Electric energy metering system consists of watt-hour meter, voltage transformer and current transformer. Hence, the error of electric energy metering system should be analyzed from the three parts. Aiming at the measurement accuracy of the power metering system under harmonics, the equivalent circuits of electronic watt-hour meter, capacitive voltage transformer and magnetic current transformer under harmonic conditions are built, and the harmonic measurement/metering error and the influencing factors are analyzed. The model of electric energy metering system is set up to analyze its error under harmonic conditions. This article provides a theoretical basis for the quantitative analysis of measurement error of the energy metering system under harmonics.

The four leg shunt active power filter has strong ability of harmonic and neutral current compensation, and is especially suitable for three-phase four-wire system harmonic suppression. At present the single inductor filter is usually used in four leg shunt active power filter, but the single inductor filter does not have enough capacity for high frequency harmonic attenuation. Due to this，this paper proposes a three-phase four-leg applied to active power filter LCL filter. This paper proposes a LCL filter which is applied to three-phase four-leg active power filter. However, LCL filter can produce resonance. Series resistance in capacitor branch can inhibit resonance. As a result, it will consume more active power. So this paper proposed control strategy using capacitive current feedback, which can not only effectively suppress resonance but also avoid consuming active power.