Research on Model-Free Control of Switching Power Supply

This article presents a model-free control method for switching power supplies. Non-modeling adaptive controller, also known as model-free controller, this approach breaks the constraints of PID control and points out a new development direction for the development of switching power supplies. Keywords: switching power supply, PID control, model-free control, PWM [b][align=center]Research of Switchiing Power Supply Based on Model Free Controller ZHANG ke ,QI Xing-Guang (Shandong Institute of Light Industry,Shandong,Jinan, 250353[/align][/b] Abstract: This paper presents a method of design a model free switch power supply.Model free adaptive controller also named non_modeling adaptive controller,the approach cancel the concepts of PID, Pointed out a new direction for development of switch power supply. Key words: switching power supply, PID control, model free controller, PWM 1. Introduction With the rapid development of power electronic technology, power electronic equipment is increasingly closely related to people’s work and life, and electronic equipment is Reliable power supply is indispensable. Switching power supply is a kind of power supply that uses modern power electronic technology to control the time ratio of switching transistors on and off to maintain a stable output voltage. Switching power supplies are generally controlled by pulse width modulation (PWM) control ICs and MOSFETs. Composition. The majority of the switching power supply control part is designed and worked according to analog signals. The disadvantage is that the anti-interference ability is very poor. Due to the rapid development of computer control technology, the processing and control of digital signals has shown obvious advantages: convenient for computers Processing and control, design flexibility is greatly improved, software debugging is convenient, etc., and PID control appears. It makes the switching power supply develop in the direction of digitization, intelligence, and multi-function. This undoubtedly improves the performance and reliability of the switching power supply. But Since the switching power supply itself is a non-linear object, the establishment of its accurate model is quite difficult, and approximate processing is often used, and its power supply system and load changes are uncertain, so it is often difficult to use the above-mentioned analog or digital PID control methods. The parameters of the PID regulator change accordingly. The control effect is not ideal. The recently developed model-free control [1] is a promising control method. It does not rely on the mathematical model of the controlled object, and integrates modeling and control. For some complex Variable or uncertain structure is very suitable for systems that are difficult to describe with accurate mathematical models. The control system of the switching power supply is improved, which not only meets the requirements of high performance and high reliability of the switching power supply. 2. The working principle of the switching power supply The principle block diagram of the switching power supply is shown in Figure 1. The grid voltage is converted into a DC voltage input to the high-frequency converter through the rectifier and filter in the input loop, and the high-frequency converter converts the input DC voltage into a high-frequency pulse square wave voltage, which passes through the high-frequency pulse in the output loop. Frequency rectifier and filter become DC voltage to supply load. [align=center] Figure 1 The working principle of switching power supply[/align] The control loop with microcomputer as the core, samples the output voltage and current of the switching power supply with the support of the control software, and compares with the given data, and then To adjust and control the inverter, change the conduction frequency or conduction/cut-off time of the MOSFET to stabilize the output, and monitor the working status of the switching power supply. 3. The composition of the switching power supply hardware system The switching power supply control system can choose different microprocessors according to the actual situation of the project. Its composition principle block diagram is shown as in Fig. 2. The power-on/reset circuit provides a stable power supply and reset function to the microprocessor. The output voltage feedback is used to adjust the output voltage value and keep the output voltage stable. The current feedback circuit has a similar function to the voltage feedback. The digital tube display circuit and keyboard input circuit realize the function of human-computer interaction. The PWM output drive circuit outputs pulses to control the switching on and off. When the output voltage is higher than the required voltage, the width of the output pulse is reduced, thereby reducing the output voltage; when the output voltage is lower than the required voltage, the output pulse The width is increased, thereby increasing the output voltage. [align=center] Figure 2[/align] 4. Model-free control principle 4.1 General overview of model-free control In the control law design, it is generally necessary to establish a mathematical model of a dynamic system. Classical methods require that this mathematical model must be established in advance, at least its structure must be determined in advance. And the more accurate the model, the better. The design of model-free control law breaks through the restriction that the control law requires the mathematical model to be established as accurately as possible in advance. Our modeling procedures are carried out with feedback control. The initial mathematical model can be inaccurate, but it must be ensured that the designed control law has a certain degree of convergence. The model-free control law we designed is to control while modeling. After obtaining new observation data, model again. Control. Continue in this way, so that the mathematical model obtained each time is gradually accurate, so that the performance of the control law is also improved. We call this procedure an integrated procedure of real-time modeling and feedback control. 4.2 The integrated approach of modeling and adaptive control In the reference, the following general model is proposed: y(k)-y(k-1)=φ(k-1)[u(k-1)- u(k-2)] (4-1) Without loss of generality, it is assumed that the time delay of the controlled dynamic system S is 1, y(k) is the one-dimensional output of system S, and u(k-1) is P Wei loses people. φ(k) is a characteristic parameter, which is estimated online using a certain identification algorithm, and k is a discrete time. We will see that φ(k) has obvious mathematical and engineering significance in the identification and control integration procedures of real-time identification-real-time feedback correction. 4.3 Integration of real-time modeling and feedback control Specifically, the framework of our integration of modeling and feedback control is as follows: (1) According to the observation data and the general model y(k)-y(k-1)=φ( k-1) [u(k-1)-u(k-2)] Using an appropriate estimation method, an estimate of φ(k-1) φ(k-1) is obtained. (2) To find the predicted value φ*(k) of φ(k-1) one step forward, a simple method is to take φ*(k) = φ*(k-1) When seeking the control law, we put φ*(k) is still recorded as φ(k). (3) Apply the control law to the system S, and get the new output y(k+1). So a new set of data {y(k+1),u(k)} is obtained. Repeating (1), (2) and (3) on the basis of this new set of data can get new data {y(k+2), u(k+1)} and so on. As long as the system S satisfies certain conditions, under the action of this procedure, the output y(k) of the system s will gradually approach y[sub]0[/sub]. 4.4 Controller program design. Most of the controllers currently used in industrial production process control are classic PID regulators and their variants. For systems that are not severely coupled, the control effect of PID regulators can still be satisfactory. , But for systems with severe coupling, the PID regulator appears powerless. The following uses the PID regulator as a benchmark to compare the model-free controller with the PID regulator to show that the model-free controller has better decoupling and resistance. Interference ability. Model-free control flow chart [align=center] Figure 3 Model-free control flow chart[/align] 5. Test results Here is a simulation comparison of the decoupling capabilities of the model-free controller and the PID regulator. For the fairness of comparison, The parameters of the model-free controller and the PID regulator are adjusted to a better state, and the following systems [1] (4-5) are controlled: The control results are shown in Figure 4 and Figure 5 [align=center] u(t ) Y(t) Fig. 4 Simulation result of PID control situation u(t) y(t) Fig. 5 Simulation diagram of model-free control[/align] From the simulation results, it can be clearly seen that the model-free controller and PID regulator are opposite to each other. The control of the linear system has received good results, but the control ability of the model-free control method for the nonlinear coupling situation is much stronger than that of the PID regulator. 6. Conclusion Model-free control is suitable for nonlinear control, and its control rules do not need to determine the model of a specific object. It has quite good stability and anti-interference ability for the control of nonlinear objects such as switching power supplies. The introduction of model-free control strategies has created a broad space for the development of switching power supplies.