Converter For Hybrid Research Articles

Transient Characteristics and Accommodative Current Limiting Strategy for Bidirectional Interlinking Converters in Hybrid AC/DC Microgrids

Transient Characteristics and Accommodative Current Limiting Strategy for Bidirectional Interlinking Converters in Hybrid AC/DC Microgrids

Resilient Distributed Secondary Control for Bidirectional Interlinking Converters in Hybrid AC/DC Microgrids Against FDI Attacks

Resilient Distributed Secondary Control for Bidirectional Interlinking Converters in Hybrid AC/DC Microgrids Against FDI Attacks

A unified decentralized framework for isolated interlinking converters of hybrid DC/AC microgrids

Due to the advantages of effectively integrating diversified loads and renewable sources, hybrid DC/AC microgrids have attracted the common attention of industry and academia. Meanwhile, with the increasing number of power electronic devices connected to the system, the complexity of the system increases, which puts forward higher requirements for galvanic isolation and intelligent control methods. This study proposes a unified decentralized framework for isolated interlinking converters (IICs) in hybrid DC/AC microgrids, which include topology and a control strategy to solve the aforementioned problems. Firstly, in terms of topology, a dual active bridge (DAB) converter is adopted to realize galvanic isolation and DC voltage conversion, which can facilitate the interconnection of DC microgrids or be combined with VSC for the interconnection of DC and AC microgrids. Secondly, in terms of the control strategy, a bidirectional voltage–supporting control strategy is proposed for IICs, in which the frequency and voltage are adopted as the indications to balance the power and strengthen the inertia interaction of microgrids. Furthermore, with the proposed control strategy, the voltage sources of different microgrids can share the power fluctuation, cooperatively. The stability of the proposed strategy is analyzed, and the effectiveness is verified by several HIL experiments.

Voltage control method based on three‐phase four‐wire sensitivity for hybrid AC/DC low‐voltage distribution networks with high‐penetration PVs

The increasing integration of distributed photovoltaics may further aggravate the over-voltage and three-phase unbalance issues of low-voltage distribution networks with three-phase four-wire structures. The voltage control method based on the AC and DC side power flow control and the three-phase power control capability of voltage source converter in hybrid AC/DC low-voltage distribution networks is a solution for the improvement of the above power quality issues. In this paper, an accurately improved sensitivity matrix calculation method considering shunt admittance based on the ABCD parameters is proposed in hybrid AC/DC low-voltage distribution networks with a three-phase four-wire structure. The presented ABCD parameters of the feeders consider the influence of the coupling effect among phases and the neutral line on sensitivity calculation, which makes the sensitivity calculation simple. Then, a power-voltage control method for voltage source converters based on three-phase four-wire sensitivity matrices of the AC side is proposed considering the constraints from the voltage source converter and DC side power flow in hybrid AC/DC low-voltage distribution networks, which can effectively address the over-voltage and unbalanced issues. Simulations are performed to verify the proposed sensitivity calculation method and voltage control method.

The Role of Front-End AC/DC Converters in Hybrid AC/DC Smart Homes: Analysis and Experimental Validation

Electrical power grids are rapidly evolving into smart grids, with smart homes also making an important contribution to this. In fact, the well-known and emerging technologies of renewables, energy storage systems and electric mobility are each time more distributed throughout the power grid and included in smart homes. In such circumstances, since these technologies are natively operating in DC, it is predictable for a revolution in the electrical grid craving a convergence to DC grids. Nevertheless, traditional loads natively operating in AC will continue to be used, highlighting the importance of hybrid AC/DC grids. Considering this new paradigm, this paper has as main innovation points the proposed control algorithms regarding the role of front-end AC/DC converters in hybrid AC/DC smart homes, demonstrating their importance for providing unipolar or bipolar DC grids for interfacing native DC technologies, such as renewables and electric mobility, including concerns regarding the power quality from a smart grid point of view. Furthermore, the paper presents a clear description of the proposed control algorithms, aligned with distinct possibilities of complementary operation of front-end AC/DC converters in the perspective of smart homes framed within smart grids, e.g., enabling the control of smart homes in a coordinated way. The analysis and experimental results confirmed the suitability of the proposed innovative operation modes for hybrid AC/DC smart homes, based on two different AC/DC converters in the experimental validation.

