Common DC Link Research Articles

Analyzing Solar PV Integrated UPQC Performance in Micro Grid Systems

The presented work proposes a methodology for the automated transition of a solar PV array and battery integrated unified power quality conditioner (PV-B-UPQC) between standalone and grid-connected modes of operation. The system consists of a shunt and series active filters connected back-to-back with a common DC link, addressing the challenge of integrating power quality improvement with clean energy generation. The automated transition ensures continuous power supply to critical loads, even during grid unavailability. Key innovations include implementing this automated transition in the PV-B-UPQC system with minimal disturbance to local loads. The system's performance is validated through experimental evaluation under various dynamic conditions, such as automated transition, supply voltage variations, grid unavailability, changes in solar power generation, and load variations - scenarios commonly encountered in modern distribution networks. The results are verified using MATLAB/Simulink simulations. Index Terms—Power Quality, shunt compensator, series compensator, UPQC, Solar PV, MPPT.

Artificial Intelligence with Metaheuristic Algorithm Based Optimization for a Hybrid Energy Storage System

This paper presents an optimization framework for a hybrid energy storage system (HESS) integrating photovoltaic (PV) and wind energy conversion systems (WECS). The PV system voltage is stepped up using a Cuk converter, controlled by a Particle Swarm Optimization (PSO) tuned Artificial Neural Network (ANN) controller to enhance dynamic performance and ensure maximum power point tracking (MPPT). The Doubly Fed Induction Generator (DFIG) based WECS is interfaced through a Pulse Width Modulation (PWM) rectifier regulated by a Proportional Integral (PI) controller, maintaining stable and efficient power conversion. Both converter outputs converge at a common DC link, whose voltage is subsequently applied to a single phase Voltage Source Inverter (VSI). This VSI is connected to the grid through an LC filter, ensuring smooth power delivery with minimal harmonics. The proposed system combines AI and metaheuristic algorithms for optimized control, enhancing overall efficiency, reliability and stability of the renewable energy integration into the grid. Simulation results demonstrate the effectiveness of the PSO ANN and PI control strategies in managing the dynamic interactions and power quality of the hybrid system. The proposed hybrid controller shows 92.47% tracking efficiency and the proposed converter shows 89.6% efficiency.

A fuzzy integrated non-linear backstepping control of a grid connected PMSG wind farm

In this paper a grid connected PMSG wind farm is controlled by non-linear backstepping control. The PMSG power is delivered to grid through two back-to-back connected IGBT based VSCs. The VSCs are controlled by individual Sin PWM techniques for which the reference signals are generated non-linear backstepping controller. A capacitor is connected at the common DC link of the back-to-back VSCs for voltage stability. The backstepping controller designed for the control of PMSG has the capability to extract maximum power from the wind farm. The machine side connected VSC operates in synchronization to the rotor angle and the grid side connected VSC operates in synchronization with the grid voltages. The DC voltage regulator of the grid side converter control should be optimum for better stability of the system. Therefore, the conventional PI controller of the voltage regulator is replaced by a 49-rule base FLC which reduces the ripple and settling time of the DC link voltage. A 2MG PMSG wind farm is considered for performance analysis with PI and FLC in the non-linear backstepping control structure. The comparative analysis is carried out in MATLAB software with Simulink block sets utilized to design the wind farm connected to grid. The graphs are compared to determine the performance of the controller with different operating conditions.

PV based Systems with Advanced Control Strategies for Load Balancing in Multilevel Inverter

In an era driven by sustainable energy solutions, the synergy of photovoltaic (PV) system stands as a beacon of hope for meeting the world's growing energy demands while minimizing environmental impact. This research ventures into the domain of renewable energy integration by seamlessly including a PV system, ingeniously controlled by Chaotic Flower Pollination Optimized Adaptive Neuro Fuzzy Inference System (ANFIS) based MPPT (Maximum Power Point Tracking) controller capable of optimizing the efficiency in the face of ever-changing weather dynamics. The PV system's quest for optimal efficiency receives a substantial boost through the implementation of the High Gain Modified Luo Converter. Designed to achieve an optimal PV output voltage, this converter's prowess finds its true calling in grid applications, where precision and efficiency are paramount. Furthermore, this research extends its purview to incorporate a bidirectional converter linked to an energy storage solution, such as a battery, through a common DC link. The output power is then passed to the Flyback Converter, seamlessly connected to a 31 level Cascaded H Bridge Multi-Level Inverter (31-level CHB MLI) controlled by PI controller. This formidable inverter architecture facilitates the efficient delivery of power to the grid, ensuring a smooth and controlled integration of renewable energy resources. This strategic integration bolsters the system's adaptability, enabling the seamless management of energy flows and grid interactions along with load balancing in MLI. The MATLAB simulation platform is used for confirming the system's overall performance. According to the simulation results, the proposed approach achieves the maximum efficiency with the lowest THD value of 94.5% and 2.5%, respectively.

