Design and analysis of underwater power generation characteristics of deflected double-stator switched reluctance generator

Abstract

The Deflectable double-stator Switched Reluctance Generator (DSRG) has the advantages of simple structure, small volume and multi-dimensional operation. The DSRG and propeller are combined into the application of underwater power generation. With the help of the deflect ability of the generator, the efficiency is improved. Due to the uncertainty of ocean current direction and the structure of switched reluctance generator, the torque ripple is one of the important factors damaging the underwater generator. In order to effectively suppress the influence of torque ripple caused by generator operation, a method of adding pole shoes on the pole side of outer stator is proposed, so as to reduce the torque ripple. The propulsion structure running at different deflection angles is simulated. The torque and speed obtained before and after pole shoe optimization are input into the propeller model. The pressure and speed characteristics of the corresponding blade structure are simulated to verify the effect of optimization and the effectiveness of the power generation system.

Keywords

Double stator finite element analysis switched reluctance motor torque ripple

1. Introduction

In recent years, due to the increasing trans-regional trade activities, the frequency of maritime transport activities has become more frequent. In order to improve the endurance of ships to adapt to long-distance maritime activities, People began to focus on the joint development and application of ocean energy and vehicle. The characteristics of simple structure, large torque, and stable operation have made the switched reluctance generators attract attention. Literature [1] proposed and analyzed a dual-stator structure switched reluctance motor. The internal and external stator characteristics of the motor increase the number of teeth, increase the output torque and effectively reduce the torque ripple. Literature [2–7] proved that the double stator structure improves the accuracy of the generator and increases the overload capacity through finite element analysis. This kind of structure has simple and compact structure, low cost, small size, high efficiency, strong adaptability, etc. The switched reluctance motor with excellent performance is suitable for use in underwater vehicles.

Because the magnetic circuit of the switched reluctance motor is highly non-linear, the torque ripple is large, which aggravates the noise and vibration of the motor. To solve this problem, literature [8–10] proposed an algorithm based on stator current to suppress the torque ripple problem and made improvements in the control of motor vibration. Literature [11] optimizes the pole-arc coefficient of the permanent magnet synchronous motor, weakens the influence of the electromagnetic harmonic generated by the air gap between the stator and rotor of the motor on the torque ripple amplitude, and achieves the purpose of reducing the torque ripple. The motor optimization method of the switched reluctance motor is the same as that of the permanent magnet synchronous motor. It is divided into two aspects: the internal current and voltage control of the motor and the motor body structure. In reference [12], an improved method was proposed to solve the problem of torque ripple in low-speed operation of switched reluctance motor in terms of control current. The neural network current injection method is used to adjust the waveform of input current to complete the optimization work of suppressing the torque ripple of the motor. Literature [13–17] adjusts the motor structure for hardware optimization from the perspective of the body structure of switched reluctance motor, and finally improves the working efficiency of the motor by reducing the torque ripple.

Based on the design of a low-power power generation system consisting of propeller and deflectable dual stator switched reluctance generator which also is called deflectable switched reluctance generator (DSRG). This paper optimized the motor torque ripple of a 2.5 kW DSRG. The finite element software was used to simulate two kinds of reluctance motors with different magnetic pole pairs of inner stators. The magnetic field distribution diagram and output current and torque curve were obtained respectively. After the optimal selection was selected, the structure of the motor pole boot was optimized [18,19]. Based on mechanical theory and fluid dynamics, provided using CFX software on the propeller pressure characteristics of a variety of deflection Angle and torque characteristics of research, finally, the underwater generator model is established by using finite element software, the simulation to verify the underwater double stator deflection type switched reluctance motor through the torque ripple is improved after optimization, the output power of the generator has been effectively improved. It lays a foundation for the design and research of high-power underwater switched reluctance generators in the future.

2. Underwater power generation system based on deflected switched reluctance generator

2.1. The power generation principle and overall structure of the underwater power generation system

The design idea of this paper is that when the vehicle stops moving, the power generation system drives the turbine blade of the motor to rotate through the ocean current, so as to transfer the mechanical energy to the prime mover of the generator, and then the generator rotates to generate electrical energy, which is input to the distributed grid inside the vehicle. When the vehicle is moving forward, it can also transfer the electricity stored in the previous generation to the power conversion system, which can then be transferred to the motor and converted into mechanical energy, so as to realize the motion of underwater navigation. The generator installed in the power generation system is a double-stator DSRG, which is characterized by the rotor can work at the deflection Angle and is combined with the propeller by connecting rod. Compared with the traditional generator, the power generation system can utilize the ocean current energy in various angles into the power generation system, effectively increasing the conversion rate of ocean current kinetic energy, and improving the endurance of the underwater vehicle. The overall structure of the underwater vehicle is shown in Fig. 1. The underwater generator is composed of propeller, connecting rod, and generator shaft, switched reluctance motor and metal shell.

