Reference Phase Voltages Research Articles

A Simplified PWM Strategy for Open-Winding Flux Modulated Doubly-Salient Reluctance Motor Drives With Switching Action Minimization

In this article, a simplified pulsewidth modulation (PWM) strategy is proposed for open-winding flux modulated doubly-salient reluctance motor (FMDRM) drives for switching action minimization and common-mode voltage (CMV) reduction. Conventionally, the open-winding converter topology is utilized to achieve the zero-sequence current flow path and dc-biased sinusoidal current excitation for the FMDRM, where the switching actions of power switches are doubled compared to the conventional modular three-phase converter, leading to higher switching losses. Different from the conventional space vector PWM scheme, the reference voltages of converter legs are directly calculated by the reference phase voltages in the proposed PWM scheme. In addition, a rotor-position-based sector division method is proposed to deal with the sector imbalance caused by the distorted back electromotive force (back EMF). Furthermore, different leg voltage clamping methods are respectively developed in odd and even sectors for switching action minimization, which can achieve voltage stress balance and CMV reduction. With the proposed scheme, the switching actions in each switching cycle can be reduced by half, which effectively increases the system efficiency of the FMDRM drive. Experiments are carried out on a three-phase 12/8 FMDRM prototype to verify the effectiveness of the proposed scheme.

Generic Carrier-Based PWM Solution for Series-End Winding PMSM Traction System With Adaptative Overmodulation Scheme

The series-end winding permanent magnet synchronous machine (SW-PMSM) drive system is a new drive topology where the phase windings are connected in series. The generic carrier-based pulsewidth modulation (CBPWM) solution of SW-PMSMs will further promote their applications and avoid the computationally complex space vector PWM in multiphase SW-PMSMs. However, the existing CBPWM solution is complex and designed for symmetrical machines. Moreover, the current approach’s lack of the overmodulation method limits its application in the traction system. This article proposes an improved generic CBPWM solution for SW-PMSMs, which utilizes the vector space decomposition concept to extend the application in both symmetrical and asymmetrical machines. First, we will introduce the concept of the virtual duty axis and divide the modulation process into two steps, where the leg voltage sequence is initialized with reference phase voltages. Then, the virtual duty cycle is utilized to ensure the feasibility of the leg voltage sequence. Furthermore, we will provide an adaptative overmodulation scheme to ensure the stable fundamental currents in the whole speed range and improve the bus voltage utilization. Finally, the experimental results in three machines verify that the proposed solution can obtain better performance with lower switching frequency and have overmodulation capability.

Dynamic Addition of Common Mode Voltage in Post Fault Operation of Cascaded H-Bridge Converter Fed Induction Motor Drive

In this article, a postfault control technique is proposed for a rotor field-oriented induction motor (RFO-IM) drive fed from a cascaded H-bridge multilevel (CHB-ML) converter. The control strategy is to vary the magnitude and phase shift of the injected fundamental common mode voltage (FCMV) according to the motor’s operating condition. The addition of the proposed FCMV with the reference phase voltages, not only ensures maximum line voltage in the postfault operating condition but also shares equal power among the remaining healthy cells of the converter. Moreover, in the postfault operation, a detailed analysis is performed on both motor and converter, and an integrated control is presented to maintain the command speed and load torque of the RFO-IM. This includes the mathematical equation explaining the new operating point of the motor for different fault configurations, traversal of operating point, and the variation in power factor of each leg of the converter in postfault conditions. From the above analysis, the dynamic FCMV is calculated from the new operating point of the stator current components in the current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -plane and the fault configuration of the CHB-ML converter. The proposed control technique is validated using simulation and experimental results conducted on a 3-hp IM.

Online Short-Circuit Current Estimation of Permanent Magnet Motors

In this article, online short-circuit estimation of permanent magnet synchronous motors (PMSMs) are presented, which is essential for postfault ac drive operations. For this purpose, initially, the PMSM model with interturn short-circuit fault (ITSC) is extended to cover motors with saliency. By utilizing ITSC model voltage equations and voltage reference equations, the amplitude and phase relationship between short-circuit current and the phase reference voltage is established. In the next step, second harmonics in the reference voltage and feedback current are used to extract the short-circuit current information. In order to efficiently use ac drive microcontroller bandwidth, the proposed short-circuit current estimation method is executed after the ITSC fault is detected, not continuously. Instead of running the proposed short-circuit current estimation continuously, it is reasonable to run it after an ITSC fault detection to efficiently use ac drive microcontroller bandwidth. Therefore, two intermediate steps, a simple ITSC fault detection and severity estimation algorithms are proposed as well. The proposed technique can estimate the fault current and severity without the knowledge of fault location and valid for all PM motors. The findings are experimentally tested using two PMSMs to demonstrate the effectiveness and practicability of the proposed estimation technique.

