120-degree conducting control of permanent magnetic synchronous motor Algorithm

Transcription

1 APPLICATIO OTE 120-degree conducting control of peranent agnetic synchronous otor Algorith uary R01A2657EJ0120 Rev.1.20 This application note ais at explaining 120-degree conducting control of peranent agnetic synchronous otors used for saple progras of Renesas Electronics Corporation s icrocontrollers. Operation checking device Contents 1. Overview degree conducting control Position detection/speed calculation at 120-degree conducting control... 3 R01A2657EJ0120 Rev.1.20 Page 1 of 13

2 120-degree conducting control of peranent agnetic synchronous otor Algorith 1. Overview This application note ais at explaining 120-degree conducting control of peranent agnetic synchronous otors (hereinafter called PMMs) used for saple progras of Renesas Electronics Corporation s icrocontrollers degree conducting control If the conduction patterns of each phase are changed at every 60 degrees as shown in Figure 2-1, a torque is generated between coil flux and peranent agnet of a rotor and the rotor rotates synchronously with the flux. As a conduction session of each switching eleent is 120 degrees, this control ethod is referred to as 120-degree conducting control. U HU U W HU V HU U (6) W HU U V (5) (4) (1) (2) W HU U V CW (3) U Phase Hall effect sensor WPhase HU W U Phase W Phase Hall effect sensor V Phase Hall effect sensor V Phase V W HU U V W V Coil flux direction Current direction Rotor Position range Figure 2-1 ix Conduction Patterns and Rotor Position Ranges (Exaple) R01A2657EJ0120 Rev.1.20 Page 2 of 13

3 120-degree conducting control of peranent agnetic synchronous otor Algorith 3. Position detection/speed calculation at 120-degree conducting control degree conducting control using Hall effect sensors Position detection The Hall effect sensors are used to detect the position of the peranent agnet, and the signals fro the Hall effect sensors are inputted to the icrocontroller as position inforation. U Phase U Phase Hall effect sensor W Phase HU W Phase Hall effect sensor V Phase Hall effect sensor V Phase Hall effect sensor HU ignals L H L Figure 3-1 Exaple of Hall effect sensors (HU,, ) position and signals As shown in Figure 3-1, the Hall effect sensors are allocated every 120 degrees and the respective Hall effect sensor signals are switched depending on change in agnetic poles of the peranent agnet. Cobining these signals of three Hall effect sensors enables to obtain position inforation every 60 degrees (six patterns for one cycle). At the switching tiing of Hall effect sensor signals, the conduction patterns of each phase are changed as shown in Figure 3-2. Change pattern (6) (1) (2) (3) (4) (5) (6) (1) (2) (3) Coil flux direction Hall Effect ensor ignals HU H L Phase pattern W phase+ U phase+ V phase+ W phase+ U phase+ V phase- W phase- U phase- V phase- W phase- V phase+ Figure 3-2 Relation between Hall effect sensor signals and conduction patterns (Rotation direction: CW) R01A2657EJ0120 Rev.1.20 Page 3 of 13

4 120-degree conducting control of peranent agnetic synchronous otor Algorith peed calculation The otor rotational speed is calculated fro a difference between the current tier value and the tier value 2π [rad] before. The tier values are obtained through the external interrupt routine by Hall effect sensor signals while having the peripheral function tier of the icrocontroller perfored free-running. With this ethod, if the Hall effect sensors are placed unequally, it is possible to calculate the rotational speed without the effect of unequalness. U phase Hall effect sensor pattern V phase Hall effect sensor pattern W phase Hall effect sensor pattern 2p 2p 2p Tier counter Check Check Check Check Check Check Check Counter value difference Motor rotational speed [rad/s] = (2π frequency of tier)/(difference of tier counts) Figure 3-3 Method of calculation for the rotational speed R01A2657EJ0120 Rev.1.20 Page 4 of 13

