Cascaded H-Bridge Multilevel Research Articles

Parallel Implementation of Model Predictive Control for Multilevel Cascaded H-Bridge STATCOM With Linear Complexity

The algorithm complexity of model predictive control (MPC) for cascaded H-bridge (CHB) static synchronous compensators (STATCOMs) was optimized to a polynomial level in previous studies. However, implementing MPC with conventional approaches still suffers from long execution time, where a low cost digital signal processor (DSP) is used to execute optimization algorithms and a small-sized field-programmable gate array (FPGA) is used to extend gate signals and sampling functions. This paper presents a parallel implementation approach to reduce the execution time of MPC, where the FPGA is configured to be used for accelerating the high-complexity sorting tasks. By running the DSP and FPGA in parallel, the algorithm execution time is only determined by the DSP, and the resource consumption is only determined by the FPGA. To minimize the resource consumption and requirement in FPGA, a parallel comparison-based sorter with multiple comparison and accumulators is proposed. The proposed implementation method can reduce the time and space complexity of the MPC from the polynomial level to a linear level without additional hardware cost, which means the MPC for medium-voltage CHB STATCOMs (e.g., 20 stages) can be implemented online with existing control platforms. Experimental results for various CHB STATCOMs are presented to validate the proposed configuration and algorithm.

Control of Cascaded H-Bridge Multilevel Inverter Based on Optimum Regulation of Switching Angles, and the FPGA Implementation

A new concept in control of cascaded H-Bridge multi-level inverters is proposed in this paper. According to this concept, switching angles are considered to be independent from the fundamental voltage. A polynomial term is presented to show the relation between switching angles and DC voltages. Based on this concept, Total Harmonic Distortion (THD) calculations are updated and proved to be independent from the fundamental voltage. Thus, once calculated for minimum THD, the switching pattern can be used for any required level of output voltage. To examine the effectiveness of the proposed method, it is applied in control of an eleven level inverter. The simulation results are demonstrated and verified through experiments with a setup controlled by Xilinx SPARTAN3 family FPGA (XC3S400-PQG208).

Switched-Capacitor-Based Single-Source Cascaded H-Bridge Multilevel Inverter Featuring Boosting Ability

Cascaded multilevel inverter (CMI) is one of the most popular multilevel inverter topologies. This topology is synthesized with some series-connected identical H-bridge cells. CMI requires several isolated dc sources which brings about some difficulties when dealing with this type of inverter. This paper addresses the problem by proposing a switched-capacitor (SC)-based CMI. The proposed topology, which is referred to as switched-capacitor single-source CMI (SCSS-CMI), makes use of some capacitors instead of the dc sources. Hence, it requires only one dc source to charge the employed capacitors. Usually, the capacitor charging process in a SC cell is companied by some current spikes which extremely harm the charging switch and the capacitor. The capacitors in SCSS-CMI are charged through a simple auxiliary circuit which eradicates the mentioned current spikes and provides zero-current switching condition for the charging switch. A computer-aid simulated model along with a laboratory-built prototype is adopted to assess the performances of SCSS-CMI, under different conditions.

Selective-Harmonic Elimination with An Optimized Multicarrier Modulation Techniques for Cascaded H-Bridge Multilevel Inverter

Selective-Harmonic Elimination with An Optimized Multicarrier Modulation Techniques for Cascaded H-Bridge Multilevel Inverter

A Modified Third Harmonic Pulse-Width Modulation for Reduced Switching Loss in Cascaded H-Bridge Multilevel Inverters

Abstract A cascaded H-bridge multilevel inverter (CHMI) is one of the promising candidates for high-voltage direct current (HVDC) distribution system. The huge number of inverter cells and switching devices, which consists CHMI, imply a great switching loss and it requires increased cost and size of the cooling components. To reduce the huge switching loss, a pulse-width modulation (PWM) strategy is proposed in this paper, which is composed of two different modulation methods. In addition, an additional cell rotation method is proposed to evenly distribute power among inverter cells which allow shaping three-phase output currents with reduced switching loss. The simulation results verify the validity of the proposed modulation scheme.