A Novel Distributed Control Method for Interlinking Converters in an Islanded Hybrid AC/DC Microgrid

In this paper, a novel distributed active power control method for interlinking converters (ICs) in an islanded hybrid ac/dc microgrid (IHMG) is proposed. The goal is to implement power sharing among all distributed generators (DGs) in an IHMG and among the ICs in a distributed manner, without the need for additional proportional-integral controllers. A mathematical formula for the active power references of the ICs is derived to achieve these objectives. Then, an estimator providing the data required for the reference calculation is proposed based on the modified dynamic consensus algorithm. In addition, a unified state-space model is derived for the entire IHMG, including the cyber-physical interactions, and a design method is presented for the parameters of the estimator. Finally, the effectiveness of the proposed method is verified by performing small-signal analysis and controller-hardware-in-the-loop verification. Compared to a previous distributed control method, the proposed method significantly improves the robustness in terms of communication delay and variation in the status of DGs while achieving the objectives.

A Modulized Three-Port Interlinking Converter for Hybrid AC/DC/DS Microgrids Featured With a Decentralized Power Management Strategy

A compact interlinking converter modular (ICM) for hybrid ac/dc microgrids with a distributed storage (DS) bus for storage integration is proposed in this article. The advanced ICM for hybrid ac/dc/ds microgrids involves the nine-switch topology with compact configuration and decreased number of active operating switches, which structurally equivalents to afford a dc interconnection port for dc subgrid, an ac interconnection port for ac subgrid, a ds interconnection port for ds subgrid, and two dc–dc converters for the interconnection ports for parallel DSs. In addition to the popular advantage of component elements saving, the suggested ICM, aggregating various interlinking converter cells (ICCs) into an ICM, is also proficient of participating computations from all ICC sensors to enhance the overall modular performance without building extra communication connection links between ICCs. With this in mind, a decentralized power management control strategy is realized by employing a coordination power control methodology to systematically handle various distributed generations (DGs), DSs, and ICM in a decentralized manner with improved communication fault ride-through capability. The controller hardware-in-the-loop experiments on a real-time digital simulator platform validates the achievement of the advanced ICM application in hybrid ac/dc/ds microgrids and the effectiveness of the associated decentralized power management scheme.

A Minimum-Phase Dual Output Hybrid Converter for Standalone Hybrid AC/DC Supply Systems

A minimum-phase dual output hybrid converter for standalone hybrid ac/dc supply systems is proposed in this article. Due to its circuit arrangement, the converter eliminates the right half-plane zero from the control-to-dc output voltage transfer function (i.e., making the system minimum-phase) and gives simultaneous ac and dc outputs using single-stage power conversion. Due to the minimum-phase behavior, the converter is capable of operating at a high load current while maintaining closed-loop stability. Further, it enables simpler controller design and faster dynamic response. As it has two inductors, one at the main input voltage terminals and another at the output dc voltage terminals, it gives continuous input/output currents. Also, it gives step-down/step-up dc output voltages along with the step-down ac output voltage based on the duty ratio. It also has inherent shoot-through protection capability, which results in reliable power conversion on the occurrence of misgating of the switches caused by electromagnetic interference. A hybrid pulsewidth modulation scheme is developed to achieve simultaneous ac and dc outputs. Detailed mathematical modeling is carried out to demonstrate the properties of the converter, and its experimental validation is done through a laboratory prototype. Moreover, at different loading conditions, efficiencies of the converter are measured for varying dc load (having constant ac load) and varying ac load (having constant dc load), to show its effectiveness.

