Small Signal Analysis and Control of High Speed PMSM Drive Consisting of LCL Filter

Permanent magnet synchronous motors (PMSM), having fundamental frequency (
$f_{1}$
) more than 500 Hz, are gaining popularity in high-speed application due to compactness in size and reduced losses. Size constraints demand better thermal management and reduction in harmonic & core losses in the motor. Further, high dv/dt of PWM voltage causes leakage currents in bearing and impacts the insulation as well. Therefore, such drives need nearly sinusoidal input voltage at the motor terminals. LCL filter-based drives improve the input power quality. However, these are inherently unstable, and suitable damping is required to stabilize the drive. This paper analyzes the LCL filter-based drive through small signal analysis. The pole-zero plot on complex s-plane of PMSM drive with and without LCL filter are plotted to identify the instability zones. Based on analysis, a suitable damping factor is proposed to stabilize the drive over complete range of
$f_{1}$
. LCL filter-based three-phase PMSM drive, rated at 916 Hz and 50 kW, is used for simulation. Active damping with the proposed damping factor is implemented to validate the theoretical findings.