A cascaded dc-dc converter

Abstract

This invention discloses a cascaded DC-DC converter, belonging to the field of DC-DC converters, comprising: a cascaded six-switch Buck-Boost circuit and a CLLLC resonant converter, as well as a current ripple optimization-power regulation unit and a pulse width generation unit. The current ripple optimization-power regulation unit is used to: calculate the converter's transmission power based on the error between the converter's output voltage and the desired output voltage; combine the functional relationship between the transmission power and d1 and d2, and the functional relationship between the converter's inductor current ripple and d1 and d2, to solve for d1 and d2 with the goal of minimizing the inductor current ripple, where d1 and d2 are the duty cycles of the P state and N state in the four switching states, respectively; the pulse width generation unit is used to control the on / off switching of the switching transistors in the six-switch Buck-Boost circuit based on the solved d1 and d2. This reduces the inductance L in the converter. b Reduce current ripple to improve its efficiency and dynamic performance.

Description

Technical Field

[0001] This invention belongs to the field of DC-DC converters, and more specifically, relates to a cascaded DC-DC converter. Background Technology

[0002] With the rapid development of DC power distribution networks and electric vehicles, the requirements for high-performance DC-DC converters are becoming increasingly stringent. Especially in the field of electric vehicles, the DC-DC converters required by on-board chargers not only need to charge the on-board lithium batteries, but also need to discharge the lithium batteries as energy storage systems in reverse. This requires the DC-DC converters to not only adapt to a wide input voltage range, but also to achieve bidirectional energy flow.

[0003] CLLLC resonant converters offer advantages such as bidirectional power transfer and zero-switching capability. However, since their voltage gain is regulated by the switching frequency, this is detrimental to the design of magnetic components, efficiency improvement, and EMI reduction. To expand the input voltage range, CLLLC resonant converters can be cascaded with DC-DC circuits. In this configuration, the CLLLC resonant converter can operate at a fixed switching frequency, with the power transfer regulated by the additional DC-DC circuit.

[0004] Existing solutions integrate a four-switch Buck-Boost circuit with a CLLLC resonant converter. In high-voltage applications, the voltage and current stress on the switching devices in this topology is excessive, leading to low converter efficiency and poor performance. Achieving stable operation of the cascaded converter and maintaining high efficiency while adjusting the power transmission of the cascaded converter is a problem that needs to be solved. Summary of the Invention

[0005] To address the shortcomings and improvement needs of existing technologies, this invention provides a cascaded DC-DC converter, which aims to simultaneously achieve optimized control of inductor current ripple during power regulation, thereby reducing the inductor current ripple of the converter and improving its efficiency and dynamic performance.

[0006] To achieve the above objectives, this invention provides a cascaded DC-DC converter, comprising: a cascaded six-switch Buck-Boost circuit and a CLLLC resonant converter, a current ripple optimization-power regulation unit, and a pulse width generation unit; the DC side of the six-switch Buck-Boost circuit is connected to the primary power supply and has four switching states: P, N, O1, and O2; the DC side of the CLLLC resonant converter is connected to the secondary load; the current ripple optimization-power regulation unit is used to: calculate the converter's transmission power based on the error between the converter's output voltage and the desired output voltage; combine the functional relationship between the transmission power and d1 and d2, and the functional relationship between the converter's inductor current ripple and d1 and d2, and solve for d1 and d2 with the goal of minimizing the inductor current ripple, where d1 and d2 are the duty cycles of the P state and N state, respectively, in the four switching states; the pulse width generation unit is used to: control the on / off state of the switching transistors in the six-switch Buck-Boost circuit based on the solved d1 and d2.

[0007] Furthermore, the functional relationship between the transmission power and d1 and d2 is as follows:

[0008]

[0009] Where p is the transmission power, V in V is the input voltage of the converter. o denoted as the output voltage of the converter, n is the transformer ratio in the CLLLC resonant converter, and R is the secondary load.

