Load Emulation Research Articles

Hardware-in-the-loop dynamic load emulation of robotic systems actuated by fluidic artificial muscles

Hardware-in-the-loop (HIL) testing is a popular control system testing method because it bridges the gap between modeling/simulation and experiments. Instead of designing a full hardware-based experiment to validate the results of a simulation, the plant hardware can be replaced with an emulator device that responds to exogenous inputs and effectively emulates the dynamic behavior of a system. This approach can be more cost-effective and modular, since the emulated plant system can be modeled in a simulation environment, implemented on a simplified piece of hardware and changed quickly without having to fabricate new parts. This paper develops the hardware and control scheme for a certain type of HIL device called a dynamic load emulator that consists of a 1-DOF linear hydraulic dynamometer equipped with in-line sensing to measure both its own position and the force exerted on it by a device-under-test. This measured force is passed to a real-time model of the emulated dynamic system. The model outputs the emulated system position, and a closed-loop controller is used to emulate this position. The emulator controller incorporates both model-based feedforward and standard feedback PI control. This paper characterizes the dynamometer-based dynamic load emulator and its controller, determining its hardware limitations and validating its capabilities when experiencing a force input from a linear spring with known parameters. Additionally, this paper demonstrates the ability of the emulator to represent the dynamics of a 1-DOF robotic joint when actuated by a pair of fluidic artificial muscles (FAMs). The primary contribution of this work is to allow for more comprehensive testing of FAM configurations, topologies, and controllers for a wide range of parameters, because the same hardware can be used to emulate multiple systems. As a result, this work will lead to more cost-effective, time-efficient, and energy-efficient designs of robotic systems and the FAMs used to actuate them.

Modeling and Load Emulation Experimental Verification of a Vehicle Powertrain System Test Bench Based on Rigid-Flexible Coupling Transmission Shaft

Modeling and Load Emulation Experimental Verification of a Vehicle Powertrain System Test Bench Based on Rigid-Flexible Coupling Transmission Shaft

An Energy-Feed Type Split-Capacitor Three-Phase Four-Wire Power Electronic Load Compatible with Various Load Demands

Energy-feed power electronic loads can precisely control the phase and magnitude of the power supply output current, achieving the emulation of loads. Moreover, they can feed energy back to the grid for energy regeneration, demonstrating significant research value. This article proposes an energy-fed power electronic load topology and control method that can realize the static and dynamic simulation of linear and non-linear loads and take into account the simulation needs of single-phase, three-phase three-wire, and three-phase four-wire loads. The main circuit uses a two-stage back-to-back AC/DC/AC structure: the front side is a three-phase four-wire split capacitor PWM rectifier bridge, which is used to simulate loads under various operating conditions; the back side is a three-phase three-wire PWM inverter bridge, which realizes the energy feeding back to the grid and reduces the waste of energy; and the intermediate side uses a split capacitor to equalize the voltage and achieve voltage stabilization. The topology is analyzed under the simulation demands of three-phase balanced, three-phase unbalanced, single-phase and non-linear loads. Finally, a MATLAB(R2022a)/Simulink simulation platform is built for a power electronic load with a rated capacity of 200 kVA. The simulation results verify the effectiveness, feasibility, and advancement of the power electronic load proposed in this article.

Load Emulation with Independent Metering for a Pump Test Bench

For the investigation of new types of internal gear pumps under realistic conditions, a test bench is presented that enables dynamic load emulation via the pressure with simultaneous dynamic speed control of the pump. For pressure control, a hydraulic half-bridge with separate control edges is used on both sides of the pump and a pressure control is presented. An error-based adaptive controller is used for pressure control and tested experimentally. It is shown that the error-based adaptive controller has a better performance compared to a simple PID control.

