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This paper develops a new control strategy for voltage source converter (VSC) based multi-terminal high voltage dc (MT-HVDC) grids for enhancing the mutual frequency support between MT-HVDC interconnected asynchronous ac systems. The existing droop control structure of VSCs is augmented with an additional feedback voltage-based loop that generates a voltage shifting term to be added to the original dc voltage reference. The addition of this integrator-based controller nullifies the difference between voltage errors seen at adjacent converter stations. This action helps to overcome inaccuracies in the mutual frequency support caused by the uneven voltages across a dc system. The proposed strategy uses only local variables for the continuous-time control; thus, it does not rely on a high-bandwidth communication network, and its performance is not affected by the change of ac systems parameters. Modal analysis is carried out to investigate the stability of the proposed controller. Finally, comprehensive simulation studies are used to verify the proposed strategys performance and compare it with recently reported alternative controllers.

This paper proposes a review map for comparative designs of wireless high-power transfer systems using single and double-resonance blocks. In-depth analyses and key guidelines are provided to design high-efficiency wireless high-power transfer systems (WHPTs) while keeping zero-phase-angle/unity power-factor property and constant-current/voltage supply to the load. Basic single-resonance LC circuits and a double-resonant block derived by combining 7 and -shaped blocks are analyzed. Then, resonant S- and T-Blocks are recommended as the best transmission blocks for competitive designs. The proposed approach is applied to map recent developments on the wireless charging technologies for electric vehicles (EVs), especially for weak-coupling systems and dynamic-charging technologies. The proposed design approach offers a systematic and effective methodology to quickly evaluate current technologies and solutions for WHPTs in EVs applications. In extension, this paper indicates different control strategies for WHPTs, especially for optimal-efficiency tracking. Design guidelines and control strategies are provided to achieve the maximum efficiency at a standard resonance-frequency against variations from loads and coupling-coefficients in operation which can easily map to recent research works and future research directions. Experimental verifications of dominant designs are also presented to validate the proposed approach.

This paper proposes a gradient descent-based transfer delay frequency-locked loop (GDTD FLL) to effectively address the challenges of existing transfer delay-based FLLs in terms of unacceptable frequency and phase angle overshoots during variations in the supply voltage amplitude and distorted voltage conditions. In the proposed GDTD FLL, a linear model of the distorted single-phase supply voltage is developed and the error term is constructed. Consequently, the gradient descent algorithm is employed to drive the error term to zero and provide an estimate of the FLL expression from which frequency estimation is achieved. By designing the learning rate employed in the gradient descent algorithm, a degree of freedom is introduced in the proposed GDTD FLL, giving it the ability to achieve improved performance during variations in the supply voltage amplitude. Furthermore, a delay-based harmonic cancellation approach is developed to reject supply voltage harmonics in the FLL’s phase angle estimation. The effectiveness of the proposed GDTD FLL is verified in comparison with other single-phase FLL schemes through experimental studies where it is shown that the proposed GDTD FLL effectively addresses the challenges of existing delay-based FLLs in terms of peak frequency and phase angle overshoots, especially when the supply voltage undergoes amplitude variation or distortion.

This paper considers applying bit loading to multicarrier non-othogonal multiple access (NOMA) systems. The objective is to maximize the system total throughput while satisfying the users' individual quality of service (QoS) constraints. Although bit loading is generally an NP-hard problem, even for orthogonal multiple access (OMA), the mutual interference between the users and the dependence of power coefficients and modulation orders are additional challenges that add substantial complexity to the optimization problem. Therefore, we propose in this paper an efficient bit loading algorithm for multicarrier NOMA systems and compares the complexity and throughput with OMA. The obtained results show that NOMA has virtual cognition and hybrid modes of operation, NOMA/OMA, that enables NOMA to outperform OMA by 100% for the two-user scenario. The complexity of the loading process for NOMA is noticeably higher than OMA, which is due to the high computational complexity of bit error rate (BER) computation for NOMA. The obtained results show that the NOMA throughput depends on which user is loaded first, and on the initially loaded bits.

Maximization of solar energy harvest and miniaturization of dc–dc converters are essential for low earth orbit (LEO) CubeSats, which are constrained by volume and weight restrictions. The state-of-the-art electric power system (EPS) architectures utilize several individual dc–dc converters to maximize solar energy harvest but it has a tradeoff with miniaturization as it requires several inductors. The main objective of this article is to propose a single-inductor-based multiport converter topology for the LEO CubeSat's EPS. The proposed topology interfaces the photovoltaic (PV) panels to the energy storage system and a control strategy have been developed to extract maximum solar power from each PV panel under wide varying irradiation conditions of the LEO CubeSat. The proposed topology consists of series-connected half-bridge modules fed by PV panels and their output is supplied to the energy storage system via a boost converter. The principle of operation is introduced followed by steady-state analysis and converter dynamics analysis. The performance of the proposed converter is verified for several case studies with an experimental prototype developed based on 1U CubeSat specifications.

