JPS6358026B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power conversion device that converts direct current power to alternating current power, and in particular converts the output power of a direct current power source such as a fuel cell or a secondary battery into alternating current power, and The present invention relates to a power conversion device having the function of performing operation.

In a power supply system that operates a power conversion device in parallel with the power grid to supply a predetermined amount of power to a load, the power conversion device generally outputs a set fixed amount of power, and the shortfall in the output power of the power conversion device is handled in parallel. The AC power supply is configured to be supplied from other AC power sources such as the connected power system.

A power conversion device having the function of converting DC power into AC power and operating in parallel with the power grid may be a device configured as shown in FIG. 1 using a self-commutated inverter. In Figure 1, 1 is a DC power source such as a fuel cell or secondary battery, and 2 is an inverter 3.
4 is a grid-side active power and grid-side reactive power detector; 5 is an inverter output active power and inverter output reactive power detector; 6 is a capacitor for stably operating the inverter 3 in parallel with the grid; 7 is a system side switch, 8 is an inverter side switch, and 9 is a load.
In such a power conversion device, parallel operation of the power system AC is always performed, and a predetermined constant power is supplied to the load from the DC power source. However, the load power consumption changes from time to time, and sometimes the output power of the power conversion device exceeds the load power consumption and becomes excessive. In such an operating state, the output power of the power conversion device flows back into the power grid, which causes a voltage increase on the power grid side, which has the disadvantage of reducing the stability of the power grid.

An object of the present invention is to provide a power conversion device that converts power obtained from a DC power source into AC power, performs stable parallel operation with the power grid, and supplies stable AC power to a load. .

The present invention is equipped with a detector that measures the active power on the grid side, and when the power of the DC power source exceeds the load power consumption and the excess power flows back to the grid side, the grid side active power detector is installed. By detecting that power is flowing backwards and controlling the inverter to reduce the inverter output, it is possible to prevent power from flowing backwards to the grid. Further, the reactive power component of the inverter output is normally controlled to a constant inverter output power factor, and is controlled to a value proportional to the active component of the inverter output power. However, when the active power component of the inverter output and the load power consumption are approximately equal, the power factor on the grid side deteriorates significantly, so the present invention further includes a detector for detecting the reactive power component on the grid side,
By determining the range of the grid side reactive power from the grid side active power and the grid side power factor range set in advance, the value of the grid side reactive power detected by the detector can be adjusted to the grid side reactive power component. If it is within the range, the above-mentioned inverter output constant rate control is performed, and if it is outside the range, the inverter compensates for the shortfall in grid side reactive power so that it is within the grid side reactive power range. Make it.

FIG. 2 shows an embodiment of the present invention. In FIG. 2, 10 is a waveform improvement filter that reduces harmonic components contained in the output of the inverter 3, 11 is a sequence control device that controls starting and stopping of the inverter and the operation of switches 7 and 8, and 12 is a main unit. This is an inverter output power controller which is the main part of the invention.
13 is the command value for the active power of the inverter output
This is a coefficient unit for giving a command value for the inverter output reactive component from P ₁ according to a preset inverter output power factor cos _1. Specifically, P ₁
The command value is multiplied by tan ₁ to obtain the command value Q ₁ for the reactive power of the inverter output. 15 is a coefficient multiplier with a dead band, and the grid side active power Pc
It operates only when the value of is negative, that is, when power flows backwards. 15 is a coefficient multiplier with a dead band, and the upper limit Q _Cnax and lower limit Q _C min of the dead band are the allowable range of the power grid side active power Pc and the grid power factor.
From cos _Cnax and cos _C min, the value obtained by multiplying Pc by tan _nax is Q _Cnax , and the value obtained by multiplying Pc by tanmin is Q _C min.
shall be. Note that the parts whose explanation is omitted are the same as those in FIG. 1.

Next, the operation shown in FIG. 2 will be explained with reference to FIG.
In the same figure, A shows active power, B shows reactive power, and C shows power factor, where a shows load consumption, b shows power system part,
c indicates the inverter output. In Fig. 3, the region T1 is the region in the normal operating state, and the output power of the power conversion device, that is, the active power portion of the inverter output, is smaller than the load power consumption, and the shortfall is supplied from the grid side. It is in a state of being. Further, the operating conditions are such that the reactive power of the load is smaller than the reactive power supplied from the power conversion device, and the system power factor is within the allowable range of the system power factor. Under these operating conditions, the numbers 14 and 15 in FIG. 2 are operating in the dead zone, so the outputs ΔPc and ΔQc of the parts 14 and 15 are zero. Therefore, the inverter uses ΔP ₁ , which is the difference between the P ₁ command value and the output power P ₁ detected in step 5, and the difference between the Q ₁ command value, which is proportional to the P ₁ command value, and the reactive power Q ₁ , detected in step 5. The phase and voltage magnitude of the output voltage e ₁ are controlled by a certain ΔQ ₁ ', and the power converter is operated to output the set power at the set power factor.

