CN116073647A - DC converter and control method thereof - Google Patents

Abstract

The invention discloses a direct current converter and a control method thereof, wherein the direct current converter comprises a plurality of cascaded power units; the power unit comprises at least two input capacitors connected in series; each input capacitor is connected with at least one switch tube in parallel; the connection midpoint of the first switching tube and the second switching tube is connected with one end of the first impedance matching inductor, and the connection midpoint of the (t-1) th switching tube and the (t) th switching tube is connected with one end of the second impedance matching inductor; the other end of the first impedance matching inductor is connected with the other end of the second impedance matching inductor through a voltage equalizing capacitor branch; the voltage-sharing capacitor branch circuit comprises at least two voltage-sharing capacitors connected in series; the connecting midpoint of two adjacent voltage-sharing capacitors is connected with one end of the resonance capacitor; the other end of the resonant capacitor is connected with one end of a primary winding of the high-frequency transformer, and the other end of the primary winding of the high-frequency transformer is connected with the connecting midpoint of the (m) th input capacitor and the (m+1) th input capacitor through a resonant inductor. The invention has the advantages of automatic input voltage equalization and automatic current equalization of the power device.

Description

A DC converter and its control method

technical field

The invention relates to power electronic circuit technology, in particular to a DC converter and a control method thereof.

Background technique

In different power occasions such as medium-voltage DC distribution network, renewable energy DC system, submarine power transmission and distribution system, and ship integrated power system, the medium-voltage DC converter can realize the transformation from the medium-voltage DC bus to the low-voltage DC bus. Electric energy conversion and electrical isolation have become research hotspots. Among them, the input series output parallel DC converter with the advantages of structural modularization and strong current output capability is widely used. However, when the traditional medium-voltage DC converter supplies power to different loads, it needs to go through multi-level voltage conversion to meet the requirements of different voltage levels. The circuit structure is more complicated and it is difficult to achieve power balance. In addition, in occasions with high reliability requirements such as submarine power transmission and distribution systems, short-circuit faults on the low-voltage side often occur. Although the protection methods adopted by traditional medium-voltage DC converters can clear the fault current, it needs to be protected. The voltage of multiple capacitors and inductors is sampled and false protection is prone to occur. At the same time, due to the different load characteristics of the output ports, when a short-circuit fault occurs at one or more output ports, it is difficult for the converter to quickly isolate the faulty output port, resulting in Multiport output system crash. The line resistance of long-distance power transmission on the seabed is large, causing the terminal voltage to drop and the input voltage range to fluctuate greatly. How to design a DC converter with a wide input range that can achieve power balance, multi-port output, and short-circuit fault isolation protection under the premise of medium-voltage input to improve system efficiency and power supply reliability is the current medium-voltage DC converter. Converter design is difficult.

The traditional switched capacitor structure (such as CN109302072A) transfers energy from Cink-1 to Cbk-1 and then to Cink step by step. According to this rule, the energy is transferred from the first capacitor to the last capacitor to achieve input capacitor voltage equalization. In the process of voltage equalization, the traditional switched capacitor structure must pass through multi-level voltage equalization energy transmission, which will lead to increased loss. The traditional switched capacitor converter cannot realize the current balance of the switching tubes, and there are problems of uneven thermal stress caused by large current impact and current inconsistency, so it is difficult to apply to high-power applications. At the same time, the existing structure or control method (CN109302072A) can only realize closed-loop control of the voltage of one output port, and indirect control of other ports, and the control accuracy is not high, so it is difficult to apply to occasions requiring high output voltage accuracy. Moreover, the traditional control method is frequency conversion or phase shift control, and it is difficult to realize wide-range voltage regulation in the resonant converter.

Contents of the invention

The technical problem to be solved by the present invention is to provide a DC converter and a control method thereof, without an additional voltage equalization process, and to reduce energy transmission loss in view of the deficiencies in the prior art.

