A method and apparatus for balancing cells of a series type dc-dc converter

Abstract

A unit balancing method of a series type direct current converter, characterized in that the method comprises the following steps: step 1, collecting a unit energy value of each DAB unit in the series type direct current converter, and comparing the unit energy value with a total energy of the direct current converter to obtain a unit energy difference of each DAB unit; step 2, establishing a correlation between a phase shift angle of the direct current converter and the unit energy difference, and adjusting the phase shift angle of each DAB unit based on the unit energy difference and the correlation. The present application has a clever idea, fully considers the balance error existing between each unit in the series type direct current converter, realizes the re-balance between the units through the adjustment of the phase shift angle, and prevents the occurrence of grid connection failure in the unstable state.

Description

Technical Field

[0001] This invention relates to the field of power equipment, and more specifically, to a unit equalization method and apparatus for a series DC-DC converter. Background Technology

[0002] In recent years, with the development of power electronics technology and the construction of flexible DC transmission projects, the stable operation of equipment in flexible DC transmission and distribution has attracted much attention. In DC distribution networks, DC converters are the core equipment, widely used due to their advantages such as electrical isolation, high power density, ease of module cascading, and bidirectional power transmission.

[0003] However, in actual operation, due to the limited precision of the DC-DC converter's manufacturing process, it is difficult to maintain perfect consistency in the main circuit parameters of each unit within the converter, such as the parameters of the energy storage inductor and the supporting capacitor. This leads to differences in energy transfer between units. Therefore, within the DC-DC converter, power imbalance between multiple units inevitably occurs in the transmission circuit. When this imbalance is severe or persists for a long time, the current stress within the unit also increases, significantly increasing the failure rate of the power devices in that unit during power level changes and even during normal operation.

[0004] Especially for branch converters with series input and series output, since the units are connected in series, the input and output currents remain the same. When one or more units become unbalanced, it is more likely that the DC-DC converter will struggle to operate in a stable state.

[0005] To address the above problems, the present invention provides a unit equalization method and apparatus for a series DC-DC converter. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a unit equalization method and apparatus for a series DC-DC converter. This method collects the energy deviation in each DAB unit, solves the correlation between the unit energy deviation and the phase shift angle, and achieves stable equalization between DAB units by fine-tuning the phase shift angle within each unit.

[0007] The present invention adopts the following technical solution.

[0008] The first aspect of the present invention relates to a cell equalization method for a series DC-DC converter, the method comprising the following steps: Step 1, collecting the cell energy value of each DAB cell in the series DC-DC converter and comparing it with the total energy of the DC-DC converter to obtain the cell energy difference of each DAB cell; Step 2, establishing the correlation between the phase shift angle of the DC-DC converter and the cell energy difference, and adjusting the phase shift angle of each DAB cell based on the cell energy difference and the correlation.

[0009] Preferably, the input current I of each DAB unit in the series DC-DC converter is... i1 Output current I i2 Input voltage U i1 Output voltage U i2 Data is collected; where i is the DAB unit number, ranging from 1 to m, and m is the number of DAB units in the DC-DC converter.

[0010] Preferably, the unit energy value of each DAB unit in the series DC-DC converter is

[0011]

[0012] Among them, C i1 C i2 These are the capacitance values ​​of the input and output capacitors in the first DAB unit, respectively.

[0013] Preferably, the unit energy difference of each DAB unit is

[0014] Preferably, the correlation between the phase shift angle of the DC-DC converter and the energy difference of the unit is as follows:

[0015] ΔE i ·k i =Δd i

[0016] Where, k i Let Δd be the correlation coefficient. i This represents the deviation of the phase shift angle of the DC-DC converter.

[0017] Preferably, the formula for calculating the correlation coefficient is as follows:

[0018]

[0019] Where f is the frequency of the AC voltage.

[0020] T is a preset multiple of the AC voltage cycle.

[0021] L i Let be the inductance value of the series inductor in the i-th DAB cell.

[0022] d represents the shift ratio.

[0023] Preferably, adjusting the phase shift angle for each DAB unit includes confirming the deviation of the phase shift angle and confirming the direction of adjustment of the phase shift angle.

[0024] Preferably, the phase shift angle deviation is |ΔE i *k i The direction of phase shift adjustment is determined based on the magnitude of the input current and output current in the DAB unit.

