Abstract: In this paper, various types of discontinuous space vector pulse-width modulation techniques for a three-leg voltage source inverter supplying balanced two-phase loads are proposed. The main objectives of the paper are to analyze switching loss characteristics associated with semiconductor devices and to reduce output current ripple by dealing with various types of zero space vector time in each switching sequence. Capabilities of reductions in switching losses and current ripple for both balanced and unbalanced output phase voltages at high modulation index and load power factor angle of 30° lagging are focused. The validity of the proposed techniques is verified by simulation and experimental results in terms of voltage spectrum, current waveforms, reductions in switching losses, and output current ripple at high modulation index when compared to a continuous space vector pulse-width modulation technique.

Abstract: Common-mode voltage (CMV) is one of the most important issues for the power electronics inverters. An interesting space vector modulation of the three-leg current-source inverter has been reported for the CMV reduction recently. However, it has the disadvantages of the bipolar current pulses and modulation index range limitation. In order to solve these problems, a four-leg current-source inverter with a new space vector modulation is proposed in this paper. With the proposed method, the system CMV can be significantly reduced without bipolar current pulses and modulation index range limitation. Finally, the experimental tests are carried out on a four-leg current-source inverter, and the experimental results verify the effectiveness of the proposed method.

Abstract: A novel hybrid time-frequency domain equalization scheme is proposed and experimentally demonstrated to mitigate the white light emitting diode (LED) nonlinearity in visible light communication (VLC) systems based on orthogonal frequency division multiplexing (OFDM). We handle the linear and nonlinear distortion separately in a nonlinear OFDM system. The linear part is equalized in frequency domain and the nonlinear part is compensated by an adaptive nonlinear time domain equalizer (N-TDE). The experimental results show that with only a small number of parameters the nonlinear equalizer can efficiently mitigate the LED nonlinearity. With the N-TDE the modulation index (MI) and BER performance can be significantly enhanced.

Abstract: This paper investigates the feasibility of extending the application of impact modulation from crack detection to the assessment of bolted joints. To support this effort, both theoretical and experimental evidence of the effectiveness of impact modulation to detect changes in bolt torque are presented. First, a nonlinear, single degree of freedom model is used to verify the correlation between changes in the nonlinear coefficient that represents the nonlinear contact forces present at a bolted interface and the amplitude of the sidebands generated in impact modulation testing. Next, a finite element representation of a two-beam, one-bolt assembly is presented to study effects not captured by the single degree of freedom model. Results of impact modulation simulations using the finite element model revealed that the amplitude of the sidebands in the response spectra depends not only on the nonlinearity present at the bolted interface, but also on other test parameters including impact amplitude and location, probing force amplitude and frequency, and sensor location. These findings are corroborated with experiments in which impact modulation was performed on a two-beam, one-bolt assembly similar to the assembly used in the simulations. Finally, impact modulation testing was conducted on the two-beam, one-bolt assembly using different bolt torque levels to demonstrate the method’s sensitivity to changes in bolt torque. A modulation index based on the amplitudes of the sidebands in the response spectrum was developed to quantify the results of the impact modulation testing. Results showed that the magnitude of the modulation index increased as the bolt torque decreased. The rate of change in the modulation index was largest when the bolt torque was $$<$$ 20 % of its maximum value.

Abstract: An open-winding permanent-magnet synchronous generator (PMSG) system with the integration of fully controlled and uncontrolled converter is investigated in this paper, in which half the amount of controllable power switches are needed compared with the conventional open winding system fed by two voltage source converters. The voltage space vector of open winding PMSG is modulated by controlled converter, which will be integrated with the voltage vector by uncontrolled converter to implement the operation of open winding PMSG. In order to analyze and compare the operation capability on the different dc voltage ratios, the available modulation range of the open winding PMSG is analyzed in detail. Moreover, unity power factor control is proposed as the optimized control method to achieve the maximum modulation index. Finally, a 1-kW experimental setup is built to validate the theoretical investigation on the open winding PMSG system.

