Load Voltage Regulation Research Articles

A New Technique for Simultaneous Load Current Sharing and Voltage Regulation in DC Microgrids

Regulating the output voltage of distributed generation units while maintaining proper power sharing among them is a challenging control issue in dc microgrids. This paper presents a new technique to regulate the voltage levels across the dc microgrid loads and achieve proper load current sharing among the distributed generation units without directly regulating their output voltages. To implement the proposed technique, a hybrid communication scheme comprising a centralized scheme for load current sharing and a decentralized scheme for load voltage regulation is proposed. The dynamic performance of the investigated dc microgrid is examined under different operating conditions through extensive digital computer simulation analyses in MATLAB. The simulation results reveal the effectiveness of the proposed technique under different operating and loading conditions including constant impedance, power, and current loads, communication link failure, and plug-and-play feature of the distributed generation units.

Joint Load Scheduling and Voltage Regulation in the Distribution System With Renewable Generators

By equipping with the advanced smart meters and two-way communications infrastructure, smart grids, as a key component of future smart cities, are able to improve the energy efficiency and reduce the energy cost through real-time monitoring and customer load scheduling. However, the high penetration of intermittent renewable energy such as solar power may cause frequent overvoltage and undervoltage problems at certain buses, making the load scheduling face new challenges on voltage regulation. In this paper, we investigate the impact of voltage constraints on load scheduling by power flow analysis in a power distribution system with renewable generators. A voltage regulator (VR) is introduced to regulate the voltage of buses in the distribution system and assist load scheduling. To jointly minimize the cost and stabilize the voltages of the distribution system, we propose a grid-customer coordinated load scheduling strategy, which simultaneously determines the tap changes of the VR and scheduling of customer electricity loads in each time slot. Finally, we evaluate the performance of the proposed strategy based on realistic power demand and renewable energy generation datasets. Extensive numerical results demonstrate that the proposed strategy can remarkably reduce the energy cost and stabilize the voltage fluctuation of distribution systems.

Simulation evaluation of capacitor bank impact on increasing supply current for alumunium production

DC current supply to power the electrolysis process in producing aluminium at PT Indonesia Asahan Aluminium (Persero) is about 193 kA. At this condition, the load voltage regulator (LVR) transformer generates 0.89 lagging power factor. By adding the capacitor bank to reduce the harmonic distortion, it is expected that the supply current will increase. This paper evaluates capacitor bank installation impact on the system by using ETAP 12.0 simulation. It has been obtained that by installing 90 MVAR capacitor bank in the secondary part of LVR, the power factor is corrected about 8% and DC current increases about 13.5%.

Analysis of efficiency improvement in wireless power transfer system

Recently, efficiency improvement of wireless power transfer (WPT) systems has been the focus of research. Conventional methods of DC-DC converters are employed for load modulation to achieve high efficiency over large variations in mutual inductance and load. However, these additional circuits degrade the performance due to their inherent losses. To address this problem, this study presents a dual-side phase shift control method for load modulation and voltage regulation in a compact WPT system. The key features of the proposed work are: attaining load modulation and voltage regulation with reduced size of the system; elimination of communication between active bridges and simple control logic. Mathematical expression of equivalent resistance versus the phase shift angles (PSAs) is deduced and the optimal PSAs for maximum efficiency are presented. Utilisation of local control, stability analysis and fault detection method are included. MATLAB/Simulink simulation and experimental results are carried out to validate the proposed method.

Radial distribution network reconfiguration for power losses reduction using a modified particle swarm optimisation

Abstract: Recently, losses reduction gained a great deal of attention in distribution system due to low-voltage level and the high-current passing through the lines, pushing the distribution utilities to improve their profit margins on one hand by reducing the unnecessary operational cost, and improving their delivered power quality on the other hand by maintaining the system reliability, and the continuity of supply for varying load demand. Load balancing, voltage regulation, network reconfiguration and others are different techniques used to reduce the losses. This study addresses the distribution network reconfiguration to minimise the network losses. A new modified form of particle swarm optimisation (PSO) is used to identify the optimal configuration of distribution network effectively. The difference between the modified PSO (MPSO) algorithms and the typical one is the filtered random selective search space for initial position, which is proposed to accelerate the algorithm for reaching the optimum solution. The suggested MPSO is tested via 33 and 69 IEEE networks. A benchmark comparison has been conducted to prove the effectiveness of MPSO compared with previous optimisation techniques.

