Abstract: A significant problem with neutral-point-clamped three-level inverters is the fluctuation in the neutral-point voltage. In this paper, a capacitor voltage balancing technique for carrier-based three-level pulsewidth modulation (PWM) is developed, with improved voltage control capability at high modulation index. The method incorporates a novel scheme that requires measurements of only the motor currents and capacitor voltages to implement voltage balancing control, and does not need to determine the direction of power flow between the inverter and the motor.

Abstract: This paper presents a method to evaluate harmonic distortion due to space vector-based pulse-width modulation (PWM) strategies for ac drives. The proposed method is general enough to deal with division of zero vector time as well as division of active vector time within a subcycle. The method is based on the notion of stator flux ripple, which is a measure of line current ripple. Expressions for RMS ripple over a subcycle are derived for six switching sequences in terms of magnitude and angle of the reference vector, and subcycle duration. The sequences considered include those involving division of active vector time within a subcycle. Further, analytical closed form expressions are derived for the total RMS harmonic distortion factor corresponding to six space vector-based synchronized PWM strategies, proposed recently, for high power drives. The square of the distortion factor turns out to be a quadratic polynomial in modulation index (M), and the coefficients differ with PWM strategies and pulse numbers. These expressions are validated through Fourier analysis as well as experimental measurements. The concept of stator flux ripple provides insight into current ripple as well as torque ripple corresponding to different sequences and strategies.

Abstract: Multilevel inverters are being increasingly used for high-power medium-voltage applications. Three-level neutral point clamped (NPC) topology is most widely used topology of multilevel inverters. However, at higher modulation index, particularly in over-modulation region, the neutral point fluctuation deteriorates the performance of the inverter. Furthermore, operating the inverter at lower modulation index implies that it is operated at lower voltages only, and the installed DC link capacity is not fully utilized. This paper proposes a simple space vector PWM scheme for operating a three-level NPC inverter at higher modulation indices including over-modulation region, with neutral point balancing. Experimental results are provided.

Abstract: This paper presents a comprehensive analysis of the 5-phase induction motor driven by voltage-source inverter drives and particularly its steady-state performance evaluation. The performance of various modulation methods are analyzed with insightful look into their harmonic content and torque ripple. Three separate methods are proposed to reduce the torque ripple for low, middle and high modulation index regions while eliminating or controlling the non-torque-producing harmonics within the current machine rating. A complete set of simulations are carried out to verify the concepts and proposed methods. The multi-level multiphase topology is introduced and it is compared to the two-level system. The modification of switching sequence for reduction of torque ripple is applied to the three-level 5-phase motor drive. Application of the multilevel multi-phase concept to high power motor drives (as well as motor design and selection) is discussed.

Abstract: It is known that any multilevel continuous phase-modulated (CPM) signal with a single modulation index can be exactly represented by a sum of pulse-amplitude modulated (PAM) waveforms. In this paper, we show how multi-h CPM signals can also be represented in this manner. The decomposition is presented in general terms as a function of the alphabet size, modulation indexes, and phase pulse of the CPM scheme. The number of pulses required to exactly construct the signal is shown to increase over that previously given for single-h schemes; this increase is in proportion to the number of modulation indexes. We propose an approximation which significantly reduces the number of signal pulses and which minimizes the mean-squared error for an arbitrary set of modulation indexes. We show that this approximation can have two objectives: 1) to reduce the number of pulses in the same manner as has been proposed for single-h schemes; and/or 2) to reduce the number of multi-h pulses; we also show the conditions where this latter objective is most practical. We compare this minimum mean-squared error approximation with another method which was recently proposed for CPM. We also give numerical results on detection performance which demonstrate the practicality of the proposed approximation.

Abstract: In recent years, the multilevel inverter synthesising the output voltage with a step pulse, has been widely used in high power and high voltage applications. To acquire the conducting angles of switches, the conventional method needs to solve simultaneous equations, corresponding to the fundamental and harmonic components, by the use of a Fourier series. Since they are calculated by an iterative method, the process is requires with a large amount of calculation and time. Moreover, they are calculated by means of an off-line operation. To overcome these drawbacks, this paper proposes a simple method of obtaining the conducting angles. This method reduces the amount of calculation needed to obtain the conducting angles and determines them through an on-line operation. It makes use of the voltage-second areas of the divided reference voltage according to the output voltage levels of the inverter. It does not solve the set of nonlinear transcendental equations, but calculates several trigonometric functions. The validity of the proposed method is demonstrated according to each modulation index through simulation and experiment results. The results indicate that the harmonic components obtained by the proposed method are similar to those from the conventional one in the high modulation index. However, in the low modulation index, the proposed method includes more harmonics than the conventional one.

