Three-phase Modulation Research Articles

A Novel Electrolytic Capacitor-Less MMC With Magnetic Power Decoupling Method

This article presents a novel flux-cancellation-based modular multilevel converter (MMC) with power decoupling capability. Conventional MMC suffers from low-frequency (fundamental and second-order) ripple power in the submodule (SM) capacitors. The low-frequency ripple power makes the SM capacitors bulky, responsible for a significant portion of the volume and weight of the whole system. The ripple power on the SM capacitor of the three-phase module is phase-shifted by 2π/3 rad from each other. The proposed flux cancellation is based on directing the low-frequency ripple power to a common core of a three-winding transformer to cancel out. A three-port bidirectional isolated dual half-bridge is introduced for flux cancellation. For this scheme, the main problem is the presence of leakage inductances of the transformer, and another one is three-port isolated bidirectional converter modeling as it has only input ports. The average model is proposed for the flux cancellation circuit. It provides a practically simple model for the complex circuit. Second, a virtual-capacitance-based power decoupling controller is proposed to overcome the leakage inductance problem by the benefits of simple current estimation and of no need for the current sensor. The proposed power decoupling method reduces the system size significantly and enables the MMC to operate with a nonelectrolytic SM capacitance of few microfarads. The operating principle and control design of the proposed MMC are presented. The proposed MMC is validated by simulation and experimentation.

Current Regulator Design for Dual Y Shift 30 Degrees Permanent Magnet Synchronous Motor

This paper gives the current regulator design for a dual Y shift 30 degrees permanent magnet synchronous motor (DT_PMSM) based on the vector space decomposition (VSD). Current regulator design in α-β subspace is insufficient and designing additional controllers in x-y subspace is necessary to eliminate the harmonic currents due to the nonlinear characteristics of the inverter. A sliding mode controller based on an internal model is proposed in α-β subspace, which is robust to the parameter uncertainties and disturbances in current control loops. In order to eliminate the harmonic currents in x-y subspace, a resonant controller is employed based on a new synchronous rotating matrix. Three-phase decomposition space vector pulse width modulation (SVPWM) technique is illustrated for the purpose of synthesizing the voltage vectors in both subspaces simultaneously. The feasibility and efficiency of the suggested current regulator design are validated by a set of experimental results.

Phase Reconfiguring Technique for Enhancing the Modulation Index of Multilevel Inverter Fed Nine-Phase IM Drive

In this article, a multilevel inverter (MLI) scheme is proposed for four-pole (4-pole), nine-phase (9-phase) induction motor (IM) drives with improved dc bus utilization as well as reduced device count. The proposed MLI is realized with nine three-switch inverter legs (3-SIL) and a single dc source. In the proposed MLI, each 3-SIL is utilized for exciting the two identical voltage profile coils/phase of the four-pole (4-pole) stator winding, which means each leg has to be modulated with two references. These two independent references/leg will limit the modulation index (M.I) of 3-SIL-based proposed MLI. This lower M.I will result in a requirement of the higher magnitude of dc-link voltage to achieve the rated load voltage requirement. In this article, an effective phase reconfiguring concept is proposed for reducing the dc-link voltage requirement of the proposed MLI. In addition, all the possibilities of phase reconfiguring details for proposed MLI-fed 9-phase IM drive are also presented. A three-phase carrier-based space vector pulsewidth modulation is implemented for improving the linear modulation range of proposed MLI configuration further. In contrast with existing 9-phase three-level inverters, like NPC and FC, the proposed MLI configuration requires only one dc link (with half of the magnitude) and lesser number of semiconductor devices. The proposed MLI-fed, 5 hp, 9-phase, 4-pole IM drive is validated by using Ansys Maxwell FEM simulation and experimental prototype for entire modulation range.

