Optical storage grid-connected / off-grid control system and control method

Abstract

The invention relates to an optical storage grid-connected / off-grid control system and method. The optical storage grid-connected / off-grid control system comprises a photovoltaic system, a storage battery, a power grid, a one-way DC / DC converter, a two-way DC / DC converter, a two-way DC / AC converter, a direct-current bus, a capacitor and an AC load. A photovoltaic system is connected with a one-way DC / DC converter through an interface, the output end of the one-way DC / DC converter is connected with the input end of a direct-current bus, the output end of the direct-current bus is connected with a DC load and a bidirectional DC / AC converter, and the bidirectional DC / AC converter is connected to a power grid; the storage battery is connected with a two-way DC / DC converter, the two-way DC / DC converter is connected to the input end of a direct current bus, the output end of the direct current bus is connected with another two-way DC / AC converter, and the two-way DC / AC converter is connected to an AC load; the output end of the direct-current bus is connected with a series circuit of the two capacitors; seamless switching between grid-connected / off-grid states of the system is realized through the one-way DC / DC converter, the two-way DC / DC converter and the two-way DC / AC converter, so that photovoltaic and energy storage power generation and grid-connected requirements are met.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy supply, and particularly to a photovoltaic energy storage parallel / isolated network control system and a control method. Background Art

[0002] With the rapid popularization of power generation technologies, the proportion of photovoltaic and energy storage access to the distribution network is continuously increasing, and photovoltaic and energy storage power generation technologies are also increasingly attracting attention. However, the output power of new energy power generation is volatile. Without suppression, power fluctuations will be transmitted to the transmission network through tie lines, which will impact the transmission network, resulting in a decline in the power quality of the distribution network, affecting electrical equipment and threatening the safety of users. Therefore, to ensure the stability of the distribution network, it is necessary to ensure the stability of new energy power generation and the reliability of grid connection. In the context of future integrated energy, traditional power generation and grid connection devices and control methods can no longer meet the operating requirements of conventional new energy. Summary of the Invention

[0003] The present invention provides a photovoltaic energy storage parallel / isolated network control system and a control method to meet the power generation and grid connection requirements of photovoltaic and energy storage, and improve the safety of the distribution network.

[0004] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0005] A photovoltaic energy storage parallel / isolated network control system includes a photovoltaic system, a storage battery, a power grid, a unidirectional DC / DC converter, a bidirectional DC / DC converter, a bidirectional DC / AC converter, a DC bus, a capacitor, and an AC load; the photovoltaic system is connected to the unidirectional DC / DC converter through an interface, the output end of the unidirectional DC / DC converter is connected to the input end of the DC bus, the output end of the DC bus is connected to a DC load and the bidirectional DC / AC converter, and the bidirectional DC / AC converter is connected to the power grid;

[0006] The storage battery is connected to the bidirectional DC / DC converter, the bidirectional DC / DC converter is connected to the input end of the DC bus, the output end of the DC bus is connected to another bidirectional DC / AC converter, and this bidirectional DC / AC converter is connected to the AC load;

[0007] The output end of the DC bus is connected to a series circuit of two capacitors.

[0008] Further, the AC load includes single-phase loads and three-phase loads.

[0009] Further, the unidirectional DC / DC converter is selected as a Boost circuit; the bidirectional DC / DC converter is selected as a bidirectional Buck / Boost circuit; the bidirectional DC / AC converter connected to the power grid is selected as a three-phase three-wire full-bridge circuit; the bidirectional DC / AC converter connected to the AC load is selected as a three-phase half-bridge circuit of a three-phase four-wire system.

[0010] Further, it further includes a controller, a host computer, and a communication module. The IO port of the controller is connected to the control signal lines of the unidirectional DC / DC converter, the bidirectional DC / DC converter, and the bidirectional DC / AC converter. The communication port of the controller is connected to the communication module, and the communication module is connected to the host computer.

