JPH0783613B2 - Inverter control device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a controller for a pulse width modulation PWM inverter having a sine wave as a fundamental wave, and particularly to an inverter for increasing the maximum output within a predetermined power supply voltage. The present invention relates to a control device for controlling.

[Prior art]

Generally, a sine wave signal is often used as a modulation signal compared with a carrier signal in a PWM inverter. First
The figure is a waveform diagram showing the relationship between a sine wave signal and a PWM signal with pulse width modulation. In FIG. 1, a is a carrier signal, b is a modulation signal for modulating the carrier signal a, and c is a pulse width-modulated PWM signal. D is the fundamental wave component included in the PWM signal C.

In this case, the comparator compares the carrier signal a and the modulated signal b, and the PWM signal c is output from the output terminal thereof. This P
The switching element of the inverter is turned on or off by the WM signal C, but the average instantaneous output is the fundamental wave component d.

Here, when a third harmonic signal of a / 6 is added to a sine wave signal having an amplitude a instead of the sine wave signal, the amplitude of the distorted wave obtained by this is as shown in FIG. Of the amplitude of the sine wave signal to become. Therefore, a PWM inverter that uses this distorted wave as a modulation signal has a higher output than one that uses a sine wave signal. Can be big. Moreover, since the third harmonic signal is canceled in principle in the three-phase AC circuit, there is no adverse effect due to the presence of the third harmonic signal.

However, PWM using a signal containing such harmonics
No important problems such as torque ripple and copper loss that occur when the electric motor is driven by the inverter are taken into consideration.

[Outline of Invention]

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional ones. By maintaining a waveform with multiple (6n-3) -order harmonics, the torque of the motor can be increased within the specified power supply voltage, and the torque ripple and harmonic copper loss can be kept low. An object is to provide a control device for an inverter.

Here, in order to understand the present invention well, the description of the waveform analysis of the modulated wave signal used in the present invention will be given.

FIG. 3 is a waveform diagram of a signal including a sine wave as a fundamental wave component and only a (6n-3) th order harmonic component. This modulated signal is Further, the period of π <θ2π is formed by inverting the sign of each waveform in the 0θπ period. Expanding this modulated signal by Fourier series, It is shown that it has only the (6n-3) th order harmonic component.

Here, a is the amplitude of the fundamental wave component, ω is the angular frequency of the fundamental wave component, and n is a positive integer of 1 or more.

FIGS. 4 and 5 are spectrum diagrams showing the respective harmonic components contained in the signals obtained by modulating the signals shown in FIGS. 2 and 3 using a triangular wave carrier. In the figure,
ωt is the angular frequency of the carrier wave, and ω is the angular frequency of the fundamental wave component of the signal wave.

The harmonic components that greatly affect the torque ripple and the copper loss of the electric motor are low-order harmonic components ωt-2ω and ωt-4ω having large energy, that is, relatively large amplitude. These harmonic components are waves that travel in opposite directions centering on the angular velocity ωt−3ω, so that they can cancel each other out if the amplitudes of these components are selected to be equal. That is, The smaller the parameter α shown by, the smaller the torque ripple. Here, the amplitude of the voltage component a _{ω t-4 ω} , a _ω
The reason why _{t-2 ω} is divided by the angular velocities ωt-4ω and ωt-2ω is that the angular velocity applied to the reactance appears because the current components serving as torque are compared. Also, the copper loss of harmonics is The smaller the parameter β shown by, the smaller the value. When these values of α and β are considered as parameters showing torque ripple and harmonic copper loss, respectively, the results are as shown in the table below. From the table, it can be seen that the values of α and β are smaller in the waveform of FIG. 3, so that the torque ripple and the harmonic copper loss can be reduced by deforming the signal wave in this way.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 8 is a block diagram of an inverter control device according to the present invention. In the figure, 1 is shown in FIG. 3, a = 1
Memory RO that stores the modulated signal as data
It is M. 2 to 4 are multipliers for multiplying the modulation signal from the memory 1 by the amplitude a, 5 are carrier wave generators for generating carrier wave signals of triangular waves, and 6 to 8 are outputs from the multipliers 2 to 4 and are compared with carrier wave signals. A modulator that outputs a PWM signal, 9 is a three-phase inverter that receives the PWM signal, and 10 is a three-phase electric motor that is a load of the inverter 9.

