A control method for prolonging the life of a dc-dc converter capacitor

Abstract

This invention discloses a control method for extending the lifespan of a DC-DC converter capacitor. The converter includes a DC-DC conversion module and a capacitor connected to a first or second side of the DC-DC conversion module. The control method includes: acquiring the ripple component Bpp of the capacitor; determining whether the capacitor has degraded based on the ripple component Bpp; and adjusting the adjustment coefficient of the loop control module of the DC-DC conversion module to suppress low-frequency ripple current on the capacitor after determining that the capacitor has degraded. This invention, by adding the adjustment coefficient to the control loop of the converter after detecting capacitor degrade, suppresses the low-frequency ripple of the capacitor on the first or second side of the DC-DC conversion module, thereby maximizing the capacitor's lifespan and improving product reliability. It also has the advantage of maintaining the original circuit structure without increasing product cost.

Description

Technical Field

[0001] This invention relates to power supply circuits, and more particularly to a control method for extending the lifespan of electrolytic capacitors in DC-DC converters. Background Technology

[0002] Electrolytic capacitors are widely used in power applications due to their larger capacitance for the same volume; however, their failure rate is relatively high in switching power supplies. (See also...) Figure 2 The equivalent model of the capacitor shown illustrates that, with increasing usage time, the capacitance of an electrolytic capacitor decreases due to electrolyte evaporation, while the ESR increases. Furthermore, the rate of capacitance decay accelerates over time. Factors affecting the lifespan of electrolytic capacitors include ambient temperature and ripple current. The load power carried by the capacitor is directly proportional to the ripple current; the larger the load, the larger the ripple current (the deeper the charge and discharge of the electrolytic capacitor), resulting in more electrolyte consumption and greater heat generation, thus reducing the capacitor's lifespan. When an electrolytic capacitor reaches the end of its service life, its capacitance decreases by approximately 30%, accelerating its failure. The lifespan of electrolytic capacitors significantly impacts the reliability of power electronic equipment, potentially causing power supply shutdowns and accidents, leading to substantial losses.

[0003] Therefore, in order to extend the service life of power electronic products and improve equipment reliability, how to detect and extend the life of electrolytic capacitors and avoid affecting the overall reliability of the equipment due to electrolytic capacitor failure is a technical problem that the industry urgently needs to solve. Summary of the Invention

[0004] To address the aforementioned deficiencies in the existing technology, this invention proposes a control method for extending the lifespan of DC-DC converter capacitors.

[0005] In a first aspect, the present invention provides a control method for extending the lifespan of a DC-DC converter capacitor. The converter includes a DC-DC converter module and a capacitor connected to a first side or a second side of the DC-DC converter module. The control method includes: acquiring the ripple component Bpp of the capacitor; determining whether the capacitor has degraded based on the ripple component Bpp; and adjusting the adjustment coefficient of the loop control module of the DC-DC converter module after determining that the capacitor has degraded to suppress low-frequency ripple current on the capacitor.

[0006] In conjunction with the first aspect, in some optional embodiments, determining whether the capacitor has degraded based on the ripple component Bpp of the capacitor specifically includes: obtaining the ripple component Bpp of the capacitor, comparing the ripple component Bpp with a ripple component threshold Bppn, and determining that the capacitor has degraded when the ripple component Bpp is greater than or equal to the ripple component threshold Bppn.

[0007] In conjunction with the first aspect, in some optional embodiments, adjusting the control parameters of the loop control module of the DC-DC converter module after determining that the capacitor has decayed specifically includes: setting a feedforward coefficient K, and generating the adjustment coefficient by multiplying the ripple component Bpp by the feedforward coefficient K.

[0008] In conjunction with the first aspect, in some optional embodiments, setting the feedforward coefficient K includes: when it is determined that the capacitor has degraded, retrieving the feedforward coefficient K from the database according to the model and operating condition of the DC-DC converter.