Selection of power sharing factor for hybrid battery/ultracapacitor energy storage‐based EV through load emulation technique

AbstractThe hybrid battery/ultracapacitor (UC) energy storage system for electric vehicles (EVs) proved more reliable and cost‐effective. Even with the best possible sizing of these energy storage devices, unforeseen EV loading cycles are causing a single‐source transition. Mainly, the UC exhaustion in acceleration or transient loading shifts the loading to the battery, causing overdischarge and reducing the life span. This paper presents a deterministic current control algorithm to restrict the maximum allowable battery discharge current. The current discharge control in the battery/UC is implemented using symmetrical carrier‐based digital average current mode (DACM). The proposed energy management algorithm (EMA) with variable battery current sharing factor typically controls the current flow between the battery and the UC so that the battery current is always within safe limits. The DC‐DC converter with proposed novel EMA allows the system to regulate the voltage and current flow between the two power sources. By sharing the currents in this way and limiting the battery current to a safe value, the system helps to prolong the battery's life and ensures that the vehicle operates safely and reliably over the long term. The EV load profile emulator provides the current sharing under dynamic operating conditions. The hardware results are supported to validate the single‐source transition under hybrid energy sources.

Neuromodel of an Eddy Current Brake for Load Emulation

The eddy current brake (ECB) is an electromechanical energy conversion device that can be used as a load emulator to load a motor according to the intended load scenario. However, conducting an analysis in the time domain is difficult due to its complex behavior involving mechanical, electrical, and magnetic phenomena. The challenges with the time domain analysis of the ECB require new modeling approaches that provide reliability, robustness, and controllability over a wide speed interval. If the ECB can be modeled with high accuracy, it can be controlled like a load emulator that can simulate nonlinear industrial loads. This paper describes a neuromodeling approach taken to develop an ECB. The nonlinear characteristic of the brake system was modeled with a high performance by using an artificial neural network (ANN), which is a potent nonlinear system identification tool. Several characteristics of a designed and optimized brake system undergoing various excitation currents in whole speed regions are described and verified experimentally. Eventually, an electromechanical brake system is proposed that aims to provide the required linear or nonlinear load model dynamics throughout an emulation process in line with the obtained neuromodel. To identify the most suitable ANN architecture for the problem, various ANN configurations, ranging from 1 neuron to 20 neurons in the hidden layer, as well as a statistical approach that differs from the existing literature, are presented. Additionally, the suggested model’s scalability is discussed.

Emulation of Mechanical Loads in Electric Drives – An Overview of Methods

Abstract The aim of the presented paper is to introduce the reader to hardware-in-the-loop (HIL) simulation in electric drives, the motivation for its usage and its benefits. Basic information about HIL simulation in general and the connection to electric drives is followed by an explanation of the main principle of the dynamic emulation of mechanical loads for electric drives, which is a special case of HIL simulation. Next, the description of the three main methods of load emulation and their mathematical background are presented in the order of historical appearance: the emulation with compensator and tracking controller, the emulation based on non-linear control and the emulation with feed-forward compensation with the use of inverse dynamics.

A cost-efficient DC active load laboratory solution

The increased use of DC renewable energy resources and DC storage systems, combined with the necessary reduction of energy waste, is boosting the development of DC smart grids. In this scenario, DC load emulation is of great importance. From the hardware point of view, DC buses stability of smart grids and the different DC/DC converter topologies must be tested. From the software point of view, smart grid strategies and job schedulers must be tested with different power absorption profiles. Moreover, DC load emulation can be useful for many other purposes, such as battery characterization, power supply testing, photovoltaic I-V curve measurements, etc. In this work, a cost-efficient DC Active Load (AL) solution is proposed. The principle of the circuit topology is a buck-boost-derived converter. This solution can be designed and tested considering the required voltage, current, and maximum input power. Both simulation and experimental results are shown on a 400 W size prototype. Thermal and electrical results validate the simulation model and the AL feasibility.

