The Experts below are selected from a list of 210 Experts worldwide ranked by ideXlab platform

Josep M Guerrero - One of the best experts on this subject based on the ideXlab platform.

  • a self sustained and flexible control strategy for islanded dc nanogrids without communication links
    IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020
    Co-Authors: Thanh Lich Nguyen, Josep M Guerrero, Gerd Griepentrog
    Abstract:

    This paper proposes a self-sustained and flexible control strategy for autonomous dc nanogrids (NGs) in remote and rural areas without the need for a communication system. The proposed control strategy of NGs is based upon a hierarchical control, in which the primary control manages the power balance inside the NG and the Secondary control is responsible for removing deviation of the dc bus voltage caused by the droop operation. The state of charge of the battery and the external dc bus signal are taken into account in the proposed control strategy in order to avoid the overcharge/deep discharge of the battery as well as the collapse of the external dc bus. Bidirectional power flow among multiple NGs is implemented through a dedicated interconnected bidirectional dual-active-bridge dc/dc converter installed inside the NG to ensure a galvanic isolation among multiple interconnected NGs. Finally, the small-signal model is developed, in which the small-signal transfer function of an entire NG is derived from the small-signal transfer functions of every single converters of the system. From the attained transfer function, the appropriate Secondary Controller is designed, and the system stability is analyzed. The proposed control strategy is validated through simulations and experiments.

  • decentralized optimal frequency control in autonomous microgrids
    IEEE Transactions on Power Systems, 2019
    Co-Authors: Yousef Khayat, Mobin Naderi, Qobad Shafiee, Yazdan Batmani, Mohammad Fathi, Josep M Guerrero, Hassan Bevrani
    Abstract:

    This paper proposes a decentralized optimal Secondary Controller for frequency regulation and accurate active power sharing in autonomous microgrids. This optimal Controller does not require any communication network. Unlike most of the existing works, a systematic approach of Secondary Controller design is introduced based on a quadratic cost function in the form of a linear quadratic regulator (LQR) solution. The design procedure only depends on the cut-off frequency of the power calculation filter. Decentralized behavior, simplicity, optimality based on a quadratic cost function, and straight forward design procedure are the main advantages of this approach. Using the proposed solution, frequency can be restored immediately following any disturbance in the system, without need of any event-driven and time-dependent protocol. Experimental results validate the effectiveness of the proposed Controller.

  • analysis of washout filter based power sharing strategy an equivalent Secondary Controller for islanded microgrid without lbc lines
    IEEE Transactions on Smart Grid, 2018
    Co-Authors: Hong Li, Lin Xu, Xin Zhao, Josep M Guerrero
    Abstract:

    As a supplement of the droop control, the concept of Secondary controlled microgrid (MG) has been extensively studied for voltage and frequency restoration. However, the low band-width communication (LBC) channels are needed to exchange information between the primary and Secondary Controllers, and the performance of the Secondary Controller degrades due to the uncertain communication delay and data drop-out in the LBC lines. Recently, a washout filter-based power sharing method was presented without communication lines and additional control loops. In this paper, the equivalence between Secondary control and washout filter-based power sharing strategy for islanded MG is demonstrated, and the generalized washout filter control scheme has been obtained. Additionally, the physical meaning of control parameters of Secondary Controllers is also presented. Besides, a complete small-signal model of the generalized washout filter-based control method for islanded MG system is built, which can be utilized to design the control parameters and analyze the stability of MG system. Finally, extensive simulation and experimental results are provided to confirm the validity and effectiveness of the derived equivalent control scheme for islanded MG.

  • low voltage ride through operation of power converters in grid interactive microgrids by using negative sequence droop control
    IEEE Transactions on Power Electronics, 2017
    Co-Authors: Xin Zhao, Juan C. Vasquez, Josep M Guerrero, Mehdi Savaghebi, Kai Sun
    Abstract:

    Due to the increasing penetration level of microgrids (MGs), it becomes a critical issue for MGs to help sustaining power system stability. Therefore, ancillary services, such as the low-voltage ride-through (LVRT) capability should be incorporated in MGs in order to guarantee stable operation of the utility grid during grid faults. In this paper, a LVRT control strategy based on positive/negative sequence droop control is proposed for grid-interactive MGs to ride-through voltage sags with not only inductive/resistive, but also complex line impedance. By using the proposed control strategy, MGs can support the grid voltage, make profits, and also ride-through the voltage dip during the whole fault period. A two-layer hierarchical control strategy is proposed in this paper. The primary Controller consists of voltage and current inner loops, a conventional droop control and a virtual impedance loop, while the Secondary Controller is based on a positive/negative sequence droop scheme which is able to coordinate the power injection during voltage sags. Experimental results are obtained to verify the effectiveness of the proposed control strategy.