[0009] In some optional embodiments, the capacitor connected to the first side of the DC-DC converter module is an electrolytic capacitor. In other optional embodiments, the capacitors connected to the first and second sides of the DC-DC converter module are electrolytic capacitors.

[0010] In conjunction with the first aspect, in some optional embodiments, the loop control module generates loop output parameters based on the output current Idc and output voltage Udc of the DC-DC converter module, and then adds the adjustment coefficient to the loop output parameters to generate PWM adjustment parameters; the PWM module in the loop control module generates a PWM control signal based on the PWM adjustment parameters, and sends the PWM control signal to the DC-DC converter module to suppress low-frequency ripple current on the capacitor.

[0011] In conjunction with the first aspect, in some optional embodiments, generating loop output parameters based on the output current Idc and output voltage Udc of the DC-DC converter module includes: subtracting the output current Idc from a preset output reference current Idc*, and modulating the resulting difference using a first PID modulator to generate an output current feedback parameter; subtracting the output voltage Udc from a preset output reference voltage Udc*, and modulating the resulting difference using a second PID modulator to generate an output voltage feedback parameter; and performing a minimum operation on the output current feedback parameter and the output voltage feedback parameter to generate the loop output parameters.

[0012] In conjunction with the first aspect, in some optional embodiments, the ripple component Bpp includes a voltage ripple component Vpp, and the ripple component threshold Bppn includes a voltage ripple component threshold Vppn; or the ripple component Bpp includes a current ripple component Ipp, and the ripple component threshold Bppn includes a current ripple component threshold Ippn.

[0013] In conjunction with the first aspect, in some optional embodiments, the control method further includes: before performing the operation of acquiring the ripple component Bpp of the capacitor, acquiring the usage time T and the adverse condition decay time Tn of the capacitor; and only performing the operation of acquiring the ripple component Bpp of the capacitor after determining that the usage time T is greater than or equal to the adverse condition decay time Tn.

[0014] In conjunction with the first aspect, in some optional embodiments, the first side of the DC-DC conversion module is connected to the AC-DC conversion module, the second side of the DC-DC conversion module is connected to the electrical load, and the capacitor includes a first capacitor C1 disposed on the first side.

[0015] In conjunction with the first aspect, in some optional embodiments, the first side of the DC-DC conversion module is connected to the AC-DC conversion module, the second side of the DC-DC conversion module is connected to the electrical load, and the capacitor includes a second capacitor C2 disposed on the second side.

[0016] The beneficial effects of the technical solution provided by this invention are:

[0017] This invention, after detecting capacitance decay, uses a control method that adds an adjustment coefficient to the control loop of the converter to suppress low-frequency ripple of the capacitors on the first or second side of the DC-DC converter module, thereby maximizing the lifespan of the electrolytic capacitors and improving product reliability; it also has the advantage of maintaining the original circuit structure without increasing product cost. Attached Figure Description

[0018] The present invention will now be described in detail with reference to the embodiments and accompanying drawings, wherein:

[0019] Figure 1 This is a schematic diagram illustrating the application of the present invention in a two-stage AC-DC converter.

[0020] Figure 2 This is the equivalent model of the capacitor in this invention;

[0021] Figure 3 This is a diagram showing the BUS voltage ripple and output current power frequency ripple when capacitor attenuation is not detected in an existing DC-DC converter.

[0022] Figure 4 This invention presents the BUS voltage ripple and output current power frequency ripple diagrams after the feedforward is changed following the detection of capacitor attenuation.

[0023] Figure 5 This is a graph showing the BUS voltage ripple and output current power frequency ripple after the DC-DC converter reduces power.

[0024] Figure 6This is a schematic block diagram of the loop control module in a preferred embodiment of the present invention;

[0025] Figure 7 This is a flowchart of the control steps of a preferred embodiment of the present invention;

[0026] Figure 8 This is a schematic diagram of the principle of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0028] The design concept of this invention is as follows: after detecting capacitance decay, a control method is used to add an adjustment coefficient to the control loop of the converter to reduce the ripple current of the bus electrolytic capacitor, thereby improving the lifespan of the bus electrolytic capacitor. The same control method can also be used to reduce the low-frequency ripple of the output-side electrolytic capacitor, thus extending its lifespan.

