Power treatment method and system suitable for two-phase voltage drop of photovoltaic inverter

Abstract

The power treatment method suitable for the two-phase voltage drop of the photovoltaic inverter is characterized by comprising the following steps: collecting the drop state of a three-phase three-wire system photovoltaic inverter when the two-phase voltage drop occurs; obtaining expressions of AC side active power, instantaneous power of a filter inductor and DC side constant power of the photovoltaic inverter based on the drop state so as to derive an expression of a frequency doubling fluctuation component of the DC side of the photovoltaic inverter; solving a fluctuation amplitude coefficient of a frequency doubling fluctuation component of the direct current side of the photovoltaic inverter on different fluctuation phases to obtain an association relationship between the fluctuation amplitude coefficient and the drop state; and calculating the DC bus power fluctuation of the photovoltaic inverter, taking the DC bus power fluctuation as a fitness function, taking the virtual phase current gains of the two phases in falling as input particles, and adopting a particle swarm algorithm to solve so as to realize the power treatment of the two-phase voltage falling of the photovoltaic inverter.

Description

Technical Field

[0001] The present invention relates to the field of power systems, and more specifically, to a power management method and system suitable for two-phase voltage drop of a photovoltaic inverter. Background Art

[0002] As the penetration rate of new energy continues to increase, the grid-connected inverter, as the key hub connecting the new energy power generation system and the AC power grid, is crucial to the stable operation of the entire power system. However, in actual grid operation, factors such as asymmetric faults and asymmetric loads may cause the grid to be in an unbalanced state, which has a negative impact on the inverter's output power and grid-connected current quality.

[0003] Background technology document: Control strategy of full-power wind power grid-connected converter when grid voltage is unbalanced. It is mentioned that under the condition of unbalanced grid voltage, the negative sequence component of voltage will cause the DC side voltage of the direct-drive permanent magnet synchronous generator (PMSG) full-power grid-connected converter to have harmonics of twice the grid frequency. Long-term operation under this condition will significantly affect the service life of the DC side capacitor and endanger the stable operation of the unit. Methods A mathematical model of the grid-side converter is established. On the basis of considering the influence of grid impedance on active power, a control strategy with the goal of enhancing the DC side voltage stability is proposed. Among them, the positive and negative sequence current instructions of the grid-side converter are obtained by ensuring that there is no active power flow with double frequency oscillation between the DC side capacitor and the grid-connected reactor. The calculation of the instructions does not require solving complex high-order matrices and does not introduce more variables. The simulation results of the direct-drive permanent magnet synchronous wind turbine verify the effectiveness of the proposed voltage control strategy. Compared with the traditional balancing control strategy, this control strategy can achieve stable control of the DC side voltage while effectively suppressing the 2-fold frequency fluctuation of the active power output to the grid, thereby improving the ability of this type of unit to operate uninterruptedly, safely and stably under unbalanced grid voltage conditions.

[0004] Although this control strategy can effectively suppress the 2-fold frequency fluctuation of the active power output to the grid, there is still a problem of large amount of calculation caused by matrix solution, which increases the difficulty and complexity of control implementation and slows down the dynamic response speed of the system.

[0005] In addition, two-phase voltage drop is one of the most common faults in voltage imbalance in the power grid. When the three-phase power grid is unbalanced, there may be a double frequency fluctuation component in the AC side active power transmitted by the inverter, which will cause the fluctuation of the DC bus power and increase the burden on the DC bus capacitor. Therefore, it is crucial to solve the problem of DC bus power fluctuation under two-phase voltage drop.

[0006] In order to meet this challenge, existing research has proposed virtual phase-current regulation (VPCR) technology. This technology suppresses the active power fluctuation on the AC side by compensating the feedback current in the current loop. However, the existing VPCR technology only manages the power fluctuation on the AC side, and does not further manage the power fluctuation on the DC side. In addition, the current discussion scenario of VPCR only targets the single-phase voltage drop, and does not study its management effect under two-phase voltage drop.

[0007] In order to address this problem, there is an urgent need for a power management method and system suitable for two-phase voltage drop of a photovoltaic inverter. Summary of the invention

[0008] In order to solve the deficiencies in the prior art, the present invention provides a power management method and system suitable for two-phase voltage drop of photovoltaic inverters. VPCR technology is introduced for compensation in the scenario of two-phase fault, and the current gain coefficients of the two virtual phases are optimally calculated through the particle swarm optimization algorithm, thereby achieving complete suppression of power fluctuations on the DC side.

[0009] The present invention adopts the following technical solution.

