Pulse Width Modulation Waveform Research Articles

Single Phase Grid-tie Inverter Design Using PLL and MPPTTechniques

This paper focuses on designing and implementing a grid-tie inverter, which can convert DC voltage from the PV systems into an AC voltage using pulse width modulation technique. The proposed inverter is synchronized with the local grid to provide an alternate solution for the energy generation. To obtain the maximum power from the inverter maximum power point tracking technology is used. Using MPPT, approximately 95% power efficiency was achieved. Boost converter is designed to boost the voltage from solar panels to 240V. Phase locked loop circuit is utilized to synchronize the output frequency of the inverter with that of the local utility grid. Phase locked loop circuit uses phase detector to detect the phase difference between the reference (utility grid) frequency and the quiescent (required) frequency set in Voltage Controlled Oscillator. This quiescent frequency is converted to match with the reference frequency. This converted or synchronized frequency is then used as a reference for pulse width modulation controller to generate Pulse Width Modulation waveform. Using PLL, phase or frequency matching between utility grid’s electricity and inverter’s electricity was achieved in just 0.6 seconds. In the end, filtering system is designed using LMS filter and KALMAN filter to remove the noise from inverter output. A total of -22.63 dB total harmonic distortion was achieved using Kalman filter and were proved to be better than LMS filter. The simulation results provided in this report show the efficacy of the proposed grid-tie inverter.

Analytical Evaluation and Reduction of Torque Harmonics in Induction Motor Drives Operated at Low Pulse Numbers

Induction motor drives operated with a low ratio of the switching frequency to the fundamental frequency (i.e., pulse number) are prone to have high magnitudes of low-order torque harmonics. This paper proposes a method to analytically evaluate the harmonic torque spectrum based on the pulsewidth-modulated voltage waveforms for low pulse number operation. The predicted torque harmonic spectra for different pulsewidth-modulated waveforms are validated through simulations and experiments. This paper also reports optimal switching angles to minimize the total rms value of torque harmonics of order 6, 12, 18 $,\dots,$ $6(N-1)$ , considering the number of switching angles per quarter ( $N$ ) to be 4 and 5. Compared to sine triangle pulsewidth modulation and selective harmonic elimination pulsewidth modulation with the same pulse number, the proposed optimal switching angles significantly reduce the total rms value of all harmonic torques of order lower than $6N$ . Extensive simulation and experimental results on a 3.7-kW induction motor drive are presented to demonstrate the superior performance of the proposed optimal pulsewidth modulation.

Sensorless Speed Control of Five-Phase PMSM Drives in Case of a Single-Phase Open-Circuit Fault

This paper introduces a new method to track saliency in a five-phase permanent magnet synchronous motor in case of a single-phase open-circuit fault. The proposed method depends on measuring the dynamic current response of the motor line currents due to the insulated-gate bipolar transistor switching actions. In case of a single-phase open-circuit fault, a fault-tolerant control strategy to control the remaining healthy currents results in minor system performance degradation. The new strategy that is proposed in this paper to track the saliency includes software modifications only to the saliency tracking algorithm used in healthy mode in order to make it applicable in the cases of a single-phase open-circuit fault. It uses the fundamental pulse width modulation waveform obtained using a symmetric multi-phase space vector pulse width modulation only. Simulation results are provided to verify the effectiveness of the proposed design over a wide speed range under different load conditions.

Low‐power pulse width modulation (PWM) for high‐frequency DC–DC converters

A low-power pulse width modulation (PWM) control circuit for high-frequency switching direct current (DC)–DC converters based on a one-shot circuit is proposed. The proposed PWM control circuit eliminates the use of a high-power comparator and ramp generator that is conventionally used to generate the PWM waveform. The design is validated through simulation in a 0.13-μm process. The proposed circuit operating at 20 MHz demonstrates greater than 20× reduction in power consumption compared with the conventional PWM circuit over a duty-cycle range of 10–90%.

