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

Abstract

The invention provides a power fluctuation suppression method and system based on two-phase virtual phase current regulation and control. The method comprises the steps that S1, a grid-connected current model and a direct-current bus power fluctuation model are constructed; a two-phase virtual phase current regulation and control technology is introduced into the grid-connected current model; the DC bus power fluctuation model corresponds to the grid-connected current model; s2, optimizing a direct current bus power fluctuation model; and S3, solving the optimized direct current bus power fluctuation model to complete the complete suppression of the power fluctuation. On the basis of the single-phase VPCR technology, one of the phases without voltage drop in the three phases is additionally selected as an auxiliary compensation phase, optimization calculation of a two-phase virtual phase current gain coefficient is carried out through a particle swarm optimization algorithm, it is proved from the theoretical level that the two-phase VPCR technology can achieve minimization and zero of direct-current side power fluctuation, and the method is suitable for large-scale popularization and application. The traditional engineering requirements are met, and the design defect of the gain coefficient of the single-phase VPCR technology is improved.

Description

Technical Field

[0001] The present invention relates to the field of alternating current, and in particular to a method and system for suppressing power fluctuations based on two-phase virtual phase current regulation. Background Art

[0002] With the construction of new power systems based on new energy, grid-connected inverters serve as a bridge for energy transmission between new energy power generation systems and AC power grids. Their stable power transmission capability plays a decisive role in the safe and reliable operation of the overall power system. However, in actual power grid operation, asymmetric faults and asymmetric loads can cause the power grid to be in an unbalanced state, thereby affecting the output power of the inverter and the quality of the grid-connected current.

[0003] When a voltage drop occurs in one phase of the power grid, causing the power grid to be in a three-phase unbalanced state, the AC side active power transmitted by the grid-connected inverter will contain a double-frequency fluctuation component, which will cause fluctuations in the DC bus voltage and power, seriously affecting the service life of the DC side capacitor, and will increase the system's requirements for capacitor stress, increasing the risk of voltage instability and voltage over-limit. Therefore, it is of practical significance to discuss the means of suppressing DC bus power fluctuations.

[0004] Virtual phase-current regulation (VPCR) technology suppresses active power fluctuations on the AC side by compensating for the three-phase grid-connected current feedback loop in the control layer. The existing VPCR technology only introduces virtual phase current gain in the voltage drop phase, so the existing VPCR technology is called single-phase VPCR technology. At present, the existing single-phase virtual phase current control technology only increases the virtual phase current gain in the phase where the voltage drops, which can weaken the power fluctuations on the DC side to a certain extent, but has limitations in the effect and cannot completely eliminate the power fluctuations on the DC side. In addition, the existing VPCR technology is relatively rough in the design of the virtual phase current gain coefficient, and only selects the voltage drop ratio as the virtual phase current gain, and does not fully exert the full suppression ability of the single-phase VPCR technology on the DC side power fluctuations.

[0005] The existing power fluctuation suppression strategy often suppresses the active power fluctuation on the AC side by adjusting the reference current of the current loop in the control strategy, thereby reducing the DC bus power fluctuation. However, this suppression method often increases the complexity of the control loop and reduces the dynamic response speed of the system. In addition, due to the change of the control loop, the existing control parameter design method is no longer applicable to the new system, which increases the difficulty of setting the system parameters. Compared with the above suppression strategy, the existing single-phase VPCR technology weakens the active power fluctuation on the AC side and the power fluctuation on the DC side by adjusting the feedback current in the control strategy, without changing the current loop structure. The control structure is simpler and can effectively eliminate the active power fluctuation on the AC side. However, the single-phase VPCR technology only compensates for the current corresponding to the voltage drop, and the ability to suppress the DC bus power fluctuation is still limited, reducing but not completely eliminating the DC bus power fluctuation.

[0006] Jin Peng, Ai Xin, Sun Yingyun, Zhou Shupeng. Optimization design of microgrid PQ control strategy for power pulsation suppression [J]. Automation of Electric Power Systems, 2013, 37(13): 30-35+131. This paper is based on a PQ control structure of dual current controllers. The expressions of active and reactive power pulsation amplitudes are established through optimization theory, and then the optimal positive and negative sequence current given values ​​are obtained. This paper first analyzes the operating state of the three-phase inverter under unbalanced voltage conditions and discusses the influence of active and reactive pulsation on the inverter output power; secondly, the optimization theory is used to solve the optimal reference value of the current in the current loop to achieve the minimum amplitude of active and reactive power pulsation. Finally, the corresponding control structure and positive and negative sequence sampling method are given, and simulation verification is completed. However, the current loop in this paper introduces a total of 4 PI controllers, which reduces the dynamic response speed and stability of the system and increases the difficulty of designing control parameters. In addition, the sampling delay and coupling of positive and negative sequence currents will interfere with the accuracy of reference current calculation and reduce the suppression effect of power pulsation. This document suppresses active power pulsation and thus smoothes the voltage fluctuation on the DC side. However, when the power pulsation on the AC side is zero, the power and voltage fluctuations on the DC side cannot be completely eliminated. The optimization theory used in this document is based on the Lagrange multiplier method, and the partial derivative of the objective function is obtained to obtain the optimal current value. However, this optimization method is only applicable to convex optimization problems. When the circuit structure changes and the complexity of the objective function increases, the solution is difficult and the scope of application is limited. The present invention does not need to change the control structure of the vector current loop, and does not require an additional PI controller. It only modifies the feedback current in the control loop and takes the DC bus power fluctuation amplitude as the direct optimization target, ensuring the complete suppression of the power pulsation on the DC side. In addition, the present invention solves the optimization model based on a meta-heuristic algorithm, which is simple to solve and has good convergence effect and strong scalability. The two-phase VPCR DC bus power fluctuation suppression technology and its coefficient design method proposed in the present invention can complete the rapid design of the virtual phase current gain coefficient under different grid imbalances, achieve complete elimination of DC bus power fluctuations, and provide theoretical support for predicting the impact of grid voltage drop on DC bus power, providing a new power fluctuation suppression strategy for three-phase three-wire grid-connected inverter DC bus power smoothing.

[0007] In the Chinese patent document with publication number CN114006388A, a grid-connected power generation system and its grid-connected power fluctuation suppression device and method are disclosed, the grid-connected power generation system includes a first DC source, an inverter and a power grid, the grid-connected power fluctuation suppression device includes: a second DC source, the second DC source is connected to the DC side of the inverter; a power distribution unit, the power distribution unit is connected to the second DC source and the inverter respectively, the power distribution unit is used to obtain the power set value of the first DC source and the power feedback value of the first DC source, and calculate the AC power set value and the power set value of the second DC source according to the power set value of the first DC source and the power feedback value of the first DC source, and control the inverter by the AC power set value and control the second DC source by the power set value of the second DC source. However, the patent document still adopts the single-phase VPCR technology, while the present invention, on the basis of the single-phase VPCR technology, additionally selects one of the three phases without voltage drop as the auxiliary compensation phase, which is essentially different from the technology and method adopted in the patent document. Summary of the invention

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

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

[0010] Step S1: constructing a grid-connected current model and a DC bus power fluctuation model;

[0011] The grid-connected current model introduces a two-phase virtual phase current control technology;

[0012] The DC bus power fluctuation model corresponds to the grid-connected current model;

[0013] Step S2: Optimizing the DC bus power fluctuation model;

[0014] Step S3: Solve the optimized DC bus power fluctuation model to completely suppress the power fluctuation.

