Speed Control of Induction Motor by Rotor Position Feedback over an RF Link

Transcription

1 Speed ontrol o Induction Motor by Rotor Position Feedback over an RF Link S.Manoj Sandeep M.Tech Student (PE) NOV ollege o Engineering Jangareddygudem,W.G(Dt),India.Suryanarayana abu HOD o EEE Dept. NOV ollege o Engineering Jangareddygudem,W.G(Dt),India G.Murali Krishna M.Tech Student (PE) NOV ollege o Engineering Jangareddygudem,W.G(Dt),India bstract There are dierent types o speed control o Induction motor. ut all the speed control methods are with wire based position eedback. In this paper, we demonstrate the easibility o controlling the speed o an induction motor using a wireless position eedback over an RF link and compare its perormance under dynamic and steady-state conditions with those obtained using a wire based position-eedback control. Due to this wireless position eed back over an RF link minimizing the eedback noise pickup and cost or some applications. This wireless position eedback has the possibility to uses the low resolution and low cost sensors. which, along with the use o simple estimation algorithms, may potentially provide an alternative to or backup support or conventional position sensor less control or a wide range o motors and speeds. 1. Introduction Speed control o an induction motor usually requires position eedback inormation rom an encoder, a resolver, or a Hall sensor to a controller unit. These eedback signals, which oten pickup noise due to electromagnetic intererence, can aect the perormance o the motor control system. s such, the eedback cable is shielded and the signals are provided in dierential orm, which increases the sensing cost. Thereore, motor-drive manuacturers have been ocusing on position sensor less control. However, universal applicability o the position sensor less algorithms or speed control, especially at or near-zero speed and at ull-load torque, has not been ully achieved yet. In this paper, we outline a technique or implementing a Volts/Hertz (V/F) (i.e., constant lux) induction motor control using real-time wireless eedback o rotor position over an RF transmission link. Today, several commercial and deence applications have addressed health monitoring and RF identiication (RFID) o motors using a wireless link. The proposed scheme can use the same RF channel (via hopping) to transmit the position eedback (typically over a 3-t transmission range). This eliminates the need or a multiwire cable, which can be expensive, especially or harsh and extended operating conditions, and much costlier than a miniaturized RF transmitter. The proposed wireless position sensing scheme can also be extended to other vector control schemes or induction and other motors. onventional position sensor less control schemes require complex estimation algorithms, and have limitations regarding the speed range and applicability. However, such schemes save the cost o an expensive position sensor. So, i a low-cost, low-resolution position sensor is used that transmits inormation over an RF link (thereby precluding the cable cost), then a simple position-estimation algorithm operating along with the lower resolution but discrete-time-interval position updates can be potentially as powerul as the complex position sensor less control (which has no position eedback). ecause the cost o the high-resolution sensor is higher to begin with, the proposed wireless inormation-exchange-based scheme, which can potentially use cheaper low-resolution sensors, can be a more cost-eective approach. However, because wireless transmission over an RF link is susceptible to channel disruptions, it is important to investigate the impact o time delay on the stability and perormance o the overall system, so that controllers can be 1

2 designed to ensure operation within the desired bounds.. 2. Description o the Scheme The proposed system consisting o an induction motor, a pulse width-modulated inverter, and a V/F eedback controller that receives the motor position eedback over a wireless channel. We use requencyshit-keying (FSK) or RF transmission. The squarewave output o the position encoder is irst multiplexed and then ed to an RF transmitter. The RF receiver antenna is tuned to a transmission requency o 9 MHz The receiver demodulates and ampliies the broadcast signal, such that the output o the receiver matches the pattern o the original encoded digital signal. Finally, the demodulated signal is ed to the motor controller. In the absence o channel disruptions, the (position-sensor-to controller or end-to-end) time delay (τd) is negligible, but it increases with deteriorating channel conditions or or reduced data rates. The RF receiver o the controller demodulates the received signal to extract the digitally encoded position eedback (θop). It is then transormed θ which represents the angular resolution o the encoder. The position eedback (θ) is ed to the controller that derives the velocity using ω = dθ/dt, which is Then compared with the velocity reerence. The error between reerence velocity and ω is ed to a proportional integral (PI) controller to obtain the slip, which is then added to ω to obtain the drive requency (ωf). Subsequently, using ωf, a desired voltage reerence magnitude (VF) is generated to maintain a V/F operation o the induction motor. Voltage reerence VF and its instantaneous electrical position (i.e., θe = pθ/2, where p represents the number o motor poles) are ed to a space-vector modulation (SVM) block to obtain the switching signals o the inverter. Fig. 1. Illustration o motor-control system (with internal control reerence) with: (a) wire-based position eedback, (b) position estimation, and (c) wireless position eedback. PS stands or position sensor. 2

3 Fig. 2. (a) lock diagram o the overall system. (b) Wireless transmission scheme or position eedback along with key waveorms at points marked 1 4 and illustration o the end-to-end time delay (τd ). 3. Modelling o Induction Machine 3.1. Modelling o Induction Machine 3

