DC suppression method and system of isolated DC-DC resonant converter for energy storage

Abstract

The invention discloses a DC suppression method and system for an isolated DC-DC resonant converter for energy storage, and aims to optimize voltage ripples of a resonant network. A voltage ripple mathematical model of a resonant network is constructed by using an instantaneous power theory, instantaneous power of a resonant inductor and a resonant capacitor is calculated, and three working conditions that the switching frequency of the resonant converter is equal to the resonant frequency, near the resonant frequency and far away from the resonant frequency are monitored. The range limitation of the switching frequency is determined according to a corresponding method when the resonant converter is in a corresponding working condition, so that the switching frequency of the resonant converter is dynamically adjusted along with different working conditions, output direct current ripples are effectively suppressed, and the reliability of an electric energy quality assurance system is improved.

Description

Technical Field

[0001] The invention belongs to the field of DC-DC resonant converter DC suppression, and in particular relates to a DC suppression method and system for an isolated DC-DC resonant converter for energy storage. Background Art

[0002] Isolated DC-DC resonant converters are widely used in the efficient transmission and distribution of energy in energy storage systems. The stability of their output voltage is crucial to the operating efficiency and safety of the system. However, since the input voltage of isolated DC-DC resonant converters is non-sinusoidal, it is easy to generate significant DC voltage ripple, which in turn leads to a decrease in the power quality of the system and even affects the life of the energy storage equipment. Conventional ripple suppression methods mainly rely on fixed frequency control, which is difficult to effectively suppress ripple under dynamic loads and wide-range power fluctuations. According to existing research, the fundamental approximation method FHA, simulation analysis method SA and time domain analysis method TDA are mainly used to analyze the voltage ripple of the resonant network. However, the effectiveness of FHA is limited to the vicinity of the resonant frequency point of the converter; SA requires a lot of analysis work and the results are not intuitive enough; TDA requires establishing the state equations under each working mode one by one, which significantly increases the computational complexity. At the same time, traditional methods usually use large-capacity electrolytic capacitors to reduce the ripple amplitude, but this increases the volume and weight of the system, which is not conducive to the improvement of power density. Summary of the invention

[0003] The present invention focuses on the problems existing in the above-mentioned prior art and provides a DC suppression method and system for an isolated DC-DC resonant converter for energy storage. The method can automatically adjust the frequency range under different load conditions through instantaneous power analysis and multi-operating frequency range design, effectively reduce DC voltage ripple, improve power quality, and ensure system reliability. The present invention is mainly used to improve the voltage output quality of the energy converter in the energy storage system, reduce the power transmission loss caused by voltage ripple, and improve the overall reliability of the system. By adopting a multi-operating frequency range design, the method can dynamically adjust the switching frequency under different working conditions to maintain the output voltage stability and extend the service life of the energy storage device. It is particularly suitable for power grid energy storage, electric vehicle charging devices and other power conversion applications that require strict voltage regulation with high power density and high conversion efficiency requirements.

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

[0005] In order to solve the problem of the response of the traditional fixed frequency method to non-sinusoidal input voltage, the present invention uses the instantaneous power theory to construct a voltage ripple mathematical model of the 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 the design of multi-operating frequency ranges.

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

[0007] The voltage ripple mathematical model of the resonant network is constructed using the instantaneous power theory, and the output DC voltage ripple amplitude model of the resonant network is obtained. According to the design goals of the system load range and gain range, the FHA analysis method is used to obtain the initialization 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.

[0008] Based on the isolated DC-DC resonant converter topology and its equivalent circuit model, it can be seen that the high-frequency transformer input voltage is set as:

[0009]

[0010] Where V in represents the input voltage amplitude, ω represents the switching angular frequency, and t represents time.

[0011] The resonant current i can be expressed as:

[0012]

[0013] Where I represents the current amplitude, Represents the current I and input voltage v in The phase difference.

[0014] According to equations (1) and (2), the instantaneous power p(t) can be obtained:

[0015]

[0016] Where p 0 and p 0-2ω They represent the average active power and ripple power (2ω), which are represented by v in and the fundamental part of I. h is the instantaneous harmonic power, including the 2ω component.