Abstract: The aim of this study is to present a modulation index considering both mechanical and dose calculation uncertainties for volumetric modulated arc therapy (VMAT). As a modulation index considering only mechanical uncertainty of VMAT, MIt has been previously suggested. In this study, we developed a weighting factor which represents dose calculation uncertainty based on the aperture shapes of fluence maps at every control point of VMAT plans. In order to calculate the weighting factor, the thinning algorithm of image processing techniques was applied to measure field aperture irregularity. By combining this weighting factor with the previously suggested modulation index, MIt, comprehensive modulation index (MIc) was designed. To evaluate the performance of MIc, gamma passing rates, differences in mechanical parameters between plans and log files and differences in dose-volume parameters between plans and the plans reconstructed from log files were acquired with a total of 52 VMAT plans. Spearman's correlation coefficients (rs) between the values of MIc and measures of VMAT delivery accuracy were calculated. The rs values of MIc (f = 0.5) to global gamma passing rates with 2%/2 mm, 1%/2 mm and 2%/1 mm were −0.728,−0.847 and −0.617, respectively (p < 0.001). Those to local gamma passing rates were −0.765,−0.767 and −0.748, respectively (p < 0.001). The rs values of MIc (f = 0.5) to multi-leaf collimator and gantry angle errors were 0.800 and −0.712, respectively (p < 0.001). The MIc (f = 0.5) showed a total of 20 rs values (p < 0.05) to the differences in dose-volumetric parameters from a total of 35 tested cases. The MIc (f = 0.5) demonstrated considerable power to predict VMAT delivery accuracy showing strong correlations to various measures of VMAT delivery accuracy.

Abstract: In the paper, an experimental comparison of pulse amplitude, carrierless amplitude-phase, and discrete multitone modulations is carried in a visible light communications link employing white phosphorescent light-emitting diode (LED) as a transmitter. By changing the modulation index, the influence of LED nonlinearity on the performance is studied. The results indicate similar performance of pulse-amplitude modulation (PAM) and carrier-less amplitude-phase (CAP) (with a slight advantage of the former) and substantially worse performance of DMT.

Abstract: This Letter demonstrates a new calibration-free 2f wavelength modulation spectroscopy (WMS) technique to measure gas concentration and pressure without the need for laser precharacterization. A 1650-nm laser diode is used for methane concentration and pressure measurements for pressures up to 4 bar and for a modulation index (m) of 2.2. All laser parameters such as the intensity, linear and nonlinear intensity modulation (IM), frequency modulation (FM) characteristics, the phase difference ψ1 between the FM and the linear IM, and the phase difference ψ2 between the FM and the nonlinear IM are accurately estimated in situ and in real time. This technique accounts for variations in these parameters that arise due to scanning of the laser's center wavelength, laser temperature variations, and aging of the laser. The laser is modulated at its phase quadrature frequency at which the linear IM and the FM are orthogonal to each other (ψ1=90°). This ensures that the two linear IM-dependent distorting Fourier components are orthogonal to the detection axis, and the undistorted 2f signal is recovered. This simplifies the simulation and gas parameter-extraction process. Finally, 2f RAM nulling is implemented to remove the significant absorption-independent 2f residual amplitude-modulation (RAM) signal that is seen to cause significant distortion of the 2f signal and detector saturation.

Abstract: Optical fringes constitute one of the major obstacles in the gas detection based on wavelength modulation spectroscopy (WMS). In order to suppress optical fringes, a convenient method of modulation index optimization was presented, using the signal-fringe ratio as a criterion. In addition to suppressing optical fringes, the optimized modulation index enables the detection of gas absorption. This method was demonstrated in a WMS based oxygen sensor. By comparing the sensor performances with and without the use of the optimized modulation index, we showed that the optical fringes are reduced by using the optimized modulation index; furthermore, the system stability and detection limit are improved. More specifically, the long-term fluctuation of the sensor measurement is dramatically reduced by a factor of 8, and a detection limit of as low as 120 ppm (with effective optical path length of 32 cm and integral time of 2.6 s), characterized by the Allan variance, was derived. This method can be applied in other existing WMS systems without the need for additional devices or complex algorithms and has the potential to be used in both laboratory and industrial settings.