[0010] The first aspect of the present invention relates to a power management method suitable for a two-phase voltage drop of a photovoltaic inverter, the method comprising the following steps: collecting a drop state when a two-phase voltage drop occurs in a three-phase three-wire photovoltaic inverter, obtaining expressions of the active power on the AC side of the photovoltaic inverter, the instantaneous power of the filter inductor, and the constant power on the DC side based on the drop state, so as to derive an expression of the double frequency fluctuation component on the DC side of the photovoltaic inverter; solving the fluctuation amplitude coefficient of the double frequency fluctuation component on the DC side of the photovoltaic inverter at different fluctuation phases, so as to obtain the correlation between the fluctuation amplitude coefficient and the drop state; using the fluctuation amplitude coefficient to calculate the DC bus power fluctuation of the photovoltaic inverter, using the DC bus power fluctuation as the fitness function, using the virtual phase current gain of the two phases where the drop occurs as the input particles, and using the particle swarm algorithm to solve the optimal particles, so as to achieve power management of the two-phase voltage drop of the photovoltaic inverter.

[0011] Preferably, collecting the drop state of the three-phase three-wire photovoltaic inverter when two-phase voltage drops, including: collecting the instantaneous value of the three-phase voltage when the two-phase voltage drops, so as to calculate the three-phase voltage as:

[0012]

[0013] Using the three-phase voltage, the two-phase voltage drop ratio k is restored a drop and k cdrop .

[0014] Preferably, the expression for obtaining the AC side active power of the photovoltaic inverter, the instantaneous power of the filter inductor, and the DC side constant power based on the drop state includes: the AC side active power of the photovoltaic inverter is:

[0015]

[0016] Wherein, U is the fundamental voltage, I1 is the current amplitude in the control loop of the photovoltaic inverter, ω is the grid angular velocity, t is time, is the initial phase of the current on the control loop of the photovoltaic inverter;

[0017] And there is

[0018] k a With k c is the virtual current gain on the two phases where voltage sag occurs.

[0019] Preferably, the expressions for obtaining the AC side active power, the instantaneous power of the filter inductor, and the DC side constant power of the photovoltaic inverter based on the drop state include: the instantaneous power of the filter inductor is:

[0020] p L =u La i a +u Lb i b +u Lc i c

[0021] In the formula, the three-phase voltage across the filter inductor is:

[0022]

[0023] The three-phase grid-connected current of the photovoltaic inverter is:

[0024]

[0025] Preferably, based on the drop state, the expressions of the AC side active power, the instantaneous power of the filter inductor, and the DC side constant power of the photovoltaic inverter are obtained, including: the DC side constant power p DC1 The calculation is based on the power grid power frequency component in the AC side power of the photovoltaic inverter.

[0026] Preferably, the expression of the double frequency fluctuation component on the DC side of the photovoltaic inverter is derived, including: based on the formula p DC =p PCC +p L =p DC1+Δp DC , extract p PCC +p L -p DC1 The double frequency component other than the power frequency component is obtained, so that the double frequency fluctuation component of the DC side of the photovoltaic inverter is obtained as follows:

[0027]

[0028] Preferably, the fluctuation amplitude coefficient of the double frequency fluctuation component on the DC side of the photovoltaic inverter at different fluctuation phases is solved to obtain the correlation between the fluctuation amplitude coefficient and the sag state, including: the sag state includes the virtual current gain k on the two phases where the voltage sag occurs a With k c ; The coefficient of fluctuation is:

[0029] In the formula,

[0030] Among them, σ1 and σ2 are parameters related to RC1, RS1, RC2, RS2, and:

[0031]

[0032] Preferably, the fluctuation amplitude coefficient is used to characterize the DC bus power fluctuation of the photovoltaic inverter, including: the DC bus power fluctuation is:

[0033]

[0034] Preferably, the DC bus power fluctuation is used as the fitness function, the virtual phase current gain of the two phases that have dropped is used as the input particle, and the particle swarm algorithm is used to solve the optimal particle, including: randomly generating a plurality of particles with the virtual phase current gain as a two-dimensional vector to obtain an initial particle swarm; iteratively updating the particle speed and position in the initial particle swarm, and ending the iteration when the fitness function takes the value of 0, thereby obtaining the optimal particle; multiplying the value result of the two-phase phase current gain in the optimal particle by the instantaneous value of the three-phase voltage when the two-phase voltage drops, and then inputting the gain voltage into the control loop to implement feedback control of the photovoltaic inverter.

