A primary side feedback half-bridge LLC resonant converter output current prediction system

Abstract

The application discloses a primary side feedback half-bridge LLC resonant converter output current prediction system, which comprises a main topology circuit and a closed-loop control system; the main topology circuit adopts a primary side feedback and LLC resonant converter structure; the closed-loop control system comprises a resonant capacitor voltage sampling module, an output current prediction module and a loop control module; the loop control module outputs a control signal duty1 of a switching tube M1 and a control signal duty2 of a switching tube M2; and the closed-loop control system is connected with a controlled switching power supply to form a closed loop. The application can measure the voltage value Vcr on the resonant capacitor Cr to accurately predict the output current through the primary side feedback control method, reduces the use of a sampling resistor, reduces the system loss, and realizes high-precision output current prediction.

Description

Technical Field

[0001] This invention relates to the field of isolated converter technology, and more particularly to an output current prediction system for a primary-side feedback half-bridge LLC resonant converter. Background Technology

[0002] With technological advancements, switching power supplies are widely used in low-to-medium power applications. Isolated switching power supplies achieve electrical isolation between input and output through transformers, offering advantages such as safety isolation and high reliability. LLC resonant converters offer unparalleled advantages over ordinary series resonant converters in terms of increasing switching frequency, reducing the size of passive components, and improving power output density. Compared to traditional half-bridge LLC resonant converters based on secondary-side feedback technology, half-bridge LLC resonant converters based on primary-side feedback technology have a simpler circuit structure and eliminate the need for nonlinear devices such as optocouplers, further improving their reliability, lifespan, and integration.

[0003] Traditional PSR output current prediction methods primarily study linear power supply current waveforms. However, LLC resonant converters exhibit significant current nonlinearity, making traditional linear current-based PSR output current prediction methods unsuitable for direct application. Therefore, researching PSR output current prediction methods applicable to LLC resonant converters with nonlinear currents is crucial for improving circuit reliability and reducing implementation costs. Currently, existing sampling resistors reduce converter system efficiency, and high-speed ADCs may be required in the sampling module to sample changing currents, leading to higher system costs. Summary of the Invention

[0004] The purpose of this invention is to provide an output current prediction system for a primary-side feedback half-bridge LLC resonant converter, which simplifies circuit control and achieves output current prediction through the input-side capacitor voltage. This system has advantages such as reducing system losses and simplifying circuit implementation.

[0005] The technical solution to achieve the purpose of this invention is as follows:

[0006] A primary-side feedback half-bridge LLC resonant converter output current prediction system includes a main topology circuit and a closed-loop control system. The main topology circuit adopts a primary-side feedback and LLC resonant converter structure. The closed-loop control system includes a resonant capacitor voltage sampling module, an output current prediction module, and a loop control module. The resonant capacitor voltage sampling module is used to collect the voltage value Vcr on the resonant capacitor Cr and output it to the output current prediction module. The output current prediction module obtains the average load current based on the voltage value and the switching transistor control signal and outputs it to the loop control module. The loop control module outputs the control signal duty1 for switching transistor M1 and the control signal duty2 for switching transistor M2. The closed-loop control system is connected to the controlled switching power supply to form a closed loop.

[0007] Furthermore, the proposed resonant capacitor voltage sampling module adopts a voltage divider sampling method, using a voltage divider circuit to reduce the input voltage to a suitable analog voltage signal, and then performs signal calculation and processing through an analog circuit or converts the analog signal into a digital signal through an ADC module before performing calculation and processing.

[0008] Furthermore, the output signal Vcr_s of the resonant capacitor voltage sampling module is proportional to the input signal Vcr, i.e., Vcr_s = k * Vcr, where k is a proportionality coefficient.

[0009] Furthermore, the voltage divider circuit converts the voltage Vcr of capacitor Cr into a smaller, proportionally smaller voltage through two voltage divider resistors R1 and R2. Therefore, the proportionality coefficient k is:

[0010]

[0011] Where N is the sampling bit depth of the ADC module, V ref Input a reference voltage value to the ADC module.

[0012] Furthermore, the output current prediction module calculates the resonant current i based on the input signal. Lr Excitation current i m Thus, the output diode current i is obtained. d and the average current of the output load i o .

