An Improved Central 60° Synchronous Modulation for High Transient Performance with PMSM Stator Flux Control Used in Urban Rail Transit Systems

Abstract

Central 60° synchronous modulation is an easy pulse-width modulation (PWM) method to implement for the traction inverters of urban rail trains at a very low switching frequency. Unfortunately, its switching patterns are determined by a Fourier analysis of assumed steady-state voltages. As a result, its transient responses are not very good with over-currents and high instantaneous torque pulses. In the proposed solution, the switching patterns of the conventional central 60° modulation are modified according to the dynamic error between the target and actual stator flux. Then, the specific trajectory of the stator flux and current vector can be guaranteed, which leads to better system transients. In addition, stator flux control is introduced to get smooth mode switching between the central 60° modulation and the other PWMs in this paper. A detailed flow chart of the control signal transmission is given. The target flux is obtained by an integral of the target voltage. The actual PMSM flux is estimated by a minimum order flux state observer based on the extended flux model. Based on a two-level inverter model, improved rules in the α-β stationary coordinate system and equations of the switching patterns amendment are proposed. The proposed method is verified by simulation and experimental results.

Simple current control of permanent magnet synchronous machines for railway traction operating in six‐steps

“…The six‐steps realisation in [11–18] does not consider the inverter switching frequency limit. With limited switching frequency, railway traction inverters usually adopt multi‐modes PWM, including asynchronous modulation, synchronous modulation and six‐step single pulse modulation [23]. Asynchronous SVPWM is widely used for low‐frequencies, while the six‐step operation is an extension of synchronous modulation.…”

“…SHEPWM is widely used for traction, although the switching angle calculation needs the solution of the transcendental equation that cannot be done in real time. In addition, there is also the problem of smooth switching to other modes [23]. SVPWM is easy to implement digitally and the overall harmonic characteristics of some types of synchronous SVPWM are not inferior to SHEPWM [28] and therefore has been adopted in this paper for application to traction inverters.…”

Current closed‐loop control and field orientation analysis of an induction motor in six‐step operation for railway applications

“…Due to the voltage limitation of the inverter DC link, IMs require flux-weakening control to extend the operating speed. In railway traction drive systems, the inverter generally enters six-step operations to utilise DC-link voltage when the motor is in the flux-weakening region [3][4][5]. Compared with the linear region of the space vector pulse width modulation (SVPWM), the inverter output fundamental voltage amplitude is improved by 10.26% in six-step operations with consequent improvement of the output torque and working area.…”