FLUX-WEAKENING-CHARACTERISTIC ANALYSIS OF ANEW PERMANENT-MAGNET SYNCHRONOUS

MOTOR USED FOR ELECTRIC VEHICLES511~515

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 ROTORTHE 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 PRINCIPLETHE 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-ADJUSTMENTCHARACTERISTICS FOR VMRPMSM

• CHARACTERISTIC OF THE MOVEMENT OF THE PMAS 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-ADJUSTMENTCHARACTERISTICS FOR VMRPMSM

• RELATIONSHIP OF THE NO-LOAD AIR-GAP MAGNETIC DENSITY AND SPEEDTHE 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-ADJUSTMENTCHARACTERISTICS FOR VMRPMSM

• RELATIONSHIP OF THE BACK EMF AND SPEEDWHEN 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 DISTRIBUTIONONLY 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 DENSITYTHE 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 EFFICIENCYWE 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 TORQUETHE 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.