The document discusses the basics of vector control in AC drives, specifically focusing on Variable Frequency Drives (VFDs) used for AC motor speed control. It details the hardware components, control schemes such as v/f control and vector control, and highlights the advantages of vector control including precise speed control and 100% torque delivery. Additionally, it covers features like auto-tuning and the architectural differences between vector drives and standard v/f drives.

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Basis of
Vector Control in AC Drives
Presentation by
Prashob P K
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VFD or AC Drive
• VFD stands for Variable Frequency Drive
• VFD is used for speed control of AC motors
• The Hardware components of VFD comprise
of
1. A Converter section with convert AC TO DC
2. A Inverter Section which convert DC back to AC of which frequency
can be varied within in a range
3. Control card or Control circuit
4. Input output interface for controlling the operation of the VFD
5. Optional Communication cards or interfaces

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AC POWER
INPUT
VECTOR BLOCK DIAGRAM
U1
V1
W1
BUS POWER
SUPPLY
POWER
OUTPUT
CIRCUT
CONTROL
POWER
SUPPLY
DRIVER
CIRCUIT
CONTROL
BOARD
CURRENT
SENSE
U2
V2
W2
EXTERNAL COMMAND
AC
MOTOR
E
POSITION , VELOCITY AND DRIRECTION FB
CURRENT FEED BACK
ENCODER/RESOLVER
CONVERTER INVERTER
DC AC
FIGURE 1
CONTROL BOARD/CIRCUIT

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Speed Control Schemes Employed in
VFD
• There are mainly two type of control schemes
employed
1. V/F control
In this output AC maintain a ration between Voltage and
Current.
V/f or V/Hz is the basic control scheme employed in AC drives
and is used for Pump applications mainly
In V/f control, current is controlled only based on fault or
over current level.

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Vector Control
• Two closed loop controls :-
Current loop and Speed loop
• Using Mathematical vectors drive can separate
toque producing current from magnetizing
current
• Vector control can tune themselves to the motor
after getting basic motor name plate parameter
• Tuning also known in certain cases as
optimization or auto tuning

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Auto tuning
• Auto tune feature measure several variable of
motor like resistance , inductance of rotor and
stator, slip
• Based on these values mathematical motor
model is setup and thus controls loops are
executed at their best
• New age drives have adaptive tuning feature
which is active continuously as the motor runs

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What are the additional configurations in Vector
drive compared to that of normal V/f drives?
• A feedback circuit with at least two current feedbacks from
the motor leads
• With above configuration vector drives are capable of
“encoder less operation”, however there is provision to
provide encoder/resolver feedback
• More powerful controller to perform vector analysis on
current and voltage feedback

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Advantages of Vector Control
• Vector control can deliver 100% torque form 0 to rated
speed
• Speed control is more precise than that of V/F
• Since closed loop control is excellent, vector control can
be implemented were PID loops or set point is
continuously coming from a process feed back or other
systems
• This control is suitable for applications involving
1. Torque control
2. Basic position control[advance control require servo drives]
3. Electronic gearing , pulse following
4. Tension control with dance adjustment etc