JP2002064983A - Power supply voltage fluctuation canceling pwm circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate for the fluctuating output voltage, without depending on negative feedback, resulting from the fluctuating main power source voltage of a PWM power converter because it is difficult to stably apply a large amount of feedback to the output voltage. SOLUTION: An oscillator 3 is controlled to generate a square wave of a carrier frequency to operate a half-bridge inverter 4. The square wave of the inverter 4 is applied to an integration circuit 7 via a transformer 5. This transformer 5 is provided to insulate between the main power source 1 and a control circuit and to supply the square wave 6 of an adequate amplitude to the integration circuit 7. A PWM signal 11 can be obtained through comparison of an input signal 9 and a PWM carrier 8 in a comparator 10. This PWM signal 11 is used to originate a control signal of a power converting circuit 12. This power converting circuit 12 switches the main power source 1 to obtain an output 13 of the PWM power converter. As a result, fluctuation of the main power source voltage can be canceled by adding a small capacity inverter to the PWM power converter. More stable operation and sufficient effect can be attained than with a method utilizing negative feedback of an output voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a PWM circuit for compensating fluctuations in a main power supply voltage.

[0002]

2. Description of the Related Art A PWM power converter applied to a stabilized DC power supply, an inverter, a general-purpose power amplifier, etc., obtains an output by switching a DC power supply as a main power supply. The main power supply voltage is originally assumed to be constant, but actually fluctuates due to output current, external factors, and the like. When the main power supply voltage changes, the output voltage also changes.
Conventionally, in order to compensate for this, means of negative feedback to the input of the output voltage has been taken. Negative feedback is a commonly used means in analog circuits, but is difficult to apply to PWM power converters. The output of the PWM power converter includes a harmonic corresponding to the PWM carrier, and a low-pass filter is used to attenuate the harmonic. Since the phase rotation of the output occurs as a side effect of the low-pass filter, it is difficult to apply a large amount of negative feedback stably. For this reason, it has been difficult to sufficiently compensate for fluctuations in the main power supply voltage.

[0003]

SUMMARY OF THE INVENTION A fluctuation of an output voltage accompanying a fluctuation of a main power supply voltage in a PWM power converter is compensated without using negative feedback of the output voltage.

[0004]

SUMMARY OF THE INVENTION The amplitude of a PWM carrier is proportional to the mains supply voltage.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A triangular wave, a saw-tooth wave, or the like is used as a carrier wave of PWM. In any case, the modulation degree is defined as follows: modulation degree = amplitude of input signal / amplitude of PWM carrier wave. The output voltage of the PWM power converter is represented by the following equation using the modulation factor: output voltage = modulation factor × main power supply voltage. This equation shows that the output voltage is proportional to the main power supply voltage. However, here, if the amplitude of the PWM carrier = main power supply voltage × constant, then the modulation degree = the amplitude of the input signal / main power supply voltage / constant, and the output voltage = the amplitude of the input signal / constant, and the output voltage becomes the main power supply No longer depends on voltage. The constant is a proportional constant between the main power supply voltage and the amplitude of the PWM carrier. Conventionally, the modulation degree of PWM is determined by the operating condition of the control circuit irrespective of the main power supply voltage, so that the output voltage also changes with the fluctuation of the main power supply voltage.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Although the present invention is based on the above simple principle, there are many possible implementation methods. FIG. 1 shows one embodiment of a PWM power conversion device using the present invention. The transmitter 3 generates a square wave having a carrier frequency. This signal causes the half-bridge inverter 4 to operate. Since this inverter only produces a carrier wave, a large power output is not required. Further, since switching is performed at the carrier frequency, switching and beat of the original power conversion circuit do not occur. The amplitude of the square wave output from the inverter 4 becomes half of the main power supply voltage 2. This square wave is connected to an integrating circuit 7 via a transformer 5. The transformer 5 is used to insulate the main power supply 1 from the control circuit and to supply a square wave 6 having an appropriate amplitude to the integration circuit 7. If the insulation between the main power supply 1 and the control circuit is not required, the transformer 5 can be omitted. The output of the integration circuit 7 becomes a triangular wave and is used as the PWM carrier 8. As described above, the portion from the transmitter 3 to the integration circuit 7 is the PWM carrier generator that characterizes the present invention. The subsequent part is a general configuration of the PWM circuit and the PWM power converter. The input signal 9 and the PWM carrier 8 are compared by a comparator 10 to obtain a PWM signal 11. A control signal for the power conversion circuit 12 is generated based on this signal, and the power conversion circuit 12 switches the main power supply 1 to obtain an output 13 of the PWM power conversion device.

FIG. 2 shows operation waveforms of the present invention. A state in which the main power supply voltage 2 decreases is shown as an example. Although the frequency of the square wave 6 obtained from the output of the inverter 4 is constant, its amplitude is proportional to the instantaneous value of the main power supply voltage 2. Therefore, the envelope of the square wave 6 is similar to the main power supply voltage 2. Similarly, the amplitude of the triangular wave obtained by integrating the square wave 6 by the integrating circuit 7, that is, the amplitude of the PWM carrier 8 is proportional to the instantaneous value of the main power supply voltage, and its envelope is similar to the main power supply voltage 2. The PWM signal 11 comprises the input signal 9 and the PWM carrier 8
At the intersection of. As can be seen, when the main power supply voltage 2 is high, the pulse width is short, and when it is low, the pulse width is long. This indicates that pulse width modulation (PWM) has been performed just to cancel the fluctuation of the main power supply voltage 2.

[0008]

According to the present invention, the fluctuation of the main power supply voltage can be canceled by adding a small-capacity inverter to the PWM power converter. Stable operation and sufficient effects can be obtained compared to the method using negative feedback of the output voltage.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a PWM power conversion device using the present invention.

FIG. 2 is an operation waveform diagram of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main power supply 2 Main power supply voltage 3 Oscillator 4 Inverter 5 Transformer 6 Square wave 7 Integrating circuit 8 PWM carrier 9 Input signal 10 Comparator 11 PWM signal 12 Power conversion circuit 13 Output

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H007 CB05 CC32 DA06 DB01 DB09 EA13 5H740 AA01 BB05 BB08 GG04 HH01 JA11

Claims (1)

[Claims] 1. A PWM circuit having a PWM carrier generator having an amplitude proportional to a main power supply voltage.