A dc-dc converter and a control method thereof

Abstract

The application discloses a kind of direct current converters and its control method, including multiple cascaded power units;Power unit includes at least two series input capacitors;Each input capacitor is connected in parallel with at least one switch tube;The connection midpoint of first switch tube and second switch tube is connected with one end of first impedance matching inductor, the connection midpoint of t-1th switch tube and tth switch tube is connected with one end of second impedance matching inductor;The other end of first impedance matching inductor, the other end of second impedance matching inductor is connected by voltage-sharing capacitor branch;Voltage-sharing capacitor branch includes at least two series voltage-sharing capacitors;The connection midpoint of adjacent two voltage-sharing capacitors is connected with one end of resonance capacitor;The other end of resonance capacitor is connected with one end of high-frequency transformer primary winding, and the other end of high-frequency transformer primary winding is connected with the connection midpoint of mth input capacitor and m+1th input capacitor by resonance inductor.The application has the advantages of input voltage automatic balancing, power device current automatic balancing.

Description

Technical Field

[0001] This invention relates to power electronic circuit technology, and in particular to a DC-DC converter and its control method. Background Technology

[0002] In various power applications such as medium-voltage DC distribution networks, renewable energy DC systems, submarine power transmission and distribution systems, and shipboard integrated power systems, medium-voltage DC converters have become a research hotspot due to their ability to convert power from medium-voltage DC buses to low-voltage DC buses and provide electrical isolation. Among them, input-series-output-parallel DC converters, which have advantages such as modular structure and strong current output capability, are widely used. However, traditional medium-voltage DC converters require multiple voltage conversion stages to meet different voltage level requirements when supplying power to different loads. This results in a complex circuit structure that is difficult to achieve power balance, and the system efficiency is reduced due to the multi-stage power processing. Furthermore, in applications with high reliability requirements, such as submarine power transmission and distribution systems, short-circuit faults on the low-voltage side frequently occur. Although the protection methods adopted by traditional medium-voltage DC converters can clear fault currents, they require sampling the voltages of multiple capacitors and inductors and are prone to false protection. Additionally, due to the different load characteristics of the output ports, when one or more output ports experience a short-circuit fault, the converter has difficulty quickly isolating the faulty output port, leading to the collapse of the multi-port output system. The high resistance of long-distance submarine power transmission lines leads to voltage drops at the terminals and large fluctuations in the input voltage range. Designing a wide-input-range DC-DC converter with power balance, multi-port output, and short-circuit fault isolation protection under medium-voltage input conditions to improve system efficiency and power supply reliability remains a key design challenge for medium-voltage DC-DC converters.

[0003] Traditional switched-capacitor converters (such as CN109302072A) transfer energy step-by-step from Cink-1 to Cbk-1 and then back to Cink. Following this pattern, energy is transferred from the first capacitor to the last to achieve input capacitor voltage equalization. However, this multi-stage voltage equalization process in traditional switched-capacitor converters leads to increased losses. Furthermore, traditional switched-capacitor converters cannot achieve current equalization between the switching transistors, resulting in large current surges and uneven thermal stress caused by current inconsistencies, making them unsuitable for high-power applications. Simultaneously, existing structures or control methods (such as CN109302072A) can only achieve closed-loop control of the voltage at one output port, with other ports controlled indirectly, resulting in low control accuracy and making them unsuitable for applications requiring high output voltage precision. Moreover, traditional control methods, such as frequency conversion or phase shift control, are difficult to implement in resonant converters with wide-range voltage regulation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a DC-DC converter and its control method that eliminates the need for an additional voltage equalization process and reduces energy transmission loss, in order to address the shortcomings of the existing technology.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a DC-DC converter, characterized in that it includes multiple cascaded power units; each power unit includes at least two input capacitors connected in series; each input capacitor is connected in parallel with at least one switching transistor; all the switching transistors are connected in series; the midpoint of the connection between the first switching transistor and the second switching transistor is connected to one end of a first impedance matching inductor, and the midpoint of the connection between the (t-1)th switching transistor and the tth switching transistor is connected to one end of a second impedance matching inductor, where t is the number of switching transistors; the other end of the first impedance matching inductor is connected to the second... The other ends of the impedance matching inductors are connected via a voltage equalization capacitor branch; the voltage equalization capacitor branch includes at least two voltage equalization capacitors connected in series; the midpoint of the connection between two adjacent voltage equalization capacitors is connected to one end of a resonant capacitor; the other end of the resonant capacitor is connected to one end of the primary winding of the high-frequency transformer, and the other end of the primary winding of the high-frequency transformer is connected via a resonant inductor to the midpoint of the connection between the m-th input capacitor and the (m+1)-th input capacitor; where m = k / 2, k is the number of input capacitors, and k is an even number; the secondary side of the high-frequency transformer is connected to a rectifier circuit; the rectifier circuit is connected to a multi-port output voltage regulator circuit.

