A Novel Grid Connected Photovoltaic System

Inthispaper, a novel grid connected photovoltaic system is proposed which can function as an Active Power Filter (APF) with Maximum Power Point Tracking (MPPT). Filter reference current is derived using Fourier Transform. Considering 33% reduction in inverter switches, cost of the grid-connect photovoltaic power plant can be reduced considerably. Using this approach, it is also possible to compensate for reactive and harmonic components of the local loads; moreover it can inject generated active power into grid at maximum power point of the photovoltaic cells. According to this, during daytime, the proposed system injects active power to the grid and at the same time compensates for the reactive power of the load. When there is no sunlight, the inverter only compensates local loads. Considering cost reduction, such capabilities may result in more application of the grid connected photovoltaic systems. Main novelty of the proposed system is simultaneous APF and MPPT functioning using single DC/AC converter. In fact, extra DC-DC converter is not required in the proposed system for MPPT. In order to verify the performance of the proposed method, some simulation is done using MATLAB/Simulink software. Also, some experimental results are presented for practical verification of the proposed grid connected inverter

Analysis of a Bidirectional DC-DC Converter with High Voltage Gain

A novel bidirectional DC-DC converter with high conversion ratio is proposed in this paper. The proposed converter uses the three windings coupled-inductor to achieved high voltage conversion ratio. The primary side consist of a winding and secondary side consist of two windings, which these two windings are series to achieved high voltage gain.In the boost mode, a capacitor is parallel charged and series discharged by the coupled inductor. Thus, high step-up voltage gain can be achieved with an appropriate duty ratio. In the buck mode, a capacitor is series charged and parallel discharged by the coupled inductor. The bidirectional converter can have high step-down voltage gain.The stress voltage of main switches can be reduced, and efficiency can be improved. The operating principle and the steady-state analyses of the voltage gain are discussed. Finally, in 24V for low voltage, and 400V for high voltage, and 200W for output power, this converter is simulated in MATLAB

A novel approach for adaptive partial sliding mode controller design and tuning in non-minimum phase switch-mode power supplies

In this article, a novel systematic approach is proposed for a partial sliding mode controller (SMC) design and tuning in non-minimum phase switch-mode power supplies (SMPS). To achieve a more simplified controller in comparison with the conventional SMCs, the partial SMC (PSMC) is introduced in this article, which just requires a part of the sliding surface for controller formulation. The accuracy of the developed PSMC is proved mathematically within the entire range of operation. Since the control parameters of the PSMC are not selected by trial and error, it can maintain the stability and robustness of the closed-loop system in a broad operational range. In this regard, and to develop a systematic approach for robust control of SMPS, a constant frequency equivalent SMC is designed using the converter nominal parameters. Then, the extracted controller is combined with an adaptive component to ensure asymptotical stability against load and line changes. Considering the Lyapunov stability criteria for nonlinear systems, it is proved that the presented SPMC can be used for output voltage regulation in both discontinuous and continuous operating modes with zero steady state error. To avoid the trial and error method during the controller tuning and parameters selection, the system characteristic equation is extracted using the Jacobian approach. Considering the roots of the characteristic equation and the stable range of the closed-loop system, the controller parameters are tuned. Furthermore, in addition to simulation, the developed approach is evaluated practically using the TMS3220F2810 digital signal processor. It is shown that the dynamic response of the proposed approach is faster than the standard double-loop SMC during load and line changes. Additionally, it is seen that the developed controller is robust against model changes in both continuous and discontinuous operations

