Different power supply requirements
供电要求不同
(1) The series intermediate frequency furnace is a constant voltage source power supply, in order to avoid the inverter's upper and lower bridge arm thyristors at the same time, resulting in short circuit of the power supply.
（1）串联中频炉是恒压源供电，为避免逆变器的上、下桥臂晶闸管同时导通，造成电源短路。
During commutation, ensure that the switch is turned off before it is turned on.
换流时，必须保证先关断，后开通。
That is, there should be a period of time for all thyristors to be turned off.
即应有一段时间内，使所有晶闸管都处于关断状态。
At this time, the stray inductance, that is, the induced electromotive force generated from the DC end to the lead inductance of the device, may damage the device, so it is necessary to select a suitable surge voltage absorption circuit of the device.
此时的杂散电感，即从直流端到器件的引线电感上产生的感生电动势，可能使器件损坏，因而需要选择合适的器件的浪涌电压吸收电路。
In addition, in order to ensure the continuity of the load current and protect the thyristor from the influence of high voltage on the converter capacitor during the shutdown of the thyristor, it is necessary to reverse parallel the fast diode at both ends of the thyristor.
此外，在晶闸管关断期间，为确保负载电流连续，使晶闸管免受换流电容器上高电压的影响，必须在晶闸管两端反并联快速二极管。
(2) The parallel intermediate frequency furnace is a constant current source power supply, in order to avoid large induced electromotive force on the filter reactor, the current must be continuous.
（2）并联中频炉是恒流源供电，为避免滤波电抗器上产生大的感生电动势，电流必须连续。
That is to say, it is necessary to ensure that the thyristors on the upper and lower bridge arms of the inverter are turned on and then turned off during commutating, that is, all thyristors are in a conducting state during the commutating period (t).
也就是说，必须保证逆变器上、下桥臂晶闸管在换流时，是先开通后关断，也即在换流期间（t）内所有晶闸管都处于导通状态。
At this time, although the inverter bridge arm is straight through, because L is large enough, it will not cause a short circuit of the DC power supply, but the long commutation time will reduce the efficiency of the system, so it is necessary to shorten the time, that is, reduce the Lk value.
这时，虽然逆变桥臂直通，由于L足够大，也不会造成直流电源短路，但换流时间长，会使体系效益降低，因而需缩短时间，即减小Lk值。