59
CHAPTER 4
APPLICATION SPECIFIC INTEGRATED TIM-CONTROL
ARCHITECTURE
4.1 INTRODUCTION
Application
specific
modules
are
developed
for
various
applications in recent years. These modules are designed to achieve simpler
design, maximum performance and less time to market features. Flexible
smart transducer interface with control is commonly used in power system
stabilizer (PSS) and capable of performing a variety of functions according to
the need. A controller, to eliminate the low frequency noise in three phase
measurement is designed (Zhijun et al. 2008).
Universal Smart Sensor Interface and Signal Conditioner for
frequency-time sensor with IEEE 1451.4 services is developed by Yurish
(2007). Modular description of IEEE 1451-based architecture for smart
transducer network is provided by Rossi et al. (2009) using FPGA. This smart
sensor interface enables reduced instrumentation costs, flexible component
integration, and shared information with internet connectivity.
Specific
purpose TEDS named Health Electronic Data Sheet (HEDS) is framed by
Jethwa et al. (2008 a) to identify noisy and dead transducers. This specially
configured TEDS assist in intelligent control of actuators such as fault
detection and isolation.
60
These smart interface modules are more application specific and do
support self-description and modularity to some extent. This has been the
motivation to develop an integrated TIM-Control architecture which can help
in enhancing the utility of resources. An AS ITIM-CA is designed in this
chapter for a class of DC/DC Converter Systems.
A brief review of DC-DC converters, in view of building new
architecture, is presented in this chapter. It is followed by detailed description
of Integrated TIM-Control architecture. The controller is designed to suit a
class of power converters and hence the architecture is categorized as
application
specific.
Application
Specific-Integrated
TIM-Controller
implementation involves generation and processing of TEDS and control
commands.
4.2 DC-DC CONVERTER SYSTEMS
DC-DC Converters are used to change the electrical voltage from
one level to another level. Depending on the voltage transformation, they are
classified into three major types called 1. Buck (Step down) Converter, 2.
Boost (Step up) Converter and 3. Buck/Boost converter. Major functional
blocks of DC-DC converters are Power components, Control circuit, Sensors
and Switching devices (Actuators). Components associated with each
functional block are listed in Table 4.1.
Table 4.1 Components of DC-DC Converter
Power components
Inductor and Capacitor
Switching devices
MOSFET or other switching device with
Freewheeling Diode, Snubber circuit
Control Circuit
Current / Voltage mode control
PID Controller, Estimator based controller
Sensors
Current/Voltage sensor, temperature sensor
61
The circuit connectivity of all the three types of DC-DC converters
are shown in Figures 4.1a, 4.1b and 4.1c. It could be seen that the components
are similar for all, except the connectivity.
Figure 4.1a Buck Converter
Figure 4.1b Boost Converter
Figure 4.1c Buck-Boost Converter
62
In general, the inductor and capacitor (power components) provide
the filtering action for the converters. Dynamic response of the converter
depends on values of these components and the switching pattern. Switching
devices are characterized by switching frequency, forward drop, reverse
recovery losses and reverse breakdown voltage. They may be provided with
appropriate snubber circuits and / or freewheeling diodes.
There are two control modes, namely voltage mode and current
mode control. Voltage control is a single loop control while the current control
is operated with two loops. The controllers could be simple PI control with
appropriate gain chosen for the application. The other commonly used
controller is estimator-based control scheme where voltage / current or both
can be measured with an estimation of load disturbance for compensation.
The block diagram representation of different control algorithms is shown in
Figures 4.2a, 4.2b and 4.2c.
Reference +
-
Controller
∑
DC-DC
Converter
Voltage
Figure 4.2a Voltage mode control
Current
Reference
Voltage
Reference
+
∑
-
Controller1
+
∑
Controller2
DC-DC
Converter
Current
Figure 4.2b Current mode control
Voltage
63
DC-DC
Converter
Disturbance
compensator
Voltage
Voltage
Estimator
Current
Figure 4.2c Estimator-based control
Depending on the controller configuration, voltage and current
sensors may be required with appropriate signal conditioning unit. The
actuator devices are to be driven by appropriate driver circuits.