[0029] There are many ways to directly reduce low-frequency ripple, such as directly controlling the loop zeros and poles. However, this method can compromise loop stability and is not recommended. In some practical products, the ripple output of the DC-DC converter module is not critical. For example, in a vehicle charger, a large-capacity capacitor is connected in parallel with the battery. This capacitor is designed for fast charging (100kW and above) and the engine. The high-frequency ripple added by slow charging is basically filtered out here. Therefore, increasing the output frequency component will not affect the actual output ripple current, but it will significantly increase the lifespan of the bus electrolytic capacitor, thereby increasing the product's lifespan.

[0030] See Figure 1 The schematic diagram shown illustrates the application of this invention in a two-stage AC-DC converter. The lifespan of the entire product depends on the capacitor with the shortest lifespan. When the lifespan of the PFC-side capacitor is detected to be degraded, the lifespan of the PFC-side capacitor is extended. When the lifespan of the load-side capacitor is degraded, the lifespan of the load-side output capacitor is extended.

[0031] In an AC-DC converter, the input voltage and current are alternating current (AC). Although it converts AC to DC, the output will not contain only DC components; a small amount of AC component will remain. This means the DC output of an AC-DC converter will have a superposition of DC and AC components, resulting in ripple. In a two-stage topology implementing AC-DC using an AC+DCDC converter, an electrolytic capacitor is used at the output of the AC-DC converter and the input of the DC-DC converter. The voltage across it is a dome-shaped wave at twice the input grid frequency. Due to the very low oscillation frequency, low-frequency ripple will appear at the output of the second-stage DC-DC converter; this ripple can only be filtered out by the output capacitor. The equivalent model of the electrolytic capacitor is as follows: Figure 2 As shown, the low-frequency ripple reaches the output capacitor through the converter. This ripple current will generate a ripple on the equivalent series resistance ESR, thereby forming an output voltage containing ripple on the DC output capacitor.

[0032] In general, in a typical AC-DC converter, because the input is AC and the output is DC, it is inevitable that some AC energy will be transferred to the bus capacitor or the output. The capacitor bears more of the load, while the output bears less. With the capacitor handling all the low-frequency ripple, only the DC and high-frequency ripple remains at the output. By controlling the DC-DC converter, reducing the output power frequency ripple can increase the ripple on the bus capacitor; increasing the output power frequency ripple can reduce the bus ripple current, reduce its heat generation, and extend its lifespan. Here, the bus ripple and output ripple are in phase.

[0033] This invention discloses a control method for extending the lifespan of capacitors in a DC-DC converter. The converter includes: a DC-DC conversion module and a capacitor connected to a first or second side of the DC-DC conversion module. See also... Figure 8 The schematic diagram of the present invention shows that the control method includes: acquiring the ripple component Bpp of the capacitor; determining whether the capacitor has degraded based on the ripple component Bpp; and adjusting the adjustment coefficient of the loop control module of the DC-DC converter module after determining that the capacitor has degraded, so as to suppress the low-frequency ripple current on the capacitor and extend the life of the capacitor.

[0034] In some optional embodiments, the capacitor connected to the first side of the DC-DC converter module is an electrolytic capacitor. In other optional embodiments, the capacitors connected to the first and second sides of the DC-DC converter module are electrolytic capacitors.

[0035] There are various methods to determine whether a capacitor has degraded. In some optional embodiments, determining whether a capacitor has degraded based on its ripple component Bpp specifically includes: obtaining the ripple component Bpp of the capacitor, comparing the ripple component Bpp with a ripple component threshold Bppn, and determining that the capacitor has degraded when the ripple component Bpp is greater than or equal to the ripple component threshold Bppn.