Fig. 1.

The overall structure of the underwater vehicle.

2.2. The structure of deflected switched reluctance generator

The body structure of the deflectable dual stator switched reluctance generator is composed of the outer stator, magnet vane, outer rotor, inner stator, inner rotor, and centralized winding coil, as shown in Fig. 2. Among them, the material of rotor and stator is silicon steel sheet formed by stacking, and its structure is a convex pole groove. The fixed rotor structure on both sides of the inside and outside can strengthen the power generation effect of the motor. There are no windings and permanent magnets on the rotor, which avoid the excitation loss on the rotor of the traditional motor. The control circuit of the external circuit is used to control the switch of motor winding. In self-excited excitation mode, the prime mover to the power switched reluctance generator, the motor rotor to counterclockwise rotation, It can be observed from Fig. 4, the path of the magnetic force lines between fixed rotors will pass through the stator yoke, stator teeth, the air gap between fixed rotors, rotor teeth, and then from the adjacent in-phase stator windings of the corresponding rotor teeth through the air gap of the fixed rotor to the adjacent in-phase stator teeth, and finally form a closed loop in the stator yoke. Figure 3 shows the two-dimensional graphic of DSRG.

Fig. 2.

The 3D diagram of deflectable dual stator switched reluctance generator.

Fig. 3.

The 2D diagram of deflectable dual stator switched reluctance generator.

3. The choice of convex pole pairs of DSRG

The deflected switched reluctance power generation system proposed in this paper can achieve different performance according to different design requirements. According to the optimal design standard of switched reluctance motor and the design optimization case of switched Reluctance motor mentioned in literature [20–24], two stator winding three-phase generator motors with the same number of outer stator poles and different number of inner stator poles are selected in this chapter, namely 12/8/8/12 structure and 12/8/16/12 structure respectively.

The specific parameters of the two motors adopted in the simulation are shown in Table 1.

Table 1
Parameters of DSRG models

Parameter 12/8/16/12 parameter 12/8/8/12 parameter

Outer radius of outer 151 151

Rotor outer diameter/mm 116 116

The stator inner diameter/mm 56 56

Outer stator tooth width/mm 30.5 30.5

Inner stator tooth width/mm 8 14.5

Outer rotor tooth width/mm 32.4 32.5

Inner rotor tooth width/mm 10 14.5

The distance of air gap/mm 0.5 0.5

Rated speed/rpm 60 60

Parameter	12/8/16/12 parameter	12/8/8/12 parameter
Outer radius of outer	151	151
Rotor outer diameter/mm	116	116
The stator inner diameter/mm	56	56
Outer stator tooth width/mm	30.5	30.5
Inner stator tooth width/mm	8	14.5
Outer rotor tooth width/mm	32.4	32.5
Inner rotor tooth width/mm	10	14.5
The distance of air gap/mm	0.5	0.5
Rated speed/rpm	60	60

It is simulated by finite element software. When phase A and F is conducting, the magnetic induction lines are shown in Fig. 4. It can be seen that the magnetic flux distribution at the salient pole tooth position in 12/8/8/12 is more regular. In contrast, the magnetic flux distribution of 12/8/16/12 is obviously more chaotic, and the edge magnetic density is high, which is more likely to cause the distortion of air gap magnetic field.

Fig. 4.

The Magnetic field distribution of the generators.

As shown in Fig. 5, A, B, C phase is the current of outer stator windings, D, E, F phase are the current of inner stator windings; the current waveforms of the two windings have the same basic trend. Obviously, the inner and outer stator winding currents of 12/8/8/12 pole motor are lower than those of the other two motors. The smaller the difference of winding current is, the more stable the output is, and the more beneficial it is to reduce the voltammetric capacity of the switch tube.

Fig. 5.

Current distribution under different magnetic poles.

The torque and torque ripple coefficient of generator are two important parameters to measure the performance of motor. When the torque value increases, the power capacity of the motor also increases. If the torque becomes smaller, the power capacity of the motor will change or even cannot work normally. When the torque ripple coefficient is larger, the stability of the output power of the motor will be worse, and the noise generated by the motor will be larger. Therefore, considering the optimal design of the motor, we need to ensure that the torque of the motor increases and the ripple coefficient decreases.

