Method and system for eliminating phase angle and power offset of power synchronous inverter

Abstract

The invention provides a method and a system for eliminating phase angle and power offset of a power synchronous inverter. The method comprises the following steps: constructing a coupling mechanism model of synchronous phase angle offset and reactive power offset; acquiring the synchronous phase error of the power grid in real time, extracting the actual phase angle of the power grid based on the phase-locked loop, and calculating the difference between the two as the synchronous phase error; dynamically generating an adaptive current reference value correction according to the coupling mechanism model; performing closed-loop control on the corrected current reference value and the actual feedback current through a vector current controller, and generating a PWM modulation signal of the inverter; the A-phase voltage amplitude is monitored in real time, the voltage drop ratio is calculated, and the asymmetric feedback gain is adjusted; filtering a second harmonic component of the d-axis voltage, extracting a direct-current voltage component, and generating an original current reference value; and setting an A-phase voltage drop working condition, comparing the synchronous phase deviation and the reactive power control effect before and after the correction strategy is added, and confirming the phase angle and power offset elimination effect.

Description

Technical Field

[0001] The present invention relates to the field of AC power transmission and distribution technology, and more particularly to a method and system for eliminating phase angle and power offsets of a power synchronous inverter. In particular, the present invention relates to a method for eliminating phase angle and power offsets of a power synchronous inverter in an unbalanced power grid. Background Art

[0002] Distributed generation, thanks to its environmentally friendly nature, strong local consumption capacity, and significant economic benefits, has seen its installed capacity continue to increase in recent years amidst energy restructuring. As distributed generation systems are increasingly deployed in weak grids, such as urban distribution networks, grid-connected stability issues in these networks have become increasingly prominent. Traditional phase-locked loop (PLL)-based grid-connected voltage source inverters can experience synchronous instability, particularly when the short-circuit ratio falls below 2. The risk of instability increases significantly with traditional PLL-controlled inverters. In contrast, power synchronous control, by mimicking the dynamic characteristics of synchronous motors, effectively improves adaptability and synchronous stability, making it a highly effective solution in weak grid scenarios. However, in unbalanced grids, the combination of negative-sequence voltage and positive-sequence current results in instantaneous active power containing a double-frequency fluctuation component, which can also cause synchronous instability in power synchronous control inverters.

[0003] Currently, to address the risk of synchronization instability in power synchronous control inverters caused by transient active power fluctuations under unbalanced voltage, the existing method is mainly the negative-sequence current regulation method, which adopts a dual-sequence decomposition control architecture of positive and negative sequences and suppresses power oscillations by adding a negative-sequence current control loop. However, sequence-based control significantly increases the complexity of system control and design. The virtual phase current regulation strategy suppresses the double-frequency oscillation power by adding an asymmetric feedback current gain and an asymmetric voltage compensation mechanism, providing a simplified solution for stable synchronization of power synchronous control inverters under unbalanced power grids without the need for sequence-based current control. However, the asymmetric feedback gain causes inconsistency between the feedback current and the actual current in the control loop, resulting in the deviation of the synchronization phase angle from the accurate value, which in turn causes the reactive power to deviate from the command value, and may eventually cause overcurrent problems.

[0004] In summary, the existing sequence control method has the defect of doubling the system complexity. Although the existing simplified solution - the virtual phase current regulation strategy can suppress active power oscillations under unbalanced power grids and enhance the synchronization stability of power synchronous inverters, its asymmetric feedback gain causes phase angle deviation and reactive power deviation problems.

[0005] The literature (Yang Ming, Gao Longjiang, Wang Haixing, etc. Power-Current Coordination Control Strategy of Virtual Synchronous Generator under Grid Imbalance [J]. Power System Protection and Control, 2019, 47(06): 17-23.) proposed a power-current coordination control strategy of virtual synchronous generator based on the stationary coordinate system. This control strategy calculates the negative-sequence current reference value according to the instantaneous power theory, establishes a unified analytical expression for three control objectives of constant active power, reactive power and current balance, realizes the coordinated control of power and current, and improves the system operation performance. Finally, the simulation results verify the effectiveness of the proposed control strategy. This literature aims at the power oscillation problem of power-synchronized inverters under unbalanced grids, proposes a sequence current control method, constructs a coordinated control architecture for positive and negative sequence currents, and effectively suppresses power fluctuations. However, this method needs to extract positive and negative sequence components by means of a finite bandwidth, and design parameters for the positive sequence control loop and the negative sequence control loop respectively. The control structure is complex and the system design is difficult, which has limitations in practical engineering applications. Summary of the Invention

[0006] Aiming at the defects in the prior art, the purpose of the present invention is to provide a method and system for eliminating the phase angle and power offset of a power-synchronized inverter.