[0036] To avoid misjudgment, in some optional embodiments, the acquisition and judgment are performed several times to increase the accuracy of the judgment. The steps are as follows:

[0037] A single acquisition judgment operation is set up, which includes acquiring the ripple component Bpp of the capacitor, comparing the ripple component Bpp with the ripple component threshold Bppn, and incrementing the first counter by 1 when the ripple component Bpp is greater than or equal to the ripple component threshold Bppn (the initial value of the first counter is zero).

[0038] Repeat the single-step judgment operation. When the value in the first counter is equal to or greater than M, increment the second counter by 1 (the initial value of the second counter is zero).

[0039] When the value in the second counter is equal to or greater than N, it is determined that the capacitor has decayed.

[0040] The values ​​of M and N can be set according to different machine models, different working conditions, and different application scenarios.

[0041] In some optional embodiments, adjusting the control parameters of the loop control module of the DC-DC converter module after determining that the capacitor has decayed specifically includes: setting a feedforward coefficient K, and generating the adjustment coefficient by multiplying the ripple component Bpp by the feedforward coefficient K.

[0042] In some optional embodiments, setting the feedforward coefficient K includes: when it is determined that the capacitor has degraded, retrieving the feedforward coefficient K from the database according to the model and operating condition of the DC-DC converter.

[0043] It should be noted that the feedforward coefficient K can be obtained in various ways, including but not limited to calculation through tables or formulas. The table shows the correspondence between ripple amplitude and feedforward coefficient obtained from multiple experiments. The formula shows the relationship between ripple amplitude and feedforward coefficient obtained from multiple experiments. The feedforward coefficient K is obtained through laboratory testing, and its value can be positive or negative. For ease of understanding, this article provides examples of the values ​​of the feedforward coefficient K, but this does not limit the range of K values ​​in this application. For example, when the feedforward coefficient K is 0, the output power frequency ripple and electrolytic capacitor ripple are generated by the loop itself. Figure 1For example, to extend the lifespan of the first capacitor C1, K < 0 can be used to reduce the capacitor ripple on the first capacitor C1. To extend the lifespan of the second capacitor C2, K > 0 can be used to reduce the capacitor ripple on the second capacitor C2.

[0044] In some optional embodiments, the loop control module generates loop output parameters based on the output current Idc and output voltage Udc of the DC-DC converter module, and then adds the adjustment coefficient to the loop output parameters to generate PWM adjustment parameters; the PWM module in the loop control module generates a PWM control signal based on the PWM adjustment parameters, and sends the PWM control signal to the DC-DC converter module to suppress low-frequency ripple current on the capacitor.

[0045] In some optional embodiments, generating loop output parameters based on the output current Idc and output voltage Udc of the DC-DC converter module includes: subtracting the output current Idc from a preset output reference current Idc*, and modulating the resulting difference using a first PID modulator to generate an output current feedback parameter; subtracting the output voltage Udc from a preset output reference voltage Udc*, and modulating the resulting difference using a second PID modulator to generate an output voltage feedback parameter; and performing a minimum operation on the output current feedback parameter and the output voltage feedback parameter to generate the loop output parameters.

[0046] In some optional embodiments, the ripple component Bpp includes a voltage ripple component Vpp, and the ripple component threshold Bppn includes a voltage ripple component threshold Vppn. In other optional embodiments, the ripple component Bpp includes a current ripple component Ipp, and the ripple component threshold Bppn includes a current ripple component threshold Ippn. The voltage ripple component threshold Vppn is the power frequency AC voltage ripple component obtained during factory testing after the electrolytic capacitor begins to decay, and the current ripple component threshold Ippn is the power frequency AC current ripple component obtained during factory testing after the electrolytic capacitor begins to decay. Relatively speaking, acquiring the voltage ripple component Vpp is easier, so in the embodiments, there are more embodiments that acquire and determine the voltage ripple component Vpp.