Extension of Negative-Sequence Current Compensation Range Based on Negative- and Zero-Sequence Voltage Injection for Hybrid Cascaded STATCOM

Negative sequence voltage (NSV) injection is an effective cluster balancing control for CHB STATCOM, which has a higher capability in eliminating unbalanced active powers than zero sequence voltage (ZSV) injection. Unfortunately, NSV is employed for negative sequence current control under unbalanced current compensation applications, and only ZSV injection is used for cluster balancing, thereby seriously limiting negative sequence current compensation range (NCCR). To extend NCCR, the converter with a common DC link, called power exchange unit (PEU), is inserted into CHB to form a hybrid cascaded structure, which can freely exchange the unbalanced active powers via the common DC link. However, only ZSV injection method fails to take the advantage of this hybrid cascaded converter (HCC) to extend NCCR. In this paper, the NSV injection with a simple algorithm in dq frame is proposed for the HCC STATCOM with negative sequence current compensation. Owing to the PEU, the NSV of CHB for cluster balancing is counteracted by superposing an opposite NSV into PEU, thus transferring unbalanced active power from CHB to PEU and not affecting the negative sequence current control. Due to the limit of PEU capacity, the ZSV injection is also employed, and thus a novel cluster balancing control based on NSV and ZSV injection is proposed, based on which the NCCR is greatly extended. Finally, the proposed control is verified by the experimental results on a 400V / 7.5kvar HCC STATCOM.

Development of constant switching frequency model predictive control for DFIG-based wind energy conversion system in standalone and grid connected operation

This paper presents a constant switching frequency (CSF) model predictive control (MPC) for a doubly-fed induction generator (DFIG)-based wind energy conversion system (WECS) in standalone and grid-connected operations. The system comprises a cascade connection of a rotor side converter (RSC) and a grid side converter (GSC) with a common DC-link. A battery energy storage system (BESS) is also connected to the common DC-link via a bi-directional dc–dc converter (BDDC). The RSC is controlled through CSF-model predictive current control (CSF-MPCC) scheme in both standalone mode (SAM) and grid-connected mode (GCM) of operations. The GSC control employs the CSF-MPCC scheme in grid-connected operation, whereas CSF-model predictive voltage control (CSF-MPVC) scheme is implemented in standalone operation. Moreover, the power balance is achieved by controlling the BDDC using MPCC to discharge or charge the BESS in response to surplus or deficient power generation. The effectiveness of the proposed control approach for DFIG-based WECS in both SAM and GCM is verified through MATLAB-based simulation and experimental results under different dynamic conditions like variable wind velocity changing from 12 m/s to 8 m/s, different grid demands from 3 kW to 1.5 kW and load change of 4 kW to 6.5 kW. Moreover, the robustness of the proposed control is corroborated by parametric sensitivity, time delay, and grid unbalance, along with its low-voltage ride-through (LVRT) capability during an LLLG fault.

Power quality stabilization system for grid connected large-scale solar power system

This paper presents solution to power quality issues when integrating a 1.5 MW photovoltaic array (PVA) with a unified power quality conditioner (UPQC) into the power grid. A modified unit vector template control scheme is used to generate a reference load voltage signal, and a synchronous reference frame (SRF) is created using a low-pass filter to control UPQC. Furthermore, the PVA is interfaced with the grid through a common DC link of shunt and series converters. The series converter mitigates power quality problems allied with the grid side, such as 3rd, 5th, and 7th harmonics, voltage sag, and voltage swell, by introducing signals in phase and out of phase voltage, respectively, at the point of common coupling (PCC). The shunt converter mitigates nonlinear load current harmonics and compensates for reactive power using SRF. The suggested methodology is implemented using MATLAB Simulink with both linear and nonlinear loads under different power quality conditions. Total harmonic distortions are maintained below 5% at PCC, as per IEEE-519 standards.

