Multilevel DC current converter, flying capacitor voltage control method and control device

Abstract

The present invention provides a multilevel DC converter, a flying capacitor voltage control method, and a control device. The multilevel DC converter includes a controller, a flying capacitor, two switching transistor groups, and an inductor. The flying capacitor control method includes adjusting a duty cycle difference between a first switching transistor of the two switching transistor groups or a phase difference between carriers of the first switching transistor of the two switching transistor groups based on the magnitude of an inductor current in response to an absolute value of a difference between a reference voltage and a sampling voltage of the flying capacitor being greater than a first threshold. According to an embodiment of the present invention, the flying capacitor voltage can be controlled, and the operation stability of the multilevel DC converter can be improved.

Description

[Technical Field]

[0001] Book The present invention relates to the field of power electronics technology, and in particular to a multilevel DC current converter, a flying capacitor voltage control method and control device. [Background technology]

[0002] Multilevel DC current converters can reduce the voltage stress of the input voltage of each switching transistor by adding flying capacitors. Taking a three-level DC current converter with flying capacitors as an example, the use of flying capacitors can store half of the input voltage, resulting in three output levels: 0, 1 / 2, and 1. The output level change amplitude is half that of a two-level topology. In this way, the performance of electronic systems can be improved by using low-voltage switching transistors.

[0003] Currently, the charging and discharging time of the flying capacitor can be adjusted by determining the inductor current direction and adjusting the difference between the duty cycles of the first switching transistor (or the second switching transistor) of the switching transistor group to control the flying capacitor voltage. However, when the inductor current is small, the inductor current is a high-frequency triangular wave, and repeatedly switches between positive and negative, controlling the flying capacitor voltage based on the instantaneous current direction places extremely high demands on the control chip and is not applicable to practical projects. Even if the difference between the duty cycles of the first switching transistor (or the second switching transistor) of the switching transistor group is greatly adjusted, the flying voltage cannot be effectively increased or decreased, and the control goal of stabilizing the flying capacitor voltage at the target value cannot be achieved. Summary of the Invention

[0004] The embodiments of the present application disclose a multilevel DC current converter, a flying capacitor voltage control method and a control device for controlling the voltage of a flying capacitor, thereby improving the operation stability of the multilevel DC current converter.

[0005] According to a first aspect, an embodiment of the present application discloses a multi-level direct current converter, the multi-level direct current converter comprising: at least one flying capacitor; two switching transistor groups connected to the flying capacitor; an inductor connected to each of the switching transistor groups and a positive electrode of a low-voltage power supply of the multi-level direct current converter; and a controller configured to control the switching transistor groups, each of the switching transistor groups comprising a first switching transistor and a second switching transistor, the on / off states of which are complementary, the first switching transistor being connected to one end of a high-voltage power supply of the multi-level direct current converter, and the second switching transistor being connected to the other end of the high-voltage power supply of the multi-level direct current converter, the controller being configured to adjust a duty cycle difference between first switching transistors of the two switching transistor groups or a phase difference between carriers of the first switching transistors of the two switching transistor groups based on the magnitude of an inductor current when an absolute value of a difference between a reference voltage of the flying capacitor and a sampling voltage is greater than a first threshold.

[0006] Multilevel DC Current Converter andA multilevel DC converter, sometimes referred to as a multilevel DC converter, is configured to perform direct current (DC) electrical energy conversion, for example, step-up conversion or step-down conversion. The specific type of the multilevel DC converter is not limited in this application and may be a three-level DC converter, a five-level DC converter, a seven-level DC converter, etc. A multilevel topology corresponding to a multilevel DC converter means that the output level has at least three states. For example, a three-level topology is one with three output levels of 1, 1 / 2, and 0. A five-level topology is one with five output levels of 1, 3 / 4, 1 / 2, 1 / 4, and 0.

[0007] The first switching transistor and the second switching transistor may be field effect transistors (FETs), metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), junction field effect transistors (JFETs), and their parallel diodes, etc., which is not limited in this specification.

[0008] The controller may be a pulse width modulation (PWM) device, a PWM-based battery management system (BMS), a micro control unit (MCU), a central processing unit (CPU), another general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or another programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, or the like. The controller may be one or more chips with a communication connection. The controller may include a control unit corresponding to each switching transistor, or may include a control unit corresponding to a group of switching transistors, e.g., a pulse width modulator corresponding to a first switching transistor and a second switching transistor of the group of switching transistors. This is not limited herein.

[0009] The flying capacitor sampled voltage is the collected real-time voltage. The flying capacitor reference voltage is the target value to which the flying capacitor is adjusted. The inductor current, also referred to as the inductor current, can be an instantaneous current value or an average value.

[0010] The first threshold is not limited in the present invention. The first threshold may be 0, for example. If the absolute value of the difference between the reference voltage and the sampling voltage of the flying capacitor is greater than the first threshold, it indicates that the flying capacitor voltage is not adjusted to the target value (for example, the target value of a three-level DC converter may be 1 / 2 the voltage of the high-voltage power supply). The duty cycle difference between the switching transistors on the flying capacitor side or the phase difference between the carriers of the first switching transistors on the flying capacitor side can be continuously adjusted to control the flying capacitor voltage and reduce the voltage stress of the multilevel DC current converter. If the difference between the sampling voltage and the reference voltage of the flying capacitor is less than the first threshold, it indicates that the flying capacitor voltage is adjusted to the target value, and the current operating state can be maintained to allow the flying capacitor to continue operating. In this way, the operating stability of the multilevel DC current converter can be improved.

[0011] Referring to the first embodiment, in a first possible implementation, when the controller determines to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current, the controller is configured to increase the phase difference between the carriers of the first switching transistors of the two switching transistor groups, and the sampling voltage of the flying capacitor is smaller than the reference voltage of the flying capacitor, thereby increasing the voltage of the flying capacitor.

[0012] Referring to the first embodiment, in a second possible implementation, when the controller determines to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current, the controller is particularly configured to reduce the phase difference between the carriers of the first switching transistors of the two switching transistor groups, and the sampling voltage of the flying capacitor is greater than the reference voltage of the flying capacitor, thereby reducing the voltage of the flying capacitor.

[0013] Referring to the first embodiment or the first possible implementation or the second possible implementation, in a third possible implementation, the controller is particularly configured to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups when the inductor current is less than a second threshold.

[0014] With reference to the first embodiment, in a possible fourth implementation, the controller is particularly configured to adjust a duty cycle difference between first switching transistors of the two switching transistor groups when the inductor current is greater than a third threshold. With reference to the first embodiment, the possible first implementation, or the possible second implementation, in a possible fifth implementation, the controller is particularly configured to adjust a duty cycle difference between first switching transistors of the two switching transistor groups or a phase difference between carriers of first switching transistors of the two switching transistor groups according to an adjustment method at a previous moment or a moment immediately before, when the inductor current is greater than or equal to the second threshold and less than or equal to the third threshold.

