A direct current suppression method and system for an isolated DC-DC resonant converter for energy storage

Abstract

The application discloses a kind of energy storage isolation type DC-DC resonant converter direct current suppression method and system, to optimize resonant network voltage ripple.The application constructs the voltage ripple mathematical model of resonant network using instantaneous power theory, by calculating the instantaneous power of resonant inductance and capacitance, and monitors the switching frequency of resonant converter is equal to the resonant frequency, is located in the resonant frequency and is away from the resonant frequency three kinds of working conditions, when in corresponding condition, according to corresponding method to determine the range limit of switching frequency, based on this, the switching frequency of resonant converter is dynamically adjusted with different working conditions, to effectively suppress output DC ripple, improve the reliability of power quality guarantee system.

Description

Technical Field

[0001] This invention belongs to the field of DC-DC resonant converter DC suppression, and particularly relates to a DC suppression method and system for an isolated DC-DC resonant converter for energy storage. Background Technology

[0002] Isolated DC-DC resonant converters are widely used in energy storage systems for efficient energy transmission and distribution. The stability of their output voltage is crucial to the system's operating efficiency and safety. However, because the input voltage of isolated DC-DC resonant converters is non-sinusoidal, they are prone to significant DC voltage ripple, which leads to a decline in power quality and even affects the lifespan of energy storage devices. Conventional ripple suppression methods mainly rely on fixed-frequency control, which is difficult to effectively suppress ripple under dynamic loads and wide power fluctuations. According to existing research, the voltage ripple analysis of resonant networks mainly employs the fundamental frequency approximation method (FHA), simulation analysis method (SA), and time-domain analysis method (TDA). However, the effectiveness of FHA is limited to the vicinity of the converter's resonant frequency; SA requires a large amount of analysis work and the results are not intuitive; TDA requires establishing state equations for each operating mode, significantly increasing computational complexity. Furthermore, traditional methods often use large-capacity electrolytic capacitors to reduce ripple amplitude, but this increases the system size and weight, which is detrimental to improving power density. Summary of the Invention

[0003] This invention addresses the problems existing in the prior art by providing a DC suppression method and system for an isolated DC-DC resonant converter used in energy storage. This method, through instantaneous power analysis and multi-condition frequency range design, can automatically adjust the frequency range under different load conditions, effectively reducing DC voltage ripple, improving power quality, and ensuring system reliability. This application primarily aims to improve the voltage output quality of energy converters in energy storage systems, reduce power transmission losses caused by voltage ripple, and improve the overall reliability of the system. By employing a multi-condition frequency range design, this method can dynamically adjust the switching frequency under different operating conditions to maintain stable output voltage and extend the service life of energy storage devices. It is particularly suitable for grid energy storage with high power density and high conversion efficiency requirements, electric vehicle charging devices, and other power conversion applications requiring strict voltage regulation.

[0004] This invention proposes a multi-condition frequency range adjustment method based on instantaneous power theory to effectively suppress DC voltage ripple in isolated DC-DC resonant converters. This method, through adaptive frequency adjustment, enables the system to achieve low ripple output over a wide frequency range and under various operating conditions, thereby meeting the requirements of energy storage systems for high voltage quality, low loss, and high stability.

[0005] To address the response issues of traditional fixed-frequency methods to non-sinusoidal input voltages, this invention utilizes instantaneous power theory to construct a mathematical model of voltage ripple in a resonant network. By calculating the instantaneous power of the resonant inductor and capacitor, the amplitude of the output voltage ripple can be accurately predicted and controlled. The instantaneous power model can capture the voltage ripple characteristics of the converter under different frequencies and loads, providing a theoretical basis for multi-operating-condition frequency range design.

[0006] By establishing an instantaneous power model of ripple voltage, the relationship between ripple amplitude and load, power factor and switching frequency is obtained, which makes frequency regulation more precise and ensures that the system achieves the best voltage ripple suppression effect across the full power range.

[0007] A mathematical model of voltage ripple in a resonant network is constructed using instantaneous power theory, and a model of the DC voltage ripple amplitude of the resonant network output is derived.

[0008] Based on the system load range and gain range design objectives, the FHA analysis method can be used to obtain the initial resonant frequency and its surrounding frequency range, so as to automatically adapt to the relevant operating conditions when the load changes, and dynamically adjust the frequency range based on the specific operating conditions.

[0009] Based on the topology of the isolated DC-DC resonant converter and its equivalent circuit model, the input voltage of the high-frequency transformer is set as follows:

[0010] (1)

[0012] In the formula V in ω represents the input voltage amplitude, ω represents the switching angular frequency, and t represents time.

