JPS6380775A - Controller for inverter - Google Patents

Abstract

PURPOSE:To reduce a distortion rate by providing means for detecting load condition, and means for varying the amplitude of a modulation wave or carrier in response to the detection. CONSTITUTION:An inverter main circuit is composed of an AC power source 1, a power reactor 3, a smoothing reactor 4, a power inverter 5, an output terminal capacitor 6, a motor 7 and a speed detector 8. A controller is composed of a current controller 10, a pulse distributor 12, a comparator 13, a modulation wave amplitude calculator 14, a modulation wave generator 15, a carrier generator 16, a vector calculator 17 and a pulse distributor 18. A current command value (i) and a phase command value theta of a current flowing to the motor 7 are obtained as the output signals of the calculator 17, and input from a current controller 19 to the gates of the reactors 3. The value theta is input from the generator 15 to the gates of the inverters 5. Thus, since the amplitude of the modulation wave is varied in response to the load condition, the allowable minimum pulse width can be always obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AC motor drive device, and more particularly to an inverter control device using a switching element having a self-extinguishing function.

[Conventional technology]

As an inverter control device, for example, the conventional pulse width modulation control device for current source inverters described in the Institute of Electrical Engineers of Japan ``Semiconductor Power Conversion Study Group Material JSPC-84-36'' is used with a fixed modulation wave amplitude or carrier wave amplitude. This reduces the ratio of the modulated wave amplitude to the carrier wave amplitude, and reduces the content of specific harmonics included in the 'r4 flow pattern.
Alternatively, it is fixed at a certain value for the purpose of reducing the strain rate. Also, the frequency of the carrier wave is
The number of switching times within a certain period of time is always fixed to be the same regardless of the load conditions.

[Problem that the invention seeks to solve]

In the above conventional technology, when the motor load increases and the DC current increases, the minimum allowable pulse width of the switching element becomes wider than when there is no load, and pulses with a narrower width than this become present in the current pattern. As a result, problems such as element destruction occur. Additionally, if the amplitude ratio is selected and fixed to ensure the minimum pulse width when the motor load is maximum, the effect of harmonic suppression at light loads will be reduced compared to the previous case where the amplitude ratio was fixed. , the problem of increased strain rate also occurs.

The present invention provides an inverter control device that enables an electric motor to be operated while minimizing harmonics and maintaining a low distortion factor by ensuring the minimum allowable pulse width of the switching element according to the load conditions. The purpose is to

[Means for solving problems]

The above object is achieved by providing means for detecting load conditions and means for varying the amplitude of the modulated wave or carrier wave in accordance with the means.

[Operation] The load condition can be obtained by detecting the DC current value, and an output voltage proportional to the DC current value can be obtained.

By varying the amplitude of the modulated wave or carrier wave according to the load conditions, the minimum pulse width of the pulse train supplied to the switching element can be varied. Therefore, it is possible to always ensure the minimum allowable pulse width of the switching element, which varies depending on the load conditions, so that there are few harmonics contained in the output current over a wide range of load conditions, and the distortion factor can be reduced.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram showing a first embodiment of the present invention, in which 1 is an AC power supply, 3 is a forward converter for controlling DC current, and 4 is a block diagram showing a first embodiment of the present invention.
5 is an inverse converter composed of a switching element with a self-extinguishing function, 6 is an output end capacitor with a function of overvoltage absorption and filtering during switching, 7 is a motor, 8 is an accelerator for smoothing DC current, is a speed detector, and the above constitutes the main circuit.

Also, 9 and 11 are gate amplifiers, 10 is a current control circuit,
12 is a pulse distribution circuit, 13 is a comparison circuit, 14 is a modulated wave amplitude calculation circuit, 15 is a modulated wave generation circuit, 16 is a carrier wave generation circuit, 17 is a vector calculation circuit, and 18 is a pulse distribution circuit. Configure.

In the figure, the output signal of the vector calculation circuit 17 is a current command value i*, a phase command value θ of the current flowing through the motor.
* is obtained. i* is input to the current control system 19, passes through the gate amplifier 9, and is input to each gate of the forward converter.

On the other hand, the phase command θ* becomes an input signal to the modulated wave generation circuit 15. This modulated wave generation circuit 15 is configured as shown in FIG. 2, for example.

FIG. 2 is a block diagram of the modulated wave generation circuit, and 155 is called a digital/analog converter (D/A).
The maximum amplitude of the output voltage Vout obtained according to the digital amount of the phase command θ* can be controlled by the comparison input (REF). Therefore, the maximum amplitude value B of the phase command θ*
can be varied. This output signal e and the output signal ee of the carrier wave generation circuit 16 shown in FIG. 1 are compared in the comparator circuit 13 to obtain a basic pulse width modulation control pattern PTN which is repeated every 60 degrees of the inverter operating period.

