Double Closed-loop Control Strategy Research Articles

An Electromagnetic Var Compensator Suitable for Wind Power Access and Its Control Strategy

As the proportion of large-scale wind farms and distributed wind power connected to the power grid increases annually, the effects of their intermittent and random characteristics on the active and reactive power fluctuations of the power grid are becoming increasingly evident, causing frequent voltage fluctuations at the grid-connected point. To solve these problems, this study proposes a new topology of an electromagnetic var compensator (EVC) based on a rotary phase-shifting transformer (RPST). The EVC can work under capacitive and inductive conditions to compensate for inductive and capacitive power, respectively. In accordance with the parallel steady-state mathematical model of the EVC, a double closed-loop control strategy with high precision and considerable robustness is proposed for the EVC on the basis of instantaneous reactive power theory. Finally, simulations show that the topology of the proposed EVC exhibits bidirectional and continuous adjustment capability that can meet the reactive power compensation requirements of power systems with a high percentage of wind power. Compared with the existing reactive power compensation device, the EVC exhibits the advantages of high voltage, large capacity, low cost, strong impact resistance, and good tolerance, imbuing it with great prospects for development.

Error allocation model and coordination control for stringer–skin T-shape structure welding robot with multiple manipulators

A new kind of 18 degrees of freedom gantry robot with multiple manipulators could be used to complete the double-sided laser beam welding of stringer–skin T-shape structure for aircraft skin. The coordination control combined with error allocation model analysis is proposed to improve the stability and accuracy of the robot in this article. Firstly, the error model of the stringer–skin T-shape structure welding robot end effectors is analyzed. The score of the robot end effectors position error caused by each joint is obtained. Secondly, according to the path-points transformation matrix of the local coordinate system relative to the base coordinate system, the desired position of stringer–skin T-shape structure welding robot end effectors is calculated to be the input of the control model aiming at the dual-beam laser welding process. Then, the double closed-loop control strategy is proposed for stringer–skin T-shape structure welding robot coordinated motion on the basis of the end error analysis results and proportional-integralderivative (PID) method. Finally, ADAMS and MATLAB are used to establish a co-simulation platform to verify the effectiveness of the proposed coordination control strategy.

Control Strategy of Flywheel Energy Storage System Based on Primary Frequency Modulation of Wind Power

As a form of energy storage with high power and efficiency, a flywheel energy storage system performs well in the primary frequency modulation of a power grid. In this study, a three-phase permanent magnet synchronous motor was used as the drive motor of the system, and a simulation study on the control strategy of a flywheel energy storage system was conducted based on the primary frequency modulation of wind power. The speed and current double closed-loop control strategy was used in the system start-up phase, and the power and current double-closed-loop control strategy were used in the power compensation phase. The model reference adaptive control was used to accurately estimate the speed and position of the rotor. The system compensates for the wind power output by using a wind turbine in real-time and conducting simulation experiments to verify the feasibility of the charge and discharge control strategy. At the same time, it can be verified that the flywheel energy storage system has a beneficial effect on wind power frequency modulation.

Research on LCL-type three-phase photovoltaic grid-connected inverter based on passive damping

The traditional LCL filter has resonance phenomenon in the working process of three-phase photovoltaic grid-connected inverter system. Based on the analysis of the frequency characteristics of LCL filter equivalent circuit before and after the introduction of passive damping resistor, it is concluded that the resonance of the system can be suppressed after the introduction of passive damping resistor. In the meantime, the current double closed-loop control strategy used in the system is introduced in detail. Finally, the simulation model is built by Matlab/Simulink simulation platform to verify the feasibility of the research method of LCL-type three-phase photovoltaic grid-connected inverter based on passive damping.

Model predictive direct power control scheme for Vienna rectifier with constant switching frequency

Model predictive direct power control (MPDPC) has strong robustness and fast dynamic response, so it is widely applied in the control system of grid-connected converter. However, the traditional FCS-MPC bears with variable switching state, which will reduce the current tracking accuracy, accidentally produce current ripple and electromagnetic noise. Here, a double closed-loop control strategy with constant switching frequency based on optimal switching sequence synthesis of model predictive direct power control (MPDPC-CF) in the inner loop and SMC control in the outer loop is proposed for the non-linear system of Vienna rectifier. Firstly, the Vienna rectifier is modelled to obtain the predicted values of input power. Then, the given values of active power and reactive power are obtained through the outer loop. Three adjacent voltage vectors with the lowest cost function in the sector are selected to synthesize the optimal voltage vector, and the pulse time of the corresponding vector is calculated according to the cost function of the voltage vector. To verify the correctness of the theoretical analysis, the Vienna rectifier is taken as the research object, and the comparison with the traditional MPDPC shows that the proposed constant frequency model predictive control has good steadystate and dynamic performance.