[0013] The resonant current i can be expressed as:

[0014] (2)

[0016] In the formula, I represents the current amplitude, and φ represents the relationship between the current I and the input voltage v. in The phase difference.

[0017] According to equations (1) and (2), the instantaneous power p(t) can be obtained:

[0018] (3)

[0020] In the formula, p0 and p 0-2ω These represent the average active power and ripple power (2ω), respectively, which are derived from v in The fundamental frequency component of I is generated. h This represents the instantaneous harmonic power, which includes a 2ω component.

[0021] The ripple component of DC voltage is mainly introduced by the 2ω component of instantaneous power (defined as p). 2ω p 2ω By p 0-2ω and p h Composed of 2ω, it is represented as:

[0022] (4)

[0024] According to the law of conservation of energy, we can conclude that:

[0025] (5)

[0027] In the formula , , and Let Lr and C represent the instantaneous power of the resonant inductor, resonant capacitor, DC-side capacitor, and DC-side capacitive load, respectively. Assuming the equivalent resonant inductance and resonant capacitance of the resonant network are Lr and C, respectively, their instantaneous power can be expressed as:

[0028] (6)

[0030] Since the resonant network filters out higher harmonics, the output DC voltage is mainly affected by the fundamental and 2ω components of p(t). The power of higher harmonics (>2ω) can be ignored, and the output power pout can be expressed as:

[0031] (7)

[0033] The specific value of the output DC voltage ripple (2ω) can be directly derived using equation (7).

[0034] The output DC voltage is defined as u dc , is represented as:

[0035] (8)

[0037] U dc and They represent u respectively dc The DC section and the ripple section.

[0038] Substituting equation (8) into equation (7), we get:

[0039] (9)

[0041] C and R are the DC-side output capacitor and equivalent load, respectively.

[0042] definition According to equations (7) and (9), it can be seen that because there are in the high-frequency converter We can obtain the solution for x in the steady state:

[0043] (10)

[0045] in

[0046] (11)

[0048] Substituting equation (8) into equation (10), we get:

[0049] (12)

[0051] this The amplitude can be used Represented as:

[0052] (13)

[0054] Equation (13) is based on the instantaneous power theory, which holds true under any operating condition. It shows that after the DC-DC resonant converter is fully parameterized, the amplitude of the DC voltage ripple (2ω) is affected by the power factor (cosφ), the switching frequency (ω), and the transmission power (R), where... The DC voltage ripple amplitude of the resonant network output,

[0055] It is worth noting that in equation (13), The value of basically increases with the increase of transmission power, that is, when the converter operates at its rated power... To achieve the maximum value. Furthermore, the power factor depends primarily on the value of ω. Therefore, to ensure that the converter's DC ripple does not exceed [a certain value] across the entire power range. The range of ω should be reasonably designed under the rated power.

[0056] This invention mainly relates to three operating conditions of resonant converters: the switching frequency of the resonant converter is at the resonant frequency, near the resonant frequency, and far from the resonant frequency.

[0057] Operating condition 1: Operating at the resonant frequency

[0058] When the resonant converter operates at its resonant frequency, the system exhibits the highest power transfer efficiency, and the voltage ripple is determined by the converter parameters and load characteristics. This operating condition is primarily used to optimize efficiency, but it is difficult to effectively suppress ripple under a fixed frequency.

[0059] If the DC-DC resonant converter operates precisely at its resonant frequency, the power factor will be 1, and the equivalent reactance Xeq will be zero. At this point:

[0060] (14)

[0062] Substituting equation (14) into equation (13), we get:

[0063] (15)

[0065] Obviously The value of is directly proportional to the output DC voltage and inversely proportional to the load, switching frequency, and DC capacitance. Therefore, in this case, The scope should meet the following requirements:

[0066] (16)

[0068] in This is the equivalent load at rated power. For u dc Permissible ripple.

[0069] Operating Condition 2: Operating within 5% of the resonant frequency

[0070] When load conditions vary slightly, the converter can operate within a range near the resonant frequency, and the frequency control method can adjust it to the minimum ripple range. Under this condition, frequency regulation can effectively reduce the amplitude of the output voltage ripple while maintaining a high power factor, making it suitable for load conditions with high ripple control requirements.

[0071] When the converter operates near the resonant frequency, the fundamental frequency analysis method (FHA) can be used to analyze the converter with good accuracy. Therefore, the range of values ​​for ω is derived using the FHA analysis method.