[0017] The ripple part of the DC voltage is mainly introduced by the 2ω part of the instantaneous power (defined as p2ω ). 2ω By p 0-2ω and p h The 2ω composition is expressed as:

[0018]

[0019] According to the law of conservation of energy, we can get:

[0020] p(t)=p Lr +p Cr +p C +p R (5)

[0021] In the formula p C and p R They represent the resonant inductor, resonant capacitor, instantaneous power of the DC side capacitor, and instantaneous power of the DC measuring capacitive load. Assuming that the equivalent resonant inductor and resonant capacitor of the resonant network are Lr and C respectively, their instantaneous power can be expressed as:

[0022]

[0023] Since the resonant network has a filtering effect on high-order harmonics, the output DC voltage is mainly affected by the fundamental part and 2ω part of p(t), and the high-order harmonic power (>2ω) can be ignored. The output power pout can be expressed as:

[0024] p out =p C +p R =p 0 +p 2ω -p Lr -p Cr (7)

[0025] The specific value of the output DC voltage ripple (2ω) can be directly derived using equation (7).

[0026] The output DC voltage is defined as u dc , expressed as:

[0027]

[0028] Among them U dc and Respectively represent u dc The DC part and the ripple part.

[0029] Substituting formula (8) into formula (7), we can obtain:

[0030]

[0031] Where C and R are the DC side output capacitor and equivalent load respectively.

[0032] definition According to equations (7) and (9), since ωRC>>1 in the high-frequency converter, the solution of x in the steady state can be obtained:

[0033]

[0034] in

[0035]

[0036] Substituting formula (8) into formula (10), we can obtain:

[0037]

[0038] this The amplitude can be obtained by A 2ω It is expressed as:

[0039]

[0040] Formula (13) is based on the instantaneous power theory, which is valid under any working conditions. It shows that after the DC-DC resonant converter is designed, the amplitude of the DC voltage ripple (2ω) will be affected by the power factor. The effect of switching frequency (ω) and transmission power (R), where A 2ω is the DC voltage ripple amplitude of the resonant network output,

[0041] It is worth noting that in formula (13), A 2ω The value of increases with the increase of transmission power, that is, when the converter works at rated power, A 2ω In addition, the power factor depends mainly on the value of ω. Therefore, in order to ensure that the DC ripple of the converter does not exceed A in the full power range 2ω , the range of ω should be reasonably designed under rated power.

[0042] The present invention mainly relates to three working conditions of the resonant converter, namely, the switching frequency of the resonant converter is at the resonant frequency, near the resonant frequency and far from the resonant frequency.

[0043] Condition 1: Working at the resonant frequency

[0044] When the resonant converter operates at the resonant frequency, the system has the highest power transmission efficiency, and the voltage ripple is determined by the converter parameters and load characteristics. This operating condition is mainly used to optimize efficiency, but it is difficult to effectively suppress the ripple under the condition of fixed frequency.

[0045] If the DC-DC resonant converter operates accurately at the resonant frequency, the power factor will be 1 and the equivalent reactance Xeq will be zero. At this time:

[0046]

[0047] Substituting formula (14) into formula (13), we can obtain:

[0048] A 2w =U dc / (3RωC) (15)

[0049] Obviously A 2ω The value of is proportional to the output DC voltage and inversely proportional to the load, switching frequency and DC capacitance. Therefore, in this case, the range of ω should satisfy:

[0050] ω>U dc / (3R N CΔ ripple ) (16)

[0051] Where R N is the equivalent load at rated power, Δ ripple for u dc Allowable ripple.

[0052] Working condition 2: Working within 5% of the resonant frequency

[0053] When the load condition changes slightly, the converter can operate in the range near the resonant frequency, and the frequency control method can be adjusted to the minimum ripple range. Under this condition, the amplitude of the output voltage ripple can be effectively reduced by frequency regulation while maintaining a high power factor, which is suitable for load conditions with high requirements for ripple control.

[0054] When the converter works near the resonant frequency point, the fundamental wave analysis (FHA) method has good accuracy in analyzing the converter. Therefore, the FHA analysis method is used to derive the value range of ω.

