Maxim A. Dybko

Mathematical simulation technique for power systems based on diode-clamped multilevel VSC

This paper presents a method for mathematical simulation of different power conversion systems based on diode-clamped multilevel power converters. The method is being a powerful tool for mathematical analysis of any system as far as it allows easy calculation of any power parameters of the system such as THD, WTHD, power factor; efficiency etc. under different operation conditions and control strategies. The base of the introduced mathematical analysis is the switching functions. As an example, three-level voltage source converter with space vector PWM is considered.

Switching frequency circulating current analysis in parallel-connected multilevel NPC converters

This paper discusses one of the major issues concerning parallel-connected voltage source converters that is the circulating currents. These currents usually flow between the converters and can be caused either unequal power sharing between the converters or nonsymmetrical PWM control. In the second case they are called switching frequency circulating currents. Detailed investigation on these currents is carried out. Analytical expressions to calculate the maximum values of these currents are obtained for the common case. Knowing the maximum value allow one to estimate semiconductor maximum current more precisely and prevent IGBT or MOSFET overcurrent fail. It is shown that number of the parallel converters has a slight influence on the switching frequency circulating currents maximum value. On the other hand the number of the voltage levels, PWM frequency and sharing reactor inductance proportionally affects this value. Simulation for several different cases is given to verify the obtained equations and prove the correctness of the assumptions made. An experimental verification on the two-level case is presented.

A power losses calculation in a four-legged three-level voltage source inverter

This paper presents analytical equations for power losses calculation in three-level VSI controlled by carrier-based PWM with third harmonic injection. A magnitude current value in the four leg devices depending on three-phase load unbalance was obtained.

Mathematical models for analysis of energy quality performance in three-phase four-level NPC converters

This paper presents an analysis of the energy quality performance of the neutral point-clamped three-phase four-level converter from the dc-link unbalance influence point of view. The analysis is carried out by the proposed mathematical models. The presented analysis technique can be applied to any n-level NPC rectifier or inverter.

Analysis of conducting losses in the single-phase three-level NPC converter

This paper offers a technique for calculating the average and RMS values of the switch currents in the singlephase three-level neutral point clamped rectifier. The presented technique is based on the space vector PWM approach. In addition, the mathematical model for the switch currents is described. The plots of conducting losses for different operating modes are obtained.

A new approach for current calculation in a single-phase three-level NPC converter with space vector PWM

This paper offers a new approach for calculating the average and RMS values of the switch currents in the single-phase three-level neutral point clamped rectifier. Th e proposed calculation method is based on the SVPWM control algorithm. Tw o sequences are considered. Plots of relative switch currents versus index modulation and power factor angle were obtained. Conducting losses for both sequences were compared.

A new grid-tied multilevel VSC for PV with leakage current suppression

This paper presents a new transformerless grid-tied multilevel voltage source converter for photovoltaic applications. An analysis of the leakage current produced by the common mode voltage is carried out. A solution to eliminate the leakage currents is given. The one uses a modified multilevel converter with space-vector PWM. The effectiveness of the proposed solution is verified by the simulation results.

Multilevel NPC Converters in Parallel Connection for Power Conditioning Systems

This paper investigates a multilevel combined NPC converter for medium-and high-power energy storage systems and active power filters. The proposed multilevel NPC converter is composed of a parallel connection of multiple NPC converters using the current sharing reactors and involves the phase shifted PWM strategy for better energy quality performance. Using the switching function-based mathematical model, the proposed multilevel converter is evaluated to show the energy quality performance and fault tolerance of an energy storage system or active power filter. In addition, the switching frequency of circulating currents is analyzed to obtain its relationship with the converter parameters and maximum sharing reactor current ripple. The performance of the proposed multilevel converter is verified by simulation.

Technical aspects of common-mode leakage current suppression in pv-generation systems

Currently in many countries much attention is paid to the power generation systems using renewable energy sources. However there is much less research is being carried out on transformerless structures and multilevel converter topologies. This paper intends to reveal some essential features of a grid-tied PV-generation system based on multilevel converter and without transformer. In particular, common-mode leakage current, a well-known problem of such systems, has some peculiarities if a multilevel converter is used. It is shown, that the common-mode voltage is the main reason of the leakage currents in single-phase and three-phase systems. The paper explores possible solutions to reduce or entirely suppress these currents and compares different known solutions. A solution for multilevel system is proposed and verified by simulation.

Active power filter with battery energy storage based on NPC inverters

Paper presents a model of a shunt active power filter combined with battery energy storage as a unified power conditioning system. It was shown that additional energy storage device in an active power filter makes it possible to extend functionality of the power system. In addition, usage of the parallel inverters with interleaved PWM allowed us to expand the bandwidth of the active power filter. A simulation results proving effectiveness of the proposed power conditioning system are given.