Fast FCS-MPC-Based SVPWM Method to Reduce Switching States of Multilevel Cascaded H-Bridge STATCOMs

Fast FCS-MPC-Based SVPWM Method to Reduce Switching States of Multilevel Cascaded H-Bridge STATCOMs

Design and Hardware Implementation Considerations of Modified Multilevel Cascaded H-Bridge Inverter for Photovoltaic System

Inverters are an essential part in many applications including photovoltaic generation. With the increasing penetration of renewable energy sources, the drive for efficient inverters is gaining more and more momentum. In this paper, output power quality, power loss, implementation complexity, cost, and relative advantages of the popular cascaded multilevel H-bridge inverter and a modified version of it are explored. An optimal number of levels and the optimal switching frequency for such inverters are investigated, and a five-level architecture is chosen considering the trade-offs. This inverter is driven by level shifted in-phase disposition pulse width modulation technique to reduce harmonics, which is chosen through deliberate testing of other advanced disposition pulse width modulation techniques. To reduce the harmonics further, the application of filters is investigated, and an LC filter is applied which provided appreciable results. This system is tested in MATLAB/Simulink and then implemented in hardware after design and testing in Proteus ISIS. The general cascaded multilevel H-bridge inverter design is also implemented in hardware to demonstrate a novel low-cost MOSFET driver build for this study. The hardware setups use MOSFETs as switching devices and low-cost ATmega microcontrollers for generating the switching pulses via level shifted in-phase disposition pulse width modulation. This implementation substantiated the effectiveness of the proposed design.

Improvement of MV Cascaded H-Bridge Inverter (CHBI) VFD Availability for High-Power ESP Oil Wells

Artificial lift systems are generally applied in the petroleum industry to provide the energy to transfer the oil from the reservoir to the surface. Electrical submersible pump (ESP) system is an artificial lift method extensively used in recovery. The maintenance cost of ESP and associate equipment is very high; therefore, the maximum availability of the system components is continuously sought. The aim of this paper is at analyzing the availability and reliability of frequency converters applied to medium voltage (MV) multilevel cascaded H-bridge inverters topology for ESP. A method to increase availability of MV frequency drives is thus proposed, enabling fewer losses in the production and a greater return on the economic investment (ROI).

A Multicarrier PWM Technique for Five Level Inverter Connected to the Grid

In this paper, a three-phase multilevel cascaded H-bridge inverter is developed for injecting renewable power energy into the grid through a filter. The main contribution of this work is to reduce the total harmonic distortion (THD) by using a passive filter and to enhance the output voltages by adopting a multicarrier pulse width modulation (MCPWM). The simulation results affirm a good performance of the proposed multicarrier PWM control using a three-phase five-level inverter. The proposed inverter is tested as well as the THD and the spectral analysis of the output voltage are calculated using Simulink/Matlab software.

Five-Level Cascaded H-Bridge MLC-Based Shunt Active Power Filter for Active Harmonics Mitigation in Distributed Network

This paper presents an investigation on mitigation of current harmonics, using Cascaded H-bridge Multilevel Converter (CHB-MLC)-based Shunt Active Power Filter (SAPF). Development and analysis of SAPF for harmonic compensation in distribution network for power quality improvement has been discussed. In the proposed work, transformer-less CHB MLC is used which reduces weight and cost of the system. Moreover, a novel controller based on average power method is adopted for generation of compensation active filter current. In order to generate switching signals, multi-carrier Alternate Phase Opposition Disposition (APOD) — Pulse Width Modulation (PWM) schemes are used. The proposed CHB-MLC SAPF reduces the source current THD below 5%. The results are simulated in MATLAB/Simulink and demonstrate the effective mitigation of current harmonics with APOD-PWM schemes. Opal-RT OP4500 real-time digital simulator is used to validate the proposed scheme under different steady state and transient conditions.

Research on the Unbalanced Compensation of Delta-Connected Cascaded H-Bridge Multilevel SVG

The paper presents the application of delta-connected cascaded H-bridge multilevel static var generator (SVG) under unbalanced compensation currents or unbalanced supply voltages. Clustered balancing control for delta-connected SVG can be realized by injecting a zero-sequence current to the delta loop. But zero-sequence current injection may cause the high peak phase current which may break converter switches. The aim of this paper is to analyze the key factors that affect the maximum output current of the SVG with injecting zero-sequence current and acquire the quantitative relationship among unbalance compensation capability, the unbalance degree of the supply voltage, the initial phase of negative-sequence voltage, the unbalance degree of the compensation current, and the initial phase of negative-sequence current. On this foundation, the valid compensation range of delta-connected SVG under unbalanced conditions is obtained. Furthermore, the compensation characteristic of the negative-sequence current is deduced with the certain supply voltage, and the influence of supply voltage variation on the maximum output current for SVG is also considered with the certain compensation current. Finally, the correctness of the relevant theoretical analysis is verified by simulation and experiment.

