Flying capacitor voltage regulation device of direct current-direct current converter and control method of flying capacitor voltage regulation device

Abstract

The present invention relates to a flying capacitor voltage regulation device and method for a DC-DC converter, having the advantages of changing a voltage regulation value for controlling a switch according to a sign of an inductive current of the DC-DC converter, thereby being able to stably regulate the voltage of a flying capacitor even if the direction of the current is changed, and improving the stability of the flying capacitor. Even if the load of the DC-DC converter is a light load, the control error can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a direct current-direct current (DC-DC) converter, and more particularly, to a voltage regulation technique of a DC-DC converter including a flying capacitor. BACKGROUND

[0002] A converter is one of representative power conversion devices together with an inverter. The inverter receives an alternating current and converts it into a direct current, and then reconverts it into an alternating current to control a motor. In contrast, the converter, particularly, a DC-DC converter is used to convert a low direct current voltage into a higher direct current voltage using a switch having a relatively low rated voltage.

[0003] A converter for electric vehicle battery charging or solar power generation, etc. requires a DC-DC converter capable of obtaining a very high voltage, and thus, a switch having a high rated voltage is required to be used. However, since the higher the rated voltage is, the higher the unit price is along with the size or weight, it is actually difficult to use a switch having a high rated voltage.

[0004] In order to solve such a problem, a DC-DC converter using a flying capacitor has been proposed.

[0005] The DC-DC converter using a flying capacitor is capable of obtaining a high output voltage with a switch having a relatively low rated voltage by connecting the switch in series and connecting a flying capacitor between the switches.

[0006] At this time, the voltage of the flying capacitor needs to be regulated to half of the output voltage, but in the case of a bidirectional DC-DC converter, if the direction of the current is reversed, a problem of being uncontrollable occurs as the voltage control loop is changed into positive feed back.

[0007] In addition, a proportional gain (P gain) is used to control the flying capacitor, but since an error of the proportional gain occurs or a voltage deviation occurs, a problem of failing to converge the voltage of the flying capacitor to half of the output voltage also occurs.

[0008] The inventors of the present application have been making efforts to solve the problems of the DC-DC converter using the flying capacitor of the related art. Even in the case where the direction of the current is reversed in the bidirectional DC-DC converter, the voltage of the flying capacitor can be controlled, and through many efforts to solve the problem of the error of the voltage of the flying capacitor caused by the error of the proportional gain, the present application has been finally completed.

[0009] [National Research and Development Projects Supporting the Present Invention]

[0010] [Subject inherent number] 1415181044

[0011] [Subject number] 20210501010020

[0012] [Ministry name] Ministry of Trade, Industry and Resources

[0013] [Subject management (special) agency name] Korea Institute of Energy Technology Evaluation and Planning

[0014] [Research business name] Development (R&D) of large-capacity high-voltage module type ESS (Energy Storage System) technology for grid connection of renewable energy power systems.

[0015] [Research subject name] Development of core equipment for MMC (Modular Multilevel Converter) type ESS and high-voltage hub station for grid connection of renewable energy.

[0016] [Contribution rate] 1 / 1.

[0017] [Subject execution agency name] Korea Electric Power Research Institute.

[0018] [Research time] November 1, 2021 to December 31, 2024. SUMMARY

[0019] Problems to be solved by the invention

[0020] The object of the present invention is to provide an apparatus and method capable of more accurately controlling the voltage of a flying capacitor in a bidirectional flying capacitor DC-DC converter.

[0021] In addition, the object of the present invention is to solve the problem that the voltage control loop of the flying capacitor does not operate normally in the case where the inductor current for power control is reversed.

[0022] On the other hand, other objects of the present invention that are not explicitly shown can be additionally considered within the scope that can be easily inferred from the following detailed description and its effects.

[0023] Means for solving the problem

[0024] The flying capacitor voltage regulating device of the DC-DC converter of the present invention,

[0025] characterized by comprising: a voltage generation part that generates an offset voltage using the difference between the output voltage of the DC-DC converter and the voltage of the flying capacitor; and a sign adjustment part that adjusts the sign of the offset voltage generated in the voltage generation part according to the sign of the inductor current of the DC-DC converter.

[0026] The feature is that if the inductor current is 0 or greater, the sign adjustment unit multiplies the offset voltage by 1; if the inductor current is less than 0, the sign adjustment unit multiplies the offset voltage by -1.

