JPS6127982B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for an inverter connected to an electric power system.

In order to operate AC power supplies from different systems in parallel, it is conventionally known to control the voltage difference between each AC power source using the deviation in reactive power, and to control the phase difference between each AC power source using the deviation in active power. . When interconnecting an inverter with a power grid, the output voltage and phase of the inverter must be controlled since the power grid cannot be controlled. A conventional example of an inverter control method will be explained with reference to FIG.

In the figure, 10 is a DC power supply, which is converted to AC by an inverter 11, and further connected to a subsequent AC filter 1.
After shaping into a sine wave in step 2, the thyristor and disconnector 1
3 to the power grid 14.

In the control circuit 100, the voltage reference 30 and the output voltage 21 of the AC filter 12 are compared, and the deviation 35a is applied to the error amplifier 33 via the changeover switch 35. The reactive power reference 31 and the output of the reactive power transducer 32 are compared, and the deviation 35b is applied to the error amplifier 33 via the changeover switch 35, and the output of the error amplifier 33 is input to the voltage control circuit 34. There is. Similarly, the active power reference 40 and the output of the active power transducer 41 are compared, and the deviation 42a is determined by the error amplifier 4.
The output of the error amplifier 42 serves as one input "I" of a phase locked loop, a so-called PLL circuit. A frequency divider 44 divides the output frequency of the PLL circuit 43, and its output becomes the other input "c" of the PLL circuit 43. The voltage 22 of the power system 14 is applied to the other input "low" of the PLL circuit 43 as a phase reference. Here, the PLL circuit 43 is a well-known circuit, but to briefly explain it, FIG. 2 is an example of a block diagram of a PLL circuit. It consists of a voltage controlled oscillator VCO. To give an overview of each of these elements, the phase error detector
The 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. The voltage controlled oscillator TCO outputs a frequency proportional to the output "H" of the low frequency filter LPF, and the output "H" of the voltage controlled oscillator VCO is connected to the frequency divider 44. If the number of stages of the frequency divider 44 is N, the oscillation frequency of the voltage controlled oscillator VCO will be N times the phase reference signal "L". Here, N is selected as an arbitrary integer depending on the number of phases of the inverter. The output of the frequency divider 44 is the phase feedback signal “H” of the phase error detector PHD.
Therefore, the oscillation frequency of the voltage controlled oscillator VCO is automatically controlled so that the phases of the phase reference signal "B" and the phase feedback signal "C" match. Here, the function of one input "A" of the PLL circuit 43 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 to Figure 1 again and explaining its operation,
Since the phase of the power system 14 is applied as the phase reference signal "b" of the PLL circuit 43, the output frequency of the PLL circuit 43 is synchronized with the phase of the power system 14, and therefore the phase of the inverter 11 is also synchronized with the phase of the power system 14.
is synchronized with the phase of Thyristor switch 13
In the open state, the switch 35 selects the deviation 35a, and the output voltage 11a of the inverter 11 is automatically controlled so that the output voltage 21 of the AC filter 12 becomes equal to the voltage reference 30. Further, the input and output of the error amplifier 42 are short-circuited by a switch (not shown), and an automatic control circuit for controlling the phase of the inverter based on the deviation 42a of active power is not formed. Next, when the thyristor and disconnector 13 are closed, the changeover switch 35 selects the deviation 35b,
The output voltage 11a of the inverter 11 is set such that the reactive power of the inverter 11 is equal to the reactive power reference 31.
is automatically controlled. Similarly, thyristor and disconnector 1
3 is closed, the short circuit between the input and output of the error amplifier 42 is released, and the phase of the inverter 11 is automatically controlled so that the active power of the inverter 11 becomes equal to the active power reference 40.

In such a conventional control method for an inverter connected to a power system, the reactive power transducer 32 and the active power transducer 41 are used, which is preferable from the viewpoint of precise power control, but the control configuration is complicated. The problem is that each power transducer is very expensive, so it cannot be called an economical system.

An object of the present invention was to solve the above-mentioned problems, and to provide an economical control method for an inverter that is connected to an electric power system and that simplifies the control configuration without impairing conventional functions. There is a particular thing.

The present invention will be explained below with reference to the drawings.

