DC Bus Voltage Regulation Research Articles

Real-time implementation of adaptive nonlinear control of Buck-Boost DC-DC power converter with a continuous input current for fuel cell energy sources

Classical Buck-Boost converter (BBC) topologies are known to drain a pulsating current from the input power source which accelerates the aging rate of the fuel cell (FC). In this paper, a Buck-Boost DC-DC converter topology with continuous input current is used. In addition to its input current, the converter offers the advantage of using a reduced number of electronic components. The point is that the internal voltage of the fuel cell is not accessible for measurement. Therefore, based on a nonlinear model of the FC-BBC system, an adaptive nonlinear controller based on the Backstepping technique is developed to meet the following requirements: (i) tracking the DC-bus voltage to its desired value despite the load uncertainties, (ii) asymptotic stability of the closed-loop system using Lyapunov stability tools. The advantage of the proposed control strategy lies in its simplicity compared to the existing nonlinear approaches. Detailed analysis, simulation, and experimental tests show that the proposed controller meets all control objectives, namely: tight dc-bus voltage regulation and asymptotic stability of the closed-loop system. The effectiveness of the proposed approach is verified by simulation using MATLAB® / Simulink®, and by experimental tests using DS 1202 MicroLabBox.

Linear quadratic regulator controllers for regulation of the dc-bus voltage in a hybrid energy system: Modeling, design and experimental validation

In this paper, linear quadratic regulator (LQR) controllers for effective operation of a hybrid energy system consisting of ultracapacitor energy storage and wind energy system have been designed and implemented. The control objective is to regulate the dc-bus voltage to a target level while extracting the maximum power from the available wind. The dc-bus voltage regulation is achieved by controlling the charging and discharging of the ultracapacitor through a bidirectional converter, and tracking the maximum power points (MPPs) is achieved by controlling a boost converter interfacing the wind turbine with the dc-bus. In addition, a boost converter-based wind turbine emulator to behavior similar to a real wind generator has been developed for testing the proposed controllers. The performance of the proposed energy system incorporating the LQR controllers has been tested under several scenarios (both in simulations and experiments), and the results presented. The simulation tests were conducted in the environment of MATLAB/Simulink, and the experimental tests implemented based on low-cost Digital Signal Processor (DSP) TMS320F2812 eZdsp board. The simulation and experimental results demonstrate their consistency and the capability of the proposed LQR controllers to (1) track the reference voltages and currents, and (2) swiftly recover the nominal operating condition of the system at all conditions including any variation in wind speed or load demand.

State-of-Charge Balancing Control for Modular Battery System With Output DC Bus Regulation

State-of-charge (SOC) balancing of battery cells is very crucial for the battery management system (BMS) to prolong the operational lifetime of the battery system. In this article, an adaptive control algorithm is proposed to balance the SOCs for a series-connected battery system. The control strategy achieves power balancing using the current-SOC droop concept while maintaining a stable dc bus voltage regulation at the battery pack. The proposed control algorithm achieves the control objectives without any communication necessity among the batteries. Moreover, the control design and the stability analysis are shown in detail using small-signal modeling. Furthermore, the simulation and experimental validation are provided to verify the effectiveness of the proposed control algorithm. In addition, the conventional centralized control method is compared with the proposed distributed control concept. The proposed approach shows higher reliability, flexibility, and scalability compared to the conventional centralized cell balancing structures.

Performance of Neutral Point Clamped Five Level Inverter Using Space Vector Modulation Control Fed by DPC-VF-SVM Rectifier

The purpose of this paper is to develop a control and regulation method for the input DC voltage of a five level neutral point clamping (NPC) inverter feeding a induction motor. In this context, the authors propose in the first part, the control strategy of three-phase pulse width modulation rectifier, they propose the virtual flux-based direct control (DPC_VF) with vector modulation (SVM), this method is applied for the enhancement of network power quality by compensation of harmonic currents produced by an non linear load, and good regulation of DC-bus voltage. The second part of the paper is dedicated to the presentation of the model of the three phase, five-level NPC voltage source inverter with its space vector modulation (SVM) control method. The performance of the proposed strategy in terms of out-put voltage and THD has studied successfully and shown using MATLAB/Simulink.