[0047] In some preferred embodiments, the control method further includes: before acquiring the ripple component Bpp of the capacitor, first acquiring the capacitor's usage time T and severe condition decay time Tn; only after determining that the usage time T is greater than or equal to the severe condition decay time Tn, is the acquisition of the capacitor's ripple component Bpp performed. It should be noted that the usage time T is the time from when the capacitor is installed in the module until the current time; the severe condition decay time Tn is the time T under the worst operating conditions when the electrolytic capacitor's capacitance begins to decay, obtained through manufacturer testing. In actual operating conditions, after the capacitor's usage time T exceeds the severe condition decay time Tn, a corresponding control mechanism to extend the capacitor's lifespan is implemented. The principle is that the time when the capacitor begins to decay is definitely greater than the severe condition decay time Tn; this constraint is added to prevent misjudgment of capacitor decay, leading to premature degradation of product parameters.

[0048] See Figure 1 The diagram illustrates the application of this invention in a two-stage AC-DC converter. The first side of the DC-DC converter module is connected to the AC-DC converter module, and the second side of the DC-DC converter module is connected to the electrical load. The capacitor includes a first capacitor C1 (also called a bus capacitor) located on the first side; in one embodiment, the bus capacitor is an electrolytic capacitor. The control method for extending the lifespan of the first capacitor C1 is as follows: The ripple component Bpp of the first capacitor C1 is obtained, and the ripple component Bpp is compared with a ripple component threshold Bppn. When the ripple component Bpp is greater than or equal to the ripple component threshold Bppn, it is determined that the first capacitor C1 has degraded. Then, a feedforward coefficient K is set, and the ripple component Bpp is multiplied by the feedforward coefficient K to generate an adjustment coefficient. The loop control module generates loop output parameters based on the output current Idc and output voltage Udc of the DC-DC converter module, and then adds the adjustment coefficient to the loop output parameters to generate PWM adjustment parameters. The PWM module in the loop control module generates a PWM control signal based on the PWM adjustment parameters and sends the PWM control signal to the DC-DC converter module to suppress the low-frequency ripple current on the first capacitor C1.

[0049] See Figure 1The diagram illustrates the application of this invention in a two-stage AC-DC converter. The first side of the DC-DC converter module is connected to the AC-DC converter module, and the second side is connected to the electrical load. The capacitor includes a second capacitor C2 (also called the output capacitor) located on the second side. In one embodiment, both the bus capacitor and the output capacitor are electrolytic capacitors. The control method for extending the lifespan of the second capacitor C2 is as follows: The ripple component Bpp of the second capacitor C2 is obtained, and the ripple component Bpp is compared with a ripple component threshold Bppn. When the ripple component Bpp is greater than or equal to the ripple component threshold Bppn, it is determined that the second capacitor C2 has degraded. Then, a feedforward coefficient K is set, and the ripple component Bpp is multiplied by the feedforward coefficient K to generate an adjustment coefficient. The loop control module generates loop output parameters based on the output current Idc and output voltage Udc of the DC-DC converter module, and then adds the adjustment coefficient to the loop output parameters to generate PWM adjustment parameters. The PWM module in the loop control module generates a PWM control signal based on the PWM adjustment parameters and sends the PWM control signal to the DC-DC converter module to suppress the low-frequency ripple current on the second capacitor C2.

[0050] The loop control module can also dynamically adjust based on the attenuation of the bus capacitor and output capacitor, thereby extending the lifespan of the entire product.

[0051] like Figure 3 As shown, the voltage of the first capacitor C1 and the output ripple of the DC-DC converter module are in phase at the power frequency. After changing the control parameters of the loop control module, the voltage ripple of the first capacitor C1 decreases, while the output ripple of the DC-DC converter module increases, as shown below. Figure 4 As shown.

[0052] Similarly, if the bottleneck in capacitor lifespan is not the first capacitor C1 (also called the BUS capacitor) but the second capacitor C2 (also called the output capacitor), the same method can be used to increase the ripple of the first capacitor C1 to reduce the ripple of the second capacitor C2 and improve the lifespan of the second capacitor C2.

