Project

# Title Team Members TA Documents Sponsor
68 Power-Factor-Corrected Musical Tesla Coil
Ali Albaghdadi
Kartik Singh Maisnam
Shengyan Liu design_document1.pdf
final_paper1.pdf
proposal1.pdf
# Gentle Giant: A Power-Factor-Corrected Musical Tesla Coil

Team Members:
- Ali Albaghdadi (aalba9)
- Kartik Maisnam (maisnam2)

# Problem

Tesla coils are impressive visual and auditory devices; some can a surprising range of sounds using arc discharges, and thus have found uses as display pieces in entertainment and STEM education. A particularly large one is permanently mounted to a ceiling inside the Museum of Science and Industry in Chicago. However, for the majority of their existence, they have been crude instruments. The way they are built and operate typically results in a suboptimal use of AC power, also known as a poor power factor, and even with the advent of "solid-state" Tesla coils (SSTCs) that use power semiconductors, the problem has not improved. Areas with lower-voltage mains like the United States are often at a disadvantage due to details in many of these implementations. Further, when scaling up to large Tesla coils for use in performances, they can have a significant effect on the grid. Solving these problems can improve the efficiency and portability of these novelty constructions.

# Solution

We aim to build, for a comparatively low cost, a Dual-Resonance Solid State Tesla Coil (DRSSTC) with an active Power Factor Correction (PFC) front end. The combination of these two advancements puts our Tesla coil at the very forefront of Tesla coil hardware technology, and solves many of the technical issues with other modern designs.

Some background: Tesla coils are effectively giant transformers, with a secondary winding that has many times more turns than the primary. Conventional SSTCs operate by first rectifying mains AC to a high-voltage DC, then using a half-bridge or full-bridge of power semiconductors to switch the primary of the Tesla coil. This results in a very large voltage being generated in the secondary, which causes it to release arc discharges.

A major benefit that DRSSTCs like ours bring over SSTCs is that it operates more like a resonant converter. In the design phase of the transformer, the primary and secondary must be tuned to have close LC resonant frequencies. During operation, feedback from the primary is used to switch it at its resonant frequency, which results in energy being built up in the system more quickly and more impressive arc discharges. This energy buildup must be stopped intermittently by an external PWM signal called an interruptor (which can simultaneously be used to modulate music into the arc discharges). The primary feedback also enables zero-current switching (ZCS), reducing thermal losses in the power stage to near zero.

We choose to improve even further by designing a digitally controlled boost-type active PFC to create the high-voltage DC rail. This brings with it several benefits of its own, like improving system power factor, making the system agnostic to mains voltage and frequency, and allowing for smooth capacitor precharging without the use of a separate precharge circuit.

With a high power factor, both of the following are possible:
1. For the same apparent AC power, the generated arcs can be larger
2. Arcs of the same size can be generated for less apparent AC power

Thus the whole system consists of the PFC, the feedback controller, the power stage, and the transformer.

# Solution Components

## Boost-type PFC Stage

This subsystem draws power from the AC mains and creates a 400-volt DC rail. It is digitally controlled using an STM32F103 microcontroller, which allows it to ramp the voltage for precharging and compensate for different mains voltages and frequencies.

A boost-type PFC consists of a bridge rectifier, an input inductance, an output capacitance, a FET and an individual diode. We plan to use the Panjit KBJB bridge rectifier, Rohm SCT3120ALHR SiC FET and Wolfspeed C6D04065A SiC diode. Since we only need one of each in the product, their costs are negligible. A Texas Instruments UCC5710x gate driver can be used to allow the STM32F103 to drive the FET. The projected frequency of switching is 50kHz.

## Feedback controller

This subsystem implements a simple ZCS feedback controller using comparators and digital logic chips, and utilizes a long plastic optical cable to safely and remotely play simple musical notes via PWM (this is the interruptor signal). The optical receiver will be an Industrial Fiber Optics IF-D95T, which is an inexpensive device that has been highly proven in Tesla coil design history. Though in theory the microcontroller could also perform the logic task, we felt that it would not have low enough latency. The feedback itself is provided by a current transformer made of a Fair-Rite #77 ferrite core, which feeds into a burden resistor. Microchip MCP6561 comparators perform the zero crossing detection, and 74HCT logic chips manipulate the signal, combine it with the interruptor signal, and create gate drive waveforms for the power stage.

## Power stage

The power stage simply consists of a full bridge of four 60N65 IGBTs, and the primary LC is connected in the middle. The switches are driven by gate drive transformers (GDTs) to save cost and complexity versus developing a solution with isolated gate drive ICs. GDTs have been by far the leading solution to drive SSTC power semiconductors, and there is little incentive to do otherwise.