The Design and Dynamic Control of a Unified Power Flow Controller with a Novel Algorithm for Obtaining the Least Harmonic Distortion

This study investigates the control and dynamic operation of the Unified Power Flow Controller made of shunt and series converters, a Static Synchronous Compensator, and a Static Synchronous Series Compensator, respectively, connected back-to-back through a common DC-link capacitor. The model of a 48-pulse Voltage Source Converter is constructed from a three-level Neutral Point Clamped converter, which allows the total harmonic distortion to be reduced. An optimal conduction angle tracking system of the three-level inverter is designed to minimize distortion by detecting proper harmonic component elimination. Starting from the six-step modulation strategy, the dq decoupled control schemes of both compensators in open and closed loops are presented. Finally, the MATLAB-Simulink model of the power flow controller is implemented and analyzed. The results show that the controller can track the power changes and apply a suitable voltage to the power system so that the power flow can be controlled. This way, the power flow controller dynamically improves the voltage and power quality across the power network while simultaneously improving the transient stability of the system. It can eliminate all system disturbances resulting from oscillations and harmonics in voltage and current within a very short time. The procedural approach used to model and simulate the Unified Power Flow Controller, as well as the new algorithm used to obtain the harmonic number that minimizes the total harmonic distortion, can be applied to any AC power system.

Simplified control of TAB converter for scalable multibattery charging system

SummaryThe integration of distributed energy resources (DERs) into DC microgrids has become commonplace in many applications, including electric vehicle (EV) systems that use batteries, fuel cells, and supercapacitors as energy storage systems. To make a sustainable charging system for electric vehicles, DERs can be used in conjunction with the grid. In many cases, charging systems based on isolated DC‐DC converters, such as the dual active bridge (DAB) converter, with various controls, are typically used. However, integrating multiple DERs at the common input DC link can result in a loss of isolation in the DAB converter and also leads to problems with circulating current. To maintain isolation, multiple DAB converters can be used, but this increases the system's size. Alternatively, the multiport isolated DC‐DC converter can address such issues but introduces complexities such as cross‐coupling between power flow. This paper proposes a hardware decoupling control methodology for a triple active bridge (TAB) based isolated DC‐DC converter, with power routing features for simultaneously charging two EV's battery stack. Through hardware decoupling control, appropriate passive components are designed and selected to connect with the individual H‐bridges of the TAB for power decoupling. The paper discusses the cross‐coupling issue in the TAB and describes a methodology derived from mathematical expressions for achieving power decoupling. For validation of the control, a 5 kW system is modeled in MATLAB Simulink, and the results demonstrate how the proposed approach overcomes cross‐coupling issues. Further, a 500 W hardware prototype has been developed to validate the proposed approach.

Comparative evaluation by two different hybrid power flow controller topologies of transient stability of machine system connected to wind-PV sources

The Hybrid Power Flow Controller (HPFC) has a simple design configuration, where the upgrading of the line functionality and controller can be performed in stages. This paper applies two HPFC configurations to a multi-machine power network. The first HPFC is a combination of two static synchronous series compensators (SSSC) connected in series, and a Static Var compensator (SVC). The second one consists of two shunt Static synchronous compensators (STATCOM) connected through a Thyristor controlled series compensator (TCSC), across a coupling transformer in a common DC link. The HPFC topologies are tested with a multi-machine power network with faults, in the presence of solar and wind energy sources. The overall model is simulated using SimPowerSystems toolbox and the performance of the two HPFC topologies is compared under various operating conditions. The comparison of simulation results shows that the second HPFC gives a better view than the first in analyzing the power system transient stability.

