JP3824445B2 - Inverter control method and apparatus for parallel operation with generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control method and apparatus for an inverter that performs parallel operation with a generator that supplies power from a commercial system together with output power from a generator to a load via an inverter in a private power generation facility or the like.
[0002]
[Prior art]
Conventionally, in a private power generation facility including a cogeneration system, power supply from a commercial system has also been used in order to ensure electric power when a generator fails and to operate the generator in an efficient state. In order to perform power supply from the commercial system and power supply from the generator in parallel operation, the power generation output of the generator is linked to the AC power supplied from the commercial system, and the system linkage matches the amplitude, frequency, phase, etc. It is necessary to drive.
[0003]
FIG. 6 shows an outline of a system in which power is supplied from a commercial system via an inverter and a generator and an inverter are operated in parallel. Such a system is provided in, for example, one factory or building, and loads 1 and 2 such as various facilities are used as a parallel operation system 3 through an output power from a generator 4 for private power generation and an inverter 5. And the electric power from the commercial electric power system 6 given. The generator 4 is desirably operated as efficiently as possible, and for that purpose, it is desirable to supply output to a load corresponding to the rated capacity. For this reason, among the plurality of loads 1 and 2, a load 1 to be supplied with power from the generator 4 and a load 2 to be supplied with power only from the commercial power system 6 are separated. Electric power is directly supplied to the load 2 from the commercial power system 6 only through the circuit breaker 7. Examples of such a load 2 include those having a high repetition frequency of turning on and off, and those that are rarely used.
[0004]
The inverter 5 is operated in synchronism with the power generation voltage and frequency of the generator 4 installed as part of the cogeneration system and outputs a differential power between the load capacity and the generator rated capacity. 8 is controlled.
[0005]
An output from the generator 4 is supplied to the load 1 within a range within the rated capacity of the generator 4. When the capacity of the load 1 exceeds the rated capacity of the generator 4, power from the power system 6 is supplied via the inverter 5. The control device 8 controls the power sharing between the power supply from the generator 4 and the power supply via the inverter 5 with respect to the load 1. When the control device 8 performs control so that the amount of power supplied to the load 1 through the inverter 5 is increased, the power supplied from the generator 4 to the load 1 is relatively decreased. Conversely, when the control device 8 controls the power supplied from the inverter 5 to the load 1 to decrease, the power supplied from the generator 4 to the load 1 relatively increases. In the parallel operation system 3 using such an inverter 5, the generator 4 continues to operate near a highly efficient rated capacity, and the amount of power supplied from the power system 6 to the load 1 is changed by changing the fluctuation of the load 1. It can be absorbed and the generator 4 can be operated at a high load. Moreover, even if the output of the generator 4 exceeds the capacity of the load 1, it is possible to prevent a reverse power flow in which surplus power flows into the power system 6.
[0006]
That is, when power is supplied from the generator 4 to the load 1 in the vicinity of the rated capacity, when the start input switch 9 is newly added and the load 1 is added, the amount of power that exceeds the rated capacity of the generator 4 Can be supplied from the power system 6 via the inverter 5. When a part of the operating load 1 is stopped, the decrease in the load capacity is adjusted as a decrease in the amount of power supplied from the inverter 5. Further, when the decrease in the capacity of the load 1 becomes larger than the amount of power supplied from the inverter 5, the output of the generator 4 decreases. Since the inverter 5 is provided between the power system 6 and the inverter 5, there is no reverse power flow in which the excess output of the generator 4 flows into the power system 6.
[0007]
[Problems to be solved by the invention]
Loads 1 and 2 used in buildings and factories include resistive loads that consume almost constant power from the start-up, such as incandescent lamps and electric furnace heaters, and reactive loads such as motors. . With a reactive load such as a motor, a large amount of power is required at the time of start-up, and during a rated operation after the start-up is completed, the operation can generally be continued with lower power consumption than at the time of start-up.
