Standard PWM Research Articles

Predictive Current Control for Six-Phase PMSM Motor With Multi-Step Synthesis Based Virtual Vectors

The concept of virtual vector has been a standard practice for the multiphase machine drives. However, simply adopting the fixed or adjustable duty-ratio virtual vectors fails to mitigate the current tracking error in the fundamental plane satisfactorily. To that end, this paper proposes a new model predictive control (MPC) method for a six-phase permanent magnet synchronous motor (PMSM) using multi-step synthesis based virtual vectors to regulate two planes simultaneously. The virtual vectors are formed through a two-step synthesis process. First, two groups of real vectors are used to synthesize 12 elementary virtual vectors to nullify the harmonic currents in the secondary plane. Subsequently, the 12 elementary virtual vectors are employed to further form other 60 composite virtual vectors to enhance the current tracking in the fundamental plane. For the sake of easy practical implementation, the pulse width modulation (PWM) switching sequence of all virtual vectors are analyzed to ensure that they present standard PWM switching sequence. The proposed multi-step synthesized composite virtual vectors can suppress the harmonic currents in the secondary plane and reduce the current tracking error in the primary plane simultaneously. Experimentations are conducted to verify the effectiveness of the proposed method.

A novel experimental procedure for lock-in thermography on solar cells

<abstract> <p>The occurrence of defects in solar cells is intrinsically related to a reduction in the efficiency and reliability of these devices. Therefore, monitoring techniques, such as lock-in thermography, electroluminescence and the I-V characteristic curve are adopted in order to evaluate the integrity of the solar cells. In the present work, a novel experimental procedure for the lock-in thermography of solar cells is proposed, aiming to improve the detection capability of the assay. Conventional techniques use pulse width modulation to operate the cell at a fixed point on the I-V curve. Instead, we propose a methodology based on a sinusoidal electric current excitation in order to extend the range of operational points that are close to the maximum power point as the cell operates in the field. Some traditional image processing techniques (principal component analysis, the fast Fourier transform and the four-step phase-shifting method) have been used to analyze the thermal images captured by an infrared camera during steady-state operation mode of the solar cells using both sinusoidal electric current signal and standard pulse width modulation procedures. Comparison between the results of both procedures found that this novel approach provides smoother and clearer delimitation of the defects. Furthermore, the contrast of the phase images was found to exhibit significant changes between the defective and non-defective regions for different modulation frequencies and types of defects. From the achieved results, it was possible to obtain a satisfactory characterization of the existing defects.</p> </abstract>

High voltage power supply controller for Electrostatic precipitators

Gaseous exhausts from various industries pollute the environment with fly-ash generally filtered by electrostatic precipitators (ESPs) before being released to the atmosphere. This paper presents the development of a controller for ESP power supply. The controller maintains the voltage applied to ESP at its maximum average value by duty cycle control that results in an improvement in dust collection-efficiency. The limiting factor for the output voltage is the breakdown of gas (spark/arc) in the electrode gap of ESP. During a spark/arc condition, the duty cycle limit imposed by the controller causes a reduction in output voltage that leads to the prevention of spark/arc. The present design has a response faster than line frequency power supply controllers. The control circuit is simpler, easy to implement and uses a standard PWM controller IC. The design of power stage uses a flyback current-fed push-pull DC-DC converter with multiple secondary circuits, which has the advantages of instantaneous current limit and less voltage stress on rectifier-diodes. Simulation is performed to obtain a 1 kV, 100 W output from a 24VDC source. The results are compared with experimental values to validate the controller’s ability to achieve good load regulation during normal operation and a reduction in output voltage during spark/arc condition.