This completes the description of DC-DC converter system. Based
on these descriptions, the following architecture is proposed for control of
DC-DC Converter systems.
4.3 PROPOSED APPLICATION SPECIFIC INTEGRATED TIMCONTROL ARCHITECTURE (AS ITIM-CA)
The architecture is designed to receive IEEE 1451.0 Standard
commands / system specifications. Sensor outputs, actuator commands and
TEDS can be accessed directly by using standard commands or TEDS can be
generated by providing system parameters. Processing module utilizes the
TEDS information to provide necessary control input to system. The major
functional blocks of the proposed architecture are shown in Figure 4.3
64
Host computer
User Interface
*Commands
*System details
IEEE 1451.0
Command Decoder
Processing
TEDS
Signal
conditioning
block
Configure
A
S
DC-DC Converter
System
Figure 4.3 Block diagram of proposed architecture
Common functions supported by the architecture are as follows
• Formation of TEDS from the specifications of the system.
• Dynamic configuration of the functional modules of TIM
• Input / Output data checks.
• Generation of IEEE 1451 control commands to be used by in-built
controller.
• Generation of control command according to circuit configuration and
user specifications.
65
It is designed to operate in two modes called ‘Configure’
and ‘Execute.’ In ‘Configure’ mode, various parameters of functional
blocks are defined and TEDS information is generated accordingly.
Functional blocks of the system are configured using TEDS information.
In the case of DC-DC converter systems, functional modules include
controller, PWM generation unit. During ‘Execute’mode, the architecture
generates the control command, using the IEEE 1451.0 compatible
controller block. Operating modules and their interconnectivity are
illustrated in Figures 4.4a and 4.4b.
DC-DC Converter
Voltage sensor
Type
Operating range
Worst case error
Calibration details
Current sensor
Type
Operating range
Worst case error
Calibration details
L,C Values
Type
Actuator 1,2 … n
Type
Operating range
Worst case error
Calibration details
Sampling rate
Bit size
ADC Parameters
Actuator TEDS
Configure
Meta TEDS
(TIM details)
Type
Operating range
Worst case error
Calibration details
Temperature Sensor
Sensor TEDS
Figure 4.4a Functional blocks in ‘Configure’ mode
66
Actuator TEDS
Sensor TEDS
Transducer Channel
I/P data size
Sampling rate
O/P data size
Sampling rate
Transducer Channel
Calibration
Calibration
coeff.
Calibration
coeff.
Calibration
Estimator
coeff.
Controller
coeff.
End User
End User
User
User
Estimator / Controller
Actuator name
Sensor name
PWM I/P to
DC-DC Converter
System O/P
(DC-DC Converter)
Figure 4.4b Functional blocks in ‘Execute’ mode
4.4 THE TRANSDUCERS AND THE CORRESPONDING TEDS
The architecture is implemented with four mandatory TEDS and
two optional TEDS. Novelty of the architecture lies in making use of the End
User Application Specific TEDS of optional TEDS to serve a specific
purpose. Information related with the system such as transfer function,
controller / estimator coefficients etc., are stored in End User Application
Specific TEDS. These TEDS are used to configure the processor according to
system requirement.
Among the mandatory TEDS, one provides information about TIM
architecture, the other three provide transducer information. Minimum TEDS
implementation for the TIM is one mandatory TEDS describing TIM details
and three mandatory TEDS for each transducer configured in the TIM. In the
proposed system, each transducer is described by three mandatory TEDS and
67
two optional TEDS. They can be accessed by standard commands such as
‘Query TEDS’, ‘Read TEDS’, ‘Write TEDS’, and ‘Update TEDS’. Details of
the TEDS are provided in Table 4.2. Formation of TEDS for various
transducers is discussed in the following section.