Single‐phase ac–dc–ac topology for grid overvoltage and voltage harmonic mitigation

A single-phase ac–dc–ac topology to improve power quality is proposed in this study. This configuration is obtained from the addition of a floating capacitor H-bridge converter on the grid side of the conventional ac–dc–ac three-leg topology. The role of the structure is not only to ensure regulated load voltage with fixed amplitude and frequency, grid current with low harmonic content and unitary power factor, but also to mitigate fundamental overvoltage and voltage harmonics at the grid. As a consequence, the proposed topology is suitable to operate as unified power quality compensator or uninterrupted power supply. It does not use isolation transformer and is capable of generating multilevel input voltages due to the cascaded H-bridge. The operation with asymmetrical dc-link voltages is considered to increase the number of voltage levels and reduce the harmonic content of the generated input voltages. Two pulse-width modulation techniques and a control system are developed to regulate the dc-link voltages and to decrease the harmonic distortion (HD), lowering the switching stress and also the power losses. The proposed configuration is compared with the conventional one with respect to HD and semiconductor losses. Simulated and experimental results are presented for validation purposes.

Microcontroller based bidirectional buck–boost converter for photo-voltaic power plant

A common configuration for a stand-alone PV power system may consist of three converters: a buck converter for the PV panel to charge the battery, a boost converter for the battery to discharge to the load and one for the load voltage regulation. Such a system requires a coordinated control scheme for three converters which can be complicated. A simple structure for a stand-alone PV plant consists of a PV array, a battery unit, and its associated bidirectional converter which is a combination of a buck and boost converter. When controlled properly the system can provide uninterrupted power to the load, despite the intermittent availability of sunlight. In this paper complete design of the converter is carried out and the simulation has been performed using Psim. From the simulation, the graphs are presented to show the converter working in buck mode and boost mode. Controller is designed to take care of mode transition, buck to boost and boost to buck mode automatically based on source voltage. Hardware implementation has been done using microcontroller (8051).

Performance Analysis of Machine-Learning Approaches for Modeling the Charging/Discharging Profiles of Stationary Battery Systems with Non-Uniform Cell Aging

The number of Stationary Battery Systems (SBS) connected to various power distribution networks across the world has increased drastically. The increase in the integration of renewable energy sources is one of the major contributors to the increase in the number of SBS. SBS are also used in other applications such as peak load management, load-shifting, voltage regulation and power quality improvement. Accurately modeling the charging/discharging characteristics of such SBS at various instances (charging/discharging profile) is vital for many applications. Capacity loss due to the aging of the batteries is an important factor to be considered for estimating the charging/discharging profile of SBS more accurately. Empirical modeling is a common approach used in the literature for estimating capacity loss, which is further used for estimating the charging/discharging profiles of SBS. However, in the case of SBS used for renewable integration and other grid related applications, machine-learning (ML) based models provide extreme flexibility and require minimal resources for implementation. The models can even leverage existing smart meter data to estimate the charging/discharging profile of SBS. In this paper, an analysis on the performance of different ML approaches that can be applied for lithium iron phosphate battery systems and vanadium redox flow battery systems used as SBS is presented for the scenarios where the aging of individual cells is non-uniform.

Optimal coordination of voltage controllable devices in distribution systems using power‐based models and quadratic programming

The incorporation of photovoltaic (PV) inverters makes the management of voltage difficult for power system operators. One solution is to consider these inverter‐based devices as controllable reactive power (VAr) sources and to coordinate them with other voltage regulating devices in the distribution system. This paper proposes some acceptable approximations to quickly formulate and solve a mixed‐integer quadratic programming problem to periodically determine the optimal voltage coordination of a load tap changer, voltage regulators, capacitor banks, and PVs on a smart grid platform. The solution to the optimization problem is aided by an iteration‐based algorithm. By using the MATLAB software to carry out the simulation and computation, the method is well verified by comparing its generated result with a trustworthy solution obtained from examining all possible coordinating combinations of voltage regulating devices and PVs in a modified IEEE 34‐bus system. The effectiveness and features of the method are clearly illustrated on that test system by considering a time‐varying load and PV generation. The obtained results demonstrate the practical application of this work to medium‐voltage systems. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Impact analysis of tap switch out of step for converter transformer

AC transformer load regulation is mainly used to adjust the load side voltage level, improve the quality of power supply, the voltage range is relatively narrow. In DC system, converter transformer is the core equipment of AC and DC power converter and inverter. converter transformer tap adjustment can maintain the normal operation of the converter in small angle range control, the absorption of reactive power, economic operation, valve less stress, valve damping circuit loss, AC / DC harmonic component is also smaller.In this way, the tap switch action is more frequent, and a large range of the tap switch adjustment is required. Converter transformer with a more load voltage regulation switch, the voltage regulation range of the switch is generally 20~30%, the adjustment of each file is 1%~2%. Recently it is often found that the tap switch of Converter Transformers is out of step in Converter station. In this paper, it is analyzed in detail the impact of tap switch out of step for differential protection, overexcitation protection and zero sequence over current protection. Analysis results show that: the tap switch out of step has no effect on the differential protection and the overexcitation protection including the tap switch. But the tap switch out of step has effect on zero sequence overcurrent protection of out of step star-angle converter transformer. The zero sequence overcurrent protection will trip when the tap switch out of step is greater than 3 for out of step star-angle converter transformer.