[0015] The values ​​of the second and third thresholds are not limited in the present invention, and the second threshold is less than the third threshold. It is understood that when the inductor current is less than the second threshold, it indicates that the inductor current is small and the current may be a light load. Assuming that the duty cycle difference is not adjusted, the phase shift control method can be used to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups. When the inductor current is greater than the third threshold, it indicates that the inductor current is large and the current may be a heavy load. Assuming that the phase difference is not adjusted, the duty cycle adjustment method can be used to adjust the duty cycle difference between the first switching transistors of the two switching transistor groups. When the inductor current is greater than the second threshold and less than the third threshold, the inductor is in an intermediate state between a light load and a heavy load, and adjustment can be performed using the adjustment method at the previous moment. For example, if the phase shift control method was used at the previous moment, the phase shift control method can be continued, or if the duty cycle adjustment method was used at the previous moment, the duty cycle adjustment method can be continued. In this way, the flying voltage can be controlled using the above three cases, and therefore the voltage of the controlled flying capacitor can continue to transition smoothly.

[0016] According to a second aspect, an embodiment of the present invention discloses a flying capacitor voltage control method. The flying capacitor is used in a multilevel DC current converter, and the multilevel DC current converter further includes two switching transistor groups, an inductor, and a controller. Each switching transistor group includes a first switching transistor and a second switching transistor, whose on / off states are complementary. The voltage control method includes: adjusting a duty cycle difference between the first switching transistors of the two switching transistor groups or a phase difference between carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current when the absolute value of the difference between the reference voltage and the sampling voltage of the flying capacitor is greater than a first threshold. In this way, when it is determined that the flying capacitor voltage is adjusted to a target value, the duty cycle difference between the switching transistors on the flying capacitor side or the phase difference between carriers of the switching transistors on the flying capacitor side can be continuously adjusted to control the flying capacitor voltage. In this way, the operating stability of the multilevel DC current converter can be improved.

[0017] Referring to the second embodiment, in a first possible implementation, the step of adjusting the duty cycle difference between the first switching transistors of the two switching transistor groups or the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current of the inductor includes the step of: when determining to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current, increasing the phase difference between the carriers of the first switching transistors of the two switching transistor groups, wherein the sampling voltage of the flying capacitor is smaller than the reference voltage of the flying capacitor.

[0018] Referring to the second embodiment, in a second possible implementation, the step of adjusting the duty cycle difference between the first switching transistors of the two switching transistor groups or the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current includes: when determining to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current, a step of reducing the phase difference between the carriers of the first switching transistors of the two switching transistor groups, wherein the sampling voltage of the flying capacitor is greater than the reference voltage of the flying capacitor.

[0019] Referring to the second embodiment, in a third possible implementation, the step of adjusting the duty cycle difference between the first switching transistors of the two switching transistor groups or the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current includes: adjusting the phase difference between the carriers of the first switching transistors of the two switching transistor groups by the controller when the inductor current is smaller than a second threshold.

[0020] Referring to the second embodiment, in a fourth possible implementation, the step of adjusting by the controller the duty cycle difference between the first switching transistors of the two switching transistor groups or the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current includes: adjusting by the controller the duty cycle difference between the first switching transistors of the two switching transistor groups in response to the current being greater than a third threshold.

[0021] Referring to the second embodiment, in a possible fifth implementation, the step of adjusting, by the controller, the duty cycle difference between the first switching transistors of the two switching transistor groups or the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the current includes the step of: when the current is greater than or equal to the second threshold and less than or equal to the third threshold, adjusting, by the controller, the duty cycle difference between the first switching transistors of the two switching transistor groups or the phase difference between the carriers of the first switching transistors of the two switching transistor groups according to the adjustment method of the previous moment.

[0022] According to a third aspect, an embodiment of the present invention discloses a control device, the control device including a controller and a memory, the memory configured to store instructions, and the controller configured to invoke the instructions stored in the memory to perform the method of the second aspect.

[0023] It should be understood that the implementations and beneficial effects of the above aspects of the present application may be cross-referenced. [Brief explanation of the drawings]

[0024] The accompanying drawings used in the embodiments of the present application will be described below.

[0025] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a photovoltaic generation system according to an embodiment of the present invention. [Figure 2] FIG. 2 shows a circuit diagram of a three-level DC current converter according to an embodiment of the present invention. [Figure 3] FIG. 3 is a diagram schematically illustrating the configuration of a multilevel DC current converter according to an embodiment of the present invention. [Figure 4] FIG. 4 shows an operation mode diagram of a three-level DC current converter according to an embodiment of the present invention. [Figure 5]FIG. 5 shows an operation mode diagram of a three-level DC current converter according to an embodiment of the present invention. [Figure 6] FIG. 6 shows an operation mode diagram of a three-level DC current converter according to an embodiment of the present invention. [Figure 7] FIG. 7 shows an operation mode diagram of a three-level DC current converter according to an embodiment of the present invention. [Figure 8] FIG. 8 shows an operation mode diagram of a three-level DC current converter according to an embodiment of the present invention. [Figure 9] FIG. 9 shows an operation mode diagram of a three-level DC current converter according to an embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing the relationship between duty cycle difference and flying voltage and the relationship between phase difference and flying voltage according to the present invention. [Figure 11] FIG. 11 is a diagram showing the relationship between duty cycle difference and flying voltage and the relationship between phase difference and flying voltage according to the present invention. [Figure 12] FIG. 12 is a diagram showing the relationship between duty cycle difference and flying voltage and the relationship between phase difference and flying voltage according to the present invention. [Figure 13] FIG. 13 is a diagram showing the relationship between duty cycle difference and flying voltage and the relationship between phase difference and flying voltage according to the present invention. [Figure 14] FIG. 14 shows a schematic flow chart of flying capacitor voltage regulation by a controller according to an embodiment of the present invention. [Figure 15] FIG. 15 is a schematic flowchart of a flying capacitor voltage control method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] A "connection" as described herein may be a direct or indirect connection. For example, when A is connected to B, it may mean that A is directly connected to B, or that A is indirectly connected to B through one or more other electrical components. For example, A may be directly connected to C, C may be directly connected to B, and A and B may be connected using C. This connection may be referred to as a coupling, an electrical connection, or the like. This is not limited herein. The terms "first" and "second" are used merely for descriptive purposes and should not be understood as an indication or implication of relative importance.

[0027] The embodiments of the present application relate to a multi-level DC current converter. child The multi-level DC current converter may be configured to perform direct current (DC)-to-direct current power conversion, for example, boost conversion or buck conversion. This is not particularly limited in the embodiments of the present application. Furthermore, the application scenario of the multi-level DC current converter is not limited in the embodiments of the present application. The multi-level DC current converter may be used in different types of electrical equipment (such as power networks or power grids, household devices, industrial and commercial electrical devices, etc.), and may be used in different application scenarios in the electrical equipment field, such as the user terminal (mobile phone, intelligent device, television, etc.) field and the vehicle field, and may be used in power supply scenarios for large electrical devices (such as power grids and industrial equipment), power supply scenarios for small and medium-sized distributed electrical equipment (such as in-vehicle electrical devices and household electrical devices), and power supply scenarios for mobile electrical equipment (such as mobile phones and intelligent equipment).