This PTN is pulse-distributed to each phase by a pulse distribution circuit 12, and is inputted to each gate of the inverter 5 via a gate amplifier 11. The relationship between the modulated wave and the carrier wave is configured as shown in FIG. 3, for example.

FIG. 3 is an operational waveform diagram showing the relationship between the modulated wave and the carrier wave, where the modulated wave e is a trapezoidal wave with an amplitude of B, and the carrier wave ec is an amplitude of A.
With the triangular wave, 6c>6. When “L”, when ec5e “
Basic pulse width modulation control pattern P
Let it be TN. This PTN is subjected to a logical operation in the distribution circuit 12 to obtain the final current pattern i. Here, a method for determining the amplitude ratio will be explained with reference to FIG.

FIG. 4 is a control characteristic diagram of the first embodiment of the present invention,
In the figure, the allowable minimum pulse width t□ at the rated point.

is a value to ensure normal operation of the motor under all load conditions, and pulses with a width less than this value must not exist. If present, the switching element will be destroyed.

Since the minimum pulse width t8 in the current pattern i in FIG. 3 is a function of the amplitude ratio as shown in FIG. 4(b), the minimum pulse width t3 is set to t□. To make it wider, the amplitude ratio needs to be set as follows. In Fig. 3, for example, when B is large, 1s is small as in (a),
In the case (b) where B is small, t becomes large. By changing B in this manner, the minimum pulse width B can be varied.

On the other hand, the modulated wave amplitude calculation circuit 14 in FIG. 1 is configured with the DC current value 14 as an input signal, as shown in FIG. 4(a).

Since the function generator has the characteristics shown in (b), the output signal, that is, the modulated wave amplitude B changes in accordance with the change in 14.

Since the carrier wave amplitude A is constant, the amplitude ratio is as shown in the figure (
It changes according to the characteristics shown in a) and (b). Therefore, even if the DC current value 14 changes, the inverter 5 can be operated with the minimum pulse width allowed at that time, so compared to the case where D is fixed at the rated value D1, as shown in Fig. 4(c).
As can be seen from , (d), electric m-operation can be performed over a wide range while reducing low-order harmonic components and keeping the distortion rate σ small.

FIG. 5 is a block diagram of main parts of a control circuit showing a second embodiment of the present invention, in which 13 is a comparison circuit, 15 is a modulated wave generation circuit, 16 is a carrier wave generation circuit, and 20 is a modulated wave amplitude calculation circuit. ,
26 is a limit circuit.

In the first embodiment, the amplitude B of the modulated wave e was directly controlled in the modulated wave amplitude calculation circuit 14, but the amplitude B of the modulated wave is constant, and the amplitude is controlled by the modulated wave amplitude calculation circuit 14.
Exactly the same effect can be obtained by limiting the output. In the embodiment shown in FIG. 5, by providing the limit circuit 26, the modulated wave e11 has an amplitude of B'.
A modulated wave limited to e, / is obtained. When comparing e and l with the output ec of the carrier wave generation circuit 16, the smaller the amplitude B', the larger the minimum pulse width t of the current pattern PTN in FIG. 3. By controlling the amplitude B' of the modulated wave in this manner, it is also possible to ensure the minimum allowable pulse width.

FIG. 6 is a block diagram of main parts of a control circuit showing a third embodiment of the present invention, in which 13 is a comparison circuit, 15 is a modulated wave generation circuit, 16 is a carrier wave generation circuit, and 20 is a modulated wave amplitude calculation circuit. It is. In the first embodiment, the amplitude ratio D (-B/A)
When changing , A is kept constant and B is made variable; however, if B is kept constant and A is made variable, exactly the same effect can be obtained as described below as the third embodiment. be able to.

In FIG. 6, if the output of the modulated wave amplitude calculation circuit 20 is set to A and is inputted to the carrier wave generation circuit 16, a carrier wave e of amplitude A can be obtained. The amplitude B of the modulated wave e1 is assumed to be constant. The relationship between the output A and the input 14 of the modulated wave amplitude calculation circuit 20 in this case will be explained below with reference to FIG.

FIG. 7 is a control characteristic diagram of a third embodiment of the present invention,
Figures (a) to (d) are characteristic diagrams similar to those in Figure 4, and Figure (13) shows the relationship between the amplitude ratio and its reciprocal 1/D, and (b) shows the relationship between the amplitude ratio and its reciprocal 1/D. Once the value of is determined (e)
The value of 1/D is determined, and since the amplitude B is constant, the value to be output is determined. The modulated wave amplitude calculation circuit 20 of FIG. 6 is a function generator having such characteristics.According to this embodiment, exactly the same effect as that of the first embodiment can be obtained.