Post-fault control strategy of rotor field-oriented induction motor drive fed from cascaded H-bridge multi-level converter

In this paper, a control technique is proposed to maintain the torque and speed of the rotor field oriented induction motor (RFOIM) fed from a cascaded H-bridge multi-level converter (CHB-MLC) in post-fault operation. In this post-fault control technique, a common mode voltage (CMV) is added to the reference phase voltages according to the motor&apos;s loading condition and the converter&apos;s fault configuration. The addition of this CMV ensures that the amount of power generated in each phase is proportional to the number of remaining healthy cells in that phase. Moreover, maximum line voltage is also obtained in the post-fault operating condition. The mathematical expression of the CMV to be added in post-fault operation for equal power sharing among the remaining healthy cells and the analysis of motor&apos;s operating point are derived and explained. Computer simulation and experimental results are presented to validate the proposed control technique.

Harmonic-Separation-Based Direct Extraction and Compensation of Inverter Nonlinearity for State Observation Control of PMSM

Nonideal switching characteristics of voltage source inverter (VSI) will result in distortions in both phase currents and reference voltages of a permanent magnet synchronous machine (PMSM) drive system, which will also consequently introduce ripples into the output speed and shaft torque, and result in a performance deterioration in the state observation control. To solve this issue, a method of directly extracting and compensating the nonlinear voltage disturbance due to VSI nonlinearity employed in PMSM drives is proposed in this paper. Firstly, the distorted voltage due to VSI nonlinearity is directly extracted via a harmonic separation scheme, which can be easily compensated by a proportional integral controller afterwards. Since both 6th harmonic and DC terms of dq -axis distorted voltages due to VSI nonlinearity are well compensated, the proposed method shows sufficiently good performance under both $i_{d}=0$ and maximum torque per ampere controls ( $i_{d} ), as verified on two prototype PMSMs being salient pole and non-salient pole, respectively, both developed for a low-speed rotary actuator. In addition, the application of proposed method to state observation controls such as the model-based sensorless control and the deadbeat predictive current control, is finally investigated. Test results manifest that the proposed method can effectively improve the accuracy of observed rotor position/speed, and the ability of current tracking.

Improved Power Converter of SRM Drive for Electric Vehicle With Self-Balanced Capacitor Voltages

The regulation of phase currents is bound by the voltage of power source for switched reluctance motor (SRM) drive with conventional asymmetric half-bridge (AHB) power converter in electric vehicle (EV). To avoid the drawback, an improved active boost power converter with self-balanced capacitor voltages is proposed. First, the problems existing in the AHB power converter are analyzed in different stages of each phase current. Then different working modes of the proposed converter are investigated. The corresponding control strategies are implemented in the light of two conduction sequences. The reference phase voltage is obtained with a new method. Then the control signals of the front-end topology are generated by comparing the reference phase voltage with the required value. One significant advantage of the proposed converter is that it can provide different voltages according to the operation condition of SRM dynamically. The other is that the maximum phase voltage the converter can boost is up to three times the supplied voltage. Comparative experiments on a three-phase 12/8 SRM drive validate the performance of the converter and the effectiveness of the control strategies.

Analysis and Control of PV Cascaded H-Bridge Multilevel Inverter With Failed Cells and Changing Meteorological Conditions

This article proposes an approach to control a photovoltaic cascaded H-bridge multilevel inverter with failed cells and changing meteorological conditions for large-scale grid-connected applications. The controller development is based on an analysis of the interaction between the inverter common-mode and differential-mode quantities, which is done in the time domain, supported by a space vector representation analysis. The proposed approach is able to produce balanced three-phase line-to-line voltages and currents even if there is a failed cell or if the fluctuating meteorological conditions cause uneven power distribution among the bridges. This is achieved through the modification of the pulsewidth modulation reference phase voltage angles combined to the injection of a dynamic homopolar component. Such an approach avoids tripping the system due to the protective functions #25 and #87 for per grid applicable codes and standards. Numerical simulations and laboratory experiments performed on a seven-level converter with different abnormal conditions to confirm the effectiveness of the suggested control strategy.

