IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 47, NO. 3, MAY/JUNE 2011 1361
High-Bandwidth Sensorless Algorithm for AC
Machines Based on Square-Wave-Type
Voltage Injection
Young-Doo Yoon, Member, IEEE, Seung-Ki Sul, Fellow, IEEE, Shinya Morimoto, and Kozo Ide, Member, IEEE
Abstract—This paper describes a new control algorithm which
can enhance the dynamics of a sensorless control system and
gives a precise sensorless control performance. Instead of the
conventional sinusoidal-type voltage injection, a square-wave-type
voltage injection incorporated with the associated signal process-
ing method is proposed in this paper. As a result, the error signal
can be calculated without low-pass filters and time delays, and
the position estimation performance can be enhanced. Using the
proposed method, the performance of the sensorless control can be
enhanced; the bandwidth of the current controller was enhanced
up to 250 Hz, and that of the speed controller was up to 50 Hz.
Index Terms—AC machines, induction machine, sensorless con-
trol, signal injection, square-wave voltage, synchronous machine.
I. INTRODUCTION
S
ENSORLESS drives of ac motors are adopted in many ap-
plications from industrial applications to home appliances.
Recently, electric vehicle applications have also been reported
[1]–[3]. The advantages of sensorless drives are not only the
reduction in the cost and size but also the improvement of
the reliability by eliminating the position sensor and related
cable connections. To achieve the advantages, many sensorless
techniques for estimating rotor position and speed have been
reported. These techniques are classified into two categories:
techniques based on back electromotive force (EMF) [4]–[7]
and techniques based on saliency in the spatial impedance of
the motor [8]–[16].
The former uses voltage models [4], [5] and/or observers
[6], [7] in the synchronous or stationary reference d–q frame.
It presents good results in the middle- and high-speed regions.
Since the amplitude of back EMF is proportional to the rotor
speed, it cannot keep the performance in the low-speed region,
Manuscript received June 7, 2010; revised November 9, 2010; accepted
December 15, 2010. Date of publication March 14, 2011; date of current
version May 18, 2011. Paper 2010-IDC-229.R1, presented at the 2009 IEEE
Energy Conversion Congress and Exposition, San Jose, CA September 20–24,
and approved for publication in the IEEE T
RANSACTIONS ON INDUSTRY
APPLICATIONS by the Industrial Drives Committee of the IEEE Industry
Applications Society.
Y.-D. Yoon is with Samsung Electronics, Suwon 443-742, Korea (e-mail:
youngdoo.yoon@gmail.com).
S.-K. Sul is with Seoul National University, Seoul 151-741, Korea
(e-mail: sulsk@plaza.snu.ac.kr).
S. Morimoto and K. Ide are with Yaskawa Electric Company, Kitakyushu
803-8530, Japan (e-mail: sinya@yaskawa.co.jp; kozo@yaskawa.co.jp).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TIA.2011.2126552
including zero speed and/or frequency, where the back EMF
disappears. The latter are exploiting the magnetic saliency.
Some algorithms inject test voltage signals in a sampling pe-
riod to estimate the rotor position [8], [9]. Since they detect
inductance difference using voltage signals in a short time,
they can be frail to parameter variation or measurement noises.
Other algorithms inject rotating high-frequency voltages and
use a tracking algorithm [10], [11]. The other algorithms inject
pulsating high-frequency voltages [12]–[16]. These rotating
and pulsating high-frequency voltage injection methods were
proposed for zero and/or low-frequency operation. These meth-
ods can be applied to general ac machines. They give reasonable
torque control capability at zero and/or low frequency, even
under heavily loaded conditions.
Based on such progresses, sensorless algorithms are adopted
in general-purpose inverters to drive interior permanent magnet
(IPM) motors. However, the performance of the conventional
sensorless control methods is still insufficient for some appli-
cations. The bandwidth of a speed controller is limited up to a
few hertz. Therefore, in some areas, a position sensor is used
in normal operations due to the limitation of the performance
of the sensorless control, and sensorless algorithms are just
utilized as the backup system for emergency when the position
sensor fails.
In this paper, a new algorithm of sensorless control for ac
servo applications is proposed to enhance the performance of
sensorless drive. Considering zero- and low-speed operations,
this paper focuses on voltage injection methods. Moreover,
the method based on back-EMF voltage is not considered.
However, the proposed method can be combined with the
method based on back-EMF voltage in middle- and high-speed
operations just like other previous methods [1], [16].
When high-frequency injection methods with conventional
manners (sinusoidal voltage injection) are used, low-pass filters
(LPFs) should be used to get an error signal. However, these
LPFs degrade sensorless control performances because of the
inherent time delay of LPFs. To enhance the performance,
the delay should be minimized. The proposed method relies
on higher frequency square-wave-type voltage injection. As
a result, the error signal can be calculated without any LPF,
and that means no time delay. Hence, the position estimation
performance can be enhanced. As a consequence, bandwidths
of current, speed, and position controllers can be increased very
much compared to those by the conventional sinusoidal-type
voltage injection method.
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