As shown in Fig. 6, taking 12/8/8/12 pole motor as an example, the periodic drop of curve is partly due to torque drop caused by mismatch between turn-off phase torque drop and turn-on phase torque rise during motor commutation. The reasons are as follows: (1) in motor control, the opening Angle of winding and turn-off Angle are not well matched, resulting in synthetic torque drop; (2) In terms of motor structure, due to magnetic circuit saturation and edge flux of the motor, the rate of change of winding inductance L to rotor position Angle decreases, resulting in torque sag. As can be seen from Fig. 6, the average torque of 12/8/8/12 pole motor is 21.34 N⋅m, and the torque ripple factor is 2.298; the average torque of 12/8/16/12 pole motor is 20.9 N⋅m, and the torque ripple is 3.613.

Fig. 6.

Torque under different magnetic poles.

Based on the above analysis, 12/8/8/12 pole switched reluctance generator with better output effect was selected as the underwater generator in this paper.

4. Torque ripple of switched reluctance generator

Based on finite element analysis and electromagnetic calculation, this section proposes a method of adding a single-pole shoe on the side of the stator against the rotation direction. After finite element analysis, the length and thickness of the pole shoe are optimized and compared, and the schemes with higher average torque and more reduced torque ripple are selected.

Because the DSRG characteristic of doubly salient structure and switch-mode power supply, lead to generator stator salient pole part during the process of running a high degree of saturation, edge flux effect is obvious, the inductance curve location in the rotor and stator line before is not zero, the phase current and the output torque of the motor trend growth is nonlinear, As the electromagnetic torque of the deflected switched reluctance generator is synthesized from the torque of two adjacent phases, the torque ripple increases.

To ensure the self-start of the reluctance motor, there is an overlap angle in the inductance rise region between salient pole structures, and the sum of stator pole width 𝛽_r and rotor pole width 𝛽_r is less than the rotor pole distance τ_r, as shown in formula (1). $\begin{eqnarray}\displaystyle \left\{\begin{array}{@{}l@{}}\displaystyle {\beta}_{s}+{\beta}_{r}\leq {\tau}_{r}=\frac{2{\pi}}{N_{r}}\\ \displaystyle {\Delta}{\theta}_{L}={\beta}_{s}-\frac{2{\pi}}{qN_{r}}>0.\end{array}\right. & & \displaystyle\end{eqnarray}$ (1)

The sum of the polar widths of the inner stator and inner rotor of a double-stator reluctance motor after the addition of polar boots with specified specifications may not meet the specified range of polar distances. In addition, under the normal operation of the motor, the addition of single-side polar boots to the inner stator has little influence on motor optimization. Therefore, the structure optimization of the external stator is carried out separately in this paper.

The upper edge magnetic density of equivalent magnetic circuit of external stator single branch is calculated by using formulas (2) and (3). In formula (3), H _s is the material magnetic field intensity, H _m is the main air gap magnetic field intensity, H _f1 edge air gap magnetic field intensity; A _s, A _m, A _f1 and A _f2 are the areas of stator, main air gap and two edge air gaps covered by magnetic field lines respectively. $\begin{eqnarray}\displaystyle \text{} & \text{} & \displaystyle \displaystyle B=\frac{{\phi}_{i}}{A_{i}}={\mu}_{i}H_{i}\end{eqnarray}$ (2) $\begin{eqnarray}\displaystyle \text{} & \text{} & \displaystyle \left\{\begin{array}{@{}l@{}}{\phi}=B_{s}(H_{s})A_{s}\\ {\phi}_{m}=B_{s}(H_{m})A_{m}\\ {\phi}_{f1}=B_{f1}(H_{f1})A_{f1}\\ {\phi}_{f2}=B_{f1}(H_{f1})A_{f2}.\end{array}\right.\end{eqnarray}$ (3)

Combined with the magnetic potential balance formula (4), (5) respectively, formula (4) is the equation of the overlapped part of the stator and rotor, formula (5) is the equation of the non-overlapping part of the rotor, l _g is the average air gap length, l _f is the edge magnetic path length, and l is the distance between stator yoke and rotor yoke; the magnetic field intensity and magnetic density of the main air gap are expressed. $\begin{eqnarray}\displaystyle N_{m}i_{m}\text{} & =\text{} & \displaystyle H_{m}l_{g}+H_{s}\end{eqnarray}$ (4) $\begin{eqnarray}\displaystyle N_{m}i_{m}\text{} & =\text{} & \displaystyle H_{f1}l_{f}+H_{s}.\end{eqnarray}$ (5)

