CN102403730A - Control method of uninterruptible power supply type distributed grid-connected power generation system - Google Patents

Abstract

The invention relates to a control method of an uninterrupted power supply type distributed grid-connected power generation system, in the system, a load is divided into an important load and a conventional load, switches which can be controlled by a controller are respectively added in front of the load, once the controller detects an island effect, the grid-connected switch and a power grid are disconnected, and meanwhile, the independent operation mode can be automatically switched without stopping and manual control, so that the continuous power supply for the important load is ensured; the overall performance of the distributed grid-connected power generation system is improved; the advantages of the distributed power generation system are fully exerted, and the advantages of the distributed power generation system are complementary with those of the power grid; an external manual switch and a double-loop output interface are not required to be arranged, so that the hardware design is simplified, and the cost is reduced; the series topology structure of the switch for grid-connected mode operation and the switch for independent mode operation improves the stability and safety of the whole system when the switch fails; when any one of the grid or the inverter is in fault and stops, the other side can continue to provide power.

Description

Control method of uninterruptible power supply type distributed grid-connected power generation system

technical field

The invention relates to a smart grid, in particular to a control method for an uninterruptible power supply type distributed grid-connected power generation system.

Background technique

When the distributed generation system and the grid are connected to the grid, if there is an accident on the grid side or a power outage for maintenance, the distributed generation system on the user side must be disconnected from the power grid to handle faults on the grid side. For the distributed generation system, at this time, the grid-connected operation mode has been converted to the island operation mode to form an island effect. If the islanding effect continues, it is very easy to cause damage to the grid equipment and bring harm to the maintenance personnel. In order to avoid the occurrence of the island effect, the distributed generation system must have an island detection function. When the island effect occurs, the grid-connected switch is disconnected, and the operation of the distributed generation system is stopped while disconnecting from the grid. This creates the following problems:

1. It cannot continuously supply power to important loads. If it is suddenly cut off, it will easily cause danger and damage to the equipment and personnel on the user side;

2. Before the power grid is repaired, the operation of the distributed power generation system is stopped;

3. Sunlight, fuel cells, and wind power cannot continue to be used, resulting in a reduction in the utilization efficiency of renewable energy;

4. When a disaster occurs, the distributed power generation system cannot effectively utilize its own independent power generation characteristics to provide power to the near-user end;

5. If you want to switch from grid-connected operation mode to independent operation mode, it can only be realized through external manual control switch and dual-loop output;

6. Only when the following two conditions are met can it be restarted to realize the conversion of the operating mode;

The distributed power generation system must be stopped for a long time before the external switch can be switched manually;

The output must be changed from the grid-tied output interface terminal to the independent output interface terminal.

Contents of the invention

The present invention aims at the problem of damage caused by the islanding effect caused by grid-connected operation, and proposes a control method for an uninterruptible power supply type distributed grid-connected power generation system. In this system, once the islanding effect is detected, the grid-connected At the same time when the switch and the grid are disconnected, it can automatically switch to the independent operation mode without stopping and manual control. If the output power of the distributed generation system is greater than or equal to the rated power of the important load, it can continuously supply power to the important load. Such important loads not only do not need to be powered off, but also the distributed generation system does not need to be stopped. In addition to the above functions, it is also possible to simply set the software to be compatible with the current requirements and implement islanding effect detection and protection.

The technical solution of the present invention is: a control method for an uninterruptible power supply type distributed grid-connected power generation system, including the following specific steps:

1) Establish an uninterruptible power supply type distributed grid-connected power generation system: the distributed power generation system includes a DC power supply, a step-up DC converter, a grid-connected inverter and a grid-connected switch. The DC power supply is directly connected to the grid-connected inverter After conversion, the load is supplied to the power grid through the switch. The load is divided into important load and normal _load . There is an independent mode operation switch at the front end of the important load, and a grid-connected mode operation switch at the rear end of the important load and the front end of the normal load. The important load is connected to the back end of the distributed power generation system, the normal load is connected to the front end of the grid, and the switch is opened and closed by the controller;

2) When connecting to the grid: first detect the grid voltage signal at the public connection point, and start the automatic synchronous grid-connecting action. After the grid-connecting conditions are met, the controller controls the grid-connected mode operation switch and the independent mode operation switch to close, and the distributed power generation system Realize grid-connected operation with the grid;

3) After grid connection: the island protection action becomes effective, and the power grid and distributed power generation system supply power to common loads and important loads at the same time;

4) When the power grid fails: When the power grid fails, the proposed distributed power generation system detects the island effect by turning on the island protection, and the detected island signal is sent to the controller. The distributed grid-connected power generation system is disconnected; the distributed power generation system continues to supply power to important loads, and the grid-connected inverter changes the control method according to the control object:

A) If the grid connection is current control, it needs to be converted to voltage control;

B) In the case of voltage control, it remains unchanged;

At this time, the distributed generation system continues to supply power to important loads as an AC voltage source just like the grid;

5) When the grid-connected inverter fails: when the grid-connected inverter fails, the controller controls the independent operation mode to switch off, and the distributed power generation system is separated from the distributed grid-connected power generation system;

If the power grid is in a normal state, common loads and important loads continue to be powered by the grid;

If the power grid is faulty, the controller controls the switch for grid-connected operation mode to be disconnected;

6) When connecting to the grid again: repeat steps 2) to 5).

