Boost-LLC self-voltage-sharing direct-current conversion circuit based on output bus voltage division and control method of Boost-LLC self-voltage-sharing direct-current conversion circuit

Abstract

The invention relates to the technical field of power electronics, and discloses a Boost-LLC self-voltage-sharing DC conversion circuit based on output bus voltage division and a control method, primary sides of two LLC circuits of an LLC voltage-sharing circuit are respectively connected to two output bus capacitors of a three-level Boost main circuit, secondary sides of the two LLC circuits are connected in parallel and output to a load, and the output bus capacitors are connected to the load. The power flow of the two LLC circuits can be utilized to forcibly maintain the voltage balance of the two output bus capacitors, a neutral-point balance algorithm or a flying capacitor is not needed, the control algorithm and the Boost module structure design are simplified, the dynamic voltage-sharing capability under the load sudden change working condition is high, the steady-state deviation of the voltage-dividing capacitor is small, the system reliability is improved, and the system cost is reduced. And the method is particularly suitable for high-voltage and high-power scenes such as electric vehicle fast charging and photovoltaic inverters, and has remarkable technical advantages and market potential.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a Boost-LLC self-balanced DC conversion circuit and a control method based on output bus voltage division. Background Art

[0002] The three-level Boost circuit has been widely and deeply used in cutting-edge fields such as new energy power generation systems and electric vehicles due to its low voltage stress characteristics, excellent power density and other significant advantages.

[0003] In application scenarios involving high-voltage DC buses, ensuring that the voltage between bus voltage divider capacitors remains balanced is an indispensable core element for maintaining stable operation of the entire system. Currently, the voltage balancing solutions commonly used in the industry mainly include two categories: one is based on active closed-loop control strategies, which achieve voltage balancing by monitoring the voltage deviation of the bus voltage divider capacitors in real time and dynamically adjusting the output duty cycle with the help of a closed-loop PI (proportional-integral) control algorithm; the other is to introduce a hardware-level voltage balancing circuit, such as flying capacitors, balancing resistors and other special components, to assist in achieving voltage balance.

[0004] However, the above-mentioned existing technologies have exposed the problem of insufficient dynamic voltage balancing ability in practical applications. Especially in the face of complex working conditions such as sudden load changes or input voltage fluctuations, active voltage balancing control may cause frequent voltage imbalance between the voltage divider capacitors due to slow response or improper PI parameter settings. This imbalance will not only cause violent oscillations in the bus voltage, but may also further cause overvoltage damage to components, seriously threatening the stability and safety of the system.

[0005] Therefore, it has become a top priority to improve and innovate based on the limitations of existing technologies.

[0006] The above information is presented as background information only to assist with understanding the present disclosure and no determination or admission is made as to whether any of the above may be used as prior art with respect to the present disclosure. Summary of the invention

[0007] The present invention provides a Boost-LLC self-balanced DC conversion circuit and a control method based on output bus voltage division to solve the problems existing in the prior art.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides a Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, comprising a three-level Boost main circuit and an LLC voltage balancing circuit; wherein:

[0010] The LLC voltage balancing circuit includes two LLC circuits;

[0011] A primary side of the LLC circuit is connected to two ends of an output bus capacitor of the three-level Boost main circuit;

[0012] The primary side of another LLC circuit is connected to two ends of another output bus capacitor of the three-level Boost main circuit;

[0013] The secondary sides of the two LLC circuits are connected in parallel to form a unified output bus to be connected to a load.

[0014] Furthermore, in the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, the three-level Boost main circuit is a three-phase staggered parallel three-level Boost main circuit.

[0015] Further, in the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, the three-level Boost main circuit includes six first switch tubes, six first diodes, six first inductors and three first capacitors;

[0016] Six of the first switch tubes are respectively connected in series with a corresponding first diode to form six bridge arm units respectively, and the six bridge arm units form a three-phase Boost circuit;

[0017] The six first inductors are respectively connected to the six bridge arm units to form six staggered branches;

[0018] The three first capacitors are respectively connected to the six interleaved branches, one of the first capacitors is an input bus capacitor, and the other two first capacitors are output bus capacitors.

