• Energy Research
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With the acceleration of energy reform, photovoltaic, energy storage, electric vehicles, and other new loads in low-voltage distribution networks have been rapidly developed. However, the distribution network with distributed power supply has some problems, such as imprecise power flow modeling and difficult coordination between various energy sources and loads, which bring challenges to the online optimization of the distribution network load curve. In this study, a multi-time scale online load optimal operation scheme of the distribution network is proposed by using the Bayesian online learning method. This scheme transforms the online power optimization of the distribution network into a Markov decision process. The output time of different energy sources is different, and the load with different user load characteristics is optimized. The scheme can track the state of the distribution network in real time and make the optimization scheme of multi-energy output online. Finally, an example is given to verify the effectiveness of the proposed method, which has theoretical significance for promoting the diversified development of low-voltage user-side load.

With the acceleration of energy reform, photovoltaic, energy storage, electric vehicles, and other new loads in low-voltage distribution networks have been rapidly developed. However, the distribution network with distributed power supply has some problems, such as imprecise power flow modeling and difficult coordination between various energy sources and loads, which bring challenges to the online optimization of the distribution network load curve. In this study, a multi-time scale online load optimal operation scheme of the distribution network is proposed by using the Bayesian online learning method. This scheme transforms the online power optimization of the distribution network into a Markov decision process. The output time of different energy sources is different, and the load with different user load characteristics is optimized. The scheme can track the state of the distribution network in real time and make the optimization scheme of multi-energy output online. Finally, an example is given to verify the effectiveness of the proposed method, which has theoretical significance for promoting the diversified development of low-voltage user-side load.

This work investigates the application of sliding mode control (SMC) on a doubly fed induction generator (DFIG). In conventional control schemes like PI controllers, the responses are relatively slow, and the transient state is often subjected to sustained oscillation. Further, the PI control achieves lesser invariance behavior against system uncertainties, and the selection of its gain parameters is a skillful task. In contrast, the SMC is well-known for its faster convergence, robustness, and better transient and steady-state behavior. In this study, the nonsingular fast terminal sliding mode control (NSFTSMC) is applied in the speed loop of the rotor side vector control of DFIG. The proposed NSFTSMC scheme results in less speed fluctuation with a change in wind speed, which is maintained by controlling the torque component of the current (iq*). This paper also presents detailed modeling of the DFIG, power converters, and the related control schemes. Moreover, stability analysis of the proposed methodology ensures the practical finite time stability of the overall system. The comparative controller performance and validation are carried out in Matlab/Simulink environment. The proposed control strategy presents much better results than conventional PI-based control.

This work investigates the application of sliding mode control (SMC) on a doubly fed induction generator (DFIG). In conventional control schemes like PI controllers, the responses are relatively slow, and the transient state is often subjected to sustained oscillation. Further, the PI control achieves lesser invariance behavior against system uncertainties, and the selection of its gain parameters is a skillful task. In contrast, the SMC is well-known for its faster convergence, robustness, and better transient and steady-state behavior. In this study, the nonsingular fast terminal sliding mode control (NSFTSMC) is applied in the speed loop of the rotor side vector control of DFIG. The proposed NSFTSMC scheme results in less speed fluctuation with a change in wind speed, which is maintained by controlling the torque component of the current (iq*). This paper also presents detailed modeling of the DFIG, power converters, and the related control schemes. Moreover, stability analysis of the proposed methodology ensures the practical finite time stability of the overall system. The comparative controller performance and validation are carried out in Matlab/Simulink environment. The proposed control strategy presents much better results than conventional PI-based control.

With the development of power grid technology, a large number of constant power loads (CPL) are introduced into the power grid system. The negative damping characteristic of CPL poses a great challenge to the stability of power grid under the condition of large signal disturbance. This paper focuses on the large signal stability and dynamic response characteristics of DC microgrid with CPL. The mixed potential function (MPF) method is adopted to model the large signal characterstic of load converter controlled by the traditional PI control strategy and the new virtual DC motor (VDM) control strategy. The large signal stability criteria and the asymptotic stability region of the DC microgrid system under the two control strategies are derived. The dynamic response characteristics of the DC microgrid are compared under three large signal operation conditions of the load step, load linear change and the load fault. The results show that VDM control strategy can effectively improve dynamic response characteristics of the DC microgrid system compared with those of PI control, and enhance the stability and anti-interference ability of the DC microgrid system.

