Load Emulation Research Articles

Dynamical effects of memristive load on peak current mode buck-boost switching converter

Abstract When an output load of switching DC-DC converter exhibits the fingerprints of frequency dependent pinched hysteresis loops, the load can be regarded as a memristive load. By substituting a resistive load with the voltage-controlled memristive load emulator, a peak current mode (PCM) memristive buck-boost converter is presented in this paper. Based on the circuit equations under two kinds of switch states, the switched conditions and normalized system model of the PCM memristive buck-boost converter operating at continuous conduction mode (CCM) are derived. Through MATLAB numerical plots, dynamical behaviors of the PCM memristive buck-boost converter are investigated and dynamical effects of the memristive load on the buck-boost converter are thereby uncovered. The results indicate that such a buck-boost converter exhibits complex dynamical behaviors including chaos, period, period-doubling bifurcation, and border collision bifurcation; the memristive load does not affect the bifurcation structures but can make the normal operation region to broaden and cause the average output voltages to drop. Additionally, the enlargement of the memristive effect of the load, the normal operation regions are further expanded and the average output voltages are further reduced. Finally, PSIM simulation model is constructed, upon which circuit simulations effectively confirm the numerical plots.

A novel road dynamic simulation approach for vehicle driveline experiments

A dynamic simulation approach for performing emulation experiments on vehicle driveline test bench is discussed in this paper. In order to reduce costs and shorten new vehicle development cycle time, vehicle simulation on the driveline test bench is an attractive alternative at the development phase to reduce the quantity of proto vehicles. This test method moves the test site from the road to the bench without the need for real chassis parts. Dynamic emulation of mechanical loads is a Hardware-in-the-loop (HIL) procedure, which can be used as a supplement of the conventional simulations in testing of the operation of algorithms without the need for the prototypes. The combustion engine is replaced by a electric drive motor, which replicates the torque and speed signature of an actual engine, The road load resistance of the vehicle on a real test road is accurately simulated on load dynamometer motor. On the basis of analyzing and comparing the advantages and disadvantages of the inverse dynamics model and the forward model based on speed closed loop control method, in view of the high order, nonlinear and multi variable characteristics of test bench system, a load simulation method based on speed adaptive predictive control is presented. It avoids the complex algorithm of closed loop speed compensation, and reduces the influence of inaccurate model parameters on the control precision of the simulation system. The vehicle start and dynamic shift process were simulated on the test bench.

Design and Modeling of a Test Bench for Dual-Motor Electric Drive Tracked Vehicles Based on a Dynamic Load Emulation Method.

Dual-motor Electric Drive Tracked Vehicles (DDTVs) have attracted increasing attention due to their high transmission efficiency and economical fuel consumption. A test bench for the development and validation of new DDTV technologies is necessary and urgent. How to load the vehicle on a DDTV test bench exactly the same as on a real road is a crucial issue when designing the bench. This paper proposes a novel dynamic load emulation method to address this problem. The method adopts dual dynamometers to simulate both the road load and the inertia load that are imposed on the dual independent drive systems. The vehicle’s total inertia equivalent to the drive wheels is calculated with separate consideration of vehicle body, tracks and road wheels to obtain a more accurate inertia load. A speed tracking control strategy with feedforward compensation is implemented to control the dual dynamometers, so as to make the real-time dynamic load emulation possible. Additionally, a MATLAB/Simulink model of the test bench is built based on a dynamics analysis of the platform. Experiments are finally carried out on this test bench under different test conditions. The outcomes show that the proposed load emulation method is effective, and has good robustness and adaptability to complex driving conditions. Besides, the accuracy of the established test bench model is also demonstrated by comparing the results obtained from the simulation model and experiments.

Load emulation technique for variable power factor and harmonic loads with energy recycling

The need for emulation of electrical load is often experienced in industrial design, development, and testing of electrical sources, especially in the case of renewable energy sources. The performance of standalone renewable energy systems is found to vary considerably with a change in load characteristics, especially with varying power factor (PF) and harmonics. Here a novel load emulation technique has been developed, using which variable PF and variable harmonic loads can be easily emulated and the energy drawn by the load can be recycled. In the proposed technique, the current drawn by the load is divided into in-phase, leading and lagging components. Each component is controlled individually. The in-phase power is then regenerated. The simulation and hardware results show exact variation in load characteristics as per the test requirements, which are difficult or impossible using passive loading and existing load emulation techniques with back to back converters. The proposed method is found to be more accurate, flexible and easier for emulation of low PF and high harmonic loads. A performance study is also conducted on a solar photovoltaic system using the developed model, substantiating the importance of this load emulation method.

