Standard PWM Research Articles

Nearly Constant Switching Frequency Hysteresis Current Controller with Fast Online Computation of Boundary for a 2-Level Induction Motor Drive

A nearly constant switching frequency current hysteresis controller for a 2-level inverter fed induction motor drive is proposed in this paper. The salient features of this controller are fast dynamics for the current, inherent protection against overloads and less switching frequency variation. The large variation of switching frequency as in the conventional hysteresis controller is avoided by defining a current-error boundary which is obtained from the current-error trajectory of the standard space vector PWM. The current-error boundary is computed at every sampling interval based on the induction machine parameters and from the estimated fundamental stator voltage. The stator currents are always monitored and when the current-error exceeds the boundary, voltage space vector is switched to reduce the current-error. The proposed boundary computation algorithm is applicable in linear and over-modulation region and it is simple to implement in any standard digital signal processor. Detailed experimental verification is done using a 7.5 kW induction motor and the results are given to show the performance of the drive at various operating conditions and validate the proposed advantages.

Single phase angle tracking method for power switches gating synchronization

This paper proposes a novel method for generating the pulses needed to fire power electronic switches that can be used for single-phase power converters. Simple operations based on the three-phase arctangent method are used within a digital signal controller or microcontroller to generate a sawtooth carrier signal phi, with an amplitude of 2pi and concurrent to the period of time of the sinusoidal input. With this signal and using standard Pulse Width Modulation techniques, gating is obtained directly. Two orthogonal signals are the basis of the arctangent method of synchronization; these signals are obtained by numerical differentiation, and normalized using frequency of the same amplitude. This strategy shortens the time consumed. The synchronizing method proposed is validated through MATLAB simulations, and used with several single-phase grid variations, such as sag, swell, flicker, frequency or phase jump. Infinite impulse response (IIR) Butterworth filter is added to take into consideration harmonic contamination on the grid. Experimental results of gating signals are presented to show the proposal's feasibility.

Experimental Study on Conducted EMI Mitigation in SMPS using a Novel Spread Spectrum Technique

Switched mode power supplies (SMPS) are power electronic circuits extensively used in a wide range of applications. High frequency switching operation of SMPS causes electromagnetic emissions and has the potential to interfere with system operation, which in turn has an impact on system performance. This makes electromagnetic compatibility (EMC) an important concern. In this paper, a new and simple spread spectrum technique is proposed by modulating chaotic pulse position modulation (CPPM) and pulse width modulation (PWM). The resulting CPWM is implemented to reduce the conducted EMI in SMPS. The proposed method is found to be effective in reducing conduction EMI. The effectiveness and simplicity of the proposed method on spreading those dominating frequencies is compared to the EMI mitigation technique using an external chaotic generator. Finally, the levels of conductive EMI with standard PWM, CPWM with an external chaos generator and the proposed method are experimentally verified to comply with the CISPR 22A regulations. The results confirm the effectiveness of the proposed method.

Analysis of the thermal management system for a pump laser

In this paper we report on a theoretical and experimental study of the steady-state response, transient response and efficiency of a thermal management system. We compare two alternative designs based on thermo-electric modules, the role of which is to control the temperature of the laser-diode pumping system for advanced fiber lasers. The performances of a standard pulse-width modulation controller and a variable-voltage controller were tested on a reference thermal management system. An experimental facility and a numerical model were set up, with the system response to various load conditions measured as well as numerically simulated. The results show that the design of the thermal management system based on the variable-voltage controller offers a significant performance advantage over the pulse-width modulation design.

A novel control scheme for buck power converters using duty-cycle modulation

A novel duty-cycle modulation control scheme for buck power converters is studied in this paper. Compared to the widely used pulse width modulation technique encountered in power electronics, the proposed control scheme offers under the same operating conditions a variety of merits, including a greater hardware simplicity, a lower modulation frequency and a better transient response. In addition, while offering new characteristics, it provides under load disturbances the same level of robustness than the standard pulse width modulation control technique. The characteristics of both control techniques are validated and compared on a well tested prototyping buck converter, using a mix of analytical reasoning, virtual simulations, and real tests on a laboratory workbench.