[0019] Further, in the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, the three-level Boost main circuit further includes a pre-charge relay, an input relay and a current limiting resistor;

[0020] The pre-charging relay is connected in series with the current limiting resistor and then connected in parallel to both ends of the input relay;

[0021] The input relay is connected between the positive pole of the input terminal and the three first inductors.

[0022] Further, in the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, the LLC circuit includes a primary circuit, a secondary circuit and a transformer;

[0023] The transformer comprises a primary winding and a secondary winding;

[0024] The primary winding is connected to the primary circuit, and the secondary winding is connected to the secondary circuit.

[0025] Further, in the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, the primary circuit includes four second switch tubes;

[0026] The four second switch tubes form a full-bridge unit.

[0027] Furthermore, in the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, the primary winding is connected in series with a group of resonant capacitors and resonant inductors and then connected to the full-bridge unit;

[0028] Further, in the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, the secondary circuit includes four second diodes;

[0029] The four second diodes constitute a rectifying circuit.

[0030] Furthermore, in the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, both the first switch tube and the second switch tube are IGBTs.

[0031] In a second aspect, the present invention provides a control method for a Boost-LLC self-equalizing DC conversion circuit based on output bus voltage division, the method being applied to the Boost-LLC self-equalizing DC conversion circuit based on output bus voltage division provided in the first aspect above, the method comprising:

[0032] S1, pre-charging stage: close the pre-charging relay in the three-level Boost main circuit, input the DC source, and charge the input bus capacitor of the three-level Boost main circuit through the current limiting resistor to raise the voltage of the input bus capacitor to a voltage close to the input DC source. After the pre-charging is completed, close the input relay of the three-level Boost main circuit, disconnect the pre-charging relay, and enter the boost stage;

[0033] S2, boost stage: the DSP digital signal processor runs the Boost control loop, and converts the loop output into the control square wave of PWM1-PWM6, drives the three-level Boost main circuit to operate, controls the output bus voltage to a given value, and maintains the voltage balance of the two output bus capacitors of the level Boost main circuit through the bus voltage equalization control loop. The boost stage is completed and enters the LLC startup stage;

[0034] S3, LLC startup stage: the DSP digital signal processor outputs control square waves PWM7 and PWM8 with fixed frequency and duty cycle to drive the two LLC circuits of the LLC voltage balancing circuit to operate, the LLC startup is completed, and the bus voltage balancing loop is closed;

[0035] S4, steady-state voltage equalization stage: At this time, the entire system is started and load addition / unloading operations can be performed; when the load changes, the LLC power flow automatically adjusts the charge and discharge rates of the two output bus capacitors to maintain voltage balance.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention provides a Boost-LLC self-equalizing DC conversion circuit and control method based on output bus voltage division. The primary sides of two LLC circuits of the LLC voltage equalizing circuit are respectively connected to two output bus capacitors of a three-level Boost main circuit, and the secondary sides of the two LLC circuits are output in parallel to the load, so that the power flow of the two LLC circuits can be used to forcibly maintain the voltage balance of the two output bus capacitors. No midpoint balance algorithm or flying capacitor is required, which simplifies the control algorithm and the Boost module structure design. The circuit has strong dynamic voltage equalization capability under load mutation conditions and small steady-state deviation of the voltage divider capacitor, thereby improving system reliability. The circuit is particularly suitable for high-voltage and high-power scenarios such as electric vehicle fast charging and photovoltaic inverters, and has significant technical advantages and market potential.

[0038] The present invention has other features and advantages, which will be apparent from or will be described in detail in the accompanying drawings and the following detailed description incorporated herein, which together serve to explain the specific principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 It is a structural schematic diagram of a Boost-LLC self-balanced DC conversion circuit based on output bus voltage division provided in the first embodiment of the present invention;

[0041] Figure 2 A schematic diagram of a control loop of a three-level Boost main circuit provided in Embodiment 1 of the present invention;

[0042] Figure 3It is a flow chart of a control method of a Boost-LLC self-equalizing DC conversion circuit based on output bus voltage division provided in the second embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to explain in detail the possible application scenarios, technical principles, specific schemes that can be implemented, and the purposes and effects that can be achieved, the following is a detailed description of the specific embodiments listed in conjunction with the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0044] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0045] Unless otherwise defined, the technical terms used in this document have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.