Considering magnetic saturation effect, the formula (6) can be obtained by combining the fitting formula of magnetic curve of classical materials. $\begin{eqnarray}\displaystyle \hspace{-18.0pt}H_{m}\text{} & =\text{} & \displaystyle \frac{B_{sat}a+N_{m}i_{m}b{\mu}}{2{\mu}}-\sqrt{\left(\frac{B_{sat}a+N_{m}i_{m}b{\mu}}{2{\mu}}\right)^{2}-c\left(B_{sat}d+{\mu}N_{m}i_{m}\right)}\end{eqnarray}$ (6) $\begin{eqnarray}\displaystyle \hspace{-18.0pt}B_{m}\text{} & =\text{} & \displaystyle {\mu}_{0}\frac{B_{sat}a+N_{m}i_{m}b{\mu}}{2{\mu}}-{\mu}_{0}\sqrt{\left(\frac{B_{sat}a+N_{m}i_{m}b{\mu}}{2{\mu}}\right)^{2}-c\left(B_{sat}d+{\mu}N_{m}i_{m}\right)}\end{eqnarray}$ (7) $\begin{eqnarray}\displaystyle \hspace{-18.0pt}B_{f1}\text{} & =\text{} & \displaystyle {\mu}_{0}\frac{2{\mu}_{0}d_{0}+B_{sat}b_{0}-{\phi}_{m}{\mu}l_{f}}{2{\mu}l_{f}a_{0}}-{\mu}_{0}\sqrt{\left(\frac{2{\mu}_{0}d_{0}+B_{sat}b_{0}-{\phi}_{m}{\mu}l_{f}}{2{\mu}l_{f}a_{0}}\right)^{2}-\frac{A_{s}({\mu}e+B_{sat}e_{0})-{\phi}_{m}c_{0}}{{\mu}l_{f}a_{0}}}.\end{eqnarray}$ (8)

In the formula (8), some variables need to be explained here. such as, μ = μ₀μ_r; a = b (l + l _g) + [(μ_r +1)∕l] − 4; b = (l + l _g)∕(l _g l); c = N _m i _m∕(μl _g l); d = (μ_r +1)(l − l _g); a ₀ = A _s l _f∕(l − l _f) + 2A _f; b ₀ = B _sat[A _s l _f(μ_r +1) + (A _f(l − l _f)]; c ₀ = Φ_m[μN _m i _m+ B _sat(l − l _f); d ₀ = N _m i _m(a ₀ − A _f); e ₀ = N _m i _m(μ_r +1). The N _m means turns of main winding; i _m means current of main winding; μ_r means relative permeability of rotor; B _sat means saturation flux; B _m means primary flux density; B _f1 means main air gap flux density; A _f means the sum of A _f1 and A _f2; l _g means equivalent magnetic circuit length of air gap.

Set the electrification of the motor windings in the finite element software to be clockwise, and add single-side pole boots to the end of the outer stator teeth. The direction of the pole boots is the opposite direction of the motor rotation, so the motor rotation direction is counterclockwise, and the single-side pole boots are located on the clockwise side of the stator pole. The switched reluctance generator used in this paper mainly analyzes the situation of partial overlap between pole boot and rotor. The segmentation diagram of the overlapped part of the motor is shown in Fig. 7.

Fig. 7.

Partially overlapping segmentation diagram of pole shoe and rotor.

𝛽_r is the length of rotor pole arc, and 𝛽_s is the length of the stator pole arc. DSRG torque ripple in the generators, the fixed, rotor salient began to overlap region, caused by the mutation of air-gap length of the air-gap magnetic field energy mutations, leading to the DSRM torque Angle characteristics appear in the corresponding position of the mutation of torque in DSRG commutation position of the rotor time is reduced, so the commutation position of a larger torque waveform fluctuations. The method of adding pole boots to the stator can optimize the stator magnetic pole structure, compensate for the torque value at the commutation position, and reduce the abrupt change of air-gap flux density between fixed rotors. Therefore, the single-side pole shoe of the stator outside the motor can moderately improve the magnetic conductivity before the convex poles of the fixed rotor overlap, and by improving the magnetic conductivity in this region, the convex poles of the fixed rotor can flow into the flux chain in advance, increase the torque within this range, and realize the improvement of the minimum torque.

As shown in Fig. 8, h is the thickness of the polar boot; 𝛼 is the Angle of the polar boot.

