JPS61251479A - Ac power source - Google Patents

Abstract

PURPOSE:To improve the utility rate of a transformer by obtaining an AC output from a square wave pulse train of the same polarity. CONSTITUTION:An oscillator 53 generates an operation reference signal of an inverter, and the inverter is driven by a pulse width controller 52' with the output of the oscillator 53 as a reference. A reference wave is generated from a reference wave generator 54, and synchronized with the operation reference signal to determine the output frequency of an AC power source. With the output of the generator 54 as a reference a changeover switch 9 is driven to switch by a switching pulse generator 55. According to the construction, since the inverter always generates pulses of the same polarity, the waveforms can be always efficiently shaped, and since the inverter output pulse is synchronized in the switching operation for generating the sinusoidal AC output of the desired frequency, smooth operation can be performed with a simple circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an AC m source device using an inverter device.

(Prior Art) Conventionally, inverter devices have been widely used in electronic computers, power supplies, uninterruptible power supplies for broadcasting, and the like.

There are various methods for controlling the output voltage of an inverter device, but among them, those that employ a PWM (pulse width control) method have fast transient responses such as sudden changes in load and are excellent in stability.

FIG. 5 shows the main part configuration of an AC power supply device using the above-mentioned pulse width control type inverter device. In the figure, 1 is an input terminal for AC input, 2 is a rectifier *a that rectifies AC input, 3 is a DC filter for smoothing, 4 is an inverter, and 5 is an inverter.
1 is an inverter control unit, 6 is an AC filter, 7 is an output terminal, and 8 is a load.

The inverter control unit 5 inputs the detected value of the inverter output voltage obtained through the AC filter 6 and the inverter output voltage set value (reference voltage), calculates the difference (set value - detected value), and generates a voltage command signal. An error amplifier (differential amplifier) 51 outputs the voltage, and an inverter 4 receives the voltage command signal.
The pulse width control circuit 52 generates a drive signal (switching control PWM signal).

The inverter 4 is configured using semiconductor switching elements (transistors) 41 and 42 and an inverter transformer 43, as shown in FIG. 6 as an example [push-pull type (center tap type) inverter]. 5, and outputs a plurality of pulse trains whose pulse widths are changed so as to bring the output voltage closer to a set value in response to output voltage fluctuations.

The output of the inverter forming this pulse train is filtered through an AC filter 6.
A sine wave AC output is obtained through the

Incidentally, recently, attempts have been made to increase the frequency of the inverter circuit and to reduce the size of the inverter transformer 43 and the AC filter 6. The output waveform of the inverter 4 (shown in FIG. 6) in this case and the output voltage waveform as a fill after passing through the AC filter 6 are shown in FIG.

FIG. 7(a) shows the output waveform of the inverter, and the pulse frequency is, for example, 20 kHz. When this output is passed through an AC filter, the AC shown in the same figure (b) <For example, 50Hz
>Output voltage is obtained.

By speeding up the operation of the inverter (higher frequency), not only can the inverter transformer and AC filter be made smaller as mentioned above, but the inverter input waveform distortion factor can be reduced, and the DC filter can also be made smaller. Secondary effects such as improved output voltage fluctuation characteristics in response to disturbances such as sudden changes in load have also been obtained.

[Problems to be Solved] Various advantages have been obtained by operating the inverter circuit at high frequencies (high frequency pulse width modulation) as described above, but there are still problems that need to be improved. The main points are that the inverter 1iIJ 111 circuit is complicated and that the inverter transformer cannot be made as small as expected.

The reason why inverter transformers cannot be made smaller is shown in Figure 7 (
As shown in a), the output waveform of an inverter consists of a positive polarity pulse and a negative polarity pulse, and when passed through an AC filter, the difference contributes to the AC output, so the use of an inverter transformer is The reason is that the rate is poor. Therefore, even if it is operated at 20kHz7, for example, 12 to 13
This is because a transformer of about the size for kHz is required.

An object of the present invention is to solve the above-mentioned problems, make full use of the advantages of increasing the frequency of operation of the inverter circuit (for example, 20 kHz >
0kHz) and the control unit can be configured with a relatively simple circuit. The objective is to provide a source device.

(Means for solving the problem) In order to achieve the above object, the inverter used in the AC power supply of the present invention is one that outputs only square wave pulses of the same polarity [see the fourth factor (■)] The polarity of the output waveform [Fig. 4 ■] obtained through the AC filter is switched every half cycle (T/2>) to obtain the AC output waveform [Fig. 4 ■].

The inverter used in the present invention has a circuit configuration as shown in FIG. 2, for example. The inverter transformer 44 is of a so-called one-stone type using one semiconductor switching element (transistor: TR) for main control, and has a reset winding WA45 on the primary side. A flywheel diode 46 is connected to the secondary side, and a semiconductor switching element (
TR) plays the role of sustaining the output current during the period when it is off. A primary current 1 and a secondary current 12 flow as shown by solid arrows in the figure, and a reset current 8113 flows as shown by a dotted line. FIG. 3 shows each waveform in correspondence with the operation of the semiconductor switching element. In Figure 3, t is the period of the PWM signal (
For example, 50 μS), and the hatched portion is the reset current 13, which plays the role of resetting the inverter transformer 44.

