WO2014079268A1

WO2014079268A1 - Bi-directional storing inverter used in grid connected power system

Info

Publication number: WO2014079268A1
Application number: PCT/CN2013/083905
Authority: WO
Inventors: 陈书生
Original assignee: 广东易事特电源股份有限公司
Priority date: 2012-11-23
Filing date: 2013-09-22
Publication date: 2014-05-30
Also published as: CN102957335A; CN102957335B

Abstract

A bi-directional storing inverter in a grid connected power system, comprising: a transformer connected between the output end of a bi-directional inverter circuit and a switching circuit; at least two bi-directional inverter circuit in parallel; the input ends of the two bi-directional inverter circuits (1, 2) respectively connecting to a storage battery, the output ends of them respectively connecting to the different windings of the transformer primary side, and the transformer secondary side connecting to the switch circuit; when the public power grid disconnects and a grid connected inverter is reconnected, if the produced power is more than the needs of the load, a sampling control circuit will control one of the bi-directional inverter circuits working in the inverter state to keep the grid based a grid connected inverter, and another bi-directional inverter circuit working in the rectification state; the excess electricity is stored in the storage battery, and there is no need to limit the output power of the grid connected inverter, which avoids the unnecessary waste of the energy.

Description

Description Bidirectional energy storage inverter for grid-connected power generation system

The invention relates to a grid-connected power generation system, and in particular to a two-way energy storage inverter.

Background technique

In distributed generation systems, grid-connected inverters are widely used today, and current-type control is generally used, that is, the grid-connected inverter is a current source. The energy of the grid-connected inverter can come from wind energy, photovoltaic modules or bio-batteries. When generating electricity, it outputs the same frequency as the grid to the utility grid. The grid-connected inverter controls only the output current, while the grid voltage is controlled by the grid. Grid company control. When the operating parameters of the utility grid exceed the requirements of the grid-connected inverter or the utility grid is de-energized, the grid-connected inverter will automatically disconnect from the utility grid and stop generating electricity. To this end, it is generally necessary to install a two-way energy storage inverter: When the utility grid is normally connected, the grid-connected inverter works normally, and the two-way energy storage inverter works in a rectified state to charge the energy storage battery; When the power is off, the bidirectional inverter works in the inverter state, adopts voltage type control, and outputs sinusoidal AC voltage. The grid-connected inverter is connected to the grid based on the local small grid, and supplies power to the load together. At this time, if more energy is generated than the load demand, since the existing bidirectional inverter can only work in one state at the same time, and cannot be rectified while inverting, the excess energy cannot be used to charge the energy storage battery. You have to use other methods to limit the output power of the grid-connected inverter and waste excess energy.

Summary of the invention

The present invention creates a two-way energy storage inverter for a grid-connected power generation system to address the problems caused by more power than the load demand after the utility grid is disconnected and the grid-connected inverter has been re-connected.

To this end, a bidirectional energy storage inverter for a grid-connected power generation system is provided, including a bidirectional inverter circuit and a sampling control circuit:

The input end of the bidirectional inverter circuit is connected to the energy storage battery, and the output end is connected to the utility grid via the switch switching circuit. Grid-connected inverter and load, specifically, a transformer is connected between the output end of the bidirectional inverter circuit and the switch switching circuit, and the bidirectional inverter circuit has at least two parallel, and the input ends of the two bidirectional inverter circuits are respectively connected to the storage The battery can be connected to the different windings of the primary side of the transformer, and the secondary side of the transformer is connected to the switch switching circuit. When the utility network is normally connected, the sampling control circuit controls the bidirectional inverter circuit to work in the rectification state, charging the energy storage battery, and the utility grid. When disconnected, the sampling control circuit controls the bidirectional inverter circuit to operate in the inverter state to provide a grid-connected basis for the grid-connected inverter. After the utility grid is disconnected and the grid-connected inverter has been re-connected, if the generated power is large In the load demand, the sampling control circuit controls one of the bidirectional inverter circuits to operate in the inverter state to maintain the grid connection of the grid-connected inverter, and the other bidirectional inverter circuit operates in the rectification state to store excess power in the storage state. Can be in the battery.

Since the bidirectional inverter circuit has two parallel circuits, the sampling control circuit can control one of the bidirectional inverter circuits to operate in an inverter state to maintain the grid-connected base of the grid-connected inverter, and the other bidirectional inverter circuit operates in a rectification state. , the excess power is charged into the energy storage battery, there is no need to limit the output power of the grid-connected inverter, and the waste of excess energy is avoided.

As for the utility grid disconnected but the grid-connected inverter has not been re-accessed, the sampling control circuit can control the two bidirectional inverter circuits to work in the inverter state, so as to provide the grid-connected inverter for the grid-connected inverter as soon as possible, so that The grid-connected inverter can be re-accessed as soon as possible.