[0053] In products where the lifespan of both BUS capacitors and output capacitors may reach a bottleneck, a more complex strategy is needed. This involves detecting BUS ripple and output ripple to identify the capacitors that begin to degrade first, and then improving the overall product lifespan by reducing their ripple.

[0054] This method of adjusting capacitor ripple by changing the control mechanism can occur more than once during the product's operating cycle. It can be adjusted multiple times under preset conditions to maximize the overall lifespan.

[0055] After detecting capacitor lifespan degradation, the ripple current of the electrolytic capacitor is reduced by decreasing the overall output power, thereby extending its lifespan. Figure 5 As shown. This would reduce the device's output power, decrease device performance, and degrade the user experience. This invention does not employ this power reduction method.

[0056] The following collection Figure 6 The schematic diagram of the loop control module of the preferred embodiment shown illustrates the working principle of the present invention:

[0057] The loop control module includes: a first subtractor J1, a second subtractor J2, a third adder J3, a first PID modulator, a second PID modulator, a smaller-than-normal module, a comparator, a feedforward coefficient K adjustment module, a multiplier, and the PWM module. The first subtractor J1 subtracts the output current Idc of the DC-DC converter module from a preset output reference current Idc*, and the difference is modulated by the first PID modulator to generate an output current feedback parameter. The second subtractor J2 subtracts the output voltage Udc of the DC-DC converter module from a preset output reference voltage Udc*, and the difference is modulated by the second PID modulator to generate an output voltage feedback parameter. The smaller-than-normal module modulates the output current feedback parameter and the output voltage feedback parameter. The loop output parameters are generated by a minimum operation. The comparator compares the ripple component Bpp with the ripple component threshold Bppn. When the ripple component Bpp is greater than or equal to the ripple component threshold Bppn, it determines that the capacitor has decayed and issues an adjustment coefficient command. The feedforward coefficient K adjustment module generates the feedforward coefficient K according to the adjustment coefficient command. The multiplier multiplies the ripple component by the feedforward coefficient K to generate the adjustment coefficient. The third adder J3 adds the adjustment coefficient to the loop output parameters to generate the PWM adjustment parameters. The PWM module generates a PWM control signal according to the PWM adjustment parameters and sends the PWM control signal to the DC-DC converter module to suppress the low-frequency ripple current on the capacitor.

[0058] See Figure 7 The flowchart of the control steps of the preferred embodiment shown is provided. The control method includes the following specific steps:

[0059] Step 1: Obtain the usage time T, the attenuation time under severe conditions Tn, and the voltage ripple component threshold Vppn;

[0060] Step 2: Determine whether the usage time T is greater than or equal to the severe condition decay time Tn. If yes, proceed to step 6; otherwise, proceed to step 3.

[0061] Step 3: Acquire the voltage ripple component Vpp of the capacitor;

[0062] Step 4: Determine whether the voltage ripple component Vpp is greater than or equal to the voltage ripple component threshold Vppn. If yes, proceed to step 6; otherwise, proceed to step 5.

[0063] Step 5: Adjust the control parameters of the loop control module of the DC-DC converter module to reduce the low-frequency ripple current on the capacitor;

[0064] Step 6: End the adjustment.

[0065] Figure 7 The control step flowchart shown primarily illustrates the voltage ripple control mechanism. The loop control module of this invention also includes a control mechanism that replaces the aforementioned voltage ripple control mechanism with a current ripple control mechanism. See [link / reference] Figure 6 The schematic diagram shows two dashed lines connecting the current ripple component Ipp and the current ripple component threshold Ippn. That is, the voltage ripple component Vpp is replaced by the current ripple component Ipp, and the voltage ripple component threshold Vppn is replaced by the current ripple component threshold Ippn, while the rest of the loop control module remains unchanged.

[0066] The above embodiments are merely illustrative and not intended to be limiting. Any equivalent modifications or alterations made without departing from the spirit and scope of this application should be included within the scope of the claims of this application.