Abstract: In this paper, power losses of 3-level NPC inverter (3LNPCI) and 3-level T-type inverter (3LTI) are classified and calculated according to the switching states. The conduction loss depends on modulation index (MI) and power factor (PF), whereas the switching loss depends on switching frequency, so the power loss analyses have been done at the different operating points of MI, PF, and switching frequency. And power losses of 3LNPCI and 3LTI with NPC and T-type inverter dedicated modules are calculated based on the theoretical formula and PSiM thermal module by using the real parameter values of switching devices. For the comparison of power losses of NPC and T-type inverters, all parameters have been referred from the data sheets of the different manufacturing companies.

Abstract: A low device switching frequency operation is essential in medium-voltage (MV) high-power drives to increase semiconductor device utilization as well as to achieve higher overall system efficiency. However, there exists a tradeoff between device switching frequency and harmonic distortion of machine currents. Synchronous optimal pulsewidth modulation (SOP) is an evolving technique for controlling multilevel inverters of MV ac drives at low device switching frequency without compromising the quality of machine currents. The state-of-the-art generalized SOP algorithm for five or higher level inverters leads to unequal device switching frequency, and also, transients in machine currents are possible due to the change in the number of switching instants at higher modulation index values. The goal of our study is to propose a new SOP technique that ensures equal device switching frequency and further reduces device switching frequency compared to the generalized SOP method. Also, it is expected that machine current transients at higher modulation index values will be reduced. The proposed SOP technique has been verified experimentally on a cascade nine-level inverter-fed 1.5-kW induction motor drive.

Abstract: Unbalanced voltage across the dc-link capacitors of classical diode clamped multilevel inverters (DCMI) generates lower order harmonics in the output voltage and increases the voltage stress on the switching devices which may result in permanent damage to the switching devices. This study proposes a space vector modulation (SVM) based voltage balancing strategy for a new 5-level multiple-pole multilevel diode-clamped inverter (M2DCI) topology to eliminate the voltage drift phenomena. The 5-level M2DCI topology which is derived from 3-level DCMI topology uses lesser number of clamping diodes compared with the conventional 5-level DCMI topology. An effective switching function model of a new multilevel inverter is derived and is used for dc-link capacitor voltage control. The method utilises the redundant vector property to balance the dc-link capacitor voltages without using any auxiliary hardware. The dependence of the capacitor voltage variation on the load power factor and modulation index has been extensively studied for 5-level M2DCI. The range of operation for the new topology with the proposed control strategy is also presented based on the simulation studies in the Matlab/Simulink® and PSIM environment and verified using experimental results.

Abstract: This paper investigates the influence of switching frequency and modulation index combined with welding on the iron losses in thin silicon–iron and nickel–iron lamination sheets of a small slotless permanent-magnet synchronous machine (PMSM). First, measurements are conducted on welded and nonwelded stator ring cores for switching frequencies between 1 and 20 kHz and modulation indexes of 0.4, 0.7, and 0.9, keeping constant fundamental flux density peak values. This is possible by changing the dc-link voltage of the inverter. The obtained measurement data are afterward used in finite-element method simulations to investigate the inverter influence on the performance of the PMSM.

Abstract: A novel filterless optical millimeter-wave signal generation scheme is proposed. In the scheme, the undesired sidebands are suppressed using two parallel dual-parallel Mach–Zehnder modulators (MZMs) with different modulation indexes and polarization multiplexing, and frequency multiplication factor as high as 16 can be achieved. Simulation results show that 80, 120, and 160 GHz signals are generated through a 10 GHz RF signal using the proposed method, and the performance of the generated signals is good when commercially available MZMs with extinction ratio of 20–30 dB are used. The scheme has large tunability of modulation index for frequency octupling and 12-tupling signals generation and high stability against the RF driving voltage deviation for frequency 16-tupling generation.