Control of Interlinking Converters in Hybrid AC/DC Grids: Network Stability and Scalability

Hybrid AC/DC networks are an effective solution for future power systems, due to their ability to combine advantages of both AC and DC networks. However, they bring new technological challenges, one key area being the control of such a network. The network, and especially the interlinking converter (ILC), must be controlled to ensure that the DC and AC subsystems coordinate to stabilize the network and allocate power appropriately. This is an area which has attracted considerable recent interest due to the non-triviality of the control design. One promising tool is passivity theory which allows the derivation of decentralized conditions through which the stability of the network can be guaranteed. This paper investigates the application of a passivity framework to AC/DC grids, using a typical lossless line assumption. By ensuring that an appropriately formulated passivity condition is satisfied by the AC and DC buses, and the interlinking converter, the stability of the interconnection can be guaranteed. We also discuss how the ILC controller may be designed to achieve an appropriate power allocation between AC and DC sources. Simulation results demonstrate that the proposed ILC control design regulates the frequency and voltages of the hybrid AC/DC network with a stable operation maintained.

Adjustable inertia implemented by bidirectional power converter in hybrid AC/DC microgrid

Hybrid AC/DC microgrid is regarded as a low inertia system due to the extensive integration of renewable energy sources. Thus, the AC bus frequency and DC bus voltage are easily damaged when a step change or random fluctuation appears, which threatens the system power quality. Focusing on this problem, this study proposes an adjustable inertia implementing method for the two-stage bidirectional power converter (BPC) to enhance the dynamic performance of the hybrid power system. Concretely, the first stage of the BPC is controlled as a virtual synchronous generator to support the AC subgrid and plays the role of imitating the inertia frequency response in the AC bus. The second stage controls the built-in capacitor of the BPC to implement adjustable inertia for the DC subgrid and improves the DC bus voltage response. Besides, the terminal voltage of the built-in capacitor will be restricted to ensure the normal operation of the BPC. The small-signal analysis of the hybrid system is provided to illustrate the stability of the proposed control method. Finally, the experimental results based on the real-time hardware-in-loop platform demonstrate the effectiveness of the proposed method.

Operation and Control of a Hybrid Coupled Interlinking Converter for Hybrid AC/Low Voltage DC Microgrids

The respective advantages of ac and dc microgrids lead to the blooming development of the hybrid ac/dc microgrid, which consists of ac and dc microgrid tied by an interlinking converter. A new structure of hybrid coupled interlinking converter (HCIC), which composed of a converter in series with a static VAR compensator (SVC), is proposed for hybrid ac and low voltage dc (LVdc) microgrids. Moreover, a new droop control method is correspondingly developed for the proposed HCIC. Its fundamental active and reactive power flow in the hybrid ac/dc microgrid is controlled by P-δ and Q-P-V droop control for converter part of the HCIC, and P-Q-α droop control is proposed for SVC part of the HCIC. Furthermore, a fast harmonic control is given based on a decoupled control strategy to improve the filtering characteristics of SVC part of the HCIC, suppress the harmonic power, and/or inject active power. Finally, simulation and experimental results are provided to verify that the proposed HCIC for hybrid ac/LVdc microgrids has the ability of good power flow control and power quality compensation, which not only meets the power flow requirements with low rating system, but also greatly promotes the development of more robust hybrid ac/dc microgrids.

Three-Port Full-Bridge Bidirectional Converter for Hybrid DC/DC/AC Systems

Sustainable solutions such as renewable energies, distributed generation, energy storage, and electric vehicles require power conversion and advance control techniques. This process is usually done in two stages by more than one power converter, specially in hybrid systems, increasing power losses and costs. The configuration with two dc stages and one ac port is widely used in several applications, such as grid-connected photovoltaic inverters; fuel cells, hybrid and electric vehicles; and ac/dc microgrids. Thus, three-port topologies have been developed to operate such systems, most of them comprising multiple power processing stages for the connection of the different elements. This article proposes a three-port full-bridge converter with a single power processing stage for dc/dc/ac systems. The ac port can be single-phase or three-phase, using two legs like an H-bridge or three legs like the conventional three-phase inverter. In both configurations, each leg is used as an inverter and as a buck-boost converter at the same time. The converter is able to manage the power flow among three ports with just four or six switches through a multivariable control strategy. Simulation and experimental results show the capability of the converter to manage the interaction between a battery and a capacitor connected to the grid achieving a fast dynamic response, bidirectional capability in all ports and reduction of components.

