Photovoltaic inverter direct current bus capacitance monitoring and service life optimization control method and system

Abstract

The invention discloses a photovoltaic inverter DC bus capacitor monitoring and life optimization control method and system, and the method comprises the steps: obtaining a voltage characteristic signal and a current characteristic signal, so as to calculate the equivalent series resistance of a DC bus capacitor; the health degree of the direct-current bus capacitor is determined through the equivalent series resistor, if the health degree is smaller than a set threshold value, the direct-current bus capacitor is replaced, and if the health degree is not smaller than the set threshold value, a voltage compensation signal is determined through the equivalent series resistor and the voltage characteristic signal; generating a voltage difference signal according to a difference value between the reference voltage of the photovoltaic array and the output voltage and the voltage compensation signal of the photovoltaic array; and the voltage difference signal passes through the PWM modulator to obtain a control signal of the boost converter. The problem that the overall service life of the photovoltaic inverter is affected due to the fact that the service life of the direct-current bus capacitor of the photovoltaic inverter is short is solved, the equivalent series resistance of the direct-current side capacitor is monitored in real time, online compensation can be conducted according to the equivalent series resistance, the decline speed of the direct-current side capacitor is effectively slowed down, and the overall service life of the photovoltaic inverter is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of monitoring and control of new energy equipment, and in particular, relates to a method and system for monitoring and optimizing the life of a photovoltaic inverter DC bus capacitor. Background Art

[0002] The number and capacity of distributed photovoltaic power generation systems connected to medium and low voltage distribution networks are rapidly increasing. As the core power conversion unit of photovoltaic power generation systems, the safe and reliable operation of photovoltaic inverters is crucial for improving grid security and the cost of photovoltaic power generation. Inverter failure rates in photovoltaic power generation systems range from 43% to 70%, and energy losses due to failures account for as much as 36%. To improve the reliability of photovoltaic inverters, manufacturers currently rely on increasing design margins to ensure safe and reliable operation of equipment, while maintenance providers primarily resort to post-installation repairs and complete replacement. These factors significantly increase the cost of photovoltaic power generation, necessitating urgent research into cost-effective methods for improving the safety and reliability of photovoltaic inverters.

[0003] The reliability of a photovoltaic inverter depends on its least reliable component. DC bus capacitors are among the most susceptible to failure in currently installed photovoltaic inverters. In distributed photovoltaic systems, DC bus capacitors are often connected in parallel with electrolytic capacitors. The film capacitors absorb high-frequency ripple current, while the electrolytic capacitors provide voltage support and absorb low-frequency ripple current. Regardless of the type of capacitor, dielectric loss increases with aging. This increased dielectric loss leads to an increase in the capacitor's operating temperature, further exacerbating aging, creating a vicious cycle that ultimately leads to device failure. Although advances in capacitor technology have improved the lifespan of electrolytic capacitors, and longer-lasting metal film capacitors have partially replaced them in some applications, documents indicate that capacitors remain the most vulnerable component in current power electronics systems, accounting for up to 30% of failures. Furthermore, compared to indoor power electronics circuits, the operating conditions of photovoltaic inverters are more complex and variable, resulting in a shorter lifespan for capacitors in photovoltaic inverters. Therefore, research on condition monitoring and lifespan optimization technologies for DC bus capacitors in photovoltaic inverters is urgently needed to improve their reliability. However, there is still a lack of effective health monitoring methods for DC bus side capacitors, and there is an even greater lack of life optimization control methods for DC bus side capacitors. Summary of the Invention

[0004] To address the deficiencies in the prior art, the present invention provides a method and system for monitoring and optimizing the life of a photovoltaic inverter's DC bus capacitor, addressing the issue of the short life of the photovoltaic inverter's DC bus capacitor affecting the overall life of the photovoltaic inverter. The method monitors the equivalent series resistance (ESR) of the DC-side capacitor in real time and performs online compensation based on the ESR, effectively slowing down the degradation rate of the DC-side capacitor and improving the overall life of the photovoltaic inverter.

[0005] The present invention adopts the following technical solutions.

