A three-phase power decoupling control method and related device based on a three-phase four-arm photovoltaic grid-connected inverter

Abstract

This invention provides a three-phase power decoupling control method and related apparatus based on a three-phase four-arm photovoltaic grid-connected inverter. Applied to a topology based on this inverter, the method includes power and current compensation for the three phases of the low-voltage distribution network; decomposing the current compensation components into positive and negative zero-sequence components to obtain the three-phase positive and negative zero-sequence current components, and performing an abc / dq0 coordinate transformation to further obtain the three-phase DC current; introducing a feedforward compensation quantity into the inner-loop current controller based on a PI element in a synchronous rotating coordinate system to obtain the output current of the independently decoupled control; and summing the output currents after coordinate transformation, using 3D-SVPWM modulation to obtain the drive signal for the inverter's switching transistors. This invention, through a three-phase power decoupling control strategy, enables the management of three-phase imbalance in grid-connected photovoltaic systems and uninterrupted intelligent power transfer of photovoltaic output under single-phase or two-phase faults.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic grid-connected technology in low-voltage distribution networks, specifically relating to a three-phase power decoupling control method and related devices based on a three-phase four-arm photovoltaic grid-connected inverter. Background Technology

[0002] With the continuous advancement of my country's energy policy, distributed new energy sources have received greater attention. In particular, the application scale of distributed photovoltaics in rural areas, buildings, and industrial parks is showing a rapid development trend. Since grid-connected photovoltaic power generation systems do not require energy storage equipment, they have become the primary choice for renewable energy power generation.

[0003] Currently, three-phase imbalance is a common problem in low-voltage distribution networks. Large-scale photovoltaic (PV) grid connection exacerbates this problem, making the operating environment of low-voltage distribution networks more complex. While rural PV energy development is increasing year by year, compared to urban low-voltage distribution networks, rural low-voltage distribution networks have relatively lower reliability and weaker grid infrastructure. Faults in rural distribution networks lead to PV systems being disconnected from the grid, resulting in a waste of PV resources. Summary of the Invention

[0004] In view of this, the purpose of this invention is to address the three-phase imbalance in low-voltage distribution networks and to ensure uninterrupted power supply of photovoltaic output power under single-phase and two-phase fault conditions in low-voltage distribution networks. A three-phase power decoupling control method and related device based on the maximum power output of a three-phase four-bridge-arm photovoltaic grid-connected inverter are proposed.

[0005] With the large-scale integration of distributed photovoltaic (PV) systems, the three-phase imbalance problem in low-voltage distribution networks has become increasingly prominent. Furthermore, the relatively weak infrastructure of low-voltage distribution networks leads to PV grid disconnection and resource waste in the event of a fault. This invention utilizes a three-phase power decoupling control strategy to address three-phase imbalance during PV grid connection and to enable uninterrupted intelligent power transfer of PV output in the event of a single-phase or two-phase fault.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter, which is applied to a topology based on a three-phase four-arm photovoltaic grid-connected inverter. The topology includes a photovoltaic array, a Boost converter, a three-phase four-arm photovoltaic inverter and a low-voltage distribution network. The photovoltaic array and the low-voltage distribution network are respectively connected to the DC bus through the Boost converter and the three-phase four-arm inverter.

[0008] The method includes the following steps:

[0009] Based on the difference between the transmission power of the photovoltaic array and the output power of the three phases of the low-voltage distribution network, power compensation is performed on the three phases of the low-voltage distribution network.

[0010] Based on the power compensation value and the voltage value of the common connection point between the three-phase four-arm photovoltaic inverter and the low-voltage distribution area, current compensation is performed on the three phases of the low-voltage distribution network.

[0011] The current compensation components are decomposed into positive and negative zero sequence to obtain the three-phase positive and negative zero sequence current components.

[0012] The positive and negative zero-sequence current components are transformed by the coordinates abc / dq0 to obtain the three-phase DC components;

[0013] In the inner loop current controller based on PI element in the synchronous rotating coordinate system, a feedforward compensation is introduced for the three-phase four-arm photovoltaic inverter to eliminate the coupling terms in the synchronous rotating coordinate coefficient mathematical model and obtain the output current of independent decoupled control.

[0014] The output current is transformed by dq0 / abc and then added together. The drive signal of the three-phase four-bridge arm inverter switching transistor is obtained by 3D-SVPWM modulation.