[0010] Furthermore, when the six-switch Buck-Boost circuit is in the first mode, the duty cycle of the P state is less than the duty cycle of the N state, and the functional relationship between the inductor current ripple of the converter and d1 and d2 is as follows:

[0011]

[0012] Where 0 < d1 < d2 ≤ 0.5, i s For inductor current ripple, V in The input voltage of the converter is T, the switching period is L. b The inductance is the connection between the midpoints of the two bridge arms in the six-switch Buck-Boost circuit.

[0013] Furthermore, the solved d1 and d2 are as follows:

[0014]

[0015] d2 = 0.5

[0016] Where n is the transformer ratio in the CLLLC resonant converter, p is the transmitted power, R is the secondary load, and v o This is the output voltage of the converter.

[0017] Furthermore, the six-switch Buck-Boost circuit is in the second mode, where the duty cycle of the P state is greater than that of the N state. The functional relationship between the inductor current ripple of the converter and d1 and d2 is as follows:

[0018]

[0019] Where 0 < d2 < d1 ≤ 0.5, i s For inductor current ripple, V in The input voltage of the converter is T, the switching period is L. b The inductance is the connection between the midpoints of the two bridge arms in the six-switch Buck-Boost circuit.

[0020] Furthermore, the solved d1 and d2 are as follows:

[0021] d1 = 0.5

[0022]

[0023] Where n is the transformer ratio in the CLLLC resonant converter, p is the transmitted power, R is the secondary load, and v o This is the output voltage of the converter.

[0024] Furthermore, the six-switch Buck-Boost circuit includes: switching transistors S1, S2, S3, S4, Q7, and Q8 with anti-parallel diodes, and a flying capacitor C. fly and inductor L b S1, S2, S3, and S4 are connected in series to form one bridge arm, and Q7 and Q8 are connected in series to form another bridge arm. S1 is connected to the positive terminal of the primary power supply, and S4 and Q8 are both connected to the negative terminal of the primary power supply. Flying capacitor C... fly One end of the inductor is connected to the connection point of S1 and S2, and the other end is connected to the connection point of S3 and S4; Inductor L b One end is connected to the connection point of S2 and S3, and the other end is connected to the connection point of Q7 and Q8.

[0025] Furthermore, the CLLLC resonant converter and the six-switch Buck-Boost circuit share the bridge arm formed by Q7 and Q8; the CLLLC resonant converter also includes: a bridge arm formed by the series connection of switching transistors Q5 and Q6, with the source of Q6 connected to the negative terminal of the primary power supply, and the drain of Q5 connected to the drain of Q7; primary-side resonant inductance L1, primary-side resonant capacitor C1, and magnetizing inductance L...m A CLLLC resonant circuit consisting of a transformer, a secondary resonant inductor L2, and a secondary resonant capacitor C2; and a secondary-side H-bridge circuit connected to the secondary side of the CLLLC resonant circuit.

[0026] Furthermore, the pulse width generation unit is specifically used to: control Q5 and Q8 to be synchronously turned on or off, control Q6 and Q7 to be synchronously turned on or off, and Q5 and Q6 to be complementaryly turned on; control the signals of Q5, Q6, Q7 and Q8 to be square wave signals with a frequency equal to the resonant frequency of the converter and a duty cycle of 50%; and control the on / off state of S1, S2, S3 and S4 according to the solved d1 and d2.

[0027] Furthermore, the switching transistors in the secondary-side H-bridge circuit are equipped with anti-parallel diodes; each switching transistor in the secondary-side H-bridge circuit is either in a state without a driving signal or in a synchronous rectification state.

[0028] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0029] (1) A cascaded DC-DC converter is provided, which cascades a six-switch Buck-Boost circuit and a CLLLC resonant converter. Compared with the cascaded four-switch Buck-Boost circuit and CLLLC resonant converter, the voltage stress on the switching transistors is halved, which can effectively expand the input voltage range of the converter, reduce the voltage level of the switching transistors, and improve the performance of the converter.