Fig. 8.

Pole shoe model structure diagram.

Fig. 9.

The profile diagram of motor model in deflection state.

Through the model section in Fig. 9, it can be observed that DSRG with pole boots can still complete the axial motion along the Z axis with the deviation φ from the X axis, without affecting the normal operation of the switched reluctance generator. Therefore, the optimization method is feasible from the perspective of structure.

As shown in Figs 10 and 11, it can be seen that the air gap reluctance decreases and the magnetic density value is more uniform. Therefore, the air gap part obtains a better linear distribution of the magnetic field and improves the magnetic field distribution in the air gap part.

Fig. 10.

Air gap magnetic density diagram of outer stator salient pole.

Fig. 11.

The optimized outer stator salient pole air gap flux density diagram.

In the motor operation process, because the current in the stator winding cannot be mutated, the instantaneous torque of the motor also changes with the current, resulting in torque ripple. The value of torque ripple is inversely proportional to the average torque, which can be expressed by formula (9). $\begin{eqnarray}\displaystyle T_{\text{ave}}=\frac{m}{2{\pi}/N_{r}}\int _{0}^{2{\pi}/N_{r}}T_{a}(i,{\theta})d{\theta}=\frac{mN_{r}}{2{\pi}}\int _{0}^{2{\pi}/N_{r}}\int _{0}^{i({\theta})}\frac{\partial L({\xi},{\theta})}{\partial {\theta}}{\xi}d{\xi}d{\theta}. & & \displaystyle\end{eqnarray}$ (9)

In formula (8), T _a is the instantaneous torque when the salient pole winding of the motor is at the position of running point a. The instantaneous torque at point a can be expressed by formula (10) using the magnetic common energy W ^′ and magnetic storage energy W of the corresponding winding. $\begin{eqnarray}\displaystyle T_{a}=\frac{\partial W^{\prime }}{\partial {\theta}_{i=\text{const}}}=-\frac{\partial W}{\partial {\theta}_{{\psi}=\text{const}}}=\int _{0}^{i({\theta})}\frac{\partial L(i,{\theta})}{\partial {\theta}}idi. & & \displaystyle\end{eqnarray}$ (10)

The formula for torque ripple is: $\begin{eqnarray}\displaystyle T_{\text{rip}}=\frac{T_{\text{max}}-T_{\text{min}}}{T_{\text{ave}}}\times 100\%. & & \displaystyle\end{eqnarray}$ (11)

According to Eq. (11), under the condition that the average torque remains unchanged, the torque ripple increases as the difference between the maximum torque value and the minimum torque value increases.

During the finite element simulation by Maxwell software, the thickness h of the pole boot on the external stator of the switched reluctance generator was kept at 2 mm, and the pole boot Angle 𝛼 was selected from 1° to 6° to evenly select 6 groups with a step size of 1 rad. The finite transient field simulation of 180° for a double-stator switched reluctance motor is carried out. Figure 12 shows the torque waveform of different pole shoe radians.

Fig. 12.

Comparison of torque characteristics under different pole shoe angles.

It can be seen from the curve trend in Fig. 12 that when the pole shoe Angle is 1°, 3° and 5°, the torque end value is smaller than that of the original structure. The maximum torque end value of the model without changing the structure after simulation can reach 48.2 N⋅m, and the minimum is only 3 N⋅m. It can be seen that compared with the torque amplitude difference of other structures, the amplitude difference of the original structure is the largest. Figure 13 shows the average torque curve and torque ripple curve at different pole shoe angles. When comparing the torque waveform at different pole shoe angles, it is found that the torque ripple tends to decrease as a whole after increasing the Angle, but the average torque of the generator keeps decreasing with the increase of pole shoe Angle. The reason is that the effect of unilateral pole shoe on improving the small inductance is significant, and vice versa, so that the maximum torque decreases to varying degrees to some extent.

Fig. 13.

Comparison chart of average torque and torque ripple under different pole shoe angles.

From Fig. 13, the angle increases the initial stage simulation model of the torque ripple is reduced gradually, when the pole shoe exceeds 3° Angle, the torque ripple starts to bounce back, the main reason is that with the rotor salient pole shoe prematurely overlap, lead to the current phase inductance up too early, after limits the torque increase, lead to torque ripple did not improve. After weighing the variation trend of average torque and torque ripple, the later simulation model selected the pole boot Angle of 3°, which can ensure that the influence of torque ripple can be minimized under the premise of losing the average torque of the motor.

Fig. 14.