[0015] Furthermore, power compensation is performed on the three phases of the low-voltage distribution network according to the three-phase fault conditions. The power compensation is performed according to the following formula:

[0016] When there is no fault in the three phases, P X =P Xload -P avgload +P all / 3, Q X =Q Xload ,

[0017] In the formula, the subscript X represents the fault-free phase among phases a, b, and c, and P X P represents the active component of phase X compensation. Xload P represents the active component of the X-phase output power in a low-voltage distribution network. all Q represents the transmission power of the photovoltaic array. X P represents the reactive component of the X-phase output power in a low-voltage distribution network. avgload =(P aload +P bload +P cload ) / 3, P aload P bload P cload These are the active components of the three-phase output power of the low-voltage distribution network, Q. Xload This represents the reactive component of the output power of phase X in a low-voltage distribution network.

[0018] During a two-phase fault, P X =P all QX =Q Xload ;

[0019] During a single-phase fault, P X =P Xload -P avgload +P all / 2, Q X =Q xload ,

[0020] In the formula, P avgload =(P X1load +P X2load ) / 3, where subscripts X1 and X2 represent two fault-free phases in phases a, b, and c, respectively.

[0021] Furthermore, current compensation is performed on the three phases of the low-voltage distribution network, including:

[0022] For the voltage values ​​of the three-phase common connection point of the three-phase four-bridge-arm photovoltaic inverter and the low-voltage distribution area, two orthogonal signals corresponding to the voltage values ​​of each phase common connection point are obtained by a second-order generalized integrator.

[0023] Based on the two orthogonal signals and power compensation values ​​of each phase, the current compensation components of the three phases of the low-voltage distribution network are determined.

[0024] Furthermore, the current compensation component is calculated according to the following formula:

[0025]

[0026] In the formula, the subscript X represents phase a, b, or c, and μ gxα and μ gXβ These are two quadrature signals of phase X, P X and Q X These represent the compensated active and reactive components of phase X, respectively.

[0027] Furthermore, the three-phase positive and negative zero-sequence current components are as follows:

[0028]

[0029] In the formula, This represents the positive and negative zero-sequence current components of phase X.

[0030] Furthermore, the positive and negative zero-sequence current components are subjected to an abc / dq0 coordinate transformation, including:

[0031] The positive sequence components are rotated into DC components using positive sequence rotating coordinates. dpref i qnref ;

[0032] The negative-order component is rotated to its flow rate i using a negative-order rotating coordinate system. dpref iqnref ;

[0033] The zero-sequence components are constructed by delaying phases B and C by 4 / 3π and 2 / 3π respectively, and then rotated into DC components using positive-sequence rotating coordinates. d0ref i q0ref .

[0034] Furthermore, the feedforward compensation is a voltage compensation, which is used to decouple the d-axis and q-axis current calculation equations, resulting in two independent current loops, thereby achieving independent decoupling of the currents.

[0035] In a second aspect, the present invention provides a three-phase power decoupling control device based on a three-phase four-arm photovoltaic grid-connected inverter, implemented based on the three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter as described in the first aspect, comprising:

[0036] The power compensation calculation component calculation unit is used to perform power compensation on the three phases of the low-voltage distribution network based on the difference between the transmission power of the photovoltaic array and the output power of the three phases of the low-voltage distribution network.

[0037] The current compensation component calculation unit is used to perform current compensation on the three phases of the low-voltage distribution network based on the power compensation value and the voltage value of the common connection point between the three-phase four-arm photovoltaic inverter and the low-voltage distribution area.

[0038] The positive and negative zero sequence separation and dq0 transformation unit is used to decompose the current compensation component into positive and negative zero sequence to obtain the three-phase positive and negative zero sequence current components; it is also used to perform abc / dq0 coordinate transformation on the positive and negative zero sequence current components to obtain the three-phase DC components.

[0039] The positive and negative zero sequence decoupling control unit is used to introduce feedforward compensation in the inner loop current controller based on PI element in the synchronous rotating coordinate system of a three-phase four-bridge photovoltaic inverter, so as to eliminate the coupling terms in the synchronous rotating coordinate coefficient mathematical model and obtain the output current of independent decoupling control.

[0040] The signal modulation unit is used to convert the output current by dq0 / abc and then add them together, and uses 3D-SVPWM modulation to obtain the drive signal of the switching transistor of the three-phase four-bridge-arm inverter.

[0041] Accordingly, the present invention also provides a computer device, the device including a processor and a memory:

[0042] The memory is used to store computer programs and send the instructions of the computer programs to the processor;

[0043] The processor executes a three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter, as described in the first aspect, according to the instructions of the computer program.

