Frequency Pulse Width Modulation Research Articles

Bipolar and unipolar schemes for confined band variable switching frequency PWM based inverter

The single phase inverter performance through the unipolar and bipolar strategies has been previously analyzed based on the constant switching frequency pulse width modulation (CSFPWM). However, the confined band variable switching frequency PWM (CB-VSFPWM) is currently proposed as a new variable switching frequency PWM technique through unipolar strategy to facilitate the design of high order filter, to reduce the switching losses, and to reduce the current total harmonics distortion (THD) as well. To evaluate the performance of a single phase inverter based on the CBVSFPWM through bipolar strategy, this paper presents a comparative study of the CB-VSFPWM based inverter performance using the unipolar PWM and the bipolar PWM strategies. The study adopts MATLAB/Simulink to simulate the inverter and to analyze the simulation results in terms of harmonics spectrum, total harmonic distortion (THD), and fundamental components. The analysis of the study results gives an indication about the appropriate type of CB-VSFPWM strategy (unipolar PWM or bipolar PWM) to guarantee the desired performance of the connected inverter in terms of the electrical grid standards like THD, and harmonics spectrum of the inverter current.

Characterization of “cool” and “warm” white light-emitting diodes for low-cost spectrophotometry

The emission properties of “cool” and “warm” white light-emitting diodes were studied in the context of low-cost spectrophotometry. The suitability of pulse-width modulation as a method to control the diode brightness was examined. Both types of light-emitting diode demonstrated emission standard deviation minima at a pulse-width modulation frequency greater than 2000 Hz. The functional wavelength ranges of the light-emitting diodes were approximated using the linearity of brightness as a function of pulse-width modulation duty-cycle and the root mean squared deviation from mean for absorbance measurements. Both light emitting diode types demonstrated good stability in absorbance measurements over long operation times. The “warm” light emitting diode demonstrated a broader range of wavelengths useful for spectrophotometry.

Analysis and Optimization of Torque Ripple Reduction Strategy of Surface-Mounted Permanent-Magnet Motors in Flux-Weakening Region Based on Genetic Algorithm

One of the parameters required for a high-performance drive of a surface-mounted permanent magnet synchronous motor (SPMSM) operating in the flux-weakening region is the torque ripple reduction. In general, the torque ripple results from many reasons, such as the machine structure, oscillations of measured speed, etc. Hence, this article proposes an optimized strategy that works in conjunction with a variable switching frequency pulsewidth modulation algorithm to reduce the torque ripple peak. For the modulating algorithm, the updated frequency changes linearly with the desired torque ripple and its predicted maximum peak. For the proposed strategy, the reflection of proportional-integral (PI) parameters is observed at the torque ripple caused by the current ripples. Therefore, a robust method for adjusting PI parameters is proposed that relies on the improved fitness function that can minimize the regulators' error and maximize the drive stability bandwidth in the flux-weakening region. This objective function is optimized offline using a genetic algorithm optimization technique. Meanwhile, a third-order generalized integral flux observer is applied in this article, providing evidence of torque ripple reduction. For driving in the flux-weakening region, the reference magnitude of the duty cycles can produce the required <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis reference current to prevent the saturation of current controllers. Finally, comprehensive simulations and experiments are presented to validate the proposed strategy effectively. In comparison with the conventional method, the proposed strategy can reduce the copper and switching losses simultaneously and control the current and speed in the flux-weakening region efficiently.

Investigation and Prediction of High-Frequency Iron Loss in Lamination Steels Driven by Voltage-Source Inverters Using Wide-Bandgap Switches

The availability of wide-bandgap (WBG) power switches makes it possible to excite electric machines with much higher pulsewidth modulation (PWM) switching frequencies. This article experimentally characterizes the magnetic and iron loss properties of lamination steels over a wide range of PWM frequencies and magnetization states excited by a voltage-source inverter using GaN-based WBG switches. With the collected hysteresis loop and iron loss data, a new frequency-interconnected dynamic Jiles-Atherton (J-A) model has been developed explicitly for PWM-induced iron loss analysis. Experiments have been conducted to verify the model prediction accuracy over a broad range of operating conditions. The proposed model has been subsequently integrated with a dynamic hysteresis model devoted to fundamental field iron loss estimation, providing an accurate and efficient tool for total iron loss estimation during PWM voltage excitation using high-frequency WBG devices. This article includes an investigation of the impact of elevated fundamental frequencies and field amplitudes on the total iron loss including comparisons between analytical predictions and experimental test results.

