Full-bridge LLC resonant converter control method based on frequency compensation

Abstract

The invention discloses a full-bridge LLC resonant converter control method based on frequency compensation. The full-bridge LLC resonant converter control method comprises the following steps: step 1, sampling; 2, setting a t1 moment; step 3, calculating to obtain frequency loss fff1 which needs to be compensated in a resonance period; 4, calculating to obtain frequency compensation fff2 in a time period delta T starting from the t1 moment; and step 5, the full-bridge LLC resonant converter carries out frequency loss according to the fff1 in a resonant period, and carries out frequency compensation according to the fff2 in a time period delta T starting from the t1 moment. According to the invention, only the input bus voltage Vin, the output voltage Vo and the load current Io need to be sampled, and the control is simple; and the output voltage is high in precision, small in ripple and high in response speed.

Description

Technical Field

[0001] The invention relates to the field of electricity, and in particular to a full-bridge LLC resonant converter control method based on frequency compensation. Background Art

[0002] LLC resonant converters have been widely used in the field of modern power electronics due to their excellent performance, such as high efficiency, high power density and low electromagnetic interference (EMI), especially in high-demand scenarios such as data centers, distributed energy systems, energy storage equipment and electric vehicles. Compared with traditional hard-switching converters, LLC resonant converters can achieve higher efficiency and lower electromagnetic interference through resonant operation, which makes them more competitive in power conversion.

[0003] However, since the core working mechanism of LLC resonant converter relies on the resonance of current and voltage, it exhibits significant nonlinear characteristics in the dynamic process. This nonlinear characteristic makes it difficult for traditional linear control methods, such as PID control and state feedback control, to effectively cope with the control requirements under complex working conditions such as load changes, input voltage fluctuations and external interference.

[0004] At present, in the application of full-bridge LLC resonant converter, the problems of excessive dynamic response overshoot and slow adjustment speed are still important factors affecting system performance. To solve these problems, the traditional approach is to increase the sampling of the output current sensor and adopt a closed-loop control strategy to accurately adjust the current. By real-time feedback of the output current change, the controller can quickly adjust the operating state of the converter to optimize the dynamic response. However, this method usually introduces additional sensor costs and hardware complexity, and relies on high-precision current measurement, which may be limited by factors such as sensor accuracy, noise interference and sensor bandwidth. This makes it difficult to achieve ideal control accuracy and response speed under some high-speed load conditions.

[0005] At the same time, the low-frequency ripple in the input power bus, especially the 100Hz secondary voltage harmonic introduced by the power factor correction (PFC) circuit, is also an important factor affecting the stability and performance of the LLC resonant converter. Since the PFC circuit is usually connected to the full-bridge LLC resonant converter, the voltage fluctuation at the input end will cause a large low-frequency ripple, which will directly affect the output performance of the converter, causing fluctuations in the output voltage and current, and even generating unnecessary noise and electromagnetic interference. In order to suppress these low-frequency ripples, traditional solutions include connecting a large number of electrolytic capacitors in parallel at the input end, adding LC filters, or using active decoupling circuits. Electrolytic capacitors can provide high charge storage capacity, which helps to smooth the input voltage and reduce low-frequency fluctuations; while LC filters can effectively reduce the impact of low-frequency ripples on converter performance by filtering out signals in specific frequency bands. However, these methods usually increase the size, cost and complexity of the system, especially in high-power and high-frequency applications, where the size and weight of electrolytic capacitors limit their effectiveness. In practical applications, traditional control methods often face problems such as excessive overshoot in dynamic response, slow adjustment speed, and high output voltage ripple. Especially in systems with high performance requirements, this control effect is difficult to meet the requirements of precise power regulation, fast response, and low output ripple. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a full-bridge LLC resonant converter based on frequency compensation.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A full-bridge LLC resonant converter control method based on frequency compensation comprises the following steps:

[0009] Step 1: Calculate the input voltage V of the full-bridge LLC resonant converter in , sampling of output voltage V0 and output current I0;

[0010] Step 2: Set the second MOS tube Q2 and the third MOS tube Q3 of the primary circuit to be in the off state, the first MOS tube Q1 and the fourth MOS tube Q4 to be in the on state, and the moment when the resonant current is equal to the excitation current is t1 in one resonant cycle of the full-bridge LLC resonant converter;

[0011] Step 3: Calculate the frequency loss f that needs to be compensated within a resonant cycle ff1 ;

[0012] Step 4: Calculate the frequency compensation f within the ΔT time period starting at time t1 ff2 ;

[0013] Step 5: In one resonant cycle, the full-bridge LLC resonant converter is switched according to f ff1 Frequency loss, starting from time t1, within the ΔT period, follow f ff2 Perform frequency compensation.

