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In this paper, a new medium voltage power converter topology using a diode rectifier, three-level boost (TLB) converter, and neutral-point-clamped (NPC) inverter is proposed for a high-power permanent magnet synchronous generator-based wind energy conversion system. The generator-side TLB converter performs the maximum power point tracking and balancing of dc-link capacitor voltages, while the grid-side NPC inverter regulates the net dc-bus voltage and reactive power to the grid. A significant improvement in the grid power quality is accomplished as the NPC inverter no longer controls the dc-link neutral point voltage. A model predictive strategy is proposed to control the complete system where the discrete-time models of the proposed power electronic converters are used to predict the future behavior of control variables. These predictions are evaluated using two independent cost functions, and the switching states which minimize these cost functions are selected and applied to the generator- and grid-side converters directly. In order to comply with the high-power application, the switching frequencies of the TLB converter and NPC inverter are minimized and maintained below 1.5 and 1 kHz, respectively. The proposed topology and control strategy are verified through MATLAB simulations on a 3-MW/3000-V/577-A system and dSPACE DS1103-based experiments on 3.6-kW/208-V/10-A prototype. [ABSTRACT FROM AUTHOR]

In this paper, a model-predictive control of medium voltage, grid-tied four-level diode-clamped inverter for use in high-power wind energy conversion systems is presented. The control objectives such as regulation of net dc-link voltage, reactive power generation to meet the grid operator request, dc-link capacitor voltages balancing, and switching frequency minimization are included in the cost function. The latter objective is an important requirement for high-power converters, and this has been achieved without any modifications to the software or hardware configuration. The future behavior of the grid currents and dc-link voltages is predicted for all the possible switching states using the discrete-time model of the inverter, dc-link, inductive filter, and grid. The switching state that minimizes the cost function has been chosen and applied to the inverter directly. During different operating conditions, the switching frequency is regulated between 750 and 850 Hz with the help of a lookup-table-based weighting factor, and thus, the proposed methodology appears as a promising tool to control the high-power grid-tied inverters. The results obtained through the MATLAB simulations on 4 MVA/4000 V system and dSPACE DS1103-based experiments on 5 kW/208 V prototype are in a close relationship and thus validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

Most research work in current-source inverter (CSI) fed motor drives has focused on general control strategies, pulsewidth modulation schemes, topologies, and efficiency evaluation. This paper, however, is dedicated to investigating zero-speed operation characteristics of CSI-fed induction motor drives (IMDs). Zero-speed operation can greatly increase the competitive value of the drive and expand its range of applications to include cranes, hoists, and draglines. The motor drive is controlled with rotor flux orientation, where stator currents and motor speed are employed for the rotor flux estimation. Unlike voltage-source-inverter-based drives, filter capacitors are required at the output of the CSI for current commutation and harmonics filtering. The influence of these capacitors on the system dynamic performance is comprehensively evaluated. Moreover, a classic load torque observer with feedforward control is employed to improve the speed dynamic response. Simulated and experimental results show that the CSI-fed IMD works well at zero speed with promising speed dynamic performance. [ABSTRACT FROM AUTHOR]

Half-cycle symmetry selective-harmonic-elimination pulsewidth-modulation (SHE-PWM) problems may have a large number of valid solutions, which are beneficial to the optimization design. This paper proposes a novel generalized formulation of half-cycle symmetry SHE-PWM problems for multilevel inverters. The advantages of the proposed formulation include simplicity in format, flexibility in PWMwaveforms, and a broad solution space. A method to obtain initial values for the SHE-PWM equations according to the reference modulation index M and the initial phase angle of output fundamental voltage is proposed and investigated thoroughly. Take a five-level inverter with M = 0.75 as an example; six sets of solutions for two typical initial phase angles of 0°? and 90°? are presented. Simulations and experiments are carried out. It is demonstrated that the experimental results agree well with simulated ones, which proves the validity and practicability of the new method proposed. [ABSTRACT FROM AUTHOR]

This paper proposes an input power factor control strategy for a current-source drive with active front-end. The proposed strategy is realized without modification of the drive's pulsewidth modulation and speed control schemes through the collaborative use of two methods: a modulation index regulation method and a flux adjustment method. Specifically, the modulation index regulation method functions to directly control the dc-link current and voltage, and it can effectively correct a leading input power factor as long as the space vector modulation is used for the inverter. On the other hand, the flux adjustment method can improve the power factor when the power factor is lagging or when the selective harmonic elimination modulation is used for the inverter at high motor speeds. When implemented together, the two methods will complement each other's functionalities and improve the overall compensation performance. Experimental results are obtained from a 600-hp and an 1100-hp drive system. [ABSTRACT FROM AUTHOR]

