Republic Of Iraq Ministry of Higher Education and Scientific Research Tikrit University Electrical Engineering Department Model Predictive Speed Control of DC Motor A graduation project is submitted to the Electrical Engineering Department in partial fulfillment of the requirements for the degree of Bachelor of Science in Electrical Engineering. By Abdul Hakim Jassim Muhammad Malaak Samir Ibrahim Supervisor Assi. Prof. Dr. Thamer Hassan Attia 1443 2022 بسم اهلل الرمحن الرحيم اَّلل اله ِذين آمنُوا ِم ْن ُكم واله ِذين أُوتُوا ال ِ ْم ل ْع يَ ْرفَ ِع هُ َ َ َْ َ َ ٍ ِ ِ ه ي ب خ ن و ل م ع ت ا ِب اَّلل و ات ُ َ َ َ َ ر َد َر َج َ ُ ْ َ صدق اهلل العظيم سورة المجادلة اآلية ()11 1 Acknowledgment First of all, I am thankful to the glory of Allah for all things. I would like to express my deepest gratitude to my supervisor Hassan Attia Dr. Thamer for his invaluable guidance, support, advice and, encouragement during the preparation of this thesis (thank you for never giving up on me). I also would like to acknowledge the staff of Electrical Engineering Department / University of Tikrit and the people who helped me (thank you very much). My sincere thanks go to my family for their help and encouragement. 2 CONTENTS Page Subject CHAPTER ONE: INTRODUCTION 1.1 General ……………………….. 5 1.2 Classification of DC motor ……………………….. 6 1.3 Permanent Magnet DC Motor ……………………….. 6 1.4 Objectives ……………………….. 8 CHAPTER TWO: DC MOTOR ……………………….. 9 2.1 Dc Motor 2.2 Advantages of Permanent Magnet DC Motor or PMDC Motor ….…….13 2.3 Disadvantages of Permanent Magnet DC Motor or PMDC Motor ……..13 2.4 Modelling of the system ……………………….. 14 CHAPTER THREE: PREDICTIVE CONTROL 3.1 Predictive Control ………………………..16 3.2 Math Presentation ………………………..17 ……………………..… 18 3.3 System Representation ………………………..23 3.4 Optimal Control Problem CHAPTER FOUR: EXPERIMENTAL WORK REFERENCES 3 List of Nomenclature Symbol Description Unit K i T P N J Torque Constant The Current Of The Armature The Torque Power Speed Rotor Inertia ---mA n.m W m.s Kg.m2 List of Figure Figure No. 1.1 1.2 2.1 3.1 3.2 DC motor Classification Of DC Motor Examples of DC drives System Representation Interactive Algorithm Page No. 5 6 11 19 25 3.3 NonIneractive Algorithm 26 3.4 Parallel Algorithm 26 3.5 Description The effect of add 𝐾𝑝 (𝐾𝑖, 𝑎𝑛𝑑 𝐾𝑑) held constant 4 27 CHAPTER ONE INTRODUCTION CHAPTER ONE INTRODUCTION CHAPTER ONE INTRODUCTION 1.1. General In a DC motor, an armature rotates inside a magnetic field. The basic working principle of a DC motor is based on the fact that whenever a current-carrying conductor is placed inside a magnetic field, there will be mechanical force experienced by that conductor [1]. All kinds of DC motors work under this principle. Hence for constructing a DC motor, it is essential to establish a magnetic field. The magnetic field is established by using a magnet. You can use different types of magnets – it may be an electromagnet or it can be a permanent magnet. A Permanent Magnet DC motor (PMDC motor) is a type of DC motor that uses a permanent magnet to create the magnetic field required for the operation of a DC motor, as shown figure (1.1). figure (1.1): DC motor [A] 5 CHAPTER ONE INTRODUCTION 1.2. Classification of DC motor Based on the type of construction and electrical connection, DC motor can be categorized into four major types. A brief chart (based on the type of construction and electrical connection) is given below: figure (1.2): Classification Of DC Motor 1.3 Permanent Magnet DC Motor In these types of DC motor, the permanent magnet is used to create a magnetic field. In this, not input current is consumed for excitation. Permanent magnet DC (PMDC) machines with brushes are being of less importance today, and they are continuously replaced by permanent magnet synchronous machines (PMSM) 6 or brushless DC (BLDC) CHAPTER ONE INTRODUCTION machines. Despite this fact, PMDC machines still have their own field of use in various types of applications, from machine tools and small home appliances to photovoltaic, robotic, and medical applications. They are widely used as auxiliary drives in automotive solutions due to the presence of a DC grid in modern vehicles, and they are especially suitable for battery-operated equipment. The biggest drawback of these machines is a commutator, which needs regular maintenance and causes