Adaptive Interconnection and Damping Assignment Passivity-Based Control of Interlinking Converter in Hybrid AC/DC Grids

In this article, a nonlinear adaptive control strategy is proposed for a power conversion system (PCS) based on the interconnection and damping assignment passivity-based control. The PCS unit includes a dc/dc boost converter cascaded with a dc/ac inverter. The PCS system injects the predetermined values of active/reactive powers from a dc grid to the ac grid while the voltage of the interlinking capacitor is fixed. A disturbance observer is designed and implemented to estimate the output voltage of the dc grid as an unknown quantity. The proposed control strategy is derived based on the extended nonlinear model of the PCS in the synchronous reference frame. This model includes the dynamics of converters, interlinking capacitor, and the output filter of dc/ac inverter. The control commands are calculated through the assignment of desired damping and interconnection matrixes to the closed-loop system using a desired Hamiltonian energy function. The proposed strategy provides soft active/reactive power and voltage/current variations following the changes in the reference commands. The proposed control law is more feasible for experimental digital signal processing modules compared to nonlinear complicated control laws. Finally, the effectiveness of the proposed controller is tested using a set of time-domain simulations using realistic models for PCS components.

Reverse droop control-based smooth transfer strategy for interface converters in hybrid AC/DC distribution networks

Hybrid AC/DC distribution networks are promising candidates for future applications due to rapid advancement in power electronics technology. They use interface converters (IFCs) to link DC and AC distribution networks. However, they possess drawbacks of the AC voltage and frequency offsets when transferring from grid-tied to islanding modes. To tackle this problem, this paper proposes a simple but effective strategy based on reverse droop method. Initially, the power balance equation of the distribution system is derived, it reveals that the cause of voltage and frequency offsets is the mismatch between IFC output power and the rated load power. Then, the reverse droop control is introduced into the IFC controller. By using a voltage-active power / frequency-reactive power (U-P /f-Q) reverse droop loop, the IFC output power enables adaptive tracking of the rated load power. Therefore, the AC voltage offset and frequency offset are suppressed during the transfer process of operational modes. In addition, the universal parameter design method is discussed based on the stability limitations of the control system and the voltage quality requirements of AC critical loads. Finally, simulation and experimental results clearly validate the proposed control strategy and parameter design method.

Implementation of Switched Reluctance Motor Using Pwm Controlled Split Phase Converter In Hybrid

This framework introduces the sun powered encouraged SRM by utilizing fluffy rationale framework. In this framework dc-dc converter, KY help converter is utilized to support the voltage from the PV board. Variable speed drives for PV-sustained electric vehicles demonstrate profoundly encouraging for financial and social development. Being increasingly affordable without winding and changeless magnets on rotor, exchanged hesitance engine (SRM) is raising as an alluring alternative in factor speed drives. Such a framework requests for an appropriate controller with basic and decreased parts. Established two switches for each stage converter is utilized to assess the execution of SRM .Performance attributes, for example, torque swell, speed and current of the SRM FUZZY rationale system is tried at different dimensions are displayed in this venture. Recreations were finished by utilizing Matlab/simulink programming. [19],[20],[21]

A Distributed Power Management Strategy for Multi-Paralleled Bidirectional Interlinking Converters in Hybrid AC/DC Microgrids

For a hybrid ac/dc microgrid (MG), bidirectional interlinking converters (BICs) enable flexible power interactions between ac and dc subgrids. In each subgrid, power sharing among diversified sources has been effectively realized by droop controllers. These power sharing concepts can also be extended to BIC applications. This paper proposes a distributed power management strategy (DPMS) for multi-paralleled BICs in the hybrid MG to avoid the overstress of a single BIC. In this strategy, each BIC is assigned with a well-devised localized distributed controller (LDC) which generates the respective power reference for the BIC. By using the LDC, BICs are allowed to exchange information with one another in the distributed communication graph. The power interactions between ac and dc subgrids can be proportionally allocated to BICs based on their different power ratings in a full distributed manner. Then the system reliability and scalability are significantly improved. Meanwhile, accurate global power sharing among all ac and dc sources in the MG would be accordingly attained. Considering the communication time delay involved in BICs, a small signal model is derived to predict the maximum tolerable delay of the studied system. The validities of the proposed DPMS and delay stability analyses are verified by a controller hardware-in-loop experimental platform.

