This page has only limited features, please log in for full access.
Integrating electric vehicles (EVs) into a microgrid improves the efficiency, flexibility, and robustness of microgrids. Unfortunately, the uncertainties of EVs, in terms of their connection/disconnection times and their initial SOC values, make integrating EVs into microgrids a more challenging issue. Contrary to the standard energy management system (EMS), integrating EVs into microgrids raises several multi-objective problems that need to be solved. In this study, a centralized power flow control scheme for an EV-connected DC microgrid (DCMG) is proposed to satisfy these multi-objective problems under several constraints. Two prime objective functions of the DCMG are presented to demonstrate the benefits to both the DCMG system and EV owners. Then, a reliable and optimized DCMG system is constructed to satisfy the selected prime objective function. The operating modes of each agent in the DCMG are defined based on information regarding the EV connection/disconnection status, the initial EV SOC values, the generation power of the wind power agent, the battery SOC levels, and the grid availability. The effectiveness and robustness of the proposed scheme have been validated by in-depth simulations and experimental tests under the uncertainties of DG power, grid availability, electricity price conditions, and EV connections. In addition, the proposed scheme reliably regulates the DC-link voltage without severe transience, even if these uncertainties cause the task of controlling the DC-link voltage to be transferred from one agent to another.
Faris Padhilah; Kyeong-Hwa Kim. A Centralized Power Flow Control Scheme of EV-Connected DC Microgrid to Satisfy Multi-Objective Problems under Several Constraints. Sustainability 2021, 13, 8863 .
AMA StyleFaris Padhilah, Kyeong-Hwa Kim. A Centralized Power Flow Control Scheme of EV-Connected DC Microgrid to Satisfy Multi-Objective Problems under Several Constraints. Sustainability. 2021; 13 (16):8863.
Chicago/Turabian StyleFaris Padhilah; Kyeong-Hwa Kim. 2021. "A Centralized Power Flow Control Scheme of EV-Connected DC Microgrid to Satisfy Multi-Objective Problems under Several Constraints." Sustainability 13, no. 16: 8863.
A robust optimized active disturbance rejection control (ADRC)-based grid voltage sensorless current controller is developed for an LCL-filtered grid-connected inverter (GCI) via a predictive control approach under various sources of disturbance including the model uncertainties, the LCL inherent resonance phenomenon, and non-ideal grid environment. Aiming to improve the sinusoidal reference tracking performance as well as to reject lumped sinusoidal disturbances in the control practice, a resonant extended state observer is integrated in the ADRC structure, which guarantees a rigorous stable operation of inverter for bounded filter parameter uncertainties and adverse grid voltage conditions. The grid frequency adaptability is thoroughly considered in controller design process and synchronization technique, offering an extra capability for GCI to operate under different grid voltage frequency levels or even the frequency deviation caused by grid fault events. Robustness against parameter uncertainty and system stability are analyzed through the discrete-time frequency analysis and pole-zero map approaches. Simulation and hardware experiments are conducted for GCI with LCL filter parameters designed for two typical regions (i.e. the resonance frequency is less and greater than 1/6 of switching frequency) to validate the theoretical analysis and the effectiveness of the proposed control method.
Thuy Vi Tran; Kyeong-Hwa Kim; Jih-Sheng Jason Lai. Optimized Active Disturbance Rejection Control With Resonant Extended State Observer for Grid Voltage Sensorless LCL-Filtered Inverter. IEEE Transactions on Power Electronics 2021, 36, 13317 -13331.
AMA StyleThuy Vi Tran, Kyeong-Hwa Kim, Jih-Sheng Jason Lai. Optimized Active Disturbance Rejection Control With Resonant Extended State Observer for Grid Voltage Sensorless LCL-Filtered Inverter. IEEE Transactions on Power Electronics. 2021; 36 (11):13317-13331.
Chicago/Turabian StyleThuy Vi Tran; Kyeong-Hwa Kim; Jih-Sheng Jason Lai. 2021. "Optimized Active Disturbance Rejection Control With Resonant Extended State Observer for Grid Voltage Sensorless LCL-Filtered Inverter." IEEE Transactions on Power Electronics 36, no. 11: 13317-13331.
An assessment of the stability and performance of current controllers with harmonic compensators is presented for an inductive-capacitive-inductive (LCL)-filtered grid-connected inverter under distorted weak grid conditions. By using two typical current control schemes which are the direct current controller with the capacitor current-based active damping and integral-resonant state feedback current controller, the closed-loop system stability and current control performance are investigated in the presence of both uncertain grid impedance and distorted grid. Even though the controller stability has been investigated under weak grid in several studies, the stability assessment of the entire current control scheme, including the harmonic resonant controllers, still needs a further comprehensive investigation. The system stability is analyzed by obtaining the movement of the closed-loop poles in the discrete-time domain when the grid impedance varies. To fully study the impact of distorted weak grid condition on the LCL filters, three LCL filter parameter sets giving the resonance frequency in different frequency bands are chosen for the purpose of evaluating the system robustness and grid-injected current quality. In order to support the presented theoretical analyses, comprehensive simulation and experimental results based on 32-bit DSP TMS320F28335 to control 2 kVA grid-connected inverter are presented in terms of grid current quality and control stability in the environment of both uncertain grid impedance and distorted grid.
