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Voltage source converter‐high voltage direct current (VSC‐HVDC) connections have become a new trend for long‐distance offshore wind power transmission. In order to facilitate the derivation of the feedforward DC voltage control based fault ride through (FRT) technique, this chapter describes the model of a VSC‐HVDC‐connected offshore wind power plant (WPP) with an external grid. It proposes a feedforward DC voltage control based FRT technique to control the AC voltage at the WPP collector network during grid‐side faults. Time‐domain simulations have been used to verify the efficacy of the proposed feedforward DC voltage control based FRT technique for VSC‐HVDC‐connected WPPs. Time‐domain simulation results shows that the proposed FRT scheme can successfully enable VSC‐HVDC‐connected WPPs to ride through balanced and unbalanced faults in host power systems, as well as faults in the WPP collector system, with a fast and robust response.

This article proposes a design of a multiphase BUCK-type DC-DC voltage converter. This buck converter allows for a high input voltage range from 3 V to 22 V and integrates two voltage modes, namely pulse width modulation control and input feedforward synchronous buck PWM control, to control dual independent voltage regulators or two-phase single output regulators. This type of step-down converter adopts multiphase cascade technology, which can effectively reduce output voltage ripple and increase output current. Multiphase cascade technology utilizes the controller to output ripples with different phases, interleaving and paralleling the ripple, ultimately reducing the ripple and improving the conversion efficiency of the controller with high stability.

There are many studies that focus on extracting harmonics from both DC and AC sides of grid-interfaced photovoltaic (PV) systems. Based on these studies, the paper introduces an efficient method depending on hybrid DC voltage, and an active and reactive power (DC-V PQ) control scheme in a single-stage three-phase grid-interfaced PV system. The proposed scheme is designed to regulate DC voltage to minimize power loss and energy share between the network reconfiguration and the utility grid. Moreover, the technique is more effective at dealing with uncertainty and has higher reliability under various operating scenarios. These operations are the insertion of linear load 1, nonlinear load, and linear load 2. Moreover, a novel objective function (OF) is developed to improve the dynamic response of the system. OF is coupled with a particle swarm optimization (PSO) algorithm and a gradient optimization (GBO) algorithm. The analysis and the comparative study prove the superiority of GBO with counterfeits algorithm.

The next-generation electric locomotive drive system has the problem of double grid frequency ripple voltage in the DC side of a single-phase PWM rectifier. In this paper, the intermediate stage dual-active-bridge DC-DC converter is studied, and an H ∞ loop shaping ripple voltage suppression control strategy is proposed to restrain the harmonic voltage and optimize the dynamic and robust performance of the closed-loop system. Firstly, the mathematical model of the DAB closed-loop control system with fluctuating input voltage is established. Then, based on the H ∞ loop shaping control theory, the dynamic performance, the ability of ripple voltage suppression, and the robust performance of the system are analyzed in the frequency domain. According to the results, a reasonable compensator is selected to reconstruct the magnitude frequency characteristic curve of the nominal system. After reconstruction, the solution of the robust stability margin of the corrected object is transformed into the H ∞ robust control problem under the coprime factor uncertainty. The suboptimal H ∞ robust controller is solved to obtain the best robustness boundary of the constructed system. Finally, the H ∞ loop shaping ripple voltage suppression controller is obtained by combining the H ∞ controller with the compensator. The experimental environment is set up in MATLAB-Simulink software. Compared with the traditional voltage loop control method and the input voltage feedforward control method, the dynamic performance of the proposed control strategy is slightly improved, and while within the allowable robust boundaries of the system, it has better ripple voltage suppression performance. When the system magnitude frequency curve is outside the tolerant robust stability margin, the ripple voltage suppression performance fails, but the harmonic content of output voltage is still far less than the other two control methods. The experiment results also prove the correctness of the theoretical analysis and that the proposed control method is effective and proper.

Renewable energy has the advantages of renewability and high temperature and has great potential for development, but its instability limits its large-scale promotion. Aiming at the stable operation of the new energy power system and ensuring the safe and reliable operation of the power grid, this project defines the basic topology of the variable multiple DC/DC converter according to the idea of switching circuit parallel factor or reducing ripple under each duty cycle. Secondly, the system structure under the boost mode is modeled, and the system is optimized by the combination of a single closed-loop current balance and duty cycle feedforward control. Finally, the model is simulated, and the results show that the method is correct and reasonable.

