Modulation method of bidirectional CLLC resonant converter with soft switching in full load range

Abstract

The application discloses a modulation method of a full-load-range soft-switching bidirectional CLLC resonant converter, and is implemented according to the following steps: step 1, sampling low-voltage-side voltage and current; step 2, calculating voltage gain and low-voltage-side output power; step 3, calculating maximum phase-shifting angle; step 4, calculating critical output power allowed under EPS, under the modulation, when the power of the system operation is less than the critical output power, all switches can realize soft switching; step 5, according to the calculation results based on steps 2 to 4, dividing the operation conditions into three cases, and obtaining state variable values according to the three cases; step 6, according to the state variable values in step 5, selecting a modulation method; and step 7, according to the modulation method selected in step 6, selecting switch signals sent by the modulation loop to drive eight switch tubes of the CLLC resonant converter. The application has the advantages of expanding the soft-switching range of the bidirectional CLLC resonant converter and improving the efficiency in the full-load range.

Description

Technical Field

[0001] This invention belongs to the technical field of bidirectional DC-DC converters and relates to a modulation method for a bidirectional CLLC resonant converter with soft switching across the entire load range. Background Technology

[0002] In clean energy power generation systems such as photovoltaic power generation, wind power generation, and fuel cell power generation, energy storage systems and bidirectional DC-DC converters are needed to ensure the continuous and stable operation of the system. The performance of bidirectional DC-DC converters directly determines the development of energy storage technology.

[0003] In recent years, among numerous bidirectional DC-DC converters, the bidirectional CLLC resonant converter has emerged as one of the mainstream topologies, possessing the following characteristics: excellent soft-switching characteristics and a wide voltage output range, and showing great promise for applications in high-voltage, high-power energy storage systems. For CLLC resonant converters, the traditional modulation method is frequency conversion modulation (PFM), while extended phase-shift modulation (EPS) is widely considered an effective method to address the problems of narrow voltage regulation range and low efficiency under light loads. PFM works well with narrow input / output voltage ranges and heavy loads, but under light loads, increasing the switching frequency may not achieve voltage reduction. EPS, on the other hand, naturally achieves synchronous rectification, enabling bidirectional step-up and step-down, facilitating rapid switching of circuit operation, and significantly improving efficiency under light loads. However, it exhibits poor soft-switching characteristics under heavy loads and large phase shift angles. Compared to PFM, the peak resonant current on the primary and secondary sides increases, increasing the turn-off losses of the switching transistors. To address the advantages and disadvantages of these two modulation strategies, this invention proposes a modulation method for a bidirectional CLLC resonant converter that achieves soft switching across the entire load range. This method optimizes the soft-switching characteristics across the entire load range and simplifies synchronous rectification control, thereby further improving the converter's efficiency. Therefore, realizing a modulation strategy based on a bidirectional CLLC resonant converter that adapts to soft switching across the entire load range is of significant research importance. Summary of the Invention

[0004] The purpose of this invention is to provide a modulation method for a bidirectional CLLC resonant converter with full load range soft switching, which has the characteristic of expanding the soft switching range of the bidirectional CLLC resonant converter.

[0005] The technical solution adopted in this invention is a modulation method for a bidirectional CLLC resonant converter with soft switching across the entire load range, which is implemented according to the following steps:

[0006] Step 1. Sample the low-voltage side voltage With current ;

[0007] Step 2. Calculate the voltage gain With low-voltage side output power ;

[0008] Step 3. Calculate the maximum phase shift angle ;

[0009] Step 4. Calculate the allowable critical output power under EPS. Under this modulation, when the system operating power is less than At that time, all switches can achieve soft switching.

[0010] Step 5. Based on the calculation results from Steps 2 to 4, the operating conditions are divided into three cases, and the state variable S value is obtained based on these three cases;

[0011] Step 6. Based on the state variable S value from Step 5, select the modulation method to ensure soft switching is achieved across the entire load range;

[0012] Step 7. Based on the modulation method selected in Step 6, select the switching signal emitted by the modulation loop. V Q1 ~ V Q8 The eight switching transistors drive the CLLC resonant converter.

[0013] The invention is further characterized by:

[0014] The formula for calculating the voltage gain in step 2 is shown in equation (1):

[0015] (1)

[0016] in, Where is the DC voltage on the high-voltage side, and n is the transformer turns ratio;

[0017] The formula for calculating the output power on the low-voltage side is shown in equation (2):

[0018] (2).

