Patent TW-202127781-A (TW)
Title: Novel tt control zvs power inversion circuits
Inventor: LEU CHING-SHAN
IPC: H02M1/08
Filed: 2020-01-09
Abstract: DC - DC converter is widely used in today’s electrical device. By using an inversion circuit cascaded with a rectification circuit and a filter circuit, the DC voltage is inverted to an AC voltage and the AC voltage is then rectified and filtered to the required DC voltage. 
 
     Several different topologies are used for different power inversion applications. Among them, four-switch inversion topologies (including full-bridge topology and three-level topology) have low voltage and current stresses on semiconductors so that these circuits are widely used for high input-voltage medium-to-high power conversion applications. 
 
     A full-bridge inversion topology with its symmetrical control scheme timing diagram is shown in FIG. 1(a) and FIG. 1(b), respectively. There are two interleaved driver signal pairs (V gs1 -V gs2  and V gs3 -V gs4 ) with two identical PWM signals in each pair. Although the topology is a totem pole circuit structure, shoot-through problem can be avoided. However, it suffers from high 
switching losses for high power density applications due to its hard-switch operation. To achieve high power density performance, phase-shifted control scheme has been invented three decades ago and their driver signals assigned to each switch (including synchronous rectifier, SR) are shown in FIG. 1(c). These four primary switch driver signals (V gs1  - V gs4 ) are all near 50% duty cycle with inserting dead-time interval. By utilizing the dead-time interval, the energies between the leakage inductance and parasitic capacitance of the MOSFET can be exchanged to achieve ZVS operation. However, it may have potential shoot-through problem at each switch’s tum-off instant. Up to date, fast recovery body-diode MOSFT with inserting a larger dead-time interval is thus used. Because of noise or radiation, however, the shoot-through problem cannot be totally avoided and becomes an issue of reliability. Besides, the inserting dead-time interval restricts the available operating switching frequency. As a result, the power density improvements are thus limited. Including two synchronous rectifier (SR) driver signals, furthermore, six drive signals have to be issued by the controller to achieve high efficiency performance. It makes the implementation of the controller complicated compared to that of the symmetrical control scheme. Accordingly, a simple control scheme is desired to have ZVS operation and less potential shoot-through problems simultaneously. 
 
     To explore the desired control scheme, both symmetrical and phase-shifted control schemes are re-investigated. It can be found that ZVS operation can be achieved if the duty cycle of one and only one driver signal in each pair is extended to near 50%. Moreover, the potential shoot-through problems can also be eliminated at the turn-off instant of the two PWM driver controlled switches. Compared to phase-shifted control scheme, potential shoot-through problems reduce to two and the circuit reliability is improved. 
 
     Due to the hieroglyph of the driver signal timing, the disclosed control scheme is named as TT control scheme. It has two interleaved drive signal pairs with one PWM signal and one near 50% duty cycle signal in each pair. Four different 
driver combinations are thus obtained as shown in FIG. 2(a) to FIG. 2(d). In addition to improving the circuit reliability, the implementation of the controller is simple because either two PWM signals or two near 50% driver signals are ready for the SR driver signals. 
 
     Accordingly, the present invention discloses several four-switch inversion circuits with TT control scheme having better reliability and high efficiency performance without increasing component count.