Pulse Width Modulation Algorithm Research Articles

Assessment of influence of rolling mill FC-AR electric drive operation mode on 10kV supply network voltage quality

Advanced rolling mill electric drives are based on frequency converters (FC) with active rectifiers (AR). Operation of such converters has negative impact on the in-plant power supply system. To improve the voltage quality of active rectifiers, special algorithms of pulse-width modulation algorithms are used. As a rule, the study of the effect of electric drives with FC-AR on the supply network are carried out based on simplified mathematical models that do not consider possible resonance phenomena in the power supply system and operating mode of electric drives. Thus, the aim of the paper is to assess the acceptability of such an approach. The trends of the main parameters of the rolling mill electric drives have been recorded during the rolling cycle using the IBA PDA software. The obtained dependencies values have been approximated and applied in a complex simulation model of the in-plant power supply system. It considers the parameters of the supply network, cable lines, step-down transformers, rolling mill electric drives and other electrical receivers of the shop substations. The main assumption in simulation modeling is to consider the loads of other electrical receivers in the form of constant values. The authors have studied the effect of the operating modes of the rolling mill electric drive on the electric power quality in the 10 kV distribution network of the in-plant power supply system of a metallurgical enterprise. It is found that the total harmonic distortion KU at 10 kV sections of the main step-down substation of a metallurgical enterprise is changing in a nonlinear manner in the dynamic modes of acceleration and deceleration of electric drives. The nature of the coefficient KU also depends on the presence of resonance phenomena in the frequency response of the medium voltage supply network. The obtained results prove the need to consider the operating modes of electric drives when studying the influence of electric drives with FC-AR on the quality of the supply network voltage. in case we conduct experimental research using the equipment of the enterprises, as well as during theoretical research using mathematical models. The adequacy of the simulation model has previously been confirmed by experimental data and previous studies.

Treating the Impacts of Connecting HVDC Link Converters with AC Power System Using Real-Time Active Power Quality Unit

The High Voltage Direct Current (HVDC) systems have been applied worldwide, due to important roles, technical benefits, and high efficiency. Usually, the HVDC network is a joining link between two separate and different technical properties of HVAC systems, which enhances its use. The joinpoint system that used to connect HVDC and HVAC links is a controlled converter circuit. Despite the importance of use and the significant benefits of the HVDC link, there are negative effects on the power quality of the electrical power of both systems connected on both ends of the HVDC network. The low quality of electric power has been addressed by known methods, whether traditional or modern. But the improvement is usually made with the assumption of load conditions and the need for the system to synthesize it. This research presents an innovative method based on real-time control strategy. This is performed by proposing dSPACE for controlling the Active Power Quality Unit (APQU). The proposed control strategy of the APQU includes a Modified Harmonics Pulse Width Modulation (MHPWM) algorithm in order to mitigate the line current THD and improve the effective power factor of the AC converter sides. The MHPWM is applicable for different nonlinear loads and can be implemented with APQU based on different topologies of H-bridge voltage source inverter. Simulation and practical results have been presented in this paper. The Experimental results are done based on real-time laboratory tests using dSPACE DS1103 board as a controller circuit. The presented results, under different operating loading conditions, show that the APQU provides almost unity power factor and significantly improving THD of the AC supply currents at both sides of the HVDC link controlled converters.

A Five-Level Converter in a Three-Level Mode for Common-Mode Leakage Current Suppression in PV-Generation Systems

Power generation systems (PGSs) based on renewable energy sources are finding ever-widening applications, and many researchers work on this problem. Many papers address the problem of transformerless PGSs, but few of them aimed at conducting research on structures with multilevel converter topologies as part of a PGS. In this paper a grid-tied transformerless PV-generation system based on a multilevel converter is discussed. There are common-mode leakage currents (CMLCs), which act as a parasitic factor. It is also known that common-mode voltage is the main cause of the common-mode leakage current in grid-tied PV-generation systems. This paper considers the space vector pulse-width modulation (PWM) technique, which is used to suppress or reduce common-mode leakage current. The proposed PWM technique with the reduction of common-mode leakage current for a generation system based on the multilevel converter controlled with a PWM technique was verified experimentally. The experimental results accurately confirmed the mathematical model and the compensation achieved without errors. In the experiment, there was an approximately six-fold decrease in the common-mode leakage current (10.3 mA in rejection mode and 61 mA in non-rejection current). This can lead to the elimination of CMLC in a multilevel semiconductor converter only by changing the modulation mode. This suggests the possibility of using these devices as part of transformerless generation systems. Suppression of CMLC can only be carried out by changing the PWM algorithm. Both considered topologies can implement this mode of operation. The proposed converter has a higher efficiency up to a frequency multiplicity of 2000.

