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

Abstract

The application provides a power fluctuation suppression method and system based on two-phase virtual phase current regulation, comprising the following steps: S1, constructing a grid-connected current model and a DC bus power fluctuation model; the grid-connected current model introduces two-phase virtual phase current regulation technology; the DC bus power fluctuation model corresponds to the grid-connected current model; S2, optimizing the DC bus power fluctuation model; S3, solving the optimized DC bus power fluctuation model to complete complete suppression of power fluctuation. On the basis of single-phase VPCR technology, one phase of three phases that does not occur voltage drop is additionally selected as an auxiliary compensation phase, and the two-phase virtual phase current gain coefficient is optimized and calculated through a particle swarm optimization algorithm, so that it is theoretically proved that the two-phase VPCR technology can minimize and be zero for DC side power fluctuation, meets the needs of traditional engineering, and improves the design drawbacks of the gain coefficient of the single-phase VPCR technology.

Description

Technical Field

[0001] This invention relates to the field of alternating current, and more specifically, to a power fluctuation suppression method and system based on two-phase virtual phase current regulation. Background Technology

[0002] With the construction of a new power system based on new energy sources, grid-connected inverters, as the bridge for energy transmission between new energy power generation systems and the AC power grid, play a decisive role in the safe and reliable operation of the overall power system due to their stable power transmission capabilities. However, in actual power grid operation, factors such as asymmetrical faults and asymmetrical loads can lead to an unbalanced state in the grid, thereby affecting the inverter's output power and grid-connected current quality.

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

[0004] Virtual phase-current regulation (VPCR) technology suppresses AC-side active power fluctuations by compensating the three-phase grid-connected current feedback loop at the control level. Existing VPCR technologies only introduce virtual phase current gain in the voltage dip phase; therefore, they are referred to as single-phase VPCR technologies. Currently, existing single-phase VPCR technologies only increase the virtual phase current gain in the voltage dip phase, which can reduce DC-side power fluctuations to some extent, but its effectiveness is limited and cannot completely eliminate DC-side power fluctuations. Furthermore, existing VPCR technologies are relatively crude in their virtual phase current gain coefficient design, only selecting the voltage dip ratio as the virtual phase current gain, and do not fully utilize the single-phase VPCR technology's ability to suppress DC-side power fluctuations.

[0005] Existing power fluctuation suppression strategies often suppress AC-side active power fluctuations by adjusting the reference current in the current loop of the control strategy, thereby reducing DC bus power fluctuations. However, this suppression method often increases the complexity of the control loop, reduces the dynamic response speed of the system, and the change in the control loop renders existing control parameter design methods unsuitable for new systems, increasing the difficulty of system parameter tuning. Compared with the above suppression strategies, existing single-phase VPCR technology weakens AC-side active power fluctuations and DC-side power fluctuations by adjusting the feedback current in the control strategy without changing the current loop structure. The control structure is simpler, and it can effectively eliminate AC-side active power fluctuations. However, single-phase VPCR technology only compensates for the current corresponding to the voltage drop, and its ability to suppress DC bus power fluctuations is still limited, reducing but not completely eliminating DC bus power fluctuations.

[0006] Jin Peng, Ai Xin, Sun Yingyun, Zhou Shupeng. Optimization Design of PQ Control Strategy for Microgrids to Suppress Power Ripple [J]. Automation of Electric Power Systems, 2013, 37(13):30-35+131. This paper is based on a PQ control structure with dual current controllers. It establishes the expression of the power ripple amplitude of active and reactive power through optimization theory, and then obtains the optimal positive and negative sequence current setpoints. The paper first analyzes the operating state of the three-phase inverter under unbalanced voltage conditions and explores the influence of active and reactive power ripple on the inverter output power. Secondly, it uses optimization theory to solve for the optimal reference value of the current in the current loop to minimize the power ripple amplitude of active and reactive power. Finally, it gives the corresponding control structure and positive and negative sequence sampling method and completes simulation verification. 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 design difficulty of control parameters. In addition, the sampling delay and coupling effect of positive and negative sequence current will interfere with the accuracy of the reference current calculation and reduce the suppression effect of power ripple. This paper addresses DC-side voltage fluctuations by suppressing active power ripples. However, even when AC-side power ripples are zero, DC-side power and voltage fluctuations cannot be completely eliminated. The optimization theory used in this paper is based on the Lagrange multiplier method, obtaining the optimal current value by taking the partial derivative of the objective function. However, this optimization method is only applicable to convex optimization problems. When changes in circuit structure increase the complexity of the objective function, the solution becomes difficult and its applicability is limited. In contrast, this invention does not require changes to the control structure of the vector current loop or an additional PI controller. It only modifies the feedback current in the control loop, using the DC bus power fluctuation amplitude as the direct optimization objective, ensuring complete suppression of DC-side power ripples. Furthermore, this invention uses a metaheuristic algorithm to solve the optimization model, resulting in a simple solution with good convergence and strong generalizability. The two-phase VPCR DC bus power fluctuation suppression technology and its coefficient design method proposed in this invention can quickly design the virtual phase current gain coefficient under different grid imbalance conditions, realize the complete elimination of DC bus power fluctuation, and provide theoretical support for predicting the impact of grid voltage drop on DC bus power. It also provides a brand-new power fluctuation suppression strategy for DC bus power smoothing in three-phase three-wire grid-connected inverters.

[0007] Chinese patent document CN114006388A discloses a grid-connected power generation system and its grid-connected power fluctuation suppression device and method. 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 connected to the DC side of the inverter; and a power distribution unit connected to both the second DC source and the inverter. The power distribution unit is used to obtain the power setpoint and power feedback value of the first DC source, calculate the AC power setpoint and the power setpoint of the second DC source based on these values, and control the inverter and the second DC source using the AC power setpoint and the power setpoint of the second DC source. However, this patent document still uses single-phase VPCR technology, while this invention, based on single-phase VPCR technology, additionally selects one phase from the three phases where no voltage drop occurs as an auxiliary compensation phase, which is fundamentally different from the technology and method used in this patent document. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the purpose of this invention is to provide a power fluctuation suppression method and system based on two-phase virtual phase current regulation.

