Latticed AC / DC power distribution area networking architecture based on power electronic transformer

Abstract

The invention discloses a grid-shaped alternating current and direct current power distribution area networking architecture based on a power electronic transformer, which comprises a plurality of distributed photovoltaic power generation arrays, a three-stage power electronic transformer for converting 10kV medium-voltage alternating current into 0.4 kV low-voltage alternating current, and a plurality of grid-shaped alternating current and direct current power distribution areas, and is characterized in that the output end of each distributed photovoltaic power generation array is connected with a direct current collection bus through a DC / DC converter; the three-stage power electronic transformer is connected with the direct-current collection bus, the low-voltage side of the three-stage power electronic transformer is connected with a 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-like AC / DC distribution station area networking architecture based on power electronic transformers. Background Art

[0002] As my country's "dual carbon" vision continues to be implemented, the proportion of new power sources such as distributed photovoltaic power generation has increased year by year. Traditional distribution networks are facing increasing pressure on line loss, power quality and power supply reliability. As the most important link between the power grid and users, the distribution network bears more and more important responsibilities. 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 node photovoltaic output characteristics 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 power electronic transformers, 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 a power electronic transformer, 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, and also includes a three-stage power electronic transformer that converts 10kV medium-voltage AC power into 0.4kV low-voltage AC power, the three-stage power electronic transformer is connected to the DC collection bus, the low-voltage side of the three-stage power electronic transformer is connected to a 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 power correspondence.

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

[0006] The three-stage power electronic transformer includes a front-stage DC / AC converter, an isolation-stage DC / DC converter, and a rear-stage DC / AC converter which are connected in sequence. The front-stage DC / AC converter is connected to a 10kV medium-voltage AC power grid, the rear-stage DC / AC converter is connected to a 0.4kV low-voltage AC power grid, and the output end of the isolation-stage DC / DC converter is also connected to a DC busbar.

[0007] The front-stage DC / AC converter adopts a three-phase bridge rectifier.

[0008] The isolation-level DC / DC converter adopts a dual active full-bridge converter, and the isolation-level DC / DC converter adopts a single-phase phase-shift modulation strategy.

[0009] The post-stage DC / AC converter includes three bridge arms connecting three phases, each bridge arm is composed of two insulated gate bipolar transistors and a diode anti-parallel therewith, the two insulated gate bipolar transistors are complementary turned on, and the output port of the post-stage DC / AC converter adopts PQ control mode to adjust active transmission and reactive transmission.

[0010] The DC busbar is connected to the DC / DC converter and multiple photovoltaic inverters through switches.

[0011] The photovoltaic inverter is a DC / AC converter. The DC side of the DC / AC converter is connected to the DC bus, and the AC side of the DC / AC converter is connected to the low-voltage AC grid.

[0012] 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 , Uq 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.

[0013] The beneficial effects of the present invention are:

[0014] The grid-like AC / DC distribution substation networking architecture based on power electronic transformers 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 selects different working modes and freely switches between the two working modes, which greatly reduces the line loss in the distribution network where the proportion of distributed photovoltaic power generation is high.

[0015] 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

[0016] Figure 1 It is a schematic diagram of the grid-like AC / DC distribution substation network architecture based on power electronic transformers of the present invention;

[0017] 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;

[0018] 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;

[0019] FIG4( a ) is a schematic diagram of a control strategy for a three-stage power electronic transformer in a grid-like AC / DC distribution substation network architecture based on a power electronic transformer according to the present invention;

[0020] FIG4( b ) is a schematic diagram of the energy management strategy of the grid-like AC / DC distribution substation network architecture based on power electronic transformers according to the present invention;

[0021] 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;

[0022] 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;

[0023] 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;

[0024] Figure 6 It is a schematic diagram of the isolation level control strategy of the three-stage power electronic converter in the grid-like AC / DC distribution substation network architecture based on the power electronic transformer of the present invention;

[0025] Figure 7 It is a schematic diagram of the back-stage control strategy of the three-stage power electronic converter in the grid-like AC / DC distribution substation network architecture based on the power electronic transformer of the present invention;

[0026] Figure 8 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 a three-stage power electronic transformer of the present invention;

[0027] Fig. 9 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 power electronic transformers of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] The present invention is based on the grid-like AC / DC distribution substation network architecture of power electronic transformers, 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, and also includes a three-stage power electronic transformer that converts 10kV medium-voltage AC power into 0.4kV low-voltage AC power. The three-stage power electronic transformer is connected to the DC bus, and the low-voltage side of the three-stage power electronic transformer is connected to the 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 three-phase electricity.