Design of a Three-Port Integrated Topology to interface electric vehicles and renewable energy sources

This work proposes the design and analysis of an off-board Three-Port Integrated Topology (TPIT). TPIT is used to interface Electrical Vehicles (EVs) and Renewable Energy Sources (RES) from solar electrical phenomenon (PV) panels with the power grid. The TPIT consists of three power converters sharing one common DC link. It can be operated in four completely different modes towards the long run sensible grids. The EV battery area unit is charged with energy from the power grid through the Grid-to-Vehicle (G2V) operation mode. The EV batteries deliver a part of the stored energy back to the power grid through the Vehicle-to-Grid (V2G) operation mode. The energy created by the PV panels is delivered to the electrical grid through the Renewable-to-Grid (R2G) operation mode and the energy created by the PV panels is employed to charge the EV batteries through the Renewable-to-Vehicle (R2V) operation mode. In addition to individual action, the reorganization of those modes leads to hybrid operational modes. This work plan is to propose a power theory to regulate the TPIT and this current control strategy controls the current in AC and DC sides of the TPIT respectively. Also, the features of the developed TPIT prototype, including the hardware and the digital control system are designed. The result portrays the analysis of TPIT operation modes are presented.

Implementation and Control of Multiport Grid Integrated Hybrid Energy Interface for EV Charging Application

EV charging combined with distributed energy storage (ES) devices could be utilized to send power to the grid during peak hours, mitigating the effects of load shedding. In order to achieve these goals, a hybrid multi-port charging system is developed in this study to properly manage power flows and balance energy. It is made up of a PFC bridge rectifier that is linked to an isolated three-port dc-dc converter that includes a series resonant (SRC) and a DAB converter for fast and slow charging applications, respectively. To maximize efficiency and power density, the ports share a 400 V common DC link. Grid-to-vehicle (G2V) mode is used to charge EV and ES vehicles from the utility grid; PV-to-grid (PV2G) mode is used to deliver PV energy to the grid; renewable-to-vehicle (R2V) mode is used to charge EV and ES batteries; and vehicle-to-grid (V2G) mode is used by EV and ES to deliver stored energy to the grid. The charging system’s performance and operation are validated in real time using MATLAB/Simulink under various operating situations. The system’s total harmonic distortion (THD) for the supply current is 2.07%. The suggested system is also compared against a state-of-the-art multiport charging system to assess its performance.

Synchronizing Control of Wind Turbine Driven Doubly Fed Induction Generator System With DG in Remote Area Involving Solar PV-Battery Energy Storage

This paper presents a synchronizing control for wind turbine (WT) driven doubly fed induction generator (DFIG) system with DG (Diesel Generator) in a remote area consisting of solar photovoltaic (PV) array and the battery energy storage. The DFIG is operated with two voltage source converters (VSCs) namely VSC on rotor side (VSCR) and VSC on load side (VSCL) by sharing common DC link with a battery. Moreover, the solar PV array is connected to the DC link through a boost converter, which is used to acquire peak power from the PV array. The microgrid is designed with minimum power converters with enhanced reliability and reduced intermittency especially for islands. Moreover, two controls are presented for successful and smooth operation of microgrid. An additional frequency loop is added in the control of VSCR for minimizing the power fluctuations and for smooth connection of DG to DFIG-solar-battery based isolated microgrid with static transfer switch. Moreover, the VSCR control is framed to build the rated voltage at the DFIG stator with control over ON/OFF operation of VSCR. It is also designed to harness the maximum power from wind. The control of VSCL is framed to regulate the DG power to operate it in optimal fuel consumption zone whenever it is synchronized. Simulations are performed at steady and varying wind speeds, varying PV insolation and at unbalanced connected loads. Moreover, a prototype of isolated microgrid is developed in the laboratory and its experimental performance is investigated at different operating scenarios to evidence its robustness.

