JPH0767346A - Control method of parallel operation of inverter for system interconnection - Google Patents

Abstract

PURPOSE:To maintain the proper value of power conversion efficiency as the whole inverter system for system interconnection consisting of a plurality of inverters and a DC power supply such as a solar cell respectively. CONSTITUTION:When the sum of the output power of both inverters 2A and 2B detected by an output voltage detector 6 is smaller than a set value thereof, an electromagnetic 3C for varying interconnection among both inverters and both solar cells 1A, 1B is closed, and either one inverter selected in both inverters is supplied with electricity from both solar cells. When the sum of both output power is larger than the set value thereof, the electromagnetic switch 3C is opened. Accordingly, the inverters are operated in both combination of the inverter 2A and the solar cell 1A and the inverter 2B and the solar cell 1B, and the operation of the inverters is controlled in conformity with a specified program in a switching control circuit 7 so as to maintain the proper value of the power conversion efficiency of the inverters by the increase of the load factor of the inverters regarding the inverters selected to be worked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a DC power source obtained by rectifying AC power from a solar cell power source or a wind power generator whose output fluctuates as an input source to output a predetermined AC power, and also to an AC system. The present invention relates to a parallel operation control method for a plurality of inverters that operate in parallel with a power source to form a grid interconnection inverter system.

[0002]

2. Description of the Related Art As a conventional parallel operation control method for this type of grid interconnection inverter, one is known which is performed according to the configuration diagram of the grid interconnection inverter system of FIG. There is. In FIG. 6, 1 is a solar cell as a DC power source whose output fluctuates, and the breakdown of the plurality of solar cells is 1A, 1B, ..., 1N, and 2 is an inverter, and the solar cells 1A, 1B, ……,
Let 2A, 2B, ..., 2N be a plurality of inverters each having 1N as its DC power source.

Reference numeral 31 is a contact of an electromagnetic switch 3 as switching means for inserting the inverter 2 into the AC system power source 4 in parallel, corresponding to the inverters 2A, 2B, ..., 2N, respectively, 31A and 31B. , ..., 31N.
That is, in the conventional system interconnection inverter system as described above, each DC / AC conversion system that is operated in parallel with the AC system power source 4 has 1A-2A-31A, ..., 1N-2N-31N.
As described above, the DC power supply 1, the inverter 2, and the electromagnetic switch 3 (or the contact 31) are configured in a fixed relationship of 1: 1 and the inverter operation / stop control is independently performed for each conversion system. The opening / closing control of the electromagnetic switch is performed.

[0004]

Generally, since the inverter has a low power conversion efficiency at the time of low output, it is desirable that the inverter is operated at a high load factor or a high output state as much as possible. On the other hand, as described above, in the conventional system interconnection inverter system, the correspondence between each inverter and its DC power source is a fixed one-to-one relationship.

Therefore, if the DC power source of the inverter is a solar cell, the generated power is small in the low sunshine state, and the individual inverters using the solar cell as the DC power source or the inverter system as a whole is There is no choice but to operate with low power conversion efficiency, and an undesired operating state occurs with an increase in power loss. Furthermore, if any of the inverters forming the inverter system fails and stops, the solar cell that supplies power to the failed inverter receives sunlight and normally generates power, and the inverter system as a whole responds to the output of the solar cell. As a result, even when there is a surplus in the power conversion capability, the output of the solar cell that feeds the faulty inverter cannot contribute to the power generation of the entire inverter system.

In view of the above, the present invention enables any combination of a plurality of inverters and a DC power source in the above-mentioned inverter system, and achieves an appropriate value of the conversion efficiency in the operating inverter by appropriately consolidating the DC power sources. It is an object of the present invention to provide a parallel operation control method of a grid interconnection inverter capable of converting all generated power of each DC power supply into AC power even when any of the inverters fails and stops.

[0007]

In order to achieve the above object, in the parallel operation control method of the grid interconnection inverter according to the present invention, 1) a first means is a plurality of DC power supplies whose outputs vary. Parallel operation of a plurality of inverters that form an inverter system for grid interconnection by converting the DC power from the AC power supply to a predetermined AC power and performing parallel operation with the AC power supply through the opening / closing means installed on the output side In the control method, connection switching means for performing any combinational connection between each inverter and each DC power supply, power detection means for detecting the total output power of each inverter operating in parallel with the AC power supply, and a predetermined value. And a switching control means for driving and controlling each of the inverters and the connection switching means in accordance with the program of FIG. A combination of each of the operating inverters and each DC power source that can be shared with the optimum conversion efficiency is selected according to the predetermined program, and the start / stop of each inverter specified according to the selection result and the above Opening / closing control of the connection switching means is performed, and 2) As a second means, a predetermined program in the first means is set to a failure stop state of each inverter and an operable state after the restoration. Correspondingly, it shall be automatically corrected regarding the number of operable inverters,
3) As a third means, the start-up of each inverter performed according to the predetermined program in the first means.
During stop control, a fixed state confirmation time is set by the time-limit element before the transition to the next stage operation.