[0009] A power fluctuation suppression method based on two-phase virtual phase current regulation according to the present invention includes:

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

[0011] The grid-connected current model incorporates two-phase virtual phase current regulation technology;

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

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

[0014] Step S3: Solve the optimized DC bus power fluctuation model to achieve complete suppression of power fluctuations.

[0015] Preferably, the two-phase virtual phase current regulation technology compensates for the voltage drop phase and the current of the auxiliary phase in the three-phase grid-connected current to maintain constant DC power, and the two-phase virtual phase current regulation 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 These represent the currents of phases A, B, and C, respectively, ua u b and u c These are the voltages of phases A, B, and C, respectively; i a v and i c v i after applying two-phase VPCR technology 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 afterwards, i d v and i q v These are the d-axis virtual current and q-axis virtual current obtained by coordinate transformation of the three-phase grid-connected current after introducing two-phase virtual phase current regulation technology, and u. d and u q These are the d-axis voltage and the q-axis virtual voltage, respectively. d * and i q *Represents the d-axis reference current and q-axis reference current of the current loop, respectively, and ω is the grid angular velocity;

[0017] Let the voltage drop ratio of phase A be k. drop Selecting phase A (voltage drop) and phase C (auxiliary phase), the three-phase voltages of the unbalanced power grid are:

[0018]

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

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

[0021]

[0022] When a voltage drop occurs in phase A, based on two-phase virtual phase current regulation technology, a virtual phase current gain k is introduced into phases A and C of the three-phase grid-connected current coordinate transformation module, respectively. a and k c The two-phase virtual phase current regulation technology does not change the current loop structure, so the reference value i of the virtual axis dq current is... d * and i q *Unchanged; if the zero-axis current in the control system is ignored, the virtual axis dq current i obtained after introducing the two-phase virtual phase current regulation technology is... d v and i q v As the input to the current loop, it will track the reference current value without steady-state error, and the virtual currents i of phases A, B, and C in the control loop will... 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 respectively. a and 1 / k c This compensates for the power drop and power fluctuation caused by voltage dips at the DC-side power calculation level.

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

[0024]

[0025] In the formula, I1 is the positive sequence current amplitude. The initial phase of the current;

[0026] Due to the introduction of two-phase virtual phase current control technology, the three-phase grid-connected current exhibits a three-phase unbalanced state. Sequence decomposition reveals that the three-phase current contains a zero-sequence current component, which contradicts the principle that zero-sequence current does not exist in a three-phase three-wire system. Therefore, the zero-axis current in the control loop cannot be ignored. Let the dq0 current in the control loop be:

[0027]

[0028] In the formula, i d Let i be the d-axis current. q Let i be the q-axis current, i0 be the zero-axis current, and I0 be the zero-axis current amplitude. The zero-axis current phase;

[0029] At this point, the three-phase currents in the control loop under the abc coordinate system are:

[0030]

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

[0032]

[0033] According to the fact that a three-phase three-wire system does not contain zero-sequence current, i a +i b +i c =0, find the amplitude and phase of the zero-axis current.

[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 grid-connected current of the dq axis is:

[0040]

[0041] AC side active power p PCC Represented as:

[0042]

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

[0044]

[0045] in,

[0046]

[0047] Let the current flow through a single inductor L f The current is

[0048]

[0049] Voltage u across the inductor L for

[0050]

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

[0052]

[0053] Find the filter inductance L f The three-phase voltages are:

[0054]

[0055] In the formula, u La u Lb u Lc These are the voltages across phases A, B, and C of the filter inductor, respectively.

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

[0057] p L =u La i a +u Lb i b +uLc i c ;

[0058] Instantaneous power p on the DC side DC From the AC side p 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 second harmonic ripple component of the DC bus power is calculated as follows:

[0061]

[0062] Where PC1, PC2, PS1, and PS2 are the coefficients of the second harmonic ripple component expression of the DC bus power, expressed as follows:

[0063]

[0064] σ1 and σ2 are the coefficients in the expressions for PC1, PC2, PS1, and PS2:

[0065]

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

[0067]

[0068] Adjusting the virtual phase current gain coefficient in the two-phase virtual phase current regulation technology reduces the DC-side power fluctuation amplitude.

[0069] Preferably, the DC bus power fluctuation model is optimized using a particle swarm optimization algorithm; the particle swarm optimization algorithm includes initializing a random particle swarm, where each particle has a random position and velocity; and...

[0070]

[0071] As the fitness function of the optimization algorithm, the power fluctuation amplitude of particles from the 1st to the i-th generation is calculated respectively; in the k-th generation, each particle has its own memory of its best position, i.e., its individual best position pbest. i k The current fluctuation amplitude is compared with the fluctuation amplitude of the individual's best position, and the position of the particle with the smallest fluctuation amplitude is retained as the new individual best position. In each generation, the entire particle swarm has a minimum fluctuation amplitude, called the global best position gbest. k In each iteration, the particle tracks two extreme values ​​(pbest).i k gbest k To update its speed v i k and position x i k The algorithm terminates when the DC-side power fluctuation is zero.

[0072] Preferably, the particle swarm optimization algorithm employs the contraction factor method, using the contraction coefficient χ to control the convergence of the system and search different regions, and the particle velocity update formula is:

[0073]

[0074]

[0075] Where the subscript i represents the i-th particle, the superscript k represents the k-th generation, and r1 and r2 are random numbers uniformly distributed between [0, 1]. and There are two learning factors. k is the number of iterations;

[0076] The particle position update formula is:

[0077]

[0078] In solving the DC bus power fluctuation optimization model, the dimension of the particles is kept consistent with the number of virtual phase current gains introduced in the two-phase virtual phase current control technology; virtual phase current gains k are introduced into phases A and C in the system respectively. a and k c If the particle dimension is 2, then the vector set of velocity and position for each particle in the two-dimensional search space is V. i =[v i1 v i2 ], X i =[x i1 x i2 ]; The two dimensions of the particle's position x i1 Corresponding virtual phase current gain k a x i2 Corresponding virtual phase current gain k c The constraints on the two dimensions of the position are consistent with the range of the voltage drop ratio, restricted to [0, 1]; in the kth generation, the set of optimal individual positions for particle i is pbest. i k =[x i1 pbest x i2 pbestIn the kth generation, the set of the global best positions for the particles is gbest. k =[x1 gbest x2 gbest ].

