Lightweight Electric/Hybrid Vehicle Design

14 Lightweight Electric/Hybrid Vehicle Design
An alternative to this arrangement is for the inverter to put power back into the mains. In case of
fault, three alternistors provide current limit protection. In the brushless DC case, the motor
permanent magnets provide 50% of the flux and the remainder comes from a 50 amp circulating
current Id at right angles to the torque producing component Iq.
The inverter is constructed using 300 amp IBGT phase leg packages which minimize the
inductance between transistors and associated bypass diodes. The inverter output is filtered by 6 x
10 μΗ capacitors plus 3 x 5 μΗ inductors. This reduces the 18 kHz carrier ripple current in the
motor to about 20 AP/P. There is a real time digital signal processor (DSP) which performs vector
control using state space techniques and this includes 3rd harmonic injection to maximize the
inverter output voltage. Comprehensive overload protection is fitted. The inverter demand is a
torque signal and a speed feedback is provided for the vehicle builder to close the speed loop.
Both signals are PWM format (10–90%) on a 400 Hz carrier. The drive can be adapted for induction
motor control but this is not so efficient, as explained in the motor section below.
1.2.13 TURBO ALTERNATOR SYSTEM FOR GAS TURBINES
Figure 1.13 illustrates a turbo alternator scheme for gas turbines. This scheme has two purposes:
it starts the turbine, and provides a stabilized DC link voltage for a 2:1 change in turbine speed and
changes in DC link current from no-load to full-load. The alternator itself is the result of many
years’ development in high speed gas compressors. It is a 4 pole unit which allows iron losses to
be kept low and in particular the tooth tip temperature reasonable whilst still using silicon steel
laminations (2 pole permanent magnet alternators are potential fireballs!). The magnet material is
samarium cobalt with a carbon fibre or Kevlar sleeve. At these speeds, one needs every bit of
strength possible. The magnets are capable of operation at 150° C. The use of metallic magnets is
not a problem here because the weight is small. Hall sensors are fitted for machine timing during
starting and voltage control purposes. A small L/C filter limits the amplitude of the carrier ripple
on the alternator windings.
BATTERY
312V DC
37 AH (1HR)
SKN/100/10
BATTERY CIRCUIT
BREAKER WITH
MOTOR REMOTE
CONTROL
DEVICES
2 ME 1300 LO60 (6C) FUJI
OR
MG300J2 YS11 TOSHIBA
CHARGING SUPPLY
220V L/L
SINGLE OR 3 PHASE
5 mH
160A
400 mF
5 mH
160A
3 0 30A
CIRCUIT
BREAKER
Fig. 1.12 Electric vehicle 45 kW inverter.
10 mF
5 mH
125A
10 mF
3 x ALTERNISTORS
CT1
250 mH
250 mH
250 mH
10 mF
5 mH
125A
10 mF
CT2 CT3
BDC MOTOR
230V 45 kw
5000 RPM
750 Hz
5 mH
10 mF
125A
10 mF
3 x OFF LOAD
ISOLATOR