sparkles, and, therefore, the machines cannot be used in an explosive environment. On the other hand, linear speed-torque curve, high torque at low speed, and the simplicity of torque/speed control are well-known advantages of the conventional PMDC machines. Coreless PMDC vibrations, and machines have smoother motor almost no running cogging at low torque, speed fewer against conventional PMDC machines. In order to work in all four quadrants, these machines are often supplied by an H-bridge DC-DC converter, which changes the mean value of the voltage on the machine terminals. This converter uses pulse-width modulation (PWM) with a 2-level or 3level type of control [2]. The PMDC machines have been extensively studied and many advanced control strategies have been presented in the past, but they are studied by many researchers even today [3–6]. Among the new approaches, a new and attractive alternative for the control of H-bridge supplied PMDC machine is finite control set model predictive control (FCSMPC) [7]. A framework for the analytical derivation of FCSMPC can be found in [8]. FCS-MPC has been applied to the control of several types of electrical drives. Techniques for reducing a steady-state error of FCS-MPC controlled H-bridge have been presented in [9]. Detailed description of the algorithm design for the commutation torque ripple minimization applied to a BLDC machine can be found in [10]. Direct speed control 7 CHAPTER ONE INTRODUCTION of a PMSM for a single-mass system has been developed in [11]. Predictive strategy for the speed control of a two-mass system driven by PMSM has been proposed in [12], introducing reduced order extended Kalman filter for mitigation of oscillations and compensation of load torque disturbances. In authors’ opinion and supported by the literature review, a FCS-MPC for the PMDC machine has not been reported yet. 1.4. Objectives The objectives of this paper lie in the following: 1. For the first time, a predictive control strategy is proposed for the combination of a DC-DC converter and a PMDC machine. 2. The proposed predictive control is compared to the conventional approach based on PI controllers. 3. In addition, we have proposed a new cost function that is different from the commonly used ones [8]. 4. In the novel cost function, two current components are introduced: a current component corresponding to a dynamic feed forward torque, iF, and a current component corresponding to a static load torque, iL 5. We will also show how these components affect the overall control performance of the FCS-MPC controller. 8 CHAPTER TWO DC MOTOR CHAPTER TWO DC MOTOR CHAPTER TWO DC MOTOR 2.1. DC MOTOR DC motors have common use and affect industrial applications such as lathes, fans, pumps, discs, and band saw drives. However, the controllability, lower cost, higher efficiency, and higher current load capacity of static power transformers have brought a significant change in the performance of electric drives. The spin-in motors spin the spin because the current flowing through the coil produces a magnetic field repulsed by a permanent magnet mounted on the rebar. When the spin coil spin brushes make contact with the coil, the polarity voltage is reversed, and the coil is alienated again [13]. It is substantial to know how the DC engine can accelerate the manipulates of robot. The voltage applied on the DC motors effects the speed of DC motors, on the characteristics of the engine, and the load on the wheels. Find out the shape of the wheel acceleration curve without sliding it is useful for the shape of the cyclic wheel acceleration curve without slide is useful for the implementation of controllers that provide traction control. Traditionally, DC models have developed close loop control systems associated with their use to propel them using classical control theory techniques, based on the transfer functions. The techniques of designing a control and system analysis are widely repressed and very valid to be utilized in real time development. In some cases we can be find the solution by advanced hardware technology and by the advanced use of software, the control system is easily analyzed and details. DC motors can be used in different applications and can be used in different sizes and rates. The processor calculates the real actual speed of the motor by sensing the voltage of the terminal. Then 9 CHAPTER TWO DC MOTOR compares the actual speed of the motor with the signal speed and it generates the comfortable control signal that is entered into the triggering unit.