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Brushless Motor Circuit EE452: Electric Drive Design Brushless Motor Wiring Switching Table for 120o Hall Spacing Clockwise Motion El-Sharkawi@University of Washington Counter-clockwise Motion 4 c c a ic b b ia a ib El-Sharkawi@University of Washington 5 c Step 1 a b a -c g El-Sharkawi@University of Washington 6 c Step 2 a b b -c g El-Sharkawi@University of Washington 7 c Step 3 a b -a g b El-Sharkawi@University of Washington 8 Step 1: With Rotor Magnet a -c m g El-Sharkawi@University of Washington 9 Step 2: With Rotor Magnet -c b m g El-Sharkawi@University of Washington 10 Step 3: With Rotor Magnet -a b g m El-Sharkawi@University of Washington 11 Power Circuit Q1 Vdc Q5 Q3 a Q4 c b Q2 Q6 o Motor windings n Step 1: Activated Transistors Q1 Vdc a c b Q2 o Motor windings n Step 2: Activated Transistors Q3 Vdc a c b Q2 o Motor windings n Step 6: Activated Transistors Q1 Vdc a c b Q6 o Motor windings n Switching Signals Phase a t Time Phase b tstep Phase c Time Time Voltage Regulation - Fixed Width Modulation Maximum Voltage Vdc Without modullation, the voltage during 𝑡𝑠𝑡𝑒𝑝 is 𝑉𝑑𝑐 tstep Time Reduced Voltage Vdc With Modulation, 𝑉𝑎𝑣𝑒 = 𝑉𝑑𝑐 𝑑 𝑑= ton toff Time 𝑡𝑜𝑛 𝑡𝑠𝑡𝑒𝑝 Voltage Regulation - Fixed Width Modulation Maximum Voltage Vdc Without modullation, the voltage during 𝑡𝑠𝑡𝑒𝑝 is 𝑉𝑑𝑐 tstep Time Reduced Voltage Vdc With Modulation, phase voltage 𝑉𝑟𝑚𝑠 ton toff Time 𝑑= 𝑡𝑜𝑛 𝑡𝑠𝑡𝑒𝑝 2𝑑 = 𝑉𝑑𝑐 3 Encoder output Problem Facts: • Transistors do not immediately commutate (open) • Transistors do not immediately close Problem: • There could be periods 𝑑𝑖 where high transient 𝑑𝑡 current exist. a Time b Time c Time Encoder output Commutation Solution • Make before break a Time b Time c Time Dynamic Braking Method 1: Q1 Vdc Q5 Q3 a Q4 Open all top transistors Close and regulate all lower transistors c b Q2 Q6 o Motor windings n Dynamic Braking Method 2: Q1 Vdc Q5 Q3 a Q4 Open all transistors Close and regulate the triacs c b Q2 Q6 o Motor windings n