Random PWM Research Articles

Study of Conducted EMI Reduction for Three-Phase Active Front-End Rectifier

The problem of electromagnetic interference (EMI) plays an important role in the design of power electronic converters, especially for airplane electrical systems. This paper explores techniques to reduce EMI noise in three-phase active front-end rectifier. The Vienna-type rectifier is used as the object. The design approach introduced in this paper is using a high-density EMI filter to satisfy the EMI standard. Design methodology is introduced in the paper by a three-stage LC- LC-L filter structure. In particular, the cause of high noise at high frequencies is studied in experiments, and the coupling effect of the final-stage capacitor and inductors is investigated. In order to reduce the EMI noise in the mid-frequency range, the application of random pulsewidth modulation (PWM) is also presented. The performance of random PWM in a Vienna-type rectifier is verified by theoretical analysis and experimental results. The approaches discussed in this paper significantly reduce the EMI noise in the Vienna-type rectifier, and therefore, the filter size can also be reduced.

Analysis and Development of Wavelet Modulation for Three-Phase Voltage-Source Inverters

This paper presents the analysis, development, and implementation of a wavelet modulation (WM) technique for three-phase voltage-source (VS) six-pulse inverters. The WM technique is based on sampling three continuous-time (CT) sinusoidal reference modulating signals in a nonuniform recurrent manner using three sets of scale-based linearly combined wavelet basis functions. These CT signals are recovered from their samples by a three-phase VS six-pulse inverter, which is activated by three sets of synthesis scale-based linearly combined wavelet basis functions. Each set of synthesis basis functions is generated for activating one leg of the three-phase inverter in order to recover one CT reference modulating signal. The WM technique is implemented for both simulation and experimental performance testing. The performances of the WM technique are compared with those obtained using the space vector modulation, random pulsewidth modulation, and hysteresis band current control techniques under the same loading conditions. Simulation and experimental test results show that the proposed WM technique is able to switch a three-phase VS six-pulse inverter to produce outputs with significantly improved fundamental components and low harmonic contents.

Spread spectrum modulation scheme for two-level inverter using vector quantised space vector-based pulse density modulation

A Space Vector based Pulse Density Modulation scheme for a two level Voltage Source Inverter is proposed in this paper. The proposed scheme employs a first order Sigma Delta Modulator. The principle of Vector Quantization is used for quantizing the reference voltage Space Vector in the Sigma Delta Modulator. For the spatial quantization, the inverter voltage vector space is divided into seven Voronoi regions. In this paper, a method is proposed to code these Voronoi regions using instantaneous reference phase amplitudes without using lookup table. The proposed scheme naturally selects the switching vectors in the over-modulation condition and hence results in a smooth transition from linear to over-modulation region. In Pulse Density Modulation scheme, the switching frequency varies randomly, resulting in the spreading of harmonic spectra. The minimum pulse width that can occur in the proposed scheme is equal to the sampling time period. Therefore, the occurrence of pulse width less than the trun on time of the switching devices is avoided. The proposed scheme is implemented for a 11.5 kVA two level inverter driving 2-HP three phase induction motor. Experimental results of proposed scheme are compared with s Space Vector PWM scheme and Random Space Vector PWM scheme.

Shaping the Noise Spectrum in Power Electronic Converters

The operation of switch-mode converters results in electromagnetic noise propagating throughout the power electronic system. Pulsewidth modulation (PWM) strategies with fixed switching frequency generate harmonics in the spectra of converter voltages and currents. Random PWM techniques allow the elimination of the harmonics, resulting in a continuous spectrum of noise, i.e., a spectrum retaining all frequency components. As a next step in advanced spectral shaping, a method presented in this paper produces spectral nulls at selected frequencies. This allows the carving of communication channels in the noise and the removal of spectral power at frequencies potentially harmful for the system. The theoretical analysis, computer simulations, implementation details, and experimental results are presented.

Harmonic Intensity Reduction Technique for Single Phase Switched Reluctance Motor Drives Using a New Random PWM Scheme

This paper proposes a new random switching strategy using a DSP TMS320F2812 to reduce the harmonics spectra of single phase switched reluctance motors. The proposed method combines the random turn-on/off angle technique and the random pulse width modulation technique. A harmonic spread factor (HSF) is used to evaluate the random modulation scheme. In order to confirm the effectiveness of the proposed method an experiment was conducted. The experimental results show that the harmonic intensity of the output voltage for the proposed method is better than that for conventional methods.

