# The Electronic Switch of Windings of a Standard BLDC Motor
## 2 Realization of the Electronic Switch with a Modified BLDC Motor  
For the experiment, a standard GBM5208 12-pole BLDC motor was used in which all the stator windings were disconnected and a separate output was made for each of them in the form of a thin wire with fluoroplastic insulation while maintaining numbering and polarity. The original BLDC motor and its modified variant are depicted in Figure 4.  
The complete circuit of the electronic switch used to switch the winding schemes of the 12-pole BLDC motor contains 3 \(\times\) 9 switching elements, see Figure 5.  
For the purpose of switching among winding schemes jumpers have been used. These commutation elements do switch the 12-stator windings among each other to obtain six working circuits with different parameters, shown in Figure 6. The higher the inductance of the switched scheme, the higher the torque of the BLDC motor and the lower its speed. Each connection scheme of the stator windings has its own dynamic range, effective operating speed, and current consumption.  
Switching during the operation of the BLDC motor of various winding connection schemes is similar to an automatic transmission in a car when the transmission stages are switched depending on the required dynamic characteristics of the ride. Such a switch can also be made by a control signal from the operator, which is similar to manual transmission in a car. Since all three phases must be switched simultaneously, for switching all 27 switching elements, there have been used 9 control signals that come from a diode matrix,  
Figure 4: Original and modified motors GBM5208—original (**left**) and modified (**right**).  
Figure 3: Possible connection schemes for four poles.  
Figure 2: Diagram connection pole phase.  
where the signal of switching a particular circuit of the windings (IN1-IN3) is divided into separate switching elements S1-S9, see Figure 7.  
Figure 5: General scheme of the electronic switch windings.  
Figure 6: Six possible winding switching schemes.  
Since the windings in the BLDC motor work in AC mode, each pair of unipolar transistors with counter-switching is selected as a power switching element to eliminate the influence of an internal security diode. The electronic circuit of the power switching element is depicted in Figure 8.  
These transistors have a very low internal resistance, which minimizes large heat losses during the operation of the switch with a high-current load. According to scheme in Figure 8, an electronic switch of the BLDC motor windings has been developed and manufactured. The modified BLDC motor is connected to the electronic switch with the preservation of the winding numbering, as seen in Figure 9.  
To compare the characteristics of a standard BLDC motor with the modified one controlled by an electronic switch, a test bench was assembled. The assembly is shown in Figure 10.  
The test set-up consisted of: 24-Volt power supply, voltmeter (V), amperemeter (A), BLDC motor (M), ESC controller for BLDC motor rotation (ESC), tachometer (RPM) for measuring the speed of rotation, and the electronic switch of the stator windings (ESW) for operational commutation of the winding connection circuits.  
Figure 8: Power switching element.  
Figure 7: Separation of the control signals by a diode matrix.