Analysis of Triangular Periodic Carrier Frequency Modulation on Reducing Electromagnetic Noise of Permanent Magnet Synchronous Motor

This paper introduces a simple approach to reduce the electromagnetic noise of permanent magnet synchronous motor (PMSM) driven by pulse width modulation (PWM) supply. Alleviating the PMSM electromagnetic noise has become an important demand due to demanding requirement on human life environment. The PMSM electromagnetic noise concentrated at multiples of switching frequency results from the concentrative current harmonic. Triangular periodic carrier frequency modulation (PCFM) is introduced to alleviate the PMSM current harmonic and electromagnetic noise in this paper. The principle of triangular PCFM in reducing PMSM current harmonic and electromagnetic noise is analyzed. The impact of modulation frequency ratio on reducing PMSM electromagnetic noise is investigated. Simulations and experiments of PMSM driven by standard PWM and triangular PCFM are implemented. The simulated and experimental results verify the disciplinarian of triangular PCFM in alleviating PMSM current harmonic and electromagnetic noise.

Techniques for Conditioning Bit-Stream Signals for Single-Phase Power Electronics Applications

Bitstream-based control, which uses one-bit-wide signals to control power electronics applications, is a new approach for controller design. Bit-Stream signals can be directly applied to control electronic devices, but the high-frequency nature of bitstream signals can lead to excessive switching losses. Thus, it is essential to downsample bitstream signals to reduce switching losses to acceptable levels. This paper presents a novel modulator, which downsamples high-frequency bitstreams to low-frequency switching signals that are suitable for driving two-level half-bridge or three-level full-bridge inverters. Methods for compensating for switch dead time and balancing switching losses of the inverter legs are presented, and the performance of the proposed modulators are compared to the standard pulse width modulation strategies. Simulation and experimental results of a 2-kW single-phase inverter show that the proposed bitstream modulators consume fewer logic resources, produce spread-spectrum output currents, and can deliver lower total harmonic distortion than similar fixed-frequency pulse width modulators.

Improved sensorless control of a permanent magnet machine using fundamental pulse width modulation excitation

A new method to estimate the rotor position of permanent magnet synchronous motor (PMSM) drives over a wide speed range, including zero frequency is introduced. The method measures the motor current derivative in response to the standard pulse width modulation (PWM) sequence to estimate rotor position. No additional signal injection or separate test vectors are required although modification is needed when narrow PWM voltage vectors occur. Three compensation techniques are proposed to improve the quality of the position estimation and reduce current distortion when narrow vectors are used for position estimation. Experimental results for sensorless speed and position control of a 4 kW PMSM verify the effectiveness of the proposed techniques.

Performance Analysis of Cascaded Multilevel Inverter with Hybrid Phase-Shifted Carrier Modulation

This paper presents the hybrid phase-shifted carrier (PSC) modulation for cascaded voltage source inverters, investigates their performance characteristics, and provides a comparison with the standard pulse-width modulation (PWM) methods. The proposed PWM combines the features of fundamental frequency PWM and high-frequency PSC-PWM in power conversion, and resolves the contradiction between high frequency and accuracy in a digital control scheme. The proposed PWM is developed based on PWM base generator and hybrid PWM control algorithm, and it is implemented using TMS320 F2407 DSP processor and Xilinx XC95108 CPLD controller, respectively. The main characteristic of this hybrid modulation is the reduction in switching losses, effectively improving harmonic performance, and solving the problem of unequal voltage stress and current stress of power devices. The performance of this hybrid modulation is analysed and compared with the original strategies. Power losses, total harmonic distortion (THD), weighted THD and the normalised weighted THD are evaluated. Simulation and experimental results verify that the proposed PWM technique is superior to standard techniques. Finally, it is concluded that the proposed strategy is highly suited to inverters with high number of voltage levels.

Using PWM-Induced Transient Excitation and Advanced Signal Processing for Zero-Speed Sensorless Control of AC Machines

The sensorless control of induction machines, particularly for operation at low speed, has received significant attention in recent years. To realize a field-oriented control of AC machines that is able to work at zero speed, the most commonly used methods are either sensor-based models or transient-signal-excitation methods. The major disadvantage of present signal-injection methods is that they are intrusive to pulsewidth modulation (PWM). An additional switching sequence has to be embedded in the control that will cause a torque and current ripple. In order to overcome these problems, a new flux-estimation algorithm that uses the phase current derivative to extract the flux-position information is presented. In contrast to previously introduced methods, this new approach operates without additional transient excitation of the machine and requires only fundamental-wave excitation using standard PWM or slightly modified PWM. Furthermore, only the current response in the two active states of PWM is used. This makes it possible to use sensorless control for the whole speed range including overmodulation and removes the distortion and parasitic influence of the zero switching states during the estimation of the flux. Experimental results are presented to validate the applicability of the presented approach.