Comparison of average torque and torque ripple under different pole shoe thicknesses.

Fig. 15.

Ratio of torque ripple to average torque under the same pole shoe thickness.

After determining the parameters of pole boot angle, the variable of pole boot thickness is used for simulation experiment, and the data shown in Fig. 14 is obtained. On the premise that the pole boot angle is 3°, the thickness of the pole boot of the model is between 0.5 mm and 2.5 mm, and the step length is 0.5 mm, for finite element simulation. It is found that the torque ripple of the motor decreases to some extent with the increase of the boot thickness. Under the same conditions, the average torque increases first and then decreases. According to Fig. 15, the ratio of torque ripple to average torque can be obtained, and the variation trends of average torque and torque ripple are weighed. Finally, 1 mm is selected as the optimal thickness value of pole shoe in this paper.

By combining the angle and thickness of the pole boot, the angle and height of 3 rad and 1 mm are finally selected as the best pole boot size of the deflecting double-stator switched reluctance motor. Compared with the initial model, the improved single-side pole shoe model increases the average torque by 6.76% and reduces the torque ripple by 9.47%.

5. Analysis of underwater propeller

In order to further adapt to the complex underwater environment [25,26], the deflection characteristics of multi-DOF generator are combined to improve the power generation performance of Marine propeller. Harnessing tidal energy at sea, the propeller blades rotate to drive a generator to generate electricity.

Propellers have a great influence on the stability, safety and speed of hull operation. In order to better match the deflection characteristics of the deflector generator, it is necessary to select propellers that are easy to change direction during operation. In combination with the power and speed characteristics of the deflector generator, the propeller shown in Fig. 16 is used for simulation in this paper. The higher compactness of the propeller can better follow the flow of water to produce higher torque. Secondly, the number of blades in this model and the arc shape of blade edges can better follow the fluctuation of water flow to achieve deflection and obtain more energy as much as possible. At the front of the model is also equipped with a hub cap device, which can better guide water through the blade, reducing a certain amount of resistance and turbulent energy loss.

In order to better highlight the power generation characteristics of deflector generator driven by underwater propeller [27,28]. In this paper, the CFX module is used to study propeller blades’ pressure and torque characteristics with a wide range of deflection angles. CFX can calculate some complex hydrodynamic and mechanical torque problems, has high stability in the calculation process, and meets the required calculation accuracy. In the simulation, the inlet velocity of water flow was set as 2 m/s, the outlet relative pressure was set as 0 Pa, and the propeller worked at 1 rad/s. Table 2 shows the specific parameters of the underwater propeller.

Fig. 16.

Underwater propeller mode.

Table 2

Specific parameters of the propeller

Symbol	Parameter
Diameter D/m	0.8
Disk ratio	0.8391
Blade valley radius: propeller	3:20
Longitudinal bevel	43.3
Leaf number	90

Fig. 17.

Propeller pressure cloud chart.

It can be seen from Fig. 17 that the pressure on the backpressure surface of the propeller is generally low, and the highest pressure is distributed in the leading part of the propeller. The distribution of front pressure is higher than that of backpressure, and the pressure is lower only at the blade root. With the increase of the deflection angle, the pressure distribution of the propeller increases first, and then decreases from the blade root part. The maximum pressure decreases by about 3%, and the negative pressure increases by about 10%.

As can be seen from Fig. 18, the maximum speed of the propeller increases to 2.94 m/s with the increase of angle, which increases by 6% compared with that without deflection. The influence range of propeller wake also increased obviously. The torque of the propeller is 24.3481 N⋅m in the X-axis direction at 0°, −2.48314 N⋅m in the Y-axis direction, 21.9468 N⋅m in the X-axis direction at 20°, and 10.0165 N⋅m in the Y-axis direction. After the propeller is deflected, the x-axis torque decreases. In the Y-axis direction, the torque fluctuation reaches 12 Nm larger than that in the case of no deflection. According to the comprehensive analysis, the deflection of propeller will cause a part of energy waste, and the increase of torque in the Y-axis direction will increase the load of the generator and reduce the service life. Deflected underwater power generation can better keep the propeller in the same direction as the current, increasing the power generation capacity. When it is used as an electric motor, it can use the torque in the Y direction to provide a greater steering force, increasing the flexibility of the hull.

Fig. 18.

Propeller speed cloud chart.

6. Experimental and data analysis

To verify the effectiveness and feasibility of the proposed generator generation strategy. In this section, DSRG would be studied under the condition of temperature 13° and rotor deflection angle 0°. The specific parameters of the experimental motor are shown in Table 3.

