JPH0640707B2 - Supply current command value calculation circuit - Google Patents

Description

The present invention relates to a plurality of power converters (for example, inverters) having different rated capacities (also simply referred to as capacities) connected in parallel to each other to supply electric power to a load. The present invention relates to a calculation circuit for calculating a current command value from the full load current according to the rated capacity ratio of each unit.

[Conventional technology]

Conventionally, most systems that connect a plurality of power converters (eg, inverters) in parallel to supply power to a load operate power converters of the same rated capacity in parallel, and therefore, power supply for each unit. The current command value can be easily obtained by simply making 1 / n the full load current.

[Problems to be Solved by the Invention]

However, in a system in which two or more machines with different rated capacities are operated in parallel, if the total load current is simply 1 / n and given as the power supply current command value, the percentage of the current flowing by each unit with respect to the rated current will differ. become. For this reason,
Depending on the full load current, some machines may exceed the rated current and some may not, or if you try to keep each machine within its rated current, the capacity of the parallel operation system will be limited by the smallest capacity machine. Problems such as being done occur.

Therefore, even when the power converters having different rated capacities are operated in parallel, the present invention distributes the full load current in accordance with the rated capacities of the respective units to easily calculate the current command value of each unit. The purpose is to provide a circuit.

[Means for Solving the Problems]

Select the resistance value so that the output of the current transformer that detects the full load current is the same as the current detection amount output by the current detector equipped in the power converter when the load is powered only by its own machine. A series circuit of a resistor that has been selected and a resistance value selected by multiplying the resistance value by the ratio of the capacity of the other machine to the capacity of the other machine, and a contact that is closed when the power supply to the other machine is started. And are connected in parallel to the current transformer that detects the full load current.

[Action]

In order to calculate the power supply current command value according to the rated capacity ratio, it is sufficient to divide the capacity of the own machine by the total capacity of the operating machine, and therefore, to flow to each machine by doing the above. Make it easy to obtain the current value (current command value).

[Embodiment] FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a configuration diagram showing an entire system to which the present invention is applied.

In FIG. 2, 1 ₁ to 1 _n are inverters, 2 ₁ to 2 _n are difference current detectors, 3 _{1 to} 3 _n are feed current command value calculators, 41 to ₁
4 _n is a current detector and 5 is a load. Differential current detector 2 ₁ -
2 _n detects the difference current between the current command value from the feeding current command value calculator 3 _{1 to} 3 _n and the current detection value from each inverter 1 ₁ to 1 _n , and the inverters 1 ₁ to 1 _n detect this difference current. Is controlled to be zero.

As shown in FIG. _{1, the} power supply current command value computing units 3 _{1 to} 3 _n have a resistor Ri connected in parallel to the current transformer CT, and contacts A _{1 to} A _n selectively connected to this resistor. This contact A ₁
~ A _n are automatically closed when the inverters 1 ₁ to 1 _n start feeding. R ₁ is a resistor with own machine current detection amount and the resistance value determined as the same detection amount when only the inverter 1 ₁ is powering the load 5, Ri is the only inverter 1 _i the load 5 It is a resistor that has a resistance value that is determined so that the amount of current detection is the same as the amount of current detection of its own device when power is supplied. Therefore, each CT of the operator 3 _i and the detector 4 _i
When the current transformation ratio is the same, the resistance Ri is equal to the resistance of the current detector 4 _i , and when the current transformation ratio is different, the resistance value is determined accordingly. Further, the resistance that is inserted in series with the contacts A ₁ and A _n is a resistance value of a ratio obtained by dividing the capacity of the own machine by the capacity of another machine.

By doing so, _{assuming that} all the contacts A _{1 to} A _n of the equivalent resistance R _ei of the feeding current command value calculation circuit 3 _i are closed, Therefore, it is possible to calculate the power supply current command value that proportionally distributes the full load current to the rated capacity ratio of each unit. Although the case where AC power is supplied to the load using the inverter has been described above, the present invention can also be applied to the case where DC power is supplied to the load using the converter.

〔The invention's effect〕

According to this invention, since the power supply current command value that is proportionally distributed according to the rated capacity ratio of each unit can be calculated, it is possible to flow up to the rated current for each unit, and the capacity of the parallel operation system can be adjusted by the minimum capacity unit. Is not limited, and the rated capacity of each unit can be effectively used. In addition, since the total load current flowing is detected and proportionally distributed, the current shared by each unit within the range (0% to 100%) of all load factors regardless of the load factor of the parallel operation system. The effect is that the percentage (percentage of the rated current of each unit) can be made the same for all units. Furthermore, if this concept is applied, it is possible to distribute at an arbitrary ratio instead of the rated capacity ratio.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a configuration diagram showing an entire system to which the present invention is applied. Code Description ₁ 1 ~1 _n ...... inverter, 2 ₁ ~2 _n ...... difference current detector,
3 ₁ to 3 _n ...... feed current command value calculator, 4 ₁ to 4 _n ...... current detector, 5 ...... load, CT ...... current transformer, A ₁ to A _n ...... contacts, R ₁ to R _i ... resistor.

Claims (1)

[Claims] 1. When a plurality of power converters having different rated capacities are connected in parallel to supply power to a load, a current command value corresponding to the rated capacity ratio of each unit is calculated from the total load current. In the arithmetic circuit, the output of the current transformer that detects the full load current is the same as the current detection amount that is output by the current detector provided in the power converter when the load is powered only by its own device. The resistor whose resistance value is selected as the value, and the other resistor whose resistance value is selected as a value obtained by multiplying the resistance value by the ratio of the capacity of the other machine divided by the capacity of the other machine and the power supply of the other machine are closed. And a series circuit with a contact that is connected to the current transformer that detects the full load current in parallel.