Buck converter pdf

The compensator is build up with resistive and capacitive elements. The figure 3. With reference to the fig 2. The error signal is minimized with the help of compensator. The output of the compensator is the duty cycle command which is given as input to the PWM. PWM will convert this into a control signal that manages the switches. This compensator is given as an example, and the primary interest of the project is modeling and simulation of the converters, and not the controllers.

The transfer function is derived as 3. These blocks along with the output filter contains a total of three blocks that complete the closed loop and helps in stabilizing the system. Equation 3. The gains of each block together contribute to the system stabilization. As a control system, the gains are multiplied to produce an input to the modulator, where the output of the compensator acts as the input to the PWM modulator.

The output of the modulator is nothing but the duty cycle with a maximum magnitude of one. The output of the modulator is given as the input to the system. This is nothing but the filter action taken at the output of the system.

Since the output through the capacitive network at the output acts as a filter, the output is regulated output.

The basic operational amplifier can be used as a proportional P gain compensation. The operational amplifier can also be used as the Integral and differential compensators. The lag filter is used as the integral I compensator and the lead filter can be used as the differential D compensator. This is the converter that is simulated and modeled. The regulators establish innovative approaches to improve system performance. This device has wide application in areas like fixed wireless networks and optical network management.

This device has several industrial and automotive applications also. The standard serial bus interface —SMBus helps in implementing the protocol to enable the communication with the system. This helps in monitoring, programming and controlling the power conversion devices. This reduces the design complexity. Many digital power techniques are used by the 3E POL regulators for its internal design. The power control techniques are used for proper utilization and management of system power and energy.

At the same time, the PMBus interface provides information like input voltage range, output voltage range, load conditions, temperature variations and delivered current and many other parameters inorder to monitor the system energy distribution.

The following figures provide the information, which can be accessed using PMBus interface. Figure 4. The fig. We can restrict the input voltage, output voltage, output current and temperature. These parameters are based upon the limitations of BMR The BMR have data of parameters for the evaluation experiments. The data is provided in a tabular format below. The following data is used to conduct experiments on BMR Different observations are taken to study the nature of BMR The device specific configuration can be selected using the interface as shown in fig.

This helps in selecting manufacture configuration, user configuration and non-linear response configuration. Even the controller and average current settings can be monitored. The device monitoring can be seen in the fig. It shows the output current, input voltage supplied, output voltage and the temperature variations according to the control inputs. This information helps in monitoring the BMR in proper direction in order to achieve defined goals.

The measurement circuit is mounted over the BMR to sense the current variations across the inductor. Since the voltage across the capacitor is proportional to the inductor current, it is easy to observe the variations in inductor current, based upon the variations in the capacitor voltage.

The rules to be followed while designing the resistor and capacitor values are: 1 The time constants of BMR and current sensing circuit should be equal. Hence the load should be selected, in such a way that, the maximum output power at the load should not cross the limit of Watts and the maximum load current should not cross 20 amperes. It supports both the linear and non-linear systems.

A graphical user interface GUI is provided by Simulink, in which the models are represented by block diagrams and the operations are click and drag mouse based. The models can be created easily by selecting the appropriate blocks from the existing block library. The block library consists of sources, sinks and several blocks which result in mathematical outputs. The blocks are connected using the connectors.

The block libraries help in modeling, simulating, implementing the design and are then used to test and verify the LTI systems like control and communication systems. SimPowerSystems: SimPowerSystems is a software package of modern design tools, which allow building and simulating the power system models. Power system is a combination of electrical circuits and electromechanical devices.

SimPowerSystems is an analysis tool which involves concepts of power electronic devices and control systems. SimPowerSystems uses the Simulink environment, in which a model is built using click and drag procedures. The tool helps in drawing and analyzing the circuit topology.

Since this uses the Simulink environment, all the parts of the power system interact with Simulink modeling library. Since the systems are often non-linear, one convenient way to understand them is through Simulation. The buck converter topology is a combination of several electronic devices and control system elements. Hence, the buck converter model is simulated with the help of Simulink and SimPowerSystems to analyze the working nature.

All the blocks shown are selected from the SimPowerSystems toolset. The model designed using SimPowerSystems looks exactly same as if we draw it on a paper. Thus, it is very easy to design the desired model. The model represents the block diagram shown in figure 3. Figure 6. The element library and electrical sources library is used to select the blocks to design the model. The model uses the measurement blocks to measure current across the wires and voltage across the nodes.

The model is designed by placing the blocks in appropriate sequence inorder to analyze the buck converter model. The purpose of simulation is to verify the condition given in equation 3. The condition states that, the product of current flowing across the inductor and the ESR across the inductor must be equal to the voltage across the capacitor in current sensing circuit.

The powergui block is very much needed for any kind of Simulink model which contains SimPowerSystems blocks, inorder to simulate the model. This block stores the equivalent Simulink circuit which represents the state-space equations of the SimPowerSystems blocks.

The third waveform shows the total input current that enters into the circuit. The elements like capacitor, resistor and inductor are chosen from the elements library. Elements are connected using wires. The connection in which an inductor is in series with a resistor is placed in parallel across the connection in which a capacitor is in series with a resistor. Description of each block used in the design: The description and performance of each individual block used in the design is explained inorder to have clear understanding over the circuit.

When the input from the sawtooth generator overtakes the input from PID, the output is 0 and if the input from sawtooth is less than the input from PID, the output is 1. The input current to the system depends on the duty cycle of the signal from PWM block.

The input is the product of the constant voltage source Vg and the duty cycle D. The dependency is shown in figure 6. The output of the pulse width modulator is a series of pulses, whose amplitude varies between 0 and 1, and the width of the each pulse depends on duty cycle.

