JPS6027272B2 - Control method of pulse width modulation inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling a pulse width modulation inverter so that the output voltage waveform is symmetrical.

In FIG. 1, a shows the principle structure of the main circuit of a three-phase pulse width modulation inverter, and b shows a specific example of the structure. In Figure 1a, each phase output terminal R, S of the inverter
, T are alternately connected to the positive terminal and negative terminal of the DC power source d by switching elements U and X, V and Y, W and Z, respectively. The figure shows an example of Toyukima's achievement of starting and killing the problem, and includes two main thyristors T,, T2, diodes D,, D2 connected in anti-parallel to each main thyristor, and a commutating capacitor C common to both main thyristors. It can be composed of a commutation reactor L, and arc-extinguishing auxiliary thyristors L and T4 attached to each main thyristor.

Pulse width modulation control in such a pulse width modulation inverter is generally performed by comparing the control signal Vc, which defines the magnitude and frequency of the desired output voltage, with the modulation signal Vm, which defines the average number of switching operations per half cycle of the output voltage. It is done.

In this case, for example, a sine wave signal having a desired output voltage magnitude and frequency is used as the control signal Vc, and a triangular signal having a sufficiently larger frequency than the sine wave signal is used as the modulation signal Vm. do. Figure 2 shows three-phase sine wave control signals Vc(R), Vc(S), Vc(
The pulse width modulated output voltages VPT(R), VPT(S), and VPT(T) generated at the output terminals R, S, and T by comparing the triangular wave modulation signal Vm with the triangular wave modulation signal Vm are illustrated.

These output voltages VPT(R), VFT(S), VPT(T
) represents the voltage at the output terminals R, S, and T of each phase with reference to the midpoint 0 of the DC voltage source Ed. In FIG. 2, at a level matching point between the three-phase sinusoidal control signals Vc(R), Vc(S), Vc(T) and the modulation signal Vm, the switching elements V and X in FIG. 1a, V and Y, The switching of W and Z, or thyristors T and L in FIG. 1b, takes place. Through such switching control, the output terminals R, S, and T of each phase receive output voltages VPT(R) and VPT with a pulse width modulated rectangular pulse width as shown in Fig. 2.
(S) and VPT(T) are generated. Since the switching point of the switching element or thyristor is carried out at a point where the levels of the control signal Vc and the modulation signal Vm match, as shown in FIG. 2, the switching point changes depending on the amplitude of the control signal Vc.

Therefore, the output voltage of the inverter is adjusted by changing the amplitude of the control signal Vc. Furthermore, in a pulse width modulation inverter with a three-phase output as shown in FIG. Synchronization is performed using an integer multiple of . Based on this, FIG. 2 shows an embodiment in which the frequency of the modulation signal Vm is set to six times the frequency of the modulation signal Vc (hereinafter referred to as frequency ratio). However, in such a conventional pulse width modulation inverter, when the frequency ratio is an even multiple as shown in FIG. 2, the output voltages VPT(R) and VPT(
S) and VPT(T) are rectangular voltages, and when looking at their one-cycle waveforms, they are point symmetrical about a half-cycle point, that is, they are expressed as odd functions.

Therefore, when such an output voltage waveform is subjected to Fourier analysis, it contains extremely low-order harmonic components. If this harmonic component is large, it will cause torque pulsation when coupled to a rotating machine or the like, leading to overheating of the crimping. Additionally, some measuring instruments produce errors if there is harmonic distortion in the alternating current voltage. For this reason, it is desired that the output voltage of the inverter has little harmonic components. In view of the above, the present invention provides a voltage control method that prevents the presence of low-order harmonic components, particularly even-order harmonic components, in the output voltage of an inverter operated at an even number multiple of the frequency ratio. The purpose is to

According to the invention, this object is achieved by comparing the control signal with a modulation signal whose phase differs by 180 degrees in the positive and negative half periods of the control signal.

That is, according to the above method, the output voltage waveform is shown as the same waveform, ie, a symmetrical waveform, although the polarity differs every half cycle. When such an output voltage waveform is subjected to Fourier analysis, the average value of even-numbered harmonics becomes zero in one cycle. Next, the present invention will be explained in detail based on embodiments shown in the drawings.

FIG. 3 illustrates switching by the voltage control method according to the present invention, and similarly to FIG. 2, the control signals Vc(R), V
c(S), Vc(T), modulation signal Vm, output voltage VPT
(R), VPT(S), VPT(T)(T) are shown,
Further, a modulating signal V' whose phase differs by 180 degrees from the modulating signal Vm is generated.
m is shown.

In addition, the modulation signal Vm and the control signals Vc(R), Vc(S),
The frequency ratio with Vc(T) is 6, which is an even multiple of 3, as described above.
It is. In FIG. 3, according to the invention, the control signal Vc
(R), Vc(S), and Vc(T) are compared with the modulation signal Vm when the value is positive, and with the modulation signal V'm when the value is negative.

