1. Introduction

2. 3-Phase BLDC Motor and Controller Design

2.2. 3-Phase BLDC Motors Winding Structure

For BLDC motors, different characteristics can be achieved depending on the winding structure of the stator. The Y-Connection is preferred for applications requiring high torque and low speed due to its simple structure and relatively high efficiency. On the other hand, the Delta-Connection is suitable for applications with low torque and high speed as it can reduce the phase impedance and widen the operating range. Especially in independent power supply drive systems powered by low-voltage batteries, the Delta-Connection is frequently used [12,13]. In contrast to the two commonly used connection methods, the approach we propose utilizes an independent 3-Phase method, known as the single-phase excitation structure, where voltage is applied independently to each winding without contact points between them.

In the case of the Independent 3-Phase system's wiring structure, there is almost no increase in the size and weight of the motor itself. Unlike the Y-Connection or Delta-Connection methods, where one voltage source is split into two or three phases, in the Independent 3-Phase system, one voltage source is allocated to each phase. This results in an increase in phase voltage. This increase in phase voltage implies an increase in phase current when resistance and inductance are constant. Therefore, this increase in phase current translates into an increase in the torque that the motor can exert at the same voltage, thereby enhancing the torque density of the motor. Since the control method is generally similar to that of commonly used wiring methods, changing only the winding method presents no significant challenge, enabling the motor to achieve higher torque density. This paper validates the efficacy of the Independent 3-Phase BLDC Motor through comparative experiments with Y-Connection BLDC motors and Delta-Connection BLDC motors.

2.2.1. Y-Connection BLDC Motor Design

In the case of a Y-Connection BLDC motor, each of the three phases forms a neutral point, as shown in Figure 1 (a). The excitation structure applied to the armature is a 2-phase excitation system, as depicted in Figure 1 (b), where two phases are excited by one voltage source. In this system, since two phases are excited by one voltage source, the available voltage per phase is reduced by half [16]. The reason why Y-connected BLDC motors are more commonly used than Delta-connected BLDC motors is that by not grounding the neutral point, they can remove the zero-sequence component of the third harmonic that causes inductive interference, thereby improving the waveform and reducing the effect of ripple on the BLDC motor operation. Additionally, the relationship between line-to-line voltage and phase voltage is advantageous for high voltages, and corona discharge and deterioration are prevented.

Figure 1. (a) Equivalent Circuit of Y-Connection BLDC Motor (b) Excitation System of Y-Connection BLDC Motor (2-Phase Excitation).

Figure 1. (a) Equivalent Circuit of Y-Connection BLDC Motor (b) Excitation System of Y-Connection BLDC Motor (2-Phase Excitation).

$$V_{line}={\sqrt{3}V}_{phase} , I_{line}= I_{phase}$$

(7)

$$\left|E_b-E_c\right|=V\left|sin\left(\omega t+\frac{2\pi }{3}\right)-sin\left(\omega t-\frac{2\pi }{3}\right)\right|$$

(8)

$$=V\left|2cos\omega sin\frac{2\pi }{3}\right|$$

(9)

$$=\sqrt{3}{k}_t\omega \left|cos\omega t\right|$$

(10)

Here, ${\mathrm{V}}_{\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}$ represents the line-to-line voltage, ${\mathrm{V}}_{\mathrm{p}\mathrm{h}\mathrm{a}\mathrm{s}\mathrm{e}}$ represents the phase voltage, ${\mathrm{I}}_{\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}$ represents the line current, ${\mathrm{I}}_{\mathrm{p}\mathrm{h}\mathrm{a}\mathrm{s}\mathrm{e}}$ represents the phase current and ${\mathrm{k}}_{\mathrm{t}}$ denotes the Back EMF constant. In the case of Y-Connection, the line-to-line voltage is $\sqrt{3}$ times greater than the phase voltage. The motor reaches saturation speed at $\mathsf{\omega }$ where Equation (10) is satisfied [17].

