LC resonant converter control method

Abstract

The invention discloses an LC resonant converter control method, which relates to the technical field of LC resonant converters, and comprises the following steps: obtaining basic parameters of each part of the LC resonant converter, obtaining a state equation of each part according to the obtained basic parameters, and when the LC resonant converter is disturbed, determining the state equation of each part according to a disturbance signal received by the LC resonant converter. Obtaining each state variable in the resonant network module; all the state variables are substituted into the state equations, and steady-state solutions corresponding to all the state equations of the LC resonant converter in the steady-state state are obtained; according to the method, time domain signals are analyzed by means of a Fourier analysis method, approximate processing is carried out on harmonic waves of all orders, the method has high accuracy, an equivalent circuit model of the converter in a steady state can be established, in addition, simulation analysis does not need to be carried out on a circuit, and only steady-state signals under the action of non-modulation signals need to be known.

Description

Technical Field

[0001] The present invention relates to the technical field of LC resonant converters, and specifically to a control method for an LC resonant converter. Background Art

[0002] The LC resonant converter has higher conversion efficiency compared with the traditional bridge converter and is widely used in power electronic conversion systems, such as electric vehicles, distributed generation systems, and energy storage systems, where it plays a crucial role in the energy conversion system. Since the LC resonant converter has non-linear characteristics, is discrete, time-varying, and high-order, there is a lack of an equivalent model for the analysis of the LC resonant converter system. How to construct a transfer function model of the LC resonant converter to evaluate the stability of the converter and optimize the converter control is an urgent problem to be solved. Therefore, a control method for an LC resonant converter is provided herein. Summary of the Invention

[0003] The purpose of the present invention is to provide a control method for an LC resonant converter.

[0004] The purpose of the present invention can be achieved through the following technical solutions: A control method for an LC resonant converter, comprising the following steps:

[0005] Step S1: Obtain the basic parameters of each part of the LC resonant converter, and obtain the state equations of each part according to the obtained basic parameters;

[0006] Step S2: When the LC resonant converter is disturbed, obtain each state variable in the resonant network module according to the disturbance signal received by the LC resonant converter;

[0007] Step S3: Obtain the steady-state solutions corresponding to the state equations of the LC resonant converter in the steady state.

[0008] Further, the LC resonant converter includes a switching network module, a resonant network module, a transformer module, a rectifying network module, a low-pass filtering module, and a load.

[0009] Further, the basic parameters of each part of the LC resonant converter obtained include:

[0010] Obtain the input voltage of the LC resonant converter, and denote the obtained input voltage of the LC resonant converter as u AB ;

[0011] Obtain the current value and voltage value of the resonant network module, and denote them as i 1 and u p ;

[0012] Obtain the output current of the rectifying network module, and denote it as i 2, obtain the resistance of the load connected to the rectifier network module, denoted as R;

[0013] Obtain the voltage value of the low-pass filter module, denoted as u C Obtain the equivalent series resistance of the low-pass filter module, denoted as r C ;

[0014] Obtain the inductance and capacitance of the resonant network module, denoted as L r and C p ;

[0015] Obtain the turns ratio of the transformer module, denoted as N.

[0016] Furthermore, obtain the state equations of each part based on the obtained basic parameters, including:

[0017]

[0018] Among them, R s is the series resistance value of the inductance and the line in the resonant network module, C is the capacitance of the low-pass filter in the low-pass filter module, u o is the output voltage of the low-pass filter module, sgn(u p ) is the sign function, and when u p is greater than 0, the value of this sign function is 1; when u p is less than 0, the value of this sign function is -1; when u p is equal to 0, the value of this sign function is 0.

[0019] 5. A method for controlling an LC resonant converter according to claim 4, characterized in that when the LC resonant converter is disturbed, the process of obtaining each state variable in the resonant network module according to the disturbance signal received by the LC resonant converter includes:

[0020] When the LC resonant converter is disturbed, the fundamental wave of the input voltage u AB of the LC resonant converter is equivalent to a corresponding frequency modulation signal, and the disturbance signal received by the LC resonant converter is obtained;

[0021] When the disturbance signal received by the LC resonant converter is a low-frequency small signal, the corresponding frequency modulation signal is a superposition of a sinusoidal signal and a cosine signal with a time-varying amplitude;

[0022] According to the frequency modulation signal, obtain each state variable in the resonant network module, then

[0023] i 1 = i s sinw s t + i c cosw s t

[0024] u p = u ps sinω s t + u pc cosω s t;

[0025] where i s is the amplitude of the sine component of the current of the resonant network module, and i c is the amplitude of the cosine component of the current of the resonant network module, and u ps is the amplitude of the sine component of the current of the resonant network module, and u pc is the amplitude of the cosine component of the current of the resonant network module, and ω s is the switching angular frequency of the switching device in the switching network module.

