Contributions Concerning the Command of the Brushless D.C. Servomotor

Transcription

1 Proceedings of the th WSEAS International Conference on SYSTEMS, Vouliagmeni, Athens, Greece, July -, (pp-) Contributions Concerning the Command of the Brushless D.C. Servomotor GHEORGHE BALUTA and NIKOLAOS PAPACHATZIS Department of Power Electronics and Electrical Drives, Department of Electrical Power Technical University Gh. Asachi of Iasi, Municipality of Larissa Blvd. D. Mangeron, No. 5-5, Iasi-75 ROMANIA, GREECE Abstract: - The authors present in this paper a reversible Brushless D.C. drive system employing a -phase Hfull bridge converter realized with complementary Darlington transistors. The servomotor is with three delta connected windings. The servomotor has the rotor position transducer composed of three Hall sensors located at the periphery of the stator and geometrically spaced at the. Key-Words: - Brushless D.C. Servomotor, -Phase H-Full Bridge Converter and Speed Adjustment. Introduction The Brushless D.C. Servomotor (BDCS) uses a reversed construction: the induced winding is located on stator and it is similar to a poly-phased induction machine, the most efficient case is threephase delta connected. The rotor is made up of a multi-polar cylindrical permanent magnet [], [], []. The block diagram of the drive system of a BDCS is shown in Fig.. D.C. POWER SUPPLY P (n) V PULSE GENERATOR T=ct. PWM SENSE START/STOP DIGITAL BLOCK (T,..., T) (T,..., T) C S O T N A V TI ER C T E R (,, ) BDCS BRUSHLESS D.C. SERVOMOTOR LOAD CCW CW RPT (TP, TP, TP) Fig.. Block diagram of the drive system of a BDCS. BDCS must be provided with a RPT device (Rotor Position Transducer) to detect the rotor position and command the static switching devices by adequate signals. Nowadays, the three-winding BDCS tipically has the rotor position transducer made up of three Hall sensors located at the periphery of the stator and geometrically spaced at the el. The TTL logical signals TP, TP and TP supplied by Hall sensors, depending on the rotor position and sense of rotation, are shown in Fig.. COUNTERCLOCK-WISE CLOCK-WISE TP TP TP Fig.. Signals supplied by Hall sensors.

2 Proceedings of the th WSEAS International Conference on SYSTEMS, Vouliagmeni, Athens, Greece, July -, (pp-) Bipolar Command A move efficient command scheme is shown in Fig., corresponding to the bipolar command of a BDCS with -stator windings star or delta connected. In such case, the copper of the windings is used in a proportion of % [], []. T D T D T T T T T D R S U S=R S. I D D i a. Windings star connected. T T T T R S D T U S=R S. I D D i i b. Windings delta connected. Fig.. Bipolar command of the BDCS. i The three statoric phase windings are supplied by a three-phase H-full bridge converter made up of six bipolar transistors. Two transistors are permenently switching-on: a T transistor in the upper part of the converter and T in the lower part [4], [5]. The transistors are switched-on for / of the command period ( el.): -T is switching-on for el. together with and and T is on another el.; -T is switching-on for el. together with T is on another el.; -T is switching-on for el. together with T T T T and is on another el. The supply voltage U is permanently applied on one winding and on the other two series connected windings in case of delta connection (see Fig. 4) and on two series connected windings in case of star connection (see Fig. 5). The electronic scheme of the digital command block of the static converter is shown in Fig.. The signals supplied to the position transducer are shaped by means of the Trigger-Schmitt structure comparators I and I, then are connected to the inputs of the BCD-to-decimal decoder I []. The command of the converter transistors is ached depending on the actual position of the rotor and rotation sense (see Table ). The following logical expressions for the digital block outputs are yielded: T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON 4 (COUNTERCLOCK-WISE) (CLOCK-WISE) 4 / E m i e B e A e C i Fig. 4. Bipolar supply in case of delta connection.

3 Proceedings of the th WSEAS International Conference on SYSTEMS, Vouliagmeni, Athens, Greece, July -, (pp-) T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON T=ON (COUNTERCLOCK-WISE) (CLOCK-WISE) i / e A E m e B i e C Fig. 5. Bipolar supply in case of star connection. V TP R R IA LM9 R V _ V- C C R4 R5 D TP IA 744 D C B A I 744 D D V C GND R SENSE K R7 CW CCW IA IA A E R8 R9 C4 V GND WA I7A 74 I7B 74 COM-T I9A 7457 ID 744 START/STOP K R OVERLOAD R5 STOP START R R I7C 74 I7D 74 R V TP R V TP R8 R4 R4 V REF R9 IB LM9 IC LM9 C7 R5 _ R5 _ C8 R R R7 D TP IB 744 R7 D7 TP IC R P (SPEED) R C9 D9 C DESC I4A 74 I4B 74 I4C 74 I4D 74 I5A 74 I5B 74 V I LM555 CV C IB IB IC IC ID ID A A A C V GND IA WA IA IA A E 7457 IB IB A WB WC WD WB COM-T I9B 7457 COM-T I9C 7457 I9D 7457 IB 7457 I8A 74 R8 R I5C 74 IA 74 IC 74 NO BRAKE K YES R9 _ ID LM9 R C5 URs I5D 74 COM-T S (I ) LIM IB 74 COM-T ID 74 COM-T D8 PS PJ OUT C T=ct. C GND R Fig.. Electronic scheme of the digital command block.

