GB2205425A

GB2205425A - Pseudo four quadrant multiplier for use in power measurement meters

Info

Publication number: GB2205425A
Application number: GB08712957A
Authority: GB
Inventors: P G Williams; A J Wilks
Original assignee: OMEGA ELECTRIC Ltd
Current assignee: OMEGA ELECTRIC Ltd
Priority date: 1987-06-03
Filing date: 1987-06-03
Publication date: 1988-12-07
Also published as: GB8712957D0

Abstract

A pseudo four quadrant multiplier is based upon rectification 1, 2; 3, 4 of both input signals followed by an interaction between a voltage to frequency converter and a pulse width modulator. The current (i) signals lead to a signal whose frequency corresponds thereto, the voltage (v) signal leading to a pulse width modulated signal of high frequency. The signals are logically combined to produce pulse trains corresponding to positive and negative power, which are fed to up/down counter 15. Full wave rectification may be used. (Fig. 2). <IMAGE>

Description

DESCRIPTION PSEUDO FOUR QUADRANT MULTIPLIER FOR USE IN POWER MEASUREMENT METERS This invention relates to pseudo four quadrant multiplier for use in power measurement systems such as solid state electricity meters.

Solid state electricity meters generally require a four quadrant multiplier to compute the actual power waveform with varying voltage, current and power factor of the load. This is generally achieved using a four quadrant multiplier based upon the variable transconductance principle. Unfortunately such four quadrant multipliers suffer from drift problems and linearity errors.

According to the present invention a pseudo four quadrant multiplier can be made which does not suffer from the type of problems detailed above.

A specific example will now be described with reference to the accompanying drawings.

Figure 1 shows in block diagram form a pseudo four quadrant multiplier using a multiplicity of half wave rectifiers, voltage to frequency converters and pulse width modulators.

Figure 2 shows in block diagram form a pseudo four quadrant multiplier using two full wave rectifiers, a single voltage to frequency converter and a single pulse width modulator.

Referring to Figure 1 the instantaneous AC current (i) and voltage (v) are applied to a network of half wave rectifiers numbered 1, 2, 3 and 4.

1 converts positive AC current to a positive voltage 2 converts negative AC current to a positive voltage 3 converts positive AC voltage to a positive voltage 4 converts negative AC voltage to a positive voltage A fast voltage to frequency converter 5 converts the output of 1 into a frequency while a similar unit 6 converts the output of 2 into a frequency.

A pulse width modulator 7 samples the output of 3 to produce a varying mark space ratio with sufficiently high frequency to effectively sample the output of 3.

Likewise 6 converts the output of 2 to a frequency and 8 samples 4 into a varying mark space ratio.

The 'AND' gates 9 gate together samples of pseudo instantaneous values of current expressed as a rate and voltage expressed as the mark space ratio of a frequency for all positive values of voltage and current. Similarly 10 gates together all negative values of voltage and current. Hence the output of 'OR' gate 11 is a pulse train representation of the positive power going into a load. This pulse train is fed to the count up input of a bidirectional counter 15.

The 'AND' gates 12 and 13 with OR gate 14 give a pulse train representation of the negative power coming from a reactive load.

This pulse train is fed onto the count down input of the counter 15.

The counter 24 may either contain a cumulative total or it may produce cumulative output pulses to a further counter.

In general the input signals (v) or (i) may be interchanged.

Referring to Figure 2 which is a more cost effective version of Figure 1, signals representing the instantaneous line current (i) and the instantaneous line voltage (v) are applied to two full wave rectifiers 16 and 17. The output of 16 is applied to 18 which is a fast voltage to frequency converter. The output of 17 is applied to 19 which is a pulse width modulator producing a varying mark space ratio with a sufficiently high frequency to sample the output of 17.

The signals (i) and (v) are applied to a power polarity detector 20 whose output is high when the power value is positive and low when it is negative.

The outputs of 18, 19 and 20 are applied to the steering logic of 21, 22 and 23 so that the output of 22 is gated samples of pseudo instantaneous values of current expressed as a rate and voltage expressed as the mark space ratio of a frequency for all positive values of power. The output of 23 is a similar pulse train for all negative values of power.

The output of 22 is fed to the count up input of a counter 24.

Likewise the output of 23 is applied to the count down input of the counter 24.

In general the input signals (v) or (i) may be interchanged.

Claims

1. A pseudo four quadrant multiplier for use in electrical power meters based upon the multiplying action of a variable frequency gated with a varying mark space ratio at a fixed frequency.

2. A pseudo four quadrant multiplier as in Claim 1 constructed using four half wave rectifiers to convert bi-polar voltage and current to individual uni-polar signals to a combination of frequency to voltage converters and pulse width modulators to provide a positive power pulse train and a negative power pulse train.

3. A pseudo four quadrant multiplier as in Claim 1 constructed using two full wave rectifiers, a single voltage to frequency convector, a single pulse width modulator and a power polarity detector to provide a positive power pulse train and a negative power pulse train.