Current Feedback Control Loop Research Articles

High Precision Hybrid Reluctance Actuator With Integrated Orientation Independent Zero Power Gravity Compensation

This article presents a novel method for enabling energy-efficient and orientation-independent gravity compensation in active vibration isolation systems by taking advantage of the inherent negative stiffness of a hybrid reluctance actuator (HRA). Counteracting the gravitational force acting on the mover of an HRA with the position dependent force of the actuator’s integrated permanent magnet, the gravitational force can be compensated without the need for an additional actuation. An HRA-system with two translational degrees of freedom (DOF) is developed, comprising a permanent magnet for generating a constant biasing flux for both system axes and two actuator coils per axis for actively controlling the position of the mover. The system prototype has an actuation range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.7 mm in both DOF, while enabling energy efficient gravity compensation of payloads up to 500 g by an additional current feedback control loop. Experiments demonstrate that the current consumption for compensation of a 500 g payload is reduced from 1.58 A to 10 mA, which corresponds to a reduction of the power consumption by a factor of 25 000.

Carrier-Based Modulated Model Predictive Control Strategy for Three-Phase Two-Level VSIs

The implementation of finite-control-set model predictive control (FCS-MPC) in voltage source inverters (VSIs) can make the system suffer from poor current harmonics performance, which may complicate the design of the required AC filter. To overcome this shortcoming, a carrier-based modulated model predictive control (CB-MMPC) strategy is proposed in this paper. This method enables the utilization of existing PWM modulation techniques with FCS-MPC, where a modulation waveform with zero-sequence signal injection is generated and compared to a triangular carrier wave, while optimizing the selection of the switching states. As it is shown, the studied CB-MMPC strategy not only considerably improves the current total harmonic distortion (THD) but also attains the performance of fast current dynamic response and robustness as the traditional FCS-MPC. Herein, the detailed implementation of the CB-MMPC control strategy is given, while considering its application to the current feedback control loop of a three-phase three-wire two-level VSI modulated at constant switching frequency. Finally, PLECS circuit simulation and a 3-kW VSI prototype are used to verify the superiority and the effectiveness of the presented CB-MMPC strategy. This is also benchmarked to the FCS-MPC and dead-beat based controllers.

A 19 μW, 50 kS/s, 0.008-400 V/s Cyclic Voltammetry Readout Interface With a Current Feedback Loop and On-Chip Pattern Generation.

A cyclic voltammetry electrochemical sensing chip was implemented with a time-based readout circuit and a current feedback control loop for wide-range and high-linearity current detection. The design utilizes a chopper-stabilized, low-noise potentiostat circuit and a delay chain time-to-digital converter to improve accuracy and the conversion rate. A current feedback loop is employed to mitigate nonlinearity of the current-to-frequency converter. Also, an on-chip pattern generator with a current reducer is used to create area-efficient, multi-rate ramp signals for cyclic voltammetry and fast-scan cyclic voltammetry measurements. The chip is fabricated using a 0.18-μm CMOS process. It achieves an 8-nA current resolution in the current range of -7 μA to 10 μA with an R2 linearity of 0.999 while consuming 19 μW. The Allan deviation floor is 4.83 Hz at the 7-second integration window, resulting in an 87-pArms input-referred current noise. The applicable limit of detection for K3[Fe(CN)6] concentration is 31 pM. To measure various reactions, the scan rate can be adjusted from 0.008 V/s to 400 V/s with a throughput data rate of up to 50 kS/s.

Modular Circulating Current and Second Harmonic Current Suppression Strategy by Virtual Impedance for DC Solid-State Transformer

This article proposes a circulating current and second harmonic current (SHC) suppression method by introducing virtual impedance into the circulating current and output current feedback control loops of the dc solid-state transformer (DCSST). The virtual impedance is employed to adjust impedance in the circulating current feedback control loop to decrease the circulating current when the transmission efficiency of each dual active bridge is different. And a SHC suppression method, which introduces the virtual impedance containing a bandpass filter, is adopted to reduce the SHC and improve the dynamic performance of the DCSST. Moreover, a relatively independent modular control method, which is conducive to the modular expansion of the DCSST, is proposed. Compared with traditional DCSST control methods, the proposed method can simultaneously realize the output current sharing and effectively reduce the SHC with modular control. Finally, a DCSST prototype is built and the results of the experiment verify the validity and effectiveness of the proposed control strategy and solutions.

Passivity-based active stabilization for DC microgrid applications

In this paper, an improved active stabilization strategy of the interface converters in microgrid applications is proposed on the basis of the passivity-based stability criterion (PBSC). As a critical part of AC and DC hybrid microgrids, the DC microgrid is taken as an example. In particular, a stabilization method with a proportional-integral (PI) controller and firstorder high-pass filter (HPF) is proposed to meet the passivity requirements of the overall control diagram with respect to the output voltage. Meanwhile, an output current feedback control loop is introduced to ensure the output impedance passivity. Moreover, a small-signal model of the parallel interface converter system is established to comprehensively study the influence of control parameters on the passivity of the converters. Based on the active stabilization method proposed in this study, by manipulating the control diagram of each interface converter, the passivity and stability of the DC microgrids with variable configuration can be guaranteed. Therefore, a generic and simplified design approach is realized. A simulation model with three interface converters is implemented in MATLAB/Simulink, and the effectiveness of the proposed passivity-based active stabilization algorithm is verified by using this simulation model.