In order to solve the above technical problems, the technical solution adopted by the present invention is: a DC converter, which is characterized in that it includes a plurality of cascaded power units; the power unit includes at least two series-connected input capacitors; each of the The above-mentioned input capacitance is connected in parallel with at least one switch tube; all switch tubes are connected in series; the connection midpoint between the first switch tube and the second switch tube is connected to one end of the first impedance matching inductor, and the t-1th switch tube is connected to the tth switch tube. The connection midpoint of each switch tube is connected to one end of the second impedance matching inductance, and t is the number of switch tubes; the other end of the first impedance matching inductance and the other end of the second impedance matching inductance are connected through a voltage equalizing capacitor branch; The voltage-balancing capacitor branch includes at least two voltage-balancing capacitors in series; the connection midpoint of two adjacent voltage-balancing capacitors is connected to one end of the resonant capacitor; the other end of the resonant capacitor is connected to one end of the primary winding of the high-frequency transformer, so The other end of the primary side winding of the high-frequency transformer is connected to the midpoint of the connection between the mth input capacitor and the m+1th input capacitor through a resonant inductance; wherein, 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 rectification circuit; the rectification circuit is connected to a multi-port output voltage stabilizing circuit.

The DC converter of the present invention realizes the direct transmission of high-frequency AC, the power transmitted by each capacitor is equal, and the capacitor voltage can be equal according to the capacitor ampere-second balance, which is realized from the perspective of equal energy transmitted by the capacitor, and does not require additional The pressure equalization process greatly reduces the energy transmission loss. In the present invention, the currents of all the switch tubes are completely consistent, and the current of the load is evenly divided, and the current stress of the switch devices is greatly reduced while realizing high voltage in series.

In the present invention, k=2, t=4; each said input capacitor is connected in parallel with two said switch tubes.

In the present invention, k=4, t=4; each of the input capacitors is connected in parallel with one of the switch tubes. The midpoint of the connection between the first input capacitor and the second input capacitor is connected to one end of the first inductance, and the other end of the first inductance is connected to the midpoint of the connection between the first switch tube and the second switch tube; the third input capacitor The midpoint of the connection with the fourth input capacitor is connected to one end of the second inductance, and the other end of the second inductance is connected to the midpoint of the connection between the third switching tube and the fourth switching tube.

Each of the 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 equalizing capacitors, and the other end of the resonant capacitor is connected to the midpoint of the connection between two adjacent clamping diodes The connecting midpoint of the two adjacent clamping diodes is connected to one end of the primary winding of the high frequency transformer.

The present invention splits the voltage equalizing capacitor of the existing DC converter into a first voltage equalizing capacitor and a second voltage equalizing capacitor, combined with a clamping circuit (clamping diode), can realize the clamping of the short-circuit current of each port, even if one or more If one output port is short-circuited, the converter can still work normally, maintain the normal output of other non-faulty ports, ensure the high reliability of multiple ports, and naturally realize short-circuit operation without any other sampling and detection control.

The rectification circuit adopts one of a half-bridge rectification circuit, a full-bridge rectification circuit and a synchronous rectification circuit.

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

The input capacitors of all power units are connected in series, the switch tubes are connected in series, and the equalizing capacitors are connected in series.

All impedance matching inductors have the same inductance value.

The present invention also provides a control method for the above DC converter, the method comprising:

When the input voltage is lower than the set threshold, the first and t-th switching tubes of all power units are turned on synchronously, and the remaining switching tubes of all power units are turned on synchronously;

When the input voltage rises above the set threshold, the first and second switching tubes of all power units are turned on complementary, and the duty cycle is less than 0.25; the phase of the t-1th switching tube in each power unit is advanced The phase of the first switching tube in the power unit is 90°, and the t-th switching tube of each power unit is complementary to the t-1-th switching tube;

and / or,

When the output voltage V _oi of the i-th power unit is lower than the expected value V _{oi_ref} of the output voltage of the power unit, the first and t-th switches of all power units are turned on synchronously, and the remaining switches of all power units are turned on synchronously; when When the output voltage V _oi is higher than the expected value V _{oi_ref} of the output voltage, the first switch tube and the second switch tube of all power units are complementary conduction, and the duty cycle is less than 0.25; the t-1th switch tube in each power unit The phase is ahead of the phase of the first switching tube in the power unit by 90°, and the t-th switching tube of each power unit is complementary to the t-1-th switching tube; 1≤i≤n;

If V _oi deviates from V _{oi_ref} and exceeds the first set value, then synchronize the switching pulse of the t-1th switching tube in each power unit, and adjust the duty cycle of the t-1th switching tube in each power unit; The voltage range across the capacitor is 2Vin/4(2n*(2n+2))～3.5Vin/4(2n*(2n+2)), Vin is the sum of the input voltages of all power units, and n is the number of power units ;

If V _oi deviates from V _{oi_ref} and exceeds the second set value, then adjust the duty cycle of the first switch tube and the last switch tube in all switch tubes, and charge all voltage-balancing capacitors; the voltage range at both ends of each voltage-balancing capacitor 3.5Vin/4(2n*(2n+2))～4Vin/4(2n*(2n+2));

Wherein, the second set value is greater than the first set value.

