Converter Control Research Articles

Symmetrical Multilevel High Voltage-Gain Boost Converter Control Strategy for Photovoltaic Systems Applications

This paper proposes a Symmetric High Voltage-Gain (SHVG) boost converter control for photovoltaic system applications. The concept is based on a multilevel boost converter configuration, which presents an advantage compared to a classic boost converter such as the ability to transfer a high amount of power with less stress on the power electronics components in the high voltage-gain conditions. This advantage allows the power losses in the converter to be reduced. A mathematical-based voltage model of the PV system using variable series resistance depending on solar irradiance and the temperature is proposed. This model is connected to an SHVG boost converter to supply the load’s power. A control strategy of the DC-bus voltage with maximum power point tracking (MPPT) from the PV system using PI controllers is developed. The contributions of the paper are focused on the SHVG operating analysis with the passive components’ sizing, and the DC-bus voltage control with maximum power point tracking of the PV systems in dynamic operating conditions. The performances of the proposed control are evaluated through simulations, where the results are interesting for high-power photovoltaic applications.

HYBRID ANTI ISLANDING PROTECTION SCHEME FOR DISTRIBUTED GENERATORS BASED ON FUZZY LOGIC CONTROLLER

Distributed generators are blessing for power grid. Distributed generators should operate properly during and after islanding process. Here in this work the main focus is earlier islanding detection and to detect islanding on earlier. Hybrid islanding protection can be preferred for islanding detection. An active oscillatory disturbance is introduced in controller of the converter and fuzzy logic controller is used, so that the introduced signal gets amplified during islanding and it is helpful to detect the islanding. Generally proportional gain controller is used for islanding detection, but its response is slow, hence fuzzy logic controller is used. Fuzzy Logic controller gives earlier trip signal to system than proportional integral controller and small signal stability issues get improved. The system performance is discussed for zero power mismatch conditions. The simulation results of this proposed method is evaluated by using MATLAB Software.

Dynamic ancillary services: From grid codes to transfer function-based converter control

Conventional grid-code specifications for dynamic ancillary services provision such as fast frequency and voltage regulation are typically defined by means of piece-wise linear step-response capability curves in the time domain. However, although the specification of such time-domain curves is straightforward, their practical implementation in a converter-based generation system is not immediate, and no customary methods have been developed yet. In this paper, we thus propose a systematic approach for the practical implementation of piece-wise linear time-domain curves to provide dynamic ancillary services by converter-based generation systems, while ensuring grid-code and device-level requirements to be reliably satisfied. Namely, we translate the piece-wise linear time-domain curves for active and reactive power provision in response to a frequency and voltage step change into a desired rational parametric transfer function in the frequency domain, which defines a dynamic response behavior to be realized by the converter. The obtained transfer function can be easily implemented e.g. via a proportional-integral (PI)-based matching control in the power loop of standard converter control architectures. We demonstrate the performance of our method in numerical grid-code compliance tests, and reveal its superiority over classical droop and virtual inertia schemes which may not satisfy the grid codes due to their structural limitations.

Investigation of grid-forming and grid-following converter multi-machine interactions under different control architectures

The proliferation of converter-interfaced generation necessitates the investigation of novel small-signal multi-machine interactions. The flexibility and lack of standardisation of converter control approaches results in a plethora of potential implementations, bringing different dynamics that can interact with each other and existing elements of the power system. This paper performs a small-signal analysis of power systems with the inclusion of grid-forming and grid-following converters for varying combinations of common control architectures, in terms of cascaded control loops, within the literature. Investigations are performed for a two-machine system and the WSCC 9-bus (three-machine) system. As well as interaction identification and characterisation, the impact of varying transmission line lengths, system loading, and generation dispatch are investigated.

Saturation-informed current-limiting control for grid-forming converters

In this paper, we investigate the transient stability of a state-of-the-art grid-forming complex-droop control (i.e., dispatchable virtual oscillator control, dVOC) under current saturation. We quantify the saturation level of a converter by introducing the concept of degree of saturation (DoS), and we propose a provably stable current-limiting control with saturation-informed feedback, which feeds the degree of saturation back to the inner voltage-control loop and the outer grid-forming loop. As a result, although the output current is saturated, the voltage phase angle can still be generated from an internal virtual voltage-source node that is governed by an equivalent complex-droop control. We prove that the proposed control achieves transient stability during current saturation under grid faults. We also provide parametric stability conditions for multi-converter systems under grid-connected and islanded scenarios. The stability performance of the current-limiting control is validated with various case studies.

