Sensorless Vector Control and Implementatio - Why and How (1)

 Challenge: Sensorless vector control increases the energy efficiency of motor control systems that drive the smart society..  Solution: This class will help you understand key challen

Sensorless Vector Control and Implementation: Why and How

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 Challenge: Sensorless vector control increases the energy efficiency of motor control systems that drive the smart

society However, understanding and implementing

sensorless vector control is a herculean task.

 Solution:

This class will help you understand key challenges associated with sensorless vector control and how to implement it using Renesas microcontrollers

‘Enabling The Smart Society’

MCU

 Need for vector control

 Theory behind vector control

 Challenges in implementing sensorless vector control

 RX62T MCU family for sensorless vector control

 Renesas motor control solutions

Macro Factors Driving Need for Energy Efficiency

Realizing Energy Efficiency in Motor Control

 Direct torque control

 Power factor correction

 Motor Design

 Motor Type

Motors (45%)

Sensorless Vector Control Theory

Permanent Magnet AC Motor

 Complex Control

 Sinusoidal stator current produces rotating field

 Rotor mounted magnetic field is rotating

 Maintain stator field orthogonal to rotor field

r s

=

Γ

X A

Vector Control Challenge

 Maintain orthogonality

 Error correction feedback loop

– In-phase current = 0 – Orthogonal current set per torque requirements

 What parameters to adjust

 Voltage magnitude (PWM duty cycle)

 Need to transform current vectors to rotor frame

Rotor Field

Stator Field

90 0

ω r

Reference Frame Transformation

 Vector control advantages

 Maximizing torque (efficiency)

 Independent control of flux and torque

 Snappy torque control for load variation

Current Transformation to 2-ph Rotor Frame

i i

i i

i

3 3

0

2

1 2

1 1

I q

d

cos θ sin θ

sin θ cos θ

q I

F q-

 Step 2 : 2-ph stationary frame to 2-ph rotor frame (rotating)

 Rotor position (θ) needed

Sensorless Vector Control

 Lower cost but more complex implementation

 Current and motor parameters to estimate rotor position

 Increased reliability

 Reduced cost of sensor ($3-$20)

 Less physical space needed

 Need to estimate θ without sensors

Speed /position sensor

Speed Calculation

Motor

PWM Generation

PI Controller

PI Controller

i

d i

Rotor Position and Speed Estimation

α λ

Renesas Flux Observer Model

dt i

α ,

e

n n

( ,

1024

1023

β α β

Low pass filter

y n

Derivative

d n

dt d

Low pass filter

β

α , 1

1024

1023

e y

) ( , β n

α

λ

 Cascaded low pass filters rather than direct integration

 First low pass filter

 Derivative

 Second low pass filter

 Negate the effect of DC offset in measured current/voltage

Flux Observer Implementation

Sensorless Vector Control Loop

abc to αβ

i a

i b

dq To αβ

v α

v β

αβ

to abc

Speed Estimation

θ

ω r

ω* r

id Regulator

i d *=0

i d

i q

iq Regulator

Speed Regulator

I q*

3-ph Inverter

6

Sine PWM

DC BUS

αβ

to dq

Implementation Challenges

High performance CPU, FPU

Implementation Challenges

1 Computation intensive routines

12Bit Simultaneous Sampling ADC

2 Multiple current/voltage measurement

Noise immunity, PWM shut off

3 Robust performance

On-chip analog, data flash, dual motor

4 Cost effective design

 32bit Barrel Shifter

 Floating point unit

• Clarke/Park Transformations

• Flux Estimation

• Rotor position and speed

Floating Point Unit Advantages

 Performance

 Wide range and high resolution

 No scaling, overflow or saturation

 Reduced code size

 Ease of Use

 Ease of coding, reading, debugging

 Compatible with the C/Matlab simulation code

Floating Point : Range and Resolution

Fixed-point Calculations Requires Scaling

X(n) = X(n-1) + A1 * E(n)

(16b, Q12.4) (16b, Q8.8) (32b,Q14.18)

(32b,Q20.12) (32b,Q14.18)

MULT

SHIFT

(32b,Q14.18)