[0035] The second aspect of the present invention relates to a power management system suitable for two-phase voltage drop of a photovoltaic inverter, and the system is used to implement the power management method suitable for two-phase voltage drop of a photovoltaic inverter described in the first aspect of the present invention; and the system includes a calculation module, an association module and a management module; wherein the calculation module is used to collect the drop state when a two-phase voltage drop occurs in a three-phase three-wire photovoltaic inverter, and obtain the expressions of the active power on the AC side of the photovoltaic inverter, the instantaneous power of the filter inductor, and the constant power on the DC side based on the drop state, so as to derive the DC power of the photovoltaic inverter. The invention discloses a method for obtaining an expression of the double frequency fluctuation component of the DC side of the photovoltaic inverter; an association module for solving the fluctuation amplitude coefficient of the double frequency fluctuation component of the DC side of the photovoltaic inverter at different fluctuation phases to obtain the correlation between the fluctuation amplitude coefficient and the drop state; a governance module for using the fluctuation amplitude coefficient to characterize the DC bus power fluctuation of the photovoltaic inverter, taking the DC bus power fluctuation as the fitness function, taking the two-phase current gain as the input particle, and using the particle swarm algorithm to solve the optimal particle to achieve power governance of the two-phase voltage drop of the photovoltaic inverter.

[0036] A third aspect of the present invention relates to a terminal, comprising a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method according to the first aspect of the present invention.

[0037] A fourth aspect of the present invention relates to a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect of the present invention.

[0038] The beneficial effect of the present invention is that, compared with the prior art, the power management method and system for two-phase voltage drop of photovoltaic inverters in the present invention introduces VPCR technology for compensation in the scenario of two-phase fault, and optimizes and calculates the current gain coefficients of two virtual phases through particle swarm optimization algorithm, thereby achieving complete suppression of power fluctuation on the DC side. The present invention performs better in eliminating power fluctuation on the DC side and power management of two-phase voltage drop, meets traditional engineering requirements, provides support at the theoretical level of control strategy, and provides a new technical path for practical application.

[0039] The beneficial effects of the present invention also include:

[0040] 1. Compared with the existing power suppression technology, the power fluctuation active management control system suitable for two-phase voltage drop of photovoltaic inverter proposed in the present invention has a more obvious suppression effect on DC bus power fluctuation and better matches the scenario of two-phase voltage drop.

[0041] 2. The present invention provides a new control strategy and coefficient design method for active power fluctuation management of two-phase voltage drop of photovoltaic inverters, and the design of virtual phase current gain coefficient is more accurate and reasonable. The method establishes a theoretical model of DC bus power fluctuation of VPCR technology under two-phase voltage drop scenario, and substitutes the model into the optimization algorithm to obtain the optimal solution of two virtual phase current gains to achieve maximum suppression of DC side power fluctuation.

[0042] 3. The method is simple and robust at the control level, and does not change the structure of the vector current loop. Since the virtual phase current gain introduced by the VPCR technology does not appear in the open-loop and closed-loop transfer functions of the system, the stability of the system is not affected by the introduced power fluctuation suppression strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of a grid-connected inverter system when a two-phase voltage drop occurs in the prior art of the present invention;

[0044] Figure 2 This is a system control block diagram of a VPCR technology in a power management method for a two-phase voltage drop of a photovoltaic inverter according to the present invention;

[0045] Figure 3 A flow chart of solving VPCR technical parameters based on particle swarm optimization algorithm in a power management method for two-phase voltage drop of a photovoltaic inverter according to the present invention;

[0046] Figure 4 It is a schematic diagram of a DC bus power curve when the VPCR technology is not introduced in an embodiment of a power management method for two-phase voltage drop of a photovoltaic inverter according to the present invention;

[0047] Figure 5 It is a schematic diagram of a DC bus power curve when only VPCR technology is introduced in one embodiment of a power management method for two-phase voltage drop of a photovoltaic inverter according to the present invention;

[0048] Figure 6 A schematic diagram of a DC bus power curve when all effects of the voltage drop on the AC and DC sides are considered in one embodiment of a power management method for a two-phase voltage drop of a photovoltaic inverter according to the present invention;

[0049] Figure 7 The figure is a waveform diagram of the compensated three-phase grid-connected current in one embodiment of a power management method for a two-phase voltage drop of a photovoltaic inverter according to the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in the present invention are only embodiments of a part of the present invention, not all embodiments. Based on the spirit of the present invention, all other embodiments not recorded in the present invention obtained by ordinary technicians in this field according to the embodiments recorded in the present invention without making creative work should belong to the protection scope of the present invention.

