Abstract: This paper presents a new space vector modulation strategy suitable for a low cost PWM-VSI inverter employing only four switches, four diodes and a split capacitor bank in the DC-link. The work is motivated by the need of an efficient and flexible modulation method, which is optimized with respect to minimum machine torque ripple. The modulation strategy is named Space Vector Modulation for Four Switch Inverter (SVMFSI) and is realized by planning the switching patterns between four active voltage vectors on the basis of a desired flux trajectory for the stator flux vector in the AC-machine (variable speed induction motor drive). The strategy is implemented in a single 8-bit microcontroller as a double sided modulation strategy. Simulations of the motor torque ripple are performed at a switching frequency of 4 kHz and indicate a torque ripple of 14% at nominal load. Finally, selected results are verified experimentally on a 1.5 kVA prototype B4 inverter. The test results indicate high quality output voltage spectra with no low-order voltage harmonics and a harmonic loss factor (HLF) of 1.12% at unity modulation index. >

Abstract: A quasi-resonant dc link soft switching inverter is presented, capable of PWM operation. It requires only two additional switches, and allows loss limitation in the resonant circuit. The modulation method adopted is able to perform true PWM operation at any modulation index. Simulated and experimental results are reported, confirming the effectiveness of the proposed solution.

Abstract: Standard low- and medium-power induction motor drives are based on the pulse width modulation (PWM) voltage-source inverter (VSI) fed from a diode rectifier. The dual topology, based on the current-source inverter/rectifier structure is used in medium- and high-power applications. This paper analyzes the existing motor drives based on current-source topologies and proposes a control strategy that addresses some of the drawbacks of this approach compared to the voltage-source approach. The proposed strategy features the following: (1) an online operated PWM CSI, using instantaneous output capacitor voltage control based on space-vector modulation; and (2) an additional inverter modulation index control loop, ensuring constant inverter modulation index and minimum DC-link current operation. The resulting additional advantages include the following: (1) fixed and reduced motor voltage distortion; (2) minimized DC-bus inductor losses; (3) minimized switch conduction losses; and (4) elimination of motor circuit resonances. Experimental results based on a DSP implementation are given.

Abstract: In this paper, the authors deal with the effects of inverter characteristics on iron losses in induction motors fed by pulsewidth modulation (PWM) controlled power converters. Laboratory tests based on no-load input power measurements were carried out and in order to avoid the influence of mechanical losses and rotor copper losses, which are difficult to be measured or computed, a special test bench with an unconventional test device was employed. In particular, the influence of the following inverter parameters are considered: modulation index; modulation waveform; and switching frequency. Complete experimental results are presented and discussed.

Abstract: Comparative studies between harmonic elimination and optimal PWM strategies are given for high power three-level inverter feeding an induction motor. An effective PWM map construction method based on the valid region on the frequency modulation index plane is suggested. Thereby, an optimal map including asynchronous space vector PWM, harmonic elimination and optimal PWM method is generated covering all of the low, middle and high modulation index regions. The PWM map was designed for 1 MVA rated general purpose GTO inverter and implemented with a digital signal processor. Experimental results are presented for 10 kVA prototype. >

Abstract: The aim of the present study was to quantitate the Hoffmann (H-) reflex modulation in the soleus muscle of spastic multiple sclerosis patients during walking at different stimulus strengths, and to quantitate the influence of the excitation level of the soleus muscle on the H-reflex. The H-reflex modulation was quantified by the minimum H-reflex in the swing phase and the modulation index introduced by Yang et al. (1). Stimulus strengths were matched between subjects, and only stimuli intensities, which reflect modulation in the H-reflex with true neurophysiological origin, were used. Based on this approach, we found that the reflex modulation is impaired in moderate spastic patients at both a strong and a weak afferent input to the motoneuron pool in consistency with studies on severe spastic patients. This study concludes that the H-reflex modulation in the spastic patients is only related to the excitation level of the muscles, whereas both the excitation level and other factors than the excitation level are known to influence the H-reflex modulation in healthy subjects.

Abstract: It is shown theoretically that the presence of amplitude modulation is necessary for optimum performance of a dispersion supported transmission system. For 10 Gbit/s nonregenerated transmission at lambda =1.5 mu m over more than 300 km standard singlemode fibre, an amplitude modulation index of 0.5 compared to 0.01 is expected to increase the receiver sensitivity by 7-14 dB.