Seung-Jin Yoon; Thuy Vi Tran; Kyeong-Hwa Kim. Stability Assessment of Current Controller with Harmonic Compensator for LCL-Filtered Grid-Connected Inverter under Distorted Weak Grid. Applied Sciences 2020, 11, 212 .
AMA StyleSeung-Jin Yoon, Thuy Vi Tran, Kyeong-Hwa Kim. Stability Assessment of Current Controller with Harmonic Compensator for LCL-Filtered Grid-Connected Inverter under Distorted Weak Grid. Applied Sciences. 2020; 11 (1):212.
Chicago/Turabian StyleSeung-Jin Yoon; Thuy Vi Tran; Kyeong-Hwa Kim. 2020. "Stability Assessment of Current Controller with Harmonic Compensator for LCL-Filtered Grid-Connected Inverter under Distorted Weak Grid." Applied Sciences 11, no. 1: 212.
A high reliability of a grid-connected inverter (GCI) system at reasonable cost is a critical requirement for maximizing renewable energy potential in the electrical energy market. Several grid voltage sensorless control approaches have been investigated not only to eliminate the vulnerability of faulty sensors but also to further reduce the GCI commercial price. In this paper, a frequency adaptive integral-resonant full-state feedback current control scheme with the facilitation of a full-state observer is adopted for a grid-connected inductive–capacitive–inductive (LCL) filtered inverter without sensing the grid voltages. The proposed scheme actively damps the filter resonance and ensures the robustness of the inverter system against unexpected severe grid conditions with low cost and simplified hardware construction. The synchronization of the inverter with the main grid is accomplished by the proposed current controller-based grid voltage estimator, in which the grid frequency and phase angle can be detected effectively. In addition, the actual grid voltages are precisely regenerated to ensure the stable performance of the full-state observer. A safe start-up procedure is also presented for the grid voltage sensorless control of the LCL-filtered inverter to avoid a critical overcurrent and long settling time during the start-up instant, offering a stable and reliable inverter system operation with low computational burden. The effectiveness and feasibility of the proposed voltage sensorless current control scheme are validated by the simulation and experimental results under non-ideal grid conditions such as the harmonic distortion, grid frequency variation, and sudden grid phase angle jump.
Thuy Vi Tran; Kyeong-Hwa Kim. Grid Voltage Estimation Based on Integral Resonant Current Controller for LCL-Filtered Grid-Connected Inverter without AC Voltage Sensors. Electronics 2020, 9, 2051 .
AMA StyleThuy Vi Tran, Kyeong-Hwa Kim. Grid Voltage Estimation Based on Integral Resonant Current Controller for LCL-Filtered Grid-Connected Inverter without AC Voltage Sensors. Electronics. 2020; 9 (12):2051.
Chicago/Turabian StyleThuy Vi Tran; Kyeong-Hwa Kim. 2020. "Grid Voltage Estimation Based on Integral Resonant Current Controller for LCL-Filtered Grid-Connected Inverter without AC Voltage Sensors." Electronics 9, no. 12: 2051.
This paper presents a power flow control strategy for a hybrid control architecture of the DC microgrid (DCMG) system under an unreliable grid connection considering the constraint of electricity price. To overcome the limitation of the existing schemes, a hybrid control architecture which combines the centralized control and distributed control is applied to control DCMG. By using the hybrid control approach, a more optimal and reliable DCMG system can be constructed even though a fault occurs in the grid or a central controller (CC). The power flow control strategy for the hybrid DCMG control architecture also takes the constraint of electricity price into account for the purpose of minimizing the electricity cost. In the proposed hybrid control, the high bandwidth communication (HBC) link is used in the centralized control to connect the CC with DCMG power agents. On the other hand, the low bandwidth communication (LBC) link is employed to constitute the distributed control. A small size of data is used to exchange the information fast between the agents and CC, or between each agent and its neighbors, which increases the reliability and robustness of the DCMG system in case of a fault in the communication link of the centralized control. A DCMG system with 400-V rated DC-link voltage which consists of a wind power agent, a battery agent, a grid agent, a load agent, and a CC is constructed in this study by using three power converters based on 32-bit floating point digital signal processor (DSP) TMS320F28335 controller. Various simulation and experimental results prove that the proposed scheme improves the system stability and robustness even in the presence of a fault in the communication link of the centralized control. In addition, the proposed scheme is capable of maintaining the DC-link voltage stably at the nominal value without severe transients both in the centralized control and distributed control, as well as both in the grid-connected case and islanded case. Finally, the scalability of the DCMG system is tested by adding and removing additional wind power agent and battery agent during a certain period.
