Patent Publication Number: US-2021163109-A1

Title: Vertical axis fluid energy conversion device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Taiwan Patent Application No. 108144016 filed on Dec. 3, 2019. The entire contents of the above-mentioned patent application are incorporated herein by reference for all purposes. 
     FIELD OF THE INVENTION 
     The present disclosure relates to a vertical axis fluid energy conversion device, and more particularly to a vertical axis fluid energy conversion device which includes Magnus rotors. The Magnus rotors drive a main shaft to rotate according to the Magnus effect, and the main shaft drives lift blades to rotate. Consequently, the kinetic energy of the fluid is converted to the mechanical energy. 
     BACKGROUND OF THE INVENTION 
     For the sustainable development of the global environment, the general trend is developing the eco-friendly green energy. All walks of life invest quite a few fund and human resources in green energy. The power generation device powered by fluid, such as wind or ocean current, has advantage of inexhaustible and powering without carbon dioxide. Consequently, energy conversion device that utilize the kinetic energy of fluids have always been the goal of development from all walks of life. 
     For instance, there are two kinds of the power generation device powered by wind according to the rotation direction of the main shaft. One is the horizontal axis wind turbine, and the other is the vertical axis wind turbine. The blades of the horizontal axis wind turbine have to face the wind direction. Consequently, the horizontal axis wind turbine is not suited for disposing in the environment with variety wind direction. Moreover, a power generator of the horizontal axis wind turbine is disposed within the cabin located at high place. Consequently, the horizontal axis wind turbine has disadvantage of difficulty maintaining, high center of gravity, weak structure and high cost. The vertical axis wind turbine does not have to face the wind direction. Consequently, the vertical axis wind turbine is suited for disposing in the environment with variety wind direction. Moreover, a power generator of the vertical axis wind turbine is disposed in the bottom of the vertical axis wind turbine. Consequently, the vertical axis wind turbine has advantage of low center of gravity, strong structure, easily maintaining and low cost. 
     There are two kinds of the vertical axis energy conversion device according to operation principle. One kind of the vertical axis energy conversion device uses drag blades, and the other kind of the vertical axis energy conversion device uses lift blades. The drag blades of the vertical axis energy conversion device can be self-starting in the flowing fluid, but the efficiency of the drag blades is worse. On the contrary, the efficiency of the lift blades of the vertical axis energy conversion device is higher, but the lift blades cannot be self-starting in the flowing fluid. Consequently, the vertical axis energy conversion device normally includes the drag blades and the lift blades working together.  FIG. 1  is a schematic perspective view illustrating a first conventional vertical axis energy conversion device. As shown in  FIG. 1 , the first conventional vertical axis energy conversion device  1 ′ includes a plurality of Darrieus lift blades  2 ′ and a Savonius drag blade  3 ′. The plurality of Darrieus lift blades  2 ′ are located in the exterior of the first conventional vertical axis energy conversion device  1 ′. Moreover, the Savonius drag blade  3 ′ is disposed on a central rotation shaft  4 ′ and located in the interior of the first conventional vertical axis energy conversion device  1 ′. The Savonius drag blade  3 ′ includes two semicircle tubes. The cross section of the Savonius drag blade  3 ′ is shown in  FIG. 2 . The Savonius drag blade  3 ′ drives the plurality of Darrieus lift blades  2 ′ to revolve.  FIG. 3  is a schematic perspective view illustrating a second conventional vertical axis energy conversion device. As shown in  FIG. 3 , the second conventional vertical axis energy conversion device  5 ′ includes a plurality of straight lift blades  6 ′ and a Savonius drag blade  3 ′. The plurality of straight lift blades  6 ′ are located in the exterior of the second conventional vertical axis energy conversion device  5 ′. The Savonius drag blade  3 ′ is disposed on a central rotation shaft  4 ′ of the second conventional vertical axis energy conversion device  5 ′ and located in the interior of the second conventional vertical axis energy conversion device  5 ′. The Savonius drag blade  3 ′ drives the plurality of straight lift blades  6 ′ to revolve. The above two conventional vertical axis energy conversion devices use the Savonius drag blade  3 ′ to overcome the problem that the lift blade is difficult to be self-starting. 
       FIG. 4  is a waveform diagram illustrating the tip speed ratio and the efficiency of the lift blade of the typical vertical axis fluid energy conversion device. As shown in  FIG. 4 , the horizontal axis represents the tip speed ratio of the lift blade. The definition of the tip speed ratio is the value between the tip speed of the blade and the flowing speed of the fluid, wherein the tip speed of the blade is the linear velocity of the blade but not the angular velocity of the blade. The vertical axis represents the efficiency of the lift blade. According to Betz law, the highest theory efficiency of converting the fluid energy is 0.59. As shown in  FIG. 4 , the highest realistic efficiency of the vertical axis fluid energy conversion device using the lift blade is about 0.45 when the tip speed ratio is 4.5. However, while the tip speed ratio is lower than 2, the efficiency of the lift blade is 0. That represents the output power of the vertical axis fluid energy conversion device is 0. Moreover, the power is equal to the torque multiplied by the rotation speed. Consequently, the vertical axis fluid energy conversion device does not output the torque, and the vertical axis fluid energy conversion device cannot be self-starting. The vertical axis fluid energy conversion device needs additional starting device. Due to the best theoretical efficiency of the above Savonius drag blade  3 ′ is occurred when the tip speed ratio of the Savonius drag blade  3 ′ is 1. For achieving the best efficiency of the lift blade and the best efficiency of the drag blade simultaneously, the revolution radius of the Savonius drag blade  3 ′ is usually equal to ¼ times of the revolution radius of the lift blade in realistic application, as shown in  FIGS. 1 and 3 . In the same rotation speed of the main shaft, the tip speed of the blade is proportional to the radius of the blade. Consequently, the speed of the lift blade is higher than four times speed of the drag blade. The best efficiency of the lift blade and the best efficiency of the drag blade are expected to achieve simultaneously. 