[0046] In the description of this application, the term "and / or" is an expression used to describe the logical relationship between objects, indicating that three relationships may exist, for example, A and / or B, which means: A exists, B exists, and A and B exist at the same time. In addition, the character " / " in this article generally indicates that the objects before and after are in an "or" logical relationship.

[0047] In the present application, terms such as “first” and “second” are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship of quantity, priority or sequence between these entities or operations.

[0048] Without further limitations, in this application, the words "include", "comprises", "has" or other similar expressions used in the sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those limited elements, but also other elements not explicitly listed, or also include elements inherent to such process, method or product.

[0049] In this application, expressions such as "greater than", "less than", "exceed" and the like are understood to exclude the number itself; expressions such as "above", "below", "within" and the like are understood to include the number itself. In addition, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups", "multiple times", etc., unless otherwise clearly and specifically limited.

[0050] In the description of the embodiments of the present application, space-related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or position relationship based on the orientation or position relationship shown in the specific embodiments or drawings, and are only for the convenience of describing the specific embodiments of the present application or facilitating the reader's understanding, and do not indicate or imply that the referred device or component must have a specific position, a specific orientation, or be constructed or operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0051] Unless otherwise expressly specified or limited, in the description of the embodiments of the present application, the terms such as "install", "connect", "connect", "fix", "set", etc. used should be understood in a broad sense. For example, the "connection" can be a fixed connection, a detachable connection, or an integrated setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. For technicians in the technical field to which the present application belongs, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0052] Embodiment 1

[0053] In view of the defects of the above-mentioned prior art, the applicant, based on many years of rich practical experience and professional knowledge in this field, and in conjunction with the application of theory, actively conducts research and innovation in the hope of creating a technology that can solve the defects of the prior art. After continuous research and design, and after repeated trial production and improvement, the present invention with real practical value was finally created.

[0054] Please refer to Figure 1 , Embodiment 1 of the present invention provides a Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, including a three-level Boost main circuit and an LLC voltage balancing circuit; wherein,

[0055] The LLC voltage balancing circuit includes two LLC circuits;

[0056] A primary side of the LLC circuit is connected to two ends of an output bus capacitor of the three-level Boost main circuit;

[0057] The primary side of another LLC circuit is connected to two ends of another output bus capacitor of the three-level Boost main circuit;

[0058] The secondary sides of the two LLC circuits are connected in parallel to form a unified output bus to be connected to a load.

[0059] It should be noted that the innovation of this embodiment is that, through the carefully designed LLC voltage-equalizing circuit, the primary sides of the two LLC circuit branches can be connected to the two output bus capacitors of the three-level Boost main circuit respectively, and their secondary sides are connected in parallel to supply power to the load together. This layout cleverly utilizes the power flow characteristics of the two LLC circuits, forcibly maintaining the voltage balance between the two output bus capacitors, thereby abandoning the reliance on the midpoint balance algorithm and the use of flying capacitors. This not only greatly simplifies the complexity of the control algorithm, but also optimizes the structural design of the Boost module.

[0060] More significantly, when faced with a sudden change in load, the circuit exhibits excellent dynamic voltage balancing capability, and the steady-state voltage deviation of the voltage divider capacitor is effectively controlled and maintained at a low level. These characteristics together improve the reliability of the entire system, making it particularly suitable for electric vehicle fast charging stations, photovoltaic inverters, and other high-voltage and high-power application scenarios. In summary, the technical solution proposed in the present invention has shown obvious technical advantages and broad market application potential in these fields.

[0061] Please refer again Figure 1 In one implementation of this embodiment, the three-level Boost main circuit is a three-phase staggered parallel three-level Boost main circuit, which improves the Boost output power density, reduces the DC bus ripple and the average module power. The Boost input side is connected to a 400V-900V DC source, and the two output bus capacitors on the output side are connected in series to form a high-voltage bus (1000V).

