage and the grid-connected active power reference value;

[0015] The initial current closed-loop regulation is obtained by processing the real-time setpoints of the inverter inductor current and active current.

[0016] In some optional real-time methods, the real-time active current setpoint is calculated based on the common coupling point voltage and the grid-connected active power setpoint, including:

[0017] The active component of the grid voltage and the real-time phase of the grid voltage are obtained by processing the voltage at the common coupling point through a phase-locked loop.

[0018] The active current amplitude is given by dividing the grid-connected active power setpoint and the grid voltage active component.

[0019] The real-time active current setpoint is calculated based on the active current amplitude setpoint and the real-time phase of the grid voltage.

[0020] In some optional real-time modes, the real-time setpoints of the inverter inductor current and active current are processed to obtain the initial current closed-loop regulation, including:

[0021] The difference between the real-time given value of the active current and the inverter inductor current is obtained;

[0022] The current difference is adjusted by a proportional-integral controller and multiple proportional-resonant controllers through a current closed-loop regulator to obtain the initial current closed-loop regulation value.

[0023] In some optional real-time modes, the expression for the current closed-loop regulator is:

[0024]

[0025] In the formula, k p k is the proportional coefficient of the proportional-integral controller. i k is the integral coefficient of the proportional-integral controller. r ω is the proportional coefficient of the proportional resonant controller.c ω is the gain bandwidth of the resonant controller, ω0 is the resonant frequency, and s is the complex frequency variable.

[0026] In some optional real-time methods, the initial current closed-loop regulation and a portion of the grid voltage feedforward are combined and phase-lead compensated to obtain the final current closed-loop regulation, including:

[0027] The initial current closed-loop regulation and part of the grid voltage feedforward are added together to obtain the compensation input.

[0028] The compensation input is fed into the phase compensation filter to perform phase lead compensation, thus obtaining the final current closed-loop regulation.

[0029] In some optional real-time modes, the expression for the phase compensation filter is:

[0030]

[0031] In the formula, ω1 is the frequency range for adjusting the phase lead, s is the complex frequency variable, A and B are both constants and B = 1 / (1-A).

[0032] In some optional real-time modes, the grid-connected inverter is controlled based on the modulated wave signal, including:

[0033] The modulated wave signal is compared with the carrier signal inside the digital controller to generate a drive control signal;

[0034] The operation of the grid-connected inverter is controlled by controlling the switching devices in the grid-connected inverter based on the drive control signal.

[0035] Secondly, the present invention provides a control device for improving the stability of a grid-connected inverter, comprising:

[0036] The voltage and current acquisition module is used to acquire the voltage at the common coupling point of the power grid and the grid-connected inverter, as well as the inverter inductor current.

[0037] The initial regulation acquisition module is used to obtain the initial current closed-loop regulation based on the common coupling point voltage and the inverter inductor current.

[0038] The feedforward quantity acquisition module is used to multiply the common coupling point voltage by a first coefficient to obtain a partial grid voltage feedforward quantity, and to multiply the common coupling point voltage by a second coefficient to obtain the full grid feedforward quantity, wherein the first coefficient is greater than 0 and less than 1, and the second coefficient is greater than or equal to 1.

[0039] The advance compensation module is used to obtain the final current closed-loop regulation by combining the initial current closed-loop regulation and part of the grid voltage feedforward through phase advance compensation.

[0040] The modulation wave acquisition module is used to add the final current closed-loop regulation and the grid voltage full feedforward to obtain the modulation wave signal;

[0041] The inverter control module is used to control the operation of the grid-connected inverter based on the modulated wave signal.

[0042] Thirdly, the present invention provides a computer device, comprising: a memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the control method for improving the stability of a grid-connected inverter as described in the first aspect or any corresponding embodiment.

[0043] The present invention has the following beneficial effects:

[0044] This invention obtains the common coupling point voltage and inverter inductor current of the power grid and the grid-connected inverter. Based on the common coupling point voltage and inverter inductor current, it obtains the initial current closed-loop regulation. The common coupling point voltage is multiplied by a first coefficient to obtain a partial grid voltage feedforward. The common coupling point voltage is multiplied by a second coefficient to obtain the full grid voltage feedforward. The initial current closed-loop regulation and the partial grid voltage feedforward are combined and subjected to phase lead compensation to obtain the final current closed-loop regulation. The final current closed-loop regulation and the full grid voltage feedforward are added to obtain a modulation wave signal, which is then used to control the operation of the grid-connected inverter. This ensures that the system phase margin meets the requirements, thereby enabling the grid-connected inverter to operate stably under a wider range of weak grid impedance conditions, thus improving the stability of the grid-connected inverter system. Attached Figure Description

[0045] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0046] Figure 1 This is a flowchart illustrating the control method for improving the stability of grid-connected inverters in an embodiment of the present invention.

