Anno Yoo

Novel Speed and Rotor Position Estimation Strategy Using a Dual Observer for Low-Resolution Position Sensors

Recently, high-performance AC motor drive technologies, including field-oriented control (FOC), have been widely used in home appliance products such as direct-drive drum washing machines. In low-cost AC machine drive systems, speed or position sensors with high resolution are not available due to high costs. Instead, a low-resolution sensor is installed to calculate the speed and rotor position. In the FOC, however, accurate rotor angle information is essential for high performance. In addition to the low resolution of the sensor, its accuracy is poor due to mechanical errors and signal processing. The inaccurate and delayed position information degrades the performance of current regulation and also increases torque ripples, which is the source of mechanical vibration and acoustic noise. In order to overcome this hardware problem, this study proposes a software technique based on a novel dual observer and a position sensor offset compensation strategy. The dual observer can estimate the rotor speed and position without time delay or bumps. Also, with the compensation algorithm for position sensor offset, the misaligned synchronous reference frame d- and q-axis can be corrected. Experimental results verify the effectiveness of the proposed method.

Design of Flux Observer Robust to Interior Permanent-Magnet Synchronous Motor Flux Variation

This paper presents a modified flux observer which is robust to the variation of the permanent-magnet flux linkage of an interior permanent-magnet synchronous motor (IPMSM). The IPMSM is driven by a current-regulated inverter, where the d-q axis currents are controlled by two proportional and integral controllers with feedforward cross-coupling decoupling terms. The integrator outputs of the current regulator reflecting flux errors are used to compensate the flux variation according to the operating temperature and manufacturing tolerance. The proposed flux observer shows satisfactory performance not only in maximum torque per ampere operating region but also in flux weakening region. The experimental results reveal the effectiveness of the proposed observer.

Flux-Weakening Strategy of an Induction Machine Driven by an Electrolytic-Capacitor-Less Inverter

This paper presents a novel flux weakening strategy of an induction machine driven by an electrolytic capacitor-less inverter. In the electrolytic capacitor-less inverter, the DC-link voltage is fluctuating at six times of frequency of input three phase source due to its small DC-link capacitance. Hence, the decoupling of the fluctuation and maximum utilization of the DC-link voltage is the major issue in the electrolytic capacitor-less inverter. In this paper, the cost function is set to increase the voltage utilization of the inverter for the flux weakening operation of an induction machine. By the proposed cost function and flux weakening strategy, the operating speed of the induction machine is extended above base speed without any stability problem. The experimental results show the effectiveness of proposed strategy.

A New Universal Isolated Converter for Grid Connection

This paper proposes an isolated universal-link ac-ac power converter suitable for grid connection. The proposed power converter can have multiple ports to connect various loads or electric energy sources, and the configuration can be arranged according to the situation. The proposed power converter does not need to employ the large interface inductor at input side and the huge electrolytic capacitor at dc link. Moreover, it utilizes high-frequency transformers for the galvanic isolation instead of bulky line-frequency transformers. These characteristics of the proposed power converter result in the reduction of the system volume and weight remarkably. The proposed power converter is the modular structure, and an H-bridge works as a basic module of the converter. By stacking the modules, the power converter can be adapted to the high-voltage grid and the various types of loads and/or sources. This paper addresses the structure of the proposed power converter and the fundamental principle of power flow. The operation of the proposed converter is verified by both computer simulations and experimental results with a laboratory-level prototype system.

Design of a Current Regulator with Extended Bandwidth for Servo Motor Drive

To increase the productivity of the manufacturing process, the high bandwidth of the current regulation should be achieved. The bandwidth of the current regulator is dependent on the switching frequency and digital delay. The limited switching frequency is inevitable to reduce the switching loss due to excessive switching frequency. Also, the digital delay is inherent problem where the Digital Signal Processor (microcontroller) and PWM are used. This paper proposes the novel current regulation strategy to enhance the performance of the current regulation by reducing the digital delay which is the sum of the execution time and PWM delay and modifying the voltage reference. The proposed strategy is robust to the parameter and reference variation. Experimental results are shown to verify the effectiveness of the proposed method.