[0044] Accordingly, the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter as described in the first aspect.

[0045] In summary, this invention provides a three-phase power decoupling control method and related apparatus based on a three-phase four-arm photovoltaic grid-connected inverter, applicable to a topology based on a three-phase four-arm photovoltaic grid-connected inverter. The method includes: power compensation for the three phases of the low-voltage distribution network based on the difference between the transmitted power of the photovoltaic array and the output power of the three phases of the low-voltage distribution network; current compensation for the three phases of the low-voltage distribution network based on the power compensation value and the voltage value at the common connection point between the three-phase four-arm photovoltaic inverter and the low-voltage distribution network; and setting the positive and negative zero values ​​for the current compensation components. Sequence decomposition yields the three-phase positive and negative zero-sequence current components. These components are then transformed using the abc / dq0 coordinate system to obtain the three-phase DC current. In the inner-loop current controller based on a PI element in the synchronous rotating coordinate system, a feedforward compensation is introduced to eliminate coupling terms in the synchronous rotating coordinate coefficient mathematical model, resulting in the output current of the independently decoupled control. The output current is then transformed using the dq0 / abc system and summed, and 3D-SVPWM modulation is used to obtain the drive signal for the switching transistors of the three-phase four-arm inverter. This invention, through a three-phase power decoupling control strategy, enables the management of three-phase imbalance in photovoltaic grid connection and uninterrupted intelligent power transfer of photovoltaic output power under single-phase or two-phase faults. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A topology diagram of a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-arm photovoltaic grid-connected inverter is provided in this embodiment of the invention.

[0048] Figure 2 A general control block diagram of a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-arm photovoltaic grid-connected inverter, provided for an embodiment of the present invention;

[0049] Figure 3 A flowchart for calculating the power compensation component of a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-arm photovoltaic grid-connected inverter, provided for embodiments of the present invention;

[0050] Figure 4 A block diagram for calculating the current compensation component of a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-arm photovoltaic grid-connected inverter, provided for embodiments of the present invention;

[0051] Figure 5 A block diagram of a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-bridge-arm photovoltaic grid-connected inverter, including positive and negative zero sequence separation and abc / dq0 transformation, is provided for an embodiment of the present invention.

[0052] Figure 6a The three-phase voltage waveform and three-phase unbalance waveform diagram of a three-phase four-arm photovoltaic converter without three-phase decoupling control are provided in the embodiments of the present invention.

[0053] Figure 6b The three-phase voltage waveform and three-phase unbalance waveform diagram of a three-phase four-arm photovoltaic converter using three-phase decoupling control are provided for embodiments of the present invention.

[0054] Figure 7 The waveform diagrams of the active power and reactive power output of the ABC three-phase photovoltaic converter provided in the embodiment of the present invention;

[0055] Figure 8 The waveform diagrams of the active power and reactive power output of the ABC three-phase photovoltaic converter provided in the embodiment of the present invention;

[0056] Figure 9 A block diagram of a three-phase power decoupling control device based on a three-phase four-arm photovoltaic grid-connected inverter provided in an embodiment of the present invention;

[0057] Figure 10 This is a block diagram of a computer device provided in an embodiment of the present invention. Detailed Implementation

[0058] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0059] This embodiment provides a three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter, which is applied to a topology based on a three-phase four-arm photovoltaic grid-connected inverter. The topology includes a photovoltaic array, a Boost converter, a three-phase four-arm photovoltaic inverter, and a low-voltage distribution network. The photovoltaic array and the low-voltage distribution network are respectively connected to the DC bus through the Boost converter and the three-phase four-arm inverter.

[0060] Please see Figure 1 , Figure 1 This is a topology diagram of a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-arm photovoltaic grid-connected inverter. The photovoltaic grid-connected system adopts a two-stage topology. The front stage is connected to both ends of the bus capacitor via a boost circuit, and controls the PV units through the MPPT algorithm to maximize their output power. The rear stage inverter circuit consists of a three-phase four-arm inverter, an LCL filter, and a low-voltage distribution network. Its function is to achieve three-phase power decoupling and power balance between the front and rear stages, and stabilize the bus voltage.