An adaptive power split strategy with a load disturbance compensator for fuel cell/supercapacitor powertrains

Electric vehicles powered by fuel cell and supercapacitor hybrid power sources are of great interest. However, the power allocation between each power source is challenging and the DC bus voltage fluctuation is relatively significant in cascaded PI control schemes. This paper develops a power control strategy with an adjustable cut-off frequency, using an artificial potential field, to adaptively split the load current between the fuel cell and the supercapacitor under various load conditions. The adaptive cut-off frequency is calculated by cutting the load frequency spectrum with an allocation ratio that changes with the supercapacitor state of charge. Therefore, the relatively lower frequency portion of the load current is provided by the fuel cell and the supercapacitor handles the higher frequency portion. To enhance the control performance of the DC bus voltage regulation against the load disturbance, a load disturbance compensator is introduced to suppress the DC bus voltage fluctuation when the load variation occurs, which is implemented by a feed-forward controller that can compensate the load current variation in advance. The effectiveness of the proposed strategy is validated by extensive experiments.

Single input qZ‐source cascaded multilevel inverters : Analysis , design, and implementation

The Single Input quasi-Z-Source Cascade Multilevel Inverter (SIqZS-CMI) has the ability to make use of a single DC input source and to share active power among all cascaded qZS modules. This unique feature, do not present in any other quasi-Z-Source (qZS) multilevel inverter in the literature, is accomplished by replacing one of its Z-impedance inductances by a coupled inductor. With this topology, it is possible to make use of a single low voltage PV string, favoring the use of small size residential rooftop systems. In addition, it simplifies the system grounding and the compliance with many Installation, Maintenance, and Safety Codes and Standards. The proposed control strategy enables high quality current injection into the grid, keeping the DC bus voltage regulation, ensuring precise power balancing with symmetric multilevel waveforms. Experimental results from a 5-level SIqZS-CMI prototype demonstrate the system's performance and its advantages.

The Coordination Control of SMES and PV in LVDC Distribution System

This paper presents a coordination scheme of superconducting magnetic energy storage (SMES) and photovoltaic (PV) generation system for regulating the DC bus voltage in the low voltage direct current (LVDC) distribution systems. Firstly, the effect of AC grid faults on LVDC distribution system is analyzed. Then, the PV is designed to operate as the backup power of SMES by adjusting the control mode automatically according to the residual energy of SMES. The proposed scheme can regulate DC bus voltage in milliseconds and maintain the bus voltage during the whole fault process by taking use of both SMES and PV. A LVDC distribution system is modelled in PSCAD/EMTDC. Simulation results have demonstrated the feasibility and effectiveness of the proposed scheme.

Fuzzy-barrier sliding mode control of electric-hydrogen hybrid energy storage system in DC microgrid: Modelling, management and experimental investigation

In this study, a novel model and nonlinear barrier function-based first order sliding mode control (NBF-FOSMC) of a hybrid hydrogen-electric energy storage system in DC microgrid has been presented. The photo-voltaic array works at its maximum power point while the fuel cell consumes hydrogen produced by the electrolyzer along with the battery and superconducting magnetic energy storage to provide fast and uninterruptible power. Fuzzy logic based power management system has been adopted for the optimal load-generation balance. Moreover, the work has been divided into two levels in which the power references generated from master level control are fed to the slave level control. NBF-FOSMC has been implemented as an underlying controller which shows insensitivity to the disturbances bounded with an unknown upper bound and prevents the system from overestimation of the gains. Global asymptotic stability of the controller has been verified using Lyapunov stability analysis. The proposed controllers have been simulated using MATLAB/Simulink® (2019a) which illustrates the tracking of desired powers and DC bus voltage regulation with minimal tracking errors. Lastly, a comparison between NBF-FOSMC and Lyapunov redesign control has been presented along with controller hardware-in-the loop experiments to validate the real-time implementation of the designed framework.

A novel communication-less fuzzy based control method to improve SOC balancing, current-sharing, and voltage restoration in a widespread DC microgrid

DC Bus Voltage Restoration, proportional current-sharing and SOCs balancing are the leading vital challenges in the field of DC microgrids. It seems that, using communication links and a central controller will solve these problems. However, microgrids under such control system will encounter some drawbacks such as low modularity, flexibility, reliability, and high cost and complexity. Besides, using communication links and the central controller is not reasonable for widespread DC microgrids. In this paper, a novel communication-less control method is proposed. First, the voltage of units is controlled by the droop controller to ensure the system stability. Next, a unit which has the least distance from critical loads, is chosen as “sender unit”. The sender unit voltage is set such that the voltage deviation of the sender bus is reduced to zero. Then, this unit injects an AC signal to the DC bus. The frequency of AC signal is determined by a fuzzy controller based on the sender unit SOC and its current. Another fuzzy controller specifies the units’ current based on the frequency of AC signal and their SOC. The units’ current determination is done such that not only the SOCs are balanced, and the voltage deviation is reduced, but also the current is appropriately shared. As the proposed method does not rely on communication links, it is applicable on both the single-bus and multi-bus microgrids (compact and geographically dispersed). The stability analysis confirms that the proposed method is strongly stable. Simulation results prove that microgrids controlled by the proposed method has a desirable performance from the standpoint of current-sharing, SOCs equalizing, and DC bus voltage regulation.