[0008]
FIG. 7 shows the load current when the starter input switch 9 is operated to start a new load by operating the generator 4 and the inverter 5 in parallel to supply power to the load 1. Changes in the instantaneous value, the inverter output instantaneous value, and the generator output current instantaneous value are indicated by (a), (b), and (c), respectively. When the additional load is activated, the load current value immediately increases, but the output current value of the inverter 5 gradually increases. Therefore, when the additional load is activated, current to the additional load is supplied from the generator 4.
[0009]
The change in the output of the inverter 5 cannot be made sufficiently early due to a delay in the control time, and a problem occurs when instantaneous power sharing is performed at the time of starting the motor. That is, when power is supplied to the load 1 in the vicinity of the rated capacity of the generator 4, if the additional load 1 is turned on, power is supplied to the load 1 that is instantaneously higher than the rated capacity of the generator 4. And the generator 4 may be stopped in some cases.
[0010]
FIG. 7 shows the experimental results under the conditions of a generator rated capacity of 60 kW, an initial load capacity of 49 kW, and an additional load capacity of 30 kW. Since the load is a heater, it is resistive, and there is almost no instantaneous load increase at startup. Nevertheless, until the output of the inverter 5 increases, the output of the generator 4 exceeds the rated capacity.
[0011]
In order to avoid the stop of the generator 4, the set value of the rated capacity of the generator 4 is set small in the inverter 5 with respect to the amount of power required by the load 1, and there is a margin with respect to the rated capacity. It is necessary to adjust the power sharing so that the generator 4 is operated and the insufficient power is supplied via the inverter 5. If the generator 4 is always operated with a margin compared to the rated capacity, the efficiency as the generator 4 is reduced, and the ratio of the amount of power supplied from the power system 6 to the load 1 via the inverter 5 is reduced. Make it bigger. The inverter 5 temporarily converts the power supplied from the power system 6 into direct current, and further converts it into alternating current by the operation of the semiconductor circuit. Therefore, the power supplied from the power system 6 and the power output as the inverter 5 In the meantime, conversion loss occurs. For this reason, giving a large margin to the output of the generator 4 causes a decrease in efficiency as the generator 4 and an increase in loss as the inverter 5.
[0012]
An object of the present invention is to provide a control method and apparatus for an inverter that performs parallel operation with a generator that can be controlled so that the generator does not enter an overload state even when the load is added and started. Is to provide.
[0013]
[Means for Solving the Problems]
The present invention provides a method for controlling an inverter that performs parallel operation with a generator so that an amount of power exceeding the rated capacity of the generator is supplied from a commercial power source via the inverter.
For the load to be supplied with power, obtain the instantaneous load capacity required at startup in advance,
Before starting by adding a load, the load is transferred from the generator to the inverter so that the power for the load capacity required for the load required for the load can be output from the generator. It is the control method of the inverter which performs parallel operation with the generator to perform.
[0014]
According to the present invention, the instantaneous load capacity required at the start-up is determined in advance for the load to be supplied with power. Before starting with the addition of a load, the load is transferred from the generator to the inverter so that the power for the load capacity required at the time of start-up can be output from the generator. When starting a load, the generator output capacity has a margin for the load capacity required when starting the load, so the instantaneous power required at startup can be generated without overloading the generator. Can be supplied from the machine.
[0015]
In addition, the present invention is characterized in that after the load shift from the generator to the inverter, after the start of the load is completed, the generator rated capacity margin of the inverter output is transferred to the generator.
[0016]
According to the present invention, at the time of additional start-up of the load, after the load shift is performed so that instantaneous power necessary for start-up can be supplied and the output of the inverter is increased, Since the generator rated capacity margin is transferred to the generator, the generator can be operated at the rated capacity after the start of the load is completed. Since the generator is operated at the rated capacity, the power generation efficiency is improved, and a decrease in power conversion efficiency in the inverter can be minimized.
[0017]
Furthermore, the present invention provides a control device for an inverter that performs parallel operation with a generator so that an amount of power exceeding the rated capacity of the generator is supplied from a commercial power source via the inverter.
