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Magnetic Field Simulator Control System for Nanosatellites

Nano- and microsatellites are becoming more and more popular in the last ten years. The main reason for this is the low cost of their development and launch.  Two such satellites of the CubeSat format have already been developed at the Igor Sikorsky Kyiv Polytechnic Institute. They have successfully completed their missions in orbit. Work on a new satellite is underway. Before flying into orbit, all satellites must pass a large number of ground tests.
An important part of almost every satellite is its subsystem of orientation and stabilization. Since it contains magnetic sensors and electromagnets, special magnetic field simulators are used to test it. Such a simulator must create a uniform magnetic field with the required parameters. The most common design used to simulate a magnetic field is a Helmholtz cage. It was built in the nanosatellite laboratory of the Igor Sikorsky Kyiv Polytechnic Institute. This paper deals with the development of a control system for it.
In the beginning, the design, parameters, and operation principle of the Helmholtz cage were described. It consists of six electromagnetic square shape coils with a side of 1.5 meters. Each coil has 52 turns of 1.29 mm wire. Such dimensions make it possible to obtain a spherical zone of uniformity of the magnetic field with a radius of 293 mm. The control system should regulate the current in the coils, change its direction and also control the parameters of the generated magnetic field. The existing solutions for such a system were analyzed. As a result, it was decided to use an H bridge circuit and pulse width regulation.
The structural and schematic diagrams of the control system were developed. Were selected all necessary components, such as power module, central processing unit, microcontroller for PWM signal generation, and magnetometer for magnetic field control. To reduce the ripple of the output current, an RLC filter for the coil driver was developed. Its frequency response, current and voltage curves of its load were calculated analytically and coincided with practical results.
An experimental layout of the control system was assembled. As a result of the tests, it was found that the system regulates the current in the coil from 0 to 6.8 A and can change its direction. The current ripple in the coils does not exceed 1 mA (peak-to-peak) at an average current of 0,574 A. The duration of the transient in the system is about 23 ms. These values meet the requirements and allow simulating any mode of satellite flight in orbit.
The developed control system for the magnetic simulator allows testing the magnetic orientation systems of nanosatellites developed at Igor Sikorsky Kyiv Polytechnic Institute and will help in their preparation for the flight.