  • Coordinated Secondary Control for Balanced Discharge Rate of Energy Storage System in Islanded AC Microgrids
    IEEE Transactions on Industry Applications, 2016
    Co-Authors: Yajuan Guan, Juan C. Vasquez, Josep M Guerrero
    Abstract:

    A coordinated Secondary control approach based on an autonomous current-sharing control strategy for balancing the discharge rates of energy storage systems (ESSs) in islanded ac microgrids is proposed in this paper. The coordinated Secondary Controller can regulate the power outputs of distributed generation (DG) units according to their states-of-charge and ESS capacities by adjusting the virtual resistances of the paralleled voltage-controlled inverters. Compared with existing Controllers, the proposed control strategy not only effectively prevents operation failure caused by overcurrent incidents and unintentional outages in DG units, but also aims to provide a fast transient response and an accurate output-current-sharing performance. A complete root locus analysis is given in order to achieve the system stability and parameter sensitivity. Experimental results are presented to show the performance of the whole system and to verify the effectiveness of the proposed Controller.

Juan C. Vasquez - One of the best experts on this subject based on the ideXlab platform.

  • Distributed Average Integral Secondary Control for Modular UPS Systems-Based Microgrids
    IEEE Transactions on Power Electronics, 2019
    Co-Authors: Santi Trujillo, Juan C. Vasquez, Albert Marzàbal
    Abstract:

    This paper presents a distributed average integral Secondary control (DAISC) method for modular uninterruptible power supply (UPS) systems-based microgrids. For each UPS unit, the local primary control level encompasses droop control and virtual impedance loops, which is commonly used in parallel inverter systems. In order to provide a fast voltage recovery performance, along with excellent power sharing capability among the parallel UPS modules, a distributed Secondary control method based on Controller area network (CAN) communication is proposed. In a sharp contrast to the existing distributed Secondary control strategies, in which the output voltage and frequency of the modules are not shared through the CAN bus, in the proposed approach, the inverter modules of the modular UPS share the integral output value of the Secondary Controller. By using the proposed novel DAISC approach, a better dynamic power sharing performance along with an inherent anti-windup capability of the integral Controller is achieved. Simulation results using PLECS and experiments from a modular UPS platform have been developed to verify the feasibility and effectiveness of the proposed distributed Secondary control. The results show that good performance of voltage recovery and power sharing of the proposed control method is obtained.

  • low voltage ride through operation of power converters in grid interactive microgrids by using negative sequence droop control
    IEEE Transactions on Power Electronics, 2017
    Co-Authors: Xin Zhao, Juan C. Vasquez, Josep M Guerrero, Mehdi Savaghebi, Kai Sun
    Abstract:

    Due to the increasing penetration level of microgrids (MGs), it becomes a critical issue for MGs to help sustaining power system stability. Therefore, ancillary services, such as the low-voltage ride-through (LVRT) capability should be incorporated in MGs in order to guarantee stable operation of the utility grid during grid faults. In this paper, a LVRT control strategy based on positive/negative sequence droop control is proposed for grid-interactive MGs to ride-through voltage sags with not only inductive/resistive, but also complex line impedance. By using the proposed control strategy, MGs can support the grid voltage, make profits, and also ride-through the voltage dip during the whole fault period. A two-layer hierarchical control strategy is proposed in this paper. The primary Controller consists of voltage and current inner loops, a conventional droop control and a virtual impedance loop, while the Secondary Controller is based on a positive/negative sequence droop scheme which is able to coordinate the power injection during voltage sags. Experimental results are obtained to verify the effectiveness of the proposed control strategy.