     However, while the revolution radius of the Savonius drag blade  3 ′ is shorter, such as ¼ times of the revolution radius of the lift blade, the torque generated by the Savonius drag blade  3 ′ is not enough. The vertical axis fluid energy conversion device still cannot be self-starting in the low flowing speed of the fluid. Consequently, the radius or the height of the drag blade is increased to enlarge the cross section and increase the torque. However, this causes the flow field inside the vertical axis fluid energy conversion device is disturbed and the performance of the lift blade is influenced. Consequently, the whole efficiency of the vertical axis fluid energy conversion device is decreased. Therefore, while the Savonius drag blade  3 ′ is served as a starting device, it is difficult to meet the self-starting and achieve high efficiency simultaneously. Moreover, while the flowing speed of the fluid is too high, the huge torque generated by the Savonius drag blade  3 ′ will drive the vertical axis fluid energy conversion device to overspeed, and danger is occurred easily. 
     Recently, the active pitch control can change the angle of the lift blade according to the flowing direction of the fluid and achieve self-starting. However, this will make the structure of the vertical axis fluid energy conversion device more complex, weak and expensive due to the increase of moving parts. Moreover, the way of disposing a starting motor in the central rotation shaft to increase the rotation speed is a solution for driving the lift blade to start revolving. However, the central rotation shaft is connected with the whole vertical axis fluid energy conversion device, so that the inertia is large. The motor has to employ a reducer to output enough torque, and the motor also has to employ an inverter and a clutch. Consequently, the cost is increased and the energy consumption is increased. So the vertical axis fluid energy conversion device has not been successfully applied for a long time. 
     Therefore, there is a need of providing a vertical axis fluid energy conversion device to solve the issues encountered by the prior arts. 
     SUMMARY OF THE INVENTION 
     An object of the present disclosure provides a vertical axis fluid energy conversion device capable of being self-starting and having advantages of high efficiency, low cost and low energy consumption. 
     In accordance with an aspect of the present disclosure, a vertical axis fluid energy conversion device for converting a kinetic energy of a fluid to a mechanical energy is provided. The vertical axis fluid energy conversion device includes at least one lift blade, a main shaft, at least one Magnus rotor and a connection component. The main shaft includes a first axis. The main shaft is rotated around the first axis. Each of the at least one Magnus rotor includes a power source and a second axis. The power source drives the corresponding Magnus rotor to rotate around the corresponding second axis selectively. The connection component is connected with the main shaft and the corresponding Magnus rotor. Each of the at least one Magnus rotor produces a lift force according to Magnus effect when the Magnus rotor is rotated on its own axis (i.e. the second axis). The connection component is served as a moment arm, and the lift force acts on the moment arm to form a torque. The main shaft is driven to rotate around the first axis in response to the torque. Each of the at least one Magnus rotor is also revolved around the first axis. The connection component is also connected with the main shaft and the corresponding lift blade. While the Magnus rotor drives the main shaft to rotate, each of the at least one lift blade is also driven to revolve around the first axis. While a revolution speed of the lift blade is greater than a speed threshold value, the efficiency of the lift blade is increased. A torque produced by the lift blade is greater than a resistance of the fluid and a friction of the main shaft, such that the main shaft is continuously driven to rotate around the first axis. A revolution radius of the Magnus rotor revolved around the first axis is less than a revolution radius of the lift blade revolved around the first axis. 
     The above contents of the present disclosure will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view illustrating a first conventional vertical axis fluid energy conversion device; 
         FIG. 2  is a cross-sectional view illustrating Savonius drag blades of the first conventional vertical axis fluid energy conversion device of  FIG. 1 . 
         FIG. 3  is a schematic perspective view illustrating a second conventional vertical axis fluid energy conversion device; 
         FIG. 4  is a waveform diagram illustrating the tip speed ratio and efficiency of lift blades of the typical vertical axis fluid energy conversion device; 
         FIG. 5A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a first embodiment of the present disclosure; 
         FIG. 5B  is a top view illustrating the vertical axis fluid energy conversion device of  FIG. 5A ; 
         FIG. 6  is a top view illustrating the operation of a Magnus rotor of the vertical axis fluid energy conversion device of  FIG. 5A ; 
         FIG. 7  is a circuit block diagram illustrating the vertical axis fluid energy conversion device of  FIG. 5A ; 
         FIG. 8  is an X-Y coordinate system illustrating the main shaft and the plurality of Magnus rotors of the vertical axis fluid energy conversion device of  FIG. 5A ; 
         FIG. 9  is a waveform diagram illustrating the driving signal of the Manus rotor of the vertical axis fluid energy conversion device of  FIG. 5A ; 
         FIG. 10  is a waveform diagram illustrating the tip speed ratio and the efficiency of the lift blade of the vertical axis fluid energy conversion device of  FIG. 5A ; 
         FIG. 11  is a control block diagram illustrating the control unit of the vertical axis fluid energy conversion device of  FIG. 5A ; 
         FIG. 12A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a second embodiment of the present disclosure; 
         FIG. 12B  is a top view illustrating the vertical axis fluid energy conversion device of  FIG. 12A ; 
         FIG. 13A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a third embodiment of the present disclosure; 
         FIG. 13B  is a top view illustrating the vertical axis fluid energy conversion device of  FIG. 13A ; 
         FIG. 14  is a top view illustrating a vertical axis fluid energy conversion device according to a fourth embodiment of the present disclosure; 
         FIG. 15  is a schematic perspective view illustrating lift blades of a vertical axis fluid energy conversion device according to a fifth embodiment of the present disclosure; 
         FIG. 16A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a sixth embodiment of the present disclosure; 
         FIG. 16B  is a top view illustrating the vertical axis fluid energy conversion device of  FIG. 16A ; 
         FIG. 17A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a seventh embodiment of the present disclosure; 
         FIG. 17B  is a cross-sectional view illustrating portion of an exemplary vertical axis fluid energy conversion device of  FIG. 17A ; and 
         FIG. 17C  is a cross-sectional view illustrating portion of another exemplary vertical axis fluid energy conversion device of  FIG. 17A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present disclosure will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this disclosure are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
       FIG. 5A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a first embodiment of the present disclosure.  FIG. 5B  is a top view illustrating the vertical axis fluid energy conversion device of  FIG. 5A .  FIG. 6  is a top view illustrating the operation of a Magnus rotor of the vertical axis fluid energy conversion device of  FIG. 5A . As shown in  FIGS. 5A, 5B and 6 , the vertical axis fluid energy conversion device  1  is disposed in the fluid W. For example, the fluid W is wind or water. The vertical axis fluid energy conversion device  1  converts the kinetic energy of the fluid W to the mechanical energy of a main shaft  2  of the vertical axis fluid energy conversion device  1  for driving the load. While the load is a generator, the vertical axis fluid energy conversion device  1  can generate electric power. The vertical axis fluid energy conversion device  1  includes a main shaft  2 , at least one lift blade  3 , at least one Magnus rotor  4  and a connection component  5 . 