Analysis of a Bidirectional DC-DC Converter with High Voltage Gain

A novel bidirectional DC-DC converter with high conversion ratio is proposed in this paper. The proposed converter uses the three windings coupled-inductor to achieved high voltage conversion ratio. The primary side consist of a winding and secondary side consist of two windings, which these two windings are series to achieved high voltage gain.In the boost mode, a capacitor is parallel charged and series discharged by the coupled inductor. Thus, high step-up voltage gain can be achieved with an appropriate duty ratio. In the buck mode, a capacitor is series charged and parallel discharged by the coupled inductor. The bidirectional converter can have high step-down voltage gain.The stress voltage of main switches can be reduced, and efficiency can be improved. The operating principle and the steady-state analyses of the voltage gain are discussed. Finally, in 24V for low voltage, and 400V for high voltage, and 200W for output power, this converter is simulated in MATLAB

Thermal Unit Commitment Solution using Priority List Method and Genetic-Imperialist Competitive Algorithm

A novel strategy including a Priority List (PL) based method and a heuristic algorithm which is named Genetic-Imperialist Competitive Algorithm (GICA) has been proposed in this paper to solve thermal Unit Commitment Problem (UCP). This problem has been confined by some constraints like minimum down time, minimum up time, spinning reserve, load demand, and limited output power of the generating units. The optimization process is carried out in three steps. At first, a strategy based PL is used to find units priority, in second step the GICA employed to solve Economic Load Dispatch (ELD), and finally a correction strategy tried to find and replace better solutions. The accuracy and effectiveness of the proposed method is verified by two different case studies with 4 and 10 generation units system. The comparison of results with some other methods shows that proposed three step method has a better performance and achieve better solution in an admissible time interval

A novel method for maximum power point tracking of the grid-connected three-phase solar systems based on the PV current prediction

In this paper, it is first attempted to provide a small signal model of the photovoltaic (PV) system, DC-DC boost converter, and pulse width modulation (PWM) generator. Then, a technique is provided for maximum power point tracking (MPPT) in grid-connected solar systems based on variable and adaptive perturbation and observation with predictive control of the PV current. An innovative aspect of the proposed predictive current control method is to use the current controller to achieve the value of PV impedance, which has been used in DC-DC boost converter. The proposed method is to obtain the coming current value on the basis of the current predictive model. The goal of the proposed method is to make the DC-DC boost converter inductor current track the current reference. Voltage and current ripple minimization is added to the cost function simultaneously as a system constraint to optimize system performance. This reduces the amount of voltage and current fluctuations around the maximum power point. The proposed method is capable of detecting rapid changes in solar radiation. A sudden and simultaneous increase in voltage and current is detected by the algorithm and then the duty cycle becomes increasing instead of decreasing. The simulation is carried out in MATLAB Simulink environment in real-time for a 26.6 kW three-phase grid-connected solar system. The simulation results of current predictive control are compared with perturbation and observation techniques and linear voltage and current proportional integral derivative (PID) controller-based adaptive control. The results show that the total harmonic distortion (THD%) of the inverter voltage with proposed method has been reduced by 0.16% compared to the PID method. In addition, the THD% of the current in the proposed method is reduced by 0.1% compared to the PID method. The solar system output voltage variation of the proposed method is less than 5 V

Sliding Mode Input Current Control of the Synchronous DC-DC Buck Converter for Electro-Mechanical Actuator Emulation in More Electric Aircrafts

The main challenges of the input current control in synchronous DC-DC buck converters are the nonlinear model of the system, changes of the operating point in a wide range, and the need to use an input LC filter for current smoothing, which may result in the instability of the closed-loop system. In this paper, a step-by-step approach is developed for the design and improvement of a PI-feedforward closed-loop controller. It is shown that a linear PI controller cannot stabilize the closed-loop system properly during wide changes in model parameters, e.g., an equivalent series resistance of the input filter. To cope with the stability issues, a fixed-frequency sliding mode controller (SMC) has been developed in this paper for the implementation of an electro-mechanical actuator (EMA) emulator. Moreover, a systematic approach is proposed for controller tuning and the selection of the SMC’s gains. To achieve high power efficiency, high-frequency GaN switches are used for the practical implementation of the DC-DC converter. Despite large changes in the load current, the designed nonlinear controller can track the input current reference satisfactorily. Steady-state and dynamic responses of the proposed SMC are compared with conventional linear controllers. Considering the Lyapunov stability theorem, it is proved that the designed SMC can stabilize the closed-loop system in the entire utilizable domain. The proposed nonlinear SMC controller enjoys a very simple control law. Hence, despite having very high switching and sampling frequencies, it can be easily implemented. The experimental response of the designed synchronous DC-DC buck converter is evaluated experimentally by implementing the control strategy in a TMS320F28335PGFA DSP from Texas Instrument. Moreover, the comprehensive comparison of the proposed SMC controller and a PI-feedforward controller proved the superior performance of the developed closed-loop system, in terms of the transient time response, robustness, and stability of the EMA emulator

