Grid-shaped AC / DC power distribution area networking architecture based on active power filter

Abstract

The invention discloses a grid-shaped AC / DC power distribution area networking architecture based on an active power filter, which comprises a plurality of distributed photovoltaic power generation arrays, the output end of each distributed photovoltaic power generation array is connected with a DC collection bus through a DC / DC converter, and the DC side of the active power filter is connected with the DC collection bus. The alternating-current side is connected with the low-voltage side of the industrial frequency transformer, the high-voltage side of the industrial frequency transformer is connected with a 10kV medium-voltage alternating-current power grid, the low-voltage side of the industrial frequency transformer is connected with a 0.4 kV low-voltage alternating-current power grid, the input ends of the plurality of photovoltaic inverters are connected with the direct-current collection bus, and the output end of each photovoltaic inverter is correspondingly connected with the low-voltage alternating-current power grid through three-phase power; according to the grid-shaped AC / DC power distribution area networking architecture, the total active power loss of existing distributed photovoltaic access can be reduced, and the electric energy quality of the power distribution area can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of AC / DC hybrid power distribution, and in particular relates to a grid-shaped AC / DC distribution station area networking architecture based on an active power filter. Background Art

[0002] With the continuous implementation of the National Energy Administration's "whole-county photovoltaic promotion" policy, as the most important connection link between the power grid and users, the distribution network is facing increasing pressure on line loss, power quality, and power supply reliability as the proportion of new power sources such as distributed photovoltaic power generation and wind power generation increases year by year. At present, distributed photovoltaic power generation mainly adopts two solutions: public low-voltage DC collection and AC collection: among them, AC collection power supply has the advantages of high reliability, simple networking architecture, and low system transformation cost, but the problem is that when the distributed photovoltaic power generation power is sent back to the grid, it needs to pass through the low-voltage AC grid, the line loss is high, and the photovoltaic output characteristics of the node do not match the load characteristics. When the distributed photovoltaic power is transferred between individual load nodes, there is still a problem of high line loss; the advantage of the public low-voltage DC collection system is that the line loss per unit length is low, the number of power conversion stages is small, and the system efficiency is high, but the problem is that this distributed photovoltaic power needs to be first concentrated in the form of DC to the low-voltage AC port of the distribution station transformer when supplying power to the system load node, and then through a DC-AC conversion to supply power to the distribution station load node, the system equivalent power supply path is long, and the overall system line loss is high. Summary of the invention

[0003] The purpose of the present invention is to provide a grid-like AC / DC distribution substation networking architecture based on active power filters, which can reduce the total active power loss of existing distributed photovoltaic access and improve the power quality of the distribution substation.

[0004] The present invention is based on a grid-like AC / DC distribution station area networking architecture of an active power filter, including multiple distributed photovoltaic power generation arrays, each distributed photovoltaic power generation array output end is connected to a DC collection bus through a DC / DC converter, the DC side of the active power filter is connected to the DC collection bus, the AC side is connected to the low-voltage side of an industrial frequency transformer, the high-voltage side of the industrial frequency transformer is connected to a 10kV medium-voltage AC power grid, and the low-voltage side is connected to a 0.4kV low-voltage AC power grid, multiple photovoltaic inverter input ends are connected to the DC collection bus, and each photovoltaic inverter output end is connected to a low-voltage AC power grid through a three-phase electrical correspondence.

[0005] The present invention is also characterized in that:

[0006] The active power filter comprises a three-phase full-bridge rectifier circuit with 180° complementary conduction formed by six bridge arms.

[0007] The control strategy of the active power filter is: collect the AC side current i of the active power filter lineLa 、i Lb 、i Lc Output i through Clark transformation α 、i β ,i α 、i β Collect line voltage U with active power filter abc The system angular frequency w is obtained through the phase-locked loop t , change i α 、i β 、w t The values ​​obtained by low-pass filter, Park inverse transform, and Clark inverse transform are the same as i La 、i Lb 、i Lc The difference is obtained by the system three-phase harmonic current and reactive current i habc +i lqabc ,i habc +i lqabc The AC side current i of the active power filter La 、i Lb 、i Lc The signals are converted into the dq coordinate system and input into the active power filter harmonic control circuit to realize the control of the active power filter.