The independent mode operation switch and the grid-connected mode operation switch may be single-pole or double-pole.

The important load is connected in series with the independent mode operation switch, and the back end of the distributed power generation system and the front end of the grid-connected mode operation switch are connected after the series connection.

The beneficial effect of the present invention is that: the uninterruptible power supply type distributed grid-connected power generation system control method of the present invention implements uninterrupted power supply for important loads, and the dual power supply mode improves the overall performance of the distributed power generation system; the distributed power supply implements continuous operation; sustainable use of renewable resources such as sunlight, fuel cells, and wind power, which improves the utilization efficiency of renewable resources; the advantages of distributed power are fully utilized, and the advantages of the grid are complementary; no need to set external manual switches and dual-loop output interface, which simplifies the hardware design and reduces the cost; the series topology of the switch for grid-connected mode operation and the switch for independent mode operation improves the stability and safety of the entire system when the switch fails; the grid or inverter When any party fails and stops, the remaining party can continue to provide power.

Description of drawings

Figure 1 is a structural diagram of a commonly used distributed grid-connected power generation system;

Fig. 2 is the structural diagram of Example 1 of the uninterruptible power supply type distributed grid-connected power generation system of the present invention;

Fig. 3 is the structural diagram of Example 2 of the uninterruptible power supply type distributed grid-connected power generation system of the present invention;

Fig. 4 is a structural diagram of Example 3 of the uninterruptible power supply type distributed grid-connected power generation system of the present invention.

Detailed ways

As shown in Figure 1, the structure diagram of a commonly used distributed grid-connected power generation system, the distributed power generation system includes a DC power supply (which can be solar cells, wind generators and fuel cells), a step-up DC converter, a grid-connected inverter and parallel Grid switch, the DC power supply is converted to DC by the grid-connected inverter, and then connected to the grid to supply power to the load through the switch.

As shown in Figure 2, the structure diagram of example 1 of the uninterruptible power supply type distributed grid-connected power generation system divides the load into important load Rs and regular load _{R o .} Mode operation switches S _a -S _b and grid-connected operation mode switches S ₁ -S ₂ , the important load Rs is connected to the rear end of the distributed power supply, the regular load R _o is connected to the front end of the grid, and the grid-connected switch is opened and closed under the control of the controller . It works like this:

1) When connected to the grid:

Firstly, detect the power grid signal at the public connection point, and start the automatic synchronous grid connection action. After the grid-connected conditions are satisfied, the grid-connected mode operation switch and the independent mode operation switch are closed through the control instructions relay_1 and relay_2, and the initial states of the switches are all set to the off state. Here, relay_1 is the control of S ₁ -S ₂ Instructions, relay_2 is the control instruction of S _a -S _b , when relay_1=1, relay_2=1, the distributed generation system and the grid are connected to the grid.

2) After grid connection:

The island protection action becomes effective. At this time, the power grid and the distributed generation system supply power to common loads and important loads at the same time.

3) When the power grid fails:

When the power grid fails, the proposed distributed generation system detects the island effect by turning on the island protection. Using the detected islanding signal as a control instruction, the switches S ₁ -S ₂ for grid-connected mode operation are turned off.

The controller issues an instruction of relay_1=0, and turns off the switches S ₁ -S ₂ for the grid-connected operation mode. At this time, the grid is separated from the distributed grid-connected power generation system.

While the grid is disconnected from the distributed grid-connected power generation system, the distributed power generation system does not need to stop and still run. However, the inverter control method may need to be changed. According to the control object, it can be divided into the following two situations:

1. If the grid connection is current control, it needs to be converted to voltage control;

2. If it is controlled by voltage, it will remain unchanged;

At this time, the distributed generation system continues to supply power to important loads as an AC voltage source just like the grid.

If you want to stop the distributed generation system, you only need to simply issue the relay_1 and relay_2 commands through the controller, so that relay_1=0 and relay_2=0.

4) When the grid-connected inverter fails:

When the grid-connected inverter fails, the controller sends a relay_2=0 command to turn off the switches S _a -S _b for independent operation mode, and at this time the distributed generation system is separated from the distributed grid-connected generation system.

If the grid is in normal state, common loads and important loads continue to be powered by the grid.

If the power grid is in a fault state, the controller sends an instruction of relay_1=0 to turn off the switches S ₁ -S ₂ for the grid-connected operation mode.

5) When connecting to the grid again: repeat the previous steps.