With the development of power grid technology, a large number of constant power loads (CPL) are introduced into the power grid system. The negative damping characteristic of CPL poses a great challenge to the stability of power grid under the condition of large signal disturbance. This paper focuses on the large signal stability and dynamic response characteristics of DC microgrid with CPL. The mixed potential function (MPF) method is adopted to model the large signal characterstic of load converter controlled by the traditional PI control strategy and the new virtual DC motor (VDM) control strategy. The large signal stability criteria and the asymptotic stability region of the DC microgrid system under the two control strategies are derived. The dynamic response characteristics of the DC microgrid are compared under three large signal operation conditions of the load step, load linear change and the load fault. The results show that VDM control strategy can effectively improve dynamic response characteristics of the DC microgrid system compared with those of PI control, and enhance the stability and anti-interference ability of the DC microgrid system.

For high-voltage (symmetric and non-symmetric) transmission networks, detecting simultaneous faults utilizing a single-end-based scheme is complex. In this regard, this paper suggests novel schemes for detecting simultaneous faults. The proposed schemes comprise two different stages: fault detection and identification and fault classification. The first proposed scheme needs communication links among both ends (sending and receiving) to detect and identify the fault. This communication link between both ends is used to send and receive three-phase current magnitudes for sending and receiving ends in the proposed fault detection (PFD) unit at both ends. The second proposed scheme starts with proposed fault classification (PFC) units at both ends. The proposed classification technique applies the Clarke transform on local current signals to classify the open conductor and simultaneous faults. The sign of all current Clarke components is the primary key for distinguishing between all types of simultaneous low-impedance and high-impedance faults. The fault detection time of the proposed schemes reaches 20 ms. The alternative transient program (ATP) package simulates a 500 kV–150-mile transmission line. The simulation studies are carried out to assess the suggested fault detection and identification and fault classification scheme performance under various OCFs and simultaneous earth faults in un-transposed and transposed TLs. The behavior of the proposed schemes is tested and validated by considering different fault scenarios with varying locations of fault, inception angles, fault resistance, and noise. A comparative study of the proposed schemes and other techniques is presented. Furthermore, the proposed schemes are extended to another transmission line, such as the 400 kV–144 km line. The obtained results demonstrated the effectiveness and reliability of the proposed scheme in correctly detecting simultaneous faults, low-impedance faults, and high-impedance faults.

For high-voltage (symmetric and non-symmetric) transmission networks, detecting simultaneous faults utilizing a single-end-based scheme is complex. In this regard, this paper suggests novel schemes for detecting simultaneous faults. The proposed schemes comprise two different stages: fault detection and identification and fault classification. The first proposed scheme needs communication links among both ends (sending and receiving) to detect and identify the fault. This communication link between both ends is used to send and receive three-phase current magnitudes for sending and receiving ends in the proposed fault detection (PFD) unit at both ends. The second proposed scheme starts with proposed fault classification (PFC) units at both ends. The proposed classification technique applies the Clarke transform on local current signals to classify the open conductor and simultaneous faults. The sign of all current Clarke components is the primary key for distinguishing between all types of simultaneous low-impedance and high-impedance faults. The fault detection time of the proposed schemes reaches 20 ms. The alternative transient program (ATP) package simulates a 500 kV–150-mile transmission line. The simulation studies are carried out to assess the suggested fault detection and identification and fault classification scheme performance under various OCFs and simultaneous earth faults in un-transposed and transposed TLs. The behavior of the proposed schemes is tested and validated by considering different fault scenarios with varying locations of fault, inception angles, fault resistance, and noise. A comparative study of the proposed schemes and other techniques is presented. Furthermore, the proposed schemes are extended to another transmission line, such as the 400 kV–144 km line. The obtained results demonstrated the effectiveness and reliability of the proposed scheme in correctly detecting simultaneous faults, low-impedance faults, and high-impedance faults.