Analysis and Verification of Two-Level Random Aperiodic PWM Schemes for DC–DC Converters

A typical two-level pulsewidth modulation scheme for a dc-dc converter generates a signal that has two values: 0 and 1. For a random aperiodic scheme, the switching period can be modulated in a random fashion with a known probability density function (pdf). In this paper, analytical expressions for both discrete and continuous spectra are provided for the case where different pdfs are used to modulate the switching signal of a dc-dc converter. Experimental results for a random aperiodic scheme that is used to optimize the output ripple of a buck dc-dc converter are provided to support the theoretical claims.

Development and Testing of Wavelet Modulation for Single-Phase Inverters

This paper introduces a novel modulation technique for single-phase (1 phi) voltage-source (VS) dc-ac power inverters. The proposed modulation technique is based on a newly designed scaling function that is capable of supporting a nonuniform recurrent sampling process. This scaling function generates sets of basis functions that span spaces, of which a collection constructs a nondyadic-type multiresolution analysis. Furthermore, the newly designed scaling function has a dual synthesis scaling function that is designed to reconstruct continuous-time signals from their nonuniform recurrent samples. The proposed wavelet modulation technique is implemented using a MATLAB code that generates switching pulses to activate a SIMULINK model of a 1 phi VS four-pulse (H-bridge) inverter. Several performance tests are conducted for the proposed wavelet-modulated (WM) inverter, when supplying linear, nonlinear, static, and dynamic loads. The results of these tests show significant reduction of the output harmonics along with high magnitude of the output fundamental component. The efficacy of the proposed WM inverter is further demonstrated through a comparison of the random pulsewidth modulation (RPWM) and the pulsewidth modulation (PWM) inverters for supplying the same loads. The comparison results show that the proposed WM inverter is capable of producing outputs with higher quality than the RPWM and PWM inverters.

Reduction of Conducted Perturbations in DC-DC Voltage Converters by a Dual Randomized PWM Scheme

Randomized Pulse Width Modulation (RPWM) deals better than Deterministic PWM (DPWM) with Electro-MagneticCompatibility (EMC) standards for conducted Electro Magnetic Interferences (EMI). In this paper, we propose a dual RPWM scheme for DC-DC voltage converters: the buck converter and the full bridge converter. This scheme is based on the comparison of deterministic reference signals (one signal for the buck converter and two signals for the full bridge converter) to a single triangular carrier having two randomized parameters. By using directly the randomized parameters of the carrier, a mathematical model of the Power Spectral Density (PSD) of output voltage is developed for each converter. The EMC advantage of the proposed dual randomization scheme compared to the classical simple randomization schemes is clearly highlighted by the PSD analysis and confirmed by FFT (Fast Fourier Transform) analysis of the output voltage.

Design and Implementation of a Novel Vector-controlled Drive by Direct Injection of Random Signal

The distribution of harmonics of an inverter output voltage in a PWM inverter can be improved by using a Random Pulse Width Modulation (RPWM) scheme. RPWM dose not affect the fundamental frequency component of voltage, however it can significantly reduce the acoustic noise and mechanical vibrations of an inverter-fed ac motor drive. Up to now, RPWM has been studied in many researches and various RPWM techniques have been introduced, but none of them have actually shown the effects of the behavior of the random signal on the frequency spectrum of the inverter output voltage and performance of the motor drive. In this paper, three different methods of random signals are employed. These different methods and the Probability Density Function (PDF) of the random signal generator will be studied and the performance of the drive is examined. Also a new method in utilizing random signal is proposed. In this method, the random signal is injected to reference value of the quadrature-axis current. It should be noted that the RPWM technique can not be utilized in hysterisis drives. Here, the random signal with different PDF is injected directly to quadrature axis current. The injection of random signal will directly affect the output responses. In this research, comparison between RSPWM technique and direct injection of random signal has been carried out. Different criteria such as total harmonic distortion (THD), torque ripple and frequency spectrum, efficiency and mechanical vibration have been analyzed. The indirect field oriented vector control drive is simulated by using Matlab-Simulink first, and the effects of various methods of employing random signal are compared and the best alternative is introduced. For the validation of the simulation results an experimental set-up is built. The experimental results confirm the simulation outputs. The simulation and experimental result show superiority of Direct Injection of Random Signal (DIRS) method in comparison with randomized Sinusoidal pulse width modulation (RSPWM) technique. Also it is realized that the DIRS method is very simple for implementation and does not need any extra hardware.

