The circuit of Figure 15.49 is used to provide regenerative braking in a traction motor. The motor constant is $0.25 \mathrm{~V} / \mathrm{rpm}$, and the supply voltage is 550 V . The armature resistance is $R_a=0.15 \Omega$. The motor speed is $1,000 \mathrm{rpm}$, and the motor current is 200 A .
a. Determine the duty cycle $\delta$ of the converter.
b. Determine the average power fed back to the battery.