No Scaling Needed

FPU Implementation Fixed-Point Implementation

SHIFT

No Saturation Check

Fixed-Point Implementation

Check for

Saturation

Reduced Code Size

FPU Implementation Fixed-Point Implementation

FPU instructions make code and the execution time smaller

FPU Brings Ease of Simulation

Inherently floating point

Floating Point Algorithm

Fixed Point CPU

Fixed Point Algorithm

Floating Point CPU

FPU Implementations

No Load/Store Instructions

Renesas RX FPU

Point Unit

Floating-2 Accurate Analog Signal Measurement

 Simultaneous sampling ADC

 Filtering to mitigate noise

 Dual registers for 1-shunt

U V W

5us

4 ADC Samples

• Estimates based on current and voltage

• Integration for flux estimation

• Multiple simultaneous measurements

Current Measurement Techniques

3-shunt

U V W

I W I W +I V

 1-Shunt Advantages

 No need for 3-ph calibration

Support for 3-shunt and 1-shunt Detection

AN0 AN1

ch0

S/H S/H

Double register for 1-shunt

 Self-diagnostic capability for UL/IEC safety requirements

PGA

PGA

Window Comparators

CPU Interrupt PWM Shut off (POE)

3 Robust Performance

 Noise immune MCU design

 Pin noise filtering

Implementing Sensorless Vector Control Using RX62T

RX62T Motor Timer Set (MTU3)

MTU3

3-phase cPWM O/P U,V,W

ch6 ch7

3 Input Captures

3-phase cPWM O/P U,V,W

Quadrature Encoder1 A,B,Z

Quadrature Encoder2 A,B,Z

Hardware Implementation

Motor Current

6

PWM Generation PWM Shut Off

PGA S/H

12-bit ADC

Analog Unit 0

RX62T

RX600 CORE

x3

3-phase inverter

Gate Driver MTU CH3/4

3

3-phase BLDC Motor

Software Implementation

Initialization

PWM Interrupt

Current Reconstruction

New Speed Estimation

Current PI

Voltage (d,q)

V BUS /Current Measurement

(u,v,w) ->

(α,β) ->(d,q)

Last θ

Reference Current

Actual Current

(d,q) -> (α,β) (u,v,w) <-

Fixed point vs FPU Comparison

 Algorithm: Sensor less Vector Control with 1-Shunt Current Detection

 PWM Carrier Frequency: 20kHz

 Current Loop: 10kHz

Renesas Inverter Board

RX62T

Starter Kit

CPU Bandwidth Usage

0% 5% 10% 15% 20% 25% 30% 35% 40%

Sine,Cosine,Atan Functions

Look-up Table

Floating Point Fixed point

CPU BW

CPU Bandwidth Usage

PI Loop Clarke and Park Position Estimation

Current Measurement

Overall

Floating Point Fixed point

us

Floating-point code 40% faster

Code Size

0 50 100 150 200 250

PI Loop Clarke and Park Position Estimation

Current Measurement

Floating Point Fixed point

Floating-point code size is 45% lower

B

Driving Two 3-Phase BLDC Motors

RX600 Motor Kit External Inverter

www.renesas.com/rxmotorkit

 Sensorless Vector Control

 Floating point math

Implementation for Two Motor Control

CPU Available

MTU.CH3/4 10KHz

MTU.CH6/7 10KHz

 Software Implementation

 Control loop executed at Timer underflow interrupt

 Both interrupts at same priority level

 Alternate Implementations

 Control loops at different rates

 Interrupt at overflow/underflow

MTU.CH3/4 10KHz

MTU.CH6/7 20KHz

Software Implementation

Initialization

PWM Interrupt

Current Reconstruction

New Speed Estimation

Current PI

Voltage (d,q)

V BUS /Current Measurement

(u,v,w) ->

(α,β) ->(d,q)

Last θ

Reference Current

Actual Current

(d,q) -> (α,β) (u,v,w) <-

Last θ

PWM Interrupt2

Performance Comparison with a High-end DSP

 RX62T offers tremendous value

16us 18us

+50%

7.8KB 7.4KB

Response to Step Change in Load

Renesas Motor Control Solutions

Motor Control MCUs

RX63TH

100 MHz, 165DMIPs 256KB – 512KB

R8C/3xM

20 MHz

8KB – 128KB

Oct.2012

Evaluation Kits for Vector Control

 Extensive Code Support

 Flexibility to Evaluate and Develop

 GUI

RX600 Motor Kit RL78 Motor Kit

High Voltage Demo Platform (2KW)

IGBTs RJH60D5DPQ-A0

Interleaved PFC

AC to DC rectifier

2KW Inverter Platform

Questions?

 Challenge: Sensorless vector control increases the energy efficiency of motor control systems that drive the smart society However, understanding and implementing

sensorless vector control is a herculean task

 We discussed key challenges associated with sensorless vector control and how to implement it using Renesas

microcontrollers

 Do you agree that we accomplished the above statement?

‘Enabling The Smart Society’

MCU