[0008] The photovoltaic inverter adopts phase-locked loop control to track the phase and frequency of the low-voltage AC grid voltage and collect the low-voltage AC grid current i La 、i Lb 、i Lc and voltage U La , U Lb , U Lc , current i La 、i Lb 、i Lc By Parker transformation, I d ,I q Actual value; voltage U La , U Lb , U Lc By Parker transformation, we can get U d , U q Actual value; where I d ,I q With given I d * ,I q * The difference is obtained by proportional integral control and I d The actual value after numerical gain is added and then added to U d , U qThe sum is performed to obtain the quantity in the dq coordinate system, and then the control quantity is obtained through the inverse Park transform and output to the photovoltaic inverter control circuit to realize the control of the photovoltaic inverter.

[0009] The DC busbar is connected to the DC / DC converter, the DC side of the active power filter, and multiple photovoltaic inverters through switches.

[0010] The photovoltaic inverter is an AC / DC converter with a DC input terminal and an AC output terminal. The DC input terminal is connected to the DC bus, and the AC output terminal is connected to the low-voltage AC grid.

[0011] The beneficial effects of the present invention are:

[0012] The grid-like AC / DC distribution substation networking architecture based on active power filters of the present invention has the same distribution characteristics of the distributed photovoltaic power generation and photovoltaic inverter combination in the system as the distribution characteristics of the load nodes. The distributed photovoltaic power generation unit can provide the required active and reactive power to the load nodes by adjusting its control strategy, thereby improving the power quality of each load node; reducing the loss of active power when the power is transferred between nodes when the photovoltaic power generation output is uneven, and its grid-like characteristics can also reduce the loss of each photovoltaic power generation unit directly supplying power to each load node; under different photovoltaic power generation outputs, the system can choose: 1. All photovoltaic power is generated and consumed on site; 2. Part of the photovoltaic power is consumed on site, and part of the photovoltaic power is fed back to the grid; the two working modes can be switched freely, which greatly reduces the line loss in the distribution network with a high proportion of distributed photovoltaic power generation.

[0013] The grid-like AC / DC distribution substation networking architecture of the present invention can improve the ability of distributed photovoltaic power generation to fully absorb and efficiently utilize it locally, reduce the loss level of distributed photovoltaic power generation lines, improve the power quality of load nodes, and improve the power supply reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the network architecture of the grid-shaped AC / DC distribution substation based on the active power filter of the present invention;

[0015] Figure 2 This is a schematic diagram of the system structure in the form of public low-voltage DC collection in the traditional distribution station area network architecture;

[0016] Figure 3 This is a schematic diagram of the system structure in the form of AC aggregation in the traditional distribution station area networking architecture;

[0017] FIG4( a) is a control block diagram of an active power filter control method in the present invention;

[0018] Figure 4(b) is a block diagram of the power management control of the central control overall distribution station area;

[0019] FIG5( a ) is a chain network structure of a 0.4 kV distribution station area according to the loss calculation method of the present invention;

[0020] FIG5( b ) is a diagram illustrating a loss comparison between the present invention and a DC collection architecture and an AC collection architecture when a single-node system operates in working mode I;

[0021] FIG5(c) is a diagram illustrating a loss comparison between the present invention and a DC collection architecture and an AC collection architecture when a single-node system operates in working mode II;

[0022] Figure 6 It is a schematic diagram of the control strategy of the active power filter in the grid-shaped AC / DC distribution substation networking architecture based on the active power filter of the present invention;

[0023] Figure 7 It is a schematic diagram of the control strategy of photovoltaic inverters at each node in the grid-like AC / DC distribution substation network architecture based on active power filters of the present invention;

[0024] Figure 8 It is a waveform simulation diagram of important nodes of the simulation model of the grid-like AC / DC distribution substation network system architecture in the grid-like AC / DC distribution substation network architecture based on the active power filter of the present invention. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] The present invention is based on the grid-like AC / DC distribution station area networking architecture of the active power filter, such as Figure 1 As shown, it includes multiple distributed photovoltaic power generation arrays, each distributed photovoltaic power generation array output end is connected to the DC bus through a DC / DC converter, the DC side of the active power filter is connected to the DC bus, the AC side is connected to the low-voltage side of the power frequency transformer, the high-voltage side of the power frequency transformer is connected to the 10kV medium-voltage AC power grid, and the low-voltage side is connected to the 0.4kV low-voltage AC power grid. Multiple photovoltaic inverter input ends are connected to the DC bus, and each photovoltaic inverter output end is connected to the low-voltage AC power grid through a three-phase electrical correspondence.