As for the normal connection of the utility grid, the sampling control circuit can control both bidirectional inverter circuits to operate in the rectification state to improve the charging efficiency.

DRAWINGS

Figure 1 is a block diagram of the structure of a grid-connected power generation system.

Figure 2 is a circuit diagram of a bidirectional energy storage inverter.

Figure 3 is a circuit diagram of another bidirectional energy storage inverter.

detailed description

As shown in FIG. 1, the bidirectional inverter circuit 1 and the bidirectional inverter circuit 2 are juxtaposed, and their input terminals are respectively connected. To the energy storage battery, their output terminals are respectively connected to the transformer primary windings N2 and N3; the transformer secondary winding N1 is the output of the bidirectional energy storage inverter. The transformer is used for energy transfer and input-output isolation, which is the core component that combines the two bidirectional inverter circuits 1, 2. The sampling and control circuits respectively sample input voltage, current, output voltage, current and other parameters, output PWM signals, and control the operation of the circuit. The secondary side of the transformer is connected to the switch switching circuit. The switch switching circuit has a detection circuit inside, and changes the connection state of the system according to the state of the utility grid and the load. The energy of the grid-connected inverter can come from wind energy, photovoltaic modules or bio-batteries.

When the utility grid is properly connected, the switch switching circuit connects the bidirectional energy storage inverter and the load to the utility grid. When the grid-connected inverter can output enough energy, the switch switching circuit connects the grid-connected inverter to the utility grid. At this time, the sampling control circuit controls the two bidirectional inverter circuits 1, 2 to operate in the rectification state, and to store energy. The battery is charged, and energy flows from the utility grid side to the energy storage battery through the bidirectional energy storage inverter.

When the operating parameters of the shared grid exceed the system requirements or the utility grid is powered off, the switch switching circuit will disconnect the utility grid. At this time, the grid-connected inverter itself will disconnect from the system by detecting no grid, and enter The so-called island state stops power generation, so the sampling control circuit controls the two bidirectional inverter circuits 1, 2 to operate in the inverter state, and the output AC power constitutes a local small grid to supply power to the load, and the energy is reversed from the energy storage battery through the two-way energy storage. The transformer flows to the load, and the grid-connected inverter detects the local small grid, and then starts and connects to the local small grid in a short time, and supplies power to the load together with the bidirectional energy storage inverter. If the grid-connected inverter generates more energy than the load demand, the sampling control circuit controls the bidirectional inverter circuit 1 to maintain the operating state in the inverter state to maintain the local small grid, and controls the bidirectional inverter circuit 2 to change from the inverter state to the rectifier. The state is to charge the energy storage battery, and the excess energy is stored. At this time, the energy is mainly converted from the grid-connected inverter to the battery after being converted by the two-way energy storage inverter, and the grid-connected inverter generates more than the load demand. Energy is stored in the battery. Under this condition, the bidirectional inverter circuit 1 operating in the inverter state mainly functions to maintain a local small power grid, and the energy consumed by the load is mainly provided by the grid-connected inverter.

Each bidirectional inverter circuit has two operating states, namely an inverter state and a rectification state. Two bidirectional inverse The combination of variable circuits can form three effective modes of operation, gp: inverter + rectification, inverter + inverter, rectification + rectification. The three working modes are switched by the sampling and control circuit of the bidirectional energy storage inverter according to the system condition, and are realized by controlling the bidirectional inverter circuit 1 and the bidirectional inverter circuit 2 to operate in an inverter state or a rectification state, respectively.

An implementation example is shown in Figure 2. The bidirectional energy storage inverter includes an input capacitor Cap, two bidirectional inverter circuits with the same circuit structure, a power frequency transformer, and a sampling control circuit. The bidirectional inverter circuit 1 comprises a DC/DC converter composed of an input inductor M1_L1, a switch M1_Q1, a switch M1_Q2 and a capacitor Ml_bus, a full bridge converter composed of M1_Q3, M1_Q4, M1_Q5, M1_Q6 and an inductor M1_L2 and a capacitor M1_C1. The bidirectional inverter circuit 2 also includes a DC/DC converter composed of an input inductor M2_L1, a switch tube M2_Q1, a switch tube M2_Q2 and a capacitor Ml_bus, and a full bridge converter composed of M2_Q3, M2_Q4, M2_Q5, M2_Q6 and A filter consisting of an inductor M2_L2 and a capacitor M2_C1. The output terminals of the bidirectional inverter circuit 1 and the bidirectional inverter circuit 2 are respectively connected to the N2 and N3 windings of the transformer, and the transformer N1 winding is the output end of the bidirectional energy storage inverter.