[0006] The present invention proposes a method for monitoring and optimizing the life of a photovoltaic inverter DC bus capacitor. A photovoltaic array is connected to the grid via a boost converter and a grid-connected inverter. A DC bus capacitor is provided on the DC bus between the boost converter and the grid-connected inverter. The photovoltaic array adopts MPPT control, and the boost converter is connected to a PWM modulator. The method includes: The voltage characteristic signal and the current characteristic signal are obtained to calculate the equivalent series resistance of the DC bus capacitor; the health of the DC bus capacitor is determined using the equivalent series resistance. If the health is less than a set threshold, the DC bus capacitor is replaced. If the health is not less than the set threshold, the voltage compensation signal is determined using the equivalent series resistance and the voltage characteristic signal; a voltage difference signal is generated based on the difference between the reference voltage of the photovoltaic array and the output voltage of the photovoltaic array and the voltage compensation signal; the voltage difference signal is passed through a PWM modulator to obtain a control signal for the boost converter.

[0007] Sampling signal from DC bus voltage The voltage characteristic signal extracted from as follows:

[0008] Where, is the upper envelope of the DC bus voltage sampling signal waveform, is the lower envelope of the DC bus voltage sampling signal waveform, is the averaging function; Sampling signal from grid current The current characteristic signal is extracted from as follows:

[0009] Where, is the absolute value of the grid-connected current sampling signal.

[0010] The equivalent series resistance of the DC bus capacitor is as follows:

[0011] Where, 、 are the sampling coefficients of DC bus voltage and grid current respectively, 、 are the amplitudes of the voltage characteristic signal and the current characteristic signal at 100Hz of the spectrum respectively.

[0012] The health of the DC bus capacitor is as follows:

[0013] Where, is the health of the DC bus capacitor, is the initial value of the equivalent series resistance, 、 Are magnification factors, calculated When Set to zero.

[0014] Voltage compensation signal as follows:

[0015] Where, is the dynamic compensation coefficient.

[0016] The dynamic compensation coefficient is defined as follows:

[0017] Where, is the health status of the DC bus capacitor.

[0018] Obtain the output voltage of the photovoltaic array and obtain the reference voltage of the photovoltaic array through the MPPT controller.

[0019] The present invention also proposes a photovoltaic inverter DC bus capacitor monitoring and life optimization control system. The photovoltaic array is connected to the grid after passing through a boost converter and a grid-connected inverter. A DC bus capacitor is set on the DC bus between the boost converter and the grid-connected inverter. The photovoltaic array adopts MPPT control, and the boost converter is connected to a PWM modulator. The control system includes: a voltage feature extraction unit, a current feature extraction unit, an equivalent series resistance calculation unit, a health assessment unit, an adaptive compensation unit, and a voltage regulator. A voltage feature extraction unit is used to extract a voltage feature signal from a DC bus voltage sampling signal; a current feature extraction unit is used to extract a current feature signal from a grid-connected current sampling signal; an equivalent series resistance calculation unit is used to calculate the equivalent series resistance of the DC bus capacitor based on the voltage feature signal and the current feature signal; a health assessment unit is used to determine the health of the DC bus capacitor using the equivalent series resistance, and if the health is less than a set threshold, a prompt is given to replace the DC bus capacitor; if the health is not less than the set threshold, a start signal is sent to the adaptive compensation unit; the adaptive compensation unit is used to determine the voltage compensation signal using the equivalent series resistance and the voltage feature signal after receiving the start signal; a voltage regulator is used to generate a voltage difference signal based on the difference between the reference voltage of the photovoltaic array and the output voltage of the photovoltaic array and the voltage compensation signal; the voltage difference signal is passed through a PWM modulator to obtain a control signal for the boost converter.

[0020] Voltage regulators include P controllers, PI controllers, and PR controllers; The reference voltage of the photovoltaic array is input to the non-inverting terminal of the voltage regulator, the output voltage of the photovoltaic array is input to the inverting terminal of the voltage regulator, and the voltage compensation signal is input to the inverting terminal of the voltage regulator.