[0072] For a series resonant circuit, the power factor of the equivalent circuit of the resonant network based on the resonant converter can be expressed as:

[0073] (17)

[0075] Where Req represents the equivalent resistance, which is related to the high-frequency transformer turns ratio n and the load R. The following four steps are then listed to determine the range of ω:

[0076] Step 1: Determine the initial range of cosφ:

[0077] Ignoring transformer, semiconductor, and line losses, output active power satisfy:

[0078] (18)

[0080] Assuming the maximum allowable current is We can obtain:

[0081] (19)

[0083] Therefore, the initial range of cosφ can be defined as:

[0084] (20)

[0086] Step 2: Limit the range of cosφ

[0087] When the converter operates near its resonant frequency, the fundamental frequency analysis (FHA) method provides good accuracy, as cosφ approaches 1. Therefore, δ ≤ cosφ ≤ 1, where δ is a constant close to 1. Combining (20), the range of cosφ is limited to:

[0088] (twenty one)

[0090] Step 3: Derive the initial range of ω:

[0091] Substituting equation (17) into equation (21), we get:

[0092] (twenty two)

[0094] Step 4: Confirm that the range of ω meets the A2ω amplitude limit.

[0095] Based on step 3, the range of ω is further determined to meet the amplitude limit of A2ω, where Step is the incremental frequency within each control cycle, and ω1 and ω2 represent the lower and upper limits in equation (22), respectively, which represent the frequency range allowed to meet the power transmission requirements. Further, according to... Figure 3 The process shown is used to determine the frequency range that meets the ripple requirements, which is expressed as:

[0096] (twenty three)

[0098] in, This refers to the minimum value within the allowed range of frequency values. This refers to the maximum value within the allowed range of frequency values.

[0099] The specific steps are as follows:

[0100] initialization , , V in n, C, i = 0;

[0101] set up and will Substituting into equation (17) yields According to equation (13), ;

[0102] Will Compare with the allowable DC ripple threshold to determine if it is acceptable. Make incremental adjustments.

[0103] Operating Condition 3: Operating far from the resonant frequency, i.e., within 5% of the resonant frequency.

[0104] When power demand changes drastically or load fluctuates significantly, the system can operate far from the resonant frequency. In this case, through dynamic adjustment of the frequency range using multi-condition frequency design, the frequency range can disperse the ripple spectrum, suppress the influence of high-frequency harmonics, and effectively control voltage quality.

[0105] When the converter operates far from the resonant frequency, the FHA method is not accurate enough. Therefore, it is necessary to combine simulation and experimental testing to further limit the range of ω in equation (23).

[0106] The task of this operating condition is to find the value of ω in equation (23) such that the DC ripple amplitude A2ω of the converter output always varies within the allowable range, and that cosφ satisfies equation (21). Therefore, the process for determining the range of ω in operating condition 3 is as follows:

[0107] Initialize p=0 ;

[0108] Set the operating frequency of the resonant converter to ;

[0109] The measurement circuit signal and the result obtained according to equation (13) ;

[0110] judge Does it meet the requirements? And satisfying the constraints in equation (21), thereby determining whether to... Make incremental adjustments;

[0111] Where Step is the incremental frequency within each control cycle, and ω is designed as follows:

[0112] (twenty four)

[0114] In the formula, ω1[j] (j=0~p-1) is used to store possible frequencies. This represents the minimum value among multiple discrete values. This represents the maximum value among multiple discrete values. To make the range of ω under the above three operating conditions easier to understand, the design range of ω is summarized. The three operating conditions consider all possible operating situations. In practical applications, operating condition 1 is too idealized and therefore rarely occurs; operating condition 2 is valid under the premise that FHA is accurate and has certain limitations. However, it is the initialization condition for operating condition 3 and is valid under all circumstances.

[0115] Multi-condition frequency adaptive adjustment

[0116] Based on the instantaneous power model and frequency design for three operating conditions of the resonant converter, this invention proposes an adaptive frequency adjustment method. This method dynamically monitors load changes and adjusts the frequency in real time to gradually optimize the frequency range. The specific steps include:

[0117] Frequency range initialization: Based on the system load range and gain range design objectives, the FHA analysis method can be used to obtain the initial resonant frequency and its surrounding frequency range, so as to automatically adapt to changes in load.

[0118] Frequency step regulation: When the load changes, the system gradually increases or decreases the frequency through a multi-condition frequency regulator to optimize the voltage ripple amplitude. This method gradually converges to the optimal frequency by adjusting the frequency step size in real time, ensuring the ripple amplitude is within acceptable limits. The stability is within the acceptable range.