[0031] Among them, the three-stage power electronic transformer includes a front-stage DC / AC converter, an isolation-stage DC / DC converter, and a rear-stage DC / AC converter connected in sequence. The front-stage DC / AC converter is connected to a 10kV medium-voltage AC power grid, the output end of the rear-stage DC / AC converter is an AC port, which is connected to a 0.4kV low-voltage AC power grid through the AC port, and the output end of the isolation-stage DC / DC converter is a DC port, which is also connected to a DC busbar through the DC port.

[0032] The three-stage power electronic transformer has a DC port and an AC port. The DC port leads to a DC busbar. The input side of the power electronic converter is electrically connected to a 10kV medium-voltage AC grid, and the output side is electrically connected to a 0.4kV low-voltage AC grid. It is used to ensure the power quality of the load and maintain the voltage level of the DC busbar under various conditions.

[0033] The DC bus is connected to the DC / DC converter and multiple photovoltaic inverters through switches. According to the power situation on the DC bus in the area, one of the following operating 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.

[0034] The photovoltaic inverter is a DC / AC converter, the DC side of the DC / AC converter is connected to the DC bus, and the AC side of the DC / AC converter is connected to the low-voltage AC grid. It has a DC input terminal and an AC output terminal, wherein the DC input terminal is electrically connected to the DC bus; the AC output terminal is electrically connected to the corresponding three-phase of the low-voltage AC grid; and the neutral line of the AC output terminal is electrically connected to the neutral line of the low-voltage AC grid.

[0035] The distributed photovoltaic power generation array has a DC output terminal, which is electrically connected to a DC busbar to output DC power.

[0036] In this embodiment, the 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 of the region, unifies the power generation voltage level of the photovoltaic array in the region to the DC busbar voltage level. The module is composed of a single insulated gate bipolar transistor IGBT, an inductor, a voltage stabilizing capacitor and a freewheeling diode; the module is composed of a single insulated gate bipolar transistor IGBT, an inductor and a voltage stabilizing capacitor. When the insulated gate bipolar transistor IGBT is turned on, the DC input allows the DC input to flow in, and the DC input charges the inductor; when it is turned off, the voltage stabilizing capacitor clamps the output voltage and outputs it outward.

[0037] Distributed photovoltaic power generation arrays specifically include:

[0038] Solar power arrays, mounted on roofs or walls;

[0039] A DC / DC converter, the input end of which is connected in series with the solar power generation array, and the output end of which is electrically connected to the DC collection busbars of each region;

[0040] The switch module is used to determine the power situation on the DC busbar in the area, and decides the working mode of consuming all photovoltaic power locally, feeding all photovoltaic power back to the grid, consuming part of the photovoltaic power locally, and feeding part of the photovoltaic power back to the grid.

[0041] 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:

[0042] The mathematical model of distributed photovoltaic power generation array is explained as follows:

[0043] 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):

[0044]

[0045] 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;

[0046] Next, we process the PI node:

[0047] Apparent power S = P + jQ, and we get formula (2):

[0048]

[0049] 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;

[0050] 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;

[0051] 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;

[0052]

[0053]

[0054] Where: (r ki ,x ki ) is the impedance of the ki branch; is the power loss of the ki feeder branch;

[0055] The calculation formula of i-node is as follows:

[0056]

[0057] 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:

[0058] 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:

[0059]

[0060] 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;

[0061] 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:

[0062]

[0063] Where: U i 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);

[0064] 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:

[0065]

[0066] 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 combining 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;

[0067] 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:

[0068] First, the active power loss of the photovoltaic inverter supplying power to each node load is calculated:

[0069]

[0070] Where: η i is the working efficiency of the i-node converter;

[0071] The following is the calculation of the active power loss of each node on the DC busbar in the power reverse working mode:

[0072]

[0073] Where: U dc_line is the rated voltage of the DC busbar; r dc is the resistivity per unit length of the DC busbar; is the physical length of the DC busbar between node i and node i-1;

[0074] 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:

[0075]

[0076] 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);

[0077] 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:

[0078]

[0079] 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;

[0080] For systems in the form of public low-voltage DC collection, Figure 2 For 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.