An integrated experimental system for gas hydrate drilling and production and a preliminary experiment of the depressurization method

The current natural gas hydrate extraction experimental research has always been carried out in a small-scale simulation test device, and the resulted boundary effect is so obvious due to the small size of samples in the reaction kettle that the experimental results will be difficult to apply in the field. In this paper, an integrated experimental system for drilling and exploitation of gas hydrate is developed innovatively based on the idea of depressurization method and the technological process. This experimental system consists of high-pressure vesselmodule, drilling & extraction module, liquid supply module, gas supply module, confining pressure loading module, back-pressure control module, three-phase separation module, temperature control module, data acquisition module and an operational platform. The hydrate-bearing samples similar to marine hydrate formations were prepared inthe experimental system with the actual geological surroundings simulated. The electrical resistance tomography was used to real-time monitor the dynamic distribution of gas hydrate in sediments inside the high-pressure vessel (521 L). This experimental system can also simulate the process of wellbore drilling in hydrate reservoirs and depressurization extraction, and realize the real-time monitoring of parameters in the whole production process such as gas production, water production, sand production, temperature, pressure, etc. We carried out a preliminary experiment on the CO2 hydrate extraction via depressurization by using this experimental system. Fundamental procedures for data acquisition and analysis were established and verified. The variations of temperature and pressure fields and gas/water output behaviors in the reservoirs were both achieved. The results show that (1) the gas and water production rate fluctuate greatly even at a constant backpressure; (2) the reservoir temperature distribution is uneven during hydrate decomposition, and the maximum temperature is decreased by 5 °C, suggesting that the hydrate decomposition is heterogeneous and stochastic. The abundant and credible experimental results based on this system are expected to provide important data support for marine gas hydrate production tests.

Research on the Simplified SVPWM for Three-Phase/Switches Y-Type Two-Level Rectifier

The three-phase/switch Y-type two-level rectifier is widely used in the unidirectional power-flowing applications such as LED illumination, communication and uninterruptible power supply. This paper presents the working principle of three-phase/switch Y-type two-level rectifier, and proposes two simple and fast modulation techniques (12-sector SVPWM and simplified equivalent SVPWM) based on the virtual vectors. The reference vectors of the 12-sector SVPWM are synthesized by utilizing real basic vectors and virtual vectors linearly combined from these real vectors in a switching period. So the created virtual vectors can reduce the error of reference voltage synthesis, contributing to better input current performance, this paper proposes a simplified 12-sector equivalent SVPWM, and shows the novel three-phase modulation wave expressions and waveforms. The proposed simplified 12-sector equivalent SVPWM does not need the process of sector determination with reducing computational processing time which is attractive for digital implementation. Finally, performance of the proposed modulation methods for a Y-type two-level rectifier using a 5kW prototype is experimentally verified.

Fast and simple space vector modulation method for multilevel converters

This study proposes a simplified space vector pulse-width modulation (SVPWM) method for multilevel converters. To avoid unnecessary coordination transformations, firstly, a further derivation is conducted on the basis of the 60° coordinate transformation. Then, all the nearest three vectors (NTVs), duty cycles and optimal switching sequence within one switching period can be identified through a simple comparison of three-phase modulation waves. To further reduce the switching frequency, detailed steps to achieve the minimum number of transitions among different NTVs are constructed. Combined with the optimal switching sequence within one switching period, the minimum number of transitions within a fundamental period can be achieved easily. Finally, a thorough discussion is conducted to simplify the procedure further and the flowchart for the proposed SVPWM is also presented. Compared with the previous methods, the proposed method does not require any iterative calculation or coordinate transformation. To the best of the authors' knowledge, the calculation amount is reduced by almost seven times compared with the methods proposed. In addition, the switching frequency and total harmonic distortions remain at the same level without any deterioration. Finally, the simulation and experiment for modular multilevel converter are performed to verify the correctness and efficiency of the proposed method.

An Output Ripple-Free Fast Charger for Electric Vehicles Based on Grid-Tied Modular Three-Phase Interleaved Converters

An off-board dc fast battery charger for electric vehicles (EVs) with an original control strategy aimed to provide ripple-free output current in the typical EV batteries voltage range is presented in this article. The proposed configuration is based on modular three-phase interleaved converters and supplied by the low-voltage ac grid. The ac/dc interleaved three-phase active rectifier is composed of three standard two-level three-phase converter modules with a possibility to slightly adjust the dc-link voltage level in order to null the output current ripple. A modular interleaved dc/dc converter, formed by the same three-phase converter modules connected in parallel, is used as an interface between the dc link and the battery. The use of low-cost, standard and industry-recognized three-phase power modules for high-power fast EV charging stations enables the reduction of capital and maintenance costs of the charging facilities. The effect of coupling on the individual input/output inductors and total input/output current ripples has been investigated as well, considering both possible coupling implementations, i.e., inverse and direct coupling. Numerical simulations are reported to confirm the feasibility and the effectiveness of the whole EV fast charging configuration, including the proposed control strategy aimed to null the ripple of the output current. Experimental results are provided by a reduced scale prototype of the output stage to verify the ripple-free output current operation capability.

