Multi-Mode Control of a Bidirectional Converter for Battery Energy Storage System

The efficient application of battery energy storage system (BESS) technology can effectively alleviate the uncertainty and volatility caused by distributed generations (DGs) and loads, and reduce their adverse effects on the power grid. More efficient applications could delay equipment capacity upgrades, improve equipment utilization, save costs, and increase the system hosting capacity for renewable energy. However, the application of BESS is restricted by its high cost and limited policy support. It is, therefore, necessary to carry out an economic evaluation of BESS, considering its flexibility and improvement of reliability, alongside incentive policy research to promote its deployment. This study on BESS involves four key aspects: 1) It proposes a reliability-benefit model for BESS, considering the value of electricity in the national economy. 2) It describes a flexibility improvement benefit calculation model for BESS, built with the definition of flexibility indexes of distribution network related to BESS, and considering the capacity, charge, and discharge constraints. 3) A reliability improvement benefit calculation model of BESS was built, and the present study proposes a detailed calculation flow of economic evaluation model for BESS users considering net present value (NPV) index and dynamic payback period (DPP) index. 4) An impact analysis of different prices and incentive policies on BESS business models is also carried out, with the present study finally presenting an incentive policy based on flexibility and reliability improvement. The results of the IEEE 33-node test system show that flexibility and reliability improvement can effectively reflect the benefit and cost of BESS, and that incentive policies can help to promote the development of BESS technology.

Application of battery energy storage systems (BESS) could help reducing wind power curtailment. Due to the uncertain nature of wind power as well as conventional generation and loads, it is more reasonable and accurate to determine the quantitative requirement for BESS probabilistically. Moreover, the effectiveness of using BESS to reduce wind power curtailment is affected by their charging and discharging control strategies. In this paper, a method based on sequential Monte Carlo simulation (SMCS) is proposed for probabilistically analyzing the requirement for BESS. Three practical charging and discharging control strategies of BESS are also proposed and compared both qualitatively and quantitatively as for their effectiveness in reducing wind power curtailment. The proposed method and control strategies are tested in a real large power system in northwest China.

This work advocates an effective way of energy management in a microgrid consisting of a synchronous reluctance generator (SynRG) based wind energy conversion system (WECS) connected to a DC bus, which voltage is maintained by a battery energy storage system (BESS). The system is capable of feeding a fairly constant value of power to the grid apart from supplying the local loads. Apart from maintaining the DC link voltage, the BESS compensates for the fluctuations in the wind power by channelizing the power in and out of the BESS as per the power generation and power demand. The SynRG is operated in direct torque control (DTC) mode corresponding to maximum power point (MPP) of the WECS by adjusting the control inputs to the machine side converter. The battery in BESS, is integrated to the DC bus using a bidirectional converter (BDC), which helps in charging and discharging of the battery. A voltage source converter (VSC) connected on the grid side evacuates the power from the common DC link and feeds it to the three-phase grid. This VSC is controlled in such a way as to maintain the required power factor on the grid side as per the reference values of the direct and quadrature axes components of currents specified. The proposed system is designed, modeled and simulated in Simulink/ MATLAB environment.

Many developing countries are now facing the problem of managing the peak demand deficit. Renewable energy resources are the best solution for this problem. Power storage devices like batteries can act as another viable solution for this by off-peak charging and peak time discharging. Efficient bidirectional converters are essential requirement for proper operation of the system. For economics, efficient and for easy applications, light weight transformer less converters exhibit superior performance over the conventional types. The work discussed below presents design and analysis of a transformer less bidirectional converter with dual power (P & Q) control scheme. The operation of this converter is controlled based on the corresponding current signal generated by the P-Q control. The proposed prototype finds its application in Battery Energy Storage System (BESS), Vehicle 2 Grid & Grid 2 Vehicle applications, where portability and efficiency are most important. Simulations are performed using Matlab.

<abstract> <p>With the increase in the integration of renewable energy resources in the grid and ongoing growth in load demand worldwide, existing transmission lines are operating near their loading limits which may experience voltage collapse in a small disturbance. System stability and security can be improved when the closeness of the system to collapse is known. In this research, voltage stability of IEEE 30 bus test network is analyzed and assessed under continuously increasing load condition, utilizing the Critical Boundary Index (CBI); and improved with continuous integration of battery energy storage system (BESS). BESS is considered to be a hybrid combination of storage units and voltage source converter to have a controllable real and reactive power output. Security constraint optimal power flow is utilized for optimally sizing the installed BESS. It is evident from the outcome of the research that the voltage stability of the system is controlled to be above the acceptable range of 0.3 pu CBI in all lines and the system voltage is kept within the acceptable and constrained range of 0.9–1.1 pu.</p> </abstract>