Claims

1. A control method for extending the lifespan of a DC-DC converter capacitor, characterized in that, The converter includes: a DC-DC converter module and a capacitor connected to a first side or a second side of the DC-DC converter module; the control method includes: Obtain the ripple component Bpp of the capacitor, and determine whether the capacitor has degraded based on the ripple component Bpp. When it is determined that the capacitor has degraded, the adjustment coefficient of the loop control module of the DC-DC converter module is adjusted to suppress the low-frequency ripple current on the capacitor. The DC-DC conversion module is connected to the AC-DC conversion module on the first side, and the DC-DC conversion module is connected to the electrical load on the second side. The capacitor includes a first capacitor C1 disposed on the first side and a second capacitor C2 disposed on the second side. The control method further includes: obtaining the capacitor with the shorter lifespan between the first capacitor C1 and the second capacitor C2; if the capacitor with the shorter lifespan is the first capacitor C1, then increasing the ripple on the second capacitor C2; if the capacitor with the shorter lifespan is the second capacitor C2, then increasing the ripple on the first capacitor C1.

2. The control method for extending the lifespan of a DC-DC converter capacitor as described in claim 1, characterized in that, The step of determining whether the capacitor has degraded based on the ripple component Bpp of the capacitor specifically includes: obtaining the ripple component Bpp of the capacitor, comparing the ripple component Bpp with the ripple component threshold Bppn, and determining that the capacitor has degraded when the ripple component Bpp is greater than or equal to the ripple component threshold Bppn.

3. The control method for extending the capacitor life of a DC-DC converter as described in claim 1 or 2, characterized in that, The step of adjusting the control parameters of the loop control module of the DC-DC converter module after determining that the capacitor has decayed specifically includes: setting the feedforward coefficient K, and multiplying the ripple component Bpp by the feedforward coefficient K to generate the adjustment coefficient.

4. The control method for extending the capacitor life of a DC-DC converter as described in claim 3, characterized in that, Setting the feedforward coefficient K includes: when it is determined that the capacitor has degraded, retrieving the feedforward coefficient K from the database according to the model and operating condition of the DC-DC converter.

5. The control method for extending the lifespan of a DC-DC converter capacitor as described in claim 4, characterized in that, The loop control module generates loop output parameters based on the output current Idc and output voltage Udc of the DC-DC converter module, and then adds the adjustment coefficient to the loop output parameters to generate PWM adjustment parameters. The PWM module in the loop control module generates a PWM control signal based on the PWM adjustment parameters and sends the PWM control signal to the DC-DC converter module to suppress the low-frequency ripple current on the capacitor.

6. The control method for extending the lifespan of a DC-DC converter capacitor as described in claim 5, characterized in that, The generation of loop output parameters based on the output current Idc and output voltage Udc of the DC-DC converter module includes: The output current Idc is subtracted from the preset output reference current Idc*, and the resulting difference is modulated by the first PID modulator to generate the output current feedback parameter. The output voltage Udc is subtracted from the preset output reference voltage Udc*, and the resulting difference is modulated by the second PID modulator to generate the output voltage feedback parameter. The loop output parameters are generated by performing a minimum operation on the output current feedback parameters and the output voltage feedback parameters.

7. The control method for extending the lifespan of a DC-DC converter capacitor as described in claim 2, characterized in that, The ripple component Bpp includes the voltage ripple component Vpp, and the ripple component threshold Bppn includes the voltage ripple component threshold Vppn. Alternatively, the ripple component Bpp may include the current ripple component Ipp, and the ripple component threshold Bppn may include the current ripple component threshold Ippn.

8. The control method for extending the lifespan of a DC-DC converter capacitor as described in claim 1, characterized in that, Also includes: Before performing the operation of obtaining the ripple component Bpp of the capacitor, the usage time T and the severe condition decay time Tn of the capacitor are first obtained. Only after determining that the usage time T is greater than or equal to the severe condition decay time Tn, the operation of obtaining the ripple component Bpp of the capacitor is performed.

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