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

Abstract

The invention provides a power pulsation suppression method and system based on three-phase virtual phase current regulation and control, and the method comprises the steps: S1, building a DC bus power pulsation overall model based on a three-phase virtual phase current regulation and control technology; according to the three-phase virtual phase current regulation and control technology, virtual phase current gains are introduced into three phases of a three-phase circuit respectively; acquiring parameters of a three-phase circuit by the direct-current bus power pulse overall model; and S2, optimizing and solving the DC bus power pulsation overall model, and completing the suppression of the power pulsation. In a control system, virtual phase current gain is introduced into feedback current of each phase, three-phase grid-connected current is in an unbalanced state through simultaneous adjustment of the three-phase feedback current, and then elimination of direct-current power pulsation under a three-phase unbalanced power grid is achieved; the optimal value of the phase current gain is solved based on the grey wolf algorithm, and it is ensured that the three-phase virtual phase current regulation and control technology completely exerts the power fluctuation suppression effect of the three-phase virtual phase current regulation and control technology.

Description

Technical Field

[0001] The present invention relates to the field of AC power generation, transmission, distribution and consumption, and in particular to a power pulsation suppression method and system based on three-phase virtual phase current regulation. Background Art

[0002] In recent years, the penetration rate of new energy in my country has been increasing, but the inertia of new energy systems 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, and it 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, resulting in a certain degree of imbalance in the power grid voltage. In my country's national standard "Power Quality Supply Voltage Deviation", it is stipulated that the three-phase power 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 when the power grid is operating normally, the negative sequence voltage imbalance does not exceed 2%. When the grid voltage has a deviation that causes the three phases to be in an unbalanced state, the power on the DC bus will have a double frequency pulsation, which will damage the life of the DC side capacitor, and in the long run will threaten the stable operation of the power grid. Therefore, when there is a supply voltage deviation in the three-phase voltage and it is in a three-phase unbalanced state, it is of practical significance to discuss how to keep the DC bus power constant.

[0003] Virtual phase-current regulation (VPCR) technology compensates for voltage deviation by adjusting the feedback current in the control system, thereby maintaining a constant power level on the DC bus. However, the existing virtual phase current technology only discusses and analyzes single-phase voltage drops, and the selection of phase current gain is not optimal, not universal, and cannot completely eliminate power fluctuations on the DC bus.

[0004] Existing power fluctuation suppression strategies often ignore the contribution of the filter circuit to the DC bus power pulsation, and directly equate the active power on the AC side with the DC bus power, resulting in the DC bus power pulsation not being completely eliminated. In addition, existing suppression strategies often achieve AC side active power pulsation suppression by modifying the positive and negative sequence reference currents of vector current control or using power compensation of direct power control. The positive and negative sequence separation delay, positive and negative sequence coupling, and increased system complexity all affect the dynamic response speed and stability of the system, which in turn interferes with the actual effect of the suppression strategy.

[0005] The existing VPCR suppression technology completely eliminates the active power fluctuation on the AC side by modifying the feedback current of the phase where the voltage drops in the control loop, and has the advantages of simple control structure and strong system robustness. However, the existing VPCR technology only analyzes the scenario of single-phase voltage drop, and does not specifically analyze the situation where the three-phase voltage is unbalanced. In actual engineering applications, the probability of single-phase voltage drop is low, and the suppression strategy for the three-phase unbalanced scenario is more general and universal. In addition, the existing VPCR technology does not propose a design method for the feedback current adjustment coefficient, that is, the virtual phase current gain, under the condition of three-phase unbalance, and the existing selection of virtual phase current gain can only eliminate the active power pulsation on the AC side, but the power fluctuation on the DC bus always exists.

[0006] Xiong Fei, Wu Junyong, Hao Liangliang, et al. Multi-objective control strategy of inverter power supply under asymmetric voltage drop [J]. Transactions of China Electrotechnical Society, 2017, 32(01): 107-116. This paper proposes a new multi-objective reference current calculation method, which uniformly expresses multiple optimization objectives in the reference current expression, and changes the proportion of different optimization objectives by adjusting the coefficient to achieve the diversity of control strategies. This paper first establishes the model of instantaneous active power and reactive power of the inverter system under the condition of grid voltage drop, and then analyzes the common control objectives of the inverter under grid voltage drop, including symmetrical three-phase current, elimination of active power fluctuation and elimination of reactive power fluctuation. This paper introduces adjustment coefficients k1 and k2 to coordinate among the three control objectives. On this basis, a selection scheme for the adjustment coefficient is proposed. However, when analyzing the optimization objectives, this paper only considers the active power and reactive power fluctuations on the AC side, and does not consider the instantaneous power fluctuations on the inverter filter circuit under grid voltage drop, and does not take the DC side power fluctuations that directly affect the DC side capacitor as the optimization objective. In addition, when solving multi-objective optimization problems, the document establishes a set of equations through the Lagrangian method to obtain the search path for the optimal power fluctuation amplitude of the adjustment coefficients k1 and k2. The complexity of the model directly affects the feasibility of solving the search path. The present invention directly takes the DC bus power pulsation amplitude as the optimization target, and additionally considers the filter circuit power fluctuation on the basis of the AC side active power fluctuation model. In addition, the present invention uses the Gray Wolf Algorithm, one of the intelligent optimization algorithms, for optimization and solution, with fast convergence speed and good convergence. Compared with the existing suppression strategies, the control strategy designed in the present invention that introduces the three-phase VPCR technology has low complexity and greatly improves the dynamic performance and calculation speed of the system.