Faris Padhilah; Kyeong-Hwa Kim. A Power Flow Control Strategy for Hybrid Control Architecture of DC Microgrid under Unreliable Grid Connection Considering Electricity Price Constraint. Sustainability 2020, 12, 7628 .
AMA StyleFaris Padhilah, Kyeong-Hwa Kim. A Power Flow Control Strategy for Hybrid Control Architecture of DC Microgrid under Unreliable Grid Connection Considering Electricity Price Constraint. Sustainability. 2020; 12 (18):7628.
Chicago/Turabian StyleFaris Padhilah; Kyeong-Hwa Kim. 2020. "A Power Flow Control Strategy for Hybrid Control Architecture of DC Microgrid under Unreliable Grid Connection Considering Electricity Price Constraint." Sustainability 12, no. 18: 7628.
Ngoc-Bao Lai; Kyeong-Hwa Kim; Pedro Rodriguez. Voltage Sensorless Control Scheme Based on Extended-State Estimator for a Grid-Connected Inverter. IEEE Transactions on Power Electronics 2020, 35, 5873 -5882.
AMA StyleNgoc-Bao Lai, Kyeong-Hwa Kim, Pedro Rodriguez. Voltage Sensorless Control Scheme Based on Extended-State Estimator for a Grid-Connected Inverter. IEEE Transactions on Power Electronics. 2020; 35 (6):5873-5882.
Chicago/Turabian StyleNgoc-Bao Lai; Kyeong-Hwa Kim; Pedro Rodriguez. 2020. "Voltage Sensorless Control Scheme Based on Extended-State Estimator for a Grid-Connected Inverter." IEEE Transactions on Power Electronics 35, no. 6: 5873-5882.
Rizka Bimarta; Kyeong-Hwa Kim. A Robust Frequency-Adaptive Current Control of a Grid-Connected Inverter Based on LMI-LQR Under Polytopic Uncertainties. IEEE Access 2020, 8, 28756 -28773.
AMA StyleRizka Bimarta, Kyeong-Hwa Kim. A Robust Frequency-Adaptive Current Control of a Grid-Connected Inverter Based on LMI-LQR Under Polytopic Uncertainties. IEEE Access. 2020; 8 ():28756-28773.
Chicago/Turabian StyleRizka Bimarta; Kyeong-Hwa Kim. 2020. "A Robust Frequency-Adaptive Current Control of a Grid-Connected Inverter Based on LMI-LQR Under Polytopic Uncertainties." IEEE Access 8, no. : 28756-28773.
In this paper, an improved power management strategy (PMS) for multi-agent system (MAS)-based distributed control of DC microgrid (DCMG) under communication network problems is presented in order to enhance the reliability of DCMG and to ensure the system power balance under various conditions. To implement MAS-based distributed control, a communication network is constructed to exchange information among agents. Based on the information obtained from communication and local measurements, the decision for the local controller and communication is optimally given to guarantee the system power balance under various conditions. The operating modes of the agents can be determined locally without introducing any central controller. Simultaneously, the agents can operate in a deliberative and cooperative manner to ensure global optimization by means of the communication network. Furthermore, to prevent the system power imbalance caused by the delay in grid fault detection and communication in case of the grid fault, a DC-link voltage (DCV) restoration algorithm is proposed in this study. In addition, to avoid the conflict in the DCV control among power agents in case of the grid recovery under communication failure, a grid recovery identification algorithm is also proposed to improve the reliability of DCMG operation. In this scheme, a special current pattern is generated on the DC-link at the instant of the grid recovery by the grid agent, and other power agents identify the grid recovery by detecting this current pattern. Comprehensive simulations and experiments based on DCMG testbed have been carried out to prove the effectiveness of the PMS and the proposed control schemes under various conditions.
Thanh Van Nguyen; Kyeong-Hwa Kim. An Improved Power Management Strategy for MAS-Based Distributed Control of DC Microgrid under Communication Network Problems. Sustainability 2019, 12, 122 .
AMA StyleThanh Van Nguyen, Kyeong-Hwa Kim. An Improved Power Management Strategy for MAS-Based Distributed Control of DC Microgrid under Communication Network Problems. Sustainability. 2019; 12 (1):122.
Chicago/Turabian StyleThanh Van Nguyen; Kyeong-Hwa Kim. 2019. "An Improved Power Management Strategy for MAS-Based Distributed Control of DC Microgrid under Communication Network Problems." Sustainability 12, no. 1: 122.
