Pole-zero Cancellation Method Research Articles

A Comparison of Classical and Reinforcement Learning-based Tuning Techniques for PI controllers

This study compares two tuning techniques for Proportional-Integral (PI) controllers. The first strategy uses the Pole-Zero Cancellation method, a well-established technique in the field of dynamic systems control. The second strategy introduces an innovative approach by using a reinforcement learning-based technique to adaptively tune a PI controller. To compare these tuning methodologies, a Heating, Ventilation and Air Conditioning (HVAC) control system was selected as a case study to guarantee users’ thermal comfort. In both cases, the HVAC process was modelled as a first-order system without time delay. In addition, the performance of the proposed controllers analysed by evaluating temperature set-point tracking and disturbance rejection caused by the occupancy of people in the room. The results demonstrate that classical methods are efficient and quick to implement, while the use of RL also enables optimization of energy consumption and reduction of operating costs.

PSO Self-Tuning Power Controllers for Low Voltage Improvements of an Offshore Wind Farm in Taiwan

A de-loaded real power control strategy is proposed to decrease the real power output and increase the reactive power output of a grid-connected offshore wind farm in order to improve the voltage profile when the wind farm is subject to a grid fault. A simplified linear model of the wind farm is first derived and a fixed-gain proportional-integral (PI) real power controller is designed based on the pole-zero cancellation method. To improve the dynamic voltage response when the system is subject to a major disturbance such as a three-phase fault in the grid, a self-tuning controller based on particle swarm optimization (PSO) is proposed to adapt the PI controller gains based on the on-line measured system variables. Digital simulations using MATLAB/SIMULINK were performed on an offshore wind farm connected to the power grid in central Taiwan in order to validate the effectiveness of the proposed PSO controller. It is concluded from the simulation results that a better dynamic voltage response can be achieved by the proposed PSO self-tuning controller than the fixed-gain controller when the grid is subject to a three-phase fault. In addition, low voltage ride through (LVRT) requirements of the local utility can be met by the wind farm with the proposed power controller.

Design of voltage and current controller parameters using small signal model-based pole-zero cancellation method for improved transient response in microgrids

Microgrids are supposed to provide stable power for seamless utility-grid interaction under all conditions as stated by IEEE-1547 standard. But, the use of power electronic inverter makes the microgrid sensitive to transients than synchronous generator-based plants. This degrades the voltage/frequency responses during transients, which can lead to transient stability problem if not controlled properly. Hence, the design of effective closed-loop voltage and current (V/I) controllers is highly desired to control the inverter output against the disturbances. The V/I controllers are based on PI (proportional-cum-integral) formulas. Thus, the effectiveness of V/I controllers relies on how accurate that their gain parameters are tuned. Many PI-tuning methods have been developed in the literature, but, it is yet difficult to identify a suitable method for an application. Also, only a few researchers have focused on the microgrids due to the complexity involved in its controller design by the presence of V/I cascaded dual-loop. Hence, to address this problem, this paper proposes a novel way of designing V/I controller parameters by using pole-zero cancellation method. This method is implemented by deriving the microgrid’s small-signal model. This improves the transient response through reduced system order and/or alleviated sluggish/marginal-stable/unstable poles by adding zeros at same places where those poles are laid, to in effect cancel them. The efficacy of the proposed method over existing methods is assessed by plotting frequency and voltage responses under different test conditions. From the simulation results, it is witnessed that the proposed method relatively improved the transient characteristics of microgrids.Article HighlightsAnalyzes the applicability of conventional PI tuning methods for microgrid controllers’ design.Proposes a novel small signal model based pole-zero cancellation method for the design of microgrid controllers.Enhances the gain margin, which improves the stabilization capacity of the system when subjected to disturbances.Improves the transient behavior of frequency and voltage responses, which ensure the safety of sensitive loads.

Pole-Zero Cancellation Method for Multi Input Multi Output (MIMO) Temperature Control in Heating Process System

With the rapid development of industrial technology, the multi-point (multi-input multi-output) heating processing systems with integrated temperature control have been increasingly needed to achieve high-quality and high-performance processing. In this paper, in response to the demand for proper transient response and to provide more accurate temperature controls, a novel pole-zero cancelation method is proposed for multi-input multi-output (MIMO) temperature control in heating process systems. In the proposed method, the temperature differences and transient characteristics of all points can be improved by compensating dead time difference and coupling effect together by matrix compensation and pole-zero cancelation with the feedforward reference model. Both simulations and experiments were carried out. The results were compared to the well-tuned conventional PI control system and PI plus decoupling compensation system to evaluate the control efficiency of the proposed method.