[0051] Traditional power fluctuation suppression strategies usually suppress active power fluctuations on the AC side by adjusting the reference current of the current loop. However, this method increases the complexity of the control loop and the computational burden of the system, affecting the dynamic response capability of the system. The existing VPCR technology simplifies the control structure and weakens the active power fluctuations on the AC side and the power fluctuations on the DC side by only adjusting the feedback current in the control loop without changing the current loop structure. However, the existing VPCR technology is only discussed in the single-phase voltage drop scenario, compensating for the current corresponding to the single-phase voltage drop, and cannot completely eliminate the DC bus power fluctuations.

[0052] The present invention makes full use of the shaping effect of VPCR technology on the feedback current of the control loop, and realizes the complete suppression of DC bus power fluctuations in the scenario of two-phase voltage drop. First, two virtual phase current gains are introduced in the current Park conversion module for the two phases where the voltage drops are located; secondly, the present invention conducts a theoretical analysis of VPCR technology in the scenario of two-phase voltage drop, establishes an overall model of DC bus power fluctuations, and intuitively reflects the influence of the two VPCR control parameters on the DC side power fluctuations; finally, according to the above DC bus power fluctuation theoretical model, the power fluctuation model is substituted into the particle swarm optimization algorithm, and the particle swarm optimization algorithm is used to obtain two optimal virtual phase current gain solutions to achieve the minimum and zero DC bus power fluctuation, that is, to achieve complete suppression of DC bus power fluctuations in the case of two-phase faults in the power grid.

[0053] Figure 1 FIG. 1 is a schematic diagram of a grid-connected inverter system when a two-phase voltage drop occurs in the prior art of the present invention. Figure 1 As shown, the first aspect of the present invention relates to a power management method suitable for two-phase voltage drop of a photovoltaic inverter, and the method includes steps 1 to 3.

[0054] Step 1: Collect the drop state of the three-phase three-wire photovoltaic inverter when two-phase voltage drops occur, and obtain the expressions of the active power on the AC side of the photovoltaic inverter, the instantaneous power of the filter inductor, and the constant power on the DC side based on the drop state, so as to derive the expression of the double frequency fluctuation component on the DC side of the photovoltaic inverter.

[0055] Three-phase three-wire grid-connected inverter system Figure 1 As shown in the figure, V dc is the DC bus voltage, C dc is the DC bus capacitance, L f is the filter inductance of the filter circuit, u PCC and i PCC is the three-phase grid voltage and grid-connected current at the common coupling point. The control block diagram of VPCR technology in the two-phase voltage drop scenario is as follows: Figure 2 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 is a phase-locked loop of dual second-order generalized integrator, θ 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 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 VPCR technology, and u d and u q are the d-axis voltage and q-axis voltage respectively, i d * and i q * are the d-axis reference current and q-axis reference current of the vector current loop, and PI is the proportional-integral controller.

[0056] Preferably, collecting the voltage drop status of a three-phase three-wire photovoltaic inverter when two-phase voltage drops, includes:

[0057] The instantaneous value of the three-phase voltage when the two-phase voltage drops is collected to calculate the three-phase voltage as follows:

[0058]

[0059] Using the three-phase voltage, the two-phase voltage drop ratio k is restored a drop and k c drop .

[0060] Take the case of voltage drop of phases A and C of a three-phase three-wire grid-connected inverter as an example, assuming that the voltage drop ratio of phase A is k a drop , the voltage drop ratio of phase C is k c drop The method also supports the analysis of two-phase voltage drops in other situations.

[0061] According to the above formula, dq transformation is performed, then:

[0062] The unbalanced voltage under the dq axis is:

[0063]

[0064] Figure 2 This is a system control block diagram of the VPCR technology in the power management method for two-phase voltage drop of the photovoltaic inverter in the present invention. In the scenario of two-phase voltage drop, the VPCR technology is applied to introduce virtual phase current gain k in the A phase and C phase of the Park conversion module of the three-phase grid-connected current. a and k c ,like Figure 2 As shown. Since the dq axis current reference value i d * and i q * unchanged, so a three-phase balanced current command will be generated in the control loop, i a v 、i b v and i c v It is still a three-phase balanced current. At this time, it is equivalent to amplifying the A phase and C phase currents of the three-phase current by 1 / k a and 1 / k c times, thereby compensating for the power fluctuation caused by the two-phase voltage drop.

[0065] Assume that the dq0 axis current in the control loop is:

[0066]

[0067] Where I1 is the command current amplitude, is the initial phase of the current, I0 is the zero axis current amplitude, is the zero axis current phase.

