JPS6243433B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generates a pulsed sinusoidal voltage in which each half period of a fundamental sinusoidal voltage is composed of a number of pulses each having a pulse width modulated. The present invention relates to a pulse width modulation inverter control circuit that controls an inverter main circuit.

In a telephone ringing signal power supply device, which is one application of an inverter, the frequency of the ringing signal voltage is 16
Since the frequency is as low as Hz, a normal square wave inverter (single pulse within a half cycle) contains many low-order harmonic components in the output, and the drawback is that the sine wave AC filter to remove these components is large. It was hot.

One way to improve this is to generate a pulsed sine wave voltage PA in which each half period of a fundamental sine wave M is composed of a large number of pulses P whose pulse width is modulated, as shown in FIG. By selecting the number of pulses and the _ratio of pulse widths α ₁ , α ₂ . has been used.

Conventionally, the control circuit 1 of the inverter main circuit in this pulse width modulation inverter generates a fundamental sine wave output a of a sine wave generator 2 and a fixed frequency triangular wave as a carrier wave, as shown in FIGS. 2 and 3 A and B. A comparator 4 compares the triangular wave output b of the generator 3, and the power of the comparison output signal c is amplified by a drive amplifier 5 to obtain a drive signal for controlling the inverter main circuit.

In this case, if the frequency of the fundamental sine wave (modulated wave) output a approaches the frequency of the triangular wave (carrier wave) output b, the tendency of the lower harmonic content to increase will increase, so the frequency of the triangular wave output b should be increased. There must be.

If this is done, the operating frequency of the inverter main circuit will become higher and loss will increase accordingly, so conventionally, from the viewpoint of emphasizing efficiency, the number of pulses n within a half period of the fundamental sine wave M shown in Fig. 1 has been It was common to use 6 to 12 pulses.

However, even in this case, the AC filter is relatively large in order to remove low-order harmonics, and in particular, the frequency of the ringing signal voltage is in the range of 16Hz to 66Hz. The drawback was that a dedicated AC filter was required depending on the frequency.

Further, as can be seen from the configuration of FIG. 2, in order to provide functions such as voltage control or load current drooping characteristics, a sine wave generator 2 with variable amplitude is required. However, such a sine wave generator 2 generally has the disadvantage that the circuit is complicated and expensive. Many methods have been developed to improve this drawback, but
In both cases, the number n of pulses is 6 to 12, so the disadvantages of the AC filter being large and the number of AC filters used cannot be improved.

Recently, when introducing electronic switching equipment, the switching equipment side has requirements for the ringing signal power supply (inverter): (a) It must be small and lightweight because it can be mounted on a rack; It is possible to set any number of frequencies in one set, (c) it is possible to share an AC filter within the frequency range used, and (d) it is possible to set the voltage value according to the frequency set in the above (b). (e) The intermittent time of output sine wave voltage on and off can be easily set or changed.

It has been difficult to realize an inverter control circuit that satisfies these requirements using conventional analog technology.

An object of the present invention is to provide a control circuit for a pulse width modulation inverter that can satisfy the above-mentioned requirements.

Hereinafter, specific examples of the present invention will be described in detail with reference to the drawings. FIG. 4 shows an example of a control circuit for a pulse width modulation inverter according to the present invention. The control circuit 1 includes a microcomputer 6, a triangular generator 7, a sine wave generator 8, a comparator 9, an automatic voltage adjustment rectifier 10, a detector 11, and a droop command circuit 12.

The microcomputer 6 includes an oscillator 13 made of, for example, a crystal oscillator and having an oscillation frequency of 6 MHz and used as a clock for the microcomputer 6, and digital quantities corresponding to the frequency, voltage value, intermittent time, etc. of the calling signal voltage, and the like. a memory circuit 14 that stores a program to obtain the
It is comprised of a microprocessor (central processing circuit) 15 and the like that has the function of sequentially processing the digital signals stored in the memory circuit 14 according to a program.

The triangular wave generator 7 has a frequency (for example, 6M) of the pulse wave output from the microcomputer 6.
Hz) (for example, 6MHz down at 12kHz), and an integrating circuit 17 that shapes the rectangular wave output from this frequency divider 16 and outputs a high-frequency triangular wave. has been done.

The sine wave generator 8 generates a digital amount (for example, this digital amount is an 8-bit 2
It is a base number, and the peak value of the sine wave is sequentially output as an 8-bit binary number based on an appropriately frequency-divided clock signal. ) is output, there is a digital-to-analog converter 18 that converts it into an analog quantity, and a polarity switch that is output every 180 degrees of the fundamental sine wave from the microcomputer 6 to convert the output of this analog quantity into alternating current. It is composed of a polarity conversion circuit 19 and the like that converts the polarity according to a signal and outputs a predetermined fundamental wave sine wave voltage.

The comparator 9 compares the high frequency triangular wave voltage from the triangular generator 7 and the fundamental wave sine wave voltage from the sine wave generator 8, and outputs a pulse width modulated drive signal.

The automatic voltage adjustment rectifier circuit 10 has a ring signal voltage
Convert e ₀ to DC voltage.