[0030] (2) The control strategy of the proposed cascaded DC-DC converter is designed. Based on the relationship between the transmission power and the duty cycle of the P state and N state, and the relationship between the inductor current ripple and the duty cycle of the P state and N state, the duty cycle of the P state and N state that can achieve the target power and minimize the inductor current ripple is obtained by solving the problem simultaneously. This reduces the inductor current ripple of the converter while regulating the power, thereby improving its efficiency and dynamic performance.

[0031] (3) The design allows the CLLLC resonant converter and the six-switch Buck-Boost circuit to share a bridge arm, and the on / off control of this bridge arm can simultaneously realize the functions of the CLLLC resonant converter and the six-switch Buck-Boost circuit. Thus, while ensuring the dynamic performance of the converter, the hardware cost is reduced and hardware resources are saved. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of a cascaded DC-DC converter provided in an embodiment of the present invention;

[0033] Figure 2This is an implementation circuit topology diagram of a cascaded DC-DC converter provided in an embodiment of the present invention;

[0034] Figure 3A , Figure 3B The main waveforms of the cascaded DC-DC converter in the first mode and the second mode provided in the embodiments of the present invention are shown respectively.

[0035] Figure 4 Equivalent circuit diagram of a cascaded DC-DC converter provided in an embodiment of the present invention;

[0036] Figure 5 A power control block diagram of a cascaded DC-DC converter provided in an embodiment of the present invention;

[0037] Figure 6 The current ripple optimization-power control (CRO-PC) strategy for cascaded DC-DC converters provided in this embodiment of the invention;

[0038] Figure 7A The main waveform diagrams for light-load switching to heavy-load switching of a cascaded DC-DC converter under closed-loop conditions provided in this embodiment of the invention;

[0039] Figure 7B The main waveform diagrams for heavy load switching to light load in the closed loop of the cascaded DC-DC converter provided in the embodiments of the present invention are as follows:

[0040] Figure 7C The main waveform diagram of the inductor current ripple of the cascaded DC-DC converter before optimization is provided in the embodiment of the present invention;

[0041] Figure 7D The main waveform diagram after optimization of the inductor current ripple of the cascaded DC-DC converter provided in the embodiment of the present invention is shown. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0043] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0044] Figure 1This is a schematic diagram of a cascaded DC-DC converter provided in an embodiment of the present invention. (See attached diagram.) Figure 1 , combined Figures 2-7D The cascaded DC-DC converter in this embodiment will be described in detail.

[0045] The cascaded DC-DC converter includes a cascaded six-switch Buck-Boost circuit and a CLLLC resonant converter, as well as a current ripple optimization-power regulation unit and a pulse width generation unit. The DC side of the six-switch Buck-Boost circuit is connected to the primary power supply and has four switching states: P, N, O1, and O2. The DC side of the CLLLC resonant converter is connected to the secondary load.

[0046] The current ripple optimization-power regulation unit is used to: calculate the converter's transmitted power based on the error between the converter's output voltage and the desired output voltage; combine the functional relationship between transmitted power and d1 and d2, and the functional relationship between the converter's inductor current ripple and d1 and d2, with the goal of minimizing the inductor current ripple, to solve for d1 and d2, where d1 and d2 are the duty cycles of the P state and N state in the four switching states, respectively. The pulse width generation unit is used to: control the on / off state of the switching transistors in the six-switch Buck-Boost circuit based on the solved d1 and d2.