[0055] For the series resonant circuit, based on the resonant network equivalent circuit of the resonant converter, its power factor can be expressed as:

[0056]

[0057] 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 listed to determine the range of ω:

[0058] Step 1: Determine The initial range is:

[0059] Ignoring transformer, semiconductor and line losses, the output active power pout0 satisfy:

[0060]

[0061] Assume that the maximum allowable current is I max , we can get:

[0062]

[0063] therefore The initial range of can be defined as:

[0064]

[0065] Step 2: Limitations Range

[0066] When the converter operates near the resonant frequency, the fundamental wave analysis (FHA) method can be used to analyze the converter with good accuracy. is close to 1. Therefore, where δ is a constant close to 1. Combining (20), The scope is restricted to:

[0067]

[0068] Step 3: Derive the initial range of ω:

[0069] Substituting formula (17) into formula (21), we can obtain:

[0070]

[0071] Step 4: Confirm the range of ω to meet the A2ω amplitude limit

[0072] Based on step 3, the ω range is further determined to meet the A2ω amplitude limit, where Step is the incremental frequency within each control cycle, ω1 and ω2 represent the lower limit and upper limit in equation (22), respectively, which represent the frequency range allowed to meet the power transmission requirements. Figure 3 The process shown obtains the frequency range that meets the ripple requirement, which is expressed as:

[0073] ω[0]≤ω≤ω[i-1] (23)

[0074] The specific steps are:

[0075] Initialize L r , C r , Δ ripple 、V in ,n,C,i=0;

[0076] Set ω = ω 1 , and substitute ω into equation (17) to obtain According to formula (13), we can obtain A 2ω ;

[0077] A 2ω It is compared with the allowed DC ripple threshold to determine whether to make incremental adjustments to ω.

[0078] Working condition 3: Working far from the resonant frequency, that is, within 5% of the resonant frequency

[0079] In the case of drastic changes in power demand or large load fluctuations, the system can operate in a range far away from the resonant frequency. At this time, through the dynamic adjustment of multi-operating frequency design, the frequency range can disperse the ripple spectrum, suppress the impact of high-frequency harmonics, and effectively control the voltage quality.

[0080] When the converter operates far away from the resonant frequency, the FHA method is not accurate enough, so it is necessary to combine simulation and experimental tests to further limit the range of ω in equation (23).

[0081] The task of this working condition is to find the value of ω in equation (23) so that the converter output DC ripple amplitude A2ω always changes within the allowable range and Satisfies equation (21). Therefore, the process for determining the ω range in working condition 3 is:

[0082] Initialize p = 0, ω = ω[0];

[0083] The operating frequency of the resonant converter is set to ω;

[0084] Measure the circuit signal and obtain A according to formula (13) 2ω ;

[0085] Judgment A 2ω Does it meet A? 2ω <Δ ripple And it satisfies the restrictions in formula (21), and determines whether to make incremental adjustments to ω;

[0086] Where Step is the incremental frequency in each control cycle, and ω is designed as:

[0087] ω 1 [0]≤ω≤ω 1 [p-1] (24)

[0088] In the formula, ω1[j] (j = 0 ~ p-1) is used to store possible frequencies. In order to make the range of ω under the above three conditions easier to understand, the design range of ω is summarized. The three conditions take into account all possible operating conditions. In practical applications, condition 1 is too idealized and therefore rarely occurs; condition 2 is established under the premise that FHA is accurate and has certain limitations. However, it is the initialization condition of condition 3 and is valid in any case.

[0089] Based on the instantaneous power model and the frequency design of three working conditions of the resonant converter, the present invention proposes an adaptive frequency adjustment method, which gradually optimizes the frequency range by dynamically monitoring the load changes and adjusting the frequency in real time. As shown, the specific steps include:

[0090] Frequency range initialization: Based on the system load range and gain range design goals, the FHA analysis method can be used to obtain the initial resonant frequency and its surrounding frequency range so that it can automatically adapt when the load changes.

[0091] Frequency step adjustment: When the load changes, the system gradually increases or decreases the frequency through the multi-condition frequency regulator to optimize the voltage ripple amplitude. This method gradually converges to the optimal frequency by adjusting the frequency step in real time to ensure the ripple amplitude A 2ω Stable within the allowable range.

