Renesas RX62T Installation and operating instructions

APPLICATION NOTE
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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
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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.

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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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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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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