Integration of energy storage components with cascaded H-bridge multilevel converters

In recent years, multilevel converters have gained considerable attention in medium-voltage motor drive and grid applications. This popularity is owed to their reduced voltage stress on the semiconductor devices used in their structure. In addition, multilevel converters generate near sinusoidal outputs with low harmonic distortions. Other advantages of such converters include inherent modularity and low dv/dt stresses. In general, multilevel power electronic converters are classified into three main topologies: diode-clamped, flying-capacitor, and cascaded H-bridge. A cascaded H-bridge multilevel converter is created when several H-bridge cells are placed in series. Each H-bridge cell must be fed by a stiff voltage source. In earlier implementations, every one of these voltage sources had to contribute to the overall power supplied to the load. Later, it was demonstrated that under certain operating conditions, one can replace all but one of these sources with energy storage devices, e.g., capacitors. In other words, the entire power can be supplied by only one source. The replacing capacitors must only maintain a constant dc voltage supplying zero net power. Although this approach benefits from cost reductions, balancing the voltages across the replacing capacitors turns out to be a challenge. In this thesis, the operating conditions under which the capacitor voltage regulation is feasible are first analytically investigated. The results show that the amplitude of the output voltage as well as the power factor of the load current determines the regulation range when the staircase modulation method is employed. In order to extend the regulation range for the replacing capacitors, a new control scheme - phase shift modulation - is proposed. This method is more robust when compared to existing methods. In this method, the main H-bridge cell of the multilevel converter operates at the fundamental frequency and the auxiliary cells run at the PWM frequency. Finally, the sigma-delta modulation method has been utilized to extend the capacitor voltage regulation range. This method benefits from simplicity in implementation in comparison to PWM techniques. The analytical and simulation results prove the effectiveness of the proposed approaches. They are also consistent with the results of the experiment --Abstract, page iv

An Improved Cascaded H-Bridge Multilevel Inverter Controlled by an Unbalanced Voltage Level Sigma-Delta Modulator

Multilevel inverters have been proven to be viable solutions for high-power automotive motor drive applications due to their high volt-ampere ratings. Cascaded H-bridge inverters are a promising breed of multilevel inverters which generally require several independent dc sources. Replacement of all but one of the dc sources with capacitors in cascaded H-bridge multilevel inverters, which leads to single-dc-source per-phase cascaded inverters, has recently gained popularity. However, very few efforts have been made to address the challenging problem of voltage regulation in the replacing capacitors. In this paper, applicability of a real-time voltage control technique named unbalanced voltage level sigma-delta modulation technique to provide voltage regulation across the replacing capacitors is examined. In addition, a new voltage ratio for the H-bridge cells is introduced, which simplifies the control tasks. Analytical and simulation results prove the effectiveness of the proposed scheme

A New Control Method for Single-DC-Source Cascaded H-Bridge Multilevel Converters using Phase-Shift Modulation

Multilevel converters have gained popularity in high-power applications due to their low switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters, which generally require several independent dc sources. Using phase-shift modulation, a new control method for cascaded H-bridge multilevel converters with only one independent dc source per phase is presented in this paper. Unlike the conventional approaches, the proposed method has a wide voltage regulation range over the capacitors replacing the dc sources in the H-bridge converter cells

Control Methods in DC-DC Power Conversion -- A Comparative Study

Several control techniques for dc-dc power conversion and regulation have been studied in this paper. Analog approaches have briefly been described since the focus is the newly developed digital techniques. Principles of operation, advantages, and disadvantages of each control method have been described. Simulation results have been used to compare the performance and accuracy of digital control techniques

Cascaded H-bridge Multilevel Inverters -- A Reexamination

Multilevel converters have gained popularity in high-power applications due to their low switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters which generally require several independent dc sources. Recently, existence of a redundant switching state has been utilized to replace the independent voltage sources with capacitors except for the one with the highest voltage level. Redundancy in the charge and discharge modes of the capacitors is assumed to be adequate for their voltage regulation. However, output current of the inverter as well as the time duration of the redundant switching states have been neglected. In this paper, the impacts of connected load to the cascaded H-bridge converter as well as the switching angles on the voltage regulation of the capacitors are studied. This study proves that voltage regulation is only attainable in a much limited operating conditions that it was originally reported

Investigation on Capacitor Voltage Regulation in Cascaded H-Bridge Multilevel Converters with Fundamental Frequency Switching

Multilevel power electronic converters have gained popularity in high-power applications due to their lower switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters which generally require several separate dc voltage sources. By utilizing the redundant switching states, it is possible to replace the separate dc voltage sources with capacitors and keep only the one with the highest voltage level. Redundancy in the charge and discharge modes of the capacitors is assumed to be adequate for their voltage regulation. However, the effects of the output current of the converter as well as the time duration of the redundant switching states have been neglected. In this paper, the impacts of the connected load to the cascaded H-bridge converter as well as the switching angles on the voltage regulation of the capacitors are studied. This paper proves that voltage regulation is only attainable in a much limited operating conditions that it was originally reported. In addition, based on the analysis of the converter, a simplified formula is found which can be used to find those modulation indices that regulate the voltage of the capacitor. This formula can be used in harmonic minimization problems while capacitor voltage regulation is ensured. Simulation and laboratory results are provided to confirm the analysis

Capacitor Voltage Regulation in Single-DC-Source Cascaded H-Bridge Multilevel Converters Using Phase-Shift Modulation

Cascaded H-bridge multilevel power electronic converters generally require several dc sources. An alternative option is to replace all the separate dc sources feeding the H-bridge cells with capacitors, leaving only one H-bridge cell with a real dc voltage source. This will yield a cost-effective converter. However, the required capacitor voltage balancing is challenging. In this paper, using the phase-shift modulation approach, a new control method for cascaded H-bridge multilevel converters fed with only one independent dc source is presented. The proposed method has a wide voltage regulation range for the replacement capacitors in the H-bridge cells. Experimental and simulation results support the proposed control method

Extended ℋ∞ Estimation for Two-Dimensional Markov Jump Systems under Asynchronous Switching

This paper is concerned with the problem of designing ℋ∞ filters for a class of two-dimensional (2D) Markov jump systems under asynchronous switching. The problem under consideration is primarily motivated by a realistic situation that the switching of candidate filters may have a lag to the switching of system modes. Different from conventional techniques, by a suitable augmentation, the jumping process of the error system is represented by a two-component Markov chain. Then, the extended transition probabilities are provided for the error system. A stochastic Lyapunov function approach is proposed for the design of desired filters that ensure a prescribed ℋ∞ performance for admissible asynchronous switching. Finally, a numerical example is given to illustrate the effectiveness of the developed method

Artificial Synapses Based on Multiterminal Memtransistors for Neuromorphic Application

10.1002/adfm.201901106ADVANCED FUNCTIONAL MATERIALS292