Bridgeless SEPIC PFC Converter for Multistring LED Driver

This paper deals with Power Factor Correction (PFC) in Low Voltage High Current (LVHC) multi-string light emitting diode (LED) using a bridgeless (BL) single ended primary inductance converter (SEPIC). This application is designed for large area LED lighting with illumination control. A multi-mode LED dimming technique is used for the lighting control. The BL-SEPIC PFC converter is used as a load emulator for high power factor. The regulated low voltage from flyback converter is a source power to the synchronous buck converters for multi-string LED driver and forced cooling system for LED junction. The BL-SEPIC PFC converter inductor design is based on Discontinuous Inductor Current Modes (DICM) which provides good PFC at low cost. Test results are found quite satisfactory for universal input AC (90–265 V). There is significant improvement in the power factor and input current Total Harmonic Distortion (THD) with good margin of harmonic limits for lighting IEC 61000-3-2 Class C.

차량 부하 모사 사이클에 따른 스택 내구 특성 평가 실험적 연구

고분자 막 전해질 연료전지(Proton Exchange Membrane Fuel Cell)는 환경 친화적이고 낮은 작동 온도를 가지고 있어 차세대 차량 동력으로서 주목되고 있지만 상용화를 저해하는 여러 문제점이 있다. 그 중 내구성 문제는 PEMFC의 기술 개발을 위해 해결되어야 하는 주요 이슈 중 하나이다. 차량용 연료전지는 부하 변동폭이 크고 시동 정지가 잦은 특성을 가지고 있기 때문에 운전 환경을 고려한 부하 변동이 반영되어야 하지만, 차량의 부하 특성을 반영한 스택 실험에 대한 연구는 아직 많지 않다. 본 연구에서는 유럽 연합 JRC 보고서에 기초하여 도심 주행과 고속도로 주행을 조합한 New European Driving Cycle(이하 NEDC)을 기반으로 900사이클 동안의 내구성 실험을 수행하여, 같은 시간 동안의 정전류 내구성 저하와 비교하였다. 0, 300, 600, 900사이클에서 분극화 곡선을 획득하여, 0사이클의 전압을 기준으로 한 전압강하율을 부하별로 분석하였다. NEDC 사이클에서의 전압 강하율은 정전류 실험에서의 전압 강하율에 비해 모든 전류밀도에서 훨씬 높은 것으로 나타났으며, 결론적으로 실차 조건에서의 내구성 저하는 정전류에서보다 잦은 부하 변동의 NEDC 사이클에서 더 큰 영향을 받는 것을 알 수 있다.

An Adaptive Digital-Control Scheme for Improved Active Power Filtering Under Distorted Grid Conditions

The operation of active power filters (APFs) under nonideal grid conditions, such as grid-frequency fluctuation and voltage harmonics, can lead to significant degradation in harmonic compensation performance. This paper proposes an adaptive digital-control scheme for a three-phase APF for use in harmonically distorted and variable-frequency grid conditions. This scheme is comprised of a grid-frequency adaptive resonant current controller and an enhanced synchronous-reference-frame phase-locked loop (SRF-PLL). The PLL uses an inherently stable adaptive-filtering stage to improve grid phase and frequency estimates in the presence of voltage harmonics. The improved PLL frequency estimate is used to update the resonant gains of a PI + vector-proportional-integral current-control scheme, implemented in the SRF. This enables the APF to maintain optimal performance in distorted grid conditions. The performance of the proposed APF control scheme is evaluated in a test microgrid, with a 15-kVA three-phase voltage-source converter configured as the APF, a 90-kVA grid emulator utilized to replicate distorted grid conditions, and a load emulator implemented to draw harmonic currents. The control scheme presented here is shown to demonstrate significant performance improvements under nonideal grid conditions compared with equivalent adaptive and nonadaptive methods.