[0119] Frequency limiting control: When the system enters a high-power or high-load fluctuation state, unnecessary frequency fluctuations are reduced by limiting the frequency range, thereby reducing ripple and improving the reliability of the converter.

[0120] This application provides a system for implementing a DC suppression method for an isolated DC-DC resonant converter for energy storage. The system includes a DC-DC resonant converter module, a switching frequency monitoring module, an FHA analysis module, a real-time test and analysis module, a step size control module, and a switching frequency adjustment module. The switching frequency monitoring module monitors the operating frequency of the DC-DC resonant converter module. The FHA analysis module analyzes and derives the range of values ​​for the switching frequency when the DC-DC resonant converter module operates near its resonant frequency. The real-time test and analysis module analyzes and derives the range of values ​​for the switching frequency when the DC-DC resonant converter module operates far from its resonant frequency. The step size control module dynamically adjusts the frequency adjustment step size by monitoring changes in the output DC voltage ripple. The switching frequency adjustment module automatically adjusts the operating frequency of the DC-DC resonant converter module.

[0121] To facilitate multi-condition frequency adjustment, this invention uses film capacitors instead of traditional electrolytic capacitors, significantly improving the system's power density and safety. Film capacitors offer higher voltage withstand capability and longer lifespan, effectively reducing the negative impacts of ripple. Furthermore, the control circuit of this invention utilizes a digital control chip or microcontroller to calculate the frequency range, frequency step, and load status in real time, achieving adaptive adjustment of the frequency range across multiple operating conditions. The controller dynamically adjusts the frequency step size by monitoring changes in output voltage ripple, enabling finer frequency control.

[0122] This invention can be widely applied to energy storage systems, especially grid-connected energy storage, electric vehicle charging systems, distributed energy storage, and power converters. Experimental verification shows that, compared with existing technologies, this invention can maintain DC-side voltage ripple suppression under different loads and power demands, effectively improving the overall efficiency and reliability of the system. Compared with traditional fixed-frequency control methods, this invention provides a flexible and adaptable frequency step adjustment scheme, which can significantly improve the voltage output quality and lifespan of energy storage systems, providing a reliable and accurate solution for the design of high-efficiency, low-ripple power electronic converters. Attached Figure Description

[0123] Figure 1 This is a circuit diagram of an isolated DC-DC resonant converter.

[0124] Figure 2 This is the equivalent circuit model of an isolated DC-DC resonant converter;

[0125] Figure 3 This is a flowchart illustrating the determination of the range of ω values ​​in working condition 2 of the present invention.

[0126] Figure 4 This is a flowchart of updating the ω range in working condition 3 of the present invention;

[0127] Figure 5 This is a schematic diagram of the design program for the ω range under three working conditions of the present invention. Detailed Implementation

[0128] The techniques described below can be modified in various ways and have multiple embodiments, which are described in detail below with reference to the accompanying drawings. However, this does not mean that the techniques described below are limited to the specific embodiments. It should be understood that the present invention includes all similar modifications, equivalents, and substitutions without departing from the spirit and scope of the techniques described below.

[0129] This invention provides a DC suppression method and system for an isolated DC-DC resonant converter used in energy storage. The invention proposes a multi-condition frequency range adjustment method based on instantaneous power theory to effectively suppress DC voltage ripple in the isolated DC-DC resonant converter. This method, through adaptive frequency adjustment, enables the system to achieve low ripple output over a wide frequency range and under various operating conditions, thereby meeting the requirements of energy storage systems for high voltage quality, low loss, and high stability.

[0130] To address the response issues of traditional fixed-frequency methods to non-sinusoidal input voltages, this invention utilizes instantaneous power theory to construct a mathematical model of voltage ripple in a resonant network. By calculating the instantaneous power of the resonant inductor and capacitor, the amplitude of the output voltage ripple can be accurately predicted and controlled. The instantaneous power model can capture the voltage ripple characteristics of the converter under different frequencies and loads, providing a theoretical basis for multi-operating-condition frequency range design.

[0131] By establishing an instantaneous power model of ripple voltage, the relationship between ripple amplitude and load, power factor and switching frequency is obtained, which makes frequency regulation more precise and ensures that the system achieves the best voltage ripple suppression effect across the full power range.

[0132] A mathematical model of voltage ripple in a resonant network is constructed using instantaneous power theory, and a model of the DC voltage ripple amplitude of the resonant network output is derived.