As shown in Figure 2, the bidirectional inverter circuit 1 is taken as an example to describe the operation mode. When the bidirectional inverter circuit 1 is operated in the inverter state, the DC/DC converter composed of the input inductor L1, the switch transistor M1_Q1, the switch transistor M1_Q2 and the capacitor Ml_bus operates in the boost mode, and the switch transistor M1_Q2 is modulated by the PWM, the switch tube M1_Q1 is off, but the body diode is in operation. The lower voltage of the battery is raised by the boosting circuit, and the voltage of the capacitor M1_bus is sampled to adjust the PWM so that the voltage of the capacitor Ml_bus is at a stable value. The full-bridge converter consisting of M1_Q3, M1_Q4, M1_Q5, and M1_Q6 is respectively modulated by 4 PWMs, and is filtered by the LC filter and isolated by the transformer to output sinusoidal AC. The energy flows out of the battery, is inverted into alternating current after the bidirectional inverter circuit, and is then isolated by the power frequency transformer to supply power to the load.

When working in the filtering state, M1_Q3, M1_Q4, M1_Q5, M1_Q6 are all in the off state, and the AC power is rectified by the full-bridge rectification formed by the body diodes of the four switch tubes, and then filtered by the capacitor Ml_bus to form a direct current, which is composed of the switch tube M1_Q1 and the switch tube. M1_Q2, DC \DC converter composed of input inductor L1 Working in the buck mode, the switch M1_Q1 is modulated by PWM, in the switch state, the switch M1_Q2 is in the off state, but the body diode is in the working state. The voltage of the capacitor M1_bus is lowered by the step-down circuit, and the PWM control battery charging process is adjusted by sampling the current of the input inductor L1 and the battery voltage. The energy is charged from the grid side through the transformer and then converted by the bidirectional inverter circuit to charge the battery.

The two operating mode control modes of the bidirectional inverter circuit 2 are the same as those of the bidirectional conversion circuit 1.

Another implementation example is shown in Figure 3. The bidirectional energy storage inverter includes an input capacitor Cap, two bidirectional inverter circuits with the same circuit structure, a power frequency transformer and a sampling control circuit. The bidirectional inverter circuit 1 includes M1_Q3, A full-bridge converter composed of M1_Q4, M1_Q5, M1_Q6 and a filter composed of an inductor M1_L2 and a capacitor M1_C1; likewise, the bidirectional inverter circuit 2 also includes a full-bridge converter composed of M2_Q3, M2_Q4, M2_Q5, M2_Q6 and the inductor M2_L2 A filter composed of a capacitor M2_C1.

As shown in Fig. 3, the bidirectional conversion circuit 1 is taken as an example to describe the operation mode. When operating in the inverter state, the full-bridge converter consisting of M1_Q3, M1_Q4, M1_Q5, and M1_Q6 is respectively modulated by 4 PWMs. After LC filtering, transformer isolation and boosting, the output sine wave AC power is used to supply the load.

When working in the filtering state, the two upper tubes M1_Q3 and M1_Q5 of the full bridge converter are in the off state, but the body diode is in the working state, and the two lower tubes M1_Q4 and M1_Q6 of the full bridge converter are respectively modulated by two PWMs. Battery charging process.

The two modes of operation of the bidirectional conversion circuit 2 are the same as those of the bidirectional conversion circuit 1.

Claims

Claim

1. A bidirectional energy storage inverter for a grid-connected power generation system, comprising a bidirectional inverter circuit and a sampling control circuit: the input end of the bidirectional inverter circuit is connected to the energy storage battery, and the output end is connected to the utility grid via the switch switching circuit, and Network inverter and load;

When the utility grid is normally connected, the sampling control circuit controls the bidirectional inverter circuit to operate in the rectification state, and the sampling control circuit controls the bidirectional inverter circuit to operate in the inverter state when the utility grid is disconnected;

Its characteristics are:

A transformer is connected between the output end of the bidirectional inverter circuit and the switch switching circuit, and the bidirectional inverter circuit has at least two parallel sides, and the input ends of the two bidirectional inverter circuits are respectively connected to the energy storage battery, and the output ends are respectively connected to the primary side of the transformer. Different windings, the secondary side of the transformer is connected to the switching circuit;

After the utility grid is disconnected and the grid-connected inverter is re-connected, if the generated electricity is more than the load demand, the sampling control circuit controls one of the bidirectional inverter circuits to operate in the inverter state, and the other bidirectional inverter circuit operates. In the rectified state.

2. The bidirectional energy storage inverter according to claim 1, wherein the sampling control circuit controls both bidirectional inverter circuits to operate when the utility grid is disconnected but the grid connected inverter is not reconnected. Inverted state.

3. The bidirectional energy storage inverter according to claim 1, wherein the sampling control circuit controls both bidirectional inverter circuits to operate in a rectified state when the utility grid is normally connected.