4 Proceedings of the th WSEAS International Conference on SYSTEMS, Vouliagmeni, Athens, Greece, July -, (pp-) SENSE S TP TP C B Table. The command of the converter transistors. TP A DECODER OUTPUTS 4 7 CONVERTER TRANSISTORS T T T T T T COM COM COM COM COM COM = (4 ) S U ( ) S = ( ) S U ( 7) S = ( 7) S U (4 ) S = ( ) S U ( 7) S = ( 7) S U ( 4) S = ( 4) S U ( ) S () The commands of the static converter transistors are for the counterclock-wise (CCW) direction or clock-wise (CW) direction of the drive, they are selected by means of six two-input data multiplexer I 9 and I (7457). The sense of rotation (address input A ) is established by means of the twoposition switch K. The PWM signal needed to the speed adjustment with frequency of 5KHz and duty cycle adjustable with the P multi-tour potentiometer within the range [5 95]%, comes from a multivibrator achieved with the LM555 timer (I ) and interferes in the command of the lower part T, T, T transistors of the static converter. The electronic scheme of the static converter is shown in Fig. 7. Complementary standard Darlington configurations of BD8A (T, T, T ) and BD8A ( T, T, T ) type, respectively, have been used [5]. With the 747 buffer with opencollector output provided at the input, the current required for the command of the converter transistors is ensured. The proper operation of the converter is also ensured by the ultra-fast diodes D D of SK9F (SEMIKRON) type (V F =.5V; I F =A; t rr 8ns). U=V C C R R5 R8 COM-T IA 747 R D7 D8 R T4 T D COM-T IB 747 R4 D9 D R T5 T D COM-T IC 747 R7 D D R9 T T D R R D D COM-T COM-T ID T IE T COM-T IF 747 D7 R D8 T D i U S=R S. I R S BRUSHLESS D.C. SERVOMOTOR (BDCS) i Fig. 7. Electronic scheme of the static converter.

5 Proceedings of the th WSEAS International Conference on SYSTEMS, Vouliagmeni, Athens, Greece, July -, (pp-) The BDCS (made in Germany) has the following nominal parameters []: -permanent magnet rotor with four pole-pair, rated power P N =W; -rated phase voltage U N =V; -rated speed n N = rev./min.; -maximum speed n max =84 rev./min.; -rated torque T N = - N m. The BDCS is loaded using a separately-excited D.C. machine with permanent magnet, which operates in a braking mode: -rated voltage V CC ; -rated current.5a; -rated speed 5 rev./min. By means a two-position switch a reduced loading system or an overload system could be imposed. Experimental Results As experimental results, are presented the oscillograms for []: -Hall sensors signals (counterclock-wise direction Fig. 8 and clock-wise direction Fig. 9); - and phase voltages (Fig. ); -Command signals for transistors T and (Fig. ). T a. TP (Ch.) and TP (Ch.). b. TP (Ch.) and TP (Ch.). Fig. 8. Hall sensors signal for counterclock-wise direction. a. TP (Ch.) şi TP (Ch.). b. TP (Ch.) şi TP (Ch.). Fig. 9. Hall sensors signal for clock-wise direction. 4 Conclusions The brushless D.C. servomotor (BDCS) present the following advantages as compared the conventional D.C. servomotor [], []: -BDCS can be used in polluted environments; -very noiseless servomotors can be built, with high service reliance, not needing surveillance or maintenance, operating with higher efficiency as compared to the conventional D.C. servomotors of equivalent nominal data;

6 Proceedings of the th WSEAS International Conference on SYSTEMS, Vouliagmeni, Athens, Greece, July -, (pp-) -BDCS itself has the overall dimensions, weight per kilowatt and copper consumption lower as the commutator, brush holder ring, auxiliary poles and compensation winding are eliminated; -servomotors of very high speed can be produced, even over rev./min., which is not possible with commutator because of mechanical and electric over-stresses; -as the commutator is missing motors of reduced rotor inertia are produced, therefore with lower electromechanical time constant than for similar conventional D.C. servomotors. a. u (Ch.) and u (Ch.), reduced loading. b. u (Ch.) şi u (Ch.), rated loading. Fig.. and phase voltages. a. T (Ch.), T (Ch.), reduced loading. b. T (Ch.), (Ch.), rated loading. Fig.. Command signals for T and T T transistors. References: [] Kuo B.C., Kelemen A., Crivii M., Trifa V., The Incremental Motion Control Systems (in Romanian), Editura Tehnica, Bucuresti, 98. [] Kenjo T., Nagamori S., Permanent-Magnet and Brushless DC Motors, Clarendon Press, Oxford, 985. [] Kenjo T., Electric Motors and their Controls, Oxford University Press, Oxford, 99. [4] Guyenot P., Hans T., Régulation et asservissement, Eyrolles, Paris, 99. [5] Hans T., Asservissements numérique, Eyrolles, Paris, 99.

7 Proceedings of the th WSEAS International Conference on SYSTEMS, Vouliagmeni, Athens, Greece, July -, (pp-) [] Băluţă Gh., Low Power Electrical Drives. Applications (in Romanian), Editura Politehnium, Iaşi, 4.