[0079] Preferably, after the k-th iteration, the two dimensions of the particle's global optimal position correspond to k in the two-phase virtual phase current control technology. a and k c The optimal value is obtained, which completely suppresses DC bus power fluctuations.

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

[0081] A power fluctuation suppression system based on two-phase virtual phase current regulation, according to the present invention, comprises:

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

[0083] The grid-connected current model incorporates two-phase virtual phase current regulation technology;

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

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

[0086] Module M3: Solve the optimized DC bus power fluctuation model to achieve complete suppression of power fluctuations.

[0087] Preferably, the two-phase virtual phase current regulation technology compensates for the voltage drop phase and the current of the auxiliary phase in the three-phase grid-connected current to maintain constant DC power, and the two-phase virtual phase current regulation 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 These represent the currents of phases A, B, and C, respectively, u a u b and u c These are the voltages of phases A, B, and C, respectively; i a v and i c v i after applying two-phase VPCR technology a and i c Multiply by the virtual phase current gain k a and k cThe virtual A-phase current and virtual C-phase current obtained afterwards, i d v and i q v These are the d-axis virtual current and q-axis virtual current obtained by coordinate transformation of the three-phase grid-connected current after introducing two-phase virtual phase current regulation technology, and u. d and u q These are the d-axis voltage and the q-axis virtual voltage, respectively. d * and i q *Represents the d-axis reference current and q-axis reference current of the current loop, respectively, and ω is the grid angular velocity;

[0089] Let the voltage drop ratio of phase A be k. drop Selecting phase A (voltage drop) and phase C (auxiliary phase), the three-phase voltages of the unbalanced power grid are:

[0090]

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

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

[0093]

[0094] When a voltage drop occurs in phase A, based on two-phase virtual phase current regulation technology, a virtual phase current gain k is introduced into phases A and C of the three-phase grid-connected current coordinate transformation module, respectively. a and k c The two-phase virtual phase current regulation technology does not change the current loop structure, so the reference value i of the virtual axis dq current is... d * and i q *Unchanged; if the zero-axis current in the control system is ignored, the virtual axis dq current i obtained after introducing the two-phase virtual phase current regulation technology is... d v and i q v As the input to the current loop, it will track the reference current value without steady-state error, and the virtual currents i of phases A, B, and C in the control loop will... 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 respectively. a and 1 / k c This compensates for the power drop and power fluctuation caused by voltage dips at the DC-side power calculation level.

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

[0096]

[0097] In the formula, I1 is the positive sequence current amplitude. The initial phase of the current;

[0098] Due to the introduction of two-phase virtual phase current control technology, the three-phase grid-connected current exhibits a three-phase unbalanced state. Sequence decomposition reveals that the three-phase current contains a zero-sequence current component, which contradicts the principle that zero-sequence current does not exist in a three-phase three-wire system. Therefore, the zero-axis current in the control loop cannot be ignored. Let the dq0 current in the control loop be:

[0099]

[0100] In the formula, i d Let i be the d-axis current. q Let i be the q-axis current, i0 be the zero-axis current, and I0 be the zero-axis current amplitude. The zero-axis current phase;

[0101] At this point, the three-phase currents in the control loop under the abc coordinate system are:

[0102]

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

[0104]

[0105] According to the fact that a three-phase three-wire system does not contain zero-sequence current, i a +i b +i c =0, find the amplitude and phase of the zero-axis current.

[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 grid-connected current of the dq axis is:

[0112]

[0113] AC side active power pPCC Represented as:

[0114]

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

[0116]

[0117] in,

[0118]

[0119] Let the current flow through a single inductor L f The current is

[0120]

[0121] Voltage u across the inductor L for

[0122]

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

[0124]

[0125] Find the filter inductance L f The three-phase voltages are:

[0126]

[0127] In the formula, u La u Lb u Lc These are the voltages across phases A, B, and C of the filter inductor, 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] Instantaneous power p on the DC side DC From the AC side p PCC and the instantaneous power p on the filter inductor L It consists of two parts:

[0131] p DC =p PCC +pL ;

[0132] The second harmonic ripple component of the DC bus power is calculated as follows:

[0133]

[0134] Where PC1, PC2, PS1, and PS2 are the coefficients of the second harmonic ripple component expression of the DC bus power, expressed as follows:

[0135]

[0136] σ1 and σ2 are the coefficients in the expressions for PC1, PC2, PS1, and PS2:

[0137]

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

[0139]

[0140] Adjusting the virtual phase current gain coefficient in the two-phase virtual phase current regulation technology reduces the DC-side power fluctuation amplitude.

[0141] Preferably, the DC bus power fluctuation model is optimized using a particle swarm optimization algorithm; the particle swarm optimization algorithm includes initializing a random particle swarm, where each particle has a random position and velocity; and...

[0142]

[0143] As the fitness function of the optimization algorithm, the power fluctuation amplitude of particles from the 1st to the i-th generation is calculated respectively; in the k-th generation, each particle has its own memory of its best position, i.e., its individual best position pbest. i k The current fluctuation amplitude is compared with the fluctuation amplitude of the individual's best position, and the position of the particle with the smallest fluctuation amplitude is retained as the new individual best position. In each generation, the entire particle swarm has a minimum fluctuation amplitude, called the global best position gbest. k In each iteration, the particle tracks two extreme values ​​(pbest). i k gbest k To update its speed v i k and position x i k The algorithm terminates when the DC-side power fluctuation is zero.