[0028] For example, Figure 1 is a diagram schematically illustrating the architecture of a photovoltaic power generation system according to an embodiment of the present application. As shown in Figure 1, the photovoltaic power generation system includes a photovoltaic cell module, a multi-level DC current converter, a battery bank, an inverter circuit, a DC load, an AC load, and a power grid. In the photovoltaic power generation system, solar energy is converted into DC energy by the photovoltaic cell module. The DC energy is boosted using the multi-level DC current converter. The boosted DC energy can be supplied to the DC load or stored in the battery bank, or can be converted into AC energy using an inverter, and the AC energy can be supplied to the AC load or connected to the power grid.

[0029] The specific type of multilevel DC current converter is not limited to that described herein and may be a three-level DC current converter, a five-level DC current converter, a seven-level DC current converter, or the like. A multilevel topology corresponding to a multilevel DC current converter means that the output level has at least three states. For example, a three-level topology is one in which the output level has three states: 1, 1 / 2, and 0. A five-level topology is one in which the output level has five states: 1, 3 / 4, 1 / 2, 1 / 4, and 0. Multilevel topology circuits are further classified into diode-clamped multilevel topology circuits, flying capacitor multilevel topology circuits, and the like. The topology circuit of the multilevel DC topology of the present invention may be a flying capacitor multilevel topology circuit including a flying capacitor.

[0030] In order to help those skilled in the art better understand the technical solutions provided in the embodiments of the present invention, the following description will take a three-level DC converter as an example. Figure 2 is a circuit diagram of a three-level DC current converter according to an embodiment of the present invention. As shown in Figure 2, the three-level DC current converter is connected to a high-voltage power supply V Ha capacitor C1, a switching transistor Q1, a switching transistor Q2, a switching transistor Q3, a switching transistor Q4, and a flying capacitor C fly , an inductor L1, a capacitor C2, and a low-voltage power supply VL.

[0031] Switching transistor Q1, switching transistor Q2, switching transistor Q3, and switching transistor Q4 may be, but are not limited to, field effect transistors (FETs), metal-oxide-semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), junction field effect transistors (JFETs), diodes connected in parallel with junction field effect transistors, etc.

[0032] The drain electrode of the switching transistor Q1 is connected to the high-voltage power supply V H The source electrode of the switching transistor Q1 is connected to the drain electrode of the switching transistor Q2 and the positive end of the flying capacitor C fly One end of the flying capacitor C fly The other end of the inductor L1 is connected to the source electrode of the switching transistor Q3 and the drain electrode of the switching transistor Q4. The source electrode of the switching transistor Q2 and the drain electrode of the switching transistor Q3 are connected to one end of the inductor L1, and the other end of the inductor L1 is connected to the low-voltage power supply V L (connected to the negative end of the parallel capacitor C2).

[0033] In an embodiment of the present invention, a flying capacitor C flyThe switching transistors are grouped based on the connection relationship between the switching transistors and the flying capacitor C fly For example, the switching transistors Q1 and Q4 are a switching transistor group, and the switching transistors Q2 and Q3 are a switching transistor group. Furthermore, the switching transistors of the multilevel DC current converter and the high-voltage power supply V H According to the connection relationship with the high-voltage power supply V H The switching transistor connected to one end of the high-voltage power supply V is called the first switching transistor. H The switching transistor connected to the other end of the high-voltage power supply V is called the second switching transistor. H When the first switching transistor is connected to the positive terminal of the high-voltage power supply V, the first switching transistor can be the switching transistor Q1 and the switching transistor Q2. H , the second switching transistor may be the switching transistor Q4 and the switching transistor Q3.

[0034] The first and second switching transistors in the switching transistor group have complementary on / off states. For example, the switching transistor Q1 and switching transistor Q4 have complementary on / off states. In this case, when the switching transistor Q1 is in the on state, the switching transistor Q4 is in the off state. The switching transistor Q1 is in the off state, and the switching transistor Q4 is in the on state. In this way, a current signal can be transmitted using the carriers of the first and second switching transistors in the switching transistor group that are in the on state.

[0035] The first and second switching transistors of the same switching transistor group have complementary on / off states, so that when the first switching transistor of the switching transistor group is in the off state, the second switching transistor of the switching transistor group should be controlled to the on state. When the first switching transistor of the switching transistor group is in the closed state, the second switching transistor of the switching transistor group should be controlled to the off state. In the following, a method for controlling the second switching transistor of the switching transistor group will be described. For the method for controlling the second switching transistor of the switching transistor group, refer to the description of the method for controlling the first switching transistor for the corresponding adjustment. 。

[0036] In this specification, one flying capacitor is used as an example for explanation. In practice, there may be two or more flying capacitors. For example, although not shown in FIG. 2, there may be a flying capacitor connected in series with the flying capacitor Cfly. Alternatively, two flying capacitors may be stored in the five-level DC current converter, with one flying capacitor connected in parallel to the first and second switching transistor groups. In the five-level DC current converter, the second switching transistor group includes a first sub-switch group and a second sub-switch group, and the first and second sub-switch groups are connected in parallel to another flying capacitor. The present invention does not limit the size or number of inductors, and the multi-level DC current converter may further include a capacitor, a resistor, etc. connected to the inductor.

[0037] The three-level DC current converter may further include a controller 101 configured to control the switching transistors of FIG. 3. The controller 101 may be a pulse width modulation (PWM) device, a battery management system (BMS) based on PWM technology, a microcontroller unit (MCU), a central processing unit (CPU), other general-purpose processors, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, individual gate or transistor logic devices, individual hardware components, etc. The controller may be understood as one or more chips with communication connections. The controller may include a control unit corresponding to each switching transistor or may include a control unit corresponding to the switching transistors, for example, a pulse width modulator corresponding to the switching transistor Q1 and the switching transistor Q4, or a pulse width modulator corresponding to the switching transistor Q2 and the switching transistor Q3. However, this is not limiting.

[0038] The carriers of switching transistors Q1, Q2, Q3, and Q4 are modulated using PWM technology to control the on and off states of the switching transistors, thereby realizing real-time bidirectional power flow. L When a load is connected to the 3-level DC current converter, the input terminal of the high-voltage power supply V H The output terminal of the three-level DC current converter is connected to the low-voltage power supply V Land the current of the three-level DC current converter is H From low voltage power supply V L The high voltage power supply V of the three-level DC current converter H When a load is connected to the 3-level DC current converter, the input terminal of the 3-level DC current converter is the low-voltage power supply VL, and the output terminal of the 3-level DC current converter is the high-voltage power supply V H and the current of the three-level DC current converter is L flows to the high-voltage power supply VH.

