Design and Implementation of a DSTATCOM for Power Factor Correction

ECE 4600 Group Design Project Progress Report G06

Group Members Matt Borody Bailey Lavallee Nyasha Machoko Chantel Reyes

Supervisor Professor Shaahin Filizadeh, Ph. D, P. Eng. January 13, 2014

Contents Glossary ......................................................................................................................................... iii 1.0 Introduction ............................................................................................................................. 1 2.0 Progress Summary .................................................................................................................. 1 2.1

Simulation ........................................................................................................................ 1

2.2

Software ........................................................................................................................... 2

2.3

Hardware .......................................................................................................................... 3

3.0 Future Work ............................................................................................................................ 4 3.1

Software ........................................................................................................................... 4

3.2

Hardware .......................................................................................................................... 5

4.0 Task List.................................................................................................................................. 5 5.0 Gantt Chart .............................................................................................................................. 6 6.0 Budget ..................................................................................................................................... 7 7.0 Conclusion .............................................................................................................................. 7

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Glossary ADC

Analog to Digital Conversion

DSC

Digital Signal Controller

DSTATCOM

Distribution Static Compensator

IGBT

Insulated Gate Bipolar Transistor

IPM

Intelligent Power Module

MIPS

Million Instructions Per Second

P/CT

Potential/Current Transformer

PCB

Printed Circuit Board

PLL

Phase-Locked Loop

PWM

Pulse-Width Modulation

THD

Total Harmonic Distortion

VSC

Voltage Source Converter

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1.0 Introduction The goal of this project is to design and implement a solid-state device for power factor correction. This will be accomplished through the use of a Distribution Static Compensator (DSTATCOM), which includes a six-pulse Voltage Source Converter (VSC) employing Insulated Gate Bipolar Transistors (IGBT) and controlled by a decoupled-indirect current controller method.

2.0 Progress Summary 2.1

Simulation We began the simulation in September and we originally used the Simulink simulation

environment. At first, Matt was assigned to build and debug the simulation file on his own, but after a few weeks this time allocation was clearly inadequate and thus a conscious decision was made to do it as a team. We encountered multiple issues while trying to get the system working as will be detailed in this section. One of the major problems encountered was with Simulink pre-made blocks. An example of this is with the Pulse-Width Modulation (PWM) block. The switching pulse generator had hard, preset limits which were not compatible with our inputs. It was also difficult to map the switching pulses generated by the block to the switches in the inverter. Other blocks shared similar problems, so we decided to create our own blocks for the PWM generation, six-pulse inverter as well as Forward and Inverse Park Transformations. This customization allowed us to be sure of the operation of the complex components in our system without relying on the functionality of the pre-made blocks. Despite these changes, the system did not function correctly and after the suggestion from Professor Filizadeh, we decided to switch from Simulink to the PSCAD simulation environment. After switching software, we still struggled to achieve stability and functionality in the simulation file. One of the problems was incorrect acquisition of the current controller inputs. In order to rectify this, we completely redesigned the current controller to allow us to monitor system variables at both the load and the output of the DSTATCOM. Furthermore, the newly 1

designed current controller allowed for complete decoupling of the active and reactive power in the DSTATCOM. Following the changes made to the control loops, there were still issues in achieving the correct operation of the system. After looking further into the derivation of the equations defining our system, we determined that there was positive feedback in the control loops, which caused an unwanted response. We were then able to determine how to achieve the correct feedback of the system. Throughout this stage we worked very closely with Professor Filizadeh to achieve a working simulation file. Upon completion of the simulation file we interrogated the system in order to determine whether it matched the specifications as originally defined, and made parameter modifications where necessary. Using the newly modified system we were able to specify various hardware components to match system requirements.

2.2

Software The software development began at the end of November, and consisted of two major

sections. The first was selecting and ordering required components, followed by setup and development of source code required for the control algorithm. We decided to develop our system in the C language as it allowed low level access to the controller while still offering a variety of integrated mathematical functionality. The software team consists of Matt and Chantel, with the duties of each member split according to difficulty and estimated time required. As stated, the first step before developing any code was to select and order the components required for the development environment. For this, we decided to select a Digital Signal Controller (DSC) over a microcontroller. The DSC provides a multitude of advantages over the microcontroller for our particular application, mainly that it offers an integrated high speed functionality for Sinusoidal PWM, multi-port simultaneous data conversion and access to an advanced library of mathematical functions. After some research, we selected a DSC made by Microchip Technology Inc. due to familiarity with the development environment MPLAB X, as well as experience using Microchip products in the past. We decided upon the dsPIC33FJ16GS402 processor which has a maximum speed of 40 MIPS as well as the required PWM outputs and simultaneous data conversion.With neither of the team members particularly well versed in the C language, comfort in the product was a major advantage. 2

The ongoing step in the software stage is development of source code for the components in the control loop. For this, the tasks were split evenly between Matt and Chantel. The sections to be divided included: Analog to Digital conversion (ADC), Forward and Inverse Park Transformations, control loop algorithm, PI controllers, Phase-Locked Loop (PLL), and PWM outputs. The exact division of labour is outlined in the software section of Table 4.1. Up to date, the testing setup has been wired, tested and verified on Project Board and is fully operational. The code required for the Forward and Inverse Park Transformations has been developed and tested with simulated data, and will be examined after completion of the ADC module. The PI controller algorithm including anti-windup functionality has been contrived as well. The setup for the high-speed PWM functionality is near completion and will be configured to operate at the highest resolution possible. The output logic of the PWM module required to properly drive the IGBT bridge has been established with the hardware team.