Experimental Investigation of Decoupled Discontinuous PWM Strategies in Open-End Winding Induction Motor Supplied by a Common DC-Link

Currently open-end winding induction motors fed by a dual inverter (OEWIM-DI) present an innovative approach to enhance the performance of modern electric drive systems; such as electrical vehicles and electric aircraft applications. However, the dual inverter topology requires a proper switching control strategy to enable the OEWIM drive to fully achieve its performance. This work aims to investigate experimentally the impact of different Decoupled Discontinuous Pulse Width Modulation (DDPWM) control strategies on the performance of the OEWIM-DI supplied by a common DC-link. The criteria performance adopted in this study are: (i) the Total Harmonic Distortion (THD) of the current and voltage, (ii) the Zero Sequence Voltage (ZSV), (iii) the Common Mode Voltage (CMV), and (iv) the dual inverters losses. The various DDPWM control schemes for the 1.5 kW OEWIM-DI motor drive are implemented on a dSPACE 1104 board and the results are compared with the popular and widely used Space-Vector PWM (SVPWM) strategy. From the results, it can be concluded that the optimised DDPWM technique gives the best performance. This technique has reduced the CMV by one level and reduce the losses by 50% while having the same THD and ZSV obtained with the SVPWM technique.

Performance Assessment of a Grid-Connected Two-Stage Bidirectional Converter for a Combined PV–Battery Energy Storage System

This paper presents a comprehensive performance assessment of a two-stage power electronic (PE) converter for interfacing the grid of a lithium-ion battery energy storage system (Li-BESS) for building-integrated PV (BIPV) applications. A performance assessment of the control system was conducted for the two-stage PE interface with a common DC-link, which consisted of a bi-directional boost converter with a cascaded PI controller and an AC/DC converter with proportional-integral (PI) and proportional-resonant (PR) controllers. The assessment covered loss analysis and useful lifetime estimation for the 10 kW PE interface with a wide-bandgap SiC power MOSFET at different loads for both the charging and discharging modes of a 50 kWh lithium-ion battery system. Additionally, a performance comparison of various switching frequencies was performed. It was observed that the system was stable up to a switching frequency of 30 kHz, and that increasing the switching frequency improved the responsiveness of the converter by decreasing the settling time; however, there were diminishing returns at higher switching frequencies. To obtain a proper balance between responsiveness and lower loss, a switching frequency of 10 kHz was selected.

Power Quality Enhancement in Solar PV and Battery Integrated UPQC Grid Connected System

This paper discusses a distributed generation system consisting of grid-connected solar PV and a battery-integrated Unified Power Quality Conditioner (UPQC). Embedded in the PV array, the UPQC consists of a series and shunt converter connected back through a common DC link. In this system, power quality problems of clean energy, such as harmonics, voltage drops, ripples, are compensated by injecting active energy into the power grid. The shunt converter is controlled to maintain a constant DC link voltage and harmonic compensation of the load current. The main voltage problem is compensated by a series converter that injects the voltage during sag and swell. The advantages of integrating renewable energy sources and enhancing power quality are brought together in this system. The performance of the system is analyzed during voltage sag, swell condition and under unbalance condition for nonlinear load along with power flow analysis through the enhancement of dc bus voltage. Finally, the simulation results are shown for the estimation of dynamic performance of PV, battery integrated UPQC system during unbalanced condition

Application of Filter Capacitor Dynamics Based Short-Circuit Fault Detection Method in Ring-Type DC Microgrid

A healthy grid always needs precise and fast isolation because this makes the system reliable and improve the power quality. To achieve this, a short-circuit (SC) fault detection method is presented for low-voltage ring-type DC microgrid (LV-RDCMG). This method uses the current dynamics of filter capacitors to identify the faulty zone. Along with fault identification, a fault isolation process is also explained decently. In the considered ring- type architecture, active sources such as AC grid, battery, and solar photovoltaic, are connected to a common DC link via power converters. The proposed method considers an averaged capacitor current as a detection parameter. Additionally, a criterion for thresholds selection is also given in detail. The presented work is validated through both digital simulation and experimental studies. All the results assure that the proposed concept can detect and isolate the fault cable within 1.98 milli second.

Research on distribution network optimal operation with a novel medium voltage photovoltaic power generation device with the soft open point function

Soft open point (SOP) realizes the normal and flexible interconnection between distribution network feeders, leading to the improvement of the flexibility and rapidity of the distribution network control. However, drawbacks such as high cost and low utilization rate limit its application. A novel medium voltage photovoltaic power generation device with the SOP function is proposed in this paper. There are two grid-connected interfaces, and both of them adopt the cascaded H-bridge topology. A common DC-link is used for both H-bridge inverters belonging to the two grid-connected interfaces respectively. The proposed device eliminates the step-up transformers, and can be connected directly to the medium voltage distribution network. Therefore, advantages such as simple structure, low cost, low power loss and fault-tolerant operation capability are able to be obtained. The stability and flexibility of the distribution network operation are improved. The topology and power flow mode of the proposed medium voltage photovoltaic power generation device with the SOP function are analyzed, and the distribution network multi-objective optimal operation model with the proposed device is established. The proposed medium voltage photovoltaic power generation device with the SOP function is connected to the modified IEEE 33-node distribution network, and the network optimal operation with the device in terms of the power flow optimization and voltage improvement is analyzed.