Abstract: Constant envelope OFDM with phase modulation (CE-OFDM-PM) was proposed. The motivation of the CE-OFDM-PM system is to alleviate the high peak-to-average power ratio of conventional OFDM systems. In this paper, we explore more details of CE-OFDM-PM systems regarding bandwidth efficiency and performance under AWGN and multipath channels. A theoretical approach instead of Carson's rule to analyze bandwidth is proposed. It indicates that bandwidth requirement is determined by factors such as input data variance and modulation index. The analytical results show that the CE-OFDM-PM systems require the same bandwidth as conventional OFDM system when appropriate (low) modulation index is applied in CE-OFDM-PM system. Under the same multipath channel and bandwidth, the performance of CE-OFDM-PM systems is compared to conventional OFDM system with one tap equalizer. The uncoded BER performance of CE-OFDM-PM is getting close when OFDM applies clipping, but power efficiency of CE-OFDM-PM still outperforms OFDM since clipping cannot eliminate PAPR issue

Abstract: It has been demonstrated that two two-level inverters connected at each end of an open end winding induction motor are capable of achieving the functionality of a three-level inverter. In this paper, a space vector based PWM switching scheme for the dual inverter fed open end winding induction motor drive is proposed. The common-mode voltages associated with such a drive are significantly reduced with the proposed PWM strategy., compared to the work reported earlier. In this work, the redundancy of the space vector combinations at a particular location is exploited, to reduce the common-mode voltages at lower indices of modulation. In the work reported earlier, the common mode voltages were enhanced with the decrement of modulation index. On the contrary, the common-mode voltages are reduced with the decrement of the modulation index with the PWM strategy presented in this paper. This PWM scheme for open-end winding induction motor drives may be suitable for applications, which call for frequent starting and run at low speeds. This scheme employs only the instantaneous reference phase voltages for the implementation. The time consuming task of sector identification is avoided with the proposed switching scheme. Another advantage with this scheme is that it does not require any look-up tables for its implementation. The scheme ensures a smooth switching all through, ensuring equal switching duty for both the inverters

Abstract: A simple method to analyse for and compare the harmonic characteristics in the multi-level inverter is presented. Generally, the magnitude of harmonic components is determined differently according to the available multi-carrier PWM techniques, the modulation index and the switching frequency. Previous papers have analysed the harmonic characteristics from the viewpoint of the space voltage vector. Hence, the calculation of harmonic vectors becomes more difficult and complex at four-level or over five-level. However, the proposed method has reduced the amount of calculation and simplified the process of it, using the relation between the reference phase voltage and the output phase voltage to the load neutral point. It is applied to a five-level cascade inverter and the harmonic characteristics for each multi-carrier PWM technique are compared through simulation.

Abstract: A static compensator (STATCOM) is a FACTS controller, whose capacitive or inductive output current can be controlled independently of the AC system voltage. A practical /spl plusmn/75 kVAr STATCOM has been designed, in which the phase difference between the converter voltage and the AC system voltage is controlled over a small region to obtain a nearly linear reactive power control. The converter voltage is synthesised using a PWM control with a fixed modulation index close to one. Here it is modelled using an averaging approach, by deriving the state-space equation of the STATCOM in the time domain. An average operator is defined, and applied to the state equation to get an averaged mathematical model. Expansion of this model will eventually lead to an average circuit model. An approximate averaged switching function represents the duty ratio as a continuous function of time. The solution is expandable as a Fourier series, which can be suitably truncated. Theoretical considerations show that the averaged model should agree well with the original system, and this is confirmed by MATLAB and PSpice simulations. Experimental results provide some practical waveforms that, compared to the corresponding simulations, validate the developed models.

Abstract: A new exact analytical model is presented to analyze the dispersive transmission in microwave fiber-optic links using a dual-drive Mach-Zehnder external modulator (DD-MZM). The model is very general and can be applied to almost all operating conditions of DD-MZM, such as bias point, drive level, phase shift, and modulation index difference between DD-MZM drives. The model results in simple new closed-form expressions for output power spectrum, permitting an accurate and fast analysis of such links. Expressions for two special cases, double sideband and single sideband modulation, are included, together with a novel presentation of some new results on power fading of fundamental and second harmonic.