[0047] Figure 2 This is a schematic diagram of the grid-connected inverter system in an embodiment of the present invention;

[0048] Figure 3 This is an open-loop Bode plot without phase compensation under a weak power grid in an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of the phase compensation filter in an embodiment of the present invention;

[0050] Figure 5 This is the Bode plot of the phase compensation filter in this embodiment of the invention;

[0051] Figure 6 This is a control structure diagram optimized for weak grid loops in an embodiment of the present invention;

[0052] Figure 7 It uses the open-loop Bode plot optimized for weak grid loops in the embodiments of the present invention;

[0053] Figure 8 This is a waveform diagram of a grid-connected experiment using a 4mH power grid after optimizing the control loop in this embodiment of the invention.

[0054] Figure 9 This is a waveform diagram of a standard power grid-connected experiment after the control loop is optimized in an embodiment of the present invention.

[0055] Figure 10 This is a structural block diagram of a control device for improving the stability of grid-connected inverters according to an embodiment of the present invention;

[0056] Figure 11 This is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] According to an embodiment of the present invention, a control method embodiment for improving the stability of a grid-connected inverter is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0059] This embodiment provides a control method to improve the stability of grid-connected inverters, such as... Figure 1 As shown, the process includes the following steps:

[0060] Step S101: Obtain the common coupling point voltage of the power grid and the grid-connected inverter, as well as the inverter inductor current.

[0061] Specifically, the point of common coupling (PCC) voltage between the grid and the grid-connected inverter refers to the voltage at the connection point between the inverter's output and the grid. In a grid-connected inverter system, the PCC is the node where the inverter's output voltage interacts with the grid voltage, and its voltage level reflects the electrical connection status between the grid and the inverter.

[0062] The inverter inductor current reflects the current characteristics of the inverter output to the power grid.

[0063] In one example, such as Figure 2 As shown, the grid-connected inverter uses a single-phase H4 bridge inverter. The inverter system mainly consists of an inverter bridge composed of four Insulated Gate Bipolar Transistors (IGBTs). The AC side uses an LC filter, which includes an inverter inductor L1 and a filter capacitor C. f From the ideal voltage source V g and L g The public power grid consists of L g To simulate the grid-side line impedance under weak grid conditions, a maximum impedance of 4mH is selected, with a switching frequency of 20kHz and a control frequency of 20kHz. The common coupling point voltage V... C That is, the filter capacitor C in the LC filter f The voltage difference between the two ends, i1 of the inverter inductor is the output current on the AC side of the grid-connected inverter.

[0064] The voltage at the common coupling point of the power grid can be obtained by sampling at the common coupling point using a voltage transformer, and the inverter inductor current can be obtained by sampling at the output side of the inverter using a Hall effect sensor or current transformer.

[0065] Step S102: Obtain the initial current closed-loop regulation amount based on the common coupling point voltage and the inverter inductor current.

[0066] The initial current closed-loop regulation is the core feedback signal of the inverter control system, used to ensure that the inverter output current can quickly and accurately track the reference value, thereby achieving stable grid-connected operation. Specifically, the real-time active current setpoint is first calculated based on the grid-connected active power setpoint. Then, the difference between the real-time active current setpoint and the inverter inductor current is calculated, and the result is adjusted through proportional-integral control and multiple proportional-resonant control to obtain the initial current closed-loop regulation.

[0067] Step S103: Multiply the common coupling point voltage by the first coefficient to obtain the partial grid voltage feedforward, and multiply the common coupling point voltage by the second coefficient to obtain the full grid voltage feedforward, wherein the first coefficient is greater than 0 and less than 1, and the second coefficient is greater than or equal to 1.

[0068] Specifically, the first coefficient is 0.1, 0.2, or 0.3, etc. The first coefficient is multiplied by the voltage at the common coupling point to obtain a portion of the grid voltage feedforward, and the first coefficient is used to adjust the compensation strength of the feedforward channel.

