Bidirectional thyristor energy consumption braking circuit

In the circuit shown in the figure, VS is a bidirectional thyristor, and its conduction angle determines the amount of braking energy; VD2 is a trigger tube, and its breakdown voltage is 30V, which can make the VS trigger reliable and stable. VD1 is a rectifier diode, and R2 is a leakage resistor, which allows the charge on C to be discharged at any time. R1 and C form a phase shift circuit to control the conduction angle of VS, thereby providing a pulsating DC voltage with an adaptive size for braking. If the value of C is large, the braking time will be long; on the contrary, the braking time will be short. Appropriately select the capacitance value of C so that the average braking voltage is 85V, the braking current is 4.5~5A, and the motor full-load braking time is 4~5 seconds. KM is the running main contactor of motor M, and KMB is the brake contactor of motor M.