Stability Improvement of Electric Ship Propulsion System Using Supercapacitor

Owing to the serious greenhouse gas emissions and inflexible control of traditional ship propulsion system, the electric ship propulsion system has been widely introduced into the ship’s power system. However, the variations of ship propellers will lead to the instability of electric propulsion system so this paper studied the transient characteristics of electric ship propulsion system by performing a series of experiments on a real electric ship propulsion system platform. Based on the experimental results, a detailed model of supercapacitor energy storage system (SCESS) is proposed to improve the voltage and frequency response for the electric ship propulsion system. To enhance the stability and reliability, a double closed-loop control method combined with Pulse-Width Modulation algorithm (PWM) is utilized to control the energy storage system for smoothing the power fluctuations caused by the electric propulsion system. The simulation results demonstrate the high efficiency of supercapacitor to improve the transient stability of the whole power system of the ship.

Generalized Approach for DCPWM Based Dual Inverter Fed OEWIM-DTC Drive

A generalized procedure of decoupled pulse width modulation (DCPWM) based on Method called Direct Torque Control (DTC) for Open Ended Winding Induction motor drive (OEWIM) is anticipated in this paper. This drive topology uses two isolated dc sources with equal magnitudes, feeding two standard two level three-phase inverters. To overcome the complexity in classical space vector pulse width modulation (SVPWM) algorithm, a simple generalized approach is presented in this research by using the phase voltages. With this procedure, various PWM algorithms can be generated by varying a constant value. The dual inverters are operating independently with half of the switching frequency. To show the usefulness of proposed PWM fed DTC drive, simulation results analysis has been carried out by using MATLAB and results obtained.

Analysis and Optimization of Torque Ripple Reduction Strategy of Surface-Mounted Permanent-Magnet Motors in Flux-Weakening Region Based on Genetic Algorithm

One of the parameters required for a high-performance drive of a surface-mounted permanent magnet synchronous motor (SPMSM) operating in the flux-weakening region is the torque ripple reduction. In general, the torque ripple results from many reasons, such as the machine structure, oscillations of measured speed, etc. Hence, this article proposes an optimized strategy that works in conjunction with a variable switching frequency pulsewidth modulation algorithm to reduce the torque ripple peak. For the modulating algorithm, the updated frequency changes linearly with the desired torque ripple and its predicted maximum peak. For the proposed strategy, the reflection of proportional-integral (PI) parameters is observed at the torque ripple caused by the current ripples. Therefore, a robust method for adjusting PI parameters is proposed that relies on the improved fitness function that can minimize the regulators' error and maximize the drive stability bandwidth in the flux-weakening region. This objective function is optimized offline using a genetic algorithm optimization technique. Meanwhile, a third-order generalized integral flux observer is applied in this article, providing evidence of torque ripple reduction. For driving in the flux-weakening region, the reference magnitude of the duty cycles can produce the required <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis reference current to prevent the saturation of current controllers. Finally, comprehensive simulations and experiments are presented to validate the proposed strategy effectively. In comparison with the conventional method, the proposed strategy can reduce the copper and switching losses simultaneously and control the current and speed in the flux-weakening region efficiently.