Table 4.2 TEDS Implementation
Mandatory TEDS
Meta TEDS
TIM details
Transducer channel TEDS
Transducer details
User Transducer Channel TEDS
User defined Transducer details
Physical TEDS
Physical Communication – details of sensors
Optional TEDS
Calibration TEDS
Calibration details
End User Application Specific TEDS Serves specific purpose of this architecture
The number and type of transducers used in systems vary,
according to the control scheme. Commonly used transducers in DC-DC
converter are
1. Current sensor,
2. Voltage sensor,
3. Temperature sensor and
4. MOSFET actuator switch.
4.4.1 Formation of Mandatory TEDS
Formation of Mandatory TEDS is as per the IEEE 1451.0
standard format. The User Transducer Channel TEDS is available to the user.
In the proposed application it is used to define the name of the transducer.
68
4.4.1.1 Meta TEDS
Details of TIM are stored in this TEDS. They occupy a memory
space of 320 bits. Following details of TIM are used to form the TEDS.
• Number of Transducers
• Physical location and identification
• Self-test timing information
• Timing out operation
Table 4.3 Meta TEDS – 320 bits
Type
Value
Description
Length
00 00 00 22
Total length
TEDS Identifier
03 04 00 01 01 01
Meta TEDS
UUID
04 0A 81 C0 F9 74 48 82 1D Physical location
C2 2E 78
identification
Time out operation
0A 04 3F 00 00 00
0.5 seconds
Self-test time out
operation
0C 04 C0 A0 00 00
0.5 seconds
No. of Transducer 0D 02 00 02
channels
Two transducers
Check sum
Validates TEDS
F8 FA
4.4.1.2 Transducer Channel TEDS
It provides information related with transducer, data converter,
timing and sampling details at the interface. Tfe Following details of sensor
and ADC are used to form the transducer channel TEDS,
• Calibration key
• Parameter being sensed
• Operating range
• Worst case error
69
• Self-test availability
• ADC bit size
• Sampling period and mode, etc.
Formation of Transducer channel TEDS for a voltage sensor is illustrated
Table 4.4
Table 4.4 Transducer Channel TEDS – Voltage sensor
Type
Length
TEDS Identifier
Value
00 00 00 68
03 04 00 03 01 01
Calibration Key
03 04 00 03 01 01
Description
Transducer channel TEDS
Provision of calibration in
TIM
Physical Units – Volts. 0C 0F 32 01 00 35 Voltage sensor
01 84 36 01 82 37
01 7A 38 01 7E
Design Operational
0D 04 F1 F8 00 00 Lower operating range
Upper limit -9V
Design Operational
0E 04 71 F8 00 00 Upper operating range
Lower limit +9V
Worst case error +/- 0F 04 44 C0 00 00 Error in output
5m
No self-test
10 01 00
Self-test option
Sample definition 812 09 28 01 00 29
Bit size of ADC
bit ADC
01 01 2A 01 08
Update time – 10
14 04 3D CC CC
No. of samples / sec
samples/s
CD
Read Set-up time –
16 04 37 D1 B7 17 Access time
25µS
Sampling period – 17 04 3D CC CC
Time between samples
0.1S
CD
Warm-up time – 30S
18 04 41 F0 00 00
Time during start up
Read delay time – 19 04 37 D1 B7 17 Delay - read operation
25µS
Self-test time – 0S
1A 04 00 00 00 00 No self-test
Sampling mode – free 1F 03 30 01 02
Synchronous sampling
running
Check sum
EB FC
Validates the TEDS
70
4.4.1.3 User Transducer TEDS
It is defined by the user to identify the transducer by a name. In
this application, the Transducer Name field indicates the type of sensor used
like Potential divider voltage sensor, Hall Effect voltage sensor, etc.
