USING MINIMAL LOAD POWER OBSERVER TO OPTIMIZE SYSTEM COST AND RELIABILITY

The previous term is made to result in the system errors converge to zero, whereas the second term is used to pay for those system uncertainties. Furthermore, the perfect load current observer can be used to optimize sys-tem cost and reliability. Particularly, the closed-loop stability of the observer-based optimal current control law is in past statistics proven by showing the whole states from the augmented observer-based control system errors tremendously converge to zero. This paper proposes an easy optimal current control way of three-phase uninterruptible-power-sup-ply systems. The suggested current controller consists of a feedback control term along with a paying control term. Unlike previous algorithms, the suggested method can produce a tradeoff between control input magnitude and tracking error simply by selecting proper performance indexes. The potency of the suggested controller is validated through simulations on MATLAB/Simulink and experiments on the prototype 600-Veterans administration test bed having a TMS320LF28335 DSP. Finally, the comparative recent results for the suggested plan and also the conventional feedback linearization control plan are given to show the suggested formula achieves a great performance for example fast transient response, small steady-condition error, and occasional total harmonic distortion under load step change, unbalanced load, and nonlinear load using the parameter variations

A Control Architecture for Regulating Voltage and Power Flows in a Networked Microgrid System

This paper presents a unique control system to regulate power exchanges and load bus voltage in a networked microgrid (NMG) system comprising AC and DC microgrids. During the islanding of a microgrid in this NMG system, load voltage and power balance can get disturbed. A control system and associated converter and inverter control methods are presented to rectify these issues. An efficient model predictive control (MPC) method, which gives a tracking error of 50% lower than a conventional proportional-integral (PI) controller, is used to control multiple inverters in the NMG system. Simulation studies are conducted to test the NMG in islanding and load change scenarios. With the help of these studies, it is verified that the MPC-controlled inverters can provide better tracking accuracy in achieving desired power flows in the NMG system

Diseño de un algoritmo de gestión basado en lógica difusa para el intercambio de potencia entre microrredes eléctricas.

El presente trabajo de investigación, detalla el diseño de un algoritmo de gestión de energía basado en lógica difusa que realiza el intercambio de potencia entre dos microrredes eléctricas (MG) interconectadas entre ellas para garantizar la provisión del suministro de energía eléctrica. Para el diseño del sistema de gestión de energía (EMS) se seleccionó el uso del Control Fuzzy Logic (FLC) por el conocimiento heurístico que se tiene del sistema, por tanto, el FLC no requiere aproximar el modelo matemático del sistema, ni tampoco necesita linealizarlo. Las microrredes en estudio se consideran de tipo residencial conectada a la red y utilizan la tasa de cambio de energía ERoC y el estado de carga de la batería (SOC) para aumentar-conservar-disminuir la potencia consumida/entregada por la red eléctrica. Para diseñar el EMS se analiza los perfiles de potencia de cada microrred tomando en cuenta el excedente de potencia generada, por lo que se planteó tres casos comprobando la hipótesis: primer caso, MG1 aporta una potencia máxima (PM) de 187,50W a la MG2; segundo caso, la MG2 aporta a la MG1 la PM de 125,00W y en el último caso el intercambio de potencia es bidireccional, aportando la MG1 a la MG2 una PM de 62,50W y la MG2 a la MG1 aporta una PM de 62,40W. En los dos primeros el SOC oscila al 75% (garantizando la vida útil de las baterías), no así en el tercer escenario, por tanto se necesitará obligatoriamente incluir a la variable SOC en el FLC para tomar acciones de control en función del estado de carga de los sistemas de almacenamiento de energía de cada microrred. La validación de las estrategias diseñadas se realizó en Matlab® evidenciando los intercambios de potencia, reduciendo las fluctuaciones y los picos de potencia, manteniendo los índices de calidad en niveles aceptables.This research work details the design of an energy management algorithm based on fuzzy logic that performs the exchange of power between two electrical microgrids (MG) interconnected between them to guarantee the provision of electrical energy supply. For the design of the energy management system (EMS), the use of the Fuzzy Logic Control (FLC) was selected due to the heuristic knowledge of the system, therefore, the FLC does not need to approximate the mathematical model of the system, nor does it need to linearize it. The microgrids under study are considered to be of a residential type connected to the grid and use the ERoC energy change rate and the state of charge of the battery (SOC) to increase-conserve-decrease the power consumed/delivered by the electrical network. To design the EMS, the power profiles of each microgrid are analyzed taking into account the excess power generated, for which three cases were proposed, testing the hypothesis: first case, MG1 provides maximum power (PM) of 187.50W to the MG2; In the second case, the MG2 provides the MG1 with a PM of 125.00W and in the latter case the power exchange is bidirectional, with the MG1 providing the MG2 with a PM of 62.50W and the MG2 providing the MG1 with a PM of 62, 40W. In the first two, the SOC oscillates at 75% (guaranteeing the useful life of the batteries), but not in the third scenario, therefore it will be necessary to include the SOC variable in the FLC to take control actions based on the state of a load of the energy storage systems of each microgrid. The validation of the designed strategies was carried out in Matlab®, evidencing the power exchanges, reducing fluctuations and power peaks, keeping the quality indices at acceptable levels