  • Coordinated Secondary Control for Balanced Discharge Rate of Energy Storage System in Islanded AC Microgrids
    IEEE Transactions on Industry Applications, 2016
    Co-Authors: Yajuan Guan, Juan C. Vasquez, Josep M Guerrero
    Abstract:

    A coordinated Secondary control approach based on an autonomous current-sharing control strategy for balancing the discharge rates of energy storage systems (ESSs) in islanded ac microgrids is proposed in this paper. The coordinated Secondary Controller can regulate the power outputs of distributed generation (DG) units according to their states-of-charge and ESS capacities by adjusting the virtual resistances of the paralleled voltage-controlled inverters. Compared with existing Controllers, the proposed control strategy not only effectively prevents operation failure caused by overcurrent incidents and unintentional outages in DG units, but also aims to provide a fast transient response and an accurate output-current-sharing performance. A complete root locus analysis is given in order to achieve the system stability and parameter sensitivity. Experimental results are presented to show the performance of the whole system and to verify the effectiveness of the proposed Controller.

  • autonomous active power control for islanded ac microgrids with photovoltaic generation and energy storage system
    IEEE Transactions on Energy Conversion, 2014
    Co-Authors: Fen Tang, Juan C. Vasquez, Tomislav Dragicevic, Josep M Guerrero
    Abstract:

    In an islanded ac microgrid with distributed energy storage system (ESS), photovoltaic (PV) generation, and loads, a coordinated active power regulation is required to ensure efficient utilization of renewable energy, while keeping the ESS from overcharge and overdischarge conditions. In this study, an autonomous active power control strategy is proposed for ac-islanded microgrids in order to achieve power management in a decentralized manner. The proposed control algorithm is based on frequency bus-signaling of ESS and uses only local measurements for power distribution among microgrid elements. Moreover, this study also presents a hierarchical control structure for ac microgrids that is able to integrate the ESS, PV systems, and loads. Hereby, basic power management function is realized locally in primary level, while strict frequency regulation can be achieved by using additional Secondary Controller. Finally, real-time simulation results under various state of charge (SoC) and irradiance conditions are presented in order to prove the validity of the proposed approach.

  • an improved droop control method for dc microgrids based on low bandwidth communication with dc bus voltage restoration and enhanced current sharing accuracy
    IEEE Transactions on Power Electronics, 2014
    Co-Authors: Josep M Guerrero, Kai Sun, Juan C. Vasquez
    Abstract:

    Droop control is the basic control method for load current sharing in dc microgrid applications. The conventional dc droop control method is realized by linearly reducing the dc output voltage as the output current increases. This method has two limitations. First, with the consideration of line resistance in a droop-controlled dc microgrid, since the output voltage of each converter cannot be exactly the same, the output current sharing accuracy is degraded. Second, the dc-bus voltage deviation increases with the load due to the droop action. In this paper, in order to improve the performance of the dc microgrid operation, a low-bandwidth communication (LBC)-based improved droop control method is proposed. In contrast with the conventional approach, the control system does not require a centralized Secondary Controller. Instead, it uses local Controllers and the LBC network to exchange information between converter units. The droop Controller is employed to achieve independent operation, and the average voltage and current Controllers are used in each converter to simultaneously enhance the current sharing accuracy and restore the dc bus voltage. All of the Controllers are realized locally, and the LBC system is only used for changing the values of the dc voltage and current. Hence, a decentralized control scheme is accomplished. The simulation test based on MATLAB/Simulink and the experimental validation based on a 2 × 2.2 kW prototype were implemented to demonstrate the proposed approach.

Lalit Chandra Saikia - One of the best experts on this subject based on the ideXlab platform.

