Design and implementation of a high accuracy sampling wattmeter under non-sinusoidal and off-nominal frequency conditions

Errors may creep in when measuring active power under non-sinusoidal and off-nominal frequency conditions by a conventional regularly spaced sampling digital wattmeter (RSSDW) due to the existence of higher order voltage and current harmonics, and asynchrony between the signal fundamental frequency and the sampling rate. This paper presents design and implementation of a modified regularly spaced sampling digital wattmeter, called M-RSSDW, immune to above mentioned drawbacks of the conventional RSSDW. The proposed method utilizes a modified/ first degree digital integrator design technique, suitable for the distorted power system signals. The harmful truncation errors of asynchronous sampling have been reduced using numerical compensation method. Compared with the well-established technique such as Liangs’ method, the proposed algorithm provides higher degree of immunity and insensitivity to harmonics and frequency deviation. Structural simplicity, wide range of application and reduced computational load are other salient features of the proposed method. Based on simulation studies, the performance and validity of the proposed algorithm at different operating conditions have been presented and its accuracy and response time have been compared with the Liangs’ approach.