[0039] Furthermore, by determining the current direction of inductor L1, the charging and discharging time of the flying capacitor can be adjusted, and the voltage of the flying capacitor can be controlled. For example, when switching transistor Q1 and switching transistor Q3 are turned on, the high-voltage power supply V H is the low voltage power supply V L The current in inductor L1 flows from the high voltage power supply VH to the low voltage power supply V L When the current flows through the flying capacitor C fly When the current in the inductor L1 flows from the low voltage power supply VL to the high voltage power supply VH (current direction is negative), the flying capacitor C fly When the switching transistor Q2 and the switching transistor Q4 are turned on, the flying capacitor C fly is the low voltage power supply V L When the current direction of the inductor L1 is positive, the flying capacitor C fly When the current flowing through the inductor L1 is negative, the flying capacitor C fly is charged and the voltage increases.

[0040] In an embodiment of the present invention, a flying capacitor C flyThe voltage of the inductor is abbreviated as flying voltage, and the current of the inductor is abbreviated as inductor current. When the inductor current is small, has a high-frequency triangular wave, and repeatedly switches between positive and negative, it can be called a light load. Conversely, when the inductor current is large, is always positive or negative, it can be called a heavy load. The difference between duty cycles can be abbreviated as duty cycle difference, and the phase shift or difference between phases can be abbreviated as phase difference. The phase shift control method is a method of adjusting the phase based on a fixed duty cycle. The duty cycle adjustment method is a method of adjusting the duty cycle based on a fixed phase. In this way, the uniformity of the adjustment can be improved, and the influence voltage can be changed smoothly.

[0041] When the three-level DC current converter operates in a steady state, the duty cycles of the switching transistor Q1 (switching transistor Q3) and the switching transistor Q2 (switching transistor Q4) are equal, and the phase shift is 180°. In other words, the phase difference between the carriers of the switching transistor Q1 and the switching transistor Q2 is 180°. Therefore, by adjusting the difference in duty cycle between the switching transistor Q1 and the switching transistor Q2 (also called the duty cycle difference for short), the steady state operation of the three-level DC current converter can be realized. For example, when the high-voltage power supply V H From low voltage power supply V L Power flows through the high voltage power supply V H From low voltage power supply V LIn the case where a current flows through the switching transistor Q1, the flying voltage can be increased by increasing the duty cycle of the switching transistor Q1 and decreasing the duty cycle of the switching transistor Q2, i.e., by increasing the duty cycle difference between the switching transistor Q1 and the switching transistor Q2. Conversely, the flying voltage can be decreased by decreasing the duty cycle of the switching transistor Q1 and increasing the duty cycle of the switching transistor Q2, i.e., by decreasing the duty cycle difference between the switching transistor Q1 and the switching transistor Q2. L From high voltage power supply V H Power flows through the low voltage power supply V L From high voltage power supply V H When the duty cycle of the switching transistor Q1 is increased and the duty cycle of the switching transistor Q2 is increased, i.e., the duty cycle difference between the switching transistor Q1 and the switching transistor Q2 is reduced, the flying voltage can be increased. Conversely, the duty cycle of the switching transistor Q1 is increased and the duty cycle of the switching transistor Q2 is decreased, i.e., the duty cycle difference between the switching transistor Q1 and the switching transistor Q2 is increased, the flying voltage can be decreased.

[0042] However, when the load is light, controlling the voltage of the flying capacitor based on the instantaneous current direction places extremely high demands on the control chip and is not applicable to practical projects. Even if the difference between the duty cycles of the first switching transistor (e.g., switching transistor Q1 and switching transistor Q2) or the second switching transistor (e.g., switching transistor Q3 and switching transistor Q4) in the switching transistor group connected in parallel to the flying capacitor is adjusted to a large value, the voltage of the flying capacitor cannot be effectively increased or decreased, and the control goal of stabilizing the voltage of the flying capacitor at the target value cannot be achieved.

[0043] Therefore, the present invention proposes a multilevel DC current converter, the controller of which is configured as follows: when the absolute value of the difference between the reference voltage of the flying capacitor and the sampling voltage is greater than a first threshold, adjust the duty cycle difference between the first switching transistors of the two switching transistor groups or the phase difference between the carriers of the first switching transistors of the two switching transistor groups according to the magnitude of the inductor current;

[0044] The sampling voltage of the flying capacitor is the collected real-time voltage. The reference voltage of the flying capacitor is the target value to be adjusted for the flying capacitor. For example, the target value of a three-level DC current converter may be half the voltage of the high-voltage power supply. The inductor current, also referred to as the inductor current, may be an instantaneous current value or an average value. The first threshold is not particularly limited and may be 0, for example. If the absolute value of the difference between the reference voltage and the sampling voltage of the flying capacitor is greater than the first threshold, it indicates that the flying capacitor voltage is not adjusted to the target value. It can be understood that the duty cycle difference between the switching transistors connected in parallel to the flying capacitor or the phase difference between the carriers of the first switching transistor on the flying capacitor side can be continued to be adjusted, the flying capacitor voltage can be controlled, and the voltage stress of the multilevel DC current converter can be reduced. If the difference between the sampling voltage of the flying capacitor and the reference voltage is less than the first threshold, it indicates that the flying capacitor voltage is adjusted to the target value, the current operating state can be maintained, and the flying capacitor can continue to operate. In this way, the operational stability of the multilevel DC current converter can be improved.

[0045] The method for adjusting the phase difference and duty cycle difference is not limited in the present invention. Here, the switching transistor Q1 and the switching transistor Q2 are taken as an example. After it is determined that the duty cycle difference needs to be adjusted, the adjustment can be performed based on the above-described adjustment method based on the current direction. For example, when a current flows from a high-voltage power supply to a low-voltage power supply, the flying capacitor C fly The sampling voltage of the flying capacitor C flyWhen the reference voltage of the switching transistor Q1 is smaller than the reference voltage of the switching transistor Q2, the duty cycle difference between the first switching transistor of the two switching transistor groups is increased. In other words, the duty cycle of the switching transistor Q1 is increased, and the duty cycle of the switching transistor Q2 is decreased, so that the flying voltage can be increased. Alternatively, when a current flows from the high voltage power supply to the low voltage power supply, the flying capacitor C fly The sampling voltage of the flying capacitor C fly If the reference voltage is greater than the reference voltage of the first switching transistor of the two switching transistor groups, the duty cycle difference between the first switching transistor of the two switching transistor groups can be reduced. In other words, the duty cycle of the switching transistor Q1 can be reduced and the duty cycle of the switching transistor Q2 can be increased to reduce the flying voltage. Alternatively, when current flows from the low voltage power supply to the high voltage power supply, the flying capacitor C fly The sampling voltage of the flying capacitor C fly If the reference voltage is smaller than the reference voltage of the first switching transistor of the two switching transistor groups, the duty cycle difference between the first switching transistor of the two switching transistor groups can be reduced. In other words, the duty cycle of the switching transistor Q1 can be reduced and the duty cycle of the switching transistor Q2 can be increased, which can increase the flying voltage. Alternatively, when current flows from the low voltage power supply to the high voltage power supply, the flying capacitor Cfly The sampling voltage of the flying capacitor C fly If the reference voltage is greater than the reference voltage of the first switching transistor of the two switching transistor groups, the duty cycle difference of the first switching transistor of the two switching transistor groups can be increased. In other words, the duty cycle of the first switching transistor Q1 can be increased and the duty cycle of the second switching transistor Q2 can be decreased, thereby reducing the flying voltage. In this way, when it is determined to adjust the duty cycle difference, the flying capacitor C is driven based on the direction of the inductor current. fly The voltage is adjusted.

