LunaDrive: A Delay-Compensated High-Voltage GaN FET-Based Motor Driver for Dynamic Robots with Flat BLDC Motors

Sota Yuzaki, Temma Suzuki, Hiromi Tada, Masanori Konishi, Kento Kawaharazuka, Kei Okada · N/A · 2026

Summary

Abstract Summary

The performance improvement of high-power flat BLDC motors has accelerated the development of dynamic robots. However, many commercially available servo motors assume operating voltages of 48 V or lower, which limits the maximum rotational speed. Dynamic robots require rapid energy generation, so this voltage constraint restricts motion performance. Therefore, driving motors beyond the rated voltage is desirable to increase the instantaneous maximum speed. On the other hand, semiconductor devices used in motor drivers have a trade-off between voltage rating and current capacity. Conventional drivers using Si MOSFETs have difficulty achieving both high-voltage and high-current operation. Although GaN FETs are promising, compact drivers that can be mounted on the rear side of flat BLDC motors remain limited. In this study, a motor driver for high-power flat BLDC motors using GaN FETs is developed. The effect of delay compensation in the high-speed region beyond the rated operating range is also investigated. In the experiments, under 96 V operation, a continuous current of 30 A was achieved with a heat sink attached. A peak current of 80 A and a maximum electrical frequency of 3110 Hz were confirmed. A high-speed load lifting experiment driven by a LiPo battery 24S (100 V) was also conducted, demonstrating applicability to dynamic robot operation.

Key Points

The performance improvement of high-power flat BLDC motors has accelerated the development of dynamic robots.
However, many commercially available servo motors assume operating voltages of 48 V or lower, which limits the maximum rotational speed.
Dynamic robots require rapid energy generation, so this voltage constraint restricts motion performance.
Therefore, driving motors beyond the rated voltage is desirable to increase the instantaneous maximum speed.
On the other hand, semiconductor devices used in motor drivers have a trade-off between voltage rating and current capacity.

Method

LunaDrive consists of two boards, as shown in Fig. 2 . One is a controller board for motor control and communication with the host system. The other is a driver board that drives the BLDC motor using GaN FETs. The diameter is $70\text{\,}\mathrm{m}\mathrm{m}$. Only the connector section used by the user protrudes outward. The thickness is $8.51\text{\,}\mathrm{m}\mathrm{m}$.

Experiments

In this experiment, switching waveforms were observed when $10\text{\,}\mathrm{A}$ was applied to the motor in order to verify proper switching operation. The oscilloscope used for the measurement was an MDO4054B-3 (Tektronix) with a bandwidth of $500\text{\,}\mathrm{MHz}$. The measurement results are shown in Fig. 9 .

Since the motor is a load with large current fluctuations, the slew rate was set to $4.5\text{\,}\mathrm{V}$ as a conservative design choice.

Experiments — LunaDrive: A Delay-Compensated High-Voltage GaN FET-Based Motor Driver for Dynamic Robots with Flat BLDC Motors — Fig. 8: Two types of heat sinks

Sources and Demonstrations

Figures are reproduced from Yuzaki et al. See the full paper for experimental details and the project page, when the paper links one, for demonstrations and videos.