[0007] In the Chinese patent document with publication number CN113400959A, a reconfigurable charging system for electric vehicles with electric drive that takes into account secondary power pulsation suppression is disclosed, including an uncontrolled rectifier bridge, a three-phase inverter, a three-phase permanent magnet synchronous motor, an energy storage capacitor, an output filter capacitor, a power battery and a switch. In the charging state, the two-phase winding of the permanent magnet synchronous motor and the two sets of half-bridges of the inverter form a parallel Boost circuit, and the remaining one-phase winding of the permanent magnet synchronous motor and the remaining set of half-bridges of the inverter form an active filter. However, this patent document only improves the power density of the charging system and does not solve the above problems. Summary of the invention

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

[0009] According to the present invention, a power pulsation suppression method based on three-phase virtual phase current regulation is provided, comprising:

[0010] Step S1: constructing a DC bus power pulsation overall model based on three-phase virtual phase current control technology;

[0011] The three-phase virtual phase current control technology introduces virtual phase current gains in the three phases of the three-phase circuit respectively;

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

[0013] Step S2: Optimize and solve the overall model of DC bus power pulsation to suppress power pulsation.

[0014] Preferably, the overall model of the DC bus power pulsation uses a phase-locked loop of a dual second-order generalized integrator to extract the positive sequence component of the grid voltage for phase locking; the parameters include the voltage offset of each phase, the three-phase virtual phase current gain, and the influence 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 control technology is introduced to make the three-phase grid-connected current unbalanced and smooth the double frequency pulsation of the DC side power; define θ PLL is the phase-locked loop output phase angle, i a v 、i b v and i c v are the virtual A-phase, B-phase and C-phase currents obtained after applying the three-phase virtual phase current control technology, i d v and i q v are virtual d-axis current and virtual q-axis current, respectively, u d and u qare the 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 the grid angular velocity.

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

[0016]

[0017] In the formula, u a 、u b and u c are the A, B and C phase grid voltages respectively, t is the time, and U is the fundamental voltage in the equilibrium state;

[0018] The dq axis voltage is:

[0019]

[0020] Three-phase virtual phase current control technology introduces virtual phase current gain k into the grid-connected current coordinate transformation module for phases A, B, and C respectively. a , k b and k c , the virtual phase current is obtained as:

[0021]

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

[0023] The three-phase virtual phase current is transformed to obtain the 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 current is 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 current meets:

[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 a zero axis current in the control loop. Let the dq0 axis current in the control loop be:

[0026]

[0027] In the formula, i d is the d-axis current, i q is the q-axis current, i 0 is the zero axis current, I 1 is the positive sequence current amplitude, is the current phase, I 0 is the zero axis current amplitude in the control loop, is the corresponding zero-axis current phase;

[0028] The three-phase current in the control circuit is:

[0029]

[0030] The three-phase grid-connected current is:

[0031]

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

[0033]

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

[0035] The three-phase grid-connected current is obtained as:

[0036]

[0037] The dq axis grid-connected current is:

[0038]

[0039] Active power P on the AC side PCC The calculation formula is:

[0040]

[0041] After the introduction of three-phase virtual phase current control technology, the active power on the AC side is:

[0042]

[0043] in

[0044]

[0045] Preferably, the DC bus power is affected by the filter inductance L f The impact of transmission power, in an unbalanced power grid, the instantaneous power transmitted on the filter inductor fluctuates, further aggravating the power fluctuation on the DC bus;

[0046] The voltage on the filter inductor is:

[0047]

[0048] In the formula, u La 、u Lb 、u Lc They are the voltages across the filter inductor phase A, phase B, and phase C respectively;

[0049] Calculate the power P on the filter inductor L for

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

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

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

[0053] Obtain the double frequency pulsation component on the DC bus for:

[0054]

[0055] Among them, FC 1 , FC 2 , FS 1 and FS 2 for The coefficients of the expression are expressed as follows:

[0056]

[0057] σ 1 and σ 2 For FC 1, FC 2 , FS 1 and FS 2 The coefficients in the expression:

[0058]

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

[0060]

[0061] Preferably, the overall model of DC bus power pulsation is optimized and solved based on the Gray Wolf Algorithm; the Gray Wolf Algorithm achieves target optimization by simulating the hierarchy and hunting mechanism in the gray wolf group; in the gray wolf group, 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, δ wolves are responsible for decision-making and dominating the predation behavior of the wolf group, and ω wolf is the bottom of the entire wolf group; α wolf corresponds to the optimal solution, β wolf corresponds to the suboptimal solution, δ wolf corresponds to the third optimal 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, and during the algorithm search process, the distance and position update formula between the individuals of the gray wolf population and the prey is:

[0063]

[0064]

[0065] In the formula, is the distance between the individual gray wolf and its 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 gray wolf;

[0066] Coefficient vector and The calculation formula is:

[0067]

[0068]

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

[0070] The gray wolf pack, led by α, β and δ wolves, identifies and surrounds the prey. α, β and δ wolves are used to determine the potential location of the prey and update the location of the ω wolf in the population. The distance between α, β and δ wolves and other gray wolf individuals in the wolf pack is:

[0071]

[0072] In the formula, and are the distances between α, β and δ wolves and other gray wolves, and is a random vector, and are the current positions of α, β and δ 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 ω wolf moving towards α wolf; is the direction and step length of ω wolf moving towards β wolf; is the direction and step length of ω wolf moving towards δ wolf;

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

[0077]

[0078] Preferably, in the gray wolf algorithm, the gray wolf population attacks prey by a convergence factor The convergence factor As the number of iterations changes, The value of is a random number in the interval [-2a, 2a]. In the interval [-1, 1], the next position of the gray wolf is any position between the current position and the prey; when When , the gray wolf attacks the prey, and the current solution falls into a local optimum; in the gray wolf algorithm, the wolves disperse when searching for prey, corresponding to the exploration process; when attacking prey, the wolves gather, corresponding to the convergence process; when When , the gray wolf will be forced to separate to escape from the local optimal state and support the exploration behavior of the gray wolf algorithm; the coefficient vector The random weight that represents the impact of the gray wolf's location on prey controls the global search capability of the algorithm.