[0133] Based on the system load range and gain range design objectives, the FHA analysis method can be used to obtain the initial resonant frequency and its surrounding frequency range, so as to automatically adapt to the relevant operating conditions when the load changes, and dynamically adjust the frequency range based on the specific operating conditions.

[0134] The topology of an isolated DC-DC resonant converter is as follows: Figure 1 As shown, its equivalent circuit model is as follows: Figure 2 As shown. High-frequency transformer input voltage:

[0135] (1)

[0137] In the formula V in ω represents the input voltage amplitude, ω represents the switching angular frequency, and t represents time.

[0138] The resonant current i can be expressed as:

[0139] (2)

[0141] In the formula, I represents the current amplitude, and φ represents the relationship between the current I and the input voltage v. in The phase difference.

[0142] According to equations (1) and (2), the instantaneous power p(t) can be obtained:

[0143] (3)

[0145] In the formula, p0 and p 0-2ω These represent the average active power and ripple power (2ω), respectively, which are derived from v in The fundamental frequency component of I is generated. h This represents the instantaneous harmonic power, which includes a 2ω component.

[0146] The ripple component of DC voltage is mainly introduced by the 2ω component of instantaneous power (defined as p). 2ω p 2ω By p 0-2ω and p h Composed of 2ω, it is represented as:

[0147] (4)

[0149] According to the law of conservation of energy, we can conclude that:

[0150] (5)

[0152] In the formula , , and Let Lr and C represent the instantaneous power of the resonant inductor, resonant capacitor, DC-side capacitor, and DC-side capacitive load, respectively. Assuming the equivalent resonant inductance and resonant capacitance of the resonant network are Lr and C, respectively, their instantaneous power can be expressed as:

[0153] (6)

[0155] Since the resonant network filters out higher harmonics, the output DC voltage is mainly affected by the fundamental and 2ω components of p(t). The power of higher harmonics (>2ω) can be ignored, and the output power pout can be expressed as:

[0156] (7)

[0158] The specific value of the output DC voltage ripple (2ω) can be directly derived using equation (7).

[0159] The output DC voltage is defined as u dc , is represented as:

[0160] (8)

[0162] U dc and They represent u respectively dc The DC section and the ripple section.

[0163] Substituting equation (8) into equation (7), we get:

[0164] (9)

[0166] C and R are the DC-side output capacitor and equivalent load, respectively.

[0167] definition According to equations (31) and (33), it can be seen that because there are in the high-frequency converter We can obtain the solution for x in the steady state:

[0168] (10)

[0170] in

[0171] (11)

[0173] Substituting equation (8) into equation (10), we get:

[0174] (12)

[0176] this The amplitude can be used Represented as:

[0177] (13)

[0179] Equation (13) is based on the instantaneous power theory, which holds true under any operating condition. It shows that after the DC-DC resonant converter is fully parameterized, the amplitude of the DC voltage ripple (2ω) is affected by the power factor (cosφ), the switching frequency (ω), and the transmission power (R), where... φ is the amplitude of the DC voltage ripple at the output of the resonant network, and cosφ is the power factor.

[0180] It is worth noting that in equation (13), The value of A2ω generally increases with the increase of transmission power, meaning that A2ω reaches its maximum value when the converter operates at rated power. Furthermore, the power factor mainly depends on the value of ω. Therefore, to ensure that the DC ripple of the converter does not exceed A2ω across the entire power range, the range of ω should be reasonably designed under rated power conditions.

[0181] This invention mainly relates to three operating conditions of resonant converters: the switching frequency of the resonant converter is at the resonant frequency, near the resonant frequency, and far from the resonant frequency.

[0182] Operating condition 1: Operating at the resonant frequency

[0183] When the resonant converter operates at its resonant frequency, the system exhibits the highest power transfer efficiency, and the voltage ripple is determined by the converter parameters and load characteristics. This operating condition is primarily used to optimize efficiency, but it is difficult to effectively suppress ripple under a fixed frequency.

[0184] If the DC-DC resonant converter operates precisely at its resonant frequency, the power factor will be 1, and the equivalent reactance Xeq will be zero. At this point:

[0185] (14)

[0187] Substituting equation (14) into equation (13), we get:

[0188] (15)

[0190] Obviously The value of is directly proportional to the output DC voltage and inversely proportional to the load, switching frequency, and DC capacitance. Therefore, in this case, The scope should meet the following requirements:

[0191] (16)

[0193] in This is the equivalent load at rated power. For u dc Permissible ripple.

