Power fluctuation suppression method and system based on three-phase virtual phase current regulation

Abstract

The application provides a power pulsation suppression method and system based on three-phase virtual phase current regulation, comprising the following steps: S1: based on three-phase virtual phase current regulation technology, a DC bus power pulsation overall model is constructed; the three-phase virtual phase current regulation technology introduces virtual phase current gain in three phases of a three-phase circuit; the DC bus power pulsation overall model obtains parameters of the three-phase circuit; S2: the DC bus power pulsation overall model is optimized and solved to complete the suppression of power pulsation. In the control system, virtual phase current gain is introduced in the feedback current of each phase, the three-phase feedback current is simultaneously adjusted, the three-phase grid-connected current is in an unbalanced state, and then the elimination of DC power pulsation under a three-phase unbalanced power grid is realized; the optimal value of phase current gain is solved based on a grey wolf algorithm, and it is ensured that the three-phase virtual phase current regulation technology fully plays its power fluctuation suppression effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of alternating current generation, transmission, distribution and utilization, and in particular, to a power pulsation suppression method and system based on three-phase virtual phase current regulation. BACKGROUND

[0002] In recent years, the penetration rate of new energy in China has been increasing, but the inertia of the new energy system is low, the damping is small, and the volatility is strong, which will have a negative impact on the power quality of the power grid. The coupling between the grid-connected inverter and the power grid will also affect the reliable and stable operation of the power grid, which is easy to cause the voltage deviation of the power grid. In addition, during the normal operation of the power grid, there will be a slight deviation in the three-phase voltage, which will cause the power grid voltage to have a certain degree of unbalance. In the national standard "Power Quality Supply Voltage Deviation", it is stipulated that the three-phase supply voltage deviation of 20kV and below is limited to 7% of the nominal voltage; in the national standard "Power Quality Three-Phase Voltage Unbalance", it is stipulated that the negative sequence voltage unbalance degree shall not exceed 2% during normal operation of the power grid. When the voltage deviation of the power grid causes the three-phase to be in an unbalanced state, the power on the DC bus will have a two-frequency pulsation, which will damage the life of the DC side capacitor, and over time will threaten the stable operation of the power grid. Therefore, when the three-phase voltage all has a supply voltage deviation and is in a three-phase unbalanced state, it is of practical significance to discuss maintaining the constant power of the DC bus.

[0003] The virtual phase current regulation (VPCR) technology compensates for the voltage deviation by adjusting the feedback current in the control system, and then maintains the constant at the DC bus power level. However, the existing virtual phase current technology only discusses and analyzes single-phase voltage drop, and the selection of phase current gain is not optimal, which is not universal and cannot completely eliminate the power pulsation on the DC bus.

[0004] Existing power pulsation suppression strategies often ignore the contribution of the filter loop to the DC bus power pulsation, directly equate the active power on the AC side to the DC bus power, and cause the DC bus power pulsation to be not completely eliminated. In addition, the existing suppression strategies often modify the positive and negative sequence reference currents of the vector current control or use power compensation of direct power control to suppress the active power pulsation on the AC side. The positive and negative sequence separation delay, the positive and negative sequence coupling effect, and the increase of system complexity all affect the dynamic response speed and stability of the system, and then interfere with the actual effect of the suppression strategy.

[0005] The existing VPCR suppression technology realizes complete elimination of active power fluctuation on the alternating current side by modifying the feedback current of the phase where the voltage drop is located in the control loop, and has the advantages of simple control structure and strong system robustness. However, the existing VPCR technology only analyzes the single-phase voltage drop scene, and does not specifically analyze the three-phase voltage imbalance condition. In actual engineering application, the probability of single-phase voltage drop is relatively low, and the suppression strategy for three-phase imbalance scene is more universal and universal. In addition, the existing VPCR technology does not propose a design method for the feedback current adjustment coefficient, i.e. the virtual phase current gain under the condition of three-phase imbalance, and the selection of the existing virtual phase current gain can only realize the elimination of active power fluctuation on the alternating current side, but the power fluctuation on the direct current bus always exists.

[0006] Xiong F, Wu JY, Hao LL, et al. Multi-objective control strategy of inverter under asymmetric voltage sag [J]. Transactions of China Electrotechnical Society, 2017, 32(01): 107-116. This document proposes a new type of multi-objective reference current calculation method, which unifies multiple optimization objectives in the expression of the reference current, and changes the proportion of different optimization objectives by adjusting the coefficient, to realize the diversity of control strategy. This document first establishes the instantaneous active power and reactive power model of the inverter under the condition of grid voltage drop, and then analyzes the common control objectives of the inverter under the condition of grid voltage drop, including symmetric three-phase current, elimination of active power fluctuation and elimination of reactive power fluctuation. This document introduces adjustment coefficients k1 and k2 to coordinate among the three control objectives, and on this basis, proposes a selection scheme for the adjustment coefficients. However, this document only considers the active power and reactive power fluctuation on the alternating current side when analyzing the optimization objectives, and does not consider the instantaneous power fluctuation on the filter circuit of the inverter under the condition of grid voltage drop, and does not take the direct current side power fluctuation which directly affects the direct current side capacitor as the optimization objective. In addition, when solving the multi-objective optimization problem, this document uses the Lagrange method to establish the equation set to obtain the search path of the optimal power fluctuation amplitude of the adjustment coefficients k1 and k2. The complexity of the model directly affects the feasibility of the search path solution. This invention directly takes the direct current bus power fluctuation amplitude as the optimization objective, and additionally considers the filter circuit power fluctuation on the basis of the active power fluctuation model on the alternating current side. In addition, this invention uses the grey wolf algorithm, one of the intelligent optimization algorithms, for optimization and solution, which has fast convergence speed and good convergence. Compared with the existing suppression strategy, the control strategy designed in this invention which introduces three-phase VPCR technology has low complexity, greatly improving the dynamic performance and calculation speed of the system.

[0007] In the Chinese patent document with publication number CN113400959A, a kind of electric drive reconfiguration type charging system for electric vehicle considering secondary power pulsation suppression is disclosed, including uncontrolled rectifier bridge, three-phase inverter, three-phase permanent magnet synchronous motor, energy storage capacitor, output filter capacitor, power battery and switching switch.In charging state, two-phase winding of permanent magnet synchronous motor and two groups of half-bridge of inverter constitute parallel Boost circuit, and the remaining one-phase winding of permanent magnet synchronous motor and the remaining one group of half-bridge of inverter constitute an active filter.But the patent document only improves the power density of charging system, and does not solve the above problems. SUMMARY

[0008] In view of the defects in the prior art, the purpose of the present application is to provide a power pulsation suppression method and system based on three-phase virtual phase current regulation.

[0009] According to the power pulsation suppression method based on three-phase virtual phase current regulation provided by the present application, the following steps are included:

[0010] Step S1: based on three-phase virtual phase current regulation technology, construct a direct current bus power pulsation overall model;

[0011] The three-phase virtual phase current regulation technology introduces virtual phase current gain in three phases of three-phase circuit respectively;

[0012] The direct current bus power pulsation overall model obtains the parameters of three-phase circuit;

[0013] Step S2: optimize and solve the direct current bus power pulsation overall model to complete the suppression of power pulsation.