[0025] Preferably, when the input current is less than 0, the deviation is added to the current phase shift angle; when the input current is equal to 0, the current phase shift angle is not adjusted; when the input current is greater than 0, the deviation is subtracted from the current phase shift angle.

[0026] A second aspect of the present invention relates to a unit equalization device for a series DC-DC converter. The device is used to implement a unit equalization method for a series DC-DC converter according to a first aspect of the present invention. The device includes a processing unit and a control unit. The processing unit is used to calculate the deviation of the phase shift angle. The control unit is used to adjust the phase shift angle in the DAB unit based on the deviation.

[0027] The beneficial effects of this invention are that, compared with the prior art, the unit balancing method and apparatus of this invention for a series DC-DC converter collects the energy deviation in each DAB unit, solves the correlation between the unit energy deviation and the phase shift angle, and achieves stable balancing between DAB units by fine-tuning the phase shift angle within each unit. This invention is ingenious, fully considering the balance error between units in a series DC-DC converter, and achieves rebalancing between units by adjusting the phase shift angle, thus preventing grid connection failures under unstable conditions. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating the steps of a unit balancing method for a series DC-DC converter according to the present invention;

[0029] Figure 2 This is a schematic diagram of the circuit structure of a series DC-DC converter according to the present invention;

[0030] Figure 3 This is a schematic diagram of the structure of the DAB unit of a series DC-DC converter in this invention. Detailed Implementation

[0031] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0032] Figure 1 This is a schematic diagram illustrating the steps of a unit balancing method for a series-type DC-DC converter according to the present invention. Figure 1 As shown, in a first aspect, the present invention relates to a unit equalization method for a series DC-DC converter, wherein the method includes steps 1 and 2.

[0033] Step 1: Collect the unit energy value of each DAB (Dual Source Bridge) unit in the ISOS (Input Series Output Series) series DC-DC converter and compare it with the total energy of the DC-DC converter to obtain the unit energy difference of each DAB unit.

[0034] It is understood that in this invention, the energy value of each DAB unit in the series DC-DC converter is first collected. In this way, the energy state within the DAB unit can be initially obtained.

[0035] Preferably, the input current I of each DAB unit in the series DC-DC converter is... i1 Output current I i2 Input voltage U i1 Output voltage U i2 Data is collected; where i is the DAB unit number, ranging from 1 to m, and m is the number of DAB units in the DC-DC converter.

[0036] Figure 2 This is a schematic diagram of the circuit structure of a series-type DC-DC converter according to the present invention. Figure 2 As shown, it is understandable that since multiple DAB units are connected in series, the input current and output current of each unit are equal. Ideally, the voltages of each unit should also be equal. However, due to various factors such as capacitors, inductors, and the state of switching transistors, imbalances often occur between DAB units, resulting in differences between the input and output voltages.

[0037] In order to adjust for the above differences, the present invention calculates the unit energy value of each DAB unit based on the basic current and voltage parameters collected.

[0038] Preferably, the unit energy value of each DAB unit in the series DC-DC converter is

[0039]

[0040] Among them, C i1 C i2These are the capacitance values ​​of the input and output capacitors in the first DAB unit, respectively.

[0041] It is understandable that since the unit energy is achieved by the energy storage capacitor at the input end and the energy storage capacitor at the output end, the total energy is the sum of the two.

[0042] Preferably, the unit energy difference of each DAB unit is

[0043] Once the energy value of each DAB unit is accurately calculated, the energy deviation of each DAB unit can be obtained based on the total energy of the DC-DC converter.

[0044] Step 2: Establish the correlation between the phase shift angle of the DC-DC converter and the energy difference of the unit, and adjust the phase shift angle of each DAB unit based on the energy difference of the unit and the correlation.

[0045] In this invention, the amount of adjustment required for each DAB unit is obtained by understanding the energy deviation of each DAB unit. Then, the delay of the switching transistor is controlled by adjusting the phase shift angle, thereby achieving compensation for the deviation.

[0046] Preferably, the correlation between the phase shift angle of the DC-DC converter and the unit energy difference is as follows:

[0047] ΔE i ·k i =Δd i

[0048] Where, k i Let Δd be the correlation coefficient. i This represents the deviation of the phase shift angle of the DC-DC converter.

[0049] Understandably, the relationship between the phase shift angle of a DC-DC converter and the energy difference between individual cells can be characterized by a correlation coefficient. If the value of this correlation coefficient is calculated, then the magnitude of the phase shift angle can be completely determined based on the magnitude of the energy difference between individual cells.