[14]. We pay attention DC motors with permanent magnets. The power provided by the engines is torque. The torque stall included in the DC motor information from data sheet and is the extreme torque produced by the engine when the torque is not grasped and prevents rotating.[15] The spin-in motors spin because the current flowing through the coil will make a magnetic field repulsed by the permanent magnet and it will be mounted in the coil producing a magnetic field repulsed by a permanent magnet mounted in the voltage polarity in a manner that the coil is repulsed back, etc. and so on. When the engine is rotating, the V voltage applied to the engine dwindles from the E voltage produced by the rotor. The rotor spin faster, the greater the value of E.[16] Due to their high reliability, flexibility and cheapness, the DC motors as shown in Fig. 1 are commonly used in industrial applications, robot maneuvers and household appliances where the speed and position of the engine is required [17]. DC machines are distinguished by their variety. Through different combinations of series- shunt, and individually-encased field coils they can be designed to display a wide range of volt-amp or torque-speed properties for a dynamic and steady-state operation. Due to of the ease with which the control systems of DC machines can be used frequently in many applications that require a wide range of engine speeds and precise control of engine output. outstanding to that of A.C. motor. Therefore, it is not astonishing to note that industrial drives. [18]. DC engines are rarely used in normal applications because all companies of electrical supply offer AC power. 10 CHAPTER TWO DC MOTOR However, for exceptional applications such as steel mills , crane tools, and electric trains, it is useful to convert AC to direct current to use DC motors. The cause of the relationship between speed and torque characteristics of dc, the engines are far Fig (2.1). Examples of DC drives In the control of closed loop system, DC is an industrial applications and researches are very common. The torsion tester is often used to provide a quick feedback to control movement [19, 20]. In the involvement of flexibility in the system, for example, shaft loader for compatible vehicles or flexible coupling, the process in the servo control becomes fully contained because the limited shaft hardness provides resonance and shaft. These are strongly unwanted effects that can be discarded by proper controller design. To be able to obtain a model, estimation, and exclude these high frequency resonance problems, it is necessary to have an estimation model of the complete system including sensors. 11 CHAPTER TWO DC MOTOR In DC motor, the position with and without velocity control by using tachometer feedback, the familiar tachometer model [21, 22] It is sufficient for less exigent motion control exercises, but is unavailing to supply high-speed and high-accuracy movement control. In fact, when this mathematical model was used to estimate the frequency response of a system with multiple shaft elasticity, it resulted in faulty results that did not conform to empirical measurements. This led to an achievement leading to a more accurate and accurate model of the torsion tester. A comprehensive analysis of a modeling has been conducted It was found that the reciprocal induction between the windings of the motor and the tachometer, however, leads to the term magnetic coupling in the expression of the output voltage of the tachometer. This effect is quantified and extracted in this paper, and the improved tachometer model is acquired using the mail rules of electromagnetic. After that, this model is then used to analyze and calculate the tachometer of a DC motor. It turns out that the new analytical estimations are in perfect agreement with empirical measurements. The result of these dynamics shows the tachometer on the response system more than everything. It is seen that the dynamics of the tachometer affect the transfer function of the system in a systemdependent manner. This is illustrated in the following sections. We find that the dynamics of the tachometer contribute to some additional zeros to the system transfer function in general. The number of these additional zeros depends on the system itself. These zeros are located in the s-plane by the relative orientation of the static field of the tachometer with respect to the static field of the motor. Having proved the model experience, we later integrated it into the feedback control design to control the motion of the engine ds, which is the ultimate 12 CHAPTER TWO DC MOTOR goal of the whole process. The importance and impact of these additional zeros are discussed in terms of the design of the controller in detail. 