[0194] Operating Condition 2: Operating within 5% of the resonant frequency range.

[0195] When load conditions vary slightly, the converter can operate within a range near the resonant frequency, and the frequency control method can adjust it to the minimum ripple range. Under this condition, frequency regulation can effectively reduce the amplitude of the output voltage ripple while maintaining a high power factor, making it suitable for load conditions with high ripple control requirements.

[0196] When the converter operates near the resonant frequency, the fundamental frequency analysis method (FHA) can be used to analyze the converter with good accuracy. Therefore, the range of values ​​for ω is derived using the FHA analysis method.

[0197] For a series resonant circuit, the equivalent circuit of the resonant network of the resonant converter is as follows: Figure 2 As shown, its power factor can be expressed as:

[0198] (17)

[0200] Where Req represents the equivalent resistance, which is related to the high-frequency transformer turns ratio n and the load R. The following four steps are then listed to determine the range of ω:

[0201] Step 1: Determine the initial range of cosφ:

[0202] Ignoring transformer, semiconductor, and line losses, output active power satisfy:

[0203] (18)

[0205] Assuming the maximum allowable current is We can obtain:

[0206] (19)

[0208] Therefore, the initial range of cosφ can be defined as:

[0209] (20)

[0211] Step 2: Limit the range of cosφ

[0212] When the converter operates near its resonant frequency, the fundamental frequency analysis (FHA) method provides good accuracy, as cosφ approaches 1. Therefore, δ ≤ cosφ ≤ 1, where δ is a constant close to 1. Combining (20), the range of cosφ is limited to:

[0213] (twenty one)

[0215] Step 3: Derive the initial range of ω:

[0216] Substituting equation (17) into equation (21), we get:

[0217] (twenty two)

[0219] Step 4: Confirm the range of ω to satisfy Amplitude Limitation

[0220] Based on step 3, further determine the range of ω to satisfy... Amplitude limits, such as Figure 3 As shown, Step is the incremental frequency within each control cycle, and ω1 and ω2 represent the lower and upper limits in equation (22), respectively. It is expressed as:

[0221] (twenty three)

[0223] in, This refers to the minimum value within the allowed range of frequency values. This refers to the maximum value within the allowed range of frequency values.

[0224] The specific steps are as follows:

[0225] initialization , , V in n, C, i = 0;

[0226] set up and will Substituting into equation (17) yields According to equation (13), ;

[0227] Will Compare with the allowable DC ripple threshold to determine if it is acceptable. Make incremental adjustments.

[0228] Operating Condition 3: Operating far from the resonant frequency, i.e., within 5% of the resonant frequency.

[0229] When power demand changes drastically or load fluctuates significantly, the system can operate far from the resonant frequency. In this case, through dynamic adjustment of the frequency range using multi-condition frequency design, the frequency range can disperse the ripple spectrum, suppress the influence of high-frequency harmonics, and effectively control voltage quality.

[0230] When the converter operates far from the resonant frequency, the FHA method is not accurate enough. Therefore, it is necessary to combine simulation and experimental testing. The comprehensive simulation uses simulation testing to obtain the theoretical power factor; the experimental testing aims to obtain the actual power factor of the resonant network and obtain the ripple based on the power factor and switching frequency. Further restrictions are placed on the range of ω in equation (23).

[0231] The task of this operating condition is to find the value of ω in equation (23) such that the DC ripple amplitude A2ω of the converter output always varies within the allowable range, and that cosφ satisfies equation (21). Therefore, the process for determining the range of ω in operating condition 3 is as follows: Figure 4 As shown,

[0232] Initialize p=0 ;

[0233] Set the operating frequency of the resonant converter to ;

[0234] The power factor cosφ of the resonant network is obtained by measuring the circuit signal, and then obtained according to equation (13). ;

[0235] judge Does it meet the requirements? And satisfying the constraints in equation (21), thereby determining whether to... Make incremental adjustments;

[0236] Where Step is the incremental frequency within each control cycle, and ω is designed as follows:

[0237] (twenty four)

[0239] In the formula, ω1[j] (j=0~p-1) is used to store possible frequencies. This represents the minimum value among multiple discrete values. This represents the maximum value among multiple discrete values. To make the range of ω under the above three operating conditions easier to understand, the design range of ω is summarized. The three operating conditions consider all possible operating situations. In practical applications, operating condition 1 is too idealized and therefore rarely occurs; operating condition 2 is valid under the premise that FHA is accurate and has certain limitations. However, it is the initialization condition for operating condition 3 and is valid under all circumstances.