[0061] The method provided in this embodiment includes the following steps:

[0062] S1: Based on the difference between the transmission power of the photovoltaic array and the output power of the three phases of the low-voltage distribution network, power compensation is performed on the three phases of the low-voltage distribution network;

[0063] S2: Based on the power compensation value and the voltage value of the common connection point between the three-phase four-arm photovoltaic inverter and the low-voltage distribution area, current compensation is performed on the three phases of the low-voltage distribution network.

[0064] S3: Perform positive and negative zero-sequence decomposition on the current compensation component to obtain the three-phase positive and negative zero-sequence current components;

[0065] S4: Perform abc / dq0 coordinate transformation on the positive and negative zero-sequence current components to obtain the three-phase DC flow;

[0066] S5: For a three-phase four-arm photovoltaic inverter, a feedforward compensation is introduced into the inner loop current controller based on the PI link in the synchronous rotating coordinate system to eliminate the coupling terms in the synchronous rotating coordinate coefficient mathematical model and obtain the output current of independent decoupled control.

[0067] S6: The output current is converted by dq0 / abc and then added together. The drive signal of the three-phase four-bridge arm inverter switching transistor is obtained by 3D-SVPWM modulation.

[0068] This control method can achieve uninterrupted power supply of photovoltaic output power under single-phase or two-phase fault conditions and address three-phase imbalance issues.

[0069] Furthermore, step S1 includes the following steps:

[0070] 1) Measure the transmission power P of the DC bus photovoltaic array. all =P pv1 +...+P pvn Measure the output power S of the three phases of the low-voltage distribution network aload =P aload +jQ aload S bload =P bload +jQ bload S cload =P cload +jQ cload Measure the phase current at the PCC point, i gabc .

[0071] 2) Determine i gabc =0 (used to determine whether a fault has occurred in the three phases A, B, and C, the circuit breaker has tripped, and no current is flowing).

[0072] Assumption 1: Three-phase fault-free I ga I gb I gc ≠0 (Managing the three-phase imbalance)

[0073] 31) Calculate the average active power P transmitted in the low-voltage distribution network. avgload =(P aload +P bload +P cload ) / 3.

[0074] 41) Phase A compensation active and reactive power components P a =P aload -P avgload +P all / 3, Q a =Q aload Phase B compensates for active and reactive power components P b =P bload -P avgload +P all / 3, Q b =Q bload C-phase compensation of active and reactive power components P c =P cload -P avgload +P all / 3, Q c =Q cload .

[0075] Assumption 2: Two-phase fault (taking AB phase fault as an example) I ga =0, I gb =0, I gc ≠0

[0076] 32) The active and reactive components P of the two-phase compensation of ABa =P b =Q a =Q b =0, C-phase compensation active and reactive power components P c =P all Q c =Q cload .

[0077] Assumption 3: Single-phase fault (taking phase A fault as an example) ga =0, I gb ≠0, I gc ≠0

[0078] 33) Calculate the average active power P transmitted between phases BC in a low-voltage distribution network. avgload =(P bload +P cload ) / 3.

[0079] 43) Phase A compensation active and reactive power components P a =Q a =0, Phase B compensation active and reactive components P b =P bload -P bvgload +P all / 2, Q b =Q bload C-phase compensation of active and reactive power components P c =P cload -P cvgload +P all / 2, Q c =Q cload .

[0080] Further, step S2 includes the following steps:

[0081] 1) Measure the phase voltage u at the PCC point gabc .

[0082] 2) Construct u using SOGI gaα u gaβ u gbα u gbβ u gcα u gcβ .

[0083] 3) Calculate the compensation current for phase A. Calculate the compensation current of phase B. Calculate the C-phase compensation current

[0084] Furthermore, steps S3 and S4 include the following steps:

[0085] 1) The compensation current components obtained from the preceding steps are decomposed into positive and negative zero sequences to obtain:

[0086] 2) Perform abc / dq0 coordinate transformation on the positive and negative zero sequence components obtained in step 1). The positive sequence component is rotated to a DC component using positive sequence rotating coordinates. dpref l qnref The negative order component uses a negative order rotating coordinate system l dpref i qnref The zero-sequence components are constructed by delaying phases B and C by 4 / 3π and 2 / 3π respectively, and then rotated into DC components using positive-sequence rotating coordinates. d0ref i q0ref .