[0144] Preferably, the particle swarm optimization algorithm employs the contraction factor method, using the contraction coefficient χ to control the convergence of the system and search different regions, and the particle velocity update formula is:

[0145]

[0146]

[0147] Where the subscript i represents the i-th particle, the superscript k represents the k-th generation, and r1 and r2 are random numbers uniformly distributed between [0, 1]. and There are two learning factors. k is the number of iterations;

[0148] The particle position update formula is:

[0149]

[0150] In solving the DC bus power fluctuation optimization model, the dimension of the particles is kept consistent with the number of virtual phase current gains introduced in the two-phase virtual phase current control technology; virtual phase current gains k are introduced into phases A and C in the system respectively. a and k c If the particle dimension is 2, then the vector set of velocity and position for each particle in the two-dimensional search space is V. i =[v i1 v i2 ], X i =[x i1 x i2 ]; The two dimensions of the particle's position x i1 Corresponding virtual phase current gain k a x i2 Corresponding virtual phase current gain k c The constraints on the two dimensions of the position are consistent with the range of the voltage drop ratio, restricted to [0, 1]; in the kth generation, the set of optimal individual positions for particle i is pbest. i k =[x i1 pbest x i2 pbest In the kth generation, the set of the global best positions for the particles is gbest. k =[x1 gbest x2 gbest ].

[0151] Preferably, after the k-th iteration, the two dimensions of the particle's global optimal position correspond to k in the two-phase virtual phase current control technology. a and k cThe optimal value is obtained, which completely suppresses DC bus power fluctuations.

[0152] Preferably, the two-phase virtual phase current regulation technology changes the input current in the control loop to indirectly regulate 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 this invention, based on single-phase VPCR technology, additionally selects one phase from the three-phase system that has not experienced a voltage drop as an auxiliary compensation phase. By adjusting the feedback current in the control loop, the constant DC-side power is ensured under unbalanced grid conditions. Furthermore, this invention uses a particle swarm optimization algorithm to optimize the gain coefficient of the two-phase virtual phase current, theoretically proving that two-phase VPCR technology can minimize and even eliminate DC-side power fluctuations, meeting the needs of traditional engineering and improving upon the design shortcomings of the gain coefficient in single-phase VPCR technology.

[0155] 2. This invention establishes a theoretical model for DC bus power fluctuation considering two-phase VPCR technology. It can theoretically predict the impact of different grid voltage drops on DC side power fluctuation. The model can be substituted into the optimization algorithm to obtain the optimal solutions for virtual phase current gains ① and ②, as well as the maximum extent to which the technology can suppress DC side power fluctuation.

[0156] 3. While retaining the vector current control structure, this invention completely eliminates DC bus power fluctuations, making the DC bus power transmission performance better meet traditional engineering requirements, effectively reducing the pressure on the DC side capacitor, and thus reducing the system size and cost; it avoids changes to the current loop structure, reduces system complexity, and eliminates the need to add an extra power compensation stage to the current loop to prevent interference with system stability.

[0157] 4. This invention constructs a DC bus power fluctuation model considering two-phase VPCR technology, theoretically analyzes the impact of different voltage drops in the power grid on DC-side power fluctuations, quantifies the factors affecting the amplitude of DC bus power fluctuations, and provides theoretical support for the power fluctuation suppression capability of two-phase VPCR technology.

[0158] 5. This invention proposes a new approach to suppressing DC-side power fluctuations. Existing suppression techniques often equate AC-side power fluctuations with DC-side power fluctuations, without considering the interference of the filter circuit on DC-side power. As a result, although AC-side power fluctuations are eliminated, DC-side power fluctuations still occur, and the burden on the DC-side capacitor remains. This invention, however, introduces two-phase virtual phase current gains at the control level to compensate for the current in the phase where the voltage drop occurs and the auxiliary phase, thereby achieving complete suppression of DC-side power fluctuations.

[0159] 6. This invention can use a 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. Furthermore, 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, which enhances the applicability and scalability of the two-phase VPCR technology in engineering.

[0160] Other beneficial effects of the present invention will be explained in detail through the introduction of specific technical features and technical solutions in specific embodiments. Those skilled in the art should be able to understand the beneficial technical effects brought about by these technical features and technical solutions through the introduction of these technical features and technical solutions. Attached Figure Description

[0161] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0162] Figure 1 This is a flowchart of the method of the present invention.

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

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

[0165] Figure 4 This is a schematic diagram illustrating the effect of VPCR technology in an embodiment of the present invention.

[0166] Figure 5 This is a flowchart illustrating the solution process of the particle swarm optimization algorithm in an embodiment of the present invention.

[0167] Figure 6 This is a graph showing the DC power and AC active power curves when the two-phase VPCR technology is not introduced in this embodiment of the invention.

[0168] Figure 7 This is a graph showing the DC power and AC active power curves after introducing single-phase VPCR technology in an embodiment of the present invention.

[0169] Figure 8 The diagram shows the three-phase grid-connected current waveform after introducing two-phase VPCR technology in an embodiment of the present invention.

[0170] Figure 9 This is a graph showing the DC-side power and AC-side active power curves after introducing two-phase VPCR technology in an embodiment of the present invention. Detailed Implementation

[0171] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

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

[0173] Reference Figure 3 As shown in the figure, i a i b and i c These represent the currents of phases A, B, and C, respectively, u a u b and u c These represent the voltages of phases A, B, and C, respectively. The DSOGI-PLL (Dual Second-Order Generalized Integrator PLL) is a phase-locked loop with two second-order generalized integrators. θ PLL Its output phase angle, i a v and i c v i after applying two-phase VPCR technology 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 afterwards, i d v and i q v These are the d-axis virtual current and q-axis virtual current obtained by coordinate transformation of the three-phase grid-connected current after introducing two-phase VPCR technology, respectively. d and u q These are the d-axis voltage and the q-axis virtual voltage, respectively. d * and i q * represents the d-axis reference current and q-axis reference current of the current loop, respectively; ω represents the grid angular velocity; PI represents the proportional-integral controller; and PWM represents pulse width modulation.

[0174] This invention provides a method for eliminating DC bus power fluctuations based on two-phase virtual phase-current regulation (VPCR) technology. It improves upon the limitations of existing single-phase VPCR technology on the DC side by introducing virtual phase current gains ① and ② in the voltage drop phase and 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, 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 kept in a balanced state and the d-axis current is kept constant, the DC power will inevitably fluctuate. If single-phase VPCR technology is introduced, the three-phase current will be asymmetrical, and the d-axis current will fluctuate, thus the DC power fluctuation will be partially suppressed. If 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 cancel each other out at the DC power calculation level, thereby achieving complete suppression of DC power fluctuation.