[0014] As a further improvement, the full-bridge LLC resonant converter includes a transformer, the primary side of the transformer is electrically connected to a primary circuit, the secondary side is electrically connected to a secondary circuit, and the secondary circuit is electrically connected to a load ZL; the primary circuit includes a first MOS transistor Q1, a second MOS transistor Q2, a third MOS transistor Q3 and a fourth MOS transistor Q4; one end of the primary side of the transformer is electrically connected to the source of the first MOS transistor Q1 and the drain of the second MOS transistor Q2 through a filter circuit, and the other end is electrically connected to the source of the third MOS transistor Q3 and the drain of the fourth MOS transistor Q4; the drain of the first MOS transistor Q1 is electrically connected to the drain of the third MOS transistor Q3, and the source of the second MOS transistor Q2 is electrically connected to the source of the fourth MOS transistor Q4.

[0015] As a further improvement, when the full-bridge LLC resonant converter is in operation, within a resonant cycle, the second MOS transistor Q2 and the third MOS transistor Q3 are in the off state, and the first MOS transistor Q1 and the fourth MOS transistor Q4 are in the on state at the time t0;

[0016] The second MOS tube Q2 and the third MOS tube Q3 are in the off state, the first MOS tube Q1 and the fourth MOS tube Q4 are in the on state, and the moment when the resonant current is equal to the excitation current is the moment t1;

[0017] The moment when the second MOS tube Q2, the third MOS tube Q3, the first MOS tube Q1 and the fourth MOS tube Q4 are all turned off is moment t2;

[0018] The first MOS tube Q1 and the fourth MOS tube Q4 remain turned off, and the second MOS tube Q2 and the third MOS tube Q3 are turned on at time t3;

[0019] The first MOS tube Q1 and the fourth MOS tube Q4 remain turned off, the second MOS tube Q2 and the third MOS tube Q3 are turned on, and the moment when the resonant current is equal to the excitation current is time t4; the moment when the first MOS tube Q1 and the fourth MOS tube Q4, the second MOS tube Q2 and the third MOS tube Q3 are turned off again is time t5;

[0020] In the next resonance cycle of the full-bridge LLC resonant converter, the second MOS transistor Q2 and the third MOS transistor Q3 are in the off state, and the first MOS transistor Q1 and the fourth MOS transistor Q4 are in the on state at time t6.

[0021] For further improvement, the specific method of step three is as follows:

[0022] The frequency loss f that needs to be compensated for the time period t1-t6 is calculated ff1 :

[0023]

[0024] Among them, L r Represents the resonant inductance, L m Represents the magnetizing inductance, C r represents the resonant capacitance, f r represents the resonant frequency, n represents the transformer turns ratio, V ref represents the output target voltage, f s represents the switching frequency of the power device, and Z0 represents the characteristic impedance value.

[0025] For further improvement, the specific method of step 4 is as follows:

[0026] The calculation results show that the required ΔT time period and frequency compensation f are needed to speed up the dynamic response. ff2 :

[0027]

[0028] Among them, t n represents the completion time of the nth iteration, V CrN Represents the normalized value of the resonant capacitor voltage, I n Represents the current value at the nth iteration; I H Indicates the maximum load current, that is, the maximum value of I0; I L Indicates the minimum load current, i.e. the low value of I0

[0029] The beneficial effects of the present invention are:

[0030] (1) Only the input bus voltage Vin and output voltage V need to be sampled. o and load current I o ;

[0031] (2) Simple control;

[0032] (3) High output voltage accuracy, small ripple and fast response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention is further described with reference to the accompanying drawings, but the contents in the accompanying drawings do not constitute any limitation to the present invention.

[0034] Figure 1 It is a full-bridge LLC resonant circuit topology.

[0035] Figure 2A FIG1 is the equivalent circuit of the full-bridge LLC resonant circuit topology during operation.

[0036] Figure 2B FIG2 is the equivalent circuit of the full-bridge LLC resonant circuit topology during operation.

[0037] Figure 2C FIG3 is the equivalent circuit of the full-bridge LLC resonant circuit topology during operation.