     The main shaft  2  includes a first axis  21 . The first axis  21  is constituted of an axis line which passes through the center of a top end of the main shaft  2  and the center of a bottom end of the main shaft  2 . The main shaft  2  is rotated around the first axis  21 . In this embodiment, the number of the lift blades  3  is two. The lift blades  3  are curved, respectively, and the profiles of the lift blades  3  are similar to that of an egg beater. Preferably but not exclusively, the lift blades  3  are curved wing blades. As shown in  FIG. 5B , the two lift blades  3  are separated from each other and disposed around the main shaft  2  evenly. The number of the Magnus rotors  4  is three. The three Magnus rotors  4  are separated from each other and disposed around the main shaft  2  evenly. Each Magnus rotor  4  includes a power source  41  and a second axis  42 . The second axis  42  is constituted of an axis line which passes through the center of a top end of the Magnus rotor  4  and the center of a bottom end of the Magnus rotor  4 . The power source  41  is for example but not limited to a motor or an engine. Each power source  41  selectively drives the corresponding Magnus rotor  4  to rotate around the second axis  42 . While the Magnus rotor  4  is disposed in the fluid W which is flowing, the Magnus rotor  4  produces the lift force of the Magnus effect by the rotation of the Magnus rotor  4 . As shown in  FIG. 6 , taking one of the Magnus rotors  4  for example, the Magnus rotor  4  is a cylinder structure. The Magnus rotor  4  is rotated on its own axis (i.e. the second axis  42 ). For example, the Magnus rotor  4  is rotated in clockwise, the angular velocity is represented as V 1  and the velocity relative to the fluid W is represented as V 2 . The Magnus rotor  4  produces lift force F according to the Magnus effect. The magnitude of the lift force F is proportional to the angular velocity V 1  of the Magnus rotor  4  and the velocity V 2  relative to the fluid W. The direction of the lift force F is perpendicular to the direction of the velocity V 2  of the Magnus rotor  4  relative to the fluid W. While the rotation direction of the Magnus rotor  4  is in counterclockwise, the direction of the lift force F is reversed. 
     In this embodiment, the connection component  5  includes a plurality of first connection parts  51  and a plurality of second connection parts  52 . Each of the plurality of first connection parts  51  is connected to the main shaft  2  and the top of the corresponding Magnus rotor  4 , or each of the plurality of first connection parts  51  is connected to the main shaft  2  and the bottom of the corresponding Magnus rotor  4 . While each of the Magnus rotors  4  is rotated on its own axis, the lift force of the Magnus effect is produced and applied on the moment arm formed by the first connection part  51  to generate torque, so that the main shaft  2  is rotated around the first axis  21  in response to the torque. Each of the plurality of second connection parts  52  is fixed on the main shaft  2  for connecting the main shaft  2  and the corresponding lift blade  3 . Consequently, while the Magnus rotor  4  drives the main shaft  2  to rotate, each lift blade  3  is also driven to revolve around the first axis  21  of the main shaft  2 . While the revolution speed of the lift blade  3  is faster than a speed threshold value, for example, the tip speed ratio of the lift blade  3  is 2.5, the efficiency of the lift blade  3  is increased. The torque produced by the lift blade  3  is greater than the resistance of the fluid W and the friction of the main shaft  2 . At this time, even though the power source  41  is turned off and the rotation of the Magnus rotors  4  is stopped, the torque produced by the lift blade  3  can still drive the main shaft  2  to accelerate. Taking wind power generation for example, at this time, the main shaft  2  can drive the generator to generate electric power. 