  • deregulated agc of multi area system incorporating dish stirling solar thermal and geothermal power plants using fractional order cascade Controller
    International Journal of Electrical Power & Energy Systems, 2018
    Co-Authors: Washima Tasnin, Lalit Chandra Saikia, More Raju
    Abstract:

    Abstract The present study highlights the attempt of incorporating geothermal power plant (GTPP), dish-Stirling solar thermal system (DSTS) and high voltage direct current transmission (HVDC) link, with the conventional thermal system, in automatic generation control of an interconnected power system under deregulated environment. Appropriate generation rate constraints are provided in thermal systems. A new fractional order (FO) cascade Controller named as FO proportional-integral-FO proportional-integral-derivative (FOPI-FOPID) is proposed as Secondary Controller and its performance is compared with the commonly used classical Controllers. A stochastic algorithm, Sine Cosine Algorithm (SCA) is used to optimize the Controller gains and other parameters. Analyses of the dynamic responses reveal the superiority of FOPI-FOPID over the others in terms of settling time, peak deviation and magnitude of oscillation. Performance index comparison is carried out and integral squared error is selected. The effect of GTPP, DSTS and HVDC link have been examined separately and the responses disclose that integration of HVDC link to the combined system having both GTPP and DSTS along with thermal leads to better dynamics. Sensitivity analysis of SCA optimized FOPI-FOPID Controller parameters obtained at nominal Disco Participation Matrix (DPM) validate that they are healthy enough and need not be optimized for change in DPMs.

  • combined voltage and frequency control of a multi area multisource system incorporating dish stirling solar thermal and hvdc link
    Iet Renewable Power Generation, 2018
    Co-Authors: Rumi Rajbongshi, Lalit Chandra Saikia
    Abstract:

    This study highlights the significance of dish-Stirling solar thermal system (DSTS) and high voltage direct current (HVDC) link in the combined automatic load frequency control (ALFC) and automatic voltage regulator (AVR) model of the multi-area thermal-diesel plant. Appropriate generation rate constraints and governor dead band for the thermal plant are considered. A maiden attempt has been made to apply fractional order integral double derivative Controller with derivative filter (FOIDDF) as a Secondary Controller for both ALFC and AVR loops. The performance of the FOIDDF Controller is compared with some commonly used classical Controllers. The lightning search algorithm is implemented for simultaneous optimisation of the Controller parameters. The comparison shows the better performance of FOIDDF than others. The effect of the AVR loop on the ALFC loop is also analysed for the first time in the combined model. The investigation of the effect of DSTS and HVDC links reveals that their inclusion improves the system dynamics. The superiority of the proposed Controller has been established for variable insolation of the DSTS. The rigorous sensitivity analysis of the different position and magnitude of disturbance, change in tie-line synchronising coefficient and different condition of the DSTS reflects the robustness of the proposed Controller parameters obtained at the nominal condition.

  • maiden application of hybrid pattern search biogeography based optimisation technique in automatic generation control of a multi area system incorporating interline power flow Controller
    Iet Generation Transmission & Distribution, 2016
    Co-Authors: Asadur Rahman, Lalit Chandra Saikia, Nidul Sinha
    Abstract:

    This study exhibits the automatic generation control (AGC) of an unequal three-area thermal system having single reheat turbine, generation rate constraint, and governor dead band, in all areas. A three-degree-of-freedom proportional-integral-derivative (3DOF-PID) Controller is used as Secondary Controller in all the areas and its dynamic performance is compared with that of classical PI, ID, and PID Controllers. The Controller parameters are simultaneously optimised using biogeography-based optimisation (BBO) technique, where 3DOF-PID Controller outperforms the other. A hybrid pattern search BBO (hPS-BBO) technique is applied for the first time in AGC, to simultaneously optimise 3DOF-PID Controller parameters. Comparison of dynamic responses corresponding to BBO and hPS-BBO optimised 3DOF-PID Controller gives better performance of the latter. This is also validated with random disturbance. The considered system is checked for optimal location of interline power flow Controller (IPFC) using BBO optimised 3DOF-PID Controller. Observations reveal that IPFC placed between Line1 and Line3 is the optimal location. A comparatively better response is observed with hPS-BBO optimised 3DOF-PID Controller parameters, having IPFC placed in its optimal location. Sensitivity analysis of the hPS-BBO optimised 3DOF-PID Controller parameters is tested and found satisfactory for variations in system loading and inertia constant H .