[0027] Its characteristic is that if the inductor current is a negative first inductor current value -I L1 The value of the first inductor current is greater than or less than the positive value of I. L1 Then the sign adjustment unit divides the inductor current by the value i of the first inductor current. L / I L1 Multiply by the offset voltage, if the inductor current is +I L1 If the above applies, the sign adjustment unit multiplies the offset voltage by 1. If the inductor current is less than -1... L1 Then the sign adjustment unit multiplies the offset voltage by -1.

[0028] Characterized by, if the inductor current I L The negative first inductor current value -i L1 If the value is above 0 and below 0, then the sign adjustment unit multiplies the offset voltage by 0. If the inductor current is greater than 0 and less than the positive first inductor current value I L1 Then the sign adjustment unit multiplies the offset voltage by If the inductor current is +I L1 If the above applies, the sign adjustment unit multiplies the offset voltage by 1. If the inductor current is less than -1... L1 Then the sign adjustment unit multiplies the offset voltage by -1.

[0029] The voltage generation unit is characterized by being composed of a proportional control device or a proportional-integral control device.

[0030] Another embodiment of the present invention provides a method for regulating the flying capacitor voltage of a DC-DC converter, characterized in that,

[0031] The method includes: receiving the output voltage of the DC-DC converter and the voltage of the flying capacitor; generating an offset voltage using the difference between the output voltage of the DC-DC converter and the voltage of the flying capacitor; and adjusting the sign of the offset voltage according to the sign of the inductor current of the DC-DC converter.

[0032] The feature is that, in the step of adjusting the sign of the offset voltage, if the inductor current is greater than or equal to 0, the offset voltage is multiplied by 1; if the inductor current is less than 0, the offset voltage is multiplied by -1.

[0033] The feature is that, in the step of adjusting the sign of the offset voltage, if the inductor current is a negative first inductor current -I L1 The first inductor current +I is greater than or less than the positive value. L1 Then divide the inductor current by the value i of the first inductor current. L / I L1 Multiply by the offset voltage; if the inductor current is +IL1 or greater, multiply the offset voltage by 1; if the inductor current is less than -IL1... L1 Then multiply the offset voltage by -1.

[0034] The feature is that, in the step of adjusting the sign of the offset voltage, if the inductor current i L The negative first inductor current value -I L1 If the value is greater than or less than 0, then the offset voltage is multiplied by 0. If the inductor current is greater than or equal to 0 and less than the positive first inductor current value I L1 Then multiply the offset voltage by If the inductor current is +I L1 Then multiply the offset voltage by 1. If the inductor current is less than -1... L1 Then multiply the offset voltage by -1.

[0035] The characteristic feature is that the step of generating the offset voltage utilizes a proportional control method or a proportional-integral control method to generate the offset voltage.

[0036] The effects of the invention

[0037] According to the present invention, the voltage of the flying capacitor can be stably controlled even for reverse inductor current in a bidirectional DC-DC converter with a flying capacitor.

[0038] In addition, when a light load is connected to the output of the DC-DC converter, it is possible to obtain the advantage of reducing control instability caused by measurement errors due to current ripple.

[0039] On the other hand, even if the effects are not explicitly mentioned herein, the effects and potential effects expected by the technical features of the present invention as described in the following description should be considered to have the same effect as those described in the description of the present invention. Attached Figure Description

[0040] Figure 1 This is a schematic structural diagram of the switching control circuit of a bidirectional DC-DC converter including a flying capacitor voltage regulation device, according to a preferred embodiment of the present invention.

[0041] Figure 2 and Figure 3 This is a more detailed structural diagram of a preferred embodiment of the flying capacitor voltage regulation device of the present invention.

[0042] Figure 4 The diagram illustrates the relationship between the inductor current and the output sign for sign regulation of a flying capacitor voltage regulation device according to a preferred embodiment of the present invention.

[0043] Figure 5 shows the main operating waveforms of different modes of the flying capacitor in a preferred embodiment of the present invention.

[0044] Figure 6 An example graph of the flying capacitor voltage controlled by a preferred embodiment of the present invention is shown.

[0045] Figure 7 This is a schematic flowchart of a method for regulating the flying capacitor voltage of a DC-DC converter according to another preferred embodiment of the present invention.

[0046] Figure 8 An example of a DC-DC converter using a typical flying capacitor is shown.

[0047] Figure 9 An example of a prior art flying capacitor voltage control circuit is shown.