Optimal control of microgrid using ALO optimization MPPT with power quality enhancement

AbstractThe paper presents a normalized, varying step size-based least mean square-based control for a standalone microgrid and Ant Lion optimization-based maximum power point tracking. This modified version of the incremental conductance algorithm addresses issues like slow dynamic response, fixed step size issues, and steady state oscillations. Comparative analysis with well-known techniques shows that Ant Lion optimizes the tracking of maximum power points more accurately, with fewer oscillations and increased efficiency. Power management and power quality are maintained through proposed adaptive voltage source converter control. The proposed voltage control shows better performance under various dynamic and steady conditions.

Modelling, design and control of power electronic converters for smart grids and electric vehicle applications

Modelling, design and control of power electronic converters for smart grids and electric vehicle applications

Modeling and control of a new multi-port converter for hybrid energy system integration

This research introduces a new topology called the quasi-Z-source integrated isolated multiport bidirectional resonant DC-DC converter. The aim is to achieve cost-effective and efficient multi-directional power flow between photovoltaic (PV), battery/supercapacitor, and DC loads. The proposed topology ensures uninterrupted power supply to the loads and supports reverse power transfer through its bidirectional power flow capability. By combining quasi z-source and H-bridge resonant converters with an existing switch, a four-port converter is achieved without the need for separate converters or additional switches. The high-gain quasi z-source converter reduces the required voltage ratings of the battery and supercapacitor packs while enabling the utilization of a high-frequency transformer (HFT) with a low turns ratio. Isolation between the ports is achieved using a secondary center-tapped HFT equipped with a controlled full-wave rectifier on the secondary side, allowing bidirectional power flow. A power flow management system and corresponding control scheme are proposed to optimize the system's performance. The proposed system's performance is evaluated under various operating conditions, demonstrating its effectiveness in power flow management and overall efficiency. The results confirm the feasibility and effectiveness of the proposed system.

A non-isolated synchronous buck DC-DC converter, ZVS topology under CCM and DCM conditions

Today, the main challenge of miniaturization and integration of power converters is reducing the volume of parts, eliminating capacitors and inductors.This paper proposes a non-isolated synchronous buck converter (NSBC) under soft switching practice. This converter uses the zero voltage switching (ZVS) topology, which not only provides soft-switching conditions for the converter switches but also prevents the voltage kicking off the two ends of the main switches from being off-state due to self-resonance. To achieve the highest voltage gain in different working cycles, complementary switching approach and use of non-isolated Dc-Dc converter for simultaneous switching of two switches will be used.The non-isolated synchronous buck DC-DC converter with ZVS is to use in some parts of the converter for providing a purpose range of output voltage. In addition, the implementation of the proposed converter control circuit is conducted very simply and needs lower costs. To confirm relations in converter theory, the results of a laboratory sample in the discontinuous and continuous modes are examined. It should be noted that the proposed converter can operate under different levels of voltage, which requires a protection heat policy. The proposed converter implements under the nominal 30-V input and 40 KHz switching frequency, which touches on issues on both sides of discontinuous conduction mode (DCM) and the continuous conduction mode (CCM) conditions and experiment as an example two rates of power 30W and 20W respectively, and also has an acceptable interest rate, which will be evaluated and compared with three different types of similar modes.

Harmonic modelling and control of dual active bridge converter for DC microgrid applications

Due to the intermittent power availability from renewable sources, the bidirectional DC-DC converter (BDC) must integrate with the energy storage system for bidirectional power flow. Among many BDCs, the Dual Active Bridge (DAB) converter is the most promising because of the system's power handling capacity and efficiency. DAB bidirectional DC-DC converter is a topology with the advantages of a decreased number of devices, soft-switching commutations, low cost, and high efficiency. This work describes the guidelines for designing a DAB converter for small DC microgrid applications. It is shown that the judicial selection of reactive elements leads to soft switching for all the switches in the converter in varying load conditions. A guideline for the controller design is given and the operations are validated through the simulation. A harmonic modelling technique has been implemented to model the DAB converter based on an efficient closed-loop regulator. A solar PV system has also been implemented here with a SEPIC converter that is used as an interfacing element between the PV system and the load bus. At last, a DC Microgrid is simulated in a PSIM environment to showcase its various modes of operation. It is shown that the battery bank can support variable loads independently through the DAB converter. In inadequate solar power generation, load power demand is shared between the battery and PV system. In case of deep discharge of the battery, the PV system can charge the battery through a DAB converter.

