JPS62254069A - Voltage and current detection system for power converter - Google Patents

Abstract

PURPOSE:To obtain a mean of an object to be detected at a highly accurate digital value irrelevant to the waveform thereof, by dividing an integrated value synchronized with a fundamental cycle of the waveform of the object being detected by the cycle to determine the mean thereof. CONSTITUTION:A voltage-frequency (V/F) converter 1 converts a voltage obtained by addition of a fixed voltage from a reference voltage generator 7 to a signal to be detected into a pulse train with the frequency equivalent thereto. A counter 3 counts the number of output pulses of the V/F converter 1 generated up to the present ignition time point from the preceding ignition time point in synchronization with the igniting action of a power converter 10 for outputting the signal to be detected. A counter 4 measures a time required for the outputting of the number of output pulses of the V/F converter 1 in synchronization with the pulse thereof. A digital processor 12 subtracts a known fixed value from a value obtained by dividing a count value of pulses from the counter 3 latched 5 by a required time from the counter 4 latched 6 to determine a mean of the signal to be detected at an ignition cycle of the power converter 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current and voltage detection method in a power conversion device such as a thyristor Leonard.

[Conventional technology]

In general, the current waveform in a power conversion device such as a thyristor Leonard has an oppressive beam pull (pulsation), and therefore the value obtained by randomly detecting one point of the instantaneous waveform is considered to be affected by the beam pull. It will show up. Thus, for example, in the above device controlled by a microcomputer, the current, 'I! Various methods have been conventionally used to detect pressure, such as the following. 5 to 7 are explanatory diagrams for explaining conventional examples of current and voltage detection methods.

(1) In the case shown in FIG. 5, a filter 22 is provided after the detection section (sensor) 21 to smooth out ripples, and then the A/D converter 23 (or V/F converter) is activated at any time. is used to convert analog quantities into digital values.

(2) In Fig. 6, the influence of ripple is avoided by sampling the instantaneous value at a point S of a constant phase of the instantaneous waveform 24, and this sampling value is converted from an analog quantity using an A/I) converter etc. This is to convert it into a digital value S5.

(6) Also, in FIG. 7, the instantaneous waveform indicated by the reference numeral 25 -
Instantaneous values V1 * V2 at multiple points in the cycle
- Sampling Vn, converting this value from an analog value to a digital value using an A/D converter, etc., and then finding the arithmetic mean S4 of the values.

[Problem that the invention seeks to solve]

However, in the method (1), even if a filter is used, the ripple component cannot be completely smoothed out, so the ripple component is affected by the sampling timing. Furthermore, since the constant of the filter is fixed regardless of the waveform of the detection target, steady state, or transient state, the signal after filter processing faithfully reflects the original enemy image, especially in a transient state where the detection target changes dynamically. Detection errors occur due to the 2nd representation.

On the other hand, in the methods (2) and (3), the relationship between the instantaneous value and the average value of the instantaneous waveform is not constant, but is a function of the circuit constant 2-phase control angle, etc., so the timing is always ideal. It is virtually impossible to sample, and therefore there are problems such as detection errors.

Therefore, when detecting voltage, current, etc. in a power converter, etc., the present invention accurately converts the waveform of the object to be detected (irrespective of the average value in the basic period of the object to be detected caused by the ignition operation of the power converter) into a digital quantity. The purpose is to provide a detection method that can detect

[Means for solving problems]

Voltage-period tfjl number C that converts the voltage obtained by adding a known constant voltage to the detection target signal into a pulse train with an equivalent frequency
Count the number of V/Ff converter output pulses from the previous firing time to the current firing time in synchronization with the firing operation of the V/F) converter and the power converter that outputs the detection target signal. A counting means and a time measuring means for measuring the time required to output the number of pulses in synchronization with the output pulses of the V/F converter are provided.

[Effect]

In this invention, the number of pulses output from a voltage-frequency V, number converter (V/F converter) in a certain period is
This was done by focusing on the fact that it is proportional to the integral value of the input voltage of the /F converter, and a predetermined constant value is added as an offset amount to the detection signal equivalent to the voltage or current of the power converter. is input to the V/F converter, and the number of output pulses is counted in synchronization with the fundamental period of the e-type to be detected, that is, the firing operation of the power converter, and is equivalent to the integral value of the detection signal during that period. In addition to measuring digital quantities,
The time required for the V/F converter to output the above number of pulses is V/F.
By subtracting the known offset amount from the average value of the period obtained by measuring in synchronization with the output pulse of the F converter and dividing the integral value by the time, the average value of the detection target can be calculated as 77Xah z< W nNRL 4 /
Old am M: No. 57 n-JR--Bubat
It is something that makes things happen.