[0006] The DC-DC converter of this invention achieves direct high-frequency AC transmission, with each capacitor transmitting equal power. Based on capacitor ampere-second balance, equal capacitor voltages are achieved, resulting in equal capacitor voltage balancing from the perspective of equal energy transmission. No additional voltage equalization process is required, significantly reducing energy transmission losses. In this invention, all switching transistors have completely identical currents, evenly distributing the load current. This allows for high voltage withstand in series while greatly reducing current stress on the switching devices.

[0007] In this invention, k = 2, t = 4; each input capacitor is connected in parallel with two switching transistors.

[0008] In this invention, k = 4, t = 4; each input capacitor is connected in parallel with one of the switching transistors. The midpoint of the connection between the first and second input capacitors is connected to one end of the first inductor, and the other end of the first inductor is connected to the midpoint of the connection between the first and second switching transistors; the midpoint of the connection between the third and fourth input capacitors is connected to one end of the second inductor, and the other end of the second inductor is connected to the midpoint of the connection between the third and fourth switching transistors.

[0009] Each of the voltage equalizing capacitors is connected in parallel with a clamping diode; one end of the resonant capacitor is connected to the midpoint of the connection between two adjacent voltage equalizing capacitors, the other end of the resonant capacitor is connected to the midpoint of the connection between two adjacent clamping diodes, and the midpoint of the connection between two adjacent clamping diodes is connected to one end of the primary winding of the high-frequency transformer.

[0010] This invention splits the voltage equalization capacitor of the existing DC converter into a first voltage equalization capacitor and a second voltage equalization capacitor. Combined with a clamping circuit (clamping diode), it can clamp the short-circuit current of each port. Even if one or more output ports are short-circuited, the converter can still work normally and maintain the normal output of other non-faulty ports, ensuring high reliability of multiple ports. It can achieve short-circuit operation naturally without any other sampling and detection control.

[0011] The rectifier circuit adopts one of the following: half-bridge rectifier circuit, full-bridge rectifier circuit, and synchronous rectifier circuit.

[0012] The multi-port output voltage regulator circuit includes a filter capacitor; or, the multi-port output voltage regulator circuit includes a filter capacitor and a voltage regulator converter connected in parallel with the filter capacitor.

[0013] The input capacitors of all power units are connected in series, the switching transistors are connected in series, and the voltage equalizing capacitors are connected in series.

[0014] All impedance-matched inductors have the same inductance value.

[0015] The present invention also provides a control method for the above-mentioned DC-DC converter, the method comprising:

[0016] When the input voltage is lower than the set threshold, the first and t-th switches of all power units are turned on simultaneously, and the remaining switches of all power units are turned on simultaneously.

[0017] When the input voltage rises to exceed the set threshold, the first and second switches of all power units are complementary and conduct, and the duty cycle is less than 0.25; the phase of the (t-1)th switch in each power unit leads the phase of the first switch in that power unit by 90°, and the tth switch and the (t-1)th switch in each power unit conduct complementary.