Partial discharge characteristics within motor insulatioi exposed to multi-level PWM waveforms

The frequent use of variable speed drives fed by pulse width modulated (PWM) inverters allow for a more efficient utilization of electric energy. The drawback is however that the stress imposed on motor winding insulation increases and partial discharges (PDs) may appear under such conditions, being considered the major contributor to the reduction of the insulation life time. This paper presents what influence the choice of PWM level and rise time has on the PD characteristics for two different motor insulations as well as introducing suitable high voltage generation test-set ups for these kinds of measurements. The two different test objects were twisted pair and a pig tail motor insulation test objects, the latter aimed for higher voltage levels. These test objects were fed from either two-, three-, four- or five level inverters of similar type, as often used in actual applications. Additionally a six level inverter was used for verification purposes. The twisted pair test objects were insulated by a polyamide-imide enamel, whereas the motor pig tail insulation objects were mica-epoxy based. To compare the performances, measurements of the PD characteristics are reported and observations concentrate on the importance of the voltage rise time, on the size of the voltage step in relation to the extinction voltages (PDEV). Specifically, the total number of PDs and their amplitude per cycle is obtained. The experimental results show that the total summed PD magnitude (exposure) drops considerably when applying the three- or higher level inverters. However the maximum PD magnitude is less dependent, which indicates that a change to a high level inverter alone may still not be sufficient condition for increasing motor insulation system life. In conclusion a combination of the PDEV level, rise time and PWM level must all together be considered in this complex design process.

Accuracy of time domain extension formulae of core losses in non‐oriented electrical steel laminations under non‐sinusoidal excitation

This study presents a comparative study on the accuracy of three iron loss prediction models. The models are based on the decomposition of core or iron losses into the hysteresis and the eddy current loss components. The time domain extensions of two frequency domain models have been used to predict the iron losses due to a number of non-sinusoidal waveforms with and without the presence of minor loops. A third model, by Boglietti, that has been proposed recently to predict core losses for non-sinusoidal and pulse-width modulated (PWM) waveforms has also been studied. The unknown coefficients of each model have been determined by data fitting iron losses obtained from Epstein frame experiments for induction levels and fundamental frequencies up to 1.6 T and 2 kHz, respectively. Core losses due to PWM waveforms have been measured at various fundamental and switching frequencies in unipolar and bipolar modes. The experimentally measured iron losses have been compared to those predicted using the three models and the accuracy and applicability of each model have been discussed.

A New SVM Method to Reduce Common-Mode Voltage of Five-leg Indirect Matrix Converter Fed Open-End Load Drives

This paper proposes a cost-effective topology to drive a three-phase open-end load based on a five-leg indirect matrix converter (IMC) and a space vector modulation (SVM) method. By sharing an inverter leg with two load terminals, the proposed topology can reduce the number of power switches when compared to topologies based on a direct matrix converter or a six-leg IMC. The new SVM method uses only the active vectors that do not produce common-mode voltage (CMV), which results in zero CMV across the load phase and significantly reduces the peak value of the CMV at the load terminal. Furthermore, the proposed drive system can increase the voltage transfer ratio up to 1.5 and provide a superior performance in terms of an output line-to-line voltage with a three-level pulse-width modulation waveform. Simulation and experimental results are given to verify the effectiveness of the proposed topology and the new SVM method.

Investigations on Optimal Pulse Width Modulation to Minimize Total Harmonic Distortion in the Line Current

High-power and high-speed motor drives have only a few switching transitions in each line cycle. Pulse width modulation (PWM) waveforms with positive voltage transition at the positive zero crossing of the fundamental voltage (type-A) are generally considered for PWM waveform with an even number of switching angles per quarter, whereas waveforms with negative voltage transition at the positive zero crossing (type-B) are considered for an odd number of switching angles per quarter. Optimal switching angles to minimize the total harmonic distortion (THD) in motor current are reported for both type-A and type-B waveforms of pulse numbers ( $P$ ) of 5, 7, 9, and 11. Based on simulation and experimental studies on a $3.7$ kW induction motor (IM) drive, optimal type-A and type-B PWM methods are shown to be better than each other in different modulation ranges for each pulse number. The space vector based analysis of optimal type-A and type-B waveforms brings out the optimal vector sequence at any modulation index for a given $P$ . Findings of the space vector based analysis lead to a new approach for determining optimal switching angles with much reduced computational effort. Compared to sine-triangle PWM, deployment of optimal vector sequences in an IM drive, having a maximum switching frequency of 250 Hz, leads to significant reduction in both THD of line current as well as motor losses over a wide range of speeds and load conditions.

