Simple Control Loop Research Articles

Modeling and analysis of digital current‐mode controlled single‐inductor dual‐output DC–DC converter with different PWM modulation modes

SummaryCurrent‐mode control is extensively used in dc–dc converters as the merits of fast transient performance, simple control loop, and elimination of right‐half‐plane zeros for boost‐type dc–dc converters. In single‐inductor multiple‐output (SIMO) dc–dc converter, the inductor current would present different trends under different circuit parameters. Therefore, the control logic changes for different inductor current trends, and the corresponding modulations are absolutely different. In this paper, a digital current‐mode control technology for SIMO dc–dc converter is proposed to expend the convenience of current‐mode control with different inductor trends. Choosing continuous conduction mode (CCM) single‐inductor dual‐output (SIDO) dc–dc converter as the research object, the principles are analyzed under different pulse width modulation modes, and the corresponding control algorithms are derived. Moreover, the discrete iterative map model is established to analyze the stability of input and output voltages varying. The results show that not only the digital current‐mode controlled SIDO buck converter has fast load transient response and small cross‐regulation but also the input and output voltages will not affect the stability in the leading edge modulation, which is different from the corresponding analog current‐mode control technology. Finally, the experimental results verify the correctness of the theoretical analysis.

Fixed-time anti-saturation control with concise system structure for the 6-DOF motion of spacecraft

Abstract This paper proposes a fixed-time anti-saturation (FT-AS) control scheme with a simple control loop for the 6-Degree-of-Freedom tracking (6-DOF) control problem of spacecraft with parameter uncertainties, external disturbances and input saturation. Considering the external disturbance and parameter uncertainties, the dynamical model of the tracking error is established. The traditional methods of handling input saturation usually add anti-saturation subsystems in the control system to suppress the impact of input overshoot. However, this paper directly inputs the input overshoot into the tracking error model, thus constructing a modified lumped disturbance term that includes the influence of input overshoot. Then, a novel fixed-time disturbance observer (FT-DO) is designed to estimate and compensate for this modified lumped disturbance. Therefore, there is no need to add the anti-saturation structures in the control loop, significantly reducing the complexity of the system. Finally, an observer-based fixed-time non-singular terminal sliding mode (FT-NTSM) controller is designed to guarantee the fixed-time stability of the whole system. In this way, the convergence time of the proposed scheme does not depend on the system’s initial conditions. Simulation results illustrate that the proposed method keeps the control input within the limit while achieving high-precision tracking control of attitude and position.

Grid power control of direct matrix converter fed three-phase induction generator

The direct matrix converter (DMC) and the modulation technique were presented in this paper, moreover the power of the grid is controlled. Due to its high flexibility and low computation demands, the DMC's most widely used modulation technique is space vector modulation. The double-side modulation is used in this paper instead of the single-side modulation because less harmonics at the input and output side can be obtained, however this would increase slightly the number of branch-switch-overs (BSO) for each switching period. In addition to being able to create input and output sinusoidal currents with various frequencies, it would adjust the input power factor. Along with that, the simple power control loop would regulate the grid power and then generate controlled three-phase reference signals for pulses generation accordingly. Results from the simulations show that the topology is appropriate for machine drive applications.

Cuk PFC Converter Based on Variable Inductor

When the input inductor operates in discontinuous current mode (DCM), the Cuk converter can automatically achieve power factor correction (PFC) function with only a simple voltage mode control loop. However, the conventional Cuk PFC converter suffers from high intermediate capacitor voltage because of the lack of feedback of the intermediate capacitor voltage and relatively low power factor (PF). In this paper, a Cuk PFC converter using variable inductor which varies with the transient rectified input voltage is proposed to enhance the PF and reduce the intermediate capacitor voltage by injecting a controlled DC bias current into the auxiliary winding of the variable input inductor. The operating principles of the proposed Cuk PFC converter based on variable inductor are analyzed in detail, and the analysis of PF, the voltage of intermediate capacitor, and design considerations are provided. To verify the feasibility of the proposed scheme and compare the characteristics of both the traditional and proposed Cuk PFC converter, a 108W experimental prototype of the proposed converter is built and tested. The experimental results show that the proposed Cuk PFC converter can significantly enhance the PF, decrease the intermediate capacitor voltage, and increase efficiency compared with the traditional Cuk PFC converter.