Self-Adaptive Firefly Algorithm with Pole Zero Cancellation Method for Controlling SMIB Power System

The accurate analysis and controller design for high-order systems are important issues. In this paper, a design of controller is suggested to Single Machine Infinite Bus (SMIB) System in which its order is reduced by the proposed self-adaptive Firefly Algorithm (FA). First, the dynamic adaption to the dominant parameters of the standard FA is proposed for overcoming its disadvantages and improving its ability in searching the global optimum solution with application to reduce the model order of SMIB. The parameters which are proposed to self-adaption are both of the light absorption based on the mean distance of fireflies’ positions and the step setting based on the fitness information to the status of preceding firefly and the current fireflies. Second, proportional–integral–derivative (PID) controller is suggested to be designed by pole zero cancellation method via the step response characteristics of the reduced-order SMIB to be applied to its high order. The efficiency of the proposed methods is tested on high-order SMIB to get its corresponding low order and to control it. The experimental results prove the efficacy of self-adaptive FA compared to the standard FA and the methods in the literature in terms of step response characteristics using error indices. The proposed methods assure the stability of the reduced order and the ability of the designed controller to handle both high and low-order model.

Discrete-Time Voltage Controller for Voltage Source Converters With <italic>LC</italic> Filter Based on State-Space Models

State-space control could provide both high dynamic performance and sufficient stability margin to voltage source converters with LC filter. However, an inherent digital delay induced by a digital control system deteriorates performance and even induces instability. In this paper, a discrete-time voltage controller is proposed based on a discrete state-space model. First, a state feedback control with a reference feedforward path is designed in the discrete-time domain with consideration for the digital delay. Second, an output current decoupling path is augmented to minimize the effects of an output current disturbance. Controller gains are derived as the functions of system parameters and design specifications, which is based on a direct pole placement and pole-zero cancellation method in a rotating reference frame. Moreover, a parameter sensitivity and digital implementation are discussed to improve the performance and stability of the proposed controller. The effectiveness of the proposed controller is verified with various experimental results. It shows that a filter resonance is well damped out while maintaining wide voltage control bandwidth.

Direct Digital Design of PIDF Controllers with ComPlex Zeros for DC-DC Buck Converters

This paper presents a new direct digital design method for discrete proportional integral derivative PID + filter (PIDF) controllers employed in DC-DC buck converters. The considered controller structure results in a proper transfer function which has the advantage of being directly implementable by a microcontroller algorithm. Secondly, it can be written as an Infinite Impulse Response (IIR) digital filter. Thirdly, the further degree of freedom introduced by the low pass filter of the transfer function can be used to satisfy additional specifications. A new design procedure is proposed, which consists of the conjunction of the pole-zero cancellation method with an analytical design control methodology based on inversion formulae. These two methods are employed to reduce the negative effects introduced by the complex poles in the transfer function of the buck converter while exactly satisfying steady-state specifications on the tracking error and frequency domain requirements on the phase margin and on the gain crossover frequency. The proposed approach allows the designer to assign a closed-loop bandwidth without constraints imposed by the resonance frequency of the buck converter. The response under step variation of the reference value, and the disturbance rejection capability of the proposed control technique under load variations are also evaluated in real-time implementation by using the Arduino DUE board, and compared with other methods.

Mechanical design and optimal control of humanoid robot (TPinokio)

The mechanical structure and the control of the locomotion of bipedal humanoid is an important and challenging domain of research in bipedal robots. Accurate models of the kinematics and dynamics of the robot are essential to achieve bipedal locomotion. Toe-foot walking produces a more natural and faster walking speed and it is even possible to perform stretch knee walking. This study presents the mechanical design of a toe-feet bipedal, TPinokio and the implementation of some optimal walking gait generation methods. The optimality in the gait trajectory is achieved by applying augmented model predictive control method and the pole-zero cancellation method, taken into consideration of a trade-off between walking speed and stability. The mechanism of the TPinokio robot is designed in modular form, so that its kinematics can be modelled accurately into a multiple point-mass system, its dynamics is modelled using the single and double mass inverted pendulum model and zero-moment-point concept. The effectiveness of the design and control technique is validated by simulation testing with the robot walking on flat surface and climbing stairs.

Reproduction of Vehicle Vibration by Acceleration-Based Multi-Axis Control

This paper presents the development of the 3-axis vibrating machine precisely reproducing vehicle's acceleration characterized with multi-mode vibration. For the reproduction in vertical axis, at first, the system identification experiment of the vibrator is carried out. Using the identified model, the feedforward control based on the pole-zero cancellation method is applied to realize the ideal transfer gain of one from the acceleration reference to its output. Next, for reproducing the acceleration in horizontal plane, the continuous-path tracking (CPT) control system is constructed using the precision XY stage. In the CPT control system, the disturbance observer is introduced focusing on the accurate reproduction within limited frequency. Finally, the experimental verification of the proposed 3-axis acceleration vibration reproduction system is shown using the developed DSP-controlled 3-axis vibrating machine.

