Analysis and simulation of a large step-up ratio four-terminal DC/DC converter

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Analysis and simulation of a large step-up ratio four-terminal DC/DC converter [Copy link]

　Boost DC/DC converter circuits are valued for their inherent boost characteristics and simple circuit topology, and are increasingly used. In many cases, it is required to output a DC voltage as high as possible under low input voltage conditions. Traditional Boost DC/DC converters only have a boost ratio of (D: duty cycle), so sometimes additional circuits have to be used to obtain a higher boost ratio [1]. This paper proposes a four-terminal combined boost DC/DC converter with a simple circuit structure and convenient control. Theoretically, it has a boost ratio of. At the same time, this paper analyzes and simulates it.

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Principle Overview The main circuit is shown in Figure 1, where the left side of the load RO is a Boost DC/DC converter and the right side is a Buck-Boost DC/DC converter. Therefore, when the circuit operates in continuous conduction mode (CCM), in the steady state, equations (1) and (2) hold true [2]: (1) (2) Figure 1 Figure 2 From (1) and (2), we can get: (3) Where: D = Ton/T, as shown in Figure 2, it can be seen that compared with the traditional Boost DC/DC converter, this circuit has a higher boost ratio and the circuit is a four-terminal structure. 3 Main parameter analysis For the convenience of analysis, the following assumptions are made: ① The components are ideal; ② The output voltage UO has no ripple. In the main circuit shown in Figure 1, V1 and V2 represent high-frequency switching tubes, and VD1 and VD2 are freewheeling diodes. The driving signals of V1 and V2 are the same, and the circuit operates in two states: Figure 3 (1) t0-t1 period. V1 and V2 are turned on at the same time, and the equivalent circuit is shown in Figure 3. At this time, Ui is added to L1 and L2 respectively, so iL1 and iL2 rise linearly, and the inductors L1 and L2 store energy, and their increments are: (4)(5) At the same time, since the switch tubes V1 and V2 are turned on, VD1 and VD2 are cut off due to the reverse pressure, so C1 and C2 discharge and release energy to provide working current to the load, U1 (positive value) decreases, and U2 (negative value) increases. (2) t1-t2 period. V1 and V2 are turned off at the same time, and the equivalent circuit is shown in Figure 4. At this time, since the currents iL1 and iL2 of L1 and L2 cannot change suddenly, VD1 and VD2 are turned on and continue to flow; at the same time, C1 and C2 are charged and store energy respectively, U1 (positive value) increases, and U2 (negative value) decreases. L1 and L2 release the energy stored during the Ton period, so iL1 and iL2 decrease linearly. Ignoring the diode voltage drop, the voltages of -(U1-Ui) and -U2 are applied to L1 and L2 respectively, and the increments are: (6)(7) Figure 4 Because in steady state, the inductance satisfies the volt-second balance in one cycle, so from equations (4) and (6) we can get: (8) Similarly, from equations (5) and (7) we can get: (9) From equations (8) and (9) we can get the output voltage: (10) That is the boost ratio. It can be seen that the boost ratio of this circuit is 1+D times that of the traditional Boost circuit. The specific working waveform is shown in Figure 5. Figure 5 (3) Realization of zero ripple. It can be seen from Figure 5 and Figure 3 that during the conduction period of V1 and V2, the following equations hold: UL1=Ui(11) UL2=Ui(12) Similarly, it can be seen from Figure 5 and Figure 4 that during the turn-off period of V1 and V2, the following equations hold: UL1=-(U1-Ui)(13) UL2=-U2(14) Moreover, equations (8) and (9) hold, so we can get: (15(16) Combining equations (11), (12), (15), and (16), it can be seen that the voltages UL1 and UL2 on inductors L1 and L2 are the same regardless of whether the switch is on or off; therefore, an integrated coupled inductor can be used to replace L1 and L2 to achieve zero ripple operation. For detailed reasoning, please refer to references [3][4]. 4 Simulation results In order to verify the correctness of the theoretical analysis, the circuit was simulated and analyzed using PSPICE circuit simulation software, and the simulation waveforms are shown in Figures 6 and 7. Among them, Ui=48V, L1=L2=1000μH, C1=C2=100μF, RO=30Ω, switching frequency f=20kHz, D=0.7. Figure 6 is the voltage waveform of the load and capacitor, and Figure 7 is a local detail diagram.