PV String-Level Isolated DC–DC Power Optimizer with Wide Voltage Range

This paper proposes a photovoltaic (PV) string-level isolated DC–DC power optimizer with wide voltage range. A hybrid control scheme in which pulse frequency modulation (PFM) control and pulse width modulation (PWM) control are combined with a variable switching frequency is employed to regulate the wide PV voltage range. By adjusting the switching frequency in the above region during the PWM control process, the circulating current period can be eliminated and the turn-on period of the bidirectional switch of the dual-bridge LLC (DBLLC) resonant converter is reduced compared to that with a conventional PWM control scheme with a fixed switching frequency, resulting in better switching and conduction loss. Soft start-up control under a no-load condition is proposed to charge the DC-link electrolytic capacitor from 0 V. A laboratory prototype of a 6.25 kW DBLLC resonant converter with a transformer, including integrated resonant inductance, is built and tested in order to verify the performance and theoretical claims.

Comprehensive Analysis of Hexagonal Sigma-Delta Modulations for Three-Phase High-Frequency VSC Based on Wide-Bandgap Semiconductors

The efficiency of wide-bandgap (WBG) power converters can be greatly improved using high-frequency modulation techniques. This article proposes using single-loop and doubleloop hexagonal sigma-delta (H-ΣΔ and DH-ΣΔ, respectively) modulations for voltage source converters (VSC) that use silicon carbide (SiC) semiconductors. These allow high switching frequencies to operate more efficiently than silicon devices. Thus, ΣΔ modulations are excellent candidates for taking advantage of WBG devices. The proposed modulation techniques allow working with a variable switching frequency, thus producing an extreme reduction in switching losses and mitigating the low-order harmonics in comparison with the classical space vector pulsewidth modulation (SVPWM) technique, and with the innovative variable switching frequency pulse-width modulation (VSFPWM). The performance and losses of both ΣΔ techniques are analyzed here using MATLAB/Simulink and PLECS, and then compared with SVPWM and VSFPWM. Furthermore, the frequency spectrum and the total harmonic distortion are evaluated. Experimental results performed on a VSC converter that uses SiC MOSFETs show how H-ΣΔ and DH-ΣΔ greatly improve efficiency and generate fewer low-order harmonics than the SVPWM and VSFPWM strategies do.

Mitigating the dead-time effects on harmonics spectrum of inverter waveform by the confined band VSFPWM technique

The dead-time is necessary to be inserted between the gates drive pulses of the two power electronic switches in a one leg of any inverter to avoid a short circuit in the leg and the DC supply as well. However, adding the dead-time increases the low order harmonics of the output voltage/current waveform of the inverter. This paper investigates the positive effects of decreasing the pulse width modulation (PWM) drive pulses number per fundamental period on the current low order harmonics. In addition, this paper evaluates the impact of the confined band variable switching frequency pulse width modulation (CB-VSFPWM) technique on inverter performance in terms of dead-time mitigating, and consequenctely lowering the low order harmonics. CB-VSFPWM technique reduces the total harmonic distortion (THD) levels in the inverter output current as well. Theoretical analysis of the CB-VSFPWM effectiveness in reducing the negative effect of the dead-time has explained in this study and confirmed by the MATLAB/Simulink simulation results.

A method for calculating the parameters of the sine filter of the frequency converter, taking into account the criterion of starting current limitation and pulse-width modulation frequency

An analysis of the method for ensuring the sinusoidality of the output voltage in power generation systems with self-commutated voltage inverters under the requirements of the international standard IEEE-519 is presented. In a number of programs, especially low-power generation systems, a low-cost solution is needed to provide the sinusoidal waveform of the output voltage with the total harmonic distortion of 5 %. This solution is to use two-level voltage inverters with an output sine LC filter. However, the feature of the sine filter with the frequency converter is that the PWM frequency affects the spectrum of higher harmonics of the output voltage. In addition, there is the starting current of the filter capacitor, which can disable the power switches of the voltage inverter. The developed method for calculating the values of the LC filter with the two-level voltage inverter in the PWM mode is presented meeting the requirements of the international standard IEEE-519, taking into account the modulation frequency and limitation of the starting current of the filter capacitor. To confirm the required quality of the output voltage of the two-level voltage inverter with the sine filter, an appropriate simulation model was created in the Matlab/Simulink computer simulation environment. The oscillograms and harmonic analysis of the input and output voltages of the sine filter, which showed the total harmonic distortion of 1.88 %, are presented. A physical prototype of the investigated system was created on the basis of a 5.5 kW OVEN PChV203-5K5-V frequency converter (Ukraine). Using the SIGLENT SDS1104X-E oscilloscope (China), the real waveform and the results of the harmonic analysis of the sine filter output voltage, confirming the implementation of the necessary sinusoidality criteria, were obtained

