Kwang-Woon Lee

Commutation Torque Ripple Reduction in a Position Sensorless Brushless DC Motor Drive

This paper presents a novel method to reduce commutation torque ripple in a position sensorless brushless DC (BLDC) motor drive. To compensate the commutation torque ripple completely, conventional methods should know commutation interval, so that they need current sensors. However, the proposed method measures commutation interval from the terminal voltage of a brushless DC motor, calculates a PWM duty ratio using the measured commutation interval to suppress the commutation torque ripple, and applies to the calculated PWM duty ratio only during the next commutation. Experimental results verify that the proposed method implemented in an air-conditioner compressor controller considerably reduces not only the pulsating currents but also vibrations of a position-sensorless BLDC motor.

A Novel Starting Method of the Surface Permanent-Magnet BLDC Motors Without Position Sensor for Reciprocating Compressor

This paper describes a new position sensorless starting method, specialized for low-cost applications, of a brushless dc (BLDC) motor with a surface permanent-magnet (SPM) rotor to prevent demagnetization of permanent magnet and vibrations due to pulsating currents during the starting period. That the magnitude of peak current causes irreversible demagnetization of permanent magnet, has been measured through experimental tests. The proposed method limits the motor currents during the starting period to lower than the demagnetization currents by doing commutation depending on the level of the measured phase currents. Experimental results show that the proposed method implemented in an inverter for a BLDC motor-driven reciprocating compressor considerably reduces not only the pulsating currents but also the vibration of the compressor during starting.

A Seamless Transition Control of Sensorless PMSM Compressor Drives for Improving Efficiency Based on a Dual-Mode Operation

The sinusoidal-wave and square-wave driving modes have been commonly used in permanent-magnet synchronous motor (PMSM) drives for household refrigerator compressors. In general, the sinusoidal-wave drive performs better in some aspects such as torque ripples, a starting performance, and a flux-weakening capability than the square-wave drive. The square-wave drive, however, has the advantage of higher efficiency at low-output-power conditions because of its relatively lower switching loss than the sinusoidal-wave drive. To selectively utilize the benefits of both driving modes, a seamless transition control between the two driving modes is proposed in this paper. Considering that the overall control structure of the sensorless PMSM drive is quite different according to the driving mode, initialization strategies, necessary for a smooth transition, for the pulse-width modulator of the inverter, speed and current controller, and sensorless position/speed estimator are presented. With the proposed method, a dual-mode operation of the sensorless PMSM drive can be achieved without stopping the compressor. The dynamic performance of the proposed transition scheme is tested using simulations and verified by experiments. Experimental result shows that the efficiency of a refrigerator increases up to 2 [%] using the dual-mode operation in comparison with the sinusoidal-wave only drive.

A Stator Core Quality Assessment Technique for Inverter-Fed Induction Machines

Localized heating caused by damage in the laminations or inter-laminar insulation of the stator core increases the core losses and can lead to machine failure. Therefore, it is important to monitor the quality of the stator core for reliable and efficient operation of the machine. The methods currently available for core quality assessment are inconvenient since they require an outage and the machine to be disassembled or operated under no load conditions. In this paper, a new method for monitoring the quality of the stator core for inverter-fed machines without motor disassembly or operation is proposed. The main concept is to use the inverter to apply a set of test signals to assess the quality of the core whenever the motor is at standstill. A set of high frequency pulsating magnetic fields are produced using the inverter, and the power loss is observed as a function of field circumferential position to detect core problems. An experimental study on 10 hp induction motor verifies that local inter-laminar core faults can be detected with high sensitivity. The proposed technique is expected to provide a simple solution for frequent stator core quality assessment without motor disassembly, motor operation, or additional hardware for reliable and efficient operation of inverter-fed induction machines.

A new strategy for condition monitoring of adjustable speed induction machine drive systems

A new strategy for monitoring the condition of adjustable speed induction machine drive systems is presented in this paper. The main concept of the new method is to use the inverter to perform off-line tests for quality assessment of the vulnerable components in the inverter, cable, and induction motor automatically whenever the motor is stopped. This new approach is suitable for monitoring system components that deteriorate gradually to failure, if the degradation is observable. Off-line test methods for monitoring the quality of the 1) dc-link aluminum electrolytic capacitor; 2) electrical connections; 3) cable and stator winding insulation; 4) stator core; and 5) rotor bar are presented along with a summary of the failure mechanism and existing test methods. It will be shown that the new strategy can be implemented with minimal hardware requirements, and that it has many advantages over existing off-line and on-line tests. An experimental study performed under simulated fault conditions for each component shows that the method provides a reliable and sensitive indication of drive system problems for reliable, efficient, and safe operation.

