Voltage Decoupling Research Articles

Dual Grid-Forming Control With Energy Regulation Capability of MMC-HVDC System Integrating Offshore Wind Farms and Weak Grids

To integrate weak onshore grids, some grid forming (GFM) control schemes taking advantage of DC voltage synchronization have been proposed for modular multilevel converter-based high-voltage direct current (MMC-HVDC) systems. In these control schemes, the sub-module (SM) capacitor energy is only used for grid synchronization. Since the SM capacitor is an energy storage device, it has the potential to actively regulate the stored energy. To fully exploit the energy management capability of MMC, a dual grid forming control scheme with energy regulation capability is presented in this paper. The proposed control scheme enables grid forming for both onshore and offshore MMC stations. Meanwhile, the capacitor energy of MMCs can be flexibly regulated to provide frequency support for the onshore grid. To verify the effectiveness of the proposed control scheme, case studies are first carried out in a point-to-point offshore wind farms (OWFs) integrated HVDC system. In addition, the frequency support performance is evaluated in a 3-area 4-machine grid integrated with two OWFs-HVDC systems. Finally, a single-terminal three-phase MMC prototype is developed to test the voltage decoupling and energy management capabilities of the proposed control strategy.

DC-link oscillation suppression method based on q-axis voltage compensation of a 180 kW PMSM traction system for urban rail transit

Under certain working conditions, the permanent magnet synchronous motor (PMSM) traction system of urban rail transit shows negative impedance characteristics, which is easy to cause voltage resonance of DC-link and lead to instability of the system. In order to ensure the stability of the system, a DC-link oscillation suppression method based on q-axis voltage compensation is proposed. Firstly, the PMSM traction system and oscillation mechanism of DC-link are analyzed. Secondly, a stable control method based on q-axis feedforward decoupling voltage compensation is adopted to realize the decoupling control of PMSM and the suppression of DC-link oscillation. Finally, the method is verified on a 180 kW PMSM traction system, simulation and experiment verify the effectiveness of the DC-link oscillation suppression method.

Multi-objective optimization of actuators and consensus ADP-based vibration control for the large flexible space structures

In this study, the multi-objective optimization and decision-making for optimal positions of actuators and consensus adaptive dynamic programming (CADP) are investigated to mitigate the vibration of large flexible space structures (LFSS). The optimization of the actuator positions maintains a balance between maximizing actuation efficiency and maximizing input voltage decoupling. Meanwhile, the CADP control method accelerates the attenuation of vibration when agents collaborate in the designed communication topology network. First, the electromechanical coupled dynamic model of the LFSS is built by the finite element method. Subsequently, the multi-objective optimization criteria are proposed, which maximize the actuation efficiency and decoupling of control inputs. Moreover, the multi-objective optimization and decision-making, which is based on the non-dominated sorting differential evolutionary algorithm (NSDE) and technique for order preference by similarity to ideal solution (TOPSIS), respectively, are performed to rapidly find the optimal position of actuators. In addition, the CADP control algorithm is designed and its stability is proven. Finally, for harmonic excitation under multi-frequency superposition, simulation comparisons based on the CADP and adaptive dynamic programming (ADP) are performed. Simulation results verify the effectiveness of the proposed optimization criterion of actuators and the CADP algorithm for vibration mitigation of LFSS.

Distributed Control for the Modular Multilevel Matrix Converter

The modular multilevel matrix converter (M3C) is a direct ac/ac topology and is promising in the medium-voltage high-power application. However, the current M3C prototypes mainly adopt the centralized control structure that may hinder its modularity and flexibility. Based on the new distributed control architecture, the corresponding design principles for the M3C are proposed to realize both the distribution of control tasks and improve the expandability. And in order to reduce the dependence of a real-time communication network, a time-dimension decoupling strategy based on a voltage decoupling and current coupling control algorithm is employed, in which the voltage loop is divided into the input side, output side, and inner circulating decoupling models that are executed in the system controller, while the real-time current loop is established on the coupling abc coordinate frame in each local controller. In order to reduce the influence of communication delay, a novel scheme to replace the direct ac current reference with dc power value and double synchronization phase information is adopted. The controller parameters of the current loop are also designed carefully after frequency decomposition. Finally, an experimental prototype is constructed to verify the feasibility of the proposed control scheme after a series of tests in steady-state and dynamic operations.