  • automatic generation control of a multi area st thermal power system using grey wolf optimizer algorithm based classical Controllers
    International Journal of Electrical Power & Energy Systems, 2015
    Co-Authors: Yatin Sharma, Lalit Chandra Saikia
    Abstract:

    Abstract This paper present automatic generation control (AGC) of a three area thermal system incorporating solar thermal power plant (STPP) in one of the area. Single reheat turbine and appropriate generation rate constraints is provided in the conventional thermal system. The performances of integral (I), proportional plus integral (PI), and proportional plus integral plus derivative (PID) Controller are evaluated in the system with and without incorporating STPP. A new computational evolutionary technique called grey wolf optimizer algorithm (GWO) is used for the optimization of Secondary Controller gains for first time in AGC. Investigations reveal that GWO optimized PID Controller’s performance is better than others in terms of settling time, peak overshoot and magnitude of oscillations in the system with or without STPP. Sensitivity analysis reveals that that GWO optimized PID Controller gains obtained in nominal conditions and parameters are healthy and not necessary to reset for large change in system conditions and parameters.

  • comparison of performances of several facts devices using cuckoo search algorithm optimized 2dof Controllers in multi area agc
    International Journal of Electrical Power & Energy Systems, 2015
    Co-Authors: Puja Dash, Lalit Chandra Saikia, Nidul Sinha
    Abstract:

    Abstract This paper presents automatic generation control (AGC) of three unequal area thermal systems with single reheat turbine and appropriate generation rate constraints (GRC) in each area. A two degree of freedom (2DOF) Controller called 2DOF-integral plus double derivative (2DOF-IDD) is proposed for the first time in AGC as Secondary Controller. Secondary Controller gains and other parameters are optimized simultaneously using a more recent evolutionary computational technique called Cuckoo Search algorithm (CS). The system dynamic responses for various 2DOF Controllers such as 2DOF-PI, 2DOF-PID, and 2DOF-DD are compared. Investigations reveal that responses with 2DOF-IDD are better than others. Performance of several FACTS devices such as Static synchronous series compensator (SSSC), Thyristor controlled series capacitor (TCSC), Thyristor controlled phase shifter (TCPS), and Interline power flow Controller (IPFC) in presence of 2DOF-IDD Controller are compared and found that the dynamic responses with IPFC are better than others. For the first time in AGC, a case study is performed with placement of IPFC and observed that IPFC present in all three areas of the system performs better. Sensitivity analysis reveals that the CS optimized 2DOF-IDD Controller parameters obtained in presence of IPFC in all three areas at nominal condition of loading and size of step load perturbation (SLP) are robust and need not be reset with wide changes in system loading and SLP. Also, the comparison of convergence curve of various algorithms reveals that CS algorithm converges much faster than others.

Frede Blaabjerg - One of the best experts on this subject based on the ideXlab platform.

  • multitask fuzzy Secondary Controller for ac microgrid operating in stand alone and grid tied mode
    IEEE Transactions on Smart Grid, 2019
    Co-Authors: Rodolpho Vilela Alves Neves, Ricardo Q Machado, Vilma A Oliveira, Xiongfei Wang, Frede Blaabjerg
    Abstract:

    A common method for load sharing is using frequency and voltage droop Controllers because there is no need to have communication links in the microgrid (MG). However, the droop control strategy has a drawback, that is, it imposes voltage and frequency deviations, which can be fixed by adding a Secondary control loop. On the other hand, if the MG operates connected to the grid, a tertiary Controller for regulating the injected power must be added. This paper proposes a multitask fuzzy Secondary Controller (FSC) applied to ac MGs acting only on the Secondary control layer. The proposed Controller allows stand-alone and grid-tied operations, regulating the voltage and frequency in the Secondary and the active and reactive powers, simultaneously, without a tertiary Controller. Stability analysis are presented showing that the FSC keeps the MG stable while operating within a proposed operation range. A MG simulation test bed based on power inverters is presented to validate the FSC operation and to compare to conventional hierarchical Controller. The proposed FSC fixes the deviations in the same way as the conventional Controller during the islanded operation tests and allows the MG to inject power into the grid.

