General Purpose Power Electronic Converter
|Duration||Spring 2018 - Fall 2018|
The goal of the project is to make the converter can increase the efficiency and be more cheap.
- 1 Introduction
- 2 Circuit Design
- 3 Design Calculations
- 4 Simulation Results
- 5 Optimization
- 6 Lagrange Mutltpiliers
- 7 Team Information
- 8 Document Archive
Converters are a commonly used device within many electronic systems that allow the voltage of the device to operate in an area with a different voltage. A well-known example of this is within portable electronic devices, such as cell phones, tablets, and laptop computers.
- Proposed Goal
In the initial stage, our goal was to design and create a control algorithm for an integrated converter which consists of 4 individual forward-converters. Moreover, our group needed to make an actual forward converter.
- Final Goal
However, our goal had to change on Nov.20th due to the failure of making an actual forward converter. Therefore, we have a new project goals which contain two parts. The first goal is to develop a modularized converter system where the output is comprised of multiple smaller converter modules while retaining high efficiency. The second goal is to output a single desired voltage from a variety of input conditions.
- Input Voltage: 12VDC to 36VDC
- Output Voltage: 24VDC (fixed Value)
- Efficiency ≥ 90%
- An integrated converter module produces 100W power. (an integrated converter contains four individual single converters)
Project learning plan
- 1. Investigate different types of DC-DC converters to know their characteristics.
- 2. Build a simulation of a schematic of a single converter module
- 3. Build a simulation of a schematic of an integrated converter module.
- 4. Find the relationship between efficiency and load currents for control algorithm.
- 5. Develop the software to automate the optimization function of the combined converter modules
- 6. Meanwhile, design a PCB for our schematic. Also, make a budget to buy components.
- 7. Build the PCBs and test them step by step.
- 8. If the hardware works successfully, hardware builder will give these PCBs to Control Algorithm designer to improve his Algorithm.
Because of the failure of making an actual forward converter, we have a new project goals. Therefore, we modified our plan. The final steps contain four parts:
- 1.Develop a voltage regulator with high efficiency
- 2.Modify the regulator for current regulation
- 3.Determine optimized output of the system
- 4.Simulate modularized system
Future work will be to assemble the modules and develop an automation control for their outputs based on the unit commitment calculations and load demand.
Choices of DC converter Modules
In the initial stage, our team had different choices of DC-DC converter. After at least two meetings, we decided to research two kinds of DC-DC converter. The first choice is forward converter. The other choice is full-bridge converter. Forward Converter The forward converter is a DC-DC converter that uses a transformer to increase or decrease the output voltage (depending on the transformer ratio) and provide galvanic isolation for the load. With multiple output windings, it is possible to provide both higher and lower voltage outputs simultaneously.
Figure 1 Tradition Forward Converter
A Bridge Converter is a DC to DC converter topology (configuration) employing four active switching components in a bridge configuration across a power transformer.
Figure 2 Full-Bridge Converter
Last semester, the simulation of the forward converter was finished successfully and earlier than the simulation of the full-bridge converter. In order to save time, we decided to use forward converter for our project in August.
Components of Forward Converter
The LT8310 is a simple-to-use resonant reset forward converter controller that drives the gate of a low side. N-channel MOSFET from an internally regulated 10V supply. The LT8310 features duty mode control that generates a stable, regulated, isolated output using a single power transformer. The chip LT8310 has two important advantages which are high efficiency and current protection.
Figure 3 Forward Converter with LT8310
Obviously, we can observe the difference between the traditional forward converter and the forward converter with the chip LT8310. It is more convenient and operable to control the forward converter with the chip LT8310.
Figure 4 Current Regulator
In current regulator, we made a little difference. We added an inductor of 1mH between the output capacitor and the load resistor. The resistor A and B prevent currents from going down. Also, the OPAMP measures the voltage of this inductor. Because we know the impedance (jwL) of the inductor, then we can know the currents that flow the inductor.
Output Current & Load Resistor
In this part, we achieve the values of the load current and the load resistor when our output power is 100W. We replace the load resistor with a current source, so we can adjust the values of load currents. This is similar to adjusting the value of load resistor.
The Transformer Ration
The Np-s is 1:3. On the schematic, the ratio of transformer is 300u: 2.7m (1: 9). When we set transformers in LTspice, (1: x) must be transformed into (1: x2). The Gate pin controls the MOSFET. The system drives the gate pin high to close the MOSFET switch.
Figure 5 The Gate Pin and the Transformer
The resistor Rt controls the frequency. We want to set the frequency to 200 KHz; therefore, the resistor is 49.9KΩ
Resistor Rset controls the duty cycle. Also, in some cases Rset affects output currents and output voltages. According to the calculation the calculation, the minimum value of Rset is 33333.33Ω. If the Rset is higher than this value, the output currents and output voltage will not be changed.