Next, the operation will be described. Maximum amplitude from memory 1 with phase signal θ as address The modulated signal of is read and three phases are generated. Multipliers 2-4
Is the modulation signal and voltage command A that controls the gain of the modulation signal
Multiply by and the amplitude A modulated signal limited to is obtained. On the other hand, the carrier wave generator 5 has a frequency (3 + 6n) times the frequency of the modulation signal (for example, 27
The carrier wave signal of the triangular wave synchronized with the modulation signal is generated at the frequency of 2 times. The carrier wave signal and the modulation signal are not shown because they can be synchronized by a usual means.

The comparators 6 to 8 generate a three-phase PWM signal by comparing the carrier wave signal with the modulation signal, thereby operating the inverter 9. The inverter 9 supplies the drive current controlled by the PWM signal to the electric motor 10. Although this drive current includes low-order harmonic components as described above, it can generate a large torque in the electric motor 10 and can keep torque ripple and copper loss of harmonics low.

In addition to the above-described embodiment, there are countless modulated signals containing only the (6n-3) th harmonic component. Figure 6 shows the amplitude of the fundamental wave It is a wave form diagram which shows the waveform of the modulation signal containing only the (6n-3) th order harmonic component. The (6n-3) th harmonic component is the period of the fundamental wave component. It is a symmetric odd-function wave with a period of. Therefore, it is sufficient to consider a period of 1/4 of the period of the third harmonic having the maximum period in the harmonic, that is, a 1/12 period of the fundamental wave period. In FIG. 6, the shaded area is the range in which the waveform of the 1/12 cycle of the modulated signal to be obtained exists.

Among these modulation signals, the one with the least distortion has the waveform ▲ v ^* _u ▼. , And the modulation signal at that time is as shown in FIG. This modulated signal has phase θ The period of The period of ,And The period of Waveform, and during the period of π <θ2π,
It is a waveform obtained by inverting the sign of each waveform in the π period.

In addition, the modulation signal with the largest distortion has a waveform of ▲ v ^* _u ▼ Becomes constant, and the modulation signal at that time has the waveform of FIG. 3 shown in the above embodiment.

As described above, there are an infinite number of modulated signals having only the (6n-3) th order harmonic component, and the waveform shown in FIG. 2 is naturally included therein.

Considering only the effect of the torque ripple among these many waveforms, it is possible to obtain a more effective waveform than the above-mentioned embodiment. That is, there is a waveform in which the parameter α corresponding to the torque ripple can be set to zero.

Further, if the waveform of the modulation signal is as shown in FIG. 7, the waveform form is very simple, so that the complexity of the circuit for generating the modulation signal is reduced.

〔The invention's effect〕

As described above, according to the present invention, the amplitude of the modulation signal is changed to the fundamental sine wave. Since it has a waveform containing a plurality of (6n-3) th order harmonics, the torque of the electric motor can be increased within a predetermined voltage range without increasing torque ripple and harmonic copper loss. effective.

[Brief description of drawings]

FIG. 1 is a waveform diagram of the operation of a conventional control device, FIGS. 2 and 3 are waveform diagrams of a modulation signal containing a harmonic component, and FIGS. 4 and 5 are shown in FIGS. FIG. 6 is a frequency spectrum diagram of a modulation signal, FIG. 6 is a waveform diagram for analyzing a modulation signal containing a harmonic component, FIG. 7 is a waveform diagram of the modulation signal, and FIG. 8 is a block diagram of a control device according to an embodiment of the present invention. Is. 1 ... memory, 2,3,4 ... multiplier, 5 ... carrier generator, 6,7,8 ... comparator, 9 ... inverter, 10 ... motor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Kamiyama 1-2-2 Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Electric Co., Ltd. Control Mfg. Co., Ltd. (56) Reference JP-A-60-200771 (JP, A)

Claims (1)

[Claims] 1. A pulse train signal pulse width modulated is generated by comparing a carrier signal and a modulation signal, the operation of an inverter is controlled by this pulse train signal, and a drive current corresponding to the modulation signal is supplied to a load. In the control device of the inverter to control, the amplitude of the fundamental wave component is a constant multiple, a memory that stores the data of a signal obtained by superimposing an odd number and a plurality of harmonic components on the fundamental wave component as the modulation signal, A multiplier for controlling the gain of the data read from the memory, and a comparator for comparing the output of the multiplier with the carrier signal to generate the pulse train signal are provided. The amplitude of And the odd harmonic component is a harmonic component of “(6n−3), where n = 1, 2 ...”, and the modulated signal has a phase θ. And a waveform in which the sign of each of the waveforms in the 0θπ period is inverted during the period of π <θ2π.