Quality Assurance Testing for Magnetization Quality Assessment of BLDC Motors used in Compressors

Quality assurance (QA) testing of mass-produced electrical appliances is critical for the reputation of manufacturer since defective units will have a negative impact on safety, reliability, efficiency, and performance of the end product. It has been observed at a brushless dc (BLDC) compressor motor manufacturing facility that improper magnetization of the rotor permanent magnet is one of the leading causes of motor defects. A new technique for postmanufacturing assessment of the magnetization quality of concentrated winding BLDC compressor motors for QA is proposed in this paper. The new method evaluates the data acquired during the test runs performed after motor assembly to observe anomalies in the zero-crossing pattern of the back-EMF voltages for screening motor units with defective magnetization. An experimental study on healthy and defective 250-W BLDC compressor motor units shows that the proposed technique provides sensitive detection of magnetization defects that existing tests were not capable of finding. The proposed algorithm does not require additional hardware for implementation since it can be added to the existing test-run inverter of the QA system as a software algorithm.

Automated monitoring of magnet quality for permanent magnet synchronous motors at standstill

Demagnetization of permanent magnets (PM) used in synchronous motors (SM) can occur due to a combination of thermal, electrical, and/or environmental operating stresses. Since PM demagnetization results in degradation of motor performance, efficiency, and reliability, it is important to monitor the quality of PMs regularly. However, there are many limitations to the off-line and on-line methods currently used for magnet quality assessment. In this paper, a new inverter-embedded technique for automated monitoring of magnet quality for permanent magnet synchronous motors (PMSM) that overcomes the limitations of existing techniques is proposed. The main concept is to use the inverter to perform a standstill test whenever the motor is stopped to detect local or uniform PM demagnetization. The machine is excited with a pulsating field at different angular positions, and the change in the current peaks caused by the change in the degree of magnetic saturation due to demagnetization is observed. An experimental study on a 10hp PMSM verifies that local and uniform PM demagnetization can be detected with high sensitivity.

Comparison of Starting Method for Position Sensorless BLDC Motor Driven Reciprocating Compressor

The magnitude of output torque in a BLDC (Brushless DC) motor depends on torque angle so that the exact initial position of rotor is essentially required for good starting performance. This paper describes starting method comparison for smooth starting in position sensorless BLDC motor drives for reciprocating compressor of refrigerator. In addition, position of rotor is determined from current response characteristics at align mode and level of the measured phase currents at the open-loop acceleration mode. The experimental results have suggested the effectiveness of starting method as starting load variations of reciprocating compressor.

A novel load variation compensation algorithm in a sensor-less brushless DC motor drive for a reciprocating compressor

This paper presents a novel load variation compensation algorithm in a sensor-less BLDC motor drive for a reciprocating compressor. Periodic load variation of a reciprocating compressor leads to commutation position error and instantaneous speed variation and causes large peak currents. The major concept of this study includes tracking the pattern of load torque and controlling the motor input voltage by the commutation point and PWM depending on the tracked load torque. The suggested method can reduce the cost because this method does not require additional current sensing or voltage comparison circuit. The utility of the suggested algorithm was confirmed by simulation and experimental results of a sensor-less BLDC motor drive.

Chronic rhinosinusitis with nasal polyps and without nasal polyps is associated with increased expression of lysophosphatidic acid-related molecules.

Background Chronic sinusitis with nasal polyps (CRSwNPs) or CRS without NPs (CRSsNPs) is associated with expression of various cytokines. Lysophosphatidic acid (LPA) generated by autotaxin (ATX), LPA-producing enzyme, initiates signaling cascade involved in the inflammatory responses and participates in diverse biological processes through LPA receptors, including cytokine production. We analyzed the expression and distribution patterns of LPA-related molecules in nasal secretion and sinus mucosa of normal controls and patients with CRSwNPs and CRSsNPs, to evaluate the possible effects of the ATX–LPA receptor axis on the pathogenesis of CRS. Methods LPA levels in nasal secretion and the expression and distribution patterns of ATX and LPA receptors 1–3 (LPA1–3) in sinus mucosa were investigated using ELISA, real-time polymerase chain reaction, Western blot, and immunohistochemistry. We elucidated the effect of CRS-relevant cytokines on the expression of ATX and LPA receptors, using cultured sinus epithelial cells, and investigated the effect of LPA on the expression of CRS-relevant cytokines, using sinus mucosa explant culture. Results LPA, ATX, and LPA1–3 levels are increased in CRSwNPs and CRSsNPs. ATX and LPA1–3 were localized to superficial epithelium, submucosal glands in normal and inflammatory mucosa, but in inflammatory mucosa, they were found in inflammatory cells. LPA1–3 were noted in endothelium. Sinus mucosa explant stimulated with LPA increasingly produced IL-4, IL-5, interferon gamma, and TNF-alpha, and in cultured epithelial cells stimulated with CRS-relevant cytokines, ATX, and LPA1–3 were differentially induced. Conclusion LPA in human sinus mucosa may play important roles in the pathogenesis of CRS, contributing to produce CRS-related cytokines. LPA-related molecules were increased in CRS, which may attribute to CRS-related cytokines.