Abstract: Flat power-envelope terahertz-wide modulation sidebands are generated by only electro-optic phase modulation of continuous-wave laser light. Generation and power equalization of widespread sidebands are realized simultaneously by spatial distribution of the modulation index within a laser beam cross section by use of simple domain-engineering processes in LiTaO3 electro-optic crystal. Generation of 46 sidebands spaced by 16.25?GHz within a ?3-dB bandwidth (over a 1-THz span for a ±3-dB bandwidth) is demonstrated.

Abstract: Voltage swells are one of the most harmful disturbances present in industrial power systems, being capable of severely damaging, breaking, or tripping converters. In the case of pulsewidth-modulation voltage-source rectifiers (PWM-VSRs), swells first saturate their control system and then force them into six-pulse operation if no precautions are taken. This paper presents an extended ride-through strategy enabling these converters to deal and cope with swells of up to 1.8 p.u. (IEEE Std. 1159 swell definition). The proposed strategy first fully exploits the dc-link voltage capacity by dynamically entering the overmodulation region, and secondly by drawing inductive current in case the former action does not suffice. Dynamic overmodulation makes possible the straight ride-through of 15% and 42% three-phase and single-phase swells, whereas the modulation index supervisor/control loop drawing inductive current enables the ride-through for greater magnitude disturbances, all the while avoiding saturation of the converter control system. This is realized using decision-making space vector modulation, and a control system built over a nonlinear control law directly obtained from the converter complex state variable model. In this way, linear and decoupled d-q axes dynamics are attained, ensuring a constant dynamic response throughout the whole operating range. Finally, experimental results from a TMS320C32 digital-signal-processor-based 5-kVA laboratory prototype subjected to typical industry single- and three-phase swells ranging from 5% to 50% are presented. These confirm the predicted performance and feasibility of the proposed voltage swell ride-through strategy for PWM-VSRs.

Abstract: In this paper, a blind estimator of the technical parameters of continuous phase modulated (CPM) signals is proposed. It consists in estimating jointly the modulation index, the symbol period and the frequency offset. It is based on the following observations. First, the inverse of the index is the smallest positive real number a CPM signal should be raised to in order to generate a deterministic harmonic signal; second, the frequencies of the harmonic signal are simply related to the symbol period and the carrier frequency. The practical implementation of this joint estimator is described and the asymptotic behavior of the estimation error is studied. If N is the number of signaling intervals, the estimate of the modulation index is shown to converge to a non-Gaussian distribution at rate 1/N, while the estimate of the frequency offset and the estimate of the symbol period converge at rate 1/N/sup 3/2/. We also investigate the case where the modulation index and the symbol period are available at the receiver side. An estimator of the frequency offset is proposed by adapting the above joint estimator to the latter case. The asymptotic behavior of this estimator is studied and compared with the case where all of the parameters are unknown, so as to evaluate the possible degradation of the performance due to the ignorance of certain technical parameters. Simulations results sustain our theoretical claims.

Abstract: Generally, the overmodulation techniques for space vector pulse width modulation (SVPWM) inverters need store lots of date in the controller beforehand, which makes a huge memory while the control resolution is not perfect. Based on amplitude control of the reference voltage vector and the vertex voltage vectors, this paper presents a novel digital over-modulation control strategy for SVPWM inverters, which can manage the transition from the linear control range to six-step operation smoothly. With avoiding the necessity of the stored data implementation, this strategy is simple and very suitable for practical digital implementation. The mathematic analyses show that the output fundamental voltage amplitude is linear proportional to the modulation index. In addition, this paper analyses the harmonic components, and the total harmonic distortion (THD) of the output voltage is compared with that of other strategy too. Both math analyses and experimental results, obtained by DSP board, verify that this strategy is very useful for the induction motor with the linear fundamental voltage output gain, low THD and simple application.

Abstract: Resonator fiber optic gyro(R-FOG) is a promising candidate for the next generation inertial rotation sensor.The signal detection system is very important in the R-FOG.The detection precision influences the ultimate resolution of the gyro directly.Optimization of the demodulation curve can enhance the detection resolution.Therefore,it has significance to optimize the demodulation curve.By the use of expansion of Bessel function and optical field overlapping method,the relation between the demodulation curve and the resonant frequency deviation was analyzed.According to the analytical expression of the demodulation curve in this phase modulation spectroscopy scheme,the changing rule for the curve was analyzed by the numerical method.Then optimized values for the modulation frequency and modulation index were obtained.The experiments verified the analytical results.

