Proportional Plus Integral Research Articles

IP controller‐based vector control of induction motor taking core loss into account

AbstractThis paper presents speed and current control of the induction motor (IM) taking core loss into account based on integral plus proportional (IP) control strategy. The proposed IP controller can overcome the problems (such as overshoot, instability under the variations of parameters and load torque) of the conventional PI controller. The performance of the proposed IP controller and PI controller is compared. The performance comparison of the IP controller and the PI controller is verified by using Matlab/Simulink. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A high-performance sensorless indirect stator flux orientation control of induction motor drive

A new method for the implementation of a sensorless indirect stator-flux-oriented control (ISFOC) of induction motor drives with stator resistance tuning is proposed in this paper. The proposed method for the estimation of speed and stator resistance is based only on measurement of stator currents. The error of the measured q-axis current from its reference value feeds the proportional plus integral (PI) controller, the output of which is the estimated slip frequency. It is subtracted from the synchronous angular frequency, which is obtained from the output integral plus proportional (IP) rotor speed controller, to have the estimated rotor speed. For current regulation, this paper proposes a conventional PI controller with feedforward compensation terms in the synchronous frame. Owing to its advantages, an IP controller is used for rotor speed regulation. Stator resistance updating is based on the measured and reference d-axis stator current of an induction motor on d-q frame synchronously rotating with the stator flux vector. Experimental results for a 3-kW induction motor are presented and analyzed by using a dSpace system with DS1102 controller board based on the digital signal processor (DSP) TMS320C31. Digital simulation and experimental results are presented to show the improvement in performance of the proposed method.

Fuzzy Algorithm for Supervisory Voltage/Frequency Control of a Self Excited Induction Generator

This paper presents the application of a Fuzzy Logic Controller (FLC) to regulate the voltage of a Self Excited Induction Generator (SEIG) driven by Wind Energy Conversion Schemes (WECS). The proposed FLC is used to tune the integral gain (KI) of a Proportional plus Integral (PI) controller. Two types of controls, for the generator and for the wind turbine, using a FLC algorithm, are introduced in this paper. The voltage control is performed to adapt the terminal voltage via self excitation. The frequency control is conducted to adjust the stator frequency through tuning the pitch angle of the WECS blades. Both controllers utilize the Fuzzy technique to enhance the overall dynamic performance. The simulation result depicts a better dynamic response for the system under study during the starting period, and the load variation. The percentage overshoot, rising time and oscillation are better with the fuzzy controller than with the PI controller type.

A New Tuning Method for PI Controllers using Features of Step Response Pattern

This paper proposes a new tuning method for PI( proportional plus integral ) controllers based on partial model matching to refer to the standard 2nd order lag model.The method consists of four steps : (1) to measure step responses of a 1st order lag plus dead time process controlled by PI controller, (2) to extract features of the step responses, (3) to estimate damping coefficient ζ and natural angular frequency ωn of the control system, and (4) to change control parameters Kp, Ti to adjust the damping coefficient and the natural angular frequency to the desired values.The result of simulation show that this method is so practical that prediction errors to step responses after changing parameters are small and it is easy to evaluate characteristics of the control system after changing parameters.

Regulation of Powder Mass Flow Rate in Gravity-Fed Powder Feeder Systems

Precise regulation of powder mass flow in laser-based manufacturing processes is critical to achieving excellent part dimensional and microstructure quality. Control of powder mass flow is challenging because low flow rates, where nonlinear effects are significant, are typically required. Also, gravity-fed powder feeder systems have significant material transport delays, making the control of powder mass flow even more challenging. This paper presents a control strategy for regulating the powder mass flow rate in a gravity-fed powder feeder system. A dynamic model of the powder feeder system, including material transport delay, is constructed, and a modified proportional plus integral (PI) controller is designed. An observer is used to estimate powder mass flow rate using the powder feeder motor encoder signal. The control strategy is implemented in a Smith Predictor Corrector Structure, which has been adjusted such that it can be applied to the modified PI controller, to account for the inherent material transport delay. Experimental studies are conducted that validate the dynamic model and controller strategy.

