P. C. Sekhar

A Seamless Control Methodology for a Grid Connected and Isolated PV-Diesel Microgrid

In this paper, a seamless control methodology has been proposed for a photo voltaic (PV)-diesel generator (DG) microgrid to operate both in the grid connected and islanded mode. It does not require any islanding detection mechanism, to change the control philosophy from the grid connected mode to the islanded mode. A second order sliding mode control has been used to control the voltage source converter of the PV source whose set points have been generated by PI controllers. The maximum power point tracking algorithm for the PV system has been augmented with an auxiliary signal obtained using the electrical power output of the DG to reduce the output power of the PV system for economical operation of the DG unit. The DG unit is regulated with the frequency of the microgrid while the inverter used in the PV system regulates the voltage at the point of common coupling. Similarly, if the DG is uncontrollable due to any reason, the PV system is further added with an auxiliary signal based on the frequency deviation to maintain frequency stability. Simulation of the system has been carried out in MATLAB/SIMULINK with different levels of insolation and load to verify the proposed control scheme.

Biogeography Based Optimal State Feedback Controller for Frequency Regulation of a Smart Microgrid

Development of “Q” and “R” matrices for designing a Linear Quadratic Regulator (LQR) is still a research challenge. The theory says they should belong to the group of positive definite matrices, so we need to find out the most suitable amongst them in order to obtain the desired response. In this paper biogeography based optimization (BBO) technique has been applied to come up with the best “Q” and “R” matrices such that the frequency excursion following a disturbance in a microgrid is minimized. As all the states in a practical system may not be measurable hence, we have used Kalman estimator to estimate them. These estimated states along with other measured states are used by the LQR to produce the desired control signal. The microgrid is made smarter by using the agent based scheme integrated with a master controller and a proper communication protocol. The simulation results show that the proposed approach improves the microgrid frequency response and also gives a new alternative method for frequency control of a smart microgrid.

Deriving inertial response from a non-inertial PV system for frequency regulation

As photovoltaic (PV) penetration is gaining its momentum in the recent past, grid codes will demand contribution by PV systems to frequency regulation. This paper presents an investigation into the frequency regulation aspect of photovoltaic systems. An inertial response from photovoltaic system is derived by making it to work away from MPPT point of operation. The case of frequency response under deloaded operation with frequency regulation is compared with the case when the photovoltaics are not contributing to frequency regulation. A microgrid with a conventional synchronous machine and six photovoltaic generators in a distributed scenario is considered for the study.

Storage Free Smart Energy Management for Frequency Control in a Diesel-PV-Fuel Cell-Based Hybrid AC Microgrid

This paper proposes a novel, smart energy management scheme for a microgrid, consisting of a diesel generator and power electronic converter interfaced renewable energy-based generators, such as photovoltaic (PV) and fuel cell, for frequency regulation without any storage. In the proposed strategy, output of the PV is controlled in coordination with other generators using neurofuzzy controller, either only for transient frequency regulation or for both transient and steady-state frequency regulation, depending on the load demand, thereby eliminating the huge storage requirements. The option of demand response control is also explored along with the generation control. For accurate and quick tracking of maximum power point and its associated reserve power from the PV generator, this paper also proposes a novel adaptive-predictor-corrector-based tracking mechanism.

Ts fuzzy based adaptive perturb algorithm for MPPT of a grid connected single stage three phase VSC interfaced PV generating system

This paper proposes an adaptive perturb maximum power point tracking algorithm for a grid connected single-stage, three-phase PV system, supplying the local load. As the Mamdanis implications based systems are complex and take more processing time for generation of outputs in real time, a Takagi-Sugeno based fuzzy system is proposed and is used to make the perturbation adaptive. Maximum power point tracking is achieved with interleaved inner current control loop and outer voltage control loop. To convert nonlinear models into linear models, a feedback linearization scheme has been formulated, which uses the nonlinear transformation by means of diffeomorphism mapping. Sliding mode control technique has been incorporated in the feedback linearized control to add robustness to the control algorithm. The developed control algorithm along with proposed maximum power point tracking technique is tested for the maximum power extraction for various percents of rapid changes in insolation along with the changes in insolation with different ramp rates. Finally, the proposed algorithm is compared with the perturb and observe technique for evaluating its performance efficacy.

