Application of Model Predictive Control in Modular Multilevel Converter for MTPA Operation and SOC Balancing

In this thesis, a one-step horizon model predictive control strategy (MPC) is implemented in a multilevel modular converter (MMC) to control the speed of an electric vehicle (EV) motor. Maximum torque per ampere (MTPA) and field weakening (FW) control strategies are used to generate reference signals for maximum torque output. The proposed control scheme aims to track the reference signal by independently regulating voltages from the MMC modules. To achieve this, the switches of the MMCs are directly controlled, eliminating the need for a pulse width modulator. A one-step horizon implementation of MPC ensures the robustness of the control system by making the real-time implementation possible. It leads to favorable performance under asymmetrical loads. The phase voltage is supplied to the motor through the MMC architecture which is composed of a large number of battery cells connected in series to supply the motor drive. Due to the non-identical characteristics of the battery, the state of charge (SOC) and the terminal voltage of the cells vary significantly at different operating conditions. The given control scheme is also incorporating a voltage balancing property that ensures the terminal voltages of all the battery cells in the MMC architecture are equalized. Finally, simulation results are presented to show the effectiveness of this control strategy and hardware is under development to validate the system performance

A Transformerless PCB Based Medium-Voltage Multilevel Power Converter with A DC Capacitor Balancing Circuit and Algorithm

This dissertation presents a new method of constructing a transformerless, voltage-sourced, medium-voltage multilevel converter using existing discrete power semiconductor devices and printed circuit board technology. While the approach is general, it is particularly well-suited for medium-voltage converters and motor-drives in the 4.16 kV, 500 - 1000 kW range. A novel way of visualizing the power stage topology is developed which allows simplified mechanical layouts while managing the commutation paths. Using so many discrete devices typically drives cost and complexity of the gate-drive system including its control and isolation; a gate-drive circuit is presented to address this problem. As with most multilevel topologies, the dc-link voltages must be balanced during operation. This is accomplished using an auxiliary circuit made up of the same power stage and an associated control algorithm. Experimental results are presented for a 4.16 kV, 746 kW, five-level power converter prototype. This dissertation also analyzes a new capacitor voltage-balancing converter along with a novel capacitor voltage balancing control algorithm. Analysis of the inverter system provides a new description of capacitor voltage stability as a function of system operating conditions

Five-Level Flying Capacitor Converter used as a Static Compensator for Current Unbalances in Three-Phase Distribution Systems

This thesis presents and evaluates a solution for unbalanced current loading in three-phase distribution systems. The proposed solution uses the flying capacitor multilevel converter as its main topology for an application known as Unbalanced Current Static Compensator. The fundamental theory, controller design and prototype construction will be presented along with the experimental results. The Unbalanced Current Static Compensator main objective is the balancing of the up-stream currents from the installation point to eliminate the negative- and zero-sequence currents originated by unbalanced single-phase loads. Three separate single-phase flying capacitor converters are controlled independently using a d-q rotating reference frame algorithm to allow easier compensation of reactive power. Simulations of the system were developed in MATLAB/SIMULINK™ in order to validate the design parameters; then, testing of the UCSC prototype was performed to confirm the control algorithm functionality. Finally, experimental result are presented and analyzed