[0015] Preferably, the two-phase virtual phase current control technology compensates for the voltage drop phase and the current of the auxiliary phase of the three-phase grid-connected current to maintain the constant power on the DC side, and the two-phase virtual phase current control technology can be applied to the scenario when a single-phase voltage drop occurs in a three-phase three-wire L-type grid-connected inverter.

[0016] Preferably, in the scenario where a single-phase voltage drop occurs in the three-phase three-wire L-type grid-connected inverter, i a 、i b and i c are the currents of phase A, phase B and phase C respectively, ua 、u b and u c are the voltages of phase A, phase B and phase C respectively; i a v and i c v After applying the two-phase VPCR technique, a and i c Multiply by the virtual phase current gain k a and k c The virtual A phase current and virtual C phase current obtained after that, i d v and i q v are the d-axis virtual current and q-axis virtual current obtained by coordinate transformation after the introduction of two-phase virtual phase current control technology, and u d and u q are the d-axis voltage and q-axis virtual voltage respectively, i d * and i q * are the d-axis reference current and q-axis reference current of the current loop, and ω is the angular velocity of the power grid;

[0017] Assume the voltage drop ratio of phase A is k drop , select the voltage drop phase A and the auxiliary phase C, the three-phase voltage of the unbalanced power grid is:

[0018]

[0019] In the formula, t is time, U is fundamental voltage;

[0020] Therefore, the voltage of the virtual axis dq is:

[0021]

[0022] When the voltage of phase A drops, based on the two-phase virtual phase current control technology, the virtual phase current gain k is introduced into the A phase and C phase of the three-phase grid-connected current coordinate transformation module. a and k c The two-phase virtual phase current control technology does not change the current loop structure, so the reference value of the virtual axis dq current i d * and i q * unchanged; if the zero-axis current in the control system is ignored, the virtual axis dq current i obtained by introducing the two-phase virtual phase current control technology is d v and i q v As the input of the current loop, it will track the reference current value without static error, and the virtual current i of phase A, phase B and phase C in the control loop a v 、ib v and i c v It is still a three-phase balanced current. The A-phase and C-phase currents in the three-phase current are amplified by 1 / k a and 1 / k c times, compensating for the power drop and power fluctuation caused by voltage drop at the DC side power calculation level.

[0023] Preferably, after the two-phase virtual phase current control technology is introduced, if the zero-axis current in the control system is ignored, the three-phase grid-connected current is:

[0024]

[0025] In the formula, I 1 is the positive sequence current amplitude, is the initial phase of the current;

[0026] The three-phase grid-connected current presents a three-phase unbalanced state due to the introduction of two-phase virtual phase current control technology. After sequence decomposition, it is found that there is a zero-sequence current component in the three-phase current, which is contrary to the principle that there is no zero-sequence current in the three-phase three-wire system. Therefore, the zero-axis current in the control loop cannot be ignored. Assume that the dq0 current in the control loop is:

[0027]

[0028] 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 0 is the zero axis current amplitude, is the zero axis current phase;

[0029] At this time, the three-phase current in the control loop under the abc coordinates is:

[0030]

[0031] The three-phase grid-connected current is:

[0032]

[0033] According to the three-phase three-wire system does not contain zero-sequence current, i a +i b +i c =0, the zero axis current amplitude and phase are obtained as

[0034]

[0035] Where sign(x) = x / |x|, x is a parameter expression, and:

[0036]

[0037] The three-phase grid-connected current is further expressed as:

[0038]

[0039] The dq axis grid-connected current is:

[0040]

[0041] AC side active power p PCC It is expressed as:

[0042]

[0043] Solve to get the AC side active power p PCC for:

[0044]

[0045] in,

[0046]

[0047] Assume that the current flowing through a single inductor L f The current is

[0048]

[0049] Voltage across the inductor u L for

[0050]

[0051] At this time, the instantaneous power p on the inductor is L for

[0052]

[0053] Calculate the filter inductance L f The three-phase voltage on is:

[0054]

[0055] 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;

[0056] Solve for the instantaneous power p on the filter inductor L :

[0057] p L =u La i a +uLb i b +u Lc i c ;

[0058] The instantaneous power p on the DC side DC From the AC side PCC and the instantaneous power p on the filter inductor L It consists of two parts:

[0059] p DC =p PCC +p L ;

[0060] The double frequency fluctuation component of the DC bus power is obtained as

[0061]

[0062] Among them, PC 1 、PC 2 ,PS 1 and PS 2 is the coefficient of the expression of the double frequency fluctuation component of the DC bus power, expressed as follows:

[0063]

[0064] σ 1 and σ 2 For PC 1 、PC 2 ,PS 1 ,PS 2 The coefficients in the expression:

[0065]

[0066] The amplitude of the DC side power fluctuation is

[0067]

[0068] The virtual phase current gain coefficient in the two-phase virtual phase current control technology is adjusted to reduce the power fluctuation amplitude on the DC side.

[0069] Preferably, the DC bus power fluctuation model is optimized and solved based on a particle swarm optimization algorithm; the particle swarm optimization algorithm includes initializing a random particle swarm, each particle having a random position and speed;

[0070]

[0071] As the fitness function of the optimization algorithm, the power fluctuation amplitudes of the 1st to i-th particles are calculated respectively; in the kth generation, each particle has its own memory of the best position, that is, the individual best position pbesti k ; Compare the current fluctuation amplitude with the fluctuation amplitude of the individual best position, and retain the particle position with the smallest fluctuation amplitude as the new individual best position; In each generation, the entire particle group has a group minimum fluctuation amplitude, which is called the global best position gbest k In each iteration, the particle tracks two extreme values ​​(pbest i k , gbest k ) to update its velocity v i k and position x i k , when the DC side power fluctuation is zero, the algorithm terminates.

[0072] Preferably, the particle swarm optimization algorithm adopts a shrinkage factor method, using the shrinkage coefficient χ to control the convergence of the system to search different areas, and the particle speed update formula is:

[0073]

[0074]

[0075] Where, the subscript i represents the i-th particle, the superscript k represents the k-th generation, and r 1 and r 2 is a random number uniformly distributed between [0, 1]. and are two learning factors, k is the number of iterations;

[0076] The particle position update formula is:

[0077]

[0078] In the process of solving the DC bus power fluctuation optimization model, the dimension of the particles is consistent with the number of virtual phase current gains introduced in the two-phase virtual phase current control technology; the virtual phase current gain k is introduced by selecting phase A and phase C in the system respectively. a and k c , then the dimension of the particle is 2; in the two-dimensional search space, the vector sets of the velocity and position of each particle are V i =[v i1 , v i2 ], X i =[x i1 , x i2 ]; the two dimensions x of the particle position i1 Corresponding virtual phase current gain k a , x i2 Corresponding virtual phase current gain kc The constraints of the two dimensions of the position are consistent with the range of the voltage drop ratio, which is limited to [0, 1]. In the kth generation, the individual best position set of particle i is pbest i k =[x i1 pbest , x i2 pbest ]; in the kth generation, the global best position set of particles is gbest k =[x 1 gbest , x 2 gbest ].