  • synchronverter enabled dc power sharing approach for lvdc microgrids
    IEEE Transactions on Power Electronics, 2017
    Co-Authors: Saeed Peyghami, Hossein Mokhtari, Pooya Davari, Poh Chiang Loh, Frede Blaabjerg
    Abstract:

    In a classical ac microgrid (MG), a common frequency exists for coordinating active power sharing among droop-controlled sources. Like the frequency-droop method, a voltage-based droop approach has been employed to control the converters in low voltage direct current (LVDC) MGs. However, voltage variation due to the droop gains and line resistances causes poor power sharing and voltage regulation in dc MG, which in most cases are solved by a Secondary Controller by using a communication network. To avoid such an infrastructure and its accompanied complications, this paper proposes a new droop scheme to control dc sources by introducing a small ac voltage superimposed onto the output dc voltage of converters. Therefore, dc sources can be coordinated together with the frequency of the ac voltage, without any communication network like synchronous generators (SGs) in conventional power systems. Small signal stability analysis, as well as mathematical calculations, is presented to demonstrate the analogy between the proposed strategy and frequency-based droop approach of the SGs. The effectiveness of the proposed control system is evaluated by simulations and verified by experiments.

  • decentralized load sharing in a low voltage direct current microgrid with an adaptive droop approach based on a superimposed frequency
    IEEE Journal of Emerging and Selected Topics in Power Electronics, 2017
    Co-Authors: Saeed Peyghami, Hossein Mokhtari, Frede Blaabjerg
    Abstract:

    Conventional droop methods for load sharing control in low-voltage direct current microgrids suffer from poor power sharing and voltage regulation, especially in the case when operating many dc sources with long feeders. Hence, the communication-based approaches are employed to improve the load sharing accuracy and voltage regulation. To avoid using such an infrastructure and the corresponding effects on the reliability and stability, an adaptive droop Controller based on a superimposed frequency is proposed in this paper. Load sharing accuracy is improved by adapting the droop gains utilizing an introduced ac power. The Secondary Controller locally estimates and compensates the voltage drop due to the droop Controller. The proposed power sharing approach can properly control the load sharing and voltage regulation without utilizing any extra communication system. The effectiveness of the proposed control system is verified by simulations and experimental tests.

  • On Secondary Control Approaches for Voltage Regulation in DC Microgrids
    IEEE Transactions on Industry Applications, 2017
    Co-Authors: Saeed Peyghami, Hossein Mokhtari, Pooya Davari, Pon Chiang Loh, Frede Blaabjerg
    Abstract:

    Centralized or decentralized Secondary Controller is commonly employed to regulate the voltage drop raised by the primary Controller. However, in the case of high capacity microgrids (MGs) and long feeders with much voltage drop on the line resistances, the conventional methods may not guarantee the voltage regulation on the load busses within a suitable range. Therefore, in addition to compensate the voltage drop of the primary Controller, it is necessary to regulate the voltage of critical loads. In this paper, a new voltage regulation strategy is proposed to regulate the voltage of MG by employing the average voltage of identified critical busses, which are determined by the proposed modal analysis. Numerical steady-state analysis and preliminary simulation results validate effectiveness of the proposed scheme. Furthermore, experimental results are performed to demonstrate the viability of the proposed approach.

  • fuzzy Secondary Controller for autonomous stand alone and grid connected ac microgrid
    Conference of the Industrial Electronics Society, 2016
    Co-Authors: Rodolpho Vilela Alves Neves, Frede Blaabjerg, Ricardo Q Machado, Vilma A Oliveira, Xiongfei Wang
    Abstract:

    The present paper addresses the AC microgrid control issue using the hierarchical control structure and droop Controllers for load sharing. Once the droop Controllers impose an operation with frequency and voltage deviations, depending on the load and droop parameters, a hierarchical control structure must be added to change the droop Controller operating points. The hierarchical Controllers operate with local measurements and shared signals from communication links among the distributed generation systems connected to the microgrid. Depending on the geographical size of the microgrid, the communication links can be economically unviable. This paper thus proposes a fuzzy Secondary Controller for AC microgrids to reduce the link communication dependency by using only local measurements. The simulation results show that the deviations as happened with the conventional Secondary Controllers can be compensated when the microgrid is operating as stand-alone mode, and can provide a certain amount of power to the connected utility bus when operating as grid-connected mode.

Hossein Mokhtari - One of the best experts on this subject based on the ideXlab platform.