This paper presents a frequency adaptive grid voltage sensorless control scheme of a grid-connected inductive–capacitive–inductive (LCL)-filtered inverter, which is based on an adaptive current controller and a grid voltage observer. The frequency adaptive current controller is constructed by a full-state feedback regulator with the augmentation of multiple control terms to restrain not only the inherent resonance phenomenon that is caused by LCL filter, but also current harmonic distortions from an adverse grid environment. The number of required sensing devices is minimized in the proposed scheme by means of a discrete-time current-type observer, which estimates the system state variables, and gradient-method-based observers, which estimate the grid voltages and frequency simultaneously at different grid conditions. The estimated grid frequency is utilized in the current control loop to provide high-quality grid-injected currents, even under harmonic distortions and the frequency variation of grid voltages. As a result, the grid frequency adaptive control performance as well as the robustness against distorted grid voltages can be realized. Finally, an inverter synchronization task without using grid voltage sensors is accomplished by a fundamental grid voltage filter and a phase-locked loop to detect the actual grid phase angle. The stability and convergence performance of the proposed observers have been studied by means of the Lyapunov theory to ensure a high accuracy tracking performance of estimated variables. Simulation and experimental results are presented to validate the feasibility and the effectiveness of the proposed control approach.
Thuy Vi Tran; Kim; Myungbok Kim; Kyeong-Hwa Kim; Tran. Frequency Adaptive Current Control Scheme for Grid-connected Inverter without Grid Voltage Sensors Based on Gradient Steepest Descent Method. Energies 2019, 12, 4266 .
AMA StyleThuy Vi Tran, Kim, Myungbok Kim, Kyeong-Hwa Kim, Tran. Frequency Adaptive Current Control Scheme for Grid-connected Inverter without Grid Voltage Sensors Based on Gradient Steepest Descent Method. Energies. 2019; 12 (22):4266.
Chicago/Turabian StyleThuy Vi Tran; Kim; Myungbok Kim; Kyeong-Hwa Kim; Tran. 2019. "Frequency Adaptive Current Control Scheme for Grid-connected Inverter without Grid Voltage Sensors Based on Gradient Steepest Descent Method." Energies 12, no. 22: 4266.
This paper presents a voltage sensorless control design for an LCL-filtered grid-connected inverter in discrete-time domain. The proposed scheme comprises a frequency adaptive current controller and a discrete current-type observer based on the linear quadratic regulator (LQR) approach, which is robust against the harmonic distortion and frequency variation of grid voltage. A frequency adaptive observer is studied in detail by means of Lyapunov stability theory to ensure high accuracy tracking performance of estimated system variables and grid voltages under different grid conditions. Since the proposed method also generates precise grid frequency and phase angle to facilitate the synchronization task, the conventional phase-locked loop (PLL) structure can be effectively eliminated. Simulation and experimental results are presented to validate the feasibility of the proposed control scheme.
Thuy Vi Tran; Kyeong-Hwa Kim. Frequency Adaptive Grid Voltage Sensorless Control of LCL-Filtered Inverter Based on Extended Model Observer. IEEE Transactions on Industrial Electronics 2019, 67, 7560 -7573.
AMA StyleThuy Vi Tran, Kyeong-Hwa Kim. Frequency Adaptive Grid Voltage Sensorless Control of LCL-Filtered Inverter Based on Extended Model Observer. IEEE Transactions on Industrial Electronics. 2019; 67 (9):7560-7573.
Chicago/Turabian StyleThuy Vi Tran; Kyeong-Hwa Kim. 2019. "Frequency Adaptive Grid Voltage Sensorless Control of LCL-Filtered Inverter Based on Extended Model Observer." IEEE Transactions on Industrial Electronics 67, no. 9: 7560-7573.
This paper presents a grid voltage-sensorless current control design based on the linear quadratic regulator (LQR) approach for an LCL-filtered grid-connected inverter. The proposed scheme relies only on the information from the grid-side current sensors to implement the control algorithm as well as to synchronize the inverter system with the utility grid. Basically, the construction of current controller consists of a full-state feedback regulator augmented with an integral control term for achieving control objectives, and a frequency-adaptive observer to estimate the system state variables and grid voltage parameters even under a non-ideal grid environment with frequency variation. A systematic design method based on the LQR approach is introduced to obtain optimal gains for the controller as well as the adaptive observer. The effectiveness of the proposed scheme is validated through the simulation results.
Thuy Vi Tran; Kyeong-Hwa Kim. A Voltage-sensorless Current Control of Grid-connected Inverter Using Frequency-adaptive Observer. IFAC-PapersOnLine 2019, 52, 63 -68.
AMA StyleThuy Vi Tran, Kyeong-Hwa Kim. A Voltage-sensorless Current Control of Grid-connected Inverter Using Frequency-adaptive Observer. IFAC-PapersOnLine. 2019; 52 (4):63-68.