[0079] Preferably, after the kth generation iteration is completed, the two dimensions of the global optimal position of the particle correspond to the k in the two-phase virtual phase current control technology. a and k c The optimal value of DC bus power fluctuation is completely suppressed.

[0080] Preferably, the two-phase virtual phase current control technology changes the input current in the control loop to indirectly control the grid-connected current.

[0081] According to the present invention, a power fluctuation suppression system based on two-phase virtual phase current regulation is provided, comprising:

[0082] Module M1: Constructing grid-connected current model and DC bus power fluctuation model;

[0083] The grid-connected current model introduces a two-phase virtual phase current control technology;

[0084] The DC bus power fluctuation model corresponds to the grid-connected current model;

[0085] Module M2: Optimize the DC bus power fluctuation model;

[0086] Module M3: Solve the optimized DC bus power fluctuation model to completely suppress the power fluctuation.

[0087] Preferably, the two-phase virtual phase current control technology compensates for the voltage drop phase and the current of the auxiliary phase of the three-phase grid-connected current to maintain the constant power on the DC side, and the two-phase virtual phase current control technology can be applied to the scenario when a single-phase voltage drop occurs in a three-phase three-wire L-type grid-connected inverter.

[0088] Preferably, in the scenario where a single-phase voltage drop occurs in the three-phase three-wire L-type grid-connected inverter, i a 、i b and i c are the currents of phase A, phase B and phase C respectively, u a 、ub and u c are the voltages of phase A, phase B and phase C respectively; i a v and i c v After applying the two-phase VPCR technique, a and i c Multiply by the virtual phase current gain k a and k c The virtual A phase current and virtual C phase current obtained after that, i d v and i q v are the d-axis virtual current and q-axis virtual current obtained by coordinate transformation after the introduction of two-phase virtual phase current control technology, and u d and u q are the d-axis voltage and q-axis virtual voltage respectively, i d * and i q * are the d-axis reference current and q-axis reference current of the current loop, ω is the angular velocity of the power grid;

[0089] Assume the voltage drop ratio of phase A is k drop , select the voltage drop phase A and the auxiliary phase C, the three-phase voltage of the unbalanced power grid is:

[0090]

[0091] In the formula, t is time, U is fundamental voltage;

[0092] Therefore, the voltage of the virtual axis dq is:

[0093]

[0094] When the voltage of phase A drops, based on the two-phase virtual phase current control technology, the virtual phase current gain k is introduced into the A phase and C phase of the three-phase grid-connected current coordinate transformation module. a and k c The two-phase virtual phase current control technology does not change the current loop structure, so the reference value of the virtual axis dq current i d * and i q * unchanged; if the zero-axis current in the control system is ignored, the virtual axis dq current i obtained by introducing the two-phase virtual phase current control technology is d v and i q v As the input of the current loop, it will track the reference current value without static error, and the virtual current i of phase A, phase B and phase C in the control loop a v 、i b vand i c v It is still a three-phase balanced current. The A-phase and C-phase currents in the three-phase current are amplified by 1 / k a and 1 / k c times, compensating for the power drop and power fluctuation caused by voltage drop at the DC side power calculation level.

[0095] Preferably, after the two-phase virtual phase current control technology is introduced, if the zero-axis current in the control system is ignored, the three-phase grid-connected current is:

[0096]

[0097] In the formula, I 1 is the positive sequence current amplitude, is the initial phase of the current;

[0098] The three-phase grid-connected current presents a three-phase unbalanced state due to the introduction of two-phase virtual phase current control technology. After sequence decomposition, it is found that there is a zero-sequence current component in the three-phase current, which is contrary to the principle that there is no zero-sequence current in the three-phase three-wire system. Therefore, the zero-axis current in the control loop cannot be ignored. Assume that the dq0 current in the control loop is:

[0099]

[0100] 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 0 is the zero axis current amplitude, is the zero axis current phase;

[0101] At this time, the three-phase current in the control loop under the abc coordinates is:

[0102]

[0103] The three-phase grid-connected current is:

[0104]

[0105] According to the three-phase three-wire system does not contain zero-sequence current, i a +i b +i c =0, the zero axis current amplitude and phase are obtained as

[0106]

[0107] Where sign(x) = x / |x|, x is a parameter expression, and:

[0108]

[0109] The three-phase grid-connected current is further expressed as:

[0110]

[0111] The dq axis grid-connected current is:

[0112]

[0113] AC side active power p PCC It is expressed as:

[0114]

[0115] Solve to get the AC side active power p PCC for:

[0116]

[0117] in,

[0118]

[0119] Assume that the current flowing through a single inductor L f The current is

[0120]

[0121] Voltage across the inductor u L for

[0122]

[0123] At this time, the instantaneous power p on the inductor is L for

[0124]

[0125] Calculate the filter inductance L f The three-phase voltage on is:

[0126]

[0127] 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;

[0128] Solve for the instantaneous power p on the filter inductor L :

[0129] p L =u La i a +u Lb i b+u Lc i c ;

[0130] The instantaneous power p on the DC side DC From the AC side PCC and the instantaneous power p on the filter inductor L It consists of two parts:

[0131] p DC =p PCC +p L ;

[0132] The double frequency fluctuation component of the DC bus power is obtained as

[0133]

[0134] Among them, PC 1 、PC 2 ,PS 1 and PS 2 is the coefficient of the expression of the double frequency fluctuation component of the DC bus power, expressed as follows:

[0135]

[0136] σ 1 and σ 2 For PC 1 、PC 2 ,PS 1 ,PS 2 The coefficients in the expression:

[0137]

[0138] The amplitude of the DC side power fluctuation is

[0139]

[0140] The virtual phase current gain coefficient in the two-phase virtual phase current control technology is adjusted to reduce the power fluctuation amplitude on the DC side.

[0141] Preferably, the DC bus power fluctuation model is optimized and solved based on a particle swarm optimization algorithm; the particle swarm optimization algorithm includes initializing a random particle swarm, each particle having a random position and speed;

[0142]

[0143] As the fitness function of the optimization algorithm, the power fluctuation amplitudes of the 1st to i-th particles are calculated respectively; in the kth generation, each particle has its own memory of the best position, that is, the individual best position pbest i k; Compare the current fluctuation amplitude with the fluctuation amplitude of the individual best position, and retain the particle position with the smallest fluctuation amplitude as the new individual best position; In each generation, the entire particle group has a group minimum fluctuation amplitude, which is called the global best position gbest k In each iteration, the particle tracks two extreme values ​​(pbest i k , gbest k ) to update its velocity v i k and position x i k , when the DC side power fluctuation is zero, the algorithm terminates.