     From above, the vertical axis fluid energy conversion device  1  of the present disclosure includes at least one lift blade  3  and at least one Magnus rotor  4 . The rotation of the Magnus rotor  4  on its own axis produces the Magnus lift force, and the Magnus rotor  4  is connected to the main shaft  2  through the connection component  5 . Consequently, the vertical axis fluid energy conversion device  1  starts up the lift blade  3  to revolve by the Magnus lift force of the Magnus rotor  4 . Moreover, the Magnus rotor  4  is driven to rotate on its own axis through the power source  41 . By increasing the rotation speed of the Magnus rotor  4 , the required Magnus lift force can be obtained. Consequently, the diameter of the Magnus rotor  4  can be designed to be shorter. Compared with the conventional Savonius drag blade, the cross-sectional area of the Magnus rotor  4  is reduced. Consequently, the flow field inside the vertical axis fluid energy conversion device  1  is less influenced. So the performance of the lift blade  3  of the present disclosure is better, that the whole efficiency of the vertical axis fluid energy conversion device  1  is enhanced. 
       FIG. 7  is a circuit block diagram illustrating the vertical axis fluid energy conversion device of  FIG. 5A .  FIG. 8  is an X-Y coordinate system illustrating the main shaft and the plurality of Magnus rotors of the vertical axis fluid energy conversion device of  FIG. 5A .  FIG. 9  is a waveform diagram illustrating the driving signal of the Magnus rotor of the vertical axis fluid energy conversion device of  FIG. 5A . As shown in  FIGS. 5A, 5B, and 6 to 9 , the vertical axis fluid energy conversion device  1  further includes a fluid detection unit  61 , a main shaft detection unit  62 , a control unit  63  and at least one driving circuit  64 . The fluid detection unit  61  detects the flowing speed and the flowing direction of the fluid W and outputs a first detection signal P 1 . The main shaft detection unit  62  detects the rotation angle of the main shaft  2  rotated around the first axis  21  and outputs a second detection signal P 2 . The control unit  63  is connected with the fluid detection unit  61  and the main shaft detection unit  62  in order to receive the first detection signal P 1  and the second detection signal P 2 . The control unit  63  calculates an angle difference according to the flowing direction of the fluid W and the rotation angle of the main shaft  21  rotated around the first axis  21  in order to calculate the angle between each Magnus rotor  4  and the flowing direction of the fluid W. Then a driving signal V is obtained, which is outputted to the corresponding power source  41  through the corresponding driving circuit  64  to drive the corresponding Magnus rotor  4  to rotate. 
     Please refer to  FIG. 8  again. The main shaft  2  is perpendicular to an original point O of the X-Y coordinate system. The positive direction of the X axis is faced to the flowing direction of the fluid W. Consequently, the vertical axis fluid energy conversion device  1  has a first side facing to the flowing direction of the fluid W and a second side facing away from the flowing direction of the fluid W. The first side is located in the right side of the Y axis of  FIG. 8 . The second side is located in the left side of the Y axis of  FIG. 8 . The rotation direction of the Magnus rotor  4  located in the first side must be opposite to the rotation direction of the Magnus rotor  4  located in the second side. So that each Magnus rotor  4  applies torque in the same direction on the main shaft  2 . As shown in  FIG. 9 , each Magnus rotor  4  has two rotation directions according to the angle between each Magnus rotor  4  and the flowing direction of the fluid W. The angle between 0 degree and 90 degrees and the angle between 270 degrees and 360 degrees are defined as a first rotation direction. The angle between 90 degrees and 270 degrees is defined as a second rotation direction. While the Magnus rotor  4  is revolved around the first axis  21 , the rotation direction of the Magnus rotor  4  on its own axis is changed continuously. In an embodiment, in order to make the rotation speed of the Magnus rotor  4  smooth and avoid vibration, the rotation speed of each Magnus rotor  4  is planned as a sine wave, as shown in  FIG. 9 . In some embodiments, the rotation speed of each Magnus rotor  4  can also be triangular wave, trapezoid wave, square wave or any other waveform with changeable direction. 
     The control unit  63  controls the power source  41  of the Magnus rotor  4  located in the first side through the corresponding driving signal V. So that each Magnus rotor  4  located in the first side is rotated on its own axis in the first rotation direction. And the rotation speed of each Magnus rotor  4  is adjusted dynamically according to the angle difference between the revolving angle of the Magnus rotor  4  and the flowing direction of the fluid W. Moreover, the control unit  63  controls the power source  41  of the Magnus rotor  4  located in the second side through the corresponding driving signal V. So that each Magnus rotor  4  located in the second side is rotated on its own axis in the second rotation direction opposite to the first rotation direction. And the rotation speed of each Magnus rotor  4  is adjusted dynamically according to the angle difference between the revolving angle of the Magnus rotor  4  and the flowing direction of the fluid W. By means of controlling the rotation of each Magnus rotor  4 , each Magnus rotor  4  obtains the Magnus lift force which is applied to the moment arm formed by the first connection part  51  to generate torque to drive the main shaft  2  to rotate in the first rotation direction. 
     In some embodiments, the control unit  63  obtains the flowing speed of the fluid W according to the first detection signal P 1  and obtains the angular velocity of the main shaft  2  according to the second detection signal P 2 . The lift blade  3  is connected with the main shaft  2  through the second connection part  52 , and the lift blade  3  is revolved around the first axis  21  of the main shaft  2 , so the angular velocity of the lift blade  3  is the same as the angular velocity of the main shaft  2 . Consequently, the linear velocity of the lift blade  3  can be obtained by multiplying the angular velocity of the main shaft  2  by the revolution radius of the lift blade  3 . Then divide the linear velocity of the lift blade  3  by the flowing speed of the fluid W detected by the first detection signal P 1  to obtain the tip speed ratio of the lift blade  3 , shown as the following formula (1). 
       tip speed ratio=linear velocity of blade/flowing speed of fluid=(angular velocity of blade×revolution radius of blade)/flowing speed of fluid   (1)
 
     The formula (1) can be converted to formula of the angular velocity of the blade as follows. 
       angular velocity of blade=(tip speed ratio×flowing speed of fluid)/revolution radius of blade   (2)
 
     The above formula (1) and the formula (2) are applicable to both the lift blade  3  and the Magnus rotor  4 . 
