Studying the effect of over-modulation on the output voltage of three-phase single-stage grid-connected boost inverter

AbstractVoltage boosting is very essential issue in renewable-energy fed applications. The classical two-stage power conversion process is typically used to interface the renewable energy sources to the grid. For better efficiency, single-stage inverters are recommended. In this paper, the performance of single-stage three-phase grid-connected boost inverter is investigated when its gain is extended by employing over-modulation technique. Using of over-modulation is compared with the employment of third order harmonic injection. The latter method can increase the inverter gain by 15% without distorting the inverter output voltage. The performance of extended gain grid-connected boost inverter is also tested during normal operation as well as in the presence of grid side disturbances. Simulation and experimental results are satisfactory

A hybrid nine-arm modular multilevel converter for medium-voltage six-phase machine drives

The nine-arm modular multilevel converter (9A-MMC) has been recently proposed as a reduced MMC topology variation for six-phase drive applications, with 25% reduction in the number of employed arms and associated components, compared to a standard dual three-phase MMC, however with a limited output voltage amplitude. This paper proposes a hybrid 9A-MMC comprised of half-bridge submodules (SMs) in both the upper and lower arms, and full-bridge SMs in the middle arms. By employing the negative-voltage state of the full-bridge SMs, the hybrid 9A-MMC avoids the limitations imposed on the dc-link voltage utilization, while achieving further reduction in the component count, compared to a standard 9A-MMC with identical half-bridge SMs. The operating principles of the proposed hybrid 9A-MMC are illustrated with mathematical analysis, while its characteristics are verified through both simulation and experimentation. An assessment of the proposed topology quantifying its employed components is also provided, in comparison to other MMC-based six-phase machine drives

High-voltage pulse generator based on sequentially charged MMC-SMs operating in a voltage-boost mode

Pulse forming networks and Marx generators are the classical rectangular waveform pulse generators (PGs). They are inflexible and their capacitors must be fully charged to the required voltage from 0V before delivering each high-voltage (HV) pulse. They are only able to generate unipolar pulses; if bipolar pulses are sought another generator fed from a negative supply voltage is added. Recently, several power electronics based PGs have been proposed. This paper presents an HV power electronics based PG, which is based on Half-Bridge Modular Multilevel Converter (HB-MMC) sub-modules (SMs) charged sequentially in a voltage boost mode. Each SM capacitor and main switch form a boost converter with the charging input supply and inductor. As a result, all SM capacitors are charged to a voltage greater than the input. During the discharging process the SM capacitors are connected in series, producing a rectangular HV pulse across the load. The proposed charging method allows a reduction in the converter footprint in comparison with recently proposed MMC sequentially charged PG topologies. Although only rectangular pulse waveforms are sought in this paper, a SM capacitor voltage balance method allows multilevel pulse generation. The viability of the proposed converter is confirmed by MATLAB/Simulink simulation and scaled-down experimentation

High voltage pulse generator based on DC-to-DC boost converter with capacitor-diode voltage multipliers for bacterial decontamination

High voltage pulse generators can be used effectively in water treatment applications, as applying a pulsed electric field on the infected sample guarantees killing of harmful germs and bacteria. In this paper, a new high voltage pulse generator with closed loop control on its output voltage is proposed. The proposed generator is based on DC-to-DC boost converter in conjunction with capacitor-diode voltage multiplier (CDVM), and can be fed from low-voltage low-frequency AC supply, i.e. utility mains. The proposed topology provides transformer-less operation which reduces size and enhances the overall efficiency. A Detailed design of the proposed pulse generator has been presented as well. The proposed approach is validated by simulation as well as experimental results.Qatar National Research FundScopu