The detector 11 detects a reference DC voltage for voltage control output from the microcomputer 6 corresponding to the frequency of the calling signal voltage e ₀ and a rectifier circuit 1 for automatic voltage adjustment.
The difference voltage is detected by comparing the DC voltage outputted from 0 and inputted to the gain adjustment section of the digital-to-analog converter 18 to perform voltage control.

The droop command circuit 12 controls the load current of the call signal voltage.
When _i0 is detected and the value exceeds the rated load current, a droop command DC voltage is output, and this is given to the gain adjustment section of the digital-to-analog converter 18 to reduce the output voltage of this digital-to-analog converter 18. By doing so, load current droop characteristics are obtained.

5A, B, C, and D show operating waveforms of such a pulse width modulation inverter control circuit 1. FIG. FIG. 5A shows the relationship between the triangular wave output voltage a of the triangular wave generator 7 and the fundamental wave sine wave output voltage b of the sine wave generator 8.

At the rated voltage, the fundamental wave sine wave output voltage RO is the fifth
The signal is output as shown by the solid line in FIG.

When the load suddenly changes and the calling signal voltage e ₀ suddenly changes and decreases, the differential voltage output of the detector 11 increases and the fundamental wave sine wave voltage 0 increases as shown by the dotted line in FIG. The voltage _e0 is increased, and the comparator 9 outputs a pulse width modulated drive signal voltage _C as shown in FIG. It operates to keep the ringing signal voltage e ₀ at the rated value.

Also, if the load current i ₀ becomes larger than the rated value,
As the drooping command circuit 12 operates, the sine wave voltage B drops extremely as shown in FIG. Output.

Note that when the microcomputer 6 does not output a digital quantity, the calling signal voltage is not output, and in this case, the content rate of the fundamental wave sine wave voltage B shown in FIG. 5D becomes zero, and the drive signal voltage C is in a state where it is output as a harmonic voltage.

FIG. 6 shows an example of a pulse width modulation inverter incorporating the control circuit 1 according to the present invention. In the figure, 20 is an amplifier, 21 is an inverter main circuit consisting of transistors Tr ₁ and Tr ₂ , a DC power source E _DC and a transformer T, 22 is an AC filter consisting of an inductance L and capacitors C ₁ and C ₂ , and 23 is a load. .

The pulse width modulated drive signal C output from the control circuit 1 is power-amplified by the amplifier 20, and is alternately applied to the bases of the transistors Tr ₁ and Tr ₂ of the inverter main circuit 21 every half cycle to make them conductive alternately. As a result, a pulse width modulated voltage containing a fundamental sine wave is induced on the secondary side of the transformer T.
The harmonic components are bypassed by the AC filter 22, and a fundamental sinusoidal calling signal voltage e ₀ is output from the output end of the AC filter 22, which is supplied to the load 23.

Such a calling signal voltage e ₀ is converted into a DC voltage by the automatic voltage adjustment rectifier circuit 10 and applied to the detector 11 . Since a reference DC voltage is applied to the detector 11 from the microcomputer 6 according to the frequency of the calling signal voltage _e0 , this reference DC voltage and the DC voltage from the rectifier circuit 10 are compared, and the difference voltage is calculated. The ringing signal voltage e0 is applied to the digital-to-analog converter 18, and the ringing signal voltage _e0 is applied to the microcomputer 6.
It is controlled to maintain a predetermined voltage according to the frequency determined by.

Furthermore, when the load 23 becomes overloaded, the load current i ₀
The droop command circuit 12 detecting the droop command signal outputs a droop command signal to the digital-to-analog converter 18, and the control circuit 1 outputs a drive signal C as shown in FIG. 5D to the transistors Tr ₁ and Tr ₂ . As a result, a harmonic voltage is applied to the primary side of the transformer T.
Almost no voltage is output to the secondary winding due to the winding inductance of the transformer T, and it is completely bypassed by the AC filter 22, so the load 23
Only a very small sinusoidal ringing signal voltage e ₀ is applied to the .

In the above embodiment, the microcomputer 6
Although the explanation has been made using one microcomputer 6, if the operating function becomes complicated, a plurality of microcomputers 6 will be required.

In addition, although it has been explained that the intermittent ringing signal voltage e ₀ is carried out without outputting a digital quantity from the microcomputer 6, in order to improve the transient characteristics, the microcomputer 6 to the detector 11
Since the characteristics can be improved by using the output voltage D (see FIG. 4) output from the microcomputer 6 in parallel, it is preferable to use the outputs D and E of the microcomputer 6 in common to perform the intermittent operation. In this way, the AC filter 22 becomes approximately 1/3 the size of the output transformer T, and even if the frequency of the calling signal voltage _e0 is any frequency between 16Hz and 66Hz, the AC filter 22
Even if you use both in common, you can obtain a sine wave as the output waveform.