Table 3
Specific parameters of DSRG

Parameter Value

Outer stator radius Ds1/mm 300

Inner stator radius Ds2/mm 13.5

Outer radius of rotor Dr1/mm 108

Inner radius of rotor Dr2/mm 43.3

Length of core la/mm 90

Range of rotor deflection 𝛼∕° 0–17

Rated current density Acd/(A/mm2) 6

Rated rotating torque n/(r/min) 200

Rated power PN/kw 2.5

Rated voltage UN/V 380

Parameter	Value
Outer stator radius Ds1/mm	300
Inner stator radius Ds2/mm	13.5
Outer radius of rotor Dr1/mm	108
Inner radius of rotor Dr2/mm	43.3
Length of core la/mm	90
Range of rotor deflection 𝛼∕°	0–17
Rated current density Acd/(A/mm2)	6
Rated rotating torque n/(r/min)	200
Rated power PN/kw	2.5
Rated voltage UN/V	380

As is shown in Fig. 19, the driving servo stepper motor with excitation voltage of 15 V was used as the prime mover to drag the DSRG for the experiment. The STM32C8T6 development board was used as the control chip to control the DSRG for power generation and measure the current and voltage data output by the DSRG at different speeds.

Fig. 19.

Experimental platform.

Fig. 20.

The output voltage and current of the experimental prototype at different speeds.

As shown in Fig. 20, experiments were performed at speeds of 30 r/min, 40 r/min, 50 r/min, 60 r/min and 80 r/min respectively to test the generator’s power generation current and voltage at different speeds. According to Fig. 20(a–h), it can be seen that DSRG can output stable current and voltage at different speeds. The feasibility of DSRG in the power generation system is verified, and the working stability of the generator is improved while the vibration and noise of DSRG is reduced.

7. Conclusion

In this paper, the underwater power generation system based on deflected switched reluctance generator is introduced, the 12/8/8/12 pole and 12/8/16 pole of stator internal salient pole are compared and analyzed. By comparison, 12/8/8/12 pole double-stator with higher average torque and smaller torque ripple are used as underwater generators. By adding stator single-pole boots, the average torque of the motor is increased by 6.76% and the torque ripple is reduced by 9.47%. The motor models with different boot heights and radians were simulated and analyzed. Finally, 3° radians and 1 mm heights were selected as optimization parameters. Maximum pressure decreased by 3% and negative pressure increased by about 10%. The actual experiments were carried out using a stepper motor to drag a generator to imitate the DSRG underwater power generation state. The power generation was tested at 30, 40, 50 and 60 r/min, and the output current of the DSRG experimental prototype was very stable and the output voltage reached the expected value, verifying the effectiveness and feasibility of the power generation system design scheme.

Footnotes

Acknowledgements

This work is supported by the National Natural Science Foundation of China (No. 51877070, U20A20198, 51577048), the Natural Science Foundation of Hebei Province of China (No. E2021208008, E2018208155), the Talent Engineering Training Support Project of Hebei Province (A201905008), the National Engineering Laboratory of Energy-saving Motor & Control Technique, Anhui University (No. KFKT201901).

References

Wang

Zhang

, Magnetic field analysis and iron loss calculation of a special switched reluctance generator, Journal of Electrical Engineering & Technology 14 (2019), 1991–2003.

Liu

and Peng

, Design study on double-stator permanent-magnet direct-driven wind turbine generator based on ansys — Maxwell, Shanghai Medium and Large Electrical Machines 2 (2021), 28–32.

Dong

Wang

, Analysis of a double-stator deflection type switched reluctance generator considering magnetostrictive effect, International Journal of Applied Electromagnetics and Mechanics 61 (2019), 1–16.

Liu

and Zhang

, Analysis of effect of winding distribution on performance in dual-stator brushless doubly-fed generator, Electric Machines and Control 25(3) (2021), 38–45.

Liu

and Xu

, Research on cogging torque weakening of dual stator wind turbine, Mechanical & Electrical Engineering Technology 49(2) (2020), 61–64.

Zhang

Chau

K.T.

Niu

and Jiang

J.Z.

, Design and analysis of a double-stator cup-rotor PM integrated-starter-generator, in: Conference Record of the 2006 IEEE Industry Applications Conference Forty-First IAS Annual Meeting, 2006, pp. 20–26.

Noroozi

M.A.

