The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

Multilevel inverter switching controller using a field programmable gate array (FPGA)

This paper presents the design and development of a switching controller using a field programmable gate array (FPGA)for a multilevel inverter application. SHE with PSO switching strategy was chosen and pre-calculated offline to obtain optimized switching angles for the power switches in the 5-level transistor-clamped H-bridge (TCHB) multilevel inverter. The designed switching controller produced 5-bit control signals, which connected to the power switches of the 5-level TCHB multilevel inverter. The switching controller utilized less than 1% of the total FPGA logic elements (LEs), which was equivalent to 96 out of 114,480 LEs. The execution speed of the switching controller using the FPGA chip was found to be 99.9% faster than microcontroller (PIC16F877A). Conducted simulation and measurement results verified and validated the switching controller design functionality and requirement.Keywords: multilevel inverter, switching controller; FPGA, general purpose processor(GPP);digital signal processing (DSP); IGBT; Verilog, power consumption;harmonic elimination (SHE).

Comparative Study of Power Semiconductor Devices in a Multilevel Cascaded H-Bridge Inverter

This thesis compares the performance of a nine-level transformerless cascaded H-bridge (CHB) inverter with integrated battery energy storage system (BESS) using SiC power MOSFETs and Si IGBTs. Two crucial performance drivers for inverter applications are power loss and efficiency. Both of these are investigated in this thesis. Power devices with similar voltage and current ratings are used in the same inverter topology, and the performance of each device is analyzed with respect to switching frequency and operating temperature. The loss measurements and characteristics within the inverter are discussed. The Saber® simulation software was used for the comparisons. The power MOSFET and IGBT modeling tools in Saber® were extensively utilized to create the models of the power devices used in the simulations. The inverter system is also analyzed using Saber-Simulink cosimulation method to feed control signals from Simulink into Saber. The results in this investigation show better performances using a SiC MOSFET-based grid-connected BESS inverter with a better return of investment

Transistor clamped five level inverter using non-inverting double reference single carrier PWM technique for photovoltaic applications

This treatise deals with transistor clamped five level inverter Using Non-Inverting Double Reference Single Carrier PWM (NIDRSC PWM) Technique. Conventional or two level inverter have drawbacks like i) Requirement of fast switching devices ii) Very high dv/dt iii) High Electromagnetic Interferences (EMI) iv) Bulky filters v) Faster heating of switches and vi) Not suitable for high voltage applications. Multilevel Inverters (MLIs) are engaged to conquer the drawbacks of conventional two levels inverter. MLIs generate an AC voltage using small voltage steps obtained with the help of DC supplies or capacitor banks. To design the proposed five level inverter 5 numbers of power control switches and 8 diodes are required. The proposed inverter circuitry is investigated by using Non-Inverting Double Reference Single Carrier PWM (NIDRSC PWM) Technique in terms of harmonics content in output waveform. Under-modulation (modulation Index =0.85), unity (modulation Index =1) and over-modulation (modulation Index =1.25) PWM signal is obtained to drive control switches. Simulation results will confirm the functionality, design and operation of the proposed MLI and NIDRSC PWM Techniqu

A New Cascaded Multilevel H-Bridge Drive

In this paper, a general structure for cascaded power converters is presented in which any number of H-bridge cells having any number of voltage levels are series connected to form an inverter phase leg. Equations are introduced for determining an optimal voltage ratio of DC voltages for the H-bridge cells which will maximize the number of voltage levels obtainable resulting in high power quality. Special cases of the generalized inverter are presented including novel 11-level and 15-level inverters. Laboratory measurements demonstrate the proposed inverter performanc

New Topologies and Advanced Control of Power Electronic Converters for Renewable Energy based Microgrids

