Capacitorless Synchronous Reluctance Motor Drives for Pump Applications With Resonance Damping and Line Current Harmonics Reduction

Due to their better efficiency, synchronous reluctance motors (SynRMs) are emerging candidates for substituting the conventional induction motors in electric pump systems. Requirements for size, cost, and reliability push toward capacitorless inverters, in which large electrolytic capacitors used to stabilize the dc-link voltage are replaced by small film capacitors. Combined with particular grid conditions, capacitorless drives can lead to dc-bus instability. The problem is not new, and the literature presents many solutions. The issue that this article addresses is the need for a rigorous and comprehensive mathematical analysis of the complex interactions among load, motor, and grid when the decoupling action of the dc capacitor bank is lacking. In cascade, the theoretical analysis leads to propose a new way to produce the required damping power, by acting on both voltage and current perturbations, that allows also a sensible reduction of line current harmonics. This article provides design guidelines for tuning the regulators and includes experiments that prove the correctness of the theoretical analysis and the effectiveness of the proposed technique.