[0007] The method for eliminating the phase angle and power offset of a power-synchronized inverter according to the present invention includes:

[0008] Step 1: Construct a coupling mechanism model of the synchronous phase angle offset and the reactive power offset. The model is based on the asymmetric feedback gain of the virtual phase current regulation method, the A-phase voltage drop ratio, the synchronous phase error, the voltage amplitude, the current amplitude and the current phase angle, and is used to quantify the correlation between the asymmetric feedback gain and the phase angle offset and the reactive power offset;

[0009] Step 2: Real-time obtain the synchronous phase error of the power grid, including generating the synchronous phase angle of the inverter through the power synchronization control loop, extracting the actual phase angle of the power grid based on the phase-locked loop, and calculating the difference between the two as the synchronous phase error;

[0010] Step 3: Dynamically generate an adaptive current reference value correction amount according to the coupling mechanism model. The correction amount is used to compensate for the influence of the asymmetric feedback gain on the consistency between the feedback current and the actual current, including amplitude and phase correction of the original dq-axis current reference value;

[0011] Step 4: Perform closed-loop control on the corrected current reference value and the actual feedback current through a vector current controller to generate a PWM modulation signal of the inverter, so as to eliminate the synchronous phase angle offset and the reactive power offset and maintain the stable synchronization between the inverter and the power grid;

[0012] Step 5: Monitor the amplitude of phase A voltage in real time, calculate the voltage sag ratio, and dynamically adjust the asymmetric feedback gain in combination with the positive and negative sequence voltage components of the power grid to adapt to the dynamically changing unbalanced grid conditions;

[0013] Step 6: Filter out the second harmonic component of the d-axis voltage in the current reference value generation module, extract the DC voltage component, and generate the original current reference value in combination with the active power and reactive power command values;

[0014] Step 7: Set the phase A voltage sag condition through the experimental verification platform, compare the synchronous phase deviation and reactive power control effect before and after adding the correction strategy, and confirm the elimination effect of phase angle and power offset.

[0015] Preferably, in the controller part, the virtual phase current regulation method VPCR is applied to the sagging phase A, a feedback gain is added, and the synchronization between the inverter and the power grid is achieved by the power synchronization control PSC. By calculating the power difference between the instantaneous active power and the command value, the synchronous frequency adjustment amount Δω is obtained, and then the phase angle θ is obtained by integration PSC ;

[0016] The current active power and reactive power command values are given in the control and Subsequently, the current reference value is obtained through the current reference value generation module The vector current controller makes the feedback current consistent with the current reference value through the dq decoupling control method, and finally outputs the PWM control signal of the inverter.

[0017] Preferably, to construct the synchronous phase angle and reactive power offset model and analyze the instantaneous power under the action of the virtual phase current regulation method, the three-phase grid-side voltage expression is:

[0018]

[0019] In the formula, ω is the grid angular frequency, U m is the voltage amplitude, k sag is the sag ratio of phase A voltage; t is the unit time;

[0020] The synchronous phase angle offset is defined as:

[0021] Δθ = θ true -θ err

[0022] In the formula, θ true is the accurate grid phase angle, θ err is the incorrect synchronous phase angle with phase offset;

[0023] Based on θ err The Park transformation is:

[0024]

[0025] After the Clarke transformation T at a synchronous phase angle with phase angle offset abc-αβ and the Park transformation T αβ-dq_dv the d-axis voltage is:

[0026]

[0027] To eliminate the oscillating component of the d-axis voltage, the DC component of the d-axis voltage is obtained through a notch filter as Subsequently, the current reference values in the dq axes are calculated through the current reference value generation module as:

[0028]

[0029] Under the virtual phase current regulation method, the asymmetric feedback gain causes zero-sequence current to be injected into the feedback current. The three-phase feedback current is defined as:

[0030]

[0031] where I m_dv is the current amplitude, is the phase angle by which the current lags behind the voltage, I 0_dv is the amplitude of the zero-sequence current, is the phase angle by which the zero-sequence current lags behind the voltage;

[0032] Based on the constraint that the zero-sequence current is zero in an actual three-phase three-wire system, the solution is:

[0033]

[0034] where k a is the feedback gain.

[0035] Preferably, when entering the steady state, the vector current controller makes the feedback current equal to the current reference value, that is, there is an equation:

[0036]

[0037] The solution is:

[0038]

[0039] According to the instantaneous power theory, the instantaneous active power is obtained as:

[0040]

[0041] Under the action of the power synchronization control loop, there is an equation in the steady state:

[0042]

[0043] Solving this equation gives the quantization expression for the phase angle offset as:

[0044]

[0045] The instantaneous reactive power is derived as:

[0046]

[0047] Wherein, the DC component of the instantaneous reactive power is:

[0048]

[0049] The oscillating component is:

[0050]

[0051] Therefore, the quantization expression for the reactive power offset is:

[0052]

[0053] Preferably, under vector current control, there is a relationship in the steady state:

[0054]

[0055] Wherein, T αβ_dq is the transformation matrix from the αβ coordinate system to the dq coordinate system; is the feedback current; is the current reference value;