Bidirectional Power Conversion of Isolated Switched-Capacitor Topology for Photovoltaic Differential Power Processors

Differential power processing (DPP) systems are among the most effective architectures for photovoltaic (PV) power systems because they are highly efficient as a result of their distributed local maximum power point tracking ability, which allows the fractional processing of the total generated power. However, DPP systems require a high-efficiency, high step-up/down bidirectional converter with broad operating ranges and galvanic isolation. This study proposes a single, magnetic, high-efficiency, high step-up/down bidirectional DC-DC converter. The proposed converter is composed of a bidirectional flyback and a bidirectional isolated switched-capacitor cell, which are competitively cheap. The output terminals of the flyback converter and switched-capacitor cell are connected in series to obtain the voltage step-up. In the reverse power flow, the converter reciprocally operates with high efficiency across a broad operating range because it uses hard switching instead of soft switching. The proposed topology achieves a genuine on-off interleaved energy transfer at the transformer core and windings, thus providing an excellent utilization ratio. The dynamic characteristics of the converter are analyzed for the controller design. Finally, a 240 W hardware prototype is constructed to demonstrate the operation of the bidirectional converter under a current feedback control loop. To improve the efficiency of a PV system, the maximum power point tracking method is applied to the proposed converter.

Modeling and control of an integrated electric parking brake system

The estimation of the frictional and clamping forces is one of the key issues in an integrated electric parking brake control system design and implementation. In this paper, we present a modeling and control system design for the integrated electric parking brake system (IEPBs). Based on the state-dependent switched IEPBs models, the whole working principles can be analyzed mathematically. Based on the mathematical models, clamping force, rotor angle position and motor current are set as the feedbacks respectively to compare the control performance. The simulation results show that with a force sensor, the clamping force can be controlled well, while the cost is increased seriously; and for the angle position feedback, the conventionally used position–force characteristic curve may change due to the external temperature and aging problem, which may result in an insufficient clamping force; the current control feedback strategy outperforms the other two strategies in terms of cost, implementation as well as the robustness with respect to the external disturbances. Finally, the proposed IEPBs model with current feedback control loop is verified through the experimental results with an on-off control method.

Simulation of the Double-closed Loop Three-phase Asynchronous Variable Voltage Control System

When controlling the voltage and speed of the asynchronous motor, to expand the speed control range and reduce the speed fluctuation, the speed control system adopts two feedback control loops, i.e. the speed feedback control loop and the current feedback control loop. The principle and components of the double-closed loop three-phase asynchronous variable voltage control system are studied, and the simulation model and the test result based on MATLAB/Simulink are provided in this article through the system modeling and the parameter setup of the main circuit and the control circuit.

A DSP-based modified slip energy recovery drive using a 12-pulse converter and shunt chopper for a speed control system of a wound rotor induction motor

This paper introduces a modified slip energy recovery drive system for speed control of a wound rotor induction motor offering improvement of drive performance, particularly line power factor and overall system efficiency. A 12-pulse line commutated thyristor converter operating in an inverter mode in conjunction with an additional IGBT shunt chopper is employed to transfer slip energy back to ac mains supply via three phase transformers. This approach offers motor speed control by varying the duty cycle of the chopper instead of changing the inverter firing angle. As a consequence, supply power factor can be improved. The servo state feedback designed by linear quadratic regulator (LQR) with observer is also included in order to keep motor speed to be constant over a certain range of operating conditions by using the estimated dc link current derived from motor speed. The advantage of this technique is absence of current transducers for current feedback control loop. The overall control system is implemented on DSP, DS1104’TMS320F240 controller board. Experimental results are illustrated in order to validate performance of the proposed system.

Adaptive cutting force control for a machining center by using indirect cutting force measurements

This paper presents an adaptive cutting force controller for the milling process, which can be attached to most commercial CNC machining centers in a practical way. The cutting forces of x, y and z axes are measured indirectly from the use of currents drawn by a.c. feed-drive servo motors. A typical model for the feed-drive control system of a horizontal machining center is developed to analyze cutting force measurement from the drive motor. The pulsating milling forces can be measured indirectly within the bandwidth of the current feedback control loop of the feed-drive system. It is shown that indirectly measured cutting force signals can be used in the adaptive controller for cutting force regulation. The robust controller structure is adopted in the whole adaptive control scheme. The conditions under which the whole scheme is globally convergent and stable are presented. The suggested control scheme has been implemented into a commercial machining center, and a cutting experiment on face milling process is performed.