Three-phase Modulation Research Articles

Study of the Modulation Schemes in the Hybrid Three-Phase Multilevel Inverter

This work proposes and analyzes modulation strategies for a hybrid three- phase multilevel inverter, which employs two different topologies in a cascade connection, a three-phase Neutral Point Clamped (NPC) converter and single- phase half-bridge converters. Two different modulation schemes are proposed: the hybrid modulation and the space vector modulation. The both modulation schemes can synthesize five voltage levels in the output phase voltage at the hybrid three- phase multilevel inverter with symmetrical dc sources. The modulation schemes operate the three-phase NPC in low-switching frequency and the half- bridge converters in high-switching frequency. Thus, semiconductors with low conduction losses can be used for three-phase NPC, decreasing the semiconductor losses. The hybrid three-phase multilevel inverter structure and modulation schemes are explained in detail and verified by simulation and experimental results.

Modified VSS‐LMS‐based adaptive control for improving the performance of a single‐stage PV‐integrated grid system

This study presents a modified variable step size (VSS) least mean square (LMS)-based control for improving the performance of a single-stage photovoltaic (PV) integrated grid system. Here, a three-phase, three-wire, single-stage grid system consists of three-phase voltage source converter, PV module, filters and loads. Main motive of the considered system with the adaptive control algorithm is to achieve desired voltage at the point of common coupling, load balancing, unity power factor and harmonics elimination while transferring power to grid as well as loads. The system with modified VSS-LMS-based control algorithm is simulated using MATLAB/Simulink environment and an experimental prototype is developed in the laboratory to verify the efficacy and performance of proposed algorithm.

Interleaved Resonant Boost Inverter Featuring SiC Module for High-Performance Induction Heating

Induction heating (IH) has become the technology of choice in many industrial, domestic, and medical applications due to its high efficiency and performance. This paper proposes an interleaved resonant boost inverter featuring SiC three-phase module to achieve high efficiency and performance IH power supply. The proposed converter achieves high efficiency by reducing the current through the devices, while the use of an interleaved full-bridge configuration reduces input current ripple and provides additional control degrees. The proposed converter has been designed, implemented, and tested experimentally, proving the feasibility of this proposal.

A Neutral-Point Voltage Balance Controller for the Equivalent SVPWM Strategy of NPC Three-Level Inverters

Based on the space vector pulse width modulation (SVPWM) theory, this paper realizes an easier SVPWM strategy, which is equivalently implemented by CBSPWM with zero-sequence voltage injection. The traditional SVPWM strategy has no effect on controlling the neutral-point voltage balance. In order to solve the neutral-point voltage unbalance problem for neutral-point-clamped (NPC) three-level inverters, this paper proposes a neutral-point voltage balance controller. The proposed controller realizes controlling the neutral-point voltage balance by dynamically calculating the offset superimposed to the three-phase modulation waves of an equivalent SVPWM strategy. Compared with the traditional SVPWM strategy, the proposed neutral-point voltage balance controller has a strong ability to balance the neutral-point voltage, has good steady-state performance, improves the output waveforms quality and is easy for digital implementation. An experiment has been carried out on a NPC three-level inverter prototype based on a digital signal processor-complex programmable logic device (DSP-CPLD). The obtained experimental results verify the effectiveness of the proposed neutral-point voltage balance controller.

Three‐level saddle space vector pulse width modulation strategy based on two‐level space vector pulse width modulation for neutral‐point‐clamped three‐level inverters

This study proposes a three-level saddle space vector pulse width modulation (SVPWM) strategy based on two-level SVPWM (TBT_SAPWM) for neutral-point-clamped (NPC) three-level inverters. According to the analysis of the conventional three-level SVPWM strategy based on two-level SVPWM (CTBT_SVPWM) and the proposed TBT_SAPWM strategy, the modulation wave expressions of the two strategies are derived. Compared to the CTBT_SVPWM strategy, each main sector has its own independent area, and determining the main sectors or regions becomes easier with the proposed TBT_SAPWM strategy. Moreover, by optimising the switching states, the proposed TBT_SAPWM strategy makes on-state duration of one selected phase equal to that of the other selected phases in a switching cycle. Therefore, the three-phase modulation waves are saddle waves at the full range of fundamental wave modulation ratios. According to the experimental results in this study, the proposed TBT_SAPWM strategy has better performances in terms of the output harmonics and the neutral-point voltage ripple, compared to the CTBT_SVPWM strategy. The feasibility and effectiveness of the proposed strategy are verified by the experimental platform of an NPC three-level inverter based on the digital signal processor and complex programmable logic device.