[0013] Furthermore, the calculation of the resonant current includes:

[0014] Define five timestamps t1, t2, t3, t4, and t5 in a single switching cycle, where t1 is the start time of the current cycle and the rising edge of duty1, t2 is the time when Vcr_s is at its lowest value in the current cycle, t3 is the time when duty1 is at its falling edge in the current cycle, t4 is the time when Vcr_s is at its highest value in the current cycle, and t5 is the time when duty1 is at its rising edge in the next cycle. Based on the five timestamps t1, t2, t3, t4, and t5, save the voltage value on Vcr_s and record it as Vcr_s(t1), Vcr_s(t2), Vcr_s(t3), Vcr_s(t4), and Vcr_s(t5).

[0015] The resonant current is determined based on the voltage Vcr:

[0016]

[0017] Furthermore, the excitation current is:

[0018]

[0019] i Lr At times t1, t3, and t5, and i m The values ​​are equal.

[0020] Furthermore, the average load current i o for:

[0021]

[0022] Where T is the period, and i is the diode current. d For i d (t)=n ps *(|i Lr (t)-i m (t)|), n ps It is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding.

[0023] Furthermore, the loop control module includes a switch control module and a loop control algorithm module. The loop control algorithm module controls the output current Io to be equal to the target reference current I. REF The loop control algorithm module is implemented through the switch control module, and the drive signal of the output switch is obtained. Based on the drive signal, duty is set to "1" to turn on the switch; duty is set to "0" to turn off the switch.

[0024] Furthermore, the loop control algorithm employs a PID control algorithm.

[0025] Compared with the prior art, the significant advantages of the present invention are:

[0026] (1) The present invention adopts a primary-side feedback control system, which realizes the prediction of the output current through the input-side capacitor voltage. Specifically, the voltage value Vcr on the resonant capacitor Cr is measured by the voltage sampling module using methods such as resistor voltage division and capacitor voltage division and is input to the closed-loop control system without increasing the circuit complexity. It can still predict the output current with high accuracy without the need for sampling resistors. It has the advantages of low cost and simple control.

[0027] (2) The present invention predicts the relevant current waveform by capacitor voltage, which can be extended to other isolated or non-isolated switching power supply circuit structures, and has the characteristics of versatility, reusability and portability. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the circuit topology and loop control of a primary-side feedback half-bridge LLC resonant converter.

[0029] Figure 2 This is a key waveform diagram of the output current prediction module of the primary-side feedback half-bridge LLC resonant converter.

[0030] Figure 3 (a) is a schematic diagram of the voltage sampling module. Figure 3 (b) is a waveform diagram of the voltage values ​​Vcr and Vcr_s on the resonant capacitor Cr.

[0031] Figure 4 (a) is a schematic diagram of the simulation results of the key signal waveforms of the current prediction module. Figure 4 (b) is a schematic diagram of the simulation results of the voltage waveform across the resonant capacitor Cr. Figure 4 (c) is i Lr Waveform of signal simulation results Figure 4 (d) is i Lr Comparison chart of signal simulation results and theoretically calculated waveforms. Figure 4 (e) is i m i Lr Simulation result waveform diagram Figure 4 (f) is i d Comparison of waveforms from simulation and theoretical analysis Figure 4 (g) is i o Signal waveform diagram. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Combination Figure 1 A primary-side feedback half-bridge LLC resonant converter output current prediction system is disclosed. This system comprises a main topology circuit and a closed-loop control system. The main topology circuit adopts a primary-side feedback and LLC resonant converter structure. Its structure is as follows: the negative terminal of the input DC voltage is connected to the input ground, the positive terminal of the input DC voltage is connected to the drain of switch M1, the source terminal of switch M1 is connected to the drain of switch M2, and the source terminal of switch M2 is connected to the input ground. The two switches M1 and M2 form a half-bridge structure, whose driving signals are complementary signals duty1 and duty2 with variable duty cycles. The inductor Lr, resonant capacitor Cr, and transformer input-side inductance L are also specified. p A series connection is formed to create an LLC resonant network, which is connected between the source terminal and ground terminal of the switching transistor M1. One end of Lr is connected to the source terminal of the switching transistor M1, and the other end is connected to the primary winding W of the transformer. p The same-named terminal, Cr, is grounded at one end and connected to the primary winding W at the other end. p The voltage value Vcr across the resonant capacitor Cr is measured by a voltage sampling circuit at the opposite terminal and input to the closed-loop control system. Output winding W s A rectifier bridge is connected, whose structure includes four diodes DR1, DR2, DR3, and DR4. The output rectifier bridge is directly connected to the output capacitor C. L Above, output capacitor C L The negative terminal is connected to the output ground, and the load R L With capacitor C L Parallel connection. The input signal of the closed-loop control system is the voltage value Vcr on the resonant capacitor Cr, and the output signals are the control signal duty1 of switch M1 and the control signal duty2 of switch M2.

