Capacity expansion technology of high-frequency induction heating power supply

Although the current capacity and voltage level of electronic devices themselves are constantly improving, even in large-capacity applications, devices sometimes need to be used in series and parallel. Sometimes it is even necessary to connect rectifiers or inverters in series and parallel to form a higher current. Yamato higher voltage AC units. In low-power applications, such as low-voltage motor control, small-capacity UPS, etc., although there are devices of corresponding levels available, the price per ampere of modular devices is far away from that of plastic-encapsulated devices, and in many cases Priority is given to using multiple tubes in parallel to achieve the required current capacity. In some situations with high operational requirements, inverters are often used to run the entire machine in parallel in order to provide redundant backup, such as UPS.

There are three levels of expansion technology commonly used for high-frequency induction heating power supplies: series and parallel connection of devices, component-level series and parallel connection, and machine-level series and parallel connection.

1. Series and parallel operation of devices

In the series-parallel operation of devices, the voltage equalization problem must be handled well, so that the voltages endured by each series-connected device when turned off are basically equal, so as to play the role of each device in blocking voltage; in parallel operation, the voltage equalization problem must be handled well. Current sharing issues after turn-on to fully utilize the conduction capability of each device.

During parallel operation of devices, dynamic and static current sharing in the devices must be considered. In static current sharing, it is mainly determined by the saturation voltage and on-resistance of the device. The discrete degree of the on-resistance value determines the actual effect of device current sharing. In dynamic current sharing, generally speaking, because the devices are connected in parallel connected so the voltages across them are equal. However, due to the unequal lead inductance during the transition process, the high di/dt effect causes voltage differences on the device. To minimize this voltage difference, we must start from two aspects: di/dt and lead inductance imbalance. . Of course, if the combined result of these differences does not exceed the rated range of the device, the critical losses caused by these differences can be ignored. On the other hand, the influence of the common lead inductance of the emitter on the switching energy cannot be ignored.

2. Series and parallel operation of components and complete machine

In dc/dc conversion, in order to increase the output current, components are often connected in parallel. For high-power parallel high-frequency induction annealing power supplies, a parallel scheme can be used to increase the overall output power. The difference from the parallel scheme of inverters is that The output of the inverter is completely independent of the two power supplies (of course the inverter trigger signal source is common). As shown in Figure 5-6, as long as the DC currents id1 and id2 of each power supply are basically equal, the operating currents of each inverter will also be basically equal, which achieves the purpose of current sharing. The inductor used as a filter link generally has a large inductance, so the first few DC links have enough time to adjust the current difference.

3. Capacity expansion plan of series inverter power supply

For the parallel connection of series resonant inverter, since the output of the inverter is voltage type and the internal resistance of the voltage source is extremely low, even if the voltages are unequal in a short period, a large circulating current will be caused, so that the current of the inverter device will be serious. Uneven, in this case, an inductor is generally inserted in series with the output end of the inverter to suppress the circulating current. There are two problems with this parallel connection of inverters:

(1) Unable to suppress DC circulation

(2) The inductor that suppresses the circulating current completely participates in the resonance of the tank circuit, which has a great impact on the series and parallel resonance characteristics of the load, and brings great inconvenience to the debugging of the circuit.