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Maximum Power Reference Tracking Algorithm for Power Curtailment of Photovoltaic Systems
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Abstract
This paper presents an algorithm for power curtailment of photovoltaic (PV) systems under fast solar irradiance intermittency. Based on the Perturb and Observe (P&O) technique , the method contains an adaptive gain that is compensated in real-time to account for moments of lower power availability. In addition, an accumulator is added to the calculation of the step size to reduce the overshoot caused by large irradiance swings. A testbed of a three-phase single-stage, 500 kVA PV system is developed on the OPAL-RT eMEGAsim real-time simulator. Field irradiance data and a regulation signal from PJM (RTO) are used to compare the performance of the proposed method with other techniques found in the literature. Results indicate an operation with smaller overshoot, less dc-link voltage oscillations, and improved power reference tracking capability.
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With increased integration of renewable resources into the power distribution system,
bidirectional ac/dc converters are gaining popularity in interfacing the utility grid and
energy storage systems. This thesis presents design and modeling of a three-phase
bidirectional PWM ac/dc converter with high power factor, low current THD, and high
efficiency. Design expressions for the passive components based on current ripple,
voltage ripple, and load transients will be proposed. A mathematical model to represent
the dynamic behavior of the converter will be derived using a Switched model and the
Generalized Averaging Method. A cascaded control system with an outer voltage
controller, an inner hysteresis current controller, and a phase-locked loop algorithm will
be designed utilizing the derived converter transfer functions. The designed system will
be set up and simulated using PLECS simulation platform. Simulation results will be
presented to validate the design and to analyze the system performance during
steady-state, start-up, load-transients, and grid-distortion conditions.
One of the major concerns associated with the increasing penetration of grid-connected photovoltaic (PV) power plants is the operational challenges (e.g., overloading and overvoltage), imposed due to the variability of PV power generation. A flexible power point tracking (FPPT), which can limit the PV output power to a specific value, has thus been defined in grid-connection regulations to tackle some of the integration challenging issues. However, the conventional FPPT algorithm based on the perturb and observe method suffers from slow dynamics. In this paper, an adaptive FPPT algorithm is thus proposed, which features fast dynamics under rapidly changing environmental conditions (e.g., due to passing clouds), while maintaining low power oscillations in steady-state. The proposed algorithm employs an extra measured sampling at each perturbation to observe the change in the operating condition (e.g., solar irradiance). Afterwards, the voltage-step is adaptively calculated following the observed condition (e.g., transient or steady-state) in a way to improve the tracking performance. Experimental results on a 3-kVA grid-connected single-phase PV system validate the effectiveness of the proposed algorithm in terms of fast dynamics and high accuracy under various operational conditions.
With a still increase of grid-connected Photovoltaic (PV) systems, challenges have been imposed on the grid due to the continuous injection of a large amount of fluctuating PV power, like overloading the grid infrastructure (e.g., transformers) during peak power production periods. Hence, advanced active power control methods are required. As a cost-effective solution to avoid overloading, a Constant Power Generation (CPG) control scheme by limiting the feed-in power has been introduced into the currently active grid regulations. In order to achieve a CPG operation, this paper presents three CPG strategies based on: 1) a power control method (P-CPG), 2) a current limit method (I-CPG) and 3) the Perturb and Observe algorithm (P&O-CPG). However, the operational mode changes (e.g., from the maximum power point tracking to a CPG operation) will affect the entire system performance. Thus, a benchmarking of the presented CPG strategies is also conducted on a 3-kW single-phase grid-connected PV system. Comparisons reveal that either the P-CPG or I-CPG strategies can achieve fast dynamics and satisfactory steady-state performance. In contrast, the P&O-CPG algorithm is the most suitable solution in terms of high robustness, but it presents poor dynamic performance.
Significant expansion of PV-grid installations have escalated new problems of PV penetration because of intermittent nature of the PV source and inertia-less interface. In this paper, a novel active and reactive power control scheme for a single stage PV-grid system is proposed to counter the potential PV penetration problems for the futuristic grid with large distributed generation system (DGS) contributions. The proposed work incorporates a PV power control algorithm, which not only facilitates maximum power point tracking (MPPT) but also provides precise PV power control, unlike conventional MPPT schemes. These features significantly overcome power and voltage fluctuations, reverse power flow problems and overvoltage issues, which are considered as major potential PV penetration problems and the main reason for limiting large PV installations. In addition, the reactive power control ability increases the effectiveness of the proposed scheme for feeder voltage profile improvement and utilization of the interfacing power converter. A 3-Ph, single stage PV-grid system is considered with the PV source directly integrated with the DC link of the inverter. The DC link voltage is controlled by the inverter. Detailed analysis, modeling and control design are included and supported by key simulation and experimental results.
Advanced grid-friendly controls demonstration project for utility-scale pv power plants
- V Gevorgian
- B O'neill
V. Gevorgian and B. O'Neill, "Advanced grid-friendly controls demonstration project for utility-scale pv power plants," National Renewable
Energy Lab.(NREL), Golden, CO (United States), Tech. Rep., 2016.
Distributed PV Monitoring and Feeder Analysis
- Epri
EPRI, "Distributed PV Monitoring and Feeder Analysis," https://
dpv.epri.com/measurement data.html, accessed: 2020-08-10.