[0092] Frequency limit 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.

[0093] The present invention is provided with a system for realizing a DC suppression method of an isolated DC-DC resonant converter for energy storage. The system is provided with a DC-DC resonant converter module, a switching frequency monitoring module, a FHA analysis module, a real-time test analysis module, a step control module and a switching frequency adjustment module. The switching frequency monitoring module is used to monitor the operating frequency of the DC-DC resonant converter module. The FHA analysis module is used to analyze and derive the value range of the switching frequency when the DC-DC resonant converter module operates near the resonant frequency. The real-time test analysis module is used to analyze and derive the value range of the switching frequency when the DC-DC resonant converter module operates far from the resonant frequency. The step control module dynamically adjusts the frequency adjustment step by monitoring the change of the output DC voltage ripple. The switching frequency adjustment module is used to automatically adjust the operating frequency of the DC-DC resonant converter module.

[0094] In order to cooperate with multi-operating frequency regulation, the present invention adopts film capacitors to replace traditional electrolytic capacitors, which significantly improves the power density and safety of the system. Film capacitors have higher voltage tolerance and longer service life, and can effectively reduce the negative impact of ripple. In addition, the control circuit of the present invention uses a digital control chip or a microcontroller to calculate the frequency range, frequency step and load status in real time to achieve adaptive regulation of the frequency range of multiple operating conditions. The controller dynamically adjusts the frequency step by monitoring the changes in the output voltage ripple to achieve more precise frequency control.

[0095] The invention can be widely used in energy storage systems, especially grid energy storage, electric vehicle charging systems, distributed energy storage and power converters. Experimental verification shows that compared with the prior art, the present invention can maintain the suppression effect of DC side voltage ripple under different loads and power requirements, effectively improving the overall efficiency and reliability of the system. Compared with the traditional fixed frequency control method, the present invention provides a flexible and adaptable frequency step adjustment scheme, which can greatly improve the voltage output quality and service life of the energy storage system, and provide a reliable and accurate solution for the design of high-efficiency, low-ripple power electronic converters. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Figure 1 This is the circuit diagram of an isolated DC-DC resonant converter;

[0097] Figure 2 It is the equivalent circuit model of isolated DC-DC resonant converter;

[0098] Figure 3 A flow chart for determining the range of ω values ​​in working condition 2 of the present invention;

[0099] Figure 4 This is a flow chart of updating the ω range in working condition 3 of the present invention;

[0100] Figure 5 Schematic diagram of the program design for the three operating conditions ω range of the present invention. DETAILED DESCRIPTION

[0101] The technology described below can be transformed in many ways and can have many embodiments, which are described in detail with reference to the accompanying drawings in specific embodiments. However, this does not mean that the technology described below is limited to specific embodiments. It should be understood that the present invention includes all similar modifications, equivalents and substitutions without departing from the spirit and technical scope of the technology described below.

[0102] The present invention first provides a DC suppression method for an isolated DC-DC resonant converter for energy storage, which is based on the multi-operating frequency range adjustment of instantaneous power theory, thereby achieving effective suppression of the DC voltage ripple of the isolated DC-DC resonant converter. The method enables the system to achieve low ripple output in a wide frequency range and multiple operating conditions through frequency adaptive adjustment, thereby meeting the requirements of the energy storage system for high voltage quality, low loss and high stability.

[0103] In order to solve the problem of the response of the traditional fixed frequency method to non-sinusoidal input voltage, the present invention uses the instantaneous power theory to construct a voltage ripple mathematical model of the 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 the design of multi-operating frequency ranges.

[0104] By establishing an instantaneous power model of the ripple voltage, the relationship between the ripple amplitude and the load, power factor and switching frequency is obtained, which makes the frequency regulation more accurate and ensures that the system achieves the best voltage ripple suppression effect within the full power range.

[0105] The voltage ripple mathematical model of the resonant network is constructed using the instantaneous power theory, and the output DC voltage ripple amplitude model of the resonant network is obtained. According to the design goals of the system load range and gain range, the FHA analysis method is used to obtain the initialization 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.