FIG. 3 is a configuration diagram showing an embodiment of the present invention. In FIG. 3, the same symbols as in FIG.
is the inverter output voltage, 46 is the voltage deviation reference, 4
7 indicates a phase difference reference for the inverter output system bus voltage. In FIG. 1, the inverter 11
By performing voltage control, the phase changes, and as a result, the active power changes, but
An error amplifier 42 operates on one input "I" of the PLL circuit 43 so that the active power of the inverter 11 becomes equal to the active power reference 40, and automatically corrects the phase.
When this is combined with an inverter that does not change the phase even when voltage control is performed as 11', controlling the phase difference between the inverter output voltage and the power system bus voltage almost controls the active power from the inverter 11'. This shows that they are equivalent to each other.
That is, if the impedance of the AC filter 12 and the power system bus voltage are known, the required amount of active power can be obtained from the above-mentioned phase difference. Here, the power system bus voltage is a certain fixed amount, and the amount of variation thereof is generally small. Regarding the control of reactive power, the voltage difference between the input and output of the AC filter 12, that is, the output voltage 11a of the inverter 11'
The error amplifier 33 and the voltage control circuit 34 operate so that the difference between the voltage difference and the power system bus voltage is always kept constant by checking the difference between the voltage deviation reference 46 and the voltage deviation reference 46, thereby controlling the output voltage 11a of the inverter 11'. FIG. 4 shows the output voltage waveform and its control point of the inverter 11', that is, an inverter with no phase change during voltage control. In Fig. 4, time points t ₁ and t ₂ are reference points, and these time points are, for example, π/2 and 3π/
It is in position 2. The output voltage phase is fixed by controlling the magnitude of Δt during voltage control.
The broken line in FIG. 4 shows a waveform in which the output voltage of the inverter is smaller than that of the solid line, and there is no phase change due to voltage control. FIG. 5 shows a specific example of the configuration of an inverter that does not change the phase when performing voltage control. In FIG. 5, 51 is a triangular wave generator, 52 is a comparator, A is a voltage control signal, and B is a comparator output signal.

To explain the operation of this configuration, the triangular wave generator 51 generates a triangular wave as shown in FIG. 6a. Further, the comparator 52 compares the magnitude of this triangular wave with the voltage control signal A, and generates a comparator output signal B. As shown in Fig. 6a, when the voltage control signal has a magnitude of A-1, the width is narrow as shown by the dotted line in Fig. 6b, and when the voltage control signal has a magnitude of E-2, the width is wide as shown by the solid line. A pulse is obtained. The output signal L of such a comparator 52 is frequency-divided by a frequency divider (not shown) and used as a gate signal of an inverter.

Therefore, as is clear from FIG. 6b, even if Δt is controlled during voltage control, the output voltage phase of the inverter does not change.

As described above, according to the present invention, by using an inverter with no phase change through voltage control, the amount of reactive power can be determined by the standard amount of voltage of the AC filter 12, that is, the voltage deviation standard 46, and the output phase and power of the inverter 11 can be adjusted. It is possible to roughly control the active power by the phase difference with the power grid 14, that is, the phase difference reference 47, which simplifies the control circuit configuration and creates an economical power system without using expensive power transducers. It becomes possible to provide a control method for interconnected inverters.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional inverter control system connected to a power system, Fig. 2 is a detailed diagram of a part of the circuit shown in Fig. 1, and Fig. 3 is a configuration showing an embodiment of the present invention. 4 is a waveform diagram showing the output voltage of the inverter used in the present invention, FIG. 5 is a diagram showing a specific configuration example of an inverter with no phase change when performing voltage control, and FIG. 6 is a waveform diagram showing the output voltage of the inverter used in the present invention. FIG. 3 is a waveform diagram for explaining the operation. 10...DC power supply, 11...Inverter, 12
... AC filter, 13 ... Thyristor circuit breaker, 14 ... Power system, 20 ... Output current, 21
... Output voltage, 22 ... Power system bus voltage, 30
...Voltage reference, 31...Reactive power reference, 32...
Reactive power transducer, 33... Error amplifier, 34... Voltage control circuit, 35... Changeover switch, 35a... Voltage deviation, 35b... Reactive power deviation, 40... Active power reference, 41... Active power transformer Jusa, 42...Error amplifier, 42a...
Active power deviation, 43... PLL circuit, 44... Frequency divider, 45... Inverter output voltage, 46... Voltage deviation reference, 47... Phase difference reference.

Claims (1)

[Claims] 1. With an inverter connected to the power grid bus,
In a device configured to control reactive power and active power, an inverter that does not cause a phase change when performing AC voltage control is used as the inverter, and the voltage between the input and output of an AC filter connected to the output side of the inverter is 1. A control method for an inverter connected to a power system, characterized in that reactive power is controlled by controlling a difference, and active power is controlled by controlling an output phase of the inverter.