This point will be explained in more detail below.

Generally, the output voltage and output current waveforms of a power converter have a pull. For example, the output voltage waveform of a three-phase pure bridge rectifier circuit with a conductive load as shown in FIG.
The i current waveforms are as shown in FIGS. 4(a) and 4(b), respectively. The average values of the output voltage and current in this case indicate that the phase control angle can be determined as α if the commutation type phenomenon is ignored.

L7 However, the result obtained by integrating a voltage or current waveform over a given period and dividing it by that integration period is expressed by formula (1), except in special cases (when the integration period is an integral multiple of the fundamental wave period). , the result is different from (2). Furthermore, in a transient state where the phase control angle α changes, the average value differs depending on the integration period and its phase.

On the other hand, since control of a power converter is not continuous but is performed intermittently over time, the control must be limited to the average value or integral value in the control period. Therefore, it is preferable that the voltage and current values in the control of the power converter are average values obtained over two periods of nine phases in synchronization with the control cycle (ignition cycle of the power converter).

Incidentally, since the output frequency of a V/F converter is proportional to its input voltage, if the input voltage is v H + v o , the output frequency f of the V/F converter is expressed by the following equation. Ta! However, k in the following equation is a constant.

fv−k x (vl+yo) --(3)
Furthermore, since the output pulse of the V/F converter is output every time the integral value of the input voltage reaches a certain value, F
The count value Fv of the pulses output from the V/F converter over D is the input voltage of the V/F converter v r + during that period.
It is proportional to the integral value of vo.

That is, if k' is a constant, It is expressed as follows.

If the average values of 1 stroke pressure Vl * V [1 in period FD are Vi and vo, respectively, then F'y - k' x (V1+Vo) X Fo
- (5), and therefore we obtain. This means that vo is known and constant (that is, ′ and V
o = Vo), it is shown that the average value ■1 of the voltage VH can be obtained from the η↑ value Fv of the output pulse of the F/V converter and the period Fo, regardless of its shape and ripple.

[Embodiments of the invention]

℃ flow detection rc in thyristor Leonardo An example in which this invention is applied is shown in Fig. 1, and its operation forming is shown in Fig. 2.
As shown in the figure. In addition, in FIG. 1, C11 is a V/F converter,
2 is a detector (sensor), 3.4 is a counter, 5 and 6 are data latch circuits, 7 is a reference voltage generator, 8 is a reference tick generator, 9 is a phase shifter, 10 is a power converter, 11 12 is a digital processing device such as a -r microcomputer, and 16 is a bus.

Here, the phase shifter 9 outputs a firing signal Gf: to the power conversion device 10 in accordance with the phase signal PK of the power source vA in accordance with the phase control angle command A given from the processing device 12 via the bus 15. The thyristor of the power converter fallD receives the firing signal G.
A commutation operation is performed by the converter output current 1 to flow through the load 11. The current detection signal Y1 as shown in FIG. 2 (a), which is converted by the sensor 2 into a voltage tBL form equivalent to the waveform of the converter output current 5, is added to the reference voltage Vo generated by the reference voltage generator 7 to obtain V. /F converter 1 is input to the pulse train fv with a frequency proportional to the input voltage.
It is converted as follows. The pulse train (the number of pulses) is counted by a counter 3. The counter 3 receives a sampling pulse S(
In synchronization with the first V/F converter output valve immediately after the input (see Fig. 2 (b)), the latch signal is output as shown in Fig. 2 (d), and the own count value Fv is As shown in FIG. 2 (e), the count is reset to 0 and the counting operation continues. The data latch 5 latches the count (direct FY) of the counter 3 immediately before being reset to 0 by a latch signal.The data latch 5 is a counter that counts the reference clock fO as shown in FIG. 4 synchronizes with the latch signal 7 and sets the count value Fo to the second
Reset to 0 as shown in figure (g). The data latch 6 is
Count value F of counter 4 immediately before OIC reset
D is latched by the latch signal.

In other words, the count value Fv of 30 latched in the data latch 5 is the count value of the V/F converter output pulse that occurred in the immediately previous firing cycle. In addition, the count value Fo of the counter 4 which is double-checked in the data latch 6 is the number of pulses 1j times the standard counted in the period required to count only the output pulse tFv of the V/F converter, and (
time) is a value proportional to K. Therefore, Fv/Fo is the V/F converter input voltage vl+v during the above period. The value is proportional to the average value of . Furthermore, V out of the input voltage of the V/F converter. Since the reference voltage is constant and known, the V that accounts for F v / F o. The average value of is a constant value, and the average value Vi of the current detection signal Vi can be obtained using the above equation (6).