For a load to be supplied with power, an activation signal input unit for inputting an activation command,
The load that is set for the load for which the start command is input to the start signal input unit, and the recognized load capacity is derived, with the instantaneous load capacity required at the start being set in advance for the load A capacity recognition unit;
A load capacity calculation unit for detecting and calculating a load capacity during power supply and deriving a calculation result;
Based on the load capacity derived from the load capacity recognition unit and the load capacity calculation unit, a transfer capacity calculation unit that calculates and derives a transfer capacity as a load to be transferred from the generator to the inverter before starting the load, and
The inverter is controlled so that the output is increased by the transfer capacity derived from the transfer capacity calculation unit, the load is transferred, and after the load is transferred, the load to which the start command is input is controlled to start. An inverter that performs parallel operation with a generator, comprising: a load transition control unit that controls the inverter output so that an inverter output is reduced by a load transition of the generator rated capacity of the inverter output to the generator after completion. It is a control device.
[0018]
According to the present invention, an activation command is input to the activation signal input unit for a load to be supplied with power. The load capacity recognizing unit recognizes the load capacity that is set for the load for which the start command is input to the start signal input unit, and the recognized load capacity is determined. To derive. The load capacity calculation unit detects and calculates a load capacity during power supply, and derives a calculation result. Based on the load capacity derived from the load capacity recognition unit and the load capacity calculation unit, the transfer capacity calculation unit calculates and derives the transfer capacity to be transferred from the generator to the inverter before starting the load. The load transition control unit controls the inverter to perform load transition so that the output increases by the transition capacity derived from the transition capacity calculation unit, and after the load transition, the load to which the start command is input starts. After the start of the load is completed, control is performed so that the generator rated capacity margin of the inverter output is transferred to the generator and the inverter output decreases. Since the inverter is shifted and increased in advance only at the time of starting the load, the instantaneous power required at the time of starting the load can be supplied from the generator. Since the generator can be operated at the rated capacity after the start of the load is completed, the generator can be operated efficiently and the loss associated with power conversion by the inverter can be minimized.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic configuration of an inverter control apparatus according to an embodiment of the present invention. In the present embodiment, for example, among the various loads 11 and 12 provided in a factory, a building, or an area, the generator 14 and the inverter 15 that constitute the parallel operation system 13 with respect to the load 11 in a certain range. Supply power. The inverter 15 rectifies the power supplied from the power system 16 which is a commercial AC power supply via the circuit breaker 17 and converts it into DC once, and synchronizes with the generated voltage and frequency of the generator 14 by a semiconductor oscillation circuit. Convert to AC power. Some of the loads 12 connected to the parallel operation system 13 are connected so as to directly supply power from the power system 16 without going through the inverter 15. Such a load 12 is not a control target of the inverter 15 that performs parallel operation with the generator 14.
[0020]
The power supply to the load 11 is controlled by the control device 18. The control device 18 controls the inverter 15 so that the power generated with the rated capacity of the generator 14 is supplied to the load 11 and the amount of power exceeding the rated capacity of the generator 14 is supplied via the inverter 15. . In the control device 18 of the present embodiment, before and after actually starting the load 11 based on an input to the start input switch 19 which is a start signal input unit operated when the load 11 is added and started. In addition, control for increasing or decreasing the output of the inverter 15 is also performed.
[0021]
FIG. 2 shows a configuration of the control device 18 of FIG. The power supplied to the load 11 shown in FIG. 1 is detected by an AC voltage transformer 20 and an AC current transformer 21. This electric power is supplied based on the parallel operation of the generator 14 and the inverter 15 of FIG. The output of the inverter 15 is controlled according to the output signal derived from the inverter output calculation unit 22. The inverter output calculation unit 22 receives a generator rated capacity setting value that is manually set in the generator rated capacity setting unit 23. Based on the outputs of the AC voltage transformer 20 and the AC current transformer 21, the inverter output calculation unit 22 is also input with the load capacity as the power actually supplied to the load calculated by the load capacity calculation unit 24. In the inverter output calculation unit 22, control is performed so as to supply the shortage of the generator rated capacity set value via the inverter 15 with respect to the actual load capacity.