[0018] And / or,

[0019] When the output voltage V of the i-th power unit oi The voltage V is lower than the expected value of the power unit's output voltage. oi_ref At that time, the first and t-th switches of all power units are turned on simultaneously, and the remaining switches of all power units are turned on simultaneously; when the output voltage V oi Higher than the expected value V of the output voltage oi_ref At this time, the first and second switches of all power units are complementary and conduct, and the duty cycle is less than 0.25; the phase of the (t-1)th switch in each power unit leads the phase of the first switch in that power unit by 90°, and the t-th switch and the (t-1)th switch in each power unit are complementary and conduct; 1≤i≤n;

[0020] If Voi Deviation from V oi_ref If the first set value is exceeded, the switching pulse of the (t-1)th switch in each power unit is synchronized, and the duty cycle of the (t-1)th switch in each power unit is adjusted; the voltage range across each equalizing capacitor is 2Vin / 4(2n*(2n+2))~3.5Vin / 4(2n*(2n+2)), where Vin is the sum of the input voltages of all power units, and n is the number of power units;

[0021] If V oi Deviation from V oi_ref If the second set value is exceeded, the duty cycle of the first and last switching transistors among all the switching transistors is adjusted to charge all the voltage equalization capacitors; the voltage range across each voltage equalization capacitor is 3.5Vin / 4(2n*(2n+2))~4Vin / 4(2n*(2n+2));

[0022] The second setting value is greater than the first setting value.

[0023] This invention proposes a multi-degree-of-freedom control method for the AC voltage amplitude of a resonant cavity, allowing multiple output ports to be independently controllable and adaptable to a wide range of input voltage variations. It possesses an ultra-wide input voltage regulation capability of 1 to 2(2n-1) times, with 2n-1 degrees of freedom for voltage regulation, enabling independent control of 2n-1 output ports. The voltage of each output port can be composed of multiple switching state combinations. Different output ports can select different switching state combinations, achieving independent direct closed-loop control of the voltage at each output port, with 2n-1 degrees of freedom for voltage regulation, enabling independent control of 2n-1 output ports. By using different switching state combinations, multiple sets of capacitors and inductors can be configured into boost or buck circuits, and step-wise boost or buck circuits can be implemented between multiple stages, further expanding the upper and lower limits of the AC voltage amplitude of the resonant cavity, enabling the output voltage to adapt to an ultra-wide input voltage variation of 1 to 2(2n-1) times.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The self-equalizing voltage and current sharing switch unit of the present invention realizes power balance; the equalizing capacitor and impedance matching inductor in this part of the circuit constitute a high-frequency AC branch, providing a circuit for capacitors at different potentials to supply power to the load, thereby realizing self-equalizing voltage of input capacitor and self-equalizing current of power device, and there is no requirement for the value of equalizing capacitor, even if there are differences in the value of capacitor, self-equalizing voltage can still be achieved.

[0026] (2) The present invention achieves multi-port output by cascading multiple power units; compared with the traditional medium-voltage DC converter, the DC converter of the present invention can output voltages of different voltage levels without multi-stage processing to meet the power supply requirements of different loads, under the premise of achieving power balance. The system efficiency is improved, and the circuit structure and control method are relatively simple.

[0027] (3) The present invention has high reliability. The overcurrent clamping circuit in the DC converter can quickly provide short-circuit protection when a short-circuit fault occurs at one or more output ports, so as not to affect the normal operation of other power units, thereby improving the reliability of the system and making it suitable for high-reliability applications.

[0028] (4) This invention can achieve voltage regulation over an ultra-wide input voltage range, and multiple output ports are independently controllable. The control method is multi-degree-of-freedom control of AC voltage amplitude of resonant cavity, which has an ultra-wide input voltage regulation capability of 1 to 2n times (n is the number of self-equalizing voltage and current sharing switch units), and the voltage regulation degree of freedom is 2n-1, which can realize independent control of multiple output ports. Attached Figure Description

[0029] Figure 1 This is a basic working principle diagram of the DC-DC converter in Embodiment 1 of the present invention.