[0069] The second coefficient is 1.25, 1.05, or 1.10, etc. The voltage at the common coupling point is multiplied by the second coefficient to obtain the full feedforward amount of the grid voltage. The second coefficient is used to compensate for the gain attenuation caused by the phase lead compensation of the feedforward channel.

[0070] Step S104: The initial current closed-loop regulation and part of the grid voltage feedforward are combined and phase lead compensation is applied to obtain the final current closed-loop regulation.

[0071] Specifically, inputting the initial current closed-loop regulation and part of the grid voltage feedforward into a phase compensation filter based on an all-pass filter modification for phase lead compensation helps to increase the system's phase margin and improve system stability.

[0072] Step S105: The final current closed-loop regulation and the grid voltage full feedforward are added together to obtain the modulated wave signal.

[0073] The final current closed-loop regulation is accumulated with the grid voltage full feedforward, and the bus voltage is normalized to obtain the final modulated wave signal.

[0074] Step S106: Control the operation of the grid-connected inverter based on the modulated wave signal.

[0075] Specifically, the modulated wave signal is compared with a carrier signal (such as a triangular wave) to generate a drive control signal. The drive control signal is used to control the switching devices in the inverter, thereby achieving output control of the inverter.

[0076] The control method for improving the stability of grid-connected inverters of the present invention obtains the common coupling point voltage of the grid and the inverter, as well as the inverter inductor current. Based on the active component of the common coupling point voltage and the inverter inductor current, an initial current closed-loop regulation is obtained. The common coupling point voltage is multiplied by a first coefficient to obtain a partial grid voltage feedforward, and the common coupling point voltage is multiplied by a second coefficient to obtain the full grid voltage feedforward. The initial current closed-loop regulation and the partial grid voltage feedforward are combined and subjected to phase lead compensation to obtain the final current closed-loop regulation. The final current closed-loop regulation and the full grid voltage feedforward are added to obtain a modulation wave signal, which is then used to control the operation of the grid-connected inverter. This ensures that the system phase margin meets the requirements, thereby enabling the grid-connected inverter to operate stably under a wider range of weak grid impedance conditions, thus improving the stability of the grid-connected inverter system.

[0077] In some implementations, step S102, obtaining the initial current closed-loop regulation amount based on the active component of the common coupling point voltage and the inverter inductor current, includes:

[0078] Step S1021: Calculate the real-time active current given value based on the common coupling point voltage and the grid-connected active power given value.

[0079] Specifically, the active component of the grid voltage and the real-time phase of the grid voltage are obtained by processing the voltage at the common coupling point through a phase-locked loop; the active current amplitude is given by performing a division operation based on the grid-connected active power setpoint and the active component of the grid voltage; and the real-time active current setpoint is calculated based on the active current amplitude setpoint and the real-time phase of the grid voltage.

[0080] Combination Figure 2 As shown, the sampled common coupling point voltage V C The active power component U of the grid voltage on the d-axis is obtained after processing by a phase-locked loop algorithm based on second-order generalized integral. d The real-time phase angle θ of the grid voltage.

[0081] Preset the grid-connected active power setpoint P ref The grid-connected active power setpoint P ref Divide by the active component of the grid voltage U d Obtain the active current amplitude setpoint I dref The active current amplitude is given by value I. dref The real-time active current reference value i is obtained by combining the real-time phase angle θ of the grid voltage. ref The calculation formula is: i ref =I dref *cosθ.

[0082] Step S1022: Process the real-time given values ​​of inverter inductor current and active current to obtain the initial current closed-loop regulation value.

[0083] Specifically, the difference between the real-time setpoint of the active current and the inverter inductor current is obtained; the current difference is then processed by a current closed-loop regulator through proportional-integral controller adjustment and multiple proportional-resonant controller adjustments to obtain the initial current closed-loop regulation value.

[0084] In one example, the current closed-loop regulator G i (s) includes a proportional-integral controller, a first-order proportional-resonant controller, a third-order proportional-resonant controller, a fifth-order proportional-resonant controller, and a seventh-order proportional-resonant controller, expressed as:

[0085]

[0086] In the formula, k p k is the proportional coefficient of the proportional-integral controller.i k is the integral coefficient of the proportional-integral controller. r ω is the proportional coefficient of the proportional resonant controller. c ω is the gain bandwidth of the resonant controller, ω0 is the resonant frequency, and s is the complex frequency variable.

