JPH0850149A - Output voltage detecting circuit - Google Patents

Abstract

PURPOSE:To provide an output voltage detecting circuit in which the control precision of a thyristor power control device can be improved, and the cost can be reduced. CONSTITUTION:The output voltage of a thyristor power control device 2 is A/D converted by an A/D converting circuit 4 in a sampling time of a period faster than the frequency of the input power. Although a voltage fluctuating component by a ripple or change of control angle is contained in the output voltage even when successively converted and smoothed by the thyristor power control device 2, it is fractionated by the A/D converting circuit 4, and averaged with a sampling number corresponding to the frequency of a first power by a voltage detecting circuit 5, whereby an output voltage never influenced by the voltage fluctuation can be detected. Since the influence of the ripple or control angle change is removed, thus, the time constant for smoothing can be also set small, and an output voltage with high precision of output voltage control and high responsiveness can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a voltage on the output side of a thyristor power control device for converting a constant voltage and a constant frequency power into a variable voltage power, and uses this as a voltage feedback value for output voltage control. The present invention relates to an output voltage detection circuit used as.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional example of an output voltage detection circuit of the above thyristor power control device. In the conventional configuration shown in FIG. 3, the output voltage detection circuit 30 for detecting the output voltage of the thyristor power control device 34 has a frequency of commercial power (50 or 60 Hz three-phase AC) input to the thyristor power control device 34. Synchronous circuit 31 for outputting synchronized pulses
A low pass filter (LPF) 33 for smoothing the output voltage of the thyristor power control device 34, and the LPF 33 at the input position of the pulse output by the synchronizing circuit 31.
And an A / D conversion circuit 32 for A / D converting the output of the. The voltage waveform of each part in the above configuration is as shown in FIG. That is, as shown in FIG.
Waveforms of the respective parts of (A) to (E) are shown in (A) to (E) of FIG. FIG. 4A shows a three-phase AC waveform of the input power, which is the waveform of the output voltage obtained by forward conversion by the thyristor power control device 34 in FIG. This output waveform is smoothed by passing through the LPF 33 as shown in (C), but has a large ripple component. Synchronization circuit 31
A / D the (D) pulse synchronized with the frequency of the input voltage
Since the signal is output to the conversion circuit 32, the A / D conversion circuit 32 performs A / D conversion of the input waveform (C) with the voltage at the pulse position. By this A / D conversion, the waveform of (C) can be detected as a substantially averaged DC voltage as shown in (E), and this is used as voltage feedback for controlling the output voltage of the thyristor power converter 34. it can.

[0003]

However, the above-mentioned conventional configuration requires the synchronizing circuit 31 as a pulse output for A / D conversion, which increases the cost of the device and is affected by the fluctuation of the input power. There was a problem that caused a malfunction. Further, the change of the thyristor control angle in the thyristor power control device 34 appears in the waveform of FIG. 4C, and this occurs as an error of the detected voltage in the output voltage feedback waveform (E), so that the control accuracy is lowered. In order to reduce this influence, it is necessary to increase the time constant of the LPF 33, but this has a problem that the control response is lowered. Therefore, the object of the present invention is to
An object of the present invention is to provide an output voltage detection circuit which solves the above-mentioned conventional problems and improves the control accuracy of the thyristor power control device, and also reduces the cost.

[0004]

In order to achieve the above object, the means adopted by the present invention is a thyristor power control device for converting the input first electric power into the second electric power of a variable voltage and outputting the second electric power. In an output voltage detection circuit for detecting an output voltage, an A / D conversion circuit for digitally converting the output voltage in a predetermined sampling time faster than the frequency of the first power, and sampling corresponding to the frequency of the first power And a voltage detection circuit that outputs the average value of the digitally converted output voltage in terms of a number, and is configured as an output voltage detection circuit.

[0005]

According to the present invention, the output voltage of the thyristor power control device is A / D converted by the A / D conversion circuit at a sampling time of a cycle sufficiently faster than the frequency of the first power. Even if the output voltage includes a voltage fluctuation component due to a ripple or a change in the control angle even if it is forward-converted and smoothed by the thyristor power control device, it is subdivided by the A / D conversion circuit and this is divided into a voltage detection circuit. Thus, averaging is performed with the number of samplings corresponding to the frequency of the first power. For example, when the first power is 50 Hz, the output voltage that is not influenced by the voltage fluctuation can be detected by averaging 6 times and 60 times when the first power is 60 Hz. Therefore, since the influence of ripples and control angle changes is removed by the above processing, the time constant for smoothing can be set small, and the output voltage with high accuracy and responsiveness of output voltage control can be detected.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. The following embodiments are examples embodying the present invention and do not limit the technical scope of the present invention. FIG. 1 is a block diagram showing the configuration of an output voltage detection circuit according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing the voltage waveform of each part in the configuration of FIG. In FIG. 1, an output voltage detection circuit 1 according to the present embodiment includes a low pass filter (LPF) 3,
It is configured to include an A / D conversion circuit 4 and a voltage detection circuit 5, detects the output voltage of the thyristor power control device 2, and the detected voltage is a voltage feedback for controlling the output voltage of the thyristor power control device 2. It is used as a value. The thyristor power control device 2 converts input commercial power (first power) having a constant voltage and constant frequency into variable voltage power (second power) and outputs the commercial power. Is a three-phase alternating current of 50 Hz or 60 Hz. The thyristor power control device 2 forward-converts the input commercial power by a thyristor assembled in a three-phase pure bridge and outputs it as variable voltage power. The control of the variable voltage is performed by changing the control angle of the thyristor, and the output voltage detection circuit 1 having this configuration is used to control the output voltage. (A) attached to each part of the circuit configuration shown in FIG.
The symbol (E) corresponds to (A) to (E) shown in FIG. 2, and shows the voltage waveforms of the respective parts (A) to (E). The operation of the output voltage detection circuit 1 will be described below with reference to FIGS.