As explained above, in the pulse width modulation inverter control circuit according to the present invention, the triangular wave is generated by the triangular wave generation circuit based on the digital output from the microcomputer, so the frequency of the triangular wave can be increased arbitrarily. be able to. As a result, when controlling an inverter used in a telephone ringing signal power supply device, this control circuit can increase the number of pulses within a half cycle of the fundamental sine wave by setting the frequency of the triangular wave to a high frequency (for example, 10kHz) compared to the conventional one. (for example, more than 100 pulses)
The content of low-order harmonics can be extremely reduced. Therefore, the AC filter can be made smaller and can be used within the frequency range (for example, 16Hz to 66Hz).
This miniaturized AC filter can be used in common for any frequency (Hz). In addition, in the present invention, drive signals of various frequencies can be freely created using a microcomputer.
When used in a control circuit for an inverter used in a telephone ringing signal power supply device, there is no need to use a large number of oscillators as in the past, and miniaturization can also be achieved in this respect. Therefore, the size and weight required for rack mounting can be easily achieved.
Furthermore, according to the present invention, the voltage can be freely set according to the set frequency by commands from the microcomputer. Furthermore, the magnitude of this voltage can be easily adjusted automatically by applying the difference voltage between the output voltage of the automatic voltage adjustment rectifier and the reference output voltage from the microcomputer to the digital-to-analog converter of the sine wave generator. can do. Furthermore, in the present invention, by applying the output of the droop command circuit to the digital-to-analog converter, it is possible to easily control the droop characteristics of the inverter load current.

[Brief explanation of the drawing]

Figure 1 is an operating waveform diagram of a conventional pulse width modulation inverter, Figure 2 is a block diagram of a conventional control circuit for a pulse width modulation inverter, Figures 3A and B are operating waveform diagrams of a conventional control circuit, and Figure 4 is a diagram of operating waveforms of a conventional control circuit. 5 is a block diagram showing an embodiment of the control circuit for a pulse width modulation inverter according to the present invention, FIGS. 5A to 5D are operational waveform diagrams of the circuit shown in FIG. 4, and FIG. 1 is a schematic diagram illustrating one embodiment of an integrated pulse width modulation inverter; FIG. 1... Control circuit, 7... Triangular wave generator, 8...
Sine wave generator, 9... Comparator, 10... Automatic voltage adjustment rectifier circuit, 11... Detector, 12... Droop command circuit, 13... Oscillator, 14... Memory circuit, 15... Micropro Setser, 16... Frequency divider, 17... Integrator, 18... Digital analog converter, 19... Polarity converter, 21... Inverter main circuit, 22... AC filter.

Claims (1)

[Scope of Claims] 1. A microcomputer that includes an oscillator, a memory circuit, and a microprocessor and outputs a high-frequency pulse for forming a triangular wave, a digital quantity for forming a fundamental sine wave, a polarity conversion signal, a reference DC voltage, etc.; A digital generator including a triangular wave generator that divides and integrates the high frequency pulse output from the microcomputer to generate a triangular wave voltage, a digital-to-analog converter, and a polarity converter, which corresponds to the fundamental sine wave voltage output from the microcomputer. a sine wave generator that converts a quantity into an analog quantity and converts the analog quantity into an alternating voltage according to a polarity signal output from the microcomputer to output a fundamental wave sine wave voltage; and a sine wave generator that outputs a fundamental wave sine wave voltage; A comparator that compares the triangular wave voltage with the fundamental sine wave voltage output from the sine wave generator and outputs a pulse width modulated drive signal voltage, and an automatic voltage adjustment that rectifies and outputs the output voltage of the inverter. A rectifier compares the reference DC voltage output from the microcomputer and the DC voltage output from the automatic voltage adjustment rectifier, and applies the difference voltage to the digital-to-analog converter of the sine wave generator to generate a voltage. 1. A control circuit for a pulse width modulation inverter, comprising a detector for controlling the pulse width modulation inverter. 2. A microcomputer that includes an oscillator, a memory circuit, and a microprocessor and outputs a high-frequency pulse for forming a triangular wave, a digital quantity for forming a fundamental sine wave, a polarity conversion signal, a reference DC voltage, etc.;
A digital generator including a triangular wave generator that divides and integrates the high frequency pulse output from the microcomputer to generate a triangular wave voltage, a digital-to-analog converter, and a polarity converter, which corresponds to the fundamental sine wave voltage output from the microcomputer. a sine wave generator that converts a quantity into an analog quantity and converts the analog quantity into an alternating voltage according to a polarity signal output from the microcomputer to output a fundamental wave sine wave voltage; and a sine wave generator that outputs a fundamental wave sine wave voltage; A comparator that compares the triangular wave voltage with the fundamental sine wave voltage output from the sine wave generator and outputs a pulse width modulated drive signal voltage, and a comparator that detects the load current of the inverter and detects an overcurrent exceeding a set value. a droop command circuit that outputs a droop command DC voltage when the voltage drops and applies it to the digital-to-analog converter of the sine wave generator to perform droop control; and an automatic voltage adjustment rectifier that rectifies and outputs the output voltage of the inverter. and voltage control by comparing the reference DC voltage output from the microcomputer and the DC voltage output from the automatic voltage adjustment rectifier, and applying the difference voltage to the digital-to-analog converter of the sine wave generator. What is claimed is: 1. A control circuit for a pulse width modulation inverter, comprising: a detector for performing the following steps.