Renesas RX62T Instrucciones de instalación y funcionamiento

APPLICATION NOTE

R01AN1192ET0100 Rev.1.00 Page 1 of 14

Jun 01, 2012

RX62T

120-degree Trapezoidal-wave with Sensorless

Introduction

This document provides an idea that using back Electromotive Force (back-EMF) signal to realize sensorless control.

Without any sensor signal input, the rotor’s location is unknown, so driving rotor to get PWM pulse via six-step

trapezoidal control method phase by phase for startup period, once the BEMF is captured by MCU successfully, change

back-EMF signal as input signal source. The control algorithm and experimental result are shown in the following

chapters.

The reader should already have some understanding of six-step commutation methods, such as Hall sensor commutation,

to provide background to the techniques described here. Besides, please read the six-step motor drive with Hall sensor

application note referred to in the Reference section at the end of this document.

Target Device

RX62T

Contents

1.System Configuration........................................................................................................................2

2.Block Diagram...................................................................................................................................3

3.Idea for Capturing BEMF Signal .......................................................................................................4

4.Flowchart...........................................................................................................................................6

5.Implementation and Testing............................................................................................................11

6.Reference........................................................................................................................................13

R01AN1192ET0100

Rev.1.00

Jun 01, 2012

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Jun 01, 2012

1. System Configuration

Target board is RX62T Motor Control Development Board designed by Renesas Electronics Taiwan. Table 1-1 lists the

jumper setting that switch input signal as BEMF source, which will be compared by VCC/2 and input into RX62T. Use

three timer channels to realize this sensorless control. The operating mode is set as input capture mode at rising and

falling edge. The detailed explanation is described in chapter 3. Table 1-2 lists the jumper setting for the CPU mode

selection.

Figure 1-1 System Configuration

Jumper J9 J10 J11

Pins 1-2 1-2 1-2

Table 1-1 Jumper Setting for Sensorless Control

Jumper J1 J2 J3 J4

Single chip mode - 1-2 1-2 2-3

Boot mode - 1-2 2-3 2-3

Table 1-2 CPU Mode Setting

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2. Block Diagram

MTU3 is the main module that is used in this application. Ch3 and ch4 are used for PWM output, which is set as reset-

synchronized mode. Ch2 is used for calculating rotational speed. Ch0, ch6 and ch7 are used for calculating BEMF

signal which is generated by phase U, V, and W. ADC receives VR value to control rotational speed.

Figure 2-1 Block Diagram

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3. Idea for Capturing BEMF Signal

Without any hall sensor detection, BEMF is one of many possible methods for sensorless control. In this application

note, it is used to realize sensorless control. As shown in Figure 3-1, Phase U BEMF is an example for explanation.

The Uis an input signal which is a compared value that gets form Phase U BEMF after comparing with VCC/2. In

Figure 3-1, a spike will be generated by 6-Step Motor Drive at the phase changed, so we know that the 3rd interrupt*1 is

the zero-crossing point. After knowing the zero-crossing point, UP PWM should output by delaying 30-degree (i.e.

output at 7th interrupt*1 in this example; note: ‘7th’ in Figure 3-1 is just an example for explanation).

*1 each interrupt is generated by a MTU3 timer which mode is set as input capture mode at rising and falling edge, and

saving the counter value per interrupt, for more detailed explanation, see Figure 3-2.

Figure 3-1 Zero-crossing Point Calculation

Figure 3-2 shows how to determine zero-crossing point at rising and falling edge by BEMF signals.

Define ‘Temp’ for saving counter value (i.e. TCNT), and TCNT is cleared at rising and falling edge of input signal;

‘CntA’ for counting the number of interrupt; and ‘Value A’ is the compared value that we set for knowing the timing of

timing.

Four points:

(1) In Figure 3-2, TCNT value will greater than ‘Value A’ only when spike is generated (refer Figure 3-1).

(2) Set ‘CntA’ to 1 when ‘Temp’ greater than ‘Value A’, and add 1 in the next interrupt (i.e. CntA++).

(3) While low condition is matched with user setting, set fictitious H1 to low (in this example is 7th). F_H1 low

represents UPPWM is outputted after delaying 30-degree, so it needs to tune ‘CntA’ for the real condition.

(4) The end of the UP phase output is uncountable, so we use the Phase V BEMF to determine the rising time of F_H1.

In figure 3-2, Vis Phase V BEMF signal, which timer mode is same as U used. Once the interrupt procedure in V is

generated and read ‘Temp’ value is greater than the minimum ‘Temp’ value (i.e. ‘Temp’= 17), set F_H1 to high.

RX62T 120-degree Trapezoidal-wave with Sensorless

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Jun 01, 2012

Figure 3-2 Calculation of Fictitious Signal

*1 ‘Temp’ value in Figure 3-2 is an example for explanation. The value should be performed in realistic condition.

Three phases BEMF relationship is shown in Figure 3-3. Red arrow ( ) indicates the rising edge of fictitious hall

signal timing. Each phase rising condition is determined by another phase, so three timer channels are realized for this

idea.