Figure 6 Feedback Resistors and their calculation
This forward converter module is in Current Mode Control. The LT8310 offers Current Mode Control to regulate the output, when the output voltage feedback pin is connected. Also, the feedback contains two resistors. According to the formula from the data sheet, the R6 is 2800Ω, and the R5 is 200Ω.
Figure 7 The output part can be seen as a LC filter
Minimum Inductor value ： Lx, min = 9.579uH Minimum Capacitor value ： Cx, min = 27.69uF
To compensate the current mode feedback loop of the chip, a series resistor-capacitor network is connected from the Vc pin to the ground.
Figure 8 The Waveforms of Output Voltages (Load Currents are changed from 0.1V to 4.1V)
Figure 9 The Output waveform
Figure 10 The Output Waveforms (13.5V—24V)
The output voltage is changed when the value of Rset is lower than 33333.33Ω. We can see the change of output voltage from 13.5V to 24V when the Rset grows from 19kΩto 34kΩ. The increment of Rset is 3000Ω.
Figure 11 Current Waveforms
when Rset changes from 19kΩ to 34KΩ Similarly, we can see many different values of currents when the Rset changes from 19kΩ to 34KΩ. The increment of Rset is 3000Ω，too.
Figure 12 design of PCB.
Figure 13. Proposed system
Figure 14. Simulated result of Regulator Module
Figure 15 Simulated system efficiency
Once the efficiency of the individual VRM and CRM modules were obtained, the datasets were extrapolated to result in quadratic equations which were then evaluated using the concepts of the economic dispatch. In power systems, the economic dispatch is defined as the immediate determination of the optimal output of a number of electrical generation facilities in order to meet a system load at the lowest possible cost while being subjected to transmission and operational constraints. It is to say that this concept takes the cost of the system and analyzes it with respect to the overall generation to provide the optimum condition of generation and power transfer to the load. In a similar manner to the power systems model, this integrated converter system can also be analyzed and optimized in the same approach. Therefore, we can assume that by obtaining the cost function of the individual modules and the overall load specifications, the optimum output would be able to be calculated with respect to the number of generation systems. Given the results of the VRM and CRMs efficiency, the cost functions were determined as the efficiency with respect to the input power. Similarly, the total power generation would be defined as the summation of all generation system in use. These equations were then solved using the method of Lagrange multipliers to provide the loading conditions of each module and the marginal efficiency per additional Watt in.
The method of Lagrange multipliers allows the system efficiency to be calculated as either a maximum or minimum while emplacing a constraint on the input conditions. The cost functions and the total generation were determined based on the data from the regulation efficiency plots, shown below:
1 (Pin1) = – 0.0395Pin12 + 0.2285Pin1 + 0.6061 (4.1)
2 (Pin2) = – 0.0509Pin22 + 0.2989Pin2 + 0.4735 (4.2)
3 (Pin3) = – 0.0486Pin32 + 0.2768Pin3 + 0.5233 (4.3)
4 (Pin4) = – 0.0480Pin42 + 0.2694Pin4 + 0.5229 (4.4)
Pin1 + Pin2 + Pin3 + Pin4 = Ptotal (4.5)
After obtaining (4.1) through (4.5), the next step is to determine the critical points of the modules that will result in the optimum output of the system. This is performed by taking the derivative of the individual efficiency equations and performing the following equation:
where y is the efficiency of the system with respect to the input power and 入 is the multiplier, to provide the following matrix:
Figure 16. Converter System Matrix
Afterwards the system is solved for the individual power distribution values and the lambda multiplier. The calculations were performed in the manner described in the prior section using the efficiency relation matrix. In the instance in figure 3, the integrated system is determining the optimum distribution for the 300-Watt load given that all four regulators are on.
Figure 17. Example System of four Converters for 300Watt Load
Figure 18. Solution for Converter System
It can be shown from the results that the efficiency of the overall system would be optimized if the four modules contained each were responsible for approximately 70 Watts. Additionally, for the efficiency of the system to change 1.0% , it would take approximately 6.68 Watts added or reduced. In order to properly consider the load distribution between the number of systems, the calculations were run with the assumptions that each of the modules would run with no less than 50 Watts if coupled. Therefore the conditions analyzed were: • 1 Module: 1 – 100 Watts • 2 Modules: 50 – 200 Watts • 3 Modules: 150 – 300 Watts • 4 Modules: 200 – 400 Watts Once the values were obtained, the switch over condition was then determined by evaluating the point which the transition would have the least change in the efficiency. The results of the table, which can be viewed in Appendix B, demonstrate that the efficiency of the system did perform better than the individual modules would have.
Major: Electrical Engineering
Major: Electrical Engineering
Major: Electrical Engineering