IEEE Industry Applications Society Annual Meeting Chicago, September 30-October 4, 2001 Implementation Issues Affecting the Performance of Carrier Signal Injection Based Sensorless Controlled AC Drives Fernando Briz, Michael W. Degner†, Juan M. Guerrero, Antonio Zamarrón††, Robert D. Lorenz‡ University of Oviedo Dept. of Elec., Computer & Systems Engineering Campus de Viesques, 2.1.07 Gijón, 33204, Spain T: 34 985-182289 F: 34-985-182068 E: fernando@isa.uniovi.es † Ford Motor Company Ford Research Laboratory 2101 Village Road P.O. Box 2053, MD 1170 Dearborn, MI 48121-2053 T: 313-322-6499 F: 313-323-8239 E: mdegner@ford.com ††Instituto Tecnológico de León Av. Tecnológico 37000, León, México ‡ University of Wisconsin-Madison Dept’s of ME & ECE 1513 University Ave. Madison, WI 53706 T: 608-262-5343 F: 608-265-2316 E: lorenz@engr.wisc.edu Abstract - This paper assesses and analyzes the practical implementation issues affecting the performance of carrier signal injection based sensorless control methods for AC drives. Included in this assessment and analysis are the following topics: selection of the carrier signal frequency and magnitude; the non- linear behavior of pulse-width modulation and power electronics; and the signal processing required for the estimation, including analog filtering, sampling, and analog-to- digital conversion. Variations in the characteristics and behavior of the saliency used for the estimation as a function of the machine's design and operating point are also addressed. The influence that each of these topics has on the robustness and accuracy of the estimate is discussed. Finally, conclusions are drawn on how the negative effects can be minimized and the performance of the estimation improved. I. INTRODUCTION Sensorless operation of AC drives is well established in applications where low speed operation is not required. The techniques developed for use in the medium to high speed range fail in applications needing true zero speed, zero frequency torque (and often also motion) control, including automotive, aerospace and industrial applications. The use of a carrier signal superimposed on the fundamental excitation to track spatial saliency images has received increasing attention recently as a viable means to provide high performance, low or zero speed, sensorless control of AC drives [1-12]. When a rotor position or saturation dependent variation in the stator transient inductance exists, its shape can be tracked by injecting a high frequency carrier signal voltage as shown in Fig. 1, [1,2]. The carrier signal current resulting from the injected voltage consists of a positive sequence component that contains no spatial information and a negative sequence component that contains the desired spatial saliency position information in its phase. Obtaining an accurate measurement of the saliency position from the negative sequence carrier signal current depends on several disciplines, including: machine design and modeling; analog and digital signal processing; sensors and power electronics. The use of machine design to affect the performance of carrier signal based sensorless control has been restricted so far to introducing relatively minor modifications in standard induction machine designs to create a rotor position dependent saliency. The design of new machines specifically for sensorless applications is expected to be an intensively explored field in the coming years. On the other hand, the modeling of existing machines, and specifically the modeling of saturation-induced saliencies, has received a lot of attention, although no satisfactory universal solution to this problem has been obtained [4-7,12]. The digital signal processing algorithms used to extract the spatial information from the negative sequence carrier signal current is a relatively developed field [1,6,7,9,11]. Modern DSP’s allow the implementation of such algorithms in real time with the short sampling periods necessary to obtain high bandwidth estimates. Less attention has been paid to the role played by the sensors, analog signal processing, and power electronics. Sensorless control algorithms have become sufficiently developed that a more detailed analysis is required to assess the influence of these issues on the overall accuracy of the estimation. In carrier signal injection based sensorless methods, the carrier signal is injected by superimposing it on the fundamental excitation, sharing the same power stage, current sensors, analog filters and analog to digital converters. The fundamental excitation that produces the electromagnetic torque is usually several orders of magnitude larger than the negative sequence carrier signal containing the desired spatial information. Techniques commonly used for the sensing and processing of the fundamental current, like synchronous sampling or antialiasing filters, can be inadequate when used to process the negative sequence carrier signal current. current regulator Three-phase drive (PWM) motor - + θr, ϖr Digital filtering high frequency carrier i qds_f s * v qds_c s * v qds_f s * v qds s * v qds s i qds s i qds_cn s i qds_f s A/D conversion Analog filtering Fig. 1. Injection of the carrier signal voltage