Region T2 in FIG. 3 is a region for constant control of inverter output power. In this region, as in region 1, if the inverter output ratio is controlled to be constant, the ratio of the reactive component to the active power supplied from the grid increases, and the power factor of the grid deteriorates. If the system power factor falls outside the preset tolerance range,
15 in FIG. 2 operates. Pc, Qc detected in 4
and ΔQc determined by the allowable range of system power factor is 1.
Output from 5. Therefore, the reactive power component of the inverter output is controlled by ΔQ 1, which is the sum of the Q ₁ command value, which is proportional to the P ₁ command value, and ΔQ _{1 '} , which is the difference between the reactive power Q ₁ detected in step 5, and the reactive power component of the inverter output is controlled. The power factor is suppressed within the set range.

Region T3 in FIG. 3 is a region in which power grid power backflow prevention control is performed. In this region, the output of the power converter exceeds the load power consumption, so
If the inverter is controlled in the same manner as in regions T1 and T2, excess power will flow back to the grid. When a part of the active power of the inverter output flows back to the grid side, the active power on the grid side detected in step 5
Pc becomes negative, and 14 operates to output ΔPc.
Therefore, it is the difference between the P ₁ command value and the effective portion P ₁ of the inverter output power detected in step 5. The active power of the inverter output power is controlled by ΔP ₁ which is the sum of ΔP ₁ ' and ΔPc, and is reduced to a value determined by the power consumption of the load. At this time, the active power Pc on the grid side becomes almost 0, so the reactive power setting range on the grid side
Q _Cnax and Q _C min become almost equal, and the dead zone of 15 disappears. Therefore, the reactive power output from the inverter is controlled to be equal to the reactive power of the load, and no reactive power is exchanged with the grid.

Note that the output power detectors used in the present invention were installed on the inverter side and the system side, respectively, but as shown in FIG. 4, similar control can be performed by installing them on the inverter side and the load side. Figure 2 Control device 12
If we use Pc, as shown in Figure 4,
All you have to do is create a value that corresponds to Qc.

According to the present invention, in a power conversion device that converts power from a DC power source into AC power and operates in parallel with another AC power source, it is possible to prevent power from flowing backward to the other AC power source, and to It is possible to prevent the power factor from deteriorating and perform stable parallel operation.

[Brief explanation of the drawing]

FIG. 1 is a general circuit configuration diagram for explaining the control method of the present invention, FIG. 2 is a configuration diagram of an embodiment of the present invention, and FIG. 3 is a diagram for explaining the operation of FIG. 2. FIG. 4 shows another embodiment of the invention. 1...DC power supply, 2...Inverter reactive power processing capacitor, 3...Self-excited inverter, 4,
5, 20... Output power detector, 6... Control device,
7, 8... Switch, 9... Load, 10... Waveform improvement filter, 11... Sequence control device, 12
...Inverter output power controller, 13... Coefficient unit, 14, 15... Coefficient unit with dead zone.

Claims (1)

[Claims] 1. In a power conversion device that uses an inverter that has the function of converting the DC power of a DC power source into AC power and running it in parallel with another AC power source, the output active power and output reactive power of the inverter are A first output power detector detects output active power and an output reactive power of another AC power source operated in parallel; It is equipped with an output power controller that controls the output power, and when the power of the DC power supply exceeds the load power consumption and the excess power flows back to other AC power supplies, a second output power detector is provided. By detecting the output active power of other AC power sources, it is detected that the power is flowing backwards, and the inverter is controlled to reduce the inverter output, thereby causing the power to flow backwards to the other AC power sources. and if the value of the output reactive power of the other AC power supply detected by the second output power detector is within the preset reactive power range, the reactive power of the inverter output is is controlled by inverter output power factor constant control to a value proportional to the active part of the inverter output, and if it is outside the range, the shortfall of the output reactive power of other AC power supplies is adjusted so that it is within the range of the reactive power. A power conversion device characterized in that it performs control that is supplemented by an inverter.