Comparative Analysis of Modulation Techniques for Modular Multilevel Converters in Traction Drives

Abstract

The spreading of electric vehicles led to a renewed interest for innovative traction drives. In this context, an electric traction drive based on a Modular Multilevel Converter and integrating batteries in each module has been recently proposed. This converter concentrates into a single unit, the control of the traction motors, the balancing and energy management of the battery cells and the vehicle recharge functions. By using different modulation techniques it is possible to optimize different aspects like efficiency or THD of output current and voltages. Performance and efficiency in balancing, traction and recharging operations have been analyzed for two modulation techniques: near level modulation and phase disposition PWM. The near level modulation reduces switching losses while the second one better follows voltage references reducing current THD and, consequently, conduction losses. In this paper an innovative modulation technique is proposed and its performance in terms of current THD and global losses are compared with the other two modulation strategies already proposed.

A High Frequency Self-Reconfigurable Battery for Arbitrary Waveform Generation

“…The number of levels in series to activate is then determined in real-time by rounding up to the nearest integer the real value given by a closed-loop control. The use of NLC for SRB driving has been compared with carrier cascaded PWM in [18]. It was shown that PWM control patterns tend to have a better THD when a low number of levels in series is used, while NLC induces less loss due to the reduced amount of commutations.…”

Windowed PWM: A Configurable Modulation Scheme for Modular Multilevel Converter-Based Traction Drives

“…LLPWM is an hybrid NLC-PWM modulation strategy proposed in [24]. LLPWM generally activates the components of the converter using NLC.…”

“…The W-PWM enables a precise control of the PWM window and the length of this window is effectively a new degree of freedom for the control system. It is worth noting that for certain values of φ that depends on the number of modules of the converter and on the magnitude of the voltage reference, W-PWM reduces to LLPWM modulation [24].…”

Integration of Stationary Batteries for Fast Charge EV Charging Stations

“…In literature different modulation techniques for this converter topology are available. The modulation techniques can be divided in two categories: nearest level control technique (NLC) and pulse width modulation (PWM) based ones [14]. NLC approximates the output voltage by turning on and off modules in order to minimize the discretization error related to the voltages of the modules, while PWM techniques add a switching signal to the output of NLC.…”