A Battery Power Bank with Series-Connected Buck–Boost-Type Battery Power Modules

The operation of a battery power bank with series-connected buck–boost-type battery power modules (BPMs) was investigated in this study. Each BPM consisted of a battery pack with an associated buck–boost converter for individually controlling battery currents. With a proposed discharging scenario, load voltage regulation with charge equalization among batteries was performed by controlling the battery currents in accordance with their state-of-charges (SOCs) estimated by real-time battery-loaded voltages detected under the same operating condition. In addition, the fault tolerance was executed to isolate exhausted or faulty batteries from the battery power bank without interrupting the system operation. Experiments were conducted to verify the effectiveness of the discharging scenario for a laboratory battery power bank with four series buck–boost BPMs.

Voltage and frequency control during microgrid islanding in a multi‐area multi‐microgrid system

This study presents a control method to regulate load voltage and system frequency during microgrid islanding in a multi-area multi-microgrid (MMG) system. In the event of islanding of a microgrid from the distribution grid in the proposed MMG system, load voltage of the islanded microgrid and system frequency are affected. To overcome these problems, a control system for the MMG system is proposed. The proposed control system facilitates desired power exchange between grid-connected and islanded microgrids, and achieves effective voltage and frequency regulation in the MMG system. The main significance of the proposed MMG system is that multiple microgrids in different locations can be interconnected to meet larger bulk power demands. This ensures improved reliability and security of power supply in the MMG system. An improved model predictive control (MPC) algorithm is used to regulate various parameters such as output voltage, frequency and power of the inverters in the MMG system. The proposed MMG system is tested during islanding and load shedding using simulation studies. The simulation studies show that the inverters can operate effectively using MPC to provide the desired voltage, frequency and power during islanding and load shedding.

Cascaded High-Voltage-Gain Bidirectional Switched-Capacitor DC–DC Converters for Distributed Energy Resources Applications

A family of bidirectional switched-capacitor (SC) converters with high-gain ratio of any positive integer is proposed in this paper for distributed energy resources applications. As compared with other existing SC converters achieving a same conversion gain, the main advantages of the proposed converters are that they require a relatively lower number of switches and capacitors, have a relatively lower switch's and capacitor's stress, and that their associated driver circuits are simpler to realize. Importantly, with the achievable conversion ratio being flexible and that the input and output of the proposed converters are of common ground, the proposed converters are widely suitable for many applications. Moreover, as the proposed converters do not possess magnetic component or any component that can severely degrade the converters’ performance at high temperature, they are especially useful for high-temperature applications. Besides, the proposed converters are capable of delivering bidirectional power, which is a key requirement for emerging applications with battery storages. Different aspects of the proposed converters, including a simple auxiliary power supply circuit for the MOSFETs’ drivers, will be discussed in this paper. A nine-time SC converter prototype that operates with 20-V input voltage, 100-W output, and at 75 kHz, is constructed and tested. Experiment results show that the maximum efficiency achievable with this prototype is over 98% (without driver's loss) and the efficiency over the entire load range between 25 and 100 W is over 95.5% including the driver's loss. The output voltage ripple of the SC converter is less than 1%. When the SC converter is open-loop controlled, the load voltage regulation is relatively well kept at less than 5% between full load and no load conditions.

Analysis of controllers for the dynamic response enhancement of the three-port full-bridge DC-DC converter interfacing photovoltaic system

Multiport DC-DC converters have been most commonly used in stand-alone renewable power systems to provide smooth and constant power to the loads. To supply the load without any interruption under various disturbances, the centralised controller in various typologies of multiport converter has been implemented only by using conventional proportional integral (PI) controller. This study presents the output voltage control of the three-port full-bridge converter interfacing photovoltaic (PV) system with three different controllers. The dynamic response of the proposed converter is analysed with the PI controller, fuzzy logic controller (FLC), and the sliding mode controller (SMC). The state space model of the three-port full-bridge converter is developed to analyse the performance using SMC. PI, FLC, and SMC-based control scheme is developed using the MATLAB/Simulink environment. The response of the PI, FLC, and SMC are analysed for line regulation, load voltage regulation, and for the converter parameter variation. The simulation results illustrate that the SMC gives a better steady state and dynamic response when compared with the PI and FLC. The results are presented to confirm the proposed control schemes.