2.2. Advantages of Permanent Magnet DC Motor or PMDC Motor The advantages of a PMDC motor are: 1. No need of field excitation arrangement. 2. No input power in consumed for excitation which improve efficiency of DC motor. 3. No field coil hence space for field coil is saved which reduces the overall size of the motor. 4. Cheaper and economical for fractional kW rated applications. 2.3. Disadvantages of Permanent Magnet DC Motor or PMDC Motor The disadvantages of a PMDC motor are: 1. The armature reaction of DC motor cannot be compensated hence the magnetic strength of the field may get weak due to the demagnetizing effect of the armature reaction. 2. There is a chance of getting the poles permanently demagnetized (partial) due to excessive armature current during the starting, reversal, and overloading conditions of the motor. 3. The field in the air gap is fixed and limited – it cannot be controlled externally. This makes it difficult for this type of motor to achieve efficient speed control of DC motor in this type of motor is difficult. 2.4. Modelling of the system A model based on the motor specifications needs to be obtained. Figure-1 shows the DC motor circuit with torque and rotor angle consideration The torque T of the motor is related to the current of the armature, i , by a torque constant K; 13 CHAPTER TWO DC MOTOR 𝑇= 𝐾𝑖 (1) The produced voltage, Ea , is proportional to angular velocity by 𝐸𝑎 = 𝐾𝑤𝑚 𝐾= (2) 𝑑ѳ (3) 𝑑𝑡 By using Newton’s law and Kirchhoff’s law in Fig 1. and we can get the following equations. b 𝑑𝜃 𝑑𝑡 𝑅𝑖 + L +J 𝑑𝑖 𝑑𝑡 𝑑𝜃 2 𝑑𝑡 =Ki = 𝑉 (𝑠) − k (4) 𝑑𝜃 𝑑𝑡 (5) Using the Laplace transform, equations (3) and (4) can be written a 𝑏𝑠 Ѳ(𝑠) + 𝐽𝑠 Ѳ(𝑠) = 𝐾 𝑖(𝑠) 𝐾 𝐼 ( 𝑠) + 𝐿𝑠 𝐼 (𝑠) = 𝑉 (𝑠) − 𝐾𝑠 Ѳ(𝑠) (6) (7) The Laplace 𝑠 operator. From (7) we can find I(s) I(s) = 𝑉(𝑠)−𝐾𝑠𝜃(𝑠) 𝑅+𝐿(𝑆) (8) and substitute it in (5) to bs θ(s) = Js θ(s) = 𝐾(𝑉(𝑠)−𝐾𝑆𝜃(𝑠)) 𝑅+𝐿(𝑠) (9) we can find the transfer function of the output angle θ to the input voltage V(s) as follow 14 CHAPTER TWO DC MOTOR Ga(s) = 𝜃(𝑠) 𝑉(𝑠) = 𝐾 {𝑆[(𝑗𝑠+𝑏)(𝑅+𝐿𝑠)+𝑘 2 ]} (10) It is simple to see that the transfer function of relationship between the input voltage V(s) with the angular velocity is ; 𝐾 Ga(s) = {𝑆[(𝑗𝑠+𝑏)(𝑅+𝐿𝑠)+𝑘 2 ]} By using m-file of the model , we can (11) To represent the model with m- file, we can implement the Fig. 2 data as follows By put the values of Power P, Speed N , Rotor Inertia J with Supply voltage , we can calculate the torque constant K Wᵐ = 𝑣𝑡 𝑘 = 2𝜋𝑛 60 (12) K=14 By using equation (3) of 𝑘𝑖 = 𝑑𝑤 𝑑𝑡 + 𝑏𝜔 (13) The values of I and ω are stabilized at the steady state ; 𝑑𝜔 𝑑𝑡 T= b= 𝑘𝑖 𝜔 𝑃 𝑊 = = 370 157 1.4∗2.3 157 =0 = 2.35 𝑁. 𝑚 (14) = 0.02 N.m /rpm (15) By applying all parameters to be used for desired DC Motor model. 15 CHAPTER THREE PREDICTIVE CONTROL CHAPTER THREE PREDICTIVE CONTROL CHAPTER THREE PREDICTIVE CONTROL 3.1. Predictive Control Predictive control or Model Predictive Control is a method of controlling and adapting systems, also known as receding horizon or moving horizon control [13-15]. The characteristic of this method is that it enters the future changes of the target inputs (that is, changing the value we want for the system outputs) in the calculation of the controller’s outputs, which makes this method used in problems of the Trajectory Tracking type. The method works as follows: 1. We have the function or path that we want to follow. 2. We take this path in a field called the Prediction Horizon field. 3. In this field, an ideal control problem is calculated or solved, i.e. an improvement is performed (usually based on an integration sign that contains certain properties as the controller output where We don't want our controllers to put a lot of effort into the system. The integration also usually contains the difference or error between the desired path and the real path). In this area, the significance is minimized. 