[0014] Preferably, the direct current bus power pulsation overall model adopts phase-locked loop of double second-order generalized integrator to extract positive sequence component of grid voltage; the parameters include phase voltage offset degree, three-phase virtual phase current gain and influence value of circuit parameters on power pulsation amplitude on direct current bus; when grid voltage is in three-phase unbalanced state, three-phase virtual phase current regulation technology is introduced to make three-phase grid-connected current unbalanced, and suppress direct current side power double-frequency pulsation; define θ PLL is the phase angle output by phase-locked loop, i a v , i b v and i c v are virtual A-phase, B-phase and C-phase currents obtained after applying three-phase virtual phase current regulation technology, i d v and i q v are virtual d-axis current and virtual q-axis current, u d and u qare d-axis voltage and q-axis virtual voltage respectively, i dref and i qref are d-axis reference current and q-axis reference current respectively, and ω is grid angular velocity.

[0015] Preferably, in the step S1, the voltage offset ratio is defined as the ratio of the current phase voltage to the phase voltage in the balanced state, and the voltage offset ratios of the three-phase voltages of phases A, B and C are respectively k a drop , k b drop , k c drop The current three-phase grid voltage is:

[0016]

[0017] In the formula, u a , u b and u c are the grid voltages of phases A, B and C respectively, t is time, and U is the fundamental voltage in the balanced state.

[0018] The dq-axis voltages are:

[0019]

[0020] The three-phase virtual phase current regulation technology introduces virtual phase current gains k a , k b and k c in the grid-connected current coordinate transformation module for three phases A, B and C respectively, and obtains the virtual phase current as:

[0021]

[0022] In the formula, i a , i b and i c are the grid-connected currents of phases A, B and C respectively.

[0023] The three-phase virtual phase current is subjected to coordinate transformation to obtain virtual dq-axis current as the input of the vector current loop, the dq-axis reference current in the current loop is maintained unchanged, and the three-phase grid-connected currents are respectively amplified by 1 / k a , 1 / k b and 1 / k c times; there is no zero sequence current in the three-phase three-wire system, and the three-phase grid-connected currents satisfy:

[0024] i a +i b +i c =0.

[0025] When k a ≠k b≠ k c When k a i a +k b i b +k c i c ≠ 0, there is zero-axis current in the control loop, and the dq0-axis currents in the control loop at this time are set as:

[0026]

[0027] where i d d is the d-axis current, i q q is the q-axis current, i0 is the zero-axis current, I1 is the positive sequence current amplitude, is the current phase, I0 is the zero-axis current amplitude in the control loop, is the corresponding zero-axis current phase;

[0028] The three-phase currents in the control loop are:

[0029]

[0030] The three-phase grid-connected currents are:

[0031]

[0032] The amplitude and phase of the zero-axis current in the control loop are:

[0033]

[0034] where sign(x) = x / |x|, x is a parameter expression;

[0035] The three-phase grid-connected currents are:

[0036]

[0037] The dq-axis grid-connected currents are:

[0038]

[0039] The active power P PCC of the AC side is calculated by the formula:

[0040]

[0041] After introducing the three-phase virtual phase current regulation technology, the active power of the AC side is:

[0042]

[0043] where

[0044]

[0045] Preferably, the DC bus power is filtered by a filter inductance L f The influence of transmission power, under unbalanced power grid, the instantaneous power transmitted on the filter inductance exists fluctuation, further aggravate the power fluctuation on the DC bus;

[0046] The voltage on the filter inductance is:

[0047]

[0048] In the formula, u La , u Lb , u Lc The voltage across the filter inductance A phase, B phase, C phase respectively;

[0049] The power P L on the filter inductance is:

[0050] P L = u La i a + u Lb i b + u Lc i c ;

[0051] The power P DC on the DC bus is the sum of the active power P PCC on the AC side and the instantaneous power P L on the filter inductance:

[0052] P DC = P PCC + P L ;

[0053] The twice frequency pulsating component on the DC bus is:

[0054]

[0055] Among them, FC1, FC2, FS1 and FS2 are The coefficients of the expression, expressed as follows:

[0056]

[0057] σ1 and σ2 are the coefficients in the expression of FC1, FC2, FS1 and FS2:

[0058]

[0059] The amplitude of the DC bus power fluctuation is:

[0060] ​

[0061] Preferably, the overall model of DC bus power pulsation is optimized based on the gray wolf algorithm. The gray wolf algorithm achieves target optimization by simulating the hierarchy and hunting mechanism in the gray wolf pack. In the gray wolf pack, the gray wolves are divided into four levels from high to low and distributed in a pyramid shape, namely α, β, δ and ω wolves. Among them, α, β and δ wolves are responsible for making decisions and dominating the predation behavior of the wolf pack, and ω wolf is the bottom level of the entire wolf pack. α wolf corresponds to the optimal solution, β wolf corresponds to the second-best solution, δ wolf corresponds to the third-best solution, and ω wolf corresponds to the candidate solution.

[0062] Preferably, in the gray wolf algorithm, the gray wolf pack surrounds the prey during the hunting process. During the algorithm's search process, the formula for updating the distance and position between individual gray wolves and their prey is:

[0063]

[0064]

[0065] In the formula, This refers to the distance between an individual gray wolf and its prey. and Let t be the coefficient vector, and t be the current iteration number. Let be the position vector of the prey. Let this be the position vector of the gray wolf;

[0066] coefficient vector and The calculation formula is:

[0067]

[0068]

[0069] In the formula, It is the convergence factor, and it decreases linearly with the number of iterations in the interval [0, 2]. and A random vector taking values ​​in the interval [0, 1];

[0070] Gray wolf packs, led by α, β, and δ wolves, identify and surround prey. They use the α, β, and δ wolves to determine the prey's potential location and update the position of the ω wolves within the pack. The distances of the α, β, and δ wolves from other individual gray wolves in the pack are:

[0071]

[0072] In the formula, and These represent the distances between α, β, and δ wolves and other individual gray wolves, respectively. and is a random vector, and are the current positions of alpha, beta and delta wolves respectively;

[0073] The position update formula of the gray wolf individual is:

[0074]

[0075] In the formula, is the direction and step length of the omega wolf advancing towards the alpha wolf; is the direction and step length of the omega wolf advancing towards the beta wolf; is the direction and step length of the omega wolf advancing towards the delta wolf;

[0076] The final position of the gray wolf individual is:

[0077]

[0078] Preferably, in the gray wolf algorithm, the attack of the gray wolf population on the prey is reflected by the decrease of a convergence factor ; the convergence factor changes with the number of iterations, so that is a random number in the interval [-2a, 2a], when is in the interval [-1, 1], the next position of the gray wolf is at any position between the current position and the prey; when , the gray wolf launches an attack on the prey, and the current solution falls into a local optimum; in the gray wolf algorithm, the wolf pack disperses when searching for prey, corresponding to the exploration process; the wolf pack gathers when attacking the prey, corresponding to the convergence process; when , the gray wolf will be forced to separate to escape from the local optimal state to support the exploration behavior of the gray wolf algorithm; the coefficient vector represents the random weight of the position of the gray wolf on the prey, which controls the global search ability of the algorithm.

[0079] Preferably, in the gray wolf algorithm, the position of each gray wolf individual has three dimensions, respectively corresponding to the virtual phase current gain of each phase; the DC bus power fluctuation overall model combines the actual operating condition of the grid-connected inverter to completely suppress the DC bus power fluctuation.