[0087] The active current is given in real time as i. ref The difference between the sampled inverter inductor current i1 and the current is calculated, and then the current is sequentially adjusted by the proportional-integral (PI) controller and the 1st, 3rd, 5th, and 7th proportional-resonant (PRR) controllers in the current closed-loop regulator to obtain the initial current closed-loop regulation value V1. By employing both PPI controller adjustment and multiple PRR controller adjustments, the fast response of the PPI controller and the error-free tracking capability of the PRR controller for specific frequency signals can be fully utilized. This composite control method effectively improves the inverter's dynamic response performance while achieving high-precision current control in steady state, further enhancing the inverter's control accuracy and stability.

[0088] In some embodiments, step S104, which involves combining the initial current closed-loop regulation and a portion of the grid voltage feedforward to obtain the final current closed-loop regulation through phase lead compensation, includes:

[0089] Step S1041: Add the initial current closed-loop regulation amount and part of the grid voltage feedforward amount to obtain the compensation input amount.

[0090] Step S1042: Input the compensation input to the phase compensation filter to perform phase lead compensation and obtain the final current closed-loop regulation.

[0091] Specifically, the voltage V at the common coupling point C It is divided into two paths. One path takes 0.1 times (which can be set according to the actual situation) of the sampled value as part of the grid voltage feedforward quantity and superimposes it with the initial current closed-loop regulation quantity V1. After processing by the phase compensation filter, the final current closed-loop regulation quantity V3 is obtained. The other path is used entirely as the grid voltage full feedforward quantity V4.

[0092] The phase compensation filter is derived from an all-pass filter. It provides an additional positive phase compensation based on the phase correction stage of a first-order all-pass filter. The expression for the all-pass filter G(s) is:

[0093]

[0094] Where ω1 is the center frequency of the all-pass filter, the all-pass filter can achieve 0dB gain and 90° phase lag for a signal with an input frequency of ω1. Cascading the all-pass filter with other components can achieve phase lead correction without affecting the gain. The control structure of the phase compensation filter is as follows: Figure 4 As shown, the phase compensation filter Gps The expression for (s) is:

[0095]

[0096] In the formula, ω1 is the frequency range for adjusting the phase lead, s is the complex frequency variable, A and B are both constants and B = 1 / (1-A) to ensure that the gain in the low frequency range is close to 1.

[0097] The phase compensator based on the all-pass filter design can accurately achieve phase lead compensation in a specified frequency range. This makes the compensation effect more targeted. The frequency range and degree of phase compensation can be flexibly adjusted according to the specific needs of the inverter system, further optimizing the dynamic performance and stability of the system and improving the control accuracy and adaptability of the inverter.

[0098] In some embodiments, step S106, controlling the operation of the grid-connected inverter based on the modulated wave signal, includes:

[0099] Step S1061: Compare the modulated wave signal with the carrier signal inside the digital controller to generate a drive control signal.

[0100] Step S1062: Control the switching devices in the grid-connected inverter to turn on and off based on the drive control signal to control the operation of the grid-connected inverter.

[0101] Specifically, the modulated wave is compared with the carrier signal inside the digital controller, such as a triangular carrier signal, to generate a drive control signal. The drive control signal is used to control the switching devices in the grid-connected inverter to control the operation of the grid-connected inverter.

[0102] In some embodiments, such as Figure 2 As shown, the grid-connected inverter uses a single-phase H4 bridge inverter. The inverter system mainly consists of an inverter bridge composed of four insulated-gate bipolar transistors. The AC side uses an LC filter, which includes an inverter inductor L1 and a filter capacitor C. f From the ideal voltage source V g and L g The public power grid consists of L1 = 600uH and C. f =4.2uF, L g To simulate the grid-side line impedance under weak grid conditions, a maximum impedance of 4mH is selected, with a switching frequency of 20kHz and a control frequency of 20kHz. The common coupling point voltage V... C That is, the filter capacitor C in the LC filter f The voltage difference between the two ends, i1 of the inverter inductor is the output current on the AC side of the grid-connected inverter.