[0062] The three-level Boost main circuit includes six first switch tubes (Q1-Q6), six first diodes (D7-D12), six first inductors (L1-L6) and three first capacitors (C1-C3);

[0063] The six first switch tubes are respectively connected in series with a corresponding first diode to form six bridge arm units (Q1 and D7, Q2 and D10, Q3 and D8, Q4 and D11, Q5 and D9, Q6 and D12), and the six bridge arm units are further combined to form a three-phase inverter bridge structure;

[0064] The six first inductors are respectively connected to the six bridge arm units to form six staggered branches, and the design of these staggered branches helps to improve the efficiency and performance of the circuit;

[0065] The three first capacitors are respectively connected to the six interlaced branches, one of the first capacitors (C1) is an input bus capacitor responsible for providing a stable input voltage, and the other two first capacitors (C2 and C3) are output bus capacitors for storing and providing an output voltage after Boost.

[0066] In summary, the three-level Boost main circuit in this embodiment achieves efficient voltage conversion and stable output voltage output through its unique three-phase staggered parallel design and carefully configured components such as switches, diodes, inductors and capacitors, laying a solid foundation for the subsequent cooperation with the LLC voltage equalization circuit.

[0067] Please refer again Figure 1 In one implementation of this embodiment, the three-level Boost main circuit is further equipped with three key components: a pre-charge relay (S2), an input relay (S1) and a current limiting resistor (R1).

[0068] Specifically, the pre-charge relay and the current limiting resistor are first connected in series, and then this series combination is connected in parallel with the input relay. This design ensures that at the beginning of power-on, the system can safely and slowly charge the capacitor through the pre-charge circuit composed of the pre-charge relay and the current limiting resistor, thereby effectively avoiding component damage caused by instantaneous high current shock.

[0069] In addition, the input relay is directly connected between the positive pole of the input terminal and the three first inductors (i.e., the first inductor corresponding to each of the three phases. Since the three phases are staggered in parallel, each phase has a corresponding first inductor connected to the input terminal). This design enables the system to flexibly control the on and off of the input power supply as needed, further improving the safety and controllability of the circuit.

[0070] In summary, by introducing the three components of the pre-charging relay, the input relay and the current limiting resistor, the three-level Boost main circuit of this embodiment further enhances its safety and reliability while maintaining the original high efficiency and stability characteristics.

[0071] Please refer again Figure 1 In one implementation of this embodiment, the LLC circuit includes a primary circuit, a secondary circuit and a transformer;

[0072] The transformer comprises a primary winding and a secondary winding;

[0073] The primary winding is connected to the primary circuit, and the secondary winding is connected to the secondary circuit, thereby realizing the transmission and conversion of electric energy.

[0074] The primary circuit includes four second switch tubes (the four second switch tubes included in the primary circuit of one LLC circuit are Q7-Q10, and the four second switch tubes included in the primary circuit of another LLC circuit are Q11-Q14);

[0075] The four second switching tubes form a full-bridge unit, which is responsible for controlling the electric energy input to the transformer.

[0076] The primary winding is connected in series with a group of resonant capacitors (one of which corresponds to the resonant capacitor of the primary winding of the LLC circuit is C4, and the other corresponds to the resonant capacitor of the primary winding of the LLC circuit is C5) and a resonant inductor (one of which corresponds to the resonant inductor of the primary winding of the LLC circuit is L7, and the other corresponds to the resonant inductor of the primary winding of the LLC circuit is L8) and then connected to the full-bridge unit, which together determine the resonant frequency of the circuit, thereby affecting the conversion efficiency and voltage gain of the circuit;

[0077] The secondary circuit includes four second diodes (the four second diodes included in the secondary circuit of one LLC circuit are D21-D24, and the four second diodes included in the secondary circuit of another LLC circuit are D25-D28);

[0078] The four second diodes form a rectifier circuit responsible for converting the alternating current output by the secondary winding of the transformer into direct current for use by the load.