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Principle Overview The main circuit is shown in Figure 1, where the left side of the load RO is a Boost DC/DC converter and the right side is a Buck-Boost DC/DC converter. Therefore, when the circuit operates in continuous conduction mode (CCM), in the steady state, equations (1) and (2) hold true [2]: (1) (2) From (1) and (2), we can get: (3) Where: D = Ton/T, as shown in Figure 2. It can be seen that compared with the traditional Boost DC/DC converter, this circuit has a higher boost ratio and the circuit is a four-terminal structure. 3 Main parameter analysis For the convenience of analysis, the following assumptions are made: ① The components are ideal; ② The output voltage UO has no ripple. In the main circuit shown in Figure 1, V1 and V2 represent high-frequency switching tubes, and VD1 and VD2 are freewheeling diodes. The driving signals of V1 and V2 are the same, and the circuit operates in two states: (1) t0-t1 period. V1 and V2 are turned on at the same time, and the equivalent circuit is shown in Figure 3. At this time, Ui is added to L1 and L2 respectively, so iL1 and iL2 rise linearly, and the inductors L1 and L2 store energy, and their increments are: (4)(5) At the same time, since the switch tubes V1 and V2 are turned on, VD1 and VD2 are cut off due to the reverse pressure, so C1 and C2 discharge and release energy to provide working current to the load, U1 (positive value) decreases, and U2 (negative value) increases. (2) t1-t2 period. V1 and V2 are turned off at the same time, and the equivalent circuit is shown in Figure 4. At this time, since the currents iL1 and iL2 of L1 and L2 cannot change suddenly, VD1 and VD2 are turned on and continue to flow; at the same time, C1 and C2 are charged and store energy respectively, U1 (positive value) increases, and U2 (negative value) decreases. L1 and L2 release the energy stored during the Ton period, so iL1 and iL2 decrease linearly. Ignoring the diode voltage drop, the voltages of -(U1-Ui) and -U2 are applied to L1 and L2 respectively, and the increments are: (6)(7) Because in steady state, the inductance satisfies the volt-second balance in one cycle, so from equations (4) and (6) we can get: (8) Similarly, from equations (5) and (7) we can get: (9) From equations (8) and (9) we can get the output voltage: (10) That is the boost ratio. It can be seen that the boost ratio of this circuit is 1+D times that of the traditional Boost circuit. The specific working waveform is shown in Figure 5. (3) Realization of zero ripple. It can be seen from Figure 5 and Figure 3 that during the conduction period of V1 and V2, the following equations hold: UL1=Ui(11) UL2=Ui(12) Similarly, it can be seen from Figure 5 and Figure 4 that during the turn-off period of V1 and V2, the following equations hold: UL1=-(U1-Ui)(13) UL2=-U2(14) Moreover, equations (8) and (9) hold, so we can get: (15(16) Combining equations (11), (12), (15), and (16), it can be seen that the voltages UL1 and UL2 on inductors L1 and L2 are the same regardless of whether the switch is on or off; therefore, an integrated coupled inductor can be used to replace L1 and L2 to achieve zero ripple operation. For detailed reasoning, please refer to references [3][4]. 4 Simulation results In order to verify the correctness of the theoretical analysis, the circuit was simulated and analyzed using PSPICE circuit simulation software, and the simulation waveforms are shown in Figures 6 and 7. Among them, Ui=48V, L1=L2=1000μH, C1=C2=100μF, RO=30Ω, switching frequency f=20kHz, D=0.7.