Field oriented control of PMSM drive with backup power supply

The primary purpose of the article is to examine the field oriented control system of permanent magnet synchronous machine (PMSM) electric drive with backup power supply. Authors pro-pose to use bi-directional DC-DC converter to ensure the «hot» backup operation mode in case of grid fault. The change-over switching system, which provide transfer of voltage-source in-verter (VSI) from DC link to the backup power source is considered. The presented system provides a good dynamic transient process; the results are confirmed by simulation in Psim software. Moreover, based on the results acquired, an electric drive based on PMSM with field oriented control and a backup power supply system from the battery via a bi-directional DC-DC converter is capable of operating according to the principles of «hot» backup.


MATERIALS AND METHODS
There are a number of industrial areas where the reliability of the electric drive system is paramount. Failure of the electric drive system in such industries as oil production, mining and others can lead to serious economic losses or be a threat to the life of personnel.
Based on the examples presented above, an obvious conclusion follows -the advantages of an adjustable speed AC drive are impossible without a stable power supply. Therefore, the main purpose of introducing backup power supply into a electric drive system is to increase the reliability, which will prevent possible man-made and economic damage in case of instability in the main supply grid.

RESULTS AND DISCUSSION
The system, operating on the principle of «hot» backup, transfers to a backup power source within a time interval from 1 ms to 20 ms, avoiding loss of electric drive performance. Currently, the main technical solutions for matching the DC link of a power converter with a backup DC source is a bi-directional galvanically isolated converter. The structural scheme presented at Figure 1.   The change-over switching system (Figure 4) is based on tracking the linear rectified voltage from the sensors, each sensor has a divider.
By isolating the DC component using a capacitor, with a resistor connected in parallel and approximating the signal through the «RMS block», it is possible to obtain the fall of the signal edge at the time of the fault operation mode ( Figure 5). After filtering the signal and comparing it to the setpoint using a comparator, the change-over switching can be carried out with good dynamic response.   Based on the obtained result, it is obviously, that the system implements the principles of «hot» backup. Moreover, the amplitudes of the values of speed and torque at the moment of switching over are insignificant, and they are unable to influence the actuator, which means that switching over to the backup supply is performed without significant ripples. Figure 8 shows the graphs of phase A current and DC link voltage at the moment of switching over to backup supply.

CONCLUSION
Based on the results of simulation and analysis of the operation of circuitry solutions, the final conclusion can be drawn -an electric drive based on PMSM with field oriented control and a backup power supply system from the battery via a bi-directional DC-DC converter is capable of operating according to the principles of «hot» backup. Moreover, the course of the transient process, based on the simulation data, occurs without a sharp increase in the amplitudes of the torque and speed, and, therefore, there are no ripples and vibrations in the mechanical part when switching over to backup DC supply. Sometimes this requirement is fundamental in the construction of low-inertia systems with backup power. The presented system provides a good dynamic transient process; the results were confirmed by simulation in Psim software.