[0080] According to the power fluctuation suppression system based on three-phase virtual phase current regulation provided by the application, the system comprises:

[0081] Module M1: based on three-phase virtual phase current regulation technology, a DC bus power fluctuation overall model is constructed;

[0082] The three-phase virtual phase current regulation technology introduces virtual phase current gain in the three phases of the three-phase circuit respectively;

[0083] The direct current bus power pulsation overall model obtains parameters of a three-phase circuit;

[0084] Module M2: optimizing and solving the direct current bus power pulsation overall model to complete the suppression of power pulsation.

[0085] Preferably, the direct current bus power pulsation overall model adopts a phase-locked loop of a double second-order generalized integrator to extract a positive sequence component of a grid voltage; the parameters include a voltage offset ratio of each phase, a three-phase virtual phase current gain, and an influence value of circuit parameters on a power pulsation amplitude on the direct current bus; when the grid voltage is in a three-phase unbalanced state, a three-phase virtual phase current regulation technology is introduced to make three-phase grid-connected currents unbalanced, thereby suppressing a direct current side power double-frequency pulsation; θ PLL is a phase angle output by the phase-locked loop, i a v , i b v and i c v are virtual A-phase, B-phase and C-phase currents obtained after the three-phase virtual phase current regulation technology is applied, i d v and i q v are virtual d-axis and q-axis currents, u d and u q are d-axis and q-axis voltages, i dref and i qref are d-axis and q-axis reference currents, and ω is a grid angular velocity.

[0086] Preferably, in the module M1, a voltage offset ratio is defined as a ratio of a current phase voltage to a phase voltage in a balanced state, and the voltage offset ratios of A-phase, B-phase and C-phase three-phase voltages are respectively k a drop , k b drop , k c drop , then the current grid three-phase voltage is:

[0087]

[0088] In the formula, u a , u b and u c are A-phase, B-phase and C-phase grid voltages, t is time, and U is a fundamental voltage in a balanced state.

[0089] The dq-axis voltages are:

[0090]

[0091] The three-phase virtual phase current regulation technology introduces virtual phase current gains k a 、 b and k c in the grid-connected current coordinate transformation module respectively, and obtains the virtual phase current as:

[0092]

[0093] wherein, i a , i b and i c are A, B and C phase grid-connected currents respectively;

[0094] The three-phase virtual phase current is subjected to coordinate transformation, and the virtual dq axis current is obtained as the input of the vector current loop, the dq axis reference current in the current loop is maintained unchanged, and the three-phase grid-connected currents are respectively amplified by 1 / k a , 1 / k b and 1 / k c times; there is no zero sequence current in the three-phase three-wire system, and the three-phase grid-connected currents satisfy:

[0095] i a +i b +i c =0;

[0096] When k a ≠k b ≠k c , k a i a +k b i b +k c i c ≠0 in the control loop, there is zero axis current in the control loop, and the dq0 axis current in the control loop at this time is:

[0097]

[0098] wherein, i d is the d-axis current, i q is the q-axis current, i0 is the zero-axis current, I1 is the positive sequence current amplitude, is the current phase, I0 is the zero-axis current amplitude in the control loop, is the corresponding zero-axis current phase;

[0099] The three-phase current in the control loop is:

[0100]

[0101] The three-phase grid-connected current is:

[0102]

[0103] The amplitude and phase of the zero-axis current in the control loop are respectively:

[0104]

[0105] In the formula, sign(x) = x / |x|, x is a parameter expression;

[0106] The three-phase grid-connected current is:

[0107]

[0108] The dq-axis grid-connected current is:

[0109]

[0110] The active power P of the AC side PCC The calculation formula is:

[0111]

[0112] After introducing the three-phase virtual phase current regulation technology, the active power of the AC side is:

[0113]

[0114] Wherein

[0115]

[0116] Preferably, the DC bus power is affected by the filter inductance L f The instantaneous power transmitted on the filter inductance fluctuates under an unbalanced power grid, further exacerbating the power fluctuation on the DC bus;

[0117] The voltage on the filter inductance is:

[0118]

[0119] In the formula, u La , u Lb , u Lc are the voltages across the filter inductance A, B, and C phases, respectively.

[0120] The power P L on the filter inductance is:

[0121] P L = u La i a + u Lb i b + u Lc i c ;

[0122] The power P on the DC side bus DC The AC side active power P PCC And the instantaneous power P on the filter inductance L The sum of:

[0123] P DC = P PCC + P L ;

[0124] The double-frequency pulsating component on the DC bus is obtained As follows:

[0125]

[0126] Wherein, FC1, FC2, FS1 and FS2 are The coefficients of the expression are expressed as follows:

[0127]

[0128] σ1 and σ2 are the coefficients in the expressions of FC1, FC2, FS1 and FS2:

[0129]

[0130] The amplitude of the DC bus power fluctuation is obtained as:

[0131]

[0132] Preferably, the overall model of the DC bus power pulsation is based on a grey wolf algorithm for optimization solution; the grey wolf algorithm realizes target optimization by simulating the hierarchical level and hunting mechanism in the grey wolf group; in the grey wolf group, the grey wolves are divided into four levels from high to low and are distributed in a pyramid shape, which are α, β, δ and ω wolves; wherein, the α, β and δ wolves are responsible for decision-making and domination of the hunting behavior of the wolf group, and the ω wolf is the bottom layer of the whole wolf group; the α wolf corresponds to the optimal solution, the β wolf corresponds to the suboptimal solution, the δ wolf corresponds to the third optimal solution, and the ω wolf corresponds to the candidate solution.

[0133] Preferably, in the grey wolf algorithm, the grey wolves surround the prey in the hunting process, and in the algorithm search process, the distance and position update formula between the individuals of the grey wolf population and the prey is:

[0134]

[0135]

[0136] In the formula, is the distance between the grey wolf individual and the prey, and is a coefficient vector, t is the current iteration number, a position vector of the prey, a position vector of the gray wolf;

[0137] a coefficient vector and is calculated by the formula:

[0138]

[0139]

[0140] wherein, is a convergence factor, and decreases linearly in the interval [0, 2] with the iteration number; and are random vectors taking values in the interval [0, 1];

[0141] The gray wolf pack led by the alpha, beta and delta wolves identifies and encircles the prey, and judges the potential position of the prey and updates the position of the omega wolves in the pack through the alpha, beta and delta wolves, and the distance between the alpha, beta and delta wolves and other gray wolves in the pack is:

[0142]

[0143] wherein, and are the distances between the alpha, beta and delta wolves and other gray wolves, respectively, and are random vectors, and are the current positions of the alpha, beta and delta wolves, respectively;

[0144] The position updating formula of the gray wolf is:

[0145]

[0146] wherein, is the direction and step length of the omega wolf moving towards the alpha wolf; is the direction and step length of the omega wolf moving towards the beta wolf; is the direction and step length of the omega wolf moving towards the delta wolf;

[0147] The final position of the gray wolf is:

[0148]

[0149] Preferably, in the gray wolf algorithm, the attack of the gray wolf pack on the prey is reflected by the decrease of the convergence factor The convergence factor causes the value of to be a random number in the interval [-2a, 2a] as the iteration number changes, and when When the interval is [-1, 1], the next position of the grey wolf is any position between the current position and the prey; when the grey wolf attacks the prey, and the current solution falls into a local optimum; the wolf pack in the grey wolf algorithm disperses when searching for the prey, corresponding to the exploration process; the wolf pack gathers when attacking the prey, corresponding to the convergence process; when the grey wolf is forced to separate to escape from the local optimum state to support the exploration behavior of the grey wolf algorithm; the coefficient vector represents the random weight of the position of the grey wolf on the prey, and controls the global search ability of the algorithm.