4. The forward-looking controller method that works on digital computers later takes the value obtained in the above process and uses it in the next time step. Although it can take this result for a longer period (the domain of prediction), it does not take this result until in the next time step and at each step, it returns the algorithm again. Therefore, there are many advantages, thus it is achieved that the calculations are always in the light of new or immediate data, i.e. new values of the sensors. 16 CHAPTER THREE PREDICTIVE CONTROL 3.2. Math Presentation The orientalist control principle is based on trying to calculate the least value of an arithmetic criterion or a (functional) parameter in each operation of the model. This criterion as this equation is the discrete form of the arithmetic criterion. This is done by using Nu number of future control entries where N1 is the minimum forecast horizon and N2 is the maximum forecast horizon. As for ρ, it is an equilibrium criterion for controlling the value of the fine resulting from the second part of the equation over the amount of the total arithmetic criterion. For non-linear systems, the equation must be optimized for each sample, which leads to predicting a set of future values for the controller input (here we have referred to a set of our consideration values for our focus on the discontinuous form of the figure in the continuous mathematical formula, a mathematical function is obtained), from this set is entered The first value (in the connected formula the first part of the function and the length of the part is the length of time between two optimizations) to the system. As for the linear systems, the optimization is achieved in advance and the control is transferred from an oriental to a linear instantaneous control. For non-linear systems, the equation must be optimized for each sample, which leads to predicting a set of future values for the controller input (here we have referred to a set of our consideration values for our focus on the discontinuous form of the figure in the continuous mathematical formula, obtained), from this set is entered a mathematical function is The first value (in the connected formula the first part of the function and the length of the part is the length of time between two optimizations) to the system. 17 CHAPTER THREE PREDICTIVE CONTROL As for the linear systems, the optimization is achieved in advance and the control is transferred from an oriental to a linear instantaneous control. Model predictive control (MPC) has gained interest both in academia and industry over the past few decades compared to other control methods, such as PID or PWM control. This is true mainly because MPC can be applied in many different processes, can implement constraints, and is easy to be understood, since its basic concepts can be explained intuitively.[23] The basic idea of model predictive control is to predict and optimize future system behaviour using the system model. The basic elements of MPC are: 1. The system model, describes the plant’s behaviour over time. 2. The control problem, where an objective function is formulated with regard to the system model to calculate the optimal control sequence for a specific number of future instances (prediction horizon) 3. Receding horizon policy, The following sections explain these elements in detail. 3.3. System Representation Modeling is a very important part of the MPC algorithms since different models produce algorithms with different complexity influencing the time needed to find the optimal solution to the control problem.[24] as shown in figure (3.1). 18 CHAPTER THREE PREDICTIVE CONTROL figure (3.1). System Representation Many different forms of modeling can be used in MPC, but for the purposes of this research, the state space representation will be used. The use of microprocessors makes MPC a discrete-time controller, thus the state-space representation in discrete-time is in order for the system model: x(k + 1) = f(x(k),u(k)) (3.1) y(k) = g(x(k)) (3.2) Where: x(k) ∈ R n is the state vector of the system at time instant kTs, u(k) ∈ R m is the input vector at time instant kTs, y(k) ∈ R p is the output vector at time instant kTs, the functions f and g are the state-update and output functions, respectively, which can be linear or nonlinear, and Ts is the sampling interval. 