Parallel connected GaN E‐HEMT VSI‐based servo drives for PMSMs

The operation of parallel-connected servo drives has the advantages of increasing the torque (hence the power) capacity, reliability, redundancy and modularity. However, smaller discrepancies of the system clocks of the independent microcontrollers, asynchronous pulse width modulation (PWM) carrier signals and hardware differences can make the output voltages of the parallel modules non-identical, which results in circulating currents. These circulating currents limit the parallel operation, introduce additional power dissipation, cause unbalanced power distribution and degrade the control performance. To eliminate the circulating currents separated DC supplies, coupled inductors (CIs), PWM techniques, modified control techniques etc. are proposed in the literature. In this study, a fault-tolerant parallel-connected gallium nitride enhancement-mode high electron mobility transistor voltage source inverter-based servo drive scheme that eliminates the need for CIs and separate DC supplies and also enables the use of a standard proportional-integral current control and a standard space vector PWM approach is proposed and tested. To evaluate the performances of the proposed scheme, up to six servo drives (limit-6 × 7 Arms) are connected in parallel and tested under various conditions with a 24 V permanent magnet synchronous motor (nominal-61.9 Arms). The results show that the parallel operation not only increases the torque capacity of the system but also increases modularity, flexibility, reliability and also redundancy.

Sensorless control for a synchronous reluctance motor based on current oversampling using standard PWM excitation

Sensorless control for a synchronous reluctance motor based on current oversampling using standard PWM excitation

Multi-vector model predictive fault-tolerant current control using reconstructed vector distribution for five-phase PM motor

<p indent=0mm>To address a single-phase open-circuit fault, this paper proposes multi-vector finite-control-set model predictive fault-tolerant current control. This method includes reconstruction of the post-fault vector distribution and introduces a vector selection method with a reduced computational burden. The reconstructed vector distribution is based on the principle of minimizing the copper loss, and is generated by combining several basic vectors. Standard PWM waveforms and an enlarged modulation area are considered simultaneously. The vector selection method adopts the basic principle of classic finite-control-set model predictive control twice, which avoids evaluation of all the candidate vectors. The computational burden can thus be reduced without a vector selection error. In addition, to further improve the operational performance, duty cycle modulation technology is adopted to optimize the amplitude of the candidate vectors. A thorough experimental evaluation is performed, which demonstrates the effectiveness and superiority of the proposed fault-tolerant method.

Improved Direct Torque Control Method for Dual-Three-Phase Permanent-Magnet Synchronous Machines With Back EMF Harmonics

In this article, we propose a novel switching-table-based direct torque control (ST-DTC) method to eliminate the current harmonics in dual-three-phase permanent-magnet synchronous machines due to the back electromotive force (back EMF) harmonics and voltage vector selection. By employing a novel space voltage vector selection strategy and the optimal action time for different groups of vectors, a novel ST-DTC method is developed. Furthermore, in order to implement standard pulsewidth modulation (PWM) switching sequence, a centralization PWM method for 36 voltage vectors is introduced. The proposed method can effectively reduce the phase current harmonics caused by both back EMF distortion and voltage vector selection, and still reserve the advantages of the conventional ST-DTC, such as fast torque response and simple structure. Its effectiveness is verified by simulations and experiments.

Enhanced Fault-Tolerant Model Predictive Current Control for a Five-Phase PM Motor With Continued Modulation

To deal with the single-phase open-circuited fault, an enhanced fault-tolerant model predictive current control with continued modulation is proposed in this article. This method includes reconstructing the postfault vector distribution and adopting a multistep vector selection method. In the reconstruction procedure, the transition vectors are generating to realize standard pulsewidth modulation waveforms. Then, the unreachable area can be filled by creating new synthetic vectors. Finally, the vectors with oversized amplitudes are optimized by using null vectors. In order to cover the full modulation area, a multistep vector selection method is used to determine the phase angle and amplitude of the optimal vector. The phase angle can be determined by defining two cost functions and adopting duty cycle modulation technology. The amplitude of the optimal vector can be optimized by utilizing the duty cycle modulation technology again. The oscillation, due to the back electromotive force, is compensated in each step. A thorough experimental evaluation has been conducted to confirm the effectiveness and superiority of the proposed fault-tolerant method.