Research on control strategy of VIENNA rectifier based on electric vehicle DC charging module

Because the VIENNA rectifier has fewer switching devices, a high power factor and no need to set dead zone time, the front rectifier of the DC charging module of ev mostly uses VIENNA circuit. However, the DC charging module has higher requirements on the dynamic response capability and stability of the VIENNA rectifier system. The traditional PI double closed loop control strategy has poor dynamic response capability. For this reason, a hybrid control strategy of PI control for current loop and sliding mode control for voltage loop is used to control the VIENNA rectifier to improve the dynamic response and stability of the system. Finally, through the simulation of the rectifier circuit, and the comparison of the simulation results, it can be proved that the dynamic response ability and stability of the hybrid control strategy is relatively good. Finally, a simulation model of VIENNA rectifier is built, and the hybrid control strategy is proved to have good dynamic performance and stability by comparison.

Computer Simulation Research of MMC Control in DC Power Network Using RTDS

With the development of DC power network, MMC has become an important AC/DC converter. MMC adopts the basic double closed-loop control composed of inner loop current control and outer loop power control. The modulation strategy adopts the nearest level approximation modulation and the capacitor voltage sequence method to ensure the capacitor voltage equalization of the sub-modules. The circulation suppression strategy can suppress the internal circulation of MMC. Finally, the simulation model of MMC was built based on RTDS, and the double closed-loop control strategy and circulation suppression strategy of MMC were verified.

A variable inductor based harmonic filter design for multi-phase renewable energy systems with double closed-loop control

Compared to L- or LC- type filters, LCL-type filters are superior in high-frequency harmonic attenuation ability. But the filtering inductors are designed with fixed values in traditional principles, which aim to limit the harmonic amplitude at the rated power. However, power converters may have to operate under load-shedding conditions due to the intermittent of both renewable energy and power consumers, which will worsen the harmonic issue on account of a skimpy filtering inductance. In this paper, in order to adapt the light-load conditions to a certain degree, an LCL-type filter with a variable converter-side inductor is designed for a multi-phase inverter system. The variable inductor can obtain about four times inductance at low currents compared to the inductance at the rated power. Meanwhile, a systematic double closed-loop control strategy is applied based on the provided extended coordinate transformation theory in multi-phase system, which can be generally applied in any n-phase systems. And in order to meet steady-state performance requirements of the system with the variable inductor, a system calibration method is proposed and introduced to design the controller parameters. Taking a five-phase inverter as an example, feasibility and validity of the proposed scheme have been verified based on the finite-element analysis (FEA), PLECS simulation platform and practical experiments.

Double Closed-Loop Compound Control Strategy for Magnetic Liquid Double Suspension Bearing

As a new type of suspension bearing, the magnetic liquid double suspension bearing (MLDSB) is mainly supported by electromagnetic suspension and supplemented by hydrostatic support. At present, the MLDSB adopts the regulation strategy of “electromagnetic-position feedback closed-loop, hydrostatic constant-flow supply” (referred to as CFC mode). In the equilibrium position, the external load is carried by the electromagnetic system, and the hydrostatic system produces no supporting force. Thus, the carrying capacity and supporting stiffness of the MLDSB can be reduced. To solve this problem, the double closed-loop control strategy of “electromagnetic system-force feedback inner loop and hydrostatic-position feedback outer loop” (referred to as DCL mode) was proposed to improve the bearing performance and operation stability of the MLDSB. First, the mathematical models of CFC mode and DCL mode of the single DOF supporting system were established. Second, the real-time variation laws of rotor displacement, flow/hydrostatic force, and regulating current/electromagnetic force in the two control modes were plotted, compared, and analyzed. Finally, the influence law of initial current, flow, and controller parameters on the dynamic and static characteristic index were analyzed in detail. The results show that compared with that in CFC mode, the displacement in DCL mode is smaller, and the adjustment time is shorter. The hydrostatic force is equal to the electromagnetic force in DCL mode when the rotor returns to the balance position. Moreover, the system in DCL mode has better robustness, and the initial flow has a more obvious influence on the dynamic and static characteristic indexes. This study provides a theoretical basis for stable suspension control and the safe and reliable operation of the MLDSB.

