Design And Research Of Direct-drive Permanent Magnet Machine For Fracturing Pump

The hydraulic fracturing technology is the most important procedure in shale gas production.In recent years,in order to increase the efficiency of system,and decrease the weight of equipment and environment pollution,the diesel-driven fracturing technology is gradually replaced by electric-driven fracturing technology.Most of production of shale gas is in the wild,which make the equipment repairing difficult,so it is important that these equipments are very reliable.There are many mechanical facilities in fracturing pump,which reduce the reliability of system.In order to increase the reliability,there are two direct-drive method used in the shale gas production.One is using the rotate direct-drive machine which is directly linked to the bent axle to reduce the gears.The other one is using the linear direct-drive machine which is directly linked to the plunger piston to reduce most of mechanical equipment of fracturing pump.The major work of this paper is shown as follows:Firstly,making a investigation of rotating direct-drive system.In order to satisfy the vehicle-mounted requirement,the radial flux permanent magnet machine which has a surface mounted rotor structure is chosen as the driven machine,which is high reliability and has high torque density.Considering that the production of shale gas needs a system which has fault-tolerant capability,the phase of machine is chosen as six.The FSCW is more suitable in direct-drive machine.The slot-pole combination of unit motor and winding structure are also confirmed.Secondly,the rotate machine is designed according the output performance of machine.The electric loading,magnetic loading,air gap length and aspect ratio are analyzed and chosen.Considering the cost,weight and efficiency,the suitable slot-pole combination and size of magnets are chosen.After the machine designed,the no-load,rated load and over load performance are analyzed,then the temperature rise and demagnetization are calculated,and the static eccentric is also analyzed.Thirdly,to improve the performance under fault-tolerant condition,the method that the rotate machine has a multilayer winding is investigated.The structure of multilayer winding is confirmed.To analyze the character of multilayer windings,both performances of double layer winding and multilayer winding are compared under different loading conditions.Finally,the linear direct-drive method is investigated.The combination of machine and pump is determined,and also the velocity planning curve of machine is confirmed.If the area of plunger piston is unchanged in linear direct driven,the mass of linear machine is more than the rotate machine.In order to reduce the mass of machine,the method of reducing area of piston and increased the length of stroke is proposed.According the working principle of machine,the optimization output force is analyzed.To save the space,a method of combining three linear machine to become one machine is proposed.The method of optimizing the thrust ripple is also proposed and verified by FEA.Comparing the rotating direct-drive method with the linear direct-drive method,the rotating direct-drive method is more suitable.