[0150] Preferably, the position of each grey wolf individual in the grey wolf algorithm has three dimensions, respectively corresponding to the virtual phase current gain of each phase; the DC bus power fluctuation overall model completely suppresses the DC bus power fluctuation in combination with the actual operation condition of the grid-connected inverter.

[0151] Compared with the prior art, the present application has the following beneficial effects:

[0152] 1. In the control system, virtual phase current gains are introduced into the feedback currents of each phase, the three-phase grid-connected currents are in an unbalanced state through simultaneous adjustment of the three-phase feedback currents, and then the elimination of DC power fluctuation under a three-phase unbalanced power grid is realized; on this basis, a design method of three-phase virtual phase current gain based on the grey wolf algorithm is proposed, and the optimal value of the phase current gain is solved by an intelligent optimization algorithm, so that the power fluctuation suppression effect of the three-phase virtual phase current regulation technology is completely ensured from the theoretical level.

[0153] 2. Compared with the existing VPCR technology, the three-phase virtual phase current regulation technology proposed by the present application has three degrees of freedom, the suppression ability of power fluctuation is further improved, and the power fluctuation of the DC bus can be completely eliminated in the face of any unbalanced operating condition of the power grid, meeting the needs of traditional engineering.

[0154] 3. The present application can be applied to any three-phase unbalanced operating condition of the power grid, and the voltage drop and voltage over-limit of any phase can be compensated at the DC bus power level by adjusting the unbalance degree of the three-phase grid-connected current, so that the existing VPCR technology is improved and improved.

[0155] 4. The present application establishes a DC bus power fluctuation theoretical model considering three-phase VPCR technology under a three-phase unbalanced power grid, and solves the optimization model by using the grey wolf algorithm to obtain the optimal value of the gain coefficient, constructs a mathematical model of the DC bus power, reflects the change of different power grid conditions and system parameters at the DC bus power level, and creatively applies an intelligent optimization algorithm to the solution of the gain coefficient.

[0156] 5、The application not only analyzes the active power of the AC side, but also considers the influence of the filter circuit on the DC bus power in the aspect of DC bus power composition, and builds a theoretical model of the DC bus double-frequency ripple considering the three-phase VPCR technology on this basis.

[0157] 6、The application proves that the designed parameters can realize complete suppression of the DC side power ripple from the theoretical level, solves the optimization solving problem of the complex power ripple amplitude model in parameter design by using the emerging swarm intelligence optimization algorithm, and has high practicability.

[0158] Other beneficial effects of the application will be described in the specific embodiments by introducing specific technical features and technical solutions, and those skilled in the art should be able to understand the beneficial technical effects brought by the technical features and technical solutions through the introduction of the technical features and technical solutions. BRIEF DESCRIPTION OF DRAWINGS

[0159] Other features, objects and advantages of the application will become more apparent through reading the detailed description of the non-limiting embodiments with reference to the following drawings:

[0160] Figure 1 The method flowchart of the application.

[0161] Figure 2 The grid-connected inverter system diagram under unbalanced power grid in the application.

[0162] Figure 3 The three-phase virtual phase current regulation technology control block diagram in the application.

[0163] Figure 4 The virtual phase current gain parameter design flowchart based on the grey wolf algorithm in the application.

[0164] Figure 5 The DC bus power curve diagram when the suppression technology is not introduced in the embodiment of the application.

[0165] Figure 6 The DC bus power curve diagram after introducing the current virtual phase current regulation technology in the embodiment of the application.

[0166] Figure 7 The grid-connected current waveform diagram after introducing the three-phase virtual phase current regulation technology in the embodiment of the application.

[0167] Figure 8 The DC bus power curve diagram after introducing the three-phase virtual phase current regulation technology in the embodiment of the application. DETAILED DESCRIPTION

[0168] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0169] Reference Figure 1 and Figure 2 As shown, C dc For DC bus capacitor, L f For the filter inductor, i a i b and i c Let u be the grid-connected current for phases A, B, and C. a u b and u c These are the grid voltages for phases A, B, and C.

[0170] Reference Figure 3 The diagram shown is a control block diagram for three-phase virtual phase-current regulation (VPCR) technology. This invention employs a dual second-order generalized integrator phase-locked loop (DSOGI-PLL) to extract the positive-sequence component of the mains voltage to achieve accurate phase locking. θ PLL For the phase angle output of the phase-locked loop, i a v i b v and i c v These represent the virtual A-phase, B-phase, and C-phase currents obtained after applying the three-phase VPCR technique, i d v and i q v These are the virtual d-axis current and the virtual q-axis current, respectively. d and u q These are the d-axis voltage and the q-axis virtual voltage, respectively. dref and i qref These are the d-axis reference current and the q-axis reference current, respectively, and ω is the grid angular velocity.

[0171] The application proposes a virtual phase current gain parameter design method based on grey wolf algorithm for eliminating DC bus power double-frequency pulsation based on three-phase VPCR technology. The existing VPCR technology only analyzes the active power fluctuation on the AC side, can only achieve partial suppression of the double-frequency pulsation of the DC bus power, and does not design an optimal selection method for the VPCR technology parameters. The VPCR technology changes the feedback current in the control loop by introducing a virtual phase current gain in the three-phase phase current, so that the three-phase grid-connected current is unbalanced, and then the three-phase unbalanced voltage is complemented on the DC bus power calculation level to achieve constant power. When the existing VPCR technology faces a three-phase unbalanced grid, the virtual phase current gain is directly selected as the voltage drop ratio, at this time the power pulsation on the DC bus is reduced but not completely eliminated, and the virtual phase current gain at this time is not the optimal value.

[0172] The three-phase VPCR technology applied in the application adds analysis of the instantaneous power fluctuation of the filter circuit on the basis of the active power fluctuation model on the AC side, and then builds a DC bus double-frequency pulsation model considering the three-phase VPCR technology. On this basis, the application proposes a design theory of the virtual phase current gain, and uses the grey wolf optimization algorithm to optimize the pulsation model to obtain a suitable virtual phase current gain value to achieve the effect of constant power.

[0173] First, consider the DC bus power pulsation theoretical model under the three-phase unbalanced grid of the three-phase VPCR technology:

[0174] When the grid voltage is in a three-phase unbalanced state, the introduction of the three-phase VPCR technology can suppress the double-frequency pulsation of the DC side power through the unbalance of the three-phase grid-connected current. Define the voltage offset ratio as the ratio of the current phase voltage to the balanced state phase voltage, and assume that the voltage offset ratios of the A, B and C phases are k a drop 、k b drop 、k c drop , then the current three-phase grid voltage is:

[0175]

[0176] In the formula, u a 、u b and u c are the A, B and C phase grid voltages, t is the time, and U is the fundamental voltage in the balanced state.