In recent years, Quasi-Z-source cascaded H-bridge multilevel inverters (qZS-CHBMLIs) have become an interesting solution for integrating renewable energy into the utility grid. The possibility of performing power conversion in a single stage, without an additional DC/DC converter, and a higher voltage gain, are their main advantages over traditional inverters. In addition, individual control of the maximum power point tracking (MPPT) can be achieved for each PV plant. Owing to the intermittent nature of PV power plants, battery energy storage systems (BESS) are commonly used to smooth out PV power fluctuations. This paper presents a control system for the active and reactive power delivered to the grid according to the system operator references and an EMS for an ES-qZS-CHBMLI. The BESS is coordinated through an energy management system (EMS) based on the state of charge (SOC) The system is evaluated under two different operation modes. One of them, where the PV power plants operate according to their MPP and the other in which the MPPT faults and thus, the PV power is decreased. A MATLAB-Simulink simulation is used to validate the proposed control system for a grid-connected single-phase configuration based on a qZS-CHBMLI with three cascade qZSI, each connected to a 4.8 kW PV power plant and a BESS.

In this paper, a simple prototype of a quasi-resonant DC link (QRDCL) voltage-fed bidirectional power converter operating in the zero voltage soft-switching PWM mode is presented for a battery energy storage system (BESS). The operating principle of this QRDCL circuit and multi-functional control-based power converter system, including PWM inverter mode in which energy flows through from the battery bank to the three phase utility-grid and an active PWM power converter mode in which energy flows through from the utility-grid to the battery bank are described. The multi-functional operating characteristics of this three-phase soft-switching ZVS-PWM bidirectional power converter with a QRDCL for BESS is demonstrated under the conditions of peak-cut mode and battery charging mode in comparison with a three-phase hard-switching PWM bidirectional power converter. Its effectiveness is proved by simulation analysis.

In this paper, a Battery Energy Storage System (BESS) dynamic model is presented, which considers average models of both Voltage Source Converter (VSC) and bidirectional buck-boost converter (dc-to-dc), for charging and discharging modes of operation. The dynamic BESS model comprises a simplified representation of the battery cells, which allows to simulate the effects of battery degradation, dc-to-dc converter, VSC, and the dynamics associated with the filter and transformer connecting the BESS to the grid. A decoupled dq-current control is used for the VSC, allowing the operation of the BESS in several modes, i.e., constant active and reactive power, constant power factor, voltage regulation, frequency regulation, oscillation damping, and a combination of the latter two. The proposed model is implemented in DSATools and tested for different contingencies on a benchmark system, and compared with a industry-grade BESS model used in power system dynamic studies. The importance of modeling the current control and dynamics of the dc-to-dc are demonstrated, especially when the battery cells are degraded due to, for instance, aging.

Global expansion of the EV market has led to widespread DC charging infrastructure. Consumers prefer DC charging over AC to reduce charging time per kilometer. However, grid-connected DC chargers can cause issues such as grid instability, power quality problems, demand imbalance, and conversion losses. This paper proposes an off-grid photovoltaic (PV) fed DC charger for EVs along with a battery energy storage system (BESS) to mitigate these challenges. The work aims to increase the use of clean energy for EV charging, to ensure uninterrupted EV charging with minimum power conversion stages, and to improve PV utilization. BESS serves as a backup power source that charges or discharges based on PV availability. Additionally, the system powers the non-critical adjustable loads of domestic/industrial sites with the available PV power when both EV and BESS are fully charged. The system can be reconfigured to operate in six distinct modes using two DC-DC converters and five relays. Among six modes, four modes operate in single-stage power conversion. A buck converter is used to extract power from PV. A bidirectional buck-boost converter is used to charge and discharge the BESS. The proposed system is validated through hardware prototype for both steady-state and transient conditions.

Wind power supply system is an effective, environmentally friendly power source for household and other applications. According to the wind speed changes in variation the output power of wind generator is not stable and constant. This paper proposes the variable speed stand-alone wind power supply system that includes Permanent Magnet Synchronous Generator, three phase diode rectifier, DC-DC boost converter, battery energy storage system, and voltage source inverter. DC-DC boost converter controls to extract maximum power from the available wind power. Battery energy storage system through bidirectional converter is to supply the load when wind power is shortage. To get the desired output voltage and frequency at the load side, the voltage source inverter with the sinusoidal pulse width modulation (SPWM) control technique has chosen. The harmonics generated from the VSI are filtered with simple passive LC filters. Simulation results of output voltages and currents, the total harmonic distortion (THD) are presented using MATLAB/Simulink.