5 120-degree conducting control of peranent agnetic synchronous otor Algorith 3.2 ensorless 120-degree conducting control Position estiation The sensorless control does not have a sensor for obtaining the peranent agnetic position, and hence an alternative to the sensor is required. The sensorless control of peranent agnetic synchronous otors generally estiates the position by detecting induced voltage. The induced voltage is generated in proportion to a change rate of agnetic flux passing through a coil, to prevent the change. For exaple, consider the case where a agnet gets close to the coil, as shown in Figure 3-4. In this case, since the agnetic flux increases within the coil, the coil generates the electrootive force that runs current in the direction of the figure to prevent the increase of agnetic flux. (The flux of opposite direction of the agnetic flux is generated by the right-handed screw rule.) A A I Figure 3-4 Induced voltage generated by coil and agnet This induced voltage E is expressed by the agnetic flux as the below forula. d E 1 dt This phenoenon also occurs in a rotating peranent agnetic synchronous otor. When the peranent agnet is rotating, the induced voltage is generated by constant change of interlinkage agnetic flux of each phase. Figure 3-5 Induced voltage in the rotating peranent agnetic synchronous otor R01A2657EJ0120 Rev.1.20 Page 5 of 13

6 120-degree conducting control of peranent agnetic synchronous otor Algorith Figure 3-6 shows the change of interlinkage agnetic flux in the U phase. ize of the interlinkage agnetic flux is shown on the vertical axis and the phase of the peranent agnet is shown on the horizontal axis. Also, a position where the pole of the peranent agnet points the coil of the U phase is defined as θ = 0. MAX - p - p/2 0 p/2 p Coil interlinkage agnetic flux q MI Figure 3-6 Change of the interlinkage agnetic flux The interlinkage agnetic flux of the U phase changes in a cosine wave forat. If considered in sae way about the V phase and W phase, they deviate respectively by 2π/3 and -2π/3 phase fro the U phase. The interlinkage agnetic fluxes of the three phases are expressed by the following forula. cosq u 2 v cos( q p ) 3 2 w cos( q p ) 3 Also, the induced voltages of the three phases are expressed by the following forulas, by using the above forula (1), when the angle speed is considered as ω. E E E u v w d d p u cosq sin q cos( q ) dt dt 2 d d 2 2 p v cos( q p ) sin( q p ) cos( q ) dt dt d d 2 2 p w cos( q p ) sin( q p ) cos( q ) dt dt These forulas show that the induced voltage leads of π/2 phase fro the peranent agnetic flux. This eans that if the induced voltage can be detected, position of the peranent agnet can be estiated. R01A2657EJ0120 Rev.1.20 Page 6 of 13

7 120-degree conducting control of peranent agnetic synchronous otor Algorith MAX Zero-crossing - p -p/2 0 p/2 p p MI Induced voltage Coil interlinkage agnetic flux Figure 3-7 Zero-crossing of the induced voltage However, the induced voltage of each phase ay not be always detected while the otor is rotating. While driving in 120-degree conduction, conduction is perfored to two phases aong the three. Therefore, in only the reaining one phase, to which current is not injected, the induced voltage can be detected. Actually, position inforation is obtained by detecting a change point of sign of induced voltage (zero-crossing) occurring in nonconducting phase. In a three-phase otor, this zero-crossing occurs for total six ties, i.e. twice in each phase, in one rotation (electrical angle) of the otor. This eans that the position for every 60 degrees can be detected by this process with resolution equivalent to Hall effect sensors. R01A2657EJ0120 Rev.1.20 Page 7 of 13

8 120-degree conducting control of peranent agnetic synchronous otor Algorith In this syste, by coparing the pseudo otor center point voltage with each phase voltage, the patterns of 1 and 0 are created according to the positional relation. In addition, the pseudo Hall effect sensor pattern is created by shifting this created pattern by π/6 phase. p/6 is a value calculated fro the estiated rotational speed. U phase induced voltage V phase induced voltage W phase induced voltage V phase- Zerocrossing Pseudo otor center point voltage Pattern created fro U phase induced voltage p/6 Pattern created fro V phase induced voltage p/6 p/6 Pattern created fro W phase induced voltage U phase pseudo Hall effect sensor pattern V phase pseudo Hall effect sensor pattern W phase pseudo Hall effect sensor pattern U phase+ V phase+ W phase+ W phase- U phase- V phase- Figure 3-8 Pseudo Hall effect sensor pattern (In case of upper ar chopping) R01A2657EJ0120 Rev.1.20 Page 8 of 13

