JPH04140924A - Signal conversion method - Google Patents

Abstract

PURPOSE:To attain signal conversion with high accuracy by sampling an analog signal in a random timing, obtaining a digital signal through filter processing and eliminating the effect of a ripple component. CONSTITUTION:A sample-and-hold circuit 8A samples and stores tentatively an analog signal being an object of signal conversion and its holding value is an analog input to an A/D converter 8B, in which the analog signal is converted into a digital signal and the digital signal is stored in an internal memory or an exclusive register of a CPU 5. The sampling signal of the circuit 8A and the converter 8B and the A/D conversion timing signal are given as a pseudo random pulse from a random number generator 9. The generator 9 generates a pulse number of the same number per unit time with respect to the sampling signal of a prescribed period from the CPU 5 and the pulse timing is used as a pseudo random timing.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a signal conversion method for sampling an analog signal of a power converter to obtain a digital signal.

B1 Summary of the Invention The present invention, when obtaining a digital signal by sampling an analog signal including ripple components, performs random timing sampling on the analog signal and averages the sample values, thereby reducing the influence of the ripple components. This is to obtain a digital signal with the .

C1 Prior Art A power converter such as a static inverter can be controlled with high precision by digitally processing its control device using a microcomputer or the like as the central part.

This digital processing requires signal conversion to convert analog signals from the power converter into digital signals.

FIG. 3 shows a block diagram of a voltage source inverter.

An AC output whose voltage and frequency are controlled by PWM control of an inverter 2 is extracted from the DC output of the rectifier 1, and variable speed control of the induction motor 3 is performed.

The control circuit 4 obtains a PWM waveform according to the frequency command, and is provided with a protection circuit, and the CP tJ 5 performs data input/output with the control circuit 4 for start/stop and forward/reverse control based on sequence commands, and furthermore, In addition to display control on the display 6, voltage control is performed according to the frequency command. Therefore, the DC heavy pressure V of the inverse converter 2 is changed between the DC-DC converter 7 and A
/ D converter 8 takes in the digital signal, a frequency signal is taken in from the control circuit 4 side to perform voltage control, and the voltage data is used for undervoltage/overvoltage protection, etc.

The acquisition of such voltage signals and current signals as digital signals is performed through an A/D converter 8 and a sample bold circuit, and the sampling timing of A/I conversion or sample hold is determined by a control program such as the CPU 5. -9 fixed intervals determined by .

D1 Problems to be Solved by the Invention In conventional signal conversion, the sampling period of A/D conversion is constant, and if the sampling period is 101118, the inverter's human power power frequency (50Hz, 60Hz)
Hz, ) and a low ratio of 125, it may be synchronized with the ripple period (such as 10 mS) of the DC voltage due to the input power frequency.

FIG. 4 shows a state in which the voltage ripple and the sampling timing are synchronized on a one-to-one basis, and the sampling timing is different from the average value VA of the DC voltage. There was a problem that the voltage control accuracy was reduced.

In addition, if surge noise etc. is superimposed on the voltage signal,
Although the ripple value is removed from the detected value by performing filter processing by software on the CPU 5 side, the ripple component cannot be averaged and corrected using the same filtering method.

An object of the present invention is to provide a signal conversion method that can remove the influence of ripples superimposed on an analog signal to be sampled.

Means and Effects for Solving Problem E1 In order to achieve the above-mentioned object, the present invention, in signal conversion for sampling an analog signal of a power converter to obtain a corresponding digital signal, solves the ripple component contained in the analog signal. By sampling the analog signal at random timing with respect to the period, filtering this sample value to obtain a digital signal, and making the sampling timing random for the analog signal including ripple components. Include the ripple in the sample value,
Through the filter processing, a digital signal with the ripples averaged is obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the present invention. 2
The analog signal to be converted is sampled and temporarily stored (held) by the sample bold circuit 8A, and this hold value is converted into a corresponding digital signal as an analog input to the A/D converter 8B. This digital signal is stored in the internal memory of the CPU 5 or in a dedicated register.

Here, sample hold circuit 8A and A/D converter 8
The sampling and A/D conversion timing signal of B is given as a pseudo-random pulse from the random number generator 9. The random number generator 9 generates the same number of pulses per unit time in response to a sampling signal of a constant period from the CPU 5, but the pulse timing is made pseudo-random. For example, if the sampling signal from the CPU 5 has a constant period of 10 ms, the random number generator 9 divides the period of the sampling signal into n equal parts and generates timing pulses for the sample hold circuit 8A and the A/D converter 8B at n types of random timing. occurs.

FIG. 2 illustrates a sampling waveform diagram. For analog signals including ripple components, the sample timing signal generated from the random number generator 9 has a period of 10 ms of the power frequency.
Evenly divided timing and random. With such random sampling, even when there is synchronization, such as when the ripple division period of the analog signal due to the power supply frequency and the sampling period of the CPU match, sampling is performed randomly on the analog signal, and the digital input of the CPU 5 By filtering, a digital signal proportional to the average value of the analog signal can be obtained.

For example, if this digital signal is used as the voltage detection signal of the inverter shown in Figure 3, it can be used for undervoltage/overvoltage protection, regenerative power control during deceleration, etc. to increase voltage detection accuracy, reduce malfunctions and erroneous control, and improve accuracy. enhance

Effects of the G9 Invention As described above, according to the present invention, sampling of an analog signal including ripple components is performed at random timing,
In order to obtain a digital signal by filtering the sample value, even when the ripple period of the analog signal and the sampling period of the CPU are the same, the influence of the ripple can be removed to perform highly accurate signal conversion. There is an effect that can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a sampling waveform diagram of the embodiment, FIG. 3 is a block diagram of a voltage source inverter, and FIG. 4 is a voltage sampling waveform diagram. 8A...Sample hold circuit, 8B...A/D converter, 9...Random number generator.

Claims (1)

[Claims] (1) In signal conversion in which an analog signal of a power converter is sampled to obtain a corresponding digital signal, the analog signal is sampled at random timing with respect to the period corresponding to the ripple included in the analog signal, and the sample value is A signal conversion method characterized by filtering and obtaining a digital signal.