Table 4.5 User Transducer TEDS – Voltage Sensor
Type
Value
Description
Length
00 00 00 28
Total length
TEDS Identifier
03 04 00 0C 01 01
User Transducer TEDS
User defined text
04 01 00
Text based data
Transducer Name
50 4F 54 45 4E 54 49 41 4C
44 49 56 49 44 45 52 56 4F
4C 54 41 47 45 53 45 4E 53
4F 52
ASCII Character
(POTENTIAL DIVIDER
VOLTAGE SENSOR)
Check sum
F7 1A
Validates TEDS
4.4.1.4 Physical TEDS
Details of physical channel used to connect the transducers are
described in this TEDS. Necessary details included in the TEDS are type of
interface and encryption, baud rate, number of bits, start and stop bits, type of
parity etc. Format of this is not defined in IEEE 1451.0-2007 and depends on
the corresponding IEEE 1451.X physical communication medium used.
Formation of Physical TEDS compatible with IEEE p1451.2-RS232 is
explained by Song and Lee (2009 a), which is used in this application.
71
4.4.2 Formation of Optional TEDS
Out of the two optional TEDS chosen, the calibration TEDS carries
the specifications as per the IEEE 1451.0 standard, whereas End User
Application Specific TEDS is defined to serve the proposed application
specific architecture.
4.4.2.1 Calibration TEDS
It is an optional TEDS. It provides all information used by
correction software on the transducer data. Two methods of calibrations are
defined, first method is single segment linear conversion of degree one and
second method is multiple segment of degree more than one. This application
utilizes single segment of degree one and the TEDS formation is given in
Table 4.6.
Table 4.6 Calibration TEDS of Voltage sensor
Type
Value
Description
Length
00 00 00 14
Total length
Header
03 04 00 05 01 01
Type, Length Value
SI Units conversion
01 03 0B 04 07
Conversion to volts
Linear conversion
11 2C 00 34 09 00 1D
Single segment of degree 1
Check sum
EF 1C
Validates the TEDS
72
4.4.2.2 End User Application Specific TEDS
Formation of End User Application Specific TEDS for various
transducers is illustrated in Tables 4.7.
Actuator End User Application Specific TEDS
• Coefficients of the controller are stored in this TEDS for all types of
controller
Table 4.7a End User Application Specific TEDS of Actuator
Type
Value
Description
Length
00 00 00 13
Total length
Identifier
03 04 00 0C 01 01 TEDS identifier
User defined data
01 10 01 10
Order of controller
(Zeros -1, Poles – 1, Bit size – 16)
Transfer function
0733 1000
Controller (Numerator and
Denominator coeffs.)
Check sum
FF 6B
Validates TEDS
Voltage Sensor End User Application Specific TEDS
• Transfer function of the system is stored in this application.
• In the case of voltage mode control, system information is provided in
this TEDS
• User defined control function can be incorporated with the knowledge
of transfer function
73
Table 4.7b End User Application Specific TEDS of Voltage Sensor
Type
Length
Identifier
User defined data
Transfer function
Check sum
Value
Description
00 00 00 15
Total length
03 04 00 0C 01 01 TEDS identifier
01 14 02 14
Order of controller
(Zeros -1, Poles – 2, Bit size – 20)
1F4017 06E817
System (Numerator and
003417
Denominator coeffs.)
FD E4
Validates TEDS
Current Sensor End User Application Specific TEDS
• Used to store State Estimator / Current controller coefficients
• Used for current mode control
• Controller may be of Estimator-based controller or Current mode
controller
• Estimator-based controller can be used in two configurations, using
one state, other state can be estimated with one sensor. Otherwise with
two sensors (two states), fault tolerance can be improved by estimating
the disturbance at the output.