Successive interference cancelation (SIC) has been considered widely for the detection of downlink nonorthogonal multiple access (NOMA) signals. However, the sequential detection inherent to SIC process may introduce additional time delay for certain users, making the SIC unsuitable for communication systems with time delay constraints such as wireless networks that utilize unmanned aerial vehicles or low earth orbit satellites. Therefore, this article considers the performance of NOMA systems using a joint multiuser detector (JMuD), which can detect the signals of all users simultaneously and, hence, reduce the detection time requirements. The performance of the JMuD is evaluated in terms of bit error rate (BER), computational complexity, and processing time and compared to the SIC detector (SICD). The exact BER of the JMuD is derived analytically using quadrature phase shift keying modulation where closed-form expressions are derived for the two- and three-user scenarios for the air-to-ground channel, which is modeled as a Rician fading channels with order statistics. The obtained analytical results corroborated by Monte Carlo simulation confirm that the BERs of the JMuD and SICD are identical; however, the processing time of the SICD is 51% more than the JMuD for several cases of interest.

The output voltage of a photovoltaic panel is greatly affected by irradiance, temperature, shading, etc. A buck–boost type inverter is, therefore, required to accommodate the wide fluctuations in dc voltage. This article proposes a class of single-phase, single-stage buck–boost inverters employing five switches (implemented using power MOSFETs with external fast recovery diodes) to provide buck–boost operation for wide variations in photovoltaic (PV) output voltage. In this article, the proposed inverters are immune from current shoot-through problems associated with voltage source inverters, easing the requirement for PWM dead-times. They also provide a common-grounding feature between the grid-neutral and the negative-terminal of the PV panel, successfully suppressing the PV leakage current. In addition, they provide reactive power support. A simple input boost inductor-based buck–boost inverter is proposed with a wide gain range; other variants are also proposed based on the switched inductor, quadratic boost, and switched coupled-inductor, achieving higher boost voltage inversions with smaller values of duty ratio. Detailed circuit operations are presented based on proposed modulation strategies. Design guidelines/requirements of components and their comparisons are provided for all of the proposed inverters. The theoretical analysis and performance characteristics of all four topologies are experimentally validated using 400 VA laboratory prototype inverters.

Dispatchable renewable generation is essential for 100% renewables power system. It is in the interest of both power system operators and customers since it reduces the need for flexibility and reserve. To this end, battery energy storage systems (BESS) are proposed for integration in the renewable power plant. This paper presents the optimal dispatch unit for a dispatchable hybrid solar‐wind power plant with BESS framework. It achieves optimal dispatchable renewable generation (from dispatchable hybrid renewable (solar‐wind) power plant with BESS, DHRB, operator perspective), subject to operational limits, by exploiting the synergy of wind and solar energy and combining it with storage capability of BESS using two different operation strategies, maximisation of revenues and maximisation of renewables harvesting. A continuous BESS degradation model is incorporated in the proposed rolling‐algorithm‐based‐optimal dispatch unit to improve the accuracy of results. The applicability of the proposed methodology and the performance of the operation strategies are demonstrated using a case study and the operation strategies are compared. Further, the effect of BESS size on its degradation and dispatchable power in a hybrid solar‐wind power plant with BESS are investigated through BESS lifetime. An indicative economic analysis is carried out to provide ground for the extra investment on and sizing of BESS for a dispatchable hybrid renewable power plant.

This paper presents a sparse quaternion‐valued minimization (SQVM) based control technique of a two‐stage grid supportive photovoltaic (PV) power system with power conditioning capabilities. The grid side converter (GSC) is controlled by utilizing an SQVM control technique. The proposed algorithm enables the GSC to mitigate the load harmonics current and provides reactive power compensation at the point of common coupling (PCC). The proposed control is tuned to mitigate the DC offset error, harmonics current and to improve the frequency response of the proposed system. A DC link pre‐predictive is incorporated to improve the dynamic response by reducing the burden on the outer Proportional‐Integral (PI) voltage controller loop. Further, it is used to extract the fundamental component of load currents for generating the reference currents. An adjustable DC link voltage loop is incorporated in the proposed control technique to adapt the PCC voltage variation, which helps in minimizing the losses of the PV system. For real‐time execution of the adjustable DC link voltage concept, the DC link voltage is adapted with a variation in the PCC voltage. The operation and control of the system topology are validated experimentally under various scenarios.