Study on Requirements for Load Emulation of the Vehicle With an Electric Braking System

For different configurations of the electric braking systems (EBS) in the vehicle, requirements for the emulation of their dynamic load on the test bench are studied in this paper, in order to determine appropriate parameters of the test equipment. First, models of three kinds of EBS as well as the test bench are built and characteristics of the transmission system including elasticity and backlash nonlinearity with their influences on the braking performance are fully considered. Two normal braking strategies, namely the maximum-motor-torque strategy and the good-pedal-feel strategy, are designed and the antilock braking strategy that includes the regenerative and friction blended torque control of the wheel slip ratio, the sliding mode control of the backlash, and the PID closed-loop control for elasticity compensation in the emergency condition is proposed. With these methods, motor and frictional braking torque are under the coordinated control to make the most of the EBS. Then, the scheme and control methods of load emulation including the PI method and the feedforward method on the test bench are put forward. Based on the models and control methods, vehicle braking results that indicate the emulation effects and requirements of different kinds of EBS in the MATLAB/Simulink environment are shown; and meanwhile, the dynamic performance parameters of the test bench containing the moment of inertia and the time constant of torque response are obtained for the selection of the test equipment. Finally, experiments on the real bench are carried out. The loading and motion of the vehicle EBS under various braking conditions can be accurately emulated on the proposed test bench and the reliable test results make it possible to investigate the EBS safely, economically, and time-efficiently in the laboratory.

Electromechanical and Electronic Integrated Harvester for Shoes Application

Energy harvesting allows making sensors or transmitters electrically autonomous. Several studies have been proposed but most cases lack electrical and mechanical parts integration and practical application purpose. Here, with the aim of supplying a Bluetooth step-counter placed in the sole of a training shoe, a complete system is presented. It consists of a magnetoinductive transducer embedded with an electronic interface for power conditioning and exploits only the energy recovered by the impact on the ground. A φ 27 × 16 mm cylindrical device containing the transducer, the electronic interface, the step-counter electronics, and the protective shell is developed. Energy recovery derives from the magnet-free oscillation following the shoe impact. The proposed interface exploits pulse-width modulation to perform transducer output rectification and to emulate optimal load impedance while charging a storage capacitor. Numerical and experimental analysis show effective optimal resistive load emulation and energy recovery gain of 2 compared with the standard ac-dc interface. Prototypes have been manufactured and tested. Considering a sample footstep, energy recovery is 360 μJ against 400 μJ dissipated on optimal resistor. Mean energy recovery over a complete run is 644 μJ/footstep. In spite of variable excitation, energy recovery at each footstep is larger than the required and allows the step-counter transmitting the information.

Industrial controller-based dynamometer with dynamic emulation of mechanical loads

Dynamic emulation of mechanical loads belongs to advanced dynamometer control strategies. The main goal of this paper is to analyse and implement a control algorithm for dynamic emulation into an industrial converter by using a standard industrial programming tool. The reference torque of a load machine is calculated through the previously developed closed-loop control algorithm using PI estimator. Proposed torque control structure is analysed and experimentally verified with a linear and a nonlinear model of a mechanical load to be emulated. Presented implementation enables the user the emulation of various mechanical loads with the industrial drive used as a dynamometer. This approach can be used for the advanced testing of motion control techniques in case where the mechanical load is not physically available. Only the equations describing its dynamic are needed.

Experimental Investigation on a Solar/Hydrogen-Based Microgrid

Abstract In this paper an experimental investigation on the performance of an integrated microgrid, installed at the laboratory of the University of Bologna, is presented. The integrated microgrid is made up of two photovoltaic solar panels, two batteries as electricity storage device, a hydrogen generator and an electronic load emulator. The direct current generated by the solar modules charges the batteries by means of a load regulator unit. The power electronics, including an inverter and a DC converter, provide the user with 12 V DC and 230 V AC to feed the electronic load and hydrogen generator, respectively. The aim of this experimental activity is to investigate batteries charging/discharging process and, as a consequence, to quantify batteries roundtrip efficiency value. Experimental trend of voltage, current and power input/output from batteries are observed during charging/discharging operation. Results of the experimental activity show that during the charging process, the voltage from the solar array tapers according to the batteries conditions and recharging needs, thus increasing the charge acceptance of the battery. Once batteries are about to reach full charged condition, the controller starts to hold constant voltage and reduce the charging current to avoid overcharging. Taking advantage of experimental activity results, average value of batteries roundtrip efficiency is determined.

