- Research and/or Engineering Questions/Objective (max. 100 words); Nowadays, automotive industries are increasing the battery voltage from 400v to 800v for shorter recharging time and longer driving range, but the occupation ratio of 800v charging station is still low now. A cost-effective approach for solving this problem is an integrated scheme which reconfigure the powertrain into a DC/DC boost converter that allows the compatibility of an 800v vehicle with the 400v charging infrastructure. But using motor windings as boost inductances have some problem:1. High winding current ripple brings the motor rotor thermal problem due to small equivalent inductance. 2.motor rotor may rotate during boost mode. - Methodology (max. 150 words) This paper proposed a new topology which has larger equivalent inductance at boost mode. New topology places a single pole triple throw switch (SP3T) between motor three phase terminals and charger port. Corresponding control scheme: at one certain position, certain switch would be closed, thus two windings are connected in parallel and then connected in series with the third winding. This connection can increase the boost circuit inductance compare to the neutral point out scheme. Meanwhile the reference current of two windings is calculated with rotor position and charge current command, making the current vector to be on d-axis (magnetizing or demagnetizing current, depending on rotor position), thus no electromagnetic torque would be generated. But demagnetizing current may make the rotor rotating, so position loop is used for solving this problem. The position controller generates two opposite corrective currents which added to original boost reference currents for holding the rotor position stable. - Results (max. 150 words); Simulation results verify the effectiveness of the system, taking rotor position -pi/6 ~ pi/6 as an example, compares to the neutral point out scheme(three phase interleave control): at rotor position 0,by using this new topology, inductance current ripple is reduced 46%,81%,81% respectively. At rotor position pi/6 and -pi/6, inductance current ripple is reduced 71%,100%,70% respectively. - Limitations of this study 1.Needing single pole triple throw switch(SP3T) which will increase the cost. 2.DCM state is involved at some position for one phase current which increase the control difficulty. 3. Total fundamental stator copper loss is larger than three-phase-out scheme, and the copper loss of each winding is not equal - What does the paper offer that is new in the field including in comparison to other work by the authors? (max. 100 words) Compare to the neutral points out scheme, the new topology has larger inductance at boost mode for saving additional inductance and controlling torque like motor without considering the homopolar torque. New control algorithm is proposed based on that topology which can achieve boost function and avoiding unintended rotor rotation. - Conclusions: (max. 100 words) This paper proposed a new topology which use electric powertrain as a boost converter to step up 400v to 800v voltage battery. This new topology uses a SP3T switch to reconfigure the motor windings’ connection at different rotor position, which not only reduces current ripple significantly compared to the neutral point out scheme, but also eliminate the electromagnetic torque through phase currents control. This new topology also has the advantage of no modification of motor structure, only need to add a switch connecting to three winding terminals.
Mr. chang Liu, Engineer, nio