     Since the efficiency of the vertical axis fluid energy conversion device  1  is closely related to the tip speed ratio of the lift blade  3 . Taking a wind power generator for example, due to the variation of the wind speed, the tip speed ratio of the lift blade  3  is changed at any time even if the rotation speed of the main shaft  2  remains unchanged. Thus, making the efficiency of the vertical axis fluid energy conversion device  1  worse. Consequently, the tip speed ratio of the lift blade  3  should be controlled to maintain at a better efficiency.  FIG. 10  is a waveform diagram illustrating the tip speed ratio and the efficiency of the lift blade of the vertical axis fluid energy conversion device of  FIG. 5A . As shown in  FIG. 10 , the horizontal axis represents the ratio between the linear velocity of the lift blade  3  and the flowing speed of the fluid W (i.e. the tip speed ratio of the lift blade  3 ). The vertical axis represents the efficiency of the vertical axis fluid energy conversion device  1 . As shown in  FIG. 10 , while the tip speed ratio of the lift blade  3  is less than or equal to a first tip speed ratio S 1 , the efficiency of the vertical axis fluid energy conversion device  1  is 0. While the tip speed ratio of the lift blade  3  is increased to a second tip speed ratio S 2 , the efficiency of the vertical axis fluid energy conversion device  1  is increased to a maximum value Emax. While the tip speed ratio of the lift blade  3  is increased to a third tip speed ratio S 3 , the efficiency of the vertical axis fluid energy conversion device  1  is decreased to 0. When the efficiency of the vertical axis fluid energy conversion device  1  is equal to the maximum value Emax, the corresponding value of the second tip speed ratio S 2  is usually between 4 and 5, which is mainly related to solidity of the lift blade  3 . The value of the second tip speed ratio S 2  can be easily obtained by those skilled in the art with experiment, and is not redundantly described herein. 
     The vertical axis fluid energy conversion device  1  controls the revolution speed of the lift blade  3  by controlling the rotation speed and the rotation direction of the Magnus rotor  4 , thereby controlling the tip speed ratio of the lift blade  3  to keep the efficiency of the vertical axis fluid energy conversion device  1  to be optimal. According to demand of user, a target tip speed ratio of the lift blade  3  is set between a first threshold value th 1  and a second threshold value th 2 . The first threshold value th 1  is less than the second tip speed ratio S 2 . The second tip speed ratio S 2  is less than the second threshold value th 2 . Consequently, the efficiency of the vertical axis fluid energy conversion device  1  is maintained between a setting value E 0  and the maximum value Emax. For example, while the tip speed ratio of the lift blade  3  is located between the first threshold value th 1  and the second threshold value th 2 , the efficiency of the vertical axis fluid energy conversion device  1  is satisfied. Meanwhile, the power source  41  can be turned off to stop the rotation of the Magnus rotor  4  to save energy consumption. However, while the tip speed ratio of the lift blade  3  is less than the first threshold value th 1  (i.e. the efficiency of the lift blade  3  is less than the setting value E 0 ), the corresponding driving signal V is outputted to the power source  41  to drive the corresponding Magnus rotor  4  to rotate to generate the torque in the same revolution direction as the lift blade  3 . Consequently, the revolution speed of the lift blade  3  is increased. The tip speed ratio of the lift blade  3  is also increased, and then back to between the first threshold value th 1  and the second threshold value th 2 , so that the efficiency of the vertical axis fluid energy conversion device  1  is maintained between the setting value E 0  and the maximum value Emax. 
     Moreover, while the tip speed ratio of the lift blade  3  is greater than the second threshold value th 2  (i.e. the efficiency of the lift blade  3  is less than the setting value E 0 ), usually it is not necessary to drive the Magnus rotor  4  to rotate to decrease the tip speed ratio. If the torque characteristic of the load (i.e. the generator) is properly matched, the torque of the load is greater than the torque generated from the main shaft  2  when the tip speed ratio is too high. Consequently, the rotation speed of the main shaft  2  is naturally decreased, and the tip speed ratio of the lift blade  3  returns between the first threshold value th 1  and the second threshold value th 2 . However, for avoiding overloaded while the flowing speed of the fluid W is too high and the rotation speed of the main shaft  2  is greater than a rated rotation speed of the load, the corresponding driving signal V is outputted to the power source  41  to drive the corresponding Magnus rotor  4  to rotate to generate the torque in the opposite revolution direction to the lift blade  3 . So the rotation speed of the main shaft  2  is decreased and danger is avoided from exceeding the rated rotation speed of the load. Hence, the vertical axis fluid energy conversion device  1  can operate safely under higher flowing speed of the fluid W without immediately activating a brake to stop the operation. Therefore, the utilization rate of the vertical axis fluid energy conversion device  1  is increased. 
     In some embodiments, while the actual rotation speed of the main shaft  2  rotated around the first axis  21  is less than a target rotation speed, the control unit  63  controls the amplitude of the rotation speed of each Magnus rotor  4  to increase. While the actual rotation speed of the main shaft  2  rotated around the first axis  21  is equal to the target rotation speed, the control unit  63  controls the amplitude of the rotation speed of each Magnus rotor  4  to maintain. While the actual rotation speed of the main shaft  2  rotated around the first axis  21  is greater than the target rotation speed, the control unit  63  controls the amplitude of the rotation speed of each Magnus rotor  4  to decrease. In order that the actual rotation speed of the main shaft  2  is controlled to track the target rotation speed. The implement method is as follows. 
