# A Review of Innovative Electromagnetic Technologies for a Totally Artificial Heart
## 3 TAH Electromechanical Components
### Electrical Drive  
According to the different projects, the electric drive implemented in a TAH can be broadly divided into speed controller-based and position (or force) controller-based arrangements. The speed control is applied to reproduce the operation for both continuous and pulsatile flow. Three-phase or multi-phase motors are generally supplied by a voltage source inverter, often operated by space vector modulation. The PID speed controller elaborates the speed signal generated by Hall-effect sensors or sensorless, estimated in more sophisticated microcontroller-based strategies (e.g., field orientation) [36]. In the latter case, a more precise and reliable control can be achieved, for instance, by providing an active braking control to decelerate the impeller motor and then allowing energy recovery during the braking operation.  
The elaboration of appropriate speed profiles enables the achievement of the pulsatile effect with a satisfactory hemodynamic response. Generally, they consist of roughly square waveforms of the desired heartbeat frequency that oscillate between two limit values. As an example, in [36] a mean aortic pressure of \(\cong\)102 mmHg and a maximum pressure slope of \(\cong\)240 mmHg/s are achieved at 30 bpm by varying the speed between 2300 and 2900 rpm. However, control parameters must be tight to the proper values, since in vivo experiments show that even slight alterations (i.e., short-term speed overshoots or control delays) can significantly alter pump outflow.  
A specific controller must be expressly designed to drive the active magnetic suspension of the rotor/impeller shaft, generally operating along the axial and possibly also the radial directions, even if a passive bearing (e.g., hydrodynamic journal bearing) can be effective in controlling the radial position. In an application based on an axial flux motor, three eddy current sensors detect the axial position and send their signals to the PID controllers [35]. Accurate coordination between the controllers of the axial position and of the motor speed enables the regulation of the LV and RV outflow. The bearing control must be tuned to cope with both hydraulic forces, depending on the motor speed and the rotor position, and the inherent magnetic attractive force between the PMs and the iron core of the motor. As an example, the power to supply the windings of the hybrid PM-electromagnet bearing for the maximum axial displacement of \(\pm\)0.15 mm at a speed of 2200 rpm is limited to \(\cong\)10 W. The overall consumption under the same conditions is below 15 W [35].  
In the LOA configuration proposed in [32], each motor coil is generally powered by a separate DC/DC full-bridge converter, with a PWM current control and a relatively low supply voltage (between 12 V and 20 V), adequate for the low coil inductance and back-e.m.f.. The drive control enforces the predefined reference sinusoidal motion using a sensor feedback signal giving the position of the pusher plates, adjusting the supply current value to the required thrust, depending, in turn, on the blood outlet back pressure and on the pump speed. A proper motor design and an effective control strategy (e.g., field orientation) should aim to maximize the thrust/current ratio, i.e., to minimize the losses/output energy ratio, in order to avoid overheating and to extend the battery range. The electromagneticogging force could possibly contribute to the thrust by taking advantage of a suitable iron core design.