Direct Power Control of a Surface-Mounted Permanent Magnet Synchronous Generator Wind Turbine for Offshore Applications

This paper proposes a direct power control scheme for an offshore wind turbine-driven surface-mounted permanent magnet synchronous generator with a full back-to-back converter situated onshore to decentralize the weight of the turbine. The proposed model is designed in a stationary reference frame and does not require a phase-locked loop as opposed to the traditional vector current control method. Simple feed-forward and feedback control loops are used in the proposed model to extract the maximum available wind power, maintain constant voltage at the coupling DC link, and ensure power injection into the electric network at unity power factor. Simulation results carried out in MATLAB/SIMULINK show that the proposed model has fast transient response and steady-state performance consistent with the vector current control model. Furthermore, eigenvalue analysis results demonstrate that the proposed method’s performance is robust to variations in different system parasitic elements, even under both stiff and weak electric network conditions. These results also indicate that the back-to-back converter can operate effectively when located onshore close to the load center, while the turbine is in close proximity offshore. This can be suitable for multiple specific offshore applications as it has the potential to reduce the overall weight, volume, and cost of the offshore wind turbine infrastructure.

Hybrid Recurrent Neural Network Modeling for Traffic Delay Prediction at Signalized Intersections Along an Urban Arterial

This paper studies the traffic delay prediction modeling for multiple signalized intersections along the Ala Moana Boulevard and Nimitz Highway in Hawaii. Several machine learning (ML) based approaches have been studied in the literature, and most of them focused on prediction accuracy rather than the end use of real-time control and implementation. These ML models tend to be very complex and non-linear in nature, making it challenging to achieve fast inferences and are computationally heavy for real-time signal control implementation. In this paper, a simple yet accurate hybrid modeling method is proposed to predict traffic delay one-step ahead with the model made suitable for real-time implementation to control traffic flow. Since real-time road-side measurements are recorded in unstructured form, the paper also discusses other issues related to data extraction and the pre-processing process. Finally, a simple signal control loop is developed to demonstrate the proposed modeling approach, which has shown advantages in model accuracy and computation efficiency compared against several existing modeling methods.

Principles of Endocrine Regulation: Reconciling Tensions Between Robustness in Performance and Adaptation to Change.

Endocrine regulation in the hypothalamic-pituitary-thyroid (HPT) axis is orchestrated by physiological circuits which integrate multiple internal and external influences. Essentially, it provides either of the two responses to overt biological challenges: to defend the homeostatic range of a target hormone or adapt it to changing environmental conditions. Under certain conditions, such flexibility may exceed the capability of a simple feedback control loop, rather requiring more intricate networks of communication between the system’s components. A new minimal mathematical model, in the form of a parametrized nonlinear dynamical system, is here formulated as a proof-of-concept to elucidate the principles of the HPT axis regulation. In particular, it allows uncovering mechanisms for the homeostasis of the key biologically active hormone free triiodothyronine (FT3). One mechanism supports the preservation of FT3 homeostasis, whilst the other is responsible for the adaptation of the homeostatic state to a new level. Together these allow optimum resilience in stressful situations. Preservation of FT3 homeostasis, despite changes in FT4 and TSH levels, is found to be an achievable system goal by joining elements of top-down and bottom-up regulation in a cascade of targeted feedforward and feedback loops. Simultaneously, the model accounts for the combination of properties regarded as essential to endocrine regulation, namely sensitivity, the anticipation of an adverse event, robustness, and adaptation. The model therefore offers fundamental theoretical insights into the effective system control of the HPT axis.