[0081] Figure 4(a) shows the three-stage power electronic transformer control strategy in the grid-like AC / DC distribution substation networking architecture based on power electronic transformers of the present invention; Figure 4(b) shows the energy management strategy of the grid-like AC / DC distribution substation networking architecture based on power electronic transformers of the present invention.

[0082] 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:

[0083] 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 load ) curve shows that the grid-shaped AC / DC distribution substation network architecture based on power electronic transformer proposed in the present invention has the lowest total active power loss;

[0084] 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 load ) curve shows that the grid-shaped AC / DC distribution substation network architecture based on power electronic transformer proposed in the present invention has the lowest total active power loss;

[0085] 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.

[0086] Example 2

[0087] The three-stage power electronic transformer used in the grid-shaped AC / DC distribution substation networking architecture based on the power electronic transformer of the present invention comprises a front-stage DC / AC converter, an isolation-stage DC / DC converter, and a rear-stage DC / AC converter which are connected in sequence, the front-stage DC / AC converter is connected to a 10kV medium-voltage AC power grid, the rear-stage DC / AC converter is connected to a 0.4kV low-voltage AC power grid, the output end of the isolation-stage DC / DC converter is connected to a DC busbar in a parallel output manner, and the rear-stage DC / AC converter is used to supply power to a low-voltage DC load.

[0088] The front-stage DC / AC converter uses a three-phase bridge rectifier. The three-phase bridge rectifier is a common topology used to convert three-phase AC power into DC power. It has six diodes and a neutral point to form a bridge rectifier circuit. The three-phase AC power is stepped down by a transformer and input into the bridge rectifier. The six diodes are switched in a specific order to convert the AC power into DC power. In this topology, the phase difference of the three-phase power supply can provide a more stable and continuous DC output.

[0089] The isolation-level DC / DC converter adopts a dual-active full-bridge converter, which includes two H-bridge converters and a medium (high) frequency transformer. The isolation-level DC / DC converter adopts a single-phase phase-shift modulation strategy. During operation, the primary and secondary H-bridges use the same switching frequency, and the upper and lower switches of each bridge arm are complementary turned on at 180°, and the diagonal switches are turned on simultaneously in sequence.

[0090] like Figure 6 As shown in the figure, the isolated DC / DC converter is mainly responsible for controlling the voltage on the right DC side. Since the second part is a DC module without a neutral line, it is not necessary to balance the neutral point voltage on the DC side, but only to stabilize the DC voltage of the entire port. The multi-active bridge (MAB) controlled by this part adopts a single-phase phase shift modulation strategy (SPS). There are two main degrees of freedom control variables, namely the external shift phase angle i of bridge 2 and bridge 3. φ MAB generates V i , which is a square wave with a duty cycle of half the total period. At the same time, a phase difference i φ , is the phase difference between the three-side H bridges. It determines the direction and magnitude of energy transfer. Therefore, the power flow of this part is mainly adjusted by adjusting i between different modules. φ to achieve.

[0091] The post-stage DC / AC converter includes three bridge arms connecting three phases, each bridge arm is composed of two insulated gate bipolar transistors and a diode anti-parallel therewith, the two insulated gate bipolar transistors are complementary turned on, and the output port of the post-stage DC / AC converter adopts PQ control mode to adjust active transmission and reactive transmission.