[0177] The dq-axis voltage can be obtained by formula (1):

[0178]

[0179] The three-phase VPCR technology introduces virtual phase current gains k a 、 b and k c into A, B and C phases respectively in the grid-connected current coordinate transformation module

[0180]

[0181] where i a , i b and i c are A, B and C phase grid-connected currents respectively

[0182] The three-phase virtual phase currents are subjected to coordinate transformation to obtain virtual dq-axis currents as the input of the vector current loop, but the dq-axis reference currents in the current loop remain unchanged, which is equivalent to amplifying the three-phase grid-connected currents by 1 / k a , 1 / k b and 1 / k c times respectively. Since there is no zero sequence current in the three-phase three-wire system, the three-phase grid-connected currents satisfy:

[0183] i a +i b +i c = 0 (4)

[0184] According to formula (4), when k a ≠ k b ≠ k c , k a i a +k b i b +k c i c ≠ 0 in the control loop, so there is zero-axis current in the control loop, and the dq0-axis current in the control loop at this time is:

[0185]

[0186] where i d is the d-axis current, i q is the q-axis current, i0 is the zero-axis current, I1 is the positive sequence current amplitude, is the current phase, I0 is the zero-axis current amplitude in the control loop, is the corresponding zero-axis current phase.

[0187] The three-phase currents in the control loop are:

[0188]

[0189] According to formulas (3) and (6), the three-phase grid-connected currents are:

[0190]

[0191] Substituting formula (7) into formula (4), the amplitude and phase of the zero-axis current in the control loop are:

[0192]

[0193] wherein sign(x) = x / |x|, x is a parameter expression;

[0194] Substituting formula (8) into formula (7), the three-phase grid-connected current is:

[0195]

[0196] Therefore, the dq-axis grid-connected current is:

[0197]

[0198] Since the calculation formula of the active power on the AC side is:

[0199]

[0200] Therefore, substituting formula (2) and formula (10) into formula (11), the active power on the AC side after introducing the three-phase VPCR technology is:

[0201]

[0202] wherein

[0203]

[0204] The power on the DC bus is not only directly related to the active power on the AC side, but also affected by the filter inductance L f transmitted on the filter inductance, which will further exacerbate the power fluctuation on the DC bus under an unbalanced grid.

[0205] The current flowing through the filter inductance is shown in formula (9), and the voltage on the filter inductance is:

[0206]

[0207] wherein u La , u Lb , and u Lc are the voltages across the filter inductance of phase A, phase B, and phase C, respectively;

[0208] Therefore, the power on the filter inductance is:

[0209] P L= u La i a + u Lb i b + u Lc i c (14)

[0210] The power on the DC side bus is the sum of the AC side active power and the instantaneous power on the filter inductance, which can be expressed as:

[0211] P DC = P PCC + P L (15)

[0212] The DC component and the double-frequency pulsating component of the DC bus power in formula (15) are separated, and the double-frequency pulsating component on the DC bus can be obtained as:

[0213]

[0214] Wherein, FC1, FC2, FS1 and FS2 are The coefficients of the expression are expressed as follows:

[0215]

[0216] σ1 and σ2 are the coefficients in the expressions of FC1, FC2, FS1 and FS2:

[0217]

[0218] The amplitude of the DC bus power fluctuation can be further obtained from formula (16) as:

[0219]

[0220] Next, the virtual phase current gain parameter design based on the grey wolf algorithm:

[0221] The grey wolf algorithm (GWO) is inspired by the hunting behavior of grey wolf packs in nature, and was first proposed by Mirjalili et al. in 2014. Through the simulation of the hierarchical level and hunting mechanism in the grey wolf population, the target optimization is achieved. The grey wolf algorithm simulates the behaviors of wolf pack hierarchical layer, surrounding prey, hunting, attacking prey and searching for prey, and has the advantages of good convergence, fast convergence speed, fewer parameters, simple structure, etc.

[0222] The grey wolf algorithm constructs a hierarchy according to the hierarchical model of the wolf pack. In the grey wolf pack, the grey wolves are divided into four levels from high to low and are distributed in a pyramid shape, namely alpha, beta, delta and omega wolves. Among them, alpha, beta and delta wolves are responsible for decision-making and dominate the hunting behavior of the wolf pack, and omega wolves are the bottom layer of the whole wolf pack and need to obey management. In the grey wolf algorithm, the alpha wolf corresponds to the optimal solution, the beta wolf corresponds to the suboptimal solution, the delta wolf corresponds to the third optimal solution, and the omega wolf corresponds to the candidate solution.

[0223] The grey wolf pack needs to surround the prey first in the hunting process. In the algorithm search process, the distance and position update formula between the individual of the grey wolf population and the prey can be expressed as:

[0224]

[0225]

[0226] In the formula, d is the distance between the grey wolf individual and the prey, and is a coefficient vector, t is the current iteration number, is the position vector of the prey, is the position vector of the grey wolf.

[0227] The calculation formula of the coefficient vector and is:

[0228]

[0229]

[0230] In the formula, c is a convergence factor, which linearly decreases in the interval [0, 2] with the iteration number, and are random vectors with values in the interval [0, 1].

[0231] The grey wolf pack can identify and surround the prey (optimal solution) under the leadership of alpha, beta and delta wolves, so the potential position of the prey can be judged by alpha, beta and delta wolves and the position of omega wolves in the population is updated. The distance between alpha, beta and delta wolves and other grey wolf individuals in the wolf pack is:

[0232]

[0233] In the formula, d is the distance between alpha, beta and delta wolves and other grey wolf individuals, are random vectors shown in formula (23), and ​​​​​These are the current positions of α, β, and δ wolves, respectively.

[0234] The formula for updating the position of individual gray wolves is:

[0235]

[0236] In the formula, and Let ω represent the direction and step length of the wolf ω moving towards α, β, and δ wolves, respectively.

[0237] The final location of the individual gray wolf is:

[0238]

[0239] The Grey Wolf Algorithm's Exploitation algorithm mimics the behavior of a grey wolf pack attacking prey, while its Exploration algorithm mimics the behavior of a grey wolf pack searching for prey. The grey wolf pack's attack on prey is determined by a convergence factor within the algorithm. The decrease reflects this. From formula (22), we can see that the convergence factor... As the number of iterations changes, The value of is a random number within the interval [-2a, 2a]. When the interval is [-1, 1], the gray wolf's next position can be anywhere between its current position and the prey. When the gray wolves attack their prey, the current solution becomes trapped in a local optimum. The gray wolf algorithm scatters the wolves during the prey search (exploration phase) and gathers them together during the prey attack (convergence phase). At this point, the algorithm forces the gray wolves to separate to escape local optima, supporting the exploratory behavior of the gray wolf algorithm. Furthermore, the coefficient vector... The random weight representing the influence of the gray wolf's location on the prey further controls the algorithm's global search capability.

[0240] Reference Figure 4 As shown, firstly, the gray wolf population and related parameters are initialized. The position of each gray wolf in the population has three dimensions, which correspond to the virtual phase current gain k of each phase. a k b and k c Secondly, the second harmonic pulsation amplitude of the DC-side bus is used as the fitness function of the optimization algorithm. The second harmonic pulsation amplitude corresponding to each gray wolf individual is calculated, and the three gray wolves with the smallest amplitude are saved as α, β, and δ wolves in this generation of the wolf pack. Then, the position of the current gray wolf is updated using formulas (25) and (26), and the position of the current gray wolf is updated. and Then, the amplitude of the second harmonic pulsation corresponding to each gray wolf individual in the gray wolf population is calculated, and the alpha, beta and delta wolves in the population are updated; finally, when the amplitude of the second harmonic pulsation corresponding to the alpha wolf is zero, the algorithm ends, and the k a , k b and k c optimal values are obtained.