[0030] Figures 2(a) and 2(b) show two circuit configurations of the self-equalizing voltage and current sharing switch unit in the DC converter of Embodiment 1 of the present invention.

[0031] Figure 3 This is a circuit diagram of the DC-DC converter when n=2 in Embodiment 1 of the present invention.

[0032] Figure 4 This is a schematic diagram of the multi-degree-of-freedom control and voltage regulation range of the AC voltage amplitude of the resonant cavity in Embodiment 2 of the present invention.

[0033] Figure 5 This is a control block diagram for multi-degree-of-freedom control of AC voltage amplitude at 2n-1 output ports, as shown in Embodiment 2 of the present invention.

[0034] Figure 6 This is the current balancing equivalent circuit of the MOSFET in Embodiment 2 of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In this document, the terms "first," "second," and other similar words are not intended to imply any order, quantity, or importance, but are merely used to distinguish different elements. The terms "one," "a," and other similar words are not intended to indicate the existence of only one of the stated things, but rather that the description pertains to only one of the two stated things, which may include one or more. The terms "comprising," "including," and other similar words are intended to indicate a logical relationship, not a spatial relationship. For example, "A includes B" means that logically B belongs to A, not that spatially B is located inside A. Furthermore, the meanings of the terms "comprising," "including," and other similar words should be considered open-ended, not closed. For example, "A includes B" means that B belongs to A, but B does not necessarily constitute all of A; A may also include other elements such as C, D, and E.

[0037] Example 1

[0038] Figure 1 This is a basic working principle diagram of a power self-balancing medium-voltage DC input multi-port output DC converter provided in Embodiment 1 of the present invention.

[0039] like Figure 1 As shown, the DC-DC converter in this embodiment includes multiple power units. Each power unit includes a self-equalizing voltage and current sharing switch unit, an overcurrent clamping circuit, a resonant circuit, a high-frequency transformer, a rectifier circuit, and a multi-port output voltage regulator circuit connected in sequence. The entire DC-DC converter has n power units, and n self-equalizing voltage and current sharing switch units are cascaded. Wherein:

[0040] The self-equalizing voltage and current sharing switch unit includes at least two input capacitors connected in series, four power switches connected in series, two impedance matching inductors, and two voltage equalizing capacitors.

[0041] The overcurrent clamping circuit includes at least one diode or an active clamping circuit, one end of which is connected to the connection point of a voltage equalizing capacitor and an impedance matching inductor in the self-equalizing voltage and current equalizing switch unit, and the other end is connected to the connection point of the resonant capacitor and the high-frequency transformer in the resonant circuit.

[0042] A resonant circuit is composed of inductors and capacitors connected in series and parallel, including series resonant circuits, LLC resonant circuits and LCC resonant circuits.

[0043] The primary side of the high-frequency transformer is connected in series in the resonant circuit, and the secondary side is connected to the rectifier circuit.

[0044] There are various types of rectifier circuits, including half-bridge rectifier circuits composed of diodes, full-bridge rectifier circuits, full-wave rectifier circuits, and synchronous rectifier circuits composed of fully controlled devices.

[0045] A multi-port output voltage regulator circuit can be constructed from a filter capacitor or a filter capacitor connected in parallel with a voltage regulator converter.

[0046] A power unit includes a self-equalizing voltage and current sharing switch unit, an overcurrent clamping circuit, a resonant circuit, a high-frequency transformer, a rectifier circuit, and a multi-port output voltage regulator circuit.

[0047] Figures 2(a) and 2(b) show two circuit configurations of the self-equalizing voltage and current sharing switch unit in this embodiment. The main difference lies in the connection method between the input capacitor and the power switch.