Experimental Study of Grid Frequency Regulation Ancillary Service of a Variable Speed Heat Pump

This paper describes an analysis of a variable speed heat pump (VSHP), which responds to direct load control (DLC) signals to provide grid frequency regulation (GFR) ancillary service, while ensuring the comfort of building occupants. A data-driven dynamic model of the VSHP is developed through real-time experimental studies with a time horizon ranging from seconds to hours. The model is simple, yet still sufficiently comprehensive to analyze the operational characteristics of the VSHP. The DLC scheme is then experimentally applied to the VSHP to evaluate its demand response (DR) capability. Two control methods are considered for a practical implementation of the DLC-enabled VSHP and a further improvement of the DR capability, respectively. Additionally, a small-signal analysis is carried out using the aggregated dynamic response of a number of DLC-enabled VSHPs to analyze their contribution to GFR in an isolated power grid. For experimental case studies, a laboratory-scale microgrid is then implemented with generator and load emulators. We show that the DLC-enabled VSHP can effectively reduce grid frequency deviations and required reserve capacities of generators.

A Simple Variable THD Load Emulation Technique for Performance Evaluation of Power Supply Equipment

Using load emulation, the performance of source side converters can be easily evaluated and improved without the need for actual load. Due to the increase in use of power electronic converters and SMPS based systems, the harmonic levels in load side has increased considerably. Hence emulation of variable THD load is very important in analysing the performance of source side converters and ensure the performance efficiency and power quality under such loads. Here a novel method of obtaining variable load using PWM control explained. The PWM is controlled in a rainbow sinusoidal fashion to obtain clipped waveform across a resistor so that harmonics is introduced in the Load. The power factor can also be varied in the system by paralleling it with leading and lagging converter circuits. The working principle, modelling and simulation are presented along with the results. Proposed technique provides accurate modulation of load THD and effect of harmonics loads on sources converter are also analysed using this.

Static and dynamic power system load emulation in a converter-based reconfigurable power grid emulator

A hardware testbed platform emulating multiple-area power system scenario dynamics has been established aiming at multiple time-scale real-time emulations. In order to mimic real power flow situations in the utility system, the load emulators have to behave like real ones in both their static and dynamic characteristics. A constant-impedance, constant-current, and constant-power (ZIP) model has been used for static load types, while a three-phase induction motor model has been built to represent dynamic load types. In this paper, ways of modeling ZIP and induction motor loads and the performance of each load emulator are discussed. Comparisons between simulation and experimental results are shown as well for the validation of the emulator behaviors. A real-time composite power load emulator is then demonstrated with desired characteristics and detailed transients for representing a power system PQ bus dynamics.

Novel load emulation technique for performance evaluation of isolated solar PV system under varying load conditions

Solar Photo Voltaic (SPV) sources are widely used in present scenario of energy crisis for various applications including grid connected PV plants and grid isolated standalone applications. The performance of solar PV system is highly dependent upon the operating conditions of source and loads especially in standalone applications. The effect on various types of loads on standalone system can be easily analyzed at design stage and testing stage by using load emulation technique, where a virtual load is used to replace actual load, giving more flexibility and accuracy to loading conditions. Here a novel load emulator model is presented which can provide accurate variation in load power factor and THD compared to existing models. The converter decouples the current in to in phase and out of phase components and the in phase component can be regenerated. The model is simulated using MATLABTM simulation and the results are validated by comparing with experimental results obtained by loading SPV inverter with actual load. Hence the proposed load emulator is very useful in design and development of application specific solar PV systems and also for performance analysis of such systems based on various standards.