## Transformer

This is the Tesla coil itself. It will stand at around three feet tall once completed. It has no electronic components, but its physical design places some constraints on the electronic components. Preliminary calculations place the resonant frequency of the primary at around 200kHz.

# Criterion For Success

A PWM generator with an optical transmitter needs to be able to remotely start and operate the Tesla coil, causing it to release arc discharges. The arc discharges should be at least 1 foot in length, and the power factor of the whole system needs to be above 0.95 during normal operation.

Illini Voyager

Cameron Jones, Christopher Xu

Featured Project

# Illini Voyager

Team Members:

- Christopher Xu (cyx3)

- Cameron Jones (ccj4)

# Problem

Weather balloons are commonly used to collect meteorological data, such as temperature, pressure, humidity, and wind velocity at different layers of the atmosphere. These data are key components of today’s best predictive weather models, and we rely on the constant launch of radiosondes to meet this need. Most weather balloons cannot control their altitude and direction of travel, but if they could, we would be able to collect data from specific regions of the atmosphere, avoid commercial airspaces, increase range and duration of flights by optimizing position relative to weather forecasts, and avoid pollution from constant launches. A long endurance balloon platform also uniquely enables the performance of interesting payloads, such as the detection of high energy particles over the Antarctic, in situ measurements of high-altitude weather phenomena in remote locations, and radiation testing of electronic components. Since nearly all weather balloons flown today lack the control capability to make this possible, we are presented with an interesting engineering challenge with a significant payoff.

# Solution

We aim to solve this problem through the use of an automated venting and ballast system, which can modulate the balloon’s buoyancy to achieve a target altitude. Given accurate GPS positioning and modeling of the jetstream, we can fly at certain altitudes to navigate the winds of the upper atmosphere. The venting will be performed by an actuator fixed to the neck of the balloon, and the ballast drops will consist of small, biodegradable BBs, which pose no threat to anything below the balloon. Similar existing solutions, particularly the Stanford Valbal project, have had significant success with their long endurance launches. We are seeking to improve upon their endurance by increasing longevity from a power consumption and recharging standpoint, implementing a more capable altitude control algorithm which minimizes helium and ballast expenditures, and optimizing mechanisms to increase ballast capacity. With altitude control, the balloon has access to winds going in different directions at different layers in the atmosphere, making it possible to roughly adjust its horizontal trajectory and collect data from multiple regions in one flight.

# Solution Components

## Vent Valve and Cut-down (Mechanical)

A servo actuates a valve that allows helium to exit the balloon, decreasing the lift. The valve must allow enough flow when open to slow the initial ascent of the balloon at the cruising altitude, yet create a tight seal when closed. The same servo will also be able to detach or cut down the balloon in case we need to end the flight early. A parachute will deploy under free fall.

## Ballast Dropper (Mechanical)

A small DC motor spins a wheel to drop [biodegradable BBs](https://www.amazon.com/Force-Premium-Biodegradable-Airsoft-Ammo-20/dp/B08SHJ7LWC/). As the total weight of the system decreases, the balloon will gain altitude. This mechanism must drop BBs at a consistent weight and operate for long durations without jamming or have a method of detecting the jams and running an unjamming sequence.

## Power Subsystem (Electrical)

The entire system will be powered by a few lightweight rechargeable batteries (such as 18650). A battery protection system (such as BQ294x) will have an undervoltage and overvoltage cutoff to ensure safe voltages on the cells during charge and discharge.

## Control Subsystem (Electrical)

An STM32 microcontroller will serve as our flight computer and has the responsibility for commanding actuators, collecting data, and managing communications back to our ground console. We’ll likely use an internal watchdog timer to recover from system faults. On the same board, we’ll have GPS, pressure, temperature, and humidity sensors to determine how to actuate the vent valve or ballast.

## Communication Subsystem (Electrical)

The microcontroller will communicate via serial to the satellite modem (Iridium 9603N), sending small packets back to us on the ground with a minimum frequency of once per hour. There will also be a LED beacon visible up to 5 miles at night to meet regulations. We have read through the FAA part 101 regulations and believe our system meets all requirements to enable a safe, legal, and ethical balloon flight.

## Ground Subsystem (Software)

We will maintain a web server which will receive location reports and other data packets from our balloon while it is in flight. This piece of software will also allow us to schedule commands, respond to error conditions, and adjust the control algorithm while in flight.

# Criterion For Success

We aim to launch the balloon a week before the demo date. At the demo, we will present any data collected from the launch, as well as an identical version of the avionics board showing its functionality. A quantitative goal for the balloon is to survive 24 hours in the air, collect data for that whole period, and report it back via the satellite modem.

![Block diagram](https://i.imgur.com/0yazJTu.png)