Research on Double Closed-Loop Control Strategy of Contactors Based on Flux Linkage Observers

In this article, a double closed-loop control structure of a contactor is proposed for the first time, in which the outer flux linkage loop controls the inner current loop to retain the merits of current closed-loop control while avoiding its defects. A voltage integral flux linkage observer is designed in the making process of the contactor. In the closing process of the contactor, the state space expression of the contactor is given, and the closed-loop flux linkage observer is formed by reconstructing the flux linkage variable. The observed flux linkage is used as the closed-loop return signal to realize flux linkage closed-loop control of the contactor in the making and closing processes. This control scheme can realize self-adjustment of the coil current; thus, contact bounces are inhibited. Meanwhile, whether the movable core is closed in place is judged according to the proportional relationship between the flux linkage and the coil current in the closing process. Finally, the feasibility of the proposed scheme is verified by simulation and experiment.

Development of Double Closed-loop Vector Control Using Model Predictive Control for Permanent Magnet Synchronous Motor

Vector control has been widely used to manipulate the permanent magnet synchronous motor (PMSM), in which the traditional double proportional integral (PI) controllers have commonly been utilized. However, it is difficult to set the suitable parameters of PI and maintain the PMSM performance under the different operating regimes. In order to solve these problems, a double closed-loop model predictive control (MPC) strategy based on the vector control has been presented for PMSM in this paper. Firstly, a simplified discrete model of PMSM is established in the d-q coordinate system without considering the interference. Then, the MPC is developed to substitute the PI controller in the speed-loop and the q-axis current-loop, respectively, and a double closed-loop MPC control system is formed. Finally, some case studies are carried out. The simulation and experimental results demonstrate that the presented MPC strategy improves the dynamic and steady-state performance of PMSM.

Research on Control Strategy of Grid-side Converter of Permanent Magnet Direct-drive Wind Turbine

In order to make the permanent magnet direct-drive wind turbines stable and grid-connected operation, a double closed-loop control strategy based on grid voltage-oriented vector and current decoupling is proposed. First, the topology of the grid-side converter of the wind turbine is determined, then the mathematical model of the control strategy is derived, and the parameters of the PI regulator are calculated. Finally, the control strategy is verified by the simulation results. Through the analysis of the experimental results, it is found that the control strategy can achieve the functions of stabilizing the DC bus voltage of the fan and controlling the input power factor, ensuring the stable operation of the fan.

A Design of Three-level Inverter Based on PCI Control

To solve the problem that the PI-controlled three-level inverter can’t achieve zero steady-state error on AC, a closed-loop control scheme using the PCI controller is proposed. The voltage and current double closed-loop control scheme is adopted. The circuit of diode-clamped three-level inverter is selected as the controlled object. And the PCI controller is designed. The zero steady-state error of three-level inverter based on the PCI control is analyzed in detail. Finally, the closed-loop control system of three-level inverter is simulated on the MATLAB/Simulink platform. The results show that the PCI control has good dynamic response ability and can accurately track various sudden loads. And then the correctness of theoretical analysis is verified.

Simulation Design of Single-phase AC Electronic Load

With the development of power electronics technology, a variety of power supplies are used in people's production and life. The characteristics of the power supply will greatly affect production and life. Therefore, it is necessary to conduct strict tests on the power supply. The traditional load has the disadvantage of consuming a lot of energy, and the AC electronic load solves the disadvantages brought by the traditional load.This paper takes single-phase AC electronic load as the research object. Based on the overall scheme design and topology research of the power electronic load system, the energy-consuming power electronic load is simulated first, the simulation model is constructed, and the main circuit is designed. Parameter, realize the load simulation function; further carry out the simulation research on the single-phase energy-fed power electronic load, the current generation unit design adopts PI+ repetitive control strategy, and the energy feedback unit adopts double closed-loop control strategy. After testing, the simulation current generation and energy are realized. The feedback function completes the overall simulation design of the single-phase AC electronic load.

Research on Boost Converter in Photovoltaic DC Boost Collection System

With the development and utilization of renewable energy, the DC collection of photovoltaics has solved the difficult problem of photovoltaic transmission, and the research of high-voltage and high-power converters has become the key. The boost full-bridge isolated converter (BFBIC) is used as the basic boost module, and the voltage level of the DC transmission line is reached through the independent input of the photovoltaic array and the parallel output of the boost converter. Moreover, after analysing the working principle of BFBIC and introducing the control transfer function of the boost module, this paper combines the principle of maximum power point tracking (MPPT), and adopts the classic double closed-loop control strategy. Finally, the simulation model is built in RTDS. By considering the operation of the system under the conditions of constant irradiation and changing irradiation, the simulation results verifies the feasibility of the system.

