This paper provides a comprehensive review of the control approaches and the power-decoupling topologies to mitigate 2ω-ripple problem in the single-phase inverters, its solutions, and discusses open challenges yet to be addressed. The cause and effects of 2ω-ripple problem and its solution based on the passive and active power-decoupling techniques are discussed. A subcategory of the active power-decoupling technique nominated as the control-oriented compensation technique is reviewed in detail, this technique can achieve the ripple-mitigation at the source through the control but not necessarily adds extra circuit or active filter to the system. The control-oriented compensation techniques can be applied in the two-stage DC-DC-AC converters and the single-stage inverters having a front-end control capability with the H-bridge such as in the quasi-switched-boost inverters. The merits and associated challenges of these techniques are listed and summarized in a tabular form. Finally, a conclusive discussion with open challenges is presented.

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Control Strategies and Power Decoupling Topologies to Mitigate 2ω-Ripple in Single-Phase Inverters: A Review and Open Challenges

Power electronic converters for electric vehicles (EVs) have been the subject of great interest over the last several decades. This article presents a thorough review of different EV power electronic converters on which the authors have worked for more than one decade. The readers will find this review interesting to design current products and to devise/invent new converters for emerging applications in EV.

Soft-Switching Power Electronics Technology for Electric Vehicles: A Technology Review

In a two-stage inverter, the instantaneous output power pulsates at twice the output frequency (2 f o), generating the second harmonic current (SHC), which will propagate into the front-end dc–dc converter. This article aims for suppressing the SHC in the front-end dc–dc converter with dc transformer (DCX)- LLC resonant converter. The small-signal model of the DCX- LLC resonant converter is proposed, and based on which, the unified small-signal model of the preregulator+ LLC converter is built. Then, the basic ideas for reducing the SHC are proposed, including the determination of the filter capacitors in the preregulator+ LLC converter and the control approach. After that, from a perspective of output impedance, the control schemes for reducing the SHC in the front-end preregulator+ LLC converter are proposed. By inserting a notch filter in the voltage loop and/or introducing a virtual impedance in series with the output rectifier of the LLC resonant converter, the output impedance of the preregulator+ LLC converter at 2 f o is increased and, thus, the SHC can be reduced. Finally, a 6-kVA two-stage three-phase inverter with boost+ LLC converter as the front-end dc–dc converter was fabricated and tested. The experimental results are provided to verify the proposed control schemes.

Second Harmonic Current Reduction for Two-Stage Inverter With DCX- LLC Resonant Converter in Front-End DC–DC Converter: Modeling and Control

Inverter connected single-phase AC loads cause second-order oscillations in source currents and DC bus voltage. These oscillations degrade the efficiency and reliability of the dc microgrid. In this paper, an adaptive sliding mode control based output impedance shaping (ASMC-OIS) methodology is proposed for voltage regulation, proportional load sharing, and second-order ripple management in a dc microgrid. By using the proposed control method, the magnitude of the output impedance of the source interfacing converter is increased at 2 $f_{ac}$ programmably, which results in the reduction of second-order ripple currents propagating through the converter. Instead, it is propagated to the dc-link capacitor or towards the nodes which consists of some ripple absorption active or passive filter. This leads to an increase in the energy density of the ripple filters. The dynamic consensus-based secondary control is incorporated to ensure proportional load current sharing. A graph theoretical analysis is presented to analyze per unit load sharing among all the nodes. Stability of the proposed controller is analyzed considering multiple source nodes using Lyapunov's approach. A dc microgrid consisting of parallel-connected dc-dc boost converters, dc load, and inverter load is simulated to verify the proposed control strategy. The proposed ASMC-OIS methodology is validated through experimentation.

Adaptive-SMC Based Output Impedance Shaping in DC Microgrids Affected by Inverter Loads

Photovoltaic microgrids provide free renewable energy solutions for Rwandans. Although solar technology keeps on its advancement, hydropower remains the principal power source in Rwanda. Other renewable power sources include wind and geothermal energies that are not yet fully exploited. Nonrenewable sources in Rwanda including methane, peat, thermal, and fuels are also used for providing energy solutions for the citizens. Rwanda Energy Group (REG) sets the energy strategic plan since 2015 for achieving the minimum of 512 MW of energy production in 2024/2025 to meet the total energy demand. The plan predicted 52% for grid-connected and 48% for off-grid (standalone) connections. The literature survey and data analysis collected on site were used to evaluate and determine the best cheaper microgrid model from the three comparison case studies for the household in Rwanda. The study focused on the economic power generation model mainly based on solar resources to minimize the electricity cost and provide income for the excess energy produced. Moreover, the study resulted in a low-cost (four times cheaper), reliable, and affordable grid-connected PV and battery microgrid model for a residential home with a minimum daily load of 5.467 kWh. The simulation results based on economic comparison analysis found the levelized cost of energy (LCOE) and net present cost (NPC) for each power-generated model by using Hybrid Optimization Model for Electric Renewable (Homer) pro software. The results show that the LCOE for electricity production by each of the Grid connected-PV-Battery system, Diesel GenSet-PV-Batteries, and PV-Batteries systems was 0.0645 US$/1 kWh, 1.38 US$/1 kWh and 1.82 US$/1 kWh, respectively, compared with 0.2621 US$/1 kWh, the current residential electricity price (2020) for Rwanda.

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Comparative Analysis of Reliable, Feasible, and Low-Cost Photovoltaic Microgrid for a Residential Load in Rwanda

A substantial pulsation of the second-order harmonic current ripple with angular frequency $2\omega$ is reflected at the input of a single-phase inverter when loads are supplied at its output with angular frequency $\omega$ . Moreover, this ripple back-propagates and injects into the source in the absence of a bulky dc-link passive filter, an active compensator or a suitable digital controller with a front-end converter in the two-stage converter. This paper proposes a new adaptive sliding mode control for a two-stage dc–dc–ac converter to reduce proliferation of ripple without compromising dynamic performance. The front-end boost converter in the considered two-stage converter interfaces a battery bank and single-phase inverter fed loads. The control shapes the output impedance of the boost converter to reduce the ripple component at battery input. Second, the proposed controller achieves good dynamic performance at line and load transients. A fast voltage recovery with small undershoot/overshoot can be achieved at transients using the proposed controller. The proposed technique is validated using a hardware of the 1-kW two-stage converter.

Kumar Gourav

Papers

Ripple Mitigation With Improved Line-Load Transients Response in a Two-Stage DC–DC–AC Converter: Adaptive SMC Approach