[0047] The DC side of a six-switch buck-boost (SSBB) circuit is connected to the primary power supply, which can be, for example, a voltage source. The six-switch buck-boost circuit includes: switching transistors S1, S2, S3, S4, Q7, and Q8 with anti-parallel diodes, and a flying capacitor C. fly and inductor L b ,like Figure 2 As shown. S1, S2, S3, and S4 are connected in series to form one bridge arm, and Q7 and Q8 are connected in series to form another bridge arm. S1 is connected to the positive terminal of the primary power supply (the positive terminal of the DC bus), and the emitter of S4 and the source of Q8 are both connected to the negative terminal of the primary power supply (the negative terminal of the DC bus). Flying capacitor C fly One end of the inductor is connected to the connection point of S1 and S2, and the other end is connected to the connection point of S3 and S4; Inductor L b One end is connected to the connection point of S2 and S3, and the other end is connected to the connection point of Q7 and Q8.

[0048] For a six-switch Buck-Boost circuit, the switching state sequence within one switching cycle is: O1→P→O2→N→O2→P→O1→N. In state P, S1 and S2 are on, and S3 and S4 are off; in state O1, S1 and S3 are on, and S2 and S4 are off; in state O2, S2 and S4 are on, and S1 and S3 are off; in state N, S3 and S4 are on, and S1 and S2 are off. Based on the self-balancing characteristic of the flying capacitor, voltage balance is achieved within two cycles. The drive waveforms for all switching devices are generated based on the switching state sequence.

[0049] The CLLLC resonant converter and the six-switch Buck-Boost circuit reuse the bridge arm formed by Q7 and Q8. The CLLLC resonant converter also includes: a bridge arm formed by the series connection of switches Q5 and Q6, with the source of Q6 connected to the negative terminal of the primary power supply, and the drains of Q5 and Q7 connected; primary-side resonant inductance L1, primary-side resonant capacitor C1, and magnetizing inductance L... m A CLLLC resonant circuit consisting of a transformer, secondary resonant inductor L2, and secondary resonant capacitor C2; and a secondary-side H-bridge circuit connected to the secondary side of the CLLLC resonant circuit, such as... Figure 1 and Figure 2 As shown. The secondary-side H-bridge circuit includes an H-bridge formed by switching transistors Q1, Q2, Q3, and Q4. That is, the CLLLC resonant converter consists of a primary-side full-bridge Q5-Q8, a secondary-side full-bridge Q1-Q4, primary and secondary-side resonant capacitors C1 and C2, primary and secondary-side resonant inductors L1 and L2, and a magnetizing inductor L... m It consists of a transformer with a turns ratio of n:1.

[0050] The DC side of the six-switch Buck-Boost circuit is connected to the primary voltage source, and a voltage regulator capacitor C is connected in parallel on its DC side. in The AC side is connected through the primary resonant inductor L1, the primary resonant capacitor C1, and the magnetizing inductor L. m It is connected to the primary side of the transformer. The AC side of the secondary H-bridge circuit is connected to the secondary side of the transformer through the secondary resonant inductor L2, the secondary resonant capacitor C2, and the DC side is connected in parallel with a voltage stabilizing capacitor C. out The DC side of the secondary H-bridge circuit is connected to the secondary load as the output terminal of the converter.

[0051] According to an embodiment of the present invention, the switching transistors in the secondary-side H-bridge circuit are equipped with anti-parallel diodes; each switching transistor in the secondary-side H-bridge circuit is either in a state without a driving signal or in a synchronous rectification state.

[0052] In this embodiment, the cascaded DC-DC converter is a six-switch Buck-Boost integrated CLLLC (SSBB-CLLLC) converter. The current ripple optimization-power regulation unit and the pulse width generation unit serve as the control section of the converter. The input terminal of the current ripple optimization-power regulation unit is connected to the DC side of the secondary-side H-bridge circuit, and its output terminal is connected to the pulse width generation unit. The output terminal of the pulse width generation unit is connected to switching transistors S1-S4.