[0176] This invention first conducts a theoretical analysis of two-phase VPCR technology, establishes an overall model of DC bus power fluctuations incorporating two-phase VPCR technology, and theoretically characterizes the impact of grid operating conditions and the selection of VPCR technology gain coefficients on DC-side power, providing theoretical support for the design of VPCR technology gain coefficients. Then, the power fluctuation optimization model is substituted into the particle swarm optimization algorithm to obtain the optimal solutions for appropriate auxiliary phases and virtual phase current gains ① and ②, thereby minimizing and eliminating DC bus power fluctuations.

[0177] In this invention, the two-phase VPCR technology maintains constant DC-side power by compensating for voltage dips in the three-phase grid-connected current and current in the auxiliary phase. Taking a single-phase voltage dip in a three-phase three-wire L-type grid-connected inverter as an example, let the voltage dip ratio of phase A be k. drop The voltage drop phase A and the auxiliary phase C were selected, and the two-phase VPCR technology was applied to smooth the DC bus power fluctuation.

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

[0179]

[0180] In the formula, t is time and U is the fundamental voltage.

[0181] Therefore, the dq axis voltage is:

[0182]

[0183] Reference Figure 3As shown, the core of the two-phase VPCR technology is to change the input current in the control loop, thereby indirectly regulating the grid-connected current. Therefore, when a voltage drop occurs in phase A, the two-phase VPCR technology is applied to introduce virtual phase current gain k into phases A and C of the three-phase grid-connected current coordinate transformation module, respectively. a and k c Since VPCR technology does not alter 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 introducing the two-phase VPCR technique is... d v and i q v As the input to the current loop, it will track the reference current value without steady-state error. At this time, the three-phase virtual current i in the control loop... a v i b v and i c v It remains a three-phase balanced current, which is equivalent to amplifying the A-phase and C-phase currents by 1 / k respectively. a and 1 / k c This doubles the power loss and power fluctuation caused by voltage drops, thereby compensating for the power decrease and power fluctuation caused by voltage drops at the DC-side power calculation level.

[0184] After introducing the 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, I1 is the positive sequence current amplitude. This represents the initial phase of the current.

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

[0188]

[0189] In the formula, i d Let i be the d-axis current. q Let i be the q-axis current, i0 be the zero-axis current, and I0 be the zero-axis current amplitude. This is the phase of the zero-axis current.

[0190] At this point, the three-phase currents in the control loop under the abc coordinate system are:

[0191]

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

[0193]

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

[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] Further calculation yields the dq-axis grid-connected current as follows:

[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 follows:

[0205]

[0206] in

[0207]

[0208] Since the instantaneous active power fluctuations of the inverter system's filter inductor can also be superimposed on the active power fluctuations on the AC side, causing DC bus power fluctuations, it is also crucial to analyze the power fluctuations on the filter.

[0209] First, let's take a single inductor as an example, and assume that current flows through inductor L. f The current is

[0210]

[0211] The voltage across the inductor is

[0212]

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

[0214]

[0215] The average power flowing through the inductor (i.e., active power) is zero within one cycle, but the power exchange between the inductor and the external circuit (i.e., reactive power) still exists, and the instantaneous power fluctuations 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 two-phase VPCR technology causes the three-phase current to be asymmetrical, resulting in the three-phase instantaneous power fluctuations on the filter inductor not being able to cancel each other out, and thus the instantaneous power fluctuations on the filter inductor still exist.

[0216] Find the filter inductance L f The three-phase voltages are:

[0217]

[0218] In the formula, u La u Lb u Lc These are the voltages across phases A, B, and C of the filter inductor, respectively.

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

[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] Further calculations reveal the second harmonic ripple component of the DC bus power as follows:

[0224]

[0225] Where PC1, PC2, PS1, and PS2 are the coefficients of the second harmonic ripple component expression of the DC bus power, expressed as follows:

[0226]

[0227] σ1 and σ2 are the coefficients in the expressions for PC1, PC2, PS1, and PS2:

[0228]

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

[0230]

[0231] As can be seen from the DC bus power fluctuation model considering the two-phase VPCR technology, by adjusting the virtual phase current gain coefficient in the two-phase VPCR technology, the DC side power fluctuation amplitude can be significantly reduced, providing sufficient theoretical support for the effectiveness of DC bus power fluctuation suppression measures.

[0232] The Particle Swarm Optimization (PSO) algorithm was developed based on the swarm behaviors of birds, such as foraging. These groups cooperate to find food, with each individual constantly changing its search pattern based on its own memory and the memories of other members. Compared to other intelligent optimization algorithms, PSO requires fewer parameters to be adjusted, making it easier to operate.

[0233] Reference Figure 5 As shown, firstly, a random particle swarm is initialized, with each particle having a random position and velocity. Secondly, the formula is...

[0234]

[0235] The fitness function of the optimization algorithm is used to calculate the power fluctuation amplitude of particles 1 through i. In the kth generation, each particle has its own memory of its best position, i.e., its individual best position pbest. i k The current fluctuation amplitude is compared with the fluctuation amplitude of the individual's best position, and the position of the particle with the smallest fluctuation amplitude is retained as the new individual best position. Then, since the entire particle swarm has a minimum fluctuation amplitude in each generation, it is called the global best position gbest. k Therefore, in each iteration, the particle tracks two extreme values ​​(pbest). i k gbest k To update its speed v i k and position x i k Finally, the algorithm terminates when the DC-side power fluctuation is zero.

[0236] Due to the large search space, to achieve a balance between search speed and accuracy, the algorithm needs strong global search capability in the early stages to obtain a suitable region, and strong local search capability in the later stages to improve convergence accuracy. Therefore, this invention employs the contraction factor method, using the contraction coefficient χ to control the convergence of the system, enabling it to effectively search different regions. At this point, the particle velocity update formula is:

[0237]

[0238]

[0239] Where the subscript i represents the i-th particle, the superscript k represents the k-th generation, and r1 and r2 are random numbers uniformly distributed between [0, 1]. and There are two learning factors. k is the number of iterations.