Abstract: A transceiver uses feedback control to monitor a transmitted continuous phase modulation (CPM) waveform, such as a spread spectrum CPM waveform, and adjust the modulation index in response thereto. Codewords are selected from a table according to a data signal and applied to a pulse shaping network. The pulse shaping network outputs a CPM waveform to a prefilter. The prefilter is connected to an FM modulator, such as a voltage controlled oscillator. In one embodiment, a correlator in the transceiver monitors the transmitted waveform during times when the transceiver is not receiving signals, and provides a correlation signal to a feedback control circuit. The feedback control circuit dynamically adjusts the gain of the prefilter, and may comprise, e.g., a second order tracking loop filter. The feedback control signal thereby tracks the amplitude of the transmitted waveform and adjusts the output gain of the prefilter so as to maintain a constant signal envelope. A tau-dither algorithm may be employed as part of the tracking circuit. In an alternative embodiment, a gradient search is used to adjust the output amplitude of the transmitted signal, wherein the step size of the gradient search is based on the slope of the signal amplitude and varied dynamically over time. In another embodiment, a two bandwidth differencing circuit is used to adjust the output amplitude of the transmitted signal.

Abstract: A method and/or apparatus for altering command voltages when a modulation index is greater than unity in order to maintain the linear relationship between the fundamental component of phase voltage and the command voltage in PWM inverter or converter usage. The method and/or apparatus calculates and provides an in phase waveform to be added to the command voltage prior to comparison of the command voltage to a carrier signal, the sum of the waveform and command voltage producing a modified command voltage which maintains said linear relationship.

Abstract: With this method for the low-noise operation of a machine driven by a pulse inverter, the amplitudes and frequencies of the harmonics of the inverter output voltages let themselves be computed. Through targeted setting of the modulation parameters, the frequency spectrum or the noise spectrum can be fanned out and harmonics, which would excite stator resonances, can be eliminated. Due to the independence of the modulation parameters of the modulation index (a0) and the fundamental oscillation frequency (f1), the fanning-out and the elimination has no influence on the fundamental oscillation (uGS) or the operating point of the machine. The control of the inverter takes place through sinusoidal pulse width modulation (PWM) and sinusoidal modulation (PFM) of the triangular carrier signal (uH). By this method, the main groups of the harmonics with two ordinate numbers (n, v) are fanned out into subgroups with three ordinate numbers (n, m, v). Apart from a more uniform distribution, also a reduction in the amplitudes of the harmonics (Unmv) arises through this fanning-out. The noise arising in that case on the one hand displays a reduced level and, on the other hand, the sound pattern no longer has any conspicuous individual frequencies and is perceived as noise.

Abstract: The performance and dynamic characteristics of a solid-state line conditioning system which simultaneously eliminates line current harmonics and compensates load power factor is presented and analysed. The line conditioning system is implemented with a pulsewidth modulated voltage-source inverter. Power factor compensation is achieved by controlling the magnitude and the phase angle (delta) of the transistorised PWM inverter output voltage. Fast response times are obtained by adjusting the amplitude of the PWM inverter output voltage through a modulation index control. The principal advantage of this scheme is that it can maintain a near unity mains overall power factor without sensing and computing the associated reactive power component. It can also substantially reduce the harmonic content of the line current when the load is nonlinear. A time domain model is derived and used to accurately predict dynamic behaviour, the stability region and to adjust system controllers. The transfer function of the line conditioning system for open-loop and closed-loop operation is derived. Experimental results confirm the operation characteristics obtained by computer simulation and mathematical analyses.

Abstract: This paper proposes a new control method of static VAr compensator (SVC) with a three-level inverter to control reactive power with fast dynamics while maintaining DC side capacitor voltage constant. Firstly, using the circuit DQ-transformation, a general and simple model of SVC with a three-level inverter is obtained, and DC and AC analyses are carried out to characterize the open-loop system. Based on the transfer function matrix of the system, modulation index control for reactive power compensation and phase angle control for DC side voltage regulation are designed. By inserting feedforward path to the voltage regulation loop the modulation index is successfully decoupled from the capacitor voltage whereby fast dynamics are achieved. The experimental results confirm the theoretical analyses and control method. >