Adaptive Phase-Shifted PWM based on Particle Swarm Optimization for Cascaded H-Bridge Inverter with Unequal Dc-link Voltages

The cascaded H-Bridge Multilevel Inverter has been found a promising technology in industrial applications because of its higher voltage with less distortion production. Various PWMs techniques have been proposed to push the harmonics frequencies higher than the switching frequency and thus reduces the THD as compared to non-carrier control technique based upon grid frequency. The Phase-Shifted PWM technique has an advantage over others PWM techniques because its harmonics orders are multiples of switching frequency and also depend on the number of levels of the inverter. The phase shifting angle is uniform when the equal voltage sources are adopted. However, in applications where sets of different voltage source levels feed the H-Bridge cells, the Phase Shifted PWM suffers its high order harmonics elimination capability. As a solution to alleviate this problem, an adaptive variable angle approach is proposed in this paper using Particle Swarm Optimization (PSO) algorithm to eliminate desired higher order harmonics. The algorithm is used to minimize the cost function based on high order sideband harmonics elimination equations. The results through MATLAB/Simulink environment shown in this paper confirm the reduction of sideband harmonics of higher orders, and the overall THD.

A Unique Pulse Width Modulation to Reduce Leakage Current for Cascaded H-Bridge Inverters in PV and Battery Energy Storage Applications

Cascaded H-bridge (CHB) inverters operate with isolated DC sources, which makes them a favorable topology for hybrid-interfaced applications. Parasitic capacitance of grounded photovoltaics (PV) results in leakage currents that may deteriorate the system performance and raise safety concerns. In order to address this problem, a common-mode equivalent circuit for a multilevel CHB is illustrated. The study reveals that common modulation techniques such as phase shifted pulse width modulation fail to suppress the leakage current. A unique modulation scheme, based on considering the switching states is proposed in order to ensure that the topology conforms to the transformerless inverter regulations and standards such as VDE-0126-1-1. Simulation study results for conventional and proposed modulation methods are presented and analyzed in a symmetrical grid inductance filter circuit.

Optimized Modeling and Control Strategy of the Single-Phase Photovoltaic Grid-Connected Cascaded H-bridge Multilevel Inverter

This paper presents the modeling and control-loop design method with an inverted decoupling scheme of a single-phase photovoltaic grid-connected five-level cascaded H-bridge multilevel inverter. For the unity power factor, the proportional and integral current controller with a duty ratio feed-forward compensation is used. In addition, in order to achieve the maximum power point tracking of each photovoltaic array, when the stacked modules are in the partial shading condition, each direct current (DC) voltage is stably controlled to their maximum power points (MPP) by dedicated voltage controllers of each H-bridge module. This paper also presents a control method that minimizes the effect of the loop-interaction in the design of an individual DC-link voltage control loop in a two-input two-output system. The proposed control methods of the cascaded H-bridge multilevel inverter are validated through the simulation and experimental results of the 2-kW prototype hardware.

A DC Link Sensor-Less Voltage Balancing Technique for Cascaded H-Bridge Multilevel Converters With Asymmetric Selective Harmonic Current Mitigation-PWM

A grid-tied cascaded H-bridge (CHB) converter with low frequency modulation techniques needs to meet power quality standards. At the same time, the effects of grid voltage harmonics on CHB converter's current harmonics must be considered in the modulation techniques. Furthermore, the dc link voltages of grid-tied converters need to be regulated. In this paper, an asymmetric selective harmonic current mitigation-pulse width modulation (PWM) (ASHCM-PWM) technique is used to meet the current harmonic limits of a power quality standard with the effects of grid voltage harmonics considered in the equation set of its optimization process. A voltage balancing technique based on the average power of each cell is derived to regulate the dc link voltages of the CHB converters without using dc voltage sensors. By using the proposed voltage balancing technique, the CHB converters do not need complicated dc link voltage controllers. As a result, the cost and complexity of the grid-tied converters can be significantly reduced. Simulations and experiments were conducted on a 7-level grid-tied CHB converter to validate the proposed voltage balancing technique with ASHCM-PWM modulation technique.

