Due to modern battery and motor drive technologies, unmanned aerial vehicles (UAV) have taken over a lot of tasks that are difficult or dangerous for humans. Thousands of new applications, from toys to military drones, have come up over the last few years. But what are the key challenges in this market? Obviously, the weight, payload, and runtime of the UAV are important. Another big challenge, especially for larger devices, is safe flight and landing, even in the case of jamming the remote signal, disturbances, or worst-case faults within the electronics or motors. A drone should never fall on anyone‘s head, cause any damage, or be lost.
Therefore, autopilot functions not only have to be implemented but, in several applications, also made redundant systems. In this case, the customer had to make sure that even in the case of a battery failure, the surveillance UAV could safely fly back over a longer distance. To achieve this redundancy, two completely separate batteries are installed in the UAV. Another important factor in this market is the readiness to redeploy after a long flight. Modern batteries allow fast charging with high power, two times 1.2kW in this case. It sounds easy, but the charger had to be portable and, therefore, as small and light as possible. The ideal solution was the combination of a very compact, 1.2kW, AC/DC power supply weighing only 1000g. With a
step-up/step-down (buck-boost) regulator it is able to charge all different types of batteries with currents up to 50A.
The
AC/DC power supply generates a 48VDC output voltage. The regulator takes this voltage and steps it up or down to the voltages needed for the complete charging process of the battery. The output voltage of the regulator is controlled by a microcontroller, which supervises the charge status and temperature of the batteries. By using two of these combinations, the customer creates the necessary, independent charging channels. Both AC/DC power supplies, two regulators, and the complete control electronics easily fit into a housing smaller than a standard briefcase. The total weight of the power components was less than 2kg.
Additionally, small RECOM converters have been used to generate 12V, 5V, and 3.3VDC supply voltages for control and supervising electronics from this 48VDC bus. The challenge of designing a 2.4kW, portable, two-channel charger was solved, and the customer can easily increase power levels in the future with a similar, very small 3kW AC/DC unit already on RECOM’s roadmap. The regulator used in the current design has enough capacity to handle this amount of power. And what if even more power is needed? Both units can be connected in parallel for 6kW of power.