[0068] After the VPCR technology is introduced in the two-phase voltage drop scenario, the three-phase grid-connected current is:

[0069]

[0070] Since the three-phase three-wire system does not contain zero-sequence current, i a +i b+i c =0, so the zero-sequence current amplitude and phase can be solved as:

[0071]

[0072] in

[0073] Therefore, the three-phase grid-connected current can be rewritten as:

[0074]

[0075] The grid-connected current under the dq axis is:

[0076]

[0077] The active power on the AC side can be calculated as:

[0078]

[0079] The active power on the AC side of the photovoltaic inverter can be obtained by calculation.

[0080] Preferably, the active power on the AC side of the photovoltaic inverter, the instantaneous power of the filter inductor, and the constant power on the DC side are calculated based on the drop state, including:

[0081] The AC side active power of the photovoltaic inverter is:

[0082]

[0083] Wherein, U is the fundamental voltage, I1 is the current amplitude in the control loop of the photovoltaic inverter, ω is the grid angular velocity, t is time, is the initial phase of the current on the control loop of the photovoltaic inverter;

[0084] And there is

[0085] k a With k c is the virtual current gain on the two phases where voltage sag occurs.

[0086] When the power grid is in a state of two-phase voltage drop, the introduction of VPCR technology amplifies the currents corresponding to the two faults, making the three-phase current unbalanced and causing instantaneous power fluctuations on the filter inductor.

[0087] Preferably, the instantaneous power of the filter inductor is:

[0088] p L =u La i a +u L bib +u Lc i c

[0089] In the formula, the three-phase voltage across the filter inductor is:

[0090]

[0091] The three-phase grid-connected current of the photovoltaic inverter is as described above.

[0092] Preferably, the constant power p on the DC side DC1 The calculation is based on the power grid power frequency component in the AC side power of the photovoltaic inverter.

[0093] The instantaneous power on the DC side can be solved by the following equation, including the constant component p DC1 and the double frequency fluctuation component Δp DC :

[0094] p DC =p PCC +p L =p DC1 +Δp DC

[0095] Preferably, solving the double frequency fluctuation component on the DC side of the photovoltaic inverter includes:

[0096] Based on the formula p DC =p PCC +p L =p DC1 +Δ pDC , extract p PCC +p L -p DC1 The double frequency component other than the power frequency component is obtained, so that the double frequency fluctuation component of the DC side of the photovoltaic inverter is obtained as follows:

[0097]

[0098] Step 2: solving the fluctuation amplitude coefficient of the double frequency fluctuation component on the DC side of the photovoltaic inverter at different fluctuation phases to obtain the correlation relationship between the fluctuation amplitude coefficient and the drop state.

[0099] The sag state includes a virtual current gain k on the two phases where the voltage sag occurs. a With k c ;

[0100] RC1, RS1, RC2, RS2 are Δp DC The fluctuation coefficient can be expressed as:

[0101]

[0102] Among them, σ1 and σ2 are parameters related to RC1, RS1, RC2, RS2, and:

[0103]

[0104] Step 3, using the fluctuation amplitude coefficient to calculate the DC bus power fluctuation of the photovoltaic inverter, taking the DC bus power fluctuation as the fitness function, taking the two-phase current gain as the input particle, and using the particle swarm algorithm to solve the optimal particle to achieve power management of the two-phase voltage drop of the photovoltaic inverter.

[0105] Then, the amplitude of the DC bus power fluctuation after the introduction of VPCR technology under two-phase voltage drop can be obtained as:

[0106]

[0107] By adjusting the virtual phase current gain introduced by the VPCR technology in the voltage drop phase, the power fluctuation amplitude on the DC side can be suppressed, and the relationship between the gain coefficient and the fluctuation amplitude can be intuitively observed.

[0108] Particle Swarm Optimization Algorithm is a group optimization algorithm that imitates the social behavior of fish and bird flocks when searching for targets or food. Particle Swarm Optimization Algorithm has the characteristics of less parameter adjustment, fast convergence speed and good convergence performance.

[0109] Figure 3 The present invention is a power management method for two-phase voltage drop of photovoltaic inverter based on particle swarm optimization algorithm VPCR technical parameter solution flow chart. The VPCR gain coefficient design method based on particle swarm optimization algorithm is as follows Figure 3 As shown, the design process is as follows:

[0110] First, the problem is defined in 2D space. Each particle i consists of two vectors, namely, velocity vector and position vector, and a particle swarm is randomly generated.