[0048] As shown in Figure 2(a), the first circuit configuration of the self-equalizing voltage and current sharing switch unit is as follows: each input capacitor is connected in parallel with two power switches connected in series, i.e., the input capacitor C in11 With power switch M 11 and M 21 Parallel, C in21 With M 31 and M 41 In parallel connection, the midpoints of two power switches connected in parallel with the same input capacitor are respectively connected to one end of two voltage-equalizing inductors, i.e., power switch M 11 and M 21 midpoint b 11 With inductor L b11 One end is connected to the power switch M 31 and M 41 midpoint b 21 With inductor L b21 One end of the capacitor is connected, and the two ends of the capacitor connected in series are respectively connected to the other ends of the two voltage-equalizing inductors, i.e., inductor L. b11 The other end c 11 With inductor L b21 The other end c 21 The voltage equalizing capacitor C connected in series b11 With C b21 The two ends.

[0049] As shown in Figure 2(b), the second circuit configuration of the self-equalizing voltage and current sharing switch unit is as follows: each input capacitor is split into two input capacitors connected in series, and then connected in parallel with two power switches respectively. An inductor, i.e., inductor L, is then connected between the midpoint of the two split input capacitors and the midpoint of the two power switches connected in parallel with them. 11 The two ends of the capacitor are connected to the input capacitor C. in11 and C in21 midpoint a 11 and power switch M 11 and M 21 midpoint b 11 Connection, inductor L 21 The two ends of the capacitor are connected to the input capacitor C. in31 and Cin41 midpoint a 21 and power switch M 31 and M 41 midpoint b 21 The connection method for the voltage equalizing capacitor and impedance matching inductor is the same as that in Figure 2(a).

[0050] In this embodiment, the resonant inductor is split into power balancing inductors Lb (Lb11~Lb22, with Lb numbering increasing as the stage increases) and Ls (Ls1~Ls3), and the voltage equalizing capacitor Cb is split into Cb1 and Cb2 (Cb11~Cb23, with Cb numbering increasing as the stage increases). Lb11~Lb22 and Cb11~Cb23 constitute a high-frequency AC branch, providing a high-frequency AC path for multiple input capacitors Cin (Cin11~Cb22, with Cin numbering increasing as the stage increases) at different potentials. Energy can be directly transferred from multiple input capacitors to multiple loads. Adjusting the impedance of the Lb and Cb AC circuits ensures that the current of all switching transistors is completely consistent.

[0051] This embodiment decouples the energy required for soft switching of the switching transistors from the resonant cavity and the load. Using an auxiliary inductor Lb11, each pair of switching transistors M11 and M21 is configured as a unit that naturally achieves soft switching, eliminating the need to consider soft switching during the design process. Because the soft switching effect of traditional LLC converters (e.g., CN109302072 A) is closely related to the resonant cavity magnetizing inductance, dead time, and load, achieving soft switching increases the difficulty of transformer design and leads to low converter bus voltage utilization due to excessive dead time. Especially in multi-port output scenarios, where the load power of multiple ports is inconsistent, traditional converters can cause differences in the soft switching effect of multiple switching transistors, or even partial soft switching failure, posing a significant risk. This embodiment decouples the soft switching effect from the load power, making it more suitable for multi-port output applications.

[0052] Figure 3 The circuit schematic of this embodiment is shown when n=2.

[0053] like Figure 3 As shown, when n = 2, at point c 21 With c 12 Two voltage-equalizing capacitors C are added in series between them. b12 and C b22 Then it can be compared with the input capacitor C. in21 and C in12 High-frequency switch M 31 M 41 M 12 and M 22 Impedance matching inductor L b21 and Lb12 Then, a self-equalizing voltage and current sharing switch unit is formed, so at this time, three power units can be formed. Figure 3 Each self-equalizing voltage and current sharing switch unit adopts the circuit configuration shown in Figure 2(a). In each power unit, the midpoint of the parallel branch of the input capacitor and the power switch is connected to the midpoint of the two equalizing capacitors and then to the input terminal of the subsequent resonant circuit.

[0054] like Figure 3 As shown, taking a diode as an overcurrent clamping circuit as an example, one end of the diode is connected to the connection point of a voltage equalization capacitor and an impedance matching inductor in the self-equalizing voltage and current equalization switch unit, and the other end is connected to the connection point of the resonant capacitor and the high-frequency transformer in the resonant circuit.