[0079] In summary, the LLC circuit in this embodiment achieves efficient power conversion and stable output voltage output through its carefully designed primary circuit, secondary circuit and transformer. This design not only improves the conversion efficiency of the circuit, but also enhances its ability to cope with load changes, providing a more reliable and efficient solution for practical applications.

[0080] It should be noted that the LLC resonant parameters, such as the resonant capacitor, resonant inductor and transformer, are strictly matched to ensure consistent gain. The secondary side of the LLC circuit uses silicon carbide (SiC) diode rectification to reduce diode conduction losses and improve LLC efficiency. At the same time, the unidirectional conductivity of the diode can prevent the occurrence of reverse circulation problems caused by LLC resonant parameter mismatch or inconsistent states.

[0081] In one implementation of this embodiment, both the first switch tube and the second switch tube are IGBTs.

[0082] As a high-performance power semiconductor device, IGBT combines the two advantages of high input impedance of MOSFET (metal oxide semiconductor field effect transistor) and low conduction voltage drop of GTR (thyristor), so it is widely used in various power electronic devices. In this embodiment, IGBT is selected as the switch tube mainly based on its excellent switching performance, high reliability and long life.

[0083] The first switch tube plays a vital role in the three-level Boost main circuit, controlling the on and off of the circuit to achieve voltage conversion and regulation. The second switch tube plays a similar role in the LLC circuit, ensuring that the electric energy can be efficiently and stably transmitted to the load end through precise control strategies.

[0084] In summary, using IGBT as the preferred solution for the switch tube in this embodiment not only improves the overall performance of the circuit, but also further enhances the stability and reliability of the system.

[0085] like Figure 2 As shown, Figure 2 The control loop diagram of the three-level Boost main circuit is shown in Figure 2. The Boost circuit uses a dual closed-loop control of “output bus voltage loop + boost inductor current loop”. busRef " is the bus voltage loop setting, and the DSP digital signal processor controls the actual voltage of the output bus by changing the setting. "V busFdb " is the bus voltage loop feedback, which is the actual bus voltage sampling value. LaPos and I LaNeg They represent the actual current sampling values ​​of the positive inductor L1 and the negative inductor L4 of the first phase Boost circuit respectively, and the average value of these two current values ​​is taken as the feedback of the inner loop of the inductor current. "PosPWM output" and "NegPWM output" are respectively driven to the upper and lower Boost tubes, and the initial phases of the two PWM waves are staggered by 1 / 2 control cycle to achieve complementarity. When the load power changes and causes the bus voltage to change, the DSP digital signal processor controls the duty cycle of the upper and lower Boost switch tubes through the output of the control loop, thereby changing the size of the input current to adapt to the load changes while maintaining the stability of the DC bus voltage.

[0086] Understandably, Figure 2The control loop diagram shown is the control loop of one phase of the three-level Boost circuit. The control loops of the other two phases are basically the same. The only difference is that the inner loop feedback of the inductor current is to take the average value of each corresponding positive and negative boost inductor current sampling, which will not be repeated here. The initial phase of the PWM square wave between phases is staggered by 1 / 3 of the control cycle to achieve staggered parallel control; in the boost stage, when the Boost is running alone, it is still necessary to superimpose the bus voltage equalization loop to perform active bus voltage equalization control. After the LLC is started, the control algorithm can be turned off to save computing resources. The voltages of C2 and C3 are collected through the sampling circuit, and the voltage deviation ΔV=Vbus+-Vbus- is calculated. ΔV is used as the feedback of the bus voltage equalization loop, and 0 is used as a given. The duty cycle of the upper and lower Boost tubes is adjusted through the output of the loop, and ΔV is controlled to zero to achieve active bus voltage equalization; the LLC circuit adopts open-loop control, and the DSP digital signal processor outputs two control square waves PWM7 and PWM8 with fixed frequency and duty cycle to the LLC primary switch tube drive to drive the LLC circuit to operate. The initial phases of the two PWM waves are staggered by 1 / 2 control cycle to achieve complementarity. The PWM wave duty cycle is fixed at 0.5, and the operating frequency is set near the LLC resonant frequency. Through actual test adjustments, it is ensured that the switch tube can achieve ZVS turn-on in the full power range to avoid the turn-on loss of the switch tube.