[0106] Isolated DC-DC resonant converter topology such as Figure 1 As shown, its equivalent circuit model is as follows Figure 2 As shown. High frequency transformer input voltage:

[0107]

[0108] Where V in represents the input voltage amplitude, ω represents the switching angular frequency, and t represents time.

[0109] The resonant current i can be expressed as:

[0110]

[0111] Where I represents the current amplitude, Represents the current I and input voltage v in The phase difference.

[0112] According to equations (1) and (2), the instantaneous power p(t) can be obtained:

[0113]

[0114] Where p 0 and p 0-2ω They represent the average active power and ripple power (2ω), which are represented by v in and the fundamental part of I. h is the instantaneous harmonic power, including the 2ω component.

[0115] The ripple part of the DC voltage is mainly introduced by the 2ω part of the instantaneous power (defined as p 2ω ). 2ω By p 0-2ω and p h The 2ω composition is expressed as:

[0116]

[0117] According to the law of conservation of energy, we can get:

[0118] p(t)=p Lr +p Cr +p C +p R (5)

[0119] In the formula p C and p R They represent the resonant inductor, resonant capacitor, instantaneous power of the DC side capacitor, and instantaneous power of the DC measuring capacitive load. Assuming that the equivalent resonant inductor and resonant capacitor of the resonant network are Lr and C respectively, their instantaneous power can be expressed as:

[0120]

[0121] Since the resonant network has a filtering effect on high-order harmonics, the output DC voltage is mainly affected by the fundamental part and 2ω part of p(t), and the high-order harmonic power (>2ω) can be ignored. The output power pout can be expressed as:

[0122] p out =p C +p R =p 0 +p 2ω -p Lr -p Cr (7)

[0123] The specific value of the output DC voltage ripple (2ω) can be directly derived using equation (7).

[0124] The output DC voltage is defined as u dc , expressed as:

[0125]

[0126] Among them U dc and Respectively represent u dc The DC part and the ripple part.

[0127] Substituting formula (8) into formula (7), we can obtain:

[0128]

[0129] Where C and R are the DC side output capacitor and equivalent load respectively.

[0130] definition According to equations (31) and (33), since ωRC>>1 in the high-frequency converter, the solution of x in the steady state can be obtained:

[0131]

[0132] in

[0133]

[0134] Substituting formula (8) into formula (10), we can obtain:

[0135]

[0136] this The amplitude can be obtained by A 2ω It is expressed as:

[0137]

[0138] Formula (13) is based on the instantaneous power theory, which is valid under any working conditions. It shows that after the DC-DC resonant converter is designed, the amplitude of the DC voltage ripple (2ω) will be affected by the power factor. The effect of switching frequency (ω) and transmission power (R), where A 2ω is the DC voltage ripple amplitude of the resonant network output, is the power factor.

[0139] It is worth noting that in formula (13), A 2ω The value of increases with the increase of transmission power, that is, A2ω reaches its maximum value when the converter works at rated power. In addition, the power factor mainly depends on the value of ω. Therefore, in order to ensure that the DC ripple of the converter does not exceed A2ω within the full power range, the range of ω should be reasonably designed at rated power.

[0140] The present invention mainly relates to three working conditions of the resonant converter, namely, the switching frequency of the resonant converter is at the resonant frequency, near the resonant frequency and far from the resonant frequency.

[0141] Condition 1: Working at the resonant frequency

[0142] When the resonant converter operates at the resonant frequency, the system has the highest power transmission efficiency, and the voltage ripple is determined by the converter parameters and load characteristics. This operating condition is mainly used to optimize efficiency, but it is difficult to effectively suppress the ripple under the condition of fixed frequency.

[0143] If the DC-DC resonant converter operates accurately at the resonant frequency, the power factor will be 1 and the equivalent reactance Xeq will be zero. At this time:

[0144]

[0145] Substituting formula (14) into formula (13), we can obtain:

[0146] A 2w =U dc / (3RωC) (15)

[0147] Obviously A 2ω The value of is proportional to the output DC voltage and inversely proportional to the load, switching frequency and DC capacitance. Therefore, in this case, the range of ω should satisfy:

[0148] ω>U dc / (3R N CΔ ripple ) (16)

[0149] Where R N is the equivalent load at rated power, Δ ripple for u dc Allowable ripple.