Abstract: We present a theoretical analysis of the performance of coherent optical FSK systems when the driving laser signal is AMI or Manchester (biphase) line-coded to counteract the nonideal FM characteristic of the transmit laser diode, and the received signal is heterodyned and detected by a delay-and-multiply demodulator. The analysis takes into account IF filtering by assuming linear filtering of the noisy signal phase, accounting, for small linewidths, for laser phase noise in a straightforward and accurate manner. A simple equivalent baseband model of the system is derived for performance evaluation, applicable to both cases of large demodulator delay and when the delay tends to zero (ideal discriminator). Noise statistics include the clicks due to both signal and phase noise. The problem of performance evaluation is reduced to a classical intersymbol interference problem which is solved by mead of the method of Gauss quadrature rules. The analysis accurately predicts the effectiveness of AMI and Manchester line coding, depending on several system parameters such as linewidth, modulation index, IF bandwidth and laser FM response, and can be easily extended to other line coding techniques. >

Abstract: This paper describes a novel technique that can be used to measure the frequency response of an optical phase modulator. An interesting feature of this technique is that it does not require the use of an interferometer for phase-to-amplitude conversion, thus alleviating stability and alignment problems. Instead, the electro-optically induced birefringence of the modulator and a simple polarizer are used to transform phase modulation into intensity modulation. The latter is detected with a high-speed photodiode and, for a sinusoidal modulating signal, the resulting output power spectrum is shown to be related to the actual phase modulation index by simple mathematical expressions involving Bessel functions. Using only a spectrum analyzer, the magnitude and the variations of the modulation index are measured over a broad frequency range. >

Abstract: The development of an implanted micro-emitter having a considerable implantation depth needs a high-efficiency magnetic transcutaneous link. This paper describes a new system for the biotelemetry of internal signals. The system associates the highest performance class E power amplifier with the impedance modulation concept. The resistive load of the transmitter is influenced by the variation of the internal equivalent resistance, modulating this latter between two rails permits to modulate the amplitude of the external transmitter current and then transmitting internal digital data. Furthermore, the dependence of the modulation index on coupling factor allows to find the external coil correct position using a position feedback loop.

Abstract: Zero-intermediate frequency (IF) zero-crossing demodulators (ZIFZCDs) have been developed for many applications to digital phase and/or frequency modulation, e.g., minimum shift keying (MSK), generalized MSK (GMSK), /spl pi//4-differentially encoded quadrature phase shift keying (/spl pi//4-DQPSK), and multi-level continuous phase frequency shift keying (CPFSK). The ZIFZCDs have exhibited better than and nearly the same performance as the existing demodulators for FM modulation index h/spl ges/1.5 and 0.5/spl les/h<1.5, respectively. The implementation complexity of the ZIFZCDs is much simpler than existing demodulators, e.g., limiter discriminator integrate and dump (LDI). Perfect symbol synchronization was assumed in the previous analyses of the ZIFZCDs. A new efficient symbol synchronization scheme is proposed for the practical application of the ZIFZCDs. The bit error rate performance of a four-level CPFSK with the ZIFZCDs using the proposed symbol synchronization shows a 2 dB and a 1 dB (average 1.5 dB) better than that of an existing scheme for the phase bit and magnitude bit, respectively. In addition, the ZIFZCDs with the proposed synchronization algorithm reduces the implementation complexity significantly compared to the existing synchronization schemes. Therefore, the battery life can be increased and the size of a portable receiver (a pager or cellular phone) can be smaller.

Abstract: Several modern systems for reverberation enhancement use time-varying electronic filters to increase their gain before instability (GBI). A computer simulation study is presented of systems with linear periodically time-varying (LPTV) filters based on an iterative frequency-domain method. Results are given from simulations and measurements of a single feedback loop with phase and delay modulators and feedback via an electronic reverberation unit. Comparisons of measured and predicted values of GBI with a sinusoidal phase modulator showed deviations typically around 0.1 dB and at most 0.3 dB for modulation frequencies between 0.5 and 4 Hz and modulation indexes of up to 4.2 radians. Phase modulators displayed GBI improvements increasing almost monotonically with a modulation index up to 4.2 radians. Delay modulators gave slight improvements when used broad band, but when high-pass filtered at 600 Hz substantial improvements resulted with variations as low as ±0.5 ms. The detrimental effects of modulation in the form of audible amplitude and frequency fluctuations were studied as well.