       FIG. 11  is a control block diagram illustrating the control unit of the vertical axis fluid energy conversion device of  FIG. 5A . As shown in  FIG. 11 , the control unit  63  includes a differentiator  161 , a subtractor  162 , a first controller  163  and a second controller  164 . The differentiator  161  is connected with the main shaft detection unit  62  to receive the second detection signal P 2  and differentiates the second detection signal P 2  which is the rotation angle of the main shaft  2  rotating around the first axis  21 , thus obtains the actual rotation speed of the main shaft  2  and outputs an actual rotation speed signal K 1  of the main shaft  2 . The subtractor  162  is connected with the differentiator  161  to receive the actual rotation speed signal K 1 . The subtractor  162  subtracts the actual rotation speed signal K 1  from a target rotation speed command K 2  to obtain a rotation speed error signal K 3 , and the target rotation speed command K 2  can be calculated by taking the second tip speed ratio S 2  corresponding to that the efficiency of the lift blade  3  is the maximum value into formula (2). The target rotation speed command K 2  must be less than the maximum rotation speed that the main shaft  2  and the load can bear. 
     The first controller  163  is connected with the subtractor  162  to receive the rotation speed error signal K 3  of the main shaft  2 . The first controller  163  outputs a waveform amplitude signal K 4  according to the rotation speed error signal K 3  by for example but not limited to the PID algorithm. The second controller  164  is connected with the first controller  163  to receive the waveform amplitude signal K 4 . In this embodiment, the driving signal V of the Magnus rotor  4  is outputted by the second controller  164 , wherein the driving signal V is the waveform amplitude signal K 4  multiplied by a cosine function. As the waveform diagram of  FIG. 9  is represented as a function which is K 4 ·COS(θ+Δ). The symbol θ of the function represents the angle between the Magnus rotor  4  and the flowing direction of the fluid W. The symbol Δ of the function represents an angle compensation value. Moreover, the Magnus rotor  4  is affected by the lift force and the drag force. In the practice, the angle compensation value Δ is utilized to adjust the phase of the waveform diagram of  FIG. 9  so as to modify the driving signal V of the power source  41  in order that the performance of the vertical axis fluid energy conversion device  1  is enhanced. In some embodiments, the angle compensation value Δ can be obtained through experiments as a function of the actual rotation speed signal K 1 . In some other embodiments, the angle compensation value Δ is 0 while the angle compensation is not used. 
       FIG. 12A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a second embodiment of the present disclosure.  FIG. 12B  is a top view illustrating the vertical axis fluid energy conversion device of  FIG. 12A . As shown in  FIGS. 12A and 12B , the vertical axis fluid energy conversion device  1   a  of this embodiment includes a main shaft  2 , at least one lift blade  3 , at least one Magnus rotor  4  and a connection component  5 . The structures and operations of the main shaft  2 , the at least one lift blade  3 , the at least one Magnus rotor  4  and the connection component  5  are similar to those of  FIG. 5A , and are not redundantly described herein. Compared with the shape of the lift blade  3  of  FIG. 5A , the shape of the lift blade  3  of this embodiment is straight line wing blade. Moreover, the number of the Magnus rotor  4  of this embodiment is two. The two ends of each Magnus rotor  4  include an end plate  43 , respectively. The end plate  43  is made by circular plate. The diameter of the end plate  43  is greater than the diameter of the corresponding Magnus rotor  4 . Moreover, the periphery surface of the Magnus rotor  4  includes bulk convex or strip convex for increasing the Magnus effect. The connection component  5  of this embodiment is for example but not limited to a rod-shaped structure. The shape of the connection component  5  can be a streamline airfoil (such as the shape of NACA0012) for decreasing the drag force. Each second connection part  52  is connected with the main shaft  2  and the corresponding lift blade  3 . Moreover, each second connection part  52  and the adjacent first connection part  51  are not limited to be located on the same level of the main shaft  2 . The angle between each second connection part  52  and the adjacent first connection part  51  is for example but not limited to 90 degrees. 
     The embodiment of the lift blade  3  usually adopts the NACA0018 or NACA2412 airfoil which has a high lift-to-drag ratio (over 20 times). So the lift blade  3  can operate at the tip speed ratio more than four, as shown in  FIG. 4 . However, as is well known, the lift-to-drag ratio of the Magnus rotor  4  is usually about three, which is much lower than the lift-to-drag ratio of the lift blade  3 . Consequently, the Magnus rotor  4  must be operated at a lower tip speed ratio than the lift blade  3 , or the Magnus rotor  4  will endure high drag force and cause poor efficiency. Because the revolution angular velocity of the Magnus rotor  4  is the same with the revolution angular velocity of the lift blade  3 , the tip speed ratio is proportional to the revolution radius according to formula (1) for both the lift blade  3  and the Magnus rotor  4 . Consequently, the revolution radius of the Magnus rotor  4  revolved around the first axis  21  must be less than the revolution radius of the lift blade  3  revolved around the first axis  21 . Usually the revolution radius of the Magnus rotor  4  revolved around the first axis  21  is less than ½ times the revolution radius of the lift blade  3  revolved around the first axis  21 . Therefore, the distance between each Magnus rotor  4  and the adjacent lift blade  3  is greater than the distance between the Magnus rotor  4  and the main shaft  2 , so each Magnus rotor  4  is far away from the adjacent lift blade  3 , so that the flow field nearby the lift blade  3  is not influenced. Consequently, the performance of each lift blade  3  can be fully utilized and the performance of the vertical axis fluid energy conversion device la is enhanced. For reducing the drag force of the Magnus rotor  4 , the height of each Magnus rotor  4  along the direction of the first axis  21  is less than the height of the lift blade  3 . Hence, the cross-sectional area of the Magnus rotor  4  is reduced, and the performance is more enhanced. 