[0241] Compared with the existing VPCR technology, the three-phase virtual phase current regulation technology has three degrees of freedom, and the suppression capability of power pulsation is further improved, and the power pulsation of the DC bus can be completely eliminated in the face of any unbalanced operating condition of the power grid, and the traditional engineering needs are met, and the three-phase unbalanced operating condition of the power grid can be applied, and by adjusting the unbalance degree of the three-phase grid-connected current, the voltage drop and voltage over-limit of any phase can be compensated on the DC bus power level, and the existing VPCR technology is improved and improved.

[0242] The three-phase unbalanced power grid under the three-phase VPCR technology is established, and the gain coefficient is solved by using the grey wolf algorithm to obtain the optimal value, and the mathematical model of the DC bus power is constructed, which reflects the change of different power grid conditions and system parameters in the DC bus power layer, and the intelligent optimization algorithm is creatively applied to the gain coefficient solving.

[0243] The above is the basic embodiment of the present application, and the technical scheme of the present application will be further described below through a preferred embodiment.

[0244] Embodiment 1

[0245] In this embodiment, the DC bus power pulsation component after introducing the three-phase VPCR technology is modeled, and the adjustable parameters in the three-phase VPCR technology are designed based on the grey wolf optimization algorithm. In order to verify the effectiveness of the proposed DC bus power double-frequency pulsation suppression method under three-phase unbalanced power grid, simulation verification is carried out.

[0246] The grid-connected inverter DC bus voltage is 700V, the filter inductance L f in the filter circuit is 1.4mH, the grid voltage amplitude U is 311V, the grid frequency f1 is 50Hz, the d-axis reference current i dref in the control circuit is 60A, the q-axis reference current i qref is-20A, the proportional gain k p of the proportional integral controller is 17.5, the integral gain k i of the proportional integral controller is 21998.2.

[0247] Referring to Figure 5 and Figure 6As shown, the following is simulated and verified by taking the A-phase voltage offset ratio of 0.9, the B-phase voltage offset ratio of 0.95 and the C-phase voltage offset ratio of 1.1 as examples. When the suppression strategy is not introduced, the power on the DC bus has a large two-frequency pulsation. When the existing VPCR technology is introduced into the system, the virtual phase current parameters of each phase are selected to be equal to the voltage offset ratio, that is, the virtual phase current gain k a = 0.9, k b = 0.95, k c = 1.1, the power fluctuation on the DC bus is partially suppressed but still exists.

[0248] When the three-phase VPCR technology is introduced into the system, the virtual phase current gain k a = 0.8089, k b = 0.8805, k c = 0.9822, then according to the theoretical model of the three-phase VPCR technology, the theoretical value of the three-phase grid-connected current can be obtained as follows:

[0249]

[0250] Referring to Figure 7 and Figure 8 , wherein the dashed line represents the theoretical current waveform, and the solid line represents the simulation current waveform, and the two are completely coincided, proving the correctness of the three-phase VPCR technology for modeling the grid-connected current. After introducing the three-phase VPCR technology, the power on the DC bus is constant, and the two-frequency pulsation is completely suppressed, proving the effectiveness of the three-phase VPCR technology for suppressing the power pulsation on the DC bus.

[0251] The method for eliminating the two-frequency pulsation of the DC bus power based on the three-phase VPCR technology proposed in the embodiment derives a three-phase grid-connected current model considering the zero-axis current component of the control loop, and further establishes a DC bus power pulsation model introducing the three-phase VPCR technology. The design method of the parameters contained in the three-phase VPCR technology is first proposed, and the optimal value of the three-phase virtual phase current gain is designed by using the grey wolf optimization algorithm to completely eliminate the power pulsation on the DC bus.

[0252] The application also provides a power pulsation suppression system based on three-phase virtual phase current regulation, which can be realized by executing the flow steps of the power pulsation suppression method based on three-phase virtual phase current regulation, that is, the power pulsation suppression method based on three-phase virtual phase current regulation can be understood by those skilled in the art as the preferred embodiment of the power pulsation suppression system based on three-phase virtual phase current regulation.

[0253] Specifically, a power pulsation suppression system based on three-phase virtual phase current regulation comprises:

[0254] Module M1: based on three-phase virtual phase current regulation technology, a DC bus power pulsation overall model is constructed;

[0255] The three-phase virtual phase current regulation technology introduces virtual phase current gain in three phases of a three-phase circuit respectively;

[0256] The DC bus power pulsation overall model obtains parameters of the three-phase circuit;

[0257] Module M2: the DC bus power pulsation overall model is optimized and solved to complete the suppression of power pulsation.

[0258] The DC bus power pulsation overall model adopts a phase-locked loop of double second-order generalized integrator to extract the positive sequence component of the grid voltage; the parameters include the voltage offset degree of each phase, the three-phase virtual phase current gain, and the influence value of the circuit parameters on the power pulsation amplitude on the DC bus; when the grid voltage is in a three-phase unbalanced state, the three-phase virtual phase current regulation technology is introduced to make the three-phase grid-connected current unbalanced, thereby suppressing the DC side power double-frequency pulsation; and θ PLL is defined as the phase angle output by the phase-locked loop, i a v , i b v and i c v are virtual A-phase, B-phase and C-phase currents obtained after the three-phase virtual phase current regulation technology is applied, i d v and i q v are virtual d-axis current and virtual q-axis current, u d and u q are d-axis voltage and q-axis virtual voltage, i dref and i qref are d-axis reference current and q-axis reference current, and ω is the grid angular velocity.

[0259] In the module M1, the voltage offset ratio is defined as the ratio of the current phase voltage to the phase voltage in the balanced state, and the voltage offset ratios of the A-phase, B-phase and C-phase three-phase are respectively k a drop , k b drop , and k c drop , then the current three-phase voltage of the grid is:

[0260]

[0261] In the formula, u a , ub and u c These are the grid voltages for phases A, B, and C, respectively; t is time; and U is the fundamental voltage under equilibrium conditions.

[0262] The dq axis voltage is:

[0263]

[0264] In the three-phase virtual phase current regulation technology, virtual phase current gains k are introduced into phases A, B, and C respectively in the grid-connected current coordinate transformation module. a k b and k c The virtual phase current is obtained as follows:

[0265]

[0266] In the formula, i a i b and i c These are the grid-connected currents for phases A, B, and C, respectively.