The invention proposes a multi-degree-of-freedom control method for the AC voltage amplitude of the resonant cavity that is independently controllable with multiple output ports and can adapt to a wide range of input voltage changes, and has a 1 to 2 (2n-1) times ultra-wide input voltage regulation capability , the degree of freedom of voltage regulation is 2n-1, and independent control of 2n-1 output ports can be realized. The voltage of each output port of the present invention can be composed of multiple switch states, and different output ports can choose different switch state combinations to realize the independent direct closed-loop controllability of the voltage of each output port, and the degree of freedom of voltage regulation is 2n-1 , can realize independent control of 2n-1 output ports. Through different switch state combinations, multiple sets of capacitors and multiple sets of inductors are used to form a step-up or step-down circuit, and step-up or step-down is performed between the multi-stage structures, which can further expand the upper and lower limits of the AC voltage amplitude of the resonant cavity. The output voltage can adapt to 1-2(2n-1) times ultra-wide input voltage variation.

Compared with prior art, the beneficial effect that the present invention has is:

(1) The self-balanced voltage and current equalizing switch unit of the present invention realizes power balance; the voltage equalizing capacitor and impedance matching inductor in this part of the circuit constitute a high-frequency AC branch circuit, which provides a circuit for supplying power to the load for capacitors of different potentials , so as to realize the self-balancing of the input capacitor and the self-balancing of the power device, and there is no requirement for the voltage-balancing capacitor value, even if there is a difference in the capacitance value, the self-balancing voltage can still be realized.

(2) The present invention realizes multi-port output through the cascading of multiple power units; compared with the traditional medium-voltage DC converter, the DC converter of the present invention does not need to go through multi-stage processing on the premise of realizing power balance. Voltages of different voltage levels can be output to meet the power supply requirements of different loads, the efficiency of the system is improved, and the circuit structure and control method are relatively simple.

(3) The present invention has high reliability. The overcurrent clamping circuit in the DC converter can quickly protect the short circuit when one or more output ports have a short circuit fault, so that it does not affect the normal operation of other power units and improves the reliability of the system. It is suitable for High reliability occasions.

(4) The present invention can realize voltage stabilization in an ultra-wide input voltage range, and multiple output ports are independently controllable. The control method is multi-degree-of-freedom control of the AC voltage amplitude of the resonant cavity, which has an ultra-wide input voltage regulation capability of 1 to 2n times (n is the number of self-voltage and current-balancing switch units), and the degree of freedom of voltage regulation is 2n-1. Realize independent control of multiple output ports.

Description of drawings

FIG. 1 is a schematic diagram of the basic working principle of a DC converter according to Embodiment 1 of the present invention.

FIG. 2( a ) and FIG. 2( b ) are two circuit forms of the self-voltage equalizing and current equalizing switch unit in the DC converter according to Embodiment 1 of the present invention.

FIG. 3 is a circuit structure diagram of a DC converter when n=2 in Embodiment 1 of the present invention.

Fig. 4 is a schematic diagram of the voltage regulation range of the resonant cavity AC voltage amplitude multi-degree-of-freedom control according to Embodiment 2 of the present invention.

Fig. 5 is a control block diagram of implementing multi-degree-of-freedom control of AC voltage amplitudes to 2n-1 output ports according to Embodiment 2 of the present invention.

FIG. 6 is a current balance equivalent circuit of MOSFET according to Embodiment 2 of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In this document, the terms "first", "second" and other similar words are not intended to imply any order, quantity and importance, but are only used to distinguish different elements. In this document, the terms "a", "an" and other similar words are not intended to mean that there is only one of said things, but that the description is for only one of said things, which may have one or more indivual. In this document, the terms "comprising", "comprising" and other similar words are intended to indicate logical interrelationships, and cannot be regarded as denoting spatial structural relationships. For example, "A includes B" is intended to mean that B logically belongs to A, but not that B is spatially inside A. Additionally, the meanings of the terms "comprising", "comprising" and other similar words are to be regarded as open rather than closed. For example, "A includes B" means that B belongs to A, but B does not necessarily constitute the whole of A, and A may also include C, D, E and other elements.

