Due to the voltage limitation of the inverter DC-link of railway traction systems, six-step operations are widely used in the high-speed region to improve the voltage utilization and increase the maximum fundamental frequency. The magnitude of the output voltage fundamental harmonic reaches the maximum for six-step operations, while only the phase angle can be adjusted. This limitation makes it challenging to control the instantaneous current of permanent magnet synchronous motors (PMSM). This paper proposes a single d-axis current regulator flux-weakening control scheme to improve the current control over six-step operations of PMSM without changing the inverter output voltage modulation ratio by controlling only one degree of freedom. The voltage in six-step operations is generated by synchronous space vector pulse width modulation based on basic bus clamping strategy with an effective limitation of the switching frequency in the full-speed region. A simplified model of the current regulator is developed for the analysis and design of the controller parameters. This paper presents clear rules for entering and quitting six-step operations effectively to achieve a smooth transition between double current regulators and the single current regulator control. The numerical results are verified by experimental measurements on a 7.5 kW PMSM drive.
|Pages (from-to)||2640 – 2647|
|Number of pages||8|
|Journal||IET Electric Power Applications|
|Early online date||4 Dec 2020|
|Publication status||Published - 18 Dec 2020|