Marcin Zygmanowski

Capacitance and inductance selection of the modular multilevel converter

The paper presents a proposal for capacitance and inductance selection procedure of the modular multilevel converter. Two analysis criteria are taken into consideration, the circulating current and voltage ripple across submodule capacitors. Results are obtained numerically by using the converter averaged model based on state equations. In the modular multilevel converter operating under a direct modulation method, based on sinusoidal modulating signals, circulating currents flows through the converter arms. These currents are strongly dependant on the component parameters of the converter, such as: submodule DC-link capacitor capacitance and arm inductor inductance. Both components form a series resonance circuit in each converter arm. Resonance that occurs in the converter arm has to be avoided and therefore it is important to properly select component parameters while taking into account all possible resonances. Such components selection should be carried out at an early stage of the converter design.

Analytical and numerical power loss analysis in Modular Multilevel Converter

This paper presents two approaches to semiconductor power loss analysis in Modular Multilevel Converters (MMC) controlled without feedback of the switching cell capacitor voltage. The first one is a novel analytical approach - basing on an averaged model of the MMC. The second one is basing on detailed model in Matlab-Simulink - used as a reference for the analytical one. Analyses are performed for five MMC switching cells scenario. The analytical method has been proven as sufficient and fast solution for the MMC power losses estimation.

DC-link voltage balancing method for a hybrid asymmetric multilevel converter

The paper presents the dc-link voltage balancing method for a five-level hybrid asymmetric multilevel converter based on a neutral point clamped (NPC) converter with H-bridge (HB) converters. The considered converter, which is referred to as NPC-HB, is treated in this paper as a modification of the classic three-level NPC converter. It improves the harmonic performance of output voltage compared to the NPC converter. This improvement is made by increasing the number of levels in the converter output voltage. Nevertheless, due to the use of floating H-bridge converters inside the NPC-HB topology, the dc voltage balancing method is implemented. Basing on the converter ac side current and HB converter dc link voltage, the proposed method modifies the PWM modulation scheme in both NPC and HB converters. This modification is applied to each switching period while the converter output voltage reference is kept unchanged. Such modulation scheme is characterized as robust and guaranteeing the low harmonic content in the output voltage. Other dc voltage balancing methods of the hybrid NPC-HB converter are compared in this paper. The proposed method is experimentally verified.

Comparison of SMES and ScES based power conditioning systems

The selection of the less expensive power conditioning system (PCS) is the aim of the work where two types of PCS are taken into consideration. The first type of PCS is based on superconducting magnetic energy storage (SMES) while the second one is based on supercapacitor energy storage (ScES). The comparison is based on installed power as the criterion. An illustrative example is given in the work

Analysis of thyristor switch in power conditioning system with SMES

Ensuring high level of power quality (PQ) is one of most important issues in supplying in industry loads. There exist some critical types of loads that should be protected from any voltage disturbance. If any voltage disturbance (like voltage sag or dip) occurs an alternative energy source is used to ensure constant voltage amplitude across protected load. In described power conditioning system (PCS), power electronic system is connected in parallel to group of protected loads. The PCS together with protected loads have to be disconnecting from the mains in the case of voltage sag or dip occurs. Disconnection is necessary, if any voltage disturbance occurs, to prevent from delivering energy to low impedance part of power system (the mains in such case) from energy storage that is contained in the PCS (in this situation high temperature superconducting magnetic energy storage (SMES)). In described system breaking the connection between the mains and the load takes place thanks to the thyristor switch (TS). Disconnection and reconnection modes of operation of the PCS are particularly described and analysed in the paper. To obtain relatively low turn off time of thyristor switch a new method of controlling the PCS has been proposed that can assist turning off process of the TS and decreasing turn off time. The resynchronisation of the load voltage and the mains voltage of the PCS is also presented in the paper. It is used to limit the amplitude of the mains current after reconnection process. Influences of resynchronisation and reconnection processes on load voltage are also analysed. To proof correctness of designed controller the simulation and experimental results have been presented and discussed in the paper

Selection of 5 kW converter leg for power electronic system for residential buildings

Three converter leg variants are analyzed for low power converter used for power electronic system for residential buildings. The two-level Si-IGBT and SiC-MOSFET converters are compared with Si-IGBT three-level T-type converter. Power losses generated in each of these converters over a predicted period of 20 years of operation are contrasted with the cost of converter options. The detailed selection procedure for output inductor is presented in this paper. This procedure shows the influence of the inductor parameters like number of turns, air gap length on its losses, cost and size. Theoretical approach is verified with simulations and experimental results.

Power loss evaluation for medium voltage drive system based on back-to-back three-level NPC converter integrated with induction machine

The paper deals with loss issues in an experimental 3.3 kV drive system consisting of back-to-back three-level NPC converter integrated with an induction machine. This integration significantly reduces the size and weight of the whole drive system. It also allows for a better understanding of loss generation and verifying the effect of operational conditions on such losses e.g. the effect of the converter switching frequency on drive system losses distribution.