[0056] The conversion relationship between the dq-axis current and the current amplitude I m and the phase is:

[0057]

[0058] Based on the instantaneous power theory, when virtual phase current modulation is not introduced, the instantaneous active power and reactive power are:

[0059]

[0060] After introducing virtual phase current modulation and adding current reference value correction at the same time, the current amplitude and phase are corrected to and Therefore, the corrected instantaneous power is:

[0061]

[0062] Let the current reference value make the DC components of the above two groups of expressions equal, and the system of equations is obtained:

[0063]

[0064] Substitute the conversion relationships of dq-axis current with current amplitude and phase into the above equations, and the expression for the adaptive current reference value is obtained as follows:

[0065]

[0066] According to the system for eliminating phase angle and power offset of a power-synchronized inverter provided by the present invention, it includes:

[0067] Module M1: Construct a coupling mechanism model of synchronous phase angle offset and reactive power offset. The model is based on the asymmetric feedback gain of the virtual phase current regulation method, the A-phase voltage drop ratio, the synchronous phase error, the voltage amplitude, the current amplitude, and the current phase angle, and is used to quantify the correlation between the asymmetric feedback gain and the phase angle offset and reactive power offset;

[0068] Module M2: Real-time obtain the synchronous phase error of the power grid, including generating the synchronous phase angle of the inverter through a power synchronization control loop, and extracting the actual phase angle of the power grid based on a phase-locked loop, and calculating the difference between the two as the synchronous phase error;

[0069] Module M3: Dynamically generate an adaptive current reference value correction amount according to the coupling mechanism model. The correction amount is used to compensate for the influence of the asymmetric feedback gain on the consistency between the feedback current and the actual current, including amplitude and phase correction of the original dq-axis current reference value;

[0070] Module M4: Perform closed-loop control on the corrected current reference value and the actual feedback current through a vector current controller to generate a PWM modulation signal of the inverter, so as to eliminate the synchronous phase angle offset and reactive power offset and maintain the stable synchronization between the inverter and the power grid;

[0071] Module M5: Real-time monitor the A-phase voltage amplitude, calculate the voltage drop ratio, and dynamically adjust the asymmetric feedback gain in combination with the positive and negative sequence voltage components of the power grid to adapt to the dynamically changing unbalanced power grid conditions;

[0072] Module M6: Filter out the second harmonic component of the d-axis voltage in the current reference value generation module, extract the DC voltage component, and generate the original current reference value in combination with the active power and reactive power command values;

[0073] Module M7: Set the A-phase voltage drop condition through an experimental verification platform, compare the synchronous phase deviation and reactive power control effect before and after adding the correction strategy, and confirm the phase angle and power offset elimination effect.

[0074] Preferably, in the controller section, the virtual phase current regulation method VPCR is applied to the dropped A phase, a feedback gain is added, and the synchronization between the inverter and the power grid is achieved by the power synchronization control PSC. By calculating the power difference between the instantaneous active power and the command value, the synchronous frequency adjustment amount Δω is obtained, and then the phase angle θ is obtained by integration. PSC ;

[0075] In the control, the current active power and reactive power command values are given. And Subsequently, the current reference value is obtained through the current reference value generation module. The vector current controller makes the feedback current consistent with the current reference value through the dq decoupling control method, and finally outputs the PWM control signal of the inverter.

[0076] Preferably, to construct the synchronous phase angle and reactive power offset model, analyze the instantaneous power under the action of the virtual phase current regulation method, the three-phase grid-side voltage expression is:

[0077]

[0078] In the formula, ω is the grid angular frequency, U m is the voltage amplitude, k sag is the drop ratio of the A-phase voltage; t is the unit time;

[0079] Define the synchronous phase angle offset as:

[0080] Δθ = θ true -θ err

[0081] In the formula, θ true is the accurate grid phase angle, θ err is the wrong synchronous phase angle with phase offset;

[0082] Based on θ err The Park transformation is:

[0083]

[0084] Under the synchronous phase angle with phase offset, the d-axis voltage after the Clarke transformation T abc-αβ and the Park transformation T αβ-dq_dv is:

[0085]

[0086] To eliminate the oscillation component of the d-axis voltage, the DC component of the d-axis voltage is obtained through the notch filter as Subsequently, the current reference values in the dq axes are calculated through the current reference value generation module as:

[0087]

[0088] Under the virtual phase current regulation method, the asymmetric feedback gain causes zero-sequence current to be injected into the feedback current. The three-phase feedback current is defined as:

[0089]

[0090] where I m_dv is the current amplitude, is the phase angle by which the current lags the voltage, I 0_dv is the amplitude of the zero-sequence current, is the phase angle by which the zero-sequence current lags the voltage;

[0091] Based on the constraint that the zero-sequence current is zero in an actual three-phase three-wire system, the solution is:

[0092]

[0093] where k a is the feedback gain.