Chicago/Turabian StyleThuy Vi Tran; Kyeong-Hwa Kim. 2019. "A Voltage-sensorless Current Control of Grid-connected Inverter Using Frequency-adaptive Observer." IFAC-PapersOnLine 52, no. 4: 63-68.
In this paper, an effective power flow control strategy (PFCS) based on the centralized control method and a reliable DC-link voltage (DCV) restoration algorithm for a DC microgrid (DCMG) under grid fault conditions are proposed. Considering the relationship of supply-demand power and the statuses of system units, thirteen operating modes are presented to ensure the power balance in DCMG under various conditions. In the PFCS, the battery charging/discharging procedure is implemented considering the battery power limit to avoid overheating and damage. Moreover, load shedding and load reconnection algorithms are presented to maintain the system power balance, even in critical cases. To prevent the system power imbalance in DCMG caused by the delay of grid fault detection, a reliable DCV restoration algorithm is also proposed in this paper. In the proposed scheme, as soon as abnormal behavior of the DCV is detected, the battery or wind power generation system instantly enters a local emergency control mode to restore the DCV rapidly to the nominal value, regardless of the control mode assigned from the central controller. Comprehensive simulations and experiments based on the DCMG testbed are carried out to prove the effectiveness of the PFCS and the proposed DCV restoration algorithm.
Thanh Van Nguyen; Kyeong-Hwa Kim. Power Flow Control Strategy and Reliable DC-Link Voltage Restoration for DC Microgrid under Grid Fault Conditions. Sustainability 2019, 11, 3781 .
AMA StyleThanh Van Nguyen, Kyeong-Hwa Kim. Power Flow Control Strategy and Reliable DC-Link Voltage Restoration for DC Microgrid under Grid Fault Conditions. Sustainability. 2019; 11 (14):3781.
Chicago/Turabian StyleThanh Van Nguyen; Kyeong-Hwa Kim. 2019. "Power Flow Control Strategy and Reliable DC-Link Voltage Restoration for DC Microgrid under Grid Fault Conditions." Sustainability 11, no. 14: 3781.
This paper proposes a frequency-adaptive current control design for a grid-connected inverter with an inductive–capacitive–inductive (LCL) filter to overcome the issues relating to both the harmonic distortion and frequency variation in the grid voltage. The current control scheme consists of full-state feedback control to stabilize the system and integral control terms to track the reference in the presence of disturbance and uncertainty. In addition, the current controller is augmented with resonant control terms to mitigate the harmonic component. The control scheme is implemented in the synchronous reference frame (SRF) to effectively compensate two harmonic orders at the same time by using only one resonant term. Moreover, to tackle the frequency variation issue in grid voltage, the frequency information which is extracted from the phase-locked loop (PLL) block is processed by a moving average filter (MAF) for the purpose of eliminating the frequency fluctuation caused by the harmonically distorted grid voltage. The filtered frequency information is employed to synthesize the resonant controller, even in the environment of frequency variation. To implement full-state feedback control for a grid-connected inverter with an LCL filter, all the state variables should be available. However, the increase in number of sensing devices leads to the rise of cost and complexity for hardware implementation. To overcome this challenge, a discrete-time full-state current observer is introduced to estimate all the system states. When the grid frequency is subject to variation, the discrete-time implementation of the observer in the SRF requires an online discretization process because the system matrix in the SRF includes frequency information. This results in a heavy computational burden for the controller. To resolve such a difficulty, a discrete-time observer in the stationary reference frame is employed in the proposed scheme. In the stationary frame, the discretization of the system model can be accomplished with a simple offline method even in the presence of frequency variation since the system matrix does not include the frequency. To select desirable gains for the full-state feedback controller and full-state observer, an optimal linear quadratic control approach is applied. To validate the practical effectiveness of the proposed frequency-adaptive control, simulation and experimental results are presented.
Rizka Bimarta; Thuy Vi Tran; Kyeong-Hwa Kim. Frequency-Adaptive Current Controller Design Based on LQR State Feedback Control for a Grid-Connected Inverter under Distorted Grid. Energies 2018, 11, 2674 .
AMA StyleRizka Bimarta, Thuy Vi Tran, Kyeong-Hwa Kim. Frequency-Adaptive Current Controller Design Based on LQR State Feedback Control for a Grid-Connected Inverter under Distorted Grid. Energies. 2018; 11 (10):2674.
Chicago/Turabian StyleRizka Bimarta; Thuy Vi Tran; Kyeong-Hwa Kim. 2018. "Frequency-Adaptive Current Controller Design Based on LQR State Feedback Control for a Grid-Connected Inverter under Distorted Grid." Energies 11, no. 10: 2674.