[0111] Secondly, the DC bus power fluctuation formula is substituted into PSO as the fitness function to calculate the DC bus power fluctuation amplitude corresponding to the 1st to ith particles.

[0112] Then, the particles are updated iteratively using the following particle velocity and position update formulas:

[0113]

[0114]

[0115] Among them, i represents the i-th particle, k represents the k-th generation, r1 and r2 are random numbers between 0 and 1, w is the inertia weight, and pbest i k is the individual best position, gbest k is the global best position.

[0116] Finally, when the fitness function corresponding to the global optimal position, that is, the power fluctuation on the DC bus, is zero, the algorithm stops. At this time, the values ​​of the two dimensions of the global optimal position correspond to the two virtual phase current gains k a and k c The optimal value of .

[0117] Power management process Figure 2 As shown, the two virtual phase current gains k a and k c The optimal value of is added to the input three-phase grid-connected current, and then feedback control of the inverter output is implemented through the original inverter control loop.

[0118] In order to verify the effectiveness of the power fluctuation active control system for two-phase voltage drop of photovoltaic inverter proposed in the present invention, simulation verification is carried out. In one embodiment, the DC bus voltage of the grid-connected inverter is 700V, and the filter inductor L in the filter is f is 1.4mH, the grid fundamental voltage amplitude U is 311V, the grid fundamental frequency f1 is 50Hz, and the current loop d-axis reference current i in the control loop d * is 50A, the current loop q axis reference current i q *For -30A, the proportional gain of the current loop PI controller is K p is 15, the integral gain K of the PI controller i is 20000.

[0119] Figure 4 FIG. 1 is a schematic diagram of a DC bus power curve when the VPCR technology is not introduced in an embodiment of a power management method for a two-phase voltage drop of a photovoltaic inverter according to the present invention. Figure 4 As shown, the grid has two phases A and C voltage drops, and the voltage drop ratio of phase A is k a drop is 0.5, C phase voltage drop ratio k c drop The simulation verification is carried out using 0.9 as an example. When the system does not introduce active power fluctuation control measures, the power on the DC bus has a large power fluctuation.

[0120] Figure 5The figure is a schematic diagram of a DC bus power curve when only VPCR technology is introduced in one embodiment of a power management method for two-phase voltage drop of a photovoltaic inverter according to the present invention. The existing VPCR technology only introduces virtual phase current gain k in the two phases A and C where the voltage drops occur. a and k c , and its value is consistent with the voltage drop ratio of each phase, that is, k a =0.5, k c =0.9, then the active power on the DC bus and AC bus is as follows Figure 5 At this time, there is still double frequency fluctuation on the DC bus.

[0121] When the method only uses the VPCR technique, the power fluctuation amplitude is significantly reduced, but the fluctuation still exists.

[0122] Figure 6 This is a schematic diagram of a DC bus power curve when all the effects of voltage drop on the AC and DC sides are considered in an embodiment of a power management method for two-phase voltage drop of a photovoltaic inverter of the present invention. When the VPCR technology proposed by the present invention is introduced into the system, considering the influence of the filter inductance, the virtual phase current gain k is solved by the particle swarm optimization algorithm. a and k c The optimal solutions are 0.5518 and 0.8285 respectively. At this time, the active power on the DC bus and AC bus is as follows: Figure 6 At this time, the double frequency fluctuation on the DC bus is completely eliminated.

[0123] In this embodiment, the theoretical value of the three-phase grid-connected current calculated by the formula is:

[0124]

[0125] Figure 7 The following is a schematic diagram of the waveform of the compensated three-phase grid-connected current in one embodiment of a power management method for a two-phase voltage drop of a photovoltaic inverter according to the present invention. Figure 7 As shown, it is consistent with the current waveform solved theoretically, which verifies the accuracy of the theoretical modeling of the VPCR technology proposed in the present invention.

[0126] The present invention proposes a power fluctuation active management control system suitable for two-phase voltage drop of photovoltaic inverter, which provides a feasible solution for suppressing power oscillation on the DC bus when the two-phase power grid voltage drops.

[0127] In summary, the present invention completely suppresses power fluctuations on the DC side: the three-phase three-wire system can completely suppress power fluctuations on the DC side in the scenario of two-phase voltage drop by introducing VPCR technology in two fault phases. Therefore, the method proposed in the present invention performs better in eliminating power fluctuations on the DC side and two-phase voltage drop power management. This is crucial to improving the stability of inverter power transmission and reducing the cost and size of DC bus capacitors. The significant advantage of the present invention is that it comprehensively solves the power fluctuation problem of photovoltaic inverters in the case of two-phase voltage drop, providing support for the stable operation of the power system.