[0034] The proposed closed-loop control system uses the voltage Vcr across the resonant capacitor Cr as its input signal and the control signals duty1 and duty2 of the switching transistor as its output signals. The closed-loop control system includes a resonant capacitor voltage sampling module, an output current prediction module, and a loop control module. The loop control module includes a switching control module and a loop control algorithm. This control system is connected to the controlled switching power supply to form a closed loop. This invention can accurately predict the output current by measuring the voltage Vcr across the resonant capacitor Cr using a primary-side feedback control method, reducing the use of sampling resistors and lowering system losses.

[0035] The proposed resonant capacitor voltage sampling module takes the voltage value Vcr on capacitor Cr as its input sampling signal and outputs the sampling result Vcr_s of Vcr, which is then passed to the output current prediction module. The high-voltage signal sampling module employs a voltage divider sampling method, using a voltage divider circuit to reduce the higher input voltage to a suitable lower analog voltage signal. The signal is then processed through analog circuitry or converted into a digital signal by an ADC module before processing. The output signal Vcr_s is proportional to the input signal Vcr, and their ratio satisfies Vcr_s = k * Vcr, where k is a constant.

[0036] The output current prediction module takes Vcr_s, duty1, and duty2 signals as inputs and outputs the average output load current i. o Calculate the resonant current i based on the input signal. Lr Excitation current i m The expression is used to obtain the output diode current i. d and the average current of the output load i o Assume that duty1 and duty2 signals are complementary. The calculation steps are as follows:

[0037] ① Define five timestamps t1, t2, t3, t4, and t5 within a single switching cycle. t1 is the start time of the current cycle, which is the rising edge of duty1. t2 is the time when Vcr_s reaches its lowest value in the current cycle. t3 is the time when duty1 falls in the current cycle. t4 is the time when Vcr_s reaches its highest value in the current cycle. t5 is the time when duty1 rises in the next cycle. Based on these five timestamps t1, t2, t3, t4, and t5, save the voltage values ​​on Vcr_s and record them as Vcr_s(t1), Vcr_s(t2), Vcr_s(t3), Vcr_s(t4), and Vcr_s(t5).

[0038] Considering the input current i Lr It is approximately a sinusoidal current, and the voltage Vcr is equal to the current i. Lr Integrating over capacitor Cr, we have:

[0039]

[0040] From the Vcr(t) voltage signal, i can be derived Lr Signal waveform. Assume i Lr The signal waveform is

[0041] i Lr (t)=I amp sin(ω(t-t2)) (2)

[0042] The Vcr voltage signal can be represented as:

[0043]

[0044]

[0045] Wherein, ω can be obtained from t2 and t4:

[0046]

[0047] Since the value of Vcr(t) can be obtained from Vcr_s(t), I can be calculated using the above formulas (3) and (4). amp The value:

[0048]

[0049] That is, i Lr Mathematical expression for signal waveform:

[0050]

[0051] ② At the rising edges t1, t5 and falling edge t3 of the duty1 signal, i Lr At times t1, t3, and t5, and i m The values ​​are equal.

[0052]

[0053] Given the coordinates of two points (t1, i) m (t1)) and (t3, i m (t3)) can be used to obtain i m (t) Signal waveform between t1 and t3.

[0054] Given (t3, i) m (t3)) and (t5, i m (t5) can be used to obtain i m The signal waveform between t3 and t5 is shown in Equation (8).

[0055]

[0056] ③ Output diode current i d The calculation formula for n is as follows, ps N is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. p and N s The ratio of the number of turns.

[0057] i d (t)=n ps *(|i Lr (t)-i m (t)|) (9)

[0058] Output load average current i o The calculation formula is as follows:

[0059]

[0060] Where T is the period.

[0061] Through loop control algorithm design, i o Equal to the target reference current I to be achieved REF The switching control module outputs a drive signal for the switching transistor, which, based on the control variable, sets duty to "1" to turn on the switching transistor and sets duty to "0" to turn it off.

[0062] This invention can accurately predict the output current by measuring the voltage Vcr on the resonant capacitor Cr using a primary-side feedback control method, thereby reducing the use of sampling resistors and lowering system losses.

[0063] Example

[0064] The following analysis uses an example of an input DC voltage of 400V, an output voltage of 60V, and an output current of 1.3A.