[0050] Preferably, the formula for calculating the correlation coefficient is as follows:

[0051]

[0052] Where f is the frequency of the AC voltage.

[0053] T is a preset multiple of the AC voltage cycle.

[0054] L i Let be the inductance value of the series inductor in the i-th DAB cell.

[0055] d represents the shift ratio.

[0056] In this invention, the correlation coefficient can be solved based on the relevant parameters in the DAB unit. Specifically, in SPS (Single Phase Shift) modulation, the known correlation between transmitted power and phase shift angle is...

[0057]

[0058] Among them, P i Let d be the transmission power of the i-th DAB unit, and d be the phase shift ratio related to the phase shift angle, which is obtained by dividing the phase shift angle by 2π. It can be seen that the value of d is between plus or minus 1 / 2.

[0059] The aforementioned transmission power is the average transmission power of the DAB unit over multiple cycles, not the instantaneous transmission power. Therefore, over a relatively long period, such as an integer multiple of the cycle length T, the total transmission energy of the DAB unit should be [value missing].

[0060]

[0061] However, if there are errors in various parameters in the formula, such as the size of the inductor, or if the parameters of other components in the circuit cause the voltage value or the shift ratio to differ from the pre-designed values, there will be problems with the energy transfer of the DAB unit.

[0062] Therefore, we assume that this error can be compensated for by adjusting the value of d. Thus, for every unit adjustment of d, E i The size of the unit will also change.

[0063] Therefore, differentiating both sides of the previous formula, we get...

[0064]

[0065] Assuming the system remains stable before and after adjustment, the changes in input and output currents in the multiple DAB units connected in series are negligible. Therefore, ΔE i The change will directly lead to a slight change in the input voltage and output voltage of the primary and secondary sides of the DAB unit.

[0066] The calculation formulas are based on the energy at the input terminal and the energy stored in the output capacitor. Then there is as well as

[0067] Substituting the two formulas above, we get:

[0068]

[0069] In addition, during steady-state operation, the input and output currents can also be obtained based on energy, duration, and voltage.

[0070]

[0071] In fact, by adjusting the value of d, the energy in the DAB unit will change, and this change will be reflected in the changes in the input voltage and output voltage.

[0072] Since the interaction between multiple DAB cells has already been taken into account to keep the current constant, the interaction between voltage and current is no longer considered here. Therefore, the change in cell energy value in the DAB cell can be calculated as follows:

[0073]

[0074] Substituting the voltage change and current formulas obtained above, we can get...

[0075]

[0076] Because this invention fully considers the changes in voltage and current parameters caused by various internal and external factors through calculation formulas, thus ensuring that ΔE i The correlation coefficient between Δd and d exhibits a correlation with higher-order states of d. This higher-order correlation makes the calculation method in this invention more accurate and with smaller errors, enabling very precise internal balance for each DAB cell by adjusting the phase shift angle.

[0077] Since the above text assumes ΔE i The correlation coefficient between Δd and Δd can be obtained using this formula. i The value of is determined.

[0078] Preferably, adjusting the phase shift angle for each DAB unit includes confirming the deviation of the phase shift angle and confirming the direction of adjustment of the phase shift angle.

[0079] It is understandable that during the adjustment of the phase shift angle, it is necessary to consider whether the DC-DC converter is operating in a mode where the input terminal outputs power to the output terminal or the output terminal outputs power to the input terminal. Based on the different operating modes, the adjustment methods of the phase shift angle are also distinguished in this invention.

[0080] Preferably, the phase shift angle deviation is |ΔE i *k i The direction of phase shift adjustment is determined based on the magnitude of the input current and output current in the DAB unit.

[0081] Preferably, when the input current is less than 0, the deviation is added to the current phase shift angle; when the input current is equal to 0, the current phase shift angle is not adjusted; when the input current is greater than 0, the deviation is subtracted from the current phase shift angle.

[0082] Specifically, when the DAB unit is in steady-state operation, the adjustment method of the phase shift angle is determined according to the direction of the input current.

[0083] Figure 3 This is a schematic diagram of the DAB unit of a series-type DC-DC converter according to the present invention. Figure 3 As shown, in a second aspect, the present invention relates to a unit equalization device for a series DC-DC converter, wherein the device is used to implement the unit equalization method for a series DC-DC converter described in the first aspect of the present invention, and the device includes a processing unit and a control unit; wherein the processing unit is used to calculate the deviation of the phase shift angle; and the control unit is used to adjust the phase shift angle in the DAB unit based on the deviation.