[0026] Furthermore, the derivatives of each state variable are obtained respectively to obtain the corresponding derivative results, that is:

[0027]

[0028] The extended description function of the input voltage of the LC resonant converter is obtained, that is:

[0029]

[0030] where is the amplitude of the fundamental component of the input-side voltage, and d is the duty cycle of the switching device in the switching network module;

[0031] u AB is the input voltage of the LC resonant converter. The state variables in the resonant network module and u AB are sinusoidal quantities with the same frequency. Therefore, if u AB is expanded into a Fourier series, only the fundamental component is the effective excitation of the resonant network module, and the remaining higher harmonics are attenuated by the resonant network module;

[0032] Furthermore, it can be known that the rectifier network module and the low-pass filter module correspond to the load effect of the resonant network module. Then, the voltage value u p of the resonant network module with the switching frequency is denoted as sgn(u p ), where:

[0033]

[0034] Since the low-pass filter module transmits energy depending on the DC component of the electric energy, u 2 is a full-wave rectified waveform. After being expanded into a Fourier series, its DC component is an effective excitation signal for the low-pass filter module. Then:

[0035]

[0036] Further, the process of obtaining the steady-state solutions corresponding to the state equations of the LC resonant converter in the steady state includes:

[0037] When the perturbation signal is a small-amplitude low-frequency signal, that is, when the frequency of the perturbation signal is much lower than the switching frequency, relative to the switching frequency, the perturbation signal is a quantity that changes very slowly. Therefore, the entire LC resonant converter can be considered a quasi-steady-state system. The above-described DC terms, DC components, and the coefficients of the sine and cosine components are made equal, and let That is:

[0038]

[0039] Then in the steady state, the steady-state quantities of each state variable are obtained, and the obtained steady-state quantities are constants. In the steady state, the increment of each state variable is 0, that is:

[0040]

[0041] According to the obtained steady-state quantities, the steady-state solutions of each state equation are obtained, that is:

[0042]

[0043] 0 = L r Ω s I s + I c R s + u pc

[0044]

[0045] Then the DC gain of the above system of equations is further obtained as:

[0046]

[0047] Wherein, A = C p Ω s , C = L r Ω s , C = R s .

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] Analyze the time-domain signal by Fourier analysis method, and perform approximate processing on the harmonic expansion of all orders. This method has high accuracy and can establish an equivalent circuit model of the converter in continuous time. In addition, this method does not require circuit simulation analysis, and only the steady-state signal under the action of the non-modulated signal needs to be known. Brief Description of the Drawings

[0050] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0051] Figure 1 It is a flowchart of the present invention. Detailed Embodiments

[0052] As Figure 1 shown, a control method for an LC resonant converter includes the following steps:

[0053] Step S1: Obtain the basic parameters of each part of the LC resonant converter, and obtain the state equations of each part according to the obtained basic parameters;

[0054] Step S2: When the LC resonant converter is disturbed, obtain each state variable in the resonant network module according to the disturbance signal received by the LC resonant converter;

[0055] Step S3: Obtain the steady-state solutions corresponding to the state equations of the LC resonant converter in the steady state.

[0056] It should be further noted that in the specific implementation process, the LC resonant converter includes a switching network module, a resonant network module, a transformer module, a rectifying network module, a low-pass filtering module, and a load.

[0057] It should be further noted that in the specific implementation process, the basic parameters of each part of the LC resonant converter obtained include:

[0058] Obtain the input voltage of the LC resonant converter, and denote the obtained input voltage of the LC resonant converter as u AB ;

[0059] Obtain the current value and voltage value of the resonant network module, and denote them as i 1 and u p ;

[0060] Obtain the output current of the rectifying network module, denote it as i 2 , and obtain the resistance of the load connected to the rectifying network module, denote it as R;

[0061] Obtain the voltage value of the low-pass filter module, denoted as u C Obtain the equivalent series resistance of the low-pass filter module, denoted as r C ;

[0062] Obtain the inductance and capacitance of the resonant network module, denoted as L r and C p ;

[0063] Obtain the turns ratio of the transformer module, denoted as N.