[0087] Although LLC circuit, output bus capacitor and other terms are used more frequently in this application, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional restrictions is contrary to the spirit of the present invention.

[0088] The present invention provides a Boost-LLC self-equalizing DC conversion circuit based on output bus voltage division, in which the primary sides of two LLC circuits of the LLC voltage equalizing circuit are respectively connected to two output bus capacitors of a three-level Boost main circuit, and the secondary sides of the two LLC circuits are output in parallel to the load, so that the power flow of the two LLC circuits can be used to forcibly maintain the voltage balance of the two output bus capacitors, without the need for a midpoint balance algorithm or a flying capacitor, thereby simplifying the control algorithm and the Boost module structure design, having a strong dynamic voltage equalizing capability under load mutation conditions and a small steady-state deviation of the voltage divider capacitor, thereby improving system reliability, and being particularly suitable for high-voltage and high-power scenarios such as electric vehicle fast charging and photovoltaic inverters, and having significant technical advantages and market potential.

[0089] Embodiment 2

[0090] Please refer to Figure 3Embodiment 2 of the present invention provides a control method for a Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, the method is applied to the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division provided in the above embodiment 1, the method comprising:

[0091] S1, pre-charging stage: close the pre-charging relay in the three-level Boost main circuit, input the DC source, and charge the input bus capacitor of the three-level Boost main circuit through the current limiting resistor to raise the voltage of the input bus capacitor to a voltage close to the input DC source. After the pre-charging is completed, close the input relay of the three-level Boost main circuit, disconnect the pre-charging relay, and enter the boost stage;

[0092] S2, boost stage: the DSP digital signal processor runs the Boost control loop, and converts the loop output into the control square wave of PWM1-PWM6, drives the three-level Boost main circuit to operate, controls the output bus voltage to a given value, and maintains the voltage balance of the two output bus capacitors of the level Boost main circuit through the bus voltage equalization control loop. The boost stage is completed and enters the LLC startup stage;

[0093] It should be noted that the given value is, for example, 1000V.

[0094] S3, LLC startup stage: the DSP digital signal processor outputs control square waves PWM7 and PWM8 with fixed frequency and duty cycle to drive the two LLC circuits of the LLC voltage balancing circuit to operate, the LLC startup is completed, and the bus voltage balancing loop is closed;

[0095] S4, steady-state voltage equalization stage: At this time, the entire system is started and load addition / unloading operations can be performed; when the load changes, the LLC power flow automatically adjusts the charge and discharge rates of the two output bus capacitors to maintain voltage balance.

[0096] It should be noted that, for example, when the voltage of C2 increases, the corresponding LLC input voltage is high. In the open-loop LLC control, the LLC gain is fixed, and the secondary output voltage also increases accordingly. The voltage difference between the two LLC secondary output voltages forms a voltage difference, and the LLC output power of C2 corresponding to the LLC increases. At the same time, because the secondary diode rectification cuts off the reverse circulation loop and the load power is stable, the output power of the other LLC naturally decreases. This is equivalent to the discharge power of C2 increasing and the discharge power of C3 decreasing until the automatic voltage equalization of the output bus capacitor is completed. This voltage equalization process does not require additional control and is fast and stable to adjust.

[0097] Finally, it should be noted that although the above embodiments have been described in the specification and drawings of this application, this does not limit the scope of patent protection of this application. All technical solutions generated by replacing or modifying equivalent structures or equivalent processes based on the essential concept of this application using the contents recorded in the specification and drawings of this application, as well as directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, are included in the scope of patent protection of this application.

