Instantaneous Current Distributing Control Collaborated with Voltage to Neutral Equalization for Grid-Tied Single-Phase Three-Wire Inverters

To provide multiple standard voltages for various load specifications, a single-phase three-wire inverter in which a neutral line tapped to the midpoint of the dc-link was adopted. Since the loads across the line to neutral are always distinct, different degrees of drop voltage across the inverter coupled filter would result unbalanced line-to-neutral voltages. This paper presents a control strategy for the inverter that is able to distribute the current for a feeder tied to the point of common coupling (PCC) while preserving a favorable voltage to neutral equalization. To equalize the line-to-neutral voltages, a simple algebraic algorithm using only the grid voltage and line current was proposed. As a result, complicated computations involved in the current control loop can be avoided. In addition, the implementation cost can be reduced to a great extent since there is no need for sensing the line-to-neutral voltage. A mathematical formulation for the proposed control scheme is first described. Then the dynamic responses subject to various loading conditions are performed on a 2kVA modified full-bridge inverter with dc bypass (FB-DCBP) platform. It is concluded from the experimental results that line-to-neutral voltage can be effectively equalized under various loading conditions with the proposed approach.