Example 1

Fig. 1 is a basic working principle diagram of a power self-balanced medium-voltage DC input multi-port output DC converter provided by Embodiment 1 of the present invention.

As shown in Figure 1, the DC converter of this embodiment includes a plurality of power units, and the power units include sequentially connected self-voltage and current equalization switch units, an overcurrent clamp circuit, a resonant circuit, a high-frequency transformer, a rectifier circuit and multiple The port output voltage stabilizing circuit, the entire DC converter has n power units, and n self-voltage equalizing and current equalizing switch units are cascaded. in:

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

The over-current clamping circuit includes at least one diode or active clamping circuit, one end of which is connected to the connection point between a voltage-balancing capacitor and an impedance-matching inductor in the self-voltage-balancing current-sharing switch unit, and the other end is connected to the resonant circuit. At the junction of the resonant capacitor and the high frequency transformer.

The resonant circuit is composed of inductance and capacitance in series and parallel, including series resonant circuit, LLC resonant circuit and LCC resonant circuit.

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.

The rectification circuit has various circuit forms, including a half-bridge rectification circuit composed of diodes, a full-bridge rectification circuit, a full-wave rectification circuit and a synchronous rectification circuit composed of fully-controlled devices.

The multi-port output voltage stabilizing circuit can be composed of filter capacitors or filter capacitor parallel-connected regulator converters.

A power unit includes a self-voltage equalizing and current equalizing switch unit, an overcurrent clamping circuit, a resonant circuit, a high frequency transformer, a rectifying circuit and a multi-port output voltage stabilizing circuit.

Fig. 2(a) and Fig. 2(b) are two circuit forms of the self-voltage equalizing and current equalizing switch unit in this embodiment, the difference mainly lies in the connection mode of the input capacitor and the power switch.

As shown in Figure 2(a), the first circuit form of the self-voltage equalizing and current equalizing switch unit is: each input capacitor is connected in parallel with two series-connected power switches, that is, the input capacitor C _in11 is connected to the power switches M ₁₁ and M ₂₁ in parallel, C _in21 is connected in parallel with M ₃₁ and M ₄₁ , and the midpoints of the two power switches connected in parallel with the same input capacitor are respectively connected to one end of the two equalizing inductors, that is, the midpoint b of the power switches M ₁₁ and M _{21 11} is connected to one end of the inductance L _b11 , the midpoint _b21 of the power switches _M31 and _M41 is connected to one end of the inductance L _b21 , and the two ends of the two equalizing capacitors connected in series are respectively connected to the other end of the two equalizing inductors One end, that is, the other end _c11 of the inductor L _b11 and the other end _c21 of the inductor L _b21 are connected to both ends of the voltage equalizing capacitors C _b11 and C _b21 after being connected in series.

As shown in Figure 2(b), the second circuit form of the self-voltage and current-sharing switch unit is: each input capacitor is split into two series-connected input capacitors and then connected in parallel with two power switches. The midpoint of an input capacitor and the midpoint of two power switches connected in parallel with it are connected with an inductor, that is, the two ends of the inductor L ₁₁ are connected to the midpoint a ₁₁ of the input capacitors C _in11 and C _in21 and the power switches M ₁₁ and M ₂₁ The midpoint b ₁₁ of the inductance L ₂₁ is connected to the midpoint a ₂₁ of the input capacitor C _in31 and C _in41 and the midpoint b ₂₁ of the power switch M ₃₁ and M ₄₁ , and the equalizing capacitor and the impedance matching inductor The connection method is the same as that in Figure 2(a).

In this embodiment, the resonant inductance is split into power balancing inductors Lb (Lb11~Lb22, the number of Lb increases as the number of stages increases) and Ls (Ls1~Ls3), and the voltage equalizing capacitor Cb is split into Cb1 and Cb2 (Cb11~Cb23 , as the number of stages increases, the number of Cb increases), Lb11~Lb22 and Cb11~Cb23 constitute a high-frequency AC branch circuit, which is a plurality of input capacitors Cin with different potentials (Cin11~Cb22, as the number of stages increases, the number of Cin increases ) provides a high frequency AC channel where energy can be transferred directly from multiple input capacitors to multiple loads. Adjusting the impedance of the Lb and Cb AC circuits can ensure that the currents of all switch tubes are exactly the same.