Optimal speed–torque control of doubly-fed induction motors: Analytical and graphical analysis

This paper proposes an optimized control approach of a Doubly-Fed Induction Motor (DFIM) based on a field weakening algorithm. This technique ensures a nearly doubled torque–speed operation region in the motor’s acceleration and deceleration operation modes. The novelty of the proposed control lies in the fact of using a DFIM for Electric Vehicle (EV) applications where both stator and rotor circuits are connected to voltage source inverters controlled by Space Vector with Pulse Width Modulation (SVPWM) algorithms. Accordingly, the active power distribution law between the stator and rotor sides is thoroughly investigated. This law imposes a relationship between the rotor and stator pulsations leading to a new variation scenario in the DFIM speed. Besides, a Stator Flux Oriented Control (SFOC) is used to provide a decoupled control between the torque and the flux. Considering the voltage and current constraints in the structure, the reference flux is chosen such that the optimal torque for any operation mode, and at any given speed range, is achieved. Nevertheless, the speed measurement as well as the sensitivity to motor parameter variations remains a major limitation in the over-speed region. Therefore, a Sliding Mode Flux Observer (SMFO) is integrated into the control scheme to ensure a sensorless command. The performance of the proposed optimized control algorithm are assessed by computer numerical simulations and its effectiveness in terms of achieving maximum torque in a wide speed range is verified.

Evaluation of SVM modulation methods for indirect two-level three-phase frequency converter and direct frequency converter

In current practice, indirectly structured frequency converters are popular because of the simple switch and control circuit diagram, and pulse width modulation (PWM) can be used to control the semiconductor switches. The PWM method has the advantage of a simple control circuit but has large switching losses and generates a common-mode voltage that causes motor damage. The development of the space vector modulation (SVM) method takes advantage of the PWM method, reducing the switching loss of the switches and reducing the harmonic at the output of the inverter. With direct converters, there are many types depending on the circuit structure and semiconductor key structure, including matrix frequency converters which are widely studied. The classical modulation method according to the duty-cycle matrix approach for matrix converter has disadvantages such as complex computational algorithms, which require many trigonometric calculations. Based on the PWM and SVM modulation algorithms for indirect converters, a space vector modulation method for matrix converters will be developed. Compared with the indirect converter, the SVM modulation method for the matrix converter will be based on two separate modulation principles: control the input current vector and control the output voltage vector. The relationship between current and voltage at the converter input is closely related to the voltage and current at the output. The relationship between current and voltage at the converter input is closely related to the voltage and current at the output. Make sure at the input of the converter, the power factor cosφ = 1 and can be adjusted, it has the quality of sine input and outputs current and the exchange power in two directions.

Improved Capacitor Voltage Balancing Algorithm for a Single-phase T-type Inverter

The paper proposes an improved pulse width modulation algorithm to solve the voltage imbalance on DC capacitors for single-phase T-type inverter. By changing the modulation index, the residual states can be applied to the discharge/charge state on the DC capacitors to balance the voltage. The proposed algorithm is validated for application in single-phase T-type inverters in independent mode. The simulation and experimental results have confirmed the effectiveness of the improved pulse width modulation method for single-phase T-type inverter. The paper proposes an improved pulse width modulation algorithm to solve the voltage imbalance on DC capacitors for single-phase T-type inverter. By changing the modulation index, the residual states can be applied to the discharge/charge state on the DC capacitors to balance the voltage. The proposed algorithm is validated for application in single-phase T-type inverters in independent mode. The simulation and experimental results have confirmed the effectiveness of the improved pulse width modulation method for single-phase T-type inverter.

A hybrid T-type (HT-type) multilevel inverter with reduced components

This paper introduces a new HT-type module for both symmetrical and asymmetrical multilevel inverters (MLIs) with reduced power electric components. The proposed module comprises of two back to back T-type inverters connected with four cross-connected switches. This MLI addresses two major drawbacks associated with the conventional and other recently proposed MLIs which are the high voltage stress of switches and higher power component counts. The structure of the proposed device is designed combining the beneficial features of both T-type inverter and cross-switched inverter. The 1st feature allows the module to produce negative voltage levels deprived of any extra H-bridge circuit and thus decreasing the overall voltage stress significantly. The latter feature allows the device to utilize reduced number of switches to produce higher voltage levels. A comprehensive comparative analysis is additionally established between other MLI topologies to confirm the superiority of the HT-type MLI. From this analysis, it is found that the proposed MLI has successfully overcome the issues associated with other MLIs, it was able to produce the results following industrial standards and it outperformed other MLIs in different aspects such as power components count, cost, efficiency and dynamic performance. Selective harmonic elimination pulse width modulation (SHE-PWM) and nearest level control (NLC) algorithm is considered in this manuscript to generate the output results from the proposed HT-type module. All the details about the operating principle and modulation techniques utilized for the proposed MLI module are stated and validated by both simulation and experimental results.