[0267] The three-phase virtual phase currents are transformed to obtain virtual dq-axis currents, which are then used as inputs to the vector current loop. The dq-axis reference current in the current loop is kept constant, and the three-phase grid-connected currents are amplified by 1 / k. a 1 / k b and 1 / k c In a three-phase three-wire system, there is no zero-sequence current, and the three-phase grid-connected current satisfies:

[0268] i a +i b +i c =0;

[0269] When k a ≠k b ≠k c At that time, k in the control loop a i a +k b i b +k c i c If ≠0, then there is a zero-axis current in the control loop. Let the dq0-axis current in the control loop at this time be:

[0270]

[0271] In the formula, i d Let i be the d-axis current. q Let I be the q-axis current, i0 be the zero-axis current, and I1 be the positive-sequence current amplitude. I0 is the phase of the current, and I0 is the amplitude of the zero-axis current in the control loop. The corresponding zero-axis current phase; the three-phase current in the control loop is:

[0272]

[0273] The three-phase grid-connected current is:

[0274]

[0275] The amplitude and phase of the zero-axis current in the control loop are respectively:

[0276]

[0277] In the formula, sign(x) = x / |x|, x is a parameter expression;

[0278] The three-phase grid-connected current is:

[0279]

[0280] The dq-axis grid-connected current is:

[0281]

[0282] The active power P of the AC side PCC The calculation formula is:

[0283]

[0284] After introducing the three-phase virtual phase current regulation technology, the active power of the AC side is:

[0285]

[0286] Wherein

[0287]

[0288] The DC bus power is affected by the filter inductance L f Transmitted power, under unbalanced grid, the instantaneous power transmitted on the filter inductance fluctuates, further aggravating the power fluctuation on the DC bus;

[0289] The voltage on the filter inductance is:

[0290]

[0291] In the formula, u La , u Lb , u Lc are the voltages across the filter inductance A, B, and C phases, respectively;

[0292] The power P L transmitted on the filter inductance is

[0293] P L = u La i a + u Lb i b + u Lc i c ;

[0294] The power P DC on the DC side bus is the sum of the AC side active power P PCC and the instantaneous power P L on the filter inductance:

[0295] P DC = P PCC + P L ;

[0296] The double-frequency pulsating component on the DC bus is obtained as:

[0297]

[0298] Wherein, FC1, FC2, FS1 and FS2 are coefficients of the expression, expressed as follows:

[0299]

[0300] σ1 and σ2 are coefficients in the expression of FC1, FC2, FS1 and FS2:

[0301]

[0302] The amplitude of the DC bus power fluctuation is obtained as:

[0303]

[0304] The overall model of the DC bus power pulsation is based on the grey wolf algorithm for optimization solution; the grey wolf algorithm realizes target optimization by simulating the hierarchical level and hunting mechanism in the grey wolf group; in the grey wolf group, the grey wolves are divided into four levels from high to low and are distributed in a pyramid shape, which are α, β, δ and ω wolves; wherein, the α, β and δ wolves are responsible for decision-making and domination of the hunting behavior of the wolf group, and the ω wolf is the bottom layer of the whole wolf group; the α wolf corresponds to the optimal solution, the β wolf corresponds to the suboptimal solution, the δ wolf corresponds to the third optimal solution, and the ω wolf corresponds to the candidate solution.

[0305] In the grey wolf algorithm, the grey wolves surround the prey in the hunting process, and in the algorithm search process, the distance and position update formula between the individuals of the grey wolf population and the prey is:

[0306] ​​

[0307]

[0308] wherein, is the distance between the grey wolf individual and the prey, and is the coefficient vector, t is the current iteration number, is the position vector of the prey, is the position vector of the grey wolf individual;

[0309] coefficient vector and is calculated by the formula:

[0310]

[0311]

[0312] wherein, is the convergence factor, and decreases linearly in the interval [0, 2] with the iteration number; and are random vectors with values in the interval [0, 1];

[0313] The grey wolf pack identifies and surrounds the prey under the leadership of the alpha, beta and delta wolves, and judges the potential position of the prey through the alpha, beta and delta wolves and updates the position of the omega wolf in the population, and the distance between the alpha, beta and delta wolves and other grey wolf individuals in the wolf pack is:

[0314]

[0315] wherein, and are the distances between the alpha, beta and delta wolves and other grey wolf individuals, and are random vectors, and are the current positions of the alpha, beta and delta wolves, respectively;

[0316] The position update formula of the grey wolf individual is:

[0317]

[0318] wherein, is the direction and step length of the omega wolf advancing towards the alpha wolf; is the direction and step length of the omega wolf advancing towards the beta wolf; is the direction and step length of the omega wolf advancing towards the delta wolf;

[0319] The final position of the grey wolf individual is:

[0320]

[0321] In the grey wolf optimization algorithm, the attack of the grey wolf population on the prey is reflected by the decrease of the convergence factor ; the convergence factor changes with the number of iterations, causing the value of to be a random number in the interval [-2a, 2a], when is in the interval [-1, 1], the next position of the grey wolf is at any position between the current position and the prey; when , the grey wolf launches an attack on the prey, and the current solution falls into a local optimum; in the grey wolf optimization algorithm, the wolf population disperses when searching for prey, corresponding to the exploration process; the wolf population gathers when attacking the prey, corresponding to the convergence process; when , the grey wolf will be forced to separate to escape from the local optimum state to support the exploration behavior of the grey wolf optimization algorithm; the coefficient vector represents the random weight of the position of the grey wolf on the prey, and controls the global search ability of the algorithm.

[0322] In the grey wolf optimization algorithm, the position of each grey wolf individual has three dimensions, respectively corresponding to the virtual phase current gain of each phase; the overall model of the DC bus power fluctuation combines the actual operating conditions of the grid-connected inverter to completely suppress the DC bus power fluctuation.

[0323] Those skilled in the art know that, in addition to implementing the system provided by the present application and each device, module and unit thereof in the form of pure computer readable program code, the same functions can also be achieved by logically programming the method steps to make the system provided by the present application and each device, module and unit thereof in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures within the hardware component; the devices, modules and units for achieving various functions can also be considered as both software modules for implementing methods and structures within hardware components.

[0324] The specific embodiments of the present application are described above. It should be understood that the present application 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 essential content of the present application. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for power pulsation suppression based on three-phase virtual phase current regulation, characterized in that, The method comprises the following steps: Step S1: constructing a DC bus power fluctuation overall model based on a three-phase virtual phase current regulation technology; The three-phase virtual phase current regulation technology introduces virtual phase current gains in three phases of a three-phase circuit respectively; The DC bus power fluctuation overall model obtains parameters of the three-phase circuit; The DC bus power fluctuation overall model adopts a double second-order generalized integrator phase-locked loop to extract a positive sequence component of a grid voltage for phase locking; the parameters include phase voltage offset degrees, three-phase virtual phase current gains, and influence values of circuit parameters on a power fluctuation amplitude on the DC bus; when the grid voltage is in a three-phase unbalanced state, the three-phase virtual phase current regulation technology is introduced to make three-phase grid-connected currents unbalanced, thereby suppressing a DC side power double-frequency fluctuation; Step S2: optimizing and solving the DC bus power fluctuation overall model to complete suppression of the power fluctuation; The DC bus power fluctuation overall model is optimized and solved based on a grey wolf algorithm; In the grey wolf algorithm, the position of each grey wolf individual has three dimensions, which respectively correspond to virtual phase current gains of the phases; the DC bus power fluctuation overall model combines actual operating conditions of a grid-connected inverter to completely suppress the DC bus power fluctuation.

