An experimental study of the effect of constant rms current with different THD to the single phase digital kWh meter is presented in this paper. The study focused on how harmonics from non-linear load with constant voltage supply and constant rms current affect the energy measurement of single phase digital watt-hour meter. Traditionally, analog electromechanical meter is using the rms current as its main measurement parameter. In digital meter, different techniques and sampling are used to measure the power consumed by the consumers. Although different techniques and sampling are used, the rms current parameter is still the dominant parameter used to measure and calculate the energy measurement. Both electromechanical and digital meter show good measurements under linear load condition. On the other hand, under non-linear load, harmonics are often neglected in energy measurement. In addition, harmonics in heavily distorted current originated from non-linear load and contributed to lot of losses and it will not be recorded in the billing. To make the situation worse, harmonics can propagate through the transformer and they will be affected the power network either if the harmonics are injected from the source or load side. Analysis from the measurement data clearly showed the effect of the harmonics to the energy measurement. In consequence, either utility company or consumer shall be affected if the harmonics parameter is neglected in the energy measurement purpose. The results showed that no significant difference when the actual digital watt-hour meter energy reading is compared to the calculated energy consumption based on rms current value. Therefore, either harmonics are taken or not taken into account during the energy measurement, the consumer is not affected and still paying the same prices. However, the utility company will be burdened by some losses if harmonics are not taken into consideration.

This paper presents an optimized and enhanced DC-DC converter design for 20V output for portable instrument application. The proposed design is based on isolated push pull topology switched mode power supply. Selfdriven synchronous rectification (SDSR) is introduced in the rectification stage in order to create an improved way of rectifying process. N-Channel and P-Channel MOSFETs are used to simplify the synchronous rectification control circuit. Both MOSFETs offer ultra low On-resistance which can be used to achieve higher efficiency than the conventional converter. This converter operates at high speed switching frequency to gain high power-to-volume ratio. In addition, minimum deadtime is set in the design to ensure high efficiency in input-output power transfer. Passive low pass filter is implemented to produce ripple free output voltage in the design. The finalize topology which is push pull with self-driven synchronous rectification is constructed using simple control circuit but maintains good efficiency in its operation. Experimental results show that the proposed converter reacts very well with the self-driven synchronous rectification method. Input voltage is set at 12V and switching frequency is set at 30 kHz in order to minimize the switching stress and conduction losses. Practical implementation of the converter shows that the converter operates at a maximum efficiency of 84.1% and only produces 50mVp-p ripple output voltage which is considered good for a regulated DC output.