2.2.2. Delta-Connection BLDC Motor Design

In the case of Delta-Connection BLDC motors, one end of each winding is connected to the neighboring end of the adjacent winding, creating a total of 3 winding junctions, as shown in Figure 2 (a). When voltage is applied to the stator, as illustrated in Figure 2 (b), it forms a 3-Phase excitation system where all three phases are energized by a single voltage source [16]. With this system, since all three phases are excited by a single voltage source. The uneven distribution of voltage applied to each phase, as seen in Figure 2 (b), creates ripples in the operation of the BLDC motor [18].

$$V_{line}=V_{phase} , I_{line}= \sqrt{3}{I}_{phase}$$

(11)

$$\left|E_b+E_c\right|=V\left|sin\left(\omega t+\frac{2\pi }{3}\right)+sin\left(\omega t-\frac{2\pi }{3}\right)\right|$$

(12)

$$=V\left|2sin\omega tcos\frac{2\pi }{3}\right|$$

(13)

$$=k_t\omega \left|sin\omega t\right|$$

(14)

$$\left|E_a\right|=k_t\omega \left|sin\omega t\right|$$

(15)

In the case of Delta-Connection, the line-to-line voltage is equal to the phase voltage, while the line current is $\sqrt{3}$ times greater than the phase voltage. The motor reaches saturation speed at $\mathsf{\omega }$ where Equations (14) and (15) are satisfied and compared to Equation (10) for Y-Connection BLDC Motor, it has a saturation point that is $\sqrt{3}$ times higher [17].

2.2.3. Independent 3-Phase BLDC Motor Design

In the Independent 3-Phase BLDC Motor, unlike Y-Connection and Delta-Connection methods, each phase is separate and distinct without any junction points, as illustrated in Figure 3 (a) Additionally, the electrical location of each phase in the motor's structure is identical to that of the Y-Connection and Delta-Connection methods. This adds no complexity to motor control and facilitates easy handling. In the Independent 3-Phase BLDC Motor, unlike the previous methods, when voltage is applied to one phase, it is exclusively applied to that phase. The voltage is not distributed among the other phases. The increase in applied voltage signifies an increase in phase current when the resistance and inductance of the stator remain constant, as indicated by Equation (3), leading to an increase in torque [13].

$$\left|E_a\right|=k_t\omega \left|sin\omega t\right|$$

(16)

$$\left|E_b\right|=k_t\omega \left|\mathrm{s}\mathrm{i}\mathrm{n}(\omega t+\frac{2\pi }{3})\right|$$

(17)

$$\left|E_c\right|=k_t\omega \left|sin(\omega t-\frac{2\pi }{3})\right|$$

(18)

In the case of the Independent 3-Phase BLDC Motor, unlike the Y-Connection BLDC Motor and Delta-Connection BLDC Motor, there is no difference in the magnitudes of line voltage and phase voltage as well as line current and phase current. The speed of the BLDC Motor saturates at ω, which satisfies Equation (16).

2.3. 3-Phase BLDC Motor Inverters Design

2.3.1. Y-Connection and Delta-Connection BLDC Motor Inverter Design

The inverter structure for both Y-Connection and Delta-Connection BLDC motors, as shown in Figure 4, is identical. It utilizes six switching components for driving the motor and comprises three half-bridge inverters. In the Y-Connection configuration, as depicted in Figure 4, junctions are formed by A-, B-, and C-. Additionally, A+, B+, and C+ are each connected to their respective half-bridge inverters. Conversely, for Delta-Connection, A+B-, B+C-, and C+A- form the junctions, connecting to the corresponding parts of the half-bridge inverter. The control sequence based on Hall Sensor signals, which is illustrated in Table 1, remains the same for both wiring configurations [19].

Figure 4. Y-Connection and Delta-Connection BLDC Motor Inverter Circuit and Connecting Schematic.

Figure 4. Y-Connection and Delta-Connection BLDC Motor Inverter Circuit and Connecting Schematic.

Table 3. Y-Connection and Delta-Connection BLDC Motor Hall Sensor and Phase Sequence.

Table 3. Y-Connection and Delta-Connection BLDC Motor Hall Sensor and Phase Sequence.

