# Analysis and Assessment of a Brushless DC Outrunner Motor for Agriculture Drones Using JMAG
## 3 Bldc Motor Analysis
### Six-Step Commutation  
Trapezoidal commutation is a low-cost technique often used in agricultural UAV applications. Its electronic simplicity lies in the six-step nature of the driving signal, disregarding the use of dead-time circuits, complex filters, and rotor position detection methods. During a complete electrical cycle, the current and voltage waveforms undergo six transitions, that is, a different current mode every 60 degrees (Figure 14). In any instant of time, current flows through two of three lines in a controlled fashion [20]. The floating line can then be used to lead the timing of the transitions required to produce a maximum torque output by detecting the zero-crossing of the BEMF [21]. Pulse width modulation (PWM) is used to control the voltage input to the motors and thus regulate the motor speed. The most popular PWM drive signal scheme in BLDC motors is that in which only high-side MOSFETs are controlled using the PWM signal (Figure 15), while the rest only receive ON-OFF states [7].  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Characteristic** & **Value** \\ \hline Winding & concentrated \\ Gauge & 23 awg \\ Stator slots & 36 \\ Rotor poles & 42 \\ Phase windings & 12 \\ Pole winding & 0.2857 \\ Pole pitch & 0.85 \\ Conductor threads & 6 \\ Slot conductor turns & 4 \\ Slot fill factor & 33\% \\ Termination & Delta \\ \hline \hline \end{tabular}
\end{table}
Table 7: Winding characteristics.  
Figure 13: BEMF: (**a**) IMAG simulation, (**b**) measured using a designed ESC with trapezoidal commutation.  
In practice, the three-half-bridge topology is used to create six-step power signal commutation and zero-crossing via resistors, filters, and comparators.  
Figure 16 shows the ESC implemented in JMAG. The circuit scheme includes a rotor position detection algorithm that commands the six-step commutation to the three-half-bridge circuit model switches. The PWM's duty cycle is regulated through a modulation ratio, emulating a radio control signal or throttle percentage from a flight controller. Additionally, the inverter is energized with a current source corresponding to experimental measurements. The circuit inputs for a 60% throttle capacity are shown in Table 9, and the corresponding electromagnetic flux density and flux lines appear in Figure 17.  
Figure 14: Six-step trapezoidal commutation for a three-phase motor with delta termination.  
Figure 15: Electronic speed controller for a three-phase electric motor with delta connection using trapezoidal commutation.  
\begin{table}
\begin{tabular}{l c c} \hline \hline
**Parameter** & **Value** & **Unit** \\ \hline Angular velocity & 3106 & rpm \\ Initial position & 7.18 & degree \\ Modulation ratio & 0.6 & - \\ Nominal voltage & 60.1 & V \\ Inverter bus current & 29 & A \\ Phase inductance & \(2.205\times 10^{-5}\) & H \\ Phase resistance & 0.03615 & ohm \\ Inverte branch resistance & 0.5 & ohm \\ PWM’s carrier frequency & 17 & kHz \\ Commutation sequence & u-v-w & - \\ \hline \hline \end{tabular}
\end{table}
Table 9: Circuit parameters for a 60% throttle capacity.  
The overall good outer-to-inner diameter ratio of the stator can be observed in the nominal magnetic flux density. The relatively thin stator yoke accounts for the larger slot depth. In keeping the magnetic flux density below 1.7 T and maintaining a good operating temperature, fewer iron losses are expected.