[0087] in:

[0088]

[0089] in:

[0090]

[0091] Furthermore, steps S5 and S6 include the following steps:

[0092] 1) In the mathematical model of a three-phase four-bridge arm PI-based inner-loop current controller in a synchronous rotating coordinate system, a feedforward compensation Δu is introduced. dk ,Δu qk , Δu d0 ,Δu q0 By eliminating coupling terms in the synchronous rotating coordinate coefficient mathematical model, the output current i of independent decoupled control is obtained. dkout i qkout i d0out i q0out (k = p, n);

[0093] In a PI-based positive and negative sequence inner loop current controller and feedforward compensation Δu dk ,Δu qk In the middle, there are:

[0094]

[0095] d-axis and q-axis currents excluding the controlled variable u cdk u cqk In addition to the influence of the current cross-coupling term ωLi, it is also affected by the current cross-coupling term ωLi qk ,ωLi dk and grid voltage u dk u qk The effect of this. To eliminate the coupling term, feedforward compensation Δu is introduced. dk ,Δuqk but:

[0096]

[0097] In the formula:

[0098]

[0099] In equation (2), v dk ,v qk i dk i qk The first-order differential voltage is expressed in equation (3), where the decoupling term can be achieved using the proportional integral of equation (4) to compensate for the voltage drop across the equivalent reactor. From (3), it can be seen that by introducing feedforward compensation Δu... dk ,Δu qk This decouples the nonlinear equations, resulting in two independent current loops, thus enabling independent decoupled control of the current.

[0100]

[0101] Output current i of independent decoupling control dkout i qkout ,as follows:

[0102]

[0103] k p ,k i These are the proportional and integral coefficients of the d-axis and p-axis PI controllers, respectively, for the inner loop of the positive and negative sequence currents of the converter.

[0104] For the zero-sequence component, in the zero-sequence inner-loop current controller of the base PI circuit, there is also

[0105]

[0106] d-axis and q-axis currents excluding the controlled variable u cd0 ,u cq In addition to the influence of 0, it is also affected by the grid voltage u sd ,u sq The impact.

[0107] Output current i of independent decoupling control outd0 i outq0 ,as follows:

[0108]

[0109] k p ,k i These are the proportional and integral coefficients of the d-axis and p-axis PI controllers, respectively, for the zero-sequence current inner loop of the converter.

[0110] 2) The output current i in step 1) dkout i qkout i d0out i q0out Perform dq0 / abc transformation to obtain i apout i anout i a0out i bpout i bnout i b0out i cpout i cnout i c0out Then add them together to get the modulation signal v a v b v c Then, the drive signal of the switching transistor of the three-phase four-bridge-arm inverter can be obtained by 3D-SVPWM modulation in the abc coordinate system.

[0111] in:

[0112]

[0113] v a =i apout +i anout +i aoout

[0114] v b =i bpout +i bnout +i aoout

[0115] v c =i cpout +i cnout +i a0out

[0116] Figure 2 This is a general control block diagram of a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-arm photovoltaic grid-connected inverter according to the present invention. The method includes a power compensation component calculation module, a current compensation component calculation module, a positive / negative zero-sequence separation and abc / dq0 conversion module, and DC bus voltage outer loop and current inner loop control. Both the voltage outer loop and the current inner loop use PI control. The command for the inner loop comes from the positive / negative zero-sequence separation and abc / dq0 conversion module, and the switching signal is output through feedforward decoupling and 3D-SVPWM modulation.

[0117] Figure 3This invention presents a flowchart illustrating the calculation of power compensation components for a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-arm photovoltaic grid-connected inverter. This method determines the inverter's operating mode (three-phase imbalance mitigation or uninterrupted power supply) by detecting the current in the low-voltage distribution network to identify whether a circuit breaker has tripped due to a fault, thereby determining the inverter's operating mode.

[0118] Figure 4 This invention presents a block diagram for calculating the current compensation component of a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-arm photovoltaic grid-connected inverter. This method constructs a two-phase stationary coordinate system using SOGI and calculates the relationship between power and current within this system (the specific calculation of the compensation current component is described above).

[0119] Figure 5 This invention presents a three-phase power decoupling control strategy based on the maximum power output of a three-phase four-arm photovoltaic grid-connected inverter, involving positive and negative zero-sequence separation and an abc / dq0 transformation block diagram. Based on the relationship between the three unbalanced components, SOGI is used to separate the three-sequence components. Positive-sequence components undergo positive-sequence coordinate transformation, negative-sequence components undergo negative-sequence coordinate transformation, and zero-sequence components are delayed by 4 / 3π and 2 / 3π respectively to construct positive-sequence components. A positive-sequence rotating coordinate transformation is then applied to obtain the command reference value in the dp0 coordinate system.

