# Problems in Residual Voltage Excitation of Diesel Generator Set 2

Nov. 11, 2022

Based on the basic requirements that the power converter of diesel generator set should match the motor structure, with high efficiency, convenient control, simple structure and low cost, an ideal power converter main circuit structure should meet the following conditions at the same time:

Minimum number of main switching elements;

All power supply voltage can be applied to motor phase winding;

The voltage rating of the main switching device is close to that of the motor;

Capable of rapidly adding phase winding current;

The phase current can be effectively controlled by modulating the main switching device; When the winding flux is reduced, the energy can be fed back to the power supply.

The following is a brief introduction to several common circuits of SRM power converter, focusing on comparing the quota size, number of components, energy feedback methods and applicable occasions of main switch devices in these different circuits.

The double winding type of diesel generator set is shown as the double winding structure used in the early days. Generally, the main and secondary windings are wound in parallel to obtain the maximum mutual inductance coefficient. After the switching element of the main winding is disconnected, the energy of the main winding is transferred to the secondary winding through mutual inductance, and then the diode continues to flow D. The rated working voltage of the main switching element of this circuit is 2 (1+D) V, Among them, V is the rectifier bridge that can be used in the rotor circuit and jointly applied by the China Resistance University Press, Pierce Hall2W1, August, 2001.

Assume that the parameters of the residual voltage excitation circuit of the unit are as follows:

The voltage drop of the two thyristors in series is 2.5V, the voltage drop of other circuits is 0.5V, the rotor circuit resistance is 1 ohm, the rotor inductance is 2 Heng, the thyristor holding current is 80mA, and the effective value of the side line voltage U2 of the rectifier transformer is 8V. Then according to formula (2), the minimum time t to make the thyristor reach the holding current can be calculated as t=1.9ms. Under the above conditions, the actual time from triggering to conduction is greater than t.

At the same time, the pulse train is used, and its duty cycle is 1. If the conduction cannot be completed at 1 of a pulse, then in the 0 segment of the pulse, the thyristor has not been conducted and will turn to the cut-off until the arrival of the next pulse "1", when the current in the rotor has not decayed to 0 last time.

In this way, after several pulse cycles of the diesel generator set, the thyristor will maintain current and conduct. If residual voltage excitation cannot be taken, the trigger voltage and current should be appropriately increased, that is, the trigger circuit resistance R1 should be appropriately reduced or the T1 turn ratio should be changed (see), and the number of turns of the secondary side coil of T1 should be added.

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