Rotor resistance tuning for indirect stator flux orientated induction motor drive based on MRAS scheme

AbstractIn this paper, the indirect stator flux orientated controlled (ISFOC) induction motor drive is presented. In order to eliminate the effect of parameter variation on the ISFOC induction motor drive, an adaptation algorithm for tuning the rotor resistance is proposed. Based on the model reference adaptive system (MRAS) scheme, the rotor resistance is tuned to obtain an exact ISFOC induction motor drive. The integral plus proportional (IP) speed controller is designed using a model‐based analytical method in order to obtain a speed step response without overshoot. The reference and adjustable models, developed in the stationary stator reference frame, are used in the MRAS scheme to estimate induction rotor resistance from measured terminal voltages and currents. The major contributions of this work are: first, taking into account the variations of the rotor resistance during start‐up and normal operations; and second, the IP gains speed controller and PI gains current controller are calculated and tuned at each sampling time according to the new estimated rotor resistance. Computer simulation results show the satisfactory behaviour of the proposed identification method. Copyright © 2005 John Wiley & Sons, Ltd.

Robust and self-tuning blood flow control during extracorporeal circulation in the presence of system parameter uncertainties

Three different discrete controllers were designed and tuned to be used in conjunction with a rotary blood pump during cardiopulmonary heart-lung support. The controllers were designed to operate in both steady and pulsatile modes. The system and methods were tested in a circulatory haemodynamic simulator. To guarantee stable control of the non-linear circulatory system in the presence of patient parameter uncertainties, a proportional plus integral (PI) and an H infinity controller were robustly tuned, using a non-linear time-varying model. (H infinity refers to the Hardy space, the set of bounded functions, analytic in the right half plane. The H infinity controller is the solution to the H infinity norm optimisation problem.) A self-tuning general predictive controller (GPC), together with an adaptive Kalman filter (KF) estimator, was compared with the two robustly tuned controllers. The closed-loop blood flow control circuit was set up in simulation routines first. The blood flow controllers were validated in a circulatory hydrodynamic simulator (MOCK) combined with a rotary blood pump. Parameters of the system simulator were changed continuously, and the controllers were tested over a wide range of different operating points. Disturbances in the form of discontinuous additive parameter uncertainties were applied. The closed-loop systems remained robustly stable. The robustly tuned H infinity controller showed the best control performance, in contrast to the GPC controller, which was near instability in regions of strongly varying non-linear system gain. Compared with the H infinity controller, the PI controller showed slightly worse behaviour, but the closed-loop response was acceptable, even in regions of strongly varying non-linear system gain and during pulsatile perfusion. The rotary blood pump could provide stationary and pulsatile perfusion under control conditions. Controlled variables were hereby mean blood flow, pulsatility index and heart rate. All three controllers were developed for an arterial mean flow of 0-6 l min(-1) and a heart rate of up to 70 beats per minute. Pulsatile closed-loop perfusion could provide up to 30 mmHg pressure variation in the simulated ascending aorta at a mean flow of 3 l min(-1).

Tuning Software Phase-Locked Loop for Series-Connected Converters

Accurate phase information is crucial for most of the modern power-electronics apparatus such as the static series compensator (SSC). A software phase-locked loop (SPLL) has been proposed in literature to obtain phase and frequency information of the grid voltage. Either a lead/lag filter or a proportional-plus-integral (PI) controller is employed to control the performance of the SPLL. In this paper, a criterion to tune the SPLL is discussed and the gains of the PI-controller are determined to obtain the desired performance. The proposed criterion is based on the fact that a phase shift of the grid voltage is sensed as a frequency deviation by the load. If the deviation of the grid frequency is kept within the range /spl plusmn/1 Hz, most of the loads function properly. Hence and by the SSC, the response of the phase angle of the load voltage is designed to follow the grid voltage angle while satisfying the frequency range at all times. Consequently, the gains of the PI-regulator of the SPLL are dependent on the maximum phase shift of the grid voltage. Unbalanced grid voltages are separated into positive- and negative-sequence components and the SPLL is locked to the positive sequence. The response of the SPLL has been evaluated by using PSCAD/EMTDC simulation package.