Design and modeling of hardware-in-loop test bench for hydraulic excavator based on dynamic load emulation

Hardware-In-Loop (HIL) testing is an effective means to improve the development process of construction machinery. This paper presents a HIL test bench for hydraulic excavator based on dynamic load emulation. The critical technology of HIL test bench is the ability to emulate realistic load. Therefore, a digging load emulating model is established and implemented in real-time environment. To improve the load emulating accuracy, the soil-bucket interaction model is calibrated based on the coupling of the discrete element method (DEM) and multibody dynamics (MBD). The experimental scheme under positive and negative load working conditions is designed to correct the testing error. The performance of the HIL test bench is evaluated from multiple perspectives of load emulating accuracy, system power flow and fuel consumption. Compared with actual excavation tests, the testing error of the proposed HIL test bench is no more than 12%.

Load Emulation Compensation Control of a Test Bench Based on Rigid-Flexible Coupling Transmission for a Vehicle Electric Drive System

A load emulation compound correction compensation control approach based on demand torque analysis of the electric drive system (EDS) and the parameter perturbation of the load emulation of rigid-flexible coupling transmission (RFCT) is proposed to address the problem of poor stability and accuracy during the load emulation of the RFCT test bench in a semi-anechoic chamber. First, a speed closed-loop tracking (SCLT) controller without the inverse dynamics model is designed by considering the demand torque decision-making link, and the influence of the RFCT nonlinearity and the perturbation parameter on the speed tracking accuracy are investigated. Subsequently, a speed feedforward correction compensator without the RFCT model is also designed. Finally, a load torque feedforward correction compensator is designed, and the compensation adjustment gain is used to accurately account for the dynamic error of the load torque caused by the inertia error of the RFCT. The simulation and experimental results show that the proposed compensation control method can accurately realize load emulation of the EDS test bench, and is suitable for application to load emulation systems that use a multi-inertia mechanical long axis to connect the device under test (DUT). Moreover, it can effectively improve the dynamic response of the SCLT and the loading torque accuracy and is robust and adaptable.

Variable Speed Drive Connected Motor Load Emulator for a Multi-Converter-Based Hardware Testbed System

Variable Speed Drive Connected Motor Load Emulator for a Multi-Converter-Based Hardware Testbed System

An emulation platform for mimicking unbalanced loads and sources

Abstract With the increasing penetration of power electronic equipment for various day to day applications, several testing methods are also gaining attention. Power level emulation is a popular technique which is typically employed for mimicking the behaviour of a source or load in real-time. Most of the available literature deals with the power level emulation of balanced loads and sources. This paper presents the details of control schemes and an emulator based on a four leg VSI, which is capable of mimicking unbalanced sources and loads. A flexible control scheme with a common inner inductor current loop is proposed for both the positive and negative sequence components, for the unbalanced load and source emulations. The proposed emulator is capable of emulating both types of unbalances — those in which only positive and negative sequence components exist (3 wire systems) and those in which the zero sequence components also exist in addition to the above mentioned components (4 wire systems). The modelling and control aspects are validated through simulations using Matlab Simulink and through experiments on the laboratory prototype emulator.

A hardware-in-the-loop wave-basin scale-model experiment for the validation of control strategies for floating offshore wind turbines

This paper presents a new hardware-in-the-loop methodology for wave-basin scale-model experiments about floating offshore wind turbines and its application as a tool for the validation of control strategies. In the hardware-in-the-loop experiments, the physical Froude-scaled wind turbine model used in conventional scale-model tests is replaced by a numerical model, measurements and a multi-fan actuator. As usual, properly-scaled waves are generated in the wave basin and the floating platform is simulated by means of a scale-model. The hardware-in-the-loop methodology was used to recreate the interaction between the collective pitch controller and the platform pitch mode that, often observed in numerical studies. In addition, the blade-root load measurement available in the numerical model of the rotor was used to implement an individual pitch control strategy. Different from in conventional experiments, the hardware-in-the-loop methodology allows to recreate a realistic three-dimensional wind field that was used to demonstrate the effectiveness of the individual pitch control. The improved emulation of the rotor loads and wind field make the hardware-in-the-loop experimental methodology an effective tool for the development and validation of control strategies for floating offshore wind turbines.