[0008]

In general, the inverter has a low power conversion efficiency when the load is low and the output is low. Therefore, it is desirable that the inverter be operated in a high load and high output state as much as possible. In response to the above, the first aspect of the present invention is to maintain an appropriate value of the power conversion efficiency of the entire grid interconnection inverter system,
Providing a connection switching means consisting of an electromagnetic switch that enables arbitrary combination connection between a plurality of inverters constituting the inverter system and a plurality of DC power sources such as solar cells,
It is necessary to determine the number of operating inverters so as to obtain the optimum high output state corresponding to the fluctuating generated power of each DC power source, and collectively connect to each operating inverter corresponding to the high output state. The determination of the number of DC power supplies and the identification of each combination of the inverter and the DC power supply performed according to both of these determinations are always performed according to a predetermined program, and the inverter system is optimized for the total generated power of the DC power supply group. It is operated at power conversion efficiency.

The second aspect of the present invention, when any one of the inverters constituting the above-mentioned inverter system fails to stop, the DC power source connected to the failed inverter is transferred to another normal inverter via the connection switching means. The connection is changed and the generated power is effectively used, and the predetermined program for controlling the connection switching means is provided in correspondence with the failure stop state of each inverter and the operable state after the restoration. The number of operable inverters is automatically corrected.

A third aspect of the present invention follows the above predetermined program in order to ensure stable operation of the inverter system with respect to a solar cell power source or the like in which the output power may suddenly change due to a sudden change in the sunshine state. During start / stop switching control of each inverter, a fixed state confirmation time is set by the time-limit element before the transition to the next stage operation.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a photovoltaic power generation system exemplifying a grid interconnection inverter system, FIG. 2 is a circuit diagram of the switching control circuit shown in FIG. 1, and FIGS. 6 is a flowchart of a control program executed.

First, FIG. 1 shows an interconnection state between two sets of a DC / AC conversion system consisting of a DC power supply and an inverter, and an AC system power supply such as a commercial power supply. A solar cell as a fluctuating DC power source has two sets of 1A and 1B, and an inverter 2 has two sets of 2A and 2B. Reference numeral 3 is an electromagnetic switch, the details of which are 3A and 3B, respectively, which form a parallel opening / closing means for inserting the inverters 2A and 2B into the AC system power supply 4 respectively, and 3C is the sun. It serves as connection switching means for changing the mutual connection between the batteries 1A and 1B and the inverters 2A and 2B.

The electromagnetic switch 3 has contact points (31).
And a contact drive coil. Reference numeral 6 denotes an output power detector for detecting the sum of the output powers of both the inverters 2A and 2B feeding the system power supply 4, and the voltage at the output busbar common to both inverters and the bus current detected by the current transformer 5. And are the inputs.

The sum of the output powers of the two inverters is used as a substitute for the total output power of the 1A and 1B solar cells. CP is a comparator, which compares the set power given as the divided voltage of the resistors R _S1 and R _S2 with the sum of the output powers of the two inverters given as the output voltage of the detector 6, The comparison result is output as a signal S _P.

The open / close control circuit 7 includes an inverter 2A.
And 2B, the optimum combination between the inverters and the solar cells is specified so that both or either of the inverters can operate in the optimum high output state according to the sum of the output powers of both inverters. At the same time, the inverter 2A has a program for controlling the start / stop of both the inverters and the switching control of the electromagnetic switches 3A, 3B, 3C.
The signals S _F1 and S _F2 indicating the failure and stop states of each of the electromagnetic switches ₂ and 2B and the power comparison signal S _P are input to the electromagnetic switch 3
Switching control signals S _C1 and S for A, 3B and 3C respectively
_It outputs _C2 and S _C3 .

Next, FIG. 2 illustrates a circuit diagram of a processing unit of the program in the opening / closing control circuit 7. As shown in the drawing, the processing unit is OR, NOR, AND, INV or a time element not shown. Is a logic circuit made up of various elements such as H / L or 1 /
A binary logical value of 0 is processed. The signal processing contents in the circuit shown in FIG. 2 will be described below with reference to the flowcharts of the control programs shown in FIGS.