A Controller for a Boost Converter With Harmonic Reduction

An adaptive controller for the compensation of output voltage ripple due to harmonic distortion in the input voltage is proposed for a pulse width modulated (PWM) boost converter. Following the Lyapunov approach, we designed an adaptive law to cope with uncertainties in the disturbance signals and parameters. Complexity of the proposed controller is reduced by rotations which transform the adaptive terms into a sum of resonant filters tuned at the frequencies of the harmonics under compensation, and operating on the output voltage error. To facilitate the implementation, we have tried to preserve the structure of the proposed controller as close as possible to the conventional one, which includes a voltage outer loop (basically a proportional plus integral (PI) control on the output voltage error) and an inner control loop (basically a proportional control plus a feedforward term). In the proposed controller, the bank of resonant filters appears as a refinement term added to the inner control loop. Indeed, they insert notches in the audio-susceptibility curve, which are tuned at the harmonics under compensation. Thus, in addition to the benefits of a conventional feedforward PWM control, the bank of resonant filters are able to cancel selected harmonics. Experimental results on a boost converter board, using a poorly regulated voltage source, are presented to assess the performance of our approach.

Lagrangian Modeling and Passivity-Based Control of Three-Phase AC/DC Voltage-Source Converters

In this paper, we investigate the dc-bus voltage regulation problem for a three-phase boost-type pulsewidth-modulated (PWM) ac/dc converter using passivity-based control theory of Euler-Lagrange (EL) systems. The three-phase PWM ac/dc converters modeled in the a-b-c reference frame are first shown to be EL systems whose EL parameters are explicitly identified. The energy-dissipative properties of this model are fully retained under the d-q-axis transformation. Based on the transformed d-q EL model, passivity-based controllers are then synthesized using the techniques of energy shaping and damping injection. Two possible passivity-based feedback designs are discussed, leading to a feasible dynamic current-loop controller. Motivated from the usual power electronics control schemes and the study of Lee, the internal dc-bus voltage dynamics are regulated via an outer loop proportional plus integral (PI) controller cascaded to the d-axis current loop. Nonlinear PI control results of Desoer and Lin are applied to theoretically validate the proposed outer loop control scheme. The PWM ac/dc converter controlled by the proposed passivity-based current control scheme with outer loop PI compensation has the features of enhanced robustness under model uncertainties, decoupled current-loop dynamics, guaranteed zero steady-state error, and asymptotic rejection of constant load disturbance. Experimental results on a 1.5-kVA PC-based controlled prototype provide verification of these salient features. The experimental responses of a classical linear PI scheme are also included for comparative study.

Voltage and Frequency Control of Self-Excited Slip-Ring Induction Generators

By varying the effective rotor resistance of a self-excited slip-ring induction generator (SESRIG), the magnitude and frequency of the output voltage can be controlled over a wide speed range. A steady-state analysis based on a normalized equivalent circuit enables the control characteristics to be deduced. For a given stator load impedance, both the frequency and the voltage can be maintained constant as the speed is varied, without changing the excitation capacitance. When the stator load is variable, simultaneous voltage and frequency control requires the excitation capacitance to be changed as the rotor resistance is varied. Experiments performed on a 1.8-kW laboratory machine confirm the feasibility of the method of control. Practical implementation of a closed-loop control scheme for an SESRIG using chopper-controlled rotor resistance is also discussed. With a properly tuned proportional-plus-integral (PI) controller, satisfactory dynamic performance of the SESRIG is obtained. The proposed scheme may be used in a low-cost variable-speed wind energy system for providing good-quality electric power to remote regions.