[0053] In this embodiment, there are two control variables, d1 and d2. d1 is the duty cycle of the P state in the four switching states, that is, the ratio of the time when switches S1 and S2 are simultaneously on to the entire switching cycle, 0≤d1≤0.5; d2 is the duty cycle of the N state in the four switching states, that is, the ratio of the time when switches S3 and S4 are simultaneously on to the entire switching cycle, 0≤d2≤0.5. The switching states and switching modes of the converter are shown in Table 1, where "1" represents that the switch is in the on state and "0" represents that the switch is in the off state.

[0054] Table 1

[0055]

[0056] The main waveforms of the first and second modes of the converter under Alternate Pulse Width Modulation (APWM) are as follows: Figure 3A , Figure 3B As shown. There are 8 switching states in one switching cycle, with the switching sequence being O1-P-O2-N-O2-P-O1-N. The duty cycles of states P, N, O1, and O2 are d1, d2, 0.5-d1, and 0.5-d2, respectively. The driving waveforms for all switching devices are generated based on the switching state sequence.

[0057] Although the front-stage six-switch Buck-Boost circuit and the rear-stage CLLLC resonant converter share a bridge arm, the voltage gains of the two stages do not affect each other. Therefore, the total voltage gain of the cascaded DC-DC converter can be expressed as:

[0058]

[0059] Among them, G BB For the voltage gain of a six-switch Buck-Boost circuit, G CLLLC This represents the voltage gain of the CLLLC resonant converter.

[0060] The following explains the principle behind establishing the functional relationship between transmission power and d1 and d2, as well as the principle behind establishing the functional relationship between the inductor current ripple of the converter and d1 and d2 in this embodiment.

[0061] Assume energy flows from the primary side to the secondary side, and there is no power loss during the flow. The expression for the transmitted power is:

[0062]

[0063] in, For v mo average voltage, For i b Average current, v mo Let i be the voltage at port mo. b For the current flowing through inductor L b The current.

[0064] Specifically, the functional relationship between transmission power and d1 and d2 is as follows:

[0065]

[0066] Where p is the transmission power, V in V is the input voltage of the converter. o denoted as the output voltage of the converter, n is the transformer ratio in the CLLLC resonant converter, and R is the secondary load.

[0067] Based on this, the transfer function v from the output current i2 and output voltage to the transmitted power of the cascaded DC-DC converter is... o (s) is:

[0068]

[0069]

[0070] From the two expressions above, it can be seen that the output current i2 is directly controlled by the transmission power p. Therefore, the entire converter can be regarded as a controlled current source controlled by p. Thus, the equivalent circuit of the SSBB-CLLLC converter is as follows: Figure 4 As shown, this is the power-based model of the converter. Based on the power model of the SSBB-CLLLC converter, the output voltage v of the SSBB-CLLLC converter can be directly controlled by controlling the transmitted power p. o Adjustments are made. The power control block diagram of the converter is as follows: Figure 5 As shown. Although p is an intermediate variable, there is a direct relationship between p and the control variables d1 and d2 under different modulation conditions. Therefore, by directly controlling p, d1 and d2 are indirectly controlled, thereby achieving rapid adjustment of the output voltage.

[0071] Inductor current ripple increases the magnetic losses of the transformer and inductor, reducing the efficiency of the SSBB-CLLLC converter. Since the control of the CLLLC resonant converter is fixed, inductor current ripple optimization should be achieved using a front-stage six-switch Buck-Boost circuit. Various combinations of d1 and d2 can achieve the desired power output (p), but different combinations of d1 and d2 result in different inductor current ripple. Therefore, the key to inductor current ripple optimization is finding a set of d1 and d2 that minimizes the inductor current ripple at a specific power transmission rate.

[0072] When the six-switch Buck-Boost circuit is in its first mode, the duty cycle of the P state is less than that of the N state. The functional relationship between the inductor current ripple of the converter and d1 and d2 is as follows:

[0073]

[0074] Where 0 < d1 < d2 ≤ 0.5, i s For inductor current ripple, V in The input voltage of the converter is T, the switching period is L. b This is the inductor connected between the midpoints of the two bridge arms in a six-switch Buck-Boost circuit.