[0240] Multi-condition frequency adaptive adjustment

[0241] Frequency design based on instantaneous power model and three operating conditions of resonant converter, such as Figure 5As shown, this invention proposes an adaptive frequency adjustment method. This method dynamically monitors load changes and adjusts the frequency in real time to gradually optimize the frequency range. Specifically, as... Figure 3 and Figure 4 As shown, the specific steps include:

[0242] Frequency range initialization: Based on the system load range and gain range design objectives, the FHA analysis method can be used to obtain the initial resonant frequency and its surrounding frequency range, so as to automatically adapt to changes in load.

[0243] Frequency step regulation: When the load changes, the system gradually increases or decreases the frequency through a multi-condition frequency regulator to optimize the voltage ripple amplitude. This method gradually converges to the optimal frequency by adjusting the frequency step size in real time, ensuring the ripple amplitude is within acceptable limits. Stable within the acceptable range.

[0244] Frequency limiting control: When the system enters a high-power or high-load fluctuation state, unnecessary frequency fluctuations are reduced by limiting the frequency range, thereby reducing ripple and improving the reliability of the converter.

[0245] This application provides a system for implementing a DC suppression method for an isolated DC-DC resonant converter for energy storage. The system includes a DC-DC resonant converter module, a switching frequency monitoring module, an FHA analysis module, a real-time test and analysis module, a step size control module, and a switching frequency adjustment module. The switching frequency monitoring module monitors the operating frequency of the DC-DC resonant converter module. The FHA analysis module analyzes and derives the range of values ​​for the switching frequency when the DC-DC resonant converter module operates near its resonant frequency. The real-time test and analysis module analyzes and derives the range of values ​​for the switching frequency when the DC-DC resonant converter module operates far from its resonant frequency. The step size control module dynamically adjusts the frequency adjustment step size by monitoring changes in the output DC voltage ripple. The switching frequency adjustment module automatically adjusts the operating frequency of the DC-DC resonant converter module.

[0246] To facilitate multi-condition frequency adjustment, this invention uses film capacitors instead of traditional electrolytic capacitors, significantly improving the system's power density and safety. Film capacitors offer higher voltage withstand capability and longer lifespan, effectively reducing the negative impacts of ripple. Furthermore, the control circuit of this invention utilizes a digital control chip or microcontroller to calculate the frequency range, frequency step, and load status in real time, achieving adaptive adjustment of the frequency range across multiple operating conditions. The controller dynamically adjusts the frequency step size by monitoring changes in output voltage ripple, enabling finer frequency control.

[0247] Although the present invention has been described in detail above with general descriptions and specific embodiments, some modifications or improvements can be made to it. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Other changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention are still included within the scope of protection of the present invention.

Claims

1. A DC suppression method for an isolated DC-DC resonant converter for energy storage, characterized in that, include: S1. Using instantaneous power theory, construct a mathematical model of the voltage ripple of the resonant network, and derive the amplitude model of the DC voltage ripple at the output of the resonant network: (13)； in, The values ​​are: DC voltage ripple amplitude of the resonant network output, cosφ is the power factor, ω is the switching frequency, R is the transmission power, and U... dc For output DC voltage u dc DC section, V in Where Cr is the input voltage amplitude, Cr is the resonant capacitor, and Lr is the resonant inductor; S2. Based on the system load range and gain range design objectives, the FHA analysis method can be used to obtain the initial resonant frequency and its surrounding frequency range, so as to automatically adapt to the working conditions corresponding to the relevant frequencies when the load changes, and dynamically adjust the frequency range based on the specific working conditions. S2.1 When the switching frequency of the resonant converter equals the resonant frequency, the power factor is 1 and the equivalent reactance Xeq is zero; at this time: (14)； Substituting equation 14 into equation 13, we get: (15)； Therefore, The range should satisfy: (16)； in, This is the equivalent load at rated power. For u dc Permissible ripple; S2.2 When the switching frequency of the resonant converter is within 5% of the resonant frequency, the range of ω is derived by analyzing the resonant converter using the fundamental frequency analysis method. Based on the equivalent circuit structure of the series resonant circuit network, the power factor model of the resonant circuit is obtained as follows: (17)； Where Req represents the equivalent resistance, which is related to the high-frequency transformer turns ratio n and the load R; assuming the maximum allowable current is Imax, using the fundamental frequency analysis method, the range of cosφ is obtained as follows: (21)； This operating condition is valid only if the FHA is effective. ≤cosφ≤1, It is a constant close to 1. Substituting Equation 17 into Equation 21, we obtain the initial range of ω as: (22)； Based on obtaining the initial range of ω, it is further determined that the range of ω satisfies Amplitude limit, which is expressed as: (23)； in, This refers to the minimum value within the allowed range of frequency values. This refers to the maximum value within the allowed range of frequency values; S2.3 When the switching frequency of the resonant converter is far from the resonant frequency, the range of ω is further limited by comprehensive simulation and experimental testing, so that ω satisfies: (24)； Where ω1[j], j=0~p-1, is used to store the frequency of possible values. This represents the minimum value among multiple discrete values. It represents the maximum value among multiple discrete values.