[0046] Flying Capacitor C flyThe principle of adjusting the phase difference is: flying capacitor C fly The charging time (area) of the flying capacitor C fly The phase difference between the carriers of the first switching transistor (or the second switching transistor) is increased so that the discharge time (area) of the flying capacitor C fly By increasing the voltage of the flying capacitor C fly The charging time (area) of the flying capacitor C fly The phase difference between the carriers of the first switching transistor (or the second switching transistor) is reduced so that the discharge time (area) of the flying capacitor C fly Therefore, in a possible embodiment, it is decided to adjust the phase difference between the carriers of the first switching transistor of the two switching transistor groups based on the magnitude of the inductor current, and to reduce the voltage of the flying capacitor C fly The sampling voltage of the flying capacitor C fly If the reference voltage is smaller than the reference voltage of the first switching transistor of the two switching transistor groups, the phase difference between the carriers of the first switching transistor of the two switching transistor groups is adjusted based on the magnitude of the inductor current, and the flying capacitor C fly The sampling voltage of the flying capacitor C fly If the reference voltage is greater than the reference voltage, the phase difference between the carriers of the first switching transistor of the two switching transistor groups is reduced.

[0047] In the present invention, it is not limited to whether the method of adjusting the phase difference or the method of adjusting the duty cycle difference is used. First, the operation state of the multi-level DC current converter will be analyzed. Figures 4 to 9 are operation mode diagrams of the three-level DC current converter according to the present invention. V0 is the flying voltage V at the start of a cycle. fly and V1 is the flying voltage V at any point during the cycle. flyand V2 is the flying voltage at the end of the cycle, V fly and;I L is the inductor current, which can also be expressed in terms of i(t) in the following equation: N / A / B / C / M are the inductor current I L where T0~T3 are the peak values ​​of the switching cycle. The deadband d may cause different freewheeling loops in different modes, and the values ​​of T0~T3 are assumed to vary; m / k / n are the slopes of the corresponding lines in the figure.

[0048] In the following, P is the switching cycle, D1 is the duty cycle of switching transistor Q1, and D2 is the duty cycle of switching transistor Q2. The duty cycle D of a three-level DC current converter can be understood as the steady-state duty cycle of the converter in an ideal case. In the ideal case, the duty cycle D of a three-level DC current converter is equal to the duty cycle D1 of switching transistor Q1 and equal to the duty cycle D2 of switching transistor Q2. In practice, if the flying voltage deviates from the target value, it is necessary to adjust the duty cycle difference between switching transistor Q1 and switching transistor Q2 or the phase difference between the carriers of switching transistor Q1 and switching transistor Q2. If the duty cycle D is less than 0.5, it indicates that both the duty cycle D1 of switching transistor Q1 and the duty cycle D2 of switching transistor Q2 are less than 0.5. If the duty cycle D is greater than 0.5, it indicates that both the duty cycle D1 of switching transistor Q1 and the duty cycle D2 of switching transistor Q2 are greater than 0.5. 4 to 9 correspond to mode 1, mode 2, mode 3, mode 4, mode 5, and mode 6, respectively.

[0049] Mode 1: The duty cycle D is less than 0.5 and the inductor current I Lis always positive, i.e., in the case of high load. Referring to Figure 4, T0 = D1P, T1 = P / 2, T2 = P / 2 + D2, T3 = P.

[0050] Mode 2: The duty cycle D is less than 0.5 and the inductor current I L is always negative, i.e., in the case of heavy load. Referring to Figure 5, T0 = (D1 + 2d)P, T1 = P / 2', T2 = P / 2 + (D2 + 2d)P, T3 = P.

[0051] Mode 3: The duty cycle D is less than 0.5 and the inductor current I L (t) can be negative or positive, i.e., in the case of light load. Referring to Figure 6, T0 = (D1 + d) P, T1 = P / 2', T2 = P / 2 + (D2 + d) P, T3 = P.

[0052] Mode 4: The duty cycle D is greater than 0.5 and the inductor current I L may always be positive, i.e., in the case of heavy load. Referring to Figure 7, T0 = (1 - D1) P, T1 = P / 2', T2 = P / 2 + (1 - D2) P, T3 = P.

[0053] Mode 5: The duty cycle D is greater than 0.5 and the inductor current I L may always be negative, i.e., in the case of light load. Referring to Figure 8, T0 = [1 - (D1 + 2d)] P, T1 = P / 2', T2 = P / 2 + [1 - (D2 + 2d)] P, T3 = P.

[0054] Mode 6: The duty cycle D is greater than 0.5 and the inductor current I L can be negative or positive, i.e., for light loads. Referring to Figure 9, T0 = [1 - (D1 + d)] P, T1 = P / 2, T2 = P / 2 + [1 - (D2 + d)] P, T3 = P.

[0055] By properly setting the coordinate system and based on the freewheeling loop of the inductor current in Figures 4 to 6, the dead band d can be combined with the duty cycle D1 and the duty cycle D2 for integrated analysis in Mode 1, Mode 2, and Mode 3. Based on the freewheeling loop of the inductor current in Figures 7 to 9, the dead band d can be combined with the duty cycle D1 and the duty cycle D2 for integrated analysis in Mode 4, Mode 5, and Mode 6. The following description will be given taking Mode 1 and Mode 4 as examples.

[0056] In a switch cycle, the voltage fluctuation of the flying capacitor can be calculated by integrating the current flowing through the flying capacitor, for example, as shown in equation (1).

number

[0057] Equation (2) is obtained by computing the intersection of equation (1).

number

[0058] The values ​​of m, n, and k refer to the following equation, where L is the size of the inductor.

number

[0059] If the phase difference between the carriers of the switching transistor Q1 (or switching transistor Q3) and the switching transistor Q2 (or switching transistor Q4) is fixed at 180°, the influence of different duty cycle differences on the flying voltage can be determined by adjusting the duty cycle D1 and the duty cycle D2. For example, when D<0.5, substituting the time T0 to time T3 of mode 1 into equation (2) gives equation (3).

number

[0060] When D>0.5, substituting time T0 to time T3 of mode 4 into equation (2) yields equation (4).

number

[0061] When the duty cycles of duty cycles D1 and D2 are fixed to D (which can be any fixed value between 0 and 1), and the phase difference between the carriers of switching transistor Q1 (or switching transistor Q4) and switching transistor Q2 (or switching transistor Q3) is adjusted to Δθ, the effect of different phase differences on the flying voltage, that is, the effect of phase shift control on the flying voltage, can be obtained. When D<0.5, substituting time T0 to time T3 of mode 1 into equation (2) gives equation (5).

number

[0062] In the case of D>0.5, substituting time T0 to time T3 of mode 4 into equation (2) yields equation (6).

number

[0063] According to equations (5) and (6), under phase-shift control, the flying voltage has a consistent adjustment direction under light load and heavy load conditions and in both positive and negative power flow directions. In other words, the larger the phase difference, the larger the flying voltage, and the smaller the phase difference, the smaller the flying voltage. This relationship is independent of the dead band.