Анализ повреждений подшипников тяговых машин на электроподвижном составе при питании от преобразователей частоты и напряжения

The technical and economic efficiency of electric rolling stock (ERS) is determined by the characteristics of its traction electric drives, the key ones of them being the manufacturing cost, repair and maintenance costs, service life, specific energy consumption, and operational reliability. The modern ERS uses induction electric drives with pulse-width control of the voltage and frequency control of the rotation frequency. The field experience gained from operation of electric drives equipped with semiconductor converters has shown a growing number of cases involving accelerated wear of the traction machine bearings. Currents through the bearings or shaft currents, which usually flow from the electrical machine shaft through the bearings, have been known since the time the electrical machines were invented. Owing to recent achievements made in power electronics, the application field of inductor motors has become much wider. In particular, the use of inverters with pulse-width modulation (PWM) and high switching frequency make it possible to operate an electric drive with a lower acoustic noise and with more efficient energy conversion; however, the use of inverters also entails the generation of bearing currents in induction motors. The article analyzes possible factors causing the occurrence of bearing currents. Typical changes occurring in the bearings as a result of electric current flowing through them are shown: the rolling surface becomes dull, grooves on the ball race occur, and lubrication becomes degraded. The influence of operating parameters on the frequency of the occurring breakdowns and the distribution of forces in the bearing system depending on the load are considered. A conclusion is drawn that the potential problem of bearing currents should be solved using design, structural, and algorithmic methods at different stages of design and operation of electrical systems involving adjustable electric drives.

Анализ повреждений подшипников тяговых машин на электроподвижном составе при питании от преобразователей частоты и напряжения

The technical and economic efficiency of electric rolling stock (ERS) is determined by the characteristics of its traction electric drives, the key ones of them being the manufacturing cost, repair and maintenance costs, service life, specific energy consumption, and operational reliability. The modern ERS uses induction electric drives with pulse-width control of the voltage and frequency control of the rotation frequency. The field experience gained from operation of electric drives equipped with semiconductor converters has shown a growing number of cases involving accelerated wear of the traction machine bearings. Currents through the bearings or shaft currents, which usually flow from the electrical machine shaft through the bearings, have been known since the time the electrical machines were invented. Owing to recent achievements made in power electronics, the application field of inductor motors has become much wider. In particular, the use of inverters with pulse-width modulation (PWM) and high switching frequency make it possible to operate an electric drive with a lower acoustic noise and with more efficient energy conversion; however, the use of inverters also entails the generation of bearing currents in induction motors. The article analyzes possible factors causing the occurrence of bearing currents. Typical changes occurring in the bearings as a result of electric current flowing through them are shown: the rolling surface becomes dull, grooves on the ball race occur, and lubrication becomes degraded. The influence of operating parameters on the frequency of the occurring breakdowns and the distribution of forces in the bearing system depending on the load are considered. A conclusion is drawn that the potential problem of bearing currents should be solved using design, structural, and algorithmic methods at different stages of design and operation of electrical systems involving adjustable electric drives.

High-Quality PWM Scheme for High-Speed Electric Drives

A pulsewidth modulation (PWM) scheme is presented for three-phase high-speed electric drives using coupled inductors with a very low series output inductance that generate multilevel output voltages with an elevated PWM frequency. Two inverter legs are used in each phase, connected in parallel using coupled inductors with magnetic cross-coupling. The PWM switching of the inverter legs is controlled using carrier signals 180° apart. Rather than changing these carrier signals on the zero crossovers of the three-phase reference signals to improve the PWM line voltage, the reference signals are modified instead: enhanced PWM control . This approach allows the use of compensation signals to eliminate flux jumps in the magnetic cores commonly associated with carrier switching. Hence, the flux in the magnetic cores follows predictable patterns, with the peak flux reduced considerably. This, in turn, allows the inductor design to be reduced in size and weight. The enhanced PWM control described is also shown to reduce the load current THDf and the load voltage harmonic volt-seconds. The feasibility of the enhanced PWM control is verified using both simulations and experimental results of a 10-kW (208 V/28 A, 300 Vdc) laboratory prototype.

Smooth Voltage PWM for Vibration and Acoustic Noise Reduction in Switched Reluctance Machines

This article proposes and investigates a control technique for vibration and acoustic noise reduction in Switched Reluctance Machines (SRMs). A large vibration generally occurs at the turn-off stage of SRM phase voltage due to a sudden decrease in the attraction force. The proposed technique is a smooth voltage Pulse-Width Modulation (PWM) method that utilizes the PWM technique to reduce the rate of change of voltage during the turn-off commutation angle. The aim of this proposed method is to control the vibration with high PWM frequency at the very beginning stage when the vibration is low before being developed into higher amplitude at the turn-off stage, without having to generate anti-phase vibration. Both simulation and experimental testing are implemented to confirm the capabilities and limitations of this technique.