Abstract: A multilevel inverter topology for a four-pole induction-motor drive is presented in this paper, which is constructed using the induction-motor stator winding arrangement. A single dc source with a less magnitude when compared with conventional five-level inverter topologies is used in this topology. Therefore, power balancing issues (which are major challenges in conventional multilevel inverters) are minimized. As this configuration uses a single dc source, it provides a path for zero-sequence currents because of the zero-sequence voltages present in the output, which will flow through the motor phase winding and power electronic switches. To minimize these zero-sequence currents, sine-triangle pulsewidth modulation (SPWM) is used, which will shift the lower order harmonics near to switching frequency in the linear modulation region. However, in the case of overmodulation, harmonic voltages will be introduced close to the fundamental frequency. In this regard, a modified SPWM technique is proposed in this paper to operate the drive in the overmodulation region up to the modulation index of 2/surd{3}. The proposed quad two-level inverter topology is experimentally verified with a laboratory prototype on a four-pole 5-hp induction motor. Experimental results show the effectiveness of the proposed topology in the complete linear modulation region and the overmodulation region.

Abstract: Constant Envelope OFDM provides a solution to the issue of high peak-to-average power ratio in OFDM by using angle modulation to transform the OFDM signal to a constant envelope signal. The modulation index of Constant Envelope OFDM controls this transformation. In this paper, we develop novel receiver structures for Constant Envelope OFDM based on the Taylor series expansion, alleviating the need for angle demodulation at the receiver. This results in immunity from phase cycle slips due to phase wrapping and the threshold effect which would otherwise cause performance degradation. These receivers allow for a simpler implementation without the need to compute the arctangent at the receiver. We show that these novel receivers perform well when compared to the conventional arctangent based receiver for small and moderate modulation indices (2 πh ≤ 0.7) for the cases of additive white Gaussian noise and multipath fading. For frequency selective fading, we show that the application of a frequency domain equalizer results in good performance when these novel receivers are employed. Finally, we study the performance of these new receivers when error correction coding is employed and show that they not only provide excellent performance but also significantly outperform the conventional arctangent based receiver for coded Constant Envelope OFDM performance.

Abstract: Power converters using deterministic switching frequency schemes have switching noise concentrated at harmonic frequencies, resulting in enhanced electromagnetic emission. To suppress the harmonic spikes in three-phase multilevel voltage source converters, a digital control scheme based on dithered sigma–delta modulation (SDM) is proposed in this paper. Introducing a dithered sequence in an SDM varies the switching frequency randomly, resulting in the suppression of the spurious harmonic spikes in the output spectrum even with a regular control input. Although the switching frequency varies randomly, the minimum pulsewidth of the proposed scheme is the sampling time period, avoiding the minimum pulsewidth problem. Instead of a conventional scalar quantizer, the quantizer in the proposed dithered sigma–delta converter uses the principle of space vector quantization. The proposed scheme is experimentally verified on a constant $v/f$ open-loop induction motor drive for a three-level inverter realized by cascading two two-level inverters. The performance of the proposed scheme is compared with different pulsewidth modulation schemes in the entire modulation index, including the overmodulation region.

Abstract: In this paper, the performance of a novel two-loop control strategy for a three-phase self-excited induction generator (SEIG), used in wind/microhydro/biogas-based isolated generation schemes, is presented. The implementation of the grid-interactive synchronization of the generalized impedance controller (GIC), an impedance-controlled operation of pulse width modulation (PWM) voltage-source converter, with SEIG is described. The SEIG frequency is tracked using digital phase-locked loop implemented on a dSpace DSP platform. The open-loop SEIG-GIC system is experimentally analyzed for the sensitivity of the SEIG voltage and frequency to GIC modulation index $m$ and phase angle $\delta$ . Based on this, a simple and practical control strategy with proportional–integral (PI)-based voltage and frequency feedback loops is evolved for the regulation of the SEIG voltage and frequency. A novel design procedure for both the PI controllers for stable closed-loop operation is presented. The performance of the proposed closed-loop system is experimentally tested under speed and load perturbations.