Abstract: The simplest and most economical method for transforming many channels of high quality video and audio analog signals into an optical signal makes use of subcarrier multiplexing. In this multiplexing scheme, a broadband analog signal consisting of the sum of many modulated subcarriers (one for each channel), is applied to amplitude modulate the intensity of a laser for transmission by optical fiber. Laser intensity modulation is also attractive for interconnecting broadband RF signals using optical fiber as, for example, between a cellular base station and its remote antenna sites, especially for implementing microcells. A fundamental, limiting transmission impairment is the nonlinear distortion of the clipped laser intensity resulting from occasional signal excursions below the laser threshold. The purpose of this paper is to apply noise theory along with numerical analysis, involving fast Fourier transforms, to determine some basic characteristics of the nonlinear distortion associated with a fully loaded system. In particular, the exact distortion spectrum and the carrier-to-nonlinear distortion ratio are determined as a function of the dynamic range and bandwidth of the multiplexed signal, and the total RMS modulation index /spl mu/. 2/spl mu//sup 2/ equals the product of the number of channels and the square of the optical modulation index per channel. The exact carrier-to-nonlinear distortion ratio per channel when all or specific orders of distortion are present is also treated. The results are presented in graphical form and they agree reasonably well with earlier theoretical and experimental works. All of the results apply to both a directly modulated laser or an externally modulated laser. >

Abstract: This invention provides a circuit for synthesizing musical sounds. In one embodiment, the circuit includes a first order FIR highpass filter that is placed between a modulation phase increment oscillator and a carrier phase increment oscillator. The invention may also include waveshaping circuits, adders, multipliers, time division multiplexing, and other types of filters. Another embodiment of the invention provides a music synthesis method where a modulation phase increment is multiplied by a modulation index to produce a modulation signal. That modulation signal is then filtered and added to a carrier phase increment. Finally, that sum is multiplied by an amplitude envelope to produce a signal representing a musical sound. The method may include using a first order FIR highpass filter, waveshaping of both sinusoidal and non-sinusoidal waveforms, additional multiplying and time division multiplexing. The invention also includes self-modulation and cascading.

Abstract: Digital pulse position modulation (PPM) has been shown to be attractive for implementation over the optical fibre channel when the laser transmitters are average power limited and the channel bandwidth is abundant. The synchronization requirements for optical fibre PPM however have not yet been addressed. We present an original mathematical formulation for the problem of spectral prediction and synchronization in PPM based on the cyclostationary properties of the format. Further we predict the conditions required to achieve and optimize both slot and frame synchronization. The major system parameters including the modulation index, data probability distribution and pulse shape are catered for and used in the analysis. A novel technique, capable of coping with the different PPM word sizes, is presented and used to achieve frame phase extraction directly from the PPM stream. Appropriate mathematical models are developed and used to predict the spectral properties at the output of the frame phase synchronizer. Original practical results measured on a PPM system are presented and shown to agree with the theoretical models and predictions to within 1 dB. >

Abstract: An attractive application of lightwave technology is cable television (CATV) transmission. In an important lightwave application known as subcarrier multiplexing, a broadband analog signal, consisting of the sum of amplitude modulated subcarriers, is used to intensity modulate a laser to produce an optical signal for transmission by optical fiber. It has been determined that the large negative excursions of the broadband signal lead to nonlinear distortion of the optical signal which also distorts the information bearing modulation on the subcarriers. The purpose of this paper is to present a general result concerning the average power of a clipped Gaussian process and apply this result to analyze the nonlinear distortion resulting from intensity modulation of a laser. In particular, a general formula for computing the average power of a stationary Gaussian process that is clipped at two arbitrary levels is applied to develop an approximation for the carrier-to-nonlinear distortion ratio (C/NLD) per channel as a function of the dynamic range of the clipping levels of the broadband analog signal, and the total RMS modulation index /spl mu/. 2/spl mu//sup 2/ equals the product of the number of channels being multiplexed and the square of the optical modulation index per channel. The approximation stems from an exact result and is especially useful because the conservative version of the approximation is independent of the bandwidth or spectral location of the broadband analog signal. Results are presented in graphical form and they are in reasonable agreement with earlier theoretical and experimental works. >