Solar energy-based microgrids are increasingly promising due to their many features, such as being environmentally friendly and having low operating costs. Power electronic converters, filters, and transformers are the key components to integrate the solar photovoltaic (PV) systems with the microgrids. The power electronic converters play an important role to reduce the size of the filter circuit and eliminate the use of the bulky and heavy traditional power frequency step-up transformer. These power converters also play a vital role to integrate the energy storage systems such as batteries and the superconducting magnetic energy storage (SMES) unit in a solar PV power-based microgrid. However, the performance of these power converters depends upon the switching technique and the power converter configuration. The switching techniques can improve the power quality, i.e. lower total harmonic distortion at the converter output waveform, reduce the converter power loss, and can effectively utilize the dc bus voltage, which helps to improve the power conversion efficiency of the power electronic converter. The power converter configuration can reduce the size of the power converter and make the power conversion system more efficient. In addition to the advanced switching technique, a supervisory control can also be integrated with these power converters to ensure the optimal power flow within the microgrid. First, this thesis reviews different existing power converter topologies with their switching techniques and control strategies for the grid integration of solar PV systems. To eliminate the use of the bulky and heavy line frequency step-up transformer to integrate solar PV systems to medium voltage grids, the high frequency magnetic linkbased medium voltage power converter topologies are discussed and compared based on their performance parameters. Moreover, switching and conduction losses are calculated to compare the performance of the switching techniques for the magnetic-linked power converter topologies. In this thesis, a new pulse width modulation technique has been proposed to integrate the SMES system with the solar PV system-based microgrid. The pulse width modulation technique is designed to provide reactive power into the network in an effective way. The modulation technique ensures lower total harmonic distortion (THD), lower switching loss, and better utilization of dc-bus voltage. The simulation and experimental results show the effectiveness of the proposed pulse width modulation technique. In this thesis, an improved version of the previously proposed switching technique has been designed for a transformer-less PV inverter. The improved switching technique can ensure effective active power flow into the network. A new switching scheme has been proposed for reactive power control to avoid unnecessary switching faced by the traditional switching technique in a transformer-less PV inverter. The proposed switching technique is based on the peak point value of the grid current and ensures lower switching loss compared to other switching techniques. In this thesis, a new magnetic-linked multilevel inverter has been designed to overcome the issues faced by the two-level inverters and traditional multilevel inverters. The proposed multilevel inverter utilizes the same number of electronic switches but fewer capacitors compared to the traditional multilevel inverters. The proposed multilevel inverter solves the capacitor voltage balancing and utilizes 25% more of the dc bus voltage compared to the traditional multilevel inverter, which reduces the power rating of the dc power source components and also extends the input voltage operating range of the inverter. An improved version magnetic-linked multilevel inverter is proposed in this thesis with a model predictive control technique. This multilevel inverter reduces both the number of switches and capacitors compared to the traditional multilevel inverter. This multilevel inverter also solves the capacitor voltage balancing issue and utilizes 50% more of the dc bus voltage compared to the traditional multilevel inverter. Finally, an energy management system has been designed for the developed power converter and control to achieve energy resiliency and minimum operating cost of the microgrid. The model predictive control-based energy management system utilizes the predicted load data, PV insolation data from web service, electricity price data, and battery state of charge data to select the battery charging and discharging pattern over the day. This model predictive control-based supervisory control with the advanced power electronic converter and control makes the PV energy-based microgrid more efficient and reliable

Active DC voltage balancing PWM technique for high-power cascaded multilevel converters

In this paper a dedicated PWM technique specifically designed for single-phase (or four wire three-phase) multilevel Cascaded H-Bridge Converters is presented. The aim of the proposed technique is to minimize the DC-Link voltage unbalance, independently from the amplitude of the DC-Link voltage reference, and compensate the switching device voltage drops and on-state resistances. Such compensation can be used to achieve an increase in the waveform quality of the converter. This is particularly useful in high-power, low supply voltage applications where a low switching frequency is used. The DC-Link voltage balancing capability of the method removes the requirement for additional control loops to actively balance the DC-Link voltage on each H-Bridge, simplifying the control structure. The proposed modulation technique has been validated through the use of simulation and extensive experimental testing to confirm its effectiveness

Design, Optimization and Implementation of a High Frequency Link Multilevel Cascaded Inverter

This thesis presents a new concept of cascaded MLI (CMLI) device reduction by utilizing low and high frequency transformer link. Two CMLI topologies, symmetric and asymmetric are proposed. Compared with counterpart CMLI topologies available in the literatures, the proposed two inverter topologies in this thesis have the advantages of utilizing least number of electronic components without compromising overall performance particularly when a high number of levels is required in the output voltage waveform