# A Review of Progress and Hydrodynamic Design of Integrated Motor Pump-Jet Propulsion
## 2 Electric Motor and Control Technology  
The IMP was first developed by the U.S. Naval Underwater Warfare Center in collaboration with the Applied Research Laboratory of Pennsylvania State University. Originally, it was used for unmanned submersibles. However, the motor was placed in the outer cover of the submersible; hence, the motor and the propulsion impeller were still two separate parts [8]. Then, the IMP was used for a light torpedo (Figure 3). The electric power which the light torpedo uses is an advanced lithium-ion battery and an integrated motor thruster. According to [PERSON] and [PERSON] (1997), this battery has a high energy density [9]. Figure 4 shows a schematic diagram of an IMP thruster. A hub, a duct, a motor stator, a rotor impeller with permanent magnets, and guiding vanes are the major components. The stator is supported by the outermost component, which is a duct similar to that of a pump-jet propeller. The stator of the motor is fixed in the outer pipe, and the outer ring of the rotor impeller is attached with permanent magnet pieces to the main shaft and can rotate around the shaft. The guide vane can be integrated with the shaft as a static blade cascade. Its function is to eliminate the rotational movement of the water sprayed from the back of the impeller so that it can effectively recover the energy of the sprayed water and balance the torque. When operating the motor, the stator coil of the motor is energized to generate a magnetic field. The impeller with permanent magnets rotates as the rotor of the motor. The blades pump water and discharge backward. The rotating energy is recovered by the stator blades, and the guide vanes are sprayed out through the nozzle to provide the device with forward momentum. Figure 3: Prototype of integrated motor propulsion developed by the U.S. Navy [8]. Figure 2: Structural diagrams of (**a**) hubless RDT, (**b**) hub-type RDT, and (**c**) hub-type IMP [3; 4]. As mentioned above, when installing the IMP integrated motor, which is required to be as thin as possible in the radial direction and as short as possible in the axial direction to reduce the duct resistance, the electromagnetic air gap should be large enough to fill in the air gap of the internal stator/rotor anticorrosion sheath [10]. The first publicly disclosed integrated motor propulsion solution was a patent authorized by [PERSON], Hannover, Germany [10], as shown in Figure 5. The types of electric motors that are applicable to IMPs are reviewed in the following section to provide a clear overview and detailed summary of the controller of the IMP system (see Table 1). Traditional permanent-magnet synchronous motors generally use vector control. The control system needs to obtain accurate position information to control the speed and current of the motor. However, because the integrated motor propulsion device stops the rotating shaft, and traditional mechanical position sensors are difficult to install, position sensor control technology [11,12] is used quite often. The control scheme mainly has two technical routes: one is to obtain the rotor position based on the basic equations of the motor, which requires a high degree of accuracy regarding the motor parameters and does not perform well at low speeds; the other is to use the salient pole characteristics of the mo  
Figure 4: Schematic diagram of integrated motor pump-jet thruster. Figure 5: The earliest patent of IMP: (**a**) rotor; (**b**) stator; (**c**) bearings; (**d**) bearings; (**e**) bearings and attachment; (**f**) propeller; and (**g**) duct [10]. position signal after injecting high-frequency signals [13]. This method can also achieve better estimation results in the low-speed and zero-speed range. However, it is not suitable for surface-mount motors with a low salient pole rate, and the algorithm is more complicated.