[0019] Maximum phase shift angle in step 3 The calculation formula is shown in equation (3):

[0020] (3)

[0021] in, V Lmin This is the minimum allowable voltage on the low-voltage side. V Hmax This is the maximum allowable voltage on the high-voltage side.

[0022] Step 4 calculates the allowable critical output power under EPS modulation. The calculation formula is shown in equation (4):

[0023] (4)

[0024] in, V Hmax This is the maximum allowable voltage on the high-voltage side. The equivalent parallel parasitic capacitance of the switching transistor, The resonant frequency, It is a primary-side resonant inductor. This is the primary-side equivalent magnetizing inductance of a high-frequency transformer. The dead time between the upper and lower bridge arms is at this power. , The switching signal of the bridge arm is delayed. , Maximum phase shift angle of the bridge arm When the system's operating power is less than At that time, all switches can achieve soft switching.

[0025] The three operating conditions in step 5 are as follows: boosting The voltage is reduced and the output power on the low-voltage side is greater than or equal to the critical output power. The voltage is reduced and the output power on the low-voltage side is less than the critical output power. ;

[0026] The expression for the value of the state variable S is shown in equation (5):

[0027] (5).

[0028] In step 5, when S=0 or S=1, the high-voltage side switch adopts the PFM modulation method, and the low-voltage side switch adopts synchronous rectification SR modulation. At this time, all switches can achieve soft switching.

[0029] The PFM modulation method is implemented according to the following steps:

[0030] Step 6.1, will With reference voltage Subtraction, the error The switching frequency is calculated by the proportional-integral (PI) controller. The calculation formula is shown in equation (6):

[0031] (6)

[0032] in, The initial value of the switching frequency is equal to the resonant frequency when the system starts running.

[0033] Step 6.2, The frequency-variable sinusoidal modulation signal U is obtained by the output of the voltage-controlled oscillator;

[0034] Step 6.3: Compare the modulation signal U with 0 to obtain the switching signal.

[0035] In step 5, when S=2, both the high-voltage and low-voltage switches adopt the EPS modulation method, and all switches can achieve soft switching at this time.

[0036] The EPS modulation method is implemented according to the following steps:

[0037] Step 6.4 will With reference output voltage Subtraction, the error The phase shift angle is calculated by a proportional-integral (PI) controller. The calculation formula is shown in equation (7):

[0038] (7);

[0039] in, This is the initial value of the phase shift angle in the EPS modulation circuit;

[0040] Step 6.5, shift the phase angle Convert to delayed signal The calculation formula is shown in equation (8):

[0041] (8)

[0042] in, The resonant frequency;

[0043] Step 6.6: The switching signal is obtained by processing the pulse signal and the delay module together.

[0044] The calculation is shown in equation (9):

[0045] (9)

[0046] in, This is the DC voltage on the high-voltage side.

[0047] The beneficial effects of this invention are:

[0048] The full-load-range soft-switching bidirectional CLLC resonant converter modulation method proposed in this invention has the advantages of expanding the soft-switching range of the bidirectional CLLC resonant converter and improving the full-load-range efficiency compared with traditional frequency conversion modulation and fixed-frequency extended phase-shift modulation. Attached Figure Description

[0049] Figure 1 This is the circuit topology diagram of the CLLC resonant converter of the present invention;

[0050] Figure 2 This is a diagram of the modulation method for the bidirectional CLLC resonant converter with full load range soft switching according to the present invention. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0052] The circuit topology of a bidirectional CLLC resonant converter, such as Figure 1 As shown, the bidirectional CLLC resonant converter consists of an inverter bridge, a rectifier bridge, a high-frequency transformer, and a resonant cavity, with switching transistors... Switching transistor Switching transistor Switching transistor A single-phase bridge is formed on the high-voltage side, with a primary resonant inductor connected in series at the midpoint of one of the bridge arms. and primary resonant capacitor And connected to the primary side of the high-frequency transformer T, wherein This is the equivalent magnetizing inductance of the primary side of the high-frequency transformer. Switching transistor. Switching transistor Switching transistor Switching transistor Together they form a single-phase bridge on the low-voltage side, with a secondary resonant inductor connected in series at the midpoint of the bridge arm. and secondary resonant capacitor and with high frequency transformer The secondary edges are connected. This is the DC voltage on the high-voltage side. This is the DC voltage on the low-voltage side. This is the high-voltage side filter capacitor. This is a low-voltage side filter capacitor. Let n be the equivalent parallel parasitic capacitance of the switching transistor, and n be the transformer turns ratio. Switching transistor To the switching transistor All use SiC MOSFETs.