Process Emulation System for High-Power Piezoelectric Ultrasonic Actuators

Abstract Ultrasonic actuators are used for a wide field of applications. The vibration energy can be used to realize many processes like ultrasonic welding or bonding. Furthermore there are many processes which run more efficient and faster combined with ultrasonic vibration like ultrasonic-assisted turning or drilling. Piezoelectric transducers are the main part of those applications. Most of the applications have a time-variant load behavior and need an amplitude feedback control to guarantee a stable process. To ensure correct function tests of the feedback control systems have to be done. In this case the processes have to be executed in association with a high number of cycles. To emulate the behavior of the environment the automotive and aerospace industries use hardware in the loop systems since a long time but there is no such a method for ultrasonic systems. This paper presents a method to realize high dynamic load emulation for different ultrasonic applications. Using a piezoelectric transformer it is possible to reproduce load curves by active damping on the secondary side of the transformer using a current proportional digital feedback circuit. A theoretical and experimental study of hardware in the loop system for ultrasonic applications is given by this paper. The present system allows testing a wide field of feedback control algorithms with high flexibility and a high number of cycles by utilization of low-cost components. This proceeding decreases design periods in association with feedback control.

Control strategy of a dual induction motor: Anti-slip control application

The paper deals with a Dual Induction Motor control. A control strategy based on the Average Differential Control (ADC) is developed and adapted to work as an anti-slip control in a railway traction system. In addition to cancel the behaviour deviation between the motors supplied by a single inverter in case of an adhesion loss (or an unbalanced load), the proposed control strategy permits an action on the torque control to cancel the differential torque between the two motors. The control strategy is validated on a laboratory test bench with a Mechanical Railway Traction Load Emulator.

Power Converter-Based Three-Phase Nonlinear Load Emulator for a Hardware Testbed System

A three-phase nonlinear load emulator using a power electronic converter is presented in this study. The proposed nonlinear load emulator is intended to be used in an ultrawide-area grid transmission network emulator, also called hardware testbed (HTB). The emulator converter is controlled in rectifier mode to act as the real nonlinear three-phase diode rectifier load. This paper presents an accurate controller for the nonlinear load emulator based on a three-phase diode rectifier system to be used in the HTB. This study also demonstrates simulation and experimental results for verification of the proposed controller.

Design and Implementation of a Two-Stage Grid-Connected High Efficiency Power Load Emulator

The need to reduce the time consumption in developing and implementing power converters, and to improve the effectiveness of the test equipment, continues to grow. This trend is further accelerated through the development of electricity-based technology, such as the electric or hybrid vehicle. As the price of energy continues to increase, regenerative test equipment used for validating power converters are gaining importance and attention. This paper focuses on the development of a two-stage regenerative power load emulator. This type of intelligent load requires a connection to the network interface, which, for some applications, should be bidirectional and must possess a galvanic isolation. The development of such grid-connected unit that processes ac-dc conversion is treated in this paper. A 5 kW prototype is used as a base to model, simulate, design, implement, and test such a system. The stability of the interconnection between the two conversion stages is established and tested in real-time applications. The prototype was tested at 180, 220, and 260 V RMS. The measured efficiency is higher than 90%, and the power factor is 0.99 over a wide range of operation.

Editorial: Special Issue on High-Frequency-Link Power-Conversion Systems, 2014

The overall objective of this IEEE Power Electronics Society (PELS) Special Issue on high-frequency-link power-conversion systems is, therefore, to bring out the highlights of the ongoing world-wide activities in this area of advanced research to expose, analyze, and resolve the critical research and developmental challenges. The Special Issue received a total of 132 manuscripts for review considerations of which 35 manuscripts have been accepted for final publication. These publications encompass all four broad categories of high-frequency-link power-conversion systems (i.e., dc/ac, ac/dc, ac/ac, and dc/dc converters) with broad applicability in the following areas of application: photovoltaic energy, wind energy, electric vehicles, fuel-cell energy, energy storage, uninterruptible power systems, motor drives, high-frequency-ac power distribution systems, high-voltage direct- current transmission, active load emulator, smart/micro grid, solid-state transformers, induction heating, railway traction drive, pulsed power, plug-in hybrid-electric-vehicle, battery charging, inductive power transfer. The contributions of the articles compiled in this special issue are multifold encompassing topologies with plurality of stages and/or levels, modulation, loss-mitigating switching, high-frequency magnetics, control, modeling, switched-capacitor power conversion, power-factor correction, and broad overview of the Special-Issue subject area.