Sliding Mode Control of a New Wind-Based Isolated Three-Phase Induction Generator System with Constant Frequency and Adjustable Output Voltage

This paper presents a new stand-alone wind-based induction generator system with constant frequency and adjustable output voltage. The proposed generator consists of a six-phase cage-rotor induction machine with two separate three-phase balanced stator windings and a three-phase space vector pulse width modulation inverter that operates as a static synchronous compensator (STATCOM). The first stator winding is fed by the STATCOM and used to excite the machine while the second stator winding is connected to the generator external load. The main frequency of the STATCOM is determined to be constant and equal to the load-requested frequency. The generator output frequency is independent of the load power demand and its prime mover speed because the frequency of the induced emf in the second stator winding is the same as this constant frequency. A sliding mode control (SMC) is developed to regulate the generator output voltage. A second SMC is used to force the zero active power exchanged between the machine and the STATCOM. Some simulation and experimental results are presented to prove the validity and effectiveness of the proposed generator system.

Robust tracking performance of linear induction motor‐based automatic picking system using a high‐gain disturbance observer

To operate the movable ejectors of an automatic picking system (APS) with high dynamics and high precision, a robust speed tracking controller design for a single-sided linear induction motor (LIM) is presented using a high-gain disturbance observer method. The thrust disturbance as well as the mechanical parameter variation due to the mass change influences directly the tracking control performance of APS. To guarantee robustness in the presence of such uncertainty, a high-gain disturbance observer-based linear quadratic regulator (LQR) is designed from the mechanical dynamics. Since the estimated disturbance effectively cancels out real uncertainties in the system, the resulting system behaves like the closed-loop system consisting of the disturbance-free nominal model and the LQR. Since MATLAB–Simulink does not support a library for a LIM, a Simulink library model has been developed using the LIM dynamics. To verify that the proposed scheme has a robust control nature, the comparative simulations are carried out based on the library. The whole control system is implemented using DSP TMS320F28335 for a LIM driven by a three-phase voltage-fed pulse-width modulation inverter. Through comparative experimental results in the presence of disturbances, the effectiveness and robustness of the proposed scheme are verified.

Study of Harmonic Detection Methods under Non-Ideal Conditions in Ship Power Network

Abstract An improved harmonic detection method based on average arithmetic is proposed. According to the research results, the designed solution uses an LPF (low-pass-filter) and a mean value module connected in series instead of the conventional mean value module, and simultaneously, a three-phase voltage phase-locked module instead of commonly used PLL (phase lock loop) module is applied in order to reduce the influence caused by three-phase distorted voltage and rapid variation of load. The experimental results show that the application of this solution leads to increase in the accuracy of harmonics detection for distorted three-phase voltage and rapid variation of load.

Modulation Techniques to Reduce Leakage Current in Three-Phase Transformerless H7 Photovoltaic Inverter

Recently, reduced common-mode voltage (CMV) pulsewidth modulation (RCMV-PWM) methods have been proposed to reduce the leakage current in three-phase transformerless photovoltaic (PV) systems. However, most of these studies only focus on leakage current elimination and neglect the overall performance of the PV systems on issues such as cost, voltage linearity, dc-link current ripples, and harmonic distortion. In this paper, a three-phase transformerless inverter, adapted from the single-phase H5 topology, is investigated. Since the H5 topology has been conventionally developed for a single-phase system, its adaptation to the three-phase system requires the development of corresponding three-phase modulation techniques. Hence, modulation techniques are proposed based on conventional PWM. The performances of the proposed PWM, in terms of CMV, leakage current, voltage linearity, output current ripples, dc-link current ripples, and harmonic distortion are studied and discussed via simulation and experiment. It is proven that the proposed topology is able reduce the leakage current without sacrificing the overall performance of the system.

Three-Phase Multimodule VSIs Using SHE-PWM to Reduce Zero-Sequence Circulating Current

A modular voltage-source inverter (MVSI) uses individual three-phase modules in a shunt connection to allow lower power rated inverters to be implemented in higher power applications. It is standard practice to implement each module with the same pulsewidth-modulation (PWM) pattern. This paper proposes a new PWM approach for MVSIs for which each module is made to operate with a different PWM pattern. It is shown in this paper how more output voltage harmonics can be eliminated with the new approach than with the standard approach and how the new approach can be expanded to significantly reduce zero-sequence current that circulates among the inverter modules. The mathematical formulations needed to generate appropriate PWM patterns for the new PWM approach and experimental results obtained from a prototype MVSI are presented in this paper as well.

