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Twenty years ago, R. Severns presented a transformer based circuit which is able to measure DC currents. However, this circuit did not experience a break-through in the industry or even academic world because it requires too many components and is unable to measure small currents. This paper enhances this circuit so that it becomes feasible to measure currents down to zero. The circuit complexity is no longer an obstacle because in digital controlled power supplies the DSP provides the required auxiliary functionalities. The feasibility of the proposed circuit has been proven by hardware experiment.

In this paper, the implementation of a shunt active power filter with a small series inductor for a three-phase system is presented. The filter consists of a three-phase current-controlled voltage source inverter (CC-VSI) with a filter inductance at the ac output and a dc-bus capacitor. The series inductor is primarily used to handle the harmonic voltage source. The main concern is the size of the series inductance so that it is as small as possible but effective in compensating the harmonics. In order to select the proper value of the series inductance, the simulation is conducted to evaluate the value for different types of load.

In this paper a novel space vector modulation method for single-phase inverters is presented. Mathematical analysis, simulation and comparison of conventional sinusoidal pulse width modulation (SPWM) techniques with the proposed space vector modulation for single-phase inverter are included. These modulation techniques are compared, evaluated and classified for different single-phase applications, including deadband effects. The proposed modulation method combines the flexibility of the well-known unipolar PWM scheme for single-phase inverters result in maximum harmonic mitigation. The new technique is suitable for simple digital implementation. Experimental results, obtained by a digital signal processor (DSP) board, are included.