A Novel Approach for grid integration of Cascaded H-bridge Multilevel Inverter Under Partial Shading Condition

<p>A modular cascaded H-bridge PV inverter system is presented in this paper. The modular structure of PV inverter helps in obtaining the maximum output power of PV system along with increase the overall efficiency of the whole system. Moreover to utilize the system up to the best a distributed MPPT controller is attached with each PV panel. As partial shading causes power imbalance at the converter output that leads to imbalance grid current, a control technique called the modulation compensation is adopted in such a way that if three phase unbalanced voltage varies directly according to unbalanced power, the injected zero sequence voltage components make the grid current balanced.</p>

Investigation of PV Connected Multilevel Cascaded H-Bridge Inverter Using Disposition Techniques

Inverters have many Technological improvements in their maximum power handling capabilities by using renewable energy sources. Multilevel inverters give effective and efficient interface for renewable energy sources and perform Transformer-less operation and increase the power quantity and quality of voltage of the PV system. In this paper, the benefits of H-bridge inverters including the total harmonic distortions are discussed. This paper has primarily focused on Sinusoidal PWM and worked on the carrier based phase disposition techniques. The performances of modulation schemes are compared. Simulations were done using MATLAB Simulink for the given PWM techniques.

Flexible Control of Photovoltaic Grid-Connected Cascaded H-Bridge Converters During Unbalanced Voltage Sags

Multilevel cascade H-bridge (CHB) converters are one of the promising solutions for medium- and large-scale grid-connected photovoltaic power plants. However, there is a lack of a complete study about their operation during voltage sags. This paper proposes a flexible control strategy for the operation of photovoltaic grid-connected CHB inverters during unbalanced voltage sags. The key novelty is that the proposed strategy is able to inject both active and reactive powers to the grid with either balanced or unbalanced currents, while ensuring that all dc-link capacitor voltages remain balanced. The simulation and experimental evaluations of a 9-kVA grid-connected seven-level CHB illustrate and validate the performance of the proposed strategy for the operation of the grid-connected CHB converter during different unbalanced voltage sags.

A Cascaded Multilevel Inverter Using Only One Battery with High-Frequency Link and Low-Rating-Voltage MOSFETs for Motor Drives in Electric Vehicles

Cascaded H-bridge (CHB) multilevel inverters are widely used in industrial applications, such as medium-voltage conversion and motor drives. However, the DC bus voltage in the electric vehicles is limited and it might not meet the requirements of the inverters for conventional motor drives. This paper presents a solution to drive the conventional motor (3Φ/AC 220 V) with inadequate DC bus voltage (DC 144 V) in an electric vehicle without any extra step-up circuits. The solution consists of a CHB inverter as a motor drive and a high-frequency (HF) transformer to balance the voltage. The multilevel CHB inverter improves the voltage and the current waveforms. High-frequency link (HFL) is used to create several isolated DC sources for the system and it can improve the power density. Besides, it replaces bulky line-transformers in the conventional CHB inverters, and the volume is reduced. Also, the inverter has bidirectional power flow ability, which can improve the efficiency in motor drives. As a result, the reduction of the step-up circuits is achieved and the topology can be used in the electric vehicles that are powered by only one 144 V-battery. The details and the principles of the control algorithm is discussed and an experiment based on a four-level CHB inverter with one DC 30 V power source is carried out to validate the proposed characteristics.

Enhance Cascaded H-Bridge Multilevel Inverter with Artificial Intelligence Control

This paper proposed a 7-level Cascaded H-Bridge Multilevel Inverter (CHBMI) with two diffenrent controller, ie, PID and Artificial Neural Network (ANN) controller to improve the output voltage performance and achieve a lower Total Harmonic Distortion (THD). A PWM generator is connected to the 7-level CHBMI to provide switching of the MOSFET. The reference signal waveform for the PWM generator is set to be sinusoidal to obtain an ideal AC output voltage waveform from the CHBMI. By tuning the PID controller as well as the self-learning abilities of the ANN controller, switching signals towards the CHBMI can be improved. Simulation results from the general CHBMI together with the proposed PID and ANN controller based 7-level CHBMI models will be compared and discussed to verifyl the proposed ANN controller based 7-level CHBMI achieved a lower output voltage THD value with a better sinusoidal output performance.