Discontinuous PWM Strategies Research Articles

Discontinuous Pulse Width Modulation Strategy for Single-phase Five-level T-type NPC Inverter considering Symmetric Thermal Loadings of Power Devices

Discontinuous Pulse Width Modulation Strategy for Single-phase Five-level T-type NPC Inverter considering Symmetric Thermal Loadings of Power Devices

Generalized discontinuous PWM strategy for Z-source inverters with switch losses optimization

Generalized discontinuous PWM strategy for Z-source inverters with switch losses optimization

Novel Space-Vector PWM Schemes for Enhancing Efficiency and Decoupled Control in Quasi-Z-Source Inverters

This paper investigates the development of pulse width modulation (PWM) schemes for three-phase quasi-Z-source inverters (qZSIs). These inverters are notable for their voltage boost capability, built-in short-circuit protection, and continuous input current, making them suitable for low-voltage-fed applications like photovoltaic or fuel cell-based systems. Despite their advantages, qZSIs confront challenges such as increased control complexity and a larger number of passive components compared to traditional voltage source inverters (VSIs). In addition, most existing PWM schemes for qZSIs lack the capability for independent control of the amplitude modulation index and duty cycle, which is essential in closed-loop applications. This study introduces innovative space-vector PWM (SVPWM) schemes, addressing issues of independent control, synchronization, and unintentional short-circuiting in qZSIs. It evaluates several established continuous and discontinuous PWM schemes, and proposes two novel decoupled SVPWM-based schemes that integrate dead time and in which the shoot-through occurrence is synchronized with the beginning of the zero switching state. These novel schemes are designed to reduce switching losses and improve qZSI controllability. Experimental validation is conducted using a custom-developed electronic circuit board that enables the implementation of a range of PWM schemes, including the newly proposed ones. The obtained results indicate that the proposed PWM schemes can offer up to 6.8% greater efficiency and up to 7.5% reduced voltage stress compared to the closest competing PWM scheme from the literature. In addition, they contribute to reducing the electromagnetic interference and thermal stress of the related semiconductor switches.

Discontinuous PWM Strategy for Reliability and Efficiency Improvements of Single-Phase Five-Level T-Type Inverter

Reliability and efficiency improvements of PV inverters have a high potential to decrease the cost of PV energy. Discontinuous PWM is an effective method to improve both the efficiency and reliability of the power devices of the single-phase five-level T-type NPC inverter. However, applying DPWM gives a negative effect on the lifetime of the DC-link capacitors and thus reduces the reliability of the inverter from the system-level reliability point of view. This paper proposes the DPWM strategy to improve the lifetime of the DC-link capacitor compared with the conventional DPWM method so that both the reliability and efficiency of the single-phase five-level T-type NPC inverter are improved. Through the proposed strategy, the lifetime of the DC-link capacitor is improved, but its negative effects on the efficiency of the inverter and the lifetime of the power devices are negligible. Therefore, the advantages of applying DPWM can be sustained. Simulation and experimental results verify the feasibility and effectiveness of the proposed DPWM strategy.

Optimal Decoupled Discontinuous Modulation for StatComs Based on the Cascaded H-Bridge Converter

Conventional discontinuous pulse width modulation (DPWM) strategies for cascaded H-bridge static compensators suffer from poor inter-phase capacitor voltage balance control during unbalanced grid voltage conditions. Specifically, the logic-based algorithm that calculates the zero-sequence voltage (ZSV) for discontinuous operation interacts with the closed-loop capacitor voltage control. This paper proposes an optimal DPWM strategy based on a finite-set optimization that chooses the best ZSV candidate that minimizes the control interactions while clamping a converter voltage. Furthermore, the effect of the different ZSV candidates on the switching loss is also considered within the optimization. Extensive experimental study is provided to demonstrate the effectiveness of the proposed approach.

Development of Various Types of Independent Phase Based Pulsewidth Modulation Techniques for Three-Phase Voltage Source Inverters

Discontinuous pulse-width-modulation (DPWM) methods have been extensively used in the industrial area to reduce overall losses, which decreases the corresponding thermal stress on the power switches of converters. However, local thermal overload can arise due to different aging conditions of semiconductor devices or failure in the cooling system. This leads to reduced reliability of the converter system due to the low expected lifespan of the most aged switches or phase legs. In this paper, the modified DPWM strategies for independent control of per-phase switching loss are introduced to deal with this matter. The proposed per-phase DPWM techniques are generated by modifying the conventional three-phase DPWM methods for reducing the switching loss in a specific leg, whereas the output performance is not degraded. This paper reports on output performance, including output current total harmonic distortion (THD) and power loss of switching devices, analysis for the various modified DPWM strategies for independent control of per-phase switching loss, which is applicable in 2-level 3-phase voltage source inverters (2L3P VSIs). The results are compared to the corresponding continuous PWM technique to verify and analyze the effectiveness and accuracy of the modified DPWM strategies for independent control of per-phase switching loss.

Discontinuous PWM Strategy with Frequency Modulation for Vibration Reduction in Asynchronous Machines

The aim of this paper is to present our research into the reduction of vibrations in induction motors. The use of power inverters results in the generation of electrical harmonics, which increase the level of the mechanical vibrations of electrical machines. To reduce these harmonics, we present a discontinuous pulse-width modulation (PWM) control strategy based on carrier-wave modulation applied to multilevel inverters. Using the proposed modulation technique, the amplitude of the electrical harmonics is reduced, as compared to other conventional techniques. These current harmonics produce the MMF (magnetomotive force) harmonics in the air gap, which are one of the main sources of vibrations. The control strategy makes it possible to vary the electrical spectrum at the output of a multilevel inverter by modifying a control parameter of the carrier wave in the PWM, thus avoiding the natural frequencies of mechanical resonance. The proposed technique also has the feature of attenuating the total harmonics distortion of the voltage of the multilevel inverters, as well as the achievement of a higher RMS value of the output voltage for the same DC level. Laboratory results for an induction motor with different modulation strategies, applied in a multilevel inverter and compared to the strategy presented, are attached.

Lifetime Extension Method for Three-Phase Voltage Source Converters Using Discontinuous PWM Scheme with Hybrid Offset Voltage

This paper proposes a lifespan extension technique for three-phase voltage inverters using hybrid offset voltage. The proposed method lengthens the inverter lifetime by independently adjusting the switching frequency of the three phases in accordance with the aging degree. To reduce the switching operation of the phase with the shortest lifetime, the proposed technique injects the offset voltage for generalized discontinuous pulse-width modulation PWM (GDPWM) into the reference voltage in the region where the switching operation of the shortest lifespan phase can be stopped. When the switching operation does not need to be stopped, the offset voltage for space vector PWM (SVPWM) is injected into the reference voltage for high inverter load current quality. An offset voltage that varies according to the need to stop the switching operation is the proposed hybrid offset voltage. Using the proposed hybrid offset voltage, the switching frequencies of the three phases are independently controllable. In addition, since only the switching operation of the phase having the shortest lifespan is reduced, the load current quality in accordance with the switching operation reduction is good compared to the conventional method to simultaneously diminish all phase switching frequencies. The proposed method significantly increases the reliability of the three-phase voltage inverter, where the thermal stress of the phase having the shortest lifespan is decreased up to 55%, whereas the inverter lifetime can be increased by 10 times. The proposed technique was verified by simulations and experiments.

Experimental Investigation of Decoupled Discontinuous PWM Strategies in Open-End Winding Induction Motor Supplied by a Common DC-Link

Currently open-end winding induction motors fed by a dual inverter (OEWIM-DI) present an innovative approach to enhance the performance of modern electric drive systems; such as electrical vehicles and electric aircraft applications. However, the dual inverter topology requires a proper switching control strategy to enable the OEWIM drive to fully achieve its performance. This work aims to investigate experimentally the impact of different Decoupled Discontinuous Pulse Width Modulation (DDPWM) control strategies on the performance of the OEWIM-DI supplied by a common DC-link. The criteria performance adopted in this study are: (i) the Total Harmonic Distortion (THD) of the current and voltage, (ii) the Zero Sequence Voltage (ZSV), (iii) the Common Mode Voltage (CMV), and (iv) the dual inverters losses. The various DDPWM control schemes for the 1.5 kW OEWIM-DI motor drive are implemented on a dSPACE 1104 board and the results are compared with the popular and widely used Space-Vector PWM (SVPWM) strategy. From the results, it can be concluded that the optimised DDPWM technique gives the best performance. This technique has reduced the CMV by one level and reduce the losses by 50% while having the same THD and ZSV obtained with the SVPWM technique.

Reliability-Oriented Optimal DPWM Strategy for Single-Phase Five-Level T-Type Inverter in PV Systems

Many efforts have been devoted to improving the reliability of PV inverters with a focus on reliability-critical components such as power devices and capacitors. Discontinuous pulsewidth modulation (DPWM) methods are representative of improving the reliability of power devices by decreasing their thermal loadings. However, although the DPWM method affects the ripple current of the DC-link capacitor, prior-art research is only focusing on the power devices. There is a lack of study on the effect of applying the DPWM method on the reliability of the DC-link capacitor. It may have a negative effect on the reliability of the DC-link capacitor and thus affects the reliability of overall PV inverters. In this article, the influence of the DPWM method with different clamping periods on the reliability of power devices and DC-link capacitors of the single-phase five-level T-type inverter is investigated, where a 7-kW PV system and annual mission profile of PV system are considered as a case study. Then, a reliability-oriented optimal DPWM strategy is presented for the target lifetime of the T-type inverter by considering system-level reliability, including the lifetimes of both power devices and DC-link capacitors.

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.

A Hybrid Discontinuous PWM Strategy for Current Ripple and Neutral-Point Fluctuation Reduction of Parallel Vienna Rectifier

Generally, discontinuous pulsewidth modulation (DPWM) strategy used in single Vienna rectifier will result in large current ripple and neutral-point fluctuation. When applied in interleaved rectifier, the issue of neutral-point voltage still exists. Besides, the input current around zero-crossing point is distorted due to the characteristics of unidirectional topology. Hence, a novel hybrid DPWM (H-DPWM) strategy for parallel Vienna rectifier is proposed in this article to reduce the distortion, current ripple, and neutral-point fluctuation. In this article, the characteristics of current ripple and neutral-point fluctuation with traditional DPWM (T-DPWM) are clarified at first. Then, the quantitative analyses on current ripple and neutral-point fluctuation with T-DPWM, classical space vector modulation, and optimized DPWM (O-DPWM) are presented in detail. To solve the issue of current distortion, the H-DPWM is proposed based on O-DPWM. Furthermore, the switching losses of these modulations are evaluated. At last, the analyses and performance of the proposed H-DPWM are verified by the experiments.

Sensorless Field Oriented Control Applied for an Induction Machine by Using the Discontinuous PWM Strategy

Sensorless Field Oriented Control Applied for an Induction Machine by Using the Discontinuous PWM Strategy

Sensorless Field Oriented Control Applied for an Induction Machine by Using the Discontinuous PWM Strategy

Sensorless Field Oriented Control Applied for an Induction Machine by Using the Discontinuous PWM Strategy

Advanced DPWM Method for Switching Loss Reduction in Isolated DC Type Dual Inverter With Open-End Winding IPMSM

This paper proposes an advanced discontinuous pulse-width modulation (DPWM) scheme for a dual inverter to reduce switching loss. A dual inverter is used to drive an open-end winding interior permanent magnet synchronous motor (OEW-IPMSM). It is composed of double two-level inverters with large switching loss owing to the use of 12 switching devices. When a current phase changes, the switching loss cannot be minimized by using a conventional DPWM scheme. As the conventional DPWM scheme uses reference voltage for switching, the switching loss cannot be minimized due to the difference between the phases of the stator current and phases of reference voltages. However, the proposed DPWM scheme with additional calculations of the current phase can minimize switching loss. When the current phase changes, the proposed DPWM is switched to ±30° of the maximum point of the current. Furthermore, the effectiveness of the proposed switching loss reduction ability is verified through simulations and experimental results.

Sideband Vibro-Acoustic Responses and Improvements With Different Pulsewidth Modulation Strategies in Permanent Magnet Synchronous Motor for Electric Vehicle

This article presents a comprehensive investigation into the sideband vibro-acoustics with continuous and discontinuous pulsewidth modulation (PWM) strategies in permanent magnet synchronous motor (PMSM). The primary motivation for the evaluation reveals the frequency distributions of the sideband components and the magnitudes suppression with the space-vector PWM (SVPWM) and the discontinuous PWM (DPWM). The principle and implementation of the conventional SVPWM and six basic DPWM modes are firstly presented. The sideband harmonic components are provided by the analytical derivations, in which the frequency distributions are established by coupling the temporal features between the current harmonics and radial electromagnetic force. To evaluate and compare the sideband current harmonics and vibro-acoustic responses among the PWM schemes, the experimental tests are presented in a study case of 12/10 PMSM. Significant deterioration is observed in each of the basic DPWMs compared with that in SVPWM. Developed with periodic dithering modulation, notable sideband harmonics suppression and vibro-acoustic improvements in DPWM schemes are observed. This work is expected to provide a guidance for a hybrid modulation strategy in electric vehicles (EVs).

Improved PWM Strategies to Mitigate Dead-Time Distortion in Three-Phase Voltage Source Converter

Pulsewidth modulation (PWM) strategies, including continuous PWM (CPWM) and discontinuous PWM (DPWM), have been efficiently applied in the three-phase voltage source converters (VSCs). In the three-phase VSCs, dead-time distortion is inevitable. The characteristics of the dead-time distortion of three-phase VSCs with CPWM strategies have been studied extensively, whereas those of DPWM strategies have not been studied in detail. In this article, a comparative analysis of the dead-time distortion of CPWM strategies and DPWM strategies is conducted. Furthermore, the improvement of the PWM strategies to mitigate dead-time distortion is presented. The improved PWM strategies inject the compensation signals to the modulation signals to reconstruct the dead-time voltage error, which can significantly reduce the dead-time distortion of various PWM strategies. Experimental tests are conducted and the experimental results are provided to verify the analysis results of the dead-time distortion of DPWM strategies and the improved PWM strategies.

Clamping Modulation Scheme for Low-Speed Operation of Three-Level Inverter Fed Induction Motor Drive With Reduced CMV

This article introduces a family of carrier-based pulse width modulation (PWM) schemes for three-level (3 L) inverter fed motor drive for low-speed operation. The proposed PWM in dual-inverter topology (DIT) simultaneously clamps two phases of each inverter throughout the fundamental cycle, which reduces the switching transition in the pole voltage and common-mode voltage (CMV). Four PWM variants in the family (i.e., PWM-1–PWM-4) are discussed and compared with conventional discontinuous PWM schemes. A mapping of the gating pulse is derived to extend the proposed PWM to a classical 3 L inverter fed star-connected motor drive. The gating pulses are generated using triangular carrier comparison with synchronous sampling. The steady-state and dynamic performances of PWM are validated both in DIT fed open-end winding induction motor (IM) drive and neutral point clamped (NPC) inverter fed star-connected IM drive. It is observed that the proposed PWM gives inherent capacitor voltage balance in the NPC topology. PWM-1 has a higher linear modulation range than conventional zero clamp PWM and leads to reduced CMV in the NPC topology. PWM-2 and PWM-3 give reduced CMV in DIT. PWM-4 has fault tolerance to single-phase open-switch and short-switch failure in DIT.

A Carrier-Based Discontinuous PWM Scheme With Optimal PWM Sequences for a Five-Level Flying Capacitor Rectifier

Five-level flying capacitor (5L-FC) rectifier is advantageous in unidirectional power applications due to its less power devices, higher power density, better reliability, etc. To further improve the efficiency, discontinuous PWM (DPWM) methods are preferred. This article investigates a carrier-based implementation of DPWM for the 5L-FC rectifier to reduce the switching losses. Since there is always a pair of redundant switching modes that have opposite effects on the neutral point (NP) in each region of the space-vector diagram, the NP voltage regulation can be easily realized by selecting suitable clamping modes in each control period, even with unbalanced dc loads. The generated PWM sequences based on the phase disposition PWM are also optimally redistributed to realize minimal switching loss with FC voltage balancing in two consecutive carrier periods. In addition, the permissible range of unbalanced dc loads is theoretically deduced. Finally, simulations and experiments are conducted to verify the performance of the proposed carrier-based DPWM scheme.

Research and Development of Adjustable Discontinuous Pulse Width Modulation Method for Three-Phase Voltage Source Inverter

Continuous pulse width modulation (CPWM) and discontinuous pulse width modulation (DPWM) strategies are used to control voltage source inverter operation. CPWM strategies allow for the reduction of total harmonic distortion values, while DPWM strategies provide a more effective reduction in inverter switching losses. The paper is devoted to the problem of improving the three-phase voltage source inverter efficiency by a controlled transition from CPWM to DPWM. The article proposes an adjustable discontinuous pulse width modulation (ADPWM) method, which means a transition from space vector PWM (refers to CPWM strategies) to DPWM in all inverter phases when the switches’ temperatures exceed the allowable value in at least one of the inverter phases. The method flowchart is presented and an algorithm for modifying the envelope curve within one sector is given. In order to test the ADPWM method a Simulink-model of a three-phase voltage source inverter and its control system were developed. A study of the proposed ADPWM method’s efficiency in comparison with CPWM, PCDPWM and NCDPWM methods was carried out using a Simulink-model. It was established that the proposed ADPWM method provides dynamic losses reduction in the inverter switches by 2.86 times compared to CPWM and by 1.89 times compared to PCDPWM and NCDPWM methods. Power supply systems for medium and high-power AC motors provide a promising area for application of the proposed ADPWM method.