[0079] Preferably, the position of each gray wolf individual in the gray wolf algorithm has three dimensions, which respectively correspond to the virtual phase current gain of each phase; the DC bus power pulsation overall model is combined with the actual operating conditions of the grid-connected inverter to completely smooth the DC bus power pulsation.

[0080] According to the present invention, a power pulsation suppression system based on three-phase virtual phase current regulation is provided, comprising:

[0081] Module M1: Based on the three-phase virtual phase current control technology, the overall model of DC bus power pulsation is constructed;

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

[0083] The DC bus power pulsation overall model obtains parameters of the three-phase circuit;

[0084] Module M2: Optimize and solve the overall model of DC bus power pulsation to suppress power pulsation.

[0085] Preferably, the overall model of the DC bus power pulsation uses a phase-locked loop of a dual second-order generalized integrator to extract the positive sequence component of the grid voltage for phase locking; the parameters include the voltage offset of each phase, the three-phase virtual phase current gain, and the influence 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 control technology is introduced to make the three-phase grid-connected current unbalanced and smooth the double frequency pulsation of the DC side power; define θ PLL is the phase-locked loop output phase angle, i a v 、i b v and i c v are the virtual A-phase, B-phase and C-phase currents obtained after applying the three-phase virtual phase current control technology, i d v and i q v are virtual d-axis current and virtual q-axis current, respectively, u d and u q are the 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 the grid angular velocity.

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

[0087]

[0088] In the formula, u a 、u b and u c are the A, B and C phase grid voltages respectively, t is the time, and U is the fundamental voltage in the equilibrium state;

[0089] The dq axis voltage is:

[0090]

[0091] Three-phase virtual phase current control technology introduces virtual phase current gain k into the grid-connected current coordinate transformation module for phases A, B, and C respectively. a , k b and k c , the virtual phase current is obtained as:

[0092]

[0093] In the formula, i a 、i b and i c They are the grid-connected currents of phases A, B and C respectively;

[0094] The three-phase virtual phase current is transformed to obtain the 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 current is 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 current meets:

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

[0096] When k a ≠k b ≠k c When k a i a +k b i b +k c i c ≠0, there is a zero axis current in the control loop. Let the dq0 axis current in the control loop be:

[0097]

[0098] In the formula, i d is the d-axis current, i q is the q-axis current, i 0 is the zero axis current, I 1 is the positive sequence current amplitude, is the current phase, I 0 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 circuit 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 solved as follows:

[0104]

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

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

[0107]

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

[0109]

[0110] Active power P on the AC side PCC The calculation formula is:

[0111]

[0112] After the introduction of three-phase virtual phase current control technology, the active power on the AC side is:

[0113]

[0114] in

[0115]

[0116] Preferably, the DC bus power is affected by the filter inductance L f The impact of transmission power, in an unbalanced power grid, the instantaneous power transmitted on the filter inductor fluctuates, further aggravating the power fluctuation on the DC bus;

[0117] The voltage on the filter inductor is:

[0118]

[0119] In the formula, u La 、u Lb 、uLc They are the voltages across the filter inductor phase A, phase B, and phase C respectively;

[0120] Calculate the power P on the filter inductor L for

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

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

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

[0124] Obtain the double frequency pulsation component on the DC bus for:

[0125]

[0126] Among them, FC 1 , FC 2 , FS 1 and FS 2 for The coefficients of the expression are expressed as follows:

[0127]

[0128] σ 1 and σ 2 For FC 1 , FC 2 , FS 1 and FS 2 The coefficients in the expression:

[0129]

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

[0131]

[0132] Preferably, the overall model of DC bus power pulsation is optimized and solved based on the Gray Wolf Algorithm; the Gray Wolf Algorithm achieves target optimization by simulating the hierarchy and hunting mechanism in the gray wolf group; in the gray wolf group, 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, δ wolves are responsible for decision-making and dominating the predation behavior of the wolf group, and ω wolf is the bottom of the entire wolf group; α wolf corresponds to the optimal solution, β wolf corresponds to the suboptimal solution, δ wolf corresponds to the third optimal solution, and ω wolf corresponds to the candidate solution.

[0133] Preferably, in the gray wolf algorithm, the gray wolf pack surrounds the prey during the hunting process, and during the algorithm search process, the distance and position update formula between the individuals of the gray wolf population and the prey is:

[0134]

[0135]

[0136] In the formula, is the distance between the gray wolf and its 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 gray wolf;

[0137] Coefficient vector and The calculation formula is:

[0138]

[0139]

[0140] In the formula, is the convergence factor, and decreases linearly with the number of iterations in the interval [0, 2]; and is a random vector with values ​​in the interval [0, 1];

[0141] The gray wolf pack, led by α, β and δ wolves, identifies and surrounds the prey. α, β and δ wolves are used to determine the potential location of the prey and update the location of the ω wolf in the population. The distance between α, β and δ wolves and other gray wolf individuals in the wolf pack is:

[0142]

[0143] In the formula, and are the distances between α, β and δ wolves and other gray wolves, and is a random vector, and are the current positions of α, β and δ wolves respectively;

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

[0145]

[0146] In the formula, is the direction and step length of ω wolf moving towards α wolf; is the direction and step length of ω wolf moving towards β wolf; is the direction and step length of ω wolf moving towards δ wolf;

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

[0148]

[0149] Preferably, in the gray wolf algorithm, the gray wolf population attacks prey by a convergence factor The convergence factor As the number of iterations changes, The value of is a random number in the interval [-2a, 2a]. In the interval [-1, 1], the next position of the gray wolf is any position between the current position and the prey; when When , the gray wolf attacks the prey, and the current solution falls into a local optimum; in the gray wolf algorithm, the wolves disperse when searching for prey, corresponding to the exploration process; when attacking prey, the wolves gather, corresponding to the convergence process; when When , the gray wolf will be forced to separate to escape from the local optimal state and support the exploration behavior of the gray wolf algorithm; the coefficient vector The random weight that represents the impact of the gray wolf's location on prey controls the global search capability of the algorithm.