[0094] Preferably, when entering the steady state, the vector current controller makes the feedback current equal to the current reference value, that is, there is an equation:

[0095] The solution is:

[0096]

[0097] According to the instantaneous power theory, the instantaneous active power is obtained as:

[0098]

[0099] Under the action of the power synchronization control loop, there is an equation in the steady state:

[0100]

[0101] Solving this equation gives the quantization expression for the phase angle offset as:

[0102]

[0103] Derive the instantaneous reactive power as:

[0104]

[0105] where the DC component of the instantaneous reactive power is:

[0106]

[0107] The oscillating component is:

[0108]

[0109] Therefore, the quantization expression of the reactive power offset is as follows:

[0110]

[0111] Preferably, under vector current control, there is a relationship at steady state:

[0112]

[0113] where T αβ_dq is the transformation matrix from the αβ coordinate system to the dq coordinate system; is the feedback current; is the current reference value;

[0114] The conversion relationship between the dq-axis current and the current amplitude I m and the phase is as follows:

[0115]

[0116] Based on the instantaneous power theory, when the virtual phase current modulation is not introduced, the instantaneous active power and reactive power are:

[0117]

[0118] After introducing the virtual phase current modulation and adding the current reference value correction at the same time, the current amplitude and phase are corrected to and Therefore, the corrected instantaneous power is:

[0119]

[0120] Let the current reference value make the DC components of the above two groups of expressions equal, and the following system of equations is obtained:

[0121]

[0122] Substitute the conversion relationship between the dq-axis current and the current amplitude and phase into the above system of equations, and the expression of the adaptive current reference value is solved as:

[0123]

[0124] Compared with the prior art, the present invention has the following beneficial effects:

[0125] (1) This method does not require adding a traditional negative-sequence current control loop to suppress power fluctuations. It retains and optimizes the simple control architecture of the existing virtual phase current regulation method, enhancing its reliability under the power synchronization type control architecture, providing support for introducing the virtual phase current regulation method in practical engineering;

[0126] (2) The control quantity offset elimination method given in this scheme can effectively adapt to the dynamically changing unbalanced grid conditions, compensating online for the dynamic asymmetric gain introduced by the virtual phase current regulation method. It has low complexity, high reliability and practicability, providing a new reference for the problem of control quantity offset of grid-connected inverters. Brief Description of the Drawings

[0127] By reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings, other features, objectives and advantages of the present invention will become more apparent:

[0128] Figure 1 is the schematic diagram of the power synchronization type inverter system;

[0129] Figure 2a and Figure 2b are the mapping relationships of the synchronous phase angle deviation, reactive power deviation and the asymmetric feedback gain k a and the voltage drop ratio k sag of phase A voltage;

[0130] Figure 3 is the control architecture with adaptive current reference value correction;

[0131] Figure 4a and Figure 4b are the experimental waveforms of the synchronous phase angle offset and current without adding the adaptive current correction method and with adding the adaptive current correction method;

[0132] Figure 5a and Figure 5b are the waveforms of the synchronous phase angle offset and instantaneous power without adding the adaptive current correction method and with adding the adaptive current correction method. Detailed Embodiments

[0133] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all belong to the protection scope of the present invention.

[0134] Embodiment

[0135] To solve the problem of the risk of synchronization instability of power synchronization control type inverters caused by the instantaneous active power fluctuation under unbalanced voltage, the existing sequence control method has the problem of high system complexity, while the existing simplified virtual phase current regulation method has the problems of phase angle deviation and reactive power deviation. Based on the existing virtual phase current regulation method, the present invention first establishes a coupling mechanism model of asymmetric gain, phase angle and power offset problems, and reveals the non-consistency problem between its feedback current and actual current; then, according to the adaptive dynamic current reference value correction method proposed by the present invention, by compensating the asymmetric feedback gain of the virtual phase current regulation method in real time, the power synchronization control type inverter maintains a stable and accurate synchronization phase angle, and at the same time realizes accurate control of power output, effectively avoiding the overcurrent problem caused by power offset. Under the control architecture of the present invention, the system has the advantages of low control complexity and high synchronization stability, providing a new reliable solution for power synchronization type inverters under unbalanced power grids. This solution has the following advantages:

[0136] This solution retains and optimizes the simple control architecture of the existing virtual phase current regulation method, without the need to add a negative sequence current control loop, improving the convenience and economy of engineering implementation.

[0137] The control quantity offset correction method given in this solution can effectively adapt to the dynamically changing unbalanced grid conditions, compensating the dynamic asymmetric gain introduced by the virtual phase current modulation method online, with low complexity and high reliability and practicability.

[0138] The technical solution of the present invention is a method for eliminating phase angle and power offset of power synchronization type inverters under unbalanced power grids.