[0144] Preferably, the particle swarm optimization algorithm adopts a shrinkage factor method, using the shrinkage coefficient χ to control the convergence of the system to search different areas, and the particle speed update formula is:

[0145]

[0146]

[0147] Among them, the subscript i represents the i-th particle, the superscript k represents the k-th generation, and r 1 and r 2 is a random number uniformly distributed between [0, 1]. and are two learning factors, k is the number of iterations;

[0148] The particle position update formula is:

[0149]

[0150] In the process of solving the DC bus power fluctuation optimization model, the dimension of the particles is consistent with the number of virtual phase current gains introduced in the two-phase virtual phase current control technology; the virtual phase current gain k is introduced by selecting phase A and phase C in the system respectively. a and k c , then the dimension of the particle is 2; in the two-dimensional search space, the vector sets of the velocity and position of each particle are V i =[v i1 , v i2 ], X i =[x i1 , x i2 ]; the two dimensions x of the particle position i1 Corresponding virtual phase current gain k a , x i2 Corresponding virtual phase current gain k cThe constraints of the two dimensions of the position are consistent with the range of the voltage drop ratio, which is limited to [0, 1]. In the kth generation, the individual best position set of particle i is pbest i k =[x i1 pbest , x i2 pbest ]; in the kth generation, the global best position set of particles is gbest k =[x 1 gbest , x 2 gbest ].

[0151] Preferably, after the kth generation iteration is completed, the two dimensions of the global optimal position of the particle correspond to the k in the two-phase virtual phase current control technology. a and k c The optimal value of DC bus power fluctuation is completely suppressed.

[0152] Preferably, the two-phase virtual phase current control technology changes the input current in the control loop to indirectly control the grid-connected current.

[0153] Compared with the prior art, the present invention has the following beneficial effects:

[0154] 1. The control strategy proposed in the present invention is based on the single-phase VPCR technology. It selects one of the three phases without voltage drop as an auxiliary compensation phase. By adjusting the feedback current in the control loop, the DC side power is guaranteed to be constant under the unbalanced power grid. In addition, the present invention uses the particle swarm optimization algorithm to optimize the two-phase virtual phase current gain coefficient, and proves from a theoretical level that the two-phase VPCR technology can minimize and zero the power fluctuation on the DC side, meet the needs of traditional engineering, and improve the design drawbacks of the gain coefficient of the single-phase VPCR technology.

[0155] 2. The present invention establishes a theoretical model of DC bus power fluctuation considering the two-phase VPCR technology, which can predict the impact of different grid voltage drop levels on DC side power fluctuations from a theoretical level, and can substitute the model into the optimization algorithm to obtain the optimal solution of virtual phase current gains ① and ② and the maximum extent to which the technology can suppress DC side power fluctuations.

[0156] 3. The present invention completely eliminates the DC bus power fluctuation while retaining the vector current control structure, so that the DC bus power transmission effect better meets the traditional engineering requirements, effectively reduces the pressure on the DC side capacitor, and thus reduces the size and cost of the system; avoids changes to the current loop structure, reduces the complexity of the system, and does not need to add additional power compensation links in the current loop to interfere with the system stability.

[0157] 4. The present invention constructs a DC bus power fluctuation model considering the two-phase VPCR technology, theoretically analyzes the impact of different voltage drop levels of the power grid on the DC side power fluctuation, quantifies the influencing factors causing the amplitude of DC bus power fluctuation, and provides theoretical support for the power fluctuation suppression capability of the two-phase VPCR technology.

[0158] 5. The present invention proposes a new idea for suppressing power fluctuations on the DC side. The existing suppression technology often equates the power fluctuations on the AC side with the power fluctuations on the DC side, without considering the interference of the filter circuit on the DC side power. As a result, although the power fluctuations on the AC side are eliminated, the power on the DC side still fluctuates, and the burden on the DC side capacitor always exists. The present invention introduces a two-phase virtual phase current gain in the control layer to perform current compensation for the phase where the voltage drops and the auxiliary phase, thereby achieving complete suppression of power fluctuations on the DC side.

[0159] 6. The present invention can utilize the particle swarm optimization algorithm based on the shrinkage factor method to obtain the global optimal solution of the model. The algorithm has good convergence and fast convergence speed. The convergence result can achieve zero DC bus power fluctuation, and the virtual phase current gain coefficient of the two-phase VPCR technology can be directly designed according to the specific needs of the engineering application scenario, thereby enhancing the applicability and scalability of the two-phase VPCR technology in engineering.

[0160] 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

[0161] 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:

[0162] Figure 1 The present invention is a flow chart of the method.

[0163] Figure 2 Schematic diagram of a three-phase three-wire grid-connected inverter system in an embodiment of the present invention.

[0164] Figure 3 4 is a control block diagram of the two-phase VPCR technology in an embodiment of the present invention.

[0165] Figure 4 Schematic diagram of the effect of VPCR technology in an embodiment of the present invention.

[0166] Figure 5 The particle swarm optimization algorithm solution flow chart in the embodiment of the present invention.

[0167] Figure 6 This is a curve diagram of DC power and AC side active power when the two-phase VPCR technology is not introduced in the embodiment of the present invention.

[0168] Figure 7 This is a curve diagram of DC power and AC side active power after the single-phase VPCR technology is introduced in the embodiment of the present invention.

[0169] Figure 8 This is a three-phase grid-connected current waveform diagram after the two-phase VPCR technology is introduced in the embodiment of the present invention.

[0170] Fig. 9 This is a curve diagram of DC side power and AC side active power after the two-phase VPCR technology is introduced in the embodiment of the present invention. DETAILED DESCRIPTION

[0171] 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.

[0172] Reference Figure 1 and Figure 2 As shown in the figure, V dc is the DC side voltage, C dc is the DC side capacitance, L f is the filter inductance of the L-type filter circuit, u PCC and i PCC It is the three-phase grid voltage and grid-connected current at the point of common coupling (PCC).

[0173] Reference Figure 3 As shown in the figure, a 、i b and i c are the currents of phase A, phase B and phase C respectively, u a 、u b and u c are the voltages of phase A, phase B, and phase C respectively. DSOGI-PLL (Dual Second-Order Generalized Integrator PLL) is a dual second-order generalized integrator phase-locked loop. PLL The output phase angle, i a v and i c v After applying the two-phase VPCR technique, a and i c Multiply by the virtual phase current gain ka and k c The virtual A phase current and virtual C phase current obtained after that, i d v and i q v are the d-axis virtual current and q-axis virtual current obtained by coordinate transformation after the introduction of two-phase VPCR technology, and u d and u q are the d-axis voltage and q-axis virtual voltage respectively, i d * and i q * are the d-axis reference current and q-axis reference current of the current loop, ω is the grid angular velocity, PI is the proportional-integral controller, and PWM is the pulse width modulation.

[0174] The present invention provides a method for eliminating DC bus power fluctuations based on two-phase virtual phase current regulation (VPCR) technology, which improves the limitations of the existing single-phase VPCR technology on the DC side. Virtual phase current gains ① and ② are introduced in the voltage drop phase and the auxiliary phase respectively to achieve complete suppression of DC bus power fluctuations. The proposed suppression strategy better meets traditional engineering requirements.

[0175] Reference Figure 4 As shown in the figure, when the power grid is in an unbalanced state, the d-axis voltage of the power grid will fluctuate. If the three-phase grid-connected current is maintained in a balanced state and the d-axis current is maintained constant, the DC side power will inevitably fluctuate. If the single-phase VPCR technology is introduced, the three-phase current will be asymmetric and the d-axis current will fluctuate, then the DC side power fluctuation will be partially suppressed. If the two-phase VPCR technology is introduced, the asymmetry of the three-phase grid-connected current will be further aggravated, so that the fluctuation of the d-axis current and the fluctuation of the d-axis voltage will offset each other at the DC side power calculation level, thereby achieving complete smoothing of the DC side power fluctuation.