[0150] Working condition 2: Working within 5% frequency range around the resonant frequency

[0151] When the load condition changes slightly, the converter can operate in the range near the resonant frequency, and the frequency control method can be adjusted to the minimum ripple range. Under this condition, the amplitude of the output voltage ripple can be effectively reduced by frequency regulation while maintaining a high power factor, which is suitable for load conditions with high requirements for ripple control.

[0152] When the converter works near the resonant frequency point, the fundamental wave analysis (FHA) method has good accuracy in analyzing the converter. Therefore, the FHA analysis method is used to derive the value range of ω.

[0153] For the series resonant circuit, the resonant network equivalent circuit of the resonant converter is as follows: Figure 2 As shown, its power factor can be expressed as:

[0154]

[0155] 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 listed to determine the range of ω:

[0156] Step 1: Determine The initial range is:

[0157] Ignoring transformer, semiconductor and line losses, the output active power p out0 satisfy:

[0158]

[0159] Assume that the maximum allowable current is I max , we can get:

[0160]

[0161] therefore The initial range of can be defined as:

[0162]

[0163] Step 2: Limitations Range

[0164] When the converter operates near the resonant frequency, the fundamental wave analysis (FHA) method can be used to analyze the converter with good accuracy. is close to 1. Therefore, where δ is a constant close to 1. Combining (20), The scope is restricted to:

[0165]

[0166] Step 3: Derive the initial range of ω:

[0167] Substituting formula (17) into formula (21), we can obtain:

[0168]

[0169] Step 4: Confirm the range of ω to satisfy A 2ω Amplitude Limit

[0170] Based on step 3, the ω range is further determined to meet A 2ω Amplitude limits, such as Figure 3As shown, Step is the incremental frequency in each control cycle, ω1 and ω2 represent the lower limit and upper limit in equation (46) respectively. It is expressed as:

[0171] ω[0]≤ω≤ω[i-1] (23)

[0172] The specific steps are:

[0173] Initialize L r , C r , Δ ripple 、V in ,n,C,i=0;

[0174] Set ω = ω 1 , and substitute ω into equation (17) to obtain According to formula (13), we can obtain A 2ω ;

[0175] A 2ω It is compared with the allowed DC ripple threshold to determine whether to make incremental adjustments to ω.

[0176] Working condition 3: Working far from the resonant frequency, that is, within 5% of the resonant frequency

[0177] In the case of drastic changes in power demand or large load fluctuations, the system can operate in a range far away from the resonant frequency. At this time, through the dynamic adjustment of multi-operating frequency design, the frequency range can disperse the ripple spectrum, suppress the impact of high-frequency harmonics, and effectively control the voltage quality.

[0178] When the converter works far away from the resonant frequency point, the FHA method is not accurate enough, so it is necessary to combine simulation and experimental testing. The comprehensive simulation uses simulation testing to obtain the theoretical power factor; the experimental test aims to obtain the actual power factor of the resonant network and obtain the ripple based on the power factor and switching frequency. Further restrict the range of ω in formula (23)

[0179] The task of this working condition is to find the value of ω in equation (23) so that the converter output DC ripple amplitude A2ω always changes within the allowable range and Satisfies equation (21). Therefore, the process of determining the ω range in working condition 3 is as follows: Figure 4 As shown,

[0180] Initialize p = 0, ω = ω[0];

[0181] The operating frequency of the resonant converter is set to ω;

[0182] Measuring circuit signals to obtain the power factor of the resonant network Then, according to formula (13), we can obtain A 2ω ;

[0183] Judgment A 2ω Does it meet A? 2ω <Δ ripple And it satisfies the restrictions in formula (21), and determines whether to make incremental adjustments to ω;

[0184] Where Step is the incremental frequency in each control cycle, and ω is designed as:

[0185] ω 1 [0]≤ω≤ω 1 [p-1] (24)

[0186] In the formula, ω1[j] (j = 0 ~ p-1) is used to store possible frequencies. In order to make the range of ω under the above three conditions easier to understand, the design range of ω is summarized. The three conditions take into account all possible operating conditions. In practical applications, condition 1 is too idealized and therefore rarely occurs; condition 2 is established under the premise that FHA is accurate and has certain limitations. However, it is the initialization condition of condition 3 and is valid in any case.

