JPH08105921A - Ac voltage detecting circuit - Google Patents

Abstract

PURPOSE: To detect an AC voltage at high speed with little ripple. CONSTITUTION: The voltage of an AC power source 1 to be detected is full-wave rectified, noises are removed by a filter circuit 4, the resulting voltage is sampled in the peak point of the full-wave rectified waveform by a sample hold circuit 5 to take the hold output as a detected output. For the sampling pulse, the phase of zero cross point is detected by a zero cross comparator 7, and this is used as a standard phase to generate a pulse of 60 deg.-interval by pulse generating circuits 9, 10, a pulse of 60 deg.-interval and the peak point phase for half period is provided by pulse shifting circuits 11, 12, the logical sum is taken by a logical sum circuit 13 to provide a pulse of 60 deg. interval and the peak point phase over the whole period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC voltage detecting circuit.

[0002]

2. Description of the Related Art A converter for obtaining a direct current controlled from an alternating current power source uses, for example, a thyristor as a control element, and controls the ignition phase to obtain a voltage-controlled direct current output to control the speed of a direct current machine.

Further, the inverter converts the DC power obtained by the converter or the rectifier into AC power whose voltage and frequency are controlled, and controls the speed of the induction machine.

In these power converters, it is often necessary to detect the voltage of the AC power supply (including the output of the inverter) as a control signal, and an AC voltage detection circuit for this purpose is provided.

In the conventional AC voltage detection circuit, as shown in FIG. 4, the voltage of the AC power supply 1 which is the output of the commercial power supply or the inverter is full-wave rectified by the diode bridge circuit 2.
A DC detection output is obtained by smoothing the rectified output with the capacitor 3.

[0006]

In the conventional AC voltage detection circuit, when the voltage of the AC power supply 1 is instantaneously changed, the filter operation of the capacitor 3 suppresses the fluctuation of the detected voltage.

Such a filter effect is very effective for general AC voltage detection, but for control such as detecting an instantaneous fluctuation of the AC power supply voltage and correcting the gate control phase of the converter, There is a detection delay in the filter operation, which has the opposite effect.

For this detection delay, it suffices to reduce the capacity of the smoothing capacitor, but in this case a large ripple occurs in the detection voltage, and when it is used as a control signal, the control circuit responds to the ripple and fails. It will be stable control.

It is an object of the present invention to provide an AC voltage detecting circuit which has a small ripple and enables high speed detection.

[0010]

In order to solve the above problems, the present invention provides a rectifier for full-wave rectifying the voltage of an AC power supply to be detected and a sampling having a phase of a peak point of the voltage of the AC power supply. A sampling signal generating unit that generates a pulse and a sample hold circuit that obtains a voltage detection output by sampling and holding the rectified output of the rectifier at the timing of the sampling pulse are provided.

[0011]

By detecting and outputting the voltage at the peak point of the full-wave rectified waveform of the voltage of the AC power supply as a detection output, the three-phase power supply is detected with a detection delay of 60 °, and detection with almost no ripple is performed. To do.

[0012]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. A full-wave rectified voltage is obtained by a rectifier 2 that receives the voltage of an AC power supply (three-phase) 1 that is a voltage detection target, and a noise component is removed from the rectified output by a low-pass filter 4.

[0013] The filter 4 is different from the conventional smoothing capacitor, in order to remove the noise component, for example the frequency of the AC power source in the case of 50 / 60H _Z removes 1 kH _Z or more frequency components.

The sample and hold circuit 5 samples and holds the voltage of the full-wave rectified waveform passed through the filter 4 to obtain a DC voltage detection signal. In this sample hold, voltage sampling is performed near the peak point of the full-wave rectified waveform. The sampling signal for this purpose is generated by the sampling signal generator 6.

The sampling signal generator 6 is composed of a zero-cross comparator 7, a logic inverter 8, pulse generators 9 and 10, pulse shifters 11 and 12, and an OR circuit 13.

