Patent ID: 12191775

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present disclosure will now be described more specifically regarding the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this disclosure are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

FIG.1is a schematic circuit diagram illustrating a three-level rectification DC/DC converter according to an embodiment of the present disclosure, andFIG.2schematically shows an equivalent circuit of the three-level rectification DC/DC converter ofFIG.1. As shown inFIG.1andFIG.2, the three-level rectification DC/DC converter1includes a primary circuit11, a resonant tank circuit12, and a secondary circuit13. The three-level rectification DC/DC converter1has the characteristic of resonant circuit and can meet the bidirectional work requirement.

The primary circuit11receives an input voltage Vin and includes a plurality of primary switches, and the primary circuit11is configured to provide a first voltage VAB. It is noted that the primary circuit11is represented by a voltage source which provides the first voltage VAB in this embodiment since the actual implementation of the primary circuit11is not limited. The specific implementation of the primary circuit11would be exemplified in the following descriptions.

The resonant tank circuit12includes a resonant inductor Lr, a resonant capacitor Cr, and a transformer Tr. A first primary terminal121and a second primary terminal122of the resonant tank circuit12are coupled to the primary circuit11. A primary winding Np of the transformer Tr is coupled between the first primary terminal121and the second primary terminal122. A secondary winding Ns of the transformer Tr is coupled between a first secondary terminal123and a second secondary terminal124of the resonant tank circuit12. The voltage between the first primary terminal121and the second primary terminal122is the first voltage VAB, and the voltage between the first secondary terminal123and the second secondary terminal124is a second voltage VCD. InFIG.1andFIG.2, Ip is the primary current, and Is is the secondary current.

The secondary circuit13includes two clamping switches D1and D2, a switch bridge arm, and a capacitor bridge arm. The switch bridge arm includes a first secondary switch S21, a second secondary switch S22, a third secondary switch S23, and a fourth secondary switch S24sequentially connected in series. The two clamping switches D1and D2are connected in series between a node between the first secondary switch S21and the second secondary switch S22and a node between the third secondary switch S23and the fourth secondary switch S24. A node C between the second secondary switch S22and the third secondary switch S23is connected to the first secondary terminal123. The capacitor bridge arm includes a first output capacitor Co1and a second output capacitor Co2connected in series. A node between the first output capacitor Co1and the second output capacitor Co2is connected to a node D between the two clamping switches D1and D2and the second secondary terminal124. Two terminals of the capacitor bridge arm are connected to two terminals of the switch bridge arm respectively, and the voltage between the two terminals of the capacitor bridge arm is an output voltage Vo.

In the embodiment shown inFIG.1, the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24are all active switches. In another embodiment, as exemplified inFIG.3A, the first secondary switch S21and the fourth secondary switch S24may be a first diode and a second diode respectively. An anode and a cathode of the first diode are coupled to the second secondary switch S22and the first output capacitor Co1respectively. An anode and a cathode of the second diode are coupled to the second output capacitor Co2and the third secondary switch S23respectively.

In addition, in the embodiment shown inFIG.1, the clamping switches D1and D2are a third diode and a fourth diode respectively. An anode and a cathode of the third diode are coupled to a cathode of the fourth diode and a node between the first secondary switch S21and the second secondary switch S22respectively. An anode of the fourth diode is coupled to a node between the third secondary switch S23and the fourth secondary switch S24. In another embodiment, as exemplified inFIG.3B, the clamping switches D1and D2may be active switches.

FIG.4is a schematic oscillogram showing the key waveforms of the three-level rectification DC/DC converter ofFIG.1. InFIGS.4, S21, S22, S23, and S24represent the driving signals of the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24respectively; is21, is22, is23, and is24represent the currents flowing through the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24respectively; and iD1and iD2represent the currents flowing through the clamping switches D1and D2respectively. As shown inFIG.4, in any two consecutive periods of the first voltage VAB, the second secondary switch S22is in an on state for a preset time length after the falling edge in the period of the first voltage VAB, and the third secondary switch S23is in an on state for the preset time length after the rising edge in the period of the first voltage VAB. The first secondary switch S21and the fourth secondary switch S24are in diode rectification mode and are maintained in an off state. The second secondary switch S22and the third secondary switch S23have the same switching frequency equal to the frequency of the first voltage VAB. The phases of the second secondary switch S22and the third secondary switch S23are out of phase by 180 degrees with respect to each other. Further, all the secondary switches in secondary circuit13can be turned on with zero voltage switching. The said preset time length is obtained based on the input voltage Vin and the output voltage Vo. By controlling the preset time length, the duty ratio of each secondary switch can be adjusted, and the gain of the output voltage Vo can be controlled. In addition, the first voltage VAB is a square wave which is at a high level in one-half period and at a low level in the other half period, where the high level and the low level may be equal to +VAB/2 and −VAB/2 respectively, or equal to +VAB and 0 respectively.