Figure 3-3 Relation between 3 Phase BEMF signal and Fictitious Signal

The program flowcharts are shown in chapter 4.

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4. Flowchart

Chapter 4 shows setting procedure of main, PWM, and BEMF in sample program. In addition, speed calculation

method is also described in this chapter, too.

Figure 4-1 Main Function Control Procedure

Four poles motor is used in this example, which means 2 cycles is generated in one revolution. Operating frequency is

1562500Hz for one timer channel (i.e. ICLK/64 = 100MHz/64) to calculate the period of fictitious hall signal at falling

edge, and the 1 rps (Revolutions Per Second) value between two falling edge is 781250. In figure 4-2, The reading

value saved in TGRA is 390625. Base on 1 rps condition, calculate the ratio of presenting value saved in TGRA, it can

get the current speed is 2 rps (i.e. 120 rpm). And that is the speed calculation method used in this application note.

Figure 4-2 Example of Speed Calculation

Main:

[1] After power on reset, initial the peripheral function

in hardware setup. Set ICLK = 100 MHz, A/D is

operated as single mode, and MTU3 timer channels

0, 6 and 7 for BEMF used; ch2 to calculate

rotational speed; and ch3 and ch4 to output PWM

command.

[2] Speed command for motor can be operated only

when BEMF control flag is set,

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Figure 4-3 shows the PWM duty output setting procedure that includes no BEMF signal input (i.e. open-loop control),

and BEMF signal input (i.e. close-loop control).

Figure 4-3 PWM Control Procedure

MTU3, MTU4 PWM Interrupt

[1] Check the hall location with previous saved value

[2] For each value, save it into an array which we

defined, such as array_Hall = [5 4 6 2 3 1], and

each value is determined at BEMF procedure,

please see Figure 4-8, step [7].

[3] Sum all value to check the status of motor, if sum

value == 21. Its means motor is activated

successfully in open loop method, then set BEMF

control flag to 1.

[4] In ‘A’, rotor will be constrained at one phase by

output particular PWM signal.

[5] In ‘B’, six phases PWM will be generated in

sequence for several times. Once the motor is

activated successfully, change motor status to

‘Close Loop Control’.

[6] In ‘C’, use fictitious hall signal as input signal.

[7] In ‘D’, if motor direction is changed or if motor

activate is fail, change status to ‘STOP’ to restart

the control procedure.

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Figure 4-4 Motor Status is ‘START’ in PWM Control Procedure

Figure 4-5 Motor Status is ‘Open Loop Control’ in PWM Control Procedure

Procedure ‘A’:

[1] Because the rotor’s location is unknown, we

enable one phase PWM to constrain rotor at a

fixed location.

[2] Check spinning direction. If changed, output

higher PWM duty to force rotor’s location.

[3] Change Motor Status to ‘Open Loop Control’.

[4] Back to Fig 4-3

Procedure ‘B’:

[1] Add PWM duty by each interrupt

[2] At this stage, each phase will follow six-step

commutation methods without any

[3] Check whether motor is running successfully

[4] Change Motor Status to ‘Close Loop Control’

[5] Back to Fig 4-3

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Jun 01, 2012

Figure 4-6 Motor Status is ‘Close Loop Control’ in PWM Control Procedure

Figure 4-7 Motor Status is ‘STOP’ in PWM Control Procedure

Procedure ‘C’:

[1] After changing Motor status to ‘Close Loop

Control’, PWM duty will be calculated according

to rotational speed.

[2] Check direction. If changed, turn off the PWM

output and set Motor Status to ‘STOP’ to restart.

[3] Clockwise and counter clockwise have its output

table respectively.

[4] Back to Fig 4-3

Procedure ‘D’:

[1] Turn off the PWM output

[2] Waiting for 0.5s, then changing Motor Status to

‘START’ to restart program.

[3] Back to Fig 4-3

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Jun 01, 2012

Three phase BEMF signals are used the same procedure, and idea for this flowchart please see Chapter 3.

Figure 4-8 BEMF Control Procedure

Note1. i = 1, 2, 3

Note 2 Three phase BEMF signals use the same procedure.

Note 3 Different condition of spinning direction has different reference table, the reference channel for falling edge of

zero-crossing point are shown in below table:

Interrupt

source

Direction

Phase U Phase V Phase W

Clockwise Phase W Phase U Phase V

Counter Clockwise Phase V Phase W Phase U

BEMF process

[1] Count operation is stopped, k = U, V, W.

[2] Check counter value bigger than 500, and save

counter value in different conditions happened.

[3] Check Hi phase to verify the timing of Spike. If

TCNT value greater than ValueA, as mentioned

in Chapter 3, clear CntA to 0 in this step.

[4] If compare match with value that user set, set

F_Hi to low.

[5] Check spinning direction

[6] Different direction has different reference signal,

see NOTE 3, and the F_Hi high condition is

determined in this step.

[7] Use saved value F_H1, F_H2, and F_H3 to

determine the latest information of rotor’s

location.

[8] Performs count operation

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