[0022]
In the load transition control in the present embodiment, the load transition capacity calculation unit 25 is equivalent to the generator rated capacity setting unit 23 that the generator rated capacity is apparently reduced before the load 11 is activated. Is derived. The calculation in the load transfer capacity calculation unit 25 is calculated by comparing the current load capacity derived from the load capacity calculation unit 24 and the load capacity derived from the load capacity recognition unit 26. In the load capacity recognition unit 26, the load capacity at the time of activation is set for each load type for the load to be activated as the load 11 in FIG. When a load start command signal for starting one of the loads is input to the start signal input unit 27 as the start input switch 19, the load capacity recognition unit 26 identifies the load type to which the load start command signal is input. Based on the above, the set load capacity is recognized, and the recognized load capacity is given to the load transfer capacity calculation unit 25. When it is going to supply the load capacity at the time of starting required for the load to be started from the generator 14 to the load 11, the load transfer capacity calculating unit 25 uses the amount of power exceeding the rated capacity of the generator 14 as the load transfer capacity. The generator rated capacity setting value set in the generator rated capacity setting unit 23 is calculated and decreased.
[0023]
Since the inverter output calculation unit 22 controls the output of the inverter 15 so that the generator 14 is operated at the rated capacity setting value of the generator set in the generator rated capacity setting unit 23, the generator rated capacity setting is performed. When the value decreases, the output power of the inverter 15 is increased. When the power supplied from the inverter 15 to the load 11 increases, the load 11 becomes lighter for the generator 14 and the power supplied from the generator 14 to the load 11 decreases. The load 11 is actually activated in accordance with the load activation signal derived from the activation signal output unit 28 based on the load transfer completion recognition unit 29 by the load transfer completion recognition unit 29. The inverter output calculation unit 22, the generator rated capacity setting unit 23, the activation signal output unit 28, and the load transition completion recognition unit 29 constitute a load transition control unit 30, and the inverter 15 when the load 11 is added and started Control related to load transfer with the generator 14 is performed.
[0024]
FIG. 3 shows a basic logic determination procedure for performing load transfer in the control device of this embodiment. When the activation input switch 19 for activating the load is turned on in step a1, a load activation command signal is given to the activation signal input unit 27 in FIG. In step a2, the load capacity recognition unit 26 and the load transfer capacity calculation unit 25 determine whether or not load transfer is necessary. This determination is made according to the following equation 1.
(Generator rated capacity)-(Generator output) <K x (Additional load capacity) ... (1)
[0025]
In Equation 1, K is a coefficient that varies depending on the load type. The coefficient K represents a multiple of the power required at startup relative to the power required in the steady state. With a resistive load, K = 1 because no particularly large power is required even at startup. With a reactive load such as a motor, K can be about 3 to 4. The load capacity recognition unit 26 can set the load type and the rated capacity for each load that can be activated as the load 11. The “generator rated capacity” in Expression 1 is manually set in the generator rated capacity setting unit 23. The “generator output” can be calculated as a difference between the load capacity derived from the load capacity calculation unit 24 and the output from the inverter 15 being controlled by the inverter output calculation unit 22.
[0026]
When it is determined in Step a2 of FIG. 3 that the condition of Expression 1 is satisfied, the process proceeds to Step a3, and the load capacity necessary for newly starting the load 11 is transferred to the inverter 15. After the load transfer at step a3 is completed, or after it is determined at step a2 that load transfer is not necessary, the procedure is ended at step a4.
[0027]
FIG. 4 shows the logic of load transfer performed by controlling the inverter 15 by the control device 18 of the present embodiment. The operation is started from step b1, and one of the start input switches 19 is operated to be an ON state as a load start switch for the additional load in step b2. In step b3, as described in step a2 of FIG. 3, load transition as shown in step a3 of FIG. 3 is performed on the activated load based on the determination logic of the load transition capacity. In step b4, the load transfer operation for the inverter 15 is performed. Since the operation of the inverter 15 becomes unstable when the output is suddenly changed, the load is transferred over, for example, about 500 ms. When the confirmation of the completion of the transition is repeated a certain number of times, an error output is derived and the process proceeds to an error processing routine provided in the system. If load transfer is completed before it is determined in step b4 that an error has occurred, load activation is performed in step b5. The activation state of the load is confirmed in step b6. If the confirmation of the start completion in step b6 is repeated a certain number of times, an error output is made and processed as an error. When it is determined in step b6 that the start is completed without causing an error, load transfer from the inverter 15 to the generator 14 is performed in step b7. In step b8, it is confirmed that the migration is completed. If the confirmation of the completion of the migration is repeated a certain number of times, an error output is made and the process proceeds to error processing. After it is determined in step b8 that the migration is complete, the procedure is terminated in step b9.
