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This paper proposes a novel polygonal voltage space vector structure (SVS) having 30 sides, for a star-connected induction motor drive. The SVS eliminates the presence of harmonics up to 25th order from motor phase voltage throughout the entire modulation range, providing a torque profile devoid of lower order pulsations. Linear modulation is extended till 99.63% of base speed without exceeding the motor phase voltage rating. Topology consists of a dc-link fed primary inverter and two equal low voltage modular capacitor fed secondary inverters. Here the harmonics generated by the primary inverter is canceled by the secondary inverter which acts as a switched capacitive filter. Detailed description of the SVS generation and timing calculations are provided in this paper. Effectiveness of the proposed scheme is validated using experimental results, inverter loss calculations, and harmonic analysis. [ABSTRACT FROM AUTHOR]

First harmonic analysis (FHA) is arguably the most widely used analytical technique for wireless power transfer (WPT) circuits due to its simplicity. Although FHA can provide closed-form solutions, the existence of rectifier diode forward voltage drop and higher order harmonics, especially the second and third harmonics at variable duty cycle operation, can significantly deteriorate its accuracy. This paper presents an accurate and efficient method called enhanced multiple harmonic analysis (eMHA) for the optimal design and optimal control of WPT systems. The eMHA method considers the nature of nonlinear rectification networks under nonsinusoidal current and reexamines the concept of the equivalent load. As a result, the rectified WPT system is transformed into a series of linear systems with complex load impedances. The steady-state electric quantities can be then explicitly calculated. This enables eMHA to seamlessly work with numerical optimization algorithms to facilitate the automated design and optimization of WPT systems. An example of optimal design and optimal control of a 10 W WPT system is demonstrated. The results obtained by eMHA and FHA are also compared. A prototype of the designed circuit was constructed. The accuracy and effectiveness of eMHA are verified by experimental measurements. This paper is accompanied by a MATLAB-based analytical tool with a graphical user interface demonstrating the effects of circuit variables on electrical quantities and waveforms. [ABSTRACT FROM AUTHOR]

This paper presents a method for generating a multilevel dodecagonal voltage space vector structure using a single dc source for induction motor drives. Multilevel dodecagonal structure combines the advantages of both multilevel and dodecagonal structures, and hence, generates low dv/dt phase voltage along with the elimination of fifth- and seventh-order harmonics over the entire modulation range. This eliminates low-order harmonic currents and prevents the generation of sixth-order torque ripple in the motor. The topology used requires only one dc source making four-quadrant operation of the drive system simpler compared to previously proposed multilevel topologies generating dodecagonal space vector structures. The topology used consists of a three-level flying capacitor (FC) inverter cascaded with a capacitor fed H-bridge. The FC inverter operates at a lower switching frequency and the low-order harmonics are eliminated by the switching action of the cascaded H-bridge inverter. The capacitors in the cascaded H-bridge modules are maintained at a substantially smaller voltage compared to the dc-link voltage and are inherently balanced during the pulsewidth modulation operation. This results in low switching loss, in the FC inverter as well as in the cascaded H-bridge inverter. Experimental results are included to validate the operation of the topology and modulation scheme presented in this paper. [ABSTRACT FROM AUTHOR]

The paper proposes a method of active switching harmonics current reduction in the dc-link capacitor of a two-level, three-phase, back-to-back converter. Based on the derived analytical solution for switching harmonic currents in the dc-link, it is shown that by specific control over the pulsewidth-modulated (PWM) carriers’ phase angles, the targeted harmonics of the rectifier and the inverter can be synchronized in phase such that their cancellation occurs in the dc-link capacitor. This synchronization is provided by harmonic phase feedback control. A three-step procedure to implement the method is detailed in the paper. The effectiveness of the proposed approach is verified experimentally. [ABSTRACT FROM AUTHOR]

This paper proposes a new fault-tolerant strategy to revamp performance of three-phase multilevel converters with a single faulty switch. The proposed fault-tolerant strategy is based on the application of a modified selective harmonic elimination (SHE) technique in conjunction with the fundamental phase-shift compensation method. The proposed fault-tolerant strategy makes the most use of the converter capacity in the faulty condition, generates balanced line voltages, and eliminates a wide range of lower order harmonics to limit the total harmonic distribution of the converter voltages in the faulty condition. In this paper, first, a brief background about cascaded H-bridge multilevel converters and SHE technique is provided. Then, the proposed fault-tolerant strategy and the modified SHE technique are presented. Finally, several experimental results are provided to validate the operation of the proposed strategy. [ABSTRACT FROM PUBLISHER]

A virtual space vector modulation technique reducing both magnitude and third-order harmonic component of the common-mode voltage (CMV) in a two-level voltage-source inverter (VSI) is proposed in this paper. The presented method employs a set of virtual space vectors constructed from original stationary space vectors to conduct modulation. Since the created virtual vectors have the lowest instantaneous and zero average CMVs, both the magnitude and third-order harmonic component of the generated CMV are reduced, contributing to better overall CMV performance and common-mode filter design in VSI applications. Three variants of the proposed modulation method using different virtual space vector combinations are presented. The concept of the virtual space vector modulation technique demonstrated with two-level inverter in this paper can also be extended to multilevel inverters. Simulation and experimental results, as well as comparisons with existing methods are provided to verify the proposed technique. [ABSTRACT FROM AUTHOR]