Therefore, in the switching control according to the present invention, the output voltage VPT
(R), VPT (S), and V gate (T) are shown as symmetrical waveforms when the positive and negative signs are removed for each half cycle. In Fig. 3, at the switching point of the modulation signals Vm and V'm, a delay element such as a timer is used to control the modulation signals Vm and V'm in order to ensure that the switching element or thyristor is turned on and off. A comparison is made with the signal Vc. FIG. 4 shows an example of a specific circuit configuration of the voltage control method according to the present invention shown in FIG.

In the figure, 1 inputs a single-phase sine wave control signal Vc,
This control signal Vc is a three-phase sine wave control signal Vc(R),
Single-phase to three-phase converter 2 converting to Vc(S), Vc(T)
is a 180° phase inversion of the modulation signal Vm to obtain a modulation signal V′m
The comparison intensifier, CP, for obtaining the control signal Vc(R)
CP2 is a control signal Vc(R).
CP3 is a comparator for comparing the control signal Vc(R) and the modulation signal V'm, and NR is a comparator for comparing the control signal Vc(R) and the modulation signal V'm.
indicates a NOR circuit, Ts indicates a timer, AND, , AND2 indicate an AND circuit, and OR indicates an OR circuit. Control signal Vc(
Since the operations for control signal Vc(R), Vc(S), and Vc(T) are the same, only the control signal Vc(R) will be described here.

First, the control signal Vc (R
) are added to the respective comparators CP, ~CP3. Comparator CP. In the control signal Vc(R), the control signal Vc(R) is compared with the "0" level to determine whether it is positive or negative. If the control signal Vc(
If R) is positive, "1" is added to the AND circuit AND, and "0" is added to the AND circuit AND2. The output of the comparator CP2 is input to the AND circuit AND, and the output of the comparator CP2 is input to the AND circuit AND2.
The output of each is added. Therefore, the control signal Vc
When (R) is positive, the output of the comparator CP3, that is, the comparison result between the control signal Vc(R) and the modulation signal Vm, and when the control signal Vc(R) is negative, the output of the comparator CP3, that is, The comparison results between the control signal Vc(R) and the modulation signal V'm are respectively applied to the switching element (thyristor) from the output terminal R' of the OR circuit PR as a control pulse width. In particular, the output of the comparator P, which is added to the AND circuit AND2, is passed through a NOR circuit NR and a timer Ts. By doing this, the control signal Vc
At the time when the polarity of (R) is switched, a control pulse with a sufficient on/off time is generated to turn on or off the switching element (thyristor) determined by the timer Ts. This means that the control signal Vc in FIG.
At the time when the polarity of (R) switches, the output voltage VPT
The previous state of (R) is shown by switching once. Control signals Vc(S) and Vc(T) are also controlled by circuits # and A3 having the same configuration as circuit A. As described above, according to the present invention, by inverting the modulation signal by 180 times in the positive half cycle and the negative half cycle of the control signal, even when the frequency ratio is an even number, the output voltage waveform is made into a symmetrical waveform, and even harmonics can be reproduced. Since wave components can be removed, the filter can be made smaller.

In the description of the embodiment of the present invention, the case was explained with three phases and a frequency ratio of 6, but in the case of three phases, the frequency ratio was 1.
Of course, the voltage control method according to the present invention can also be applied to cases such as 2, 18, . . . .

Further, in the above explanation, it is preferable that the control signal is a sine wave and the modulation signal is a triangular wave, but the symmetrical modulation method according to the present invention can be applied to other waveforms, such as a rectangular wave or a square wave.

Furthermore, the same applies to single-phase pulse width modulation inverters, and when the frequency ratio is set to an integer multiple of two, a part of the output voltage is removed by switching the modulation signal in the positive and negative half cycles of the control signal. Removal of harmonic components is achieved.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of the main circuit configuration of a conventional pulse width modulation inverter, Fig. 2 is a diagram showing a conventional pulse width modulation method, and Fig. 3 is a voltage control method for a pulse width modulation inverter according to the present invention. FIG. 4 shows a specific circuit configuration diagram for implementing the voltage control method for a pulse width modulation inverter according to the present invention. Vc (R), Vc (S), Vc (T)...control signal, Vm
, V′m...Modulation signal, VM(R), VPT(S),
V.P. (T)...Inverter output voltage, 1...Single-phase to three-phase converter, 2...Proportional multiplier, CP,, CP2, CP
3... Comparator, Ts... Timer, NR... NOR circuit,
AND,,AND2...AND circuit, OR...OR circuit. Figure 1 Figure 2 Figure 3 Figure O 4

Claims (1)

[Claims] 1. In a pulse width modulation inverter that controls the pulse width of an output voltage based on a comparison result between a control signal and a modulation signal having a frequency ratio of an even number, a positive half period and a negative half period of the control signal are A method for controlling a pulse width modulation inverter, characterized in that, as the modulation signals to be compared, different signals whose phases are inverted by 180° are used.