An industrial control loop decoupler for process control applications

The paper describes a simple and efficient control loop decoupler for TITO (two inputs, two outputs) control systems. The inverted decoupling approach is used, and the feedforward filters are just static gains. The feedforward gains are determined in two ways, from a static analysis and from optimization. By investigating several cases found in literature, it is found that the two sets of feedforward gains are very close. The control loop decoupler is implemented in an industrial DCS system and simulation experiments as well as laboratory tests show that a significant reduction of the coupling is accomplished. Automatic tuning of the feedforward gains is derived and implemented in the system as well.

Reliability Enhancement of Power IGBTs under Short-Circuit Fault Condition Using Short-Circuit Current Limiting-Based Technique

Like the widely-used semiconductor switch, Insulated Gate Bipolar Transistors (IGBTs) are subject to many failures and degradation in power electronic converters. In Short Circuit Fault (SCF), as the most reported failures in IGBTs, drastic, sudden temperature rise, and peak SCF current are widespread failures owing to a relatively long delay of the protection subsystem. This paper proposes a protection strategy to limit the junction temperature rise by limiting the SCF current by adding a small value resistor in the IGBT emitter. Second, it reduces the SCF current to a value much less than the saturated current. With the proposed control approach, sudden temperature rise during SCF is controlled, preventing significant failure in IGBTs. The extension of the permissible SCF time is achieved even for the cases with temporary arcs. A simple control loop activates in the SCF condition and does not create slow transients for the IGBT. The results of this paper are validated through simulation and experiment.

1kW Bidirectional 48V-12V DCDC Converter Design Based on Full Bridge CLLC Topology and FDP Controlling Method for Electric Vehicles Application

Present electric vehicles market calls for 1kW bidirectional 48V-12V DCDC converters with high performances. The requirements that isolation and soft switching determine the power stage topology choosing range. Based on previous research results and actual requirements of this application, full-bridge CLLC topology is chosen for further analyses and designs. By properly choosing resonant devices, operating frequency (F), phase shift (P) between power side and load side, and duty (D) of power side, the power system achieves high efficiency with soft switching. Soft switching comes from a small extra time per period with no power transfer. The FPD has respective influences on the performances of the power system. For each one of FDP, there is a balance and two important performances that are conversion efficiency and output voltage accuracy which are listed for illustrating influences of F P D and choosing a best FPD for the whole system. The whole system includes power stage design on PCB and controlling stage design on integrated circuits. FPD can be designed self-adapting respectively and a simple control loop is proposed with adjustable D and settled F P. A proper FPD can achieve over 98.9% efficiency and control loop can be verified workable for load variation.

Three-Phase Buck–Boost Derived PFC Converter for More Electric Aircraft

In more electric aircraft (MEA), three-phase power factor correction (PFC) rectifiers of several kilowatts are required. In this paper, a three-phase buck–boost derived PFC converter with three switches and with input inductors connected in delta configuration for use in MEA is presented. The proposed converter is operated in a discontinuous conduction mode to achieve PFC at ac input. This avoids the inner current control loop which further eliminates the current sensors. It requires only one output voltage sensor unlike five sensors in conventional PFC converter for its control implementation. This makes the system cost effective, more reliable, and robust. A simple voltage control loop is used to generate the gate signals. The steady state operation of the converter and detailed design calculations are presented. For each power component, the analytical expressions for calculating the average and rms current ratings are derived to facilitate the converter design. The small-signal model of the converter is presented to aid the controller design. The experimental results from a 2 kW laboratory prototype are presented to confirm the operation of the proposed converter. An input power factor of 0.999, an input current total harmonic distortion of as low as 2.76%, and a high conversion efficiency of 96% are achieved from the prototype.

Robotic Light Following System

This project demonstrates the creation of a robot using low cost light controlled variable resistor to follow a flash light. It also demonstrates a very simple control loop. A control loop is an important concept in the world of robotics. Control loops are used for everything from regulating the speed of the motors to helping the robot travel in the path of higher luminescence across all directions. It is based on the principle that resistance of a LDR changes with the amount of light falling on it. The resistance of an LDR will decrease with increase in luminescence. This variation is fed to a comparator with a reference voltage set. This drives the robot in the desired direction with the help of DC motors.

