In the last decades, multilevel converters have been developed usually for medium-voltage high-power applications. They have become a mature solution for the increasing power demand of multiple applications such as renewable energy systems, power quality improvement, and motor drives. In this paper, the operation of multilevel converters is addressed focusing on control and modulation techniques for different well-known applications. The new developments are presented as an extension of conventional methods for two-level voltage-source converters which are still the mainstream solution for most cases.

Multilevel Converters: Control and Modulation Techniques for Their Operation and Industrial Applications

New breed of solid-state transformer mainly combing hybrid cascaded multilevel converter with resonant DC-DC converters

A sliding mode control (SMC) strategy with dc capacitor voltage balancing is proposed for three-phase three-level T-type rectifiers. The proposed SMC strategy is designed in the abc frame rather than the dq frame. In this case, the necessity of three-phase current transformations is eliminated. The proposed SMC is based on the errors of the line currents. The amplitude of line current references is generated by controlling the dc voltage using a proportional-integral (PI) controller. In order to obtain unity power factor, the generated reference amplitude is multiplied by the corresponding sinusoidal waveform obtained from the phase locked loop (PLL) operating with grid voltages. The dc capacitor voltage balancing is achieved by adding a proportional control term into the line current reference obtained for each rectifier leg. The performance of the proposed control strategy is validated by simulations and experiments during steady-state, transients caused by load change, and unbalanced grid conditions. The results show that the proposed control strategy offers excellent steady-state and dynamic performances with low THD in the line currents, zero steady-state error in the output voltage, and very fast dynamic response.

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Sliding-Mode Control Strategy for Three-Phase Three-Level T-Type Rectifiers With DC Capacitor Voltage Balancing

This paper presents a comprehensive literature review for mine hoist drives. Both DC and AC drives with their control techniques are discussed with a comparative study on their performance. Many recent control techniques using power electronic based systems are also discussed. The future trend in this area is also addressed. This review paper is the first of its kind information source provider for mine winder drives to be useful for researchers, designers and application engineers in the mining industry.

Recent developments in mine hoists drives

This paper proposes the zero-crossing distortion inhibition method of three-phase dual-buck inverter with LCL filter. The half-cycle pulse-width modulation (PWM) of the dual-buck inverter would cause zero-crossing distortion. The cause of zero-crossing distortion is analyzed and the inhibition method is presented. Half-cycle space vector PWM (SVPWM) is applied as the control strategy of the inverter. The negative feedback of grid current harmonic components can change the reference of the space vector at zero-crossing period. Thus the amplitude of the current ripple can be reduced. When it is close to zero, the zero-crossing distortion can be inhibited. A prototype of three-phase dual-buck inverter has been built and tested to verify the theoretical analysis.

Zero-crossing distortion inhibition method of three-phase dual-buck inverter

In this study, a novel individual voltage balancing control scheme for multilevel cascade active-front-end rectifier is proposed to allow a different voltage setting capability among different dc outputs in series. First, the proportional resonant controller and admittance compensation controller are introduced for the active inner-current control loop of cascade active-front-end rectifier to achieve better steady-state and dynamic performance. Second, an assumption based on conservation of energy is proposed to decouple a series connected ac-dc system into several individual subsystems to facilitate the individual dc-bus controller design. Both simulation and experimental results based on the cascade two-unit cascade dual-buck/boost-type active-front-end rectifier proved the effectiveness of the proposed individual balancing control scheme, which also verified the proposed assumption.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2012.0257

Fangyi Zhao

Papers

Novel individual voltage balancing control scheme for multilevel cascade active-front-end rectifier