[0028]
FIG. 5 shows an example of changes in the generator output and the inverter output when the load shift control is performed according to the procedure shown in FIG. When a load input command is issued by operating the start input switch 19 at time t0, the load transfer capacity is calculated according to the load transfer capacity determination logic in step b3 of FIG. 4 by time t1. This is performed by the calculation unit 25 and the generator rated capacity setting unit 23. The inverter output calculation unit 22 in FIG. 2 performs control to increase the output of the inverter 15 from 0 to P3 from time t1 to time t2. Since the power supplied from the inverter 15 to the load 11 increases, the generator output decreases from P1 to P2. That is, P1-P2 = P3. When the load transition to the inverter 15 is completed at time t2, and the completion is recognized by the load transition completion recognition unit 29 shown in FIG. 2, the activation signal output unit 28 activates the load from time t3. When the load is activated, a large amount of power is instantaneously supplied to the load 11, and this power is mainly supplied from the generator 14. Since the output of the generator 14 is lowered in advance before starting the load at the time t3, the generator 14 does not exceed the rated capacity P0 even if the power necessary for starting the load is supplied. be able to.
[0029]
After the load activation at time t3, the increase in load accompanying the load activation decreases at time t4, and it is determined that the load activation is completed. However, in practice, as indicated by the solid line, the output of the inverter 15 gradually increases from P3 so as to cancel the increase in the output of the generator 14, so that the output of the generator 14 correspondingly decreases. The determination of the start completion in step b6 in FIG. 4 can be made by detecting such a change in the decrease tendency of the generator output or by detecting an increase in the inverter output. After confirming the completion of load activation at time t4, load transition from the inverter to the generator shown in step b7 of FIG. 4 is started. In the load transition, the rated capacity margin as the load transition capacity is calculated so that the generator 14 operates at the rated capacity P0, and the output of the inverter 15 is reduced by the rated capacity margin at time t5. Start load transition to increase the output of When the output of the rated capacity is supplied from the generator 14 to the load 11 at time t6, the load transfer procedure is completed. Since a load is newly added, power is supplied from the inverter 15 at time t6, and the generator 14 and the inverter 15 are operated in parallel.
[0030]
As described above, in the present embodiment, power supply when starting the additional load 11 is performed from the generator 14. However, before the load 11 is started, the load is transferred so that the capacity of the generator 14 is substantially supplied from the inverter 15 by the amount corresponding to the start current of the load 11 such as a motor. After the load is added, the load is transferred to the generator 14 again, and the output from the generator 14 is increased to the rated capacity, so that a high operation rate can be obtained and power can be generated efficiently. From these things, it becomes possible to obtain the effect similar to system cooperation, without performing system cooperation.
[0031]
【The invention's effect】
As described above, according to the present invention, when a load is added, a load transition is performed in advance so that an instantaneous load capacity necessary for starting the load is supplied from the inverter, and the output of the generator is started. Since the load capacity that is sometimes required is provided, it is possible to supply the power necessary for starting the load from the generator without causing the generator to be overloaded. Even when starting a load that needs to supply a large amount of electric power instantaneously, the generator does not enter an overload state, so that it is possible to avoid a situation such as a generator operation stop.
[0032]
Further, according to the present invention, the load is transferred to the inverter side at the time of starting the load, the instantaneous electric power required at the time of starting is supplied from the generator, and after the start of the load is completed, from the inverter to the generator Since the rated capacity margin is transferred to the load, the generator is operated at the rated capacity, so that the efficiency can be improved and the loss in the inverter can be reduced.