2.3

Hardware The hardware section of the project began in November, and was split into three basic

sections: signal conditioning and measurement, isolation, and mounting of the VSC. For a breakdown of task division, see Table 4.1. The first task that needed to be completed was the signal conditioning circuit. To execute our current controller algorithm, three sinusoidal signals and one DC signal have to be measured; these signals are the source voltage, load current, DSTATCOM current, and capacitor voltage. The first thing we have to do is to step down these signals to safe values which can be fed to the DSC. The AC signals are measured by current and potential transformers which step down the sinusoidal quantities to a range between ±5V, however, the DSC ADC requires signals which are between 0 and 3.6V. A signal conditioning circuit is then required to shift the ±5V signal output by the PT/CTs to a range between 0 and 3.6V. One of our major concerns when planning hardware implementation was protection and isolation. Proper isolation is required to keep the low and high voltage components separate for safety considerations. The transformers being used to step down and measure AC signals also provide isolation between the controller and high voltage/amperage signals. A precision isolation amplifier is used to isolate the DC link voltage from the DSC. The signals from the DSC that turn on the IGBTs cannot be directly connected to the IGBT, so we had to use digital isolators. 3

Usually opto-isolators are used for this, however, we chose digital isolators because of their speed and reliability. We are also implementing protective measures such as circuit breakers and fuses to ensure currents above our rated 15A do not flow through the DSTATCOM. Once we had figured out how to keep the system properly isolated, we began to look into how we were going to mount the VSC. Originally, we wanted to use a soldering board due to its ease of use, however, the IGBT bridge IC package is non-standard - the pins are of an irregular size and spacing - which made a soldering board a non-option. Due to these restrictions, we opted to design a PCB to accommodate the IGBT bridge. In summary, to date we have selected most of the hardware components, sketched out the PCB and begun the digital design, and begun work on the signal conditioning circuit.

3.0 Future Work 3.1

Software Coming to the completion of this project, there are still a few software modules that will

have to be developed and tested. These include the ADC, the PI testing, PWM module and PLL. We are aiming to complete the following modules by the beginning of February in order to facilitate the final system integration process. Firstly, the ADC module must be completed. For this, we must develop the source code that will initialize the module on the controller, and come up with a timing scheme to determine how quickly we can convert the data. The PI controller algorithm is complete and must be tested following the completion of the ADC module. To do so, we will construct a virtual feedback loop in the DSC source code and using this loop we can examine the response of a step input to the PI controller. The PWM module must be completed and tested for its functionality. Using the ADC module to process a sinusoidal test signal, we can determine if the outputs of the device are correct. In the final stages of testing, we will combine these outputs with the IGBT module to attempt a reconstruction of the same test signal. The PLL algorithm must be completed and then translated into source code. Because of the complexity of the system, a decision must be made as to whether we will implement the PLL on a separate DSC or within the source code of the main controller. 4

As stated, we are aiming to complete all the modules individually before combining the processes into a single control loop algorithm. We will have the complete system operational in early February in order to combine the controller with the hardware team.

3.2

Hardware The final stage of the project encompasses the bulk of the hardware work. Some of the

hardware components are already in progress, such as the PCB design, and signal conditioning implementation; outstanding tasks include PCB construction, the low voltage board design and construction, and system compilation and testing. The low voltage board needs to be designed and implemented; this includes testing the signal conditioning circuit, planning the location of the low voltage components, and constructing the low voltage part of the project. The high voltage board requires the completion of the design of the PCB, as well as the printing and construction. Following completion of the high and low voltage boards, we will begin work on system construction. This will involve connecting the high and low voltage boards to each other to form the DSTATCOM, and then connecting the DSTATCOM to the source and load. We will then proceed with testing the system to ensure it performs satisfactorily.

4.0 Task List Table 4.1: Tasks List

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Figure 5.1: Gantt Chart

5.0 Gantt Chart

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6.0 Budget

7.0 Conclusion With two months left remaining in the project, we are currently in the beginning stages of hardware and software implementation. We are planning to spend a total of $347.88 of our $400 budget, leaving us with just over $50 in emergency funds. Although we have fallen slightly behind on our original schedule, due to planned contingency time we are confident the project will be finished on time and within the expected budget.

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