[0150] Preferably, the position of each gray wolf individual in the gray wolf algorithm has three dimensions, which respectively correspond to the virtual phase current gain of each phase; the DC bus power pulsation overall model is combined with the actual operating conditions of the grid-connected inverter to completely smooth the DC bus power pulsation.

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

[0152] 1. In the control system of the present invention, a virtual phase current gain is introduced into the feedback current of each phase respectively, and the three-phase grid-connected current is made unbalanced by adjusting the three-phase feedback current simultaneously, thereby eliminating the DC power pulsation under the three-phase unbalanced power grid; 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 the intelligent optimization algorithm, which ensures from a theoretical level that the three-phase virtual phase current control technology fully exerts its power fluctuation suppression effect.

[0153] 2. Compared with the existing VPCR technology, the three-phase virtual phase current control technology proposed in the present invention has three degrees of freedom, and the ability to suppress power pulsation is further improved. In the face of any unbalanced working conditions of the power grid, the power pulsation of the DC bus can be completely eliminated to meet the needs of traditional engineering.

[0154] 3. The present invention is applicable to any unbalanced three-phase operating condition of the power grid. By adjusting the imbalance of the three-phase grid-connected current, the voltage drop and voltage over-limit of any phase can be compensated at the DC bus power level, thereby promoting and improving the existing VPCR technology.

[0155] 4. The present invention establishes a theoretical model of DC bus power pulsation under a three-phase unbalanced power grid considering the three-phase VPCR technology, and uses the Grey Wolf algorithm to solve the optimization model to obtain the optimal value of the gain coefficient. A mathematical model of DC bus power is constructed, which reflects the performance of different grid conditions and changes in system parameters at the DC bus power level, and creatively applies the intelligent optimization algorithm to the solution of the gain coefficient.

[0156] 5. In terms of the DC bus power composition, the present invention not only analyzes the active power on the AC side, but also takes into account the impact of the filter circuit on the DC bus power, and on this basis constructs a theoretical model of the DC bus double frequency pulsation considering the three-phase VPCR technology.

[0157] 6. The present invention proves theoretically that the designed parameters can achieve complete suppression of power pulsation on the DC side, and utilizes the emerging swarm intelligence optimization algorithm to solve the optimization problem of complex power pulsation amplitude model in parameter design, which has high practicality.

[0158] Other beneficial effects of the present invention will be explained in the specific implementation manner through the introduction of specific technical features and technical solutions. Through the introduction of these technical features and technical solutions, those skilled in the art should be able to understand the beneficial technical effects brought about by the technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0159] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0160] Figure 1 The present invention is a flow chart of the method.

[0161] Figure 2 This is a diagram of a grid-connected inverter system under an unbalanced power grid in the present invention.

[0162] Figure 3 This is a control block diagram of the three-phase virtual phase current regulation technology in the present invention.

[0163] Figure 4 The figure is a flow chart of virtual phase current gain parameter design based on the Grey Wolf algorithm in the present invention.

[0164] Figure 5 This is a DC bus power curve diagram when the suppression technology is not introduced in the embodiment of the present invention.

[0165] Figure 6 This is a DC bus power curve diagram after the current virtual phase current control technology is introduced in the embodiment of the present invention.

[0166] Figure 7 This is a grid-connected current waveform diagram after the three-phase virtual phase current control technology is introduced in the embodiment of the present invention.

[0167] Figure 8 This is a DC bus power curve diagram after the three-phase virtual phase current control technology is introduced in the embodiment of the present invention. DETAILED DESCRIPTION

[0168] The present invention is 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 are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0169] Reference Figure 1 and Figure 2 As shown, C dc is the DC bus capacitance, L f is the filter inductor, i a 、i b and i c is the grid-connected current of phases A, B and C, u a 、u b and u c is the A, B and C phase grid voltage.

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

[0171] The present invention proposes a virtual phase current gain parameter design method based on the Grey Wolf algorithm to eliminate the double frequency pulsation of the DC bus power based on the three-phase VPCR technology. The existing VPCR technology only analyzes the active power fluctuation on the AC side, and can only partially suppress the double frequency pulsation of the DC bus power, and the optimal selection method of the VPCR technical parameters is not designed. The VPCR technology introduces a virtual phase current gain in the three-phase phase current to change the feedback current in the control loop, so that the three-phase grid-connected current is unbalanced, and then complements the three-phase unbalanced voltage at the DC bus power calculation level to achieve power constancy. When facing a three-phase unbalanced power grid, the existing VPCR technology directly selects the virtual phase current gain as the voltage drop ratio. At this time, the power pulsation on the DC bus is reduced but not completely eliminated. At this time, the virtual phase current gain is not the optimal value.

[0172] The three-phase VPCR technology applied by the present invention adds the analysis of instantaneous power fluctuation of the filter circuit on the basis of the active power fluctuation model on the AC side, and then constructs a DC bus double frequency pulsation model considering the three-phase VPCR technology. On this basis, the present invention proposes a design theory of virtual phase current gain, optimizes the pulsation model using the gray wolf optimization algorithm, and obtains a suitable virtual phase current gain value to achieve the effect of constant power.