This paper presents an experimental application of LiFePO4 battery energy storage systems (BESSs) to primary frequency control, currently being performed by Terna, the Italian transmission system operator (TSO). BESS performance in the primary frequency control role was evaluated by means of a simplified electrical-thermal circuit model, taking into account also the BESS auxiliary consumptions, coupled with a cycle-life model, in order to assess the expected life of the BESS. Numerical simulations have been carried out considering the system response to real frequency measurements taken in Italy, spanning a whole year; a parametric study taking into account different values of governor droop and of BESS charge/discharge rates (C-rates) was also performed. Simulations, fully validated by experimental results obtained thus far, evidenced a severe trade-off between expected lifetime and overall efficiency, which significantly restricts the choice of operating parameters for frequency control.

This paper focuses on the applications of the battery energy storage system (BESS) to be installed in distribution systems for deferment of the distribution reinforcement investment in the short-term power distribution planning. The distribution system in this paper refers to the cost and standard criteria of Provincial Electricity Authority (PEA). The existing system is 22-kV voltage level includes 115/22 kV substation, the 45-km. distribution feeder, 1 photovoltaic plant and 8 load points with mixed customer types. The technical problem often occurred in 22-kV distribution feeders is the power demand exceeds the line thermal limit in short time (1-4 hour per day) every day. Following PEA’s standard and criteria, distribution network owners (DNO) has 2 choices to solve this problem; taking the risk of fault or reinforce feeders. Nowadays, energy storage technologies play the interested role in smart grid era. It illustrates from the analysis that BESS can solve this problem and postpone the time of system reinforcement such as construction of the new distribution line with worthy investment. Power flow of the study system is calculated by DIgSILENT PowerFactory software. The best alternative is chosen based on the maximum net present value (NPV).

Battery Monitoring is very important for most of the electric vehicle(EV) and battery energy storage system (BESS) since the safety, operation and even the life of the passenger/operator depends on the battery system. Checking and controlling the status of battery within their specified safe operating conditions is exactly the major function of battery management system (BMS). The state of charge (SOC) is a critical parameter of a Li-ion battery, an accurate on-line estimation of the SOC is important for forecasting the EV driving range and BESS power dispatching. A widely used method to estimate SOC is based on coulomb counting, due to the uncertainty, including unit-to-unit variation, measurement noise, operational uncertainties, and model inaccuracy, it's difficult to estimate the SOC by using coulomb counting, an online inference of open-circuit voltage (OCV) is used to calibrate the SOC, however, a relatively flat OCV curve of LiFePO4 will lead to the error of SOC is large. In this paper, an algorithm using the derivation curve (dV/dQ vs Q) to calibrate the SOC on-line is bring out. The SOC estimation has been implemented using coulomb counting and derivation curve methods thereby eliminating the limitation of the stand-alone coulomb counting method. Finally, by utilizing the actual operation data, experiments and numerical table were conducted, show that this SOC calibrate algorithm based on characteristic curve has better robust performance of the practical application of LiFePO4 battery energy storage system.

This paper presents a novel concept of system energy demand reduction by simultaneous optimization of line loss reduction and Conservation Voltage Reduction (CVR). This is accomplished by a new smart inverter control of Battery Energy Storage Systems (BESS) and PV solar system as STATCOMs, both during night and day. Both the BESS and PV systems provide dynamic voltage control utilizing inverter capacities available after real power exchange, for reactive power control. The combination of BESS and PV system enhances the total available reactive power capacity for voltage control more than with BESS alone for achieving the above-stated objective. The effectiveness of the proposed control is demonstrated on a modified IEEE 14 bus system using optimal power studies performed with PSS/E software. With the rapid growth of PV systems and BESS in power systems, the proposed combined smart inverter control of BESS and PV systems can be effectively employed to reduce overall system energy demand.

This paper reviews the procedures, layouts and metrics described in the new test manual issued by the Electric Power Research Institute (EPRI), in order to determine the performance and functionality of a utility scale battery energy storage system (BESS). In this approach, the large battery unit is connected to the dc-link of a bidirectional power conversion system (PCS), which may be interfaced with either the utility grid or a load bank for the purpose of estimating the BESS operation and performance characteristics, some of which includes; available charge/discharge energy at rated power, continuous charge/discharge duration, battery ramp rate, and ac round trip efficiency (RTE). The bidirectional converter is operated with different charge and discharge cycles relevant to each specification and the battery state of charge along with electrical measurements at the ac and dc side are monitored and recorded. Also, an electrical equivalent circuit for a utility scale battery unit was developed based on the 1MW/2MWh operational BESS at the LG &E and KU E.W. Brown facility. This model was formulated using an improved method for estimating the battery cell parameters.