Motor current reconstruction via DC bus current measurement

Abstract

A technique for reconstructing phase currents based on measurements of a DC bus current. Non-observable regions of DC bus current samples to reconstruct phase currents are reduced in size by using two phase space vector modulation. The non-observable regions can be further reduced by omitting deadtime insertions for switch actuations when output current is higher than a given threshold. Voltage command vectors in non-observable areas can be formed by two additive vectors of differing phase and magnitude to obtain an observable DC bus current reflecting phase current. The additive vectors have the same combined time average value as that of the voltage command vector.

Description

RELATED APPLICATION [0001] The application is based on and claims benefit of U.S. Provisional Application No. 60 / 368,860, filed on Mar. 28, 2002, entitled Motor Current Reconstruction Via DC Bus Current Measurement, to which a claim of priority is hereby made.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates generally to motor current feedback measurements, and relates more specifically to a computational reconstruction of motor current obtained through measurement of a DC bus current. [0004] 2. Description of Related Art [0005] Inverters for three phase motor drives are well known in the industry. Typically, a DC bus supplies switched power to different phases of an AC motor. A design approach used to supply switching commands and sequences to the inverter involves the use of space vector modulation. For example, a switch vector plane is illustrated in FIG. 1 with specific switch states noted at the vertices of the hexagon. [0006] Wit...

AI Technical Summary

Benefits of technology

This approach effectively reduces the non-observable domain, enabling more accurate motor current reconstruction and reducing the controller execution cycle by half, thereby improving motor drive performance.

Problems solved by technology

However, it is often difficult to accurately measure motor phase current over wide current and temperature ranges.

For example, Hall effect sensors can be used, but are inherently bulky and costly.

However, if a basic vector is used only for a very short period of time, motor phase current cannot be directly determined from the DC bus current.

This lack of observability of motor phase current is due to practical considerations in the implementation of the PWM inverter drive system.

For example, time delays caused by A / D converter sample and hold times, slewing of voltage during turn on, and other delay factors prevent the effects of basic vectors used for a very short time from being observed.

Without being able to observe motor phase currents during these control periods, it is difficult to achieve a robust and high performance motor drive.

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