[0021] The beneficial effects of the present invention are as follows, compared with the prior art, at least including: based on the parameter monitoring of the DC bus capacitor, the present invention introduces the monitored parameters into the control loop, slows down the decay rate of the DC bus capacitor, and realizes the life optimization control of the DC bus capacitor; dynamically adjusts the size of the compensation amount according to the calculated ESR size, reduces the current stress of the capacitor, and further improves the life. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of a photovoltaic inverter DC bus capacitor monitoring and life optimization control method proposed by the present invention; Figure 2 This is a schematic diagram of a photovoltaic inverter DC bus capacitor monitoring and life optimization control method system proposed by the present invention; Figure 3 The waveform diagram of the DC bus voltage and the inductor current of the grid-connected inverter when ESR=0.2 and the life optimization control method proposed in the present invention is not adopted; Figure 4 The waveform diagram of the DC bus voltage and the inductor current of the grid-connected inverter when the life optimization control method proposed by the present invention is adopted when ESR=0.2; Figure 5 The waveform diagram of the DC bus voltage and the inductor current of the grid-connected inverter when the life optimization control method proposed in the present invention is adopted when ESR=0.25. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] The present invention proposes a method for monitoring and optimizing the life of a photovoltaic inverter DC bus capacitor. Figure 1 As shown, the following steps are included: Step 1: Acquire voltage characteristic signals and current characteristic signals.

[0025] Specifically, obtain the DC bus voltage sampling signal , and send it to the voltage feature extraction unit to obtain the voltage feature signal , the specific extraction formula is:

[0026] Where, is the upper envelope of the DC bus voltage sampling signal waveform, is the lower envelope of the DC bus voltage sampling signal waveform, is an averaging function; in the present invention, when monitoring the DC bus capacitance of the photovoltaic inverter, it is necessary to perform denoising on the DC bus voltage to obtain a voltage characteristic signal, and both the upper envelope and the lower envelope are signals that change with time t and only the low-frequency AC component is retained in the envelope. Therefore, the present invention adopts the method of extracting the low-frequency AC component using the upper and lower envelopes to effectively remove the high-frequency noise in the DC bus voltage sampling signal, thereby improving the sampling and monitoring accuracy.

[0027] Specifically, the grid current sampling signal is obtained , and send it to the current feature extraction unit to obtain the current feature signal , the specific extraction formula is:

[0028] Where, is the absolute value of the grid current sampling signal, since is the AC component, so Approximately 1 steamed bun wave, and is the average value of the steamed bun wave, i.e. the DC component, so the purpose of this formula is to extract The AC component in .

[0029] Step 2: Calculate the equivalent series resistance of the DC bus capacitor using the voltage characteristic signal and the current characteristic signal.

[0030] Specifically, and The equivalent series resistance of the DC bus capacitor is obtained by sending it to the ESR calculation unit. The calculation formula of ESR is:

[0031] Where, 、 are the sampling coefficients of DC bus voltage and grid current respectively, 、 are the amplitudes of the voltage characteristic signal and the current characteristic signal at 100 Hz of the spectrum, respectively. In the embodiment, the calculated ESR does not take the resistance dimension into account and only takes the numerical value.

[0032] The present invention realizes targeted monitoring. Since the DC bus capacitor of the photovoltaic inverter mainly bears the electrical stress at 100 Hz, the present invention proposes a high-precision monitoring method of characteristic parameters at 100 Hz.

[0033] Step 3: Use the equivalent series resistance to determine the health of the DC bus capacitor. If the health is less than a set threshold, a prompt is given to replace the DC bus capacitor. If the health is not less than the set threshold, proceed to step 4.

[0034] In the embodiment, the threshold value is set to 10%. When the health level is less than 10%, the DC bus capacitor is replaced.

[0035] Specifically, the ESR is sent to the health assessment unit to assess the health of the DC bus capacitor. The specific assessment method is as follows:

[0036] Where, is the health of the DC bus capacitor, is the initial value of the equivalent series resistance, 、 are the magnification factors, for 1.2 to 1.3 times of; In the embodiment, The value is 10. The value is 13, then the method proposed by the present invention is 1.3 times of is taken as the point where health is 0. If the calculated If it is a negative value, Set to 0.

[0037] Step 4: Determine a voltage compensation signal using the equivalent series resistance and the voltage characteristic signal.

[0038] Specifically, ESR is compared with At the same time, it is sent to the adaptive compensation unit to obtain the voltage compensation signal , the formula is:

[0039] Where, It is the dynamic compensation coefficient. ESR-ESR0 is only used to dynamically adjust the compensation amount. It does not take the resistance dimension into account and only takes the numerical value. In order to achieve accelerated compensation for aging of the DC bus capacitor, the dynamic compensation coefficient is defined as follows:

[0040] Where, is the health status of the DC bus capacitor. ; In the embodiment, When the capacitor is >70%, dynamic compensation is performed based on the health of the DC bus capacitor. The smaller the health, the greater the compensation coefficient. When the DC bus capacitor aging warning is issued and the compensation coefficient is 1, When the DC bus capacitor is less than or equal to 50%, the DC bus capacitor must be replaced.