Fuzzy Logic Versus PI Speed Control in High-Performance AC Drives: A Comparison

A frequently discussed application of artificial intelligence inmotion control is the replacement of a standard Proportional Plus Integral (PI)speed controller with a fuzzy logic (FL) speed controller. A common conclusionthat emerges from such studies is that the FL control provides superior performance. However, such a conclusion usually is based on a limited simulation and/or experimental study. It appears that a thorough comparison of the drive behavior under PI and FL speed control, using simulations and an experimental rig, is still missing. This paper attempts to provide such an in-depthcomparison of the operation of a vector-controlled permanent magnet synchronous motor. Speed responses under PI and FL speed control are at first simulated and then measured on the experimental rig for a variety of operating conditions. Twodifferent machines are used in simulation and experimentation, enabling a better generalization of the results. The transients studied include response to a large step speed command from standstill with nominal inertia and an increased inertia, response to a small step speed reference change, response to a step load torque application, and a reversing transient. The transient behavior is examined for various initial speed settings, so that a thorough comparison is enabled. It is shown that superiority of the FL speed control is much less pronounced than it is often portrayed in literature on the basis of limited comparisons. Indeed, in a number of cases PI speed control provided a superior speed response. Predictions obtained by simulations and experimental results are found to be in reasonable agreement, considering all the differences between the simulation and experimental study.

Input-output linearization and zero-dynamics control of three-phase AC/DC voltage-source converters

Nonlinear differential-geometric techniques are proposed for the design of a feedback controller for three-phase voltage-source pulsewidth modulation (PWM) AC/DC boost converters under a cascade control structure. The input-output linearizability of the system modeled in d-q synchronous reference frames is examined. The results lead to a decoupled d-q current control scheme. For the internal DC-bus voltage dynamics (zero dynamics), by considering the d-axis current command as control input and using a square transform on DC-bus voltage, it is shown that this remaining system contains an input memoryless nonlinearity of conic sector type and satisfies the conditions for a Lur'e plant. This suggests a new outer-loop control strategy to control the square of the DC output voltage, rather than DC output voltage itself, utilizing a simple proportional plus integral (PI) controller cascaded to the d-axis current loop. Since most results do not consider the control of zero dynamics, the strategy for the control of zero dynamics via cascade control structure may provide valuable insight for the design of input-output linearized systems in which zero dynamics contain some desired control variables. The absolute tracking concept for Lur'e plants is introduced to prove the global tracking capability with zero steady-state error of the voltage loop. The controlled PWM AC/DC converter has the features of global stability, fast (exponential) tracking of DC-bus voltage command with zero steady-state error, asymptotic rejection of load disturbance, robustness against parameter uncertainties and decoupled dynamical responses between d and q current loops. Also, measurement of load current is not required. All these features are confirmed via laboratory experiments on a 1.5 kVA PC-based controlled prototype.

A fuzzy-logic-based controller for active rectifier

This paper presents a current-sensorless active rectifier specifically designed for low-cost applications. Both the control and the modulation use fuzzy logic. A simple model of the system is given in order to explain the current feedforward control using fuzzy logic and the fuzzy-logic-based modulation, then, the new algorithm is analyzed looking for high performance even using small passive elements and low switching frequency. Performance are compared with those of a closed-loop proportional-plus-integral (PI)-based rectifier with space-vector modulation (SVM). This comparison has been carried out either considering the whole systems or a combination of their components (PI control + fuzzy modulation or fuzzy feedforward control + SVM). The results show that even without current sensors, the low-frequency distortion of the line currents and the DC voltage oscillations produced by the proposed system are very limited, ensuring performance similar to those of PI-based closed loop active rectifiers.

A comparative analysis of fuzzy logic and PI speed control in high-performance AC drives using experimental approach

One of the frequently discussed applications of artificial intelligence in motion control is the replacement of a standard proportional plus integral (PI) speed controller with a fuzzy logic (FL) speed controller. Regardless of all the work, it appears that a thorough comparison of the drive behavior under PI and FL speed control is still missing. This paper attempts to fill in this gap, by providing an in-depth comparison of operation of a vector-controlled permanent-magnet synchronous motor, using at first an experimental rig. Speed responses, obtained under PI and FL speed control, are recorded and compared for a variety of operating conditions. The transients studied include response to a large step speed command from standstill with nominal inertia and an increased inertia, response to small step speed reference change, and response to step load torque application. The transient behavior is examined for various initial speed settings, so that a thorough comparison is enabled. Experimental results are further supplemented with a set of simulation results, obtained using a different permanent-magnet machine and a different FL controller. Better generalization of the results is enabled in this way. It is shown that superiority of the FL speed control is less pronounced than it is often portrayed in the literature on the basis of limited comparisons. Indeed, in a number of cases, PI speed control provides a superior speed response.

