JPS5935534A - Power converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] The present invention relates to a power conversion device that converts DC power to AC power, and in particular converts the output power of a DC power source such as a fuel cell or a secondary battery to AC power. The present invention relates to a power conversion device having a function of performing parallel operation with a power grid.

In a power supply system that supplies a predetermined amount of power to a load by reversing a power converter in parallel with the power grid, the power converter generally outputs a set fixed amount of power, and any shortfall in the output power of the power converter is output 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 first current power into alternating current power and operating in parallel with a power system and a power system may be a device configured as shown in FIG. 1 using a self-commutated inverter.

In Figure 1, 1.1 is a DC power source such as a fuel cell or secondary battery, 2 is a capacitor that processes the reactive power of the inverter 3, 4 is the thread KOi11 effective power and grid-side reactive power detector, and 5 is the inverter output. A ringing power and inverter output reactive power detector, 6 a control device for stably operating the inverter 3 in parallel with the grid, 7 a grid side switch,
8 is an inverter side switch, and 9 is a load. In such a power conversion device, the power system AC is always operated in parallel, and a predetermined constant power is supplied to the load from the DC power source. but,
The load power consumption changes from moment to moment, 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 backward 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 power source into AC power, performs stable parallel operation with the power grid at all times, and supplies stable AC power to a load. It is in.

The present invention includes a detector for measuring effective power on the grid side,
When the power of the DC power supply exceeds the load power consumption and the excess power flows back to the grid, the active power detector on the grid side detects the backflow of power and controls the inverter. By reducing the inverter output, power is prevented from flowing back to the grid. In addition, the reactive power component of the inverter output is normally controlled to have a constant inverter output power factor, and is proportional to the active component of the inverter output power.
control to m. However, when the load power consumption is approximately equal to the active power of the inverter output, the power factor on the grid side deteriorates significantly, so the present invention further includes a detector for detecting the reactive power on the grid side, By determining the range for one grid side reactive power from the range of one grid side reactive power and the preset grid side power factor, the value of grid side reactive power detected by the detector can be adjusted to include only a portion of the grid side reactive power. If it is within the E1λ range, the above-mentioned inverter output constant rate control is performed, and if it is outside the range, control is performed to compensate for the shortage of grid-side reactive power from the inverter so that it becomes a grid-side reactive power detector. Do it like this.

FIG. 2 shows an embodiment of the present invention. In Figure 2, 1
0 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 the switches 7 and 8; and 12 is the main part of the present invention. An inverter output power controller.

13 is the inverter output power factor cosψX set in advance from the command value Pt other than the active power of the inverter output.
It is a coefficient multiplier for giving a command value for the inverter output invalid portion according to P! The command value is multiplied by tanψI to obtain a command value Q■ corresponding to the reactive power of the inverter output. The device 6 is a coefficient multiplier with a dead band, and operates only when the grid side active power PcO value becomes negative, that is, when power flows backward. 15 is a coefficient multiplier with a dead band, and the upper limit Qcゎ,
Cmmx and cosψcmin, Pc as tanψ□
The value multiplied by 8 is set as Qcm8, and the value obtained by multiplying PC by janψ is set as Qcm=. 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.

(2) in the same figure is the effective power, -[F]) is the reactive power, (0 is the power factor diagram, a is the load consumption, b is the power system reading, and C is the inverter output). In Fig. 3, the region T1 is the region of normal operating state, and the output power of the power converter, that is, the active current portion of the inverter output, is small compared to the load power consumption, and the shortfall is In addition, the reactive power of the load is in a smaller range than the reactive power supplied from the power conversion device, and the operating condition is that the system power factor is within the permissible range of the system power factor.

Under these operating conditions, the symbol 14.15 in Figure 2 is operating in the dead zone, so the output of 14.15 is ΔP.
c and ΔQc become 0. Therefore, the inverter
Output power P detected with command value and 5! ΔPr', which is the difference between
And P! Q proportional to the command value.

Reactive power Q detected with command value and 5! ΔQl', which is the difference between
The output voltage e! The phase and magnitude of the voltage are controlled, and the power converter is operated to output the set power at the set power factor.

Region T2 in FIG. 3 is a region in which inverter output power is controlled to be constant. 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. When the system power factor falls outside a preset tolerance range, 15 in FIG. 2 operates. P detected in 4
c.

Qc and ΔQc determined by the allowable range of system power factor are 15
It will be outputted. Therefore, Q! is proportional to the Pl command value!
ΔQI' required by the difference between the command value and the reactive power Q10 detected in 5
The reactive power portion of the inverter output is controlled by ΔQt, which is the sum of

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 way as in regions Tl 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 Pc on the grid side detected in 5 becomes negative, and 14
operates and outputs ΔPc". Therefore, the active power of the inverter output power is controlled by ΔPx, which is the sum of ΔPr', which is the difference between the PI command value and the effective portion P! of the inverter output power detected in step 5, 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 Q c ya□ and Q Cmin of the reactive power setting range on the grid side are almost equal. 1
The dead zone of 5 will disappear. 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 grid side, respectively, but as shown in Fig. 4,
Similar control can be achieved even when installed on the inverter side and load side. If the control device 12 shown in FIG. 2 is used, it is better to create a suitable value for PceQc as shown in FIG. 4.

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 current source,
It is possible to stably perform parallel operation by preventing power from flowing backward to other AC power sources and from deteriorating the power factor on the side of other AC power sources.

[Brief explanation of drawings]

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.

Claims (1)

[Claims] 1. In a power conversion device having a function of converting DC power of a DC power source into AC power and operating in parallel with another AC power source, detecting the output power of the power conversion device. 1st
A second output power detector that detects the output power of another AC power supply that operates in parallel with the output power detector of the power converter, or a first output power detector that detects the output power of the power converter and the power converter of the load. A third output power detector detects the difference between the output power of the power converter and the device output, and an output power controller that controls the output power by changing the magnitude and phase of the output voltage of the power conversion device. A power conversion device characterized in that an effective portion and a reactive portion of output power are controlled according to a detection signal. 2. The second output power detector recited in claim 1 outputs zero output when the detected value of active power is positive, outputs detected ringing power when it is negative, and outputs reactive power. A power conversion device characterized in that when a detected value of reactive power is within a set range, the output is zero, and when it is outside the set range, a value proportional to the detected reactive power is output. 3. The output power controller according to claim 1 is configured to control the difference between the set output power of the power conversion device and the active power output of the first output power detector and the active power output of the second output power detector. The output power is controlled by the sum of the difference between the set reactive power of the power converter, the reactive power output of the first output power detector, and the reactive power output of the second output power detector. A power conversion device characterized in that the reactive component of the power converter is controlled. 4. The value of the set output power of the output power controller according to claim 1 is given from an external circuit, and the value of the set reactive power is determined from the set output power and the fCC power converter output rate, which is set in advance. Alternatively, the percentage value is defined by the value of the power converter output power detected by the first output power detector and a preset power converter output ratio. Power converter.