DFIG Controller

The goal of this project is to design and implement a rotor side converter (RSC) that monitors a doubly-fed induction generators (DFIGs) torque, current and voltage output in order to command an input waveform that will stabilize the DFIG with the grid at 60Hz. The completion of this project will aid in the advancement of wind energy systems by allowing further research to be conducted on doubly-fed inductions generators.

Background
As the principal generator used in Type III wind energy conversion systems, the doubly fed induction generator (DFIG) is widely accepted in today's wind energy industry. As society shifts toward renewable energy, these systems are becoming more prevalent. This brings an increasing need for research into how these systems interact with the grid. To achieve this end, the University of Idaho has created a wind turbine simulator which uses an AC induction motor to drive a DFIG at variable speeds and monitor power delivery and stability. In order to use this test bench, a full featured controller is needed operator the DFIG properly. That is the motivation for this project. The DFIG is essentially a wound rotor induction generator in which the rotor circuit can be controlled by external devices to achieve variable speed operation. The stator of the generator is connected to the grid through a transformer, whereas the rotor connection to the grid is done through power converters, harmonic filters, and the transformer. The stator of the generator delivers power from the wind turbine to the grid. In the rotor, the power can be delivered from the rotor to the grid and vice versa through rotor-side converter depending on rotor speed, and power factors. Two of the main components in the control system of the DFIG are the grid-side converter (GSC) and the rotor-side converter (RSC). The GSC is responsible for managing power delivery to the grid and generating a stable DC rail value from the grid to power the inverters. The RSC is responsible for controlling the power applied to the rotor in order to facilitate smooth, clean, and efficient power generation. The scope of this project is assembling and testing the components to create the RSC to be used with the wind turbine simulator test bench that the University of Idaho has built.

Deliverables
The focus for the first semester is understanding the systems involved and getting components ordered and tested. The process for this is the following: Once hardware procurement and testing is completed, the plan for the second semester is the following: This outlines the process, and the final deliverables will be:
 * Learning to understand systems involved and components required
 * Developing and verifying a design for the system using simulations
 * Developing specifications and selecting hardware components based on design and verification
 * Ordering components and testing individually to ensure expected function and specification compliance
 * Perform component integration and subsystem tests
 * Develop control code and test sub routines involved
 * Complete any fabrication of custom components
 * Mount components to power electronics stand
 * Final integration and full scale tests
 * 1) A capable Microcontroller programmed with the required algorithms to run on the wind turbine simulator
 * 2) Power electronics components including Gate Driver, IGBTs, snubbers, rectifiers, etc.
 * 3) System connection components including any breakout boards and cables required to connect components
 * 4) Isolation components, in this case Optic Fiber links for noise immunity and isolation of high and low voltage components
 * 5) Sensors connected and tested in the final layout

Specifications and Constraints
Specifications for the project are listed below:
 * Prototype must be modular
 * Prototype must be robust
 * Utilize startup and fail safe procedures in code
 * Incorporate adequate isolation

Constraints of the RSC design were as follows:
 * Integration must be designed to handle a DC bus voltage value up to 340V
 * Must be able to stabilize a generator operating in a range of 0-60Hz with the grid (ie. 60Hz)
 * Read sensor inputs and command the 3-phase inverter at a minimum frequency of 20kHz

=Project Outline= Below you will find the schedule that was followed to complete this project. The gantt chart shown is a broad outline of the design steps taken. A detailed version can be found in the additional documents section of this page.

=Project Learning= Since our team members weren't really familiar with DFIG, we had to do a lot of readings and researches to get the ideas of how DFIG works and control over it. Also, it is a hard project that was out there for several semesters and even graduate students worked on it, our progress can be very slow. We took three weeks in the power lab to test the machine in sub-synchronous and super-synchronous mode and did the locked-rotor test, the no-load test and the DC test. Below is the result we got for our first parameter tests.