[0011] A control method for a photovoltaic energy storage grid-connected / off-grid control system includes the following steps:

[0012] S1. When the controller determines that the power grid has an abnormality or a power outage, the bidirectional DC / AC converter connected to the power grid stops working;

[0013] S2. The bidirectional DC / DC converter takes over the control power of the DC bus voltage and controls the DC bus voltage at a set value;

[0014] S3. When the power grid returns to normal and switches from off-grid to grid-connected, the bidirectional DC / AC converter connected to the power grid is operated in a current source mode, and the bidirectional DC / AC converter connected to the AC load remains in a voltage source mode and operates continuously during the entire switching process;

[0015] R soc is the charging power of the battery, and P pv and P load respectively refer to the photovoltaic power that the photovoltaic system can generate and the load power; in the off-grid state, if R pv >R load there are two cases:

[0016] 1) If the battery is not fully charged, that is, R soc <R socmax , R socmax is the maximum value of the battery power, then the unidirectional DC / DC converter performs maximum power point tracking MPPT;

[0017] The bidirectional DC / DC converter controls the DC bus voltage and charges with a constant current, and the bidirectional DC / AC converter connected to the AC load controls the load voltage;

[0018] 2) If the battery is already fully charged and no further charging is allowed, that is, R soc ≥R socmax, the unidirectional DC / DC converter controls the DC bus voltage, the bidirectional DC / DC converter charges with constant voltage and current limit, and the bidirectional DC / AC converter connected to the AC load controls the load voltage;

[0019] S4. In the off-grid state, if P pv <P load , there are two cases:

[0020] 1) The battery still has power to discharge, that is, R soc >R socmin , then the unidirectional DC / DC converter performs maximum power point tracking MPPT, the bidirectional DC / DC converter controls the DC bus voltage and discharges with constant current, and the bidirectional DC / AC converter connected to the AC load controls the load voltage;

[0021] 2) The battery has no power to discharge, that is, R soc ≤R socmin , then the battery is unloaded or shut down, and the photovoltaic system or the power grid takes over the power supply;

[0022] S5. Perform simulation analysis; at t = 0.04 s, the power grid loses power, the grid voltage disappears, and the grid-connected current becomes 0 A; the bidirectional DC / AC converter connected to the AC load still maintains a stable operation state.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1) Simple and effective control for photovoltaic and energy storage power generation in grid-connected / off-grid mode;

[0025] 2) Reduce the deficiency of voltage fluctuation during photovoltaic and energy storage power generation;

[0026] 3) High safety performance. Adopting a dual-control strategy for the power generation end and the grid-connected end greatly improves the reliability of photovoltaic and energy storage power generation and grid connection, and also improves the safety of the distribution network;

[0027] 4) Connect the controller through the upper computer, and the controller connects the unidirectional DC / DC converter, the bidirectional DC / DC converter, and the bidirectional DC / AC converter to form a microgrid system, providing high-quality and efficient power for local DC and AC loads. The upper-layer control system can also perform energy management and scheduling on the system according to certain optimization goals, enabling users to obtain the maximum economic benefits;

[0028] 5) When the power grid loses power, only need to switch the DC bus voltage control to the bidirectional DC / DC converter control. The bidirectional DC / AC converter connected to the power grid stops working, and the bidirectional DC / AC converter connected to the AC load keeps working normally, which can ensure seamless switching between the grid-connected / off-grid states of the system, and the local critical loads are not affected. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of the control system described in the present invention.

[0030] Figure 2 It is a flowchart of the control method described in the present invention.

[0031] Figure 3 It is a simulation analysis diagram described in the present invention. Detailed implementation manners

[0032] The following further describes the detailed implementation manners of the present invention with reference to the accompanying drawings:

[0033] See Figure 1 , which is a schematic structural diagram of the control system described in the present invention. A photovoltaic energy storage grid-connected / off-grid control system of the present invention includes a photovoltaic system, a storage battery, a power grid, a unidirectional DC / DC converter, a bidirectional DC / DC converter, a bidirectional DC / AC converter, a DC bus, a capacitor, an AC load, a controller, a host computer, and a communication module; the photovoltaic system is connected to the unidirectional DC / DC converter through an interface, the output end of the unidirectional DC / DC converter is connected to the input end of the DC bus, the output end of the DC bus is connected to a DC load and the bidirectional DC / AC converter, and the bidirectional DC / AC converter is connected to the power grid; the IO port of the controller is connected to the control signal lines of the unidirectional DC / DC converter, the bidirectional DC / DC converter, and the bidirectional DC / AC converter, the communication port of the controller is connected to the communication module, and the communication module is connected to the host computer; the output end of the DC bus is connected to a series circuit of two capacitors;

[0034] The storage battery is connected to the bidirectional DC / DC converter, the bidirectional DC / DC converter is connected to the input end of the DC bus, and the output end of the DC bus is connected to another bidirectional DC / AC converter, and this bidirectional DC / AC converter is connected to a single-phase AC load or a three-phase AC load.