[0103] The open-loop transfer function expression of the grid-connected inverter system is:

[0104]

[0105] Among them, G d (s) represents the time from trigger sampling to the final execution of the drive control signal PWM when using a digital controller, which is approximately 2 switching cycles T. s The delay, G d The expression for (s) is:

[0106]

[0107] K pwm The voltage gain of the inverter bridge arm is determined by the DC side voltage V. bus and modulated carrier V tri The decision is made jointly, and its expression is:

[0108]

[0109] Considering non-ideal power grid conditions, the grid-side impedance L g If it is not 0, then the inverter voltage V inv The voltage to the filter capacitor is the voltage at the common coupling point V. C The transfer function expression is:

[0110]

[0111] Inverter voltage V inv The transfer function expression for the inverter current i1 is:

[0112]

[0113] In the formula, C is the capacitance value of the filter capacitor.

[0114] like Figure 3 As shown, the open-loop amplitude-frequency curve of the grid-connected inverter under a weak grid has two resonance peaks, one of which is a positive resonance peak, influenced by the grid-side impedance L. g The impact is relatively small; the other is the reverse resonance peak, which is affected by the grid-side impedance L. g The impact is significant, affecting the grid-side impedance L. g When the frequency changes from 0 to 4mH, the negative resonance peak moves rapidly to the lower frequency band, causing the phase margin of the grid-connected inverter system to become lower and lower, and the system to gradually become unstable.

[0115] The expressions for the frequencies of the two resonant peaks are:

[0116]

[0117] This invention provides an additional positive phase compensation based on the phase correction stage of a first-order all-pass filter, thereby constructing a phase-compensated filter. The expression for the all-pass filter G(s) is:

[0118]

[0119] An all-pass filter can achieve 0dB gain and a 90° phase lag for an input frequency of ω1. Cascading an all-pass filter with other components can achieve phase lead correction without affecting the gain. The control structure of a phase compensation filter is as follows: Figure 4 As shown, the phase compensation filter G ps The expression for (s) is:

[0120]

[0121] In the formula, ω1 is the frequency range for adjusting phase advance, s is the complex frequency variable, A is the strength of adjusting phase advance, A and B are both constants and B = 1 / (1-A) to ensure that the gain in the low frequency range is close to 1.

[0122] With the design objective of ensuring stable operation of the grid-connected inverter system at a grid impedance of 4mH, the negative resonance peak is 1.2kHz. The current loop and inductance parameters selected in this embodiment determine a control bandwidth of 500Hz–900Hz from no-load to full-load. Therefore, a phase lead compensation frequency of 800Hz is chosen to reduce the impact of the negative resonance peak on the system's phase margin. The required compensation phase angle is approximately 30°, satisfying the following conditions:

[0123]

[0124] From the above relationships, we can deduce that A = 0.6, B = 1 / (1-A) = 2.5. Figure 5 The Bode plot for the phase compensation circuit will yield a positive phase shift of 30° at 800Hz.

[0125] Grid-side impedance l g and digital control delay G d The presence of (s) will affect the feedforward channel through G. vc (s) and closed-loop channel via G vi (s) respectively produce negative phase shifts, therefore, as Figure 6 As shown, in this embodiment of the invention, a phase compensation link G is introduced into the initial current closed-loop regulation V1 and part of the grid voltage feedforward V2, respectively. ps (s). K1 is set to 0.2 to adjust the compensation strength of the feedforward channel, and K2 is set to 1.05 to compensate for the gain attenuation caused by phase compensation in the feedforward channel. Figure 7 With the grid-side impedance set to 4mH, the open-loop Bode plots before and after various loop optimization strategies show that, compared to other strategies, the phase margin of the control strategy is significantly improved in these frequency bands between each resonant control point, loop cutoff frequency, and negative resonant peak.

[0126] The effectiveness of the control strategy was verified on a 1.5kW actual prototype platform. Figure 8 The full-load grid-connected waveform under the condition of connecting to a 4mH high-impedance power grid shows that the inverter current and grid-connected current waveforms have no low-frequency oscillations, indicating that the system can operate stably under weak power grid conditions. Figure 9 The waveform of the grid-connected current under full load under standard power grid conditions is shown. The lower harmonics such as the 3rd, 5th, 7th and 9th are all effectively suppressed, indicating that a high-quality grid-connected current waveform can be maintained under strong power grid conditions.