InFIG.4, the duration from time t0to t6is regarded as one period of the secondary switches.FIGS.5A to5Fshow the working state of the three-level rectification DC/DC converter ofFIG.1in one period. In specific,FIGS.5A to5Fshow the switching state and the current flowing direction of the three-level rectification DC/DC converter1within one period. The duration from time t1to t2(FIG.5B) and the duration from time t4to t5(FIG.5E) respectively correspond to the durations of the third secondary switch S23and the second secondary switch S22being turned on positively.FIGS.5B and5Eshow the corresponding working states of the three-level rectification DC/DC converter1. The equivalent circuit of the three-level rectification DC/DC converter1during the duration from time t1to t2is shown inFIG.6A. The equivalent circuit of the three-level rectification DC/DC converter1during the duration from time t4to t5is shown inFIG.6B. FromFIGS.5B,5E,6A, and6B, it can be seen that the secondary circuit13is equivalent to be in a short-circuit state when the third secondary switch S23and the second secondary switch S22are turned on positively. At this time, the energy is stored in the resonant inductor Lr through the first voltage VAB, which prepares for the high-gain energy output in the next duration.

From the above descriptions, in the three-level rectification DC/DC converter1of the present disclosure, through controlling the four secondary switches, the energy is stored in the resonant inductor Lr during the operating process, thereby achieving the high-gain voltage output.

In an embodiment, to further improve the work efficiency of the three-level rectification DC/DC converter1, the secondary switches may be controlled with synchronous rectification. Namely, the secondary switch is driven during the current flowing reversely therethrough, thereby reducing the conduction loss of the secondary switches.

FIG.7is a schematic oscillogram showing the key waveforms of the three-level rectification DC/DC converter ofFIG.1while applying complete synchronous rectification to the secondary switches. As shown inFIG.7, while applying the complete synchronous rectification, in addition to the durations of being in the on state shown inFIG.4, the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24are further in the on state during all durations within the duration of the currents flowing reversely through the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24respectively. In this embodiment, the driving signals of the second secondary switch S22and the third secondary switch S23are complementary and have the same duty ratio of 50%. A phase difference between the driving signals of the first secondary switch S21and the fourth secondary switch S24is 180 degrees, and a phase difference between the driving signals of the second secondary switch S22and the third secondary switch S23is 180 degrees.

In addition, depending on whether the switching frequency of primary switches is variable, the control for the three-level rectification DC/DC converter1of the present disclosure may be divided into a variable frequency control and a fixed-frequency control.

FIG.8Ais a schematic block diagram illustrating the variable frequency control applied to the three-level rectification DC/DC converter ofFIG.1. While applying the variable frequency control, as shown inFIG.8A, the three-level rectification DC/DC converter1further includes a control module14a.The control module14ais configured to acquire an input voltage signal Vin_FB, an output voltage signal Vo_FB, and an output current signal Io_FB reflecting the input voltage Vin, the output voltage Vo, and the output current Io respectively through detection, and to control the operation of all the primary and secondary switches. The control module14aincludes a regulator141, and the regulator141generates a regulating signal according to the output voltage signal Vo_FB, the output current signal Io_FB, an output reference voltage Vo_ref, and an output reference current Io_ref. In this embodiment, the control module14afurther includes a voltage-controlled oscillator142and a controller143. The voltage-controlled oscillator142is coupled to the regulator141and generates a switching frequency fs of all the primary switches according to the regulating signal. The controller143is coupled to the voltage-controlled oscillator142, and generates an on-time Ton of all the secondary switches according to the input voltage signal Vin_FB, the output voltage signal Vo_FB, and the switching frequency fs of all the primary switches. When the turns ratio n of the transformer Tr is fixed, the relations among the on-time Ton of all the secondary switches, the input voltage Vin, the output voltage Vo and the switching frequency fs of all the primary switches are conformed with the curve shown inFIG.8A. In actual applications, the on-time Ton of the secondary switches may be obtained through calculation or look-up table.

FIG.8Bis a schematic block diagram illustrating the fixed-frequency control applied to the three-level rectification DC/DC converter ofFIG.1. While applying the fixed-frequency control, the switching frequency fs of all the primary switches is fixed and is larger than the resonant frequency of the resonant tank circuit12. As shown inFIG.8B, the three-level rectification DC/DC converter1further includes a control module14b.The control module14bis configured to acquire an input voltage signal Vin_FB, an output voltage signal Vo_FB and an output current signal Io_FB reflecting the input voltage Vin, the output voltage Vo and the output current Io respectively through detection, and to control the operation of all the primary and secondary switches. The control module14bincludes a regulator141, and the regulator141generates a regulating signal according to the output voltage signal Vo_FB, the output current signal Io_FB, an output reference voltage Vo_ref, and an output reference current Io_ref. In this embodiment, the control module14bfurther includes a PWM controller144. The PWM controller144is coupled to the regulator141, and generates the driving signals of all the primary and secondary switches according to the regulating signal.