In order to alleviate the negative impacts of harmonically distorted grid conditions on inverters, this paper presents a linear quadratic regulator (LQR)-based current control design for an inductive-capacitive-inductive (LCL)-filtered grid-connected inverter. The proposed control scheme is constructed based on the internal model (IM) principle in which a full-state feedback controller is used for the purpose of stabilization and the integral terms as well as resonant terms are augmented into a control structure for the reference tracking and harmonic compensation, respectively. Additionally, the proposed scheme is implemented in the synchronous reference frame (SRF) to take advantage of the simultaneous compensation for both the negative and positive sequence harmonics by one resonant term. Since this leads to the decrease of necessary resonant terms by half, the computation effort of the controller can be reduced. With regard to the full-state feedback control approach for the LCL-filtered grid connected inverter, additional sensing devices are normally required to measure all of the system state variables. However, this causes a complexity in hardware and high implementation cost for measurement devices. To overcome this challenge, this paper presents a discrete-time current full-state observer that uses only the information from the control input, grid-side current sensor, and grid voltage sensor to estimate all of the system state variables with a high precision. Finally, an optimal linear quadratic control approach is introduced for the purpose of choosing optimal feedback gains, systematically, for both the controller and full-state observer. The simulation and experimental results are presented to prove the effectiveness and validity of the proposed control scheme.
Thuy Vi Tran; Seung-Jin Yoon; Kyeong-Hwa Kim. An LQR-Based Controller Design for an LCL-Filtered Grid-Connected Inverter in Discrete-Time State-Space under Distorted Grid Environment. Energies 2018, 11, 2062 .
AMA StyleThuy Vi Tran, Seung-Jin Yoon, Kyeong-Hwa Kim. An LQR-Based Controller Design for an LCL-Filtered Grid-Connected Inverter in Discrete-Time State-Space under Distorted Grid Environment. Energies. 2018; 11 (8):2062.
Chicago/Turabian StyleThuy Vi Tran; Seung-Jin Yoon; Kyeong-Hwa Kim. 2018. "An LQR-Based Controller Design for an LCL-Filtered Grid-Connected Inverter in Discrete-Time State-Space under Distorted Grid Environment." Energies 11, no. 8: 2062.
Inductive-capacitive-inductive (LCL)-type filters are currently preferred as a replacement for L-type filters in distributed generation (DG) power systems, due to their superior harmonic attenuation capability. However, the third-order dynamics introduced by LCL filters pose a challenge to design a satisfactory controller for such a system. Conventionally, an LCL-filtered grid-connected inverter can be effectively controlled by using a full-state feedback control. However, this control approach requires the measurement of all system state variables, which brings about more complexity for the inverter system. To address this issue, this paper presents a systematic procedure to design an observer-based integral state feedback control for a LCL-filtered grid-connected inverter in the discrete-time domain. The proposed control scheme consists of an integral state feedback controller and a full-state observer which uses the control input, grid-side currents, and grid voltages to predict all the system state variables. Therefore, only the grid-side current sensors and grid voltage sensors are required to implement the proposed control scheme. Due to the discrete-time integrator incorporated in the state feedback controller, the proposed control scheme ensures both the reference tracking and disturbance rejection performance of the inverter system in a practical and simple way. As a result, superior control performance can be achieved by using the reduced number of sensors, which significantly reduces the cost and complexity of the LCL-filtered grid-connected inverter system in DG applications. To verify the practical usefulness of the proposed control scheme, a 2 kW three-phase prototype grid-connected inverter has been constructed, and the proposed control system has been implemented based on 32-bit floating-point digital signal processor (DSP) TMS320F28335. The effectiveness of the proposed scheme is demonstrated through the comprehensive simulation and experimental results.
Seung-Jin Yoon; Ngoc Bao Lai; Kyeong-Hwa Kim. A Systematic Controller Design for a Grid-Connected Inverter with LCL Filter Using a Discrete-Time Integral State Feedback Control and State Observer. Energies 2018, 11, 437 .
AMA StyleSeung-Jin Yoon, Ngoc Bao Lai, Kyeong-Hwa Kim. A Systematic Controller Design for a Grid-Connected Inverter with LCL Filter Using a Discrete-Time Integral State Feedback Control and State Observer. Energies. 2018; 11 (2):437.
Chicago/Turabian StyleSeung-Jin Yoon; Ngoc Bao Lai; Kyeong-Hwa Kim. 2018. "A Systematic Controller Design for a Grid-Connected Inverter with LCL Filter Using a Discrete-Time Integral State Feedback Control and State Observer." Energies 11, no. 2: 437.