[0187] Frequency design based on instantaneous power model and three working conditions of resonant converter, such as Figure 5 As shown, the present invention proposes an adaptive frequency adjustment method, which gradually optimizes the frequency range by dynamically monitoring load changes and adjusting the frequency in real time. Figure 3 and Figure 4 As shown, the specific steps include:

[0188] Frequency range initialization: Based on the system load range and gain range design goals, the FHA analysis method can be used to obtain the initial resonant frequency and its surrounding frequency range so that it can automatically adapt when the load changes.

[0189] Frequency step adjustment: When the load changes, the system gradually increases or decreases the frequency through the multi-condition frequency regulator to optimize the voltage ripple amplitude. This method gradually converges to the optimal frequency by adjusting the frequency step in real time to ensure the ripple amplitude A 2ω Stable within the allowable range.

[0190] Frequency limit 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.

[0191] The present invention further provides a system for implementing the DC suppression method of the isolated DC-DC resonant converter for energy storage, wherein the system comprises a DC-DC resonant converter module, a switching frequency monitoring module, a FHA analysis module, a real-time test analysis module, a step control module and a switching frequency adjustment module, wherein the switching frequency monitoring module is used to monitor the operating frequency of the DC-DC resonant converter module, the FHA analysis module is used to analyze and derive the value range of the switching frequency when the DC-DC resonant converter module operates near the resonant frequency, the real-time test analysis module is used to analyze and derive the value range of the switching frequency when the DC-DC resonant converter module operates away from the resonant frequency, the step control module dynamically adjusts the frequency adjustment step by monitoring the change of the output DC voltage ripple, and the switching frequency adjustment module is used to automatically adjust the operating frequency of the DC-DC resonant converter module.

[0192] In order to cooperate with multi-operating frequency regulation, the present invention adopts film capacitors to replace traditional electrolytic capacitors, which significantly improves the power density and safety of the system. Film capacitors have higher voltage tolerance and longer service life, and can effectively reduce the negative impact of ripple. In addition, the control circuit of the present invention uses a digital control chip or a microcontroller to calculate the frequency range, frequency step and load status in real time to achieve adaptive regulation of the frequency range of multiple operating conditions. The controller dynamically adjusts the frequency step by monitoring the changes in the output voltage ripple to achieve more precise frequency control.

[0193] Although the present invention has been described in detail above with general description and specific embodiments, some modifications or improvements can be made on the basis of the present invention. The above description is only a preferred embodiment of the present invention and is not limited to 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 protection of the present invention are still included in 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. Use the instantaneous power theory to construct the voltage ripple mathematical model of the resonant network, and obtain the output DC voltage ripple amplitude model of the resonant network: Among them, A 2ω is the DC voltage ripple amplitude of the resonant network output, is the power factor, ω is the switching frequency, R is the transmitted power, U dc is the output DC voltage u dc The DC part, V in is the input voltage amplitude, C r is the resonant capacitor, L r is the resonant inductor; S2. Based on the system load range and gain range design goals, 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 is equal to the resonant frequency, the power factor is 1 and the equivalent reactance X eq is zero; at this time: Substituting formula (14) into formula (13), we can get: A 2w =U dc / (3RωC) (15) It can be concluded that the range of ω should satisfy: ω>U dc / (3R N CΔ ripple ) (16) Among them, R N is the equivalent load at rated power, Δ ripple for u dc Allowable ripple; S2.