Three-phase 50 Hz or 60 Hz commercial power (A) input to the thyristor power control device 2 is forward-converted and converted into a waveform as shown in FIG. This output waveform has a saw-tooth shape as shown in the figure, and the required voltage cannot be detected as the output voltage feedback value. Therefore, this output voltage is input to the output voltage detection circuit 1 and detected as an averaged voltage. By inputting the output voltage (B) into the LPF 3, the output voltage (B) in FIG.
Although the waveform is smoothed as shown in Fig. 5, it still has a large ripple. This ripple can be reduced by increasing the time constant of the LPF 3, but the responsiveness of voltage control deteriorates. Also, because the waveform of (B) changes due to the change of the control angle of the thyristor,
The waveform of (C) contains a varying ripple component. The waveform (C) is input to the A / D conversion circuit 4. A sampling clock signal fixed at 555 μs as the sampling time for A / D conversion is applied to the A / D conversion circuit 4, and the voltage of the input (C) waveform is A / D at the sampling time of 555 μs. To be converted. Since this sampling time is a timing sufficiently faster than the frequency of the commercial power source, the voltage of the waveform (C) shows a voltage fluctuation state as shown in FIG. A / D conversion is performed as it is.

The (D) waveform A / D converted in the above sampling time is input to the voltage detection circuit 5. An average sampling number signal that can be switched according to the frequency of the commercial power supply is applied to the voltage detection circuit 5,
A / D with sampling time of 555 μs when Hz
The converted voltage is averaged 6 times, and 5 times when 60 Hz. That is, at 50 Hz, 555 μs × 6 =
At 3.33 ms, 60 Hz, 555 μs × 5 = 2.7
The waveform of (D) is averaged at the timing of 7 ms and is shown in FIG.
The voltage waveform shown in (E) is output. 50Hz / 6 above
Since switching of 0 Hz is a change in commercial power frequency depending on the area as is well known, the number of samplings to be averaged can be switched by a switch depending on the place where the device is used.
As described above, in the configuration of this embodiment, it is not necessary to generate a signal synchronized with the input power as in the conventional configuration in order to A / D-convert the output voltage having a voltage fluctuation. There are advantages that you do not need. Further, the synchronous circuit causes a malfunction due to the fluctuation of the input power, but in the above configuration, since the fixed sampling signal is A / D converted, it is not affected by the fluctuation of the input power. Furthermore, since the A / D conversion values are averaged by the number of samplings corresponding to the frequency of the input power, the occurrence of detection errors due to ripples and changes in the control angle is eliminated, and control accuracy is improved. Since this averaging operation also assists the action of the LPF 3, the time constant of the LPF 3 can be set as small as possible, which can improve the responsiveness of voltage control.

[0009]

As described above, according to the present invention, the output voltage of the thyristor power control device is A / D converted by the A / D conversion circuit at a sampling time of a cycle sufficiently faster than the frequency of the input power. . Even if the thyristor power control device performs forward conversion and smoothing, the output voltage contains ripples and voltage fluctuation components due to changes in the control angle.
It is subdivided by the A / D conversion circuit, and this is averaged by the voltage detection circuit by the sampling number corresponding to the frequency of the input power. Therefore, the influence of ripples and changes in control angle is removed by this processing, so that the time constant for smoothing can be set small and the output voltage with high accuracy and responsiveness of output voltage control can be detected.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an output voltage detection circuit according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing voltage waveforms of respective parts shown in FIG.

FIG. 3 is a block diagram showing a configuration of an output voltage detection circuit according to a conventional example.

FIG. 4 is a waveform diagram showing voltage waveforms of respective parts shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Output voltage detection circuit 2 ... Thyristor power control device 3 ... Low pass filter (LPF) 4 ... A / D conversion circuit 5 ... Voltage detection circuit

Claims (1)

[Claims] 1. The input first electric power is changed to a second variable voltage.
An output voltage detection circuit for detecting an output voltage of a thyristor power control device for converting to the electric power of the above and outputting the electric power, and an A / D conversion circuit for digitally converting the output voltage at a sampling time faster than the frequency of the first electric power. An output voltage detection circuit comprising: a voltage detection circuit that outputs an average value of the digitally converted output voltage at a sampling number corresponding to the frequency of the first power.