Multiphysics Simulation Analysis and Design of Integrated Inverter Power Module for Electric Compressor Used in 48-V Mild Hybrid Vehicles

This paper presents designs, multiphysics finite-element method (FEM) and circuit simulations, and experimental validations of a three-phase inverter power module for an electric compressor (e-Compressor) used in 48-V mild hybrid vehicles. The inverter module is integrated with its motor and scroll. The integration and e-Compressor operation situations raise sequential challenges in the module design and analysis. Thus, the e-Compressor module employs a direct bonded copper (DBC) substrate on which MOSFET dies, shunt resistors, and other electronics are soldered. Multiphysics FEM and circuit simulations are conducted to analyze (and minimize) the parasitic and loop inductances, current concentration, and temperature elevation of the design. The modeling and simulation processes are customized to represent the integrated DBC-based e-Compressor module, including the determination of loop inductance and overshoot voltage by considering systemic current conduction and reasonable simplification of cooling fluid effects. The simulation process and module performances are validated by experiments. The designed e-Compressor inverter module is improved to fully satisfy all the required specifications. Moreover, an excellent agreement between the simulation and the experimental results is confirmed, demonstrating the similar reductions of: 1) loop inductances simulated by FEM (~57%); 2) circuit-simulated overshoot voltages (~47%); and 3) experimentally measured overshoot voltages (~53%).

Fuzzy Logic Based Robust DVC Design of PWM Rectifier Connected to a PMSG WECS under wind/load Disturbance Conditions

Permanent Magnet Generator has been widely used in Variable-Speed Wind Energy Conversion System (VSWECS). Fuzzy Logic Control (FLC) of the generator side converter has the ability to have good regulation of the DC-link voltage to meet the requirements necessary to achieve optimal system operation, regardless of the disturbances caused by the characteristics of the drive train or some changes into the DC-load. The main focus of this paper is to present a model for a three-phase voltage source space vector pulse width modulation (SVPWM) rectifier which is connected to a PMSG in a wind turbine system, where a direct voltage control (DVC) using FLC based on voltage orientation strategy is used to control the mentioned rectifier. The control algorithm employs a fuzzy logic controller to effectively achieve a smooth control of DC-link voltage under wind/load perturbation conditions. Some simulation results, using Matlab/Simulink, are presented to show the effectiveness of the SVPWM rectifier Connected to a PMSG WECS with the proposed control strategy.

Diagnosis and Tolerance of Common Electrical Faults in T-Type Three-Level Inverters Fed Dual Three-Phase PMSM Drives

In this paper, diagnosis and tolerant control schemes have been studied for common electrical faults in T-type three-level inverter fed dual-three phase permanent magnet synchronous motor (PMSM) drives for safety-critical applications. Based on vector space decomposition and double three-phase space vector modulation, diagnostic and tolerant control methods have been developed comprehensively for open-phase faults, open-switch faults, and short-switch faults in T-type three-level inverter fed dual-three-phase PMSM drives, in such way that misdiagnosis of different faults sharing similar faulty features can be avoided. In particular, a two-step diagnostic scheme is proposed in order to simplify the diagnostic process. The first step is to identify the faulty phase and fault category by analyzing current trajectories on harmonic subspace, and the second step is to determine the specific fault type in a small fault-searching area obtained from the first step. In the aspect of fault-tolerant control, a novel current compensation method is proposed for open-phase fault without changing the machine model, space vector diagram, and control framework. Open-switch faults and short-switch faults are tolerated by making full use of the remaining vectors after faults. The validity of the proposed fault diagnosis and tolerance schemes has been verified by experiments.

Assessment of Efficiency and Reliability of Wide Band-Gap Based H8 Inverter in Electric Vehicle Applications

This paper analyzes the performance of a three-phase converter architecture with a reduced common mode voltage to be used in electric motor drives. Starting from the classical three-phase bridge architecture, two additional switches are inserted in the DC link, in order to decouple the source from the load during the freewheeling intervals. Ad-hoc modulation strategies are introduced and evaluated against the classical three-phase space vector modulation. Three main parameters are analyzed: common mode voltage, efficiency and reliability. Experimental measurements on a converter prototype are used to evaluate the common mode performance. The efficiency in the case of Si-IGBT and SiC-MOSFETs is experimentally evaluated. Reliability analysis performed with a Coffin-Mason model showed that the higher efficiency offered by the SiC devices allows for a marked extension of the lifetime.