Study of Power Generation for Permanent Magnet Motor Elevator by Energy Regenerative Unit (EERU)

This paper presents Power Generation for Permanent Magnet Motor Elevator by Energy Regenerative Unit (ERU). The study reveals that permanent magnet motors with rated 5.5kW in elevators which is working by transferring mechanical energy into electricity when the motor is rotating without power therefore the motor is capable of producing electrical energy back into the grid system. This situation is call “Regenerative mode” which is the wasted energy can be used once again [1]. The study is done by simulation using MATLAB/Simulink program. This investigated ERU and inverter in this study can be applied for future use of in existing elevator system. The Proposed ERU is used to convert DC voltage to AC voltage for gird synchronization. The investigated ERU is operating as three-phase module. From experiment, it is observed that when the motor operates as a generator then ERU will receive DC voltage from the elevator inverter system then convert to AC voltage that can be fed into the grid system.

A Novel Single-Reference Six-Pulse-Modulation (SRSPM) Technique-Based Interleaved High-Frequency Three-Phase Inverter for Fuel Cell Vehicles

This paper presents a hybrid modulation technique consisting of singe-reference six-pulse-modulation (SRSPM) for front-end dc/dc converter and 33% modulation for three-phase inverter. Employing proposed novel SRSPM to control front-end dc/dc converter, high frequency (HF) pulsating dc voltage waveform is produced, which is equivalent to six-pulse output at 6× line frequency (rectified 6-pulse output of balanced three-phase ac waveforms) once averaged. It reduces the control complexity owing to single-reference three-phase modulation as compared to conventional three-reference three-phase SPWM. In addition, it relives the need of dc-link capacitor reducing the cost and volume. Eliminating dc link capacitor helps in retaining the modulated information at the input of the three-phase inverter. It needs only 33% (one third) modulation of the inverter devices to generate balanced three-phase voltage waveforms resulting in significant saving in (at least 66%) switching losses of inverter semiconductor devices. At any instant of line cycle, only two switches are required to switch at HF and remaining switches retain their unique state of either ON or OFF. Besides, inverter devices are not commutated when the current through them is at its peak value. Drop in switching loss accounts to be around 86.6% in comparison with a standard voltage source inverter (VSI) employing standard three-phase sine pulse width modulation. This paper explains operation and analysis of the HF two-stage inverter modulated by the proposed novel modulation scheme. Analysis has been verified by simulation results using PSIM9.0.4. Experimental results demonstrate effectiveness of the proposed modulation.

Precise Braking Torque Control for Attitude Control Flywheel With Small Inductance Brushless DC Motor

In this paper, a newly designed braking torque control scheme with improved toque estimation and control characteristics in a small inductance brushless DC motor is presented. The motor torque is estimated according to the back electromotive force (EMF) shape function that is fitted by neural network and corrected by temperature. Upon this, a hybrid braking torque control structure that combines dynamic braking and plug braking is proposed for the smooth and continuous braking torque. These two braking modes operate, respectively, in the relatively high- and low-speed ranges. During dynamic braking, a predictive torque control method is proposed to suppress the torque fluctuation that is induced by the supplying voltage namely back EMF descent. During plug braking, an effective torque ripple reduction method is designed to weaken the large torque ripple which is caused by high winding voltage, low winding impedance, and three-phase inverter modulation. In addition, different pulse width modulation patterns and the most suitable operating conditions for each braking mode have been studied. Finally, experimental results are presented to demonstrate the validity and effectiveness of the proposed braking torque control scheme.

DSPIC BASED POWER ASSISTED STEERING USING BRUSHLESS DIRECT CURRENT MOTOR

This study illustrates the Electrically Assisted power Steering (EAS) using BLDC motor for a vehicle. Earlier the Electrically Assisted power Steering (EAS) was implemented with DSP. This study shows the usage of a dsPIC to control the BLDC motor with an encoder. The BLDC motor here is driven by dsPIC through a three phase inverter system. IRAMS type of inverter is used which is cost efficient and space efficient. The dsPIC supplied with the input of the steering. In its higher capacity the vehicles speed controller acts as the assistance level controller for steering effort. At the lower capacity, the torque controller gives the effort level control. In reality this can be realized as torque sensor and vehicle sensor interfaced in the dsPIC. For actual implementation in the system, a dsPIC-based BLDC motor controller with three-phase inverter module is used with Hall-effect sensor feedback. It is designed in such a way that the driver assistance can be varied at any time without any difficulty.

