Cascaded PI Control Research Articles

Torque ripple minimization of multi-level inverter fed PMSM drive using modified MPTC

Abstract This paper focuses on investigating the steady-state and dynamic performance of the permanent magnet synchronous motor (PMSM) drive using modified model predictive torque control (MPTC) method with multi-level inverters (MLIs). The MPTC method is simple and easy to implement for motor control as they don’t involve cascaded PI controllers unlike required the conventional controllers, such as field oriented control (FOC) and direct torque and flux control (DTFC). The proposed modified MPTC method eliminates the use of weighing factors and it is a fusion of model predictive current control (MPCC) and MPTC. Initially, the proposed modified MPTC fed PMSM drive is implemented using two-level inverter. It provides better steady-state and dynamic performance, but the ripple contents of torque, flux, and currents are high. In order to reduce the ripple contents and improve the performance of the PMSM drive, a modified MPTC is implemented using three-level inverter. The proposed modified MPTC fed PMSM drive using two-level and three-level inverters are simulated in MATLAB/SIMULINK environment under different operating conditions, such as no-load, loading, speed reversal, step change in speed operations. In order to show the effectiveness and feasibility of the proposed method, it is also validated with the experimental results.

Robust plug-in repetitive control for speed smoothness of cascaded-PI PMSM drive

Non-ideal factors can cause steady-state speed ripples for Permanent Magnet Synchronous Motor (PMSM). In this paper current measurement error is mainly analyzed since it can cause multiple (not only 1st- or 2nd-order as analyzed in the existing literature) harmonics when considering its influence on electrical angle. In order to suppress the ripples, a robust plug-in repetitive controller with phase compensation is designed in the outer speed loop of PMSM cascade PI control system. Compared with the repetitive controller added in the current loop, there are two technical challenges: more stringent requirement of high-frequency disturbance suppression and more complex phase compensation design. Hence, a third-order Butterworth filter with phase correction is proposed which can ensure the system’s ability to resist low-frequency periodic disturbances and the high-frequency stability of the system. A hybrid phase correction method combining lead, lag and linear correction is designed which can ensure the stability and the fast convergence of the system at low frequencies. The designed repetitive controller is robust to PMSM parameters variation within a normal range. The experimental results prove that the proposed control strategy can effectively suppress motor speed fluctuation with good steady-state and transient performance.

A Sliding Surface for Controlling a Semi-Bridgeless Boost Converter with Power Factor Correction and Adaptive Hysteresis Band

This paper proposes a new sliding surface for controlling a Semi-Bridgeless Boost Converter (SBBC) which simultaneously performs Power Factor Correction (PFC) and DC bus regulation. The proposed sliding surface is composed of three terms: First, a normalized DC voltage error term controls the DC bus and rejects DC voltage disturbances. In this case, the normalization was performed for increasing system robustness during start-up and large disturbances. Second, an AC current error term implements a PFC scheme and guarantees fast current stabilization during disturbances. Third, an integral of the AC current error term increases stability of the overall system. In addition, an Adaptive Hysteresis Band (AHB) is implemented for keeping the switching frequency constant and reducing the distortion in zero crossings. Previous papers usually include the first and/or the second terms of the proposed sliding surface, and none consider the AHB. To be best of the author’s knowledge, the proposed Sliding Mode Control (SMC) is the first control strategy for SBBCs that does not require a cascade PI or a hybrid PI-Sliding Mode Control (PI-SMC) for simultaneously controlling AC voltage and DC current, which gives the best dynamic behavior removing DC overvoltages and responding fast to DC voltage changes or DC load current perturbations. Several simulations were carried out to compare the performance of the proposed surface with a cascade PI control, a hybrid PI-SMC and the proposed SMC. Furthermore, a stability analysis of the proposed surface in start-up and under large perturbations was performed. Experimental results for PI-SMC and SMC implemented in a SBBC prototype are also presented.

Comparative Analysis Between PI Conventional and Cascade Control in Heater-PFR-Series

The goals of this work are to compare and analyze the use of PI conventional and Cascade control configuration in heater-plug-flow-reactor-series (Heater-PFR-series) to produce benzene through the reaction of hydrodealkylation of toluene (HDA).The two control configurations were rigorously examined in UniSim dynamic simulation environment. The PI control parameters were tuned by using “autotuner” mode of UniSim. As shown in dynamic simulation study, the two control configurations with its tuning parameters gave the fast and stable responses. This study revealed that the Cascade control acted very well and its responses were better and faster than those in PI-conventional.Keywords: cascade control; dynamic simulation; PFR; PI conventional; UniSim