New Control Technique Applied in Dynamic Voltage Restorer for Voltage Sag Mitigation

The Dynamic Voltage Restorer (DVR) was a power electronics device that was able to compensate voltage sags on critical loads dynamically. The DVR consists of VSC, injection transformers, passive filters and energy storage (lead acid battery). By injecting an appropriate voltage, the DVR restores a voltage waveform and ensures constant load voltage. There were so many types of the control techniques being used in DVR for mitigating voltage sags. The efficiency of the DVR depends on the efficiency of the control technique involved in switching the inverter. Problem statement: Simulation and experimental investigation toward new algorithms development based on SVPWM. Understanding the nature of DVR and performance comparisons between the various controller technologies available. The proposed controller using space vector modulation techniques obtain higher amplitude modulation indexes if compared with conventional SPWM techniques. Moreover, space vector modulation techniques can be easily implemented using digital processors. Space vector PWM can produce about 15% higher output voltage than standard Sinusoidal PWM. Approach: The purpose of this research was to study the implementation of SVPWM in DVR. The proposed control algorithm was investigated through computer simulation by using PSCAD/EMTDC software. Results: From simulation and experimental results showed the effectiveness and efficiency of the proposed controller based on SVPWM in mitigating voltage sags in low voltage distribution systems. It was concluded that its controller also works well both in balance and unbalance conditions of voltages. Conclusion/Recommendations: The simulation and experimental results of a DVR using PSCAD/EMTDC software based on SVPWM technique showed clearly the performance of the DVR in mitigating voltage sags. The DVR operates without any difficulties to inject the appropriate voltage component to correct rapidly any anomaly in the supply voltage to keep the load voltage balanced and constant at the nominal value.

Delta Modulation with PI Controller—A Comparative Study

The paper discusses the application of PWM delta modulation with PI controller as an alternative to the standard PWM techniques for providing gating signals to the voltage source inverters. Its inherent characteristics of constant volts/Hertz control without feedback complexity and boosting of the fundamental voltage makes it an excellent choice for motor drive applications. This paper discusses the comparison between a basic delta modulation, the advanced Delta modulation with PI controller and an optimized DMPI. It is shown that in addition to the aforementioned advantages, VSI with optimized DMPI produces superior load current/voltage waveforms compared to simple DMPI, when IGBT is employed as a switching device for the inverter. Since the tacho feedback or other traditional speed sensing means is not permissible in sealed motor or the pump, a novel method is used to monitor the motor speed from the terminal quantities like voltage, current, and motor input power factor.

Performance Analysis of Reduced Common-Mode Voltage PWM Methods and Comparison With Standard PWM Methods for Three-Phase Voltage-Source Inverters

This paper surveys the reduced common-mode voltage pulsewidth modulation (RCMV-PWM) methods for three-phase voltage-source inverters, investigates their performance characteristics, and provides a comparison with the standard PWM methods. PWM methods are reviewed, and their pulse patterns and common-mode voltage (CMV) patterns are illustrated. The inverter input and output current ripple characteristics and output voltage linearity characteristics of each PWM method are thoroughly investigated by analytical methods, simulations, and experiments. The research results illustrate the advantages and disadvantages of the considered methods, and suggest the utilization of the near-state PWM and active zero state PWM1 methods as overall superior methods. The paper aids in the selection and application of appropriate PWM methods in inverter drives with low CMV requirements.

Two PWM techniques for single-phase shunt active power filters employing a direct current control strategy

This paper presents a comparison of two pulse-width-modulation (PWM) control techniques applied to a single-phase shunt active power filter (SPSAPF) using theoretical and experimental validation methods. A direct current control strategy is implemented using a standard PWM (S-PWM) and a modified PWM (M-PWM) in order to compensate the current harmonics and the reactive power generated by a nonlinear load. The M-PWM technique is based on two comparisons of a triangular high-frequency carrier signal with a low-frequency modulating signal (which represents the load current harmonics) and its opposite. The M-PWM shifts the first significant harmonic rays towards twice the switching frequency and eliminates the spectral rays that are centred around the odd multiples of the switching frequency. The simulation and experimental results are presented with a view to determine which of the M-PWM or the S-PWM performs better in terms of source current total harmonic distortion and reactive power compensation.