As shown in Figures 3 and 4, the uninterruptible power supply type distributed grid-connected power generation system examples 2 and 3 structure diagrams, the load is divided into important load Rs and regular load R _o , and the front ends of important load Rs and regular load R _o are respectively set The single-pole independent mode operation switch S _a and the grid-connected operation switch S ₁ , the important load Rs is connected to the back end of the distributed generation system, the normal load R _o is connected to the front end of the grid, and the grid-connected switch is opened and closed under the control of the controller, where The grid-connected operation mode of the conventional load R _o is connected to the main circuit with the switch S ₁ , as shown in Figure 3 and 4, the independent mode operation switch S _a of the important load Rs can be connected to the main circuit, and can also be connected in series with the important load Rs Parallel to both ends of the distributed generation system.

1) When connected to the grid:

Firstly, detect the power grid signal at the public connection point, and start the automatic synchronous grid connection action. After the grid-connected conditions are satisfied, the grid-connected mode operation switch and the independent mode operation switch are closed through the control commands relay_1 and relay_2, and the initial states of the switches are all set to be off. Here, relay_1 is the control signal of S ₁ , and relay_2 is the control signal of S _a . When relay_1=1 and relay_2=1, the distributed generation system and the grid are connected to the grid.

2) After grid connection:

The island protection action becomes effective. At this time, the power grid and the distributed generation system supply power to common loads and important loads at the same time.

3) When the power grid fails:

When the power grid fails, the proposed distributed generation system detects the island effect by turning on the island protection. Using the detected islanding signal as a control command, the switch S ₁ for grid-connected mode operation is turned off.

The controller issues an instruction of relay_1=0, and turns off the switch S ₁ for the grid-connected operation mode. At this time, the grid is separated from the distributed grid-connected power generation system.

While the grid is disconnected from the distributed grid-connected power generation system, the distributed power generation system does not need to stop and still run. However, the inverter control method may need to be changed. According to the control object, it can be divided into the following two situations:

If the grid connection is current control, it needs to be converted to voltage control;

In the case of voltage control, it remains unchanged;

At this time, the distributed generation system continues to supply power to important loads as an AC voltage source just like the grid.

If you want to stop the distributed generation system, you only need to simply issue the relay_1 and relay_2 commands through the controller, so that relay_1=0 and relay_2=0.

4) When the grid-connected inverter fails:

When the grid-connected inverter fails, the controller sends relay_1=0 and relay_2=0 commands to disconnect the switch S ₁ for grid-connected mode operation and the switch S _a for independent operation mode. At this time, the distributed generation system starts from the distributed Disengage and disconnect important loads in the grid-connected power generation system.

5) When connecting to the grid again: repeat the previous steps.

Claims (3)

1. the distributed grid-connected system control method of uninterrupted power supply type is characterized in that, comprises following concrete steps:

1), set up the distributed grid-connected system of uninterrupted power supply type: distributed generation system comprise DC power supply,, voltage boosting dc transducer, combining inverter and the switch that is incorporated into the power networks; After DC power supply carries out the orthogonal conversion through combining inverter; Through switch and to the electrical network powering load, load is divided into important load and conventional load _o, being provided with the stand-alone mode run switch at the important load front end, important load rear end and conventional load front end are provided with the mode operation switch that is incorporated into the power networks, and important load connects the distributed generation system rear end, the open and close that are controlled by the controller of the conventional load front end that gets access to grid, switch;

When 2), being incorporated into the power networks: at first detect the points of common connection mains voltage signal; Begin to be incorporated into the power networks synchronously automatically action; After satisfying the condition that is incorporated into the power networks, the controller control command mode operation switch that is incorporated into the power networks is closed with the stand-alone mode run switch, and distributed generation system and electrical network realization are incorporated into the power networks;

3), the back of being incorporated into the power networks: isolated island protection action beginning is effective, and electrical network and distributed generation system are given the power supply of common load and important load simultaneously;

4), during electric network fault: when electrical network breaks down; The distributed generation system of motion detects island effect through opening the isolated island protection, and detected isolated island signal send controller; Controller is controlled the mode operation that is incorporated into the power networks and is broken off with switch, and electrical network breaks away from from distributed grid-connected system; Distributed generation system continues to the important load power supply, and combining inverter changes control mode according to controlling object:

A) when being incorporated into the power networks, need convert voltage control into to Current Control;

B) when being voltage control, remain unchanged;

At this moment, distributed generation system continues to supply power to important load as alternating-current voltage source just as electrical network;

5), during the combining inverter fault: when combining inverter broke down, controller control independent operation mode broke off with switch, and at this moment distributed generation system breaks away from from distributed grid-connected system;

If during the electrical network normal condition, common load and important load continue by mains supply;

If during grid failure state, the controller control pattern that is incorporated into the power networks is broken off with switch;

When 6), being incorporated into the power networks again: repeating step 2)～5).

2. according to the distributed grid-connected system control method of the said uninterrupted power supply type of claim 1, it is characterized in that, said stand-alone mode run switch be incorporated into the power networks the mode operation switch can be the hilted broadsword formula also can be the double-pole formula.

3. according to the distributed grid-connected system control method of the said uninterrupted power supply type of claim 1, it is characterized in that said important load and stand-alone mode run switch are connected in series, connect the distributed generation system rear end after the series connection and be incorporated into the power networks mode operation switch front end.

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