[0041] By introducing a dynamic compensation coefficient related to the health state of the DC bus capacitor, the dynamic compensation coefficient increases with the health state of the DC bus capacitor when the health state is within the allowable range. The compensation voltage increases as the ESR decreases, realizing dynamic adjustment of the compensation voltage under aging of the DC bus capacitor and implementing a life optimization control strategy. When the health state is in the warning range, the dynamic compensation coefficient takes a value of 1, and the compensation voltage depends entirely on the deviation between the ESR and the initial value and the voltage characteristic signal, realizing a complete following compensation strategy.

[0042] Step 5: Based on the reference voltage of the photovoltaic array The output voltage of the photovoltaic array , voltage compensation signal The difference between the two generates a voltage difference signal; the voltage difference signal is modulated by the PWM modulator to obtain the control signal of the boost converter.

[0043] Specifically, the voltage regulator includes a P controller, a PI controller, and a PR controller; those skilled in the art can select different types of controllers as voltage regulators according to actual needs. The reference voltage of the photovoltaic array is input to the non-inverting terminal of the voltage regulator, the output voltage of the photovoltaic array is input to the inverting terminal of the voltage regulator, and the voltage compensation signal is input to the inverting terminal of the voltage regulator; wherein, the output voltage of the photovoltaic array is obtained. and , get the reference voltage of the photovoltaic array through the MPPT controller .

[0044] The voltage difference signal output by the voltage regulator is converted into a control signal for the boost converter after passing through a PWM modulator. The control signal of the boost converter drives the boost converter to operate, thereby achieving life optimization control of the photovoltaic grid-connected inverter.

[0045] The present invention also proposes a photovoltaic inverter DC bus capacitor monitoring and life optimization control system, such as Figure 2 As shown, the photovoltaic array is connected to the grid after passing through a boost converter and a grid-connected inverter. A DC bus capacitor is set on the DC bus between the boost converter and the grid-connected inverter. The photovoltaic array adopts MPPT control, and the boost converter is connected to a PWM modulator. The control system includes: a voltage feature extraction unit, a current feature extraction unit, an equivalent series resistance calculation unit, a health assessment unit, an adaptive compensation unit, and a voltage regulator. Among them, the voltage feature extraction unit is used to sample the signal from the DC bus voltage The voltage characteristic signal is extracted from ; Current feature extraction unit, used to sample the signal from the grid current The current characteristic signal is obtained by extracting the current characteristic extraction unit ; Equivalent series resistance calculation unit, used to calculate the equivalent series resistance according to the voltage characteristic signal and current characteristic signal The equivalent series resistance (ESR) of the DC bus capacitor is calculated; the health assessment unit is used to determine the health of the DC bus capacitor using the equivalent series resistance (ESR). If the health is less than a set threshold, a prompt is given to replace the DC bus capacitor. If the health is not less than the set threshold, a start signal is sent to the adaptive compensation unit; the adaptive compensation unit is used to use the equivalent series resistance (ESR) and voltage characteristic signal after receiving the start signal. Determine the voltage compensation signal ; Voltage regulator, used to adjust the reference voltage of the photovoltaic array The output voltage of the photovoltaic array , voltage compensation signal The difference between the two generates a voltage difference signal; the voltage difference signal is modulated by the PWM modulator to obtain the control signal of the boost converter.

[0046] Figure 3 The DC bus voltage when ESR=0.2 is not adopted the life optimization control method proposed by the present invention and the inductor current of the grid-connected inverter The waveform diagram, Figure 4 The DC bus voltage when the life optimization control method proposed by the present invention is used when ESR=0.2 and the inductor current of the grid-connected inverter The waveform diagram of Figure 3 and Figure 4 It can be seen that after using the control method of the present invention, the ripple voltage of the DC bus voltage can be reduced, the ripple current borne by the capacitor can be reduced, and the heat generated by the capacitor can be reduced, thereby extending the working life of the capacitor. Figure 5 The DC bus voltage when the life optimization control method proposed by the present invention is used when ESR=0.25 and the inductor current of the grid-connected inverter The waveform diagram simulates the aging of the DC bus capacitor. After using the control method of the present invention, the ripple voltage on the capacitor is further reduced, thereby further extending the working life of the capacitor.

