JPH098618A - Pulse width modulation signal generator - Google Patents

Abstract

(57) [Summary] [Construction] The carrier peak signal output from the carrier signal generation unit 12, the carrier up / down signal 13, and the comparison signal which determines the magnitude of the carrier signal and the modulated wave signal output from the comparator 3 The pulse generator 4 that receives the input determines the output level of the pulse width modulation signal from the comparison signal level when the carrier peak signal is generated and the comparison signal level and the up / down signal level immediately after the change of the comparison signal. [Effect] Since a correct level signal can be output without applying a narrow pulse width to the switching element of the power converter and even during overmodulation, destruction of the switching element and a correct level voltage with less output distortion Can be output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse width modulation signal generator.

[0002]

2. Description of the Related Art Conventionally, in a pulse width modulation signal generator for comparing a carrier wave and a modulated wave, a method of preventing the output of a pulse having a narrow width is to generate a pulse depending on whether the carrier signal is increasing or decreasing. A method for determining the output level of a width modulation signal is known, and an example thereof is Japanese Patent Laid-Open No. 6-18870.
There is a pulse width modulator described in Japanese Patent No. 2 publication.

[0003]

In the pulse width modulation signal generator according to the above-mentioned prior art, when the carrier wave is increasing, the output signal is changed to the high level (or low level) at the time when the carrier wave signal and the modulated wave signal coincide with each other. ), And conversely, when the carrier wave is decreasing, the output signal is set to low level (or high level). That is, a pulse width of a narrow width is prevented by fixing the output level at the time when the carrier wave and the modulated wave coincide with each other due to the up / down movement of the carrier wave. However, in the case of overmodulation in which the modulated wave signal is larger than the carrier wave signal, the carrier wave signal and the modulated wave signal do not match. Therefore, when the modulated wave signal changes stepwise and is overmodulated, the output level of the pulse width modulated signal becomes opposite, and there is a problem that a pulse of a correct level cannot be output.

An object of the present invention is to prevent the output of a narrow pulse which causes a breakdown of a switching element of a power converter and a voltage distortion even when a modulated wave changes stepwise. The purpose is to output a pulse width modulation signal of the correct level even when overmodulation occurs.

[0005]

In order to achieve the above object, the present invention provides an up-down signal indicating whether a carrier signal is increasing or decreasing and a peak signal indicating a peak point of the carrier signal in addition to the carrier signal. And a comparison means for determining the magnitude relation between the carrier wave signal and the modulated wave signal and outputting a comparison signal as a level signal, and an up-down signal, a peak signal and a comparison signal as input, There is provided pulse generation means for determining the output level of the pulse width modulation signal according to the comparison signal level, and for determining the output level of the pulse width modulation signal from the comparison signal level immediately after the change of the comparison signal and the up / down signal level.

[0006]

