Electromagnetic simulation of electric motors for automotive applications Adrian Scott Market Development Manager Low Frequency Applications
Agenda Quick introduction to CST EMS for LF simulation and applications Short summary of motors in automotive applications Typical motor design parameters Simulation example of a PMSM model set up and useful design parameter extraction Other motor examples : Induction and reluctance motors Outlook CST EMS 2016
CST EM STUDIO Solvers Electrostatics Frequency Domain Stationary Currents Magnetostatics Time Domain
Traction motor candidates for HEV/EVs Rotating machines Synchronous Asynchronous PMSM (Brushless DC) Externally excited (ESM) Reluctance IM Switched Reluctance (SRM) Variable Reluctance (VRSM)
Typical synchronous motor parameters Requirement Open Circuit MMF Characteristic Torque versus torque angle Torque optimization Cogging torque Lq/Ld Extraction Iron loss calculation Permanent magnet demagnetization Flux weakening capability Goal Parameterization V versus Flux Parameterization Maximize Minimize - vibration Equivalent circuit Efficiency Short circuit risk Wide range of operating speed
Electrical machine features 2D Transient and Magnetostatic
Key features : 2015 1. 2D LT Motion solver 2. Permanent magnet transformation 3. Coil grouping 4. State-Space (Ms) 5. Transient Inductance monitors (LT) + Back EMF (LT) 6. Impedance Matrix (LF) 7. Core Loss models (LT)
Iron Loss Calculation Methods
Conceptual example PMSM Optimization
Permanent Magnet Synchronous Motor Stator consisting of three-phase rotating field winding system, non-linear steel Rotor consisting of Permanent magnets Air barriers for flux diversion
Coil Grouping / Colouring Multi-phase winding/coil systems Voltage and/or current groups Reduced inductance matrix Summation of coils inductances Terminals i.e. single or 3-phase systems... Colouring helps to ensure correct coil definition
Permanent magnet definition
Air-Gap Definition (rotional)
Stator and Rotor steel M19 BH Data
Mesh with local mesh properties
PMSM optimization Average torque and torque ripple (check also cogging torque?) Permanent magnet radial position, angle between magnets, magnet lengths, barrier geometry Motivation : difficult to derive analytical expressions due to non-linear effects e.g. Barrier shape, proximity to rotor surface Conflict of interests : maximum torque, reduced ripple!
Steady state torque and ripple Minimize Maximize
Rotor permanent magnets and barriers
Average Torque
Torque ripple
Sum of all goals
Initial and Optimized Steady State Torque
Steady-State torque
Cogging torque (stator open circuit)
Optimized PMSM geometry
B-Field (Abs) versus time
Core losses in Stator and Rotor
Incremental Inductance versus time
Back-EMF results
Back EMF vs. Speed (Frequency)
Other motor types
Induction motor performance Performance characteristic Torque vs. Speed vs. Frequency Squirrel Cage Type 4 Pole, 400 Hz 3-Phase Stator Winding (AC Supply) Synchronous speed proportional to applied frequency Rotor slips behind synchronous field Torque, Nm 100 400 Hz Standstill Speed, rev/min 12000 rpm S = 1 Slip S = 0 Constant Voltage/frequency (V/f) control scheme for induction motors
Induction motor B-Field
Acceleration CPU Acceleration Pyhsical cores/multi-threading Distributing Computing Parametric/optimisation Induction motor simulation Single simulation (e.g. @ Slip_T_max) Total time 1 Thread: 9m : 23s Total time 4 Threads: 5m : 15s Acceleration: 1.8
Switched Reluctance Machine
Salient Pole Synchronous Motor Salient pole rotor with DC excitation 4 Pole, 50 Hz, 3-Phase Stator Winding (AC Supply) Synchronous speed proportional to FREQUENCY / Number of magnetic poles
Salient Pole Synchronous Motor Open circuit (no-load) test Rotor speed = synchronous speed Stator RMS voltage (phase A) versus field current, I_field
Multiple rotations : magnetic gear
Shaded-Pole Induction Motor (SPIM) 2D Transient motion Eddy currents in cage and shaded-pole rings, non-linear magnetic materials Standard Torque-Speed curves
New features in EMS 2016
Key features : 2016 1. Voltage driven coils in 2D (LT) 2. Zero NET current constraint in LT 2D in magnets 3. Permanent magnet demagnetization Monitor (LT) 4. Periodicity LT (subvolume) 5. Equation of motion (LT) 6. Linear motion (LT) 7. Additional core loss models 8. 2D Forces, 3D LT Force density (Ms, LT) 9. H-Field calculation for (LF EQS) 10. Moment calculation (Ms)
Motor Control PMSM : Pulse Width Modulation New voltage sources in 2D LT Transient User-Defined PWM stator voltage signals PWM Signals from inverter unit
Summary New features in EMS 2015 for the simulation of electrical machines Efficient 2D simulations Simulation example of a PMSM model set up and useful design parameter extraction The possibilities to optimize design parameters of a PMSM was shown Same principles can also be applied to induction and reluctance motors Outlook CST EMS 2016