A New Hybrid Random PWM Scheme

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper proposes a new hybrid random pulsewidth modulation (PWM) scheme based on a TMS320LF2407 DSP, in order to disperse the acoustic switching noise spectra of an induction motor drive. The proposed random PWM pulses are produced through the logical comparison of a pseudorandom binary sequence (PRBS) bits with the PWM pulses corresponding to two random triangular carriers. For this reason, the PWM pulses of the proposed scheme possess the hybrid characteristics of the random pulse position PWM and the random carrier frequency PWM. In order to verify the validity of the proposed method, the simulations and experiments were conducted with a 1.5-kW three-phase induction motor under the 2.5-A load condition. The DSP generates the random numbers, the PRBS bits with a lead-lag random bit (8 bit) and the three-phase reference signals. Also, a frequency modulator MAX038 makes the randomized frequency triangular carrier (3 <formula formulatype="inline"><tex Notation="TeX">$\pm$</tex></formula> 1 kHz). From the results, the proposed scheme shows good randomization effects of the voltage, current, and acoustic noise of the motor as compared with conventional scheme (3 kHz). </para>

브리시리스 직류 전동기에 랜덤 PWM을 적용한 저가형 센서리스 드라이브에 관한 연구

Recently, it is increased to apply sensorless drive for BLDC (Brushless DC) motor to household electrical appliances, especially in the refrigerators and air conditioners, to reduce the cost and the acoustic noise by the operation and to make their functions more comfortable for human beings. In this paper, low-cost sensorless drive for BLDE motor is implemented by random PWM (Pulse Width Modulation). The experimental results show that the electromagnetic noise was reduced and the sound quality was improved by BLDC motor sensorless random PWM Control.

A New Random Current Control Technique for a Single-Phase Inverter with Bipolar and Unipolar Modulations

Although a hysteresis current control is a simple and a reliable modulation technique in switching control systems, its spectral contents around switching sideband are not distributed broadly. Random Pulse Width Modulation (RPWM) technique is an effective scheme which distributes the spectral contents of a load current and can reduce acoustic noise and mechanical vibrations of an inverter-fed motor drive. This paper presents a Random-Band Hysteresis Current Control (RBHCC) technique with bipolar and unipolar modulations. Mathematical analysis and simulation results show the RBHCC with the unipolar modulation has no significant effect on distributing the spectral contents of the load current compared to the bipolar modulation technique. Finally, the effect of the random-band hysteresis current control is analysed to determine the best hysteresis band height variation for the bipolar modulation.

A comparison between random hysteresis current control technique with bipolar and unipolar modulations

Current control methods play an important role in power electronic circuits. Among them, a hysteresis current control method has been used largely on AC motor drives due to a good dynamic response and simple operation. The Random Pulse Width Modulation (RPWM) technique distributes the spectrum contents of load current without affecting the fundamental component, and it may reduce the acoustic noise and mechanical vibration of an inverter-fed induction motor drive when the amplitude of harmonics around side bands is decreased. This paper presents a Random Band Hysteresis Current Control (RBHCC) technique with bipolar and unipolar modulations, and compares spectrum contents of a load current. Mathematical analysis and simulation results show that the RBHCC with unipolar modulation has no considerable effect on distributing the spectrum contents of the load current compared to the bipolar modulation technique.

A novel random hysteresis current control for a single-phase inverter

Although a hysteresis current control technique is a simple and a reliable modulation scheme in switching control systems, its harmonic spectrum around the switching side band may not distribute properly. Random pulse width modulation technique is an effective scheme that distributes the harmonic spectrum of the load current, and it can reduce the acoustic noise and the mechanical vibration of inverter-fed motor drives. This paper presents a new method for hysteresis current control based on random band control for a better spreading of the harmonic spectrum of the load current. In this paper, the effect of the random-band hysteresis current control is analysed to determine the best hysteresis band variation and the results have been compared with the traditional hysteresis current control. Theoretical analysis and simulations have been performed to describe the method.

Application of chaotic modulation to AC motors for electro magnetic interference suppression

Instead of avoiding occurrence of chaos in motor drives, chaos is positively utilized in this paper. A new chaotic pulse width modulation (PWM) scheme is proposed and implemented for AC motors, which functions to significantly suppress harmonic peaks and hence acoustic noise. The key is to employ the Chua’s circuit for generating a desired chaotic sequence. By using a practical induction motor, computer simulation and experimental results verify that the chaotic PWM has advantages of harmonic peak suppression and simple hardware implementation over the conventional PWM and random PWM.