[0038] Figure 3 This is the current and voltage analysis diagram of LLC working process.

[0039] Figure 4A The resonant voltage and current trajectory curve Figure 1 .

[0040] Figure 4B Figure 2 is the resonant voltage and current trajectory curve.

[0041] Figure 5 This is the frequency prediction control block diagram.

[0042] Fig. 6A is the resonant current and voltage when the load changes Figure 1 .

[0043] Figure 6B Figure 2 shows the resonant current and voltage when the load changes.

[0044] Figure 7 This is the frequency compensation algorithm flow chart.

[0045] Figure 8 This is the output ripple effect diagram.

[0046] Fig. 9 This is a dynamic response effect diagram. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0048] System principle description

[0049] The topology of the full-bridge LLC resonant converter is as follows: Figure 1 As shown. Among them, V i is the input voltage, V out is the output voltage, Z L is the output equivalent impedance. Q1~Q4 are the upper and lower power tubes of the primary side, respectively, and Q5~Q6 are the rectifier tubes of the secondary side. L r is the resonant inductor, C r is the resonant capacitor, L m is the magnetizing inductance, C o is the output filter capacitor, and n is the transformer turns ratio. Lr 、V Cr 、iLm They are resonant inductor current, resonant capacitor voltage and magnetizing inductor current respectively. The equivalent circuit in the working process can be summarized into the following three states: Figure 2A , Figure 2B , Figure 2C As shown. According to the different actual working processes, the essence of the change process is to switch through the following three states through permutations and combinations.

[0050] By equivalent Figure 2A According to Kirchhoff's voltage law:

[0051]

[0052] From (1) and (2), we can find the general solution of the quadratic differential equation:

[0053]

[0054] k1 and k2 are determined by the initial value conditions, and it can be deduced that:

[0055]

[0056] Where V Cr0 ,I Cr0 is the initial value of the resonant voltage and current at t=t0, is the characteristic impedance value, is the resonant frequency. Normalize (3) and (4) and multiply all voltage quantities by the coefficient 1 / V in , the current is multiplied by the coefficient Z0 / V in , can be obtained

[0057]

[0058] In (5) and (6), N represents the normalized variable. Combining (5) and (6), we can get

[0059]

[0060] Similarly, we can get the equivalent graphs (2) and (3)

[0061]

[0062] in,.

[0063]

[0064] From (7), (8), and (9), we can see that Figure 2A , Figure 2B The stable working state is about V CrN ,I CrN The trajectory circle, Figure 2Cis the trajectory ellipse. The center of the trajectory circle and the focus of the trajectory ellipse are determined by the specific working state. During the full-bridge LLC resonant operation, the drive signal, voltage and current waveforms are as follows: Figure 3 As shown, t0-t1 corresponds to the equivalent circuit Figure 2A , t1-t3 corresponds to the equivalent circuit Figure 2C , t3-t4 corresponds to the equivalent circuit Figure 2B .

[0065] Implementation of Frequency Predictive Control Strategy

[0066] According to the above rules, this paper proposes a control strategy based on frequency compensation. The implementation block diagram of the strategy is as follows: Figure 5 The control target is the output voltage, and the frequency compensation method is used to speed up the dynamic response and eliminate the output voltage ripple. Figure 4B It can be seen that to eliminate the voltage ripple, it is necessary to compensate for the frequency loss f in the time periods t1-t3 and t4-t0 (t6). ff1 To speed up the dynamic response, a frequency compensation f is required for a period of ΔT. ff2 .

[0067] (1) In the time periods t1-t3 and t4-t0 (t6), the resonant current can be regarded as a constant value i Lr_1 , and the trajectory is symmetrical; the resonant voltage change value, that is, the voltage u between O1 and O2 13 .

