We provided third party design review services for a major electrical power systems manufacturer to improve the electrical reactive and real power calculation accuracy of a power system measuring device. Upon completion of the design review, solutions were proposed for reducing the measurement errors. The proposed unique solution was then implemented in software resolving the existing measured distortion. This was designed to use no additional CPU resources, a major requirement for real time equipment, while fixing the measured errors consistently. The solution was fully tested to prove the new measurement algorithm to be a success.
These power measurement errors were found to be caused by phase distortion introduced in both the existing electronics and real time software of the power system measurement device. In the electronics, the relative phase angle differences between each of the CTs (current transformer) and VTs (voltage transformer) were created by the various input stages before the ADC (Analog to Digital Converter).
The analogue circuits were analysed by creating mathematical models of the system and confirmed with the measuring results. We conducted both analytical and numerical analysis of the phase distortion through modelling of both the CT and VT circuits, and analysed the signal propagation timing. The firmware was also analysed for improvements to better control the ADC. Computer modelling and circuit simulations were also performed to determine the transfer functions (impedance models) of the various stages of the circuit. The simulations, transfer functions and measured results all matched confirming where each of the errors were introduced.
Upon the completion of reviewing the power calculations, we proposed a unique software solution involving correction matrix mathematics. Other optimisations were also introduced which actually reduced the overall CPU usage of the power calculations performed. This software algorithm was first simulated numerically before developing to correct all of these errors with our in-house engineering testing matching the numerical simulation. Our final solution provided significant improvements to the power measurement accuracy. The firmware was then fully tested by a third party tester to confirm the reliable operation of the measurement device with accurately measured power.
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