This enhancement has been incorporated in Release 2009b (R2009b). For previous product releases, read below for any possible workarounds:
The BJT transistor when used for power switching applications operates as an IGBT.
When it is conducting (BJT operating in the saturated region) a forward voltage "Vf" develops between collector and emitter (in the range of 1 V).
Therefore the IGBT can be used to model the BJT.
SimPowerSystems does not simulate the gate current controlling the BJT or IGBT. The switch is controlled by a Simulink signal (1/0).
The attached demo is an example of an H-Bridge being used to generate a chopped voltage and control speed of a DC motor, in open loop, in both directions.
The DC motor is the preset model (5 HP 24V 1750 rpm). It simulates a fan type load (load torque is proportional to square of speed).
The armature mean voltage can be varied from 0 to 240 V when the duty cycle (specified in the Pulse Generator block) is varied from 0 to 100%.
The H-Bridge consists of four BJT/diode pairs (BJT simulated by IGBT models). Two transistors are switched simultaneously Q1-Q4 or Q2-Q3.
When Q1 and Q4 are fired, a positive voltage is applied to the motor and diodes D2-D3 operate as free-wheeling diodes when Q1 and Q3 are switched off.
When Q2-and Q3 are fired, a negative voltage is applied to the motor and diodes D1-D4 operate as free-wheeling diodes when Q2 and Q3 are switched off.
The demo illustrates motor starting in the positive direction with a duty cycle of 75% (mean DC voltage = 180V).
Then, at t = 0.5s, armature voltage is suddenly reversed and the motor runs in the negative direction.
Scope1 shows motor speed, armature current, and load torque.
Scope2 shows currents flowing in BJT Q3 and diode D3.
Two files are included: a discrete model (sample time Ts=20e-6s) and a continuous model.
The demo is built in SimPowerSystems 4.1.1 (R14SP3).