Decoupled direct control for PWM inverter-fed induction motor drives

A new direct torque and stator flux control method is presented for pulsewidth modulation (PWM) inverter-fed induction motors. This new strategy, called decoupled direct control (DDC), is based on a decoupling matrix that allows for the separate control of the stator flux and the torque. This method is compared to the well-known direct field-oriented control (FOC) and stator flux vector control (SFVC) methods. Two DDC-based methods are presented. The first determines the stator voltage vector such that the torque and the flux track their respective reference trajectories in one sampling time. The second sets separately the dynamic behavior of the torque and stator flux errors by the use of proportional-plus integral (PI)-type controllers. These methods take into account the full motor dynamics without the need of a coordinate transformation and reduce significantly computation requirements compared to FOC and SFVC. The two proposed strategies have been implemented experimentally and comparisons with FOC and SFVC were carried out. The obtained results show the effectiveness of the proposed PI-DDC strategy.

Real-time gain tuning of PI controllers for high-performance PMSM drives

In this paper, a new and practical real-time gain-tuning method for proportional plus integral (PI) controllers has been formulated and implemented, using the speed control of a permanent-magnet synchronous motor drive system as a testbed. While the novel strategy enhances the performance of traditional PI controller greatly and proves to be a completely model-free approach, it also preserves the simple structure and features of PI controllers. The essential idea is as follows: (1) according to the system dynamics to step variation, define a performance index to evaluate the system response; (2) based on the monotonous relationship between the performance index and an intermediate PI gain parameter, this latter parameter is estimated with a modified binary search algorithm in order to improve the performance index; and (3) finally, PI gains are calculated and renewed according to the estimated intermediate gain parameter. Experiments have been thoroughly carried out to test the proposed method under different conditions. Besides being simple and easy to implement for real-time applications, the proposed method also possesses features such as versatility, stability, and effectiveness.

Feedforward maximum power point tracking of PV systems using fuzzy controller

A feedforward maximum power (MP) point tracking scheme is developed for the interleaved dual boost (IDB) converter fed photovoltaic (PV) system using fuzzy controller. The tracking algorithm changes the duty ratio of the converter such that the solar cell array (SCA) voltage equals the voltage corresponding to the MP point at that solar insolation. This is done by the feedforward loop, which generates an error signal by comparing the instantaneous array voltage and reference voltage. The reference voltage for the feedforward loop, corresponding to the MP point, is obtained by an off-line trained neural network. Experimental data is used for off-line training of the neural network, which employs back-propagation algorithm. The proposed fuzzy feedforward peak power tracking effectiveness is demonstrated through the simulation and experimental results, and compared with the conventional proportional plus integral (PI) controller based system. Finally, a comparative study of interleaved boost and conventional boost converter for the PV applications is given and their suitability is discussed.

Design and implementation of a gain scheduling controller for a water level control system

Abstract The design of a gain-scheduled proportional plus integral (PI) controller for a nonlinear water-tank level control system is presented. A novel approach of determining operating points in terms of interpolation error is also given. The controller is implemented in LABVIEW in the laboratory. The field test results of the system response at different operating conditions clearly illustrate the controller's improved performance over a fixed PI controller.

Active control of resistive wall modesin the large-aspect-ratio tokamak

The large-aspect-ratio model for current-driven external kinks is applied to study control of non-axisymmetric resistive wall modes in tokamaks. Comparison with toroidal computations indicates that the cylindrical instabilities react in similar ways to feedback as the pressure-driven toroidal modes, when the feedback and sensor coils are placed on the low-field side of the torus. However, higher gain is required in the cylindrical case. The cylindrical model is used to gain insights into design issues concerning a feedback system for ITER, with a double wall and superconducting coils. Good control performance and acceptable coilvoltages are found in an initial value problem, where the initial conditions correspond to expected noise levels, when sensors for the poloidal field are placed inside the first wall. This can be accomplished with a PI (proportional plus integral) controller from the voltages of the sensor loops to the voltage over the active coils. The two-wall structure of ITER makes control somewhat more demanding than for tokamaks with a single wall. Adequate control can be achieved also when poloidal sensors are placed outside a single wall, but this requires additional derivative action (PID) and the resulting voltages are significantly higher.