Protection coordination for the microgrid system in both islanded and grid connected modes is considered a challenge for microgrid operation. The variation in short circuit currents in each mode of operation, limitation of protection curves in the relays, and the need for fast and reliable communication are the main challenges tackled in research. Direction overcurrent relays are considered the main protection instrument for the microgrid. However, one protection setting for both (main and backup) operation does not provide a fast-operating time. On the contrary, the dependence on communication to maintain the proper backup protection operation is not a reliable solution for protection system. Therefore, this paper introduces a fast, reliable, and simple protection scheme for secure microgrid operation in both islanded and grid connected modes. In this context, one set of protection settings is optimized and used in both modes of operation. A protection setting consists of two time-dial settings and one pickup current setting for each relay. The proposed design technique minimizes the total operating time for both main and backup relays. As all protection functions are executed in the forward direction, no communication is needed among relays. The proposed scheme is tested and verified on a modified portion of IEEE 30 bus test system equipped with distributed generation units. A comparative analysis is carried out and the results demonstrate superior performance by the proposed scheme in comparison with the dual setting scheme with communication.

This paper introduces a new framework for optimum design and operation of hybrid renewable energy plants (HREP) augmented with battery energy storage systems (BESS). A new renewable energy management system (REMS) is developed comprising three components: 1) Enhanced joint forecasting of wind and solar outputs based on deep neural networks and also multiplicative weights update (MWU); 2) an advanced optimization model for sizing the HREP-BESS components and the policy of BESS operation; and 3) Augmenting the rolling hourly dispatch for HREP-BESS with a novel dynamic ramping limit and a criterion for reduction of deviations from the hour-ahead dispatch schedule. The proposed REMS tool enables maintaining the inter-hourly ramping of the HREP-BESS output within a threshold. In this context, a novel dynamic ramp limit is proposed to minimize the energy curtailment during operation and maximize energy sales to the power grid. The advantage of the proposed REMS tool over the classical renewable energy systems operation scheme is the mitigation of the volatility of renewable energy sources (RES) by suppressing extreme ramping events with minimum curtailment. Moreover, the costs and revenues of the HREP-BESS design and operation are assessed over a 25 years period. The design problem is solved for different scenarios, and the optimal solution always encloses a hybrid mix of renewables where the share of the PV plant can reach up to 37.1% of the total plant size. With the proposed REMS, the curtailment of RES never exceeds 12.9% even when the HREP is operated without a reserve margin. For the selected design, the optimum BESS capacity is 12.9% of the HREP capacity. The number of hours which observe a ramping violation event is 2.4% of the season's length (2184 hours). 99% of all ramping events fall within the defined ramping limits. The use of the MWU method increases the total profit by 2.53% compared with adopting the average forecast.

A high-frequency isolated multilevel cascaded-type bipolar direct PWM ac–ac converter is proposed. By cascading N -unit cells, the converter can produce symmetric bipolar voltage gain of ± ND. It does not require a separate ac source for each unit cell, and can provide higher ac output voltages with multiple levels using low-voltage rating devices, decreasing output voltage harmonics and filtering requirements. Moreover, phase-shift PWM switching is employed, increasing the effective frequency of the output filter, further reducing its requirements. The converter can be utilized as a dynamic voltage restorer (DVR) for grid voltage regulation, with the following features: No need for an external dc source, separate ac sources, and a line-frequency voltage injection transformer. Injection of higher voltage magnitudes than the line voltage, mitigating deep voltage sags. Injection of a negative series voltage to provide compensation for voltage swells. The detailed circuit operation is explained together with component design guidelines and application as DVR. Finally, experimental results are provided using an 800-W scale-down laboratory prototype.

This article proposes a DR program characterized by a novel compensation scheme. The proposed scheme recognizes the different characteristics of curtailment, such as the total length of curtailments within a window of time, or the number of separate curtailment events (i.e., curtailment startup), and compensates the end-user accordingly. The proposed compensation scheme features a piece-wise reward function comprised of two intervals. DR participants receive a onetime reward upfront when they enroll in the DR program and accept a set of predefined curtailment aspects. Curtailment aspects in excess of the agreed quantities are rewarded at a linear rate. This design is tailored to appeal to residential DR participants, and aims to secure sufficient flexibility at minimum cost. The parameters of the smart contract are optimized such that the system’s social welfare is maximized. The optimization problem is modeled as a mixed-integer linear program. Consequently, this article updates the unit-commitment (UC) formulation with the commitment aspects of DR units. The proposed extension to the UC problem considers the critical aspects of DR participation, such as: the total length of interruptions within a window, the frequency of interruptions within a time-window irrespective of their length, and the net energy deviation from the original load profile. Deployment of the smart DR contract in the unit dispatch problem requires translating DR participants’ characteristics to their equivalent aspects in conventional thermal generators, such as minimum up time, minimum down-time, start-up and shutdown costs. The obtained results demonstrate significant improvement in social welfare, notable reduction of curtailed renewable energy and reduction in extreme ramping events of conventional generators.