Direction	Operating Range		Hall Sensor			Switching Signal
	Degree	Interrupt	HA	HB	HC	A1	A2	B1	B2	C1	C2
Forward	0~60	HA↑	1	0	1	1	0	0	PWM	0	0
	60~120	HC↓	1	0	0	1	0	0	0	0	PWM
	120~180	HB↑	1	1	0	0	0	1	0	0	PWM
	180~240	HA↓	0	1	0	0	PWM	1	0	0	0
	240~300	HC↑	0	1	1	0	PWM	0	0	1	0
	300~360	HB↓	0	0	1	0	0	0	PWM	1	0
Reverse	0~60	HA↑	1	1	0	0	0	0	PWM	1	0
	60~120	HB↓	1	0	0	0	PWM	0	0	1	0
	120~180	HC↑	1	0	1	0	PWM	1	0	0	0
	180~240	HA↓	0	0	1	0	0	1	0	0	PWM
	240~300	HB↑	0	1	1	1	0	0	0	0	PWM
	300~360	HC↓	0	1	0	1	0	0	PWM	0	0

2.3.2. Independent 3-Phase BLDC Motor Inverter Design

Unlike the six-step inverters of Y-Connection BLDC motors and Delta-Connection BLDC Motors, the inverter structure of the Independent 3-Phase BLDC Motor, as shown in Figure 5, consists of three full-bridge inverters, with each full-bridge inverter controlling the on/off of one phase. The connection between the stator and a single pole in the inverter is as illustrated in Figure 5. Furthermore, the Independent 3-Phase BLDC Motor has an identical electrical location with Y-Connection BLDC motors and Delta-Connection BLDC Motors. As a result, controlling the signals output based on the Hall Sensor signals is easily achievable using the same Hall Sensor signals as shown in Table 2 [20].

3. Experiment Comparing the Motor Dynamics

3.2. Speed Experiment of Each BLDC Motor

The speed was calculated using the M method, using signals from the Hall sensors that were amplified sixfold to increase resolution. The equations for the M method are as provided in (4) and (5), and the parameters used for speed calculation are detailed in Table 4 [2]. The first comparative analysis of motor dynamics was conducted with PWM ranging from 30% to 90%, measuring the RPM changes corresponding to each duty ratio. In the second comparative analysis experiment, the characteristics of speed and current were compared at a 90% duty ratio.

$$\theta =\frac{m1}{PPR}\times 2\pi \left[rad\right]$$

(4)

$${\omega }_m=\frac{60}{2\pi }\times \frac{\theta }{t}=\frac{60}{2\pi }\times \frac{m1}{PPR}\times 2\pi \times \frac{1}{T_s} \left[RPM\right]$$

(5)

Here, $\mathsf{\theta }$ represents the rotation angle, poles indicate the number of poles in the motor, and PPR (Pulse Per Revolution) refers to the maximum number of output pulses per revolution of the motor. ${\mathrm{T}}_{\mathrm{s}}$ represents the sampling time.

Table 4. Independent 3-Phase BLDC Motor Hall Sensor and Phase Sequence.

Table 4. Independent 3-Phase BLDC Motor Hall Sensor and Phase Sequence.

Direction	Operating Range		Hall Sensor			Switching Signal
	Degree	Interrupt	HA	HB	HC	A1	A2	A3	A4	B1	B2	B3	B4	C1	C2	C3	C4
Forward	0~60	HA↑	1	0	1	1	0	0	PWM	0	PWM	1	0	0	0	0	0
	60~120	HC↓	1	0	0	1	0	0	PWM	0	0	0	0	0	PWM	1	0
	120~180	HB↑	1	1	0	0	0	0	0	1	0	0	PWM	0	PWM	1	0
	180~240	HA↓	0	1	0	0	PWM	1	0	1	0	0	PWM	0	0	0	0
	240~300	HC↑	0	1	1	0	PWM	1	0	0	0	0	0	1	0	0	PWM
	300~360	HB↓	0	0	1	0	0	0	0	0	PWM	1	0	1	0	0	PWM
Reverse	0~60	HA↑	1	1	0	0	0	0	0	0	PWM	1	0	1	0	0	PWM
	60~120	HB↓	1	0	0	0	PWM	1	0	0	0	0	0	1	0	0	PWM
	120~180	HC↑	1	0	1	0	PWM	1	0	1	0	0	PWM	0	0	0	0
	180~240	HA↓	0	0	1	0	0	0	0	1	0	0	PWM	0	PWM	1	0
	240~300	HB↑	0	1	1	1	0	0	PWM	0	0	0	0	0	PWM	1	0
	300~360	HC↓	0	1	0	1	0	0	PWM	0	PWM	1	0	0	0	0	0

Table 5. Speed Calculation Parameters for the M Method.

Table 5. Speed Calculation Parameters for the M Method.

	Number of Poles	PPR	${\mathbf{T}}_{\mathbf{s}}$(Sampling time) [sec]
BLDC motor	26	$78$	0.04

4. Results

5. Discussion

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