[0092] like Figure 7 As shown: The rear stage DC / AC converter includes output port 2 and output port 3. Both ports use PQ control mode to adjust the overall active and reactive power transmission between the three ports. According to the instantaneous power theory, the following table can be obtained:

[0093]

[0094] where v d and i d is the active component of the inverter voltage and current, v q and i q is the reactive component of the inverter output voltage and current. The reactive power reference value is determined by the load current to compensate for the reactive power caused by the non-resistive load. The reactive power reference value is as follows, where i load_q Represents the reactive component of the load current.

[0095]

[0096] Reference value P ref Determined by the grid demand, the reference value Q ref Determined by the reactive power output by the unresistance load. Compare the reference signal with the inverter output current and adjust the error through the PI controller. Add the voltage feedforward signal to the modulation wave, compare it with the carrier wave, and generate a switching signal.

[0097] Example 3

[0098] The present invention is based on the grid-like AC / DC distribution substation network architecture of power electronic transformers.

[0099] like Figure 8 As shown, 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.

[0100] The grid-shaped AC / DC distribution substation network architecture based on power electronic transformers of the present invention is adopted, and the simulation waveform diagram is explained as follows:

[0101] like Fig. 9 As shown, the waveform Fig. 9 The first and second figures from the top are the three-phase voltage waveform and three-phase current waveform of the load node respectively; Fig. 9 The third one from the top is the photovoltaic inverter output current waveform; Fig. 9 The fourth figure from the top shows the equivalent power of two distributed photovoltaic arrays after passing through the DC / DC converter; waveform Fig. 9 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.

[0102] like Fig. 9As 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 full power local consumption; 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 that the system control time is within about 1 cycle (0.02s).

Claims

1. A grid-like AC / DC distribution substation network architecture based on power electronic transformers, 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, and also includes a three-stage power electronic transformer that converts 10kV medium-voltage AC power into 0.4kV low-voltage AC power, the three-stage power electronic transformer is connected to the DC busbar, the low-voltage side of the three-stage power electronic transformer is connected to a low-voltage AC power grid, multiple photovoltaic inverter input ends are connected to the DC busbar, and each photovoltaic inverter output end is connected to a low-voltage AC power grid through three-phase electricity.

2. The grid-like AC / DC distribution substation network architecture based on power electronic transformers according to claim 1 is characterized in that: The three-stage power electronic transformer includes a front-stage DC / AC converter, an isolation-stage DC / DC converter, and a rear-stage DC / AC converter connected in sequence, wherein the front-stage DC / AC converter is connected to a 10kV medium-voltage AC power grid, the rear-stage DC / AC converter is connected to a 0.4kV low-voltage AC power grid, and the output end of the isolation-stage DC / DC converter is also connected to a DC busbar.

3. The grid-like AC / DC distribution substation network architecture based on power electronic transformers according to claim 2 is characterized in that: The front-stage DC / AC converter adopts a three-phase bridge rectifier.

4. The grid-like AC / DC distribution substation network architecture based on power electronic transformers according to claim 2 is characterized in that: The isolation-level DC / DC converter adopts a dual active full-bridge converter, and the isolation-level DC / DC converter adopts a single-phase phase-shift modulation strategy.

5. The grid-like AC / DC distribution substation network architecture based on power electronic transformers according to claim 2 is characterized in that: The post-stage DC / AC converter includes three bridge arms connected to three phases, each bridge arm is composed of two insulated gate bipolar transistors and a diode anti-parallel therewith, the two insulated gate bipolar transistors are complementary and turned on, and the output port of the post-stage DC / AC converter adopts a PQ control mode to adjust active transmission and reactive transmission.

6. The grid-like AC / DC distribution substation network architecture based on power electronic transformers according to claim 1 is characterized in that: The DC busbar is connected to the DC / DC converter and multiple photovoltaic inverters through switches.

7. The grid-like AC / DC distribution substation network architecture based on power electronic transformers according to claim 1 is characterized in that: The photovoltaic inverter is a DC / AC converter, the DC side of the DC / AC converter is connected to a DC bus, and the AC side of the DC / AC converter is connected to a low-voltage AC power grid.

8. The grid-like AC / DC distribution substation network architecture based on power electronic transformers 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 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.

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