[0075] By establishing the functional relationships between the inductor current ripple of the combined converter and d1 and d2, and the functional relationships between the transmitted power and d1 and d2, and eliminating the intermediate variable d2, we can obtain the expression for the inductor current ripple with respect to the transmitted power p and the control variable d1:

[0076]

[0077] Using this expression as the optimization objective and the boundary condition 0 < d1 < d2 ≤ 0.5 of the first mode as the constraint, we solve for the extreme values ​​of the inductor current ripple. We find that the inductor current ripple is minimized when d2 = 0.5. At this point, the solved d1 and d2 are respectively:

[0078]

[0079] d2 = 0.5

[0080] Where n is the transformer ratio in the CLLLC resonant converter, p is the transmitted power, R is the secondary load, and v o This is the output voltage of the converter.

[0081] When the six-switch Buck-Boost circuit is in the second mode, the duty cycle of the P state is greater than that of the N state. The functional relationship between the inductor current ripple of the converter and d1 and d2 is as follows:

[0082]

[0083] Where 0 < d2 < d1 ≤ 0.5, i s For inductor current ripple, V in The input voltage of the converter is T, the switching period is L. b This is the inductor connected between the midpoints of the two bridge arms in a six-switch Buck-Boost circuit.

[0084] Similar to the solution principle in the first mode, in the second mode, the solved d1 and d2 are as follows:

[0085] d1 = 0.5

[0086]

[0087] Where n is the transformer ratio in the CLLLC resonant converter, p is the transmitted power, R is the secondary load, and v o This is the output voltage of the converter.

[0088] According to an embodiment of the present invention, the pulse width generation unit is specifically used to: control Q5 and Q8 to be synchronously turned on or off, control Q6 and Q7 to be synchronously turned on or off, and Q5 and Q6 to be complementaryly turned on; control the signals of Q5, Q6, Q7 and Q8 to be square wave signals with a frequency equal to the resonant frequency of the converter and a duty cycle of 50%; and control the on / off state of S1, S2, S3 and S4 according to the solved d1 and d2, such as... Figure 6 As shown.

[0089] Converter resonant frequency f r for:

[0090]

[0091] Figure 7A , Figure 7B These are the main waveform diagrams for light-load switching to heavy-load and heavy-load switching to light-load switching in the closed-loop configuration of the cascaded DC-DC converter provided in this embodiment of the invention. (See also...) Figure 7A and Figure 7B It can be seen that during load switching, v o v cfly The basic structure remains unchanged. Experimental results show that the power control of the cascaded DC-DC converter in this embodiment has good steady-state performance and dynamic response speed, while maintaining the balance of the flying capacitor voltage.

[0092] Figure 7C , Figure 7D respectively in V in =300V, v o The main waveforms of the inductor current ripple before and after optimization are shown under the conditions of 500V and p=800W. (See also...) Figure 7C and Figure 7D As can be seen, before optimized control, the inductor current ripple was 10.78A; after optimized control, the inductor current ripple decreased to 2.85A. In both cases, v cfly All values ​​remained stable at 150V. Experimental results show that, in this embodiment, under the proposed CRO-PC optimized control strategy, the inductor current ripple of the cascaded DC-DC converter decreased from 10.78A to 2.85A, achieving a stable voltage level while maintaining a stable voltage. cfly While maintaining stability, it reduced inductor current ripple by 73.5%, significantly reducing the magnetic loss of the device.