[0055] like Figure 3 As shown, the resonant circuit takes an LLC resonant circuit as an example, which is connected in series with the primary side of the high-frequency transformer; the rectifier circuit takes a full-bridge rectifier circuit as an example, which is connected in series with the secondary side of the high-frequency transformer; the multi-port output voltage regulator circuit takes a filter capacitor as an example, which is connected to the output side of the rectifier circuit.

[0056] Example 2

[0057] Figure 4 This is a diagram showing the multi-degree-of-freedom control range of AC voltage amplitude in the resonant cavity of the DC converter in Embodiment 2 of the present invention.

[0058] like Figure 4 As shown, the control method for the DC-DC converter is multi-degree-of-freedom control of the AC voltage amplitude in the resonant cavity. The output voltage V... o2 Taking control as an example, control M 31 M 41 M 12 and M 22 The frequency doubling low-gain and high-gain modes can achieve a 2-fold adjustment of the amplitude of the AC input voltage to the resonant cavity. The implementation details are as follows: when the input voltage is low, the high-gain mode is used, i.e., controlling M... 11 M 41 M 12 and M 42 Simultaneous activation, M 21 M 31 M 22 and M 32 Simultaneous activation, at this time for V Cb11 V Cb21 V Cb12 V Cb22 V Cb13 V Cb23 Charging, i.e., V AC1 V AC2 and V AC3 When the input voltage increases, a high-gain mode is activated; when the input voltage increases, a low-gain mode is activated, i.e., M is controlled...11 M 12 Simultaneous activation, duty cycle less than 0.25, M 21 With M 11 Complementary, M 31 M 32 The phases lead M respectively 11 and M 12 90 degrees, M 41 M 42 With M 31 M 32 Complementary, at this time V Cb11 V Cb21 V Cb12 V Cb22 V Cb13 V Cb23 The charging voltage drops to half that of high-gain mode, i.e., V. AC1 V AC2 and V AC3 The voltage is reduced to achieve a low-gain mode.

[0059] For M 11 ~M 42 All switching transistors according to Figure 5 The stepped charging control in the circuit can expand the gain range by 2-3 times, 4-6 times, etc., to achieve 1-n times adjustment of the AC input voltage amplitude of the resonant cavity. Combining the above two control strategies, the converter can achieve an ultra-wide input voltage regulation of 1-2n times, which is far superior to traditional converters. The control strategy block diagram is as follows. Figure 5 As shown.

[0060] Figure 5 This is a control block diagram for multi-degree-of-freedom control of AC voltage amplitude at 2n-1 output ports in this embodiment. The specific control process includes:

[0061] Degree of freedom #1: Figure 4 The frequency multiplication low-gain and high-gain mode switching described in the document, V o1 V is the output voltage of port 1. o1_ref Let V be the desired value of the output voltage at port 1. o1 Below V o1_ref If V o1 Higher than V o1_ref Then switch to low gain mode.

[0062] Degree of freedom #2: If the input voltage change amplitude is too large, causing V o1 Deviation from V o1_ref If the gain is too large, exceeding the gain range of 1-2 times that of degree of freedom #1, then voltage regulation of degree of freedom #2 will be activated. The implementation details are as follows: M... 21 and M 32 The switching pulse synchronization is achieved by adjusting M.21 and M 32 The duty cycle can be used for V Cin11 V Cin21 V Cin12 V Cin22 Charge and discharge simultaneously, while controlling V Cb11 V Cb21 V Cb12 V Cb22 V Cb13 V Cb23 To charge and discharge, V Cb11 V Cb21 V Cb12 V Cb22 V Cb13 V Cb23 The voltage range is 2Vin / 4(2n*(2n+2)) to 3.5Vin / 4(2n*(2n+2)), further extending the adjustable gain range.

