Five-level parallel current source converter for high power drives with DC current balance control and superior harmonic performance

In this thesis, space vector modulation is developed for a 5-level parallel current source converter for high power drives. The modulation scheme is designed to bring superior harmonic performance to the currents on the AC sides. This method synthesizes the rotating reference current vector in the converter's space vector's plane with three adjacent switching vectors. Unbalanced currents of DC links become a practical challenge when two converters are connected in parallel. To balance the DC currents, the proper switching state for every Small and Medium switching vector is chosen from redundant switching states corresponding to the vector based on circuit circumstances and the designed switching sequence. Simulated results verify the effectiveness of the method. In addition, the switching sequence is designed to lower the switching frequency and minimize the switching loss. Finally, the proposed converter and switching scheme are simulated and steady state and dynamic performance are investigated in detail.

Sensorless Current Source-Fed PM Drive System For Low Speed Operations

In this thesis, a sensorless method for low and zero speed operation is proposed for a high-power medium-voltage pulse-width-modulated Current–Source-Converter (CSC)-fed Interior Permanent Magnet Motor (IPM) drive system. The proposed method is based on injection of a high-frequency (HF) pulsating sinusoidal signal into the estimated synchronous reference frame of the drive’s Field Oriented Control (FOC) scheme. The conventional FOC control scheme, low switching frequency, dc-link inductor and the inverter output three-phase filter capacitor of the medium-voltage high-power current-source drive present some challenges in the generation and design of the HF injection signal. To overcome the challenges, the FOC scheme is modified by introducing a modulation index control with a suitable dc-link current compensation to enhance the dynamic response of the injected signal and prevent any clamp in the injected signal. In addition, a Multisampling Space Vector Modulation (MS-SVM) method is proposed to prevent the distortion in the HF signal due to a low switching frequency to injected signal ratio. It is found that by using the proposed FOC scheme and multisampling modulation scheme, and proper design of the HF signal, an accurate rotor flux angle can be estimated for sensorless zero/low speed operation. Moreover, a novel input power factor compensation method is proposed for a high-power pulse-width-modulated Current-Source-Converter (CSC)-fed Permanent Magnet Synchronous Motor (PMSM) drive system. The proposed method is based on controlling the d-axis stator current component in the field-oriented control scheme of the drive system. The main feature of the proposed scheme is to compensate for the line-side power factor without the need for modulation index control in either the rectifier or the inverter. Simulation and experimental verification for various objectives are provided throughout the thesis. The results validate the proposed solutions for the main challenges of zero/low speed operation of sensorless Current-Source-Converter (CSC)-fed Permanent Magnet Synchronous Motor (PMSM) drive system.

Five-level parallel current source converter for high power drives with DC current balance control and superior harmonic performance

In this thesis, space vector modulation is developed for a 5-level parallel current source converter for high power drives. The modulation scheme is designed to bring superior harmonic performance to the currents on the AC sides. This method synthesizes the rotating reference current vector in the converter's space vector's plane with three adjacent switching vectors. Unbalanced currents of DC links become a practical challenge when two converters are connected in parallel. To balance the DC currents, the proper switching state for every Small and Medium switching vector is chosen from redundant switching states corresponding to the vector based on circuit circumstances and the designed switching sequence. Simulated results verify the effectiveness of the method. In addition, the switching sequence is designed to lower the switching frequency and minimize the switching loss. Finally, the proposed converter and switching scheme are simulated and steady state and dynamic performance are investigated in detail.