The six-step operation of surface-mounted permanent magnet machine drives in a flux weakening region has many advantages compared to the pulse width modulation mode, such as the reduced switching loss and fully utilized inverter output voltage. However, if the ratio of the sampling frequency to the fundamental frequency is low in fixed sampling system, the low-frequency oscillation in the current can be incurred in the six-step operation. The low-frequency current causes a system stability problem and reduces system efficiency due to an excessive heat and high power loss. Therefore, this paper proposes the variable time step controller for six-step operation. By updating an output voltage, sampling phase currents, and executing the digital controller synchronized with the variable sampling time, the turn on and off switch signals for six-step operation can be generated at the exact moment. As a result, the low-frequency oscillation in the phase current can be eliminated. In addition, the system transfer function of the proposed control method is discussed for the system stability and system dynamic analysis. The effectiveness of the proposed method is verified by the comparative simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper addresses the inverter nonlinearity of a three-level T-type inverter. The main causes of the nonlinearity are pulse shaping, pulse skipping due to narrow pulses for the dead time, and voltage drop of the switching devices. Although the same causes have existed in two-level inverters, the pulse skipping phenomenon and results are quite different in the case of the three-level T-type inverter. The effects of pulse shaping and skipping have been investigated and discussed. In addition, the voltage drop of the switching devices has been considered in conjunction with the conduction path of the T-type inverter. Compensation methods based on the pulse width modulation (PWM) of T-type inverter to alleviate the inverter nonlinearity have been proposed from research results. The proposed methods could be easily implemented by adding appropriate offset voltages to the voltage references of the inverter in PWM. Furthermore, a neutral voltage balancing method of a three-level T-type inverter has been proposed in conjunction with the proposed PWM methods using offset voltage. Through extensive experimental tests, the fifth- and seventh-harmonic components of the current are conspicuously reduced along with the even harmonics. The neutral voltage of the inverter can be balanced effectively with the proposed offset voltage adjustments as well. [ABSTRACT FROM AUTHOR]

For multilevel converters, as their selective harmonic elimination (SHE) equations are highly related to the switching patterns, it is almost impossible to give a complete study for all the switching patterns under the traditional SHE framework. In this paper, a unified SHE approach is proposed, in which the various SHE equations for different switching patterns are merged into one group of unified SHE equations and the inequality constraints on the switching angles are eliminated at all. This unified SHE equations can be solved by any methods, which have been used in solving the traditional SHE problems. By using the theory of Groebner bases and symmetric polynomials, all the possible switching patterns and the corresponding switching angles can be solved simultaneously. The study on the case for four switching angles discovers some unusual switching patterns that have the lowest total harmonic distortion for low-modulation indices. Also, the case for nine switching angles with modulation index m=\text0.72 is studied; in total, there exist 43 groups of switching angles, which belong to 33 different switching patterns. Experiments on a 13-level cascaded-H bridge converter verify the correctness of this unified multilevel SHE approach. [ABSTRACT FROM PUBLISHER]

The two common three-leg, two-level voltage source inverters of a six-phase drive are able to produce 64 different switching states, representable as voltage space vectors in two orthogonal subspaces. The discrete output voltage of the inverter legs is usually controlled by means of a space vector modulation (SVM) technique, the aim of which is to produce the same volt-seconds as the continuous reference voltage vectors in both subspaces within a certain time frame (switching cycle). Using a simplified phase model of the machine consisting in each subspace of a voltage source and a leakage inductance, the phase currents are found to exhibit unwanted distortion harmonics. A proper sequence of voltage vectors has to be applied in order to reduce these harmonics. By allowing each inverter leg to change its output twice during the switching cycle (continuous modulation), 518400 different space vector sequences can be generated. This paper demonstrates that, among these sequences, only 11 need to be considered to modulate the reference vectors. Further simulation shows that, for a certain pair of reference vectors and leakage inductance ratio, only one of them reduces the distortion to a minimum. Due to the high computational effort, however, this optimization problem is not solvable online. To overcome this drawback, four different modulation strategies, the standard three-phase SVM, the fragmented sector mapping, the optimal interleaved and the approximated interleaved SVM, are derived from and compared with an offline optimization. Each strategy is evaluated regarding the resulting current distortion and the influence of the reference vectors as well as the inductance ratio. The harmonic current of these online modulation strategies is calculated in simulation and validated by experiments. Applying the proposed modulation techniques leads to a great reduction in the machine losses caused by switching. [ABSTRACT FROM AUTHOR]