Development and research of improved PWM algorithm of an active rectifier with variable switching angle tables

Modern electric drives of rolling mills are based on frequency converters with active rectifiers (AR). During operation, active rectifiers consume non-sinusoidal current, having a negative effect on the supply network. In order to improve the performance index of voltage quality, AR special algorithms of pulse-width modulation are used. Selective harmonic elimination (SHE) PWM algorithm has become widespread. However, application of SHE PWM algorithm does not always allow to optimize the operation of the AR under the conditions of changing parameters of the electro-technical complex under various operating modes. Therefore, a solution is needed to improve the electrical power quality index of plant networks with powerful frequency converter with AR. To carry out the research, a mathematical model of the frequency converter with active rectifiers was implemented with an improved PWM algorithm in the Matlab-Simulink environment based on the parameters of the main electric drive of the 2000 cold rolling mill “LPC-11” of PJSC “ММК”. The main assumption of the simulation model is that the inverter is represented as a current source. An improved algorithm with the ability to select tables of switching angles based on SHE PWM has been developed. The operation of the FC with AR with the proposed improved PWM algorithm with variable tables of switching angles has been investigated. A comparative analysis of the instantaneous values of AR voltages and currents when transferring to the tables with similar switching angles and significantly different ones has been made. It has been found that changing the tables of switching angles does not have a significant negative effect on the operation of the FC with AR. The proposed improved PWM algorithm can be used to improve the performance index of power quality in electrotechnical complexes with FC and AR by using optimal tables of switching angles in conditions of various modes of the power supply system. The adequacy of the simulation model has previously been confirmed by experimental data and previous studies.

A study on performances of carrier-based pulse-width modulation techniques for three-phase three-level t-type neutral-point-clamped inverter under switch-open-circuit fault on two neutral-point-connected legs

Multilevel voltage source inverters (VSIs) have been used for several decades thanks to their advantages compared with traditional two level VSI. Among various types of multilevel configuration, the T-type neutral-point-clamped VSI (3L TNPC VSI or 333-type VSI) has gained the attention in recent years. Due to the unique structure, the 333-type VSI has critical issues in reliability in operation such as switch-open-circuit (SOC) and switch-short-circuit (SSC), which lead to several unrequired issues, for instance, reduction of system performance, distorted and unbalanced output voltages and currents, or triggering the protection circuits. In some applications, the amplitude reduction and harmonics distortion of output voltages in SOC faults are not acceptable. Therefore, it is necessary to develop a pulse-width modulation (PWM) algorithm for 333-type VSI working under SOC fault which guarantees the desired output fundamental component voltage. The simultaneous SOC fault on two neutral-point-connected legs in the 333-type VSI may cause a large reduction in the output voltage. Under this circumstance, the 333-type VSI becomes an asymmetrical one called 322-type VSI. Certain studies regarding to the operation of 333-type VSI under SOC faults have been carried out. However, these studies require more semiconductor devices in order to create a redundant switching circuit. This leads to higher system cost with reduced inverter effieciency due to the additional loss. In this study, two carrier-based pulse-width modulation (CBPWM) techniques, i.e. 322-sinusoidal PWM (322-SPWM) and 322-medium offset CBPWM (322-MOCBPWM) are proposed for 322-type VSI. The proposed techniques are firstly simulated in MATLAB/Simulink and then implemented on a hardware setup. Performances of the proposed techniques are evaluated in terms of total harmonic distortion (THD) and weighted-THD (WTHD) of output voltages. Simulation results show that considering the worst output voltage under SOC fault, vBC, the proposed 322-SPWM technique could improve the THD by 40% and the WTHD by 94% compared with the uncompensated case with m=0.8. The corresponding results of 322-MOCBPWM technique are 42% and 96%, respectively. Characteristics of THD and WTHD values are also presented for demonstration the effectiveness of the proposed algorithm.

Control of an Ultracapacitor-Based Energy Storage System for Source and Load Support Applications

This paper presents a simple pulse width modulation algorithm for control of an ultracapacitor based energy storage system used for source and load support applications. As opposed to dual loop control philosophy that is widely used for backup applications, this paper presents a simple single loop current control that is only useful for controlling the ultracapacitor based DC/DC converters used in source and load support applications. The proposed PWM blocking method necessitates the DC/DC converter to operate in five states and takes into consideration the essential operational limits associated with the ultracapacitors. The performance of the proposed algorithm is verified experimentally using a 24 V laboratory prototype setup. Further, the shortcomings of dual loop control when applied to source and load support applications are demonstrated.