Detection errors in the embodiments of the present invention can be divided into errors due to non-synchronization between the fundamental period of the detection target (waveform) and the measurement period during which averaging is performed, and errors due to the measurement itself. In the former case, in Fig. 2, the current waveform [current detection signal Vl] and the output pulse fv of the V/F converter 1 are not strictly synchronized, so the period during which the actual average value is taken is the waveform to be detected. This is an error caused by not matching.

However, this synchronization deviation is at most one period of the output pulse fv of the V/F converter. Moreover, even if the current detection signal Vi is the minimum, the maximum value of the period, that is, the minimum output frequency of the V/F converter, is guaranteed to be the minimum value of the V/F converter input terminal by adding the reference voltage v00, and as a result, Since the minimum value of the output frequency, that is, the maximum value of the period, is guaranteed, the reference voltage V. By appropriately selecting , the detection error due to this synchronization shift can be reduced to a practically negligible level. In addition, in the case of , the average value itself for the measurement period has high detection accuracy as described later, and the average value or integral value of the error due to this synchronization shift is OK.

On the other hand, the error caused by the latter measurement itself is the reference clock in the measurement of the integration period! ! This is due to the quantization error of the i' number. In other words, the detection error Δ(
From equation (5), VB+Vo) is vFv Vl+V,) Fv k'F.

becomes. Therefore, the reference clock f is set so that FD is sufficiently large for the fine period. This error can be easily reduced by selecting the frequency of .

〔Effect of the invention〕

According to the present invention, the average value is obtained by dividing an integral value synchronized with the fundamental period of the waveform to be detected by that period.

It is possible to realize average value detection that is extremely faithful to the principle regardless of ripples. In addition, by using a V/F converter as a means for performing an integral operation, the integral value can be directly converted into a digital value in the form of the number of pulse outputs at the same time as the integral operation, making analog-to-digital conversion extremely easy and inexpensive. Can be done. Furthermore, V/F
By adding a constant input to the input of the converter, a) the minimum output frequency of the V/F converter can be limited and synchronized with the waveform to be detected.

A) The V/F converter can be used only in areas where the linearity of its conversion operation is good.

...), iE・For detection targets that change negatively, ■
By making the input of the /F converter unipolar, there is no need to provide an external means for determining polarity.

Effects such as this can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram of each part to explain its operation, Fig. 6 is a circuit diagram showing a general three-phase pure bridge rectifier circuit, and Fig. 4 is a waveform diagram showing the output voltage and current, and FIGS. 5 to 7 are explanatory diagrams for explaining conventional examples of voltage and current detection methods. Code explanation 1... Voltage-frequency converter, 2.21...
...detector (sensor),! 1, 4... Counter, 5, 6... Data latch circuit, 7...
・Reference voltage generator, 8... Reference clock generator, 9... Phase shifter, 10... Power converter, 11... Load, 12... ...Digital processing device (microcomputer), 13...
bus, 22...filter, 23...analog/digital (A/D) converter, 24.25.
...Detection signal, vA... AC voltage, i.
...Converter output current, VB...Current detection signal, %'a...Reference voltage (offset), f
v...V/F converter output pulse, Fv. Fo...Count value, fo...Reference clock, S...Sampling pulse, L...Latch signal, P...Phase signal, A...
... Phase side elevation angle command, G... Firing signal. Agent Patent Attorney Akio Namiki Agent Patent Attorney Kiyoshi Matsuzaki Figure 1 Figure 2 Figure 3 Diagram Figure 4 0-〜〜−−−−−−−−−−−−−−−−−−− ---
−−−−−−−−−−−−−−−−(b)

Claims (1)

[Claims] A voltage-frequency converter (V/F converter) that converts a voltage obtained by adding a known constant voltage to a signal to be detected into a pulse train of an equivalent frequency; a counting means for counting the number of V/F converter output pulses from the previous ignition time to the current ignition time in synchronization with the ignition operation of the output power converter; and the output of the V/F converter. a time measuring means for measuring the time required to output the number of pulses in synchronization with the pulse; A voltage and current detection method for a power converter, characterized in that an average value of a signal to be detected in a firing cycle of the power converter is obtained by subtracting the known constant value.