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

[0174] When the grid voltage is in a three-phase unbalanced state, the introduction of three-phase VPCR technology can smooth the DC side power double frequency pulsation by unbalancing the three-phase grid current. The voltage offset ratio is defined as the ratio of the current phase voltage to the phase voltage in the balanced state. Assume that the voltage offset ratios of phases A, B, and C are k a drop , k b drop , k c drop , then the current three-phase voltage of the power grid is:

[0175]

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

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

[0178]

[0179] The three-phase VPCR technology introduces virtual phase current gain k into the grid-connected current coordinate transformation module for phases A, B, and C respectively. a , k b and k c , the virtual phase current is obtained as:

[0180]

[0181] In the formula, i a 、i b and i c They are the grid-connected currents of phases A, B and C respectively;

[0182] The three-phase virtual phase current is transformed to obtain the virtual dq axis current as the input of the vector current loop, but the dq axis reference current in the current loop is kept unchanged, which is equivalent to amplifying the three-phase grid-connected current by 1 / k a , 1 / k b and 1 / k c Since there is no zero-sequence current in the three-phase three-wire system, the three-phase grid-connected current satisfies:

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

[0184] From formula (4), we can get that when k a ≠k b ≠k c When k a i a +k b i b +k c i c ≠0, so there is a zero axis current in the control loop. Let the dq0 axis current in the control loop be:

[0185]

[0186] In the formula, i d is the d-axis current, i q is the q-axis current, i 0 is the zero axis current, I 1is the positive sequence current amplitude, is the current phase, I 0 is the zero axis current amplitude in the control loop, is the corresponding zero axis current phase.

[0187] The three-phase current in the control circuit is:

[0188]

[0189] From formulas (3) and (6), the three-phase grid-connected current can be obtained as:

[0190]

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

[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 can be obtained as:

[0195]

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

[0197]

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

[0199]

[0200] Therefore, by substituting formula (2) and formula (10) into formula (11), we can get the active power on the AC side after the introduction of the three-phase VPCR technology:

[0201]

[0202] in

[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 Influence of transmission power: In an unbalanced power grid, the instantaneous power transmitted on the filter inductor fluctuates, which will further aggravate the power fluctuation on the DC bus.

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

[0206]

[0207] In the formula, u La 、u Lb 、u Lc They are the voltages across the filter inductor phase A, phase B, and phase C respectively;

[0208] Therefore, the power on the filter inductor can be obtained as

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

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

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

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

[0213]

[0214] Among them, FC 1 , FC 2 , FS 1 and FS 2 for The coefficients of the expression are expressed as follows:

[0215]

[0216] σ 1 and σ 2 For FC 1 , FC 2 , FS 1 and FS 2 The coefficients in the expression:

[0217]

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

[0219]

[0220] Then the virtual phase current gain parameters are designed based on the Grey Wolf algorithm:

[0221] The Grey Wolf Optimizer (GWO) was inspired by the predation behavior of grey wolves in nature. It was first proposed by Mirjalili et al. in 2014. It achieves target optimization by simulating the hierarchy and hunting mechanism of grey wolf groups. The Grey Wolf Optimizer simulates the hierarchical stratification, encircling prey, hunting, attacking prey and searching prey of wolf groups. It has the advantages of good convergence, fast convergence speed, fewer parameters and simple structure.

[0222] The Gray Wolf Algorithm constructs a hierarchy of solutions according to the hierarchical model of the 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 decision-making and controlling the predation behavior of the wolf pack, and ω wolves are at the bottom of the entire wolf pack and must obey management. In the Gray Wolf Algorithm, α wolf corresponds to the optimal solution, β wolf corresponds to the suboptimal solution, δ wolf corresponds to the third optimal solution, and ω wolf corresponds to the candidate solution.

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

[0224]

[0225]

[0226] In the formula, is the distance between the gray wolf and its 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 gray wolf.

[0227] Coefficient vector and The calculation formula is:

[0228]

[0229]

[0230] In the formula, is the convergence factor, which decreases linearly with the number of iterations in the interval [0, 2]. and is a random vector with values ​​in the interval [0, 1].

[0231] The gray wolf pack can identify and surround the prey (optimal solution) under the leadership of α, β and δ wolves, so the potential location of the prey can be determined by α, β and δ wolves and the location of ω wolf in the population can be updated. The distance between α, β and δ wolves and other gray wolf individuals in the wolf pack is:

[0232]

[0233] In the formula, and are the distances between α, β and δ wolves and other gray wolves, and is the random vector shown in formula (23), and are the current positions of wolves α, β and δ respectively.

[0234] The position update formula of the gray wolf individual is:

[0235]

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

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

[0238]

[0239] The exploitation of the gray wolf algorithm imitates the behavior of the gray wolf population attacking prey, and the exploration of the gray wolf algorithm imitates the behavior of the gray wolf population searching for prey. The attack of the gray wolf population on prey is determined by the convergence factor in the algorithm. It is reflected by the decreasing of. From formula (22), we can see that the convergence factor As the number of iterations changes, The value of is a random number in the interval [-2a, 2a]. In the interval [-1, 1], the next position of the gray wolf can be anywhere between the current position and the prey. When the gray wolf attacks the prey, the current solution falls into a local optimum. When the gray wolf algorithm searches for prey, the wolf pack disperses, and when it attacks the prey, the wolf pack gathers. When , the algorithm will force the gray wolf to separate to escape from the local optimal state, supporting the exploration behavior of the gray wolf algorithm. In addition, the coefficient vector The random weights representing the impact of the wolf’s location on prey further control the algorithm’s global search capability.

[0240] Reference Figure 4As shown, first, initialize the gray wolf population and related parameters. The position of each gray wolf individual in the population has three dimensions, corresponding to the virtual phase current gain k of each phase. a , k b and k c ; Secondly, the double frequency pulsation amplitude of the DC bus is used as the fitness function of the optimization algorithm, and the double frequency pulsation amplitude corresponding to each gray wolf individual is calculated respectively, and the three gray wolf individuals with the smallest amplitude are saved as α, β and δ wolves in this generation of wolf pack; then, the position of the current gray wolf is updated using formula (25) and formula (26), and and Next, the double frequency pulsation amplitude corresponding to each individual gray wolf in the gray wolf population is calculated, and the α, β and δ wolves in the population are updated; finally, when the double frequency pulsation amplitude corresponding to the α wolf is zero, the algorithm ends and the k is obtained. a , k b and k c Optimal value.