4 Stator urrents (pu) t The steady-state model and equivalent circuit are useul or studying the perormance o machine in steady state. This implies that all electrical transients are neglected during load changes and stator requency variations. Such variations arise in applications involving variable-speed drives. The dynamic model considers the instantaneous eects o varying voltages/currents, stator requency and torque disturbances. The dynamic model o induction motor is derived by using a two-phase motor in direct and quadrature axes. This approach is desirable because o the conceptual simplicity obtained with the two sets o the windings, one on the stator and the other on the rotor. wide variety o rotating machines are polyhase a.c. machines constructed in a dierent manner than the primitive machine. In such cases, the primitive machine can also be employed in the analysis, provided the rotating polyphase winding on the rotor and the stationary polyphase winding on stator. The process o replacing one set o variables by another related set o variables is called winding transormation. The equivalence between the three-phase and two-phase machine models is derived rom the simple observation, and this approach is suitable or extending it to model an n-phase machine by means o a two phase machine. The concept o power invariance is introduced: the power must be equal in the three-phase machine and its equivalent two-phase model. The required transormation in voltages, currents, or lux linkages, is derived in generalized way. The reerence rames are chosen to arbitrary and particular cases such as stationary, rotor, and synchronous reerence rames, are simple instances o the general case. Derivations or electromagnetic torque involving the currents and lux linkages are given. The space-phase model is derived rom the dynamic model in direct and quadrature axes. The space-phasor model powerully evokes the similarity and equivalence between the induction machines and D machines rom the modeling and control points o view. 3.2 D-Q Stationary and Synchronous Reerence Frames s mentioned earlier, there is seldom a need to simulate an induction machine in the arbitrary rotating reerence rame. For power system studies, induction machine analysis about some operating condition, a synchronously rotating reerence rame which speed drives, it is usually more convenient to simulate an induction machine and its converter to a stationary reerence rame. nd or small signal-dynamic stability yields steady values o steady-state voltages and currents under balanced conditions is used. 4. Results and Discussion 4.1 Introduction Speed control o an induction motor usually requires position eedback inormation rom an encoder, a resolver, or a Hall sensor to a controller unit which increases the sensing cost. To overcome this problem RF link is used in place o wire eedback. Speed control with wire eed eedback and with RF link has been stimulated and rotor speed, stator currents are observed 4.2 Simulation with wire eed back Discrete, s = 5e-5 s powergui r Wm W* in out PI Saturation 1/3 Gain2 supply + Supply - v/ lock ommand Voltage v Va Vb Vc Theta Vam Vbm Vcm PWM Voltage Inverter Sine Wave Generator 4v D Supply Three-Phase V-I Measurement Vabc Iabc a b c.142 Tm (N-m) Tm m synchronous Machine <Stator current is_a ()> <Stator current is_b ()> <Stator current Mux7 is_c ()> <Rotor speed (wm)> -Krpm <Rotor angle thetam (rad)> Figure 4.1 Induction Motor ontrol with Wire Feed ack x 1 5 Figure 4.2 Stator urrents with Wire Feed ack Is() speed 4

5 Stator urrents (pu) Rotor Speed (rpm) t Rotor Speed (rpm) x 1 5 Figure 4.3 Rotor Speed with Wire Feed ack x 1 5 Figure 4.6 Rotor Speed with RF Link Feed ack The graphical diagrams ig 4.2 and ig 4.3 illustrates the stator currents and rotor speed obtained by simulating the speed o induction motor with wire eedback. The rotor speed is limited to 5 rpm. 4.2 Simulation with RF eed back The graphical ig 4.5 and ig 4.6 illustrates the stator currents and rotor speed obtained by simulating the speed o induction motor using RF link. The graphs obtained are similar to that o wire eedback. y this we can conclude that instead o electric link, we can use RF link or speed control o induction motor. Discrete, s = 5e-5 s powergui 4v D Supply 5. onclusion r Figure 4.4 Induction Motor ontrol with RF Link Feed ack Wm W* in out PI Saturation 1/3 Gain2 supply + Supply - v/ lock PWM Voltage Inverter ommand Voltage v Va Vb Vc Theta Vam Vbm Vcm Sine Wave Generator du/dt Derivative Three-Phase V-I Measurement Vabc Iabc a b c.142 Tm (N-m) Tm -Krpm <Rotor speed (wm)> synchronous Machine Out1In1 r link m <Stator current is_a ()> <Stator current is_b ()> <Stator current Mux7 is_c ()> <Rotor angle thetam (rad)> Is() speed y simulation results we can conclude that we can use RF link eedback instead o wire eedback to control the speed o induction motor. The advantages o using RF link eedback are as ollows: This eliminates the need or multi wire cable. The proposed scheme can be extended to other vector control schemes. Speed control o the motor especially at or near-zero speed and at ull-load torque can be achieved. Perormance o the motor can be improved 6. Reerences x 1 5 Figure 4.5 Stator urrents with RF Link Feed ack [1] W. Leonhard, ontrol o Electrical Drives. New York: Springer-Verlag,1996. [2] P. Vas, Sensorless Vector and Direct Torque ontrol. London, U.K.: Oxord Univ. Press, [3] K. Rajashekara,. Kawamura, and K. Matsuse, Sensorless ontrol o Motor Drives: Speed and Position Sensorless Operation. Piscataway, NJ: IEEE Press, [4] Digital control system group, I3 1 system documentation Variable speed control o 3-phase induction motor, Texas Instrument, Villeneuve-Loubet edex, France, Project Rep., Sep. 2. [5]. Lu, T. G. Habetler, R. G. Harley, and J.. Gutirrez, On the application o wireless sensors networks in condition monitoring and energy usage 5

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