A Composite Voltage-Balancing Method for Four-Level NPC Inverters

Four-level neutral-point-clamped (NPC) inverter suffers from the neutral-point (NP) voltage-balancing problem, which seriously hinders its application in the industry. Carrier-overlapped pulsewidth modulation (COPWM) is a newly proposed carrier-based modulation method which can solve this problem. However, the total switching transitions under this modulation method are doubled, and hence the switching losses are increased. In order to alleviate this problem, a composite modulation and voltage-balancing method is proposed in this article. For a low modulation index range under 0.5, phase-disposition pulsewidth modulation (PDPWM) is utilized and the relationship between the NP currents and the reference phase voltage is derived. A zero-sequence voltage injection-based NP voltage balancing method is proposed. For a high modulation index range more than 0.5, a decoupled voltage-balancing method based on COPWM is used. By combining the two modulations and voltage-balancing methods, the NP voltages can be balanced under the full modulation index range with reduced switching losses. Simulation and experimental results are presented to confirm the validity of this method.

Fuzzy logic-based multi-level shunt active power filter for harmonic reduction

In this paper, using a three level diode clamped multilevel inverter and DC capacitor, a shunt active power filter (SAPF) is implemented to mitigate the supply current harmonics and compensate reactive power drawn from nonlinear load. The advantage of using three-level inverter paves way to reduced harmonic distortion and switching losses. Fuzzy logic control and unit sine vector control are proposed in this paper for generating reference current for the SAPF. The advantage of fuzzy control is that it is based on a linguistic description and does not require a mathematical model of the system. The implementation of fuzzy logic control (FLC) algorithm is executed using MATLAB fuzzy logic tool box. The proposed pulse width modulation (PWM) method produces the switching signals to the inverter from the sampled reference phase voltage magnitudes as in the case of conventional space vector PWM (SVPWM). The simulation results illustrate that the proposed three-level SAPF with low harmonic content in supply current and in phase with the line voltage. The simulation results are validated with prototype model for demonstrating the effectiveness of the system.

Fuzzy logic-based multi-level shunt active power filter for harmonic reduction

In this paper, using a three level diode clamped multilevel inverter and DC capacitor, a shunt active power filter (SAPF) is implemented to mitigate the supply current harmonics and compensate reactive power drawn from nonlinear load. The advantage of using three-level inverter paves way to reduced harmonic distortion and switching losses. Fuzzy logic control and unit sine vector control are proposed in this paper for generating reference current for the SAPF. The advantage of fuzzy control is that it is based on a linguistic description and does not require a mathematical model of the system. The implementation of fuzzy logic control (FLC) algorithm is executed using MATLAB fuzzy logic tool box. The proposed pulse width modulation (PWM) method produces the switching signals to the inverter from the sampled reference phase voltage magnitudes as in the case of conventional space vector PWM (SVPWM). The simulation results illustrate that the proposed three-level SAPF with low harmonic content in supply current and in phase with the line voltage. The simulation results are validated with prototype model for demonstrating the effectiveness of the system.

Three-Phase PLL for Grid-Connected Power Converters Under Both Amplitude and Phase Unbalanced Conditions

This paper proposes a technique for accurate phase estimation of distorted three-phase grid voltages including unbalanced amplitudes and/or phase angles. An adaptive cascaded delayed signal cancellation (CDSC) strategy is used for the generation of the amplitude balanced three-phase voltages. The CDSC strategy also eliminates both odd and even harmonics from the input voltage. An algorithm is also reported for removing the phase angle deviations from the three-phase voltages including unbalanced phase angles. Finally, a phase-locked loop (PLL) is applied to estimate the phase angle of the reference phase voltage. It requires only one PLL to estimate three phase angles of the thee-phase voltages, respectively, suffering from the unbalanced amplitudes and phase angles. It is also immune to harmonic distortions at changeable frequency environment. When compared to the CDSC-PLL and dqCDSC-PLL techniques reported in the technical literature, it can provide improved phase estimation under amplitude and phase unbalanced condition. Simulated and experimental results of the technique are acquired from the MATLAB/Simulink and dSPACE1104 control board platform, respectively, for a number of case studies observed in the grid voltage.

