Battery Emulation Research Articles

Mobile AC/DC test device for electric vehicle charging infrastructure communication

The large-scale deployment of charging infrastructure poses challenges to the distribution grid stability. In Hamburg, the project Electrify Buildings for Electric Vehicles (ELBE) implements and tests a demand side management communication protocol that allows the distribution grid operator to reduce the charging power of electric vehicle charging stations if necessary. For this purpose, a test device capable of testing the signal chain as well as a real load reduction is presented for DC charging infrastructure. The standardized high-level communication protocols are described. With the charger’s power electronics located in the DC charging station, the need for a battery emulation arises, which is also discussed. Finally, a novel concept for a mobile and modular test setup for combined testing signal and real load reduction of AC and DC charging infrastructure is presented.

Control of a Multiphase Buck Converter, Based on Sliding Mode and Disturbance Estimation, Capable of Linear Large Signal Operation

Power-hardware-in-the-loop systems enable testing of power converters for electric vehicles (EV) without the use of real physical components. Battery emulation is one example of such a system, demanding the use of bidirectional power flow, a wide output voltage range and high current swings. A multiphase synchronous DC-DC converter is appropriate to handle all of these requirements. The control of the multiphase converter needs to make sure that the current is shared equally between phases. It is preferred that the closed-loop dynamic model is linear in a wide range of output currents and voltages, where parameter variations, control signal limits, dead time effects, and so on, are compensated for. In the case presented in this paper, a cascade control structure was used with inner sliding mode control for phase currents. For the outer voltage loop, a proportional controller with output current feedforward compensation was used. Disturbance observers were used in current loops and in the voltage loop to compensate mismatches between the model and the real circuit. The tuning rules are proposed for all loops and observers, to simplify the design and assure operation without saturation of control signals, that is, duty cycle and inductor current reference. By using the proposed control algorithms and tuning rules, a linear reduced order system model was devised, which is valid for the entire operational range of the converter. The operation was verified on a prototype 4-phase synchronous DC-DC converter.

A Reconfigurable Solar Photovoltaic Grid-Tied Inverter Architecture for Enhanced Energy Access in Backup Power Applications

In this paper, a photovoltaic (PV) reconfigurable grid-tied inverter (RGTI) scheme is proposed. Unlike a conventional GTI that ceases operation during a power outage, the RGTI is designed to act as a regular GTI in the on-grid mode but it is reconfigured to function as a DC-DC charge-controller that continues operation during a grid outage. During this period, the RGTI is tied to the battery-bank of an external UPS based backup power system to augment it with solar power. Such an operation in off-grid mode without employing communication with the UPS is challenging, as the control of RGTI must not conflict with the battery management system of the UPS. The hardware and control design aspects of this requirement are discussed in this paper. A battery emulation control scheme is proposed for the RGTI that facilitates seamless functioning of the RGTI in parallel with the physical UPS battery to reduce its discharge current. A system-level control scheme for overall operation and power management is presented to handle the dynamic variations in solar irradiation and UPS loads during the day, such that the battery discharge burden is minimized. The design and operation of the proposed RGTI system are independent of the external UPS and can be integrated with an UPS supplied by any manufacturer. Experimental results on a 4~kVA hardware setup validate the proposed RGTI concept, its operation and control.

Estimation and compensation of DC-Link voltage disturbances in a DC–DC converter for battery emulation

ABSTRACT Battery emulation is essential for reliable testing of powertrains of electric and hybrid vehicles under repeatable conditions. For that purpose, a DC voltage controller provides fast reference tracking capabilities. Due to imperfect conversion of AC current to DC current, the DC voltage source of the battery emulator does not provide constant voltage but is subject to periodic fluctuations. This disturbance is propagated through the system to the battery emulator's output. In this paper, an observer-based compensation strategy is deployed. As the structure of the multiplicative perturbation is known, it is integrated into the battery emulator model yielding a state-affine system. An appropriate observer provides asymptotically correct estimates of the disturbance, which are then used to adequately manipulate the control variable without interfering with stability properties of the closed-loop system. Simulation and experimental results show the improvements achieved by the disturbance rejection.

Off-the-Shelf Power Supply-Based Battery/Supercapacitor Emulator for Charger Functionality Testing

This paper presents a method of battery/supercapacitor emulator (BSE) rapid prototyping, based on modified off-the-shelf components. Low-cost commercial constant output voltage switching power supply, transformed into an input-voltage-controlled converter, is utilized as emulator power stage. The control over input voltage of the power supply is gained by appropriately altering the voltage feedback branch of the control circuitry. Consequently, it becomes possible to tightly regulate the input voltage of the device according to a predefined current–voltage relation and hence emulate any static and/or dynamic behavior by sensing the input current of the power supply and varying its input voltage appropriately. For battery or supercapacitor emulation, the desired charging characteristics may be either derived from manufacturer provided datasheet, obtained experimentally or estimated by solving the appropriate electrical equivalent circuit of the emulated storage device. In order to demonstrate the validity of the proposed method, a prototype was designed and built using an off-the-shelf boost dc–dc converter-based low-cost power supply. Dynamic input characteristics of the prototype were experimentally evaluated and two commercial storage devices (namely MR-2791 lithium ion battery and Maxwell BMOD0058-E016-B02 supercapacitor packs) charging sequences were emulated. The resulting I – V input relations were shown to closely resemble the charging behavior of real devices.

Battery Emulation for Power-HIL Using Local Model Networks and Robust Impedance Control

Battery emulation with a controllable high-power dc supply enables repeatable hardware-in-the-loop testing of powertrains for hybrid and electric vehicles. For this purpose, not only the power flow but also the nonlinear characteristic and dynamic impedance of batteries need to be emulated. In this paper, nonlinear local model networks are used to obtain dynamic battery models with high fidelity that can be computed in real time. This approach also allows the extraction of local linear impedance models for high-bandwidth impedance emulation, leading to a tighter coupling between the test bed and simulation model with predictable closed-loop dynamics. A model predictive controller that achieves optimal control with adherence to system constraints is extended to impedance control and robustness against constant power loads. This results not only in superior dynamic performance but also in stable dc-bus voltage control even for testing of tightly controlled electric motor inverters with negative differential input resistance. Since the controller design is based on a model of the test bed setup including the virtual battery model, emulator hardware, and input characteristics of the powertrain under test, it is possible to systematically analyze stability.

Model predictive control of a DC–DC converter for battery emulation

A battery emulator is used instead of a real traction battery to supply an electric motor inverter on a test bed for hybrid and electric powertrains under deterministic conditions. The use of virtual battery models eliminates the need for expensive battery prototypes. Virtual battery properties such as chemistry, state of charge or state of health can be changed instantly. However, the control of a battery emulator is a challenging problem. Very fast reference tracking is required for battery impedance emulation but motor inverters act as constant power loads that have a negative influence on the tracking performance and can even lead to instability. In this paper an MPC strategy is proposed for solving this problem. Scheduling of local controllers is utilized in order to handle the nonlinear and destabilizing load. Furthermore, a fast algorithm is presented that allows real-time MPC subject to input and output constraints. Experimental results obtained with a battery emulator supplying an electric drive inverter demonstrate the performance of the stabilizing controller.