[0127] Based on the analysis of the above embodiments, the control method for improving the stability of grid-connected inverters in this invention adds the initial current closed-loop regulation and part of the grid voltage feedforward to the phase advance compensation, which can ensure that the system phase margin meets the requirements, thereby enabling the inverter to operate stably under a wider range of grid weak impedance conditions.

[0128] Furthermore, by adding the initial current closed-loop regulation and part of the grid voltage feedforward to the phase lead compensation, the loop gain in the low-frequency band will not be affected. Therefore, while improving the adaptability of the grid-connected inverter to different grid impedances, it can still output a high-quality grid-connected current waveform under strong grid conditions, thus ensuring the consistency of the grid-connected control algorithm.

[0129] This invention also provides a control device for improving the stability of grid-connected inverters, such as... Figure 10 As shown, it includes:

[0130] The voltage and current acquisition module 1101 is used to acquire the common coupling point voltage of the power grid and the grid-connected inverter, as well as the inverter inductor current.

[0131] The initial regulation acquisition module 1102 is used to obtain the initial current closed-loop regulation based on the common coupling point voltage and the inverter inductor current.

[0132] The feedforward quantity acquisition module 1103 is used to multiply the common coupling point voltage by a first coefficient to obtain a partial grid voltage feedforward quantity, and multiply the common coupling point voltage by a second coefficient to obtain the full grid voltage feedforward quantity, wherein the first coefficient is greater than 0 and less than 1, and the second coefficient is greater than or equal to 1.

[0133] The advance compensation module 1104 is used to obtain the final current closed-loop regulation by combining the initial current closed-loop regulation and part of the grid voltage feedforward through phase advance compensation.

[0134] The modulation wave acquisition module 1105 is used to add the final current closed-loop regulation amount and the grid voltage full feedforward amount to obtain the modulation wave signal;

[0135] Inverter control module 1106 is used to control the operation of the grid-connected inverter based on the modulated wave signal.

[0136] The control device for improving the stability of grid-connected inverters according to embodiments of the present invention acquires the common coupling point voltage of the grid and the grid-connected inverter, as well as the inverter inductor current. Based on the common coupling point voltage and the inverter inductor current, an initial current closed-loop regulation is obtained. The common coupling point voltage is multiplied by a first coefficient to obtain a partial grid voltage feedforward, and the common coupling point voltage is multiplied by a second coefficient to obtain the full grid voltage feedforward. The initial current closed-loop regulation and the partial grid voltage feedforward are combined and subjected to phase lead compensation to obtain the final current closed-loop regulation. The final current closed-loop regulation and the full grid voltage feedforward are added to obtain a modulation wave signal, which then controls the operation of the grid-connected inverter, ensuring that the system phase margin meets the requirements. This allows the grid-connected inverter to operate stably under a wider range of weak grid impedance conditions, thereby improving the stability of the grid-connected inverter system.

[0137] Furthermore, the initial adjustment amount acquisition module 1101 includes:

[0138] The real-time current setpoint calculation module is used to calculate the real-time active current setpoint based on the common coupling point voltage and the grid-connected active power setpoint.

[0139] The current processing module is used to process the real-time given values ​​of inverter inductor current and active current to obtain the initial current closed-loop regulation value.

[0140] Furthermore, the real-time current setpoint calculation module includes:

[0141] The phase acquisition module is used to obtain the active component of the grid voltage and the real-time phase of the grid voltage after the common coupling point voltage is processed by a phase-locked loop.

[0142] The amplitude acquisition module is used to obtain the active current amplitude setpoint by performing a division operation based on the grid-connected active power setpoint and the active component of the grid voltage.

[0143] The current and voltage processing module is used to calculate the real-time active current setpoint based on the active current amplitude setpoint and the real-time phase of the grid voltage.

[0144] Furthermore, the current processing module includes:

[0145] The current difference module is used to calculate the difference between the real-time given value of the active current and the inverter inductor current to obtain the current difference value.

[0146] The current regulation module is used to adjust the current difference through a proportional-integral controller and multiple proportional-resonant controllers to obtain the initial current closed-loop regulation value.

[0147] Furthermore, the expression for the current closed-loop regulator is:

[0148]

[0149] In the formula, k p k is the proportional coefficient of the proportional-integral controller. i k is the integral coefficient of the proportional-integral controller. r ω is the proportional coefficient of the proportional resonant controller. c ω is the gain bandwidth of the resonant controller, ω0 is the resonant frequency, and s is the complex frequency variable.