An effective compensation control strategy for power quality enhancement of unified power quality conditioner

The unified power quality conditioner (UPQC) has become one of the most proficient solutions for compensating the effects of voltage fluctuations, harmonics, sudden load changes and enhancing the power quality of distribution networks. Aiming at the shortcomings of conventional compensation control strategies and enhancing the compensation effect of UPQC, this paper proposes an effective control strategy for UPQC based on dq0 detection method. Furthermore, the space vector pulse width modulation (SVPWM) algorithm is improved in this paper. The fundamental and harmonic detection on the power supply side current and load side voltage are performed through the proposed strategy. In order to verify the effectiveness of the proposed control strategy, the simulation model of the system is established by MATLAB/Simulink under three-phase voltage unbalance conditions, voltage sag and load sudden changes. In addition, an experimental verification is carried out on an installed experimental platform. Under normal and unbalance operating conditions of the three-phase power supply voltage, the proposed control strategy has a better fundamental and harmonic detection effect compared with the conventional detection-based control strategy. Furthermore, under different load sudden changes conditions, it is verified that the proposed control strategy has better voltage tracking performance. Finally, the outcomes showed the effectiveness of the proposed control strategy in maintaining load side voltage stability, maintaining power side current sinusoidal, and enhancing the power quality of the distribution network.

Self-Balanced 13-Level Inverter Based on Switched Capacitor and Hybrid PWM Algorithm

A 13-level inverter based on switched-capaci-tor technique is proposed in this article. It consists of ten transistors, four diodes, and four capacitors with self-balanced voltages. The ten transistors form two H-bridges and one half-bridge resulting in simple structure and easy design of gate drivers. With a hybrid of level-shifted and phase-shifted pulsewidth modulation algorithm, voltage ripples of capacitors and low harmonic components of output voltage are suppressed simultaneously. Compared with the existing solutions, the proposed 13-level inverter has a simpler structure and the lower cost per level. Experimental results demonstrate that the proposed inverter has the advantages of high boosting factor, self-balanced capacitor voltages, low harmonics, and high efficiency, and the maximum efficiency is up to 97.2%.

Increasing the Utilization Factor of an Autonomous Inverter under Space Vector Control

Control systems for ac electric drive frequency converters are based on pulse width modulation (PWM) algorithms. Their use leads to problems: significant output voltage and current distortion, the appearance of shaft torque pulsation and its rotation frequency, and, as a result, an increase in vibrations and noise of the drive motor. Semiconductor PMW converters are also characterized by underutilized voltage. The solution to these problems is possible through applying space vector modulation (SVM) algorithms, however the voltage efficiency remains at the PWM level. To solve these problems, it is reasonable to use modified SVM algorithms that will provide semiconductor converter operation in the overmodulation mode. This article considers the development of overmodulation algorithms, the application of which will solve these problems. The following developed algorithms for the overmodulation of spatial vector control systems are presented: an alternating active overmodulation algorithm, adaptive overmodulation algorithm, and synchronous overmodulation algorithm. Their mathematical formulation is given. It is shown that overmodulation algorithms provide an increased voltage utilization factor of the autonomous inverter. When using the developed overmodulation algorithms, the output current of the autonomous inverter has a quasi-sinusoidal shape. The minimum autonomous inverter output current distortion coefficient is provided when using the synchronous overmodulation algorithm at a level of no more than 10%. The switching frequency of the autonomous inverter becomes lower, which leads to reduced switching losses. It is shown that the use of overmodulation algorithms is feasible and provides higher values of such indicators of electric energy conversion efficiency as: output current and voltage distortion coefficients, voltage utilization factor of the autonomous inverter, amplitude of the fundamental harmonic at the same value of the space vector modulation period and switching frequency.