       FIG. 13A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a third embodiment of the present disclosure.  FIG. 13B  is a top view illustrating the vertical axis fluid energy conversion device of  FIG. 13A . As shown in  FIGS. 13A and 13B , the vertical axis fluid energy conversion device  1   b  of this embodiment includes a main shaft  2 , at least one lift blade  3 , at least one Magnus rotor  4  and a connection component  5 . The structures and operations of the main shaft  2 , the at least one lift blade  3 , the at least one Magnus rotor  4  and the connection component  5  are similar to those of  FIG. 5A , and are not redundantly described herein. Compared with the shape of the lift blade  3  of  FIG. 5A , the shape of the lift blade  3  of this embodiment is straight line wing blade. Moreover, the connection component  5  only includes two first connection parts  51 . Two ends of each first connection part  51  are connected with the lift blade  3  and the main shaft  2 , respectively. Each Magnus rotor  4  is connected with the middle section of the corresponding first connection part  51 , so that each Magnus rotor  4  is located between the corresponding lift blade  3  and the main shaft  2 . The distance between each Magnus rotor  4  and the adjacent lift blade  3  is greater than the diameter of the cylinder of the Magnus rotor  4  for avoiding influencing the performance of the lift blade  3 . 
       FIG. 14  is a top view illustrating a vertical axis fluid energy conversion device according to a fourth embodiment of the present disclosure. As shown in  FIG. 14 , the vertical axis fluid energy conversion device  1   c  of this embodiment includes a main shaft  2 , at least one lift blade  3 , at least one Magnus rotor  4  and a connection component  5 . The structures and operations of the main shaft  2 , the at least one lift blade  3 , the at least one Magnus rotor  4  and the connection component  5  are similar to those of  FIG. 5A , and are not redundantly described herein. Compared with the shape of the lift blade  3  of  FIG. 5A , the shape of the lift blade  3  of this embodiment is straight line wing blade. In some embodiments, the shape of the lift blade  3  of this embodiment is spiral wing blade, as shown in  FIG. 15 . The number of the lift blade  3  is three and the number of the Magnus rotor  4  is three. The second connection part  52  of this embodiment is a rod-shaped structure. The second connection part  52  is connected between the main shaft  2  and the corresponding lift blade  3 . The angle between each second connection part  52  and the adjacent first connection part  51  is for example but not limited to 60 degrees. 
       FIG. 16A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a sixth embodiment of the present disclosure.  FIG. 16B  is a top view illustrating the vertical axis fluid energy conversion device of  FIG. 16A . As shown in  FIGS. 16A and 16B , the vertical axis fluid energy conversion device  1   d  of this embodiment includes a main shaft  2 , at least one lift blade  3 , at least one Magnus rotor  4  and a connection component  5 . The structures and operations of the main shaft  2 , the at least one lift blade  3 , the at least one Magnus rotor  4  and the connection component  5  are similar to those of  FIG. 5A , and are not redundantly described herein. Compared with the shape of the lift blade  3  of  FIG. 5A , the shape of the lift blade  3  of this embodiment is straight line wing blade. The number of the lift blade  3  is one, and the number of the Magnus rotor  4  is one. Moreover, the number of the first connection part  51  of this embodiment is one, and the number of the second connection part  52  is one. The second connection part  52  of this embodiment is a rod-shaped structure. The second connection part  52  is connected between the main shaft  2  and the lift blade  3 . 
       FIG. 17A  is a schematic perspective view illustrating a vertical axis fluid energy conversion device according to a seventh embodiment of the present disclosure.  FIG. 17B  is a cross-sectional view illustrating portion of an exemplary vertical axis fluid energy conversion device of  FIG. 17A . As shown in  FIGS. 17A and 17B , the vertical axis fluid energy conversion device le of this embodiment includes a main shaft  2 , at least one lift blade  3 , at least one Magnus rotor  4  and a connection component  5 . The structures and operations of the main shaft  2 , the at least one lift blade  3 , the at least one Magnus rotor  4  and the connection component  5  are similar to those of  FIG. 5A , and are not redundantly described herein. Compared with the main shaft  2  of  FIG. 5A , the main shaft  2  of this embodiment includes a main body  22 , a sleeve  23  and a first bearing  24 . The first axis  21  is constituted of an axis line which passes through the center of a top end of the main body  22  and the center of a bottom end of the main body  22 . The main body  22  is rotated around the first axis  21 . The sleeve  23  is a hollow tubular structure. The inner diameter of the sleeve  23  is greater than the outer diameter of the main body  22 , so that the sleeve  23  can be sleeved on the outside of the main body  22 . The first bearing  24  is disposed between the main body  22  and the sleeve  23 . The sleeve  23  and the main body  22  are formed as a concentric structure by the first bearing  24 , so that the sleeve  23  and the main body  22  can rotate around the first axis  21  independently. The rotation speed of the sleeve  23  can be different from the rotation speed of the main body  22 . 
     Moreover, in this embodiment, the main shaft  2  further includes a clutch  26 . The clutch  26  controls the sleeve  23  and the main body  22  to engage or disengage. The clutch  26  is a bidirectional clutch or a unidirectional clutch. The clutch  26  includes a first side  261  and a second side  262 . The first side  261  of the clutch  26  is fixed on the main body  22 . The second side  262  of the clutch  26  is fixed on the sleeve  23 . The number of the Magnus rotor  4  is for example but not limited to two, and the number of the lift blade  3  is for example but not limited to two. Each Magnus rotor  4  is connected with the sleeve  23  through the corresponding first connection part  51 . Each lift blade  3  is connected with the main body  22  through the corresponding second connection part  52 . Moreover, the level of the first connection part  51  disposed on the first axis  21  is different from the level of the second connection part  52  disposed on the first axis  21 . Consequently, the Magnus rotor  4  connected with the first connection part  51  and the lift blade  3  connected with the second connection part  52  can revolve around the first axis  21  independently and respectively without collision. 