[0068]

[0069] From (10), (11), (12), (13), and using V ref Replace V o Available

[0070]

[0071] (2) When the load changes, the resonant current and voltage change as follows Fig. 6A and Figure 6B As shown. Fig. 6A , the inductor current cannot change suddenly. The inductor current remains unchanged during the time t1-t3:

[0072]

[0073] Depend on Figure 6B According to geometric operations, we can get:

[0074]

[0075] After iterative calculation, we can deduce:

[0076]

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A full-bridge LLC resonant converter control method based on frequency compensation, characterized in that: The steps include: Step 1: Calculate the input voltage V of the full-bridge LLC resonant converter in , sampling of output voltage V0 and output current I0; Step 2: Set the second MOS tube (Q2) and the third MOS tube (Q3) of the primary circuit to be in the off state, the first MOS tube (Q1) and the fourth MOS tube (Q4) to be in the on state, and the moment when the resonant current is equal to the excitation current is t1 in one resonant cycle of the full-bridge LLC resonant converter; Step 3: Calculate the frequency loss f that needs to be compensated within a resonant cycle ff1 ; Step 4: Calculate the frequency compensation f within the ΔT time period starting at time t1 ff2 ; Step 5: In one resonant cycle, the full-bridge LLC resonant converter is switched according to f ff1 Frequency loss, starting from time t1, within the ΔT period, follow f ff2 Perform frequency compensation.

2. The full-bridge LLC resonant converter control method based on frequency compensation according to claim 1, characterized in that: The full-bridge LLC resonant converter comprises a transformer, wherein the primary side of the transformer is electrically connected to a primary circuit, the secondary side is electrically connected to a secondary circuit, and the secondary circuit is electrically connected to a load (ZL); the primary circuit comprises a first MOS transistor (Q1), a second MOS transistor (Q2), a third MOS transistor (Q3) and a fourth MOS transistor (Q4); one end of the primary side of the transformer is electrically connected to a source electrode of the first MOS transistor (Q1) and a drain electrode of the second MOS transistor (Q2) through a filter circuit, and the other end is electrically connected to a source electrode of the third MOS transistor (Q3) and a drain electrode of the fourth MOS transistor (Q4); the drain electrode of the first MOS transistor (Q1) is electrically connected to a drain electrode of the third MOS transistor (Q3), and the source electrode of the second MOS transistor (Q2) is electrically connected to a source electrode of the fourth MOS transistor (Q4).

3. The full-bridge LLC resonant converter control method based on frequency compensation according to claim 2, characterized in that: When the full-bridge LLC resonant converter is in operation, within a resonant cycle, the moment when the second MOS tube (Q2) and the third MOS tube (Q3) are in the off state and the first MOS tube (Q1) and the fourth MOS tube (Q4) are in the on state is t0; The second MOS tube (Q2) and the third MOS tube (Q3) are in the off state, the first MOS tube (Q1) and the fourth MOS tube (Q4) are in the on state, and the moment when the resonant current is equal to the excitation current is the moment t1; The moment when the second MOS tube (Q2), the third MOS tube (Q3), the first MOS tube (Q1) and the fourth MOS tube (Q4) are all turned off is moment t2; The first MOS tube (Q1) and the fourth MOS tube (Q4) remain turned off, and the second MOS tube (Q2) and the third MOS tube (Q3) are turned on at time t3; The first MOS tube (Q1) and the fourth MOS tube (Q4) remain turned off, the second MOS tube (Q2) and the third MOS tube (Q3) are turned on, and the moment when the resonant current is equal to the excitation current is moment t4; The moment when the first MOS tube (Q1), the fourth MOS tube (Q4), the second MOS tube (Q2) and the third MOS tube (Q3) are all turned off again is moment t5; In the next resonance cycle of the full-bridge LLC resonant converter, the second MOS transistor (Q2) and the third MOS transistor (Q3) are in the off state, and the first MOS transistor (Q1) and the fourth MOS transistor (Q4) are in the on state at time t6.

4. The full-bridge LLC resonant converter control method based on frequency compensation according to claim 3, characterized in that: The specific method of step three is as follows: The frequency loss f that needs to be compensated for the time period t1-t6 is calculated ff1 : Among them, L r Represents the resonant inductance, L m Represents the magnetizing inductance, C r represents the resonant capacitance, f r represents the resonant frequency, n represents the transformer turns ratio, V ref represents the output target voltage, f s represents the switching frequency of the power device, and Z0 represents the characteristic impedance value.

5. The full-bridge LLC resonant converter control method based on frequency compensation according to claim 4, characterized in that: The specific method of step 4 is as follows: The calculation results show that the required ΔT time period and frequency compensation f are needed to speed up the dynamic response. ff2 : Among them, t n represents the completion time of the nth iteration, V CrN Represents the normalized value of the resonant capacitor voltage, I n Represents the current value at the nth iteration; I H Indicates the maximum load current, that is, the maximum value of I0; I L Indicates the minimum load current, that is, the minimum value of I0.

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