[0176] The present invention firstly conducts a theoretical analysis of the two-phase VPCR technology, establishes an overall model of DC bus power fluctuation introducing the two-phase VPCR technology, characterizes the influence of the grid operating conditions and the selection of the gain coefficient of the VPCR technology on the DC side power from a theoretical level, and provides theoretical support for the design of the VPCR technology gain coefficient; then, the power fluctuation optimization model is substituted into the particle swarm optimization algorithm to obtain the optimal solution of the appropriate auxiliary phase and virtual phase current gains ① and ②, so as to achieve the minimum and zero DC bus power fluctuation.

[0177] In the present invention, the two-phase VPCR technology maintains the constant power on the DC side by compensating the voltage drop phase and the current of the auxiliary phase of the three-phase grid-connected current. Taking the single-phase voltage drop of the three-phase three-wire L-type grid-connected inverter as an example, assuming that the voltage drop ratio of phase A is k drop, select the voltage drop phase A and the auxiliary phase C, and apply the two-phase VPCR technology to smooth the DC bus power fluctuation.

[0178] At this time, the three-phase voltage of the unbalanced power grid is:

[0179]

[0180] Where t is time and U is fundamental voltage.

[0181] Therefore, the dq axis voltage is:

[0182]

[0183] Reference Figure 3 As shown in the figure, the core of the two-phase VPCR technology is to change the input current in the control loop, thereby indirectly regulating the grid current. Therefore, when the voltage of phase A drops, the two-phase VPCR technology is applied to introduce virtual phase current gains k in the coordinate transformation module of phase A and phase C of the three-phase grid current. a and k c Since the VPCR technology does not change the current loop structure, the dq axis current reference value i d * and i q *Unchanged. If the zero-axis current in the control system is ignored, the virtual dq-axis current i obtained after the introduction of the two-phase VPCR technology is d v and i q v As the input of the current loop, it will track the reference current value without static error. At this time, the three-phase virtual current i in the control loop a v 、i b v and i c v It is still a three-phase balanced current, which is equivalent to amplifying the A-phase and C-phase currents in the three-phase current by 1 / k respectively. a and 1 / k c times, thereby compensating for the power drop and power fluctuation caused by voltage drop at the DC side power calculation level.

[0184] After the introduction of two-phase VPCR technology, if the zero-axis current in the control system is ignored, the three-phase grid-connected current is:

[0185]

[0186] In the formula, I 1 is the positive sequence current amplitude, is the initial phase of the current.

[0187] It can be seen that the three-phase grid-connected current presents a three-phase unbalanced state due to the introduction of the two-phase VPCR technology. There is a zero-sequence current component in the three-phase current after sequence decomposition, which is contrary to the principle that there is no zero-sequence current in the three-phase three-wire system. Therefore, the zero-axis current in the control loop cannot be ignored. Therefore, the dq0-axis current in the control loop is set to:

[0188]

[0189] 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 0 is the zero axis current amplitude, is the zero axis current phase.

[0190] At this time, the three-phase current in the control loop under the abc coordinates is:

[0191]

[0192] The three-phase grid-connected current is:

[0193]

[0194] According to the three-phase three-wire system does not contain zero-sequence current, i a +i b +i c =0, the zero axis current amplitude and phase can be obtained as

[0195]

[0196] Where sign(x) = x / |x|, x is a parameter expression, and:

[0197]

[0198] Therefore, the three-phase grid-connected current can be further expressed as:

[0199]

[0200] The dq axis grid-connected current is further obtained as:

[0201]

[0202] Since the active power on the AC side can be expressed as:

[0203]

[0204] The active power on the AC side can be solved as

[0205]

[0206] in

[0207]

[0208] Since the instantaneous active power fluctuation of the inverter system filter inductor will also be superimposed on the active power fluctuation on the AC side to cause DC bus power fluctuation, it is also crucial to analyze the power fluctuation on the filter.

[0209] First, take a single inductor as an example. Suppose the current flowing through the inductor L f The current is

[0210]

[0211] The voltage across the inductor is

[0212]

[0213] At this time, the instantaneous power on the inductor is

[0214]

[0215] The average power (i.e., active power) flowing through the inductor in a cycle is zero, but the power exchange between the inductor and the external circuit (i.e., reactive power) still exists, and the instantaneous power fluctuation on the inductor cannot be ignored. When the system is in a three-phase balanced state, the three-phase instantaneous power fluctuations on the filter inductor in the grid-connected inverter cancel each other out, and the sum is zero. However, when the system is in a three-phase unbalanced state, the introduction of the two-phase VPCR technology makes the three-phase current asymmetric, resulting in the inability of the three-phase instantaneous power fluctuations of the filter inductor to cancel each other out, causing the instantaneous power fluctuations on the filter inductor to still exist.

[0216] Calculate the filter inductance L f The three-phase voltage on is:

[0217]

[0218] 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;

[0219] The instantaneous power on the filter inductor can be solved:

[0220] p L =u La i a +u Lb i b +u Lc i c ;

[0221] The instantaneous power on the DC side consists of two parts: the instantaneous power on the AC side and the instantaneous power on the filter inductor, which can be expressed as:

[0222] p DC =p PCC +p L ;

[0223] The double frequency fluctuation component of the DC bus power is further obtained as

[0224]

[0225] Among them, PC 1 、PC 2 ,PS 1 and PS 2 is the coefficient of the expression of the double frequency fluctuation component of the DC bus power, expressed as follows:

[0226]

[0227] σ 1 and σ 2 For PC 1 、PC 2 ,PS 1 ,PS 2 The coefficients in the expression:

[0228]

[0229] Therefore, the amplitude of the DC side power fluctuation is

[0230]

[0231] From the DC bus power fluctuation model considering the two-phase VPCR technology, it can be seen that by adjusting the virtual phase current gain coefficient in the two-phase VPCR technology, the power fluctuation amplitude on the DC side can be greatly reduced, providing sufficient theoretical support for the effectiveness of the DC bus power fluctuation suppression method.

[0232] The particle swarm optimization algorithm (Particle Swarm Optimization Algorithm) is developed based on the research of group behaviors such as bird hunting. Such groups find food through cooperation, and each individual constantly changes its search mode according to its own memory and the memory of other members. Compared with other intelligent optimization algorithms, the particle swarm algorithm has fewer parameters to adjust and is easy to operate.

[0233] Reference Figure 5 As shown in Figure 1, first, a random particle swarm is initialized, and each particle has a random position and velocity. Secondly, the formula

[0234]

[0235] As the fitness function of the optimization algorithm, the power fluctuation amplitude of the 1st to i-th particles is calculated respectively. In the kth generation, each particle has its own memory of the best position, i.e., the individual best position pbest i k , compare the current fluctuation amplitude with the fluctuation amplitude of the individual best position, and retain the particle position with the smallest fluctuation amplitude as the new individual best position; then, since the entire particle group in each generation has a group minimum fluctuation amplitude, it is called the global best position gbest k , so in each iteration, the particle tracks the two extreme values ​​(pbest i k , gbest k ) to update its velocity v i k and position x i k Finally, when the DC side power fluctuation is zero, the algorithm terminates.