Gain scheduling control scheme for improved transient response of DC/DC converters

In this study, a gain scheduling control scheme for DC/DC converters is proposed to improve the transient response to load current step inputs with high slew rate. The proposed control scheme is designed with pole-zero cancellation method to adaptively auto-tuning parameters of the compensator for efficiently improving the output transient response. The adaptive voltage position (AVP) function is also included in multiphase buck converter for voltage regulator (VR) application to verify the proposed gain scheduling scheme. Owing to the improved transient response, output capacitance can be significantly reduced with the proposed scheme. The proposed gain scheduling scheme is implemented on single-phase and multiphase DC/DC synchronous buck converter by 12 V input, 1.2 V output, individually. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed scheme.

Design of PID Controller for Higher Order Continuous Systems using MPSO based Model Formulation Technique

This paper proposes a new algebraic scheme to design a PID controller for higher order linear time invariant continuous systems. Modified PSO (MPSO) based model order formulation techniques have applied to obtain the effective formulated second order system. A controller is tuned to meet the desired performance specification by using pole-zero cancellation method. Proposed PID controller is attached with both higher order system and formulated second order system. The closed loop response is observed for stabilization process and compared with general PSO based formulated second order system. The proposed method is illustrated through numerical example from literature.

Two-Degree-of-Freedom Self-Tuning Control for Motor Drives Using Pole-Zero Cancellation Method

In this paper, we present an excellent method named pole-zero cancellation (PZC) for designing motor control systems. PZC is performed in the z plane. A control system consists of three controllers, i.e., a speed controller, a position controller, and an adaptive identifier. The speed controller has two degrees of freedom: disturbance suppression and tracking speed, both of which can be regulated. The pulse transfer function used for regulating the tracking speed has two poles and one zero. When one pole and one zero coincide and cancel each other, the pulse transfer function is of the first-order lag type, and overshoots do not appear. The adaptive controller determines the coefficients of the pulse transfer function and adjusts the speed controller automatically so that the poles and zeros coincide. The transfer function of the position controller also has one pole and one zero, which cancel another pole and zero; pole 1 in the closed loop is not cancelled, and hence, position overshoots do not appear.A 2.2-kW induction motor is tested. The motor torque is controlled using a rapid torque control method. In this paper, first, the tracking-speed characteristics and the tracking-position characteristics are presented. Next, the identified transient coefficients are given, and finally, the disturbance-suppression characteristics are discussed. The experimental results prove the usefulness of the proposed method.

Designing of PID Controller for Discrete Time Linear System Using Balanced Approach Reduced Order Model

Modeling physical systems usually results in complex high-order dynamic models. It is often desirable to approximate these models by simpler models with reduced order. This study deals with the design of discrete time linear system using a balanced approach reduced order model. The reduced order model retains the desired state variable which contains a significant contribution. A PID controller is designed for the reduced second order model to meet the desired performance specifications by using pole-zero cancellation method. The stabilization of linear discrete time system is achieved by selection of parameters of the PID controller. A numerical example is given to illustrate the design method.

Design of an optical servosystem using a structural optimizing method considering controllability. (2nd report. The structural optimization of an optical pick-up model using the pole-zero cancellation method).

The optical servosystem requires a high degree of controllability. However, it is very difficult to realize a servosystem with higher controllability since the dynamic characteristics of an optical pick-up influence the stability of the servosystem. Therefore, both a control system and a structural system must be considered simultaneously in the design stage of the optical servosystem. The purpose of this paper is to determine the structural system in order to obtain higher controllability. Firstly, the authors investigate the structural characteristics of an optical pick-up model and explain the necessity of structural optimization to improve servo characteristics. Secondly, the structure of the optical pick-up model is optimized by using the Pole-Zero Cancellation Method proposed by the authors. The servosystem is comprised of the optical pick-up model with the phase-lead compensator. Finally, the characteristics of the servosystem are investigated and the improvements are confirmed. The practicability of this design method is verified by the experiments.

Design of an optical servosystem using a structural optimizing method considering controllability. (3rd report. An application of the pole-zero cancellation method to development of optical pick-up).

The design method of an optical servosystem and its practicability were discussed in the first and second reports. In this paper, the authors develop a practical optical pick-up. Firstly, we propose a new type of optical pick-up which is a simple monobloc hinge-type structure and investigate its structural characteristics. As a result, it is confirmed that the structural characteristics of the optical pick-up influence the stability of the servosystem; accordingly, a structural optimization is necessary to obtain a high degree of controllability. Secondly, the optical pick-up is optimized by using the Pole-Zero Cancellation Method and the servosystem is comprised of the optimal pick-up with the phase-lead compensator. The results of both analytical and experimental investigations verify that the servo characteristics are improved and sufficient characteristics are satisfied such that the servo specifications are realized