Claims

1. A Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, characterized in that: It includes a three-level Boost main circuit and an LLC voltage equalization circuit; wherein, The LLC voltage balancing circuit includes two LLC circuits; A primary side of the LLC circuit is connected to two ends of an output bus capacitor of the three-level Boost main circuit; The primary side of another LLC circuit is connected to two ends of another output bus capacitor of the three-level Boost main circuit; The secondary sides of the two LLC circuits are connected in parallel to form a unified output bus to be connected to a load.

2. The Boost-LLC self-balanced DC conversion circuit based on output bus voltage division according to claim 1, characterized in that: The three-level Boost main circuit is a three-phase staggered parallel three-level Boost main circuit.

3. The Boost-LLC self-balanced DC conversion circuit based on output bus voltage division according to claim 2, characterized in that: The three-level Boost main circuit includes six first switch tubes, six first diodes, six first inductors and three first capacitors; Six of the first switch tubes are respectively connected in series with a corresponding first diode to form six bridge arm units respectively, and the six bridge arm units form a three-phase Boost circuit; The six first inductors are respectively connected to the six bridge arm units to form six staggered branches; The three first capacitors are respectively connected to the six interleaved branches, one of the first capacitors is an input bus capacitor, and the other two first capacitors are output bus capacitors.

4. The Boost-LLC self-balanced DC conversion circuit based on output bus voltage division according to claim 3 is characterized in that: The three-level Boost main circuit also includes a pre-charge relay, an input relay and a current limiting resistor; The pre-charging relay is connected in series with the current limiting resistor and then connected in parallel to both ends of the input relay; The input relay is connected between the positive pole of the input terminal and the three first inductors.

5. The Boost-LLC self-balanced DC conversion circuit based on output bus voltage division according to claim 3, characterized in that: The LLC circuit includes a primary circuit, a secondary circuit and a transformer; The transformer comprises a primary winding and a secondary winding; The primary winding is connected to the primary circuit, and the secondary winding is connected to the secondary circuit.

6. The Boost-LLC self-balanced DC conversion circuit based on output bus voltage division according to claim 5, characterized in that: The primary circuit includes four second switch tubes; The four second switch tubes form a full-bridge unit.

7. The Boost-LLC self-balanced DC conversion circuit based on output bus voltage division according to claim 6, characterized in that: The primary winding is connected in series with a group of resonant capacitors and resonant inductors and then connected to the full-bridge unit.

8. The Boost-LLC self-balanced DC conversion circuit based on output bus voltage division according to claim 7, characterized in that: The secondary circuit includes four second diodes; The four second diodes constitute a rectifier circuit.

9. The Boost-LLC self-balanced DC conversion circuit based on output bus voltage division according to claim 6, characterized in that: The first switch tube and the second switch tube are both IGBTs.

10. A control method of a Boost-LLC self-balanced DC conversion circuit based on output bus voltage division, characterized in that: The method is applied to the Boost-LLC self-balanced DC conversion circuit based on output bus voltage division according to any one of claims 1 to 9, and the method comprises: S1, pre-charging stage: close the pre-charging relay in the three-level Boost main circuit, input the DC source, and charge the input bus capacitor of the three-level Boost main circuit through the current limiting resistor to raise the voltage of the input bus capacitor to a voltage close to the input DC source. After the pre-charging is completed, close the input relay of the three-level Boost main circuit, disconnect the pre-charging relay, and enter the boost stage; S2, boost stage: the DSP digital signal processor runs the Boost control loop, and converts the loop output into a control square wave of PWM1-PWM6, drives the three-level Boost main circuit to operate, controls the output bus voltage to a given value, and maintains the voltage balance of the two output bus capacitors of the three-level Boost main circuit through the bus voltage equalization control loop. The boost stage is completed and enters the LLC startup stage; S3, LLC startup stage: the DSP digital signal processor outputs control square waves PWM7 and PWM8 with fixed frequency and duty cycle to drive the two LLC circuits of the LLC voltage balancing circuit to operate, the LLC startup is completed, and the bus voltage balancing loop is closed; S4, steady-state voltage equalization stage: At this time, the entire system is started and load addition / unloading operations can be performed; when the load changes, the LLC power flow automatically adjusts the charge and discharge rates of the two output bus capacitors to maintain voltage balance.

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