Diseño de un algoritmo de gestión basado en lógica difusa para el intercambio de potencia entre microrredes eléctricas.

El presente trabajo de investigación, detalla el diseño de un algoritmo de gestión de energía basado en lógica difusa que realiza el intercambio de potencia entre dos microrredes eléctricas (MG) interconectadas entre ellas para garantizar la provisión del suministro de energía eléctrica. Para el diseño del sistema de gestión de energía (EMS) se seleccionó el uso del Control Fuzzy Logic (FLC) por el conocimiento heurístico que se tiene del sistema, por tanto, el FLC no requiere aproximar el modelo matemático del sistema, ni tampoco necesita linealizarlo. Las microrredes en estudio se consideran de tipo residencial conectada a la red y utilizan la tasa de cambio de energía ERoC y el estado de carga de la batería (SOC) para aumentar-conservar-disminuir la potencia consumida/entregada por la red eléctrica. Para diseñar el EMS se analiza los perfiles de potencia de cada microrred tomando en cuenta el excedente de potencia generada, por lo que se planteó tres casos comprobando la hipótesis: primer caso, MG1 aporta una potencia máxima (PM) de 187,50W a la MG2; segundo caso, la MG2 aporta a la MG1 la PM de 125,00W y en el último caso el intercambio de potencia es bidireccional, aportando la MG1 a la MG2 una PM de 62,50W y la MG2 a la MG1 aporta una PM de 62,40W. En los dos primeros el SOC oscila al 75% (garantizando la vida útil de las baterías), no así en el tercer escenario, por tanto se necesitará obligatoriamente incluir a la variable SOC en el FLC para tomar acciones de control en función del estado de carga de los sistemas de almacenamiento de energía de cada microrred. La validación de las estrategias diseñadas se realizó en Matlab® evidenciando los intercambios de potencia, reduciendo las fluctuaciones y los picos de potencia, manteniendo los índices de calidad en niveles aceptables.This research work details the design of an energy management algorithm based on fuzzy logic that performs the exchange of power between two electrical microgrids (MG) interconnected between them to guarantee the provision of electrical energy supply. For the design of the energy management system (EMS), the use of the Fuzzy Logic Control (FLC) was selected due to the heuristic knowledge of the system, therefore, the FLC does not need to approximate the mathematical model of the system, nor does it need to linearize it. The microgrids under study are considered to be of a residential type connected to the grid and use the ERoC energy change rate and the state of charge of the battery (SOC) to increase-conserve-decrease the power consumed/delivered by the electrical network. To design the EMS, the power profiles of each microgrid are analyzed taking into account the excess power generated, for which three cases were proposed, testing the hypothesis: first case, MG1 provides maximum power (PM) of 187.50W to the MG2; In the second case, the MG2 provides the MG1 with a PM of 125.00W and in the latter case the power exchange is bidirectional, with the MG1 providing the MG2 with a PM of 62.50W and the MG2 providing the MG1 with a PM of 62, 40W. In the first two, the SOC oscillates at 75% (guaranteeing the useful life of the batteries), but not in the third scenario, therefore it will be necessary to include the SOC variable in the FLC to take control actions based on the state of a load of the energy storage systems of each microgrid. The validation of the designed strategies was carried out in Matlab®, evidencing the power exchanges, reducing fluctuations and power peaks, keeping the quality indices at acceptable levels