With the increasing importance of power accumulator batteries in electric vehicles, the accurate characteristics of power accumulator batteries have an important role. In order to evaluate the power accumulator battery, battery charging and discharging is indispensable. In this article, a H-bridge bidirectional DC-DC converter is presented which can charge and discharge the battery with different voltage levels and one of the merits of this topology is that a wide output voltage range can be easily achieved. In the control part, a proportional-integral (PI) control strategy is adopted to ensure a stable and reliable operation of the converter. Furthermore, compared with the PI control strategy, a duty ratio feedforward control is utilized to obtain the rapid current dynamic response. In this article, firstly, the system configuration for battery charging and discharging is introduced, then the operating principles and mathematical model of the DC-DC converter are analyzed and derived. Secondly, for bidirectional DC-DC converters, the PI control method and duty ratio feedforward control method are put forward and designed. Finally, the simulation model is established based on PSIM software and the experiment platform is also built in lab. The results of the simulation and experiment research show that the H-bridge bidirectional DC-DC converter can operate reliably and stably during the charging, discharging and power flow reverse modes. In addition, the dynamic response of the charging and discharging current can also be further improved by introducing the duty ratio feedforward control method.

The dynamic performance of the DC bus significantly influences the impedance characteristics of MMC and the system stability in a high-voltage direct current system. However, most of the existing MMC-HVDC system stability research simplifies the DC side as an ideal voltage source and ignores the impacts of voltage feedforward control, which affects the accuracy and practicability of stability analysis. In this paper, a sequence impedance model considering both DC voltage control and voltage feedforward control is developed, and the necessity of considering DC control and voltage feedforward control for MMC-HVDC stability analysis is illustrated. Then, the impact of control parameters on MMC-HVDC impedance is discussed, and the boundary conditions of control parameters are also derived. Finally, a method of control parameters design and impedance optimization for MMC-HVDC based on the stability boundary is proposed. Compared to the traditional optimization method, the system stability is further improved by the impedance optimization method proposed this paper.

The low-harmonic (LOH) voltage of the DC link of three-phase voltage source converter (VSC) requires a large aluminum electrolytic capacitor for suppression under nonlinear AC current. Consequently, this work proposes an active decoupling control method combining DC-link LOH voltage closed loop and LOH current feedforward based on a DC–DC converter. This methodology effectively transfers the DC-link LOH voltage to the smaller-sized decoupling capacitor in the DC–DC converter, thereby reducing the number of capacitors required to stabilize of the VSC DC-link voltage. This work first investigates the relationship between the DC-link LOH voltage and the VSC nonlinear current. Second, a mathematical model for the decoupling capacitor voltage is derived, indicating that its voltage form is complex under nonlinear AC current, making direct voltage control arduous. Subsequently, the principle and design process of the proposed active decoupling control strategy are analyzed in detail. A dedicated fast-response filter structure is also utilized to extract the feedback LOH voltage and feedforward LOH current in the DC link. Meanwhile, a simple control strategy for the DC component of the decoupling capacitor voltage is proposed to improve the utilization of the decoupling capacitor. Finally, the effectiveness and correctness of the method are experimentally verified.

In this paper, a sample voltage dead-beat control based on differentiative voltage prediction (DVP) and switching-cycle extension (SCE) is presented to achieve optimal transient response for DC-DC converters under discontinuous conduction mode (DCM) operation. Firstly, to improve load transient response, a DVP method is proposed to estimate the load. With the estimated load, the controller realizes load current feedforward and thus improves the transient response with a wide load range. Secondly, an SCE strategy is proposed to enlarge the output current range and output voltage slew rate, both of which have limited value under conventional digital pulse width modulation (DPWM). When the output current reaches the limited value, the proposed strategy increases the switching cycle to enlarge the current range without losing DCM operation. Finally, combining DVP with SCE, the converter not only achieves optimal response in large signal transients, but also doubles the load range in DCM operation.

This research delves into the comparative effectiveness of two MPPT strategies within wind energy conversion systems that utilize a self-excited induction generator (SEIG). The first strategy is a hybrid approach that integrates variable step size perturb and observe (VSS-P&O) with feed-forward artificial neural network (FF-ANN) control, while the second is the conventional FF-ANN-based MPPT method. We investigate the limitations associated with VSS-P&O, such as its susceptibility to environmental conditions and wind speed fluctuations, which can result in suboptimal tracking accuracy. By combining the duty cycles produced by both techniques and applying them to a DC-DC boost converter, the hybrid MPPT method offers a promising solution to alleviate these limitations. Through extensive simulations conducted in MATLAB/Simulink under various operating conditions, we assess the performance of both strategies. Our analysis indicates that the hybrid approach not only enhances tracking accuracy and convergence speed but also improves system stability compared to the standalone FF-ANN-based MPPT method. These findings highlight the potential of hybrid MPPT solutions in overcoming the constraints of traditional variable step size P&O algorithms, thus contributing to the development of more efficient and dependable wind energy conversion systems (WECSs).