In this embodiment, the energy required for the soft switching of the switching tube is decoupled from the resonant cavity and the load, and each group of switching tubes M11 and M21 is configured as a unit that naturally realizes soft switching by using the auxiliary inductance Lb11, and there is no need to consider the switch in the design process. Tube soft switching problem. Because the soft switching effect of traditional LLC converters (such as CN109302072 A) is closely related to the excitation inductance of the resonant cavity, dead time and load, etc., in order to achieve soft switching, it will increase the difficulty of transformer design and cause excessive dead time. The problem of low utilization rate of converter bus voltage. Especially in the case of multiple output ports, the load power of multiple ports is inconsistent, and traditional converters will cause differences in the soft switching effects of multiple switching tubes, and even some soft switching failures, which poses a huge hidden danger. This embodiment realizes the decoupling of the soft switching effect and the load power, and is more suitable for the occasion of multi-port output.

FIG. 3 is a circuit schematic diagram of this embodiment when n=2.

As shown in Figure 3, when n=2, add two series voltage equalizing capacitors C _b12 and C _b22 between points c ₂₁ and c ₁₂ , then they can be connected with input capacitors C _in21 and C _in12 , high-frequency switching M ₃₁ , M ₄₁ , M ₁₂ and M ₂₂ , impedance matching inductors L _b21 and L _b12 form a self-voltage equalizing and current equalizing switch unit, so three power units can be formed at this time. In Fig. 3, each self-voltage-balancing and current-balancing switch unit adopts the circuit form shown in Fig. 2(a), and the midpoint of the parallel branch between the input capacitor and the power switch in each power unit is connected to the midpoint of the two voltage-balancing capacitors The input end of the post-stage resonant circuit.

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

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

Example 2

Fig. 4 is a diagram of the multi-degree-of-freedom control voltage regulation range of the AC voltage amplitude of the resonant cavity of the DC converter according to Embodiment 2 of the present invention.

As shown in Figure 4, the control method of the DC converter is multi-degree-of-freedom control of the AC voltage amplitude of the resonant cavity. Taking the control of the output voltage V _o2 as an example, controlling the double-frequency low-gain and high-gain modes of M ₃₁ , M ₄₁ , M ₁₂ and M ₂₂ can realize the adjustment of the resonant cavity input AC voltage amplitude by 2 times. The implementation details are as follows: when the input When the voltage is low, adopt high-gain mode, that is, control M ₁₁ , M ₄₁ , M ₁₂ and M ₄₂ to be turned on synchronously, and M ₂₁ , M ₃₁ , M ₂₂ and M ₃₂ to be turned on synchronously. At this time, V _Cb11 , V _Cb21 , V _Cb12 , V _Cb22 , V _Cb13 , and V _Cb23 are charged, that is, the voltages of V _AC1 , V _AC2 , and V _AC3 rise to realize high-gain mode; when the input voltage rises, low-gain mode is adopted, that is, M ₁₁ and M ₁₂ are controlled to be turned on synchronously , the duty cycle is less than 0.25, M ₂₁ and M ₁₁ are complementary, M ₃₁ and M ₃₂ are 90 degrees ahead of M ₁₁ and M ₁₂ in phase respectively, M ₄₁ and M ₄₂ are complementary to M ₃₁ and M ₃₂ , at this time V _Cb11 and V _Cb21 , V _Cb12 , V _Cb22 , V _Cb13 , and V _Cb23 charging voltages drop to half of those in high-gain mode, that is, the voltages of V _AC1 , V _AC2 , and V _AC3 drop to realize low-gain mode.

For all the switch tubes of M ₁₁ ~ M ₄₂ , according to the step charging control in Fig. 5, the gain range can be expanded by 2-3 times, 4-6 times, etc., and the resonant cavity input AC voltage amplitude can be adjusted by 1-n times. Combining the above two control strategies, the converter can realize 1-2n times ultra-wide input voltage regulation, which is much higher than that of traditional converters. The block diagram of the control strategy is shown in Figure 5.

FIG. 5 is a control block diagram of the present embodiment for performing AC voltage amplitude multi-degree-of-freedom control on 2n-1 output ports. The specific control process includes:

Degree of Freedom #1: It is the multiplication low-gain and high-gain mode switching described in Figure 4. V _o1 is the output voltage of port 1, and V _{o1_ref} is the expected value of the output voltage of port 1. If the output V _o1 is lower than V _{o1_ref} , Then switch to a high gain mode, and if V _o1 is higher than V _{o1_ref} , switch to a multiplier low gain mode.