Shafiei

and Milimonfared

, Novel single phase e-shaped double-stator flux switching permanent magnet generator, in: 2020 11th Power Electronics, Drive Systems, and Technologies Conference (PEDSTC), 2020, pp. 1–5.

Chang

and Yang

, Research on torque Ripple suppression of magnet Synchronous Motor, Electronic Test 24 (2020), 55–56.

Zhao

and Sun

, Harmonic suppression and torque ripple reduction of a high-speed permanent magnet spindle motor, IEEE Access 9 (2021), 51695–51702.

10.

Chu

Dutta

Pouramin

and Rahman

M.F.

, Analysis of torque ripple of a spoke-type interior permanent magnet machine, Energies 13(11) (2020), 2886.

11.

Cui

Sh.

and Dou

, Reduction method of torque ripple and vibration and noise of permanent magnet synchronous motor, Micromotors 53(10) (2020), 11–16.

12.

Dang

and Pan

, Torque ripple reduction of switched reluctance motor based on current injection method, Modular Machine Tool Automatic Manufacturing Technique 5 (2021), 115–119.

13.

Wang

Jiang

Wang

Williams

B.W.

and Wang

, A novel step current excitation control method to reduce the torque ripple of outer-rotor switched reluctance motors, Energies 15(8) (2022), 2852.

14.

Kocan

Rafajdus

Bastovansky

Lenhard

and Stano

, Design and optimization of a high-speed switched reluctance motor, Energies 14(20) (2021), 6733.

15.

Pupadubsin

Kachapornkul

Jitkreeyarn

Somsiri

and Tungpimolrut

, Investigation of torque performance and flux reversal reduction of a three-phase 12/8 switched reluctance motor based on winding arrangement, Energies 15(1) (2022), 284.

16.

Bao

and Xu

, Rotor topology optimization of a synchronous reluctance motor based on deep neural network model, International Journal of Applied Electromagnetics and Mechanics 66(3) (2021), 445–459.

17.

Raj

M.A.

and Kavitha

, Effect of rotor geometry on peak and average torque of external-rotor synchronous reluctance motor in comparison with switched reluctance motor for low-speed direct-drive domestic application, IEEE Transactions on Magnetics 53(11) (2017), 1–8.

18.

Nalinashini

and Tamilselvi

, Experimental investigation of modified in-wheel switched reluctance motor with reduced torque ripple for electric vehicles, Electrical Engineering 103 (2021), 2837–2845.

19.

Hosseini

S.A.

and Beromi

, Noise reduction in switched reluctance motor by modifying the structures, IET Electric Power Applications 14 (2020), 2863–2872.

20.

Toda

Senda

Morimoto

and Hiratani

, Influence of various non-oriented electrical steels on motor efficiency and iron loss in switched reluctance motor, IEEE Transactions on Magnetics 49(7) (2013), 3850–3853.

21.

Song

and Cho

, Comparison of 12/8 and 6/4 switched reluctance motor: noise and vibration aspects, IEEE Transactions on Magnetics 44(11) (2018), 4131–4134.

22.

Diao

Zhang

and Yan

, Design of comprehensive experiment for switched reluctance motor driving system, Experimental Technology and Management 37(12) (2020), 63–66.

23.

Wang

and Du

, Design and comparison of a high force density dual-side linear switched reluctance motor for long rail propulsion application with low cost, IEEE Transactions on Magnetics 53(6) (2017), 16914231.

24.

Liu

Chau

K.T.

and Lin

, A new hybrid-structure machine with multimode fault-tolerant operation for mars rover, IEEE Transactions Magnetics 51(11) (2015), 1–4.

25.

Nounou

Charpentier

J.F.

Marouani

Benbouzid

and Kheloui

, Emulation of an electric naval propulsion system based on a multiphase machine under healthy and faulty operating conditions, IEEE Transactions on Vehicular Technology 67(8) (2018), 6895–6905.

26.

Ojaghlu

and Vahedi

, Specification and design of ring winding axial flux motor for rim-driven thruster of ship electric propulsion, IEEE Transactions on Vehicular Technology 68(2) (2019), 1318–1326.

27.

Toporkov

J.V.

Hwang

P.A.

Sletten

M.A.

, Surface velocity profiles in a vessel’s turbulent wake observed by a dual-beam along-track interferometric SAR, IEEE Geoscience Remote Sensing Letters 8(4) (2011), 602–606.

28.

Bowker

J.A.

Tan

and Townsend

N.C.

, Forward speed prediction of a free-running wave-propelled boat, IEEE Journal Oceanic Engineering 46(2) (2021), 402–413.