Soft start-up scheme for the hybrid distribution transformer

Abstract

Hybrid distribution transformer (HDT) is an integrated system of the conventional distribution transformer and the PWM converters, which can greatly enhance the controllability of the conventional distribution transformer and is important for the intelligence of the future distribution network, since HDT can support the AC–DC power network and control the voltage and current in real time. However, the impact current, over voltage, and saturation will lead to the start-up failure when an incorrect start-up scheme is adopted in HDT. Therefore, it is significant to design a reliable start-up scheme to guarantee a safe operation for HDT. Here, a three-phase circuit scheme and the control system of HDT are proposed. Then, a soft start-up scheme that can realise the constant-current charging for the DC bus capacitor is proposed. Specifically, the soft start-up scheme is based on the following measures, bypassing the DC-bus current-limiting resistors when the voltage of DC-bus capacitor exceeds the threshold, limiting the output of PI controllers during the start-up, separating the integral coefficient according to the DC-bus voltage error. Finally, the proposed start-up scheme is verified in MATLAB, which lays the foundation for the optimal design of the start-up scheme of HDT.

Keywords

• PI control
• PWM power convertors
• power transformers
• distribution networks
• power capacitors
• voltage control
• controllability
• electric current control
• soft start-up scheme
• hybrid distribution transformer
• HDT
• AC–DC power network
• start-up failure
• three-phase circuit scheme
• constant-current charging
• DC-bus capacitor
• DC-bus voltage error
• distribution network
• PWM converters
• controllability
• DC-bus current-limiting resistors
• PI controllers
• integral coefficient