[0064] Next, reference is made to Figs. 10 to 13, which respectively show the relationship between duty cycle difference and flying voltage, and between flying voltage, phase difference and inductor current in the present invention. Using Figs. 10 and 11, we will explain the influence of different loads on the change in flying voltage in the case of a fixed phase difference and a fixed duty cycle difference. The horizontal axis represents the inductor current IL, and the vertical axis represents the amount of change in flying voltage ΔV. fly The solid line corresponding to a fixed duty cycle difference indicates the magnitude of the flying capacitor voltage adjustment under different loads when the same duty cycle difference is adjusted for the first switching transistor. The dashed line corresponding to a fixed phase difference indicates the magnitude of the flying capacitor voltage adjustment under different loads when the same duty cycle difference is adjusted for the first switching transistor. Figure 10 uses an application scenario where D<0.5, D=0.34, and Equations (3) and (5) are used as an example. Figure 11 uses an application scenario where D>0.5, D=0.8, and Equations (4) and (6) are used as an example. Figures 10 and 11 show that the flying voltage change is small under light loads (where the inductor current is a high-frequency triangular wave, repeatedly fluctuating between positive and negative, and is relatively small; the dashed line is larger than the solid line and may be close to zero in the figures). Adjusting the duty cycle also results in an inverse change in the flying voltage. As the load gradually increases, the change in flying voltage gradually increases, so the flying voltage can be controlled by adjusting the duty cycle at high loads. In other words, with the method of adjusting the duty cycle, the control strength of the flying voltage rapidly decreases as the load gradually decreases. In contrast, the control strength of the phase shift control is strong under light loads and weak under heavy loads, so the phase shift can be controlled under light loads. In other words, the flying voltage can be controlled by adjusting the phase difference.

[0065] 12 and 13, the influence of a fixed duty cycle difference and a fixed phase difference on the change in flying voltage when a fixed load is applied will be explained. The horizontal axis represents the duty cycle D, and the vertical axis represents the change in flying voltage ΔV. fly12 is applied to a heavy load, and FIG. 13 is applied to a light load. From FIG. 12 and FIG. 13, it can be seen that in the phase-shift control method, as the duty cycle gradually increases, the control strength of the flying voltage rapidly decreases. However, at light loads, the phase-shift control method can maintain a greater control strength than the duty cycle adjustment method. Thus, at light loads, the flying voltage can be controlled using the phase-shift control method. At heavy loads, the flying voltage can be controlled by adjusting the duty cycle.

[0066] Therefore, in possible embodiments, the controller may be configured to adjust a phase difference between carriers of first switching transistors of the two switching transistor groups in response to the inductor current being less than the second threshold. Alternatively, the controller may be configured to adjust a duty cycle difference between first switching transistors of the two switching transistor groups in response to the inductor current being greater than a third threshold. Alternatively, the controller may be configured to adjust a duty cycle difference between first switching transistors of the two switching transistor groups or a phase difference between the carriers of first switching transistors of the two switching transistor groups in response to the inductor current being greater than or equal to the second threshold and less than or equal to the third threshold, according to the adjustment method at the previous moment.

[0067] The values ​​of the second and third thresholds are not limited in the present invention, and the second threshold is smaller than the third threshold. Note that if the inductor current is smaller than the second threshold, it indicates that the inductor current is small, which may indicate a light load. Assuming that the duty cycle difference is not adjusted, the phase shift control method may be used to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups. If the inductor current is larger than the third threshold, it indicates that the inductor current is large, which may indicate a heavy load. Assuming that the phase difference is not adjusted, the duty cycle adjustment method may be used to adjust the duty cycle difference between the first switching transistors of the two switching transistor groups. If the inductor current is greater than the second threshold and less than the third threshold, the inductor is in an intermediate state between a light load and a heavy load, and adjustment may be performed using the adjustment method used at the previous moment. For example, if the phase shift control method was used at the previous moment, the phase shift control method may be continued, or if the duty cycle adjustment method was used at the previous moment, the duty cycle adjustment method may be continued. In this way, the flying voltage can be controlled using the above three cases, and therefore the voltage of the controlled flying capacitor can continue to transition smoothly.

[0068] For example, the hysteresis module may include a hysteresis module and a first pulse-width modulator and a second pulse-width modulator connected to the hysteresis module. The first pulse-width modulator is configured to adjust the phase or duty cycle of a first switching transistor (or a second switching transistor) of a group of switching transistors connected to the flying capacitor, and the second pulse-width modulator is configured to adjust the phase or duty cycle of a first switching transistor (or a second switching transistor) of another group of switching transistors connected to the flying capacitor. For example, the first pulse-width modulator is configured to adjust the phase or duty cycle of the switching transistor Q1 or the switching transistor Q4, and the second pulse-width modulator is configured to adjust the phase or duty cycle of the switching transistor Q2 or the switching transistor Q3. The hysteresis module may include a duty cycle controller and a phase controller. The duty cycle controller is configured to control the first pulse-width modulator and the second pulse-width modulator to implement a duty cycle control loop and adjust the duty cycle difference between the two switching transistors. The phase controller is configured to control the first pulse width modulator and the second pulse width modulator to implement a phase control loop and adjust the phase difference between the carriers of the two switching transistors.

[0069] The hysteresis module is configured to: control the first pulse width modulator and the second pulse width modulator based on the magnitude of the inductor current in response to the absolute value of the difference between the reference voltage and the sampling voltage of the flying capacitor being greater than a first threshold, and adjust a phase difference between carriers of first switching transistors of the two switching transistor groups or a duty cycle difference between the first switching transistors of the two switching transistor groups.

[0070] The hysteresis module: when the hysteresis module determines to adjust the phase difference between carriers of a first switching transistor of the two switching transistor groups based on the magnitude of the inductor current, if the sampling voltage of the flying capacitor is smaller than the reference voltage of the flying capacitor, the hysteresis module increases the phase difference between carriers of the first switching transistor of the two switching transistor groups, or if the sampling voltage of the flying capacitor is larger than the reference voltage of the flying capacitor, the hysteresis module decreases the phase difference between carriers of the first switching transistor of the two switching transistor groups.