Optimal Design and Performance Investigation of Artificial Neural Network Controller for Solar- and Battery-Connected Unified Power Quality Conditioner

Nowadays, integration of renewable sources into the local distribution system and the nonlinear behavior of advanced power electronic equipment have made a large impact on the power quality (PQ). The unified power quality conditioner (UPQC) is a multifunctional FACTS device, which is a combination of both shunt active filter and series active filters via a common DC link. Presently, the artificial intelligence is playing a vital role in the development of the intelligent control methods. Traditional training methods of artificial neural network (ANN) like back propagation and Levenberg-Marquardt may get stuck in local optimal solution which leads to the invention of ANN trained optimally by metaheuristic algorithms. This paper develops a firefly algorithm-trained ANN (FF-ANNC) controller for the shunt active filter and proportional integral controller (PI-C) for the series active filter of the UPQC integrated with the solar energy system and battery energy storage via boost converter (B-C) and buck boost converters (B-B-C). The main aim of the proposed FF-ANNC is to reduce the mean square error (MSE) thereby achieving the constant DC link capacitor voltage (DLCV) during load and irradiation variations, reduction of imperfections in current waveforms, improvement in power factor (PF), and mitigation of sag, swell, disturbances, and unbalances in the grid voltage. The working of developed FF-ANNC was tested on five test studies with different types of loads and source voltage balancing/unbalancing conditions. However, to demonstrate supremacy of the suggested FF-ANNC, a comparative study with the training methods like genetic algorithm (GA) and ant colony optimization (AC-O) and also with other methods that exist in literature like PI-C, fuzzy logic controller (FL-C), and artificial neuro fuzzy interface system (ANFI-S) was conducted. The proposed method reduces the total harmonic distortion to 2.39%, 2.32%, 2.27%, 2.45%, and 2.66% which are lower than the existing methods that are available in literature. The FF-ANNC shows an excellent performance in reducing voltage fluctuations and total harmonic distortion (THD) successfully and thereby improving PF.

Active voltage damping method with negative DC link current feedback in electric and hybrid electric transmissions

Electric and hybrid electric transmissions in traction drive have a limited capacity power source. Since the traction drive operates in the torque source mode, the DC link voltage becomes unstable and goes into oscillatory mode. This leads to the software protection reaction which prevents the traction inverter overvoltage breakdown. The transition boundary to the oscillatory mode is determined by the power and the value of the capacitance installed in the electric transmission DC link. To increase reliability of the traction inverters, large-capacity electrolytic capacitors are replaced with small-capacity film capacitors which makes the system more prone to oscillations. To solve this problem, active damping methods are used allowing changing the engine dynamic characteristics by means of the control system. The software methods with power and torque proportional control are most widely used. Proportional power control is the simplest method in which the traction drive simulates an RL load. The torque proportional control method adjusts the torque reference according to the change in the DC link voltage. This paper proposes a new negative DC link feedback method. In this case, the torque is adjusted dynamically depending on the current consumed by the traction inverter from the electric transmission common DC link. Mathematical modeling methods were used to compare the known and proposed methods of DC link voltage active damping. Mathematical models have been developed in the MATLAB Simulink environment which makes it possible to investigate the damping capacity at various values of the power consumed by the traction inverter. It is shown that the proposed method with negative DC link current feedback demonstrated tuning simplicity. In comparison with proportional power and torque control methods, the proposed option is robust when setting parameters, provides a large damping coefficient over the entire range of traction drive power, and has a short duration of the transient process. The proposed method can be used to suppress DC link voltage oscillations on any type of hybrid electric and all-electric vehicles traction inverters and ensures stable and reliable equipment operation.