[0139] Compared with the existing power fluctuation suppression method based on sequence control under unbalanced power grids, the present invention has lower system complexity and higher convenience and economy in engineering implementation. Based on the simple virtual phase current modulation method, the present invention first analyzes the non-consistency problem between the feedback current and the actual current caused by its asymmetric feedback gain, and quantifies the coupling mechanism of the asymmetric feedback gain, phase angle offset and power offset; then gives a current reference value correction method suitable for dynamically changing unbalanced conditions, compensating the negative impact of the asymmetric feedback gain online to obtain an accurate synchronization phase angle and accurate reactive power control. The specific implementation means are as follows:

[0140] A. Construct a synchronization phase angle and power offset model

[0141] The schematic diagram of the power synchronization control type inverter system is as Figure 1 shown. In the power stage part of the figure, i abc and v abc are the grid-side current and voltage respectively, U m is the voltage amplitude, k sagis the voltage dip ratio of phase A. In the controller part, the Virtual Phase Current Regulation (VPCR) is applied to the sagging phase A, and the feedback gain k is added. a The synchronization between the inverter and the grid is achieved by Power Synchronization Control (PSC). By calculating the power difference between the instantaneous active power and the command value, the synchronous frequency adjustment amount Δω is obtained, and then the phase angle θ is obtained by integration. PSC The current active power and reactive power command values are given in the control. and Subsequently, the current reference value is obtained through the current reference value generation module. The vector current controller makes the feedback current consistent with the current reference value through the dq decoupling control method, and finally outputs the PWM control signal of the inverter.

[0142] To construct the synchronous phase angle and reactive power offset model, it is necessary to analyze the instantaneous power under the action of the virtual phase current regulation method. The expressions of the three-phase voltage and current are defined as:

[0143]

[0144] where ω is the grid angular frequency.

[0145] The synchronous phase angle offset is defined as:

[0146] Δθ = θ true - θ err

[0147] where θ true is the accurate grid phase angle, and θ err is the incorrect synchronous phase angle with phase offset. Thus, the Park transformation based on θ err is:

[0148]

[0149] The d-axis voltage after the Clarke transformation T abc-αβ and the Park transformation T αβ-dq_dv under the synchronous phase angle with phase offset is:

[0150]

[0151] To eliminate the oscillating component of the d-axis voltage, the DC component of the d-axis voltage is obtained through a notch filter as Subsequently, the current reference values in the dq axes are calculated through the current reference value generation module as:

[0152]

[0153] Under the virtual phase current regulation method, the asymmetric feedback gain injects zero-sequence current into the feedback current. The feedback current is defined as:

[0154]

[0155] where, I m_dv is the current amplitude, is the phase angle by which the current lags behind the voltage, I 0_dv is the amplitude of the zero-sequence current, is the phase angle by which the zero-sequence current lags behind the voltage. Based on the constraint that the zero-sequence current is zero in an actual three-phase three-wire system, the following can be solved:

[0156]

[0157] Then, when entering the steady state, the vector current controller makes the feedback current equal to the current reference value, that is, there is an equation:

[0158]

[0159] The above equation can be solved to obtain:

[0160]

[0161] According to the instantaneous power theory, the instantaneous active power can be obtained as:

[0162]

[0163] Under the action of the power synchronization control loop, there is an equation in the steady state:

[0164]

[0165] Solving this equation can obtain the quantization expression of the phase angle offset as:

[0166]

[0167] Furthermore, the instantaneous reactive power can be derived as:

[0168]

[0169] where, the DC component of the instantaneous reactive power is:

[0170]

[0171] The oscillating component is:

[0172]

[0173] Therefore, the quantization expression of the reactive power offset is:

[0174]

[0175] So far, a mapping relationship model of the synchronous phase angle offset, reactive power offset, and asymmetric gain has been constructed. The phase angle offset Δθ and reactive power offset Δq g vary with the voltage sag ratio k of phase A sag and the gain k of the virtual phase current regulation method a as shown in Figure 2a and Figure 2b . When the virtual phase current regulation method is not introduced, that is, when the feedback gain k a is set to one, both the synchronous phase angle offset and reactive power offset remain at 0° and 0 Var. This shows that the asymmetric feedback gain of the virtual phase current regulation method is the root cause of the synchronous phase angle offset and reactive power offset.

[0176] B. Introduction of the adaptive current reference value correction method

[0177] Considering that the virtual phase current regulation method eliminates the oscillating component of the instantaneous active power by modifying the current in the feedback branch, which is exactly the essence of the phase angle and reactive power deviation. To correct these deviations in the virtual phase current modulation control structure, the present invention proposes an improved control structure as shown in Figure 3 . An adaptive current reference value correction strategy is added to the improved control structure to compensate for the change of the feedback parameters and improve the virtual phase current control architecture.