Theoretical harmonic analysis of cascaded H‐bridge inverter under hybrid pulse width multilevel modulation

This study investigates the analytical approach for determining the spectral components of a hybrid pulse width modulation (HPWM) strategy for cascaded H-bridge (CHB) multilevel inverters. By decomposing the HPWM voltage into a staircase waveform and a non-sinusoidal pulse width modulation waveform and applying the one-dimensional Fourier series as well as double Fourier series methods, the closed-form solution for arbitrary level HPWM voltage is derived. Based on the derived solution, analysis of HPWM output with a changed modulation index is also performed, with good stability and control dynamic demonstrated. The spectral analytical expression is verified extensively by comparison of theoretical calculation results with those of the simulation and laboratory experiment, which coincide with each other very well. Furthermore, a brief switch function rotation balancing method for HPWM-based CHB inverter is utilised, and is also validated by experimental results.

PWM Strategy With Minimum Harmonic Distortion for Dual Three-Phase Permanent-Magnet Synchronous Motor Drives Operating in the Overmodulation Region

This study presents a novel overmodulation strategy for a six-phase voltage source inverter (VSI)-fed dual three-phase permanent-magnet synchronous motor. The proposed strategy can achieve minimum harmonic injection in the overmodulation region. Four-vector space vector pulse width modulation (SVPWM) renders mathematic foundations for this given method. However, the classical four-vector SVPWM used in six-phase VSI has asymmetrical pulse width modulation waveform, which makes it difficult for hardware implementation. In this paper, the modulation algorithms in both linear and overmodulation regions have been unified and implemented with the double zero-sequence injection PWM strategy. This strategy is able to overcome the inherent shortcomings of the four-vector SVPWM, and it achieves smooth transitions from linear to overmodulation region. Simulation analysis and experimental results demonstrate the effectiveness and feasibility of the proposed strategy.

Reducing the stroboscopic effects of LED luminaires with pulse width modulation control

Pulse width modulation for dimming the light output of LEDs has become common. When pulse width modulation is used at low frequencies unwanted visual artefacts including flicker perception and stroboscopic effects may occur. These artefacts need to be avoided or at least reduced to a minimum in order to obtain high user acceptance. In this paper, an optimized phase-shifted pulse width modulation method is described, implemented and validated in a visual experiment. The method is intended to minimize the stroboscopic effect on a reference surface by first optimizing the LED units of a single LED luminaire and then co-optimizing several of these luminaires. The optimized pulse width modulation waveforms are then compared to standard pulse width modulation dimming methods. In the visual experiment, 13 subjects rated the extent of the stroboscopic effect of standard and optimized waveforms in a white painted experimental room. The results indicate that the optimized waveforms are indistinguishable from constant light.

One-Dimensional Spectral Analysis of Complex PWM Waveforms Using Superposition

This paper takes a new look at the mechanisms underlying the double-edge pulse-width modulation (PWM) process. It presents a novel way of deriving equations for the spectrum of double-edge PWM using basic mathematical techniques. In the process the underlying nonlinearities that generate the PWM sidebands are identified. Unlike the classical double Fourier series approach, the proposed method of deriving the PWM spectrum does not require the construction of the so-called unit cell. The interaction between this new model of the pulse-width modulator and the regular sampling process is studied, and generalized equations for the Fourier transforms of regularly sampled PWM waveforms are derived. A general solution to the important question of what happens to the PWM spectrum when the PWM reference consists of a summation of signals is presented. It is shown that the addition of reference signals in the time domain results in a double convolution of the PWM sidebands in the frequency domain. As an application of this result, it is shown how new analytic equations for the harmonics of third-harmonic injection PWM and space vector modulation can easily be derived. Finally, the new theoretical results are benchmarked against results from the well-established double Fourier series method.