Abstract: Purpose – In this paper, a new application of the Selected Harmonic Elimination Pulse Width Modulation (SHEPWM) technique used in the cascade multilevel inverter topology which is formed by series connections of one‐phase bridge type inverters (H‐bridge) is introduced. The advantage of the SHEPWM technique is its ability to operate in low switching frequency that makes it suitable for high power applications.Design/methodology/approach – First, the switching angles are calculated using constrained optimization technique. By using these switching angles, the fundamental harmonic can be controlled and the selected harmonics can be eliminated. Then, using these calculated switching angles, a set of equation is formed which calculate the switching angles with respect to the modulation index. The switching angles at any modulation index can be easily obtained by solving the equation set. In this study, this equation set has been solved online using dSPACE DS1103 controller board. Using this technique, three‐ph...

Abstract: A mathematical approach of modelling and analysing three-phase pulse width modulation (PWM) is presented. The three-phase flyback converter required a unique pattern of PWM to optimise the power transfer in the magnetic circuit used in the converter. The three-phase PWM is generated digitally based on uniform symmetrical sampling technique using Xilinx chip. The generated PWM pattern is able to reduce the magnitude of the low order of harmonic components present in the input AC supply. Although software simulation could simulate the PWM pattern, it does not represent the exact pattern as been generated digitally. The mathematical approach used is to model the PWM pattern exactly as been created digitally. The proposed mathematical technique could also be used to analyse any digital PWM. The result of the mathematical analysis on the PWM pattern could be used to study the characteristics of the pattern such as maximum and minimum value of duty cycle, pulse width, turn-on time, turn-off time and modulation index. To verify the validity of the proposed technique, the results obtained from the mathematical model, experimental and simulation using PSpice were compared

Abstract: The main goal of this paper is to analyze and compare the evolution of magnetic hysteresis losses in silicon-steel sheets submitted to three different supplies: sinusoidal and two and three-level PWM voltages. The influence of the magnetic induction amplitude, the triangular frequency and the modulation index are considered. This experimental investigation was performed using a workbench constituted by a PWM inverter, an oscilloscope and computers for signal generation, data acquisition and calculations

Abstract: A system and method for transmitting a UWB or WB signal over a wireless network using a CP-FSK modulated carrier waveform. The system and method comprises selecting a wireless communication channel that is free of at least one of interference and multipath distortion and transmitting a CP-FSK modulated signal over the selected channel having a modulation index of ≦0.707, a bandwidth of at least 500 MHz, a power spectral density of ≦−41.3 dBm/MHz, and a frequency range of 3.1 GHz to 10.6 GHz.

Abstract: The space vector PWM (SVPWM) control of multi-phase inverter has more flexibility for the additional voltage vectors. According to vectors analyzing, the advantages of multi-phase inverter SVPWM control is presented in this paper. Two new SVPWM control methods for five-phase inverter are proposed comparing to the traditional Near Two Vectors SVPWM (NTV-SVPWM) control, and here they are called Near Four Vectors SVPWM (NFV-SVPWM) control and Minimum Switch Loss SVPWM (MSL-SVPWM) control. The target voltage functions and waveforms of three kind of SVPWM are deduced and compared. The conclusions can be drawn that there are much low frequency harmonics with NTV-SVPWM control, and which is not suitable for multi-phase inverter control; NFV-SVPWM has the best harmonics performance and is fit for low modulation index operation; MSL-SVPWM has the lowest switching loss and is fit for high modulation index operation. MATLAB is adopted to simulate the five-phase variable speed system, and the simulation results validate the conclusions above.

Abstract: This paper quantifies effects of using three different pulse width modulation (PWM) schemes on the losses in the inverter and induction motor of a 1 kW drive Direct measurements of losses have been made with a calorimeter Results show that for the inverter, discontinuous PWM excitation reduces losses by up to 15% compared to sine and symmetrical space vector PWM methods However, at a low modulation index the greater harmonic content with discontinuous PWM increased motor losses by nearly 20% This study demonstrates the importance of careful choice of modulation scheme to achieve high overall drive efficiency

Abstract: The detection issues of UWB signals depend on the type of modulation scheme used during the transmission. The cross-modulation interference (CMI) for pulse position modulated (PPM) UWB signaling is introduced. The effects of CMI on the detection mechanism of selective-Rake (SRake), transmitted-reference (TR) and energy detector (ED) receivers are analyzed. The bit-error-rate (BER) performance of all three receivers in the presence and absence of CMI are studied through computer simulations. The results show that the CMI amount varies according to the modulation index and the performance degradation due to CMI can be extremely severe depending on the modulation index for all three receivers. The validity of the conventional optimal and orthogonal PPM criteria are checked considering the CMI effects. The results demonstrate that the conventional orthogonal PPM for all three receivers and the conventional optimal PPM criterion for N-SRake and TR receivers can be used in the presence of CMI. On the other hand, the BER performance of ED receivers using the conventional optimal PPM criterion result in error floor and this criterion is not valid to be used for ED receivers