[0178] Under vector current control, there is a relationship at steady state:

[0179]

[0180] The conversion relationship between the dq-axis current and the current amplitude and phase can be obtained as:

[0181] Or

[0182] Based on the instantaneous power theory, when the virtual phase current modulation is not introduced, the instantaneous power is:

[0183]

[0184] After introducing the virtual phase current modulation and adding the current reference value correction at the same time, the current amplitude and phase are corrected to and Therefore, the corrected instantaneous power is:

[0185]

[0186] Let the current reference value be such that the DC components of the above two sets of expressions are equal, and the following system of equations is obtained:

[0187]

[0188] Substitute the conversion relationships between dq-axis current, current amplitude, and phase into the above system of equations, and the expression for the adaptive current reference value is solved as:

[0189]

[0190] Therefore, according to the voltage imbalance situation in practice, after correcting the original current reference value through the above formula, the asymmetric feedback gain introduced by the virtual phase current regulation method can be dynamically compensated, thereby correcting the inconsistency between the feedback current and the actual current, and eliminating the synchronous phase angle offset and reactive power offset of the power synchronous inverter under unbalanced power grids.

[0191] Embodiment 2

[0192] In order to solve the problem that the instantaneous active power fluctuation under unbalanced voltage causes the risk of synchronization instability of the power synchronous control inverter, the existing sequence control method has the problem of high system complexity, while the existing simplified virtual phase current regulation method has the problems of phase angle deviation and reactive power deviation. Based on the existing virtual phase current regulation method, the proposed adaptive dynamic current reference value correction method can maintain a stable and accurate synchronous phase angle of the power synchronous control inverter by compensating the asymmetric feedback gain of the virtual phase current regulation method in real time, and at the same time achieve accurate control of power output, effectively avoiding the overcurrent problem caused by power offset. To verify the effect of the present invention, a power synchronous grid-connected inverter experimental platform was built. Set the reference values of active power and reactive power to be 240W and 180Var respectively, and the voltage amplitude of phase A in the three-phase voltage drops to 0.5 times the rated value. The experimental waveforms of the synchronous phase angle deviation and current are as Figure 4a and Figure 4b shown. Under the control structure of the traditional virtual phase current regulation method, when the adaptive current correction method is not added, the phase deviation is about 12.8°; under the control structure of the improved virtual phase current regulation method, when the current reference value correction method is added, the phase deviation is eliminated to 0°, achieving zero phase deviation and accurate and stable power synchronization. In addition, it can be observed that the effective value of the current is significantly reduced, solving the overcurrent problem that may be caused by inaccurate reactive power control. Figure 5a and Figure 5b show the experimental waveforms of the phase deviation and instantaneous power under the switching of the control architectures of the traditional and improved virtual phase current regulation methods. Under the control structure of the traditional virtual phase current regulation method, when the adaptive current correction method is not added, the average value of the reactive power is about 310Var, and compared with (240Var) There is a significant power control deviation of approximately +29.17%. Under the control structure of the improved virtual phase current regulation method, when the current reference value correction method is added, the reactive power control deviation is corrected to zero. Therefore, the above experimental results successfully verify the effectiveness of the proposed concept.

[0193] Under unbalanced voltages, existing power fluctuation suppression methods based on sequence control will increase system complexity, which is not conducive to the design and reliable operation of practical systems. However, the above experimental verification shows that by using the adaptive current reference value correction method proposed in the present invention, power fluctuations can be suppressed based on the virtual phase current regulation method in a simple control architecture without adding a negative sequence control loop, while eliminating the synchronous phase angle offset and reactive power offset caused by the asymmetric feedback gain, enhancing the stability and reliability of the power synchronization type inverter under unbalanced voltages.

[0194] Those skilled in the art know that in addition to implementing the systems, devices, and their respective modules provided by the present invention in the form of pure computer-readable program code, the method steps can be logically programmed to enable the systems, devices, and their respective modules provided by the present invention to be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers, etc., to achieve the same program. Therefore, the systems, devices, and their respective modules provided by the present invention can be regarded as a kind of hardware component, and the modules included therein for implementing various programs can also be regarded as the structure within the hardware component; the modules for implementing various functions can also be regarded as either software programs for implementing the method or the structure within the hardware component.

[0195] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined arbitrarily with each other.

Claims

1. A method for eliminating the phase angle and power offset of a power-synchronized inverter, characterized in that, Including: Step 1: Construct a coupling mechanism model of the synchronous phase angle offset and the reactive power offset. The model is based on the asymmetric feedback gain of the virtual phase current regulation method, the A-phase voltage drop ratio, the synchronous phase error, the voltage amplitude, the current amplitude, and the current phase angle, and is used to quantify the correlation between the asymmetric feedback gain and the phase angle offset and the reactive power offset; Step 2: Obtain the synchronous phase error of the power grid in real time, including generating the synchronous phase angle of the inverter through the power synchronization control loop, extracting the actual phase angle of the power grid based on the phase-locked loop, and calculating the difference between the two as the synchronous phase error; Step 3: Dynamically generate an adaptive current reference value correction amount according to the coupling mechanism model. The correction amount is used to compensate for the influence of the asymmetric feedback gain on the consistency between the feedback current and the actual current, including amplitude and phase correction of the original dq-axis current reference value; Step 4: Perform closed-loop control on the corrected current reference value and the actual feedback current through the vector current controller to generate the PWM modulation signal of the inverter, so as to eliminate the synchronous phase angle offset and the reactive power offset and maintain the stable synchronization between the inverter and the power grid; Step 5: Monitor the A-phase voltage amplitude in real time, calculate the voltage drop ratio, and dynamically adjust the asymmetric feedback gain in combination with the positive and negative sequence voltage components of the power grid to adapt to the dynamically changing unbalanced power grid conditions; Step 6: Filter out the second harmonic component of the d-axis voltage in the current reference value generation module, extract the DC voltage component, and generate the original current reference value in combination with the active power and reactive power command values; Step 7: Set the A-phase voltage drop condition through the experimental verification platform, compare the synchronous phase deviation and the reactive power control effect before and after adding the correction strategy, and confirm the elimination effect of the phase angle and power offset.