[0033]
Further, according to the present invention, for the load to be activated by inputting the activation command at the activation signal input unit, the instantaneous load capacity required at the time of activation is set in advance and derived from the load capacity recognition unit. The load capacity currently being supplied is derived by detecting the voltage value and current value in the load capacity calculation unit, and the transition capacity calculation unit is based on the load capacity derived from the load capacity recognition unit and the load capacity calculation unit. The transfer capacity to be transferred from the generator to the inverter is calculated and derived, and the load transfer control unit controls so as to increase by the transfer capacity of the inverter. Since the load to which the load transition activation command is input is activated, the instantaneous electric power required when the load is activated can be supplied from the generator, and the generator is not overloaded. After starting the load, the generator rated capacity margin of the inverter output is controlled so that the load shifts to the generator and the inverter output decreases, so that the generator can be operated at the rated capacity. The time to increase the output of the inverter so that the output of the generator is reduced for power supply at the start of the load is a short time at the start of the load. It can be operated and power generation efficiency can be increased. Since only the minimum necessary power is supplied from the inverter, the loss associated with the conversion can be minimized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic concept of a parallel operation system of a generator and an inverter according to an embodiment of the present invention.
2 is a block diagram showing an electrical configuration of an inverter 15 and a control device 18 of FIG.
FIG. 3 is a flowchart showing basic load transfer capacity determination logic performed to add and start a load 11 in the embodiment of FIG. 1;
FIG. 4 is a flowchart showing a load transfer control operation performed in the embodiment of FIG. 1;
5 is a time chart showing changes in generator output and inverter output accompanying the control of FIG. 4; FIG.
FIG. 6 is a block diagram showing a schematic configuration of a conventional parallel operation system of a generator and an inverter.
7 is a time chart showing changes in instantaneous values of load current, inverter output current, and generator output current when the load 1 is added and started in the parallel operation system of FIG. 6;
[Explanation of symbols]
11, 12 Load 13 Parallel operation system 14 Generator 15 Inverter 16 Power system 18 Control device 19 Start input switch 20 AC voltage transformer 21 AC current transformer 22 Inverter output calculation unit 23 Generator rated capacity setting unit 24 Load capacity calculation unit 25 Load transfer capacity calculation unit 26 Load capacity recognition unit 27 Start signal input unit 28 Start signal output unit 29 Load transfer completion recognition unit 30 Load transfer control unit

Claims (3)

In the control method of the inverter that operates in parallel with the generator so that the amount of power exceeding the rated capacity of the generator is supplied from the commercial power source via the inverter,
For the load to be supplied with power, obtain the instantaneous load capacity required at startup in advance,
Before starting by adding a load, the load is transferred from the generator to the inverter so that the power for the load capacity required for the load required for the load can be output from the generator. Control method of the inverter that operates in parallel with the generator. 2. The generator according to claim 1, wherein after the load is transferred from the generator to the inverter, after the start of the load is completed, the generator rated capacity margin of the inverter output is transferred to the generator. Inverter control method for parallel operation. In the inverter control device that operates in parallel with the generator so that the amount of power exceeding the rated capacity of the generator is supplied from the commercial power supply via the inverter,
For a load to be supplied with power, an activation signal input unit for inputting an activation command,
The load that is set for the load for which the start command is input to the start signal input unit, and the recognized load capacity is derived, with the instantaneous load capacity required at the start being set in advance for the load A capacity recognition unit;
A load capacity calculation unit for detecting and calculating a load capacity during power supply and deriving a calculation result;
Based on the load capacity derived from the load capacity recognition unit and the load capacity calculation unit, a transfer capacity calculation unit that calculates and derives a transfer capacity as a load to be transferred from the generator to the inverter before starting the load, and
The inverter is controlled so that the output is increased by the transfer capacity derived from the transfer capacity calculation unit, the load is transferred, and after the load is transferred, the load to which the start command is input is controlled to start. An inverter that performs parallel operation with a generator, comprising: a load transition control unit that controls the inverter output so that an inverter output is reduced by a load transition of the generator rated capacity of the inverter output to the generator after completion. Control device.

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