Novel space vector PWM technology with lower common‐mode voltage for dual three‐phase PMSM

Pulse width modulation (PWM) converters generate switching common-mode voltages (CMV) across the load terminals. These voltages cause common mode currents, leading to bearing failure in motor loads and electromagnetic interference problems. This study proposes a novel space vector PWM strategy to reduce the CMV in the dual three-phase permanent magnet synchronous motor (PMSM) driven by two-level six-phase inverter. The novel space vector PWM algorithm discards the use of zero vectors. Firstly, the two largest voltage vectors of each sector are selected as main vectors to synthesise reference vector. Then, three groups voltage vector, which are opposite to the main vectors, have been selected as auxiliary vectors. Appropriate auxiliary vector selected is based on the length of zero voltage vector working time. Next, zero vector working time is distributed to the main and selected auxiliary vectors based on voltage-second principle. In addition, CMV and the harmonic component in z1z2 subspace of the proposed space vector PWM are analysed in detail. Finally, the expected CMV reduction to one-sixth of DC voltage and change rate of CMV in each cycle promised by the proposed novel space vector PWM are demonstrated with simulation and experimental results.

Position control of a pneumatic cylinder actuator using modified PWM algorithm

Pneumatic cylinders are used as actuators for modern automatedsystems in many industries applications for their numerous advantages.Basically, those applications are implemented using components suchas proportional and servo pneumatic control valves that are relativelyexpensive because of their high accuracy even in applications thatdo not require such high accuracy. Recently, binary (on/off) solenoiddirectional control valves (DCVs) have been used to replace many ofthe expensive components and consequently reduce the system costwith achieving acceptable accuracy. This paper presents a controltechnique for a positioning system of a pneumatic double acting cylindercontrolled by pair of on/off solenoid DCVs. The control technique hasbeen developed based on a parametric study presented previously by theauthors[1]. The control technique depends on operating the DCVs usinga pulse width modulation (PWM) algorithm that is modified to employa valve dead-zone compensator (DZC) along with using optimumpneumatic parameters gained from the performed parametric study. Anexperimental test bed for a pneumatic double acting cylinder positioningsystem that uses a pair of on/off solenoid DCVs has been installed to testthe accuracy of the presented control technique. A comparison betweenthe performance of the positioning control technique using the modifiedPWM control algorithm and the traditional one has been carried outto experimentally show the enhancement of the positioning accuracywith acceptable maximum steady state error less than 0.7 mm whenusing the modified PWM control technique due to reducing the systemnonlinearity associated with its dynamics.

A Single-Stage Fault-Tolerant Three-Phase Bidirectional AC/DC Converter With Symmetric High-Frequency Y-Δ Connected Transformers

This article presents a single-stage isolated three-phase bidirectional ac/dc converter with symmetric Y-Δ connected transformers, which implements ac/dc buck conversion, high-frequency electrical isolation, and high power factor for ac side (PF > 0.99). The converter can be utilized between the ac bus and the dc bus in ac–dc hybrid microgrid and in other applications where three-phase bidirectional ac/dc conversion is needed. With two operating modes available, the converter possesses the fault-tolerant ability and the improved light-load efficiency. When the converter works in the high power application with all the components operating normally, the transformers operate in the symmetric mode and share the power equally. Then, the switch current stress can be reduced. The converter can also operate in dual transformer mode for light-load conditions or with some abnormal components. The Y-Δ connected transformers provide an additional step-down conversion ratio and make the converter suitable for buck conversion. Furthermore, to guarantee the voltage-second balance of the transformers, the corresponding space vector pulse width modulation (SVPWM) algorithm is proposed. Experimental results based on a 2.4-kW prototype are presented in detail, which verify the theoretical analysis and demonstrate the converter's performance well.

Research on Three-phase Variable Frequency Power Supply Based on DSP and SVPWM Technology

Starting from the defects of analog power supply. Based on the analysis of space vector pulse width modulation algorithm, a three-phase variable frequency variable amplitude inverter power supply based on SVPWM technology is studied. On this basis, the PI control algorithm for closed-loop control of inverter power supply is also proposed. In order to improve the system response speed, the DSP with powerful digital signal processing capability was designed as the hardware platform, and various related verification experiments were completed. The results show that the system realizes a voltage-regulated output with a step of 1 V and a range of 40 V and an FM output with a step of 2Hz and a range of 50Hz to 1kHz. The system has small load regulation rate, excellent performance and good application prospects.