Performance analysis of three port full bridge converter for hybrid photovoltaic/battery management system

In this paper, performance analysis of three port full bridge converter based hybrid photovoltaic (PV)/battery management system is explained. The overall control system of the three port full bridge converter based PV/battery management system is created and simulated using MATLAB. Maximum power point tracking of solar PV system is controlled by perturb and observe method. Load regulation of PV/ battery management system is controlled by phase shift pulsewidth modulation technique. The system is tested for various real time operating conditions of the power system such as variation of PV panel voltage, change of battery voltage, and change of load power. The experimental verification also is carried out for developed system. Finally, simulation result and experimental result are compared for the developed system.

A Unified Control for the DC–AC Interlinking Converters in Hybrid AC/DC Microgrids

A novel unified control of the dc–ac interlinking converters (ICs) for autonomous operation of hybrid ac/dc microgrids (MGs) has been proposed in this paper. When the slack terminals in the ac and dc MGs are available, the ICs will operate in autonomous control of interlinking power between the ac and dc subgrids, with the total load demand proportionally shared among the existing ac and dc slack terminals. With a flexible control variable added in power control loop, design of the interlinking power control, and droop features of ac and dc MGs can be decoupled. Moreover, this control variable can be tuned flexibly according to different power control objectives, such as proportional power sharing in terms of capacity (which is considered in this paper), interlinking power dispatch, and other optimal power dispatch algorithms, ensuring a well-designed flexibility and compatibility. Furthermore, if the dc MG or the ac MG loses dc voltage control or ac voltage and frequency control capability due to failures of operation of its slack terminals, the ICs can automatically and seamlessly transfer to dc MG support or ac MG support control modes without operation mode detection, communication, control scheme switching, and control saturation. In order to enhance the stability of the proposed unified control in different modes with different control plants, a phase compensation transfer function has been added in the power control loop. After thorough theoretical analysis and discussions, detailed simulation verifications based on PSCAD/EMTDC and experimental results based on a hardware experimental MG platform have been presented.

Modelling and analysis of a synchronous machine‐emulated active intertying converter in hybrid AC/DC microgrids

The integration of renewable energy resources into the electrical distribution systems faces several stability challenges especially in the low inertia conditions. To address these issues, this study introduces a virtual synchronous machine (VSM) control strategy for the intertying power electronic converters in the autonomous AC/DC hybrid microgrids. It is shown that the VSM-based controller improves the system damping following the frequency disturbances and the AC/DC voltage variations. Moreover, a power management regulation topology is implemented in the active intertying converter to achieve an accurate bidirectional power flow under different loading conditions. A small-signal state-space model for the entire hybrid system is developed to assess the overall system performance. Time-domain simulation results under the PSCAD/EMTDC environment are also presented to investigate the effectiveness of the proposed techniques. The introduction of the VSM control for the intertying converters in the hybrid AC/DC microgrids provides a significant improvement in the dynamic performance and increases the robustness against external disturbances.

Improved Control Strategy for Bidirectional Single Phase AC-DC Converter in Hybrid AC/DC Microgrid

This paper presents the improved control strategy with optimal switching scheme to improve the bidirectional converter's power flow control capability and to allow for different modes of operation in hybrid AC/DC microgrid. Also, this improved control strategy eliminates the need of PI controller for independent reactive power control. With the improvements in digital controllers, it is possible to implement complex control circuitry easily. The performance of bidirectional converter with improved control strategy is verified first in simulation environment and then on lab scale experimental set-up with the control circuit is implemented using hardware in loop in the real-time digital simulation platform. The simulation and experimental results for all the cases show that the controller is highly capable for power transfer between AC and DC grid with very fast response and also control reactive power without additional PI controller. Also, it maintains the current total harmonic distortion (THD) within standard limits.