[0035] The unidirectional DC / DC converter is selected as a Boost circuit; the bidirectional DC / DC converter is selected as a bidirectional Buck / Boost circuit; the bidirectional DC / AC converter connected to the power grid is selected as a three-phase three-wire full-bridge circuit; the bidirectional DC / AC converter connected to the AC load is selected as a three-phase half-bridge circuit of a three-phase four-wire system.

[0036] The photovoltaic system PV has a photovoltaic interface, the battery has a battery interface, and the power grid has a power grid interface. The photovoltaic interface, the battery interface, and the power grid interface are energy ports, which are respectively connected to the DC bus through a unidirectional DC / DC converter (U1), a bidirectional DC / DC converter (U3), and a bidirectional DC / AC converter (U2). The AC load is connected to the DC bus through a bidirectional DC / AC converter (U4) and can connect to three-phase or single-phase loads. In addition, the DC bus also serves as a load port to directly supply energy to the DC load. The DC bus, as the energy exchange point of the four converters, uses two parallel capacitors for energy buffering during grid-connected / off-grid switching and facilitates decoupling control between the converters.

[0037] See Figure 2 , in the grid-connected case, the unidirectional DC / DC converter (U1) starts or stops according to the situation of the photovoltaic system PV; the bidirectional DC / AC converter (U2) controls the DC bus voltage and the grid-connected current and operates in four quadrants; the bidirectional DC / DC converter (U3) starts or stops working according to the command of the upper computer controller; the bidirectional DC / AC converter (U2) disconnects from the grid and stops working; the bidirectional DC / DC converter (U3) takes over the power of controlling the DC bus voltage; the bidirectional DC / AC converter (U4) keeps running in the voltage source state to supply power to the critical load. The differences between the grid-connected and off-grid operation modes mainly lie in whether the bidirectional DC / AC converter (U2) works. At the same time, the bidirectional DC / AC converter (U4) keeps running in the voltage source mode without interruption. The specific steps are as follows:

[0038] S1. When the controller determines that the grid has an abnormality or power failure, the bidirectional DC / AC converter (U2) stops working;

[0039] S2. The bidirectional DC / DC converter (U3) takes over the power of controlling the DC bus voltage and controls the DC bus voltage at the set value;

[0040] S3. When the grid returns to normal and switches from off-grid to grid-connected, make the bidirectional DC / AC converter (U2) operate in the current source mode, and the bidirectional DC / AC converter (U4) keeps running in the voltage source mode without interruption during the whole switching process;

[0041] R soc is the charging power of the battery, P pv and P load respectively refer to the photovoltaic power that the photovoltaic system can generate and the load power; in the off-grid state, if R pv >R load there are two cases:

[0042] 1) If the battery is not fully charged, that is, R soc <R socmax, R socmax is the maximum battery power, then the single - way DC / DC converter (U1) performs maximum power point tracking MPPT;

[0043] The bidirectional DC / DC converter (U3) controls the DC bus voltage and charges at a constant current, and the bidirectional DC / AC converter (U4) connected to the AC load controls the load voltage;

[0044] 2) If the battery is already fully charged and no further charging is allowed, that is, R soc ≥R socmax , then the single - way DC / DC converter (U1) controls the DC bus voltage, the bidirectional DC / DC converter (U3) charges at a constant voltage and limited current, and the bidirectional DC / AC converter (U4) controls the load voltage;

[0045] S4. In the off - grid state, if P pv <P load there are two cases:

[0046] 1) The battery still has power to discharge, that is, R soc >R socmin , then the single - way DC / DC converter (U1) performs maximum power point tracking MPPT, the bidirectional DC / DC converter (U3) controls the DC bus voltage and discharges at a constant current, and the bidirectional DC / AC converter (U4) controls the load voltage;

[0047] 2) The battery has no power to discharge, that is, R soc ≤R socmin , then the battery is unloaded or the system shuts down, and the photovoltaic system or the power grid takes over the power supply;

[0048] S5. Conduct a simulation analysis for this system; the single - way DC / DC converter (U1) is selected as a Boost circuit; the bidirectional DC / DC converter (U3) is selected as a bidirectional Buck / Boost circuit; the bidirectional DC / AC converter (U2) is selected as a three - phase three - wire full - bridge circuit; the bidirectional DC / AC converter (U4) is selected as a three - phase half - bridge circuit of a three - phase four - wire system. The simulation analysis is shown in Figure 3 , at t = 0.04 s, the power grid loses power, the grid voltage disappears, and the grid - connected current becomes 0 A; the bidirectional DC / AC converter (U4) still maintains a good operating state, without any impact on critical loads, and truly achieves seamless grid - connected / off - grid switching.

