JPH0458261B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an AC interconnection system that is operated in conjunction with another AC power source, and in particular to a system that stably supplies a predetermined reactive power even when the voltage of the AC power source fluctuates. The present invention relates to a method of operating a self-excited power converter suitable for supplying power to a specific load in the event of an AC power failure.

[Technical background of the invention]

Conventionally, in order to operate AC power supplies from different systems in parallel, the voltage difference between each AC power supply is calculated by the deviation of reactive power.
It is known to control the phase between each AC power source by the deviation of the active power.

When connecting a DC-AC power converter, such as an inverter, to a power system, the power system cannot be controlled, so a self-excited power converter (hereinafter referred to as a power converter) is used as the converter. A method of controlling active power and reactive power is adopted.

FIG. 1 shows a block diagram showing a conventional control method for a power converter.

The DC output of the DC power source 1 is converted into AC by a power conversion device 2, converted to a predetermined voltage by a transformer 3, and connected to a power grid 5 via a switch 4.

In the control circuit 100, the voltage reference 21 is compared with the secondary detection voltage 12 of the transformer 3 connected to the power converter 2, and the difference 25a is applied to the error amplifier 24 via the changeover switch 25. The reactive power reference 22 is compared with the output of a reactive power detection circuit 23 that detects reactive power from the secondary detection voltage 12 of the transformer 3 and the secondary detection current 11 of the transformer 3, and the deviation 25b is detected by the changeover switch 24. The output of the error amplifier 24 is applied to the voltage control circuit 26 through the voltage control circuit 26.

Similarly, the active power reference 31 is compared with the output of the active power detection circuit 32 that detects active power from the secondary detection voltage 12 of the transformer 3 and the secondary detection current 11 of the transformer 3, and the deviation 33a is the error. Amplifier 33
The output of the error amplifier 33 serves as one input "I" of a phase locked loop, so-called PLL circuit 34. 35 is a frequency divider which divides the output frequency of the PLL circuit 34, and its output is divided into other parts of the PLL circuit 34.
This results in two inputs “ha”. Another one of the PLL circuit 34
The power system detection voltage 13 is applied to the two inputs "b" as a phase reference.

Here, the PLL circuit 34 is a well-known circuit, but
Explain briefly. FIG. 2 is an example of a block diagram of the PLL circuit 34. The PLL circuit 34 is composed of a phase error detector PHD, a low frequency filter LPF, and a voltage controlled oscillator VCO. To give an overview of each of these elements, the phase error detector PHD generates a signal "D" proportional to the phase difference between the phase reference signal "B" and the phase feedback signal "C". A signal "2" proportional to this phase difference is input to the low-pass filter LPF, which removes harmonic components and amplifies the phase error. And the voltage controlled oscillator VCO is the output “H” of the low frequency filter LPF.
This voltage controlled oscillator outputs a frequency proportional to
The output “H” of the VCO is given to the frequency divider 35.
If the number of stages of the frequency divider 35 is N, then the voltage controlled oscillator
The oscillation frequency of the VCO is N times that of the phase reference signal "L". Here, N is selected as an arbitrary integer depending on the number of phases of the inverter circuit of the power conversion device 2. Since the output of the frequency divider 35 is the phase feedback signal "c" of the phase error detector PHD, the voltage controlled oscillator
The oscillation frequency of the VCO is automatically controlled so that the phases of the phase reference signal "L" and the phase feedback signal "C" match. Here, the function of one input "A" of the PLL circuit 34 is that the phase difference between the phase reference signal "B" and the phase feedback signal "C" can be arbitrarily set by giving a signal to the low frequency filter LPF. becomes.

Returning again to the explanation of the operation in FIG. PLL circuit 34
Since the phase of the power system 5 is applied as the phase reference signal “b” of Synchronized with phase.

When the switch 4 is open, the switch 25 has a deviation of 2.
5a is selected, and the secondary detection voltage 1 of transformer 3 is selected.
2 is automatically controlled to be equal to the voltage reference 21. In addition, the input and output of the error amplifier 33 are connected to the switch 3.
6 is short-circuited, and an active power control circuit that controls the phase of the power converter 2 based on the active power deviation 33a is not formed.

Next, when the switch 4 is closed, the changeover switch 25 selects the deviation 25b, and the output voltage of the power conversion device 2 is automatically controlled so that the reactive power of the power conversion device 2 becomes equal to the reactive power reference 22. .

Further, at the same time as the switch 4 is closed, the switch 36 is opened, the input/output short circuit of the error amplifier 33 is released, and the power converter 2 is adjusted so that the active power of the power converter 2 becomes equal to the active power reference 31. Voltage phase is automatically controlled.

Therefore, in the description of the operation of the present invention, active power is not particularly relevant, so in the following description, it is assumed that the voltage phases of the power conversion device 2 and the power system 5 are completely equal.