[0128] Compared with the existing VPCR technology, this method not only manages the power fluctuation on the AC side, but also further handles the power fluctuation on the DC side. In the case of a two-phase voltage drop, the system achieves comprehensive management of power fluctuations by compensating for the currents of the two faulty phases. Compared with the existing VPCR technology, the present invention introduces an advanced power fluctuation active management control system, which not only performs well in the management of power fluctuations on the AC side, but also breaks through the limitations of the existing technology, effectively handles the power fluctuations on the DC side, and achieves comprehensive suppression of the unbalanced state of the power grid. This innovative method performs excellently in solving common problems in the power grid. It can not only cope with two-phase voltage drops, but also has excellent management effects on the three-phase unbalanced state of the power grid, effectively reducing the burden on the DC bus capacitor and improving the stability of the inverter power transmission.

[0129] The present invention uses a particle swarm optimization algorithm to optimize the current gain coefficients of the two virtual phases, proving that the VPCR technology can minimize the power fluctuation on the DC side in the scenario of two-phase voltage drop and meet the needs of traditional engineering. This provides a new technical path for practical applications and provides support at the theoretical level. This theoretical support provides a reliable technical path for practical applications, making this control strategy the preferred choice for the connection between new energy power generation systems and AC power grids.

[0130] In general, the present invention has made significant contributions in improving the stability of the connection between the new energy power generation system and the AC power grid and reducing the negative impact of the unbalanced state of the power system on the inverter output power and the grid-connected current quality.

[0131] The second aspect of the present invention relates to a power management system suitable for two-phase voltage drop of a photovoltaic inverter, the system is used to implement the power management method suitable for two-phase voltage drop of a photovoltaic inverter in the first aspect of the present invention; and the system includes a calculation module, an association module and a management module; wherein the calculation module is used to collect the drop state when the two-phase voltage drops in the three-phase three-wire photovoltaic inverter, and calculate the active power of the AC side of the photovoltaic inverter, the instantaneous power of the filter inductor, and the constant power of the DC side based on the drop state to solve the double frequency fluctuation component of the DC side of the photovoltaic inverter; the association module is used to solve the fluctuation amplitude coefficient of the double frequency fluctuation component on the DC side of the photovoltaic inverter at different fluctuation phases to obtain the correlation between the fluctuation amplitude coefficient and the drop state; the management module is used to use the fluctuation amplitude coefficient to characterize the DC bus power fluctuation of the photovoltaic inverter, take the DC bus power fluctuation as the fitness function, take the two-phase current gain as the input particle, and use the particle swarm algorithm to solve the optimal particle to achieve power management of the two-phase voltage drop of the photovoltaic inverter.

[0132] A third aspect of the present invention relates to a terminal, comprising a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method according to the first aspect of the present invention.

[0133] A fourth aspect of the present invention relates to a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method in the first aspect of the present invention.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A power management method for two-phase voltage drop of photovoltaic inverter, characterized in that: The method comprises the following steps: The voltage drop state of a three-phase three-wire photovoltaic inverter when two-phase voltage drops occurs is collected, and expressions of the active power on the AC side of the photovoltaic inverter, the instantaneous power of the filter inductor, and the constant power on the DC side are obtained based on the voltage drop state, so as to derive an expression of the double frequency fluctuation component on the DC side of the photovoltaic inverter; Solving the fluctuation amplitude coefficient of the double frequency fluctuation component on the DC side of the photovoltaic inverter at different fluctuation phases to obtain the correlation relationship between the fluctuation amplitude coefficient and the drop state; The DC bus power fluctuation of the photovoltaic inverter is calculated by using the fluctuation amplitude coefficient, the DC bus power fluctuation is used as the fitness function, the virtual phase current gains of the two phases where the voltage drop occurs are used as input particles, and the particle swarm algorithm is used to solve the optimal particles to achieve power management of the two-phase voltage drop of the photovoltaic inverter.

2. A power management method for two-phase voltage drop of a photovoltaic inverter according to claim 1, characterized in that: The collecting of the voltage drop status of a three-phase three-wire photovoltaic inverter when two-phase voltage drops occurs includes: The instantaneous value of the three-phase voltage when the two-phase voltage drops is collected to calculate the three-phase voltage as follows: Using the three-phase voltage, the two-phase voltage drop ratio k is restored a drop and k c drop .