[0048] *The accompanying drawings are provided for illustrative purposes to understand the technical concept of the present invention, and the scope of the present invention is not limited thereto. Detailed Implementation

[0049] Hereinafter, with reference to the accompanying drawings, we will observe the configuration of the present invention guided by various embodiments and the effects produced by such configuration. In describing this specification, detailed descriptions of well-known functions that are obvious to those skilled in the art and deemed likely to unnecessarily obscure the spirit of the invention will be omitted.

[0050] The terms "first," "second," etc., can be used to describe various constituent elements, but these constituent elements should not be limited to the terms used above. The terms used above are only used to distinguish one constituent element from another. For example, without departing from the scope of the invention, "first constituent element" can be named "second constituent element," and similarly, "second constituent element" can be named "first constituent element." Furthermore, unless the context clearly specifies otherwise, singular expressions include plural expressions. Unless otherwise defined, the terms used in the embodiments of the invention can be interpreted as having meanings known to those skilled in the art.

[0051] Hereinafter, with reference to the accompanying drawings, we will observe the configuration of the present invention as guided by various embodiments thereof and the effects produced by such configuration.

[0052] Figure 8 An example of a typical DC-DC converter employing a flying capacitor is shown.

[0053] exist Figure 8 In the DC-DC converter, a plurality of switches S1, S'1, S2, and S'2 with relatively low rated voltages are connected in series, and a flying capacitor V is connected between the switches. F This allows for the use of switches with low rated voltage to obtain high output voltage.

[0054] Figure 9 An example of a prior art flying capacitor voltage regulation circuit is shown in a DC-DC converter using a flying capacitor.

[0055] The voltage V across the flying capacitor is usually... C Regulated to output voltage V out Half of it. Therefore, it has been used to compare the voltage corresponding to 1 / 2 of the output voltage with the voltage across the flying capacitor, or as... Figure 8 As shown, the voltage is adjusted by comparing the voltage corresponding to twice the voltage of the flying capacitor with the output voltage, thereby increasing or decreasing the voltage of the flying capacitor.

[0056] At this point, the voltage transfer function of the flying capacitor is: In cases requiring bidirectional power control, if I L If the value is less than 0, that is, if reverse current flows, the feedback loop for the flying capacitor will turn into a feedforward loop and cause an uncontrollable problem.

[0057] Figure 1 An example of a voltage control circuit for a DC-DC converter of the present invention for solving the problems described above is shown.

[0058] The flying capacitor voltage regulation device 100 of the DC-DC converter of the present invention may include a voltage generation unit 110 and a sign control unit 120.

[0059] The flying capacitor voltage regulator 100 receives the inductor current I of the DC-DC converter. L Output voltage V O and the flying capacitor voltage V F To generate a voltage V for operation M offset voltage D offset .

[0060] Figure 2 This is a more detailed structural diagram of the voltage generation unit of the present invention.

[0061] The voltage generation unit 110 utilizes the output voltage V O 1 / 2 and flying capacitor voltage V F The difference is used to generate an offset voltage in the voltage control unit 112.

[0062] In the voltage control unit 112, due to the flying capacitor voltage V F It needs to be controlled as the output voltage V O Half of that, therefore utilizing the output voltage V O 1 / 2 and the flying capacitor voltage V F The difference between them is used to generate the offset voltage.

[0063] The voltage control unit 112 can generate an offset voltage using proportional control or proportional-integral control.

[0064] Figure 3 This is a more detailed structural diagram of the symbol determination part of the present invention.

[0065] The symbol determination unit 120 may be composed of a low-pass filter unit 122 and a symbol operation unit 124.

[0066] The low-pass filter section 122 can be configured with a low-pass filter (LPF) and can calculate the average value of the inductor current. The low-pass filter can have a frequency band of 3 kHz, but is not limited to this.

[0067] The sign arithmetic unit 124 determines the sign of the inductor current.

[0068] In its simplest form, the sign arithmetic unit 124 can determine the sign of a variable and use the sign(x) function, which outputs a value of 1 or -1. The sign(x) function outputs 1 if the value of x is positive and -1 if the value of x is negative.

[0069] Therefore, in a bidirectional DC-DC capacitor, when the inductor current is less than 0, that is, when the direction of the inductor current is opposite, the sign calculation unit 124 can convert the sign of the offset voltage generated in the voltage generation unit 110 into a negative value to adjust the operating voltage value. Thus, the voltage of the flying capacitor can be adjusted by controlling the switch of the DC-DC converter.

[0070] Figure 4 Other examples of operations performed on symbols are shown in the symbolic arithmetic unit 124.