Experimental Analysis of an Air Heat Pump for Heating Service Using a “Hardware-In-The-Loop” System

Estimating and optimizing the dynamic performance of a heat pump system coupled to a building is a paramount yet complex task, especially under intermittent conditions. This paper presents the “hardware-in-the-loop” experimental campaign of an air-source heat pump serving a typical dwelling in Pisa (Italy). The experimental apparatus uses real pieces of equipment, together with a thermal load emulator controlled by a full energy dynamic simulation of the considered building. Real weather data are continuously collected and used to run the simulation. The experimental campaign was performed from November 2019 to February 2020, measuring the system performances under real climate and load dynamics. With a water set point equal to 40 °C, the average heat pump coefficient of performance was about 3, while the overall building-plant performance was around 2. The deviation between the two performance indexes can be ascribed to the continuous on-off signals given by the zone thermostat due to the oversized capacity of the heat emission system. The overall performance raised to 2.5 thanks to a smoother operation obtained with reduced supply temperature (35 °C) and fan coil speed. The paper demonstrates the relevance of a dynamic analysis of the building-HVAC system and the potential of the “hardware-in-the-loop” approach in assessing actual part-load heat pump performances with respect to the standard stationary methodology.

Enhanced Frequency Control Method for Microgrid-Connected Flywheel Energy Storage System

Flywheel energy storage system (FESS) can be used for frequency regulation in microgrids. In this article, an enhanced frequency control system is presented for FESS to reduce the frequency variations of microgrid. A three-layer control system is proposed for machine-side converter of the FESS including dc-link voltage controller, speed controller, and field-oriented control system. Unlike the conventional control methods, in the proposed method, the frequency controller is implemented in the grid-side converter to increase the ramp rate of the FESS and reduce the frequency deviation against load changes. Also, the proposed three-layer control system of the machine-side converter reduces the dc-link voltage variations. Furthermore, a mode coordination system is proposed to reduce the dc-link voltage variations when the operation mode of FESS changes from flywheel speed control mode to the microgrid frequency control mode. To demonstrate the advantageous of the proposed method in comparison to the conventional method, at first, the linearized model of the FESS in microgrid is extracted, and then the small-signal analysis is carried out for optimal design of proportional integral (PI) controllers. Two control strategies are theoretically presented and experimentally compared in a prototype microgrid including a diesel generator emulator and a load emulator. The frequency control system is studied in different loading conditions. Experimental results verify the theoretical concepts proposed in this article, and show the superiority of the proposed method over the conventional method.

Teaching Digital Control of Substation and IEC 61850 With a Test Bench Validation

This paper proposes an original Smart-Grid test bed aimed at teaching the IEC 61850 standard to students and professionals. It includes emulation of medium voltage loads and generators, with a supervisory control and data acquisition system. With this test bed, lab classes focused on the setup and configuration of protection relays using semantics of xml language are proposed. For this, GOOSE services and their functionalities are taught and tested with experiments involving real cases. The presented lab classes are part of a dedicated complete pedagogic module comprising lectures and experiments. Through the development, the test and the deployment of their own solutions in an actual distribution grid, the students learn by integrating theory and practice through the complete chain of Smart-Grid solutions: from the electrical to the communication layers.