[0065] The main topology parameters of the primary-side feedback half-bridge LLC resonant converter are shown in the table below:

[0066]

[0067] Figure 2 These are key waveforms of the output current prediction module for a primary-side feedback half-bridge LLC resonant converter. From top to bottom, they are duty1, duty2, and i. Lr (t), Vcr(t), Vcr_s(t), i d The signal waveform of (t).

[0068] Figure 3 (a) is a voltage sampling module implementation method, which converts the high voltage Vcr of capacitor Cr into a proportional small voltage through voltage divider resistors R1 and R2. After voltage division by resistors, the output voltage is Vcr_d, which is then input to the ADC module for sampling to obtain the digital quantity Vcr_s.

[0069] Assuming the voltage divider resistors are R1 and R2, the ADC sampling bit depth is N bits, and the ADC input reference voltage value is V... ref The formula for calculating the proportionality coefficient K is as follows.

[0070] Vcr_s=k×Vcr

[0071]

[0072]

[0073] Figure 3 (b) is a waveform diagram of the voltage values ​​Vcr and Vcr_s on the resonant capacitor Cr. Given that the voltage divider resistors R1 and R2 are 1K and 99K respectively, the ADC sampling bit is 10 bits, and the ADC input reference voltage is 4V, the value of K can be calculated as 2.56 according to formula (11).

[0074] Figure 4 (a) is a schematic diagram of the simulation results of the key signal waveforms of the current prediction module. From top to bottom, they are duty1, duty2, and i. Lr (t), i m (t), Vcr(t), i d The signal waveform of (t). The loop control algorithm design yields the output current i. o Then, the output current Io can be controlled to equal the target reference current I. REF This achieves constant output current and can also be used for load detection. A loop control algorithm is implemented through a switch control module, which obtains the drive signal for the output switch. Based on the drive signal, duty is set to "1" to turn on the switch; duty is set to "0" to turn off the switch.

[0075] Figure 4 (b) is a schematic diagram of the simulation results of the voltage waveform across the resonant capacitor Cr. The simulation results show the Vcr voltage values ​​at five times t1, t2, t3, t4, and t5 within a single switching cycle, recorded as Vcr(t1), Vcr(t2), Vcr(t3), Vcr(t4), and Vcr(t5). At t1 = 6.243 * 10⁻⁶, the voltage value is... -3 At time t1, Vcr is 134.6V; t2 = 6.244 * 10 -3 At time t3, Vcr is 120.3V; t3 = 6.25 * 10 -3 At time t4, Vcr is 265.4V; t4 = 6.251 * 10 -3 At time t5, Vcr is 279.7V, and t5 = 6.258 * 10⁻⁶. -3 At time t1, Vcr is 134.4V; based on the ratio k, the values ​​of Vcr_s(t1), Vcr_s(t2), Vcr_s(t3), Vcr_s(t4), and Vcr_s(t5) can be calculated to be 344.576, 307.968, 679.424, 716.032, and 344.064, respectively.

[0076] Figure 4 (c) is i Lr The waveform diagram of the signal simulation result shows that I is obtained from the simulation. amp The value is 0.875. I is calculated according to formula (5).amp The theoretical result is 0.892, from Figure 4 (b) The data shows that ω is 418879 rad / s, and the theoretically calculated ω is 418879.0205 rad / s. Comparative analysis reveals that the internal resistance of the system components and the impedance of capacitors and inductors affect i. Lr The error between the theoretical value and the simulation result of the signal amplitude is about 1.9%, which is within the acceptable range.

[0077] Figure 4 (d) is i Lr Signal simulation results and theoretical calculations Lr_cal Waveform comparison chart, where the upper waveform is i Lr The waveform diagram of the signal simulation result is shown below. The waveform diagram of the theoretical calculation is shown below. Through comparative analysis, the simulation result and the calculated theoretical sine wave basically coincide.

[0078] Figure 4 (e) is i m i Lr The simulation result waveform diagram shows the waveform represented by the dashed line i. m Waveform diagram, solid line waveform is i Lr The waveform diagram of the signal simulation results shows that it satisfies formula (7), and the simulation results are consistent with the theoretical analysis.

[0079] Figure 4 (f) is i d i d_cal Waveform comparison chart, where the solid line waveform represents i. d The waveform diagram of the signal simulation result shows that the dashed line represents the theoretically calculated i. d_cal The waveform diagram shows that, due to I... amp The theoretical calculation results are higher than the simulation results. amp The value needs to be large. From formula (9), the theoretically calculated waveform i d_cal in i d Above the simulated waveform.