= Design Evaluation and Verification =

= Hardware Procurement =

Optic Links
= Implementation and Testing =

=Previous project revising= Starting from the second semester, our team focused on both hardware and software by first revising previous project done by graduate students and former senior design teams. For the hardware, we looked at a grid side converter(GSC) design built by Rebecca Dong, it consists of power converter module, DC/DC converter, voltage/current sensor and a single 16V power supply. We came up with a brief schematic of this GSC and learned the function of each component of the board, even though our goal is to design a converter for the rotor side, we can still use it as a reference. However, this board is too complicated, we want to build a controller system with multiple boards perform individual tasks, so we turn to a project done in 1996 led by Dr.Joseph Law, this project is a controller system for a induction machine, we particularly looked at the gate driver delay circuit and the gate driver board. In the delay circuit, 2 sets of input go into 1 of the 3 lines that are used to drive the gate of the power converter, the purpose of the delay circuit is to prevent the situation when the upper and lower transistor of the inverter closed at the same time to cause a short around the DC bus. The delay circuit then sends its output information to the gate driver board through fiber optics to eliminate the interference of other equipment in this system. The gate driver board converts fiber optic light signals to pulse signals to trigger the transistor and provide reference for the emitter on each of the transistor.

=Field orientation Control= Using an already provided assembly language for a squirrel cage induction machine partial c++ code was developed that can be used in conjunction with hardware decided to use in the future.

=PID control= To start we first developed a simple RL circuit with current across the inductor as output and simple step function as voltage input and developed simulink Matlab files for it. In future using the simulink files provided by DR. Law, which can be found in project portfolio Matlab code needs to be developed in simple C/C++ language that can be easily imported to any hardware decided to use.

=Conclusion= The goal of the project was to model a wind-energy system based on type-3 DFIG. In the Spring semester we studied DFIG and conducted tests to get the parameters of the machine being used. In the Fall semester we tested existing hardware and back tracked the circuitry of the hardware and documented the progress. We also learned about space-vector and dq axis. Used existing assembly language code to develop a simple C++ code and started working on the PID control.

=Future work= Future work needed to be completed for this project can be broken down into five topics, all of which have been partially completed but have some advancements needing to be implemented. These topics include PCB fabrication, high voltage side stand configuration, low voltage side stand configuration, coding, and system testing. Tasks involved with the future work associated with PCB fabrication are as follows: The PCB board needing to be printed is for the gate driver and its external components utilized in the protection abilities that the gate driver device provides. Steps needing to be completed to finish the high voltage side of the prototype include: Low voltage side stand configurations tasks needing to be completed are: In terms of coding the only task needing to be completed is to write and verify the field oriented control algorithm. Following these tasks the last item involved with future work is to run tests utilizing the wind turbine simulator and the RSC design. It is advised to run a few small scale tests verifying system integration before performing tests with the wind turbine simulator.
 * PCB printing (gerber files provided)
 * RCin port capacitor chosen
 * ITrip port capacitor chosen
 * ITrip port resistor chosen
 * Mounting the PCB and making gate driver connections (mounting hardware already in place)
 * Twist soldering snubber components (snubber components already in place)
 * Drilling extra holes on the heatsink for proper IGBT mounting
 * Mounting the positive rail
 * Connecting power supply outputs to the optics and gate driver(devices already mounted in a layout that provides easy interconnections to be made)
 * Mounting uC and making connections to the optics and sensors
 * Creating the breakout boards that will aid in the connection process of the uC (schematics for these boards are provided)

=Team Members= Mason Ulrich Major: Electrical Engineering Email: ulri3329@vandals.uidaho.edu Bio: Mason Ulrich was born and raised in Lewiston, Idaho. During his academic career he studied Electrical Engineering with an emphasis on Power. Following his graduation he will be moving to Olympia, Washington to work for Electrical Power Systems Inc. (EPS) as a substation design engineer. In his free time you will find Mason rock climbing, skiing, on top of a mountain, or getting lost in the presence of the beautiful outdoors.

=Additional Documentation=

=Meeting Minutes=