Three-Phase Single-Stage-Isolated Cuk-Based PFC Converter

In this paper, analysis and design of a three-phase-isolated Cuk-based power factor correction (PFC) converter have been proposed. The proposed converter is operated in discontinuous output inductor current mode to achieve PFC at ac input. This avoids the inner current control loop which further eliminates the sensing of current. This makes the system more reliable and robust. The converter requires only one simple voltage control loop for output voltage regulation, and all the power switches are driven by the same gate signal which simplifies the gate driver circuit. The detailed operation of the converter and design calculations are presented. And also a small-signal model of the converter by using current injected equivalent circuit approach is presented to aid the controller design. The experimental results from a 2-kW laboratory prototype with 208-V line-to-line input voltage, 400-V output voltage are presented to confirm the operation of the proposed converter. An input power factor of 0.999, an input current total harmonic distortion of as low as 4.06%, and a high conversion efficiency of 95.1% are achieved from laboratory prototype.

Optimal Operation of a DWC by Self-Optimizing Control: Active Vapor Split Approach

Dividing Wall Column(DWC) offers the large potential for operating and capital cost saving in compared with conventional distillation sequence. In the studied DWC in this study, the aid of Vmin diagrams, it is shown that without a suitable value for vapor split fraction bellow the dividing wall in different operating conditions, the energy requirement increases from optimal value and it will lead to the suboptimal operation. Accordingly, a control structure based on the self-optimizing concept is designed using vapor split fraction as the control degree of freedom (active vapor split). To find the best self-optimizing Controlled Variables (CV) the exact local method is used. It is shown that the value of loss with the aid of active vapor split is lower than 0.7 percent of nominal value with using the conventional single measurement self-optimizing CV, which is a reasonably small value, and using a more complex combination of measurement as a self-optimizing CV provides a little enhancement in reducing the loss. So, including vapor split fraction in the self-optimizing control structure of the DWC can save energy and in the meantime avoid the complexity of combination of measurement. Moreover, the dynamic simulation studies show that the proposed control structure with the simple decentralized control loops can conveniently stabilize the plant and reject the effects of disturbances.

New Modulated Carrier Controlled PFC Boost Converter

A new modulated carrier control (MCC) method is proposed in this paper for a power factor correction (PFC) boost converter, which provides high power factor (PF) and low total harmonic distortion (THD) in wide input voltage and load range. The proposed MCC method employs a zero current duration (ZCD) demodulator that detects ZCD in each switching cycle to estimate current conduction duration of the boost inductor. Using the estimated signal of the ZCD demodulator, the proposed controller generates a compensated duty signal with a PFC converter to properly operate in continuous conduction mode (CCM) or discontinuous conduction mode (DCM). Unlike the conventional MCC PFC converter where the line current is distorted in DCM resulting in poor PF and high THD, the proposed MCC method can provide higher PFC performance regardless of CCM and DCM while maintaining the simple control loop of conventional MCC control method that does not require inner current loop and using relatively small inductance. In this paper, the operational principle of the proposed method has been discussed. To verify the proposed method, it has been tested on a 400-W PFC boost converter.

Use of the benchmark for PID control in engineering studies at the University of Almería

This paper presents the methodology followed to evaluate students ability to face the challenge of controlling a refrigeration system based on vapour compression proposed as a benchmark for PID control design in the PID18 Conference. This benchmark has been also proposed as test-bed plant for the design of controllers in the subject Industrial Control Techniques at the University of Almería, Spain. The solutions proposed by the students range from simple SISO PID control loops (including anti-windup effect) to MIMO ones, including decoupling, filters and feedforward action to reject disturbances. All these solutions rely on models obtained from the reaction curve method. The selection of adequate specifications is encouraged, although students creativity has led them to exploit very aggressive specifications taking into account the different system restrictions, and obtaining very good values of the proposed evaluation indexes. © Copyright IFAC 2018.