The up / down signal output by the carrier wave generating means is a level signal which, for example, outputs a high level while the carrier wave signal is increasing, and outputs a low level when the carrier wave signal is decreasing. The peak signal outputs a pulse signal at both the upper peak point where the carrier wave changes from increase to decrease and the lower peak point where the carrier wave changes from decrease to increase. The comparing means determines the magnitude relationship between the carrier wave signal and the modulation wave signal, and outputs a high level, for example, when the modulation wave signal is large, and outputs a level signal which is a low level when the modulation wave signal is small. The pulse generation means that receives these three types of up-down signals, peak signals, and comparison signals must determine the output level of the pulse generation means from the level of the comparison signal immediately after the comparison signal changes and the level of the up-down signals. Then, as for the output pulse level of the pulse generating means at the time when the comparison signal changes, only a specific output level can be obtained according to the up or down of the carrier signal. That is, during the up period or down period of the carrier wave signal, the change occurs only once at most, so that the operation is performed so as to prevent the generation of the output pulse having a narrow width. Further, by determining the comparison signal level at the time of the peak signal generation as the output level of the pulse generating means, it is possible to output an accurate comparison signal level for each half cycle of the carrier signal even during overmodulation.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pulse width modulation signal generator to which the present invention is applied will be described below with reference to FIG. The carrier wave signal generation unit 1 has a triangular wave carrier wave signal 11, a pulsed peak signal 12 indicating upper and lower peak points of the carrier wave signal, and an up / down signal 13 indicating whether the carrier wave signal is increasing or decreasing. Is output. In addition, the modulated wave signal generator 2 outputs a sinusoidal modulated wave signal 21 which is a control signal.
The comparator 3 inputs the carrier wave signal 11 and the modulated wave signal 21,
A comparison signal 31 that discriminates the magnitude of these two signals is output. The pulse generator 4 receives the peak signal 12, the up / down signal 13, and the comparison signal 31 and outputs the pulse width modulation signal 41. An embodiment of a specific detailed circuit of the pulse generator 4 is shown in FIG. Shown in. First, the comparison signal 31
Becomes a signal shifted by one cycle of the reference clock by the flip-flops 51 and 52, and each of them is an EXOR circuit 53.
And becomes an edge signal 42 having a pulse width corresponding to one cycle of the reference clock. That is, the edge signal 42 is a pulse signal indicating immediately after the comparison signal 31 changes, and becomes the clock signal of the flip-flop 57 that outputs the pulse width modulation signal 41. Further, the comparison signal 31 is the up / down signal 13
Becomes an input to the EXOR circuit 54 together with the EXOR circuit 5
If the comparison signal 31 and the up / down signal 13 are at the same level 4, the change permission signal 43 is set to the low level
The circuit 55 outputs the edge signal 42 to the flip-flop 5
It is masked that it is input as the 7 clock signal.
The output clock 44, which is the clock signal of the flip-flop 57, is the edge signal 4 which is permitted by the OR circuit 56 by the carrier peak signal 12 and the change permission signal 43.
Both signals will be two. Since the data input of the flip-flop 57 is the comparison signal 31, the output clock 4
The comparison signal level when 4 is input becomes the level of the pulse width modulation signal 41. Next, the operation of this embodiment will be described with reference to the time chart of FIG. FIG. 3 shows an operation waveform when the modulated wave signal changes stepwise. In this case, the comparator signal 31 generates a pulse having a narrow width between the points A, B and C. However, in the edge signal 42, the up / down signal 13 and the comparator output 31 cause EXO.
Since the R change permission signal 43 becomes low level at the point B, the output clock 44 is masked at the point B, so that a pulse having a narrow width is not generated in the output pulse width modulation signal 41. The peak signal 12 is also superimposed on the output clock 44 at the point D, and the level of the comparator output 31 at the peak time D is output. Next, operation waveforms in the case of overmodulation in which the modulated wave signal is larger than the carrier wave signal will be described with reference to FIG. In FIG. 4, the modulated wave signal changes stepwise at point F and is overmodulated, so that the comparator signal 31 generates a pulse having a narrow width between points E and F. Also in this case, since the output clock 44 at the point F is masked by the same operation as in FIG. 3, a pulse having a narrow width is not generated in the pulse width modulation signal 41. Further, the peak signal 12 is also superimposed on the output clock 44 at the point G, and the comparator output 31
The correct level of is output. Therefore, even if the modulated wave is overmodulated, a pulse width modulated signal 41 having a correct level can be output without generating a pulse having a narrow width.

In this embodiment, since it is possible to cope with overmodulation without outputting a pulse having a narrow width, it is possible to realize a power converter having a high voltage utilization rate.

In this embodiment, a triangular wave is used as the carrier signal, but a sawtooth wave can also be applied, and the modulating wave signal can be various waveforms such as a sine wave and a trapezoidal wave. The good news is clear.

[0010]

According to the present invention, since a pulse having a narrow width, which causes the destruction of the switching element used in the power converter, is not applied, it is possible to realize the protection against the destruction of the switching element and to prevent the overmodulation. However, since a correct level signal can be output, a correct level voltage with little output distortion can be output.

[Brief description of drawings]

FIG. 1 is a block diagram of a pulse width modulation signal generator to which the present invention is applied.

FIG. 2 is a block diagram of a pulse generation unit in FIG.

FIG. 3 is a time chart explaining the operation of FIG.

FIG. 4 is a time chart explaining the operation of FIG. 1 during overmodulation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Carrier wave signal generation part, 2 ... Modulation wave signal generation part, 3 ... Comparator, 4 ... Pulse generation part, 51, 52 ... Flip-flop, 53, 54 ... EXOR circuit, 54 ... AND circuit, 5
6 ... OR circuit, 57 ... Flip-flop.

Claims (2)

[Claims] 1. A carrier wave signal generating means, a modulated wave signal generating means which is a control signal, and a comparing means for comparing a carrier wave signal output by the carrier wave signal generating means and a modulated wave signal output by the modulated wave signal generating means. In a pulse width modulation signal generator that performs pulse width modulation using a comparison signal that determines the magnitude of the carrier wave signal and the modulated wave signal by the comparison means, the comparison signal and the carrier wave signal are increasing or decreasing. A pulse characterized by comprising pulse generation means for inputting an up-down signal indicating whether or not, and determining the output level of the output pulse from the comparison signal level and the up-down signal level immediately after the change of the comparison signal. Width modulation signal generator. 2. In order to determine the output level of the pulse generating means according to claim 1, the output level of the output pulse is determined from the comparison signal level and the up / down signal level immediately after the change of the comparison signal. A pulse width modulation signal generator for determining an output level of an output pulse according to the comparison signal levels at the upper and lower peak points of the carrier signal.