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This article presents a new optimized hybrid modulation and control systems based on symmetrical and asymmetrical operations of a dual-active-bridge converter to minimize the transformer root-mean-square (RMS) current and extend the zero-voltage-switching (ZVS) range. Various modulation modes are analyzed, and their corresponding power, RMS current equations, and soft-switching conditions are derived. The RMS equations are minimized using the multivariable optimization method, and the corresponding parametric equations are obtained. A hybrid control system has been proposed to regulate the battery current, to ensure smooth inductor current transients, and eliminate the need for a blocking capacitor on the low-voltage side. Using asymmetrical-extended-phase-shift and conventional symmetrical modes, a wider ZVS range is achieved compared to advanced modulations, such as triple phase shift. Moreover, in the low-power region, an optimized RMS current is achieved by applying an optimum dc voltage on the blocking capacitor at the HV side. Hybrid modulation that extended ZVS range and improved RMS current makes the proposed approach a suitable modulation for high-frequency applications and also high-voltage or high-current applications with high $C_{\text{oss}}$ losses. The efficiency, ZVS operation, and control system performance are validated by a 5 kW converter. [ABSTRACT FROM AUTHOR]

This article presents approaches for efficient modeling and systematic design of enhanced phase-locked loop (ePLL) structures. While different ePLL structures have found a wide acceptance for various applications, their modeling and design aspects have not been fully and systematically reported in the existing literature. This article fills this gap by presenting an effective modeling approach for both the single- and three-phase ePLLs. The models are derived with a view to minimize the number of parameters to be adjusted to simplify the design. The models are then used to develop systematic design algorithms for their parameters. As an example, application of the ePLL in a grid-connected inverter is formulated and studied through simulation and experimental results. The design and simulation files are made available. [ABSTRACT FROM AUTHOR]

This article proposes a controller for dc–dc converters to achieve fast load-transient responses. The controller is developed for both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) of operation. The main idea is developed for buck converters, but it is shown that the proposed controller can be applied to other topologies, such as the noninverting buck–boost converter. The controller derivation, analysis, and experimental verifications are provided in both CCM and DCM, and its performance is compared with other methods. The main advantage of the proposed controller is that it minimizes the recovery times associated with load-transient responses in dc–dc converters while maintaining component sizes and other system parameters within the acceptable range. The proposed controller can be used to minimize load transients in electronic portable devices and electric vehicle charging. [ABSTRACT FROM AUTHOR]

Steady-state models of power converters that provide accurate closed-form expressions for converter waveforms are extremely valuable for converter analysis and design, and enable comparative evaluation of different converter topologies. An obstacle in the development of such models is the inherent nonlinearity of switching power converters. This article presents a systematic procedure to model a broad class of power converters using ordinary differential equations (ODEs) with periodic and discontinuous inputs, and provides an approach to determine closed-form expressions for their steady-state waveforms. The formal mathematical proof of the proposed approach to finding closed-form expressions for the steady-state solution of ODEs with periodic and discontinuous inputs, Laplace-based theorem (LBT), is also presented. The presented modeling procedure and LBT, collectively called Laplace-based steady-state modeling (LBSM), serves as an effective analysis and design tool for power converters. The value of LBSM is demonstrated by using it to obtain closed-form expressions for the steady-state waveforms of different types of converters. In particular, two commonly used topologies—the series resonant converter and the phase-shift converter—are analyzed and compared using LBSM and their optimum operating conditions and applications are discussed. The converter waveforms, soft switching ranges and other characteristics obtained using LBSM are also validated through simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper presents Weighted Dynamic aggregation (WD agg) method to obtain an equivalent Wind Turbine Generator (WTG) for an induction machine-based wind farm using its dynamic model. The suggested approach obtains the equivalent d-q model of the induction generators considering the contribution of each unit in the model. The challenges in the aggregation of a large-scale wind farm are the variation of wind speeds at different zones and differences in the WTGs parameters. Compared with the existing methods such as Full aggregation (Full agg), Zone aggregation (Zone agg), and Semi aggregation (Semi agg), the suggested WD agg method provides an accurate single unit equivalent model for a large-scale wind farm while taking into account various wind speed zones and unequal WTG parameters. The proposed method is evaluated through time-domain simulation of a 4-WTG and a large-scale 20-WTG Doubly-Fed Induction Generator (DFIG) wind farms and their aggregated models. These simulations cover combinations of different wind speeds and WTGs parameters. Also, a 4-WTGs fixed-speed wind farm is studied to show the generality of the proposed method. Comparing WD model with the detailed response of the wind farm verifies the accuracy of the method in both steady-state and transient behaviors. [ABSTRACT FROM AUTHOR]