2. The method according to claim 1, characterized in that, The high-frequency input voltage of the isolated DC-DC resonant converter is: (1)； The resonant current i is: (2)； Based on the high-frequency input voltage and the resonant current, the instantaneous power p(t) of the isolated DC-DC resonant converter is: (3)； Where p0 and p0-2ω represent the average active power and ripple power, respectively, which are generated by the fundamental components of Vin and I, and Ph is the instantaneous harmonic power, which includes the 2ω component.

3. The method according to claim 2, characterized in that, The isolated DC-DC resonant converter is a CLLLC resonant converter or an LLC resonant converter.

4. The method according to claim 1, characterized in that, Based on obtaining the initial range of ω, further determining that the range of ω satisfies the A2ω amplitude limit specifically includes: initialization , , V in n, C, i = 0; set up and will Substituting into equation 17 yields According to Equation 13, ; Will Compare with the allowable DC ripple threshold to determine if it is acceptable. Make incremental adjustments.

5. The method according to claim 3, characterized in that, The capacitor of the resonant converter is a thin-film capacitor.

6. The method according to claim 2, characterized in that, The 2ω portion of the instantaneous power p(t) is introduced, where p2ω is composed of p0-2ω and ph2ω, and is expressed as: (4)； According to the law of conservation of energy, we can conclude that: (5)； In the formula , , and Let Lr and C represent the instantaneous power of the resonant inductor, resonant capacitor, DC-side capacitor, and DC-side capacitive load, respectively. Assuming the equivalent resonant inductance and resonant capacitance of the resonant network are Lr and C, respectively, their instantaneous power can be expressed as: (6)； Since the resonant network filters out higher harmonics, the output DC voltage is mainly affected by the fundamental and 2ω components of p(t). Ignoring higher harmonic power, the output power is obtained. It can be represented as: (7)。 7. The method according to claim 6, characterized in that, The specific value of the output DC voltage ripple is derived using Equation 7, and the output DC voltage u is... dc Specifically: (8)； Among them, U dc and They represent u respectively dc The DC portion and the ripple portion; Substituting equation 8 into equation 7, we get: (9)； Where C is the DC-side output capacitor and R is the DC-side equivalent load.

8. The method according to claim 7, characterized in that, definition According to equations 7 and 9, and in high-frequency converters... We can obtain the solution for x in the steady state: (10)； in (11)； Substituting Equation 8 into Equation 10, the DC component and ripple component of the output DC voltage can be expressed as follows: (12)； The amplitude of the ripple portion of the output DC voltage can be obtained based on the DC portion and the ripple portion of the output DC voltage.

9. The method according to claim 1, characterized in that, After deriving the power factor model of the resonant circuit based on the equivalent circuit structure of the series resonant circuit network, the initial range of cosφ is further determined: (18)； Assuming the maximum allowable current is Imax, we can obtain: (19)； Therefore, the initial range of cosφ can be defined as: (20)； The limited range of cosφ can be obtained based on the initial range of cosφ.

10. A system for implementing the DC suppression method for an isolated DC-DC resonant converter for energy storage according to any one of claims 1-9, characterized in that, The system includes a DC-DC resonant converter module, a switching frequency monitoring module, an FHA analysis module, a real-time test and analysis module, a step size control module, and a switching frequency adjustment module. The switching frequency monitoring module monitors the operating frequency of the DC-DC resonant converter module. The FHA analysis module analyzes and derives the range of values ​​for the switching frequency when the DC-DC resonant converter module operates near its resonant frequency. The real-time test and analysis module analyzes and derives the range of values ​​for the switching frequency when the DC-DC resonant converter module operates far from its resonant frequency. The step size control module dynamically adjusts the frequency adjustment step size by monitoring changes in the output DC voltage ripple. The switching frequency adjustment module automatically adjusts the operating frequency of the DC-DC resonant converter module.

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