[0028] Among them, the industrial frequency transformer can convert 10kV medium voltage AC power into 0.4kV low voltage AC power.

[0029] The active power filter has a DC port and an AC port. The DC port leads to a DC busbar, and the AC side is electrically connected to a 0.4kV low-voltage AC grid to ensure the power quality of the load and maintain the voltage level of the DC busbar in various situations.

[0030] The distributed photovoltaic power generation array has a DC output terminal, which is electrically connected to a DC busbar to output DC power.

[0031] A DC / DC converter, wherein the input end is electrically connected to the distributed photovoltaic power generation array, and the output end is electrically connected to the DC busbar in the area, unifying the power generation voltage level of the photovoltaic array in the area at the DC busbar voltage level.

[0032] The photovoltaic inverter has a DC input terminal and an AC output terminal, wherein the DC input terminal is electrically connected to the DC busbar; the AC output terminal is electrically connected to the corresponding three-phase of the low-voltage AC power grid; and the neutral line of the AC output terminal is electrically connected to the neutral line of the low-voltage AC power grid.

[0033] The DC bus is used to connect photovoltaic inverters and active power filters.

[0034] The DC busbar is connected to the DC / DC converter, the DC side of the active power filter, and multiple photovoltaic inverters through switches. According to the power situation on the DC busbar in the area, one of the following working modes is selected: 1. All photovoltaic power is consumed locally; 2. Part of the photovoltaic power is consumed locally, and part of the photovoltaic power is fed back to the grid.

[0035] In order to illustrate the specific calculation method of reducing the overall line loss of distributed photovoltaic power generation in the present invention, the following description is made in conjunction with the accompanying drawings:

[0036] The mathematical model of distributed photovoltaic power generation array is explained as follows:

[0037] The photovoltaic inverter of the present invention adopts the control form of current-controlled voltage source. At this time, the distributed photovoltaic power supply node of the distributed photovoltaic power generation array and the photovoltaic inverter in the present invention is equivalent to a PI node that provides active power and constant current to the distribution network. The reactive power of the node can be calculated by formula (1):

[0038]

[0039] Where: P is the active power output by the photovoltaic power source; I is the current provided by the photovoltaic power source; e is the real part of the voltage provided by the photovoltaic power source; f is the imaginary part of the voltage provided by the photovoltaic power source;

[0040] Next, we process the PI node:

[0041] Apparent power S = P + jQ, and we get formula (2):

[0042]

[0043] After the photovoltaic power generation system introduces the inverter, the active power and the injected current are constant. For this type of PI constant distributed power source, the reactive power is first calculated by formula (1). Through the processing of formula (2), this type of node can be regarded as a PQ node, and the node is converted into a PQ node in the second iteration process;

[0044] Figure 5(a) is a chain distribution line, k, i are parent and child nodes, i, j are parent and child nodes, branch ij and branch ki are parent and child branches, and Ci is a node set consisting of child nodes of node i;

[0045] The k-th iteration formula of the power flow algorithm adopted by the present invention is as follows (3) and (4), where the load voltage and impedance characteristics can be regarded as constant values;

[0046]

[0047]

[0048] Where: (r ki , x ki ) is the impedance of the ki branch; is the power loss of the ki feeder branch;

[0049] The calculation formula for the i-node is formula (5):

[0050]

[0051] The following is a calculation of the three-phase active power loss in the power reverse transmission mode of the n-node AC aggregation architecture:

[0052] First, a preliminary calculation is performed on the incoming current of each load node in the AC collection form when the iteration number k = 0:

[0053]

[0054] Where: is the active power flowing out of node i; is the distributed photovoltaic active power output of node i; is the reactive power flowing out of node i; is the conjugate of the rated voltage of node i;

[0055] The following is a preliminary calculation of the total active power loss of each node when the AC collection system works in the working mode of partial power feedback to the grid and partial power local consumption based on the input current of each node calculated in formula (6) and taking into account the conversion loss of the converter:

[0056]