2. When the switching frequency of the resonant converter is within 5% of the resonant frequency, the fundamental wave analysis method is used to analyze the resonant converter to derive the value range of ω. Based on the equivalent circuit structure of the series resonant circuit network, the power factor model of the resonant circuit is obtained as follows: Among them, R eq Represents the equivalent resistance, which is related to the high-frequency transformer turns ratio n and the load R; assuming that the maximum allowable current is I max , using the fundamental wave analysis method, we can get The range is: This working condition is established under the premise that FHA is valid, that is, δ is a constant close to 1. Substituting equation (17) into equation (21), the initial range of ω is obtained as: On the basis of obtaining the initial range of ω, further determine the range of ω to satisfy A 2ω Amplitude limit, that is, expressed as: ω[0]≤ω≤ω[i-1] (23) S2.

3. When the switching frequency of the resonant converter is far away from the resonant frequency, the range of ω is further limited by comprehensive simulation and experimental testing so that ω satisfies: ω1[0]≤ω≤ω1[p-1] (24) Among them, ω1[j], j=0~p-1 is used to store the frequencies of possible values.

2. The method according to claim 1, characterized in that The high-frequency input voltage of the isolated DC-DC resonant converter is: The resonant current i is: According to the high-frequency input voltage and the resonant current, the instantaneous power p(t) of the isolated DC-DC resonant converter is obtained as follows: where p0 and p 0-2ω They represent the average active power and ripple power, which are generated by the fundamental part of Vin and I, P h is the instantaneous harmonic power, including 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: On the basis of obtaining the initial range of ω, further determining the range of ω satisfies A 2ω Amplitude limits include: Initialize L r , C r , Δ ripple 、V in ,n,C,i=0; Set ω = ω1, and substitute ω into equation (17) to obtain According to formula (13), we can obtain A 2ω ; A 2ω It is compared with the allowed DC ripple threshold to determine whether to make incremental adjustments to ω.

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 part of the instantaneous power p(t) is introduced, p 2ω By p 0-2ω and p h The 2ω composition is expressed as: According to the law of conservation of energy, we can get: p(t)=p Lr +p Cr +p C +p R (5) In the formula p C and p R They represent the resonant inductance, resonant capacitance, instantaneous power of the DC side capacitor, and instantaneous power of the DC measuring capacitive load. Assume that the equivalent resonant inductance and resonant capacitance of the resonant network are L r and C, then its instantaneous power can be expressed as: Since the resonant network has a filtering effect on high-order harmonics, the output DC voltage is mainly affected by the fundamental part and 2ω part of p(t). Ignoring the high-order harmonic power, the output power p is obtained. out0 It can be expressed as: p out =p C +p R =p0+p 2ω -p Lr -p Cr (7)。 7. The method according to claim 6, characterized in that The specific value of the output DC voltage ripple is derived using formula (7), and the output DC voltage u dc Specifically: Among them, U dc and Respectively represent u dc The DC part and ripple part; Substituting formula (8) into formula (7), we can obtain: Among them, 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 the high-frequency converter, ωRC>>1, the solution of x in the steady state can be obtained: in Substituting equation (8) into equation (10), the DC part and the ripple part of the output DC voltage can be expressed as: The amplitude of the ripple part of the output DC voltage can be obtained based on the DC part and the ripple part of the output DC voltage.

9. The method according to claim 1, characterized in that: After the power factor model of the resonant circuit is obtained based on the equivalent circuit structure of the series resonant circuit network, it is further determined The initial range is: Assuming the maximum allowable current is Imax, we can get: therefore The initial range of can be defined as: Based on the The initial range can be obtained as described scope of restrictions.

10. A system for executing the DC suppression method of an isolated DC-DC resonant converter for energy storage according to any one of claims 1 to 9, characterized in that: The system is provided with a DC-DC resonant converter module, a switching frequency monitoring module, a FHA analysis module, a real-time test analysis module, a step control module and a switching frequency adjustment module. The switching frequency monitoring module is used to monitor the operating frequency of the DC-DC resonant converter module. The FHA analysis module is used to analyze and derive the value range of the switching frequency when the DC-DC resonant converter module operates near the resonant frequency. The real-time test analysis module is used to analyze and derive the value range of the switching frequency when the DC-DC resonant converter module operates far from the resonant frequency. The step control module dynamically adjusts the frequency adjustment step by monitoring the change of the output DC voltage ripple. The switching frequency adjustment module is used to automatically adjust the operating frequency of the DC-DC resonant converter module.

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