Saravana Ilango Ganesan

A Hybrid Algorithm for Tracking of GMPP Based on P&O and PSO With Reduced Power Oscillation in String Inverters

Maximum power point tracking (MPPT) is essential for photovoltaic (PV) string inverter systems. Partially shaded PV strings with bypass diodes exhibit multiple peaks in the power-voltage characteristic. Under partial shading conditions, conventional algorithms get trapped in a local maximum power point, and fail to track the global MPP (GMPP). To overcome this problem, global search algorithms such as particle swarm optimization (PSO) have been proposed. However, these can cause excessive oscillations in the output power before converging onto the GMPP. In this paper, a new GMPPT technique combining the PSO and Perturb and Observe (P&O) algorithms has been presented. The P&O technique is used to track the MPP under uniform irradiance, and the same is used to detect the occurrence of partial shading. Only on the onset of partial shading conditions, PSO is employed. Furthermore, the search space of PSO is reduced by using a window-based search in order to reduce the power oscillations and convergence time. The effectiveness of the proposed algorithm in tracking the GMPP, both under uniform and nonuniform irradiance conditions, is demonstrated experimentally.

Control Scheme for a Bidirectional Converter in a Self-Sustaining Low-Voltage DC Nanogrid

Local dc distribution systems or dc nanogrids for residential and commercial buildings are growing popular due to the increased focus on energy savings. Using low-voltage dc for the nanogrid provides various advantages such as easier integration with renewable sources and battery banks, increased savings, etc. Future systems would use renewable sources and storage devices to become self-sufficient in generation with bare minimum consumption from the grid. The objective of this paper is to develop an energy management system (EMS) to provide uninterrupted power supply to the dc loads and achieve self-sufficiency by minimizing grid power consumption. This is achieved by developing a control scheme for a cascaded two-stage bidirectional converter interface between the nanogrid and the ac distribution network. In addition, an empirical relation for power flow through the converter is obtained, and an optimal capacitor link voltage range is derived to achieve power transfer between rated limits. The efficacy of the proposed control algorithm for the EMS is analyzed and proved to be well suited for the self-sustained dc nanogrid. A 5-kVA prototype of the converter is designed and developed in hardware, and the system operation is verified with experimental results.

Fireworks Enriched P&O Algorithm for GMPPT and Detection of Partial Shading in PV Systems

Global maximum power point tracking (GMPPT) strategies for photovoltaic systems are effective under nonuniform irradiation conditions but cause unnecessary power loss due to wide search under uniform irradiance. This paper proposes a scheme for detecting the type of irradiation, viz., uniform or nonuniform, using the trend observed in the string maximum power point (MPP) voltage and current. This partial shading detection scheme is implemented in a GMPPT control strategy combining the conventional perturb and observe (P&O) algorithm and the Fireworks Algorithm (FWA). Under uniform irradiation conditions, the P&O algorithm is used owing to the lower magnitude of power oscillations during tracking as compared to the FWA. On the other hand, under partial shading conditions, the FWA is employed due to its global search and fast tracking capability. The proposed GMPPT method is tested experimentally to verify its effectiveness under different shading patterns.

Dragonfly Algorithm Based Global Maximum Power Point Tracker for Photovoltaic Systems

This paper presents the application of the Dragonfly Algorithm (DA) for tracking the Global Maximum Power Point (GMPP) of a photovoltaic (PV) system. Optimization techniques employed for GMPP tracking (GMPPT) are required to be fast and efficient in order to reduce the tracking time and energy loss respectively. The DA, being a meta-heuristic algorithm with good exploration and exploitation characteristics, is a suitable candidate for this application. Due to its simplicity, the DA is implemented on a low cost microcontroller, and is proven to track the GMPP effectively under various irradiation conditions. The performance of the proposed DA based GMPPT scheme is compared with that of the conventional PSO based GMPPT scheme, and proves to be superior in terms of tracking time and energy loss during tracking.

A Control Strategy for Reliable Power Output From a Stand-alone WRIG With Battery-Supported DC Link

This paper proposes a versatile control strategy for a standalone wound rotor induction generator (WRIG) with back-to-back converters supported by a battery at dc-link. The principal feature of the study is the operation of the generator as a commanded current source, to supply only sinusoidal current as desired, and the operation of battery fed Front End Converter (FEC) as a constant voltage source, which adapts to varying load conditions. Further, in implementing this feature, in a significant deviation from conventional approaches, to Rotor Side Converter (RSC) and FEC are redefined with a view to achieve versatility and reliability in stand-alone operation. In particular, the RSC is employed to track the maximum power (instead of load voltage and frequency control), whereas the FEC maintains a constant load voltage and frequency. It is revealed that there are multiple benefits of the proposed strategy such as inherent load balancing; capability to support critical loads solely by battery through the FEC as in an uninterruptible power supply (UPS), especially at low wind speeds; compensating unbalanced or harmonic load currents via FEC (as in an active power filter); and smooth transition between the MPPT mode and the UPS mode by synchronization. Simulation results of a 2-MW wind turbine, along with test results of a 2.3-kW laboratory setup, validate the proposed strategy.

Performance Evaluation of Type-3 PLLs Under Wide Variation in Input Voltage and Frequency

This paper presents a detailed analysis of Type-3 phase locked loop (PLL) under wide variation in input voltage and frequency. Using small signal modeling, the performance of both single loop and dual loop Type-3 PLL for variation in input voltage and frequency is studied. The analysis shows that for the same bandwidth, both the single loop and dual loop Type-3 PLLs exhibit similar dynamics provided the supply voltage is balanced. However, under voltage sag conditions, dual loop PLL shows improved dynamic response without affecting its stability. Further, the tracking time is reduced as the feed forward frequency is a function of supply frequency. To improve the filtering characteristics under frequency deviations, a dual loop Type 3 adaptive PLL which accurately tracks the phase and frequency of the input signal under wide frequency deviations is developed. Simulations are carried out in MATLAB and experimentally verified by implementing in ALTERA cyclone II Field Programmable Gate Array (FPGA) board.