This paper presents a novel power-factor (PF) control strategy for a high-power pulsewidth-modulated current-source rectifier-current-source inverter-fed motor drive system. The PF regulation is realized by adjusting the motor flux in the drive's fieldoriented control scheme. The relationship between the motor flux and the drive's input reactive power is first investigated. Based on this analysis, a flux-adjustment PF regulation scheme is proposed. The proposed PF regulation method, together with a properly designed input line capacitor, can ensure a unity PF throughout the whole speed range (including flux-weakening range). Furthermore, unlike all the other PF compensation techniques, the proposed fluxadjustment approach does not require online modulation index control of the rectifier and the inverter, and therefore, offline selective harmonic elimination modulation can be implemented on both the rectifier and the inverter to minimize the line-side and motorside waveform distortions. Medium-voltage simulation results and experimental results from a low-voltage 30-hp induction motor drive are provided to verify the effectiveness of the PF correction strategy. [ABSTRACT FROM AUTHOR]

A generalized formulation of quarter-wave symmetrical selective harmonic elimination (SHE) problems according to the rising and falling edges of the pulsewidth modulation (PWM) waveforms for multilevel inverters is proposed. The SHE modulation scheme features a broad solution space and can eliminate a large number of low-order harmonics. An effective method for obtaining initial values of switching angles is proposed. This method is based on rules of equal area and superposition of center of gravity (cg) of the PWM section with the sine reference signal. To illustrate the effectiveness of the proposed SHE method, a five-level voltage source inverter with elimination of 11 low-order harmonics is investigated. The SHE-PWM equations that can eliminate harmonics from 5th to 35th with modulation index M varying from o to 1.15 are formulated, and solutions are presented. Simulations and experiments based on two sets of solutions are carried out. It is demonstrated that the experimental results agree well with simulated ones, which proves the validity and practicability of the new method proposed. [ABSTRACT FROM AUTHOR]

In this paper, a loss reduction and dc-link current minimization strategy for a high-power current-source inverter (CSI) fed drive is proposed. The proposed strategy consists of an inverter maximum modulation index control scheme and a flux optimization algorithm. Specifically, in the inverter modulation index control, the CSI modulation index is kept at the maximum value while the current-source rectifier (CSR) is used to regulate a reduced variable dc-link current, and therefore, to control the motor current magnitude. This control scheme can effectively reduce the dc-link current, and at the same time, improve the line-side and motor-side waveforms. On the other hand, for the optimized flux control, the relationship between the rotor flux and the dc-link current is first investigated thoroughly. Based on this analysis, the dc-link current from the maximum inverter modulation index control can be minimized further by optimizing the rotor flux according to system variables such as the motor speed, the applied torque, and the motor-side capacitor size. With the proposed dc current minimization strategy, the losses in the semiconductor devices and the dc link can be reduced, and the drive current rating could be lowered. Both simulation and experimental results on a 4.16-kV 600-hp CSI-fed drive system are obtained to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper presents a technology review of voltage-source-converter topologies for industrial medium-voltage drives. In this highly active area, different converter topologies and circuits have found their application in the market. This paper covers the high-power voltage-source inverter and the most used multilevel-inverter topologies, including the neutral-point- clamped, cascaded H-bridge, and flying-capacitor converters. This paper presents the operating principle of each topology and a review of the most relevant modulation methods, focused mainly on those used by industry. In addition, the latest advances and future trends of the technology are discussed. It is concluded that the topology and modulation-method selection are closely related to each particular application, leaving a space on the market for all the different solutions, depending on their unique features and limitations like power or voltage level, dynamic performance, reliability, costs, and other technical specifications. [ABSTRACT FROM AUTHOR]

This paper presents a novel switching sequence design for the space-vector modulation of high-power multi- level converters. The switching sequences are optimized for the improvement of harmonic spectrum and the minimization of device switching frequency. Compared to other commonly used switching sequences, the output spectrum of the proposed design shows higher inverter equivalent switching frequency. Meanwhile, the device switching frequency is reduced by using a flexible switching pattern. The proposed switching sequence has been simulated and experimentally tested on a 5-level neutral point clamped H-bridge based inverter. The results from both simulations and experiments consistently verify the above-mentioned features. [ABSTRACT FROM AUTHOR]