Table 4.7c End User Application Specific TEDS of Current sensor
Type
Value
Description
Length
00 00 00 20
Total length
Identifier
03 04 00 0C 01 01 TEDS identifier
User defined data
02 14 02 14
Order of estimator and controller
(Order – 2, Bit size – 20)
State space
parameters
000603 000400
001904 000200
Estimator and controller
coefficients
Check sum
FF 09
Validates TEDS
74
Temperature Sensor End User Application Specific TEDS
• State model of the system is stored
• It can be used to predict losses due to temperature rise
Table 4.7d End User Application Specific TEDS of Temperature sensor
Type
Value
Description
Length
00 00 00 22
Total length
Identifier
03 04 00 0C 01 01 TEDS identifier
User defined data
02 14
Order of estimator
(Order – 2, Bit size – 20)
State space
parameters
0030B0 7FCF07
000000 000000
001000 000000
00000 003007
State space parameters
Check sum
FB 84
Validates TEDS
Advantages of having the End User Application Specific TED are
• Details of transducers as well as system are available to user.
• Updates / changes can be easily incorporated.
• Processor can be configured for any application by changing TEDS
contents.
4.5 ‘CONFIGURE’ MODE - FUNCTIONAL MODULES
Active functional blocks of this mode include Input buffers, Data
Conversion Units and Memory blocks. Input buffers are designed to receive
information regarding the converter and transducers. These parameters are
converted into the format defined for TEDS and stored in the memory blocks.
75
Data conversion units are used to transform the system parameters into TEDS
form. On request, the TEDS information can be displayed in the output.
Formation of TEDS from the input specifications is explained in the following
section.
Converter specifications
The inputs to be given in this module are
• Type of converter (Buck, Boost and Buck-Boost)
• Power component values
• Controller type (PI, PID, Voltage / Current mode, Estimator based
controller)
• Controller coefficients
• Estimator coefficients
• According to the type of converter, transfer function is formed as
follows.
H (s) =
V
D (1 + sL / R + s 2 LC )
Buck converter
(4.1)
H ( s) =
V (1 − sL / D '2 R )
D ' (1 + sL / D ' 2 R + s 2 LC / D ' 2 )
Boost converter
(4.2)
H (s) =
V (1 − sDL / D '2 R )
D ( D ' 2 + sL / R + s 2 LC )
Buck-Boost converter
(4.3)
• Conversion of specifications to End User Application TEDS is
provided in Table 4.8
76
Table 4.8 Converter specifications
Specification
Representation
Data generated
Sensor used
Type of converter
8 – bit fixed
point
Number of numerator and
denominator coefficients
Power component
values
20 – bit fixed
point
Transfer function
coefficients
Voltage
sensor
Power component
values
20 – bit fixed
point
State model of converter
Temperature
sensor
Voltage mode
control
20 – bit fixed
point
Voltage controller
coefficients
Actuator
Current /
estimator based
control
20 – bit fixed
point
Current
controller/estimator
coefficients
Current
sensor
--
Sensor Specifications
Transducer Channel TEDS and User Transducer Channel TEDS
are generated for each transducer.
•
Specifications are converted into fixed point or floating point
representation as defined in the standard.
•
Data converter units are used to convert the input specifications into
proper TEDS.
•
Various specifications, and their representation in the TEDS are given
in Table 4.9
77
Table 4.9 Sensor specifications
Transducer Channel TEDS
Specifications
Representation
Operating range – Upper limit
32–bit floating point
Operating range – lower limit
32–bit floating point
Worst case error
32–bit floating point
Self test details
32–bit unsigned integer
Calibration details
32–bit unsigned integer
User Transducer channel TEDS
Transducer name
Text data – user defined
Actuator specifications
Formation of TEDS is similar to sensor, except that the TEDS
contents indicate the transducer as an actuator.
Signal Conditioning Unit Specifications
Specifications of analog to digital converter such as output word
length, sampling rate, timing details, etc., are used to form part of Transducer
Channel TEDS. It is used to configure the input/output data size and sampling
rate of controller accordingly. Specifications and their representation in the
TEDS are given in Table 4.10
Table 4.10 Signal Conditioning Unit Specifications
Transducer channel TEDS
Specification
Representation
Data size of ADC
32–bit unsigned integer
Sampling rate
32–bit floating point
Timing details
32–bit unsigned integer
78
TIM Specifications
Physical location, number of transducers used, model number,
time-out period and other TIM details are used to form the Meta TEDS, which
provide TIM details.