FIG. 3 is a flow chart showing the operation processing state of the grid interconnection inverter system corresponding to the sum of the output powers of both inverters 2A and 2B, showing the first and third embodiments of the invention. The process proceeds in the following order. The inverter 2A and the electromagnetic switch 3A, as well as 2B and 3B, simultaneously perform both start and close operations and stop and open operations.

1) Both the inverters are in a normal state (S _F1 ; 0, S _F2 ; 0), and the sum of the output powers of both (hereinafter, the detected value is referred to as P _T ) is the set value (hereinafter referred to as P _T ). _S )) (P _S > P _T , S _P ; 0); Inverter 2A: Start [Electromagnetic switch 3A closed (S _C1 ;
1)] Electromagnetic switch 3C: closed circuit (S _C3 ; 1) Inverter 2B: stop [electromagnetic switch 3B open circuit (S _C2 ;
0)] and both of the power generated by the solar cells 1A and 1B are supplied to the inverter 2A.

2) After that, if the above power relation is reversed as P _S <P _T ; electromagnetic switch 3C: open circuit (S _C3 ; 0), but S _C3 ; 1 after a lapse of time ΔT after establishment of P _S <P _T → 0 Inverter 2B: Start-up However, it is started after a time ΔT has elapsed since P _S <P _{T is} established, and power generated by the solar cells 1A and 1B is supplied to the inverters 2A and 2B, respectively. Note that ΔT is a set time for confirming the state variation of the power P _T , and is programmed by setting and resetting the timer circuit.

3) After that, if the above-mentioned power relation is reversed again as P _S > P _T ; electromagnetic switch 3C: closed circuit (S _C3 ; 1) However, after the time ΔT has elapsed since P _S > P _T , S _C3 ; 0 → 1 Inverter 2B: Stop However, it will be stopped after the time ΔT has elapsed since P _S > P _{T is} established, and the solar cell 1 will be connected to the inverter 2A that continues its operation.
Power generated by both A and 1B is supplied again.

Further, FIG. 4 shows an inverter 2A operating simultaneously.
2B is a flowchart showing an operation processing state of the inverter system in the case where a failure occurs in any one of 1 and 2B, showing an embodiment of the second invention, and the processing proceeds in the following order. 1) Inverters 2A and 2B with the electromagnetic switch 3C open.
If a failure occurs in the inverter 2B while both are in operation; electromagnetic switch 3C: closed circuit (S _C3 ; 1) inverter 2B: stop and the inverter 2A that continues its operation has the solar cell 1
Power generated by both A and 1B is supplied.

2) Subsequently, if the failure of the inverter 2B is recovered and the failure closed state is reset (RESET) successfully, the electromagnetic switch 3C: open circuit (S _C3 ; 0) the inverter 2B: start, and the solar cells 1A and 1B. The operation of supplying the generated electric power to the inverters 2A and 2B is restarted.

3) Further, if the failure of the inverter 2B is not recovered and further failure occurs in the inverter 2A; inverter 2A: stop, and operation of both inverters 2A and 2B is stopped. 4) Also, if the failure of the inverter 2A in the previous section 3) is recovered and reset (RESET) of the failure closed state is successful; .

Each of the control states described in 1) to 4) above is a case where the inverter failure occurs prior to 2B. However, by replacing the inverters 2A and 2B in each of the above items, the inverter failure is detected. The same can be said for the case where the occurrence occurs prior to 2A. Further, at the time of starting / stopping each inverter or controlling the opening / closing of each electromagnetic switch according to the above 1) to 4), the confirmation of the failure state by a set time not shown is performed in the same manner as in FIG. And

FIG. 5 is a flow chart showing the operation processing state of the inverter system in the case where a failure occurs in either one of the inverters 2A or 2B during the independent operation. The present invention shows an example of the above, and the processing proceeds in the following order. 1) If a failure occurs in the inverter 2A that is operating independently with the electromagnetic switch 3C closed, stop it and check the failure status of the inverter 2B; if the inverter 2B is normal; inverter 2B: start inverter If 2B is in a failure state, at the stage where the failure is recovered and reset (RESET) of the failure closed state is successful; Inverter 2B: Start, and the inverter 2B is operated independently instead of the original inverter 2A.

2) If the failure of the inverter 2A recovers and the resetting of the failure closed state succeeds (RESET) during the independent operation of the inverter 2B instead of the failed inverter 2A; inverter 2A: start inverter 2B: stop , The original operation of the inverter 2A is restored.