[0240] The particle position update formula is:

[0241]

[0242] In solving the DC bus power fluctuation optimization model, the particle dimension is kept consistent with the number of virtual phase current gains introduced in the two-phase VPCR technique. This is because virtual phase current gains k are introduced in phases A and C of the system respectively. a and k c Therefore, the dimension of the particle is 2. In the two-dimensional search space, the vector sets of velocity and position of each particle are V. i =[v i1 v i2 ], X i =[x i1 x i2 The two dimensions of the particle's position, x. i1 Corresponding virtual phase current gain k a x i2 Corresponding virtual phase current gain k c The constraints on the two dimensions of position are consistent with the range of the voltage drop ratio, restricted to [0, 1]. In the kth generation, the set of optimal individual positions for particle i is pbest. i k =[x i1 pbest x i2 pbest In the kth generation, the set of the global best positions for the particles is gbest. k =[x1 gbest x2 gbestAfter iteration, the two dimensions of the particle's global optimal position correspond to k in the two-phase VPCR technique. a and k c The optimal value is determined to ensure complete suppression of DC bus power fluctuations.

[0243] The control strategy proposed in this invention, based on single-phase VPCR technology, additionally selects one phase from the three-phase system that has not experienced a voltage drop as an auxiliary compensation phase. By adjusting the feedback current in the control loop, the constant DC-side power is ensured under unbalanced grid conditions. Furthermore, this invention uses a particle swarm optimization algorithm to optimize the gain coefficient of the two-phase virtual phase current, theoretically proving that two-phase VPCR technology can minimize and even eliminate DC-side power fluctuations, meeting the needs of traditional engineering and improving upon the design drawbacks of the gain coefficient in single-phase VPCR technology.

[0244] The above are basic embodiments of the present invention. The technical solution of the present invention will be 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 The voltage is 1.3mH, the fundamental voltage amplitude U is 311V, the fundamental frequency f1 is 50Hz, and the d-axis reference current i in the control loop is... d * is 60A, current loop q-axis reference current i q *The proportional gain K of the current loop PI controller is -30A. p The integral gain K of the PI controller is 16.3. i It is 20426.9.

[0247] The following will consider a voltage drop in phase A of the power grid and a drop ratio k. drop Simulation verification was performed using 0.6 as an example.

[0248] Reference Figure 6 and Figure 7 As shown, when two-phase VPCR technology is not introduced into the system, the DC-side power exhibits significant fluctuations under unbalanced grid conditions. Existing single-phase VPCR technology only introduces a virtual phase current gain k in phase A, where the voltage drop occurs. a And take k a =k drop In this system, k is taken 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] In grid-connected inverters, two-phase VPCR technology is applied, introducing a virtual phase current gain k in phase A where the voltage drop occurs. a The virtual phase current gain k is 0.6216, introduced by the auxiliary phase C phase. c The value is 0.9227, at which point the three-phase grid-connected current is given by the formula.

[0250]

[0251] The corresponding theoretical value is calculated as follows:

[0252]

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

[0254] Reference Figure 9 As shown, after introducing the two-phase VPCR technology, 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 has been verified.

[0255] The method for eliminating DC bus power fluctuations based on two-phase VPCR technology proposed in this embodiment establishes a DC bus power fluctuation model considering two-phase VPCR technology. Furthermore, by combining particle swarm optimization algorithm, the virtual phase current gain coefficient of the two-phase VPVR technology is designed to ensure constant DC-side power under unbalanced grid conditions. This embodiment provides a novel approach to the design of DC bus power fluctuation suppression strategies.

[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 implemented 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 embodiment 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: Constructs the grid-connected current model and the DC bus power fluctuation model;

[0259] The grid-connected current model incorporates two-phase virtual phase current regulation technology;

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

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

[0262] Module M3: Solve the optimized DC bus power fluctuation model to achieve complete suppression of power fluctuations.

[0263] Preferably, the two-phase virtual phase current regulation technology compensates for the voltage drop phase and the current of the auxiliary phase in the three-phase grid-connected current to maintain constant DC power, and the two-phase virtual phase current regulation 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 These represent the currents of phases A, B, and C, respectively, u a u b and u c These are the voltages of phases A, B, and C, respectively; i a v and i c v i after applying two-phase VPCR technology 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 afterwards, i d v and i q v These are the d-axis virtual current and q-axis virtual current obtained by coordinate transformation of the three-phase grid-connected current after introducing two-phase virtual phase current regulation technology, and u. d and u q These are the d-axis voltage and the q-axis virtual voltage, respectively. d * and i q *Represents the d-axis reference current and q-axis reference current of the current loop, respectively, and ω is the grid angular velocity;

[0265] Let the voltage drop ratio of phase A be k. drop Selecting phase A (voltage drop) and phase C (auxiliary phase), the three-phase voltages of the unbalanced power grid are:

[0266]

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

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

[0269]

[0270] When a voltage drop occurs in phase A, based on two-phase virtual phase current regulation technology, a virtual phase current gain k is introduced into phases A and C of the three-phase grid-connected current coordinate transformation module, respectively. a and k c The two-phase virtual phase current regulation technology does not change the current loop structure, so the reference value i of the virtual axis dq current is... d * and i q *Unchanged; if the zero-axis current in the control system is ignored, the virtual axis dq current i obtained after introducing the two-phase virtual phase current regulation technology is... d v and i q v As the input to the current loop, it will track the reference current value without steady-state error, and the virtual currents i of phases A, B, and C in the control loop will... 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 respectively. a and 1 / k c This compensates for the power drop and power fluctuation caused by voltage dips at the DC-side power calculation level.

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

[0272]

[0273] In the formula, I1 is the positive sequence current amplitude. The initial phase of the current;

[0274] Due to the introduction of two-phase virtual phase current control technology, the three-phase grid-connected current exhibits a three-phase unbalanced state. Sequence decomposition reveals that the three-phase current contains a zero-sequence current component, which contradicts the principle that zero-sequence current does not exist in a three-phase three-wire system. Therefore, the zero-axis current in the control loop cannot be ignored. Let the dq0 current in the control loop be:

[0275]

[0276] In the formula, i d Let i be the d-axis current. q Let i be the q-axis current, i0 be the zero-axis current, and I0 be the zero-axis current amplitude. The zero-axis current phase;

[0277] At this point, the three-phase currents in the control loop under the abc coordinate system are:

[0278]

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

[0280]

[0281] According to the fact that a three-phase three-wire system does not contain zero-sequence current, i a +i b +i c =0, find the amplitude and phase of the zero-axis current.