A Novel Hybrid Packaging Structure for High-Temperature SiC Power Modules

This paper presents a novel hybrid packaging structure for high-temperature SiC power modules that combines the benefits of the wirebond packaging structure and the planar packaging structure. With the proposed hybrid structure, the power modules can achieve the same footprint and similar parasitic to planar structures but with a much easier fabrication process and more reliable top-side interconnections. Meanwhile, no double-side solderable devices are required. The new structure and its fabrication process are presented, and a prototype module is built based on an SiC JFET. Detailed comparisons are also conducted between the hybrid, planar, and wirebond structures. The results reveal better performances of the hybrid structure in smaller parasitic, lower switching loss, and more flexible routing than the wirebond structure and easier fabrication, more reliable top-side connection, and more flexible die attachment material selection than the planar structure. A three-phase multiple-chip SiC JFET hybrid-structure power module is built and tested with 250 °C junction temperature for verification.

Wireless Paralleled Control Strategy of Three-phase Inverter Modules for Islanding Distributed Generation Systems

This paper presents a control strategy for distributed systems, which can be used in islanded microgrids. The control strategy is based on the droop method, which uses locally measured feedback to achieve load current sharing. Instead of the traditional droop method, an improved one is implemented. A virtual inductor in the synchronous frame for three-phase inverters is proposed to deal with the coupling of the frequency and the amplitude related to the active and reactive power. Compared with the traditional virtual inductor, the proposed virtual inductor is not affected by high frequency noises because it avoids differential calculations. A model is given for the distributed generation system, which is beneficial for the design of the droop coefficients and the value of the virtual inductor. The effectiveness of the proposed control strategy is verified by simulation and experiment results.

The Low Voltage Ride through Simulation Analysis for Wind Turbines to Grid

According to the provisions of low voltage ride through capability of wind turbines in the “large-scale design and technical specifications for wind farm to grid” of china, proposed a method to simulate this low voltage ride through grid voltage by computer simulation software. The simulation method is mainly used to simulate whether the wind turbines grid can meet the low voltage ride through requirements. In order to obtain the required grid voltage, the fault simulation circuit is divided into voltage dip part and voltage recovery part, which were used to simulated 20% & 90% voltage dip and the 20% grid voltage gradually recovered to 90% grid voltage. Three-phase fault modules for the voltage dip part, Three-phase programmable voltage source module for the voltage recovery part. The simulation results show that simulation system we build can simulate the required grid voltage.

Instantaneous Torque Control of Small Inductance Brushless DC Motor

Due to the small inductance, modulation of three-phase inverter induces serious torque ripple. In addition, the increase in modulation frequency is limited by the processor speed. Therefore, the traditional torque control approaches are not suitable. In order to solve the aforementioned problems, a new instantaneous torque control method for small inductance brushless dc motor is proposed by improving the torque estimation and control. First, instantaneous torque is estimated through improved position information and back electromotive force (EMF) coefficient estimation. The former is achieved by the proposed hall sensors position calibration and compensation method, and the latter is obtained by neural network fitting. Second, the torque ripple reduction is realized in the conduction and commutation region. The ripple caused by three-phase inverter modulation is suppressed by the dc-link buck converter pulsewidth modulation control method. Upon this, an asymmetry compensation function is designed to solve the problem of unbalance among three phase windings. After that, back EMF disturbance, which is applied to current dynamics, is compensated through feedforward control. Subsequently, the commutation ripple is reduced by the outgoing phase control. Finally, the validity of the proposed torque control method is verified through experimental results.

Design on Parameters of Power Circuit of AC Servo System

Power circuit is the core of high precision permanent magnet synchronous motor (PMSM) AC servo system. It is composed of three-phase AC-DC circuit and Intelligence Power Module (IPM). Three-phase AC electric currents flows through the major power circuit and changed to sinusoidal symmetrically AC currents to drive PMSM to work. For the high precision PMSM AC servo system, a design method of the system’s power circuit was given and the specific parameters of the circuit were calculated. According to the circuit, system simulation was carried on and simulation results show that the design of power circuit is feasible and the high precision PMSM AC servo system has good performances such as high position and trace accuracy, large range of adjustable speed, fast response and strong robustness. So the power circuit designed not only guarantee system’s robustness but also system’s following performance.

Analysis and Characterization of a Square-Wave Modulation Method for Single-Phase Cascaded H-Bridge Multilevel Inverters

Cascaded multilevel inverters offer several advantages over other multilevel structures: modularity, high voltage capability, reliability. Additionally, a large number of cascaded inverters using a square wave modulation method allow low losses in the inverter and low harmonic distortion in the output voltage. This paper analyzes the main features of one of these modulation methods especially in what concerns to real- time implementation in a FPGA, output voltage distortion in single- and three-phase systems and modulation range in static and dynamic conditions. Also, scalability is addressed in order to evaluate the method's capability to be used in high voltage applications. Simulation results with a different number of H- bridge inverters are presented and they allow obtaining the main conclusions; experimental results verify and support those conclusions.