Innovative Control And Modulation Methods Exploiting Logic-Equations For Novel Multilevel Converter Topologies

An unremitting and persistent research for developing advanced multilevel converter topologies with improved characteristics, performance, modulation methods, and control techniques still goes on. The multilevel converters are well-suited for power conversion areas demanding more power density, reliablity, efficiency, and power quality. The emergence of new power conversion areas such as grid integration of large-scale renewable energy sources and large-capacity energy storage necessitate the evolution of the classic multilevel converters. This dissertation proposes innovative logic-equation-based modulation techniques and control methods for new multilevel converter topologies. Chapter I reviews the classic multilevel converter configurations. Chapter II proposes an enhanced topology for the flying-capacitor multilevel converters to reduce the voltage diversity and stored energy of the flying-capacitors within switching-power-cells in order to improve the multilevel converter integrity and modularity. Chapter III provides general solutions for nonlinear transcendental equations of the cascaded H-bridge converters modulated under the selective harmonic elimination method to eliminate the significant low-order line-to-line voltage harmonics. Chapters IV, V, VI investigate the conduction and switching power losses in the flying-capacitor-based multilevel converter topologies utilizing the proposed closed-form formulas. Chapter VII proposes a duo-active-neutral-point-clamped multilevel converter topology with an innovative control technique and modulation method. The proposed converter reduces the number of the high-frequency medium-voltage semiconductor power switches in the active-neutral-point-clamped multilevel converter family by 50%. The substantial reduction in the number of the switching-power-cells by 50% in comparison with the classic active-neutral-point-clamped converter along with a drastic decrease in the total voltage rating and the stored energy of the flying-capacitors are the paramount advantages of the proposed multilevel converter topology. Chapter IIX suggests an improved configuration for the active-neutral-point-clamped multilevel converters to reduce the flying-capacitors in this breed. Moreover, logic-equation-based control technique is developed in chapter IIX to modulate the proposed multilevel converter topology. Chapter IX proposes a novel multilevel converter topology which is realized by the cascaded connection of the classic two-level or multilevel converters and modular-concatenated-cell H-bridge converters. This results in a significant improvement in the harmonic spectra of the generated voltage at the converter output stage along with a reduction in the dv/dt-stress on the semiconductor power switches. Utilizing the flying-capacitors instead of the isolated dc-voltage sources is the major distinction between the proposed modular-concatenated-cell multilevel converter topology and the cascaded H-bridge inverters. The voltage rating of the power switches and the flying-capacitors are 1 p.u. in the proposed configuration. This boosts the integrity and modularity of the flying-capacitor-based multilevel converters. Moreover, chapter IX derives an innovative modulation method exploiting logic-equations for balancing the flying-capacitor voltages at their reference voltage-levels within modular-concatenated-cells of the proposed multilevel converter. Chapter X proposes a novel active capacitor voltage balancing technique for flying-capacitor multilevel converters using logic-equations. The foremost advantage of the proposed active control technique is that it does not require any complex computations

Phase-Disposition PWM Based Active Voltage Control of Seven-Level Nested Neutral-Point-Piloted (NNPP) Inverters

This paper introduces logic-equations for active voltage balancing of seven-level nested neutral-point-piloted (NNPP) inverters. It measures the load current and voltage of floating-capacitors (FCs). These instantaneous measurements are then translated into logic-variables on basis of their reference values. Next, the interpreted logic-variables are employed in a set of logic-equations that are specifically derived for the 7-level NNPP inverters. These equations aim to actively balance the FC voltages at their target operating levels and to generate the reference voltage-level according to the adopted PWM strategy. As an outstanding advantage, the proposed logic-equations-based active-voltage balancing method eliminates all the complicated and time-consuming computations that are necessary in the conventional active balancing approaches since it is not utilizing or optimizing any cost/energy functions. The experimental results obtained from a 7-level prototype of the NNPP converter are provided to verify the logic-equations and active control method

Flying-Capacitor Voltage-Balancing Control in Five-Level Active Neutral-Point-Clamped (A-NPC) Converters Using Phase-Disposition PWM

A new control technique for five-level active neutral-point-clamped (A-NPC) inverters is proposed in this paper. The introduced method is based on a set of simple and effortless logic-variables and logic-equations. It actively balances the voltage of the flying-capacitor (FC) at its requisite value, and controls the 5-level A-NPC converter\u27s synthesized voltage according to phase-disposition pulse-width-modulation (PD-PWM) strategy. These logic-variables and equations are derived using the instantaneous measurements of output current and FC\u27s voltage. The regulation of the FC\u27s voltage at its reference operating level and generating the commanded voltage-levels of PD-PWM modulator at output with the less computational requirements are the control targets. The logic-equations and the proposed active balancing technique are validated using the experimental results which are obtained from the prototype of a five-level A-NPC inverter

Novel multi-terminal MMC-based dc/dc converter for MVDC grid interconnection

Multi-terminal modular multilevel converter (MMC)-based dc/dc converter with the medium-frequency ac-link transformer is an attractive and feasible solution for interconnecting medium-voltage direct-current (MVDC) grids. This study proposes a novel multi-terminal dc/dc converter which features significantly reduced number of components compared with the conventional converter topology. The proposed dc/dc converter is capable of interconnecting multiple MVDC grids with different voltage levels as well as controlling the power flow between them. A combination of sine wave modulation scheme and phase disposition level-shifted pulse-width modulation is developed and employed for voltage balancing and controlling the power flow in the proposed converter. Several simulations, experimental and real-time hardware-in-the-loop case studies are carried out to demonstrate the dynamic response and capacitor voltage balancing capability of the proposed MMC and dc/dc converter under the developed control strategy

Exploring the trade-off between competing objectives for electricity energy retailers through a novel multi-objective framework

Energy retailer is the intermediary between Generation Companies and consumers. In the medium time horizon, in order to gain market share, he has to minimize his selling price while looking at the profit, which is dependent on the revenues from selling and the costs to buy energy from forward contracts and participation in the market pool. In this paper, the two competing objectives are engaged proposing a new multi-objective framework in which a ε-constraint mathematical technique is used to produce the Pareto front (set of optimal solutions). The stochasticity of energy prices in the market and customer load demand are coped with the Lattice Monte Carlo Simulation (LMCS) and the method of the roulette wheel, which allow the stochastic multi-objective problem to be turned into a set of deterministic equivalents. The method performance is tested into some case studies

Analytical Approach to Calculate Inductor Current Ripple Cancellation in Two-Phase Interleaved Single-phase Inverter

Single-phase inverters have very wide range of applications such grid-tied inverter to inject any absorbed solar energy into power grid in residential areas. This paper presents closed-form equations to analytically calculate the required inductance of an LC filter in a single-phase full-bridge inverter controlled with unipolar switching pattern. According to the derived equations, required inductance value of LC filter varies with the modulation index value. Furthermore, the derived equations show that the maximum peak-to-peak ripple of the inductor current happens at angle which depends on the modulation index value. In addition, this paper provides an analytical approach to calculate current ripple cancellation in two-phase interleaved single-phase inverter. Real-time experimental results obtained from OPAL-RT for two cases of modulation index M=0.4 and M =0.8 are provided to confirm derived closed-form equations