Interface Specifications
Details of interfacing the TIM with other modules are provided in
Physical TEDS. Information required to access a particular channel and the
information common to all channels is described in this TEDS.
4.6 ‘EXECUTE’ MODE – FUNCTIONAL MODULES
Active modules of this mode are Transducers, TEDS and
Estimator/ Controller modules. Functional modules are configured for voltage
mode control or current mode control. For voltage mode control, voltage
sensor output is compared with the reference and the error signal is processed
by controller to generate PWM control command. Controller input data size
and sampling frequency are derived from Transducer Channel TEDS of
Voltage sensor. Output data size and sampling frequency are derived from
Transducer Channel TEDS, whereas coefficients are derived from End User
Application Specific TEDS of actuator. Interconnectivity of the functional
modules for voltage mode control is shown in Figure 4.5.
79
Actuator
Transducer
Channel TEDS
O/P data size &
sampling rate
Voltage
Sensor
-
End User
TEDS
Controller
coefficients
PWM
Controller
Generator
∑
+
Reference
Actuator
I/P data size &
sampling rate
Transducer
Channel TEDS
Voltage sensor
Figure 4.5 Processing blocks of Voltage mode control
For current mode control, estimator-based controller is used to
generate the PWM output. Estimator coefficients are derived from End User
Application Specific TEDS of current sensor. Remaining parameters are
derived similar to voltage mode control. Interconnectivity of the functional
modules for voltage mode control is shown in Figure 4.6.
Transducer
Channel TEDS
Voltage
Sensor
O/P data size &
sampling rate
Estimator
Current
Sensor
End User
TEDS
Controller
Estimator
coefficients
Transducer
Channel TEDS
Current sensor
Controller
coefficients
PWM
Generator
I/P data size &
sampling rate
Transducer
Channel TEDS
Voltage sensor
Figure 4.6 Processing blocks for Current mode control
Actuator
80
4.7 STATE FLOW DIAGRAM OF THE ARCHITECTURE
TIM operates in any of the states shown in state flow diagram
shown in Figure 4.7. TIM enters into receive mode after power on and checks
for the mode input. With mode equal to zero, it accepts either system
parameters to generate the TEDS or IEEE 1451.0 service command. For
invalid commands, the TIM again enters initial stage to receive next
command. Valid commands are decoded to provide enable signal for various
blocks of TIM. Control signals include enabling of signal processing unit of
sensor and memory block used for TEDS and registers. With mode equal to
one, controller is configured using TEDS information and actuator command
is generated according to sensor information.
Power on
Initialization
Done
Actuator
output
Mode = 1
Check
mode
Smart
controller
Mode = 0
Receive Parameters /
Commands
Done
TEDS &
Data Read
Parameters
Command
TEDS
Generator
Invalid
Command
Command
Decoder
Valid Memory/ data
R/W command
TEDS / Registers
Transducer Data
R/W
Figure 4.7 State flow diagram of AS ITIM-CA
81
Flow chart representation of the command execution is shown in Figure 4.8
Power On
Actuator command
output
Configure
controller
Mode = 0
Reset invalid
command bit
No
Read
TEDS/Data
Yes
Receive 56 bits of
Commands
Read/Write/
Validate TEDS
TEDS Access
command
Valid
command
Set invalid
command
bit
No
Data Read &
Write command
Enable Sensors
and Actuators
Enable output
module
Data --> output
Figure 4.8 Flow Chart for the AS ITIM-CA
82
4.8
COMMAND DECODING AND EXECUTION UNIT
The timing and control unit provides two operating modes based
on the input signal ‘mode’ as follows.