A Low THD Three-Level Rectifier For Gen-Set Applications

A low input current total harmonic distortion (THD) rectifier is presented, tailored around an open-end winding permanent magnet synchronous generator. Specifically, a six-level converter topology is obtained by connecting the generator stator winding to a three level T-type unidirectional rectifier on one side, and to an auxiliary two-level inverter on the other side. The T-type rectifier manages the entire active power stream and operates at the line frequency in order to minimize the switching power losses. The auxiliary inverter is instead driven by a standard PWM technique, being tasked to sinusoidally shape the input current and to actively balance the voltage across the dc-bus capacitors of the T-type rectifier. Such an inverter, being rated at a lower power and at a lower voltage than the T-type rectifier, can exploit low-cost power mosfet s. The proposed topology, featuring a very low input current THD, could well supplement in aircraft, portable or distributed generation applications, modern high-speed permanent magnet synchronous generators featuring a quite small stator impedance. Simulation and experimental results confirm the effectiveness of the proposed configuration.

A Simple Voltage Modulator Scheme for Torque Ripple Minimization in a Permanent Magnet Brushless DC Motor

This paper presents a simple dc-link voltage modulation scheme to minimize the commutation torque ripple in a permanent magnet brushless dc motor (PMBLdcM). Maintaining a constant current in the noncommutating (NC) phase helps to minimize the torque ripple, which can be achieved by boosting the motor input voltage whenever two phase currents are undergoing commutation. At low speeds, since the required ac voltage at commutation is also less than nominal, the standard pulsewidth modulation operation of the inverter with nominal dc-link voltage suffices. However, at higher speeds, a momentary (only during the commutation interval) boost in the dc-link voltage (above the nominal level) is needed to ensure a boost in motor voltage, and hence, a steady current in the NC phase. In the proposed scheme, the dc voltage boost at higher speeds is obtained by connecting two capacitors in series, which are normally connected in parallel, across the dc-link. The proposed scheme is verified for a 1-hp PMBLdcM drive through simulations and experiments in the laboratory. Results exhibit a notable improvement in reducing the torque ripple.

Elimination of Harmonic Currents Using a Reference Voltage Vector Based-Model Predictive Control for a Six-Phase PMSM Motor

This paper proposes a novel deadbeat current control (DBCC)-based model predictive control for an asymmetrical six-phase permanent magnet synchronous machine. First, the solution of DBCC is adopted to obtain the expected reference voltage vector (RVV). Then, two groups of virtual vectors, in the total number of 24 with different magnitudes, are defined for the sake of current harmonics suppression. Subsequently, two in-phase virtual vectors which are closest to the RVV are selected as the prediction vectors. The next step is to define a cost function which is composed of the error between the RVV and the available prediction vectors. Then, the selected two virtual vectors are evaluated and the one that minimizes the cost function will be applied in the next instant. In this way, only two prediction vectors need to be evaluated and the computation burden is highly alleviated. In the meantime, the weighting factor involved in predictive torque control is avoided. In addition, to achieve the readily implementation with standard pulsewidth modulation switching sequence, 18 virtual vectors are artfully replaced by their corresponding equivalent virtual vectors. Finally, the proposed method is comparatively studied and compared with other benchmark methods. Simulation and experimental results are offered to confirm the effectiveness of the proposed method.

Analysis and Reduction of the Output Voltage Error of PWM for Modular Multilevel Converters

Standard pulsewidth modulation (PWM) schemes for modular multilevel converters (MMC) have neglected deviations of the module voltages from the mean module voltage of an MMC arm as well as the dynamic change in the module voltages since their last measurement and during the switching period. This induces an output voltage error. Large output voltage errors disturb the higher level closed-loop control of the MMC, such that control targets cannot be met anymore. The output voltage error can be reduced using advanced PWM methods that predict and include the dynamic change of the individual module voltages during a switching period in the calculations for the duty cycle. This paper shows measurement results obtained from an experimental medium-voltage prototype, proving that advanced methods lead to much lower output voltage errors than the standard methods, but cannot fulfill the expectations raised by the simulations documented in the literature. In order to overcome the limitations of the old method, a new method that includes the semiconductor voltage drop and parasitic resistances is introduced and evaluated with measurements in this paper. Furthermore, simulation results showing the influence of the considered modulation methods on the closed-loop current control performance are presented.