Effect of state feedback coupling and system delays on the transient performance of stand-alone VSI with LC output filter

The influence of state feedback coupling in the dynamics performance of power converters for stand-alone microgrids is investigated. Computation and pulsewidth-modulated (PWM) delays are the main factors that limit the achievable bandwidth of current regulators in digital implementations. In particular, the performance of state feedback decoupling is degraded because of these delays. Two decoupling techniques to improve the transient response of the system are investigated, named nonideal and ideal capacitor voltage decoupling, respectively. In particular, the latter solution consists in leading the capacitor voltage on the state feedback decoupling path in order to compensate for system delays. Practical implementation issues are discussed with reference to both the decoupling techniques. A design methodology for the voltage loop that considers the closed-loop transfer functions developed for the inner loop is also provided. A proportional resonant voltage controller is designed according to Nyquist criterion taking into account application requirements. For this purpose, a mathematical expression based on root locus analysis is proposed to find the minimum value of the fundamental resonant gain. Experimental tests performed in accordance to UPS standards verify the theoretical analysis.

Benchmark of AC and DC Active Power Decoupling Circuits for Second-Order Harmonic Mitigation in Kilowatt-Scale Single-Phase Inverters

This paper presents the benchmark study of ac and dc active power decoupling (APD) circuits for the second-order harmonic mitigation in kilowatt-scale single-phase inverters. First, a brief comparison of recently reported APD circuits is given, the best solution that can achieve high efficiency and high-power density is identified and comprehensively studied, and the commercially available film capacitors, the circuit topologies, and the control strategies adopted for APD are all considered. Then, an adaptive decoupling voltage control method is proposed to further improve the performance of dc decoupling in terms of efficiency and reliability. The feasibility and superiority of the identified solution for APD together with the proposed adaptive decoupling voltage control method are finally verified by both the simulation and experimental results obtained on a 2-kW single-phase inverter.

DTC Based Induction Motor Speed Control Using 10-Sector Methodology for Torque Ripple Reduction

A direct torque control (DTC) drive allows direct and independent control of flux linkage and electromagnetic torque by the selection of optimum inverter switching modes. It is a simple method of signal processing which gives excellent dynamic performance. Also transformation of coordinates and voltage decoupling are not required. However, the possible discrete inverter switching vectors cannot always generate exact stator voltage required, to obtain the demanded electromagnetic torque and flux linkages. This results in the production of ripples in the torque as well as flux waveforms. In the present paper a torque ripple reduction methodology is proposed. In this method the circular locus of flux phasor is divided into 10 sector as compared to six sector divisions in conventional DTC method. The basic DTC scheme and the 10-sector method are simulated and compared for their performance. An analysis is done with sector increment so that finally the torque ripple varies slightly as the sector is increased.

Anti-Islanding Detection for Single-Stage Photovoltaic System Based on Passivity

Based on the basic principles of anti-islanding detection, this paper puts forward an anti-islanding (AI) detection method which combined/q-axis voltage decoupling and positive feedback with Euler-Lagrange (EL) model .The proposed method is classified as an passive islanding detection method and it is based on the voltage change at the point of common coupling (PCC) that occurs in islanding .In the method, Add the d-axis decoupling voltage of PCC to the d-axis reference current of the EL model. A simulation study shows that the method is simple and feasible.

Robust Miller Compensation With Current Amplifiers Applied to LDO Voltage Regulators

This paper presents a general methodology for compensating LDO regulators which exploits a current amplifier to effectively multiply the Miller capacitor. After a general theoretical analysis that takes into account both the external and internal loop stability, it is examined the feasibility of applying this kind of compensation in different LDO applications, showing the role of the design parameters and proposing a specific design procedure for each practical cases which differ in terms of load capacitance and the adoption of a decoupling voltage buffer. Simulations and experimental results which validate the methodology are also included.