 '1' : Configure − mod e − IEEE − 1451.0 Services
Operate − mod e − UserDefined
Services
'0' :
‘Mode’ = 
Commands are received through input module and stored
temporarily in input buffer. First 56 bits of received data are transferred to
instruction register and decoded by the instruction decoder. Proper timing and
control signals are generated by the decoding unit to enable corresponding
functional blocks of TIM. The IEEE 1451.0 service commands are grouped
into 7 octets (group of 8 bits). Each octet is formed according to the command
class, command function, destination transducer, length of the command and
check sum. The structure of the command is explained in Table 4.11
Table 4.11 Command message structure
1 Octet
7
6
5
4
3
2
1
Destination Transducer Channel Number (most significant octet)
Destination Transducer Channel Number (least significant octet)
Command class
Command function
Length (most significant octet)
Length (least significant octet)
Command dependant octets
.
.
0
83
The functionality of the command is defined by command class
and command function. Transducer activated by the command is indicated in
Destination transducer channel number. Total length of the command is
provided in the length. Command dependant octets provide offset into TEDS.
Complete functionality of the command is provided in transducer channel,
command class, command function and length fields. Assuming the offset as
zeros and excluding the offset field, 56 bits are used to represent the IEEE
1451.0 service command. The command for read transducer channel TEDS of
transducer number 0001 is given below.
0001 01 02 0001 03
|
|
|
|
|____ TEDS access code (Transducer channel TEDS)
|
|
|
|_________ Length
|
|
|____________ Command Function (Read TEDS)
|
|_______________ Command class (Common command)
|___________________ Destination Transducer number (0001)
TIM is designed to implement five major standard commands with 17
command subclasses. Detailed description of commands is provided by Song
and Lee (2010). A brief description of the commands executed by TIM is
provided in Appendix 1.
4.9 LAB-VIEW BASED IMPLEMENTATION OF PROPOSED
ARCHITECTURE
The proposed architecture is implemented in Lab-View based
virtual instrumentation platform. Functionality of the system is illustrated for
Buck converter. Various design issues of the functional modules are discussed
in the following section.
84
4.9.1 Illustrative Example
Major design parameters of the converter are the coefficients of
converter transfer function, controller/estimator gain and state space
parameters. Derivation of these parameters for Buck type DC-DC Converter
is explained in the following section.
DC / DC
Load
Converter
Actuator
Sensor
Driver circuit
Controller
Signal
Conditioner
Figure 4.9.a Voltage loop control of DC/DC Converter
Figure 4.9.b DC/DC Converter
85
A buck type DC-DC converter with L = 330µH, C = 100µF to get
regulated voltage of 3V at 1A at the output is chosen for this application. A
resistive load of value R3 = 3Ω are considered for the DC-DC converter.
For the given values of components, transfer function and the state
space representations is derived as follows
G( s) =
1 + (500 × 10 −9 ) s
1 + (110.5 × 10 −9 ) s + (3.3 × 10 −9 ) s 2
 − 3000 − 3.0303e7 
A=

0

 0
1 
B= 
0 
(4.4)
C = [0.0015e7 3.0303e7]
Digitizing the transfer function with a sampling period of T = 0.00001 results
in
H (Z ) =
0.1503Z − 0.1474
Z 2 − 1.963Z + 0.9658
0.9613 − 297.66
F =
0.9985 
 0
0.982e − 5
G=

0


(4.5)
C = [0.0015e7 3.0303e7]
Control of DC-DC Converter is illustrated for voltage mode
control. Voltage mode control is achieved with simple PI controller with a
zero at -0.45 and a pole at -1. Current mode controller is designed with a state
feedback controller, consisting state estimator and a controller in feedback
path. Estimator and controller gains are calculated using Matlab for poles at
0.63 and 0.65.
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4.9.2 Lab View Integrated TIM-Controller
Functionality of the controller is verified in Lab View-based virtual
instrumentation platform. Control input ‘mode’ determines operating mode of
the controller. Control input and user interfaces are provided in front panel
diagram shown in Figure 4.10. With control input 'mode' = 0, the architecture
operates in 'Configure' mode. Type of converter is assigned as 0 for buck
converter, 1 for boost converter and 2 for Buck-Boost converter.