LQG controller in cascade loop tuned by PSO applied to a DC–DC converter

AbstractThis work presents a Linear Quadratic Gaussian (LQG) controller in cascade loop applied to a Two‐Switch Forward Converter (2SFC). This arrange is suitable for low power battery chargers and provides both performance for reference tracking and disturbance rejection. Once the weighting matrices of the LQG have several parameters to be selected, they are here adjusted by Particle Swarm Optimization (PSO), in a strategy called LQG‐PSO. This allows working intuitively with complex characteristics, such as noise, uncertainties and saturation, just by inserting them into the simulation used for PSO. Since this algorithm is a metaheuristic, this work shows a convergence analysis of PSO for this LQG‐problem. The obtained solutions from different trials resulted in LQG gains contained in a well‐defined region, suggesting that optimality was reached. Simulation results have also shown good dynamic behavior with LQG‐PSO strategy, which has outperformed a cascade PI controller for different scenarios. Experimental results comparing the LQG‐PSO and PI controllers applied to the 2SFC confirmed that LQG‐PSO provided superior performance.

Performance Optimization of Brushless DC Motors for the Mitigation of Voltage Dips, Swells and Short Interruptions in Weak Grids

Normally, the BLDC motor drives a sensitive load which is severely influenced by such disturbances. The main aim of this work is to investigate the performance of BLDC motors when they are tied to weak grids. Thus, this paper presents a study on the performance of the BLDC motor under disturbed utility conditions and implements an efficient solution in order to guarantee a soft operation in the case that a BLDC drives a sensitive load. A buck-boost DC converter is merged with the BLDC drive inverter in order to be able to mitigate voltage dips as well as voltage swells. A short interruption of one or two phases of the grid voltage can also be mitigated. The BLDC motor is controlled via cascade PI-controller layout that has an outer loop for the speed control and inner loop for the DC voltage control. The PI controllers’ gains are optimized by using the ant-colony optimization technique and then implemented in a simulation model using MATLAB/SIMULINK. Six cases of disturbances have been simulated including balanced and unbalanced dips, swells and short interruption of one or two phases of the grid. Simulation results with various disturbances show the ability of the proposed controller to mitigate the grid disturbances with good transient and steady-state responses.

Stability analysis and nonlinear current‐limiting control design for DC micro‐grids with CPLs

In this study, a DC micro-grid consisting of multiple paralleled energy resources interfaced by both bidirectional AC/DC and DC/DC boost converters and loaded by a constant power load (CPL) is investigated. By considering the generic dq transformation of the AC/DC converters' dynamics and the accurate nonlinear model of the DC/DC converters, two novel control schemes are presented for each converter-interfaced unit to guarantee load voltage regulation, power sharing and closed-loop system stability. This novel framework incorporates the widely adopted droop control and using input-to-state stability theory, it is proven that each converter guarantees a desired current limitation without the need for cascaded control and saturation blocks. Sufficient conditions to ensure closed-loop system stability are analytically obtained and tested for different operation scenarios. The system stability is further analysed from a graphical perspective, providing valuable insights of the CPL's influence onto the system performance and stability. The proposed control performance and the theoretical analysis are first validated by simulating a three-phase AC/DC converter in parallel with a bidirectional DC/DC boost converter feeding a CPL in comparison with the cascaded PI control technique. Finally, experimental results are also provided to demonstrate the effectiveness of the proposed control approach on a real testbed.

A signal compensation based cascaded PI control for an industrial heat exchange system

Since the characteristics of the industrial heat exchange system (HES) are drastically affected by variations of the steam pressure, ambient temperature and water quality, it is difficult for the classical cascade PI control system to meet the desirable control objectives. Therefore, in this paper, a deterministic linear model with unmodeled dynamics is used to describe the dynamic characteristics of the HES. It should be noted that the unmodeled dynamics at the previously sampled instant can be calculated using actual measurements and that the tracking error, which includes effects of the rate of changes of unmodeled dynamics on the controlled model, can be accurately determined. An additional compensating signal is obtained with the feedforward control together with a one-step optimal control law. Consequently, the cascade PI control strategy with the signal compensation is established. The simulation and industrial application show that the proposed method can effectively improve the performance of the cascade PI control system, especially when the unmodeled dynamics is subjected to unknown variations.

선박용 전기추진시스템을 위한 PMSM의 센서리스 제어성능에 영향을 미치는 SMO와 PI 제어기의 영향 분석

This paper analyzes some effects on sensorless speed control performance of a sliding mode observer (SMO) for building electric propulsion system of small ships using a permanent magnet synchronous motor (PMSM). An adaptive observer gain and switching function in the SMO are analyzed in detail to reduce the chattering phenomenon in estimated back electromotive force information. Furthermore, cascade low pass filter and PI controller gains are also investigated to progress speed sensorless control performance especially in low speed area. The results of simulations and experiments considering a 1.5 kW PMSM are provided to assure the effectiveness of the optimized SMO and controllers. The results show that the optimized SMO, cascade low pass filter, and controllers can give good speed sensorless control performances even when the PMSM operates at 5rpm.