Degree of freedom #2: If the amplitude of the input voltage change is too large, causing V _o1 to deviate too much from V _{o1_ref} , exceeding the 1-2 times gain range of degree of freedom #1, then start the voltage regulation of degree of freedom #2, and its implementation details are as follows: Synchronize the switching pulses of M ₂₁ and M ₃₂ , and by adjusting the duty cycle of M ₂₁ and M ₃₂ , V _Cin11 , V _Cin21 , V _Cin12 , V _Cin22 can be charged and discharged, and V _Cb11 , V _Cb21 , V _Cb12 , V _Cb22 , V _Cb13 , V _Cb23 are charged and discharged, and the voltage range of V _Cb11 , V _Cb21 , V _Cb12 , V _Cb22 , V _Cb13 , V _Cb23 is 2Vin/4(2n*(2n+2))～3.5 Vin/4(2n*(2n+2)), to further expand the adjustable gain range.

Degree of freedom #3: If the amplitude of the input voltage change is further increased, causing V _o1 to deviate too much from V _{o1_ref} , exceeding the gain range of degree of freedom #1 and degree of freedom #2, then start the voltage regulation of degree of freedom #3, its implementation details In order to increase the pulses for individually adjusting the duty cycle of M ₁₁ and M ₄₂ in the control period, by adjusting the duty cycle of M ₁₁ and M 42, V _Cb11 , V _{Cb21 , V Cb12 ,} V _Cb22 , V _Cb13 , V _Cb23 , for charging, the voltage range is 3.5Vin/4(2n*(2n+2))～4Vin/4(2n*(2n+2)), which further expands the adjustable gain range.

According to the above three degrees of freedom, a three-level stepped ultra-wide adjustable gain is realized. There are 2n-1 degrees of freedom in the multi-degree-of-freedom control of the AC voltage amplitude of the resonator. By adjusting these 2n-1 degrees of freedom, the output voltage at different ports can be adjusted. The ratio among them realizes that the output voltages of 2n-1 ports can be adjusted independently. Compared with the prior art, the remarkable effect of this embodiment is that the converter can realize 1-2n times ultra-wide input voltage regulation, and the voltage regulation range is much larger than that of traditional converters, and is more suitable for wide input voltage range applications.

FIG. 6 is a current balance equivalent circuit of MOSFET according to Embodiment 2 of the present invention. The structure of the embodiment of the present invention is described below to realize the current balance of the switch tube.

MOSFET current balance principle:

The MOSFET current can be decomposed into multiple voltage sources supplying current to multiple loads. In the 0-T _s /2 phase, the equivalent circuit of supplying power to the load Z _ac1 is shown in Figure 6. v ₁₁ -v ₃₂ is the equivalent voltage source, take C _in1k ＝C _in2k ＝C _in , C _b1k ＝C _b2k ＝C _b , then v ₁₁ -v ₃₂ is

v ₁₁ =v ₃₁ =v ₁₂ =v ₃₂ =v _in /(4k) (2)

The current through M ₁₁ -M ₃₂ is

i _M11Z1 -i _M11Z3 are currents flowing through M ₁₁ , supplying power to loads Z _ac1 , Z _ac2 and Z _ac3 respectively. Z _M11Z1 -Z _M32Z1 is the equivalent internal resistance of the power supply supplying power to the load Z _ac1 . If the line DC resistance is ignored, then Z _M11Z1 -Z _M32Z1 is

ω _s is the switching angular frequency. The equivalent internal resistance Z _M11Z2 -Z _M32Z2 and Z _M11Z3 -Z _M32Z3 can also be calculated by the same method. The current ratio of M ₁₁ -M ₃₂ is

k _iM1k ＝i _M1k /(i _M11 +i _M31 +i _M12 +i _M32 ) (6)

If the impedance matching inductance ω _s L _b is much larger than the bus capacitance impedance, the current ratio is

The current flowing through M ₁₁ -M ₃₂ is

While preferred embodiments of the present application have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, the appended claims are intended to be construed to cover the preferred embodiment and all changes and modifications which fall within the scope of the application.