2. The method for eliminating the phase angle and power offset of a power-synchronized inverter according to claim 1, characterized in that, In the controller section, the virtual phase current regulation method (VPCR) is applied to the dropped A phase, with a feedback gain added. The synchronization between the inverter and the grid is achieved by power synchronization control (PSC). By calculating the power difference between the instantaneous active power and the command value, the synchronous frequency adjustment amount Δω is obtained, and then the phase angle θ is obtained by integration. PSC ; Given the current active power and reactive power command values in the control and Subsequently, the current reference value is obtained through the current reference value generation module The vector current controller makes the feedback current consistent with the current reference value through the dq decoupling control method, and finally outputs the PWM control signal of the inverter.

3. The method for eliminating the phase angle and power offset of a power synchronization type inverter according to claim 2, characterized in that To construct a synchronous phase angle and reactive power offset model and analyze the instantaneous power under the action of the virtual phase current regulation method, the expression of the three-phase grid-side voltage is: where ω is the grid angular frequency, U m is the voltage amplitude, and k sag is the voltage sag ratio of phase A voltage; t is the unit time; Define the synchronous phase angle offset as: Δθ = θ true -θ err where θ true is the accurate power grid phase angle, and θ err is the incorrect synchronization phase angle with a phase offset; Based on θ err The Park transformation is as follows: After the Clarke transformation T at a synchronous phase angle with phase angle offset abc-αβ and the Park transformation T αβ-dq_dv the d-axis voltage is: To eliminate the oscillating component of the d-axis voltage, the DC component of the d-axis voltage is obtained through a notch filter as Subsequently, the current reference values in the dq axes are calculated through the current reference value generation module as follows: Under the virtual phase current regulation method, the asymmetric feedback gain causes zero-sequence current to be injected into the feedback current. Define the three-phase feedback current as: Where, I m_dv is the current amplitude, is the phase angle by which the current lags behind the voltage, and I 0_dv is the amplitude of the zero-sequence current, is the phase angle by which the zero-sequence current lags behind the voltage; Based on the constraint that the zero-sequence current is zero in the actual three-phase three-wire system, it is solved that: where k a is the feedback gain.

4. The method for eliminating the phase angle and power offset of a power synchronization type inverter according to claim 3, characterized in that, When entering the steady state, the vector current controller makes the feedback current equal to the current reference value, that is, there is an equation: It is solved that: According to the instantaneous power theory, the instantaneous active power is obtained as: Under the action of the power synchronization control loop, there is an equation in the steady state: Solving this equation gives the quantization expression of the phase angle offset as: Derive the instantaneous reactive power as: In the formula, the DC component of the instantaneous reactive power is: The oscillation component is: Therefore, the quantization expression of the reactive power offset is:

5. The method for eliminating the phase angle and power offset of a power synchronization type inverter according to claim 4, characterized in that, Under vector current control, there is a relationship in the steady state: Among them, T αβ_dq is the transformation matrix from the αβ coordinate system to the dq coordinate system; is the feedback current; is the current reference value; Obtain the conversion relationship between the dq-axis currents and the current amplitude I m and the phase as follows: Based on the instantaneous power theory, when the virtual phase current modulation is not introduced, the instantaneous active power and reactive power are: After introducing virtual phase current modulation and adding current reference value correction at the same time, the current amplitude and phase are corrected to and Therefore, the corrected instantaneous power is Let the current reference value make the DC components of the above two groups of expressions equal, and obtain the system of equations: Substitute the conversion relationship between the dq-axis current and the current amplitude and phase into the above system of equations, and solve the expression of the adaptive current reference value as:

