Three phase active harmonic rectifier (AHR) to improve utility input current THD in telecommunication power distribution system

Modern telecommunication power supply systems have several parallel connected switch mode rectifiers to provide -48 V DC. Typical switch mode rectifier configuration includes a three phase diode rectifier followed by a DC-DC converter. Such a system draws significant harmonic currents for the utility resulting in poor input power factor and high total harmonic distortion (THD). In this paper, a three phase active harmonic rectifier (AHR) scheme is proposed. In AHR scheme, a diode rectifier module is replaced by 6-IGBT PWM rectifier to supply load harmonics as well as its own active power. Each DC-DC converter module is connected to a shared 48 V dc-link. The AHR module together with parallel connected switch mode rectifiers is controlled to achieve clean input power characteristics. The VA ratings of AHR scheme is compared with an active power filter (APF) approach. The control design is based on the synchronous reference frame approach. Analysis, simulation and experimental results show that AHR offers several advantages such as lower VA rating, better current control response, efficient use of AHR dc-link, small size, and stable dc-link voltage control.