[0093] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cascaded DC-DC converter, characterized in that, include: A cascaded six-switch Buck-Boost circuit and a CLLLC resonant converter, as well as a current ripple optimization-power regulation unit and a pulse width generation unit; The DC side of the six-switch Buck-Boost circuit is connected to the primary power supply and has four switching states: P, N, O1, and O2; the DC side of the CLLLC resonant converter is connected to the secondary load. The current ripple optimization-power regulation unit is used to: calculate the converter's transmission power based on the error between the converter's output voltage and the desired output voltage; and combine the transmission power with... d 1 and d The functional relationship between 2 and the inductor current ripple of the converter and d 1 and d The functional relationship between the two is solved with the goal of minimizing the inductor current ripple. d 1 and d 2, of which, d 1. d 2 represents the duty cycle of the P state and N state in the four switching states, respectively; The pulse width generation unit is used to: based on the solution obtained d 1 and d 2. Control the on / off state of the switching transistors in the six-switch Buck-Boost circuit; Transmission power and d 1 and d The functional relationship between 2 is: in, For transmission power, The input voltage of the converter. The output voltage of the converter. The transformer ratio in the CLLLC resonant converter is given. For secondary side load; The six-switch Buck-Boost circuit is in the first mode, where the duty cycle of the P state is less than that of the N state, and the inductor current ripple of the converter is... d 1 and d The functional relationship between 2 is: in, , For inductor current ripple, The input voltage of the converter. For the switching cycle, The inductance connecting the midpoints of the two bridge arms in the six-switch Buck-Boost circuit; The solution obtained d 1 and d 2 are respectively: in, The transformer ratio in the CLLLC resonant converter is given. For transmission power, For secondary side load, The output voltage of the converter; The six-switch Buck-Boost circuit is in the second mode, where the duty cycle of the P state is greater than that of the N state, and the inductor current ripple of the converter is... d 1 and d The functional relationship between 2 is: in, , For inductor current ripple, The input voltage of the converter. For the switching cycle, The inductance connecting the midpoints of the two bridge arms in the six-switch Buck-Boost circuit; The solution obtained d 1 and d 2 are respectively: in, The transformer ratio in the CLLLC resonant converter is given. For transmission power, For secondary side load, The output voltage of the converter; The six-switch Buck-Boost circuit comprises: switch tubes S1, S2, S3, S4, Q7 and Q8 with reverse-parallel diodes, and a flying capacitor C fly and an inductor L b ; S1, S2, S3 and S4 are connected in series to form a bridge arm, Q7 and Q8 are connected in series to form a bridge arm, S1 is connected to the positive terminal of the primary power supply, and S4 and Q8 are both connected to the negative terminal of the primary power supply. flying capacitor C fly one end connected to the connection point of S1 and S2, the other end connected to the connection point of S3 and S4; inductor L b one end connected to the connection point of S2 and S3, the other end connected to the connection point of Q7 and Q8; The CLLLC resonant converter and the six-switch Buck-Boost circuit share the bridge arm formed by Q7 and Q8; The CLLLC resonant converter further includes: a bridge arm formed by the series connection of switching transistors Q5 and Q6, with the source of Q6 connected to the negative terminal of the primary power supply, and the drains of Q5 and Q7 connected; a primary resonant inductor L1, a primary resonant capacitor C1, and a magnetizing inductor L... m A CLLLC resonant circuit consisting of a transformer, a secondary resonant inductor L2, and a secondary resonant capacitor C2; and a secondary-side H-bridge circuit connected to the secondary side of the CLLLC resonant circuit.

2. The cascaded DC-DC converter as described in claim 1, characterized in that, The pulse width generation unit is specifically used for: Control Q5 and Q8 to turn on or off synchronously, control Q6 and Q7 to turn on or off synchronously, and Q5 and Q6 to turn on complementaryly. The signals controlling Q5, Q6, Q7 and Q8 are square wave signals with a frequency equal to the resonant frequency of the converter and a duty cycle of 50%. According to the solution d 1 and d 2. Control the on / off state of S1, S2, S3 and S4.

3. The cascaded DC-DC converter as described in claim 1, characterized in that, The switching transistors in the secondary-side H-bridge circuit are equipped with anti-parallel diodes; each switching transistor in the secondary-side H-bridge circuit is either in a state without a driving signal or in a synchronous rectification state.

Images