Modulating the output of a voltage source inverter (VSI) inherently causes current distortions on the load side due to the switching behavior of the inverter. This paper describes a method to reduce these distortions for a drive setup with six phases. The setup consists of a six-phase machine connected to two three-leg two-level VSIs. The phases within the machine are symmetrically arranged and spatially shifted by $60^\circ$ . The phases are grouped so that two conventional three-phase sets are formed, each fed by one inverter. The output of each inverter leg is modulated by comparing a triangle carrier waveform with the desired fundamental wave. Arranged in this way, the drive setup offers an additional degree of freedom, the phase shift of the two carrier waveforms. It is shown that, depending on the machine parameters, there exists an optimal angle, which reduces the harmonic losses of the drive for a certain amplitude of the fundamental wave. The resulting overall current distortion can even be lower compared to a conventional three-phase drive with a two- or three-level inverter topology. For three different modulation techniques, the optimal phase shift angles are derived in an exact form, naturally, symmetrical regular and asymmetrical regular sampled pulse width modulation. An approximation with reasonable accuracy is achieved out of the exact solution. Simulations and experimental tests validate the theoretical considerations. [ABSTRACT FROM AUTHOR]

An algebraic method is proposed for selective harmonic elimination PWM (SHEPWM). By computing its Groebner bases under the pure lexicographic monomial order, the nonlinear high-order SHE equations are converted to an equivalent triangular form, and then a recursive algorithm is used to solve the triangular equations one by one. Based on the proposed method, a user-friendly software package has been developed and some computation results are given. Unlike the commonly used numerical and intelligent methods, this method does not need to choose the initial values and can find all the solutions. Also, this method can give a definite answer to the question of whether the SHE equations have solutions or not, and the accuracy of the solved switching angles are much higher than that of the reference method. Compared with the existing algebraic methods, such as the resultant elimination method, the calculation efficiency is improved. Experimental verification is also shown in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analytical investigation of the four-switch three-phase (B4) voltage source inverter. The double Fourier integral analysis is used as an analytical approach to determine the phase-leg switched voltage spectrum under condition of natural sampling. The performance of two proposed switching sequences are subsequently evaluated when the harmonic copper losses are chosen as performance criterion. For a clear identification of dc-link voltage, the spectrum of dc-link current is characterized by convolution of switching function spectrum and corresponding phase current spectrum, in which fundamental component appears causing offset and fluctuation in dc-link two-capacitor voltages. The offset can be suppressed by certain switching states, whereas the effect of fluctuation must be neutralized through analytical compensation for modulating waveforms. Otherwise, symmetry of three-phase output currents and reliable operation of the system will not be retained. Finally, the analytically calculated spectrum of output voltage and dc-link current are demonstrated by comparing with those obtained by fast Fourier transform (FFT) analysis of simulated waveforms in MATLAB/SIMULINK. The capacitor voltage offset suppression and fluctuation effect neutralization are carried out by simulations and experiments, in which the results confirm the validity of the analytical investigation. [ABSTRACT FROM AUTHOR]

In medium-/high-power inverters, optimal pulse-width modulation (OPWM) is often used to reduce the switching frequency and at the same time, realize selective harmonic elimination (SHE). For both two-level and multilevel inverters, most selective harmonic elimination (SHE) studies are based on solving multiple variable high-order nonlinear equations. Furthermore, for multilevel inverters, SHE has been often studied based on the assumption of balanced dc levels and single switching per level. In this paper, the authors further developed harmonics injection and equal area criteria-based four-equation method to realize OPWM for two-level inverters and multilevel inverters with unbalanced dc sources. For the cases, where only small number of voltage levels are available, weight oriented junction point distribution is utilized to enhance the performance of the four-equation method. A case study of multilevel inverter at low-modulation index is used as an example. Compared with existing methods, the proposed method does not involve complex equation groups and is much easier to be utilized in the case of large number of switching angles, or multiple switching angles per voltage level in multilevel inverters. [ABSTRACT FROM AUTHOR]

This paper presents the real-time implementation and experimental performances of the wavelet-modulation technique for single-phase voltage-source (VS) inverters. The wavelet-modulation technique is realized through constructing a nondyadic-type multiresolution analysis, which supports sampling of a sinusoidal reference-modulating signal in a nonuniform recurrent manner, then reconstructing it using the inverter-switching actions. The required nonuniform recurrent sampling is carried out by using dilated and translated sets of wavelet basis functions, which are generated by the scale-base linearly combined scaling function. The reconstruction of the sampled signal is accomplished by using dilated and translated sets of wavelet basis functions, which are generated by the scale-base linearly combined synthesis scaling function. The dilated and translated sets of wavelet basis functions used in the reconstruction are employed as switching signals to activate the inverter-switching elements. The wavelet-modulation technique is implemented in real time by using a digital signal processing board to generate switching pulses for a single-phase VS H-bridge (four-pulse) inverter. Experimental performances of the single-phase inverter, which is operated by the wavelet-modulation technique are investigated while supplying linear, dynamic, and nonlinear loads with different frequencies. Experimental test results show that high magnitude of fundamental components and significantly reduced harmonic contents of the inverter outputs can be achieved using the wavelet-modulation technique. The efficacy of the developed modulation technique is further demonstrated through performance comparisons with the pulsewidth- and random-pulsewidth-modulation techniques for similar loading conditions. [ABSTRACT FROM AUTHOR]