[0053] To address the problems of voltage regulation difficulties under light load conditions in frequency conversion modulation of CLLC resonant converters in existing technologies, and the inability to soft switch under heavy load and large phase shift angle when using fixed frequency extended phase shift modulation, this invention provides a technical solution: a bidirectional CLLC resonant converter modulation method with soft switching across the entire load range.

[0054] Modulation methods for a bidirectional CLLC resonant converter with soft switching across the entire load range, such as... Figure 2 As shown, please follow these steps:

[0055] Step 1, sample the low-voltage side voltage With current ;

[0056] Step 2, calculate voltage gain With low-voltage side output power The formula for calculating voltage gain is shown in equation (1), and the formula for calculating low-voltage side output power is shown in equation (2).

[0057] (1)

[0058] (2)

[0059] Step 3, calculate the maximum phase shift angle Maximum phase shift angle The calculation formula is shown in equation (3):

[0060] (3)

[0061] in, V Lmin This is the minimum allowable voltage on the low-voltage side. V Hmax This is the maximum allowable voltage on the high-voltage side;

[0062] Step 4: Calculate the allowable critical output power under EPS modulation. Under this modulation, when the system operating power is less than At this time, all switches can achieve soft switching;

[0063] Maximum operating power during extended phase-shift modulation The calculation formula is shown in equation (4):

[0064] (4)

[0065] in, The resonant frequency, The dead time between the upper and lower bridge arms is at this power. , The switching signal of the bridge arm is delayed. , Maximum phase shift angle of the bridge arm When the system's operating power is less than At this time, all switches can achieve soft switching;

[0066] Step 5: Based on the calculation results from Steps 2 to 4, the operating conditions are divided into three cases, and the state variable S value is obtained based on these three cases.

[0067] The three operating conditions are: boost voltage The voltage is reduced and the output power on the low-voltage side is greater than or equal to the critical output power. The voltage is reduced and the output power on the low-voltage side is less than the critical output power. ;

[0068] The expression for the value of the state variable S is shown in equation (5):

[0069] (5);

[0070] Step 6: Select a modulation method based on the state variable S value described in Step 5;

[0071] When S=0 or S=1, the high-voltage side switch adopts the PFM modulation method, and the low-voltage side switch adopts synchronous rectification SR modulation. At this time, all switches can achieve soft switching.

[0072] The PFM modulation method is implemented according to the following steps:

[0073] Step 6.1, will With reference voltage Subtraction, the error The switching frequency is calculated by the proportional-integral (PI) controller. The calculation formula is shown in equation (6):

[0074] (6)

[0075] in, The initial value of the switching frequency is equal to the resonant frequency when the system starts running.

[0076] Step 6.2, The frequency-variable sinusoidal modulation signal U is obtained by the output of the voltage-controlled oscillator;

[0077] Step 6.3: Compare the modulation signal U with 0 to obtain the switching signal;

[0078] When S=2, both the high-voltage and low-voltage switches adopt the EPS modulation method, and all switches can also achieve soft switching at this time.

[0079] The EPS modulation method is implemented according to the following steps:

[0080] Step 6.4 will With reference output voltage Subtraction, the error The phase shift angle is calculated by a proportional-integral (PI) controller. The calculation formula is shown in equation (7):

[0081] (7);

[0082] in, This is the initial value of the phase shift angle in the EPS modulation circuit;

[0083] Initial value of phase shift angle in EPS modulation circuit The calculation formula is shown in equation (9):

[0084] (9);

[0085] Step 6.5, shift the phase angle Convert to delayed signal The calculation formula is shown in equation (8):

[0086] (8)

[0087] Step 6.6: The switching signal is obtained by processing the pulse signal and the delay module together.

