ps basics of a dc drive

7/29/2019 PS Basics of a DC Drive

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DC DRIVE BASICS


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Purpose of a DC Drive

Alternating

Voltage

V

T

T

V

Direct Voltage

A DC drive converts AC power to DC voltage

in order to vary the speed and torque of the motor


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DC Motor Review

Speed is primarily determined by Armature Voltage

Torque is determined by Armature Current


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DC Motor Review

Rotation is the result of two independent electromagnetic

fields.

Armature windings

Field windings

Extended motor speeds above base speed are achieved

by reducing the field voltage (current)

Field Weakening


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DC Drive

Shunt

Field

M

Field Supply

3 Phase AC

Power

SCR

Gate

DC Armature

T1 T3 T5

T2 T4 T6

L1L2

L3

+

-

Firing Circuit

Regulator

Operator

Control Station

Current

Feedback

Voltage

Feedback


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DC Drive Components

Shunt

Field

M

Field Supply

3 Phase AC

Power

SCR

Gate

DC Armature

T1 T3 T5

T2 T4 T6

L1L2

L3

+

-

Firing Circuit

Regulator

Operator

Control Station

Current

Feedback

Voltage

Feedback

DC DRIVE

INPUT

Alternating

Voltage

V

T


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Shunt

Field

M

Field Supply

3 Phase AC

Power

SCR

Gate

DC Armature

T1 T3 T5

T2 T4 T6

L1L2

L3

+

-

DC Drive Components

Firing Circuit

Regulator

Operator

Control Station

Current

Feedback

Voltage

Feedback

SiliconControl

Rectifiers

(SCR)

Permits current to flow in 1 direction

Gate signals when conduction occurs

T

V

Direct Voltage


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Shunt

Field

M

Field Supply

3 Phase AC

Power

SCR

Gate

DC Armature

T1 T3 T5

T2 T4 T6

L1L2

L3

+

-

DC Drive Components

Firing Circuit

Regulator

Operator

Control Station

Current

Feedback

Voltage

Feedback

Field Supply

Used to Control

Field Voltage/Current


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Shunt

Field

M

Field Supply

3 Phase AC

Power

SCR

Gate

DC Armature

T1 T3 T5

T2 T4 T6

L1L2

L3

+

-

DC Drive Components

Firing Circuit

Regulator

Operator

Control Station

Current

Feedback

Voltage

Feedback

Operator ControlStation

Sends Instructions

to Regulator


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Shunt

Field

M

Field Supply

3 Phase AC

Power

SCR

Gate

DC Armature

T1 T3 T5

T2 T4 T6

L1L2

L3

+

-

DC Drive Components

Firing Circuit

Regulator

Operator

Control Station

Current

Feedback

Voltage

Feedback

Regulator

Compares instructions

feedback signals and

send appropriate signal to

firing circuit

Current (Torque)

Voltage (Speed)


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Shunt

Field

M

Field Supply

3 Phase AC

Power

SCR

Gate

DC Armature

T1 T3 T5

T2 T4 T6

L1L2

L3

+

-

DC Drive Components

Firing Circuit

Regulator

Operator

Control Station

Current

Feedback

Voltage

Feedback

Firing Circuit

Supplies the gate pulses

that fire the SCRs


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Speed Power Curve

Armature Voltage Control

Constant Field Current

Field Current Control

Constant Armature

Voltage

Constant Power

Con

stantT

orque

Speed (% of Base Speed)

Power(%o

fRated)

100

100


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Speed Torque Curve


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Forms of Stopping

Coast to Rest

Ramp Stop

Dynamic Braking

Regeneration


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Dynamic Braking Dynamic Braking

- Dissipates rotating mechanical energy to heat

- Faster than coasting to rest

- Not Controllable (except by changing the resistor)

Firing Circuit

Regulator

Operator Control

Station

Current

Feedback

Voltage

Feedback

M

Foward

Current

DB

Resistor

Drive Powering Motor

M

Foward

Current

Dynamic

Braking

Resistor

Stop Signal

Sent

DynamicBraking

Current


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Regeneration Regeneration

- Occurs when load overhaul motor

- Puts power back into drive through 2nd set of

SCRs

M

Forward Reverse Foward

Current

Reverse

Current

Firing Circuit

Regulator

Operator Control

Station

Current

Feedback

Voltage

Feedback

Benefits

- Stop High Inertia Loads Faster

- Return Energy to AC Power Line


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Stopping Time

CoastStop

Ramp

Stop

Dynamic

Braking

RegenerativeBraking


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Speed Regulation

How Much Will the Speed Change

Between No Load and Full Load?

Expressed as a Percentage

of Base Speed


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Speed Regulation


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Feedback Options

Speed Feedback Type Regulation

Voltage - 2 %

AC Tachometer RE O45 1 %

DC Tachometer 5PY 1 %

Encoder (pulse) RD-120-1 .01%

Encoder (pulse) RL - 1024 .01 %

Feedback device can determine speed regulation


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Types of Regulation

Voltage

Current (Torque)

Speed Position

For discussion purpose, the regulation discussedwill be from 0 to base speed.


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Types of Regulation

Voltage Regulator

Drive Regulates Armature Voltage

Feedback = Voltage & Current Speed Changes based on loading (5%)

IR Compensation

Improves regulation Measures current feedback


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Types of Regulation

Current (Torque) Regulation

Adjusts armature voltage to change armature current

Feedback = Voltage & Current Drive will provide only the current (torque) it is told


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Types of Regulation

Speed Regulation

Drive regulates speed of motor by changing armature

voltage Feedback = Speed &Current


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Types of Regulation

Position Regulation

Drive regulates positioning device by changing the

armature voltage Feedback = Position & Current


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Power Distribution Options

FlexPak 3000

Drive

M

Isolation Transform

Circuit Breaker

Line Reactor

Inverting Fault

Circuit BreakerContactor


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FlexPak 3000

Drive

M

Isolation Transform

Circuit Breaker Provides Impedance Reduce Electrical Noise

Isolation from ground

Protect from external

transients

Preferred for regenerative

applications

Provide power off switch

Overload capability

Thermal

Instantaneous

Current


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FlexPak 3000

Drive

M

Line Reactor

Inverting Fault

Circuit Breaker Contactor

Provides Impedance

Reduces Electrical

Noise

Mechanical disconnectto Motor

Provides power off switch

Overload

(Instantaneous Current)


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FlexPak 3000

Drive

M

Disconnect Switch

Provides power off

switch to drive

Less expensive

than circuit breaker


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DC Drive Modifications

Blower Motor Starter

115 V Control Interface

Enhanced Field Supply

Electronic Field Trim (240 V Drives only)

Field Economy

Field Current Regulator


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Blower Motor Starter

AC motor starter

Control of 3-phase blower motor

Fused with adjustable overload & interlocking


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115 V Control Interface

Converts customer supplied 115 V to

24 VDC Inputs & Outputs

Run

Stop

Jog

Fwd/Rev

Auto/Man

Coast Stop

Customer Interlock


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Enhanced Field Supply

Adjust field voltage to control field flux

Electronic Field Trim Changes Field Voltage/Current

Field Economy

Supply minimum voltage to keep motor warm


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Field Current Regulator

Actually regulates field current

Improves regulation performance


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DC Drive Terms

Constant Torque Variable Hp

Cogging

Full Wave / Half Wave Regulation (% of rated)

M Contactor

Contactor

Turn down Ratio

Enclosures (Page XIV)


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Questions ???

ps basics of a dc drive

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