Proximate Time-Optimal Digital Control for Synchronous Buck DC–DC Converters

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper introduces an approach to near time-optimal control for synchronous buck dc–dc converters. The proposed proximate time-optimal digital (PTOD) controller is a combination of a constant-frequency pulsewidth modulation (PWM) controller employing a linear PID compensator close to a reference point, and a linear or nonlinear switching surface controller (SSC) away from the reference, together with smooth transitions between the two. A hybrid capacitor current estimator enables switching surface evaluation and eliminates the need for current sensing. The SSC, which is implemented as a small Verilog HDL module, can be easily added to an existing digital PWM controller to construct the PTOD controller. In steady state, the controller operates exactly the same as a standard constant-frequency PWM controller with a linear PID compensator. Simulation and experimental results are shown for a 6.5 V-to-1.3 V, 10A synchronous buck converter. </para>

Genome-wide analysis of chlamydiae for promoters that phylogenetically footprint

Currently, there is a lack of phylogenetic footprinting programmes that can take advantage of multiple whole genome sequences of different species within the same bacterial genus. Therefore, we have developed and tested a position weight matrix-based programme called Footy, that performs genome-wide analysis of bacterial genomes for promoters that phylogenetically footprint. When Footy was used to analyse the non-coding regions upstream of genes from three chlamyidal species for promoters that phylogenetically footprint, it predicted a total of 42 promoters, of which 41 were new. Ten of the 41 new promoters predicted by Footy were biologically assayed in Chlamydia trachomatis by mapping the 5′ end of the transcripts for the associated genes. The primer extension assay validated seven of the 10 promoters. When Footy was compared to two other accepted methods for genome-wide prediction of promoters in bacteria (the standard PWM method and MITRA), Footy performed equally as well or better than these programmes. This paper, therefore, shows the value of a bioinformatics programme able to perform genome-wide analysis of bacteria for promoters that phylogenetically footprint.

Use of a High-Temperature Superconducting Coil for Magnetic Energy Storage

A high temperature superconducting magnetic energy storage device (SMES) has been realised using a 350 m-long BSCCO tape wound as a ‘‘pancake’’ coil. The coil is mounted on a cryocooler allowing temperatures down to 17.2 K to be achieved. The temperature dependence of coil electrical resistance R(T) shows a superconducting transition at T = 102.5 K. Measurements of the V(I) characteristics were performed at several temperatures between 17.2 K and 101.5 K to obtain the temperature dependence of the critical current (using a 1 µV/cm criterion). Critical currents were found to exceed 100 A for T < 30 K. An electronic DC-DC converter was built in order to control the energy flow in and out of the superconducting coil. The converter consists of a MOS transistor bridge switching at a 80 kHz frequency and controlled with standard Pulse Width Modulation (PWM) techniques. The system was tested using a 30 V squared wave power supply as bridge input voltage. The coil current, the bridge input and output voltages were recorded simultaneously. Using a 10 A setpoint current in the superconducting coil, the whole system (coil + DC-DC converter) can provide a stable output voltage showing uninterruptible power supply (UPS) capabilities over 1 s.

Implementation and simulation of modified PWM with two current control techniques applied to single-phase shunt hybrid power filter

Filter and source current control strategies are applied to a single-phase shunt hybrid power filter (SPSHPF). These techniques are implemented with a modified pulse width modulation (M-PWM) in order to compensate for the harmonics and reactive power required by nonlinear loads and the high-frequency harmonics generated by the switching process. Contrarily to the existing methods, the proposed source current control eliminates switching spikes in the supply current and appears to be more suitable than the filter current control method. Furthermore, the M-PWM technique ensures the elimination of all groups of harmonics that are centred on the odd multiples of the switching frequency. It requires a relatively reduced size input passive filter. In addition, it attenuates the harmonics that are located around twice the switching frequency four times less than the S-PWM. The measured power losses of the M-PWM hybrid filter are also one-fourth compared to that of the standard PWM control. Experimental results obtained on a 1 kVA developed laboratory prototype system and through simulations validate the effectiveness of the SPSHPF adopting the source current control with the modified PWM technique.

Optimized PWM Strategy Based on Genetic Algorithms

A genetic algorithm is applied to optimize a pulsewidth modulation (PWM) inverter, which cannot only spread harmonic energy but also reduce harmonic distortion. Simulation and experimental results verify that the optimized PWM technique is superior to standard triangular PWM and random PWM techniques.

Hysteresis controller with constant switching frequency

Switch mode audio power amplifiers are showing up on market in still greater numbers because of advantages in form of high efficiency and low total system cost, especially for high power amplifiers. Several different modulator topologies have been made, ranging from standard PWM to various self-oscillating and digital modulators. Performance in terms of low distortion, noise and dynamic range differs significantly with the modulator topology used. Highest system performance is generally achieved with analog modulators made as a modulator loop including at least the power stage of the amplifier, because of benefits from continuous time operation and non-quantized resolution. This type of modulator uses no external carrier signal, and is called self-oscillating modulators. The work presented in this paper refers to switch mode audio power amplifier, but can be used within a wide range of DC-DC or DC-AC converters as well.