[0057] Where: Ui is the phase voltage at the output of the i-node converter; I i is the current at the output of the i-node converter; η i is the conversion efficiency of the i-node converter; Q i is the reactive power flowing out of node i; r ac is the single-phase resistivity per unit length of low-voltage AC power grid; l ac is the physical length of the low-voltage AC power grid between node i and node (i-1);

[0058] The three-phase active power loss of each node obtained in formula (7) is taken into account and multiple iterations are performed until the iteration result meets the accuracy requirements. At this time, after k iterations, the total three-phase active power loss of the AC aggregation system that meets the accuracy requirements is calculated as follows:

[0059]

[0060] when When , the AC collection architecture works in a mode where part of the power is consumed locally and part of the power is fed back to the grid. At this time, distributed photovoltaic power generation has met all load requirements in the distribution station area. The low-voltage AC power grid does not circulate active power and only serves as a support for system reliability. The total system loss only needs to take into account the active power loss of the photovoltaic inverter at each node and use an iterative calculation method to calculate sequentially from the end node to the transformer export node; when When the AC collection architecture works in the local consumption mode of all photovoltaic power, the low-voltage AC power grid not only supports the system reliability, but also needs to provide power support for the load in the system. At this time, the total system loss needs to be iteratively calculated by comprehensively considering the active output of distributed photovoltaic power generation at each node and the node load, and the active power loss of photovoltaic inverters at each node needs to be taken into account;

[0061] The following is a calculation of the active power loss in the power reverse transmission mode of the n-node grid distribution station network architecture:

[0062] First, the active power loss of the photovoltaic inverter supplying power to each node load is calculated:

[0063]

[0064] Where: η i is the working efficiency of the i-node converter;

[0065] The following is the calculation of the active power loss of each node on the DC busbar in the power reverse working mode:

[0066]

[0067] Where: U dc_line is the rated voltage of the DC busbar; r dcis the resistivity per unit length of the DC busbar; is the physical length of the DC busbar between node i and node i-1;

[0068] The following is a preliminary calculation of the active power loss of each node on the low-voltage AC power grid in the power reverse working mode when the iteration number k = 0:

[0069]

[0070] Where U ac_N is the average rated voltage of node i; Q i is the reactive power flowing out of node i; is the reactive power output of distributed photovoltaic power generation at node i; r ac is the single-phase resistivity per unit length of low-voltage AC power grid; l ac is the physical length of the low-voltage AC power grid between node i and node (i-1);

[0071] The following is a comprehensive calculation of the total active power loss of the grid-shaped distribution substation network architecture system working in the partial power reverse transmission and partial power local consumption working mode based on the active power loss of the photovoltaic inverter of each node calculated in equations (9), (10) and (11), the active power loss of each node on the DC busbar in the power reverse transmission working mode, and the active power loss generated by the reactive power transmission demand of each node on the low-voltage AC power grid after k iterations that meet the accuracy requirements:

[0072]

[0073] when When , the grid-like distribution architecture works in a mode where part of the power is consumed locally and part of the power is fed back to the grid. At this time, distributed photovoltaic power generation has met all the load requirements in the distribution station area. The low-voltage AC power grid does not circulate active power and only serves as a support for system reliability. The total active power loss in the system only needs to calculate the excess distributed photovoltaic active power through the DC busbar feedback loss and take into account the active power loss of the photovoltaic inverter; when When the grid-like power distribution architecture works in the local consumption mode of all photovoltaic power, the low-voltage AC power grid not only supports the system reliability, but also needs to provide power support for the load in the system. The total active power loss in the system needs to be calculated by taking into account the load demand of the active output of distributed photovoltaic power generation at each node, and then iteratively calculated and taking into account the active power loss of photovoltaic inverters at each node;

[0074] For systems in the form of public low-voltage DC collection, Figure 2For example, consider the extreme case where PV1 supplies power to BUS1 busbar. The distributed photovoltaic active power output not only needs to flow through the DC busbar, but also needs to flow through the low-voltage DC busbar, thus generating additional line losses. Figure 3 As shown, the system in the AC collection form and the distribution system using the architecture of the present invention can directly supply power to the load node only through the photovoltaic inverter; in this working mode, the loss of the low-voltage public DC collection architecture is much greater than that of the other two system architectures.