[0150] Furthermore, the advance compensation module 1104 includes:

[0151] The input acquisition module is used to add the initial current closed-loop regulation and part of the grid voltage feedforward to obtain the compensation input.

[0152] The phase compensation module is used to input the compensation input to the phase compensation filter to perform phase lead compensation and obtain the final current closed-loop regulation.

[0153] Furthermore, the expression for the phase compensation filter is:

[0154]

[0155] In the formula, ω1 is the frequency range for adjusting the phase lead, s is the complex frequency variable, A and B are both constants and B = 1 / (1-A).

[0156] Furthermore, the inverter control module 1106 includes:

[0157] The signal comparison module is used to compare the modulated wave signal with the carrier signal inside the digital controller to generate a drive control signal;

[0158] The switching control module is used to control the on / off state of the switching devices in the grid-connected inverter based on the drive control signal to control the operation of the grid-connected inverter.

[0159] This invention also provides a schematic diagram of the structure of a computer device, such as... Figure 11As shown, the computer device includes one or more processors 10, memory 20, and interfaces for connecting the components, including high-speed interfaces and low-speed interfaces. The components communicate with each other via different buses and can be mounted on a common motherboard or otherwise installed as needed. The processors can process instructions executed within the computer device, including instructions stored in or on memory to display graphical information of a GUI on external input / output devices (such as display devices coupled to the interfaces). In some alternative implementations, multiple processors and / or multiple buses can be used with multiple memories and multiple memory modules, if desired. Similarly, multiple computer devices can be connected, each providing some of the necessary operations (e.g., as a server array, a group of blade servers, or a multiprocessor system). Figure 11 Take a processor 10 as an example.

[0160] Processor 10 may be a central processing unit, a network processor, or a combination thereof. Processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The programmable logic device may be a complex programmable logic device (CAMP), a field-programmable gate array (FPGA), a general-purpose array logic (GDA), or any combination thereof.

[0161] The memory 20 stores instructions executable by at least one processor 10 to cause at least one processor 10 to perform the method shown in the above embodiments.

[0162] The memory 20 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the computer device. Furthermore, the memory 20 may include high-speed random access memory and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some alternative embodiments, the memory 20 may optionally include memory remotely located relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0163] The memory 20 may include volatile memory, such as random access memory; the memory may also include non-volatile memory, such as flash memory, hard disk or solid-state drive; the memory 20 may also include a combination of the above types of memory.

[0164] The computer device also includes an input device 30 and an output device 40. The processor 10, memory 20, input device 30, and output device 40 can be connected via a bus or other means. Figure 11 Taking the example of a connection between China and Israel via a bus.

[0165] Input device 30 can receive input numerical or character information, and generate key signal inputs related to user settings and function control of the computer device, such as a touchscreen, keypad, mouse, trackpad, touchpad, joystick, one or more mouse buttons, trackball, joystick, etc. Output device 40 may include display devices, auxiliary lighting devices (e.g., LEDs), and haptic feedback devices (e.g., vibration motors). The aforementioned display devices include, but are not limited to, liquid crystal displays, light-emitting diodes, displays, and plasma displays. In some alternative embodiments, the display device may be a touchscreen.

[0166] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code, which, when accessed and executed by the computer, processor, or hardware, implements the methods shown in the above embodiments.

[0167] A portion of this invention can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to the invention through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0168] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and all such modifications and variations fall within the scope of protection.

Claims

1. A control method for improving the stability of a grid-connected inverter, characterized in that, include: Obtain the common coupling point voltage of the power grid and the grid-connected inverter, as well as the inverter inductor current; The initial current closed-loop regulation is obtained based on the common coupling point voltage and the inverter inductor current. The common coupling point voltage is multiplied by a first coefficient to obtain a partial grid voltage feedforward, and the common coupling point voltage is multiplied by a second coefficient to obtain the full grid voltage feedforward, wherein the first coefficient is greater than 0 and less than 1, and the second coefficient is greater than or equal to 1. The initial current closed-loop regulation and part of the grid voltage feedforward are combined and phase lead compensation is applied to obtain the final current closed-loop regulation. The modulated wave signal is obtained by adding the final current closed-loop regulation and the grid voltage full feedforward. The grid-connected inverter is controlled based on the modulated wave signal.