In addition, in the three-level rectification DC/DC converter1of the present disclosure, the resonant inductor Lr and the resonant capacitor Cr of the resonant tank circuit12have various kinds of actual implementations.FIG.9schematically shows a specific implementation of the resonant tank circuit12. In the embodiment shown inFIG.9, the resonant inductor Lr, the primary winding Np, and the resonant capacitor Cr are sequentially connected between the first primary terminal121and the second primary terminal122in series, but not limited thereto. For example, the resonant capacitor Cr may be connected in series between the secondary winding Ns and the second secondary terminal124, and the resonant inductor Lr may be connected in series between the secondary winding Ns and the first secondary terminal123. Further, as exemplified inFIG.10, in an embodiment, the resonant inductor Lr includes a primary resonant inductor Lrp and a secondary resonant inductor Lrs, the primary resonant inductor Lrp is connected in series between the primary winding Np and the first primary terminal121, and the secondary resonant inductor Lrs is connected in series between the secondary winding Ns and the first secondary terminal123. In an embodiment, the resonant capacitor Cr includes a primary resonant capacitor Crp and a secondary resonant capacitor Crs, the primary resonant capacitor Crp is connected in series between the primary winding Np and the second primary terminal122, and the secondary resonant capacitor Crs is connected in series between the secondary winding Ns and the second secondary terminal124.

Moreover, in the three-level rectification DC/DC converter1of the present disclosure, the actual circuit topology of the primary circuit is not limited, and the primary circuit is for example but not limited to a full-bridge circuit, a half-bridge circuit, a serial-half-bridge circuit, a three-level circuit with a flying capacitor, or a three-level circuit with the clamped midpoint. Two kinds of actual circuit topologies of the primary circuit are exemplified as follows.

In an embodiment, as shown inFIG.10, the primary circuit11ais a full-bridge circuit, and the primary circuit11aincludes an input capacitor Cin, a first bridge arm, and a second bridge arm connected to each other in parallel. The voltage on the input capacitor Cin is the input voltage Vin. The first bridge arm includes a first primary switch S11and a second primary switch S12connected in series, and a node B between the first primary switch S11and the second primary switch S12is connected to the second primary terminal122. The second bridge arm includes a third primary switch S13and a fourth primary switch S14, and a node A between the third primary switch S13and the fourth primary switch S14is connected to the first primary terminal121. All the primary switches in the primary circuit11acan be turned on with zero voltage switching.FIG.11is a schematic oscillogram showing the key waveforms of the three-level rectification DC/DC converter ofFIG.10.FIG.12is a schematic oscillogram showing the key waveforms of the three-level rectification DC/DC converter ofFIG.10while applying complete synchronous rectification to the secondary switches.

In an embodiment, as shown inFIG.13, the primary circuit11bis a three-level circuit with a clamped midpoint, and the primary circuit11bincludes two primary clamping switches D3and D4, a first bridge arm, and a second bridge arm. The voltage between the two terminals of the first bridge arm is the input voltage Vin, and the two terminals of the first bridge arm are connected to two terminals of the second bridge arm respectively. The first bridge arm includes a first input capacitor C1and a second input capacitor C2connected in series. The second bridge arm includes a first primary switch S11, a second primary switch S12, a third primary switch S13, and a fourth primary switch S14sequentially connected in series. The two primary clamping switches D3and D4are connected in series between a node between the first primary switch S11and the second primary switch S12and a node between the third primary switch S13and the fourth primary switch S14. A node A between the second primary switch S12and the third primary switch S13is connected to the first primary terminal121, and a node between the first input capacitor C1and the second input capacitor C2is connected to a node B between the two primary clamping switches D3and D4and the second primary terminal122. All the primary switches in the primary circuit11bcan be turned on with zero voltage switching.FIG.14is a schematic oscillogram showing the key waveforms of the three-level rectification DC/DC converter ofFIG.13.FIG.15is a schematic oscillogram showing the key waveforms of the three-level rectification DC/DC converter ofFIG.13while applying complete synchronous rectification to the secondary switches.

In summary, the present disclosure provides a three-level rectification DC/DC converter which has the characteristic of a resonant circuit and can meet the bidirectional work requirement. In addition, the three-level rectification DC/DC converter has the characteristic of storing energy through short-circuiting the secondary circuit thereof, thereby achieving the output with high voltage gain. Since the highest voltage on the secondary switch equals one-half of the output voltage, the secondary switch can be implemented by switch components with low withstand voltage, which makes the selection for switch components easier and reduces the cost. Moreover, through controlling the four secondary switches, the energy is stored in the resonant inductor during the operating process by the secondary circuit equivalent to be short-circuited, thereby achieving the high-gain voltage output.

While the disclosure has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the disclosure needs not to be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation to encompass all such modifications and similar structures.