Pulse Width Modulation Switching Research Articles

Impact of close proximity pulse width modulation switching events on electric machine terminal voltages

AbstractElectric machines form an essential part of a wide range of modern systems. When speed control is required, the use of pulse width modulation‐based inverters is generally the solution of choice. It is also usual to connect the machine to the inverter using a cable. The combination of these three elements produces the potential for voltages which exceed the dc link voltage to occur at the machine terminals. Methods for predicting the terminal voltage exist; however, these methods assume that the pulses applied to the system can be considered as isolated, discrete events. The authors highlight an issue with this assumption. When a switching event occurs, it will cause a voltage disturbance in the unswitched phases of the system due to the mutual coupling between the phases. If a second switching event occurs within a short time of this event the resultant voltage will interact with the previous switching event resulting in a higher terminal voltage than would be the case for an isolated event. This effect can be problematic for insulation design if it is not considered. This issue is demonstrated, with the worst‐case scenarios identified and potential methods of reducing terminal voltage being proposed.

Generalized Pulse Width Modulation Switch Model for Converters Based on the Multistate Switching Cell in Discontinuous Conduction Mode.

This work introduces a generalized version of the pulse width modulation (PWM) switch model applied in the small-signal modeling of converters based on the multistate switching cell (MSSC) operating in discontinuous conduction mode (DCM). It consists of extending the concept formerly introduced by Vorperian for the representation of multiphase converters in DCM, yielding a circuit-based approach that does not rely on matrix manipulations unlike state-space averaging (SSA). The derived dc and ac models are valid for any number of switching states and any operating region defined in terms of the duty cycle, thus allowing for determining the voltage gain and distinct transfer functions. A thorough discussion of results is presented to demonstrate the applicability of the derived models to represent distinct configurations of the MSSC.

High-Speed Controller to Enhance Responsiveness and Stability of Dynamic Characteristics for DC–DC Converter

In general, the DC load is electrically sensitive to the input voltage and current compared to the AC load. As the demand for digital systems that require DC power increases rapidly, the importance of stable DC power supply methods is increasing. Various elements such as renewable energy and load are configured in the power grid that supplies DC, and they are connected in various forms and power patterns. These elements have different starting and operating characteristics, which can be disadvantageous to the design of controllers for power converters to maintain a stable bus voltage in the DC power grid. Therefore, in a DC power system, an energy storage system with active bi-directional power control technology that can minimize transient conditions, such as overshoot, which can occur when a load is connected or power accelerates rapidly, is significantly important. This paper proposes a novel power control method capable of compensating for the instability of the DC bus voltage owing to the transient state in the DC power supply system. This method minimizes overshoot and ensures fast responsiveness and system stability by calculating the flux linkage of an inductor in a bi-directional DC/DC converter and applying an excitation voltage without pulse-width modulation (PWM) switching. The performance and validity of the proposed transient high-speed controller (THSC) were verified through simulations and experiments.

Maximum power point tracking and space vector modulation control of quasi-z-source inverter for grid-connected photovoltaic systems

The quasi-Z-source inverter (qZSI) become one of the most promising power electronic converters for photovoltaic (PV) applications, due to its capability to perform a buck-boost conversion of the input voltage in a single stage. The control strategy based maximum power point tracking (MPPT) and proportional integral (PI) controller are well known in grid-connected with traditional configuration but not in qZSI. This paper presents a control strategy for qZSI grid-connected based on the MPPT algorithm and the linear control by PI controllers. This is complemented by the capability to efficiently transfer the harvested power to the grid, ensuring a unity power factor. The proposed control strategy effectively separates the control mechanisms for the direct current (DC) and alternating current (AC) sides by utilizing the two control variables, the shoot-through duty ratio and the modulation index. An adapted space vector modulation technique is then utilized to generate the switching pulse width modulation (PWM) signals, using these two control variables as inputs. The proposed approach was tested and validated under MATLAB/Simulink and PLECS software.

Accurate asymmetrical minor loops modeling with the modified arctangent hysteresis model

In the area of automotive propulsion, electric motors experience core losses due to the presence of higher harmonic frequencies, particularly those arising from pulse width modulation switching. Consequently, it is required to establish a practical model capable of characterizing the hysteresis loops in electrical steel when subjected to harmonic excitations. Nonetheless, existing dynamic models may be inappropriate for real-world applications due to their inherent complexity and their tendency to neglect the influence of minor loops arising from harmonics. In the present work, the minor and major hysteresis curves of non-oriented silicon steel sheets are measured under variable frequency excitation containing harmonic components. To reproduce the asymmetrical minor hysteresis loops, a modified arctangent model is employed. The evaluation of the accuracy of this hysteresis model is conducted by comparing the fitted results of static and dynamic hysteresis loops against experimental data, both with and without harmonic excitation.

Analysis of the Performance of a 5-Level Modular Multilevel Inverter for a Solar Grid-Connected System

The main purpose of a multilevel inverter is to combine numerous levels of dc voltage to create a nearly sinusoidal voltage. The synthesized output waveform has more stages as the number of levels rises, creating a staircase ripple which resembles the preferred waveform. As the number of voltage levels rises, the output wave's harmonic distortion diminishes and eventually approaches zero. In particular, the performance analysis of a five-level inverter with variable loads is highlighted in this paper. This topology has fewer devices than traditional multilevel inverters for the same five output levels, which makes it more affordable due to lesser driver circuits. The proposed modular five level topology is simulated using both high frequencies switching pulse width modulation and basic frequency switching modulation techniques. The output voltage, current waveform, and THD are examined and compared using Simulink to confirm the viability of the modular multilevel inverter topology.

Terminal Voltage and Common Mode Voltage Analysis for Various PV Inverter Topologies

The switching function method is critical for understanding the effect of different switching mechanisms or Pulse Width Modulation (PWM) designs on both terminal voltage and common mode voltage. The switching patterns of numerous five-level inverter topologies are determined using modified PWM in this study. The switching function technique is used in this study to investigate the terminal voltage of the PV array and the common mode voltage of the inverter. Notably, as compared to normal PWM approaches, five-level common mode voltage source inverters (CMLIs) need less carrier waves. The study gives thorough insights into the overall architecture of the examined converter, as well as terminal and common mode voltage expressions. When compared to normal PWM, any five-level CMLI requires less carrier waves. This document also details the converter’s overall structure, terminal and common mode voltage expressions, and switching patterns.

Skin Effect and Losses in Soft Magnetic Sheets: From Low Inductions to Magnetic Saturation

High frequencies are ubiquitous in present-day power applications: most electrical equipment, like rotating machines, are supplied by Pulse Width Modulation (PWM) switching inverters, often working at tens or hundreds of kilohertz. PWM is responsible of minor cycles along the major hysteresis loop of the magnetic core, lasting a few microseconds. Such minor loops can cause deep skin effect, even if the thinnest today available laminations (0.1 - 0.2 mm thick sheets) are used. Common mode currents in the megahertz range, flowing from the electrical machine windings to the machine chassis through capacitive effects, can engender strong electromagnetic disturbances and bearing damages. A correct prediction of high frequency phenomena is necessary, for example, for the accurate calculation of common mode filters, requiring a magnetic model of the laminated cores suited to high frequencies and low induction values and the ensuing dramatic skin effect. For power conversion applications, such as embedded planar transformers, the mandatory reduction of volume and cross-sectional area of the core, often made of high-permeability grain-oriented (HGO) sheets, imposes the increase of the conversion frequency from a few hundred hertz to several kilohertz and high peak induction values. The skin effect in this case is affected by the non-linear saturable magnetic response of the material and its treatment requires non-trivial experimental methods and modeling approaches. In this work, we discuss physically based modeling of magnetization process and energy loss in magnetic sheets at high frequencies. We focus first on the low induction regimes occurring in thin non-oriented (NO) Fe-Si laminations. We consider then the case of high inductions, as encountered in power conversion devices using NO, HGO, and Fe-Co alloys, where non-linear models, possibly validated by magneto-optical observations of the domain wall dynamics, are developed and implemented.

PWM harmonics reduction for dual-branch three-phase PMSMs using interleaving topology

High-frequency pulse width modulation (PWM) acoustic noise is generated by PWM switching harmonics in the dual-branch three-phase permanent magnet synchronous motor (PMSM) systems during the switching process of the drivers. Because of the special winding structure of the double branch motor, the sum of the current of the two branches reflects the high frequency vibration of the motor. This paper proposes a method using four voltage source inverters and coupled inductors with a special connection method to eliminate the carrier frequency as well as its twice, triple noise for dual-branch three-phase PMSMs. Carrier-phase-shift technique is used to change the direction of the current harmonics. Compared with the conventional method, four paralleled VSIs can be saved. The simulation results verify the effectiveness of the method.

Unified small‐signal model for DC‐DC converters based on the three‐state switching cell operating in discontinuous conduction mode

SummaryUnified small‐signal modeling approaches are of paramount importance for the design of controllers and closed‐loop control systems in power electronic converters. In this sense, this work proposes the small‐signal analysis of non‐isolated dc‐dc converters employing the three‐state switching cell (3SSC) in discontinuous conduction mode (DCM). The modeling technique relies on the very same principles of the pulse width modulation (PWM) switch while not involving matrix operations, but only basic concepts related to electric circuits. Considering that the waveforms associated with the terminals of the 3SSC in DCM have a common behavior in all basic dc‐dc converters, it is possible to derive the small‐signal models for both operating regions of the 3SSC, that is, non‐overlapping mode (NOM) and overlapping mode (OM). Thus, one can effectively demonstrate that the same circuit can represent both modes, even though the coefficients that describe the models are calculated from distinct equations. The theoretical claims are validated in the frequency and time domains while comparing the model with the converter. The obtained results evidence that the unified model can accurately represent converters based on the 3SSC in DCM.

Investigation of high gain DC/DC converter for solar PV applications

Integration of solar photovoltaic (PV) systems into a microgrid is accomplished with the help of a dual-diode, dual-capacitor, and single-switch DC-DC boost converter. At the output, a power of 400W transfer is achieved together with a voltage gain of 3.92. The converter may be operated in two primary forms, both of that are based on the ON/OFF switches. The benefits that may be noticed in practice from the hardware output are high reliability and decreased switching losses. The properties of the converter are determined via an open loop system that uses pulse width modulation (PWM) switching at 20 kHz. An examination of the step response is carried out. The validations of the proposed converter topology has been compared with the recent converter topologies. The performance of the converter has been evaluated in terms of voltage gain.

Small-Signal Model of the NPC + GCC Multilevel Transformerless Inverter in Single-Phase Photovoltaic Power Systems

Photovoltaic transformerless inverters are very efficient and economical options for solar-power generation. The absence of the isolation transformer improves the converters’ efficiency, but high-frequency voltage to ground can appear in the photovoltaic string poles. The high capacitance to ground of the photovoltaic generator leads to undesirable high-leakage currents. Using half-bridge topologies dramatically reduces the leakage to ground, and using a multilevel half-bridge inverters improves the output quality compared with classical inverters. The neutral point clamped + generation control circuit (NPC + GCC) topology is a multilevel single-phase transformerless inverter capable of tracking the maximum power point of two photovoltaic sources at the same time. This paper presents the control structure and the dynamic modeling of the NPC + GCC inverter. The pulse-width modulated (PWM) switch model in continuous conduction mode (CCM) was used to obtain the small-signal model of the two switching converters that make up the inverter. The resulting dynamic model was used to quantify the stability margins of both converters’ current and voltage loops.

Highly Efficient Three-Phase Bi-Directional SiC DC–AC Inverter for Electric Vehicle Flywheel Emulator

Flywheels are nowadays a solution for the dynamic charging of electric vehicles since they act as transient energy storage. The need for a top efficient reversible power converter for the flywheel system is crucial to assure high dynamic performance. The paper presents the design of a 50 kW highly efficient reversible three-phase DC–AC inverter involving the most recent silicon carbide metal oxide semiconductor field effect transistors, and its experimental validation on a home-made emulator. Highest efficiency in reversible mode, compactness, and thermal enhancement are the targeted objectives that have been achieved. The power converter prototype evaluated on an original pulse width modulation testing-bench is able to emulate the working of the flywheel system. High frequency pulse width modulation switching, speed cycle operating, and thermal losses are evaluated. In addition, an efficiency above 99% for the converter has been attained, enabling robust functioning of the flywheel system emulator to perform specific charging profiles for electric vehicles.

A Modified PWM Scheme to Improve the Power Quality of NPC Inverter Based Solar PV Fed Induction Motor Drive for Water Pumping

This paper proposes a modified modulating signal-based pulse width modulation (PWM) scheme for a neutral point clamped (NPC) inverter-based induction motor drive (IMD) for enhancing the efficiency of solar photovoltaic (PV) fed water-pumping systems. During the previous several decades, the use of sustainable source-based power generation systems has benefited water pumps in household life, irrigation-based activities, and industrial sectors, especially in areas where the electric grid is less available. A critical concern has long been the power quality, speed, and torque of an induction motor used in solar PV-powered water pumping. This paper focuses on the improvement of power performance by minimizing total harmonic distortions (THDs), switching losses and conduction losses, and torque ripples in the induction motor driving the PV-fed water pump by using a modified PWM scheme that generates symmetrical and balanced gate driving signals for the NPC inverter employed in the IMD. The IMD with the suggested PWM switching strategy has been tested in all feasible induction motor operating situations. To demonstrate the effectiveness of the suggested PWM scheme, a performance comparison of the proposed PWM scheme with conventional PWM schemes is performed, and also the IMD with the suggested PWM switching strategy is tested in all feasible induction motor operating situations using the MATLAB/Simulink platform.

An improved modulation method for modular multilevel converters based on particle swarm optimization

Modular multilevel converter (MMC) is the first topology choice for flexible DC transmission systems. This paper presents a particle swarm optimization (PSO) algorithm aided modulation method to calculate the improved selective harmonic elimination pulse width modulation (iSHE-PWM) switching angles with the aim of reducing the total harmonic distortion (THD) and output voltage error of MMC. The SHE-PWM has more controllable variables compared with the staircase modulation so that it can be used to improve the output current waveform quality. This method retains the advantages of easy to control and low frequency from the staircase modulation. But amplitude of its high-order harmonic is high and this paper improves it. Firstly the mathematical model of MMC is set up and corresponding expressions of THD and voltage error are given. The joint function of THD and voltage error is considered as the fitness function. The PSO algorithm was used to minimize the joint function for solving the optimal switching angles. Finally the proposed method is verified through simulation results showing its potential to successfully solve the problem of difficulty in obtaining the iSHE-PWM switching angles while minimizing the THD and output voltage error of the MMC.

Redesign of common dc-link capacitors for dual-three phase machine drive system based on PWM sequence reorder

The dual three phase machine drive system with the common dc-link capacitors has been widely used in many industrial applications due to the advantages such as small stallion volume, reduced cost and flexibility. The large ripple current caused by the pulse width modulation (PWM) switching has to be reduced by choosing the large capacitor, while the bulky dc-link capacitor is still the main drawback for the improvement of power density. Therefore, this paper proposes a common dc-link capacitors reduced design method for dual three phase machine drives system with the proposed PWM sequence reorder aiming at the cost, volume and lifetime. First, the derived dc-link current expression are given according to the phase current and average current. Secondly, the PWM sequence reorder method on two inverters is used to reduce the dc-link capacitors switching frequency harmonics. Finally, the design principle of the new capacitors is proposed considering the cost, volume, lifetime. The results show that the lifetime of the capacitors with the proposed reorder PWM method can be extended significantly. The experiment results are given to verify the effectively of the proposed method. The results could provide a good guideline for the dual-three phase drive system design with low cost and high reliability.

Predictive Current Control for Six-Phase PMSM Motor With Multi-Step Synthesis Based Virtual Vectors

The concept of virtual vector has been a standard practice for the multiphase machine drives. However, simply adopting the fixed or adjustable duty-ratio virtual vectors fails to mitigate the current tracking error in the fundamental plane satisfactorily. To that end, this paper proposes a new model predictive control (MPC) method for a six-phase permanent magnet synchronous motor (PMSM) using multi-step synthesis based virtual vectors to regulate two planes simultaneously. The virtual vectors are formed through a two-step synthesis process. First, two groups of real vectors are used to synthesize 12 elementary virtual vectors to nullify the harmonic currents in the secondary plane. Subsequently, the 12 elementary virtual vectors are employed to further form other 60 composite virtual vectors to enhance the current tracking in the fundamental plane. For the sake of easy practical implementation, the pulse width modulation (PWM) switching sequence of all virtual vectors are analyzed to ensure that they present standard PWM switching sequence. The proposed multi-step synthesized composite virtual vectors can suppress the harmonic currents in the secondary plane and reduce the current tracking error in the primary plane simultaneously. Experimentations are conducted to verify the effectiveness of the proposed method.

Dual Inverter-Fed Open Winding IPMSM Drive System for High-Power Premium Class EV

Recently, the class of electric vehicles (EVs) with high-power (250 kW) motor drive systems and high energy/high voltage (100 kWh/800 V) batteries has been the prominent focus of various automotive makers. Considering the drive system efficiency, motor acoustic noise, system fail-safe features, and cost, the dual inverter with a dual battery and an open-winding interior permanent magnet motor is considered to be a highly promising drive system configuration for premium class EVs. Therefore, considering the high drive system efficiency and low motor acoustic noise, the authors propose selecting different pulse width modulation (PWM) switching pattern modes in the frequent vehicle operating area based on the vehicle driving modes for the system configuration of premium class EVs. The authors performed suitable simulations and experiments with a 65 kW motor drive system. The experimental results are validated to verify the effectiveness of selecting different PWM switching modes based on the vehicle driving pattern.

Simple Discontinuous Pulse-Width Modulation Scheme for the Loss Reduction of a Dual Inverter Fed an Open-End Winding Induction Motor

This paper presents a simple discontinuous pulse width modulation (DPWM) switching scheme to reduce the switching loss of a single DC-link dual two-level inverter fed an open-end winding (OW) induction motor (IM). The dual inverter system is attractive in many applications due to higher DC-link voltage utilization. Additionally, the OW motor has the potential fault-tolerant capability. However, the use of the dual inverter results in reduced system efficiency due to increased power losses in the inverter. Moreover, an OW motor inherently suffers from a zero-sequence current (ZSC) issue because the open neutral point of the stator windings provides the ZSC path. The ZSC causes negative effects in the system, such as an additional power loss and total harmonic distortion (THD). Thus, this work proposes an optimal DPWM scheme to reduce the inverter loss while suppressing the ZSC. Additionally, this work proposes a strategy to make the average power loss of each inverter equal. The performance of the proposed method is discussed in terms of switching power loss reduction and ZSC suppression. Simulation and experimental results are provided to verify the effectiveness of the proposed DPWM scheme.

New Acoustic Noise Reduction Method for Signal-Injection-Based IPMSM Sensorless Drive

Many signal-injection-based sensorless methods have been developed to drive the interior permanent magnet synchronous motor without a position sensor at low speed. By these methods, rotor position can be estimated by measuring the output current ripple of inverter caused by the injected signal. However, this ripple is able to generate the undesirable acoustic noise, which decreases the usefulness and practicality of method while preventing the increase of signal-to-noise ratio. This article proposes the new acoustic noise reduction method by injecting signals to both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> - and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axes, respectively, to reduce torque ripple components for position estimation. In particular, the frequency of injected signals is matched with the pulsewidth modulation switching frequency to maximize the bandwidth for position estimation. By the proposed method, the sensorless drive with high performance can be achieved while suppressing the acoustic noise caused by injecting signals. The compensation for signal distortion is first studied by simulation with the analysis of nonlinear properties of high-frequency signal. Then, the practical effectiveness of the proposed method is verified by experimental results.