A Three-Port DC-DC Converter with Partial Power Regulation for a Photovoltaic Generator Integrated with Energy Storage

A novel integrated DC-DC converter is proposed for the first stage of two-stage grid connected photovoltaic (PV) systems with energy storage systems. The proposed three-port converter (TPC) consists of a buck–boost converter, interposed between the battery storage system and the DC-AC inverter, in series with PV modules. The buck–boost converter in the proposed TPC is utilized for maximum power point tracking by regulating two power switches. The output power of the proposed converter is regulated by controlling the DC-AC converter. During the battery-charging mode, partial power regulation is employed with a direct power flow path (the series-connection of the PV panel, the battery and the output). As resistances in this path are almost negligible, the power conversion efficiency is higher than existing topologies. During battery-discharging mode, the power conversion is processed through a buck–boost converter with only two active power switches and one inductor. With fewer components, higher power conversion efficiency is also achieved. The circuit operation and analysis are presented in detail. To illustrate the simplicity of the converter control, the performance of the converter is tested with a straightforward maximum power point tracking on a PV system with battery cells. Simulation and experimental tests are carried out to demonstrate circuit operation and power conversion efficiency.

Advanced Control Solutions for DFIG Wind Turbines: From Vector to Predictive Control

This paper investigates advanced control strategies for a doubly-fed induction generator-based wind turbine (DFIG-WT), focusing on vector control and model predictive control (MPC). Initially, it introduces the DFIG-WT structure and general control methods, then explores vector control for effective decoupled power management of active and reactive power. Despite vector control's efficiency, its limitations in handling constraints are highlighted, leading to the adoption of MPC. The study examines MPC's application in current control for three-phase two-level converters, showing its capability for fast tracking and response. Further, it explores MPC's model predictive torque control, demonstrating its proficiency in handling various requirements through a well-designed cost function. Overall, this research emphasizes MPC's adaptability and efficiency in optimizing DFIG-WT performance under varying operational conditions.

Design of a Switching Strategy for Output Voltage Tracking Control in a DC-DC Buck Power Converter

This work proposes the design of a commutation function to solve the output voltage trajectory tracking problem in the DC-DC Buck power electronic converter. Through a Lyapunov-type analysis, sufficient conditions are established, taking into account the discontinuous model, to ensure asymptotic convergence to the desired trajectories. Based on this analysis, a state-dependent switching function was designed to guarantee the closed-loop stability of the tracking error. To validate the control performance, circuit numerical simulations were carried out under abrupt disturbances in the source and load of the converter. The results demonstrate that the voltage tracking at the output of the converter is satisfactorily achieved.

Optimised linear active disturbance rejection control of multiport-isolated DC-DC converter for hydrogen energy storage system integration

Hydrogen energy storage systems are becoming increasingly accepted owing to their environmental friendliness. The efficiency and performance of these systems largely depend on the attributes of their power electronic interface systems. Among the promising solutions is a multiport-isolated DC-DC converter with characteristics of reduced component count, fewer conversion stages, and galvanic isolation. However, this system presents a challenge due to its inherent cross-coupling effect, complicating precise control. To address this, linear active disturbance rejection control (LADRC) is a viable option, leveraging dynamic/disturbance properties observed by linear extended state observers. LADRC serves as a decoupling controller, mitigating the cross-coupling effect. However, LADRC has several gains, and selecting them can be a difficult task, often requiring manual tuning. To streamline this process, this paper proposes utilising particle swarm optimisation to determine the optimum gains of LADRC. By employing this approach, the implementation of LADRC is facilitated with reduced design efforts while ensuring effective decoupling control within the system. Simulations are conducted to validate the performance of the optimised gain LADRC.