Advanced Controls Of Cyber Physical Energy Systems

Cyber system is a fairly important component of the energy systems. The network imperfections can significantly reduce the control performance if not be properly treated together with the physical system during the control designs. In the proposed research, the advanced controls of cyber-physical energy systems are explored in depth. The focus of our research is on two typical energy systems including the large-scale smart grid (e.g. wide-area power system) and the smart microgrid (e.g. shipboard power system and inverter-interfaced AC/DC microgrid). In order to proactively reduce the computation and communication burden of the wide-area power systems (WAPSs), an event/self-triggered control method is developed. Besides, a reinforcement learning method is designed to counteract the unavoidable network imperfections of WAPSs such as communication delay and packet dropout with unknown system dynamics. For smart microgrids, various advanced control techniques, e.g., output constrained control, consensus-based control, neuro network and game theory etc., have been successfully applied to improve their physical performance. The proposed control algorithms have been tested through extensive simulations including the real-time simulation, the power-hardware-in-the-loop simulation and on the hardware testbed. Based on the existing work, further research of microgrids will be conducted to develop the improved control algorithms with cyber uncertainties

Improvement of Stability of a Grid-Connected Inverter with an LCL filter by Robust Strong Active Damping and Model Predictive Control

This study addresses development and implementation of robust control methods for a three-phase grid-connected voltage source inverter (VSI) accompanied by an inductive-capacitive-inductive (LCL) filter. A challenge of current control for the VSI is LCL filter resonance near to the control stability boundary, which interacts with the inverter control switching actions and creates the possibility of instability. In general, active damping is needed to stabilize the system and ensure robust performance in steady-state and dynamic responses. While many active damping methods have been proposed to resolve this issue, capacitor-current-feedback active damping has been most widely used for its simple implementation. There has been no clear consensus regarding design of a control system including capacitor-current-feedback active damping. This is due to the fact that simulation/experiment results are not congruent with the design analyses on which the control is designed. This study explains the incoherence between theory and practice when it comes to a capacitor-currents-feedback active damping system. Proposed capacitor-current-estimate active damping utilizing a developed posteriori Kalman estimator gives coherent simulation results as expected from the design analyses. This reveals that the highly oscillatory capacitor currents containing the inverter switching effects bring about uncertainty in the system performance. The switching effects are not incorporated in the analyses and control system design. Therefore, it is required to remove the switching noise from the capacitor currents in order to yield consistent results. It has been confirmed that the proportional-negative feedback of the capacitor current is equivalent to virtual impedance connected in parallel with the filter capacitor. In a digitally controlled system, the computation delay causes the equivalent resistance of the virtual impedance to become negative in the frequency range of fs/6 to fs/2, which produces a pair of open-loop unstable poles in RHP. This happens when the displaced resonance peak by active damping is in that region. Thus, an a priori Kalman estimator has been developed to generate one-sample-ahead state variable estimates to reconstruct the capacitor currents for active damping, which can compensate for the delay. The one-sample-ahead capacitor-current estimates are computed from the inverter-side and grid-side current estimates. The proposed method provides extended limits of the active damping gain that improve robustness against system parameter variation. It also allows strong active damping which can sufficiently attenuate the resonance. Grid condition is another significant factor affecting the stability of the system. In particular, a weak grid tends to provide high impedance. The system employing the proposed active damping method stably operates in a weak grid, ensuring robustness under grid impedance variation. The developed Kalman estimators offer an effective and easy way of determining the stability status of a system in addition to the functions of filtering and estimation. Stability analysis can be easily made since state variable estimates go to infinity when a system is unstable. As a promising approach, model predictive control (MPC) has been designed for the system. This study suggests that MPC including active damping can be employed for a grid-connected VSI with an LCL filter with good dynamic performance