Barrier Function Based Adaptive Sliding Mode Controller for a Hybrid AC/DC Microgrid Involving Multiple Renewables

Conventional electricity generation methods are under the major revolution, and microgrids established on renewable energy sources are playing a vital role in this power generation transformation. This study proposes a hybrid AC/DC microgrid with a barrier function-based adaptive sliding mode controller, in which 8 kW wind energy system and 4.5 kW photovoltaic energy system perform as the hybrid RESs, and 33 Ah of battery works as the energy storage system. Barrier function-based adaptive sliding mode controller ensures the convergence of the system’s output variable independent of the knowledge of the upper bound of the disturbances. Firstly, global mathematical modeling of the suggested system is ensured. Then, the control laws are defined, providing the DC bus voltage regulation during islanding mode and AC/DC link bus voltage regulation during the grid-connected mode. The proposed barrier function-based adaptive sliding mode controller technique is analyzed through 20 s simulations on MATLAB/Simulink, which validates the controller’s robustness and effectiveness. Furthermore, a comparison of the proposed controller is made with the proportional integral derivative controller, Lyapunov controller, and sliding mode controller. In the end, hardware-in-loop tests are performed using C2000 Delfino MCU F28379D LaunchPad, showing the proposed structure’s real-time performance.

A novel power management algorithm for a residential grid-connected PV system with battery-supercapacitor storage for increased self-consumption and self-sufficiency

The increasing penetration of renewable energy technologies causes major problems in the power network, as their generation cannot be totally predicted. Along with fluctuations in the generation of renewables due to weather uncertainties, storage is very important for mitigating several problems that may arise, affecting the stability and reliability of the grid. In particular, in recent years there has been an emphasis on residential storage applications (behind-the-meter storage), with the aim of increasing the energy self-consumption and therefore reducing electricity bills. The proposed model consists of a 3 kWp rooftop solar photovoltaic (PV) system connected to the grid through converters and a battery-supercapacitor hybrid energy storage system. The model is developed and simulated in the MATLAB/Simulink software environment, based on mathematical analysis and average modeling. The supercapacitor handles rapid changes that occur within 0.2 s, and this can relieve the battery stress and extend the battery lifetime. The building’s electricity demand is satisfied through the PV, hybrid energy storage and/or grid. A new filtration-based power management algorithm (PMA) is proposed here, prioritizing the utilization of the PV and battery-supercapacitor instead of the grid, thus achieving a reduced power exchange between the building and the grid and increasing the PV self-consumption and self-sufficiency of the building. The dynamic performance of the proposed model is verified through several simulations over short time periods (10–30 s) for different scenarios that could occur. The obtained results show that the model works properly and responds extremely fast during the different mode transitions, exhibiting a very fast DC-bus voltage regulation with a very small ripple voltage of up to 5 V (a maximum of ± 0.625%). Additionally, both battery and supercapacitor remain between their minimum and maximum limits. Finally, an effective power sharing is achieved between the PV, the battery-supercapacitor storage, the building load and the grid.

A Bidirectional Versatile Buck-Boost Converter Driver for Electric Vehicle Applications.

This work presents a novel dc-dc bidirectional buck–boost converter between a battery pack and the inverter to regulate the dc-bus in an electric vehicle (EV) powertrain. The converter is based on the versatile buck–boost converter, which has shown an excellent performance in different fuel cell systems operating in low-voltage and hard-switching applications. Therefore, extending this converter to higher voltage applications such as the EV is a challenging task reported in this work. A high-efficiency step-up/step-down versatile converter can improve the EV powertrain efficiency for an extended range of electric motor (EM) speeds, comprising urban and highway driving cycles while allowing the operation under motoring and regeneration (regenerative brake) conditions. DC-bus voltage regulation is implemented using a digital two-loop control strategy. The inner feedback loop is based on the discrete-time sliding-mode current control (DSMCC) strategy, and for the outer feedback loop, a proportional-integral (PI) control is employed. Both digital control loops and the necessary transition mode strategy are implemented using a digital signal controller TMS320F28377S. The theoretical analysis has been validated on a 400 V kW prototype and tested through simulation and an EV powertrain system testing.