The zero-cross comparator 7 is an AC power supply 1
The zero crossing point of the voltage signal of one phase of
Is detected as a 1/2 duty (180 ° width) pulse. The logic inverter 8 obtains an inverted signal of the detection pulse of the zero cross comparator 7.

The pulse generation circuits 9 and 10 obtain pulses at intervals of 60 ° with the pulse outputs of the zero cross comparator 7 and the logic inverter 8 as reference phases. This circuit is realized by, for example, a tripler circuit or a PLL (phase locked loop) circuit. Further, it is realized by using a shift register having an input pulse as a shift start phase and using the shift pulse as pulses at 60 ° intervals in synchronization with the power supply voltage.

The pulse shift circuits 11 and 12 generate pulses at the timing of the trailing edge of the output of the pulse generation circuits 9 and 10. This circuit is realized by, for example, a monostable multivibrator.

The OR circuit 13 is a double-pulse shift circuit 1
The logical sum of 1 and 12 is taken as the sampling signal of the sample and hold circuit 5.

The operation waveforms of this embodiment are shown by a to i of the respective parts in FIG.
It is shown in FIG. 2 in association with the points. The output (point a) of the filter circuit 4 with respect to the U-phase voltage of the AC power supply 1 has a waveform obtained by full-wave rectifying the u, v, and w phases.

On the other hand, the zero-cross comparator 7
Output (point b) is a 1/2 duty pulse having a u-phase zero-cross point as a leading edge and a trailing edge. Further, the output (point c) of the logic inverter 8 becomes a pulse of its inverted phase.

Outputs (d, e) of the pulse generation circuits 9 and 10
Points) are pulses at 60 ° intervals with reference to the leading and trailing edges of the input pulse. The width of this pulse is 20 °.

Outputs of the pulse shift circuits 11 and 12 (f,
At point g), a pulse having a constant width is generated from the trailing edge of the output pulse of the pulse generation circuits 9 and 10. The width of this pulse is 10
Let be °.

Therefore, the pulse shift circuits 11 and 12
Has a width of 10 ° around the peak point of the three-phase full-wave rectified waveform. These pulses are added to the OR circuit 13
The output (point h) passed through becomes a sampling pulse having a peak point phase over the entire period of the full-wave rectified waveform.

The output (point i) of the sample-hold circuit 5 for sampling the full-wave rectified waveform by this sampling pulse is sampled at the peak point of the full-wave rectified waveform and held to obtain an AC voltage detection signal.

From the above operation, in the present embodiment, the level of the peak point of the AC voltage is detected at intervals of 60 ° as shown in FIG. The maximum delay is a phase delay of 60 °, which enables high-speed detection. In addition, the detection signal has almost no ripple.

As the sampling pulse width becomes narrower, the true peak point can be detected and the detection error can be reduced.

Further, this embodiment can be applied to voltage detection of a single-phase power supply. In this case, the detection delay is 180 °,
It can be detected with a half cycle delay.

Further, the filter circuit 4 can be omitted when the AC power supply 1 contains little noise or when the sampling pulse has a narrow width at the peak point.

[0030]

As described above, according to the present invention, the voltage at the peak point of the full-wave rectified waveform of the voltage of the AC power source is sampled and held to be detected.
It is possible to perform high-speed detection such as detection with the detection delay of, and it is possible to perform detection with almost no ripple.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a waveform chart of each part of the embodiment.

FIG. 3 shows an example of detection signals of the embodiment.

FIG. 4 is a conventional detection circuit diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... Rectifier 4 ... Filter circuit 5 ... Sample hold circuit 6 ... Sampling signal generation unit 7 ... Zero cross comparator 9, 10 ... Pulse generation circuit 11, 12 ... Pulse shift circuit

Claims (1)

[Claims] 1. A rectifier for full-wave rectifying the voltage of an AC power supply to be detected, a sampling signal generation unit for generating a sampling pulse having a phase of a peak point of the voltage of the AC power supply, and a timing of the sampling pulse. An AC voltage detection circuit, comprising: a sample and hold circuit that samples and holds the rectified output of the rectifier to obtain a voltage detection output.