Analysis of controllers for the dynamic response enhancement of the three-port full-bridge DC-DC converter interfacing photovoltaic system

Multiport DC-DC converters have been most commonly used in stand-alone renewable power systems to provide smooth and constant power to the loads. To supply the load without any interruption under various disturbances, the centralised controller in various typologies of multiport converter has been implemented only by using conventional proportional integral (PI) controller. This study presents the output voltage control of the three-port full-bridge converter interfacing photovoltaic (PV) system with three different controllers. The dynamic response of the proposed converter is analysed with the PI controller, fuzzy logic controller (FLC), and the sliding mode controller (SMC). The state space model of the three-port full-bridge converter is developed to analyse the performance using SMC. PI, FLC, and SMC-based control scheme is developed using the MATLAB/Simulink environment. The response of the PI, FLC, and SMC are analysed for line regulation, load voltage regulation, and for the converter parameter variation. The simulation results illustrate that the SMC gives a better steady state and dynamic response when compared with the PI and FLC. The results are presented to confirm the proposed control schemes.

Optimization of Synchronous Non-Isolated Bidirectional DC-DC Switching Power Converter

This paper presents a high-efficiency non-isolated synchronous bidirectional DC-DC switching power converter. The circuit is made to operate in Synchronous Discontinuous Conduction Mode (SDCM)/Forced Continuous Conduction Mode (FCCM) of operation for minimum inductor value, to reduce the size, weight and cost of the converter. A snubber capacitor is used across the switch to minimize turn-off loss. The power dissipation through snubber capacitor and inductor is minimized by proper selection of their value, which improves the efficiency of the converter. Complementary gate signals are used to control the ON and OFF of main and auxiliary switch. By use of SDCM of operation, complementary gate signals control scheme and snubber capacitor, turn-on loss and parasitic ringing effect is minimized. State space averaging method is used to obtain control-to-current transfer function module. Using the transfer function module, Proportional Integral Derivative (PID) controller is tuned using PID tuner software, available in MATLAB simulink control design block to regulate load voltage and load current for change in inductor reference current (I*), change in load resistance and change in input voltage. The modules are verified using MATLAB simulink simulator.

A Smart Load Interface and Voltage Regulator for Electrostatic Vibration Energy Harvester

This paper presents a new implementation in ams 0.35μm HV technology of a complete energy management system for an electrostatic vibrational energy harvester (e-VEH). It is based on the Bennet's doubler architecture and includes a load voltage regulator (LVR) and a smart Load Interface (LI) that are self-controlled with internal voltages for maximum power point tracking (MMPT). The CMOS implementation makes use of an energy harvester that is capable of producing up to 1.8μW at harmonic excitation, given its internal voltage is kept within its optimum. An intermediate LI stage and its controller makes use of a high side switch with zero static power level shifter, and a low power hysteresis comparator. A full circuit level simulation with a VHDL-AMS model of the e-VEH presented was successfully achieved, indicating that the proposed load interface controller consumes less than 100nW average power. Moreover, a LVR regulates the buffer and discharge the harvested energy into a generic resistive load maintaining the voltage within a nominal value of 2 Volts.

Implementation of FPGA based DPWM-Digital PI Closed Loop Controller for Voltage Regulation

Objectives: In this paper, a Field Programmable Gate Array (FPGA) based real time implementation of a closed loop controller for regulating the load voltage under line and load disturbances by generating Digital Pulse Width Modulation (DPWM) is developed. Digital Proportional Integral (DPI) controller is designed to generate the DPWM. Methods: DPWM are developed by two methods: Counter based and Delay line based. The closed loop DPWM activated DC-DC buck converter is simulated using MODELSIM and tested in real time using Xilinx Spartan 3A DSP FPGA. Findings: Hardware results show the regulated load voltage by updating the DPWM control signal duty cycle to compensate the line and load disturbances. FPGA based DPWM provides less complexity in design. Improvements: Hybrid based DPWM method with closed loop control for DC-DC Buck converter could be used for voltage regulation.

An Efficient Switched-Capacitor DC-DC Buck Converter for Self-Powered Wearable Electronics

This paper introduces an efficient reconfigurable, multiple voltage gain switched-capacitor dc-dc buck converter as part of a power management unit for wearable electronics. The proposed switched-capacitor converter has an input voltage of 0.6 V to 1.2 V generated from an energy harvesting source. The switched-capacitor converter utilizes pulse frequency modulation to generate multiple regulated output voltage levels, namely 1 V, 0.8 V, and 0.6 V based on two reconfigurable bits over a wide range of load currents from 10 $\mu\text{A}$ to 800 $\mu\text{A}$ . The switched-capacitor converter is designed and fabricated in 65-nm low-power CMOS technology and occupies an area of 0.493 mm2. The design utilizes a stack of MIM and MOS capacitances to optimize the circuit area and efficiency. The measured peak efficiency is 80% at a load current of 800 $\mu\text{A}$ and regulated load voltage of 1 V.

Enhancement of Load Voltage Regulation by Series Reactance Emulation of SSSC

Enhancement of Load Voltage Regulation by Series Reactance Emulation of SSSC