JPH06138959A - Ac power voltage detector - Google Patents

Abstract

PURPOSE:To stably and accurately detect the AC power source voltage by detecting directly the peak value of the power source voltage by a delay time equal to a half cycle of synchronization of the power voltage. CONSTITUTION:When the signal SA produced by a rectifier circuit 512 has a higher level than a reference signal VB, the output SB of a comparator 515 is turned to 1 and a counter 516 counts the clock signals. Then the output SB is turned to 0 when SA<=VB is satisfied. Under such conditions, the count value of the counter 516 is held on an output stage and cleared. At the same time, a CPU 514 reads the count value T5 of the counter 516. The time (T5-T3) during a period when SA>VB is kept is known from the value T5. The voltage peak level is defined as a T7 that adds the half time of the (T5-T3) to the rising edge T6 of the next SB. The CPU 514 reads the value of the signal SA in the time T7 via an A/D converter 517. Thus the AC power source voltage can be stably and accurately detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power supply voltage detecting device which is used in a power converter or the like which receives an AC power supply as an input and which is used as condition information for establishing an input power supply.

[0002]

2. Description of the Related Art An AC power supply voltage detecting device is one for detecting the power supply in a device using an AC power supply as an input.
Widely adopted. An example of a general power converter to which this is applied is shown in FIG.

FIG. 3 shows an example of a power converter to which a power supply detection circuit is applied. 1 is a converter, 2 is a smoothing capacitor, 3 is an inverter, 4 is an induction motor, 5 is a power supply detection circuit, and 6 is a drive. A signal generation circuit, 7 is a drive circuit. In FIG. 3, a DC output is converted by a converter 1 having a three-phase AC power supply as an input, and a DC output obtained through a smoothing capacitor 2 is input to an inverter 3. Further, the inverter 3 drives the induction motor 4 by the drive signal generation circuit 6 and the drive circuit 7, and the inverter driving of the induction motor is commonly used, and the detailed description thereof will be omitted.

Here, the power supply detection circuit 5 is provided to monitor the AC power supply and protect the power conversion device when the voltage value thereof falls below a specified value. Generally, a power conversion device using an AC power supply as an input cannot operate when the power supply voltage is exhausted, and when the power supply voltage is lower than a specified voltage value, predetermined performance cannot be obtained even if the power converter can be operated. This is because in the inverter drive shown in FIG. 3, an attempt is made to output a current by an amount corresponding to a decrease in voltage in order to output the required torque, and, for example, an excessive current flows in a switching element forming the inverter 3. Therefore, the life of the power conversion device itself is shortened and other adverse effects are exerted.

When the AC power supply falls below a specified voltage, the power supply voltage detection circuit 5 can generally give a stop command signal to the drive circuit 7 to stop the power conversion and cut off the output. This is as shown in FIG. FIG. 4 shows the relationship between the AC power supply drop and the output cutoff. VAC is the power supply voltage, VA is the specified voltage, IU is the output current of the inverter, and HV and HI are envelope routes.

Now, such a power supply voltage detection circuit 5 is shown in FIG.
It had a structure as shown in. FIG. 5 shows a conventional power supply voltage detection circuit. 511 is a step-down transformer, 512 is a rectifier circuit, 513 is a smoothing circuit, and 514 is a microcomputer (CPU). Here, the smoothing circuit 513 comprises a capacitor and a resistor for reducing the signal ripple, and the CPU 514 detects the voltage and obtains, for example, the above-mentioned stop command signal. Further, FIG. 6 is shown to facilitate understanding of the operation of FIG.
D is the input voltage taken into the CPU 514 and the specified voltage.

Now, assuming that the power supply voltage has disappeared until time T1, the waveform of the input voltage VDC becomes as shown in FIG. When the CPU 514 obtains this input voltage VDC and, as a result, it becomes smaller than the specified voltage VDC after the time T2, it can be regarded as a power failure.

[0008]

However, although the power failure can be detected by such a conventional power point pressure detection method, the detection time T2 depends on the discharge time constant of CR of the smoothing circuit 513, and further It was greatly affected by the performance variations of the components.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to eliminate the above-mentioned problems, and is a means for obtaining a signal proportional to an AC voltage input to a power converter or the like, and a means for obtaining the signal. Means for comparing the received signal with a reference signal,
By obtaining the rectangular wave obtained by the comparison means,
It comprises at least means for adding the time width (1/2) of this rectangular wave to the rising time of the rectangular wave to be generated next time, and means for detecting the AC voltage at the time determined by this adding means. It is a thing.

