Hypercube 100A Dual H-Bridge Board

2018-11-09

• The final tweaks before launch of board ready
• The H-bridge is fully optically isolated from the CPU
• Each quarter of the H-bridge can be independently turned on from the CPU
  • This in turn allows phase shifted bridges with software control of each bridge configuration to be implemented
  • Phase shifted bridges are some of the most advanced efficient designs around today for aircraft power supplies
• 3 Phase waveforms can be generated with PWM to drive drone motors of very high power.
• More importantly, the PWM can be generated in software, and with sensor added, motor stall and recovery is easily implemented to prevent drones falling out of the sky
• Circuits to be released in KiCAD and open sourced along with software

History

• The Hypercube 100A Dual H-Bridge board is based around peripheral boards for the open sourced ARM Linux SoC board
• Soon to be open sourced after testing. Design work is finished, sent for manufacturing, now awaiting manufactured board and testing.

• The connectors are 20A rated. Big pads added to allow direct soldering of wire to the connector to get more current in and out of the board.

Uses

Driving High Power Drone Motors

• High power drone motors are 3 phase motors.
• The Hypercube Dual H-bridges are actually 4 half bridges that are wired externally to make them into Dual H-bridge
• 3 of the half bridges can be used to drive one 3 phase drone motor
• To drive 4 drone motors require 3 Hypercube Dual H-bridge boards.
• Each half H-bridge can drive 100A load.
• Higher power is possible by paralleling up the half bridges. So 6 Hypercube Dual H-bridge boards can supply up to 200A drive current at around 25V safely.
• The power to the motor is controlled by feeding PWM signals to the MOSFETs so that they are on for a fraction of the time needed to drive them.
• The PWM signals are three phases set 120 degrees apart.
• The kind of signals needed to drive the PWM is easily possible with Arduino for slow drone motors.
• For faster drone motors, the software needs to be written in C.
• The Hypercube STDuino++ board runs both Arduino code and C code. So you can develop test software in Arduino, and progress to C code
• We will be making fully functional multi-tasking code for Arduino mode and C and release it as open source so you can go build the more powerful drones your imagination has set its eyes on :)
• Don't forget our Lithium boards for managing reconfigurable battery arrays. We will be releasing software for battery management systems as well so that you can integrate both the drone drivers and the battery management system in true real time multi-tasking systems with open sourced code that we will provide.
• Soon we will release circuit diagrams, documentation and software - watch this space :)

Cooling & Safety

• The MOSFETs are 2mR. At 100A, you can expect it to consume about 0.2W. But this is only true if the MOSFET is cool and the MOSFET is not being switched on and off at high speed. As the temperature rises to around 100 degrees, the resistance will increase to about 4mR and so the device will absorb around 0.4W. As the switching frequency increases, there is a finite amount of time when the MOSFET is going from 2mR to near infinite off resistance. During this brief switching period, it will absorb a lot of power. The faster the switching frequency, the more energy that gets absorbed by the MOSFET. The typical switching frequency before MOSFET's efficiency becomes a problem is 100kHz upwards. They can be driven up to 10MHz with good cooling. But be careful, if the system is radiating energy because of improperly wired coils, and the total energy in the radiation is running into a couple of of watts to kilowatts, then this radiated energy is dangerous and life threatening, as well as damaging to any electronic items in its vicinity including biomedical devices such as pacemakers. If you are cranking up the power, be sure to know your electronics, and if uncertain get help from a suitably qualified electronics engineer.
• When driving high current motors and coils, imagine what might happen if the load is suddenly removed. There is nowhere for the currents and voltages to go, and so it is all returned back to the H-bridge! There are flywheel diodes built into the MOSFETs to handle this energy surge, but the bigger the currents and voltages, the bigger the surge. The surge is returned to the power supply by the flywheel diodes. For a short instant a 25V power supply can surge to thousands of volts. Usually that never matters because there will always be another coil that the surge power will get dumped into. But if all of those coils are simultaneously seeing the load lightening, then the power is returned to the battery. Usually the battery or the power source can handle this returned power. Despite this being a requirement, high wattage power supplies are not always designed to handle this kind of surge power being returned to it. So be careful - know your power supply limits when driving high wattage loads. And if the power source is a battery, it most definitely will not handle large amounts of returned power. It takes a long time (about 4 to 20 minutes) for a battery to go from discharging mode to re-charging mode because it is a chemistry change. So it will not accept the returned power, and thus the returning energy pulse builds up in the wires generating thousands of volts ready to arc across electronics, batteries and terminals. To avoid this, you can fit a supercapacitor to absorb the returning energy pulse. Many electric vehicles have it. They are big capacitors with instant reaction able to absorb a lot of power. Again take care if using supercapacitors when large amounts of energy is involved. A third of the energy in the pulse is lost as heat - this is down to basic physics of capacitors. This lost energy is heating up the supercapacitor! So if regular amounts of pulse energy is being mitigated by supercapacitors, then be sure to fit cooling for them. Fitting supercapacitors in general not a good idea - better to have some other method to mitigate damaging pulse energy - for example fitting some kind of sensor that directs pulse energy to a rectifier circuit, rectifies it, and use it to charge another set of batteries.
• These advisories do not provide full coverage about safety. You need to know your electronics and rely on your training to guide you to safe usage of high power electronics when designing products such as electric vehicles, high power drone motors, large 3D printers and so on.