Arto Sankala

Modeling and Analysis of the Dead-Time Effects in Parallel PWM Two-Level Three-Phase Voltage-Source Inverters

This paper addresses modeling and analysis of the dead-time effects in parallel pulsewidth-modulated (PWM) two-level three-phase inverters. The main objective is to gain understanding of how the effects caused by the necessary blanking time, the finite turn-on and turn-off times of the switching devices, and the forward voltage drops of the switching devices and the antiparallel diodes, i.e., the dead-time effects, influence the circulating current generation between the parallel-connected units. To meet this objective, a circulating current model taking these effects into account is developed for the parallel connection of n units. The model, which is an average model by nature, can be used to study the circulating current behavior with different types of PWM methods and to estimate the resulting circulating current values when there are differences in the dead-time effect parameters. In other words, the model provides an analytical way to consider the significance of these effects. To verify the validity of the developed model, the circuit simulation and experimental results are shown and compared with the analytical results. The illustrations show that the results obtained with the developed model are in good agreement with the circuit simulations and the experiments.

Modular double-cascade converter

A new multilevel converter topology with cascaded H-bridges and a multi-winding medium frequency isolation transformer is introduced. The proposed converter topology has a modular structure, which is achieved using cascaded H-bridges. The isolation for the H-bridges is provided by medium frequency isolation transformers which are small compared with line frequency transformers with the same power rating. The building blocks of the proposed converter topology can be connected in series or in parallel. Series connection adds voltage steps to output voltage, and parallel connection increases the power rating of the converter.

Modular Double-Cascade converter with soft switching DC/DC isolation converter

In power electronic converters soft switching is an efficient way to reduce losses. A resonant tank in series with the windings of the isolation transformer in a Modular Double-Cascade converter is presented. Positive effects such as switching loss reduction, prevention of flux walking and saturation of transformer core are analyzed and discussed.

Five-level inverter with a neutral point connection and a flying capacitor

Multilevel inverters have become a well proven technology in medium voltage drives, especially due to their improved power quality. This paper presents a new five-level inverter topology that is based on a neutral point connection and a flying capacitor. The operation of the topology is presented, taking into account the balancing of the flying capacitors. The performance of the topology is demonstrated with simulations, and compared with five-level active neutral point clamped inverter.

Power direction control of medium frequency isolation DC/DC converter for modular double cascade converter

Multilevel converters have strongly arrived to the medium voltage drive market. A new voltage source multilevel converter topology, called modular double cascade converter, is discussed. The converter uses cascaded H-bridges as input and output converters and a medium frequency DC/DC converter for galvanic isolation between the H-bridge modules. The key feature for the DC/DC converter is the six-winding transformer, that is able to balance the DC link voltages of the connected converters. It also enables power delivery in both directions, making four quadrant operation feasible. In this paper, different DC/DC converter control schemes are researched. The objective is to find the best method for balancing the DC link voltages between the isolated modules, and to minimize the transformer winding currents.

Hybrid five-level T-type inverter

Multilevel inverters have proven to be a solid technology in electrical drive applications. A new voltage source multilevel converter topology, that is a hybrid between three-level flying capacitor and T-type inverters, is introduced. The proposed topology can produce live output voltage levels. This paper presents the principle of operation for the topology, including the control of the flying capacitor voltage. The inverter operation is simulated and the loss distribution over the phase leg devices is presented.

Design of an active front end for a Modular Double-Cascade converter

Modular Double-Cascade converter is a multilevel frequency converter which has two sets of cascaded H-bridges as input and output power stages. This paper presents the topology-specific advantages that an active front end offers to the system together with an example design of the active front end controller and LCL filter.

Flux and winding current balancing control for a medium-frequency six-winding transformer

Solid state transformers normally include a transformer whose operating frequency is well above the usual grid frequencies. These transformers are supplied by power electronic inverters such as an H-bridge. The average value of transformer supply voltage can drift to a non-zero value which may lead to saturation of the magnetic core. This paper presents an active control method to prevent saturation of a multi-winding medium-frequency transformer. The control method comprises two control loops: the first balances the flux of the transformer and the other balances the currents in different windings. Simulation results which show the feasibility of the proposed control method are shown.