2. The method of claim 1, wherein the method is characterized by: Definitions θ PLL is the phase angle of the output of the phase-locked loop, i a v , i b v and i c v are the virtual A-phase, B-phase and C-phase currents, respectively, obtained after applying the three-phase virtual phase current regulation technique, i d v and i q v are the virtual d-axis and q-axis currents, respectively, d q u d and u q are the d-axis and q-axis voltages, respectively, d q i dref and i qref are the d-axis and q-axis reference currents, respectively, d q ω is the grid angular speed.​​​​​​ 3. The method of claim 2, wherein the method is characterized by: In the step S1, the voltage offset ratio is defined as the ratio of the current phase voltage to the phase voltage in the balanced state, and the voltage offset ratios of the three phases A, B and C are respectively denoted as k a drop , k b drop , k c drop The current three-phase voltage of the power grid is ； wherein u a , u b and u c are the A, B and C phase grid voltages, respectively, t is time, U is the fundamental voltage in balanced state; dq The shaft voltage is: ； The three-phase virtual phase current regulation technology introduces virtual phase current gain in A, B and C three phases respectively in the grid-connected current coordinate conversion module k a 、 k b and k c , and obtains the virtual phase current as ； wherein i a , i b and i c are the A, B and C phase grid currents, respectively; The three-phase virtual phase currents are coordinate-transformed to obtain virtual dq The shaft current is taken as the input of the vector current loop to maintain the current loop dq The shaft reference current remains unchanged, and the three-phase grid-connected currents are respectively amplified by 1 k a , 1 k b , and 1 k c times; the zero-sequence current does not exist in the three-phase three-wire system, and the three-phase grid-connected currents satisfy: ； When k a ≠ k b ≠ k c , the zero-axis current in the control loop is k a i a + k b i b + k c i c ≠ 0, the zero-axis current in the control loop exists, and the zero-axis current in the control loop at this time is dq 0 ； wherein i d is d shaft current, i q is q shaft current, i 0 is zero shaft current, I 1 is positive sequence current magnitude, φ i is current phase, I 0 is zero shaft current magnitude in control loop, φ 0 is corresponding zero shaft current phase; The three-phase currents in the control loop are: ； The three-phase grid-connected currents are: ； The amplitude and phase of the zero-axis current in the control loop are: ； wherein sign ( x )= x / | x |, x is a parameter expression; The three-phase grid-connected currents are obtained as: ； dq The shaft-connected grid current is: ； Active power on the ac side The formula for calculating the active power on the ac side is: ； After the three-phase virtual phase current regulation technology is introduced, the active power on the AC side is: ； wherein 。 4. The method of claim 3, wherein the method is characterized by, The direct current bus power is affected by the filter upper filtering inductance L f The transmission power is affected by the fluctuation of the instantaneous power transmitted on the filtering inductance under the unbalanced power grid, which further aggravates the power fluctuation on the direct current bus. The voltage on the filter inductance is: ； In the formula, u La , u Lb , u Lc are the filtered inductance voltages across the A-phase, B-phase, and C-phase, respectively. Power on filter inductance is found To ； the sum of the instantaneous power on the dc side bus for the ac side active power and the filter inductance the sum: ； obtaining a double frequency ripple component on the dc bus is: ； wherein FC 1、 FC 2、 FS 1 and FS 2 are coefficients of the expression, expressed as follows: ； σ 1 and σ 2 are FC 1, FC 2, FS 1 and FS 2 coefficients in the expressions: ； The amplitude of the DC bus power fluctuation is obtained as: 。 5. The method of claim 1, wherein the method is characterized by: The gray wolf algorithm optimizes the target by simulating the hierarchy and hunting mechanisms within a gray wolf pack. In the gray wolf pack, the wolves are divided into four ranks from highest to lowest, arranged in a pyramid shape. α、β、δ and ω wolves; among them, α、 β、δ Wolves are responsible for making decisions and directing the hunting behavior of the wolf pack. ω Wolves are at the very bottom of the wolf pack; α The wolf corresponds to the optimal solution. β The wolf corresponds to the suboptimal solution. δ The wolf corresponds to the third optimal solution. ω The wolf corresponds to the candidate solution.

6. The method of claim 5, wherein the method is characterized by: In the grey wolf algorithm, the grey wolf population surrounds the prey in the process of predation, and the distance and position updating formula between the individuals of the grey wolf population and the prey in the algorithm search process is: ； ； wherein is the distance between the grey wolf individual and the prey, and is the coefficient vector, t is the current iteration number, is the position vector of the prey, is the position vector of the grey wolf; coefficient vector and The calculation formula is: ； ； wherein is a convergence factor and decreases linearly in the interval [0, 2] with the iteration number; and is a random vector taking values in the interval [0, 1]; Gray wolf packs in α , β and δ under the leadership of a wolf identify and surround prey, determine the potential location of prey by α , β and δ wolves and update the location of ω wolves in the pack, the distance of α , β and δ wolves in the pack from other gray wolf individuals is: ； wherein , and are respectively α , β and δ the distance between the wolf and the other wolf individual, , and are random vectors, , and are respectively α , β and δ the current position of the wolf; The position updating formula of the grey wolf individual is: ； wherein is ω the wolf moves towards α the direction and step length the wolf moves towards; is ω the wolf moves towards β the direction and step length the wolf moves towards; is ω the wolf moves towards δ the direction and step length the wolf moves towards; The final position of the grey wolf individual is: 。 7. The method of claim 6, wherein, In the grey wolf algorithm, the attack of the grey wolf population on the prey is reflected by the decrease of the convergence factor ; the convergence factor changes with the number of iterations, causing the value of the convergence factor to be a random number in the interval [-2 a , 2 a ]; when the value of the convergence factor is in the interval [-1, 1], the next position of the grey wolf is any position between the current position and the prey; when the value of the convergence factor is greater than 1, the grey wolf attacks the prey, and the current solution falls into a local optimum; in the grey wolf algorithm, the wolf population disperses when searching for the prey, corresponding to the exploration process; the wolf population gathers when attacking the prey, corresponding to the convergence process; when the value of the convergence factor is greater than 2, the grey wolf will be forced to separate to escape from the local optimum state, supporting the exploration behavior of the grey wolf algorithm; the coefficient vector represents the random weight of the position of the gray wolf on the prey, controlling the global search ability of the algorithm.

8. A power pulsation suppression system based on three-phase virtual phase current regulation, characterized by, The method comprises the following steps: Module M1: constructing a DC bus power fluctuation overall model based on a three-phase virtual phase current regulation technology; The three-phase virtual phase current regulation technology introduces virtual phase current gains in three phases of a three-phase circuit respectively; The DC bus power fluctuation overall model obtains parameters of the three-phase circuit; The DC bus power fluctuation overall model adopts a double second-order generalized integrator phase-locked loop to extract a positive sequence component of a grid voltage for phase locking; the parameters include phase voltage offset degrees, three-phase virtual phase current gains, and influence values of circuit parameters on a power fluctuation amplitude on the DC bus; when the grid voltage is in a three-phase unbalanced state, the three-phase virtual phase current regulation technology is introduced to make three-phase grid-connected currents unbalanced, thereby suppressing a DC side power double-frequency fluctuation; Module M2: optimizing and solving the DC bus power fluctuation overall model to complete suppression of the power fluctuation; The DC bus power fluctuation overall model is optimized and solved based on a grey wolf algorithm; In the grey wolf algorithm, the position of each grey wolf individual has three dimensions, which respectively correspond to virtual phase current gains of the phases; the DC bus power fluctuation overall model combines actual operating conditions of a grid-connected inverter to completely suppress the DC bus power fluctuation.

9. The power pulsation suppression system based on three-phase virtual phase current regulation of claim 8, wherein, Definitions θ PLL is the phase angle of the output of the phase-locked loop, i a v , i b v and i c v are the virtual A-phase, B-phase and C-phase currents, respectively, obtained after applying the three-phase virtual phase current regulation technique, i d v and i q v are the virtual d-axis and q-axis currents, respectively, d q u d and u q are the d-axis and q-axis voltages, respectively, d q i dref and i qref are the d-axis and q-axis reference currents, respectively, d q ω is the grid angular speed.​​​​​​

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