9 120-degree conducting control of peranent agnetic synchronous otor Algorith There are soe kinds of ethod to detect the zero-cross. For exaple, (1) Using A/D converters in a icrocontroller (2) Using the coparators and so on. oe representative exaples are explained below. (1) Using A/D converters in a icrocontroller In this ethod, at first actual voltage on each U/V/W phases are converted by A/D converter. Then pseudo center voltage is generated with the su of these values. The zero-cross is detected by coparing this pseudo center voltage and voltage of each phases. ince there is no need for a coparator to copare voltages, this ethod is called coparator-less ethod. Basic iage of this ethod is shown below. BLDC otor ix-phase inverter To A/D input of icrocontroller Circuit for voltage dividing Figure 3-9 Coparator-less ethod R01A2657EJ0120 Rev.1.20 Page 9 of 13

10 120-degree conducting control of peranent agnetic synchronous otor Algorith (2) Using the coparators In the ethod with using the coparators, the zero-cross is detected by the coparators with coparing the actual voltage of each U/V/W phases and a pseudo center voltage which is generated by an electrical circuit. Then, the outputs of the coparators are input as external interrupts into a icrocontroller. Basic iage of this ethod is shown below. BLDC Motor 6Phase Invertor Circuit for pseudo center voltage + - Circuit for voltage dividing Coparators (Micro Coputer Peripheral) To Interrupt Figure 3-10 Method with using coparators (with a circuit for pseudo center voltage) As for induced voltage to be detected actually, ipact of coutation voltage generated when switching conducting patterns and PWM of other phases ust be considered. The ipact is expressed as shown in Figure To reduce the ipact, soe countereasures such as a ethod using a siple filter circuit or software filtering can be taken. on-conduction interval Ipact of coutation Ipact of other phase PWM Figure 3-11 Conceptual Diagra of Ipact of Coutation and Other Phase PWM R01A2657EJ0120 Rev.1.20 Page 10 of 13

11 120-degree conducting control of peranent agnetic synchronous otor Algorith peed calculation The otor rotational speed is calculated fro a difference between the tier value confired 2p [rad] before and the current tier value. The tier values are generated with a free-running tier in a icrocontroller at the zero-cross point in which the conductive pattern change. Pattern created fro U phase induced voltage Pattern created fro V phase induced voltage Pattern created fro W phase induced voltage 2p 2p 2p Tier counter Check Check Check Check Check Check Check Counter value difference Motor rotational speed [rad/s] = (2π frequency of tier)/(difference of tier counts) Figure 3-12 Method of calculation for the rotational speed R01A2657EJ0120 Rev.1.20 Page 11 of 13

12 120-degree conducting control of peranent agnetic synchronous otor Algorith tart-up ethod Induced voltage does not occur unless the peranent agnet is rotating. This eans that position of the agnet cannot be estiated by using induced voltage at the tie of start-up. Therefore, as a start-up ethod, there is a ethod to lead the synchronous speed by generating a rotating agnetic field by forcibly switching conduction patterns regardless of position of the peranent agnet. For ore details, please refer to the Ipleentation (application note). R01A2657EJ0120 Rev.1.20 Page 12 of 13

13 120-degree conducting control of peranent agnetic synchronous otor Algorith Website and upport Renesas Electronics Website Inquiries All tradearks and registered tradearks are the property of their respective owners. R01A2657EJ0120 Rev.1.20 Page 13 of 13

14 Revision History Rev. Date Description Page uary First edition issued Issued in accordance with the revision 24V Motor Control Evaluation yste for RX23T Addition of the explanation about the detection zero cross by the coparator. Reconsideration of the sentences

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