In order to overcome the limitations of conventional diagnosis methods, this paper proposes a reliable and practical on-line fault localization scheme for a pulse width modulation (PWM) inverter-fed permanent magnet synchronous machine (PMSM) drive system even when the inverter has simultaneous open faults in up to three switches. An open-switch fault is usually initiated by an accidental over-current, or electrical and thermal stresses. This fault may induce crucial secondary damage in the drive system since it is easily propagated and produces a continuous harmful effect on other system components. The open-switch faults in inverters often occur in a very complicated manner. Due to this reason, it was only recently that real-time diagnosis schemes under the open-switch faults in multiple switches have been presented in a few references. However, to alleviate the complexity and exactness issues, most of the conventional diagnosis schemes have considered the open faults only in two simultaneous switches until now, which is not generally the case. Even though the fault detection is simple and immediate, the exact fault localization is not a simple task, especially when there are open faults in three simultaneous switches because different open-switch fault locations may develop the same fault signature. To deal with such a problem, free-wheeling mode detection is introduced in this paper for the purpose of identifying the exact fault group and the faulty switch location. Then main objective of this paper is to realize a reliable fault localization algorithm under the condition of simultaneous open-switches (up to three) on an online basis without requiring any extra hardware or sensors in order that the algorithm can be easily installed in main CPU of a commercial drive system. For this purpose, the open faults in simultaneous switches are categorized into seven different fault groups. The entire system is implemented on a digital controller by using TMS320F28335 digital signal processor (DSP). The experimental results are presented under various open fault conditions to validate the usefulness of the proposed open-switch fault localization scheme.
Jae-Hwan Song; Kyeong-Hwa Kim. A Practical Approach to Localize Simultaneous Triple Open-Switches for a PWM Inverter-Fed Permanent Magnet Synchronous Machine Drive System. Energies 2018, 11, 101 .
AMA StyleJae-Hwan Song, Kyeong-Hwa Kim. A Practical Approach to Localize Simultaneous Triple Open-Switches for a PWM Inverter-Fed Permanent Magnet Synchronous Machine Drive System. Energies. 2018; 11 (1):101.
Chicago/Turabian StyleJae-Hwan Song; Kyeong-Hwa Kim. 2018. "A Practical Approach to Localize Simultaneous Triple Open-Switches for a PWM Inverter-Fed Permanent Magnet Synchronous Machine Drive System." Energies 11, no. 1: 101.
LCL filters are being more and more preferred over the L filter in a grid-connected inverter due to the smaller physical size and better harmonic attenuation characteristics. However, additional control loops are often required to control inverter-side current as well as capacitor voltage. These additional control loops complicate the controller design process. To overcome such a limitation, a discrete-time control design for a three-phase grid-connected inverter using a full state observer is presented in this paper. The controller design is accomplished based on the state-space model of the inverter system. Furthermore, to reduce the steady-state error in output currents, a discrete-time integral state feedback controller is employed. Generally, all state variables should be available to implement a state feedback controller. For the purpose of reducing the number of sensors in a practical system, an observer which uses the measured grid-side currents, grid voltages, and control inputs is constructed in discrete-time domain to predict the inverter-side currents and capacitor voltages. As a result of using both the feedback controller and the observer, the proposed control scheme provides a better control performance in a systematic design approach. Simulation results are given to demonstrate the feasibility and performance of the proposed control scheme.
Seung-Jin Yoon; Ngoc-Bao Lai; Kyeong-Hwa Kim; Hwachang Song. Discrete-Time Control Design for Three-Phase Grid-Connected Inverter Using Full State Observer. 2018 International Conference on Platform Technology and Service (PlatCon) 2018, 1 -6.
AMA StyleSeung-Jin Yoon, Ngoc-Bao Lai, Kyeong-Hwa Kim, Hwachang Song. Discrete-Time Control Design for Three-Phase Grid-Connected Inverter Using Full State Observer. 2018 International Conference on Platform Technology and Service (PlatCon). 2018; ():1-6.
Chicago/Turabian StyleSeung-Jin Yoon; Ngoc-Bao Lai; Kyeong-Hwa Kim; Hwachang Song. 2018. "Discrete-Time Control Design for Three-Phase Grid-Connected Inverter Using Full State Observer." 2018 International Conference on Platform Technology and Service (PlatCon) , no. : 1-6.
This paper presents an observer-based control scheme for a grid-connected LCL-filtered inverter with only grid-side current feedback. The proposed control scheme is composed of a state feedback regulator and an augmented state observer. The augmented state observer is used to estimate the inverter states which are then employed to construct the regulator. In addition to inverter states, the observer also estimates the grid voltages which are utilized to remove the effects of abnormal grid voltage and system parameter variations, as well as to synchronize the inverter with the grid. As a result of using the observer, only grid-side current sensors are required to control the inverter system even under unbalanced and distorted grid voltages. The effectiveness of the suggested control approach is verified through numerical results.