Enhancing electric vehicle performance through buck‐boost converters with renewable energy integration using hybrid approach

AbstractThe electrification of vehicles has emerged as a pivotal technique for addressing environmental concerns and reducing reliance on conventional fuel sources. Conversely, the best way to incorporate renewable energy into electric vehicles (EVs) is still a challenging task, particularly in enhancing the performance of EVs through efficient energy management. The transition to EVs has gained momentum as part of global efforts to mitigate environmental impacts and reduce dependence on fossil fuels. This paper proposes a hybrid method for enhancing EV performance through buck‐boost converters with renewable energy integration. The proposed technique is the joined execution of Flying Foxes Optimization (FFO) and Viscoelastic Constitutive Artificial Neural Networks (vCANNs) techniques. The proposed method's goal is to enhance the energy efficiency, minimize EV charging cost, and mitigating environmental impacts. The renewable energy sources: solar panels, fuel cells, and wind turbines, are integrated into the EV power system through buck‐boost converters. The buck‐boost converter's control signal is optimized through the FFO method. vCANNs are used to predict these control parameters. The proposed strategy is executed in MATLAB software and is compared with existing strategies. In comparison with other current approaches like particle swarm optimization, heap based optimizer, and wild horse optimize, the proposed method achieves a high efficiency of 99% and low cost of 0.05 €/KWh.

Power converters analyzed in energy storage systems to enhance the performance of the smart grid application

This paper implements and compares the existing power supply converters for an energy storage system to determine the best suited for the smart grid application. A survey of different DC-DC converters is carried out to analyze the battery's overall performance. The main objective is to identify this application's most appropriate energy storage device. The advantages of this technology have high efficiency and reliability, which can connect various energy sources and reduce conduction losses in the power converters. Through the converter control, reference currents are imposed to charge the battery. The battery nominal voltage needs to change to see which type of converter is the most suitable and robust. Simulation results show that the operating ranges of boost-buck, buck-boost, and buck-boost converters with negative output voltage enhance the efficiency of battery and renewable energy sources and compared the DC converters to know the functional voltage for the energy storage system. The power converter's efficiency and control facility will allow us to link the energy storage system with the power grid. The overall installation is established using MATLAB/Simulink software.

Comparing fuzzy logic and backstepping control for a buck boost converter in electric vehicles

Significant advances have been made in the control of DC/DC converters, owing to the effective combination of linear and nonlinear approaches. The above-mentioned approaches have greatly improved the efficiency as well as stability of the converter, even when faced with changing conditions. Nevertheless, the emergence of artificial intelligence has introduced new perspectives in the domain. The objective of the article is to examine two separate methodologies for controlling a boost-buck converter: using a nonlinear approach, especially backstepping, and utilizing artificial intelligence through fuzzy logic. The main aim of this work is to illustrate the inherent stability and robustness of fuzzy logic controllers compared to backstepping control in managing effectively various variations and challenges encountered in converter control.

Multipurpose Design of Optimized Current Controller for Bridgeless Totem-Pole Power Factor Correction Converters

Multipurpose Design of Optimized Current Controller for Bridgeless Totem-Pole Power Factor Correction Converters

Modeling and Control of a New Five-Level Converter for Medium-Voltage Drive Systems

Modeling and Control of a New Five-Level Converter for Medium-Voltage Drive Systems

Investigation of bidirectional three-phase four-leg converter with LCL filter

A three-phase four-leg bidirectional power converter used as an input stage of an energy storage system using the inductance (L), capacitance (C), and inductance (L) or LCL filter on the grid side is considered. The article provides a variant of the three-phase four-leg bidirectional converter control system implementation based on 3D space vector pulse-width modulation and per-phase voltage control. A brief analysis of the applied control algorithms of the three-phase four-leg bidirectional converter in inverter and rectifier modes is given. A computer model has been built to investigate the operating modes of the converters of the designated class with both balanced and unbalanced load. Studies were carried out by computer modeling methods in order to optimize the parameters of the LCL filter on the grid side with bidirectional energy exchange. Optimal LCL filter parameters and modulation frequencies are determined for the developed converter, providing acceptable quality indicators when operating in bidirectional mode.