M

THREEPHASE INPUT

VOLTAGE

THREE PHASEBRUSHLESS SERVO

MOTOR WITHPERMANENT

MAGNETS

SHUNTS, USED ASCURRENT SENSORS.

CURRENT (TORQUE)FEEDBACK CIRCUIT

POSITION/SPEED

ENCODER

POSTION/SPEED FEEDBACK

POWERTRANSISTOR CONTROL

CIRCUIT

THIS COMMONLY USED INVERTER TOPOLOGY WAS USED IN THE DESIGNOF LOW VOLTAGE, SMALL CAPACITY SERVO DRIVE FOR ROBOTICS

APPLICATION( INPUT POWER 48V AC, SPEED 3000 RPM, TORQUE UP TO1N*M.

THREE CURRENT DETECTING SHUNTS WERE THE MAJOR FEATURE OF THE INVERTER- SPECIAL ALGORITHM ALLOWED TO FETCH THE MODULE OF CURRENT FROM THESE

SHUNTS. ( BIG CURRENT TRANSFORMERS IN THE PHASE LINES AND OPTICALINSULATION OF THE POWER CIRCUIT MAY BE AVOIDED WITH THIS ENGINEERING

DECISION.THIS CIRCUIT WAS PATENTED BY 3 PATENTS.

T1

T2

T3

T4

T5

T6

D1

D2

D3 D5

D4 D6

R2 R4 R6

LET US TAKE THE PERIOD OF TIME, WHEN ONLY TWO PHASESARE UNDER VOLTAGE (ACCORDING TO THE POSITION OF THE

ROTOR) AND PWM CURRENT IS FLOWING THROUGH THEM.THERE COULD BE AT LEAST 3 CONDITIONS: 1. BOTH

TRANSISTORS ARE ON, 2. BOTH TRANSISTORS ARE OFF, 3. ONETRANSISTOR IS ON.

LET US OBSERVE ALL THESE CONDITIONS AND VERIFY THAT,CURRENT FETCHED FROM THE SHUNT REPRESENT THE CURRENT

IN THE PHASES.

1 CONDITION: T1 AND T4 ARE IN ON STATE.

T1

T4

R4CURRENT IS DETECTED FROMR4 (IT REPRESENT CURRENT,

FLOWING THROUGH PHASES UAND V.

U

V

W

2 CONDITION: TRANSISTORS T1 AND T4 ARE INOFF STATE, CURRENT FLOWS THROUGH DIODES

D1 AND D4 BACK TO THE POWER SOURCE(REGENERATIVE MODE)

T2T4

R4CURRENT IS DETECTED FROMR4 (IT REPRESENT CURRENT,

FLOWING THROUGH PHASES UAND V.

U

V

W

T1

T4

R4

CURRENT IS DETECTEDFROM R4 (IT REPRESENT

CURRENT, FLOWINGTHROUGH PHASES U AND V.

THE VALUE MAY BEREVERSED TO GET THE

MODULE OF THE CURRENT

U

V

W

D1

D4

D2

R2

3 CONDITION: ONLYTRANSISTOR T4 IS IN ON

STATE (CURRENT FLOWS INTHE CLOSED LOOP THROUGH

T4 AND D2)

SWITCH MODE FLY BACK POWER SUPPLY (IT WAS DESIGNEDAS A SECONDARY POWER SOURCE FOR SERVO DRIVES).

PATENTED

CONTROLCIRCUIT

INPUT DCVOLTAGE

OUTPUT DCVOLTAGE

CURRENT DIAGRAMTHE SPECIAL FEATURE ABOUT THIS POWER

SUPPLY WAS A CIRCUIT, WHAT DETECTSTHAT THE OUTPUT CURRENT BECOMES

"ZERO" AND ACTIVATES THE INPUT CIRCUIT.IT ALLOWED TO MAKE THE WORKING

FREQUENCY STABLE, WHAT LED TO LESSOUTPUT PULSATION AND EFFICIENCY OF

POWER SUPPLY.

TIME

TIME

INPUTCURRENT

OUTPUTCURRENT

CURRENT ZERO,DETECTION POINT

T1

T1 ON T1 ON T1 ONT1 OFF T1 OFFT1 OFF

INPUTCURRENT

OUTPUTCURRENT

TWO PULSE PER PERIOD SWITCH MODE FLY BACKPOWER SUPPLY (IT WAS DESIGNED AS A SECONDARY

POWER SOURCE FOR DC MOTOR DRIVES)PATENTED

SPECIAL FEATURE ABOUT THIS POWER SUPPLY ISSYNCHRONISATION CIRCUIT. OUTPUT VOLTAGE IS MORE

STABLE, LESS PULSATION.

CONTROL

CIRCUIT

INPUT DCVOLTAGE

OUTPUTDC

VOLTAGE

T1

INPUTCURRENT I1

OUTPUTCURRENT

IO2

CONTROL

CIRCUIT

INPUT DCVOLTAGE

T2

INPUTCURRENT I2

OUTPUTCURRENT

IO1

SYNCHRONISATIONCIRCUIT

TIME

TIME

TIME

INPUTCURREN

T I1

INPUTCURRENT

I2

OUTPUTCURRENT

OUTPUTCURRENT

IO2

OUTPUTCURRENT

IO2OUTPUT

CURRENTIO2

OUTPUTCURRENT

IO1

OUTPUTCURRENT

IO1

SYNCHRONISATIONPOINT