Figure 4.10 Front panel display during ‘Configure’ mode
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Numerical Values assigned for type of controller is 0 for voltage
mode controller, 3 for current mode controller and 4 for estimator-based
controller. Specifications of the converter are provided through another input
interface named specifications. According to the type of converter and
controller, system details are converted into corresponding TEDS.
With ‘mode = 0’, specifications in user interfaces are converted
into proper TEDS information, using data converters. Major functional blocks
in this mode include input modules, data conversion units, write and read
measurement files. Measurement files are used to store the TEDS information
and TEDS contents are displayed in the front panel. Parameters of concern
only, are shown in front panel. Measurement files of interest are enabled
according to the instruction. Information flow for the command ‘Read User
TEDS’ is shown in Figure 4.11
Figure 4.11 Files activated according to the instruction –
“00010103000107”
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4.9.3 ‘Execute’ Mode
Real time operation of the system is achieved in this mode. Active
functional modules of this mode are controller, TEDS and PWM generation
unit. Coefficients of controller are derived from the End User Application
Specific TEDS of actuator.
DC-DC Converter is developed with the components presented in
the previous section. The output of the converter is sensed by potential divider
voltage sensor. Voltage sensor output is interfaced through NI Data
Acquisition Module to the TIM. Controller module of TIM calculates the
error between DC – DC converter output and reference. A simple PI controller
provides PWM output signal to the actuator of DC – DC Converter, based on
the error signal. PI controller is chosen with zero at -0.45 and pole at -1.
ȉ
PWM signal is fed to the MOSFET switch after proper driving circuit.
Switching frequency of the transistor is fixed at 100 KHz. The block diagram
representation, experimental set-up and functional modules of operate mode
are shown in Figures 4.12a, 4.12b and 4.12c.
DC/DC
Converter
Voltage Sensor
Actuator
Data
Acquisition
Module
Virtual Instrumentation
Platform - TIM
Architecture
(IEEE 1451.0 Services and
Controller)
Figure 4.12a Block diagram of smart control of DC/DC Converter
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DC/DC CONVERTER
DATA AQCUISITION
MODULE
Figure 4.12b Experimental set-up
Figure 4.12c Block diagram of ‘Execute’ mode for voltage mode control
of Buck Converter
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Controller operation is verified by the PWM signal and converter
output for various reference voltages. Simulation waveforms for reference
voltages of 4V and 6V are shown in Figure. 4.13a. Duty cycle input to PWM
generator is shown in Figure 4.13b. Figure 4.14 illustrates the Converter
output capture in CRO.
Figure 4.13a. DC-DC Converter output for reference voltage of 4V and 6V
Figure 4.13b. Duty cycle input to PWM generator
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Figure 4.14 Buck converter output
4.10 CONCLUSION
Demand for smart system with intelligence at each level is
increasing in industrial and commercial applications. This chapter proposed
Integrated TIM-Control architecture, which meets the requirements of smart
system. It is implemented using commonly available low cost transducers
with smart interface. Self-configuration of system is achieved with the TEDS
information of smart transducers. The architecture is developed for a class of
DC-DC Converters used in power systems and classified under application
specific module. Features of the proposed system are listed as follows.
• TEDS are generated automatically by using system parameters.
• Specific purpose TEDS are formed for the purpose of control and smart
readout.
• Design parameters of individual modules are formulated using TEDS
information.
• Upgrades / Changes in system parameters are easily incorporated.
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• The architecture can be utilized for any application by replacing the
configure module accordingly.
This chapter illustrated the architecture suitable for Buck, Boost
and Buck-Boost converters. Experimental set-up is shown for voltage mode
control of Buck type converter. The architecture can be used for any DC-DC
Converter system.