[0063] Degree of freedom #3: If the amplitude of the input voltage change further increases, causing V o1 Deviation from V o1_ref If the value is too large, exceeding the gain range of degrees of freedom #1 and #2, then voltage regulation of degree of freedom #3 will be activated. The implementation details are as follows: a separate adjustment M is added during the control cycle. 11 and M 42 The duty cycle pulse, through M 11 and M 42 The duty cycle can be used for V Cb11 V Cb21 V Cb12 V Cb22 V Cb13 V Cb23 It is charged with a voltage range of 3.5Vin / 4(2n*(2n+2)) to 4Vin / 4(2n*(2n+2)), further extending the adjustable gain range.

[0064] Based on the aforementioned three degrees of freedom, a three-stage stepped ultra-wide adjustable gain is achieved. The AC voltage amplitude control of the resonant cavity has a total of 2n-1 degrees of freedom. By adjusting the proportion of these 2n-1 degrees of freedom in the output voltage regulation at different ports, the output voltage at each of the 2n-1 ports can be independently adjusted. Compared with existing technologies, the significant advantages of this embodiment are: it can achieve an ultra-wide input voltage regulation range of 1 to 2n times, with a voltage regulation range far exceeding that of traditional converters, making it more suitable for applications with a wide input voltage range.

[0065] Figure 6 This is the equivalent circuit for current balancing of the MOSFET in Embodiment 2 of the present invention. The following explains how the structure of the embodiment of the present invention can achieve current balancing of the switching transistor.

[0066] MOSFET current balance principle:

[0067] The current in a MOSFET can be decomposed into multiple voltage sources supplying current to multiple loads. In the 0-T... s / 2 phase, to load Z ac1 The equivalent circuit of the power supply is as follows Figure 6 As shown. v 11 -v 32 As an equivalent voltage source, take C in1k =C in2k =C in C b1k =C b2k =C b Then v 11 -v 32 for

[0068]

[0069] v 11 =v 31 =v 12 =v 32 =v in / (4k) (2)

[0070] Through M 11 -M 32 The current is

[0071]

[0072]

[0073] i M11Z1 -i M11Z3 For flow through M 11 The current is respectively directed to the load Z. ac1 Z ac2 and Z ac3 Power supply. Z M11Z1 -Z M32Z1 To load Z ac1 The equivalent internal resistance of the power supply. If the DC resistance of the line is ignored, then Z... M11Z1 -Z M32Z1 for

[0074]

[0075] ω s It is the switching angular frequency. The equivalent internal resistance Z... M11Z2 -Z M32Z2 and Z M11Z3 -Z M32Z3 The same method can also be used to calculate M. 11 -M32 The current ratio is

[0076] k iM1k =i M1k / (i M11 +i M31 +i M12 +i M32 (6)

[0077] If impedance matching inductance ω s L b If the current ratio is much greater than the bus capacitance impedance, then the current ratio is:

[0078]

[0079] Flowing through M 11 -M 32 The current is

[0080]