More specifically, a means for obtaining a rectified signal based on the AC power supply voltage, a means for giving a pulse output synchronized with the rectified signal, and a time of (1/2) pulse width of the pulse output are described below. A means for adding the rising time of the generated pulse and a means for judging the rectified signal level by the output of the adding means are provided.

[0011]

With such a solution, the peak value of the power supply voltage is directly detected in the delay time of the half cycle of the power supply voltage synchronization to obtain a high-level comparison input value that is robust against noise, and the power supply voltage is regulated. It can be judged whether or not it is lower than the value. Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of the essential part of an embodiment of the present invention represented in a manner similar to FIG. 5, in which 515 is a comparison circuit, 516 is a counter, and 517 is an analog-digital converter. In the figure,
Those having the same reference numerals as those in FIG. 5 are components having the same function. Further, FIG. 2 shows waveforms of respective parts for facilitating understanding of the operation of FIG.

The AC power supply passes through the step-down transformer 511 and is input to the rectifier circuit 512. The signal SA generated by the rectifier circuit 512 is input to the comparison circuit 515, compared with the signal VB given as a reference value by the resistors R1 and R2 connected between the constant power sources, and the output of the comparator CP is compared with the signal SB. Become. Here, the pulse width of the signal SB (T5-
It is clear that T3) does not have to be an accurate value in this embodiment, so that even if the values of the constant power source and the resistors R1 and R2 that determine the value of the signal VB vary, it does not cause any trouble.

The signal SB output from the comparison circuit 515 is the counter 51.
6 is applied to the clear terminal (CLR) of the counter 6 (when the signal SA is larger than the signal VB), the counter 516 outputs the clock signal C.
LK is counted, (when the signal SA becomes smaller than the signal VB), the count value at that time is held in the output stage, and the internal counter is cleared.

The signal SB is also given to the CPU 514 and CP
U514 reads through the signal line SM the count value T5 of the counter 516 when the signal changes from the high level to the low level. As a result, (T5-T4) where {T3 =
0} is the time of (SB> VB), and half the time {(T5-T3) / 2} is the time when the voltage reaches the peak value. Therefore, it is apparent that the voltage also reaches the peak value at the time when the previous half time is added to the rising edge T6 of the next signal SB. At this time T7, the value of the signal SA is read by the CPU 514 via the analog-digital converter 517.

Therefore, according to the present embodiment, the voltage value can be accurately detected with a half cycle delay of the power supply synchronization, and the voltage value can be compared with a preset specified value to determine whether the power supply has dropped at a stable and robust level. It can be carried out.

[0017]

As described above in detail, according to the present invention, it is possible to provide an AC power supply voltage detecting device which can make a stable and robust judgment without being influenced by the variation of parts and the power supply frequency with a delay of only a half cycle. The practical effect of preventing the performance deterioration of the power conversion device and the like and the adverse effect on the device itself is remarkable.

[Brief description of drawings]

[0018]

FIG. 1 is a system diagram showing a main part configuration of an embodiment of the present invention.

FIG. 2 is a waveform diagram shown to facilitate understanding of the operation of FIG.

FIG. 3 is a system block diagram showing an example of a power conversion device to which a power supply detection circuit is applied.

FIG. 4 is a waveform diagram showing the relationship between the AC power supply drop and the output cutoff.

FIG. 5 is a circuit diagram showing a conventional power supply voltage detection circuit.

FIG. 6 is a waveform diagram shown to facilitate understanding of the operation of FIG.

[0019]

[Explanation of symbols]

 1 Converter 2 Inverter 5 Power Supply Detection Circuit 6 Drive Signal Generation Circuit 7 Drive Circuit 511 Step Down Transformer 512 Rectifier Circuit 513 Smoothing Circuit 514 Microcomputer (CPU) 515 Comparison Circuit 516 Counter 517 Analog-to-Digital Converter

Claims (1)

[Claims] 1. A comparison means for obtaining a rectangular wave obtained from a proportional signal of an AC power supply voltage and a reference signal, and a rising edge of the rectangular wave which generates (1/2) of a temporal width of the rectangular wave next time. An alternating-current power supply voltage detection device comprising: an addition unit that obtains a value added to the time; and a unit that detects the level of the proportional signal at the time determined by the addition unit.