JPS6328276A - Controller of three-phase pwm inverter - Google Patents

Abstract

PURPOSE:To obtain triple harmonic wave signals from three-phase voltage command signals with given frequency and ampltude in a simple circuit, by using the sum voltage of or means value voltage between the maximum value synthesizing voltage and the minimum value synthesizing voltage so as to obtain the triple harmonic wave signals. CONSTITUTION:The three-phase sinusoidal wave voltage command signals eA-eC are connected to a three-phase all-wave rectification circuit composed of diode bridges. The potential at point A becomes the maximum value signal eH of each phase, while the potential at point B the minimum value signal eL of each phase. By resistances R1 and R2 the sum of the maximum value signal eH and the minimum value signal eL are found, so that the triple harmonic wave signals can be obtained. Modulated waveforms are made by synthesizing these triple harmonic wave signals and carrier waves and then by synthesizing them with the original waves, the PWM control of the inverter can be implemented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for a voltage source three-phase PWM inverter used in a variable speed drive device for an AC motor or an AC uninterruptible power supply.

[Conventional technology]

A voltage type three-phase PWM inverter is used when driving an AC motor at variable speed or to obtain an AC voltage of a constant frequency from a generator.

FIG. 7 shows a block diagram of a typical voltage source three-phase PWM inverter, and FIG. 8 shows waveforms at various parts.

In FIG. 8, ta+ indicates the relationship between a three-phase sine wave that is a signal wave and a carrier wave that is a triangular wave, fbl, (cl,
fdl indicates the pulse width modulation waveform of each phase.

In these figures, the fundamental wave component of the phase voltage with respect to the neutral point n of the DC circuit, taking the U phase as an example, is eu −'Ak
Eacsinωt (where k is the modulation rate).

Also, the line voltage between UV is euv=! 4k Edt
(Sjnωt-5incωt-120°))-Fushi/2
・kE, ts4 direct ωt+30°), and even in the case of k=1, the peak value of the output line voltage is
It is not possible to fully utilize the DC voltage, which only produces 2 (=, 0.87) times the voltage.

As a final measure to solve this problem, a method was developed in 1983 to superimpose harmonics (3rd harmonics) of 3 times the frequency (and its harmonics) on the PWM command signal waveform. He is widely known for his presentation at the National Conference of the Institute of Electrical Engineers of Japan. For a three-phase inverter, this will fit the tertiary and its multiples.
The wave component becomes the same II (component, and does not appear in the line voltage,
1 in the load! This takes advantage of the fact that as long as the ↓ point is in the floating Φ) state, it does not affect the current.

FIG. 9 shows the effect of triple harmonic superposition using waveforms. In the same figure, eu and ev are phase voltages, "lI'+eV° is phase voltage e
. + "This is the waveform after injecting the third harmonic of the amplitude of 176 of the fundamental wave into V. When e u' = ev'
Since the peak value of is lower than the phase voltage e, ev, eu
, it is possible to raise the ev's beak (hold it until the end).

e. +, e, = are the waveforms after lifting. Also, eu-v is the line voltage when the third harmonic is not included, eu
Hl-v・, is the line voltage after injecting the third harmonic,
In the latter case, the voltage increases by 2/fuki=], 15 times as much as the former.

[Problem that the invention seeks to solve]

However, this proposal remains theoretical, and no proposal has been made as to how to actually achieve it. Generally, in order to obtain the third harmonic, the formula 3 of the trigonometric function is applied, a fundamental wave cube circuit and a summation circuit are combined, and a correction circuit is added in case each phase is unbalanced. Etc. is required, quite a bit? It is necessary to have a JfM composition and four nodes.

As described above, in order to superimpose the third harmonic, there is a problem in that, in practical terms, it is not easy to generate a signal of the third harmonic.

If the voltage has a predetermined frequency and amplitude, the signal generator can be programmed to obtain a waveform with triple harmonics superimposed, but any frequency can be used.

Obtaining the third harmonic from a three-phase voltage command signal with amplitude is not easy.

The present invention has been made in view of these current problems, and aims to obtain triple harmonics by a simple method.

[Means for solving problems]

In order to achieve this object, the three-phase PWM inverter control device of the present invention provides a voltage that combines the maximum value and a voltage that combines the minimum value of the amplitudes of each phase of the voltage command signal of the three-phase sine wave PWM inharc. , and the sum voltage or average (
means for obtaining a third harmonic signal of the voltage command signal using the lYf voltage; and superimposing the third harmonic signal and the voltage command signal to increase the peak value of the output line voltage to the DC m line voltage. It is characterized by comprising a means for disposing of the dead body.