Ngoc-Bao Lai; Kyeong-Hwa Kim. Observer-based Control for Grid-connected LCL-filtered Inverter with Only Grid Current Feedback. DEStech Transactions on Engineering and Technology Research 2017, 1 .
AMA StyleNgoc-Bao Lai, Kyeong-Hwa Kim. Observer-based Control for Grid-connected LCL-filtered Inverter with Only Grid Current Feedback. DEStech Transactions on Engineering and Technology Research. 2017; (ameme):1.
Chicago/Turabian StyleNgoc-Bao Lai; Kyeong-Hwa Kim. 2017. "Observer-based Control for Grid-connected LCL-filtered Inverter with Only Grid Current Feedback." DEStech Transactions on Engineering and Technology Research , no. ameme: 1.
The grid voltage, especially under unbalanced and harmonically distorted grid conditions, often distorts the injected currents of grid-connected inverters. To address this problem, a robust control scheme of grid-connected inverters is presented in this paper. The proposed scheme is achieved by an internal model (IM)-based current controller and a robust phase-locked loop (PLL) scheme. The robust PLL scheme employs open-loop filtering technique to offer exact steady-state performance as well as fast transient response. The IM-based current controller is stabilized using the linear matrix inequality approach to optimize the feedback gains, and implemented in the synchronous reference frame to reduce computational efforts. A state estimator is also introduced into current controller for the purpose of reducing the number of current sensors which are often required in state feedback controller to damp the unstable dynamics of LCL filters. The validity of the proposed control scheme is demonstrated through comparative simulations and experimental results using a prototype grid-connected inverter.
Ngoc-Bao Lai; Kyeong-Hwa Kim. Robust Control Scheme for Three-Phase Grid-Connected Inverters With LCL-Filter Under Unbalanced and Distorted Grid Conditions. IEEE Transactions on Energy Conversion 2017, 33, 506 -515.
AMA StyleNgoc-Bao Lai, Kyeong-Hwa Kim. Robust Control Scheme for Three-Phase Grid-Connected Inverters With LCL-Filter Under Unbalanced and Distorted Grid Conditions. IEEE Transactions on Energy Conversion. 2017; 33 (2):506-515.
Chicago/Turabian StyleNgoc-Bao Lai; Kyeong-Hwa Kim. 2017. "Robust Control Scheme for Three-Phase Grid-Connected Inverters With LCL-Filter Under Unbalanced and Distorted Grid Conditions." IEEE Transactions on Energy Conversion 33, no. 2: 506-515.
This paper presents an improved current control strategy for a three-phase grid-connected inverter under distorted grid conditions. In terms of performance, it is important for a grid-connected inverter to maintain the harmonic contents of inverter output currents below the specified limit even when the grid is subject to harmonic distortion. To address this problem, this paper proposes a modulated finite control set–model predictive control (FCS-MPC) scheme, which effectively mitigates the harmonic components in output current of a grid-connected inverter. In the proposed scheme, the system behavior in the future is predicted from the system model in the discrete-time domain. Then, the cost function is selected based on the control objective of system. This cost function is minimized during the optimization process to determine the control signals that minimize the cost function. In addition, since the proposed scheme requires pure sinusoidal reference currents in the stationary frame to work successfully, the moving average filter (MAF) is employed to enhance the performance of the traditional phase lock loop (PLL). Due to the control performance of the FCS-MPC scheme as well as the harmonic disturbance rejection capability of the MAF-PLL, the proposed scheme is able to suppress the harmonic distortion even in the presence of distorted grid condition, while retaining fast transient response. Comparative simulation results of different controllers verify the effectiveness of the proposed control scheme in compensating the harmonic disturbance. To validate the practical feasibility of the proposed scheme, the whole control algorithm is implemented on a 32-bit floating-point digital signal processor (DSP) TMS320F28335 to control a 2 kW three-phase grid-connected inverter. As a result, the proposed scheme is a promising approach toward improving the current quality of a grid-connected inverter under distorted grid conditions.
Tien Hai Nguyen; Kyeong-Hwa Kim. Finite Control Set–Model Predictive Control with Modulation to Mitigate Harmonic Component in Output Current for a Grid-Connected Inverter under Distorted Grid Conditions. Energies 2017, 10, 907 .
AMA StyleTien Hai Nguyen, Kyeong-Hwa Kim. Finite Control Set–Model Predictive Control with Modulation to Mitigate Harmonic Component in Output Current for a Grid-Connected Inverter under Distorted Grid Conditions. Energies. 2017; 10 (7):907.
Chicago/Turabian StyleTien Hai Nguyen; Kyeong-Hwa Kim. 2017. "Finite Control Set–Model Predictive Control with Modulation to Mitigate Harmonic Component in Output Current for a Grid-Connected Inverter under Distorted Grid Conditions." Energies 10, no. 7: 907.