Obviously, those skilled in the art can make various changes and modifications to the application without departing from the spirit and scope of the application. In this way, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims (10)

1. A DC converter, characterized in that it comprises a plurality of cascaded power units; the power unit comprises at least two input capacitors connected in series; each of the input capacitors is connected in parallel with at least one switching tube; all switches tubes in series; the midpoint of the connection between the first switching tube and the second switching tube is connected to one end of the first impedance matching inductor, and the midpoint of the connection between the t-1th switching tube and the tth switching tube is connected to the second impedance matching inductor One end is connected, and t is the number of switch tubes; the other end of the first impedance matching inductance and the other end of the second impedance matching inductance are connected through a voltage equalizing capacitor branch; the voltage equalizing capacitor branch includes at least two series connected Voltage equalizing capacitor; the connection midpoint of two adjacent voltage equalizing capacitors is connected to one end of the 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 to the The connection midpoint of the mth input capacitor and the m+1th input capacitor; wherein, 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 The rectifier circuit is connected to the multi-port output voltage stabilizing circuit. 2. The DC converter according to claim 1, wherein k=2, t=4; each of the input capacitors is connected in parallel with two of the switching tubes. 3. The DC converter according to claim 1, wherein k=4, t=4; each of the input capacitors is connected in parallel with one of the switch tubes. 4. The DC converter according to claim 3, wherein the connection midpoint between the first input capacitor and the second input capacitor is connected to one end of the first inductance, and the other end of the first inductance is connected to the first switch The midpoint of the connection between the third and fourth input capacitors; the midpoint of the connection between the third input capacitor and the fourth input capacitor is connected to one end of the second inductor, and the other end of the second inductor is connected to the third switch tube and the fourth The connection midpoint of the switching tube. 5. The DC converter according to claim 1, wherein each of the equalizing capacitors is connected in parallel with a clamping diode; one end of the resonant capacitor is connected to a connection midpoint between two adjacent equalizing capacitors, so The other end of the resonant capacitor is connected to the connection midpoint of two adjacent clamping diodes, and the connection midpoint of the two adjacent clamping diodes is connected to one end of the primary winding of the high frequency transformer. 6. The DC converter according to claim 1, wherein the rectifier circuit is one of a half-bridge rectifier circuit, a full-bridge rectifier circuit, and a synchronous rectifier circuit. 7. The DC converter according to claim 1, wherein the multi-port output voltage stabilizing circuit includes a filter capacitor; or, the multi-port output voltage stabilizing circuit includes a filter capacitor and a capacitor connected in parallel with the filter capacitor regulator converter. 8 . The DC converter according to claim 1 , wherein the input capacitors, switch tubes, and voltage equalizing capacitors of all power units are connected in series. 9 . The DC converter according to claim 1 , wherein the inductance values of all impedance matching inductors are equal. 10. A control method for a DC converter according to any one of claims 1 to 9, characterized in that the method comprises: When the input voltage is lower than the set threshold, the first and t-th switching tubes of all power units are turned on synchronously, and the remaining switching tubes of all power units are turned on synchronously; When the input voltage rises above the set threshold, the first and second switching tubes of all power units are turned on complementary, and the duty cycle is less than 0.25; the phase of the t-1th switching tube in each power unit is advanced The phase of the first switching tube in the power unit is 90°, and the t-th switching tube of each power unit is complementary to the t-1-th switching tube; and / or, When the output voltage V _oi of the i-th power unit is lower than the expected value V _{oi_ref} of the output voltage of the power unit, the first and t-th switches of all power units are turned on synchronously, and the remaining switches of all power units are turned on synchronously; when When the output voltage V _oi is higher than the expected value V _{oi_ref} of the output voltage, the first switch tube and the second switch tube of all power units are complementary conduction, and the duty cycle is less than 0.25; the t-1th switch tube in each power unit The phase is ahead of the phase of the first switching tube in the power unit by 90°, The tth switching tube of each power unit is complementary to the t-1th switching tube; 1≤i≤n; If V _oi deviates from V _{oi_ref} and exceeds the first set value, then synchronize the switching pulse of the t-1th switching tube in each power unit, and adjust the duty cycle of the t-1th switching tube in each power unit; The voltage range across the capacitor is 2Vin/4(2n*(2n+2))～3.5Vin/4(2n*(2n+2)), Vin is the sum of the input voltages of all power units, and n is the number of power units ; If V _oi deviates from V _{oi_ref} and exceeds the second set value, then adjust the duty cycle of the first switch tube and the last switch tube in all switch tubes, and charge all voltage-balancing capacitors; the voltage range at both ends of each voltage-balancing capacitor 3.5Vin/4(2n*(2n+2))～4Vin/4(2n*(2n+2)); Wherein, the second set value is greater than the first set value.

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