Investigation of parallel-connected GaN E-HEMT VSI-based servo drives

Yürük, Hüseyin
Nonlinearities in voltage source inverters (VSIs) are thought to be the primary cause of output voltage distortions which cause low-order harmonics in the output current. These nonlinearities also considerably degrades control performance and system stability for low-speed applications with low-inductance motors, particularly when the system operates in the low-torque area. The impact of the nonlinearities on the phase current and current control of a silicon (Si) metal-oxide-semiconductor field-effect transistor (MOSFET) based VSI are examined in this thesis using a coreless permanent magnet synchronous motor (PMSM). To address this issue, a gallium nitride (GaN) enhancement-mode high electron mobility transistor (E-HEMT) based VSI is proposed. Based on the results, a GaN E-HEMT VSI-based servo drive is being developed to replace its Si MOSFET VSI-based counterpart. It is about half the size of the previous one, allowing for the use of two servo drives in parallel rather than one for redundancy. The use of parallel-connected servo drives offers the benefit of increased torque capacity, reliability, redundancy, and modularity. Smaller variances in the system clocks of the separate microcontrollers, asynchronous pulse width modulation (PWM) carrier signals, and hardware differences, on the other hand, might cause non-identical output voltages of the parallel modules, resulting in circulating currents. These circulating currents limit parallel operation, increase power consumption, induce imbalanced power distribution, and degrade control performance. A fault‐tolerant parallel‐connected GaN E-HEMT VSI based servo drive scheme is proposed to reduce the circulating currents and to eliminate the need for extra inductors at the output and separate DC supplies at the input of the inverters. Various experimental tests are conducted with up to six parallel-connected servo drives and a PMSM for validation.


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Nonlinearities in voltage source inverters (VSIs) such as; dead time, switching time, delay time, voltage drops on the power switches, parasitic capacitance, etc., are considered to be the main sources of the output voltage distortions. These distortions result in low-order harmonics in the output current, which in turn increase core losses and create torque ripples. In particular, for low-speed applications with low-inductance motors, the control performance and the stability of the system degrades substan...
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Citation Formats
H. Yürük, “Investigation of parallel-connected GaN E-HEMT VSI-based servo drives,” Ph.D. - Doctoral Program, Middle East Technical University, 2022.