The simulation was run for duration of 0. The following results were obtained after simulation. Output Voltage 2. Output Current 3. Voltage across modeled capacitor Figure 6.

Current through Inductor 5. Voltage across Inductor 6. Current to the modeled capacitor I. The Output voltage is maintained constant at 3 Volts. Since the load of 1. The output voltage and the output current are in proportion, due to the resistive load. Since the circuit has to maintain or regulate the voltage at 3 Volts, the designed circuit is succeeded in providing the desired result.

Many observations are taken with different load values to verify the circuitry design and were successfully observed. The first waveform shows the Output Current and the second waveform shows the Output Voltage. Voltage across modeled Capacitor Vs Current through Inductor The measurement circuit as described in section 5.

The capacitor is denoted C1 in figure 5. In the figure 6. This is shown in figure 6. One more interesting information is observed. The Voltage across inductor is found proportional to the current through the Capacitor.

This observation is shown in the following figure 6. The first waveform shows the current across the Capacitor and the second waveform shows the Voltage across the Inductor. The Simulink model of the buck converter is shown in the figure 6. The above model is an exact representation of the equations obtained in the section 3. The number of integrators used in the figure 3. The product of the duty cycle from sawtooth generator and the input voltage provides the pwm signal for the buck converter system.

The output voltage and current are duty cycle controlled outputs. The SimPowerSystems model shown in the figure 6. Log in with Facebook Log in with Google.

Remember me on this computer. Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. Download Free PDF. Buck Converter Design. A short summary of this paper. Download Download PDF. Translate PDF. In this paper, firstly, general information about Buck Converter will be given and the working principle will be explained. Secondly, design criterions will be determined and component selection issues will be discussed.

Finally, Buck Converter Circuit will be implemented, and the paper will be ended displaying test results. It uses a power semiconductor device as a switch to turn on and off the DC supply to the load.

Figure 1 shows a simplified block diagram of a buck converter that accepts a DC input and uses pulse- width modulation PWM of switching frequency to control the switch. An external diode, together with external inductor and output capacitor, produces the regulated dc output. Buck, or step down converters produce an average output voltage lower than the input source voltage. The first mode is when switch Q close, and the second one is when switch Q open. When switch Q closes, current flows from the supply voltage Vi through the inductor and into the load, charging the inductor by increasing its magnetic field and increasing Vo.

Diode D will be on reverse bias, thus blocking the path for current. At the same time, the current through the inductor increases and the energy stored in the inductor increases. When Vo reaches the desired value, switch Q is open and diode D is turned on. Figure 2 shows this mode. When the switch Q opens, the inductor acts as a source and maintains the current through the load resistor.

During this period, the energy stored in the inductor decreases and its current falls. Current continues to flow in the inductor through the diode D as the magnetic field collapses and the inductor discharges. Before the inductor completely discharges, diode D is open and Q is closed and the cycle repeats. It is important that there is continuous conduction through the load for this circuit. Figure 3 shows this mode. The longer Q is turned on, the greater Vout will be.

Figure 4 shows variation of duty cycle. Duty cycle is always being presented in percentage value. The difference between the two is that in CCM the current in the inductor does not fall to zero. A buck converter operates in continuous mode if the current through the inductor never falls to zero during the commutation cycle.

In DCM, the current through the inductor falls to zero during part of the period. Practically, converter can be operated in either operation mode. Capacitor is large enough that the output voltage ripple is small relative to its average value. Inductor is large enough to ensure that the inductor current stays positive for the switching period. In terms of the circuit operation, a DC-DC converter can be described as a piece-wise switched electrical circuit whose topology toggles between a number of linear circuits in some predefined manner.

In simple DC-DC converters such as the buck, boost and buck-boost converters the involved circuits are second-order circuits containing an inductor, a capacitor, a switch externally controlled switch and a diode internally controlled switch. The simple buck, boost and buck-boost converters having two independent storage elements are second- order systems.

Nevertheless, a close inspection of the inductor current waveform reveals that the inductor current is identically zero at the start of each switching period when operating in discontinuous conduction mode DCM , i. Thus the inductor current is no longer a dynamic variable. As a result, the converter reduces to first-order, with the capacitor voltage serving as the only state variable.

The resulting first-order iterative map describes the open-loop dynamics of the system. Then with the loop closed, the feedback factor becomes a parameter that can be varied at will. On the other hand, when dn is varied according to input, the system is termed as closed-loop system.

Obviously the usefulness of this map lies in its ability to predict the flow of the system. In particular, if the system has a contraction it is guaranteed it will converge to a unique fixed value.

This discrepancy can be removed by focusing attention on the system controlled by the simple feedback scheme. In practice, DC- DC converters are controlled via feedback mechanism. The usual control objective is to keep the output voltage fixed. For simplicity, we consider a proportional feedback which effectively samples the output voltage and generates an error signal from which the duty cycle is derived, i.

An example will help visualize the situation. Direct substitution gives 1. They represent typical unimodal map, i. In this process, at each step in the iteration, the current value of vn is fed back to produce the next value, then this value is used to produce the next and so on.

Period-1 In fig. These solutions to the buck converter map repeat every second value, i. This is termed as period-2 orbit. Period-4 In fig. This is called period-4 orbit. Chaotic aperiodic Fig. In it the iterated solutions do not converge and further iterations will never produce a repeating and hence periodic sequence of solutions.

This aperiodic behaviour is known as chaotic orbit or simply chaos. Still chaotic aperiodic In fig. Still chaotic aperiodic Fig. Again period-1 Fig. Bifurcation diagram of buck converter with comparing do V.