An acoustic remote sensing method for high-precision propeller rotation and speed estimation of unmanned underwater vehicles.

Understanding the dominant sources of acoustic noise in unmanned underwater vehicles (UUVs) is important for passively tracking these platforms and for designing quieter propulsion systems. This work describes how the vehicle's propeller rotation can be passively measured by the unique high frequency acoustic signature of a brushless DC motor propulsion system and compares this method to Detection of Envelope Modulation on Noise (DEMON) measurements. First, causes of high frequency tones were determined through direct measurements of two micro-UUVs and an isolated thruster at a range of speeds. From this analysis, common and dominant features of noise were established: strong tones at the motor's pulse-width modulated frequency and its second harmonic, with sideband spacings at the propeller rotation frequency multiplied by the poles of the motor. In shallow water field experiments, measuring motor noise was a superior method to the DEMON algorithm for estimating UUV speed. In negligible currents, and when the UUV turn-per-knot ratio was known, measuring motor noise produced speed predictions within the error range of the vehicle's inertial navigation system's reported speed. These findings are applicable to other vehicles that rely on brushless DC motors and can be easily integrated into passive acoustic systems for target motion analysis.

Single‐phase hybrid multilevel inverter topology with low switching frequency modulation techniques for lower order harmonic elimination

A new single-phase asymmetrical multilevel inverter (MLI) is presented in this study. The proposed topology generates a staircase output voltage waveform with a maximum number of levels using less number of components compared to several existing and recent topologies. The basic module consists of a combination of two isolated DC sources with ten switches that produce all the possible number of levels. Other advantages of the proposed MLI include improved output voltage performance and a low blocking voltage of the switches. The low switching frequency pulse width modulation (LSF-PWM) technique has been used for the generation of gate pulses. In the LSF technique, selective harmonic elimination (SHE) and fundamental switching frequency PWM techniques have been discussed for the better output voltage waveform. The optimised switching angles with SHEPWM has been calculated using particle swarm optimisation considering the different combination of the elimination of lower order harmonics. Simulation work was carried out using MATLAB/SIMULINK, and a prototype was implemented to validate the proposed MLI module. Simulation and experimental results have been provided in the study to show the performance of the proposed topology with these modulation techniques.

Demonstration of Superior Electrical Characteristics for 1.2 kV SiC Schottky Barrier Diode-Wall Integrated Trench MOSFET With Higher Schottky Barrier Height Metal

In this letter, the authors demonstrated superior electrical characteristics of a 1.2 kV SiC Schottky barrier diode-wall integrated trench MOSFET (SWITCH-MOS) with the higher Schottky barrier height of nickel. It was confirmed that a significant improvement in short-circuit capability was achieved with no sacrifice of on resistance, because the electron leakage current through the integrated Schottky barrier diode (SBD), caused by thermionic-field emission, could be successfully suppressed. Further, although the integrated SBD with nickel showed 0.25 V greater forward voltage drop than that with titanium, the on resistance and switching characteristics were similar in the two devices. The results of the study showed that the SWITCH-MOS with nickel can achieve 21.0% less power dissipation in high frequency pulse width modulation inverters, compared to standard SiC trench MOSFETs.

Reduction of Electromagnetic Interference for Permanent Magnet Synchronous Motor Using Random PWM Switching Method Based on Four-Switch Three-Phase Inverters

The four-switch three-phase inverters have become an effective approach for fault-tolerant reconstruction and operation of the six-switch three-phase topology. However, the conventional control strategy for four-switch three-phase inverters can result in a large number of current harmonic components, high electromagnetic acoustic noise, and electromagnetic interference (EMI). Therefore, this paper proposes a random switching frequency pulse width modulation method under the centrosymmetry period with a two-state Markov chain based on four-switch three-phase inverters (RSFPWM-CPTMC). In this method, random numbers are optimized and evenly distributed on both sides of the center frequency within a specific frequency bandwidth range, which significantly reduces the current harmonics and EMI at the switching frequency and frequency multiplication. The spectral characteristics generated by the random switching frequency under the centrosymmetry period with the two-state Markov chain are evaluated and compared to that provided by the traditional fixed switching frequency pulse width modulation (FSFPWM). Simulations and experiments are carried out to illustrate the superiority of the proposal.