[0236] Since the search space is large, in order to achieve a balance between search speed and accuracy, the algorithm must have a strong global search capability in the early stage to obtain a suitable area, and a strong local search capability in the later stage to improve the convergence accuracy. Therefore, the present invention adopts the shrinkage factor method, and uses the shrinkage coefficient χ to control the convergence of the system, so that it can effectively search different areas. At this time, the particle speed update formula is:

[0237]

[0238]

[0239] Among them, the subscript i represents the i-th particle, the superscript k represents the k-th generation, and r 1 and r 2 is a random number uniformly distributed between [0, 1]. and are two learning factors, k is the number of iterations.

[0240] The particle position update formula is:

[0241]

[0242] In the process of solving the DC bus power fluctuation optimization model, the dimension of the particles is consistent with the number of virtual phase current gains introduced in the two-phase VPCR technology. Since the virtual phase current gain k is introduced by selecting phase A and phase C in the system, a and k c, so the dimension of the particle is 2. In the two-dimensional search space, the vector sets of each particle’s velocity and position are V i =[v i1 , v i2 ], X i =[x i1 , x i2 The two dimensions x of the particle position i1 Corresponding virtual phase current gain k a , x i2 Corresponding virtual phase current gain k c The constraints of the two dimensions of the position are consistent with the range of the voltage drop ratio, which is limited to [0, 1]. In the kth generation, the individual best position set of particle i is pbest i k =[x i1 pbest , x i2 pbest ]; in the kth generation, the global best position set of particles is gbest k =[x 1 gbest , x 2 gbest After the iteration is completed, the two dimensions of the global optimal position of the particle correspond to k in the two-phase VPCR technique. a and k c to ensure complete suppression of DC bus power fluctuations.

[0243] The control strategy proposed in the present invention is based on the single-phase VPCR technology. It selects one of the three phases without voltage drop as an auxiliary compensation phase. By adjusting the feedback current in the control loop, the DC side power is guaranteed to be constant under the unbalanced power grid. In addition, the present invention uses the particle swarm optimization algorithm to optimize the two-phase virtual phase current gain coefficient, and proves from a theoretical level that the two-phase VPCR technology can minimize and zero the power fluctuation on the DC side, meet the needs of traditional engineering, and improve the design drawbacks of the gain coefficient of the single-phase VPCR technology.

[0244] 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.

[0245] Example 1

[0246] In this embodiment, the DC side voltage of the grid-connected inverter is 700V, and the filter inductor L in the L-type filter is f is 1.3mH, the grid fundamental voltage amplitude U is 311V, and the grid fundamental frequency f 1 is 50Hz, and the reference current i of the current loop d axis in the control loop d* is 60A, the current loop q axis reference current i q *For -30A, the proportional gain of the current loop PI controller is K p is 16.3, the integral gain K of the PI controller i It is 20426.9.

[0247] The following example assumes that the A phase voltage of the power grid drops and the drop ratio is k drop Take 0.6 as an example for simulation verification.

[0248] Reference Figure 6 and Figure 7 As shown in Figure 1, when the two-phase VPCR technology is not introduced into the system, the DC side power fluctuates greatly under the condition of unbalanced power grid. The existing single-phase VPCR technology only introduces a virtual phase current gain k in the phase A where the voltage drops. a , and take k a =k drop , in this system, take k a =0.6. It can be seen that although the active power fluctuation on the AC side is completely eliminated, the power fluctuation on the DC side still exists.

[0249] The two-phase VPCR technology is applied in the grid-connected inverter, and a virtual phase current gain k is introduced in the phase A where the voltage drops. a The auxiliary phase C introduces a virtual phase current gain k c is 0.9227. At this time, the three-phase grid-connected current is given by the formula

[0250]

[0251] The corresponding theoretical value is calculated as:

[0252]

[0253] Reference Figure 8 As shown, the dotted line represents the theoretical current waveform, and the solid line represents the simulated current waveform. It can be seen that the simulated and theoretical current waveforms are completely consistent, which further verifies the reliability of the theoretical modeling of the two-phase VPCR technology proposed in the present invention.

[0254] Reference Fig. 9 As shown, after the two-phase VPCR technology is introduced, it can be seen that the power fluctuation on the DC bus has been completely eliminated, and the effectiveness of the suppression method proposed in this embodiment is verified.

[0255] The method for eliminating DC bus power fluctuation based on two-phase VPCR technology proposed in this embodiment establishes a DC bus power fluctuation model considering two-phase VPCR technology, and designs the virtual phase current gain coefficient of two-phase VPVR technology in combination with particle swarm optimization algorithm, thereby ensuring the constant power on the DC side under unbalanced power grid. This embodiment provides a new idea for the design of DC bus power fluctuation suppression strategy.

[0256] The present invention also provides a power fluctuation suppression system based on two-phase virtual phase current regulation. The power fluctuation suppression system based on two-phase virtual phase current regulation can be realized by executing the process steps of the power fluctuation suppression method based on two-phase virtual phase current regulation, that is, those skilled in the art can understand the power fluctuation suppression method based on two-phase virtual phase current regulation as a preferred implementation of the power fluctuation suppression system based on two-phase virtual phase current regulation.

[0257] Specifically, a power fluctuation suppression system based on two-phase virtual phase current regulation includes:

[0258] Module M1: Constructing grid-connected current model and DC bus power fluctuation model;

[0259] The grid-connected current model introduces a two-phase virtual phase current control technology;

[0260] The DC bus power fluctuation model corresponds to the grid-connected current model;

[0261] Module M2: Optimize the DC bus power fluctuation model;

[0262] Module M3: Solve the optimized DC bus power fluctuation model to completely suppress the power fluctuation.

[0263] Preferably, the two-phase virtual phase current control technology compensates for the voltage drop phase and the current of the auxiliary phase of the three-phase grid-connected current to maintain the constant power on the DC side, and the two-phase virtual phase current control technology can be applied to the scenario when a single-phase voltage drop occurs in a three-phase three-wire L-type grid-connected inverter.

[0264] Preferably, in the scenario where a single-phase voltage drop occurs in the three-phase three-wire L-type grid-connected inverter, i a 、i b and i c are the currents of phase A, phase B and phase C respectively, u a 、u b and u c are the voltages of phase A, phase B and phase C respectively; i a v and i c v After applying the two-phase VPCR technique,a and i c Multiply by the virtual phase current gain k a and k c The virtual A phase current and virtual C phase current obtained after that, i d v and i q v are the d-axis virtual current and q-axis virtual current obtained by coordinate transformation after the introduction of two-phase virtual phase current control technology, and u d and u q are the d-axis voltage and q-axis virtual voltage respectively, i d * and i q * are the d-axis reference current and q-axis reference current of the current loop, and ω is the angular velocity of the power grid;

[0265] Assume the voltage drop ratio of phase A is k drop , select the voltage drop phase A and the auxiliary phase C, the three-phase voltage of the unbalanced power grid is:

[0266]

[0267] In the formula, t is time, U is fundamental voltage;

[0268] Therefore, the voltage of the virtual axis dq is:

[0269]

[0270] When the voltage of phase A drops, based on the two-phase virtual phase current control technology, the virtual phase current gain k is introduced into the A phase and C phase of the three-phase grid-connected current coordinate transformation module. a and k c The two-phase virtual phase current control technology does not change the current loop structure, so the reference value of the virtual axis dq current i d * and i q * unchanged; if the zero-axis current in the control system is ignored, the virtual axis dq current i obtained by introducing the two-phase virtual phase current control technology is d v and i q v As the input of the current loop, it will track the reference current value without static error, and the virtual current i of phase A, phase B and phase C in the control loop a v 、i b v and i c v It is still a three-phase balanced current. The A-phase and C-phase currents in the three-phase current are amplified by 1 / k a and 1 / k ctimes, compensating for the power drop and power fluctuation caused by voltage drop at the DC side power calculation level.