Attenuation of Electromagnetic Interference in a Shunt Active Power Filter

Shunt active power filters (APF) are commonly used for the reduction of current harmonics and improvement of the power factor in power systems with nonlinear loads, such as diode rectifiers. A pulsewidth modulation (PWM) power converter constitutes the main component of the APF. The low-order harmonics of the line current are attenuated, but the switch-mode operation of the converter results in electromagnetic interference (EMI) spreading to the grid. Specifically, clusters of harmonics appear in the frequency spectra of voltages and currents of the converter at multiples of the switching frequency. In this paper, transferring the discrete spectral power of those harmonics to the continuous spectral power density is proposed as means for mitigation of the EMI. It is accomplished by randomization of the switching periods using a novel random PWM method (RPWM II). In contrast to the existing random PWM methods, in RPWM II the sampling frequency of the digital modulator is constant and equal to the average switching frequency. Computer simulations and experimental investigation of an APF designed for shipboard power systems are described, and the results are presented. They demonstrate significant reduction of the EMI, a feat achieved at practically no expense.

Application of Random PWM Technique for Reducing the Conducted Electromagnetic Emissions in Active Filters

A pulsewidth modulation (PWM)-controlled active filter generates harmonics at the switching frequency and its multiples in the RF range, and the concentrated power spectrum may produce electromagnetic interference (EMI) problems. In this paper, the random PWM (RPWM) technique is applied in order to spread the noise spectrum over a wide range, thus, considerably reducing the amplitudes of these harmonics and the consequent EMI problems. To study the operation of active filters, the case of an ac/dc converter along with a power-factor corrector is considered as a nonlinear load and a series active filter, respectively. A line impedance stabilization network is used to study the RF noise emanating from the converter. A noise model to study the EMI emission is presented and used in this paper. Theoretical analysis of the RF noise power spectrum is carried out in order to demonstrate the advantages of the RPWM technique over conventional PWM. Experimental results confirm the validity of the theoretical calculations and simulation results, and demonstrate the effectiveness of applying the RPWM technique in reducing the RF noise level.

Improvement of Electromagnetic Compatibility of Motor Drives Using Chaotic PWM

In this paper, a new chaotic pulse width modulation (PWM) scheme is proposed and implemented to reduce the conducted electromagnetic interference (EMI) in motor drives. The key is the use of logistic mapping to chaoize a frequency-modulated signal which then modulates the carrier frequency. Compared with the sinusoidal PWM and random PWM, the proposed scheme not only suppresses the peaky EMI, but also avoids the occurrence of low-order noises and mechanical resonance. Both simulation and experimental results are given to support the validity

Implementation of Variable-Delay Random PWM for Automotive Applications

This paper presents the implementation of variable-delay random pulsewidth modulation (VD-RPWM) for an automotive traction drive inverter. RPWM is desirable as a means of reducing electromagnetic emissions from the inverter and minimizing electromagnetic-compatibility filtering requirements. It can also serve in reducing acoustic noise generated by the drive. The algorithm is implemented on a power-PC-based microprocessor. Experimental results are presented to verify the operation of the algorithm and its compatibility with basic motor-control functions. Spectrum plots of the phase current and voltage demonstrate the effectiveness of the technique in mitigating electromagnetic interference. The effects on torque ripple and acoustic noise are also investigated

Reduced Conductive EMI in Switched-Mode DC–DC Power Converters Without EMI Filters: PWM Versus Randomized PWM

This paper addresses improved electromagnetic compatibility (EMC) in switched-mode power converters (SMPCs), without using electromagnetic interference (EMI) filters. A practical solution is proposed for minimizing conductive EMI in a pulsewidth modulated (PWM), and random PWM dc-dc power converters. A comparative investigation is performed into the use of different random modulation schemes (driven by the DSP-2 board with the TMS320C32) as against the normal PWM. The effectiveness of randomization on spreading those dominating frequencies that normally exist in constant frequency PWM schemes is evaluated by power spectral density (PSD) estimations in the low-frequency range. Some parasitical- and topology-based EMI sources in devices are presented and frequency analysis is shown by using the discrete Fourier transform (DFT). SPICE simulations are also used to verify practical solutions for eliminating negative EMI sources and achieving EMC improvements. Finally, levels of conductive EMI are estimated with DFT, and experimentally verified to comply with the CISPR 25 (or EN 55025) regulations. Moreover, it is clearly shown, that limited speed PWM driving of the power switches with appropriate snubber circuits guarantees reduced conductive EMI. When considering the price and high EMC, in the final solution the power converter is driven by the mu-controller PIC16F876 with limited numerical and peripheral capabilities, where only normal PWM and randomized PWM can be implemented