2. The control method for improving the stability of a grid-connected inverter according to claim 1, characterized in that, The step of obtaining the initial current closed-loop regulation amount based on the common coupling point voltage and the inverter inductor current includes: The real-time active current reference value is calculated based on the common coupling point voltage and the grid-connected active power reference value. The initial current closed-loop regulation value is obtained by processing the real-time given values ​​of the inverter inductor current and the active current.

3. The control method for improving the stability of a grid-connected inverter according to claim 2, characterized in that, The calculation of the real-time active current reference value based on the common coupling point voltage and the grid-connected active power reference value includes: The voltage at the common coupling point is processed by a phase-locked loop to obtain the active component of the grid voltage and the real-time phase of the grid voltage. The active current amplitude is obtained by performing a division operation based on the given value of the grid-connected active power and the active component of the grid voltage. The real-time active current setpoint is calculated based on the given active current amplitude and the real-time phase of the grid voltage.

4. The control method for improving the stability of a grid-connected inverter according to claim 2, characterized in that, The process of processing the real-time given values ​​of the inverter inductor current and the active current to obtain the initial current closed-loop regulation includes: The difference between the real-time given value of the active current and the inverter inductor current is used to obtain the current difference value; The current difference is adjusted by a proportional-integral controller and multiple proportional-resonant controller adjustments through a current closed-loop regulator to obtain the initial current closed-loop regulation value.

5. The control method for improving the stability of a grid-connected inverter according to claim 4, characterized in that, The expression for the current closed-loop regulator is: In the formula, k p k is the proportional coefficient of the proportional-integral controller. i k is the integral coefficient of the proportional-integral controller. r ω is the proportional coefficient of the proportional resonant controller. c ω is the gain bandwidth of the resonant controller, ω0 is the resonant frequency, and s is the complex frequency variable.

6. The control method for improving the stability of a grid-connected inverter according to claim 1, characterized in that, The step of obtaining the final current closed-loop regulation by combining the initial current closed-loop regulation and a portion of the grid voltage feedforward through phase lead compensation includes: The initial current closed-loop regulation and the partial grid voltage feedforward are added together to obtain the compensation input. The compensation input is input to the phase compensation filter to perform phase lead compensation and obtain the final current closed-loop regulation.

7. The control method for improving the stability of a grid-connected inverter according to claim 6, characterized in that, The expression for the phase compensation filter is: In the formula, ω1 is the frequency range for adjusting the phase lead, s is the complex frequency variable, A and B are both constants and B = 1 / (1-A).

8. The control method for improving the stability of a grid-connected inverter according to claim 1, characterized in that, The control of the grid-connected inverter based on the modulated wave signal includes: The modulated wave signal is compared with the carrier signal inside the digital controller to generate a drive control signal; The operation of the grid-connected inverter is controlled by controlling the switching devices in the grid-connected inverter based on the drive control signal.

9. A control device for improving the stability of a grid-connected inverter, characterized in that, include: The voltage and current acquisition module is used to acquire the voltage at the common coupling point of the power grid and the grid-connected inverter, as well as the inverter inductor current. The initial adjustment amount acquisition module is used to obtain the initial current closed-loop adjustment amount based on the common coupling point voltage and the inverter inductor current. The feedforward quantity acquisition module is used to multiply the common coupling point voltage by a first coefficient to obtain a partial grid voltage feedforward quantity, and multiply the common coupling point voltage by a second coefficient to obtain the full grid voltage feedforward quantity, wherein the first coefficient is greater than 0 and less than 1, and the second coefficient is greater than or equal to 1. The advance compensation module is used to obtain the final current closed-loop regulation by combining the initial current closed-loop regulation and part of the grid voltage feedforward through phase advance compensation. The modulation wave acquisition module is used to add the final current closed-loop regulation amount and the grid voltage full feedforward amount to obtain the modulation wave signal; The inverter control module is used to control the operation of the grid-connected inverter based on the modulated wave signal.

10. A computer device, characterized in that, include: A memory and a processor are interconnected, the memory stores computer instructions, and the processor executes the computer instructions to perform the control method for improving the stability of a grid-connected inverter as described in any one of claims 1 to 8.

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