POWER CONDITIONING UNIT FOR SMALL SCALE HYBRID PV-WIND GENERATION SYSTEM

Small-scale renewable energy systems are becoming increasingly popular due to soaring fuel prices and due to technological advancements which reduce the cost of manufacturing. Solar and wind energies, among other renewable energy sources, are the most available ones globally. The hybrid photovoltaic (PV) and wind power system has a higher capability to deliver continuous power with reduced energy storage requirements and therefore results in better utilization of power conversion and control equipment than either of the individual sources. Power conditioning units (p.c.u.) for such small-scale hybrid PV-wind generation systems have been proposed in this study. The system was connected to the grid, but it could also operate in standalone mode if the grid was unavailable. The system contains a local controller for every energy source and the grid inverter. Besides, it contains the supervisory controller. For the wind generator side, small-scale vertical axis wind turbines (VAWTs) are attractive due to their ability to capture wind from different directions without using a yaw. One difficulty with VAWTs is to prevent over-speeding and component over-loading at excessive wind velocities. The proposed local controller for the wind generator is based on the current and voltage measured on the dc side of the rectifier connected to the permanent magnet synchronous generator (PMSG). Maximum power point tracking (MPPT) control is provided in normal operation under the rated speed using a dc/dc boost converter. For high wind velocities, the suggested local controller controls the electric power in order to operate the turbine in the stall region. This high wind velocity control strategy attenuates the stress in the system while it smoothes the power generated. It is shown that the controller is able to stabilize the nonlinear system using an adaptive current feedback loop. Simulation and experimental results are presented. The PV generator side controller is designed to work in systems with multiple energy sources, such as those studied in this thesis. One of the most widely used methods to maximize the output PV power is the hill climbing technique. This study gives guidelines for designing both the perturbation magnitude and the time interval between consecutive perturbations for such a technique. These guidelines would improve the maximum power point tracking efficiency. According to these guidelines, a variable step MPPT algorithm with reduced power mode is designed and applied to the system. The algorithm is validated by simulation and experimental results. A single phase H-bridge inverter is proposed to supply the load and to connect the grid. Generally, a current controller injects active power with a controlled power factor and constant dc link voltage in the grid connected mode. However, in the standalone mode, it injects active power with constant ac output voltage and a power factor which depends on the load. The current controller for both modes is based on a newly developed peak current control (p.c.c.) with selective harmonic elimination. A design procedure has been proposed for the controller. Then, the method was demonstrated by simulation. The problem of the dc current injection to the grid has been investigated for such inverters. The causes of dc current injection are analyzed, and a measurement circuit is then proposed to control the inverter for dc current injection elimination. Characteristics of the proposed method are demonstrated, using simulation and experimental results. At the final stage of the study, a supervisory controller is demonstrated, which manages the different operating states of the system during starting, grid-connected and standalone modes. The operating states, designed for every mode, have been defined in such a hybrid model to allow stability and smooth transition between these states. The supervisory controller switches the system between the different modes and states according to the availability of the utility grid, renewable energy generators, the state of charge (SOC) of energy storage batteries, and the load. The p.c.u. including the supervisory controller has been verified in the different modes and states by simulation