6. A system for eliminating the phase angle and power offset of a power synchronization type inverter, characterized in that, Including: Module M1: Construct a coupling mechanism model for synchronous phase angle offset and reactive power offset. The model is based on the asymmetric feedback gain of the virtual phase current regulation method, the A-phase voltage drop ratio, the synchronous phase error, the voltage amplitude, the current amplitude, and the current phase angle, and is used to quantify the correlation between the asymmetric feedback gain and the phase angle offset and reactive power offset; Module M2: Real-time obtain the synchronous phase error of the power grid, including generating the synchronous phase angle of the inverter through the power synchronization control loop, extracting the actual phase angle of the power grid based on the phase-locked loop, and calculating the difference between the two as the synchronous phase error; Module M3: Dynamically generate an adaptive current reference value correction amount according to the coupling mechanism model. The correction amount is used to compensate for the influence of the asymmetric feedback gain on the consistency between the feedback current and the actual current, including amplitude and phase correction of the original dq-axis current reference value; Module M4: Perform closed-loop control on the corrected current reference value and the actual feedback current through a vector current controller to generate a PWM modulation signal for the inverter to eliminate the synchronous phase angle offset and reactive power offset and maintain the stable synchronization between the inverter and the power grid; Module M5: Real-time monitor the A-phase voltage amplitude, calculate the voltage drop ratio, and dynamically adjust the asymmetric feedback gain in combination with the positive and negative sequence voltage components of the power grid to adapt to the dynamically changing unbalanced power grid conditions; Module M6: Filter out the second harmonic component of the d-axis voltage in the current reference value generation module, extract the DC voltage component, and generate the original current reference value in combination with the active power and reactive power command values; Module M7: Set the A-phase voltage drop condition through an experimental verification platform, compare the synchronous phase deviation and reactive power control effect before and after adding the correction strategy, and confirm the elimination effect of the phase angle and power offset.

7. The system for eliminating the phase angle and power offset of a power synchronization type inverter according to claim 6, characterized in that In the controller section, the virtual phase current regulation method (VPCR) is applied to the dropped A phase, and a feedback gain is added. The synchronization between the inverter and the grid is achieved by the power synchronization control (PSC). By calculating the power difference between the instantaneous active power and the command value, the synchronous frequency adjustment amount Δω is obtained, and then the phase angle θ is obtained by integration. PSC ; Given the current active power and reactive power command values in control and Subsequently, the current reference value is obtained through the current reference value generation module The vector current controller makes the feedback current consistent with the current reference value through the dq decoupling control method, and finally outputs the PWM control signal of the inverter.

8. The system for eliminating the phase angle and power offset of a power synchronization type inverter according to claim 7, characterized in that, To construct a synchronous phase angle and reactive power offset model and analyze the instantaneous power under the action of the virtual phase current regulation method, the expressions of the three-phase grid-side voltages are: where ω is the grid angular frequency, U m is the voltage amplitude, and k sag is the voltage sag ratio of phase A voltage; t is the unit time; Define the synchronous phase angle offset as: Δθ = θ true -θ err where θ true is the accurate grid phase angle, and θ err is the wrong synchronization phase angle with a phase offset; Based on θ err The Park transformation is as follows: After the Clarke transformation T at a synchronous phase angle with phase angle offset abc-αβ and the Park transformation T αβ-dq_dv the d-axis voltage is: To eliminate the oscillating component of the d-axis voltage, the DC component of the d-axis voltage is obtained through a notch filter as Subsequently, the current reference values in the dq axes are calculated by the current reference value generation module as follows: Under the virtual phase current regulation method, the asymmetric feedback gain causes a zero-sequence current to be injected into the feedback current. Define the three-phase feedback current as: Where, I m_dv is the current amplitude, is the phase angle by which the current lags behind the voltage, and I 0_dv is the amplitude of the zero-sequence current, is the phase angle by which the zero-sequence current lags behind the voltage; Based on the constraint that the zero-sequence current is zero in the actual three-phase three-wire system, the solution is: where k a is the feedback gain.

9. The system for eliminating the phase angle and power offset of a power-synchronized inverter according to claim 8, characterized in that, When entering the steady state, the vector current controller makes the feedback current equal to the current reference value, that is, there is an equation: The solution is: According to the instantaneous power theory, the instantaneous active power is obtained as: Under the action of the power synchronization control loop, there is an equation at steady state: Solving this equation gives the quantization expression for the phase angle offset as: Derive the instantaneous reactive power as: Where the DC component of the instantaneous reactive power is: The oscillating component is: Therefore, the quantization expression for the reactive power offset is:

10. The system for eliminating the phase angle and power offset of a power-synchronized inverter according to claim 9, wherein Under vector current control, there is a relationship at steady state: Among them, T αβ_dq is the transformation matrix from the αβ coordinate system to the dq coordinate system; is the feedback current; is the current reference value; Obtain the conversion relationship between the dq-axis current and the current amplitude I m , phase is as follows: Based on the instantaneous power theory, when the virtual phase current modulation is not introduced, the instantaneous active power and reactive power are: After introducing virtual phase current modulation and adding current reference value correction at the same time, the current amplitude and phase are corrected to and Therefore, the corrected instantaneous power is Let the current reference value make the DC components of the above two sets of expressions equal, and obtain a system of equations: Substitute the conversion relationship between the dq-axis current and the current amplitude and phase into the above system of equations, and the expression for the adaptive current reference value is obtained as:

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