General Purpose Power Electronic Converter

The goal of the project is to make the converter can increase the efficiency and be more cheap.

Background
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.

Project Goals
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. 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.
 * Proposed Goal
 * Final Goal

Project Specifications

 * 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)

Proposed Steps

 * 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.

Final Steps
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
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

Full-Bridge 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

Final Decision
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
Chip LT8310 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.

Circuit
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.

Current Regulator
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

Frequency
The resistor Rt controls the frequency. We want to set the frequency to 200 KHz; therefore, the resistor is 49.9KΩ

Duty cycle
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.

Feedback Divider
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.

LC Filter
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

Vc pin
To compensate the current mode feedback loop of the chip, a series resistor-capacitor network is connected from the Vc pin to the ground.

Simulation Results
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

Budget

 * Budget

Contract

 * Contract

Meeting Minutes

 * Meeting minutes

Design Review Presentation

 * Presentation 1
 * Presentation 2

Final expo

 * Expo