[0075] FIG4(a) shows the control strategy of the active power filter in the grid-type AC / DC distribution substation network architecture based on the active power filter; FIG4(b) shows the energy management strategy in the grid-type AC / DC distribution substation network architecture based on the active power filter.

[0076] In order to further demonstrate the function of reducing the overall line loss of distributed photovoltaic power generation in the present invention, the following description is made in conjunction with the accompanying drawings:

[0077] Based on the two graphs of FIG. 5( b ) and FIG. 5( c ), the optimal system architecture in the distribution network with a high proportion of photovoltaic power generation access is the grid-like distribution station area networking system architecture of the present invention.

[0078] As shown in Figure 5(b), the working mode of consuming part of the power locally and sending part of the power back to the grid is adopted. The P loss -(P PV -P laod ) curve shows that the grid-like AC / DC distribution substation network architecture based on active power filter proposed in the present invention has the lowest total active power loss.

[0079] As shown in Figure 5(c), the working mode of consuming all power locally is adopted, and the P under the grid-like distribution substation network architecture, AC collection architecture, and public low-voltage DC collection architecture are compared. loss -(P PV -P laod ) curve shows that the grid-like AC / DC distribution substation network architecture based on active power filter proposed in the present invention has the lowest total active power loss.

[0080] Example 2

[0081] Based on the grid-like AC / DC distribution substation network architecture of active power filter, the structure of active power filter is as follows:

[0082] The active power filter structure includes a three-phase full-bridge rectifier circuit with 180° complementary conduction formed by six bridge arms VD1 to VD6, a DC port on the DC side directly leads out an 800V DC bus and is electrically connected to the bus, and an AC side is electrically connected to a 0.4kV low-voltage AC power grid; the topology of the module is not limited to the structure used in the present invention, and other structures can also be used, which can realize the flexible voltage regulation, reactive power compensation, high availability, fault management and other functions of the active power filter.

[0083] like Figure 6 As shown: The control strategy of the active power filter is: collect the AC side current i of the active power filter line La 、i Lb 、i Lc Output i through Clark transformation α 、i β ,i α 、i β Collect line voltage U with active power filter abc The system angular frequency w is obtained through the phase-locked loop t , change i α 、i β 、w t The values ​​obtained by low-pass filter, Park inverse transform, and Clark inverse transform are the same as i La 、i Lb 、i Lc The difference is obtained by the system three-phase harmonic current and reactive current i habc +i lqabc ,i habc +i lqabc The AC side current i of the active power filter La 、i Lb 、i Lc The signals are converted into the dq coordinate system and input into the active power filter harmonic control circuit to realize the control of the active power filter.

[0084] Figure 7 The control block diagram is a control strategy for photovoltaic inverters at each node in the grid-like AC / DC distribution substation network architecture based on active power filters.

[0085] Example 3

[0086] The present invention is based on the grid-like AC / DC distribution area networking architecture of the active power filter. The photovoltaic inverter control strategy is as follows: the photovoltaic inverter adopts phase-locked loop control to track the phase and frequency of the low-voltage AC grid voltage and collect the low-voltage AC grid current i La 、i Lb 、i Lc and voltage U La , U Lb, U Lc , current i La 、i Lb 、i Lc By using Parker transformation, I d ,I q Actual value; voltage U La , U Lb , U Lc By Parker transformation, we can get U d , U q Actual value; where I d ,I q With given I d * ,I q * The difference is obtained by proportional integral control and I d The actual value after numerical gain is added and then added to U d , U q The sum is performed to obtain the quantity in the dq coordinate system, and then the control quantity is obtained through the inverse Park transform and output to the photovoltaic inverter control circuit to realize the control of the photovoltaic inverter.

[0087] The DC / DC converter structure is as follows:

[0088] The module is composed of a single insulated gate bipolar transistor IGBT, an inductor, a voltage-stabilizing capacitor and a freewheeling diode. The insulated gate bipolar transistor IGBT allows a DC input to flow in when it is turned on, and the DC input charges the inductor; when it is turned off, the voltage-stabilizing capacitor clamps the output voltage and outputs it outward. The topology of the module is not limited to the structure used in the present invention, and other structures can also be used, as long as it can achieve the output of photovoltaic power generation to the DC bus voltage.