Now, the output voltage 211 of the power converter 2 is E〓 ₁ ,
If the voltage at the connection point with the power grid 5, that is, the secondary voltage 14 of the transformer 3, is E = ₂ , then the transformer 3 has a third
A voltage of E〓 ₁ −E〓 ₂ of the vector in the figure will be applied, and the current I・_L flowing through the transformer 3 will be the voltage vector E〓 ₁ , assuming that the impedance of the transformer 3 is only the reactance component. It is expressed as a vector E〓 _L whose phase is delayed by 90° with respect to E〓 ₂ .

The power at this time is reactive power, and the output voltage control of the power converter 2 involves giving and receiving reactive power. In other words, the transfer of reactive power to and from the power grid 5 through the reactive power control of the power converter 2 can stabilize the voltage at the interconnection point. That is, if the voltage of the power grid 5 is lower than a predetermined value, a predetermined command is given to the reactive power standard 22, and reactive power is supplied from the power conversion device 2 to the power grid 5, thereby reducing the voltage at the interconnection point. If the voltage of the power system 5 is greater than the predetermined value, the reverse will occur. That is, assuming that the voltage of the power system 5 cannot be changed, the reactive power between the two power sources can be controlled by changing the voltage of the power conversion device 2.

[Problems with background technology]

However, if the capacity of the power system 5 is very large relative to the power converter 2, or if the so-called AC power source is strong, even if the reactive power control of the power converter 2 is performed, it will not be possible to stabilize the voltage at the interconnection point. The contribution is small. Moreover, the conventional method shown in FIG.
In response to sudden changes in the voltage of the power system 5, the reactive power detection circuit 23 requires a circuit that calculates the reactive power, so this calculation circuit is delayed, and the output voltage control function of the power converter 2 is also delayed. Put it away.

This delay in the output voltage control function causes a sudden change in the current I・_L caused by the voltage difference E〓 ₁ −E〓 ₂ shown in Fig. 3.
Depending on the sudden change in the voltage of the power system 5, a well-known overcurrent detection value is reached for the protection of the power converter 2, resulting in the disadvantage that the power converter 2 performs a protective interlocking operation and stops. .

Also, at the same time as the switch 4 is operated, the changeover switch 2
Since the output voltage control and reactive power control of the power converter 2 are switched in step 5, there is a drawback that the power of the power converter 2, especially the reactive power, is forced to suddenly change when the switch 4 is opened/closed.

[Purpose of the invention]

In view of this point, the present invention provides an AC grid-connected system that is operated in conjunction with other so-called strong AC power supplies, which continues to operate stably even in the face of sudden changes in the voltage of the power grid 5, and which maintains the opening/closing operation of the switch 4. Operation of a self-excited power converter that can suppress sudden changes in voltage at interconnection points during times of failure, and can quickly open the switch 4 and shift to single load operation of only a predetermined load in the event of an accident in the power system 5. Its purpose is to provide a method.

[Summary of the invention]

In the present invention, a self-excited power converter that converts the output of a DC power source into alternating current is connected to another AC power source via a switch, and the reactive power and active power of this AC power source are transferred to the self-excited power converter. A power conversion system for controlling an output voltage control system of the self-excited power converter, comprising a selection circuit that selects either a predetermined setting value or the AC power supply voltage detection value as a voltage reference of an output voltage control system of the self-excited power conversion device, the voltage of the AC power supply If is within the specified range,
The AC power supply voltage detection value is selected as a voltage reference, and the output voltage control circuit inputs the AC power supply voltage detection value, the output voltage detection value of the self-excited power converter, and the control deviation of the reactive power control circuit. , while controlling the output voltage of the self-excited power converter, if the voltage of the AC power supply is outside a predetermined range,
The switch is opened to stop the reactive power control circuit and the active power control circuit, the predetermined set value is selected as a voltage reference, and the predetermined set value and the detected output voltage value of the self-excited power converter are This is a method of operating a self-excited power converter, in which the output voltage of the self-excited power converter is controlled by an output signal of the voltage control circuit that receives as an input.

[Embodiments of the invention]

An embodiment of the present invention will be explained with reference to a block diagram showing its configuration in FIG. 4.

In FIG. 4, the same reference numerals as in FIG. 1 have the same functions.

The differences between this embodiment (Fig. 4) and the conventional example (Fig. 1) are as follows. That is, the error amplifier 24
a changeover switch 42 for selecting either the power system detection voltage 13 or the voltage reference 21 as the voltage reference;
The reference signal 42a selected via the power converter 2, the output detection voltage 15 of the power converter 2, and the output signal 43a of the error amplifier 43 for reactive power control are input.

Now, the operation of the present invention will be described.

In FIG. 4, if the power grid 5 is established within a predetermined range, the voltage discrimination circuit 41 which receives the power grid detection voltage 13 as an input causes the changeover switch 42 to select the power grid detection voltage 13 and control the voltage. This is used as a reference signal 42a for the system.

When the switch 4 is open, that is, when the power converter 2 is supplying power only to the load 6, the input and output of the error amplifiers 33 and 43 are short-circuited by the switches 36 and 44, respectively, so that the effective power
Both reactive power control systems have stopped functioning, and the error amplifier 24 performs voltage control using the deviation 24a between the reference signal 42a and the output detection voltage 15 of the power converter 2 as input. That is, the output voltage of the power conversion device 2 is automatically controlled to be equal to the voltage of the power system 5.