[0071] Figure 4 (a) and (b) are examples of using a derating factor to prevent noise that may occur when the sign is suddenly changed around 0.

[0072] When the load on a DC-DC converter is light, it is difficult to determine the sign due to inductor current ripple and measurement errors. Furthermore, the lighter the load, the smaller the change in duty cycle leads to a smaller change in the flying capacitor voltage. Therefore, if... Figure 4 As shown, a derating factor is used for control.

[0073] In such Figure 4 In the function shown in (a), if the inductor current is at a preset value I L1 Within the range, that is, if it is -I L1 <Inductor current i L L1 Then the sign arithmetic unit 124 does not output -1 or 1, but instead outputs the value i, which is the inductor current divided by a preset value. L / I L1 .

[0074] If the inductor current is I L1 Above or -I L1 The following outputs are the same as those of the sign(x) function, either 1 or -1.

[0075] In such Figure 4 In the function shown in (b), if it is -I L1 ≤Inductor current i L If <0, the output can be set to If 0 ≤ inductor current i L <I L1 Then the output can be set to

[0076] ​Thus, the output generated in the symbol generation unit 120 is multiplied by the offset voltage generated in the voltage generation unit 110, and the symbol is changed or the offset voltage with a derating factor is used as the operating voltage for the switching control of the DC-DC converter. As a result, the voltage across the flying capacitor can also be controlled as desired.

[0077] Figure 5 illustrates the switching mode of the flying capacitor with the switch duty cycle D and the direction of the inductor current.

[0078] Figure 5a It shows that D < 0.5 and I L In the case of >0, Figure 5b It shows that D > 0.5 and I L In the case of >0, Figure 5c It shows that D < 0.5 and I L In the case of <0, Figure 5d It shows that D > 0.5 and I L The case where <0.

[0079] As can be seen in Figure 5, the change in the flying capacitor voltage will occur in opposite directions, even at the same duty cycle, depending on the direction of the inductor current.

[0080] This can be expressed using the following mathematical formula.

[0081]

[0082] In this mathematical formula, it can be confirmed that, according to the inductor current I... L The direction of change in the voltage across the capacitor is opposite to that of the direction of change in the capacitor voltage.

[0083] Figure 6 An example is shown of controlling the output voltage of a DC-DC converter and the voltage of the flying capacitor using the flying capacitor voltage regulation device of the present invention as described above.

[0084] It can be confirmed that, for the input voltage (1200V) to be controlled to the output voltage of 1500V, although the direction of the inductor current (input current) changes from -66A to 66A, the voltage of the flying capacitor is controlled to half of the output voltage, 750V, by using the flying capacitor voltage regulation device of the present invention.

[0085] Figure 7 A schematic flowchart of a method for regulating the flying capacitor voltage of a DC-DC converter according to a preferred embodiment of the present invention is shown.

[0086] The method for regulating the flying capacitor voltage of the DC-DC converter of the present invention can be executed using a control unit including one or more processors and a memory.

[0087] The processor can execute various operations and commands for voltage regulation, and can store instructions for processor actions and data for voltage regulation in memory.

[0088] In order to regulate the voltage across the flying capacitor, the input of voltage and current values ​​as references is first received (S110).

[0089] The reference voltages include the output voltage of the DC-DC converter and the voltage across the flying capacitor, while the reference currents include the inverter current of the DC-DC capacitor.

[0090] Next, the offset voltage is generated using the received input voltage (S120).

[0091] An offset voltage is generated by using the difference between half of the output voltage of a DC-DC converter and the voltage of a flying capacitor.

[0092] Therefore, while proportional control methods or proportional-integral control methods can be used, they are not limited to these.

[0093] After the offset voltage is generated, a sign adjustment step S130 is performed to respond to the sign of the inductor current.

[0094] To adjust the sign, you can use the sign(x) function, which outputs 1 or -1 depending on the sign of the inductor current.

[0095] However, in the range where the inductor current is close to zero, due to inductor current ripple and measurement errors, a situation may arise where the correct sign determination is not formed. Therefore, as... Figure 4 As shown in the example, the output uses a sign adjustment value with a derating factor.

[0096] That is, if the inductor current is within the preset value I L1 The range within, that is, if it is -I L1 <Inductor current i L <I L1 Then it can output the value i, which is the inductor current divided by a preset value. L / I L1 or able to output or Instead of outputting -1 or 1, as mentioned earlier.