Fault-Tolerant Predictive Control of Six-Phase PMSM Drives Based on Pulsewidth Modulation

Multiphase machines are famous for their fault-tolerant capability. Conventional fault-tolerant model predictive current control (FT-CMPC) of multiphase machines suffers from high computational burden, low switching frequency, and relatively high current harmonics. This paper proposes a fault-tolerant PWM predictive control (FT-PWMPC) to enhance the performance of fault-tolerant predictive control strategy without using complex enumeration method. The reference phase voltages are generated by a postfault mathematical model in stationary reference frame and transformed to duty cycles with a properly set common-mode voltage. Then, a comparative study of fault-tolerant predictive control strategies is presented, including FT-CMPC, FT-two-vector-based-predictive control, and the proposed FT-PWMPC. The control strategies are implemented with the same sampling frequency or switching frequency on a six-phase permanent magnet synchronous machine test bench. Experimental results of dynamic response, steady-state currents, vibration, and parameter sensitivities are given to identify the advantages and limitations of each control strategy.

Fractal‐based autonomous partial discharge pattern recognition method for MV motors

On-line partial discharge (PD) monitoring is being increasingly adopted to improve the asset management and maintenance of medium-voltage (MV) motors. This study presents a novel method for autonomous analysis and classification of motor PD patterns in situations where a phase-reference voltage waveform is not available. The main contributions include a polar PD (PPD) pattern and a fractal theory-based autonomous PD recognition method. PPD pattern that is applied to convert the traditional phase-resolved PD pattern into a circular form addresses the lack of phase information in on-line PD monitoring system. The fractal theory is then presented in detail to address the task of discrimination of 6 kinds of single source and 15 kinds of multi-source PD patterns related to motors, as outlined in IEC 60034. The classification of known and unknown defects is calculated by a method known as centre score. Validation of the proposed method is demonstrated using data from laboratory experiments on three typical PD geometries. This study also discusses the application of the proposed techniques with 24 sets of on-site PD measurement data from 4 motors in 2 nuclear power stations. The results show that the proposed method performs effectively in recognising not only the single-source PD but also multi-source PDs.

Indirect Vector Controlled Asynchronous Motor Drive’s Dynamic Performance and Analysis with A New Modified MPPT Controller

Generation of electricity from the PV system has nowadays chosen as a best energy collecting source, due to its abundance availability and also to save the conventional energy sources to the future generation. Because all the conventional sources are coming to an extinct. That is the reason, everybody are looking towards the available renewable energy resources like wind, solar, bio mass, ocean, tidal and geothermal. But, upon those, solar and wind sources are maximum preferred sources, due to their easy availability and easy way of collection of energy. This paper presents a modeling of solar photovoltaic (PV) array with a new modified maximum power point tracking (MPPT) controller, which enhances the PV system performance even at abnormal weather conditions. That the existed MPPT controllers were developed based upon the ideal characteristics of constant irradiance with variable temperature and constant temperature with variable irradiance. To overcome the above problem a practical data is considered for designing of MPPT controller which is based upon variable irradiance. But here, it is developed with the variable irradiance and variable temperature with better performance of the system. The output obtained from the PV with a new modified MPPT is given to the boost converter with an inverter to find the dynamic performance of an indirect vector controlled asynchronous motor drive under different operating conditions. For inverter control, a space vector modulation (SVM) algorithm is used, in which the calculation of switching times is proportional to the instantaneous values of the reference phase voltages. The dynamic performance responses like phasor current, torque and speed of the drive by the new modified MPPT along with SVM controlling technique of the inverter are compared and analyzed with the existed method for different operating conditions.

Performance Improvements in Open End Winding Induction Motor Drive Using Decoupled PWM Techniques

This Paper presents a decoupled space vector modulation algorithm for a three level open-end winding induction motor drive. In the proposed scheme, switching vectors for the 2- two level inverters are generated separately using the instantaneous reference phase voltages along with the simple digital logic. So that, each inverter can be operated as a two level inverter isolately. This modulation scheme does not require any complex computations. This algorithm generates different pulse width modulation (PWM) schemes by phase shifting one inverter phase voltages with respect to the other inverter. A common- mode voltage is identified in the dual inverter, all the PWM schemes presented in this paper mitigating and also eliminating the common-mode voltage (CMV) in a dual inverter. All the pulse width modulation (PWM) schemes generated in the proposed decoupled algorithm are simulated using MATLAB/SIMULINK environment, and the corresponding results are presented.