Abstract: The characteristics of a buck type three phase PWM rectifier are analyzed using the circuit DQ transform method. An exact DQ equivalent circuit model is induced and a full set of equations are derived in explicit form. Using the signal flow graph to describe the internal relations of power converter operation, the unique behavior of the power converter is analyzed from several practical viewpoints. Various power converter characteristics such as gain, real and reactive power, power factor and unity power factor condition including the effects of component values and load variations are analyzed as a function of modulation index and PWM phase angle variation. >

Abstract: The method involves acquiring patient attenuation data from a slice which indicates patient attenuation of an x-ray beam at two substantially orthogonal gantry angles. A modulation index is then calculated using information derived from the acquired patient attenuation data which indicates the reduction in x-ray dose applicable to the patient. The method also entails calculating a modulation profile using the modulation index. The profile includes a set of values which indicate the x-ray dose applied to the patient at successive gantry angles during the acquisition of attenuation data from the single slice. Each value in the modulation profile is then compared with a value indicative of minimum x-ray dose.

Abstract: Pulsewidth modulation, similar to voltage-space vector control in switches utilizing a field programmable gate array, is compared with PSpice simulation in a three switches converter is presented. The PSpice simulation is used in time domain simulation of the rectifier and inverter circuit. The PSpice PWM simulation modelled is compared with the experiment which is implemented in a field programmable gate array based on a carrier frequency of 19.2 kHz. The PWM is applied to the converter operated as a step-down converter where the output voltage can be controlled by the modulation index in the range of 0 to 1.5 V/spl circ//sub ph/. Simulation and experimental results are provided to demonstrate the effectiveness of the proposed model.

Abstract: Degradation in carrier-to-interference ratio (CIR) due to optical beat interference (OBI) in subcarrier multiplexed wavelength division multiple Access (SCM/WDMA) networks using direct photodetection is evaluated. The subcarriers are assumed to directly intensity modulate separate lasers. A large signal model for the modulated laser light is used. The discrepancy in CIR between this model and the small signal model commonly used in the literature is important at high modulation indices (4.5 dB at about unity modulation index). This justifies the introduction of the large signal model for analyzing OBI. It is found from analytical results that OBI is lower for higher intensity modulation indices. >

Abstract: Two novel trellis-coding techniques, called nonlinear multi-h signaling and nonlinear asymmetrical multi-h signaling, which achieve higher constraint length than ordinary multi-h signals, are introduced with CPFSK signals. In contrast to ordinary multi-h signaling where the modulation index is changed at the end of every symbol interval, nonlinear multi-h signals are constructed by changing the modulation index based on the previous symbol, and the current symbol interval. A class of nonlinear asymmetrical multi-h signals, which change the modulation index based on the current symbol too, is then constructed by extending nonlinear multi-h signals and combining them with asymmetrical multi-h signals. Binary full-response nonlinear multi-h and nonlinear asymmetrical multi-h CPFSK signals are constructed and analyzed. Minimum Euclidean distances and spectral properties of these signals are calculated at different phase states and various selected modulation index patterns. Numerical results indicate that nonlinear multi-h and nonlinear asymmetrical multi-h signals achieve significantly higher distance than other existing multi-h formats reported in the literature. >

Abstract: The harmonic content in the output of the rectifier can be reduced by employing pulse-width modulation. Sinusoidal pulse-width modulation (SPWM) is commonly used to reduce the harmonic content in the output and to vary the average voltage. However, the SPWM technique gives a large second harmonic component in the output and a low fundamental output voltage. The paper describes a novel PWM scheme called inverted-sine PWM (ISPWM) which uses a sinusoidal reference signal and an inverted-sine carrier. The ISPWM has a better spectral quality and a higher average voltage compared to the SPWM. The paper computes the harmonic content of the ISPWM output for different values of modulation index and compares them with the results obtained for a conventional SPWM. The complete control circuit for generating the ISPWM control signal for a PWM rectifier is developed. Experimental waveforms of voltages and currents and their frequency spectra are presented. >

Abstract: In this paper, based on multilevel coding and multistage decoding techniques, multilevel schemes for M-ary continuous phase frequency shift keying (CPFSK) with modulation index 1/2 are introduced. At each level of the multilevel system classical or punctured convolutional codes and at the last level, where the phase continuity is satisfied, fast frequency shift keying (FFSK) codes are used. The new systems with M=4, 8 and 16 are compared with corresponding previously designed schemes and uncoded cases. It is shown that the proposed systems have coding gain and decoding complexity advantages.