[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 grid-connected current of the dq axis is:

[0288]

[0289] AC side active power p PCC Represented as:

[0290]

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

[0292]

[0293] in,

[0294]

[0295] Let the current flow through a single inductor L f The current is

[0296]

[0297] Voltage u across the inductor L for

[0298]

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

[0300]

[0301] Find the filter inductance L f The three-phase voltages are:

[0302]

[0303] In the formula, u La u Lb u Lc These are the voltages across phases A, B, and C of the filter inductor, 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] Instantaneous power p on the DC side DC From the AC side p PCC and the instantaneous power p on the filter inductor L It consists of two parts:

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

[0308] The second harmonic ripple component of the DC bus power is calculated as follows:

[0309]

[0310] Where PC1, PC2, PS1, and PS2 are the coefficients of the second harmonic ripple component expression of the DC bus power, expressed as follows:

[0311]

[0312] σ1 and σ2 are the coefficients in the expressions for PC1, PC2, PS1, and PS2:

[0313]

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

[0315]

[0316] Adjusting the virtual phase current gain coefficient in the two-phase virtual phase current regulation technology reduces the DC-side power fluctuation amplitude.

[0317] Preferably, the DC bus power fluctuation model is optimized using a particle swarm optimization algorithm; the particle swarm optimization algorithm includes initializing a random particle swarm, where each particle has a random position and velocity; and...

[0318]

[0319] As the fitness function of the optimization algorithm, the power fluctuation amplitude of particles from the 1st to the i-th generation is calculated respectively; in the k-th generation, each particle has its own memory of its best position, i.e., its individual best position pbest. i k The current fluctuation amplitude is compared with the fluctuation amplitude of the individual's best position, and the position of the particle with the smallest fluctuation amplitude is retained as the new individual best position. In each generation, the entire particle swarm has a minimum fluctuation amplitude, called the global best position gbest. k In each iteration, the particle tracks two extreme values ​​(pbest). i k gbest k To update its speed v i k and position x i k The algorithm terminates when the DC-side power fluctuation is zero.

[0320] Preferably, the particle swarm optimization algorithm employs the contraction factor method, using the contraction coefficient χ to control the convergence of the system and search different regions, and the particle velocity update formula is:

[0321]

[0322]

[0323] Where the subscript i represents the i-th particle, the superscript k represents the k-th generation, and r1 and r2 are random numbers uniformly distributed between [0, 1]. and There are two learning factors. k is the number of iterations;

[0324] The particle position update formula is:

[0325]

[0326] In solving the DC bus power fluctuation optimization model, the dimension of the particles is kept consistent with the number of virtual phase current gains introduced in the two-phase virtual phase current control technology; virtual phase current gains k are introduced into phases A and C in the system respectively. a and k cIf the particle dimension is 2, then the vector set of velocity and position for each particle in the two-dimensional search space is V. i =[v i1 v i2 ], X i =[x i1 x i2 ]; The two dimensions of the particle's position x i1 Corresponding virtual phase current gain k a x i2 Corresponding virtual phase current gain k c The constraints on the two dimensions of the position are consistent with the range of the voltage drop ratio, restricted to [0, 1]; in the kth generation, the set of optimal individual positions for particle i is pbest. i k =[x i1 pbest x i2 pbest In the kth generation, the set of the global best positions for the particles is gbest. k =[x1 gbest x2 gbest ].

[0327] Preferably, after the k-th iteration, the two dimensions of the particle's global optimal position correspond to k in the two-phase virtual phase current control technology. a and k c The optimal value is obtained, which completely suppresses DC bus power fluctuations.

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

[0329] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0330] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A power fluctuation suppression method based on two-phase virtual phase current regulation, characterized in that, include: Step S1: Construct the grid-connected current model and the DC bus power fluctuation model; The grid-connected current model incorporates two-phase virtual phase current regulation technology; The two-phase virtual phase current regulation technology compensates for the voltage drop phase and auxiliary phase current of the three-phase grid-connected current to maintain constant DC power. The two-phase virtual phase current regulation 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. The DC bus power fluctuation model corresponds to the grid-connected current model; Step S2: Optimize the DC bus power fluctuation model based on the grid-connected current model; Step S3: Solve the optimized DC bus power fluctuation model to achieve complete suppression of power fluctuations.

2. The power fluctuation suppression method based on two-phase virtual phase current regulation according to claim 1, 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 These are the currents for phases A, B, and C, respectively. u a , u b and u c These are the voltages for phases A, B, and C, respectively. i a v and i c v After applying two-phase virtual phase current regulation technology i a and i c Multiplied by virtual phase current gain k a and k c The virtual A-phase current and virtual C-phase current obtained afterwards i d v and i q v These are the coordinate transformations obtained from the three-phase grid-connected currents after introducing two-phase virtual phase current regulation technology. d Axis virtual current and q Axis virtual current, u d and u q They are respectively d shaft voltage and q Axis virtual voltage, i d * and i q * Current loops d Shaft reference current and q Shaft reference current, ω The angular velocity of the power grid; Let the voltage drop ratio of phase A be... k drop Selecting phase A (voltage drop) and phase C (auxiliary phase), the three-phase voltages of the unbalanced power grid are: ； In the formula, t For time, U The fundamental voltage; Therefore, virtual axis dq The voltage is: ； When a voltage drop occurs in phase A, virtual phase current gain is introduced into phases A and C of the three-phase grid-connected current coordinate transformation module based on two-phase virtual phase current regulation technology. k a and k c The two-phase virtual phase current regulation technology does not change the current loop structure, thus the virtual axis... dq Reference value of current i d * and i q * constant; If the zero-axis current in the control system is ignored, the virtual axis obtained after introducing two-phase virtual phase current regulation technology is... dq Current i d v and i q v As the input to the current loop, it will track the reference current value without steady-state error, and the virtual currents of phases A, B, and C in the control loop will be... i 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 This compensates for the power drop and power fluctuation caused by voltage dips at the DC-side power calculation level.