[0120] The effectiveness of the method proposed in this invention will be verified and analyzed through simulation:

[0121] A simulation model of a photovoltaic grid-connected inverter was built using Matlab / Simulink software, and the method proposed in this invention was compared with the simulation results. The simulation model parameters are shown in the table below.

[0122]

[0123] Simulation Example 1: Three-phase power decoupling control to address three-phase imbalance

[0124] Figure 6(a) shows the three-phase voltage waveform and three-phase unbalance waveform of a three-phase four-arm photovoltaic converter without three-phase decoupling control. Under the same conditions, the three-phase voltage waveform and three-phase unbalance waveform of the three-phase four-arm photovoltaic converter with three-phase decoupling control proposed in this invention are shown in Figure 6(a). The active power and reactive power waveforms of the three-phase output of the three-phase four-arm photovoltaic converter (A, B, and C) are shown in Figure 6(b).

[0125] As shown in Figure 6(a), under the condition of a three-phase four-arm photovoltaic converter without three-phase decoupling control, the three-phase imbalance is about 5%, exceeding the three-phase imbalance limit of 2%. Under the condition of using a three-phase four-arm photovoltaic converter with three-phase decoupling control, the three-phase imbalance is about 0%, effectively addressing the system's three-phase imbalance problem. Figure 6(b) shows that after the inverter decoupling control, the 10kW photovoltaic power compensates for 5.08kW of active power in phase A, 4.22kW of active power in phase B, and 0.7kW of active power in phase C. The photovoltaic inverter compensates for 5.15kVar of reactive power in phase A, 4.54kVar of active power in phase B, and 2.88kVar of active power in phase C.

[0126] Simulation Example 2: Single-phase fault (power supply uninterrupted when switching from three-phase to two-phase grid connection)

[0127] In the simulation, phase A disconnects due to a fault in 0.1s, and phase A is disconnected from the grid. Figure 7 The waveforms show the active and reactive power outputs of the ABC three-phase photovoltaic converter. Figure 7 It can be seen that after the photovoltaic power of 10kW is decoupled and controlled by the inverter, the active power of phase A is compensated to be 0kW, the active power of phase B is 6.76kW, and the active power of phase C is 3.24kW. The photovoltaic inverter compensates for the reactive power of phase A to be 0kVar, the active power of phase B to be 4.54kVar, and the active power of phase C to be 2.88kVar.

[0128] Simulation Example 3: Two-phase fault (uninterrupted power supply switching from three-phase grid connection to single-phase grid connection)

[0129] In the simulation, phases A and B disconnected due to a fault in 0.1s, and phases A and B were disconnected from the grid. Figure 8 The waveforms show the active and reactive power outputs of the ABC three-phase photovoltaic converter. Figure 8 It can be seen that after the photovoltaic power of 10kW is decoupled and controlled by the inverter, the active power of phase A is 0kW, the active power of phase B is 0kW, and the active power of phase C is 10kW. The photovoltaic inverter compensates for the reactive power of phase A (0kVar), the active power of phase B (0kVar), and the active power of phase C (2.88kVar).

[0130] Compared with the prior art, the present invention has the following advantages:

[0131] This invention addresses the problem that large-scale photovoltaic grid connection exacerbates three-phase imbalance in low-voltage distribution networks and leads to photovoltaic off-grid issues during low-voltage distribution network faults. This invention proposes a three-phase power decoupling control strategy based on a three-phase four-arm photovoltaic inverter, which can achieve uninterrupted intelligent power transfer and three-phase imbalance mitigation for photovoltaic grid connection.

[0132] Based on the same inventive concept, this application also provides a three-phase power decoupling control device for implementing the aforementioned three-phase power decoupling control method for a three-phase four-arm photovoltaic grid-connected inverter. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations in the embodiments of the three-phase power decoupling control device for a three-phase four-arm photovoltaic grid-connected inverter provided below can be found in the limitations of the three-phase power decoupling control method for a three-phase four-arm photovoltaic grid-connected inverter described above, and will not be repeated here.

[0133] Please see Figure 9 This embodiment provides a three-phase power decoupling control device based on a three-phase four-arm photovoltaic grid-connected inverter, implemented based on the three-phase power decoupling control method for a three-phase four-arm photovoltaic grid-connected inverter as described in the previous embodiment, including:

[0134] The power compensation calculation component calculation unit is used to perform power compensation on the three phases of the low-voltage distribution network based on the difference between the transmission power of the photovoltaic array and the output power of the three phases of the low-voltage distribution network.