Permanent-Magnet Machine-Based Starter–Generator System With Modulated Model Predictive Control

This paper describes a hybrid control scheme for a permanent magnet machine-based starter–generator (S/G) system. There has been increased usage of electric drive systems in the transportation sector for increased efficiency and reduced emissions. One of the advantages of utilizing suitable electric drives is the capability to operate as a starter or generator. The control design of such a system should be considered due to the operating requirements and fast load changes. Different control approaches should therefore be considered in order to achieve these goals, which are a current trend in the transportation sector. Model predictive control (MPC) is considered due to its very fast dynamic performance. In particular, modulated MPC (M2PC) was recently introduced and showed significantly better performance than the standard MPC. The control scheme used in this paper utilizes M2PC for the current inner loop and PI controllers for the outer loop. The use of M2PC allows very fast transient-current response for the S/G system. The proposed overall control benefits from reduced current ripple when compared with a full cascaded PI control scheme. Simulation analyzes and experimental results show the capability and performance of the designed controller across both starter and generator modes.

Multi-objective optimization for advanced superheater steam temperature control in a 300 MW power plant

Control of superheater steam temperature (SST) is critical for the safety and efficiency of the coal-fired power plant. However, the conventional cascaded PI controller is faced with great challenges in regulating the SST within a satisfactory range in the environment of extensive load changes, which is inevitably becoming even worse due to the growing integration of the intermittent renewables. To this end, this paper introduces advanced control and multi-objective optimization (MOO) to improve the SST control performance and thus to enable the load being quickly adjusted in a wider range. The inner-loop PI controller parameters are optimized based on the tracking and regulation performance objectives subject to a robustness constraint. The improvement of the outer-loop controller involves two steps, (i) the outer-loop PI controller is upgraded to active disturbance rejection controller (ADRC) in order to eliminate the sluggish response to the external load disturbances; (ii) a mathematical algorithm is developed to depict the stable region for the ADRC parameters, serving as the MOO search space. Comparative simulations show the advantage of the proposed strategy, which is confirmed by a field test in an in-service 300MW power plant. It shows that the proposed strategy leads to a much smaller temperature deviation in both constant-load and load-varying conditions than the conventional control, making it less sensitive to the external disturbances. Furthermore, the load demand can be shifted more flexibly in a wide range (from 10MW to 15MW) while the SST is strictly confined within the allowable range, indicating a promising prospect of the proposed strategy in a power grid with high renewables penetration.

Cascaded PI Controller Tuning for Power Plant Superheated Steam Temperature based on Multi-Objective Optimization

To improve the superheated steam temperature (SST) control performance, this paper considers the conflicting objectives in SST control, multi-objective optimization (MOO) algorithm is employed in this paper. Firstly, the inner-loop PI controller is optimized by considering the objectives of set-point tracking and disturbance rejection, with and without constraints on robustness level. It is found that robustness constraint is essential in the optimization. Secondly, the regulation performance of the outer-loop PI controller is addressed by optimizing the disturbance rejection and robustness simultaneously. The parameter are determined based on the simulation comparison between the non-dominated solutions. The simulation results demonstrate a promising prospect of promoting the proposed strategy to more industrial practices.

Experimental evaluation of control performance of MPC as a regulatory controller

Proportional-integral-derivative (PID) control is widely practised as the base layer controller in the industry due to its robustness and design simplicity. However, a supervisory control layer over the base layer, namely a model predictive controller (MPC), is becoming increasingly popular with the advent of computer process control. The use of a supervisory layer has led to different control structures. In this study, we perform an objective investigation of several commonly used control structures such as ‘Cascaded PI controller’, ‘DMC cascaded to PI’ and ‘Direct DMC’. Performance of these control structures are compared on a pilot-scale continuous stirred tank heater (CSTH) system. We used dynamic matrix control (DMC) algorithm as a representative of MPC. In the DMC cascaded to PI structure, the flow-loops are regulated by the PI controller. On top of that a DMC manipulates the set-points of the flow-loops to control the temperature and the level of water in the tank. The ‘Direct DMC’ structure, as its name suggests, uses DMC to manipulate the valves directly. Performance of all control structures were evaluated based on the integrated squared error (ISE) values. In this empirical study, the ‘Direct DMC’ structure showed a promise to act as regulatory controller. The selection of control frequency is critical for this structure. The effect of control frequency on controller performance of the ‘Direct DMC’ structure was also studied.