[0271] Preferably, after the two-phase virtual phase current control technology is introduced, if the zero-axis current in the control system is ignored, the three-phase grid-connected current is:

[0272]

[0273] In the formula, I 1 is the positive sequence current amplitude, is the initial phase of the current;

[0274] The three-phase grid-connected current presents a three-phase unbalanced state due to the introduction of two-phase virtual phase current control technology. After sequence decomposition, it is found that there is a zero-sequence current component in the three-phase current, which is contrary to the principle that there is no zero-sequence current in the three-phase three-wire system. Therefore, the zero-axis current in the control loop cannot be ignored. Assume that the dq0 current in the control loop is:

[0275]

[0276] 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 0 is the zero axis current amplitude, is the zero axis current phase;

[0277] At this time, the three-phase current in the control loop under the abc coordinates is:

[0278]

[0279] The three-phase grid-connected current is:

[0280]

[0281] According to the three-phase three-wire system does not contain zero-sequence current, i a +i b +i c =0, the zero axis current amplitude and phase are obtained as

[0282]

[0283] Where sign(x) = x / |x|, x is a parameter expression, and:

[0284]

[0285] The three-phase grid-connected current is further expressed as:

[0286]

[0287] The dq axis grid-connected current is:

[0288]

[0289] AC side active power p PCC It is expressed as:

[0290]

[0291] Solve to get the AC side active power p PCC for:

[0292]

[0293] in,

[0294]

[0295] Assume that the current flowing through a single inductor L f The current is

[0296]

[0297] Voltage across the inductor u L for

[0298]

[0299] At this time, the instantaneous power p on the inductor is L for

[0300]

[0301] Calculate the filter inductance L f The three-phase voltage on is:

[0302]

[0303] 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;

[0304] Solve for the instantaneous power p on the filter inductor L :

[0305] p L =u La i a +u Lb i b +u Lc i c ;

[0306] The instantaneous power p on the DC side DC From the AC sidePCC and the instantaneous power p on the filter inductor L It consists of two parts:

[0307] p DC =p PCC +p L ;

[0308] The double frequency fluctuation component of the DC bus power is obtained as

[0309]

[0310] Among them, PC 1 、PC 2 ,PS 1 and PS 2 is the coefficient of the expression of the double frequency fluctuation component of the DC bus power, expressed as follows:

[0311]

[0312] σ 1 and σ 2 For PC 1 、PC 2 ,PS 1 ,PS 2 The coefficients in the expression:

[0313]

[0314] The amplitude of the DC side power fluctuation is

[0315]

[0316] The virtual phase current gain coefficient in the two-phase virtual phase current control technology is adjusted to reduce the power fluctuation amplitude on the DC side.

[0317] Preferably, the DC bus power fluctuation model is optimized and solved based on a particle swarm optimization algorithm; the particle swarm optimization algorithm includes initializing a random particle swarm, each particle having a random position and speed;

[0318]

[0319] As the fitness function of the optimization algorithm, the power fluctuation amplitudes of the 1st to i-th particles are calculated respectively; in the kth generation, each particle has its own memory of the best position, that is, the individual best position pbest i k ; Compare the current fluctuation amplitude with the fluctuation amplitude of the individual best position, and retain the particle position with the smallest fluctuation amplitude as the new individual best position; In each generation, the entire particle group has a group minimum fluctuation amplitude, which is called the global best position gbestk In each iteration, the particle tracks two extreme values ​​(pbest i k , gbest k ) to update its velocity v i k and position x i k , when the DC side power fluctuation is zero, the algorithm terminates.

[0320] Preferably, the particle swarm optimization algorithm adopts a shrinkage factor method, using the shrinkage coefficient χ to control the convergence of the system to search different areas, and the particle speed update formula is:

[0321]

[0322]

[0323] Where, the subscript i represents the i-th particle, the superscript k represents the k-th generation, and r 1 and r 2 is a random number uniformly distributed between [0, 1]. and are two learning factors, k is the number of iterations;

[0324] The particle position update formula is:

[0325]

[0326] In the process of solving the DC bus power fluctuation optimization model, the dimension of the particles is consistent with the number of virtual phase current gains introduced in the two-phase virtual phase current control technology; the virtual phase current gain k is introduced by selecting phase A and phase C in the system respectively. a and k c , then the dimension of the particle is 2; in the two-dimensional search space, the vector sets of the velocity and position of each particle are V i =[v i1 , v i2 ], X i =[x i1 , x i2 ]; the two dimensions x of the particle position i1 Corresponding virtual phase current gain k a , x i2 Corresponding virtual phase current gain k c The constraints of the two dimensions of the position are consistent with the range of the voltage drop ratio, which is limited to [0, 1]. In the kth generation, the individual best position set of particle i is pbest i k =[x i1pbest , x i2 pbest ]; in the kth generation, the global best position set of particles is gbest k =[x 1 gbest , x 2 gbest ].

[0327] Preferably, after the kth generation iteration is completed, the two dimensions of the global optimal position of the particle correspond to the k in the two-phase virtual phase current control technology. a and k c The optimal value of DC bus power fluctuation is completely suppressed.

[0328] Preferably, the two-phase virtual phase current control technology changes the input current in the control loop to indirectly control the grid-connected current.

[0329] 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.

[0330] 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 fluctuation suppression method based on two-phase virtual phase current regulation, It is characterized in that include: Step S1: constructing a grid-connected current model and a DC bus power fluctuation model; The grid-connected current model introduces a two-phase virtual phase current control technology; The DC bus power fluctuation model corresponds to the grid-connected current model; Step S2: Optimizing the DC bus power fluctuation model; Step S3: Solve the optimized DC bus power fluctuation model to completely suppress the power fluctuation.

2. According to claim 1, a method for suppressing power fluctuations based on two-phase virtual phase current regulation, It is characterized in that The two-phase virtual phase current control technology compensates for the voltage drop phase and the current of the auxiliary phase of the three-phase grid-connected current to maintain the constant power on the DC side, and the two-phase virtual phase current control technology can be applied to the scenario when a single-phase voltage drop occurs in a three-phase three-wire L-type grid-connected inverter.