[0135] The current compensation component calculation unit is used to perform current compensation on the three phases of the low-voltage distribution network based on the power compensation value and the voltage value of the common connection point between the three-phase four-arm photovoltaic inverter and the low-voltage distribution area.

[0136] The positive and negative zero sequence separation and dq0 transformation unit is used to decompose the current compensation component into positive and negative zero sequence to obtain the three-phase positive and negative zero sequence current components; it is also used to perform abc / dq0 coordinate transformation on the positive and negative zero sequence current components to obtain the three-phase DC components.

[0137] The positive and negative zero sequence decoupling control unit is used to introduce feedforward compensation in the inner loop current controller based on PI element in the synchronous rotating coordinate system of a three-phase four-bridge photovoltaic inverter, so as to eliminate the coupling terms in the synchronous rotating coordinate coefficient mathematical model and obtain the output current of independent decoupling control.

[0138] The signal modulation unit is used to convert the output current by dq0 / abc and then add them together, and uses 3D-SVPWM modulation to obtain the drive signal of the switching transistor of the three-phase four-bridge-arm inverter.

[0139] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0140] Reference Figure 10 The present invention also provides a computer device 3, including: a memory 302 and a processor 301, and a computer program 303 stored in the memory 302. When the computer program 303 is executed on the processor 301, it implements the three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter as described in any of the above methods.

[0141] The computer device 3 may be a desktop computer, laptop, handheld computer, or cloud server, etc. The computer device 3 may include, but is not limited to, a processor 301 and a memory 302. Those skilled in the art will understand that... Figure 10 The computer device 3 is merely an example and does not constitute a limitation on the computer device 3. It may include more or fewer components than shown in the figure, or combine certain components, or different components, such as input / output devices, network access devices, etc.

[0142] The processor 301 may be a Central Processing Unit (CPU), or it may be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0143] In some embodiments, the memory 302 may be an internal storage unit of the computer device 3, such as a hard disk or memory of the computer device 3. In other embodiments, the memory 302 may be an external storage device of the computer device 3, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., equipped on the computer device 3. Furthermore, the memory 302 may include both internal and external storage units of the computer device 3. The memory 302 is used to store the operating system, applications, bootloader, data, and other programs, such as the program code of the computer program. The memory 302 can also be used to temporarily store data that has been output or will be output.

[0144] This invention also provides a computer-readable storage medium storing a computer program thereon. When the computer program is run by a processor, it implements the three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter as described in any of the above methods.

[0145] In this embodiment, if the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include at least: any entity or device capable of carrying computer program code to a photographing device / terminal device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium. Examples include USB flash drives, portable hard drives, magnetic disks, or optical disks. In some jurisdictions, according to legislation and patent practice, computer-readable media cannot be electrical carrier signals or telecommunication signals.

[0146] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0147] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0148] In the embodiments disclosed in this application, it should be understood that the disclosed devices / terminal equipment and methods can be implemented in other ways. For example, the device / terminal equipment embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual coupling or direct coupling or communication connection may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0149] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter, characterized in that, This is applied to a topology based on a three-phase four-arm photovoltaic grid-connected inverter. The topology includes a photovoltaic array, a Boost converter, a three-phase four-arm photovoltaic inverter, and a low-voltage distribution network. The photovoltaic array and the low-voltage distribution network are respectively connected to the DC bus through the Boost converter and the three-phase four-arm photovoltaic inverter. The method includes the following steps: Based on the difference between the transmission power of the photovoltaic array and the output power of the three phases of the low-voltage distribution network, power compensation is performed on the three phases of the low-voltage distribution network. Based on the power compensation value and the voltage value of the common connection point between the three-phase four-arm photovoltaic inverter and the low-voltage distribution network, current compensation is performed on the three phases of the low-voltage distribution network. The current compensation components are decomposed into positive and negative zero sequence to obtain the three-phase positive and negative zero sequence current components. The positive and negative zero-sequence current components are subjected to an abc / dq0 coordinate transformation to obtain the three-phase DC flow. The three-phase four-arm photovoltaic inverter is based on the synchronous rotating coordinate system. In the inner loop current controller of the circuit, a feedforward compensation is introduced to eliminate the coupling terms in the synchronous rotating coordinate coefficient mathematical model and obtain the output current of independent decoupled control. The output current is transformed by dq0 / abc and then added together. The driving signal of the switching transistor of the three-phase four-arm photovoltaic inverter is obtained by 3D-SVPWM modulation.