The overall configuration of the AC power supply device of the present invention is almost the same as the conventional one (FIG. 5), but as described above, a changeover switch (
What is interesting is that 9) in Figure 1 has been added. A circuit for driving the changeover switch is provided in the inverter control section. In other words, the inverter control section is
an oscillator that generates an operating reference signal for the inverter, a pulse width control circuit that drives the inverter based on the oscillator output, and a reference wave generation circuit that also determines the AC power output frequency based on the oscillator output; The device is configured to include a switching pulse generation circuit that receives the reference wave output and drives the changeover switch.

[Effect]

As described above, according to the present invention, since the inverter always generates pulses of the same polarity, efficient waveform shaping is facilitated, and a changeover switch is required to generate a sine wave AC output of a desired frequency. Since the operation is synchronized with the inverter output pulse, it can be performed smoothly with a simple circuit.

(Example) Next, the present invention will be explained by examples.

FIG. 1 is a block diagram showing the configuration of an AC power supply device of the present invention. In the figures, the same reference numerals as those mentioned above indicate the same or equivalent parts, and the explanation will be omitted as appropriate.

9 is the output waveform 1. This is a changeover switch (AC switch composed of two semiconductor switching elements) that switches the polarity every 2 cycles.

5' is an inverter control unit that switches the changeover switch 9! ! ! It is equipped with a circuit for operation.

That is, the inverter operation reference signal (for example, 20k
Hz), and a pulse width control circuit 52- that drives an inverter based on the output of the oscillator 53.
and a reference wave generation circuit 54 that generates a reference wave (ideal sine wave) that is synchronized with the operation reference signal and determines the output frequency (for example, 50H2) of the AC power supply; A switching pulse generation circuit 55 for switching and driving the changeover switch 9 is provided.

Note that the pulse width control circuit 52' controls the pulse @1bIJI1
This is a well-known circuit that is commonly used as a drive circuit for a 1-system inverter, and includes a triangular wave generating circuit 56 that generates a triangular wave from a reference signal generated by an oscillator 53, and an output of the triangular wave generating circuit and M! ! It is configured to include a pulse generation circuit 57 that receives the output (voltage command signal) of the amplifier 51 and generates pulses for inverter drive control, and an amplifier 58 that amplifies the output.

FIG. 4 shows each part of the apparatus of the present invention [labeled in FIG. 1].
-■] is a waveform diagram. ■ is the output of the oscillator 53,
■ is a reference wave that determines the frequency of the AC output, and ■ is a switching pulse that drives the changeover switch. As shown in the figure, the high frequency (e.g., 20 kHz) inverter output is converted to a desired frequency (e.g., 50 Hz).
) sine wave AC output ■ can be obtained.

(Effects) As explained above, the inverter device used in the AC power supply device of the present invention obtains AC output from a square wave pulse train of the same polarity, so the utilization rate of the transformer is improved compared to the conventional method. Well, by increasing the frequency, it becomes possible to downsize the inverter transformer according to the frequency.

Furthermore, the control circuit can be simplified.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the present invention, the second factor is a circuit diagram of an inverter used in the present invention, and FIG. 3 is an explanatory diagram of the operation of the inverter shown in FIG. 2. FIG. 4 is a waveform diagram at each part of the device of the present invention, and shows ■~■
correspond to the portions ① to ② shown in FIG. 1, respectively. Fig. 5 is a block diagram of a conventional device, Fig. 6 is a circuit diagram of an inverter used in the conventional device, Fig. 7(a) is an output waveform diagram of the inverter shown in Fig. 6, Fig. 7 (b)
2 is a waveform diagram obtained by passing the inverter output in (a) through an AC filter. 4...Inverter, 5.5-...Inverter control section, 6...
・AC filter, 9...changeover switch, 51...error amplifier, 52.52'...pulse width 1111!1 circuit,
53... Oscillator, 54... Reference wave generation circuit, 55... Switching pulse generation circuit.

Claims (1)

[Claims] 1. An inverter that outputs a high-frequency pulse width modulated square wave pulse train of the same polarity, an AC filter that shapes the pulse train output from the inverter into a sinusoidal waveform, and a pulse train that is obtained through the AC filter. A switch that switches the polarity every 1/2 period of the output waveform, and a pulse width control of the inverter to monitor the voltage fluctuation of the AC output voltage obtained through the changeover switch and keep the output voltage constant. An AC power supply device comprising: an oscillator that generates an operation reference signal for the inverter; a pulse width control circuit that drives the inverter based on the output of the oscillator; a reference wave generation circuit that generates a reference wave that is synchronized with the operation reference signal and determines the output frequency of the AC power supply; and a switching pulse generation circuit that switches and drives the changeover switch based on the output of the reference wave generation circuit. An AC power supply device comprising: