Synchronous Optimal Pulsewidth Modulation Research Articles

Synchronous Optimal Pulsewidth Modulation for High-Power AC Motor Drives: A Review

Synchronous Optimal Pulsewidth Modulation for High-Power AC Motor Drives: A Review

Comparative Study of Advanced Modulation and Control Schemes for Dual Three-Phase PMSM Drives With Low Switching Frequencies

In this paper, multiple advanced low-switching-frequency modulation and control schemes are investigated for dual three-phase permanent-magnet synchronous motor (PMSM) drives. The modulation schemes under investigation include multisampling space vector modulation (MS-SVM), selective harmonic elimination pulse width modulation (SHEPWM) and synchronous optimal pulse width modulation (SOPWM) while the control schemes include complex vector control, model predictive control (MPC) and flux trajectory control-based model predictive pulse pattern control (MP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C). The difference between three-phase and dual three-phase PMSM drives at low switching frequencies is analyzed. Moreover, an optimal pulse width modulation (PWM)-based MP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C scheme is proposed for the dual three-phase PMSM, where the optimal PWM modulation and MP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C control are combined such that the optimal steady-state and dynamic control performance is achieved among the modulation and control schemes investigated. Experimental results are given to compare and validate the proposed control scheme.

Synchronous Optimal PWM With Continuous Switching-to-Fundamental Frequency Ratio

In high-power applications, the synchronous optimal pulse width modulation (SOPWM) serves as a vital modulation method that achieves an excellent tradeoff between the switching losses and the current harmonic. However, the optimized pulse patterns of SOPWM are constrained due to the discrete pulse numbers, which leads to the underutilization of the allowable maximum switching frequency. Therefore, the corresponding current harmonic could not be reduced as low as possible. In response to this issue, the SOPWM with a continuous switching-to-fundamental frequency ratio is proposed in this article. First, the deduction of the traditional pulse patterns is introduced based on the symmetry of the voltage pulse waveform. Then, the principle of the proposed strategy is illustrated in detail, and an overall comparison with traditional SOPWM is given theoretically. With the proposed strategy, a considerable reduction of the current THD is achieved over almost the whole high-speed range, and the losses and efficiency of the system are analyzed by the finite element method (FEM). Finally, theoretical results are verified by simulation and experimental tests.

DC-Link Capacitor and Inverter Current Ripples in Anisotropic Synchronous Motor Drives Produced by Synchronous Optimal PWM

An accurate approximation of the dc-link capacitor current is crucial for the design of the dc-link capacitor as the capacitor current ripple affects lifetime, size, weight, and cost of the voltage source inverter (VSI). In this article, analytical expressions for the dc-link capacitor current and the inverter current are derived for two-level VSIs feeding anisotropic interior permanent magnet synchronous machines (IPMSMs) controlled by synchronous optimal pulsewidth modulation (SOPWM). The magnetic anisotropic properties of the IPMSM are considered and half-wave symmetric SOPWM signals are utilized. Experimental results evaluate the effect of various pulse patterns on the produced inverter current and dc-link capacitor current ripples and validate the correctness of the derived expressions.

Synchronous Optimal Pulsewidth Modulation for Synchronous Machines With Highly Operating Point Dependent Magnetic Anisotropy

The performance of synchronous optimal pulsewidth modulation is investigated for the control of an automotive low voltage electrical drive system, which consists of a two-level voltage source inverter and an interior permanent magnet synchronous motor. The machine magnetic anisotropy varies due to magnetic saturation and cross-saturation effects and depends on the motor operating point. The main objective of this article is to investigate the influence of the varying magnetic anisotropy on the optimized half-wave symmetric inverter pulse patterns. For this purpose, the optimized inverter switching angles are derived by minimizing the current harmonic distortion of an isotropic and anisotropic permanent magnet synchronous motor. Their performance is evaluated and compared by experimental results.

Simple Fundamental Current Estimation and Smooth Transition Between Synchronous Optimal PWM and Asynchronous SVM

In this article, two aspects of a synchronous optimal pulsewidth modulation (SOPWM) strategy for inverter control are considered. First, a fundamental current estimation method is proposed, which eliminates the undesired harmonics in the measured currents and allows us to integrate the SOPWM strategy into a field-oriented control scheme without the need of an observer. The main features of this method are its implementation simplicity and its independence of the load parameters. Second, a smooth transition between asynchronous space vector modulation (SVM) and SOPWM is introduced to avoid performance degradation and overcurrent in the current control loops. The proposed transition strategy transforms the asynchronous SVM into a frequency- and phase-synchronous SVM before the transition to SOPWM takes place. Experimental results for a two-level inverter-fed three-phase inductive load confirm the accurate steady-state and transient performance of the proposed estimation and transition strategies.

Hybrid SVM-SOPWM Modulation of Current-Fed Three-level Inverter for High Power Application

The goal of the paper is to develop a hybrid modulation technique to combine space vector modulation (SVM) scheme and synchronous optimal pulsewidth modulation (SOPWM) technique for current source inverter (CSI). SVM provides better dynamic performance, but is unable to produce less total harmonic distortion (THD) on inverter current at low device switching frequency (<; 1 kHz). SOPWM provides less THD even at low device switching frequency, however it needs a conversion technique to operate CSI and it needs an additional control technique to improve dynamic performance. Hence to overcome these limitations, this paper develops a single modulation technique called optimal SVM technique that can achieve less THD as well as better dynamic performance. To develop optimal SVM technique, three methods have been proposed in this paper. These three methods do not require an additional conversion technique to operate CSI and they provide less THD even under low device switching frequency of 450 Hz. Experimental results prove that the proposed modulation technique can provide better steady-state performance as well as dynamic performance.

A novel hybrid Phase Shifted-Modified Synchronous Optimal Pulse Width Modulation based 27-level inverter for grid-connected PV system

In grid connected Photovoltaic (PV) systems, Multilevel Inverters (MLI) are commonly employed for providing better reliability and getting minimal harmonics. Most of the MLIs function with Phase-Shifted Pulse Width Modulation (PSPWM) techniques for achieving high level performance. However, in the in existing PSPWM techniques, the harmonic voltage profiles are not efficient. This paper aims to improve the harmonic voltage profile of the 4 KW grid-connected PV system using a novel hybrid PSPWM-Modified Synchronous Optimal PWM (PS-MSOPWM) technique for a 27-level inverter. With the combination of these hybrid PSPWM-Modified SOPWM techniques, optimum switching angles are computed to match the switching frequency with the fundamental frequency. From the results, it is identified that the proposed hybrid modulation method effectively reduces the Total Harmonic Distortion (THD) and exhibits improved reliability of the grid-connected solar system.

Performance and Implementation of Modular Converter Based on Advanced Control Topology

In high power industrial drive use the multi modular converter for high voltage dc transmission system. The reduction of switching frequency, reduce thermal stress and harmonic distortion in the output of the converter by using the modular converter. Synchronous optimal pulse width modulation (SOP) is a developing low gadget exchanging recurrence regulation system for high power converters, which keeps up the nature of converter output current. SOP system has been effectively exhibited for established multilevel topologies and it has been demonstrated that greatest gadget exchanging recurrence can be restricted to evaluated principal recurrence for seven or larger amount inverters without trading off on the nature of yield streams. Be that as it may, execution of SOP procedure for MMC topology is as yet pending. One of the primary difficulties for control of MMC is to keep up drifting capacitor voltages around their ostensible esteem. The objective of our investigation is to propose, break down and actualize improved SOP strategy for MMCs to accomplish low device exchanging recurrence operation, better quality of converter output current and keep up capacitor voltages around their perceived value.

Generalized Synchronous Optimal Pulse Width Modulation for Multilevel Inverters

With the growing interest of the industry in high-power medium-voltage multilevel inverters and the technological limitation in high voltage power semiconductors switches, synchronous optimal pulse width modulation techniques, originally developed for two-/three-level inverters, became again a topic of interest, now to optimize multilevel waveforms. This work proposes a novel formulation for the problem of optimizing the modulation pattern of multilevel converters, including in a single optimization problem the decision of the directions for each step transition in addition to the switching angles and, thus, completely defining the optimized multilevel waveform at a given modulation index. In addition, experimental results are presented in order to demonstrate the effectiveness of this optimized modulation technique exemplar applied to a five-level NPC H–bridge feeding a permanent magnet synchronous motor.

Modified Synchronous Pulsewidth Modulation of Current-Fed Five-Level Inverter for Solar Integration

Large-scale photovoltaic (LSPV) energy conversion systems have been installed at many places across the world. The essential component of the LSPV system is the dc-ac conversion stage. The usage of multilevel converters is one of the recent advances in the dc-ac conversion stage of the LSPV system to enable transformer-less inversion. Current-fed multilevel inverter has been chosen in this paper as it provides high power inversion with inherent voltage boosting, and thus, avoids the usage of transformer. High power conversion necessitates low device switching frequency operation in order to satisfy thermal constraint of semiconductor devices and also to improve efficiency. However, low device switching frequency operation leads to higher harmonic distortion of inverter output currents. Synchronous optimal pulsewidth modulation (SOP) technique is an emerging low device switching frequency modulation technique that has been successfully implemented for voltage-source multilevel inverters. However, the state-of-the-art SOP technique cannot be directly applied to modulate current-source multilevel inverter topologies due to additional constraints on the switching commutations. Therefore, the purpose of our study was to propose a modified SOP technique to achieve: low device switching frequency and minimal harmonic distortion of inverter output currents. The topology of current-fed five-level inverter was used for demonstrating the performance of proposed technique. A generalized conversion method was introduced in the modified SOP technique for including switching constraints of the current-fed inverter. In addition, a state-sequencing machine was developed by utilizing redundant inverter states to produce equal switching commutation among all semiconductor devices at minimal switching frequency of 350 Hz. The experimental results obtained from the five-level current-source inverter of 1.2 kW demonstrated the effectiveness of the proposed SOP technique.

Current-Fed Multilevel Converters: An Overview of Circuit Topologies, Modulation Techniques, and Applications

Multilevel converters (MLCs) have emerged as standard power electronic converters in high power as well as quality demanding applications. They are classified into current-fed MLCs and voltage-fed MLCs. Voltage-fed MLCs have widely researched whereas the current-fed MLCs are the recent topic of research. Based on the principle of duality between voltage and current sources, several current-fed MLCs analogous to voltage-fed MLCs have been identified. Current-fed MLCs offer several advantages in terms of high power capability, transformerless operation, short-circuit protection, and excellent quality of output current waveform. The goal of this paper is: 1) to present review of circuit topologies, modulation schemes, and applications of current-fed MLCs; and 2) to review an emerging low-device switching frequency modulation technique known as synchronous optimal pulsewidth modulation for current-fed MLCs. The circuit configuration and advantages of each topology along with various modulation techniques are discussed in detail. Compared to voltage-fed MLCs, the operation of current-fed MLCs need to satisfy additional switching constraints. A survey of classical methods for realization of these operational constraints has been done and a new generalized method has been proposed. Finally, future scope of research has been presented to encourage further development of topologies and modulation techniques for current-fed MLCs.

Optimal Pulsewidth Modulation for Common-Mode Voltage Elimination Scheme of Medium-Voltage Modular Multilevel Converter-Fed Open-End Stator Winding Induction Motor Drives

Multilevel converter topologies for open-end stator winding medium-voltage (MV) induction motor drives have been researched from the last two decades. In this paper, a dual $n$ -level modular multilevel converter (MMC) topology has been proposed for open-end stator winding MV induction motor drives. The control requirements of the proposed system are low device switching frequency, minimal harmonic distortion of machine stator currents, elimination of common-mode voltages in machine stator windings, and maintaining floating capacitor voltages around their nominal value. Based on these requirements, an emerging modulation technique for MV induction motor drives known as synchronous optimal pulsewidth modulation has been developed for the proposed dual $n$ L-MMC topology. The laboratory measurements from a dual three-level MMC fed 1.5-kW open-end stator winding induction motor drive demonstrate the performance of proposed technique.

Optimal Low Switching Frequency Pulsewidth Modulation of Current-Fed Three-Level Converter for Solar Power Integration

Large-scale photovoltaic energy conversion systems have been installed at many places across the world and they handle higher power levels. In high power conversion, low device switching frequency operation is preferred in order to satisfy the thermal constraints of semiconductor devices and also to improve efficiency. However, low device switching frequency operation leads to higher total harmonic distortion (THD) of the converter output currents. Synchronous optimal pulsewidth modulation (SOP) is an emerging low device switching frequency modulation technique, which has been successfully implemented for voltage source inverters without compromising on THD. The goal of our research is to propose, analyze, and implement a modified SOP technique for current source inverter topologies. The additional switching constraints for these inverter topologies have been included in the modified SOP technique. The experimental results obtained from a low-power prototype demonstrated its effectiveness.

Optimal Pulsewidth Modulation of Medium-Voltage Modular Multilevel Converter

Modular multilevel converter (MMC) is now the state-of-the-art converter topology for high-voltage dc transmission (HVDC) systems. Another potential application for MMC is medium-voltage (MV) high-power industrial ac drives. In high-power applications, thermal constraints of power semiconductor devices limit device switching frequency to a few hundred hertz. However, there exists a tradeoff between device switching frequency and harmonic distortion of converter output currents. Synchronous optimal pulsewidth (SOP) modulation is an emerging low-device switching-frequency-modulation technique for high-power converters, which maintains the quality of converter output currents. SOP technique has been successfully demonstrated for classical multilevel topologies and it has been proved that maximum-device switching frequency can be limited to rated fundamental frequency for seven or higher level inverters without compromising on the quality of output currents. However, implementation of SOP technique for MMC topology is still pending. One of the main challenges for control of MMC is to maintain floating-capacitor voltages around their nominal value. The goal of our study is to propose, analyze, and implement enhanced SOP technique for MMCs to achieve low-device switching-frequency operation, better quality of converter output currents, and maintain capacitor voltages around their nominal value. The proposed technique has been validated using low-power prototype of five-level MMC feeding an 1.5-kW induction motor.

A Survey of Low Switching Frequency Modulation Techniques for Medium-Voltage Multilevel Converters

Multilevel converters (MLCs) have emerged as standard power electronic converters for medium-voltage high-power industrial applications. Owing to dominating device switching losses in high-power applications, it is preferable to use low device switching frequency (LDSF) modulation techniques. Then, it is possible to achieve higher device utilization, higher converter efficiency, and reduced cooling requirements. However, there exists a tradeoff between device switching frequency and harmonic distortion of converter output currents. Therefore, the main challenge for LDSF modulation techniques is to minimize the harmonic distortion of the output currents. The goal of this paper is to provide a review of various LDSF modulation techniques proposed in the literature and also discuss in detail about one of the emerging LDSF control techniques known as synchronous optimal pulsewidth modulation. Finally, challenges to LDSF modulation techniques for emerging multilevel topologies and future trends in applications of MLCs are discussed to motivate further research, to enhance the proposed LDSF techniques, and to explore for new alternatives.

Fundamental Switching Frequency Optimal Pulsewidth Modulation of Medium-Voltage Nine-Level Inverter

A low device switching frequency operation is essential in medium-voltage (MV) high-power drives to increase semiconductor device utilization as well as to achieve higher overall system efficiency. However, there exists a tradeoff between device switching frequency and harmonic distortion of machine currents. Synchronous optimal pulsewidth modulation (SOP) is an evolving technique for controlling multilevel inverters of MV ac drives at low device switching frequency without compromising the quality of machine currents. The state-of-the-art generalized SOP algorithm for five or higher level inverters leads to unequal device switching frequency, and also, transients in machine currents are possible due to the change in the number of switching instants at higher modulation index values. The goal of our study is to propose a new SOP technique that ensures equal device switching frequency and further reduces device switching frequency compared to the generalized SOP method. Also, it is expected that machine current transients at higher modulation index values will be reduced. The proposed SOP technique has been verified experimentally on a cascade nine-level inverter-fed 1.5-kW induction motor drive.

Optimal Low-Switching Frequency Pulsewidth Modulation of Medium Voltage Seven-Level Cascade-5/3H Inverter

Low-switching frequency modulation of multilevel inverters for medium-voltage high-power industrial ac drives is essential to reduce switching losses and, thus, improve the overall energy efficiency of the system. However, minimizing the switching frequency increases the total harmonic distortion (THD) of machine currents. Synchronous optimal pulsewidth modulation (SOP) is an emerging technique for controlling multilevel inverters at low-switching frequency without compromising on the THD of machine currents. The goal of our experiment was to implement SOP technique for controlling seven-level cascade inverter for an induction motor drive at an average device switching frequency limited to rated fundamental frequency. First, optimal seven-level waveforms were obtained by ofline optimization assuming steady-state operating conditions. Then, the switching angles for each semiconductor device were obtained that ensure equal distribution of switching losses as well as minimal unbalance in dc-link capacitor voltages. The proposed SOP technique is validated by experimental results obtained from the seven-level cascade inverter feeding a 1.5-kW induction motor.

Optimal Low Switching Frequency Pulsewidth Modulation of Nine-Level Cascade Inverter

Synchronous optimal pulsewidth modulation (SOP) permits low switching frequency modulation of multilevel inverter for medium-voltage high-power industrial ac drives without compromising on total harmonic distortion (THD). An aim of our experiment was to operate a nine-level cascade inverter of an induction motor drive at an average device switching frequency limited to rated fundamental frequency by using SOP technique. To reduce the number of separate dc sources, a three-level diode clamped converter was used as a cell in the nine-level cascade inverter. Using SOP technique, optimal nine-level waveforms were obtained by ofline optimization assuming steady-state operation of the induction machine. The switching angles for each semiconductor switch are then obtained from optimal nine-level waveforms based on the criteria to minimize the switching frequency as well as unbalance in dc-link capacitor voltages. Experimental results obtained from the 1.5-kW induction motor drive show THD 5% for stator currents. The results indicate that SOP technique reduces the switching frequency of operation without compromising on THD.

Control of Large Salient Pole Synchronous Machines using Synchronous Optimal Pulsewidth Modulation

High-power grinding mills are used in the cement and mining industries to crush clinker or copper ore and grind these materials to fine powder. The multimegawatt speed-controlled mill drives operate at a very low angular speed. Synchronous motors with a high number of pole pairs are used as the prime movers. They are traditionally fed by load-commutated thyristorized cycloconverters. These are prone to failure modes that can lead to excessive torque pulsations and high overcurrents. The huge stator, which was built as a separate ring-shaped structure around the tubular mill, may then get mechanically displaced, and the operation of the plant is interrupted. A novel and reliable direct drive uses a voltage source inverter that operates at the unity power factor for increased efficiency. Synchronous optimal pulsewidth modulation ensures a low harmonic current distortion and reduced switching losses at a very low switching frequency. The optimization of the pulse patterns takes the anisotropic magnetic properties of a separately excited synchronous motor into account. The implementation in a 23-MW semiautonomous grinding mill installed in a Zambian copper mine is intended.