Control of a 9-Phase PMSM with Stacked Polyphase Bridge Converter including DC Source Impedance

This paper presents a control concept for a drive system consisting of a 9-phase PMSM connected to a stacked polyphase bridge converter (SPBC) under consideration of the DC source impedance (Rb,Lb). When the converter is connected to the DC source with a cable, the cable impedance represents a source impedance that could cause instabilities affecting the total DC link voltage and the module voltage balance. In this paper, a control concept is presented for stabilising the module voltage balance via an appropriate definition of the module reference voltage. The total DC link voltage is not controlled but stability is ensured by sufficiently large DC link capacitors. The complete drive controller concept is validated in a simulation of a 1.5kW drive system.

I. Introduction

A promising solution to fulfil the need for more efficient, smaller, and less expensive electrical drives is the concept of integrated motor drives (IMDs) [1]. IMDs combine an electric motor and its driving inverter in one mechanical unit. A converter topology that is particularly suited to IMDs is the stacked polyphase bridge converter (SPBC, [2]) due to its modularity and due to its lower ^dv/_dt on the motor windings compared to conventional two-level topologies [3]. Furthermore, the SPBC can be used in combination with multiphase motors. Multiphase motor windings such as for example 9-phase motor windings enable a higher winding factor than conventional 3-phase windings. The higher winding factor results in a higher efficiency/power density of the drive system [4]. In addition, DC cables are used to connect IMDs to a DC voltage source that is located with some distance to the IMDs. Possible applications for such cables are electric cars (for connecting the inverter(s) to the battery) or factories with a single DC supply connected to multiple distributed IMDs.