The 30th Annual Conference of the IEEE Industrial Electronics Society, November 2
-
6, 2004, Busan, Korea
Sensorless Direct Power and Torque Control of PWM Back-To-Back Converter-Fed Induction Motor M. Jasinski I Student, IEEE, M.P. Kazmierkowski, Fellow, IEEE ,
1,2Institute of Control & Industrial Electronics, Warsaw University of Technology, Warsaw, Poland, e-rnail :
mja@isep,pw,edu.pl,
[email protected]
Absttllct-
A
novel
fectifier-invertef system
control
scheme
fOf
PWM
is PfOPOSed. Fast contfol strategies
such as line voltage Sensorless VirtuaJ Flux (VF) based Direct Power Control with Space Vectof Modulatof (DPC-SVM) fOf PWM rectifier and Direct Torque Control with Space VectOf Modulator (DTC-SVM) for PWM inverter side afe used. These strategies lead to good dynamic and static behaviofS of the proposed conn-ol system - Difect Power and Torque Control Space
Vector
Modulated
(DPT-SVM).
Simulations
and
experiment results obtained show good performances of the proposed system. Additional power feedforward loop from a motof to PWM rectinef control side improved
dynamic
behaviofS of the powef now control As a result, better
input-output energy matching aJlows decreasing the size of the dc-link capacitor.
I. INTRODUCTION The adjustable speed drives (ASD) with diode rectifier nowadays is the most popular on the marked. Large electrolytic capacitor is used as an energy-storing device to decouple rectifier and the inverter circuits. The capacitors have some drawbacks: low reliability, big size, weight and cost. Hence, reliability of the dc-link capacitor is the major factor limiting the lifetime of the ASD systems [1]. Development of control methods for Pulse Width Modulated ( PWM) boost rectifier ( active rectifier) was possible thanks to advances in power semiconductors devices andDigital Signal Processors (DSP). Therefore, the Insulated Gate Bipolar Transistors (lGBT) ACIDC/AC (back-to-back) converter controlled by PWM is used in motor drive systems (Fig. 1). Thanks to active rectifier the dc-link capacitor can be reduced [2). Fartber reduction of the capacitor can be achieved by power feedforward loop from motor side to the control ofthe PWM rectifier. A lot of works are given attention to reduce the dc-link capacitor. However, a small capacitance leads to a high dc-voltage fluctuation. To avoid this drawback various dc-voltage control schemes have been proposed. Some of them take into account the inverter dynamics to improve the PWM rectifier current control by feedback linearization [3J and master-slave [1] manner. Another control methodology proposed a fast dc-link voltage controller which works with dc-voltage and motor variables as inputs [4]. Moreover, various methods of the output power estimation have been discussed in [5]. In the mentioned methods active and reactive powers of the PWM rectifier are indirectly controlled via current control loops. Besides, stator current controllers control the
0-7803-8730-9/04/$20.00 ©2004 IEEE
torque and flux of the motor too. In this paper a line voltage sensorless Virtual Flux (VF) based Direct Power Control with Space Vector Modulator (DPC-SVM) is applied to control of the PWM rectifier. The inverter with induction motor is controlled via Direct Torque Control with Space Vector Modulator (DTC-SVM). Contrary to the scheme presented in [6], this solution works not in cascade but in parallel manner. Hence, a back-to-back converter of Fig.l, is controlled by Sensorless Direct Power and Torque Control-Space Vector Modulated (DPT-SVM) scheme. In comparison to methods that control an active and reactive power, torque and flux in indirect manner the coordinates transformation and decoupling are not required. Moreover, the current control loops are avoided. In respect of dynamic, of dc-voltage control the power balance between line and motor is very important. Therefore, to improve instantaneous input/output power matching, the additional feedforward power control loop is introduced. Thanks to better control of the power flow the fluctuation of the dc-link voltages will be decrease. So the size of the dc-link capacitor can be reduced. 11_ DIRECT POWER AND TORQUE CONTROL SPACE VECTOR MODULATED (DPT-SVM) SCHEME
Direct Power Control (DPC) for PWM rectifier is based on instantaneous control of active p and reactive q power flow from/to the line and to/from active load. In classical approach [7], I8] ofDPC there are two power control loops with hysteresis comparators and switching table. .0)
line
(Virtual MOI01')
Fig. 1. Representation oftbree-phase back-to-backoonverter; vector diagram and coordinate system for: a) PWM rectifier side b) PWM inverter side.
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Therefore, the key point of the DPC implementation is sufficiently precise and fast estimation of the instantaneous line
powers.
The
most significant
of
drawbacks
the
hysteresis.based DPC are variable Switching and high sampling frequency. Introducing a Space Vector Modulator
(SYM) in control strategy [9,10] allows to eliminate the both mentioned problems. Moreover, the line voltage sensors can
be replaced by Virtual Flux (VF) estimator, which introduces and
economical
(simplification,
technical
reliability,
advantages galvanic
to
the
system
isolation,
cost
reduction). Such control system is called: Virtual Flux Based Direct Power Control Space Vector Modulated (DPC·SVM) scheme
[11].
Summarized,
in
this
method
linear
PWM R1ol�� "Lo
Ullc\lv--:
. .. ..
y. .. ..••� "':.r::r._IJ_���
(a, b) with diode rectifier, (c,d) back-ta-back converter. Udc- dc·link voltage 100 V/div, p- active power at the input oflbe converter, Is- stator current, n.",. mechanical speed, M,- electromagnetic torque. Fig. 7. Transients to commanded torque changes (.0.25 to 0.25 MN). ACIDC/AC
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