3. The power fluctuation suppression method based on two-phase virtual phase current regulation according to claim 2, characterized in that, After the introduction of the two-phase virtual phase current regulation technology, if the zero-axis current in the control system is ignored, the three-phase grid-connected current is: ； In the formula, I 1 represents the positive sequence current amplitude. φ i This is the initial phase of the current; The three-phase grid-connected current exhibits a three-phase unbalanced state due to the introduction of two-phase virtual phase current regulation technology. Sequence decomposition reveals the presence of a zero-sequence current component in the three-phase current, contradicting the principle that zero-sequence current does not exist in a three-phase three-wire system. Therefore, the zero-axis current in the control loop cannot be ignored. Let the zero-axis current in the control loop... dq 0 current is: ； In the formula, i d for d shaft current, i q for q shaft current, i 0 represents the zero-axis current. I 0 represents the zero-axis current amplitude. φ 0 represents the zero-axis current phase; At this time, abc The three-phase currents in the control loop under coordinates are: ； The three-phase grid-connected current is: ； Since a three-phase three-wire system does not contain zero-sequence current, that is... i a + i b + i c =0, calculate the amplitude and phase of the zero-axis current. ； in, sign ( x )= x / | x |, x For the parameter expression, and: ； The three-phase grid-connected current is further expressed as: ； dq The shaft-connected grid current is: ； AC side active power Represented as: ； Solve for the active power on the AC side for: ； in, ； Suppose that the current flows through a single inductor L f The current is ； Voltage across the inductor for ； At this time, the instantaneous power on the inductor for ； Find the filter inductance L f The three-phase voltages are: ； In the formula, u La , u Lb , u Lc These are the voltages across phases A, B, and C of the filter inductor, respectively. Solve for the instantaneous power on the filter inductor : ； DC side instantaneous power From the communication side Instantaneous power on the filter inductor It consists of two parts: ； The second harmonic ripple component of the DC bus power is calculated as follows: ； in, PC 1. PC 2. PS 1 and PS 2 represents the coefficients of the expression for the second harmonic ripple component of the DC bus power, expressed as follows: ； σ 1 and σ 2 is PC 1. PC 2. PS 1. PS 2. Coefficients in the expression: ； The amplitude of DC-side power fluctuation is ； Adjusting the virtual phase current gain coefficient in the two-phase virtual phase current regulation technology reduces the DC-side power fluctuation amplitude.

4. The power fluctuation suppression method based on two-phase virtual phase current regulation according to claim 3, characterized in that, The DC bus power fluctuation model is optimized and solved using a particle swarm optimization algorithm. The particle swarm optimization algorithm includes initializing a random particle swarm, where each particle has a random position and velocity; and then... As the fitness function of the optimization algorithm, the fitness of the 1st to 5th generations is calculated respectively. i The power fluctuation amplitude of the first particle; k In this generation, each particle has its own memory of its optimal position, that is, its individual optimal position. pbest i k The current fluctuation amplitude is compared with the fluctuation amplitude of the individual's optimal position, and the position of the particle with the smallest fluctuation amplitude is retained as the new individual optimal position. In each generation, the entire particle swarm has a minimum fluctuation amplitude, called the global optimal position g. best k In each iteration, the particle tracks two extreme values ​​( pbest i k g best k To update its speed v i k and location x i k The algorithm terminates when the DC-side power fluctuation is zero.

5. The power fluctuation suppression method based on two-phase virtual phase current regulation according to claim 4, characterized in that, The particle swarm optimization algorithm employs the shrinkage factor method, utilizing the shrinkage coefficient. χ The convergence of the control system is searched in different regions, and the particle velocity update formula is: ； ； Among them, subscript i Representing the i One particle, superscript k Representing the k generation, r 1 and r 2 is a random number uniformly distributed between [0, 1]. φ 1 and φ 2 represents two learning factors. φ = φ 1 +φ 2>4, k It is the number of iterations; The particle position update formula is: ； In solving the DC bus power fluctuation optimization model, the dimension of the particles is kept consistent with the number of virtual phase current gains introduced in the two-phase virtual phase current control technology; virtual phase current gains are introduced into phases A and C in the system respectively. k a and k c Then the dimension of the particle is 2; in the two-dimensional search space, the vector sets of velocity and position of each particle are respectively V i =[ v i1 , v i2 ], X i =[ x i1 , x i2 ]; Two dimensions of particle position x i1 Corresponding virtual phase current gain k a , x i2 Corresponding virtual phase current gain k c The constraints on the two dimensions of the location are consistent with the range of the voltage drop ratio, limited to [0, 1]; k generation, particles i The set of optimal individual positions is pbest i k =[ x i1 pbest , x i2 pbest ]; No. k In this case, the set of global optimal positions for the particle is g. best k =[ x 1 gbest , x 2 gbest ].

6. The power fluctuation suppression method based on two-phase virtual phase current regulation according to claim 5, characterized in that, The first k After the iteration is completed, the two dimensions of the particle's global optimal position correspond to the two-phase virtual phase current control technology. k a and k c The optimal value is obtained, which completely suppresses DC bus power fluctuations.

7. The power fluctuation suppression method based on two-phase virtual phase current regulation according to claim 1, characterized in that, The two-phase virtual phase current regulation technology changes the input current in the control loop to indirectly regulate the grid-connected current.

8. A power fluctuation suppression system based on two-phase virtual phase current regulation, characterized in that, include: Module M1: Constructs the grid-connected current model and the DC bus power fluctuation model; The grid-connected current model incorporates two-phase virtual phase current regulation technology; The two-phase virtual phase current regulation technology compensates for the voltage drop phase and auxiliary phase current of the three-phase grid-connected current to maintain constant DC power. The two-phase virtual phase current regulation 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. The DC bus power fluctuation model corresponds to the grid-connected current model; Module M2: Optimizes the DC bus power fluctuation model based on the grid-connected current model; Module M3: Solve the optimized DC bus power fluctuation model to achieve complete suppression of power fluctuations.

Images