[0064] It should be further noted that in the specific implementation process, the state equations of each part obtained according to the obtained basic parameters include:

[0065]

[0066] Among them, R s is the series resistance value of the inductance and the line in the resonant network module, C is the capacitance of the low-pass filter in the low-pass filter module, u o is the output voltage of the low-pass filter module, sgn(u p ) is the sign function, and when u p is greater than 0, the value of this sign function is 1; when u p is less than 0, the value of this sign function is -1; when u p is equal to 0, the value of this sign function is 0.

[0067] It should be further noted that in the specific implementation process, when the LC resonant converter is disturbed, the process of obtaining each state variable in the resonant network module according to the disturbance signal received by the LC resonant converter includes:

[0068] When the LC resonant converter is disturbed, the fundamental wave of the input voltage u AB of the LC resonant converter is equivalent to the corresponding frequency-modulated signal, and the disturbance signal received by the LC resonant converter is obtained;

[0069] When the disturbance signal received by the LC resonant converter is a low-frequency small signal, the corresponding frequency-modulated signal is a superposition of a sine signal and a cosine signal with a time-varying amplitude;

[0070] It should be further noted that in the specific implementation process, because the frequency of the disturbance signal is much lower than the switching frequency of the switching network module, within a high-frequency period, it can be considered that the amplitudes of the sine signal and the cosine signal are constant;

[0071] According to the frequency-modulated signal, obtain each state variable in the resonant network module, then

[0072] i 1= i s sin w s t + i c cos w s t

[0073] u p = u ps sin w s t + u pc cos w s t;

[0074] where i s is the amplitude of the sine component of the current of the resonant network module, and i c is the amplitude of the cosine component of the current of the resonant network module, and u ps is the amplitude of the sine component of the current of the resonant network module, and u pc is the amplitude of the cosine component of the current of the resonant network module, and w s is the switching angular frequency of the switching tube in the switching network module;

[0075] Derive the derivative of each state variable respectively to obtain the corresponding derivative result, that is:

[0076]

[0077] Obtain the extended description function of the input voltage of the LC resonant converter, that is:

[0078]

[0079] where, is the amplitude of the fundamental component of the input-side voltage, and d is the duty cycle of the switching tube in the switching network module;

[0080] u AB is the input voltage of the LC resonant converter. The state variables in the resonant network module and u AB are sinusoidal quantities with the same frequency. Therefore, if u AB is expanded into a Fourier series, only the fundamental component is the effective excitation of the resonant network module, and the remaining higher harmonics are attenuated by the resonant network module;

[0081] Furthermore, it can be known that the load effects of the rectifier network module and the low-pass filter module on the resonant network module can be represented by a square-wave signal with a frequency of the switching frequency. Then, the voltage value u p of the resonant network module with a frequency of the switching frequency is denoted as sgn(u p ), where:

[0082]

[0083] Since the low-pass filter module transmits energy relying on the direct current (or average value) of electric energy, thus u 2 is a full-wave rectified waveform. After expanding it into a Fourier series, its DC component is an effective excitation signal for the low-pass filter module, then:

[0084]

[0085] It should be further noted that in the specific implementation process, the process of obtaining the steady-state solutions corresponding to the state equations of the LC resonant converter in the steady state includes:

[0086] When the perturbation signal is a small-amplitude low-frequency signal and the frequency of the perturbation signal is much lower than the switching frequency, relative to the switching frequency, the perturbation signal is a quantity that changes very slowly. Therefore, the entire LC resonant converter can be considered as a quasi-steady-state system. The above-mentioned DC term, DC component, and the coefficients of the sine and cosine components are made equal respectively to obtain the description. Let That is:

[0087]

[0088] Then in the steady state, the steady-state quantities of each state variable are obtained, and the obtained steady-state quantities are constants. In the steady state, the increment of each state variable is 0, that is:

[0089]

[0090] According to the obtained steady-state quantities, the steady-state solutions of each state equation are obtained, that is:

[0091]

[0092] 0=L r Ω s I s +I c R s +u pc

[0093]

[0094] Then the DC gain of the above equations is further obtained as:

[0095]

[0096] Among them, A=C p Ω s , C=L r Ω s , C=R s .

[0097] The above are only the preferred embodiments of the present invention and do not impose any formal limitations on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any modification or equivalent replacement made to the above embodiments based on the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for controlling an LC resonant converter, characterized in that: The following steps are involved: Step S1: obtaining basic parameters of various parts constituting the LC resonant converter, and obtaining state equations of various parts according to the obtained basic parameters; Step S2: when the LC resonant converter is disturbed, obtaining various state variables in the resonant network module according to the disturbance signal received by the LC resonant converter; Step S3: Obtain the steady-state solutions corresponding to the state equations of the LC resonant converter in the steady-state state.