Multimodule Boost-Converter-Based Pulse Generators: Design and Operation

In this article, three different types of pulse generators based on multimodule boost converter ringing circuit are presented, namely, interleaved, stacked, and interleaved-stacked with full design and operational concept. The interleaved version is advantageous in generating a burst of pulses with moderate voltage magnitude, where the used modules are fed from a common dc source. On the other hand, the stacked multimodule version can be used to generate high-voltage pulsed output from synchronized modules with a moderate voltage rating. This can be done by feeding the modules from isolated dc sources while connecting their outputs in series. Finally, the interleaved-stacked version can be used for generating a burst of pulses with high-voltage magnitude. The presented pulse generators are valid for resistive loads with exponential decay pulses. The suggested pulse generators are simple and require semiconductor devices with moderate voltage ratings. For given pulse specifications, a detailed design for the passive components of each version is presented in this article. The simulation and experimental results are used to validate the suggested topologies.Qatar Foundation; Qatar National Research FundScopu

HVDC shunt tap based on three single-phase half-bridge series-connected MMCs operated under 2L modulation

In this study, a cost-effective HVDC shunt tap with low-number of relatively low-voltage semiconductor devices and small-sized passive components is proposed. The proposed architecture is based on employing three single-phase half-bridge Modular Multilevel Converters (MMCs), where the DC sides of MMCs are connected in series across the total DC-link voltage. The MMCs are adopted instead of conventional Two-Level Voltage Source Converters (2L-VSCs) to avoid the complications of series connection of Insulated Gate Bipolar Transistors (IGBTs). The involved MMCs in the suggested architecture are operated with the conventional 2L modulation, which results in insignificant arm inductors and Sub-Modules (SMs) capacitances (in range of ?H and ?F, respectively). This, in turn, affects positively the converter cost and footprint. Each arm of the involved MMCs can be considered as a high-voltage valve of a 2L-VSC. To maintain the balance of SMs capacitors, each arm of the involved (N + 1)-level MMC has an extra SM (a balancing SM) to select N out of N + 1 SMs during the turn-off condition. The operational concept, design, and assessment of the proposed architecture are presented in this study. Simulation results are provided for substantiation of the proposed concept. Finally, a scaled down single-phase prototype is used for experimental validation.Qatar National Research FundScopu

Flywheel energy storage system based on boost DC-AC converter

An additional DC-DC boost converter is used in conventional configuration of Flywheel Energy Storage System (FESS) to regulate the output voltage during flywheel low speeds. This paper presents a new FESS based on the boost inverter topology. The proposed system facilitates voltage boost capability directly in single stage. A three-phase boost inverter consisting of three DC-DC boost converters is employed in this paper. The main advantage of the boost inverter is the deployment of only six switches and undersized passive elements to obtain a boosted up AC output voltage weighed against the input DC supply. The boosting capability of boost inverter is also verified experimentally in this paper. The boost inverter in Flywheel Energy Storage System is modeled and simulated using MATLAB/SIMULINK.Qatar National Research FundScopu

Modular Multilevel Converter-Based Bipolar High-Voltage Pulse Generator with Sensorless Capacitor Voltage Balancing Technique

In order to generate bipolar high-voltage (HV) pulses across certain load from HV dc (HVdc) power supply, a voltage source inverter (VSI) stage should be inserted between the load and the supply. In order to meet the required HV level, series connection of semiconductor devices should be employed with dynamic voltage sharing between the involved devices. Modular multilevel converter (MMC) can be used instead of the conventional two-level VSI to alleviate the complexity introduced by the deployment of series-connected devices. The voltage level of the HVdc power supply and the voltage rating of the available semiconductor devices determine the suitable number of MMC voltage levels ( N ). Capacitor voltage balancing is a vital issue for proper operation of the MMC. In general, conventional sensor-based balancing techniques require a significant amount of measurements, which increases the complexity of the system. In addition, the high dv/dt during switching times causes electromagnetic interference, which may adversely affect the accuracy of the measurements. In this paper, a sensorless voltage balancing technique is proposed for the MMC-based bipolar HV pulse generator that reduces the system sensitivity, cost, and complexity. A detailed illustration of the proposed approach is presented in this paper. The simulation and experimental results are used to validate the proposed concept. 1973-2012 IEEE.Scopu