Current limiting soft starter for three phase induction motor drive system using PWM AC chopper

This study presents a new current-limiting soft-starter for a three-phase induction motor drive system using pulse width modulation (PWM) AC chopper. A novel configuration of three-phase PWM AC chopper using only four insulated gate bipolar transistors (IGBTs) is also proposed. The proposed control strategy does not require zero crossing detection circuits, which employed in thyristorised soft starters. It requires only one current sensor. The duty ratio of the chopper IGBTs is obtained from the closed-loop current control in order to limit the motor starting current at a preset value. Only two complementary gate pulses are obtained from the control circuit to control the four IGBT switches. The proposed control strategy is characterised by a simple control loop; thus, a low-cost processor can be used due to the low-computation burden. The superiority of the proposed strategy is proved theoretically and confirmed experimentally. The experimental work is developed using a laboratory prototype system composed of DSP-DS1104 digital control board and 1.5 HP induction motor. The proposed starter offers a smooth start-up for the motor speed, torque ripple minimisation, less number of semiconductor switches, less switching and conduction losses, less harmonics and improved input power factor.

A new model predictive control algorithm by reducing the computing time of cost function minimization for NPC inverter in three-phase power grids

This paper presents a new control strategy based on finite-control-set model-predictive control (FCS-MPC) for Neutral-point-clamped (NPC) three-level converters. Containing some advantages like fast dynamic response, easy inclusion of constraints and simple control loop, makes the FCS-MPC method attractive to use as a switching strategy for converters. However, the large amount of required calculations is a problem in the widespread of this method. In this way, to resolve this problem this paper presents a modified method that effectively reduces the computation load compare with conventional FCS-MPC method and at the same time does not affect on control performance. The proposed method can be used for exchanging power between electrical grid and DC resources by providing active and reactive power compensations. Experiments on three-level converter for three Power Factor Correction (PFC), inductive and capacitive compensation modes verify the good and comparable performance. The results have been simulated using MATLAB/SIMULINK software.

Simulation of control loops in wireless networks: Relating QoS with QoC

Considering the flexibility of network-based control systems and the wide adoption of wireless IP networks, the relationship between Quality of Service (QoS) and Quality of Control (QoC) parameters is studied in a simple control loop implemented over a wireless ad hoc network. This relationship is investigated using ns-2 simulator in three scenarios: static without packet loss, static with packet loss and mobile. The first scenario was compared to a case study for wired networks presented in the literature. Similar results were obtained, according to the prediction that different packet-switched technologies would present similar results because the concepts of QoS parameters are general enough. Results related to the other two scenarios qualitatively show QoC problems that appear due to the high utilization rate of the network and route disruption due to mobility. These problems can be summarized by the “inertia” of the controlled variable. A proof-of-concept experiment was also implemented to complement and to evaluate simulations.

Dynamic and Control of an Absorber - Desorber Plant at Heilbronn

The present work is based on an MEA absorption test campaign performed November 2013–January 2014 at EnBW's amine test pilot located in Heilbronn, Germany. The test campaign included transient step responses in steam, exhaust gas, solvent flow rate and in exhaust gas CO2 concentration. In addition, a test with simultaneous steps in all flow rates (exhaust gas, solvent and steam) was included.A dynamic model of the Heilbronn plant was then implemented in the dynamic simulator K-Spice® and tested against the step responses at the plant. In spite of some stead state deviations, the model was able to capture the process dynamics very well. For dynamic studies one can therefore assume that the model is representative for the plant. In the work presented here, two different control configurations were tested: 1) Ratio control in combination with a slow feed back control on the CO2 out of the absorber and 2) Control of CO2 out of the absorber by lean liquid flow rate and a temperature sensor up in the desorber packing. Both structures involve only simple PID control loops and are thus easy to implement. The proposed control configurations were tested by simulations with 30% changes in flue gas flow and composition. Both configurations showed good performance during the simulation testing, but the second one was superior as well as excellent with respect to tight CO2 recovery control. This may be an important property in supervisory control schemes.