Modeling a residential grid-connected PV system with battery–supercapacitor storage: Control design and stability analysis

The increased penetration of renewables and the variable behavior of solar irradiation makes the energy storage important for overcoming several stability issues that arise in the power network. The current paper examines the design and stability analysis of a grid-connected residential photovoltaic (PV) system with battery–supercapacitor hybrid energy storage. The battery and supercapacitor packs are connected to the common 400 V DC-bus in a fully active parallel configuration through two bidirectional DC–DC converters, hence they have different voltage levels and their power flow is controlled separately. A detailed small-signal stability analysis is considered for the design of the current controllers for the bidirectional converters of the battery and supercapacitor. An important contribution here is that a detailed stability analysis is performed for both the boost and the buck mode of operation for the battery and supercapacitor converters, resulting in more accurate tuning of the controllers. Moreover, the small-signal stability analysis of the voltage source inverter (VSI) is considered in order to design the DC-bus voltage controller, where a reference output current is obtained using a phase-locked loop (PLL) for grid synchronization. The proposed model is developed and simulated in the MATLAB/Simulink software environment, based on mathematical analysis and average modeling. The simulation results verify the dynamic performance of the proposed model, through several rapid changes in PV generation and in load demand. Also, the model works properly and responds extremely fast during different mode transitions, exhibiting a very fast DC-bus voltage regulation with a very small ripple voltage (a maximum of ± 0.625%). Finally, the supercapacitor handles the rapid changes occurring within 0.2 s, hence this can relieve the battery stress and extend the battery lifetime.

Nonlinear control strategy of single-phase unified power flow controller

In this work we propose a nonlinear control strategy of single-phase unified power flow controller (UPFC), using in order to enhance energy quality parameters of a perturbed single-phase power grid supplying nonlinear loads. The control objectives are: i) The current harmonics and the reactive power compensation, that ensure a satisfactory power factor correction (PFC) at the point of common coupling (PCC); ii) compensation of the voltage perturbations (harmonics and sags of voltage) in order to ensure the desired level, of load voltage, without distortion; iii) DC bus voltage regulation. The considered control problem entails several difficulties including the high system dimension and the strong system nonlinearity. The problem is dealt with by designing a nonlinear controller with structure including three control loops. The inner-loop regulator is designed using the Lyapunov technique to compensate the current harmonics and reactive power. The intermediary-loop regulator is designed using the Backstepping technique to compensate the voltage perturbations. The outer-loop regulator is designed using a linear PI to regulate the DC bus voltage. The control stability is proved theoretically and through simulations, these latter show the effectiveness and strong robustness of the proposed control, and prove that the above-mentioned objectives are achieved.

Design and stability analysis of a control system for a grid-independent direct current microgrid with hybrid energy storage system

This paper proposes the design and stability analysis of a control system for a hybrid energy storage system (HESS). The control method is framed to address the demand-generation disparity and DC bus voltage regulation. In the proposed control method, battery is utilized to address slow-frequency power surges. Meanwhile, supercapacitor (SC) has been used to manage fast-frequency power surges. Furthermore, the proposed control method enhances the battery life cycle by diverting uncompensated battery currents to SCs for quick compensations. The advantages of the proposed control method over the conventional control method show its robustness for DC bus voltage in terms of settling time and voltage overshoot/undershoot. Additionally, total harmonic distortion (THD) of 3-phase voltage is presented. The test scenarios have been verified in a MATLAB/SIMULINK environment. The experimental results authenticate the viability and feasibility of the proposed control method.

COMPARATIVE STUDY OF SINGLE-PHASE PWM RECTIFIER CONTROL TECHNIQUES

In this study, 2.5 kW single-phase pulse-width modulated rectifier is simulated with three different control techniques to investigate the performance of controllers. Rectifier simulation is performed in Matlab / Simulink environment by using hysteresis current control, sinusoidal pulse width modulation and voltage oriented control techniques. In the performance comparison of the control techniques, considering the switching frequencies, the total harmonic content of the current drawn from the grid, the phase difference between the grid voltage and the grid current, and the DC bus voltage regulation at the output are considered as comparison criteria. The switching frequency is set to 35 kHz in sinusoidal pulse width modulation and voltage oriented control techniques. Since the switching frequency is variable in the hysteresis current control technique, the average and instantaneous switching frequency are calculated for different hysteresis band values. In the results with the technique, the switching frequency varies between 18.52 kHz and 47.6 kHz, while the average switching frequency is 34.6 kHz. As a result, the total harmonic distortion of the grid current with hysteresis current control, sinusoidal pulse width modulation and voltage oriented control techniques is 3.69%, 1.12% and 1.82%, respectively. The synchronization with the grid voltage is achieved with all techniques, and the DC voltage is regulated with active power.

