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FLUX-WEAKENING-CHARACTERISTIC ANALYSIS OF A
NEW PERMANENT-MAGNET SYNCHRONOUS
MOTOR USED FOR ELECTRIC VEHICLES
511~515
KOU BAOQUAN, LI CHUNYAN, AND CHENG SHUKANG
老師:王明賢
學生:方偉晋
ABSTRACT
• THE PERMANENT-MAGNET (PM) SYNCHRONOUS MOTOR (PMSM) TAKES ADVANTAGES OF SMALL
CAPACITY, HIGH EFFICIENCY, AND HIGH POWER DENSITY AND HAVE BECOME COMMONPLACE IN
ELECTRICVEHICLE DRIVING SYSTEMS.
• ANALYSIS IS DISCUSSED, INCLUDING THE FORCE ON THE MAIN PM, THE MOVEMENT PROCESS OF THE PM
IN THE PM SLOT, THE CHARACTERISTICS OF THE MOVEMENT OF THE PM, AND THE FW PERFORMANCE OF
THE NEW PMSM USED FOR ELECTRIC VEHICLES.
OUTLINE
• INTRODUCTION
• PRINCIPLE OF THE VMRPMSM
• MOVEMENT ANALYSIS OF THE PM
• AIR MAGNETIC-FIELD-ADJUSTMENT CHARACTERISTICS FOR VMRPMSM
• FEM FW ANALYSIS OF THE VMRPMSM
• EXPERIMENTAL RESEARCH
INTRODUCTION
• THE EMPHASIS OF THE RESEARCH AND DEVELOPMENT ON ELECTRIC VEHICLES LIES IN HIGH EFFICIENCY,
HIGH-POWER-DENSITY DRIVING DEVICES (MOTOR AND CONTROLLER), AND FUEL BATTERY.
• THE TERMINAL VOLTAGE IS PROPORTIONAL TO THE SPEED, AND THE LIMITATION OF THE STORAGE
BATTERY OF ELECTRIC VEHICLES AND THE SATURATION OF THE CURRENT CONTROLLER CONSTRAIN THE
APPLICATION OF THE PMSM ABOVE THE BASE SPEED; THEREFORE, FLUX-WEAKENING (FW) CONTROL IS
NECESSARY.
• THE NEW PMSM HAS THE ADVANTAGES OF ADAPTING DIFFERENT LOADS BY THE AUTOMATICALLY
ADJUSTABLE MAGNETIC FLUX AND BECOMES AN EXCELLENT COMPETITOR IN DRIVE SYSTEMS FOR
ELECTRIC VEHICLES.
PRINCIPLE OF THE VMRPMSM
• NEW STRUCTURE OF THE ROTOR
THE STATOR OF A FRACTIONAL 18-SLOT
WINDING IS THE SAME AS THE GENERAL
STRUCTURE OF A PMSM. THE ROTOR SHOWN
IN FIG. 1 IS COMPOSED OF A PM SLOT, MAIN
AND SECONDARY PMS, AND A NONMAGNETIC
CONDUCTOR.
Fig. 1. Rotor structure of the VMRPMSM. (a) The rotor structure.
(b) The prototype rotor.
PRINCIPLE OF THE VMRPMSM
• FW PRINCIPLE
THE CENTRIFUGAL FORCE ON THE MAIN PMS INCREASES WHEN THE SPEED INCREASES ABOVE THE BASE SPEED. THE
MAGNETS THEN MOVE OUTWARD ALONG THE PM SLOT UNTIL THE CENTRIFUGAL FORCE AND ELECTROMAGNETIC
FORCE REACH A BALANCE.
MOVEMENT ANALYSIS OF THE PM
• THE POSITION OF THE PM IN THE PM SLOT DETERMINES THE RELUCTANCE OF THE PATH THROUGH WHICH
THE FLUX PRODUCED BY THE PM PASSES. THIS, IN TURN, AFFECTS THE FLUX DENSITY B IN THE AIR GAP.
• A SIMPLIFIED MODEL WHICH INCLUDES THE MOVABLE PM IN THE PM SLOT AND THE IRON SLOT IS
SHOWN AS FIG. 2.
Fig. 2. Force-analysis model of the PM.
MOVEMENT ANALYSIS OF THE PM
• WE USE THE FINITE-ELEMENT METHOD (FEM) TO CALCULATE THE ELECTROMAGNETIC FORCE WHEN THE
PM IS IN DIFFERENT POSITIONS IN THE SLOT. WE DEFINE THE VARIABLE L AS THE DISTANCE BETWEEN THE
PM AND THE SLOT.
• THE ELECTROMAGNETIC FORCE INCREASES WITH DECREASING S, AND THE MAGNITUDE IS SMALLER
WHEN L IS WIDER. THE DIRECTION OF THE ELECTROMAGNETIC FORCE IS 270◦ APPROXIMATELY, WHICH
MEANS THAT THE FORCE POINTS TOWARD THE CENTRAL SHAFT. THE FRICTIONAL FORCE DUE TO
PRESSURE OF THE PM AGAINST THE SIDES OF THE SLOT IS NEARLY ZERO, SO IT IS NEGLECTED.