As a method for obtaining a triple harmonic signal, a three-phase sinusoidal voltage command signal can be subjected to full-wave rectification, and the neutral point potential of the DC output circuit can be made into a triple harmonic signal.

[Operation] FIG. 1 shows the basic configuration of triple harmonic synthesis according to the present invention. This circuit is composed of a circuit that takes the maximum value and minimum value of the three-phase sinusoidal voltage command signal and a sum signal e3 of these values. These circuits can be easily constructed using operational amplifiers.

eA+"s, ec are three-phase sinusoidal voltage command signals.

When the maximum and minimum values of these three-phase sinusoidal voltage command signals eA, e@, and ec are taken by the maximum value circuit and the minimum value circuit, the values are shown by thick lines in FIG. 2, respectively.

e5. becomes. Furthermore, since these maximum value signal eH and minimum l1fi signal e have a frequency three times that of eA, ell, and ec, they are effective as third harmonics to be superimposed. Also, conveniently, the origin of eA, em, and ec (
Since the origin of (zero cross) and e2 coincide, the symmetry of the waveform after superimposition is ensured.

In this way, the third harmonic signal can be easily obtained.

〔Example〕

Examples of the present invention will be described below.

FIG. 3 shows the first embodiment, in which three-phase sinusoidal voltage command signals eA, eB, and e (are connected to a three-phase full-wave rectifier circuit composed of a diode bridge.The Δ point potential becomes the maximum value signal e of each phase, and the four-point potential also becomes the minimum value signal eL (see Figure 2)., - maximum (+
/! A third harmonic signal e3 can be obtained by adding the signal ell and the minimum value signal e1.

FIG. 4 shows a second embodiment of the present invention which compensates for the voltage drop due to dimation when the signal voltage Y(: is low). After compensating for the voltage below the bridge 7, the operational amplifier AI calculates the sum of the maximum value signal eu and the minimum value signal e, thereby obtaining the third harmonic signal e3.

FIG. 5 shows an example of a circuit that synthesizes 3tfl harmonics using the circuit of FIG. 3, synthesizes them into the original signal wave, and performs PWM control f311. As shown in Figure 6, the third harmonic e3 and &
By combining the transmitted wave and the operational amplifier 0PA2, fb
By creating a Bozu modulation waveform on l and combining it with the original signal wave, the inverter's PWM control can be achieved. 3ff can be performed.

〔Effect of the invention〕

As explained in 1-1 above, in the present invention, the triple feather wave signal is obtained using the sum voltage of the maximum value composite voltage and the minimum value composite voltage or the average M voltage. This allows any frequency with a simple circuit.

It is possible to obtain a triple harmonic signal from a three-phase voltage command signal having an amplitude, increase the output voltage, and improve the output in a device that uses the same current.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the Hiroki configuration of the present invention, Fig. 2 is a waveform diagram showing its operation, Fig. 3 is a circuit diagram showing the first embodiment of the invention, and Fig. 4 is a block diagram showing the Hiroki configuration of the present invention. A circuit diagram showing the second embodiment, FIG. 5 is a circuit diagram for performing PWMli control using the control device of the present invention, FIG. 6 is a waveform diagram showing the operation of the circuit, and FIG. 7 is a conventional PWM control. A circuit diagram showing the control circuit configuration,
FIG. 8 is an operating waveform diagram of the same circuit, and FIG. 9 is a waveform diagram showing the effect when using third harmonic.

Claims (1)

[Scope of Claims] 1. Means for obtaining a voltage that synthesizes the maximum value and a voltage that synthesizes the minimum value of the amplitudes of each phase of the voltage command signal of a three-phase sine wave PWM inverter, and a method for synthesizing these maximum values. means for obtaining a third harmonic signal of the voltage command signal using a sum voltage or an average value voltage of the voltage and the minimum value composite voltage;
A control device for a three-phase PWM inverter, comprising means for superimposing a harmonic signal and the voltage command signal to increase a peak value of an output line voltage to a DC bus voltage. 2. The three-phase sine wave voltage command signal is subjected to full-wave rectification, and the neutral point potential of the DC output circuit is obtained as a third harmonic signal. PWM
Inverter control device.