Control and Validation of a Reinforced Power Conversion System for Upcoming Bioelectrochemical Power to Gas Stations

This paper presents a proposal for potential bioelectrochemical power to gas stations. It consists of a two-level voltage source converter interfacing the electrical grid on the AC side and an electromethanogenesis based bioelectrochemical system (EMG-BES) working as a stacked module on the DC side. The proposed system converts CO2 and electrical energy into methane, using wastewater as the additional chemical energy input. This energy storage system can contribute to dampening the variability of renewables in the electrical network, provide even flexibility and grid services by controlling the active and reactive power exchanged and is an interesting alternative technology in the market of energy storage for big energy applications. The big challenge for controlling this system lays in the fact that the DC bus voltage of the converter has to be changed in order to regulate the exchanged active power with the grid. This paper presents a cascade approach to control such a system by means of combining external control loops with fast inner loops. The outer power loop, with a proportional-integral (PI) controller with special limitation values and anti-windup capability, is used to generate DC bus voltage reference. An intermediate loop is used for DC bus voltage regulation and current reference generation. A new proportional resonant controller is used to track the current reference. The proposed scheme has been validated through real-time simulation in OPAL OP4510.

Industrial Robots Fuel Cell Based Hybrid Power-Trains: A Comparison between Different Configurations

Electric vehicles are becoming more and more popular. One of the most promising possible solutions is one where a hybrid powertrain made up of a FC (Fuel Cell) and a battery is used. This type of vehicle offers great autonomy and high recharging speed, which makes them ideal for many industrial applications. In this work, three ways to build a hybrid power-train are presented and compared. To illustrate this, the case of an industrial robot designed to move loads within a fully automated factory is used. The analysis and comparison are carried out through different objective criteria that indicate the power-train performance in different battery charge levels. The hybrid configurations are tested using real power profiles of the industrial robot. Finally, simulation results show the performance of each hybrid configuration in terms of hydrogen consumption, battery and FC degradation, and dc bus voltage and current regulation.

DC Bus Voltage Regulation Strategy in Maritime DC Power System for Minimized Converter Loss

In a maritime dc power system, the rectified dc-bus voltage of a permanent magnet synchronous generator is generally regulated by the pulsewidth modulation (PWM) operation of an active ac/dc converter. This article proposes a dc bus voltage regulation strategy exploiting the six-step operation. Under the six-step operation, the switching loss of the converter can be significantly reduced, compared to the PWM operation. Moreover, due to the higher modulation index and the less flux-weakening current of the six-step operation, the conduction loss can also be reduced. By employing diode rectification mode at light load, the conduction loss induced by the non-negligible ripple current of the six-step operation could be minimized. This article implements a controller for the proposed dc bus voltage regulation strategy and verifies its validity with simulation and experimental setup. According to the simulation and the experimental test, the converter efficiency at the rated load is enhanced by 0.6% and 0.4%, and the converter loss is reduced by up to 70% and 19%, respectively.

Hybrid energy storage system control analogous to power quality enhancement operation of interlinking converters

Increasing nonlinear loads and power electronic converters lead to various power quality issues in microgrids (MGs). The interlinking converters (ILCs) can participate in these systems to harmonic control and power quality enhancement. However, ILC participation deteriorates the dc link voltage, system stability, and storage lifetime due to oscillatory current phenomena. To address these problems, a new control strategy for a hybrid energy storage system (HESS) is proposed to eliminate the adverse effects of the harmonic control operation of ILC. Specifically, battery and super-capacitor (SC) are used as HESSs that provide low and high power frequency load, respectively. The proposed strategy tries to compensate the current oscillation imposed by ILC with fuzzy control of HESS. In this method, a proportional-resonant (PR) controller integrated with harmonic compensator (HC) is employed to control the ILC for power quality enhancement and oscillatory current elimination. The main advantages of the proposed strategy are to reduce DGs power fluctuations, precise DC bus voltage regulation for generation and load disturbances, improved grid power quality under nonlinear load and transition conditions. The performance of the proposed method for isolated and grid-connected modes is verified using simulation studies in the MATLAB software environment.