[0047] DC bus voltage and the inductor current of the grid-connected inverter The data was imported into the Matlab Workspace for data processing. The simulation results under different conditions are shown in Table 1. It can be seen that the two-stage single-phase inverter DC bus capacitor ESR monitoring method provided by the present invention has high tracking accuracy.

[0048] Table 1

[0049] Therefore, the method proposed in the present invention can accurately monitor the ESR of the DC bus capacitor of the photovoltaic inverter. On the one hand, it can be used to evaluate the health status of the DC bus capacitor. On the other hand, the ESR monitoring value is introduced into the life optimization control. The ripple size on the DC bus voltage can be autonomously adjusted by dynamically generating a compensation voltage signal according to the size of the ESR: when the DC bus capacitor decays, the ESR increases, and the voltage ripple compensation amount of this method increases. Through closed-loop control, the DC bus voltage ripple is reduced, that is, the ripple current borne by the DC bus capacitor is reduced, the loss on the DC bus capacitor is reduced, and the heat generation is reduced, thereby improving the life of the DC bus capacitor. The advantage of the photovoltaic inverter DC bus capacitor monitoring and life optimization control method provided by the present invention is that there is no need to introduce new measurement points. The method is simple and easy to implement, can accurately identify the ESR of the DC bus capacitor, and can autonomously adjust the compensation amount according to the size of the DC bus capacitor ESR, thereby extending the working life of the DC bus capacitor.

[0050] The present invention also proposes a photovoltaic inverter DC bus capacitor monitoring and life optimization control system. The photovoltaic array is connected to the grid after passing through a boost converter and a grid-connected inverter. A DC bus capacitor is set on the DC bus between the boost converter and the grid-connected inverter. The photovoltaic array adopts MPPT control, and the boost converter is connected to a PWM modulator. The control system includes: a voltage feature extraction unit, a current feature extraction unit, an equivalent series resistance calculation unit, a health assessment unit, an adaptive compensation unit, and a voltage regulator. A voltage feature extraction unit is used to extract a voltage feature signal from a DC bus voltage sampling signal; a current feature extraction unit is used to extract a current feature signal from a grid-connected current sampling signal; an equivalent series resistance calculation unit is used to calculate the equivalent series resistance of the DC bus capacitor based on the voltage feature signal and the current feature signal; a health assessment unit is used to determine the health of the DC bus capacitor using the equivalent series resistance, and if the health is less than a set threshold, a prompt is given to replace the DC bus capacitor; if the health is not less than the set threshold, a start signal is sent to the adaptive compensation unit; the adaptive compensation unit is used to determine the voltage compensation signal using the equivalent series resistance and the voltage feature signal after receiving the start signal; a voltage regulator is used to generate a voltage difference signal based on the difference between the reference voltage of the photovoltaic array and the output voltage of the photovoltaic array and the voltage compensation signal; the voltage difference signal is passed through a PWM modulator to obtain a control signal for the boost converter.

[0051] The control system proposed by the present invention is simple, easy to implement, and low-cost. The existing technology requires the introduction of new detection points or the addition of high-precision measuring elements. However, the DC bus voltage and grid-connected current in the present invention are based on the existing detection points, without the need for adding new detection hardware. Voltage regulators include P controllers, PI controllers, and PR controllers; The reference voltage of the photovoltaic array is input to the non-inverting terminal of the voltage regulator, the output voltage of the photovoltaic array is input to the inverting terminal of the voltage regulator, and the voltage compensation signal is input to the inverting terminal of the voltage regulator.

[0052] The present disclosure may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0053] A computer-readable storage medium can be a tangible device that can hold and store instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punched card or raised structure in a groove on which instructions are stored, and any suitable combination thereof. As used herein, a computer-readable storage medium is not to be construed as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse passing through a fiber optic cable), or an electrical signal transmitted through an electrical wire.

[0054] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in the computer-readable storage medium in each computing / processing device.