Sliding mode controller design for stabilization of the three-phase grid-connected inverters in the presence of unbalanced local loads

Considering the presence of different model parameters and controlling variables, as well as the nonlinear nature of DC to AC inverters; stabilizing the closed-loop system for grid current balancing is a challenging task. To cope with these issues, a novel sliding mode controller is proposed for the current balancing of local loads using grid-connected inverters in this paper. The closed-loop system includes two different controlling loops: a current controller which regulates the output current of grid-connected inverter and a voltage controller which is responsible for DC link voltage regulation. The main features of the proposed nonlinear controller are reactive power compensation, harmonic filtering and three-phase balancing of local nonlinear loads. The developed controller is designed based on the state-space averaged modelling its stability and robustness are proved analytically using the Lyapunov stability theorem. The accuracy and effectiveness of proposed controlled approach are investigated through the PC-based simulations in MATLAB/Simulink

A novel Lyapunov-based robust controller design for LCL-type shunt active power filters using adaptive sliding-mode backstepping approach

In this paper, a novel hybrid two-loop nonlinear controller is designed for stabilization and robust control of the LCL-type shunt active power filter (SAPF). To cope with the instability issue of the closed-loop system and the inherent resonance of the LCL coupling, backstepping, sliding mode and adaptive controllers are combined. DC link voltage of the grid-connected inverter is regulated in an outer control loop by determining a proper reference value for an inner loop. In addition to DC link voltage control, a major objective of the proposed closed-loop system is to make the grid current in phase with the grid voltage directly. Hence, active power filtering of the grid-connected inverter can be achieved without any current feedback from the local load. To stabilize the LCL-type SAPF in a wide range of changes, all uncertain parameters of the model including the DC link capacitor and equivalent impedances of the LCL coupling network are estimated by employing a proper Lyapunov function. For practical evaluation of the developed approach, the closed-loop system is implemented by using Texas Instruments’ digital signal processor (DSP-TMS28F335). Considering the application of an adaptive-robust nonlinear controller, it is proved that the system enjoys a stable and robust performance over the whole range of utilization, and it doesn't suffer from resonance issues of the LCL-type SAPFs. Moreover, considering the experimental results, it is observed that the steady-state error of the proposed nonlinear controller is zero in a wide range of operations

Effect of support on power output of ethanol/O2 biofuel cell

Enzymatic biofuel cells have many great usages as a small power source for medical and environmental applications. In this paper, we employed carboxylated multiwall carbon nanotube- (1-ethyl-3-methylimidazolium bis (trifluoromethyl sulfonyl) imide) ionic liquid nanocomposite on two different electrodes (glassy carbon and carbon felt) for immobilizing alcohol dehydrogenase. The properties of the two types of electrodes were characterized by cyclic voltammetry analysis. Polarization analysis and field emission scanning electron microscopy were used to show differences in the nanobiocomposite immobilization on two electrodes. Compared to glassy carbon, carbon felt achieved much more gains in electrochemical activity and power by catalyst coating. Power density of 10.027μWcm−2, has been achieved by carbon felt, but glassy carbon showed 1.7 μWcm−2 respectively