[0080] Figure 4 (g) is i o Signal waveform diagram. As can be seen from the diagram, the simulation output i... o The current prediction error is 2.1%, which is 1.3275A, while the design specification is 1.3A. This is within an acceptable error range.

[0081] Comparative observation shows that the simulated waveforms are consistent with the theoretical analysis, proving the feasibility of the output current prediction algorithm proposed in this patent.

[0082] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the invention is limited to these descriptions. Many variations of the invention described herein are possible, and constant current algorithms can be used for control in other switching power supplies. Such variations should not deviate intentionally from the spirit and scope of the invention. Therefore, all modifications that are obvious to those skilled in the art should be included within the scope of these claims.

Claims

1. A primary-side feedback half-bridge LLC resonant converter output current prediction system, comprising a main topology circuit and a closed-loop control system, wherein the main topology circuit adopts a primary-side feedback and LLC resonant converter structure, characterized in that: The closed-loop control system includes a resonant capacitor voltage sampling module, an output current prediction module, and a loop control module. The resonant capacitor voltage sampling module is used to collect the voltage value Vcr on the resonant capacitor Cr and output it to the output current prediction module. The output current prediction module obtains the average load current based on the voltage value and the switching transistor control signal and outputs it to the loop control module. The loop control module outputs the control signal duty1 for switching transistor M1 and the control signal duty2 for switching transistor M2. The closed-loop control system is connected to the controlled switching power supply to form a closed loop. The output current prediction module calculates the resonant current i based on the input signal. Lr Excitation current i m Thus, the output diode current i is obtained. d and the average current of the output load i o ; The calculation of the resonant current includes: Five timestamps t1, t2, t3, t4, and t5 are defined in a single switching cycle. Here, t1 is the start time of the current cycle, which is the rising edge of duty1. t2 is the time when Vcr_s is at its lowest value in the current cycle. t3 is the time when duty1 is at its falling edge in the current cycle. t4 is the time when Vcr_s is at its highest value in the current cycle. t5 is the time when duty1 is at its rising edge in the next cycle. Vcr_s is the output signal of the resonant capacitor voltage sampling module. Based on the five timestamps t1, t2, t3, t4, and t5, the voltage values ​​on Vcr_s are saved and recorded as Vcr_s(t1), Vcr_s(t2), Vcr_s(t3), Vcr_s(t4), and Vcr_s(t5). The resonant current is determined based on the voltage Vcr: The excitation current is: i Lr At times t1, t3, and t5, and i m The values ​​are equal; The average current of the output load i o for: Where T is the period, and i is the output diode current. d for n ps It is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding.

2. The primary-side feedback half-bridge LLC resonant converter output current prediction system according to claim 1, characterized in that, The proposed resonant capacitor voltage sampling module adopts a voltage divider sampling method. It uses a voltage divider circuit to reduce the input voltage to a suitable analog voltage signal, and then performs signal calculation and processing through an analog circuit or converts the analog signal into a digital signal through an ADC module before performing calculation and processing.

3. The primary-side feedback half-bridge LLC resonant converter output current prediction system according to claim 2, characterized in that, The output signal Vcr_s of the resonant capacitor voltage sampling module is proportional to the input signal Vcr, i.e., Vcr_s = k * Vcr, where k is the proportionality coefficient.

4. The primary-side feedback half-bridge LLC resonant converter output current prediction system according to claim 2, characterized in that, The voltage divider circuit converts the voltage Vcr across capacitor Cr into a smaller, proportionally smaller voltage using two voltage divider resistors R1 and R2. Therefore, the proportionality coefficient k is: Where N is the sampling bit depth of the ADC module, V ref Input a reference voltage value to the ADC module.

5. The output current prediction system for a primary-side feedback half-bridge LLC resonant converter according to claim 1, characterized in that, The loop control module includes a switch control module and a loop control algorithm module. The loop control algorithm module controls the output current Io to be equal to the target reference current I. REF The loop control algorithm module is implemented through the switch control module, and the drive signal of the output switch is obtained. Based on the drive signal, duty is set to "1" to turn on the switch; duty is set to "0" to turn off the switch.

6. The output current prediction system for a primary-side feedback half-bridge LLC resonant converter according to claim 5, characterized in that, The loop control algorithm uses the PID control algorithm.

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