Минимизация и перераспределение коммутационных потерь в инверторе напряжения при использовании алгоритма широтно-импульсной модуляции с прогнозированием

The article deals with testing a combined PWM method for a voltage source inverter, which is aimed at minimizing the switching losses and distributing them among the power converter modules. To reduce switching losses in the inverter, duty cycles are calculated for several possible PWM shaping methods, and a PWM method in which the phase with the largest value of current flowing through it is not switched is chosen. Another advantage of this method is its ability to control the thermal operating conditions of the inverter’s IGBT modules. This is especially important for designs in which the power IGBT modules are installed on a common heat sink, because with such configuration, the modules of a three-phase converter operate under different thermal conditions. To avoid overheating of a particular IGBT module, an algorithm is proposed using which losses can be redistributed among the modules. Since it is difficult to establish an exact mathematical relationship between the desired behavior and the controlled parameters, a prediction method is used. The total losses anticipated for each possible PWM method are calculated, and the objective function that takes into account several variable parameters is determined. By varying the objective function’s weighting coefficients, different system operation modes can be specified. Three system operation modes defined by three objective function configurations are analyzed. In its first configuration, the objective function makes it possible to select the PWM method in which the total losses in the system are kept to a minimum. In its second configuration, the objective function allows the user to calculate the minimum losses in the inverter’s most heavily heated leg. In its third version, the objective function is a combination of the first two configurations and is aimed at simultaneously reducing the total losses in the system and losses in its most heavily heated module. The performance characteristics of each of these three objective functions and of the standard vector PWM are tested on a heat sink thermal model. The presented simulation results show that application of the first objective function helps to decrease the total losses in the system as compared with those in the case of using the standard vector PWM; application of the second objective function makes it possible to decrease losses in one phase, whereas the temperature in the other legs tends to grow; and the third objective function was found to be the most effective one, because its application made it possible to achieve the minimal losses in the system and a lower temperature of the most heavily heated module.

Active EMI Reduction Using Chaotic Modulation in a Buck Converter with Relaxed Output LC Filter

DC-DC buck converters are widely used in portable applications because of their high power efficiency. However, their inherent fast switching releases electromagnetic emissions, making them prominent sources of electromagnetic interference (EMI). This paper proposes a voltage-controlled buck converter that reduces EMI by using a chaotic pulse-width modulation (PWM) technique based on a chaotic triangular ramp generator. The chaotic triangular ramp generator is constructed from a simple on-chip chaotic circuit linked with a symmetrically triangular ramp circuit. The proposed converter can thus operate in the chaotic mode reducing the EMI without requiring any EMI filters. Additionally, using the triangular ramp signal can relax the requirement for a large LC output filter in chaotic mode. The effectiveness of the proposed scheme was experimentally verified with a chaotic triangular ramp generator embedded in a voltage-mode controller buck converter using a 0.18 µm Complementary Metal Oxide Semiconductor (CMOS) process. The measurement results from a prototype showed that the EMI improvement from the proposed scheme is approximately 14.53 dB at the fundamental switching frequency with respect to the standard fixed-frequency PWM reference case.

Assessment and improvements of inorganic insulation for high temperature low voltage motors

The increase of internal temperature capability of electrical machines is a major challenge for building high power density actuators for many applications in transport systems and in aerospace industry. Today, the main limit is the thermal class of the organic Electrical Insulation System (EIS), but a breakthrough toward very high temperature is possible with inorganic insulation technologies. An inorganic EIS is proposed and tested for designing motors able to work permanently up to 500 °C in the heart of windings. After a review of several high temperature (HT°) insulation solutions, the paper focuses on currently available ceramic-coated wires insulated with a very thin inorganic layer, which is a favorable solution for high current densities in machines of small sizes. The electrical limits of this technology are investigated, the weak points of the HT° wire are circumvented using impregnating cements able to provide adequate mechanical and electrical properties up to 500°C for designing HT ° electrical machines fed by a standard PWM inverter connected to the HVDC bus of the more electric aircraft, for example.