[0071] The hysteresis module is particularly configured as follows: when the hysteresis module determines to adjust the phase difference between the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current, when a current flows from the high-voltage power supply to the low-voltage power supply, the duty cycle difference between the first switching transistors of the two switching transistor groups increases, and the sampling voltage of the flying capacitor is smaller than the flying capacitor reference voltage; or when a current flows from the high-voltage power supply to the low-voltage power supply, the duty cycle difference between the first switching transistors of the two switching transistor groups decreases, and the sampling voltage of the flying capacitor is larger than the flying capacitor reference voltage; or when a current flows from the low-voltage power supply to the high-voltage power supply, the duty cycle difference between the first switching transistors of the two switching transistor groups decreases, and the sampling voltage of the flying capacitor is smaller than the flying capacitor reference voltage; or when a current flows from the low-voltage power supply to the high-voltage power supply, the duty cycle difference between the first switching transistors of the two switching transistor groups increases, and the sampling voltage of the flying capacitor is larger than the flying capacitor reference voltage.

[0072] The hysteresis module is particularly configured to: in response to the current being smaller than a second threshold, control the first pulse width modulator and the second pulse width modulator to adjust a phase difference between carriers of first switching transistors of the two switching transistor groups; or in response to the current being larger than a third threshold, control the first pulse width modulator and the second pulse width modulator to adjust a duty cycle difference between the first switching transistors of the two switching transistor groups; or in response to the current being greater than the second threshold and less than the third threshold, control the first pulse width modulation and the second pulse width modulation according to an adjustment method at a previous moment to adjust a phase difference between carriers of first switching transistors of the two switching transistor groups or a duty cycle difference between the first switching transistors of the two switching transistor groups.

[0073] An example will be described in which the first switching transistor is a switching transistor Q1 and a switching transistor Q2. Figure 14 is a schematic flow chart of the voltage regulation of the flying capacitor by the controller according to the present invention. As shown in Figure 14, the hysteresis module first adjusts the sampling voltage V of the flying capacitor. fly_ad and the reference voltage V of the flying capacitor fly_ref It is determined whether the absolute value of the difference between the sampling voltage V of the flying capacitor is greater than a first threshold value. fly_ad and the reference voltage V of the flying capacitor fly_ref The difference between the inductor current and the average value i LAVGIf the second threshold is less than the second threshold, the phase shift control loop corresponding to the phase controller is controlled to keep the duty cycle unchanged (the output limiting the linear change of the duty cycle control loop is set to 0). Therefore, the first pulse width modulator applies the current output result of the duty cycle control loop to a steady-state duty cycle based on the direction of the inductor current. Then, the second pulse width modulator adds the output result of the phase shift control loop to the carrier of the switching transistor corresponding to the second pulse width modulator, thereby dynamically adjusting the phase difference between the carriers of the switching transistor Q1 corresponding to the first pulse width modulator and the switching transistor Q2 corresponding to the second pulse width modulator around 180°. LAVG When the third threshold is greater than the third threshold, the duty cycle control loop corresponding to the duty cycle controller is controlled on the premise that the control phase difference is not changed, and therefore the first pulse width modulator and the second pulse width modulator apply the current output result of the phase shift control loop to the carrier corresponding to the second pulse width modulator according to the direction of the inductor current, so as to dynamically adjust the duty cycle difference between the switching transistor Q1 and the switching transistor Q2 around 0. LAVG is between the second threshold and the third threshold, maintain the adjustment method at the previous moment and control the phase shift control loop corresponding to the phase controller for operation, so that the first pulse width modulator and the second pulse width modulator adjust the phase difference between the carriers of the switching transistor Q1 and the switching transistor Q2, or control the duty cycle control loop corresponding to the duty cycle controller for operation, so that the first pulse width modulator and the second pulse width modulator adjust the duty cycle difference between the switching transistor Q1 and the switching transistor Q2.

[0074] 15 is a schematic flowchart of a flying capacitor voltage control method according to an embodiment of the present invention. The flying capacitor is used in a multilevel DC current converter, which includes at least one flying capacitor, two switching transistor groups connected to the flying capacitor, an inductor connected to each of the switching transistor groups and a positive electrode of a low-voltage power supply of the multilevel DC current converter, and a controller configured to control the switching transistor groups. Each of the switching transistor groups includes a first switching transistor and a second switching transistor, whose on / off states are complementary. As shown in FIG. 15, the voltage control method can include step S101.

[0075] S101: When the absolute value of the difference between the reference voltage and the sampling voltage of the flying capacitor is greater than a first threshold, the controller adjusts the duty cycle difference between the first switching transistors of the two switching transistor groups or the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current.

[0076] If the absolute value of the difference between the reference voltage and the sampling voltage of the flying capacitor is greater than the first threshold, it indicates that the voltage of the flying capacitor is not adjusted to the target value, and the phase difference between the switching transistors connected in parallel on the flying capacitor side or the duty cycle difference between the switching transistors connected in parallel on the flying capacitor side can be further adjusted to control the voltage of the flying capacitor, thereby improving the operating stability of the multi-level DC current converter.

[0077] In a possible embodiment, a method for adjusting the duty cycle difference between the first switching transistors of two switching transistor groups or the phase difference between the carriers of the first switching transistors of two switching transistor groups based on the magnitude of the inductor current includes the following steps: increasing the phase difference between the carriers of the first switching transistors of the two switching transistor groups when it is determined to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current and the sampling voltage is smaller than the reference voltage of the flying capacitor; or decreasing the phase difference between the carriers of the first switching transistors of the two switching transistor groups when it is determined to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current. In this way, increasing the phase difference between the carriers of the first switching transistors of the two switching transistor groups increases the voltage of the flying capacitor. Reducing the phase difference between the carriers of the first switching transistors of the two switching transistor groups reduces the voltage of the flying capacitor.

[0078] In a possible embodiment, a method for adjusting a duty cycle difference between first switching transistors of two switching transistor groups or a phase difference between carriers of first switching transistors of two switching transistor groups based on the magnitude of an inductor current includes the following steps: when the hysteresis module determines to adjust the duty cycle difference between the first switching transistors of the two switching transistor groups based on the magnitude of the inductor current, increasing the duty cycle difference between the first switching transistors of the two switching transistor groups when a current flows from the high-voltage power supply to the low-voltage power supply, and the sampling voltage of the flying capacitor is smaller than the reference voltage of the flying capacitor; or When current flows to the power supplies, decreasing the duty cycle difference between the first switching transistors of the two switching transistor groups, the flying capacitor sampling voltage being greater than the flying capacitor reference voltage; or when current flows from the low voltage power supply to the high voltage power supply, decreasing the duty cycle difference between the first switching transistors of the two switching transistor groups, the flying capacitor sampling voltage being less than the flying capacitor reference voltage; or when current flows from the low voltage power supply to the high voltage power supply, increasing the duty cycle difference between the first switching transistors of the two switching transistor groups, the flying capacitor sampling voltage being greater than the flying capacitor reference voltage. Thus, when it is determined that the duty cycle difference should be adjusted, the flying capacitor voltage is adjusted based on the direction of the inductor current.