[0081] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0082] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A control method for a DC-DC converter, the DC-DC converter comprising multiple cascaded power units; each power unit comprising at least two input capacitors connected in series; each input capacitor connected in parallel with at least one switching transistor; all switching transistors connected in series; the midpoint of the connection between the first and second switching transistors connected to one end of a first impedance matching inductor, the midpoint of the connection between the (t-1)th and tth switching transistors connected to one end of a second impedance matching inductor, where t is the number of switching transistors; the other ends of the first and second impedance matching inductors are connected via a voltage-equalizing capacitor branch; the voltage-equalizing capacitor branch comprising at least two voltage-equalizing capacitors connected in series; the midpoint of the connection between two adjacent voltage-equalizing capacitors connected to one end of a resonant capacitor; the other end of the resonant capacitor connected to one end of the primary winding of a high-frequency transformer, the other end of the primary winding of the high-frequency transformer connected via a resonant inductor to the midpoint of the connection between the m-th and (m+1)-th input capacitors; wherein, m = k / 2, where k is the number of input capacitors and k is an even number; the secondary side of the high-frequency transformer is connected to a rectifier circuit; the rectifier circuit is connected to a multi-port output voltage regulator circuit; the method is characterized by comprising: When the input voltage is lower than the set threshold, the first and t-th switches of all power units are turned on simultaneously, and the remaining switches of all power units are turned on simultaneously. When the input voltage rises to exceed the set threshold, the first and second switches of all power units are complementary and conduct, and the duty cycle is less than 0.25; the phase of the (t-1)th switch in each power unit leads the phase of the first switch in that power unit by 90°, and the t-th switch and the (t-1)th switch in each power unit are complementary and conduct. And / or, When the output voltage of the i-th power unit V oi The voltage is lower than the expected value of the power unit's output voltage. V oi_ref At that time, the first and t-th switches of all power units are turned on simultaneously, and the remaining switches of all power units are turned on simultaneously; when the output voltage V oi Higher than the expected value of the output voltage V oi_ref At this time, the first and second switches of all power units are complementary and conduct, and the duty cycle is less than 0.25; the phase of the (t-1)th switch in each power unit leads the phase of the first switch in that power unit by 90°, and the t-th switch and the (t-1)th switch in each power unit are complementary and conduct; 1≤i≤n; like V oi Deviation V oi_ref If the first set value is exceeded, the switching pulse of the t-1th switching transistor in each power unit is synchronized, and the duty cycle of the t-1th switching transistor in each power unit is adjusted; the voltage range across each voltage equalizing capacitor is 2Vin / 4(2n*(2n+2))~3.5Vin / 4(2n*(2n+2)), where Vin is the sum of the input voltages of all power units, and n is the number of power units; like V oi Deviation V oi_ref If the second set value is exceeded, the duty cycle of the first and last switching transistors among all switching transistors is adjusted to charge all equalizing capacitors; the voltage range across each equalizing capacitor is 3.5Vin / 4(2n*(2n+2))~4Vin / 4(2n*(2n+2)); The second setting value is greater than the first setting value.

2. The control method for a DC-DC converter according to claim 1, characterized in that, k=2, t=4; each of the input capacitors is connected in parallel with the two switching transistors.

3. The control method for a DC-DC converter according to claim 1, characterized in that, k=4, t=4; each of the input capacitors is connected in parallel with one of the switching transistors.

4. The control method for a DC-DC converter according to claim 3, characterized in that, The midpoint of the connection between the first and second input capacitors is connected to one end of the first inductor, and the other end of the first inductor is connected to the midpoint of the connection between the first and second switching transistors; the midpoint of the connection between the third and fourth input capacitors is connected to one end of the second inductor, and the other end of the second inductor is connected to the midpoint of the connection between the third and fourth switching transistors.

5. The control method for a DC-DC converter according to claim 1, characterized in that, Each of the voltage equalizing capacitors is connected in parallel with a clamping diode; one end of the resonant capacitor is connected to the midpoint of the connection between two adjacent voltage equalizing capacitors, the other end of the resonant capacitor is connected to the midpoint of the connection between two adjacent clamping diodes, and the midpoint of the connection between two adjacent clamping diodes is connected to one end of the primary winding of the high-frequency transformer.

6. The control method for a DC-DC converter according to claim 1, characterized in that, The rectifier circuit adopts one of the following: half-bridge rectifier circuit, full-bridge rectifier circuit, and synchronous rectifier circuit.

7. The control method for a DC-DC converter according to claim 1, characterized in that, The multi-port output voltage regulator circuit includes a filter capacitor; or, the multi-port output voltage regulator circuit includes a filter capacitor and a voltage regulator converter connected in parallel with the filter capacitor.

8. The control method for a DC-DC converter according to claim 1, characterized in that, The input capacitors of all power units are connected in series, the switching transistors are connected in series, and the voltage equalizing capacitors are connected in series.

9. The control method for a DC-DC converter according to any one of claims 1 to 8, characterized in that, All impedance-matched inductors have the same inductance value.

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