[0055] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, and conventional procedural programming languages ​​such as "C" or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, the state information of the computer-readable program instructions is used to personalize an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), so that the electronic circuit can execute the computer-readable program instructions, thereby implementing various aspects of the present disclosure.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for monitoring and optimizing the life of a photovoltaic inverter DC bus capacitor, wherein a photovoltaic array is connected to the grid via a boost converter and a grid-connected inverter, a DC bus capacitor is provided on the DC bus between the boost converter and the grid-connected inverter, the photovoltaic array is controlled using MPPT, and the boost converter is connected to a PWM modulator; characterized in that: include: The voltage characteristic signal and the current characteristic signal are obtained to calculate the equivalent series resistance of the DC bus capacitor; the health of the DC bus capacitor is determined using the equivalent series resistance. If the health is less than a set threshold, the DC bus capacitor is replaced. If the health is not less than the set threshold, the voltage compensation signal is determined using the equivalent series resistance and the voltage characteristic signal; a voltage difference signal is generated based on the difference between the reference voltage of the photovoltaic array and the output voltage of the photovoltaic array and the voltage compensation signal; the voltage difference signal is passed through a PWM modulator to obtain a control signal for the boost converter.

2. The photovoltaic inverter DC bus capacitance monitoring and life optimization control method according to claim 1, characterized in that: Sampling signal from DC bus voltage The voltage characteristic signal extracted from as follows: Where, is the upper envelope of the DC bus voltage sampling signal waveform, is the lower envelope of the DC bus voltage sampling signal waveform, is the averaging function; Sampling signal from grid current The current characteristic signal is extracted from as follows: Where, is the absolute value of the grid-connected current sampling signal.

3. The photovoltaic inverter DC bus capacitance monitoring and life optimization control method according to claim 2, characterized in that: The equivalent series resistance of the DC bus capacitor is as follows: Where, 、 are the sampling coefficients of DC bus voltage and grid current respectively, 、 are the amplitudes of the voltage characteristic signal and the current characteristic signal at 100Hz of the spectrum respectively.

4. The photovoltaic inverter DC bus capacitance monitoring and life optimization control method according to claim 3, characterized in that: The health of the DC bus capacitor is as follows: Where, is the health of the DC bus capacitor, is the initial value of the equivalent series resistance, 、 Are magnification factors, calculated When Set to zero.

5. The photovoltaic inverter DC bus capacitance monitoring and life optimization control method according to claim 4, characterized in that: Voltage compensation signal as follows: Where, is the dynamic compensation coefficient.

6. The photovoltaic inverter DC bus capacitance monitoring and life optimization control method according to claim 5, characterized in that: The dynamic compensation coefficient is defined as follows: Where, is the health status of the DC bus capacitor.

7. The photovoltaic inverter DC bus capacitor monitoring and life optimization control method according to claim 1, characterized in that: Obtain the output voltage of the photovoltaic array and obtain the reference voltage of the photovoltaic array through the MPPT controller.

8. A photovoltaic inverter DC bus capacitor monitoring and life optimization control system, wherein a photovoltaic array is connected to the grid through a boost converter and a grid-connected inverter, a DC bus capacitor is provided on the DC bus between the boost converter and the grid-connected inverter, the photovoltaic array adopts MPPT control, and the boost converter is connected to a PWM modulator; characterized in that: The control system includes: a voltage feature extraction unit, a current feature extraction unit, an equivalent series resistance calculation unit, a health assessment unit, an adaptive compensation unit, and a voltage regulator; A voltage feature extraction unit is used to extract a voltage feature signal from a DC bus voltage sampling signal; a current feature extraction unit is used to extract a current feature signal from a grid-connected current sampling signal; an equivalent series resistance calculation unit is used to calculate the equivalent series resistance of the DC bus capacitor based on the voltage feature signal and the current feature signal; a health assessment unit is used to determine the health of the DC bus capacitor using the equivalent series resistance, and if the health is less than a set threshold, a prompt is given to replace the DC bus capacitor; if the health is not less than the set threshold, a start signal is sent to the adaptive compensation unit; the adaptive compensation unit is used to determine the voltage compensation signal using the equivalent series resistance and the voltage feature signal after receiving the start signal; a voltage regulator is used to generate a voltage difference signal based on the difference between the reference voltage of the photovoltaic array and the output voltage of the photovoltaic array and the voltage compensation signal; the voltage difference signal is passed through a PWM modulator to obtain a control signal for the boost converter.

9. The photovoltaic inverter DC bus capacitance monitoring and life optimization control system according to claim 8, characterized in that: Voltage regulators include P controllers, PI controllers, and PR controllers; The reference voltage of the photovoltaic array is input to the non-inverting terminal of the voltage regulator, the output voltage of the photovoltaic array is input to the inverting terminal of the voltage regulator, and the voltage compensation signal is input to the inverting terminal of the voltage regulator.

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