Abstract: This paper concerns the effect of symmetric supply voltage harmonics in a space-vector modulated three-phase indirect matrix converter (IMC). The IMC is controlled using indirect space-vector modulation. The effect of symmetric supply harmonics on load voltages and currents is analysed using space-vector presentation. The measurement and simulation results with distorted supply voltages are compared to the results with pure sinusoidal supply voltage. Three compensation methods are tested in simulations and measurements: 1) calculation of modulation index using measured supply voltages (method I), 2) feedback control of output currents (method II), and 3) combination of methods I and II, i.e. output current control with supply voltage measurement (method III). All methods are easy to implement and do not require complicated computing. It is noted that the methods I and III, where modulation index is calculated using measured supply voltages, compensate the effects of harmonics most effectively

Abstract: Cancellation of common-mode intensity noise in microwave-photonic links is found to be limited by the applied intensity modulation. A model is developed and verified experimentally for the dependence of the maximum noise suppression on modulation index, for two-tone and multichannel modulation. For example, for a root-mean-square modulation index of 0.3, suppression is limited to 5 dB.

Abstract: We demonstrate a simple scheme to multiply the repetition rate in an actively mode-locking fiber laser by using a phase modulated optical fiber loop mirror (PMOLM). The PMOLM can convert phase modulation to amplitude modulation at double the modulation frequency. In principle, it is easy to double the repetition rate. However, the PMOLM also induces residual chirp which can disable this method in some cases. Numerical simulation shows that the best results can be obtained when the intracavity dispersion is negative and the modulation frequency is an odd harmonic of half of the cavity fundamental frequency. This agrees with the experimental results, in which an 80-GHz 1.74-ps transform limited pulse was obtained. By using rational harmonic modulation which requires detuning the modulation frequency and adjusting the modulation index, the repetition rate can be increased by three or four times.

Abstract: This paper concern on a new application of selected harmonic elimination pulse width modulation technique (SHEPWM) for multilevel inverters. In this paper, first, the switching angles are calculated using constrained optimization technique. With these switching angles both the fundamental harmonic can be controlled and the selected harmonics can be eliminated. Then, using these calculated switching angles, a set of equation is formed which calculates the switching angles with respect to modulation index. Using this technique three-phase voltage has been obtained from a five-level cascade inverter. This voltage is applied to an induction motor. The dynamic behaviour of the induction motor has been examined for constant v/f operation and the simulation results have been given.

Abstract: The optimal linear modulation approximation of any M-ary continuous-phase modulated (CPM) signal under the minimum mean-square error (MMSE) criterion is presented in this paper. With the introduction of the MMSE signal component, an M-ary CPM signal is exactly represented as the superposition of a finite number of MMSE incremental pulses, resulting in the novel switched linear modulation CPM signal models. Then, the MMSE incremental pulse is further decomposed into a finite number of MMSE pulse-amplitude modulated (PAM) pulses, so that an M-ary CPM signal is alternatively expressed as the superposition of a finite number of MMSE PAM components, similar to the Laurent representation. Advantageously, these MMSE PAM components are mutually independent for any modulation index. The optimal CPM signal approximation using lower order MMSE incremental pulses, or alternatively, using a small number of MMSE PAM pulses, is also made possible, since the approximation error is minimized in the MMSE sense. Finally, examples of the MMSE-optimal CPM signal approximation and its comparison with the Laurent approximation approach are given using raised-cosine frequency-pulse CPM schemes.

Abstract: Gaussian frequency shift keying is the modulation scheme specified for Bluetooth. Signal adversities typical in Bluetooth networks include AWGN, multipath propagation, carrier frequency, and modulation index offsets. In our effort to realise a robust but efficient Bluetooth receiver, we adopt a high-performance matched-filter-based detector, which is near optimal in AWGN, but requires a prohibitively costly filter bank for processing of K bits worth of the received signal. However, through filtering over a single bit period and performing phase propagation of intermediate results over successive single-bit stages, we eliminate redundancy involved in providing the matched filter outputs and reduce its complexity by up to 90% (for K = 9). The constant modulus signal characteristic and the potential for carrier frequency offsets make the constant modulus algorithm (CMA) suitable for channel equalisation, and we demonstrate its effectiveness in this paper. We also introduce a stochastic gradient-based algorithm for carrier frequency offset correction, and show that the relative rotation between successive intermediate filter outputs enables us to detect and correct offsets in modulation index.