Even during the independent operation of the inverter 2A in the closed state of the electromagnetic switch 3C, the confirmation of the failure state of the inverter 2B and the reset operation of the failure closed state when the failure occurs are always performed. In addition, at the time of starting / stopping each inverter described in 1) and 2) above, it is possible to confirm the failure state by the set time shown in FIG.
The same shall apply as in the case of.

[0028]

According to the present invention, DC power from a plurality of DC power supplies whose outputs fluctuate is converted into a predetermined AC power, and the AC power supply is connected to the AC power supply via the opening / closing means installed on the output side. In a parallel operation control method of a plurality of inverters that perform parallel operation and constitute an inverter system for system interconnection, a connection switching means for performing an arbitrary combination connection between each inverter and each DC power source, and the AC system power source And an opening / closing control means for driving and controlling each of the inverters and the connection switching means according to a predetermined program, and a power detection means for detecting the total output power of the inverters in parallel operation. The combination of each operation inverter and each DC power source, which is configured such that each operation inverter can share the optimum conversion efficiency, As well as selected according to the program,
Start-up of each inverter specified according to the selection result
By performing the stop and the opening / closing control of the connection switching means, even in the low output state of each DC power source such as a solar cell whose output fluctuates, it is possible to properly integrate the DC power source into the operation inverter with the number limited. This makes it possible to maintain an appropriate value of the power conversion efficiency in the operating inverter, and hence the power conversion efficiency of the entire inverter system, as the load factor increases.

Further, the predetermined program is automatically corrected with respect to the number of operable inverters corresponding to the failure stop state of each inverter and the operable state after the restoration, thereby stopping the failure of any inverter. Also in this case, it is possible to disconnect the faulty inverter from the inverter system and transfer the generated power of the DC power supply to another normal inverter, so that it is possible to effectively use all the generated power of each DC power supply.

Furthermore, during the start / stop control of each inverter and the open / close control of the connection switching means, which are performed according to the predetermined program, a constant state confirmation time is set by the time-limiting element before the transition to the next stage operation. By doing so, it is possible to prevent chattering when the operating state is changed due to a sudden change in the output of each DC power source such as a solar cell, and to perform stable operation of the inverter system.

That is, the above-mentioned various measures can make the inverter system as a whole highly efficient and highly reliable.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a grid interconnection solar power generation system showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of an opening / closing control circuit in FIG.

FIG. 3 is a flowchart showing an embodiment of the first and third inventions.

FIG. 4 is a flowchart (2) showing an embodiment of the second invention.
(When operating simultaneously)

FIG. 5 is a flowchart showing an embodiment of the second invention (during single operation).

FIG. 6 is a configuration diagram of a grid interconnection inverter system showing an example of a conventional technique.

[Explanation of symbols]

1 Solar cell (1A, 1B, ..., 1N) 2 Inverter (2A, 2B, ..., 2N) 3 Electromagnetic switch (3A, 3B) 4 System power supply (AC) 5 Current transformer 6 Output power detector 7 Switching control circuit 31 Contact points of electromagnetic switch 3 (31A, 31B, ...,
31N) CP comparator

Claims (3)

[Claims] 1. A DC power supplied from a plurality of DC power supplies whose outputs fluctuate is converted into a predetermined AC power and is operated in parallel with an AC power supply through an opening / closing means installed on the output side. A parallel operation control method for a plurality of inverters that form an inverter system for grid interconnection,
Connection switching means for performing an arbitrary combination connection between each inverter and each DC power supply, power detection means for detecting the total output power of each inverter operating in parallel with the AC power supply, and according to a predetermined program, And a switching control means for driving and controlling the respective inverters and connection switching means, so that the respective operating inverters can share the total sum of the inverter output power with the optimum conversion efficiency and the respective operating inverters. In addition to selecting a combination with a DC power supply according to the predetermined program, starting / stopping each inverter specified according to the selection result and controlling the opening / closing of the connection switching means are performed. Parallel operation control method. 2. The parallel operation control method for a grid interconnection inverter according to claim 1, wherein the selection program corresponds to a failure stop state of each of the inverters and an operable state after the restoration, and the operation is possible. Parallel operation control method of inverters for grid interconnection, characterized in that the number of inverters is automatically corrected. 3. A parallel operation control method for a grid interconnection inverter according to claim 1, wherein at the time of starting / stopping control of each inverter according to the selection program, a constant state is established by a timed element before shifting to the next stage operation. A parallel operation control method of a grid interconnection inverter characterized by setting a confirmation time.