     While the lift blade  3  is required to revolve, the Magnus rotor  4  is driven to rotate by the power source  41  and the Magnus lift force is produced, which is applied to the moment arm formed by the first connection part  51  to produce the torque, so that the sleeve  23  is rotated around the first axis  21  in response to the torque. Meanwhile, control the clutch  26  in an engaged state. The sleeve  23  will drive the main body  22  to rotate around the first axis  21 , so that the lift blade  3  is also driven to revolve around the first axis  21  through the second connection part  52 . While the revolution speed of the lift blade  3  is greater than a speed threshold value, the lift blade  3  can produce sufficient torque to make the main body  22  continue to rotate without relying on the torque provided by the Magnus rotor  4 , so that the Magnus rotor  4  can be stopped from rotating for saving energy and the clutch  26  can be disengaged, so the sleeve  23  is not driven by any torque and stops rotating. Since the main body  22  is disengaged from the sleeve  23 , the torque produced by the lift blade  3  is totally utilized to drive the main body  22  to rotate without being dragged by the resistance of the Magnus rotor  4 . Consequently, the efficiency of the vertical axis fluid energy conversion device  1   e  is enhanced. In an embodiment, the length of the first connection part  51  used to connect the sleeve  23  and the Magnus rotor  4  can be designed to be longer to obtain greater torque for reducing the start time of the lift blade  3 . After the vertical axis fluid energy conversion device le is started and the clutch  26  is disengaged. The rotation of the main body  22  is not influenced by the drag force of the Magnus rotor  4  and the first connection part  51 . Moreover, while the flowing speed of the fluid W is too high, the rotation speed of the main body  22  is too fast and the main body  22  is dangerous, only by engaging the clutch  26 , the main body  22  will be decelerated to stop by the drag force of the Magnus rotor  4  and the first connection part  51 . Consequently, an additional safety mechanism is provided, and the wear of the brake can be reduced. 
     Moreover, in this embodiment, the vertical axis fluid energy conversion device  1   e  is disposed on a base  9 . The base  9  is a fixed surface or a tower. The vertical axis fluid energy conversion device  1   e  includes a holder  8 . The holder  8  is fixed on the base  9  and includes a circular through hole  81 . The main body  22  of the main shaft  2  is penetrated through the circular through hole  81  and is contacted with the holder  8  through a plurality of second bearings  25 . So the main body  22  is supported on the base  9  through the holder  8  and can be rotated around the first axis  21 . 
       FIG. 17C  is a cross-sectional view illustrating portion of another exemplary vertical axis fluid energy conversion device of  FIG. 17A . In some embodiments, as shown in  FIG. 17C , the holder  8  is a hollow tubular structure. The inner diameter of the holder  8  is greater than the outer diameter of the main body  22 . The outer diameter of the holder  8  is less than the inner diameter of the sleeve  23 . Consequently, the holder  8  is disposed between the main body  22  and the sleeve  23 . The holder  8  is contacted with the sleeve  23  through the plurality of first bearings  24 , and the holder  8  is contacted with the main body  22  of the main shaft  2  through the plurality of second bearings  25 . Consequently, the main body  22  of the main shaft  2  and the sleeve  23  are both supported by the holder  8 , and the main body  22  of the main shaft  2  and the sleeve  23  both can be rotated around the first axis  21  independently. Therefore, while the clutch  26  is disengaged, the main body  22  does not need to drive the sleeve to rotate, nor does it need to support the weight of the sleeve  23  and the weight of the Magnus rotor  4 , since the sleeve  23  is supported by the holder  8  through the plurality of first bearings  24 , therefore, the weight supported by the main body  22  of the main shaft  2  is lighter, resulting in less friction. So the efficiency of the vertical axis fluid energy conversion device  1   e  is enhanced. 
     From the above descriptions, the vertical axis fluid energy conversion device of this disclosure includes at least one lift blade and at least one Magnus rotor. The rotation of the Magnus rotor produces the Magnus lift force. The Magnus rotor is connected with the main shaft through the connection component. The vertical axis fluid energy conversion device starts up the lift blade to revolve by the Magnus lift force of the Magnus rotor. Moreover, the Magnus rotor of the present disclosure is driven to rotate by the power source, and the required lift force can be obtained by increasing the rotation speed of the Magnus rotor. Consequently, the diameter of the Magnus rotor can be designed to be shorter. Compared with the conventional Savonius drag blade, the cross-sectional area of the Magnus rotor of this disclosure is reduced. Consequently, the flow field inside the vertical axis fluid energy conversion device is less influenced. So the performance of the lift blade of the present disclosure is better, that the whole efficiency of the vertical axis fluid energy conversion device is enhanced. 
     Furthermore, the lift blade of the present disclosure does not need to have a variable pitch design. The lift force generated by the Magnus rotor can drive the vertical axis fluid energy conversion device to achieve self-starting. So there are fewer moving parts, that the structure is more stable. Compared with the traditional vertical axis fluid energy conversion device that directly use the power source to drive the main shaft to rotate, the power source of the vertical axis fluid energy conversion device of the present disclosure only drives the Magnus rotor to rotate instead of driving the main shaft which is bulky. Consequently, the required power is smaller. So the vertical axis fluid energy conversion device of the present disclosure has advantages of low cost and low energy consumption. 
     While the disclosure has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the disclosure needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.