Analysis on Core Loss of Brushless DC Motor Considering Pulse Width Modulation of Inverter

In this paper, characteristics of blushless direct current (BLDC) motor including core loss are analyzed considering pulse width modulation (PWM) of inverter. Input voltage of BLDC motor due to PWM is calculated considering duty ratio and carrier frequency of inverter in order to control torque or speed of BLDC motor. For the calculation of core loss, the input current with harmonics due to PWM voltage is calculated by using equivalent circuit model of BLDC motor according to switching pattern and carrier frequency. Next, core loss is analyzed by inputting the currents as a source of BLDC motor for FEM. Characteristics including core loss are compared with ones without PWM waveform according to reference speed.

Analysis of Losses and Thermal in Induction Motors

This paper presents an investigation into the losses and thermal characteristics of induction motors operated from pulse width-modulated (PWM) voltage supply in comparison to that operated from sinusoidal voltage supply. It was concluded that due to the abundant harmonics in the PWM waveforms, significant losses are induced in the motor by the inverter supply. The temperature ascends correspondingly. Experiments were conducted with no load and with load conditions. The losses and thermal characteristics were calculated using finite element analysis (FEA) and validated by the experiments.

A New Approach to Theoretical Analysis of Harmonic Content of PWM Waveforms of Single- and Multiple-Frequency Modulators

This paper presents a new approach to the spectral analysis of a carrier-based pulse width modulation (PWM) signal with continuous modulating function, and natural or regular sampling. The method is based on 1-D Fourier series and an expansion of the implicitly defined functions of the pulse edge angles of a PWM signal to power series. Expressions for the individual harmonics are given in closed form, allowing direct the calculation of the harmonic components, and can readily be implemented by a computer software package, such as MATLAB. Similarly, analytical expressions for the edges of the naturally sampled output PWM signal are determined. Cases of single- and multiple-modulation wave are analyzed in detail. As modulation of the half-bridge, single-phase inverter and the resulting spectrum constitute the basic building block from which the spectrum content of modulated multiphase, multilevel converters can readily be discerned, the spectrum of harmonics of the output PWM signal of an ideal half-bridge, single-phase inverter is analyzed. The method is evaluated and validated by comparing the spectrum obtained using the present method with those obtained by applying double Fourier series or by direct numerical procedure.

Grid Interfacing of Multimegawatt Photovoltaic Inverters

This paper investigates the suitability of selective harmonic elimination (SHE) for low-loss multimegawatt grid-connected photovoltaic (PV) inverters. The proposed system is able to meet utilities regulations, IEEE and IEC standards. In an attempt to substantiate the potential superiority of SHE over carrier-based or space-vector pulsewidth modulation (PWM), this paper demonstrates that SHE may allow grid-connected PV inverters to be controlled using a switching frequency of less than 1 kHz, while the inverter is still able to provide necessary operation features such as independent control of active and reactive powers and operation control simplicity. For system validation, experimental results with SHE are compared to the case when the inverter is controlled using third-harmonic injection PWM, with a 2-kHz switching frequency. Furthermore, the paper proposes a new implementation technique for SHE that utilizes the third harmonics to spread the switching angles over 90° instead of being located in a narrow range as generated when using conventional techniques, along with increases in modulation index. The advantages of the proposed technique include simplicity in implementation and flexibility in PWM waveforms. Simulation and experimentation demonstrate agreement, which validates the practicability of the proposed system.

Design of an integrated single-input dual-output 3-switch buck converter based on sliding mode control

This paper presents the design, implementation, and testing of a proof-of-concept monolithic single-input dual-output buck converter. The proposed architecture implements an analog hysteretic controller. This avoids the use of extra circuitry to generate a dedicated reference carrier signal to create the pulse-width modulated waveform, thus saving area, and reducing static power consumption. Furthermore, the proposed topology implements only three switches (instead of four switches in conventional solutions), and can save additional silicon area with proper design of the power switches in the voltage regulator. The IC prototype was fabricated in standard 0.5 μm CMOS technology (VTHN = 0.78 V, VTHP = ?0.93 V), operates with a single voltage supply of 1.8 V, generates 1.2 and 0.9 V output-voltage levels, and supplies a maximum total current of 200 mA (100 mA provided by each output), reaching up to 88 % efficiency.