19 CHAPTER THREE PREDICTIVE CONTROL Starting from the current state x(k), this model is used for the calculation of the state and the output future values over a finite number N of planed control actions {u(k),u(k + 1), . . . ,u(k + N)}. starting from the step k + 1 for the state it holds: x(k + 1) = f(x(k),u(k)) x(k + 2) = f(x(k + 1),u(k + 1)) = f(f(x(k),u(k)),u(k + 1)) (3.3) x(k + N) = f(x(k + N − 1),u(k + N − 1)) = f(f . . .(f(x(k),u(k)),u(k + 1)), ...u(k + N − 1)) Thus the output over N steps is: y(k + 1) = g(f(x(k),u(k))) y(k + 2) = g(f(x(k + 1),u(k + 1))) = g(f(f(x(k),u(k)),u(k + 1))) (3.4) y(k + N) = g(f(x(k + N − 1),u(k + N − 1))) = g(f(f . . .(f(x(k),u(k)),u(k + 1)), ...u(k + N − 1))) Linear model For a linear model the discrete time state-space representation is: x(k + 1) = Ax(k) + Bu(k) y(k) = C x(k) (3.5) (3.6) where A, B and C are the system matrices. Following the same procedure as in (3.3) and (3.4), the state over a finite number of planed actions N is: 20 CHAPTER THREE PREDICTIVE CONTROL Or in a matrix form: Using the last applied control action u(k − 1) (which is known) it is possible to write the future control actions u(k),u(k + 1), . . . ,u(k + N − 1) in the form: u(k) = u(k) − u(k − 1) + u(k − 1) = ∆u(k) + u(k − 1) u(k + 1) = ∆u(k + 1) + ∆u(k) + u(k − 1) u(k + N − 1) = ∆u(k + N − 1) + • • • + ∆u(k) + u(k − 1) where ∆u(k + l − 1) = u(k + l − 1) − u(k + l − 2), l = 1, . . . , N. Combining (3.7) and (3.9) we get: 21 (3.9) CHAPTER THREE The equations PREDICTIVE CONTROL describing the state evolution over a prediction horizon N are of course equivalent and for the system’s output in both representations it holds 22 CHAPTER THREE PREDICTIVE CONTROL 3.4. Optimal Control Problem In order to obtain the control law a cost function is needed. In general, the cost function is formulated in regard to the output difference to a specific reference signal and the required control effort. Such a function is of the form: The most commonly used norms in MPC are p = 1 , p = ∞, which produce a linear function, and p = 2, which produces a quadratic function. The aim of the optimization problem is, using the formulated cost function J, to find the control sequence U(k) that results in the best performance of the system: 23 CHAPTER FOUR EXPERIMENTAL WORK CHAPTER FOUR EXPERIMENTAL WORK CHAPTER FOUR EXPERIMENTAL WORK CHAPTER FOUR EXPERIMENTAL WORK SIMULINK 30 CHAPTER FOUR EXPERIMENTAL WORK MATLAB 1 clear all clc R=4.88;% resistance of the Motor (Ohm) L=0.0384;%inductance of the Motor (Henry) F=0.0131;%friction coefficient J=0.0091;%moment of inertia K=0.9533;%Torque Constant num1=K; den=[J*L J*R F*L (F*R+K^2)]; sys1=tf(num1,den); [A1,B1,C1,D1] = tf2ss(num1,den) Ts=0.001; MV=struct('Min',-inf,'Max',Inf,'RateMin',-inf,'RateMax',inf); OV=struct('Min',-inf,'Max',100); % range of output signal p=50; % Prediction Horizon m=4; % Control Horizon mpccon=mpc(ss(A1,B1,C1,D1),Ts,p,m,[],MV,OV); Tstop=5; xo=[0 0 0]'; outc=sim('MPC_for_DC_Motor_V1'); save SIM_speed_change_step.mat outc figure (1) plot(T(1:10:end,1),r(1:10:end,1),'--k',T(1:10:end,1),W(1:10:end,1),'b','LineWidth',2,... 'MarkerEdgeColor','k',... 'MarkerFaceColor','g',... 'MarkerSize',16) title('Reference Speed & Motor Speed Versus Time') xlabel('Time in Sec') ylabel('Speed (rad/Sec)') ylim([0 100]) legend('Refernce Speed','Motor Speed') 31 CHAPTER FOUR EXPERIMENTAL WORK MATLAB 2 p=40; % Prediction Horizon m=4; % Control Horizon MATLAB 3 p=70; % Prediction Horizon m=4; % Control Horizon 32 REFERENCES References ________ References [A] publié le 03 avr 2015 par Richard ALLARD [1] W. Yeadon and A. Yeadon, Handbook of small electric motors. 2001. [2] Šlapák, Viktor; Kyslan, Karol; Lacko, Milan; Fedák, Viliam; Ďurovský, František (2016). Finite Control Set Model Predictive Speed Control of a DC Motor. Mathematical Problems in Engineering, 2016(), 1–10. doi:10.1155/2016/9571972. [3] M. G. Guerreiro, D. Foito, and A. Cordeiro, “A sensor less PMDC motor speed controller with a logical overcurrent protection,” Journal of Power Electronics, vol. 13, no. 3, pp. 381–389, 2013. [4] M. Tuna, C. B. Fidan, S. 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