2. The LC resonant converter control method according to claim 1, characterized in that: The LC resonant converter includes a switch network module, a resonant network module, a transformer module, a rectifier network module, a low-pass filter module and a load.

3. The LC resonant converter control method according to claim 2, characterized in that: The basic parameters of the various parts that make up the LC resonant converter include: Obtain the input voltage of the LC resonant converter, and record the obtained input voltage of the LC resonant converter as u AB ; Get the current and voltage values ​​of the resonant network module, recorded as i1 and u respectively p ; Obtain the output current of the rectifier network module, recorded as i2, and obtain the resistance of the load connected to the rectifier network module, recorded as R; Get the voltage value of the low-pass filter module, recorded as u C Get the equivalent series resistance of the low-pass filter module, denoted as r C ; Get the inductance and capacitance of the resonant network module, denoted as L r and C p ; Get the transformation ratio of the transformer module, denoted as N.

4. The LC resonant converter control method according to claim 3, characterized in that: The state equations of each part obtained according to the basic parameters include: Among them, R s is the series resistance value of the inductor and line in the resonant network module, C is the capacitance value of the low-pass filter in the low-pass filter module, u o is the output voltage of the low-pass filter module, sgn(u p ) is a sign function, when u p When u is greater than 0, the sign function value is 1. p When u is less than 0, the sign function value is -1. p When it is equal to 0, the sign function value is 0.

5. The LC resonant converter control method according to claim 4, characterized in that: When the LC resonant converter is disturbed, the process of obtaining various state variables in the resonant network module according to the disturbance signal received by the LC resonant converter includes: When the LC resonant converter is disturbed, the input voltage u AB The fundamental wave is equivalent to the corresponding frequency modulation signal, and the disturbance signal received by the LC resonant converter is obtained; When the disturbance signal to which the LC resonant converter is subjected is a low-frequency small signal, the corresponding frequency-modulated signal is a superposition of a sine signal and a cosine signal with a time-varying amplitude; According to the frequency modulation signal, various state variables in the resonant network module are obtained, then i1=i s sin w s t+i c cosw s t u p =u ps sin w s t+u pc cos w s t; where i s The amplitude of the sinusoidal component of the resonant network module current, i c is the amplitude of the cosine component of the resonant network module current, u ps The amplitude of the sinusoidal component of the resonant network module current, u pc is the amplitude of the cosine component of the resonant network module current, w s is the switching angular frequency of the switch tube in the switching network module.

6. The LC resonant converter control method according to claim 5, characterized in that: Derivate each state variable separately to obtain the corresponding derivative results, namely: The extended description function of the input voltage of the LC resonant converter is obtained, namely: in, is the amplitude of the fundamental component of the input voltage, and d is the duty cycle of the switch tube in the switch network module; u AB is the input voltage of the LC resonant converter, the state variable in the resonant network module and u AB is a sinusoidal quantity with the same frequency, so if u AB Expanded into Fourier series, only the fundamental component is the effective excitation of the resonant network module, and the remaining high-order harmonics are attenuated by the resonant network module; It can be known that the rectifier network module and the low-pass filter module correspond to the load effect of the resonant network module, so the voltage value u of the resonant network module with the switching frequency is p The square wave signal is recorded as sgn(u p ),in: Since the low-pass filter module relies on the DC amount of electrical energy to transmit energy, u2 is a full-wave rectified waveform. After being expanded into a Fourier series, its DC component is an effective excitation signal for the low-pass filter module. Then:

7. The LC resonant converter control method according to claim 6, characterized in that: The process of obtaining the steady-state solutions corresponding to the state equations of the LC resonant converter in the steady-state state includes: When the disturbance signal is a low-frequency signal with a small amplitude, the frequency of the disturbance signal is much lower than the switching frequency. Compared with the switching frequency, the disturbance signal is a very slowly changing quantity. Therefore, the entire LC resonant converter can be considered as a quasi-steady-state system. The coefficients of the above DC term, DC component, and sine and cosine components are equal to each other. Let Right now: Then, in the steady state, the steady-state quantity of each state variable is obtained, and the obtained steady-state quantity is a constant. In the steady state, the increment of each state variable is 0, that is: According to the obtained steady-state quantities, the steady-state solutions of each state equation are obtained, namely: 0=L r Ω s I s +I c R s +u pc Then the DC gain of the above equations is further obtained as: Among them,A=C p Oh s , C=L r Oh s ,C=R s 。

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