JPH027872A - Method of controlling system tie inverter - Google Patents

Abstract

PURPOSE:To stably control a device by setting effective power subtracting a device loss from output effective power, when output wattless power is changed of an inverter tied to a power system. CONSTITUTION:In controlling a system tie inverter, a deviation between an effective power preset value P and an effective power actual value PAC is calculated and input to an effective power adjusting circuit 21. This adjusting circuit 21 outputs a control signal, zeroing the input deviation, to a pulse arithmetic generating circuit 23, and a deviation between a wattless power preset value Q and a wattless power actual value QAC is calculated and input to a wattless power adjusting circuit 22. This adjusting circuit 22 outputs a control signal, zeroing the input deviation, to the pulse arithmetic generating circuit 23, and being based on these signals, firing and arc-extiguishing pulses are given to the inverter 4. Here a loss arithmetic circuit 30 being provided, a device loss of the inverter 4 is calculated. And the effective power preset value P is reduced by the amount of this loss. Thus, effective power PDC is controlled to have a fixed value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling an inverter that is connected in parallel to a power system and operated in conjunction with the power system.

[Conventional technology]

The capacity of power generation systems such as solar cells and fuel cells has increased, and there are many opportunities for them to be operated in conjunction with the power grid, but since these power sources are direct current, it is necessary to convert this direct current to alternating current using an inverter. , this inverter is operated in parallel with the power grid.

FIG. 3 is a circuit diagram showing a conventional example of an inverter that converts a DC w source into AC and operates in conjunction with the power grid. b) is the third
The inside of the control device 14 shown in FIG.

In this FIG. 3 (a), the DC power from the DC power source 2 such as the solar cell or fuel cell mentioned above is indicated by the symbol 4.
It is converted into alternating current by a self-supporting inverter, and connected in parallel to the power grid 6 via a transformer 5, but this direct current type a2 and inverter 4 control the output active power as well as the output reactive power. However, depending on the case, only the inverter 4 may be operated in a linked manner and used as a reactive power compensator. In this way, in order to control the active power and reactive power output by the inverter 4, the current and voltage of the inverter 4 are transferred to the current transformer 11 and the voltage transformer 1.
2 and input these to the power detection circuit 13 to extract the actual active power value P and the actual reactive power value Q from the power detection circuit 13, and set these as the active power setting value P.
0 and the reactive power setting value Q1 is input to the control device 14, and the inverter 4 is appropriately controlled by the output of this control device 14.
n, the active and reactive power are controlled according to the set values.

As shown in FIG. 3(b), the control device 14 is composed of an active power adjustment port 1821, a reactive power adjustment circuit 22, and a pulse calculation generation circuit 23, and an active power setting device 15.
The deviation between the active power setting value P0 output from the power detection circuit 13 and the active power actual value P output from the power detection circuit 13 described above is determined, and this deviation is inputted to the active power adjustment circuit 21 described above. Regarding reactive power, the deviation between the reactive power set value Q0 outputted from the reactive power setting device 16 and the reactive power actual value (!IQ) outputted from the power detection circuit 13 is calculated, and this deviation is calculated as 22.

These active power adjustment circuit 21 and reactive power adjustment circuit 22
Each outputs a control signal 3'll to make the input deviation zero to the pulse calculation generation circuit 23, and based on this, the ignition/extinguishing pulse is generated from this pulse calculation generation circuit 23 to form the inverter 4. active power and reactive power are maintained at their respective set values.

FIG. 4 is a basic circuit diagram showing an example of the configuration of the inverter 4 shown in FIG. 3. In FIG. That is, a gate turn-off thyristor (hereinafter abbreviated as GTO thyristor) 41 as a switching element and a freewheel diode 42 are connected in antiparallel to each other to form an arm, and six sets of these arms are connected in a three-phase bridge. This constitutes the inverter 4.
The DC power supply 2 is connected to the DC side of the inverter 4 via a smoothing capacitor 43, and the AC side of the inverter 4 is connected to the power system 6.

FIG. 5 is a diagram showing the flow of power when active power and reactive power are controlled by the inverter 4 shown in FIG. 4.

In FIG. 5, DC power PDC passes through an inverter 4 and is output as active power pAc. on the other hand,
It can be seen that the reactive power QAc is the power circulating between the power system and this inverter 4. Therefore, ideally a) Poc=PAC b) Qac should be independent of PAC and PDC.

[Problems to be Solved by the Invention] However, since the inverter 4 has a configuration as shown in FIG. In reality, conditions a) and b) described above are not satisfied, and conditions c) and d) below occur.

c) Poc=Pac+equipment loss PL d) Device loss PL is affected by Q AC.

By the way, inverters that operate in conjunction with the power grid,
It is often necessary to suppress fluctuations in DC output from becoming excessive due to requests from DC power sources such as fuel cells.

Further, even when used as the above-mentioned reactive power compensator, fluctuations on the DC circuit side lead to fluctuations and instability of the entire system, so it is desirable to suppress them as much as possible. Therefore, the change in active power that accompanies the change in DC output must be made slowly so that the rate of change is within an acceptable range.

On the other hand, as mentioned above, changes in reactive power should not cause fluctuations on the DC side (see condition b) above).
So, is it a control of reactive power? Although there is no restriction on ffU, in reality, the loss of PL in the device causes a change in the DC output PDC (see condition C), so reactive power cannot be freely controlled, and changes in this There are restrictions.

FIG. 6 is a graph showing the influence of changes in reactive power on DC power, with the horizontal axis representing reactive power Q and the vertical axis representing DC power poc. That is,
By changing the reactive power Q output by the inverter 4, the DC power P, which is originally desirable to be a constant value, can be obtained. C
There was a problem where the value fluctuated.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to perform reactive power control of an inverter connected to a power system without causing output fluctuations on the DC circuit side.