AIR MAGNETIC-FIELD-ADJUSTMENT
CHARACTERISTICS FOR VMRPMSM
• CHARACTERISTIC OF THE MOVEMENT OF THE PM
AS THE PM MOVES ALONG THE SLOT, IT TAKES THE FOLLOWING FEATURES.
1) THE MOTION PROCESS IS A VARIABLE LINEAR MOVEMENT.
2) THE PM LOCATES IN DIFFERENT POSITIONS IN THE PM SLOT WITH INCREASING AND DECREASING SPEEDS OF THE
MOTOR.
3) THE CRITICAL POINT WHERE THE PM BEGINS TO MOVE IS DIFFERENT WITH INCREASING AND DECREASING
SPEEDS OF THE MOTOR.
AIR MAGNETIC-FIELD-ADJUSTMENT
CHARACTERISTICS FOR VMRPMSM
• RELATIONSHIP OF THE NO-LOAD AIR-GAP MAGNETIC DENSITY AND SPEED
THE PM MOVES IN THE PM SLOT WHEN THE SPEED EXCEEDS THE BASE SPEED. THE MAGNETIC RELUCTANCE IS
VARIABLE FOR THE EXITS OF THE NONMAGNETIC CONDUCTOR IN THE MAGNETIC CIRCUIT, AND THE AIRGAP
MAGNETIC FLUX WILL ALTERNATE. THE NO-LOAD AIR-GAP MAGNETIC DENSITY IS INFLUENCED BY THE MOVEMENT
OF THE PM.WE DEFINE THE DISTANCE BETWEEN THE MAIN PMAND THE SECONDARY MAGNET AS THE VARIABLE S.
AIR MAGNETIC-FIELD-ADJUSTMENT
CHARACTERISTICS FOR VMRPMSM
• RELATIONSHIP OF THE BACK EMF AND SPEED
WHEN THE PM IS MOVING, THE AIR-GAP MAGNETIC DENSITY IS VARIABLE, AND THE RELATIONSHIP BETWEEN THE
NO-LOAD MAGNETIC DENSITY AND SPEED COULD BE DIVIDED INTO THREE STAGES.
THE VALUE OF THE BACK EMF IS DECIDED BY THE COMPARISON OF THE INCREASING SPEED AND THE DECREASING
MAGNETIC DENSITY. WE TAKE THE INCREASING-SPEED PROCESS OF THE MOTOR AS AN EXAMPLE TO ANALYZE THE
BACK EMF. THE RULE OF THE BACK EMF IN THE DECREASING-SPEED PROCESS OF THE MOTOR IS SIMILAR EXCEPT
THAT THE CRITICAL SPEED IS DIFFERENT.
FEM FW ANALYSIS OF THE VMRPMSM
• MAGNETIC-FLUX DISTRIBUTION
ONLY THE EXCITATION OF THE PM IS PRESENT WHEN THE VMRPMSM IS OPERATED IN A NO-LOAD MODE. THE
DENSER THE MAGNETIC FLUX IS, THE STRONGER IS THE MAGNETIC FIELD. THE RESULTS INDICATE THAT THE VALUE OF
S IS SMALLER, THE MAGNETIC FLUX IS WEAKER, AND THE MAGNETIC FIELD IS WEAKER.
FEM FW ANALYSIS OF THE VMRPMSM
• AIR-GAP MAGNETIC DENSITY
THE COMPARISON OF THE NO-LOAD AIR-GAP
MAGNETIC-DENSITY WAVEFORMS IS SHOWN IN
FIG. 3.
Fig. 3. Comparison of no-load air-gap magnetic-density waveforms.
EXPERIMENTAL RESEARCH
• PERFORMANCE OF THE EFFICIENCY
WE MANUFACTURED A PROPORTIONAL LOW-POWER 600-W PROTOTYPE. THE TEST SYSTEM FOR THE VMRPMSM IS
SHOWN IN FIG. 4. THE EFFICIENCY REACHES 92% WHEN OPERATED AT THE RATED POWER; THE SPEED RANGE IS
INCREASED TO 2.3 TIMES BY THE SPECIFIC STRUCTURE OF THE VMRPMSM ITSELF WITH NO FW CONTROL METHOD.
THE AREA OF EFFICIENCY OVER 80% EXCEEDS 60% (FIG. 5).
EXPERIMENTAL RESEARCH
Fig. 4. Test system.
Fig. 5. Efficiency map of the motor.
EXPERIMENTAL RESEARCH
• PERFORMANCE OF THE TORQUE
THE TORQUE PERFORMANCE IS SHOWN IN
FIG. 6. HERE, 1 IS THE CALCULATED CURVE
OF THE TRADITIONAL PMSM, WHICH TAKES
THE SAME ROTOR STRUCTURE WITH FIXED
PMS, 2 IS THE TEST CURVE OF THE
VMRPMSM, AND 3 IS THE CALCULATED
CURVE OF THE VMRPMSM.
Fig. 6. Comparison of the traditional PMSM and the VMRPMSM.