자동 조립 및 공급을 위한 BLDC 서보 전동기 제어시스템 설계

본 논문은 DSP 제어기와 IGBT 구동기를 이용하는 조립과 공급의 자동처리를 위한 BLDC 서보 모터 제어시스템 설계를 제안한다. 조립, 공급 자동처리 시스템은 다양한 동작을 위해 서보모터의 토크, 속도, 위치 제어를 필요로한다. 본 논문은 이러한 서보제어를 벡터제어와 공간벡터 PWM 기법을 이용하여 구현한다. 제어기의 CPU 로서 PWM 파형발생기, A/D 컨버터, SPI 통신 포트 및 많은 입/출력 포트를 갖는 TMS320F240 DSP를 채택하였다. 이 제어시스템은 메인 호스트 PC 가 위로부터의 명령을 전달하고 끝단의 서보제어기의 상태들을 모니터링하는 세 개의 부 DSP시스템을 관리하는 3레벨의 계층적 구조로 이루어져 있다. 각 부 DSP 시스템은 DSP와 IPM을 사용하여 BLDC 서보모터를 제어하는 8개의 BLDC 서보모터제어부를 운영한다. 호스트 시스템과 중간의 DSP는 RS-422을 이용하여 통신하며, 주프로세서와 제어기는 SPI 포트를 이용하여 통신한다. This paper presents a design of a BLDC servo motor control system for the auto process of assembly and supply using DSP(Digital Signal Processor) controller and IGBT driver. The assembly and supply auto processing system needs torque, speed, position control of servo motor for variable action. This paper implements those servo control with vector control and space vector PWM(Pulse Width Modulation) technique. As CPU of controller, TMS320F240 DSP was adopted because it has PWM waveform generator, A/D converter, SPI(Serial Peripheral Interface) port and many input/output port etc. This control system consists of 3-level hierarchy structure that main host PC manages three sub DSP system which transfer downward command and are monitoring the states of end servo controllers. Each sub DSP system operates eight BLDC servo controllers which control BLDC motor using DSP and IPM. Between host system and sub DSP communicate with RS-422, between main processor and controller communicate with SPI port.

Understanding the PWM Nonlinearity: Single-Sided Modulation

This paper provides a new look at the mechanisms underlying pulse width modulation (PWM). A simple approach to analyze the behavior of a single-sided pulse width modulator is presented. By using elementary methods, the pulse-width-modulated waveform is written as the sum of two sawtooth functions and the original modulating waveform. Simply applying the well-known Fourier series expansion of the sawtooth function, an equivalent model of the pulse width modulator, which shows that it is in essence a sequence of phase modulators, is derived. This model provides a clear understanding of the nonlinearities involved in the PWM process. It is shown how the superposition of modulating waveforms in the time-domain translates into the convolution of the sidebands in the frequency domain. Finally, the interaction of the pulse width modulator and a sample-and-hold register is studied and a general expression for the Fourier transform of a regular-sampled PWM waveform is derived. The analysis applies to periodic as well as aperiodic modulating waveforms.

The Sampling Theorem With Constant Amplitude Variable Width Pulses

This paper proves a novel sampling theorem with constant amplitude and variable width pulses. The theorem states that any bandlimited baseband signal within ±0.637 can be represented by a pulsewidth modulation (PWM) waveform with unit amplitude. The number of pulses in the waveform is equal to the number of Nyquist samples and the peak constraint is independent of whether the waveform is two-level or three-level. The proof of the sampling theorem uses a simple iterative technique that is guaranteed to converge to the exact PWM representation whenever it exists. The paper goes on to develop a practical matrix based iterative technique to generate the PWM waveform that is guaranteed to converge exponentially. The peak constraint in the theorem is only a sufficient condition. In fact, many signals with higher peaks, e.g., lower than Nyquist frequency sinusoids, can be accurately represented by a PWM waveform.