[0088] Step 7: Based on the modulation method selected in Step 6, select the switching signal emitted by the modulation loop. V Q1 ~ V Q8 The eight switching transistors drive the CLLC resonant converter.

Claims

1. A modulation method for a bidirectional CLLC resonant converter with soft switching across the entire load range, characterized in that, The specific steps are as follows: Step 1. Sample the low-voltage side voltage With current ; Step 2. Calculate the voltage gain With low-voltage side output power ; Step 3. Calculate the maximum phase shift angle ; Step 4. Calculate the critical output power under EPS modulation. Under this modulation, when the system operating power is less than At this time, all switches can achieve soft switching; Step 5. Based on the calculation results from Steps 2 to 4, the operating conditions are divided into three cases: boosting... The voltage is reduced and the output power on the low-voltage side is greater than or equal to the critical output power. The voltage is reduced and the output power on the low-voltage side is less than the critical output power. ; The state variable S is obtained based on these three cases, as shown in equation (5): （5） When S=0 or S=1, the high-voltage side switch adopts the PFM modulation method, and the low-voltage side switch adopts the synchronous rectification SR modulation method. At this time, all switches can achieve soft switching. When S=2, both the high-voltage side and the low-voltage side switches adopt the EPS modulation method. At this time, all switches can also achieve soft switching. Step 6. Based on the state variable S value described in Step 5, select a modulation method to ensure soft switching is achieved across the entire load range; Step 7. Based on the modulation method selected in Step 6, select the switching signal emitted by the modulation loop. V Q1 ~ V Q8 The eight switching transistors drive the CLLC resonant converter.

2. The modulation method for a bidirectional CLLC resonant converter with full load range soft switching according to claim 1, characterized in that, The formula for calculating the voltage gain in step 2 is shown in equation (1): （1） in, Where is the DC voltage on the high-voltage side, and n is the transformer turns ratio; The formula for calculating the output power on the low-voltage side is shown in equation (2): （2）。 3. The modulation method for a bidirectional CLLC resonant converter with full load range soft switching according to claim 1, characterized in that, The maximum phase shift angle in step 3 The calculation formula is shown in equation (3): （3） in, V Lmin This is the minimum allowable voltage on the low-voltage side. V Hmax This is the maximum allowable voltage on the high-voltage side.

4. The modulation method for a bidirectional CLLC resonant converter with full load range soft switching according to claim 1, characterized in that, Step 4 involves calculating the critical output power under EPS modulation. The calculation formula is shown in equation (4): （4） in, V Hmax This is the maximum allowable voltage on the high-voltage side. The equivalent parallel parasitic capacitance of the switching transistor, The resonant frequency, It is a primary-side resonant inductor. This is the primary-side equivalent magnetizing inductance of a high-frequency transformer. The dead time between the upper and lower bridge arms is at this power. , The switching signal of the bridge arm is delayed. , Maximum phase shift angle of the bridge arm When the system's operating power is less than At that time, all switches can achieve soft switching.

5. The modulation method for a bidirectional CLLC resonant converter with full load range soft switching according to claim 1, characterized in that, The PFM modulation method is implemented according to the following steps: Step 6.1, will With reference voltage Subtraction, the error The switching frequency is calculated by the proportional-integral controller. The calculation formula is shown in equation (6): （6） in, The initial value of the switching frequency is equal to the resonant frequency when the system starts running. Step 6.2, The frequency-variable sinusoidal modulation signal U is obtained by the output of the voltage-controlled oscillator; Step 6.3: Compare the modulation signal U with 0 to obtain the switching signal.

6. The modulation method for a bidirectional CLLC resonant converter with full load range soft switching according to claim 1, characterized in that, The EPS modulation method is implemented according to the following steps: Step 6.4 will With reference output voltage Subtraction, the error The phase shift angle is calculated by the proportional-integral controller. The calculation formula is shown in equation (7): （7）； in, This is the initial value of the phase shift angle in the EPS modulation circuit; Step 6.5, shift the phase angle Convert to delayed signal The calculation formula is shown in equation (8): （8）； in, The resonant frequency; Step 6.6: The switching signal is obtained by processing the pulse signal and the delay module together.

7. The modulation method for a bidirectional CLLC resonant converter with full load range soft switching according to claim 6, characterized in that, The The calculation formula is shown in equation (9): （9） in, This is the DC voltage on the high-voltage side.

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