(Means for Solving the Problems) In order to achieve the above object, the control method of the present invention includes:
In a method for controlling a grid-connected inverter, in which an inverter that converts direct current to alternating current is connected in parallel to a power grid, and the output active power and output reactive power of this inverter are controlled to respective set values, the output reactive power of the inverter is The loss of the inverter that occurs in response to this is calculated, and this loss is subtracted from the set value of the output active power.

(Function) When the inverter is operated in conjunction with the power system, reactive power circulating between the power system and the inverter generates device loss inside the inverter, and this device loss is caused by the direct current power. This method focuses on the effect on DC circuit voltage output by subtracting the equipment loss that occurs in response to changes in reactive power from the set value of output active power (in this way, it suppresses fluctuations in DC circuit voltage output. This is what I am trying to do.

[Embodiment] FIG. 1 is a control block diagram showing an embodiment of the present invention.

In FIG. 1, the deviation between the separately set active power setting value P"AC and the actual dynamic power value PAe detected by the power detection circuit 13, etc. described above is calculated, and this deviation is used to adjust the active power. When input to the circuit 21, this active power adjustment circuit 21 outputs a control signal that makes the input deviation to zero to the pulse calculation generation circuit 23, and also outputs a separately set reactive power setting value Q"Ac and the power detection circuit. When the deviation from the actual reactive power value QAc outputted from 13 etc. is calculated and inputted to the reactive power adjustment circuit 22, this reactive power adjustment circuit 22 sends a control signal to make the manual deviation to zero to the pulse calculation generation circuit 23. Therefore, applying ignition/extinguishing pulses based on these control signals to the inverter 4 is the same as in the conventional circuit described in FIG. 3(b).

In the present invention, a loss calculation circuit 30 is installed, and when the reactive power setting value Q"ac changes, the device loss of the inverter 4 corresponding to this change is calculated by the loss calculation circuit 30, so that only this loss can be calculated. Active power setting value P□.

We are trying to reduce this.

By reducing the AC output active power in this way, the DC power PDC can be maintained at a constant value.

Here, the device loss due to reactive power is GTO shown in Fig. 4.
Thyristor 41 If the on-voltage of a power device such as a freewheeling diode 42 can be considered constant, the loss calculation circuit 30 shown in FIG. 1 can be configured with a simple amplifier with a proportional gain of K. This is usually sufficient to achieve the required performance.

FIG. 2 is a circuit diagram showing an example in which the embodiment circuit shown in FIG. 1 is applied to a reactive power compensator.

Inverter 4, transformer 5, power system 6, current transformer 11, voltage transformer 12, power detection circuit 13 shown in FIG.
, the reactive power setting device 16, the reactive power adjustment circuit 22, the pulse calculation generation circuit 23, and the loss calculation circuit 30.
Since they have already been explained in FIGS. 1 and 3, explanations of their names, uses, and functions will be omitted.

In the present invention, the DC circuit is provided with a capacitor 9, a DC voltage detector 31, a DC voltage setter 32, and a DC voltage adjustment circuit 33.

The DC circuit voltage of the reactive power compensator shown in FIG. . is detected, and the deviation between the DC voltage setting value E set by the DC voltage setting device 32 and the above-mentioned actual value E is manually inputted to the DC voltage adjustment circuit 33, and a 1tNI control signal is generated to zero this input deviation. Feedback control is performed to output the power, and the DC voltage adjustment circuit 33 takes in power from the power system 6 to compensate for the loss of one circuit member. Therefore, the h
By calculating the a loss in the loss calculation circuit 30 and adding it to the output of the DC voltage adjustment circuit 33 described above, fluctuations in the DC voltage can be quickly suppressed and the system can be stabilized.

〔Effect of the invention〕

According to this invention, when changing the output reactive power of an inverter that is operated in connection with the power grid, it is possible to prevent the DC output from fluctuating due to the influence of the device loss of the inverter that increases or decreases in response to this change. In order to avoid this, the active power is set by subtracting it from the output active power of the W tll bone, which has the effect of avoiding adverse effects on DC power sources, such as fuel cells, and reactive power compensation. If applied to a device, this device can be controlled stably.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram showing an embodiment of the present invention;
Fig. 2 is a circuit diagram showing an example in which the embodiment circuit shown in Fig. 1 is applied to a reactive power compensator, and Fig. 3 is a circuit diagram of an inverter that converts DC power into AC and operates in connection with the power grid. A circuit diagram showing a conventional example, Fig. 4 is a basic circuit diagram showing an example of the configuration of the inverter 4 shown in Fig. 3, and Fig. 5 shows control of active power and reactive power by the inverter 4 shown in Fig. 4. Figure 6 shows the flow of power when
...DC power supply, 4...Inverter, 5...Transformer,
6... Power system, 9... Capacitor, 11... Current transformer, 12... Instrument transformer, 13... Power detection circuit, 14... Control device, 15... Effective power setting device,
16... Reactive power setting device, 21... Active power adjustment circuit, 22... Reactive power 9A node circuit, 23... Pulse calculation generation circuit, 30... Loss calculation circuit, 31... DC Voltage detector, 32... DC voltage setting device, 33...
DC voltage regulation circuit. After the 21st station exchange, the town turned silkworms 31 Tamo 3 Figure 2

Claims (1)

[Claims] 1) In a control method for a grid-connected inverter, in which an inverter that converts DC to AC is connected in parallel to a power grid, and the output active power and output reactive power of this inverter are controlled to respective set values, the output of the inverter is disabled. A method for controlling a grid-connected inverter, comprising calculating a loss of the inverter that occurs in response to electric power, and subtracting this loss from a set value of the output active power.