Cluster Voltage Regulation Strategy to Eliminate Negative-Sequence Currents Under Unbalanced Grid for Star-Connected Cascaded H-Bridge STATCOM

Under unbalanced grid, three cluster voltages are typically controlled balanced and unchanged for the star-connected cascaded H-bridge static synchronous compensator (CHB STATCOM), however, to deal with the unbalanced grid voltages, the modulation voltages become unbalanced, which would result in fewer steps of the staircase voltages and unbalanced double-line-frequency ripples across the cluster voltages. Thus, the harmonic performance of the currents is deteriorated. In addition, the negative sequence currents are always injected for active power redistribution, which degrades the power quality. To improve the current performance under the unbalanced grid, three cluster voltages are regulated to different values and three-phase modulation voltages can maintain balance. Based on this concept, three cluster voltages can be derived by decomposing the positive- and negative-sequence components from the converter voltages to meet the balance of three-phase currents. To ensure the cluster voltages stable, the zero-sequence voltage is further extracted to analyze the active power distribution. It is interesting to find that the total active power in each phase induced by both the negative and zero-sequence voltages is equal to zero, which reveals the CHB STATCOM has the natural zero-active-power feature. To keep three unequal cluster voltages within a certain boundary, the relationship between the unbalanced grid voltages and the cluster voltages is established, based on which the algorithm of limiting the cluster voltages is proposed. The theoretical analysis and the proposed control scheme are verified by the simulation and experimental results.

Photovoltaics literature survey (no. 149)

Photovoltaics literature survey (no. 149)

Three-Phase ZVR Topology and Modulation Strategy for Transformerless PV System

Leakage current reduction is crucial for operating transformerlss photovoltaic (PV) systems. In this letter, a new three-phase topology and modulation strategy is proposed. It is derived from the single-phase zero-voltage state rectifier topology, but the operation mechanism is quite different. Therefore, a new modulation strategy based on the Boolean logic function is proposed to achieve the constant common-mode voltage, so as to eliminate the leakage current. Finally, the experimental tests are carried out to verify the feasibility and effectiveness of the proposed solution.

Design of Brushless Direct Current Motor Control System Based on DSP

As the energy and environment crises become more and more intense, people are becoming more and more conscious of environment protection and energy conservation. Electrical vehicles are gradually being accepted and becoming the development trend for vehicles, which are characterized by free pollution, low noise, high energy efficiency and simple structure compared with traditional internal combustion engine automobile vehicles. In selecting the driving motor of electric vehicle, the brushless DC motor is favored by many auto dealers with its advanced features. As a result, based on motor’s mathematical model and controlling theory, this paper started from the basic structure and working mechanism of brushless DC motor, to build the simulation model based on Matlab/Simulink platform control system, which mainly includes speed and current regulation module, logic commutation module, dual-mode converter module, motor module, overlapping commutation module, and three-phase full-bridge inverse module. Then, the simulation results are obtained to provide references for the subsequent design of hardware circuit and software programs. Besides, the overall scheme of control system is determined by taking performance indexes into consideration, and the circuit design for the system hardware based on DSP2812 is completed, which mainly includes central processing unit, main power circuit, driving circuit, detection circuit, dual-mode switching circuit, display circuit, speed adjustment circuit, power supply circuit and reset circuit, of which the working principle and functions are presented in this study.

A Physical RC Network Model for Electrothermal Analysis of a Multichip SiC Power Module

This paper is concerned with the thermal models which can physically reflect the heat-flow paths in a lightweight three-phase half-bridge two-level SiC power module with six MOSFETs and can be used for coupled electrothermal simulation. The finite-element (FE) model was first evaluated and calibrated to provide the raw data for establishing the physical resistor–capacitor (RC) network model. It was experimentally verified that the cooling condition of the module mounted on a water cooler can be satisfactorily described by assuming the water cooler as a heat exchange boundary in the FE model. The compact RC network consisting of 115 R and C parameters to predict the transient junction temperatures of the six MOSFETS was constructed, where cross-heating effects between the MOSFETs are represented with lateral thermal resistors. A three-step curve fitting method was especially developed to overcome the challenge for extracting the R and C values of the RC network from the selected FE simulation results. The established compact RC network model can physically be correlated with the structure and heat-flow paths in the power module, and was evaluated using the FE simulation results from the power module under realistic switching conditions. It was also integrated into the LTspice model to perform the coupled electrothermal simulation to predict the power losses and junction temperatures of the six MOSFETs under switching frequencies from 5 to 100 kHz which demonstrate the good electrothermal performance of the designed power module.