Reducing the stroboscopic effects of LED luminaires with pulse width modulation control

Pulse width modulation for dimming the light output of LEDs has become common. When pulse width modulation is used at low frequencies unwanted visual artefacts including flicker perception and stroboscopic effects may occur. These artefacts need to be avoided or at least reduced to a minimum in order to obtain high user acceptance. In this paper, an optimized phase-shifted pulse width modulation method is described, implemented and validated in a visual experiment. The method is intended to minimize the stroboscopic effect on a reference surface by first optimizing the LED units of a single LED luminaire and then co-optimizing several of these luminaires. The optimized pulse width modulation waveforms are then compared to standard pulse width modulation dimming methods. In the visual experiment, 13 subjects rated the extent of the stroboscopic effect of standard and optimized waveforms in a white painted experimental room. The results indicate that the optimized waveforms are indistinguishable from constant light.

Analysis of Discontinuity Induced Bifurcations in a Dual Input DC-DC Converter

DC-DC power converters with multiple inputs and a single output are used in numerous applications where multiple sources, e.g. two or more renewable energy sources and/or a battery, feed a single load. In this work, a classical boost converter topology with two input branches connected to two different sources is chosen, with each branch independently being controlled by a separate peak current mode controller. We demonstrate for the first time that even though this converter is similar to other well known topologies that have been studied before, it exhibits many complex nonlinear behaviors that are not found in any other standard PWM controlled power converter. The system undergoes period incrementing cascade as a parameter is varied, with discontinuous hard transitions between consecutive periodicities. We show that the system can be described by a discontinuous map, which explains the observed bifurcation phenomena. The results have been experimentally validated.

A multilevel converter with reduced number of switches in STATCOM for load balancing

In this paper, a 3-phase, delta-connected, 5-level Static Synchronous Compensator with a novel AC to DC converter is analyzed and implemented for load balancing in three-phase systems. The level shifted carrier based sinusoidal pulse width modulation (SPWM) method is used as the switching technique. This converter has less number of power switches than conventional H-bridge structure and it can be controlled from the standard PWM ports of microcontrollers. The control algorithm depends on sequence decomposition of load current and compensation of its negative sequence component in addition compensation of imaginary component of positive sequence. The simulation results obtained from Matlab are compared with the experimental results. The system is implemented in the laboratory by using DSP TMS320F28335.

Adaptive Hysteresis Current Controlled Multilevel Inverter for Solar Photovoltaic Applications

This paper presents a five-level cascaded multilevel inverter controlled by an adaptive hysteresis band current controller for photovoltaic system. Due to increasing the number of levels, the proposed five-level cascaded multilevel inverter further reduces its total harmonic distortion (THD). The solar system is simulated using MATLAB/Simscape software and it is integrated with DC–DC boost converter and single-phase five-level cascaded multilevel inverter controlled by the proposed control strategy. The simulation results show that the proposed controller provides constant switching frequency, reduced harmonics and can reach its steady state quickly compared to the conventional fixed hysteresis controller and standard PWM controller. Also, the proposed five-level cascaded multilevel inverter reduces THD of the output voltage and current. The proposed controller is also implemented Xilinx Spartan 3E field programmable gate array using the Atmel AT90USB2 USB controller on the Basys2 development board. The simulation and experimental results describe and verify the current control technique for the multilevel inverter.

Six-phase Voltage Forming Method using the Largest Magnitude Space Vectors

In this paper, a six-phase voltage source inverter with a single-neutral star connected load is investigated. A space vector PWM (SVPWM), which uses largest magnitude vectors is proposed and implemented. Simulation results of the six-phase voltage source inverter (VSI), which uses the proposed SVPWM method, are compared to the results when a standard sinusoidal PWM scheme is used. Analysis of the results shows that proposed SVPWM scheme is suitable to form a six-phase sinusoidal output voltage. The main advantage of proposed SVPWM scheme is that it requires the same computational resources as the three-phase SVPWM. DOI: http://dx.doi.org/10.5755/j01.eee.19.10.5904