Photovoltaic system based transient mitigation and frequency regulation

New grid codes demand contribution by Distributed Generation like photovoltaics, wind power and the like in frequency regulation. In this paper, contribution of a battery connected to standard nine bus system to provide primary control is studied. A photovoltaic system is simulated in which rather than using battery along with PV as is conventionally done, deloaded PVs are used to enhance the frequency regulation capability of the systems. Photovoltaic system is to operate at a point away from Maximum Power Point Tracking (MPPT). The case of frequency response under deloaded operation with frequency regulation is compared with the case when the photovoltaics are working at their MPPT point and thereby not contributing to frequency regulation. A microgrid with a conventional synchronous machine and six photovoltaic generators is considered for the simulation.

Sliding mode based feedback linearizing controller for a PV system to improve the performance under grid frequency variation

This paper proposes an effective control strategy for a single-stage, three-phase PV system, supplying local load and integrated with the grid. Maximum power tracking is achieved with interleaved inner current control loop and outer voltage control loop. The output of PV generator is processed by the voltage source converter, a well established dc/ac converter. But these converter systems are highly non linear and coupled. Since the conventional PI controller will not give the satisfactory performance for the changing operating conditions and uncertain load changes, the feedback linearization scheme has been formulated. Sliding mode control technique has been incorporated in the feedback linearized control to address the issues of uncertainty and to add robustness to the control algorithm. The developed control algorithm is tested for the maximum power extraction at different insolations, controlling the dc/ac converter as an ancillary service to supply reactive power, load uncertainties and finally for variable grid frequency within a small band.

Voltage and Frequency control of wind diesel hybrid system with variable speed wind turbine

This paper deals with dynamic performance of wind diesel system with variable wind speed turbine. The quality of power supplied to the autonomous system is improved by controlling the frequency to the rated value. To improve the system characteristics, a variable speed operative wind generator: Doubly-Fed Induction Generator along with diesel generator in the isolated hybrid system is used. The simulation results of the proposed hybrid system are presented to demonstrate its effectiveness in meeting change in load demands along with change in wind speed. The system is also studied for a short circuit fault to ensure the stability. The performance of the proposed system is analyzed using MATLAB/SIMULINK and it is found that the fluctuations in power and frequency are minimum.

A novel controller for frequency regulation in a hybrid system with high PV penetration

In high penetration scenario of renewable, it is important that these sources contribute to the frequency control of power system. This paper investigates the frequency control aspects of an hybrid system with photovoltaic generation and conventional generators. A multi bus system with two conventional generators and twelve PV systems which are working away from the maximum power point of operation is the system used for the study. Frequency control contribution of the deloaded PVs with frequency control is simulated and the dependency of output power on the control parameters is shown with the help of simulations done on DigSILENT platform. An improved controller which considers not only the frequency deviation of the system but also the available reserve in the photovoltaic is proposed. This ensures that the PV with more reserve will participate more in the frequency control compared to those with less reserve so that distribution of the reserve over the different generators is achieved.

Control of single-phase grid connected PV power plant for real as well as reactive power feeding

This paper presents a methodology for the control of active and reactive power feeding to the utility and the load through a single phase grid connected photovoltaic power plant. A two stage control strategy has been used to provide an effective and simplified control to extract maximum power from the PV array as well as to control the reactive power. This paper focuses on simplifying the control topology by using proportional resonant controller and reducing the number of control variables. The time domain simulation has been done to analyze the performance of the controller and justify the robustness at different operating conditions.