Analysis, design and implementation of a fixed frequency PWM-based sliding-mode controller for quadratic buck converter

The DC-DC converters are well-known due to their nonlinear and time-variant nature. This paper addresses the investigation of a fixed frequency pulse width modulation (PWM) based sliding mode current controller applied to quadratic buck converter (QBC). The QBC is well-suited for very low voltage central processing unit (CPU) voltage regulator applications with high-step-down DC-DC conversion ratios. The sliding mode current control features the reference current profile generation, satisfaction of hitting, existence and stability conditions besides the selection of sliding surface parameters. The simulation of QBC is realised for 19 V~8 V/1V at 50 KHz using PSIM software. The experimental results are presented in order to validate the simulation results. The strength of this control strategy is analysed for both line and load regulations.

GaN-Based Tri-Mode Intelligent Solid-State Circuit Breakers for Low-Voltage DC Power Networks

The purpose of this article is to provide a comprehensive and integrated discussion on the basic concept and general design methodology of a gallium nitride (GaN)-based, tri-mode, intelligent solid-state circuit breaker, referred to as iBreaker. The iBreaker concept explores the use of GaN devices in the low-voltage (<; 1000 V), mΩ-resistance SSCB designs and new SSCB topology and control techniques beyond the commonly used on/off switch configuration in order to integrate more intelligent functions without increasing component count. The iBreaker adopts a distinct pulsewidth modulation (PWM) current limiting (PWM-CL) state in addition to the conventional on and off states to facilitate soft startup, fault authentication, and fault location functions. Key design elements, such as use of wide bandgap (particularly GaN) switches, tri-mode operation, combined digital and analog control, and universal hardware/software architecture, are discussed in detail. In particular, the bidirectional buck topology, changes among operation states, variable PWM frequency control, fault locating techniques, GaN FET hardware, and thermal design are discussed. Two iBreaker prototypes, rated at 380 V/20 A and 1000 V/10 A, respectively, are built and tested to validate the proposed SSCB design concept. 99.95% transmission efficiency, passive cooling, and μs-scale response time are demonstrated experimentally.

An acoustic remote sensing method for high-precision speed estimation of micro-UUVs

Understanding the dominant sources of acoustic noise in unmanned underwater vehicles (UUVs) is important for passively tracking UUVs and for designing quieter propulsion systems. This work describes how the speed of a vehicle can be passively measured by the unique high frequency acoustic signature of a brushless DC motor propulsion system. First, the causes of high frequency tones were determined through direct measurements of two micro-UUVs and an isolated thruster. From this analysis, the vehicle noise was mapped to speed and the common and dominant features of noise were established: strong tones at the motor's pulse-width modulated frequency and its second harmonic, each of which is a carrier with sidebands at frequency intervals equivalent to the propeller rotation frequency multiplied by the poles of the motor. Field experiments were performed where the speed of two micro-UUVs was predicted by measuring the sidebands of the two dominant tones. When the mapping of rotational to translational speed of the UUV was known, this method produced speed predictions with 0.004 m/s accuracy. These findings are applicable to many off-the-shelf vehicles available today which rely on brushless DC motors and can be easily integrated into passive acoustic security systems for target motion analysis. [Work supported by the Department of Defense NDSEG program, ONR, and Draper.]

A Variable-Frequency Current-Dependent Switching Strategy to Improve Tradeoff Between Efficiency and SiC MOSFET Overcurrent Stress in Si/SiC-Hybrid-Switch-Based Inverters

Reliability remains an issue for the Si/SiC hybrid switch adopting the conventional switching strategy of the internal SiC MOSFET that turns on earlier, and off later. Such issue is attributable to the overcurrent stress under the heavy load operating condition, which adversely affects the SiC MOSFET during the gate delay time. To solve this problem without increasing the extra power loss, a novel variable-frequency current-dependent switching strategy combining the variable switching pattern strategy, and the variable pulsewidth modulation (PWM) frequency strategy is proposed. Variable switching pattern strategy can avoid the overcurrent stress of the SiC MOSFET at the heavy load operating condition, and the designed optimal delay time in different switching patterns can achieve the compromise between the excellent reliability, and the power loss of Si/SiC hybrid switch. Variable PWM frequency strategy can effectively reduce the switching loss of the Si/SiC hybrid switch by decreasing the switching frequency around the peak current region. An Si/SiC-hybrid-switch-based single-phase inverter platform is constructed and tested. Test results show that the power loss of the single-phase inverter adopting such switching strategy outperforms the current-dependent switching strategy with 9.4% reduction of power loss, and overcurrent stress of SiC MOSFET is avoided.