Explore the vast range of titles available.

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.

Modular multilevel converter (MMC) tends to cause resonance instability in interconnected systems. Current studies on the stability of MMC mainly focus on high-voltage and large-capacity power systems, while the impedance modeling process of MMC ignores the harmonics of the submodule (SM) capacitor voltages and the influence of voltage feedforward control. The applicability of the MMC impedance model with fewer submodules is doubtful. According to the circuit structure and control mode, the AC-side sequence impedance model of the MMC is established, which takes into account the capacitor voltage balance control of submodules and voltage feedforward control. Based on the RT-Lab control hardware-in-loop (CHIL) test platform, the MMC impedance frequency scanning was carried out to verify the accuracy of the impedance modeling method. The influence of control parameters in different frequency bands on the impedance characteristics of MMC was studied. The AC terminal voltage feedforward causes phase lag in the mid-/high-frequency range and increases the risk of resonance. In the low-frequency range, the dynamics and control of capacitor voltages reduce the impedance magnitude of MMC. Using the resonance phenomenon of an MMC connected to a weak grid as an example, the high-frequency resonance mechanism caused by control parameters is analyzed from the perspective of the negative damping effect. The simulation results show that the detailed wideband impedance model can improve the accuracy of the stability analysis results.

The current quality is an important indicator to evaluate the performance of a grid-connected inverter. In practice, many factors including the grid voltage distortion, dead-time effect, non-ideal switches and dc-link disturbances would result in many low-order harmonics in the injected grid current. The inverter with either the typical grid voltage feedforward or the harmonic resonant (HR) control had some difficulties in rejecting the impact of multi-harmonic sources. In this study, the combination of the grid voltage feedforward and the multi-HR control is proposed to suppress low-order harmonics. It is found that all those harmonic sources are classified into two kinds, and a general way is provided to analyse the harmonic rejection of the inverter with the typical or the proposed strategy. The low-order current harmonics of the inverter with different strategies are clearly explained. The comparative analysis, simulations and experiments all indicate that the proposed strategy greatly improves the ability of the inverter to reject the current harmonics induced by multi-harmonic sources as long as the grid feedforward and the resonant control are complementary.

A low-cost position sensorless speed control method for permanent magnet synchronous motors (PMSMs) is proposed using a space vector PWM based four-switch three-phase (FSTP) inverter. The stator feedforward d q -axes voltages are obtained for the position sensorless PMSM drive. The q-axis current controller output with a first order low-pass filter formulates the rotor speed estimation algorithm in a closed-loop fashion similar to PLL (Phase Lock Loop) and the output of the d-axis current controller acts as the derivative representation in the stator feedforward voltage equation. The proposed method is quite insensitive to multiple simultaneous parameter variations such as rotor flux linkage and stator resistance due to the dynamic effects of the PI current regulator outputs that are used in the stator feedforward voltages with a proper value of K gain in the q-axis stator voltage equation. The feasibility and effectiveness of the proposed position sensorless speed control scheme for the PMSM drive using an FSTP inverter are verified by simulation and experimental studies.

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.

To meet the application requirements of flexible power flow control in local power systems across voltage levels, the PFCT circuit topology and its power flow control strategy are studied. A PFCT circuit topology and its equivalent model are proposed. The mathematical modeling for the series and parallel components of the PFCT are established, along with corresponding control strategies. Flexible control of power flow transmission along the line is accomplished by cross-decoupling power flow control and feedforward decoupling control. A simulation model was built by using the MATLAB/Simulink platform to analyze and validate the PFCT’s control of power flow transmission across voltage levels in a typical local power system. A prototype was constructed to validate further the correctness and feasibility of the proposed mathematical models and control strategies.

Piezoelectric ceramic actuators show nonlinear hysteresis characteristics due to material properties. In order to modify the inverse piezoelectric effect as an ideal linear execution, the classical Prandtl–Ishlinskii (PI) model is usually used on compensation by feedforward control. The PI model performs well on the simple hysteresis characteristics. However, when the output requirements are complex, the PI model has uneven compensation accuracy on the complex hysteresis characteristics and cannot achieve the accuracy as same as the simple hysteresis. This paper proposes a simplification of the complex hysteresis: Separated level-loop PI (SLPI) model. Firstly, use a loop separation logic algorithm simplification of the complex hysteresis characteristics to obtain hysteresis single loops with loop levels and vertexes. Secondly, hysteresis characteristics of each loop are independently modeled using the PI model. Finally, the inverse model is reconstructed by the rollback method to restore a positive sequence of the feedforward voltage and then input the feedforward voltage as a compensation to achieve higher and more uniform accuracy. Experiments and discussions show that the SLPI model can effectively improve the compensation results of complex hysteresis characteristics by 50.3%, and the average compensation accuracy difference between single hysteresis loops is reduced by 53.7%.

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.

To mitigate the effects of motor load torque variations on the control performance of a 126 kV high voltage vacuum circuit breaker equipped with a motor driven operating mechanism, this paper presents the derivation of dynamic equations for the motor load torque. These equations, formulated using the Euler-Lagrange equation, Lagrange multipliers, and geometric constraints, are expressed in terms of a single independent variable: the angular displacement of the motor. Utilizing these equations, the load torque can be calculated in real-time using the motor position sensor feedback, and the motor control strategy is optimized through a feedforward method designed to actively compensate for load disturbances. Subsequently, an angular displacement trajectory has been designed to serve as a positional reference for the motor control, with the aim of enhancing the operational reliability of the operating mechanism. Furthermore, comparative control experiments have been conducted in the motor-breaker integrated experimental platform to assess the reduction in the motor’s position tracking error, contact bouncing duration, and mechanical collision duration under the optimized motor control strategy. The obtained experimental results reveal the efficacy of the load torque dynamic equations established and their contribution to enhancing control accuracy and improving the operational reliability of the operating mechanism.

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.