When the switch 4 is turned on in this state, the output voltage 211 of the power converter 2 and the voltage of the power grid 5 are equal, so there is no exchange of reactive power due to the voltage difference between the two, so fluctuations in the voltage at the interconnection point can be suppressed. Can be done.

The error amplifiers 33, 43 are connected to the respective switches 36,
When 44 is opened, a starting circuit (not shown) operates to gently control predetermined active power and reactive power.

The output signal 43a of the error amplifier 43 is the reference signal 4
2a and the output detection voltage 15 of the power converter 2, and works to correct the deviation 24a of the voltage control system with the reactive power control amount, and as a result, the reactive power between the power converter 2 and the power system 5 is The transfer of power is automatically controlled to be equal to the reactive power standard 22.

Furthermore, even if the voltage of the power system 5 suddenly changes, the reference signal 42a of the voltage control system changes instantaneously, so the deviation 2
4a allows the error amplifier 24 to respond quickly and suppresses changes in the amount of reactive power. In other words, since the increase in current between the two power supplies is suppressed, the power converter 2 does not detect an overcurrent and perform a protective interlock operation.

If the power system 5 fluctuates beyond a predetermined range, the voltage discrimination circuit 41 detects this and opens the switch 4, and switches the changeover switch 42 to the voltage reference 21, thereby switching the power converter The output voltage 211 of No. 2 can be controlled at a constant voltage, and stable power can be supplied to the load 6.

By the way, in this embodiment, the power system detection voltage 1
3 is within a predetermined range, the voltage discrimination circuit 41 causes the selector switch 42 to select the power system detection voltage 13, and if it is outside the predetermined range,
Although the voltage reference 21 is selected, the detection range by the voltage discrimination circuit 41 may be determined in accordance with the output voltage control range of the power conversion device 2.

In other words, even if a temporary short-circuit accident occurs in some branch circuits of the power system 5, by widening the output voltage control range of the power conversion device 2, the power conversion device 2 can maintain the voltage of the power system 5. This allows it to continue operating without detecting overcurrent.

Further, the changeover switch 42 selects the voltage reference 21 so as to supply a constant voltage to the load 6 when the switch 4 is open, and when the switch 4 is turned on, the changeover switch 42 is switched to control the power system 5. The voltage may be controlled to be equal to the voltage.

〔Effect of the invention〕

As explained above, according to the present invention, in an AC interconnection system that connects a power conversion device that converts direct current from a DC power source to alternating current and another different AC power source, at the time of interconnection by turning on a switch, By suppressing the transmission and reception of transient reactive power, without changing the voltage at interconnection points, and by quickly responding to voltage control systems even if the voltage of the power grid suddenly changes, unnecessary reactive power can be reduced. Since the transmission and reception of power is suppressed, the power conversion device can continue to operate without detecting overcurrent. Even if an accident occurs in the power system, by promptly opening the switch 4, power can be continuously supplied to the specified load.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the control method of a conventional AC interconnection system, Fig. 2 is a specific circuit configuration diagram of the PLL circuit shown in Fig. 1, and Fig. 3 is a vector diagram explaining the generation of reactive power. FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention. 1... DC power supply, 2... Self-excited power converter (211 is its output voltage), 3... Transformer, 4...
Switch or circuit breaker, 5... Power system, 6...
Load, 11...Output current, 12...2 of transformer 3
Next detection voltage, 13... Power system detection voltage, 14...
...Secondary voltage of transformer 3, 15...Power converter 2
output detection voltage, 21... voltage reference, 22... reactive power reference, 23... reactive power detection circuit, 24...
...error amplifier, 24a...deviation, 25...changeover switch, 25a, 25b...deviation, 26...voltage control circuit, 31...active power reference, 32...active power detection circuit, 33...error amplifier, 34...
PLL circuit, 35... Frequency divider, 36... Switch,
41... Voltage discrimination circuit, 42... Changeover switch,
43...Error amplifier, 43a...Output signal, 44
...Switch.

Claims (1)

[Scope of Claims] 1. A self-excited power converter that converts the output of a DC power source into alternating current is connected to another AC power source via a switch, and the reactive power and active power of this AC power source are converted into the self-excited power converter. A power conversion system controlled by the device, comprising a selection circuit that selects either a predetermined setting value or the AC power supply voltage detection value as a voltage reference of the output voltage control system of the self-excited power conversion device, If the voltage of the power supply is within the specified range,
The AC power supply voltage detection value is selected as a voltage reference, and the output voltage control circuit inputs the AC power supply voltage detection value, the output voltage detection value of the self-excited power converter, and the control deviation of the reactive power control circuit. , while controlling the output voltage of the self-excited power converter, if the voltage of the AC power supply is outside a predetermined range,
The switch is opened to stop the reactive power control circuit and the active power control circuit, the predetermined set value is selected as a voltage reference, and the predetermined set value and the detected output voltage value of the self-excited power converter are A method of operating a self-excited power converter, characterized in that an output voltage of the self-excited power converter is controlled by an output signal of the voltage control circuit which receives as an input.