Abstract: For medium-voltage high-power drives fed by current-source converters (CSCs), a transformerless configuration has benefits in both cost and volume. Removing the isolation transformer necessitates a common-mode choke to undertake the major portion of the drive's common-mode voltage (CMV) stress, which would otherwise cause premature failure of the motor insulation system. On the other hand, as device switching frequency in high-power CSCs is normally limited to a few hundred hertz, improving harmonic performance via modulation has always been a challenge. Selective harmonic elimination (SHE) is a preferred modulation scheme in such a system owing to its ability to eliminate several unwanted low-order harmonic currents. Alternatively, conventional space vector modulation (SVM) provides continuous modulation index adjustment capability, but its output current contains low-order harmonics with high magnitudes that may arouse harmful resonances in the system. Aiming at reducing CMV and improving harmonic performance at the same time, this paper proposes a new SVM-based modulation strategy for high-power CSCs using synthesized reference trajectory on the hexagon in the αβ plane. Along with the proposed strategy, two methods of reference trajectory optimization (RTO) are investigated. By introducing a coefficient to the duty-cycle function for RTO, the first method can remove an extra low-order harmonic component, or minimize the weighted total harmonic distortion. The second method, with a different approach of RTO, eliminates the unwanted low-order harmonics by combining the proposed SVM with the SHE. The proposed concepts are verified by both simulation and experimental results.

Abstract: This paper has introduced a four-level π-type converter for low-voltage applications which has a simple structure with six switches per phase leg. The line output voltage has seven levels and the output harmonics is much lower than the conventional two-level converter. The switching states and their associated output voltage levels have been analyzed. A simple carrier-based modulation method with zero-sequence signal injection has been devised to modulate the converter and regulate dc-link neutral points' voltages. The two neutral points' voltages can be well controlled with a back to back configuration even under high modulation index and high power factor. Simulation and experimental results have validated the topology, modulation and control strategy for the four-level π-type converter.

Abstract: This paper investigates time-domain analysis of sampling effect in digital pulsewidth modulation (DPWM) of dc–dc converters. The relation between the sampling delay, duty ratio, and multisampling factor (sampling to carrier frequency ratio) has been characterized. The sampling delay of the digital controller used for DPWM of the dc–dc converter has close relation with the actual pulsewidth-modulation output. An increase in the multisampling factor can reduce the delay effect of the DPWM. The output voltage varies as a stepped function of the duty ratio instead of the linear function as observed in ideal modulation. It is shown in this paper that this delay is a periodic function of the duty ratio. The effect of variations in the sampling frequency, switching frequency, and modulation index has been analyzed. The proposed sampling effect has been verified analytically for the buck, boost, and buck–boost dc–dc converters. The experimental results for the buck and boost converters have been obtained with the control circuit realized through a field-programmable gate array-based digital controller.

Abstract: This paper reports the extraction of concentration and pressure of methane using a 1650-nm laser diode operated at its phase quadrature frequency (f q ) and using the calibration-free residual amplitude modulation (RAM) method. Although the RAM method is the simplest calibration-free technique, it has low signal levels compared with the phasor decomposition (PD) method for small values of the phase difference ψ between the laser intensity modulation and frequency modulation (FM). For the laser diode used in this paper, ψ turned out to be 90° at a very modest modulation frequency of 125.5 kHz, which is an order of magnitude lower than values reported elsewhere. The RAM signal and FM signal are at phase quadrature at this frequency and each can be fully and simultaneously recovered along a detection axis of a lock-in amplifier free from distortion by the other. The absolute absorption profile is accurately recovered with the signal-to-noise ratio (SNR) maximized for this laser. The gas parameters are extracted by fitting a Voigt line shape to the experimental data. These results show that when operating at f q , the PD method offers no advantage over the RAM method and is therefore redundant. In addition, the background RAM is eliminated by an automatic fiber-optic RAM nulling technique. Finally, the RAM method is also implemented at high values of modulation index to increase the SNR ratio. The time resolution of measurements is currently 10 s. The prospect of using the RAM method with a 2004-nm vertical cavity surface emitting laser is also explored.