EMI Noise Reduction for the Single-Phase Grid-Connected Inverter With A Modified Harmonic Filter Design

Harmonics and conducted electromagnetic interference (EMI) are two main issues in grid-connected inverter system. In this article, a modified LCL-LC harmonic filter is structured to strengthen its EMI suppression ability. Considering the common mode and differential mode EMI propagation paths, the traditional LCL-LC filter is split into a symmetrical topology, and with the midpoint of the split filtering capacitors connected to the midpoint of the dc-link capacitor. Compared to the traditional LCL-LC filter, the modified one can maintain the satisfied harmonic attenuation ability and strengthen the EMI suppression. Also, a double closed-loop control strategy is employed to solve the severe resonance problem caused by the harmonic filter. Moreover, a system calibration method is proposed and introduced to design the controller parameters to improve the high-order grid-connected system's stability. A comprehensive analysis and discussions concerning the traditional and modified LCL-LC filters are conducted in simulation and experiment on a 2 kW/220 V/50 Hz single-phase grid-connected inverter. The results have verified the feasibility of the proposed design method, and shown the superiority of the modified LCL-LC filter and active damping strategy in EMI mitigation. Besides, the weight and volume of the harmonic filter can be significantly reduced through this strategy.

Research on the Control Method of UPS Inverter Circuit Considering Additional Filtering Branch

Improving the electric power quality of the Uninterruptible Power Supply (UPS) is an important part of ensuring the reliability of the power system. In order to optimize the output voltage waveform of the UPS, a filtering branch can be added to the existing UPS inverter circuit. This paper studies the circuit control problem after adding the RLC filter branch in the UPS inverter circuit. Through the analysis of the inverter circuit directly considering the added filtering branch, the system state function of the circuit is constructed. A double closed-loop PI control strategy is designed to control the inverter circuit, and the effectiveness of the method is verified by simulation. Using the method in this paper, the output of the inverter circuit with the added filter branch can reach a stable state quickly. The research conclusions of this paper are helpful to improve the output power quality of UPS.

Research on Topology, Control and Simulation of DVR

Dynamic voltage restorer (DVR) is a series compensation device with energy storage device, which can compensate reactive power and active power. DVR is composed of power module, action module, control module and sampling module. The core of the research lies in its topology and control strategy. This paper starts from the above two aspects, studies the working principle and structural characteristics of the dynamic voltage restorer, and analyzes the topological structure and the function of the structure of the dynamic voltage restorer. A voltage and current double closed-loop control strategy is proposed, which can effectively compensate the transient voltage. A DVR model is built in Matlab/Simulink, and power failure and three-phase short circuit are simulated. A double closed-loop control strategy based on voltage and current is applied. The simulation results show the feasibility and effectiveness of the control strategy.

Sliding mode and predictive current control strategy of the three-phase Vienna rectifier

This study involves the design and implementation of a novel double closed-loop control of the three-phase Vienna rectifier. To achieve the unit power factor operation of the rectifier and reduce the harmonic content of the grid side, the double closed-loop control strategy is proposed on the basis of the voltage control of the outer loop and the current control of the inner loop. The voltage outer loop adopts the sliding-mode variable structure control strategy based on the improved reaching law; this strategy can effectively suppress switching jitter. The current inner loop adopts an improved predictive current control strategy that combines the traditional finite control set model predictive control (FCS-MPC) with the space vector modulation method (SVPWM), such that the optimal switching state obtained by the predictive controller is modulated to generate a switching signal. Moreover, the switching frequency can be controlled by adjusting the frequency of the carrier, and the switching frequency is fixed while preserving the advantages of model prediction control. The primary advantages of the proposed double closed-loop control strategy are as follows: (1) it does not require proportional–integral controllers in the current control loops, and (2) it keeps the output voltage stable. The Vienna rectifier simulation is performed on MATLAB. Then an experimental prototype based on SiC devices is developed to verify the excellent performance of the proposed strategy in steady and transient states.

Efficiency Improvement of Wireless Power Transfer Based on Multitransmitter System

Multitransmitter wireless power transfer system gets more and more applications as it can maintain high efficiency in a large space range. This article focuses on modeling the multitransmitter system, and proposes an impedance matching method to improve efficiency under lateral-misalignment conditions. The theoretical analysis shows that the maximum transfer efficiency can be achieved as long as the equivalent input impedance of the transmitters is regulated to be the same under misalignment condition. Hence, a double closed-loop control strategy is proposed to realize maximum efficiency point tracking, where the primary control loop adjusts the input impedance of the transmitters through pulsewidth modulation, while the second control loop maintains constant output power by a dc–dc converter. A 500-W prototype is built to validate the feasibility of the proposed method. The efficiency is always higher than 90% with an improvement of up to 20.3% compared to that without such a method when the lateral misalignment increases from 0 to 10 cm (0%–41% of maximum coil size).