[0089] The simulation waveform is explained as follows:

[0090] like Figure 8 As shown, the waveform Figure 8 The first and second figures from the top are the three-phase voltage waveform and three-phase current waveform of the load node respectively; Figure 8 The third figure from the top is the waveform of the photovoltaic inverter output current; Figure 8 The fourth figure from the top shows the equivalent power of two distributed photovoltaic arrays after passing through the DC / DC converter; waveform Figure 8 The fifth figure from the top shows the difference between the active power demand Pload of the load nodes in the system and the equivalent active power output Ppv of each photovoltaic array in the system.

[0091] like Figure 8As shown in the fifth figure, in the simulation model established by the present invention, the system operates in a working mode of partial power reverse transmission and partial power local consumption at 0.1s to 0.2s; a new load is added to the load node in the system for parallel operation at 0.2s, and the system operates in a mode of local consumption of all power; consistent photovoltaic active output fluctuations and inconsistent photovoltaic active output fluctuations are added at 0.3s and 0.4s respectively. It can be seen from the waveform diagram that the system control time is within about 1 cycle (0.02s). It can be seen that the grid-like AC / DC distribution substation networking architecture based on active power filters of the present invention can operate stably under the condition of sudden increase and decrease of photovoltaic output, and the system dynamic process is fast.

Claims

1. A grid-like AC / DC distribution substation network architecture based on active power filters, characterized in that: It includes multiple distributed photovoltaic power generation arrays, each of which has an output end connected to a DC busbar through a DC / DC converter, an active power filter DC side connected to a DC busbar, an AC side connected to a low-voltage side of an industrial frequency transformer, a high-voltage side of the industrial frequency transformer connected to a 10kV medium-voltage AC grid, and a low-voltage side connected to a 0.4kV low-voltage AC grid, multiple photovoltaic inverter input ends connected to the DC busbar, and each photovoltaic inverter output end connected to a low-voltage AC grid through a three-phase electrical correspondence.

2. The grid-like AC / DC distribution substation network architecture based on active power filter according to claim 1 is characterized in that: The active power filter comprises a three-phase full-bridge rectifier circuit with 180° complementary conduction formed by six bridge arms.

3. The grid-like AC / DC distribution substation network architecture based on active power filter according to claim 1 is characterized in that: The control strategy of the active power filter is: collecting the AC side current i of the active power filter line La 、i Lb 、i Lc Output i through Clark transformation α 、i β ,i α 、i β Collect line voltage U with active power filter abc The system angular frequency w is obtained through the phase-locked loop t , change i α 、i β 、w t The values ​​obtained by low-pass filter, Park inverse transform, and Clark inverse transform are the same as i La 、i Lb 、i Lc The difference is obtained by the system three-phase harmonic current and reactive current i habc +i lqabc ,i habc +i lqabc The AC side current i of the active power filter La 、i Lb 、i Lc The signals are converted into the dq coordinate system and input into the active power filter harmonic control circuit to realize the control of the active power filter.

4. The grid-like AC / DC distribution substation network architecture based on active power filter according to claim 1 is characterized in that: The photovoltaic inverter adopts phase-locked loop control to track the phase and frequency of the low-voltage AC grid voltage and collect the low-voltage AC grid current i La 、i Lb 、i Lc and voltage U La , U Lb , U Lc , current i La 、i Lb 、i Lc By Parker transformation, I d ,I q Actual value; voltage U La , U Lb , U Lc By Parker transformation, we can get U d , U q Actual value; where I d ,I q With given I d * ,I q * The difference is obtained by proportional integral control and I d The actual value after numerical gain is added and then added to U d , U q The sum is performed to obtain the quantity in the dq coordinate system, and then the control quantity is obtained through the inverse Park transform and output to the photovoltaic inverter control circuit to realize the control of the photovoltaic inverter.

5. The grid-like AC / DC distribution substation network architecture based on active power filter according to claim 1 is characterized in that: The DC busbar is connected to the DC / DC converter, the DC side of the active power filter, and a plurality of photovoltaic inverters through switches.

6. The grid-like AC / DC distribution substation network architecture based on active power filter according to claim 1 is characterized in that: The photovoltaic inverter is an AC / DC converter having a DC input terminal and an AC output terminal, wherein the DC input terminal is connected to a DC busbar, and the AC output terminal is connected to a low-voltage AC power grid.

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