Dual Observers for the Disturbance Rejection of a Motion Control System

The conventional motion control system simply consists of a PID position controller and a disturbance observer. The estimated speed from the observer has been used to control the speed as a feedback and the estimated disturbance force, which is a byproduct of the observer, has been used to reject the disturbance. However, in this case the disturbance rejection performance should be traded off with speed estimation performance. This paper explains this trade-off using Bode analysis and presents a dual observer system for the motion control application. The proposed method uses two observers, where one is dedicated to the speed estimation and the other to disturbance compensation. The disturbance rejection performance is enhanced by the custom tuned disturbance observer in the proposed method. The feasibility of the proposed method has been verified by the experimental results using a high precision linear motion control system as well as by the analysis based on Bode plot.

Input filter analysis and resonance suppression control for electrolytic capacitor-less inverter

This paper presents an analysis on electrolytic capacitor-less inverter and proposes a strategy for resonance suppression control for a DC-link voltage and input current in electrolytic capacitor-less inverter. The proposed electrolytic capacitor-less inverter can operate both in the motoring mode and regenerating mode owing to its inherent bidirectional power flow capability of the active front-end rectifier whose switching frequency is equal to the input line frequency. However, in the electrolytic capacitor-less inverter, the DC-link voltage is fluctuating with six times of the frequency of input three phase source due to its small DC link capacitance. Also, an input filter should be employed to remove the high frequency component generated by PWM inverter. By the input filter, the DC-link voltage can be resonant, and a specific resonance suppression control is required when the input line-to-line voltage is low and the demanded power is large. In this paper, a novel resonance suppression strategy is proposed for a stable operation of the electrolytic capacitor-less inverter. The experimental results show the effectiveness of proposed strategy.

Novel speed and rotor position estimation strategy using a dual observer for low resolution position sensors

Recently, high performance AC motor drive technologies including a field oriented control (FOC) are widely used in home appliance products such as a direct- drive drum washing machine. In home appliance, speed or position sensors with high resolution are prohibitive due to the cost problems. Usually, a low resolution sensor is installed to calculate the speed and rotor position. In the FOC, however, accurate rotor angle information is essential for high performance torque control. On top of the low resolution of the sensor, the accuracy of the sensor is poor due to mechanical errors of sensor itself and installation. The inaccurate and delayed position information degrades the performance of current regulation and also increases torque ripples, which is the source of vibration and acoustic noise. In order to overcome the hardware problems, this paper proposes a software technique using a novel dual observer and position sensor offset compensation strategy. The dual observer can estimate the rotor speed and position without any time delay and bumps with the compensation algorithm for the position sensor offset by adjusting the misaligned synchronous reference frame d and q-axis. Experimental results verify the effectiveness of the proposed method.

An AC/DC power conversion based on Series-connected Universal Link converter

This paper presents a novel AC/DC power converter topology for the future energy conversion network. The proposed Series-connected Universal Link (SUL) converter transfers the power via the high frequency transformers and single phase full bridge converters. The shape of input AC source current is sinusoidal without PWM switching of the input side converter. Thanks to the reduced reactive components and high frequency transformer, the proposed converter can increase the power density and the efficiency significantly. It is expected that the SUL converter can be easily adapted to various renewable energy sources and energy storage system. Experimental results with prototype show the effectiveness of the proposed power converter topology.

Design of Flux Observer Robust to Parameter Variation of Interior Permanent Magnet Synchronous Motor

This paper presents a modified flux observer which is robust to the parameter variation. In this paper, the mathematical modeling of an interior permanent magnet synchronous motor (IPMSM) is shown and the proportional and integral (PI) current regulator with decoupling strategy is analyzed. The flux error terms from the current regulator are used to compensate the parameter variation. The proposed flux observer shows satisfactory performance not only in maximum torque per ampere (MTPA) region, but also in flux weakening region. The experimental results reveal the effectiveness of the proposed observer.