Abstract: The standard solution for the traction system in battery powered electric vehicles (EVs) is a two-level (2L) inverter feeding a three-phase motor. A simple and effective way to achieve a three-level (3L) inverter in battery-supplied electric vehicles consists of using two standard three-phase 2L inverters with the open-end winding connection of standard three-phase ac motors. The 3L inverter solution can be usefully adopted in EVs since it combines several benefits such as current ripple reduction, increment of phase motor voltage with limited voltage ratings of the two battery banks, improvement in system reliability, etc. The reduction in current ripple amplitude is particularly relevant since it is a source of electromagnetic interference and audio noise from the inverter-motor power connection cables and from the motor itself. By increasing the inverter switching frequency the ripple amplitude is reduced, but the drive efficiency decreases due to the proportionally increased switching losses. In this paper the peak-to-peak ripple amplitude of the dual-2L inverter is evaluated and compared with the corresponding ripple of the single-2L inverter, considering the same voltage and power motor ratings. The ripple analysis is carried out as a function of the modulation index to cover the whole modulation range of the inverter, and the theoretical results are verified with experimental tests carried out by an inverter-motor drive prototype.

Abstract: The paper addresses optimal voltage and current quality (minimal Total Harmonic Distortion — THD) for a singlephase multilevel inverter staircase modulation. The previous research mostly addressed optimal THD problem in frequency domain accounting for a limited harmonics count. The novelty of this research is that voltage and current minimal THD problems are formulated in time domain as a constrained optimization ones in order to find theoretically optimal switching angles accounting for all switching harmonics. The optimal switching angles and respective minimal THD values are obtained for different inverter level counts and the whole fundamental voltage (modulation index) range. Suggested are smooth ripple-free approximations for accurate voltage and current THD for arbitrary level counts and modulation indices. While these simple hyperbolic formulas accurately approximate the average trend, local maxima and minima of voltage and current THD may be considered on separate. In fact, the obtained current THD is frequency weighted THD that assumes inductance dominated RL-load. For grid-connected applications, normalized current fundamental harmonic is smaller than voltage modulation index and current THD is essentially larger than frequency weighted voltage one.

Abstract: In this paper, Selective Harmonic Mitigation (SHM) and Selective Harmonic Elimination (SHE) modulation techniques are combined to generate the appropriated firing pulses for a 4-leg 3-Level Neutral Point Clamped (NPC) inverter. SHM modulation technique is applied to the phase legs in order to get a desired modulation index (ma) and to mitigate the lower order odd non-triplen harmonics (5th, 7th, …) while the fourth leg firing pulses are generated using SHE modulation technique to eliminate the major low order odd triplen harmonics (3rd, 9th, …) completely. It is demonstrated that this hybrid modulation technique can reduce significantly a vast range of harmonic orders in the NPC inverter output voltage when compared with the results achieved when using only SHE modulation technique in the four legs of the inverter. To avoid the generation of odd non-triplen harmonics in the SHM phase legs that can not be eliminated with the fourth SHE leg, the Simulated Annealing (SA) heuristic algorithm used to find the SHM switching angles is tuned in order to provided suitable odd-non-triplen harmonics distortions which can be eliminated with SHE technique. Moreover, since in dynamical applications the modulation index has to be changing continuously, the SA algorithm has also been designed in order to provide a smooth switching angles set to avoid undesired transients harmonic contents.

Abstract: We consider soft-output detection of a binary continuous phase modulation (CPM) generated through a low-cost transmitter, thus characterized by a significant modulation index uncertainty, and sent over a channel affected by phase noise. The proposed detector is designed by adopting a simplified representation of a binary CPM signal with the principal component of its Laurent decomposition and is obtained by using the framework based on factor graphs and the sum-product algorithm. It does not require an explicit estimation of the modulation index nor of the channel phase and is very robust to large uncertainties of the nominal value of the modulation index. Being soft-output in nature, this detector can be employed for iterative detection/decoding of practical coded schemes based on a serial concatenation, possibly through a pseudo-random interleaver, of an outer encoder and a CPM modulation format.