Maximum power point tracking (MPPT) control is a key functionality in solar photo-voltaic (PV) based power generation systems that enhances the efficacy of energy extraction. A pulse-width modulated (PWM) power converter connected to the PV is designed to perform this essential function. A variety of MPPT control schemes are available in literature, many of which are voltage based techniques wherein the PV bus voltage is controlled in closed loop to the required level that achieves MPP tracking. However, a suitable plant model of the PV fed converter system that facilitates the design of such a PV voltage control loop for MPPT purpose, is not fully covered in literature. In this paper, a small-signal model is developed for a buck converter based charger system fed by a PV source, which is a nonlinear active source. Based on this model, the relevant transferfunctions are analytically derived. The control to converter input voltage transfer-function vin/ d thus obtained, is useful in the systematic design of voltage controller bandwidth, that facilitates the selection of perturbation period of a typical perturb & observe (P&O) MPPT controller. Such an approach for control design is verified in this work on a PV system with energy storage, which is typically used in dual-mode or standalone PV applications. The P&O MPPT control is validated on a buck PV charge controller system employing a 36 V battery bank. Experiments conducted on a 1 kW hardware prototype verify the accuracy of the proposed analytical transfer-functions and the performance of the PV-charger system.
This paper discusses concepts of a 20 kVA power converter design and key differences between discrete IGBT and module-based design approaches. Module-based power converters have been typically employed in academic and research institutes for power levels of 10 kVA and more. However, with advancement in IGBT technologies and the growing need to minimize system size and weight, designs based on discrete devices are now an attractive alternative for such power levels. A simple procedure is presented for power converter design that includes power loss evaluation, heat-sink thermal characterization, thermal model of overall system and sizing of DC link capacitor. Using the same, a state-of-the-art discrete device and modulebased power converters are designed. A comparison is subsequently made, where it is shown that discrete approach yields a compact and economic design up to a power level of 20 kVA. A key objective of this work is to lay emphasis on laboratory design of power converters. This enables a graduate level student to build a converter from start and in the process gain insights into the underlying engineering design aspects.
Grid-forming (GFM) control offers promising performance features for inverter-based resources (IBRs) across scales. However, design, analysis, and benchmarking of GFM IBRs during unbalanced faults remains largely unexplored. In this paper, we outline a stationary-reference-frame nested-loop control architecture for GFM IBRs and integrate the same with novel current-limiting strategies. The architecture improves on virtual-impedance and current-reference-saturation limiting as well as state-of-the-art methods for control of voltage-source inverters. Electromagnetic-transient simulations for a modified IEEE 14-bus network validate salient features of the proposed control architectures. The proposed virtual-impedance limiter is shown to provide better voltage support during faults than the current-reference-saturation limiter (quantified via sequence voltages). On the other hand, the current-reference-saturation limiter offers better (and more accurate) fault-current contribution.
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