Generalized Theory and Analysis of Scalar Modulation Techniques for a $m {\;\times\;} n$ Matrix Converter

The basic requirement of all the scalar modulation strategies employed for matrix converter, is to define the desired output voltages. The output phase voltages, if not optimized, results in underutilization of semiconductor device ratings. For better utilization, the output reference phase voltages are modified such that the sinusoidal nature of line voltages is not altered. Multiphase drives are in consideration and much work is being done and reported on multiphase matrix converter-based system. New modulation strategies for such systems are being formulated. Most of these new strategies are based on scalar approach; which in contrast to the space vector pulse width modulation, require addition of friendly harmonics in order to achieve optimized output reference phase voltages and maximum utilization of the matrix converter semiconductor switches. On the other hand, in space vector pulse width modulation, the maximum voltages are inherently achieved. This paper presents a generalized theory, explained in mathematical as well as graphical manner, defining the optimized output reference phase voltages for any number of input and output phases, whether odd or even, for m × n matrix converter. Further, this paper also explores the Venturini method for m × n case. It is found that the method is extendable to 3 × n matrix converters only. Finally, a simple and generalized algorithm, applicable to all m × n matrix converter configurations, is discussed. Results for 3 × 5 matrix converter are validated by simulation and experimental results.

On design and implementation of three phase three level shunt active power filter for harmonic reduction using synchronous reference frame theory

Shunt active power filter is commonly used to eliminate current harmonics generated in the source side due to presence of non-linear loads. This scheme consists of three phase three level diode clamped multilevel inverter and a DC capacitor that act as a shunt active power filter to mitigate the supply current harmonics and inject the required reactive power to non-linear loads. In this paper, using synchronous reference frame algorithm, a three phase three level SAPF is implemented on an embedded platform. In SRF theory, reference signals are transformed from a–b–c stationary frame to 0–d–q rotating frame. The reference signals in the 0–d–q rotating frame are controlled to get the desired reference signals using PI controller. The PWM signal generation for the three phase three level inverter is computed directly from the sampled amplitudes of the reference phase voltages. The practical implementation of the SAPF is realized using Xilinx XC3SD1800A – FG676-4 Spartan 3A DSP FPGA controller. This system is simulated using MATLAB/SIMULINK and the simulation results are compared with prototype hardware model for validating the effectiveness of the proposed system. Based on the studies, it is concluded that the SAPF is easy for implementation for reducing the Total Harmonic Distortion below 5% as per IEEE-519 standard.

Space‐vector pulse width modulation scheme for open‐end winding induction motor drive configuration

This study proposes a novel space-vector pulse width modulation scheme for an induction motor with open-end windings. The proposed PWM scheme requires two two-level inverters with isolated power supplies. This PWM scheme uses instantaneous phase reference voltages for the generation of gating signals. Open-end winding induction motor (OEWIM) offers significant switching redundancy. Thus, with the proposed scheme the required gating pulses can be generated to reduce the voltage stress on the switching devices. In addition, the switching scheme is capable of equalising the junction temperature rise during the switching and conduction state of the devices. In the present switching scheme when one inverter is switching while the other inverter is clamped and vice versa. The proposed scheme is simulated using MATLAB/Simulink. The PWM scheme is experimentally validated on dSPACE for a three-level OEWIM.

VCMIPWM Scheme to Reduce the Neutral-Point Voltage Variations in Three-Level NPC Inverter

ABSTRACTThis paper presents variable common mode injection pulse width modulation (VCMIPWM) technique to reduce the neutral-point voltage variations in three-level neutral-point-clamped (NPC) inverter. The neutral-point voltage varies with the modulation index and the variation is high in the low modulation index region. Therefore, proper common mode voltages are calculated for various modulation index regions and are carefully injected with the reference phase voltages. The calculation is based on equalizing the switching times of the zero/redundant vectors in a switching cycle for various modulation index regions. The simulation results show the improvement in the neutral-point voltage balancing of the inverter in the VCMIPWM scheme compared with the sinusoidal pulse width modulation (PWM). The proposed PWM is implemented in field programmable gate array (FPGA) and the experimental results are shown to verify the practicability of the proposed method.