3. A method for suppressing power fluctuations based on two-phase virtual phase current regulation according to claim 2, It is characterized in that In the scenario where a single-phase voltage drop occurs in the three-phase three-wire L-type grid-connected inverter, i a 、i b and i c are the currents of phase A, phase B and phase C respectively, u a 、u b and u c are the voltages of phase A, phase B and phase C respectively; i a v and i c v After applying the two-phase VPCR technique, a and i c Multiply by the virtual phase current gain k a and k c The virtual A phase current and virtual C phase current obtained after that, i d v and i q v are the d-axis virtual current and q-axis virtual current obtained by coordinate transformation after the introduction of two-phase virtual phase current control technology, and u d and u q are the d-axis voltage and q-axis virtual voltage respectively, i d * and i q * are the d-axis reference current and q-axis reference current of the current loop, ω is the angular velocity of the power grid; Assume the voltage drop ratio of phase A is k drop , select the voltage drop phase A and the auxiliary phase C, the three-phase voltage of the unbalanced power grid is: In the formula, t is time, U is fundamental voltage; Therefore, the voltage of the virtual axis dq is: When the voltage of phase A drops, based on the two-phase virtual phase current control technology, the virtual phase current gain k is introduced into the A phase and C phase of the three-phase grid-connected current coordinate transformation module. a and k c The two-phase virtual phase current control technology does not change the current loop structure, so the reference value of the virtual axis dq current i d * and i q * unchanged; if the zero-axis current in the control system is ignored, the virtual axis dq current i obtained by introducing the two-phase virtual phase current control technology is d v and i q v As the input of the current loop, it will track the reference current value without static error, and the virtual current i of phase A, phase B and phase C in the control loop a v 、i b v and i c v It is still a three-phase balanced current. The A-phase and C-phase currents in the three-phase current are amplified by 1 / k a and 1 / k c times, compensating for the power drop and power fluctuation caused by voltage drop at the DC side power calculation level.

4. A method for suppressing power fluctuations based on two-phase virtual phase current regulation according to claim 3, It is characterized in that After the two-phase virtual phase current control technology is introduced, if the zero-axis current in the control system is ignored, the three-phase grid-connected current is: In the formula, I 1 is the positive sequence current amplitude, is the initial phase of the current; The three-phase grid-connected current presents a three-phase unbalanced state due to the introduction of two-phase virtual phase current control technology. After sequence decomposition, it is found that there is a zero-sequence current component in the three-phase current, which is contrary to the principle that there is no zero-sequence current in the three-phase three-wire system. Therefore, the zero-axis current in the control loop cannot be ignored. Assume that the dq0 current in the control loop is: 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 0 is the zero axis current amplitude, is the zero axis current phase; At this time, the three-phase current in the control loop under the abc coordinates is: The three-phase grid-connected current is: According to the three-phase three-wire system does not contain zero-sequence current, i a +i b +i c =0, the zero axis current amplitude and phase are obtained as Where sign(x) = x / |x|, x is a parameter expression, and: The three-phase grid-connected current is further expressed as: The dq axis grid-connected current is: AC side active power p PCC It is expressed as: Solve to get the AC side active power p PCC for: in, Assume that the current flowing through a single inductor L f The current is Voltage across the inductor u L for At this time, the instantaneous power p on the inductor is L for Calculate the filter inductance L f The three-phase voltage on 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; Solve for the instantaneous power p on the filter inductor L : p L =in La and a +in Lb and b +in Lc and c ; The instantaneous power p on the DC side DC From the AC side PCC and the instantaneous power p on the filter inductor L It consists of two parts: p DC =p PCC +p L ; The double frequency fluctuation component of the DC bus power is obtained as Among them, PC 1 、PC 2 ,PS 1 and PS 2 is the coefficient of the expression of the double frequency fluctuation component of the DC bus power, expressed as follows: σ 1 and σ 2 For PC 1 、PC 2 ,PS 1 ,PS 2 The coefficients in the expression: The amplitude of the DC side power fluctuation is The virtual phase current gain coefficient in the two-phase virtual phase current control technology is adjusted to reduce the power fluctuation amplitude on the DC side.

5. A method for suppressing power fluctuations based on two-phase virtual phase current regulation according to claim 1, It is characterized in that The DC bus power fluctuation model is optimized and solved based on a particle swarm optimization algorithm; the particle swarm optimization algorithm includes initializing a random particle swarm, each particle having a random position and speed; As the fitness function of the optimization algorithm, the power fluctuation amplitudes of the 1st to i-th particles are calculated respectively; in the kth generation, each particle has its own memory of the best position, that is, the individual best position pbest i k ; Compare the current fluctuation amplitude with the fluctuation amplitude of the individual best position, and retain the particle position with the smallest fluctuation amplitude as the new individual best position; In each generation, the entire particle group has a group minimum fluctuation amplitude, which is called the global best position gbest k In each iteration, the particle tracks two extreme values ​​(pbest i k , gbest k ) to update its velocity v i k and position x i k , when the DC side power fluctuation is zero, the algorithm terminates.

6. A method for suppressing power fluctuations based on two-phase virtual phase current regulation according to claim 5, It is characterized in that The particle swarm optimization algorithm adopts the shrinkage factor method, and uses the shrinkage coefficient χ to control the convergence of the system to search different areas, and the particle speed update formula is: Among them, the subscript i represents the i-th particle, the superscript k represents the k-th generation, and r 1 and r 2 is a random number uniformly distributed between [0, 1]. and are two learning factors, k is the number of iterations; The particle position update formula is: In the process of solving the DC bus power fluctuation optimization model, the dimension of the particles is consistent with the number of virtual phase current gains introduced in the two-phase virtual phase current control technology; the virtual phase current gain k is introduced by selecting phase A and phase C in the system respectively. a and k c , then the dimension of the particle is 2; in the two-dimensional search space, the vector sets of the velocity and position of each particle are V i =[v i1 , v i2 ], X i =[x i1 , x i2 ]; the two dimensions x of the particle position i1 Corresponding virtual phase current gain k a , x i2 Corresponding virtual phase current gain k c The constraints of the two dimensions of the position are consistent with the range of the voltage drop ratio, which is limited to [0, 1]. In the kth generation, the individual best position set of particle i is pbest i k =[x i1 pbest , x i2 pbest ]; in the kth generation, the global best position set of particles is gbest k =[x 1 gbest , x 2 gbest ].

7. A method for suppressing power fluctuations based on two-phase virtual phase current regulation according to claim 6, It is characterized in that After the kth generation iteration is completed, the two dimensions of the global optimal position of the particle correspond to k in the two-phase virtual phase current control technology. a and k c The optimal value of DC bus power fluctuation is completely suppressed.

8. A method for suppressing power fluctuations based on two-phase virtual phase current regulation according to claim 2, It is characterized in that The two-phase virtual phase current control technology changes the input current in the control loop to indirectly control the grid-connected current.

9. A power fluctuation suppression system based on two-phase virtual phase current regulation, It is characterized in that include: Module M1: Constructing grid-connected current model and DC bus power fluctuation model; The grid-connected current model introduces a two-phase virtual phase current control technology; The DC bus power fluctuation model corresponds to the grid-connected current model; Module M2: Optimize the DC bus power fluctuation model; Module M3: Solve the optimized DC bus power fluctuation model to completely suppress the power fluctuation.

10. A power fluctuation suppression system based on two-phase virtual phase current regulation according to claim 9, It is characterized in that The two-phase virtual phase current control technology compensates for the voltage drop phase and the current of the auxiliary phase of the three-phase grid-connected current to maintain the constant power on the DC side, and the two-phase virtual phase current control technology can be applied to the scenario when a single-phase voltage drop occurs in a three-phase three-wire L-type grid-connected inverter.

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