[0241] Compared with the existing VPCR technology, the three-phase virtual phase current control technology proposed in the present invention has three degrees of freedom, and the ability to suppress power pulsation is further improved. In the face of any unbalanced working condition of the power grid, the power pulsation of the DC bus can be completely eliminated, meeting the needs of traditional engineering projects. It can be applicable to any three-phase unbalanced operating condition of the power grid. By adjusting the imbalance of the three-phase grid-connected current, the voltage drop and voltage over-limit of any phase can be compensated at the DC bus power level, thereby promoting and improving the existing VPCR technology.

[0242] The present invention establishes a theoretical model of DC bus power pulsation under a three-phase unbalanced power grid considering the three-phase VPCR technology, and uses the Grey Wolf algorithm to solve the optimization model to obtain the optimal value of the gain coefficient. A mathematical model of the DC bus power is constructed, which reflects the performance of different grid conditions and changes in system parameters at the DC bus power level, and creatively applies the intelligent optimization algorithm to the solution of the gain coefficient.

[0243] The above is a basic embodiment of the present invention. The technical solution of the present invention is further described below through a preferred embodiment.

[0244] Example 1

[0245] This embodiment models the DC bus power pulsation component after the three-phase VPCR technology is introduced, and designs the adjustable parameters in the three-phase VPCR technology 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 DC bus voltage of the grid-connected inverter is 700V, and the filter inductor L in the filter circuit isf is 1.4mH, the grid voltage amplitude U is 311V, and the grid frequency f 1 is 50Hz, the d-axis reference current i in the control loop dref is 60A, q-axis reference current i qref For -20A, the proportional gain k of the proportional-integral controller is p is 17.5, the integral gain k of the proportional integral controller i It is 21998.2.

[0247] Reference Figure 5 and Figure 6 As shown, the following simulation verification is carried out using the three-phase unbalanced power grid with a voltage offset ratio of 0.9 for phase A, 0.95 for phase B, and 1.1 for phase C. When the suppression strategy is not introduced, the power on the DC bus has a double frequency pulsation and the pulsation amplitude is large. The existing VPCR technology is introduced into the system, and the virtual phase current parameter of each phase is selected to be equal to the voltage deviation 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] The three-phase VPCR technology is introduced into the system, and the virtual phase current gain parameter design method based on the Grey Wolf algorithm can obtain the virtual phase current gain k a =0.8089, k b =0.8805, k c =0.9822, then according to the three-phase VPCR technical theoretical model, the theoretical value of the three-phase grid-connected current can be obtained as:

[0249]

[0250] Reference Figure 7 and Figure 8 As shown in the figure, the dotted line represents the theoretical current waveform and the solid line represents the simulated current waveform. The two completely overlap, proving the correctness of the three-phase VPCR technology in modeling the grid-connected current. After the introduction of the three-phase VPCR technology, the power on the DC bus is constant and the double frequency pulsation is completely suppressed, proving the effectiveness of the three-phase VPCR technology in suppressing the power pulsation of the DC bus.

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

[0252] The present invention also provides a power pulsation suppression system based on three-phase virtual phase current regulation. The power pulsation suppression system based on three-phase virtual phase current regulation can be realized by executing the process steps of the power pulsation suppression method based on three-phase virtual phase current regulation, that is, those skilled in the art can understand the power pulsation suppression method based on three-phase virtual phase current regulation as a preferred implementation 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 includes:

[0254] Module M1: Based on the three-phase virtual phase current control technology, the overall model of DC bus power pulsation is constructed;

[0255] The three-phase virtual phase current control technology introduces virtual phase current gains in the three phases of the three-phase circuit respectively;

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

[0257] Module M2: Optimize and solve the overall model of DC bus power pulsation to suppress power pulsation.

[0258] The overall model of DC bus power pulsation uses a phase-locked loop of a dual second-order generalized integrator to extract the positive sequence component of the grid voltage for phase locking; the parameters include the voltage offset of each phase, the three-phase virtual phase current gain, and the influence 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 control technology is introduced to make the three-phase grid-connected current unbalanced and smooth the double frequency pulsation of the DC side power; define θ PLL is the phase-locked loop output phase angle, i a v 、i b v and i c v are the virtual A-phase, B-phase and C-phase currents obtained after applying the three-phase virtual phase current control technology, i d v and i q v are virtual d-axis current and virtual q-axis current, respectively, u d and u q are the 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 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 equilibrium state. Suppose the voltage offset ratios of the three phases A, B, and C are k a drop , k b drop , k c drop , then the current three-phase voltage of the power grid is:

[0260]

[0261] In the formula, u a 、u b and u c are the A, B and C phase grid voltages respectively, t is the time, and U is the fundamental voltage in the equilibrium state;

[0262] The dq axis voltage is:

[0263]

[0264] Three-phase virtual phase current control technology introduces virtual phase current gain k into the grid-connected current coordinate transformation module for phases A, B, and C respectively. a , k b and k c , the virtual phase current is obtained as:

[0265]

[0266] In the formula, i a 、i b and i c They are the grid-connected currents of phases A, B and C respectively;

[0267] The three-phase virtual phase current is transformed to obtain the 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 current is 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 current meets:

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

[0269] When k a ≠k b ≠k c When k a i a +k b i b +k c ic ≠0, there is a zero axis current in the control loop. Let the dq0 axis current in the control loop be:

[0270]

[0271] In the formula, i d is the d-axis current, i q is the q-axis current, i 0 is the zero axis current, I 1 is the positive sequence current amplitude, is the current phase, I 0 is the zero axis current amplitude in the control loop, is 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 solved as follows:

[0276]

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

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

[0279]

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

[0281]

[0282] Active power P on the AC side PCC The calculation formula is:

[0283]

[0284] After the introduction of three-phase virtual phase current control technology, the active power on the AC side is:

[0285]

[0286] in

[0287]

[0288] The DC bus power is affected by the filter inductance L fThe impact of transmission power, in an unbalanced power grid, the instantaneous power transmitted on the filter inductor fluctuates, further aggravating the power fluctuation on the DC bus;

[0289] The voltage on the filter inductor is:

[0290]

[0291] In the formula, u La 、u Lb 、u Lc They are the voltages across the filter inductor phase A, phase B, and phase C respectively;

[0292] Calculate the power P on the filter inductor L for

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

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

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

[0296] Obtain the double frequency pulsation component on the DC bus for:

[0297]

[0298] Among them, FC 1 , FC 2 , FS 1 and FS 2 for The coefficients of the expression are expressed as follows:

[0299]

[0300] σ 1 and σ 2 For FC 1 , FC 2 , FS 1 and FS 2 The coefficients in the expression:

[0301]

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

[0303]

[0304] The DC bus power pulsation overall model is optimized and solved based on the gray wolf algorithm; the gray wolf algorithm achieves target optimization by simulating the hierarchy and hunting mechanism in the gray wolf group; 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, δ wolves are responsible for decision-making and dominating the predation behavior of the wolf pack, and ω wolf is the bottom of the entire wolf pack; α wolf corresponds to the optimal solution, β wolf corresponds to the suboptimal solution, δ wolf corresponds to the third optimal solution, and ω wolf corresponds to the candidate solution.

[0305] In the gray wolf algorithm, the gray wolf pack surrounds the prey during the hunting process. During the algorithm search process, the distance and position update formula between the individuals of the gray wolf population and the prey is:

[0306]

[0307]

[0308] In the formula, is the distance between the individual gray wolf and its 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 gray wolf;

[0309] Coefficient vector and The calculation formula is:

[0310]

[0311]

[0312] In the formula, is the convergence factor, and decreases linearly with the number of iterations in the interval [0, 2]; and is a random vector with values ​​in the interval [0, 1];

[0313] The gray wolf pack, led by α, β and δ wolves, identifies and surrounds the prey. α, β and δ wolves are used to determine the potential location of the prey and update the location of the ω wolf in the population. The distance between α, β and δ wolves and other gray wolf individuals in the wolf pack is:

[0314]

[0315] In the formula, and are the distances between α, β and δ wolves and other gray wolves, and is a random vector, and are the current positions of α, β and δ wolves respectively;

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

[0317]

[0318] In the formula, is the direction and step length of ω wolf moving towards α wolf; is the direction and step length of ω wolf moving towards β wolf; is the direction and step length of ω wolf moving towards δ wolf;

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

[0320]

[0321] In the gray wolf algorithm, the gray wolf population attacks prey by the convergence factor The convergence factor As the number of iterations changes, The value of is a random number in the interval [-2a, 2a]. In the interval [-1, 1], the next position of the gray wolf is any position between the current position and the prey; when When , the gray wolf attacks the prey, and the current solution falls into a local optimum; in the gray wolf algorithm, the wolves disperse when searching for prey, corresponding to the exploration process; when attacking prey, the wolves gather, corresponding to the convergence process; when When , the gray wolf will be forced to separate to escape from the local optimal state and support the exploration behavior of the gray wolf algorithm; the coefficient vector The random weight that represents the impact of the gray wolf's location on prey controls the global search capability of the algorithm.

[0322] The position of each individual gray wolf in the gray wolf algorithm has three dimensions, which correspond to the virtual phase current gain of each phase respectively; the DC bus power pulsation overall model is combined with the actual operating conditions of the grid-connected inverter to completely smooth the DC bus power pulsation.

[0323] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0324] The above describes the specific embodiments of the present invention. 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. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A power pulsation suppression method based on three-phase virtual phase current control, It is characterized in that include: Step S1: constructing a DC bus power pulsation overall model based on three-phase virtual phase current control technology; The three-phase virtual phase current control technology introduces virtual phase current gains in the three phases of the three-phase circuit respectively; The DC bus power pulsation overall model obtains parameters of the three-phase circuit; Step S2: Optimize and solve the overall model of DC bus power pulsation to suppress power pulsation.

2. According to claim 1, a power pulsation suppression method based on three-phase virtual phase current regulation, It is characterized in that The overall model of DC bus power pulsation uses a phase-locked loop of a dual second-order generalized integrator to extract the positive sequence component of the grid voltage for phase locking; the parameters include the voltage offset of each phase, the three-phase virtual phase current gain, and the influence 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 control technology is introduced to make the three-phase grid-connected current unbalanced and smooth the double frequency pulsation of the DC side power; define θ PLL is the phase-locked loop output phase angle, i a v 、i b v and i c v are the virtual A-phase, B-phase and C-phase currents obtained after applying the three-phase virtual phase current control technology, i d v and i q v are virtual d-axis current and virtual q-axis current, respectively, u d and u q are the d-axis voltage and q-axis virtual voltage respectively, i dref and i qref are the d-axis reference current and q-axis reference current respectively, and ω is the grid angular velocity.