This paper proposes a robust current controller (CC) and dc-link voltage controller based on $\mu $ -synthesis and $H_{\infty }$ method, respectively, for a single-phase photovoltaic (PV) converter with an LCL-filter under weak grid operation. The $\mu $ -synthesis CC guarantees system robustness against weak grid uncertainties such as grid impedance variations and voltage harmonics. Moreover, the controller compensates the system delays arising from the calculation, pulsewidth modulation, and zero order hold, as well as delay uncertainties. The CC only uses the grid current feedback which eliminates the requirement for additional loops or state measurements utilized in partial or full state-feedback systems. In addition, the $H_{\infty }$ dc-link voltage controller minimizes the bus voltage fluctuations caused by variations of PV system power generation. Also, the controller ensures system robustness against such power variations, which conventional controllers fail to perform. Moreover, power decoupling is achieved by the control system without any auxiliary circuit. In addition, the stability and robust performance of the phase-locked loop in a weak grid with major impedance changes is verified. Simulation and experimental results prove the superior performance of the proposed controllers in both cases of a nominal system and a system with deviated parameters. [ABSTRACT FROM AUTHOR]

A virtual synchronous machine (VSM) approach is proposed to integrate inverter-based distributed energy resource units into the power and energy system. VSMs emulate the model of a synchronous machine in the inverter's controller. Among different aspects, emulating the damper windings or devising an alternative damping strategy is critical. The damper has a major stabilizing effect against system disturbances and change. An effective damping method to improve the VSM responses is proposed in this paper. It is shown that the proposed method offers two degrees of freedom, which allows flexible adjustment of response damping without compromising the inertial response. Mathematical analysis, comparative simulations, and experimental results are presented to prove and validate this claim. [ABSTRACT FROM AUTHOR]

A new distributed control scheme and charge flow analysis is presented for voltage balancing of series connected battery cells using nondissipative modular power electronics. Each modular bridge is connected across two battery cells using a high frequency transformer and an asymmetrical half-bridge. This results in using one switch and one diode per battery cell. Intrabridge charge transfer equalizes the voltage of two battery cells within a module using coupled transformer windings. Each modular bridge is connected to adjacent bridges by connecting transformer windings within each module. This allows interbridge charge transfer and the balancing of pairs of battery cells, both within adjacent bridge modules and modules more removed. The proposed controller uses a distributed control strategy whereby the control of each modular bridge monitors its own battery cell voltages and also those of adjacent bridges, thus reducing the number of feedback sensors. Detailed analysis is presented that quantifies the flow of charge between a number of series connected battery cells ($ N$ battery cells). A per-unit design methodology is used to illustrate the system charge flow characteristics. Simulations, design guidelines and experimental results are presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

A fast and robust fixed switching frequency peak current controller for DC–AC converters is presented. The proposed method tends to mimic the switching behavior of pulse width modulation (PWM) techniques, so it features all the advantages of peak current controllers (such as simplicity, fast transient, and optimum dynamic response), with the superiority of fixed switching frequency and harmonic free output. The proposed method is a generalized approach that can be applied to different PWM schemes. The method is specifically elaborated for single-phase distributed generation applications, using various inverter topologies and mimicking different PWM schemes. Moreover, adaptive bands are proposed to provide active damping for the controller, to extend use of the proposed method for inverters with LCL output filters. Feasibility and performance of the controller is shown by means of simulations and experiments. [ABSTRACT FROM AUTHOR]

The sparse modular multilevel converter (MMC) is a new type of high-voltage ac/ac MMC topology suitable for high-power applications. It is based on an alternative configuration of half/full-bridge submodules, and voltage unfolder stages on each side of the converter. This topology has fewer components compared to conventional approaches and as an additional benefit, more than half of the switches operate under the soft switching condition. A comprehensive control strategy is proposed to ensure capacitor voltage balancing while exploiting the full power capability of the converter. A modified unfolder is also suggested to eliminate the inherent zero-crossing circulating current. The effectiveness of the proposed control strategy is confirmed by simulation and experimental results. [ABSTRACT FROM PUBLISHER]

An alternative transmission line design method is proposed that reduces the required conductor-to-ground clearance by injecting third harmonic voltage. In this method, third harmonic voltage is injected to the line, such that the peak amplitude of phase voltages is reduced by 13.4% while the fundamental component remains intact. The injected third harmonic voltage does not influence the load or generation sides. The objective is to utilize the insulating strength of the conductor-to-ground clearance almost continuously rather than only during the crest voltage, as opposed to conventional ac lines. With this approach, for the same fundamental voltage level, the proposed line requires lower conductor-to-ground clearance. This could considerably reduce the line construction capital investment by using shorter transmission towers. Furthermore, the existing ac lines could be upgraded with this method to increase their ground clearance, if desired. Injection of third harmonic voltage can also increase the loadability of existing ac lines, if the new phase-to-phase clearance is met. In this paper, the operation of a power transmission line with injected third harmonic voltage and practical consideration for its implementation are studied. [ABSTRACT FROM AUTHOR]

A new bidirectional multilevel converter topology called the sparse modular multilevel converter suitable for high power ac/ac applications is presented. The proposed topology has fewer insulated-gate bipolar transistor switches and capacitors compared with conventional approaches. Moreover, a salient feature of the proposed topology is that more than half of the switches are operating in soft switching conditions, which considerably decreases the switching losses of the converter. The theoretical calculations and simulation results are provided to verify the feasibility of the proposed topology. [ABSTRACT FROM PUBLISHER]