The Optimal Controller Design of Buck-Boost Converter by using Adaptive Tabu Search Algorithm Based on State-Space Averaging Model

Normally, the artificial intelligence algorithms are widely applied to the optimal controller design. Then, it is expected that the best output performance is achieved. Unfortunately, when resulting controller parameters are implemented by using the practical devices, the output performance cannot be the best as expected. Therefore, the paper presents the optimal controller design using the combination between the state-space averaging model and the adaptive Tabu search algorithm with the new criteria as two penalty conditions to handle the mentioned problem. The buck-boost converter regulated by the cascade PI controllers is used as the example power system. The results show that the output performance is better than those from the conventional design method for both input and load variations. Moreover, it is confirmed that the reported controllers can be implemented using the realistic devices without the limitation and the stable operation is also guaranteed. The results are also validated by the simulation using the topology model of MATLAB and also experimentally verified by the testing rig.

Design and Implementation of Cascade LQR Controller for Stabilization of Two-Wheeled Robot

Abstract In this paper the developed two-wheeled robot and cascade LQR controller, Kalman filters, PI and PID controllers are presented. The cascade LQR controller stabilizes the two-wheeled robot in upright position. The PID controller ensures good tracking of wheel position reference and the PI controller steers two-wheeled robot rotation around the vertical axis. A software in MATLAB®/Simulink environment intended for design and generation of control code which is embedded in a Texas Instruments Digital Signal Controller is developed. Simulation and experimental results of system performance are given that confirm the efficiency of the control system developed.

Enhancement of feed drive dynamics using additional table speed feedback

The tracking performance and disturbance response of feed drive systems with P–PI cascade control principle are limited by the first natural frequency of mechanical transmission elements. In order to overcome this limitation, a new control principle for feed drives with large inertia ratio is presented. It synthesizes a weakly set motor speed controller with an additional table speed control loop. The bandwidth is increased without any extra sensor or actuator. The large inertia ratio can be achieved by using a high dynamic motor with small inertia and a ball screw with high pitch.

Fictitious Reference Iterative Tuning for Cascade PI Controllers of DC Motor Speed Control Systems

Fictitious Reference Iterative Tuning for Cascade PI Controllers of DC Motor Speed Control Systems

X4-MaG: A Low-Cost Open-Source Micro-Quadrotor and its Linux-Based Controller

The new open-source quadrotor platform called X4-MaG presented here was developed for academic and research applications. X4-MaG is a small, low-cost open quadrotor of only 307–grammes which offers two levels of controllers providing a manual mode and an automatic mode thanks to powerful Linux-based controller embedded onboard. The experiments presented here show the reliability of the open hardware and software embedded onboard the quadrotor. To estimate the robot s attitude, a quaternion-based complementary filter requiring very few computational resources was developed and implemented on an 8-bit Arduino board. It was also established that the stabilization feedback system based on quaternions tracks the attitude setpoints with precision up to twice greater than a classical cascaded PI controller. The controllers and estimators were designed in the Matlab/Simulink environment and directly implemented onboard the tiny Linux-based autopilot board using a custom made toolbox (RT-MaG toolbox). The autopilot was tested in the brand-new Marseilles Flying Arena with various 3-D flight trajectories and found to be highly accurate with errors of only 0.7cm in hover and less than 3.2cm at 1.2m.s−1. The X4-MaG quadrotor was able to reach speeds greater than 2m.s−1 and reject attitude disturbances of 20′ within 0.8s.

Nonlinear Control of a Hybrid Batch Reactor

This paper introduces a new class of advanced control algorithms for batch-reactor temperature control where a nonlinear PI controller with a feed-forward part in a cascade combination with a P controller is used. The main goal of the algorithm is to optimize the production by lowering the costs of the temperature control and increasing the quantity and quality of the chemical, biological, pharmaceutical, food and beverage products produced in these reactors. The algorithm is designed to cope with the constraints and the mixed discrete and continuous nature of the process by manipulating variables for heating and cooling. The stability and robustness of the control algorithm is proven through the Popov Stability Criterion. The simulation results of the proposed algorithm show much better performance compared to a conventional cascade PI control structure, which is most commonly used in industry. Furthermore, the study also contains a real-time implementation on a bioreactor with the proposed algorithm.

State and control system variables sensitivity to rotor asymmetry in the induction motor drive

Purpose – The aim of this paper is to undertake analysis and comparison of the closed‐loop and sensorless control systems sensitivity to the broken rotor for diagnostic purposes. For the same vector control system induction motor drive analysis concerning operation with the asymmetric motor, broken rotor fault handling and operation were investigated. Reliability, range of stable operation, fault symptoms and application of diagnosis methods based on control system variables utilization was analyzed.Design/methodology/approach – Induction motor drive vector control system synthesis was applied using the multiscalar variables of the machine model with nonlinear feedback linearization applied to use classical cascaded PI controllers for the speed‐torque and flux decoupled control. Speed observer was applied for the rotor flux and rotor speed estimation for the sensorless control system synthesis.Findings – Relative sensitivity of the state and control system variables to broken rotor fault based on experime...