Commutation Torque Ripple Reduction of Brushless DC Motor in Braking Operation

In this paper, the commutation torque ripple is studied in the brushless DC motor (BLDCM) braking operation. As the phase currents flow in the reversed directions in the braking operation, the current circuits in the braking operation are different from those in the motor operation. For this reason, it is found that the commutation torque ripple can be reduced in the speed range from the rated speed to zero just by the common braking pulse width modulation strategies, where the three-phase modulation is not needed. However, it is impossible in motor operation. Under the common braking pulse width modulation strategies, the speed ranges where commutation torque ripple can be reduced are derived and compared. Based on the analysis of these speed ranges, a simple braking method is proposed. With this method, the BLDCM can be slowed down without commutation torque ripple in the whole braking process from the rated speed to zero. Experiment results verify the effectiveness of the method and the correctness of the theory.

Fault-Tolerant Direct Torque Control of Five-Phase FTFSCW-IPM Motor Based on Analogous Three-Phase SVPWM for Electric Vehicle Applications

High reliability is important in motor driving system for electric vehicle applications. In this paper, a fault-tolerant direct torque control for a five-phase fault-tolerant fractional-slot concentrated-winding interior-permanent-magnet (FTFSCW-IPM) motor under the open-circuit condition of a single phase is proposed, in which an analogous three-phase space vector pulse width modulation (SVPWM) control strategy is adopted. The DTC system for the five-phase PM motor based on healthy SVPWM has several advantages of improved currents and low torque and flux ripples. To achieve the fault-tolerant operation of the SVPWM-DTC system, an analogous three-phase SVPWM strategy is proposed. The proposed SVPWM fault-tolerant control scheme is achieved by the division of six sectors and the reconfiguration of six equal nonzero voltage vectors, which is quickly computed and easily realized. In addition, based on a 2-kW FTFSCW-IPM motor prototype, the good performances of the proposed fault-tolerant drive are validated by both simulations and experiments, in which the average torque and low torque ripple during fault can be maintained. Finally, the dynamic performances under healthy and fault-tolerant conditions are measured. The results show that the proposed analogous three-phase SVPWM control can offer good dynamic performance, which is comparable to the healthy SVPWM.

An Instantaneous Average Current Sharing Scheme for Parallel UPS Modules

The instantaneous average current sharing (IACS) control strategy ensures accurate transient and steady-state current sharing among uninterruptible power supply (UPS) modules connected in parallel, but is dependent on a communication backbone. This paper proposes a new IACS scheme that is more reliable and economically efficient. In the process of deriving this control scheme, two existing IACS schemes are examined in detail. It is shown that both the schemes offer distinct structural and performance related advantages and disadvantages. The proposed scheme is shown to provide more reliable operation without sacrificing the system performance and incurring extra control cost. Performance of the proposed approach is analytically predicted and validated through experimental results with a 22.5-kW system supported by three parallel-connected three-phase UPS modules.

Multilevel Converter Based on Cascaded Three-Leg Converters with Reduced Voltage and Current

In this paper, a modularity concept using standard three-leg converters is addressed. Three-phase cascaded topologies composed of standard three-leg converters are investigated. They are composed of three, nine, twenty-one, or $n$ three-leg converters. It permits the reduction levels of currents and voltages on switches when compared with a conventional three-phase module or a cascaded H-bridge structure. In this way, three-leg cascaded converters are suitable to be applied in scenarios of high current in which other cascaded topologies become less attractive and high voltage. Furthermore, the proposed arrangement brings advantages such as modularity that leads to convenient construction, easy maintenance, and extension to higher voltage and current levels. A dynamic model is developed and a pulse-width modulation strategy is designed to the converter command accordingly with reference voltage. Discussions about fault tolerance and dc-link capacitor currents are also carried out. Comparisons in terms of converter rating, harmonic distortion, and semiconductor power losses between the proposed and conventional cascaded H-bridge topologies have been carried out. Simulation and experimental results are presented as well.