[0084] It is understood that, in order to implement the various functions in the methods provided in the embodiments of this application, the unit equalization device in this invention includes hardware structures and / or software modules corresponding to the execution of each function. Those skilled in the art should readily recognize that, in conjunction with the algorithm steps of the examples described in the embodiments disclosed herein, this application can be implemented in hardware or a combination of hardware and computer software. Whether a function is executed in hardware or by computer software driving hardware depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0085] This application embodiment can divide the unit equalization device into functional modules according to the above method example. For example, each function can be divided into a separate functional module, or two or more functions can be integrated into one processing module. The integrated module can be implemented in hardware or as a software functional module. It should be noted that the module division in this application embodiment is illustrative and only represents one logical functional division. In actual implementation, there may be other division methods.

[0086] The beneficial effects of this invention are that, compared with the prior art, the unit balancing method and apparatus of this invention for a series DC-DC converter collects the energy deviation in each DAB unit, solves the correlation between the unit energy deviation and the phase shift angle, and achieves stable balancing between DAB units by fine-tuning the phase shift angle within each unit. This invention is ingenious, fully considering the balance error between units in a series DC-DC converter, and achieves rebalancing between units by adjusting the phase shift angle, thus preventing grid connection failures under unstable conditions.

[0087] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A method of balancing cells of a series type DC converter, characterized by, The method comprises the following steps: Step 1, collecting the unit energy value of each DAB unit in the series type DC converter and comparing it with the total energy of the DC converter to obtain the unit energy difference of each DAB unit; Step 2, establishing the correlation between the phase shift angle of the DC converter and the unit energy difference, and adjusting the phase shift angle of each DAB unit based on the unit energy difference and the correlation; The correlation between the phase shift angle of the DC converter and the unit energy difference is ΔE i ·k i = Δd i where k i is a correlation coefficient, Δd i is a deviation of the phase shift angle of the direct current converter.

2. The unit balancing method of the series type DC converter according to claim 1, characterized in that: The input current I i1 , the output current I i2 , the input voltage U i1 , the output voltage U i2 are collected; Wherein, i is the number of DAB unit, the value range is 1 to m, m is the number of DAB unit in the DC converter.

3. The unit balancing method of the series type DC converter according to claim 2, characterized in that: The unit energy value of each DAB unit in the series type DC converter is wherein C i1 , C i2 are the capacitance values of the input and output capacitors of the first DAB cell, respectively.

4. The unit balancing method of the series type DC converter according to claim 3, characterized in that: the unit energy difference of each DAB unit is 5. The unit balancing method of the series type DC converter according to claim 4, characterized in that: The calculation formula of the correlation coefficient is Wherein, f is the frequency of the alternating voltage, T is the preset multiple of the alternating voltage period, L i L is the inductance value of the series inductance in the i-th DAB unit, d is the phase shift ratio, c1 is the equivalent capacitance of the input DC port of the series type DC converter, c2 is the equivalent capacitance of the output DC port of the series type DC converter.

6. The unit balancing method of the series type DC converter according to claim 5, characterized in that: Adjusting the phase shift angle of each DAB unit includes confirming the deviation amount of the phase shift angle and confirming the adjustment direction of the phase shift angle.

7. The unit balancing method of the series type DC converter according to claim 6, characterized in that: The deviation amount of the phase shift angle is |ΔE i / k i The adjustment direction of the phase shift angle is determined based on the magnitude of the input current, the output current in the DAB unit.

8. The unit balancing method of the series type DC converter according to claim 7, characterized in that: When the input current is less than 0, the deviation amount is added to the current phase shift angle; When the input current is equal to 0, the current phase shift angle is not adjusted; When the input current is greater than 0, the deviation amount is subtracted from the current phase shift angle; wherein n i is the winding ratio in the i-th DAB cell.

9. A unit balancing device of a series type DC converter, characterized in that: The device is used to realize the unit balancing method of the series type DC converter according to any one of claims 1-8, and the device comprises a processing unit and a control unit; Wherein, the processing unit is used to calculate the deviation amount of the phase shift angle; The control unit is used to adjust the phase shift angle of the DAB unit based on the deviation amount.

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