3. A power pulsation suppression method based on three-phase virtual phase current regulation according to claim 2, It is characterized in that In step S1, the voltage offset ratio is defined as the ratio of the current phase voltage to the phase voltage in the equilibrium state. Suppose the voltage offset ratios of phases A, B, and C are k a drop , k b drop , k c drop , then the current three-phase voltage of the power grid is: In the formula, u a 、u b and u c are the A, B and C phase grid voltages respectively, t is the time, and U is the fundamental voltage in the equilibrium state; The dq axis voltage is: Three-phase virtual phase current control technology introduces virtual phase current gain k into the grid-connected current coordinate transformation module for phases A, B, and C respectively. a , k b and k c , the virtual phase current is obtained as: In the formula, i a 、i b and i c They are the grid-connected currents of phases A, B and C respectively; The three-phase virtual phase current is transformed to obtain the 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 current is 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 current meets: i a +i b +i c =0; When k a ≠k b ≠k c When k a i a +k b i b +k c i c ≠0, there is a zero axis current in the control loop. Let the dq0 axis current in the control loop be: In the formula, i d is the d-axis current, i q is the q-axis current, i 0 is the zero axis current, I 1 is the positive sequence current amplitude, is the current phase, I 0 is the zero axis current amplitude in the control loop, is the corresponding zero-axis current phase; The three-phase current in the control circuit is: The three-phase grid-connected current is: The amplitude and phase of the zero-axis current in the control loop are solved as follows: Wherein, sign(x)=x / |x|, x is a parameter expression; The three-phase grid-connected current is obtained as: The dq axis grid-connected current is: Active power P on the AC side PCC The calculation formula is: After the introduction of three-phase virtual phase current control technology, the active power on the AC side is: in 4. A power pulsation suppression method based on three-phase virtual phase current regulation according to claim 3, It is characterized in that The DC bus power is affected by the filter inductance L f The impact of transmission power, in an unbalanced power grid, the instantaneous power transmitted on the filter inductor fluctuates, further aggravating the power fluctuation on the DC bus; The voltage on the filter inductor is: In the formula, u La 、u Lb 、u Lc They are the voltages across the filter inductor phase A, phase B, and phase C respectively; Calculate the power P on the filter inductor L for P L =in La and a +in Lb and b +in Lc and c ; Power P on the DC bus DC is the AC side active power P PCC And the instantaneous power P on the filter inductor L sum: P DC =P PCC +P L ; Obtain the double frequency pulsation component on the DC bus for: Among them, FC 1 , FC 2 , FS 1 and FS 2 for The coefficients of the expression are expressed as follows: σ 1 and σ 2 For FC 1 , FC 2 , FS 1 and FS 2 The coefficients in the expression: The amplitude of the DC bus power fluctuation is obtained as:

5. The power pulsation suppression method based on three-phase virtual phase current regulation according to claim 1, It is characterized in that The DC bus power pulsation overall model is optimized and solved based on the Grey Wolf algorithm; The gray wolf algorithm achieves target optimization by simulating the hierarchy and hunting mechanism in the gray wolf group; 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, δ wolves are responsible for decision-making and dominating the predation behavior of the wolf pack, and ω wolf is the bottom of the entire wolf pack; α wolf corresponds to the optimal solution, β wolf corresponds to the suboptimal solution, δ wolf corresponds to the third optimal solution, and ω wolf corresponds to the candidate solution.

6. A power pulsation suppression method based on three-phase virtual phase current regulation according to claim 5, It is characterized in that In the gray wolf algorithm, the gray wolf pack surrounds the prey during the hunting process. During the algorithm search process, the distance and position update formula between the individuals of the gray wolf population and the prey is: In the formula, is the distance between the gray wolf and its 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 gray wolf; Coefficient vector and The calculation formula is: In the formula, is the convergence factor, and decreases linearly with the number of iterations in the interval [0, 2]; and is a random vector with values ​​in the interval [0, 1]; The gray wolf pack, led by α, β and δ wolves, identifies and surrounds the prey. α, β and δ wolves are used to determine the potential location of the prey and update the location of the ω wolf in the population. The distance between α, β and δ wolves and other gray wolf individuals in the wolf pack is: In the formula, and are the distances between α, β and δ wolves and other gray wolves, and is a random vector, and are the current positions of α, β and δ wolves respectively; The position update formula of the gray wolf individual is: In the formula, is the direction and step length of ω wolf moving towards α wolf; is the direction and step length of ω wolf moving towards β wolf; is the direction and step length of ω wolf moving towards δ wolf; The final position of the gray wolf individual is:

7. A power pulsation suppression method based on three-phase virtual phase current regulation according to claim 6, It is characterized in that In the gray wolf algorithm, the gray wolf population attacks prey by the convergence factor The convergence factor As the number of iterations changes, The value of is a random number in the interval [-2a, 2a]. In the interval [-1, 1], the next position of the gray wolf is any position between the current position and the prey; when When , the gray wolf attacks the prey, and the current solution falls into a local optimum; in the gray wolf algorithm, the wolves disperse when searching for prey, corresponding to the exploration process; when attacking prey, the wolves gather, corresponding to the convergence process; when When , the gray wolf will be forced to separate to escape from the local optimal state and support the exploration behavior of the gray wolf algorithm; the coefficient vector The random weight that represents the impact of the gray wolf's location on prey controls the global search capability of the algorithm.

8. A power pulsation suppression method based on three-phase virtual phase current regulation according to claim 6, It is characterized in that The position of each individual gray wolf in the gray wolf algorithm has three dimensions, which correspond to the virtual phase current gain of each phase respectively; the DC bus power pulsation overall model is combined with the actual operating conditions of the grid-connected inverter to completely smooth the DC bus power pulsation.

9. A power pulsation suppression system based on three-phase virtual phase current control, It is characterized in that include: Module M1: Based on the three-phase virtual phase current control technology, the overall model of DC bus power pulsation is constructed; The three-phase virtual phase current control technology introduces virtual phase current gains in the three phases of the three-phase circuit respectively; The DC bus power pulsation overall model obtains parameters of the three-phase circuit; Module M2: Optimize and solve the overall model of DC bus power pulsation to suppress power pulsation.

10. A power pulsation suppression system based on three-phase virtual phase current regulation according to claim 9, It is characterized in that The overall model of DC bus power pulsation uses a phase-locked loop of a dual second-order generalized integrator to extract the positive sequence component of the grid voltage for phase locking; the parameters include the voltage offset of each phase, the three-phase virtual phase current gain, and the influence 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 control technology is introduced to make the three-phase grid-connected current unbalanced and smooth the double frequency pulsation of the DC side power; define θ PLL is the phase-locked loop output phase angle, i a v 、i b v and i c v are the virtual A-phase, B-phase and C-phase currents obtained after applying the three-phase virtual phase current control technology, i d v and i q v are virtual d-axis current and virtual q-axis current, respectively, u d and u q are the d-axis voltage and q-axis virtual voltage respectively, i dref and i qref are the d-axis reference current and q-axis reference current respectively, and ω is the grid angular velocity.

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