International Journal of Power Electronics and Drive Systems (IJPEDS) Vol. 15, No. 4, December 2024, pp. 2058~2067 ISSN: 2088-8694, DOI: 10.11591/ijpeds.v15.i4.pp2058-2067  2058 Journal homepage: http://ijpeds.iaescore.com Single observer speed sensorless field weakening control of two parallel motors Agus Suprajitno, Feri Yusivar, Abdul Halim Faculty of Engineering, Department of Electrical Engineering, Universitas Indonesia (UI), Jakarta, Indonesia Article Info ABSTRACT Article history: Received Mar 12, 2024 Revised Aug 26, 2024 Accepted Sep 5, 2024 Two induction motors with parallel connected stator windings supplied by a single inverter (single observer) with a field weakening control system. The objective of this study is to propose a torque production speed sensorless vector control technique for each parallel connected rotor by adding field weakening control to improve the performance of each motor and reducing the number of adaptive observers on each motor to a single observer. Design of a rotor flux-oriented control (RFOC) system. Simulation results with the C-MEX S-function of MATLAB/Simulink 2015b show that the proposed method works better and can be operated at speeds that exceed the nominal speed of the motor. Keywords: Field weakening Induction motor Nominal speed RFOC Single observer This is an open access article under the CC BY-SA license. Corresponding Author: Feri Yusivar Faculty of Engineering, Department of Electrical Engineering, Universitas Indonesia UI Depok Campus, Jakarta, 16424 Indonesia Email: yusivar@eng.ui.ac.id 1. INTRODUCTION Industry uses induction motors with cage rotors extensively due to their robust design and affordable cost in comparison to other motors of the same class. In use, a speed adjustment is required to control the set point or the desired speed, and then a feedback system is required, which is rotor speed information. Two methods were used to collect the rotor speed information: sensor-based and speed-sensorless. In systems with sensors, the use of encoders often cannot detect very low and very high speeds. To overcome this problem, a sensorless speed control system is designed by applying current vector control to control and estimate the rotor speed, which is fed back to the system [1]-[8]. Induction motors can be precisely driven by a single inverter running a single induction motor by the use of the field-oriented control approach of sensorless vector control. On the other hand, a single inverter can power several induction motors connected in parallel for industrial uses such electric propulsion, as in railroad traction systems [9], [10]. Due to hardware minimization and cost reduction, multiple induction motors, considered one large motor, can be driven by a single inverter under the same specifications and rating. However, when an uneven load torque is applied, the performance becomes unstable [11]. Control with field weakening is one method to improve the performance of induction motors. With this method, speeds that can exceed the nominal speed can be achieved. S.H. Kim and S.K. Sul used field weakening in maximum torque operations [12], Briz et al. [13] used current and voltage regulation to achieve revolutions above nominal revolutions. Kerkman et al. using indirect field-oriented control in the application of field weakening [14]. In this research, the motor rotation is estimated with an observer on the ab-axis reference frame using the motor flux weakening control or field weakening control method while taking into account the limits of the motor nominal voltage and current so that the motor rotation can be achieved beyond