DC boost converter and bidirectional DC converter

Q: What is the primary function of a boost converter? 

A: 

Steps up input voltage ((V_d)) to higher output voltage ((V_a)) 

Key equation: (V_a = \frac{V_d}{1-D}) 

(Unlike AC transformers, uses inductor energy storage) 

Q: How does a boost converter's topology differ from a buck converter? 

A:  

• Inductor on input side  

• Transistor (IGBT) in parallel with output  

• Diode in series with output 

Q: What are the inductor voltage equations during switch states? 

A:  

• Switch ON: (\Delta V_L = V_d) (charges inductor)  

• Switch OFF: (\Delta V_L = V_d - V_a) (discharges to output) 

Q: What is the steady-state condition for inductor current? 

A: 

(\Delta I_{on} + \Delta I_{off} = 0) → (V_d t_{on} = (V_a - V_d) t_{off}) 

(Energy balance over switching cycle) 

Q: How does duty cycle ((D)) affect boost converter output? 

A: 

(V_a = \frac{V_d}{1-D})  

• (D=0): (V_a = V_d)  

• (D→1): (V_a→∞) (theoretically) 

Q: Why is a large capacitor used in boost converters? 

A:  

• Maintains constant output voltage ((V_a))  

• Filters ripple during switching  

• Assumed infinite in steady-state analysis 

Q: What is the key advantage of a 2-quadrant bidirectional converter? 

A:  

• Allows power flow in both directions  

• Combines buck (step-down) and boost (step-up) modes  

• Enables motoring/regenerative braking 

Q: How does a bidirectional converter achieve 2-quadrant operation? 

A:  

• Buck mode (Q1): (S_1) active → power to motor  

• Boost mode (Q2): (S_2) active → regeneration to source  

• Uses complementary switches/diodes 

Q: Describe current paths during buck vs. boost modes: 

A:  

• Buck: Current through (S_1) (ON) or (D_2) (OFF)  

• Boost: Current through (S_2) (ON) or (D_1) (OFF)  

• Inductor voltage determines diode conduction 

Q: A boost converter has (V_d=20V), (D=0.6). What is (V_a)? 

A: 

(V_a = \frac{20V}{1-0.6} = 50V) 

(Step-up ratio: 2.5×)  

Q: What are limitations of boost converters? 

A:  

• High output voltage stresses components  

• Requires precise duty cycle control  

• Discontinuous conduction at light loads 

Q: How is power conserved in ideal converters? 

A: 

(P_{in} = P_{out}) → (V_d I_d = V_a I_a) 

(Assuming 100% efficiency, no losses)