[0079] In a possible embodiment, a method for adjusting a duty cycle difference between first switching transistors of two switching transistor groups or a phase difference between carriers of the first switching transistors of two switching transistor groups based on the magnitude of the inductor current includes the following steps: adjusting the phase difference between carriers of the first switching transistors of two switching transistor groups when the inductor current is smaller than a second threshold; or adjusting the duty cycle difference between the first switching transistors of two switching transistor groups when the inductor current is larger than a third threshold; or adjusting the phase difference between carriers of the first switching transistors of two switching transistor groups or the duty cycle difference between the first switching transistors of two switching transistor groups according to the adjustment method at the previous moment when the inductor current is equal to or larger than the second threshold and smaller than the third threshold. In this way, the flying voltage can be controlled using the above three cases, and thus the voltage of the controlled flying capacitor can be maintained smoothly.

[0080] An embodiment of the present invention further provides a control device, the control device including a controller and a memory, the memory configured to store instructions, and the controller configured to invoke the instructions stored in the memory to perform the method of any one of the above aspects.

[0081] Those skilled in the art will understand that all or part of the steps of the method embodiments can be implemented by a program instructing relevant hardware. The program can be stored in a computer-readable storage medium. When the program is executed, the steps of the method embodiments are performed. The aforementioned storage medium includes any medium that can store program code, such as a removable storage device, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0082] The above description is merely a specific embodiment of the present invention and does not limit the scope of protection of the present invention. Any modifications or substitutions that can be easily understood by a person skilled in the art within the technical scope disclosed in the present invention are included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be governed by the scope of protection of the claims.

Claims

1. 1. A multi-level DC current converter comprising: at least one flying capacitor; two switching transistor groups connected to the flying capacitor; an inductor connected to each of the switching transistors and a positive electrode of a low-voltage power supply of the multilevel DC current converter; a controller configured to control the group of switching transistors; Each of the switching transistor groups includes: a first switching transistor and a second switching transistor, the on / off states of which are complementary; the first switching transistor is connected to one end of a high-voltage power supply of the multi-level DC current converter; the second switching transistor is connected to the other end of the high voltage power supply of the multilevel DC current converter; The controller configured to adjust a duty cycle difference between first switching transistors of the two switching transistor groups or a phase difference between carriers of first switching transistors of the two switching transistor groups based on the magnitude of an inductor current when an absolute value of a difference between a reference voltage and a sampling voltage of the flying capacitor is greater than a first threshold value; the controller is configured to increase the phase difference between the carriers of the first switching transistor of the two switching transistor groups when the controller determines to adjust a phase difference between the carriers of the first switching transistor of the two switching transistor groups based on the magnitude of the inductor current; the sampling voltage on the flying capacitor is less than the reference voltage on the flying capacitor; or the controller is configured to reduce the phase difference between the carriers of the first switching transistor of the two switching transistor groups when the controller determines to adjust a phase difference between the carriers of the first switching transistor of the two switching transistor groups based on the magnitude of the inductor current; the sampling voltage of the flying capacitor is greater than the reference voltage of the flying capacitor; Multilevel DC current converter.

2. the controller is configured to adjust the phase difference between the carriers of the first switching transistors of the two switching transistor groups when the inductor current is less than a second threshold.

2. The multilevel DC current converter according to claim 1.

3. A multilevel DC current converter comprising: at least one flying capacitor; two switching transistor groups connected to the flying capacitor; an inductor connected to each of the switching transistors and a positive electrode of a low-voltage power supply of the multilevel DC current converter; a controller configured to control the group of switching transistors; Each of the switching transistor groups includes: a first switching transistor and a second switching transistor, the on / off states of which are complementary; the first switching transistor is connected to one end of a high-voltage power supply of the multi-level DC current converter; the second switching transistor is connected to the other end of the high voltage power supply of the multilevel DC current converter; The controller configured to adjust a duty cycle difference between first switching transistors of the two switching transistor groups or a phase difference between carriers of first switching transistors of the two switching transistor groups based on the magnitude of an inductor current when an absolute value of a difference between a reference voltage and a sampling voltage of the flying capacitor is greater than a first threshold value; the controller is configured to adjust the duty cycle difference of the first switching transistors of the two switching transistor groups when the inductor current is greater than a third threshold. Multilevel DC current converter.

4. the controller is configured to adjust, when the inductor current is greater than or equal to a second threshold and less than or equal to a third threshold, a duty cycle difference between the first switching transistors of the two switching transistor groups or a phase difference between the carriers of the first switching transistors of the two switching transistor groups according to an adjustment method of a previous moment.

4. A multilevel DC current converter according to claim 1 or 3.

5. A method for controlling a voltage of a flying capacitor, comprising: The flying capacitor is used in a multilevel DC current converter, The multi-level DC current converter comprises two switching transistor groups, an inductor, and a controller; each of the switching transistor groups includes a first switching transistor and a second switching transistor, the on / off states of which are complementary to each other; The voltage control method includes: and when an absolute value of a difference between a reference voltage and a sampling voltage of the flying capacitor is greater than a first threshold, adjusting, by the controller, a duty cycle difference between first switching transistors of the two switching transistor groups or a phase difference between carriers of first switching transistors of the two switching transistor groups based on the magnitude of an inductor current; The step of adjusting, by the controller, a duty cycle difference between first switching transistors of the two switching transistor groups or a phase difference between carriers of first switching transistors of the two switching transistor groups based on the magnitude of the inductor current includes: When determining to adjust the phase difference between the carriers of the first switching transistor of the two switching transistor groups based on the magnitude of the inductor current, increasing the phase difference between the carriers of the first switching transistor of the two switching transistor groups by the controller, wherein the sampling voltage of the flying capacitor is smaller than the reference voltage of the flying capacitor; or when determining to adjust the phase difference between the carriers of the first switching transistor of the two switching transistor groups based on the magnitude of the inductor current, reducing the phase difference between the carriers of the first switching transistor of the two switching transistor groups by the controller, wherein the sampling voltage of the flying capacitor is greater than the reference voltage of the flying capacitor. method.

6. The step of adjusting, by the controller, a duty cycle difference between first switching transistors of the two switching transistor groups or a phase difference between carriers of first switching transistors of the two switching transistor groups based on the magnitude of the inductor current includes: adjusting, by the controller, the phase difference between the carriers of the first switching transistors of the two switching transistor groups when the inductor current is less than a second threshold; or adjusting, by the controller, the duty cycle difference between the first switching transistors of the two groups of switching transistors when the inductor current is greater than a third threshold; or adjusting, by the controller, a duty cycle difference between the first switching transistors of the two switching transistor groups or a phase difference between the carriers of the first switching transistors of the two switching transistor groups according to an adjustment method of a previous moment, when the inductor current is equal to or greater than a second threshold and equal to or less than a third threshold; The method of claim 5.

7. A control device, A controller and a memory, the memory configured to store instructions; The controller is configured to invoke the instructions stored in the memory to perform the method of claim 5 or 6. Control device.

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