  • synchronverter enabled dc power sharing approach for lvdc microgrids
    IEEE Transactions on Power Electronics, 2017
    Co-Authors: Saeed Peyghami, Hossein Mokhtari, Pooya Davari, Poh Chiang Loh, Frede Blaabjerg
    Abstract:

    In a classical ac microgrid (MG), a common frequency exists for coordinating active power sharing among droop-controlled sources. Like the frequency-droop method, a voltage-based droop approach has been employed to control the converters in low voltage direct current (LVDC) MGs. However, voltage variation due to the droop gains and line resistances causes poor power sharing and voltage regulation in dc MG, which in most cases are solved by a Secondary Controller by using a communication network. To avoid such an infrastructure and its accompanied complications, this paper proposes a new droop scheme to control dc sources by introducing a small ac voltage superimposed onto the output dc voltage of converters. Therefore, dc sources can be coordinated together with the frequency of the ac voltage, without any communication network like synchronous generators (SGs) in conventional power systems. Small signal stability analysis, as well as mathematical calculations, is presented to demonstrate the analogy between the proposed strategy and frequency-based droop approach of the SGs. The effectiveness of the proposed control system is evaluated by simulations and verified by experiments.

  • decentralized load sharing in a low voltage direct current microgrid with an adaptive droop approach based on a superimposed frequency
    IEEE Journal of Emerging and Selected Topics in Power Electronics, 2017
    Co-Authors: Saeed Peyghami, Hossein Mokhtari, Frede Blaabjerg
    Abstract:

    Conventional droop methods for load sharing control in low-voltage direct current microgrids suffer from poor power sharing and voltage regulation, especially in the case when operating many dc sources with long feeders. Hence, the communication-based approaches are employed to improve the load sharing accuracy and voltage regulation. To avoid using such an infrastructure and the corresponding effects on the reliability and stability, an adaptive droop Controller based on a superimposed frequency is proposed in this paper. Load sharing accuracy is improved by adapting the droop gains utilizing an introduced ac power. The Secondary Controller locally estimates and compensates the voltage drop due to the droop Controller. The proposed power sharing approach can properly control the load sharing and voltage regulation without utilizing any extra communication system. The effectiveness of the proposed control system is verified by simulations and experimental tests.

  • On Secondary Control Approaches for Voltage Regulation in DC Microgrids
    IEEE Transactions on Industry Applications, 2017
    Co-Authors: Saeed Peyghami, Hossein Mokhtari, Pooya Davari, Pon Chiang Loh, Frede Blaabjerg
    Abstract:

    Centralized or decentralized Secondary Controller is commonly employed to regulate the voltage drop raised by the primary Controller. However, in the case of high capacity microgrids (MGs) and long feeders with much voltage drop on the line resistances, the conventional methods may not guarantee the voltage regulation on the load busses within a suitable range. Therefore, in addition to compensate the voltage drop of the primary Controller, it is necessary to regulate the voltage of critical loads. In this paper, a new voltage regulation strategy is proposed to regulate the voltage of MG by employing the average voltage of identified critical busses, which are determined by the proposed modal analysis. Numerical steady-state analysis and preliminary simulation results validate effectiveness of the proposed scheme. Furthermore, experimental results are performed to demonstrate the viability of the proposed approach.

  • distributed Secondary control in dc microgrids with low bandwidth communication link
    The Power Electronics Drive Systems & Technologies Conference, 2016
    Co-Authors: Poh Chiang Loh, Frede Blaabjerg, Saeed Peyghamiakhuleh, Hossein Mokhtari
    Abstract:

    In this paper, a distributed Secondary power sharing approach with low bandwidth communication network is proposed for low voltage direct current (LVDC) microgrids. Conventional droop control causes voltage drop in the grid and also a mismatch on the current of converters in the case of consideration of the line resistances. Proposed control system carry out the current value of the other converters to reach the accurate current sharing and suitable voltage regulation as well. Voltage and current Controllers locally regulate the voltage and current of converters as a Secondary Controller. Secondary Controller is realized locally and the communication network is only used to transfer the data of dc currents. Therefore, the Secondary Controller can regulate the average voltage by only using the data of currents. The proposed approach is verified with simulations based on PLECS.