[0049] The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The methods used in the following embodiments are all conventional methods unless otherwise specified.

Claims

1. A photovoltaic energy storage grid-connected / off-grid control system, characterized in that: It includes a photovoltaic system, a battery, a power grid, a unidirectional DC / DC converter, a bidirectional DC / DC converter, a bidirectional DC / AC converter, a DC bus, a capacitor and an AC load; the photovoltaic system is connected to the unidirectional DC / DC converter through an interface, the output end of the unidirectional DC / DC converter is connected to the input end of the DC bus, the output end of the DC bus is connected to the DC load and the bidirectional DC / AC converter, and the bidirectional DC / AC converter is connected to the power grid; The battery is connected to a bidirectional DC / DC converter, the bidirectional DC / DC converter is connected to a DC bus input terminal, the DC bus output terminal is connected to another bidirectional DC / AC converter, and the bidirectional DC / AC converter is connected to an AC load; The DC bus output end is connected to a series circuit of two capacitors.

2. A photovoltaic energy storage grid-connected / off-grid control system according to claim 1, characterized in that: The AC load includes a single-phase load and a three-phase load.

3. A photovoltaic energy storage grid-connected / off-grid control system according to claim 1, characterized in that: The unidirectional DC / DC converter is selected as a Boost circuit; the bidirectional DC / DC converter is selected as a bidirectional Buck / Boost circuit; the bidirectional DC / AC converter connected to the power grid is selected as a three-phase three-wire full-bridge circuit; the bidirectional DC / AC converter connected to the AC load is selected as a three-phase four-wire three-phase half-bridge circuit.

4. A photovoltaic energy storage grid-connected / off-grid control system according to claim 1, characterized in that: It also includes a controller, a host computer and a communication module. The IO port of the controller is connected to the control signal lines of the unidirectional DC / DC converter, the bidirectional DC / DC converter and the bidirectional DC / AC converter. The communication port of the controller is connected to the communication module, and the communication module is connected to the host computer.

5. A control method for a photovoltaic energy storage grid-connected / off-grid control system according to any one of claims 1 to 4, characterized in that: The steps include: S1. When the controller determines that the grid is abnormal or power is off, the bidirectional DC / AC converter connected to the grid stops working; S2, the bidirectional DC / DC converter takes over the DC bus voltage control power and controls the DC bus voltage at the set value; S3. When the grid returns to normal and the switch is made from off-grid to grid-connected, the bidirectional DC / AC converter connected to the grid is operated in the current source mode, and the bidirectional DC / AC converter connected to the AC load is kept in the voltage source mode for uninterrupted operation during the whole switching process; R soc is the charge capacity of the battery, P pv and P load They refer to the photovoltaic power and load power generated by the photovoltaic system respectively; in the off-grid state, if R pv >R load There are two situations: 1) If the battery is not fully charged, R soc <R socmax , R socmax is the maximum power of the battery, the unidirectional DC / DC converter performs maximum power point tracking MPPT; The bidirectional DC / DC converter controls the DC bus voltage and charges with constant current, and the bidirectional DC / AC converter connected to the AC load controls the load voltage; 2) If the battery is already fully charged, no further charging is allowed, i.e. R soc ≥R socmax , then the unidirectional DC / DC converter controls the DC bus voltage, the bidirectional DC / DC converter charges with constant voltage and current limitation, and the bidirectional DC / AC converter connected to the AC load controls the load voltage; S4, in off-grid state, if P pv <P load There are two situations: 1) The battery still has discharge, that is, R soc >R socmin , the unidirectional DC / DC converter performs maximum power point tracking MPPT, the bidirectional DC / DC converter controls the DC bus voltage and discharges at a constant current, and the bidirectional DC / AC converter connected to the AC load controls the load voltage; 2) The battery is not discharged, that is, R soc ≤R socmin , the battery is unloaded or shut down, and the photovoltaic system or grid takes over the power supply; S5. Perform simulation analysis. At t=0.04s, the grid loses power, the grid voltage disappears, and the grid current becomes 0A. The bidirectional DC / AC converter connected to the AC load still maintains a stable operation state.

Images