In order to fully exploit the design advantages of the system, the three-level neutral point clamped (NPC) topology, which used to be mainly used in high-power applications, has gradually appeared in medium and low-power applications in recent years. The improved spectrum characteristics and lower switching loss of low-voltage components can benefit the UPS system, solar inverter and other equipment that need filter. So far, in order to complete the three-level circuit, only the use of discrete components or at least three modules in one. Nowadays, choosing chip technology for higher breakdown voltage, integrating three-level bridge arms into independent modules, coupled with driving circuits, can make this kind of topology more attractive in new applications.
Principle of three level NPC topology
In the topology of three-level NPC, each bridge arm is connected in series by four IGBTs with anti parallel diodes, and two diodes DH and DL are equipped to connect the nodes between them to the neutral point of DC bus. All the selected power semiconductors have the same breakdown voltage. According to the characteristics of output voltage and current, the fundamental frequency output of a cycle has four different freewheeling operation states.
Figure 1. Commutation circuit of a bridge arm in three-level NPC. a) Short commutation circuit; b) long commutation circuit
It can be seen from figure 1A that the voltage and current are in the positive direction, T1 and DH constitute the working mode of Buck line, while T2 outputs the current in the form of constant current. While the voltage and current are in the negative period, T4 and DB constitute the working mode of boost line, and T3 outputs current in the normal mode. In the above two states, commutation only occurs in two components, which is called short freewheeling. However, when the output current is negative and the voltage is positive, the current passing through T3 and DB must be commutating to D2 and D1 as shown in Fig. 1b). This kind of commutation involves four components, so it is called long commutation circuit.
The above is the description of IGBT power module manufacturer inheritor electronics on its power module. Inheritor electronics is a power semiconductor power module manufacturer with power electronics technology as its professional field. It supplies the formulation, manufacturing and processing of power semiconductor power modules for various enterprises and companies, and also supplies the OEM production or OEM processing business for various companies. The main products are: IGBT power module, thyristor power module, ultra fast recovery epitaxial diode power module, single-phase rectifier bridge power module, three-phase rectifier bridge power module, rectifier diode power module, Schottky diode power module and other power semiconductor components.
