Mutual Inductance-Type Current Sensing

Apparatus for processing signals received from a mutual inductance current sensor having a first transfer function, the apparatus comprising:

• a low-pass filter which receives a signal from the current sensor, the low-pass filter having a second transfer function configured to attenuate one or more harmonic components of the signal;
• an analogue-to-digital converter which receives and digitises a filtered signal output from the low-pass filter;
• a controller configured to process a digitised current signal from the analogue-to-digital converter using a digital processing chain configured to compensate for the frequency and phase responses of the first transfer function and the second transfer function;
• wherein the apparatus is for measuring a signal corresponding to an alternating current having a fundamental frequency and wherein the apparatus is configured to measure up to a predetermined harmonic of the fundamental frequency;
• wherein the second transfer function of the low-pass filter has a −3 dB corner frequency which lies between the fundamental frequency and the predetermined harmonic.

A method comprising:

• receiving a signal from a mutual inductance current sensor having a first transfer function;
• filtering the received signal in the analogue domain using a low-pass filter having a second transfer function configured to attenuate one or more harmonic components from the signal;
• converting the filtered current signal to the digital domain to generate a digitised signal;
• processing the digitised current signal using a digital processing chain configured to compensate for the frequency and phase responses of the first transfer function and the second transfer function;
• wherein the signal corresponds to an alternating current having a fundamental frequency and wherein the method is intended to measure up to a predetermined harmonic of the fundamental frequency;
• wherein the second transfer function of the low-pass filter has a −8 dB corner frequency which lies between the fundamental frequency and the predetermined harmonic.