2. The three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter according to claim 1, characterized in that, Based on the three-phase fault conditions, power compensation is performed on the three phases of the low-voltage distribution network according to the following formula: When all three phases are functioning correctly , In the formula, the subscript X represents the fault-free phase among phases a, b, and c. This indicates the active component of phase X compensation. This represents the active component of the X-phase output power of the low-voltage distribution network. This indicates the transmission power of the photovoltaic array. This indicates that phase X compensates for the reactive component. , , , These are the active components of the three-phase output power of the low-voltage distribution network, respectively. This represents the reactive component of the X-phase output power of the low-voltage distribution network; During a two-phase fault, ; In the event of a single-phase fault, , In the formula, The subscripts X1 and X2 represent two fault-free phases in phases a, b, and c, respectively.

3. The three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter according to claim 1, characterized in that, Current compensation for the three phases of the low-voltage distribution network includes: For the voltage values ​​of the three-phase four-bridge-arm photovoltaic inverter and the three-phase common connection point of the low-voltage distribution network, two orthogonal signals corresponding to the voltage values ​​of each phase common connection point are obtained by a second-order generalized integrator. Based on the two orthogonal signals of each phase and the power compensation value, the current compensation components of the three phases of the low-voltage distribution network are determined.

4. The three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter according to claim 3, characterized in that, The current compensation component is calculated according to the following formula: ； In the formula, the subscript X represents phase a, b, or c. and These are the two orthogonal signals of phase X. and These represent the compensated active and reactive components of phase X, respectively.

5. The three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter according to claim 4, characterized in that, The three-phase positive and negative zero-sequence current components are as follows: ， ， ， ， ， ， ， ， ； In the formula, This represents the positive and negative zero-sequence current components of phase X. These represent the compensation currents for phase a, phase b, and phase c, respectively.

6. The three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter according to claim 1, characterized in that, The positive and negative zero-sequence current components are subjected to an abc / dq0 coordinate transformation, including: The positive sequence components are rotated into DC components using a positive sequence rotating coordinate system. , ; The negative-sequence component is rotated into a DC component using a negative-sequence rotating coordinate system. , ; The zero-sequence components delay phases B and C by 4 / 3 respectively. and 2 / 3 The components are constructed as positive-sequence components, and then rotated into DC using positive-sequence rotating coordinates. , .

7. The three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter according to claim 1, characterized in that, The feedforward compensation amount is a voltage compensation amount, which is used to decouple the d-axis and q-axis current calculation equations to obtain two independent current loops, thereby achieving independent decoupling of the currents.

8. A three-phase power decoupling control device based on a three-phase four-arm photovoltaic grid-connected inverter, characterized in that, The method is implemented based on the three-phase power decoupling control method of a three-phase four-arm photovoltaic grid-connected inverter as described in any one of claims 1-7, including: The power compensation calculation component calculation unit is used to perform power compensation on the three phases of the low-voltage distribution network based on the difference between the transmission power of the photovoltaic array and the output power of the three phases of the low-voltage distribution network. The current compensation component calculation unit is used to perform current compensation on the three phases of the low-voltage distribution network based on the power compensation value and the voltage value of the common connection point between the three-phase four-arm photovoltaic inverter and the low-voltage distribution network. The positive and negative zero sequence separation and dq0 transformation unit is used to decompose the current compensation component into positive and negative zero sequence to obtain three-phase positive and negative zero sequence current components; it is also used to perform abc / dq0 coordinate transformation on the positive and negative zero sequence current components to obtain three-phase DC components. The positive and negative zero sequence decoupling control unit is used to control the three-phase four-arm photovoltaic inverter in a synchronous rotating coordinate system based on... In the inner loop current controller of the circuit, a feedforward compensation is introduced to eliminate the coupling terms in the synchronous rotating coordinate coefficient mathematical model and obtain the output current of independent decoupled control. The signal modulation unit is used to convert the output current by dq0 / abc and then add them together, and use 3D-SVPWM modulation to obtain the drive signal of the switching transistor of the three-phase four-arm photovoltaic inverter.

9. A computer device, characterized in that, The device includes a processor and a memory: The memory is used to store computer programs and send the instructions of the computer programs to the processor; The processor executes, according to the instructions of the computer program, a three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the three-phase power decoupling control method based on a three-phase four-arm photovoltaic grid-connected inverter as described in any one of claims 1-7.

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