[0097] The flying capacitor voltage regulation device and method for DC-DC converter of the present invention, as described above, have the following effects: even when the direction of the inductor current in the bidirectional DC-DC converter is reversed, the voltage of the flying capacitor can be stably controlled; and even when the load of the DC-DC converter is light, the voltage of the flying capacitor can be stably adjusted by reducing the measurement error, even when the inductor current is small.

[0098] The scope of protection of this invention is not limited to the embodiments described and depicted above. Furthermore, it should be reiterated that even obvious modifications or substitutions within the technical field to which this invention pertains shall not limit the scope of protection of this invention.

Claims

1. A flying capacitor voltage regulation device for a DC-DC converter, characterized in that, include: The voltage generation unit generates an offset voltage by utilizing the difference between the output voltage of the DC-DC converter and the voltage of the flying capacitor; as well as The sign adjustment unit adjusts the sign of the offset voltage generated in the voltage generation unit according to the sign of the inductor current of the DC-DC converter.

2. The flying capacitor voltage regulation device for a DC-DC converter according to claim 1, characterized in that, If the inductor current is 0 or greater, the sign adjustment unit multiplies the offset voltage by 1; if the inductor current is less than 0, the sign adjustment unit multiplies the offset voltage by -1.

3. The flying capacitor voltage regulation device for a DC-DC converter according to claim 1, characterized in that, If the inductor current is a negative first inductor current value -I L1 The value of the first inductor current is greater than or less than the positive value of I. L1 Then the sign adjustment unit divides the inductor current by the value i of the first inductor current. L / I L1 Multiply by the offset voltage, If the inductor current is +I L1 In the above, the sign adjustment unit multiplies the offset voltage by 1. If the inductor current is less than -I L1 Then the sign adjustment unit multiplies the offset voltage by -1.

4. The flying capacitor voltage regulation device for a DC-DC converter according to claim 1, characterized in that, If the inductor current i L The negative first inductor current value -I L1 If the value is above 0 and below 0, then the sign adjustment unit multiplies the offset voltage by 0. If the inductor current is greater than 0 and less than the positive first inductor current value I L1 Then the sign adjustment unit multiplies the offset voltage by If the inductor current is +I L1 In the above, the sign adjustment unit multiplies the offset voltage by 1. If the inductor current is less than -I L1 Then the sign adjustment unit multiplies the offset voltage by -1.

5. The flying capacitor voltage regulation device for a DC-DC converter according to claim 1, characterized in that, The voltage generation unit is composed of a proportional control device or a proportional-integral control device.

6. A method for regulating the flying capacitor voltage of a DC-DC converter, wherein the method is executed using a control unit comprising one or more processors and a memory, characterized in that, include: The step of receiving the output voltage of the DC-DC converter and the voltage of the flying capacitor; The step of generating an offset voltage using the difference between the output voltage of the DC-DC converter and the voltage of the flying capacitor; as well as The step of adjusting the sign of the offset voltage according to the sign of the inductor current of the DC-DC converter.

7. The method for regulating the flying capacitor voltage of a DC-DC converter according to claim 6, characterized in that, In the step of adjusting the sign of the offset voltage If the inductor current is 0 or higher, then the offset voltage is multiplied by 1. If the inductor current is less than 0, then the offset voltage is multiplied by -1.

8. The method for regulating the flying capacitor voltage of a DC-DC converter according to claim 6, characterized in that, In the step of adjusting the sign of the offset voltage If the inductor current i L The negative first inductor current value -I L1 If the value is greater than or less than 0, then the offset voltage is multiplied by 0. If the inductor current is greater than or equal to 0 and less than the positive first inductor current value I L1 Then multiply the offset voltage by If the inductor current is +I L1 The above, then multiply the offset voltage by 1, If the inductor current is less than -I L1 Then multiply the offset voltage by -1.

9. The method for regulating the flying capacitor voltage of a DC-DC converter according to claim 6, characterized in that, In the step of adjusting the sign of the offset voltage If the inductor current is the negative first inductor current -I L1 The first inductor current +I is greater than or less than the positive value. L1 Then divide the inductor current by the value i of the first inductor current. L / I L1 Multiply by the offset voltage, If the inductor current is +I L1 The above, then multiply the offset voltage by 1, If the inductor current is less than -I L1 Then multiply the offset voltage by -1.

10. The method for regulating the flying capacitor voltage of a DC-DC converter according to claim 6, characterized in that, In the step of generating the offset voltage, the offset voltage is generated using a proportional control method or a proportional-integral control method.

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