Electronic Emulator of Biological Tissue as an Electrical Load during Electroporation

Electroporation is an emerging technology, with great potential in many different medical and biotechnological applications, food engineering and biomass processing. Large variations of biological load characteristics, however, represent a great challenge in electroporator design, which results in different solutions. Because a clinical electroporator is a medical device, it must comply with medical device regulative and standards. However, none of the existing standards directly address the operation or electroporator’s performance requirements. In order to evaluate clinical, laboratory and prototype electroporation devices during the development process, or to evaluate their final performance considering at least from the perspective of output pulse parameters, we present a case study on the design of an electronic emulator of biological tissue as an electrical load during electroporation. The proposed electronic load emulator is a proof of concept, which enables constant and sustainable testing and unbiased comparison of different electroporators’ operations. We developed an analog electrical circuit that has equivalent impedance to the beef liver tissue in combination with needle electrodes, during high voltage pulse delivery and/or electroporation. Current and voltage measurements during electroporation of beef liver tissue ex vivo, were analyzed and parametrized to define the analog circuit equation. An equivalent circuit was simulated, built and validated. The proposed concept of an electronic load emulator can be used for “classical” electroporator (i.e., not nanosecond) performance evaluation and comparison of their operation. Additionally, it facilitates standard implementation regarding the testing protocol and enables quality assurance.

Research on Multifunctional High-Power Grid Source Simulator System with Synchronous Generator, Line Impedance Imitation, and ZIP Load Emulator

As the penetration of distributed power sources in the power grid is getting higher and higher, the adverse effects are also increasing. It is necessary to adopt control technology to make the distributed power source participate in the power regulation of the power system. In this paper, a multifunctional high-power grid source simulator system is presented. For wider control bandwidth and better performance, a high-power, back-to-back converter and an auxiliary lower-power, back-to-back converter connected in cascade mode topology is proposed in this paper. The basic principle and implementation method of virtual synchronous generator (VSG) in the high-power, back-to-back converter are described to reflect the same power frequency characteristics and voltage regulation characteristics as synchronous generators. Amplitude closed-loop control is proposed to realize zero steady-state error in the lower-power, back-to-back converter, also with line impedance imitation. Meanwhile, a constant-impedance, constant-current, and constant-power (ZIP) load model is used to emulate static load in the grid simulator system. At last, a set of experimental results for a 2 MW grid simulator system is provided to verify the effectiveness and validity of the proposed approach.

High-Accuracy Dynamic Load Emulation Method for Electrical Drives

This article addresses the problem of dynamic load emulation (DLE) with high accuracy of any mechanical load for which the mathematical model is known. The control strategy of a load machine is used to design tasks of control algorithms of variable speed and torque drives for educational purposes and several engineering applications, as transportation and renewable energy. The structure uses a set-point feed-forward compensator with speed-tracking controller, which provides robustness under parametric variation and nonmodeled dynamics. Nonlinear effects and constraints of the experimental setup shaft can be included in the compensator, which makes the strategy an alternative method for systems operating under different degrees of uncertainty. Moreover, different control approaches can be applied to both compensator and speed controller. The method can be applied with any rotary machines, where two induction motors (IMs) with directly coupling are adopted. The method was compared to two other DLE methods and was validated through nonlinear models whose inertia and friction are not constant. The simulated and experimental results are very similar, even when high uncertainty is assumed.

Monitoring 3-D Temperature Distributions and Device Losses in Power Electronic Modules

This paper presents a methodology for real-time monitoring of 3-D temperature distributions and device losses within power electronic modules. It allows precise thermal management, empirical lifetime prognosis, and detection of critical degradation of the power module. By effective combination of thermal 3-D finite difference modeling, parametric loss models, and model truncation techniques, a compact thermal real-time model is derived. It enables the computation of device losses and temperatures at critical locations within a power module, e.g., at the devices, solder interfaces or the base plate, on a conventional digital signal processor. The real-time model as well as real-time junction temperature information are combined in a new Luenberger-style observer structure. Applying bandwidth partitioning, the observer estimates the temperatures throughout the power module every switching period and averaged over one excitation period with nearly zero lag, even if the junction temperature measurement exhibits delays and has noisy signals. Furthermore, it estimates errors in the loss prediction process that can be tracked over the lifetime of the power module to detect degradation of the devices or the power module. The observer and its features are experimentally evaluated under realistic operating conditions on a load emulator using a state-of-the-art automotive power module.