In addition, in FIG. 6, the output AfewI of the modulated wave amplitude calculation circuit 20 may be used as a signal for changing the transmission frequency. That is, when the input 14 increases, the pulse width of the current pattern can be maintained at the minimum allowable pulse width by decreasing the output A and lowering the frequency of the carrier wave ec.

FIG. 8 is a block diagram of main parts of a control circuit showing a fourth embodiment of the present invention, in which 21 is an arithmetic circuit, 22 is an output multiplexer, 23 is a current pattern storage circuit, and 24 is a current pattern storage circuit. 2, 25 is a read demultiplexer, and 26 is a write demultiplexer. In this figure, the same reference numerals as in FIG. 1 indicate the same parts.

In the case of the embodiment shown in FIG. 8, the comparison between the modulated wave and the carrier wave is as follows.
The comparison circuit does not perform this, but the calculation circuit 21 performs the third
Based on the concept shown in FIG. Circuit [0 stored in 24
During normal operation, the pattern P T N & of either the current pattern storage circuit I23 or the current pattern storage circuit [24 is read out and input to the distribution circuit 12 according to the phase command θ*. At this time, the pattern having the minimum pulse width for the DC current value l obtained by the arithmetic circuit 21 is the current pattern storage circuit 1 which is not used at that time.
23 or written into the current pattern storage circuit [24]. A write demultiplexer 26 is a circuit that specifies which storage circuit to write to. The read demultiplexer 25 and the output multiplexer 22 are circuits that select a memory circuit to be used for PTN generation.

When the output pattern of the arithmetic circuit 21 is written to one memory circuit via the write demultiplexer 26, that memory circuit is used for control, and the next pattern is written to the other memory circuit by the write demultiplexer 26. According to this embodiment, it is possible to change the minimum pulse width of the current pattern PTN to a permissible value according to the DC current value ld, so that the same effect as in the previous embodiment can be obtained. Obtainable.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to ensure that the width of the pulse having the minimum width in the current pattern is greater than or equal to the allowable minimum pulse width of the switching element, regardless of the load conditions. Destruction can be prevented, lower-order shoulder inertia components of the motor current can be reduced, and the distortion rate can be reduced. Therefore, it is possible to drive the electric motor with high efficiency and low noise, and it is possible to provide an inverter control YaN with excellent functions without the drawbacks of the above-mentioned prior art.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the first embodiment of the present invention, Fig. 2 is a block diagram of a modulated wave generation circuit, Fig. 3 is an operating waveform diagram showing the relationship between modulated waves and carrier waves, and Fig. 4 is a block diagram of the present invention. A control characteristic diagram of the first embodiment of the invention, FIG. 5 is a configuration diagram of main parts of a control circuit showing a second embodiment of the invention, and FIG. 6 is a control circuit showing a third embodiment of the invention. 7 is a control characteristic diagram of a third embodiment of the present invention, and FIG. 8 is a diagram of a main part of a control circuit showing a fourth embodiment of the present invention. 1: AC power supply, 3: Forward converter, 5: Inverse converter, 7: 'W
1 motive, 8: speed detector, 9.11: gate amplifier, 1
2: Pulse distribution circuit, 13: Comparison circuit, 14: Modulated wave amplitude calculation circuit, 15: Modulated wave generation circuit, 16: Carrier wave generation circuit, 17: Vector calculation circuit, 18: Pulse distribution circuit 3: m unit 13: Comparison circuit, 6. :WIMMA em: ``Drum B:'MMM@
ee: Tsuden Figure 3 t,: Most l" series width
iI: Current ρ TN ρ TN: Lv main cap diagram is latent frying (a) TN ts ts ts: Maximum series width tsad: License maximum series width Fig. 4 20: Modulated wave near-width calculation circuit 15: Modulated wave generation circuit 16: Carrier wave generation circuit 13: Comparison circuit 26: Limit circuit (Figure 5) 24: Current flow memory circuit ■ 25: Demultiplexer for readout 4 d N” -

Claims (1)

[Claims] 1. A current comprising an AC power source, a forward converter that converts the AC current from the AC power source into a DC current, and an inverse converter that converts the DC current into an AC current, which is composed of a semiconductor switching element having a self-extinguishing function. an inverter control device for controlling a load connected to the output of the inverter, the inverter control device comprising: a detection means for detecting the state of the load; means for varying the minimum pulse width of the switching pulses supplied to the semiconductor switching element to ensure the allowable minimum pulse width of the semiconductor switching element according to the load conditions, and to reduce the harmonics and maintain the distortion factor small while controlling the load. An inverter control device characterized by being configured to be operable.