Multiloop control method for high-performance microgrid inverter through load voltage and current decoupling with only output voltage feedback

This paper proposes a multiloop controller with voltage differential feedback, and with output voltage decoupling and output current decoupling by only using the output voltage feedback. The output voltage differential feedback loop actively damps the output LC filter resonance and thus increases the system stability margin. The decoupling of output voltage and current makes the inner loop equivalent to a first-order system and thus improves the system dynamic response to load disturbance. The pole placement technique has been used here to design the inner loop and outer loop gain, with considering the effect of system control delay. The proposed control scheme possesses very fast dynamic response at load step change and can also achieve good steady-state performance at both linear and nonlinear loads. In addition, it only uses the output voltage as the feedback variable, which reduces the system complexity. The theoretical conclusion has been verified by simulation and experiment results. This method is proved to be an effective solution for voltage control in stand-alone mode of three-phase microgrid inverters.

Vectorial command of an asynchronous motor fed by a photovoltaic generator

In order to promote renewable energy, Tunisia has developed a large program to exploitate photovoltaïc systems (PV) to provide electric power in rural electrification. These needs increase continually following standard of living improvements, from lighting and media communication (radio, TV) to motors, refrigeration and pumping. The fluctuation of solar energy on one hand, and the necessity to optimise available solar energy on the other, it is useful to develop new efficient and flexible modes to control motors. A vectorial control of an asynchronous motor fed by a photovoltaïc system is proposed. In this case, the control of the circulating current becomes an important objective in the algorithm design. This paper presents an efficient current controller scheme that can achieve high accuracy and a fast dynamic response of induction machine. This scheme uses voltage decoupling and proportional integral controller loops (PI). Furthermore, to operate the PV array at its maximum power point for every instant, the PV system must contain a maximum power point tracking controller (MPPT). Good static and dynamic performances were obtained in simulation of the proposed structure.

A deadbeat current controller for field oriented induction motor drives

Accurate stator current control is essential in high performance field orientation-controlled induction motor drives. Any current error degrades the drive's performance in the same way as an incorrectly tuned field orientation. This paper presents an efficient current control scheme that can achieve high accuracy and a fast dynamic response. This scheme uses voltage decoupling and deadbeat control loops. The decoupling controller provides the voltage needed to oppose the motor's back EMF. The deadbeat controller reduces the current error as fast as possible and stabilizes the system. The control law does not require knowledge of the rotor flux and is independent of the field orientation control tuning. Good static and dynamic performances were obtained in both the simulation and experimental verifications. Because the motor leakage inductance and resistance information were required for this control method, the influence of the estimation errors for these parameters was also investigated. The results show that the leakage inductance model error might cause a current ripple. However, this parameter can be tuned to its correct value easily by inspecting the current response.

Interphase power controller with voltage injection

This paper introduces a new family of interphase power controllers (IPC) based on the principle of voltage injection commonly used in phase-shifting transformers (PST). The voltage injection IPC exhibits power (active and reactive) control characteristics similar to previously defined IPCs and retains their inherent qualities: passive control, short circuit limitation and voltage decoupling. It also provides more flexibility for the adjustment of the operating point. Two promising topologies are described in more detail. One of them offers the potential of retrofitting existing phase-shifting transformers into full-fledged IPCs. The application of the IPCs is in flexible AC transmission systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

PARROT: A fiber optic link for particle detectors

The fiber optic technology has been used to build a transmitter-receiver system capable of delivering channeltron or PM tube signals through a few hundred meter span. The intrinsic immunity of optical fibers to e.m. noise has been used to reduce noise problems in an experimental apparatus equipped with two electrostatic analyzers for coincidence (e, 2e) spectroscopy. A coincidence energy separation spectrum of He, used for calibration of the apparatus energy scale, has been measured using fiber optic links instead of coaxial cables. The system was completely built using cheap and easily available commercial components. The results show that fiber optic links could become a viable technique for noise reduction, high voltage decoupling and low temperature calorimeters signal transfer.