**5. Experimental Setup**

The experimental verification of the proposed algorithm was performed using the test rig demonstrated in Figure 12. It included a prototype of the three phase PMSM developed for rotary and reciprocating compressors, the rated parameters are shown in Table 1. However, motor direct and quadrature inductances strongly depend on the stator current and vary as depicted in Figure 6.

**Figure 12.** Experimental setup.

The IPMSM control system implemented for verification of the proposed algorithm, was taken from a commercial motor drive discussed in [46] (Figure 13). It performs a sensorless control of IPM motors, using a back-EMF based speed and position estimation technique discussed in [47]. In order to exclude reverse rotation at the start, the estimator is enhanced with an initial rotor position estimation algorithm [48]. The performance of the estimation algorithm was verified with the help of an incremental position encoder [49,50], which demonstrated that it operates at speeds over 10 Hz with the maximum estimation error of 3~4 electrical degrees. Since the control system was designed for operation with compressors, it was enhanced with a silent stoppage algorithm considered in [51].

The control scheme contains an outer speed loop and inner current loops in the synchronous reference frame, where the rotor speed and position are provided by the estimation algorithm. The information on the motor electrical signals is provided by the DC-link voltage and two shunt-based current sensors, placed at the bottom legs of the inverter.

The IPMSM control system includes a field-weakening algorithm, which increases the maximum operation speed by up to +50% of the rated one by demagnetizing the rotor field with a negative *id* current. The motor drive includes an adaptive MTPA control algorithm, required to increase efficiency. This algorithm uses a seeking technique, which was considered in [31]; therefore, this method for MTPA control can be used for the experimental validation of the proposed idea.

**Figure 13.** Control block diagram of the IPM motor drive with seeking MTPA algorithm.

The motor under test was connected with a Magtrol water cooling power brake 1-PB-65 capable of providing load torque up to 10 N·m. This power brake was controlled by the Magtrol DSP6001 dynamometer controller, which received commands from the computer and reported speed and torque. This load equipment provided low-ripple and precise torque application, which is necessary for the accurate measurements of speedtorque characteristics of the motor drive. The electrical signals were measured by the Yokogawa DL 850 oscilloscope, capable of operating with raw data and oscillograms and a Yokogawa WT-1800E power analyzer used for measurements of power and efficiency.

The inverter involved in these experiments was a commercial device designed for the control of rotary compressors of air conditioners. It was based on the FSBB15CH60F (15 A/600 V) Fairchild smart power module and designated for operation in 220 V (50/60) Hz standard grids. This inverter had a conventional structure for low-cost applications, which involved two shunt-based current sensors in the inverter legs and one voltage sensor in the DC-link. The signals from the sensors were pre-amplified by internal operational amplifiers of the microcontroller and then processed by a 12-bit ADC. The control system of the inverter used in the experiments included the iHart i910 Cortex M3 core microcontroller operating at 80 MHz and controlled the inverter switches at 10 kHz. The experimental sample of the inverter was extended with an RS-232 communication interface used for the connection with the computer in order to send commands and monitor the internal data.