3. A power management method applicable to two-phase voltage drop of photovoltaic inverter according to claim 2, characterized in that: The expression for obtaining the AC side active power, the instantaneous power of the filter inductor, and the DC side constant power of the photovoltaic inverter based on the drop state includes: The AC side active power of the photovoltaic inverter is: Wherein, U is the fundamental voltage, I1 is the current amplitude in the control loop of the photovoltaic inverter, ω is the grid angular velocity, t is time, is the initial phase of the current on the control loop of the photovoltaic inverter; And there is k a With k c is the virtual current gain on the two phases where voltage sag occurs.

4. A power management method applicable to two-phase voltage drop of photovoltaic inverter according to claim 3, characterized in that: The expression for obtaining the AC side active power, the instantaneous power of the filter inductor, and the DC side constant power of the photovoltaic inverter based on the drop state includes: The instantaneous power of the filter inductor is: p L =in La and a +in Lb and b +in Lc and c In the formula, the three-phase voltage across the filter inductor is: The three-phase grid-connected current of the photovoltaic inverter is:

5. A power management method applicable to two-phase voltage drop of photovoltaic inverter according to claim 4, characterized in that: The expression for obtaining the AC side active power, the instantaneous power of the filter inductor, and the DC side constant power of the photovoltaic inverter based on the drop state includes: The constant power p on the DC side DC1 The calculation is based on the power grid power frequency component in the AC side power of the photovoltaic inverter.

6. A power management method applicable to two-phase voltage drop of photovoltaic inverter according to claim 5, characterized in that: The expression for deriving the double frequency fluctuation component on the DC side of the photovoltaic inverter includes: Based on the formula p DC =p PCC +p L =p DC1 +Δp DC , extract p PCC +p L -p DC1 The double frequency component other than the power frequency component is obtained, so that the double frequency fluctuation component of the DC side of the photovoltaic inverter is obtained as follows:

7. A power management method applicable to two-phase voltage drop of photovoltaic inverter according to claim 6, characterized in that: The step of solving the fluctuation amplitude coefficient of the double frequency fluctuation component on the DC side of the photovoltaic inverter at different fluctuation phases to obtain the correlation between the fluctuation amplitude coefficient and the drop state includes: The fluctuation amplitude coefficient is: In the formula, Among them, σ1 and σ2 are parameters related to RC1, RS1, RC2, RS2, and:

8. A power management method applicable to two-phase voltage drop of photovoltaic inverter according to claim 7, characterized in that: The method of using the fluctuation amplitude coefficient to characterize the DC bus power fluctuation of the photovoltaic inverter includes: The DC bus power fluctuation is:

9. A power management method applicable to two-phase voltage drop of photovoltaic inverter according to claim 8, characterized in that: The method uses the DC bus power fluctuation as the fitness function, uses the virtual phase current gains of the two phases that have dropped as input particles, and uses a particle swarm algorithm to solve the optimal particle, including: randomly generating a plurality of particles with virtual phase current gain as a two-dimensional vector to obtain an initial particle group; Iteratively updating the particle speed and position in the initial particle group, and ending the iteration when the fitness function takes a value of 0, thereby obtaining the optimal particle; After multiplying the value of the two-phase current gain in the optimal particle by the instantaneous value of the three-phase voltage when the two-phase voltage drops, the gain voltage is input into the control loop to implement feedback control of the photovoltaic inverter.

10. A power management system suitable for two-phase voltage drop of photovoltaic inverter, characterized by: The system is used to implement the power management method applicable to two-phase voltage drop of photovoltaic inverters as described in any one of claims 1 to 9; and The system includes a calculation module, an association module and a governance module; wherein, The calculation module is used to collect the drop state of the three-phase three-wire photovoltaic inverter when two-phase voltage drops occur, and obtain the expressions of the AC side active power, the instantaneous power of the filter inductor, and the DC side constant power of the photovoltaic inverter based on the drop state, so as to derive the expression of the double frequency fluctuation component on the DC side of the photovoltaic inverter; The association module is used to solve the fluctuation amplitude coefficient of the double frequency fluctuation component on the DC side of the photovoltaic inverter at different fluctuation phases to obtain the association relationship between the fluctuation amplitude coefficient and the drop state; The management module is used to use the fluctuation amplitude coefficient to characterize the DC bus power fluctuation of the photovoltaic inverter, use the DC bus power fluctuation as the fitness function, use the two-phase current gain as the input particle, and use the particle swarm algorithm to solve the optimal particle to achieve power management of the two-phase voltage drop of the photovoltaic inverter.

11. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1-9.

12. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 9 are implemented.

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