Half-bridge LLC circuit for aerospace

Abstract

The half-bridge LLC circuit comprises an LC filter circuit, an MOS tube bridge arm, a capacitor bridge arm, a resonant inductor Lr, a transformer, a diode D1, a diode D2, a diode D3, a diode D4, a filter capacitor Co, a resistor RL, a compensator, an amplitude limiter, a voltage-controlled oscillator, a PWM controller, an isolation driver, a comparator and a PI controller. According to the invention, the problems of loss, electromagnetic interference and the like caused by improvement of the switching frequency of the existing hard switching circuits such as forward and half-bridge circuits in the space navigation secondary power supply system are solved.

Description

Technical Field

[0001] This invention belongs to the field of LLC circuit technology, and particularly relates to a half-bridge LLC circuit for aerospace applications. Background Technology

[0002] Networked satellites are characterized by low cost, small size, light weight, and complex functional requirements, which places more stringent demands on the size and efficiency of space secondary power supplies. Increasing the switching frequency of existing hard-switching circuits such as forward converters and half-bridge converters in current space secondary power supply systems can lead to problems such as power loss and electromagnetic interference. Summary of the Invention

[0003] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a half-bridge LLC circuit for aerospace applications, which solves the problems of loss and electromagnetic interference caused by increasing the switching frequency of existing hard switching circuits such as forward converters and half-bridge converters in aerospace secondary power supply systems.

[0004] The objective of this invention is achieved through the following technical solution: a half-bridge LLC circuit for aerospace applications, comprising: an LC filter circuit, a MOS transistor bridge arm, a capacitor bridge arm, and a resonant inductor L. r Transformer, diode D1, diode D2, diode D3, diode D4, filter capacitor C o Resistance R L The circuit includes a compensator, a limiter, a voltage-controlled oscillator, a PWM controller, an isolation driver, a comparator, and a PI controller; wherein the LC filter circuit is connected to the MOS bridge arm, and the MOS bridge arm is connected in parallel with the capacitor bridge arm; the cathode of diode D1 is connected to one end of the capacitor bridge arm, the anode of diode D1 is connected to the cathode of diode D2, and the anode of diode D2 is connected to the other end of the capacitor bridge arm; the resonant inductor L... r One end is connected to the middle of the capacitor bridge arm, and the resonant inductor L r The other end is connected to one end of the primary winding of the transformer, and the other end of the primary winding of the transformer is connected to the middle of the MOS bridge arm; the anode of diode D3 is connected to one end of the secondary winding of the transformer, and the cathode of diode D3 is connected to the filter capacitor C. o One end of the resistor R L One end of the capacitor is connected to the negative terminal of diode D4, and the positive terminal of diode D4 is connected to the other end of the secondary side of the transformer. The filter capacitor C... o The other end, the resistor R LThe other end and the middle of the secondary side of the transformer are both grounded; the compensator is connected to the limiter, the limiter is connected to the voltage-controlled oscillator, the voltage-controlled oscillator is connected to the PWM controller, the PWM controller is connected to the isolation driver, and the isolation driver is connected to the MOS bridge arm; the comparator is connected to the PWM controller, and the PI controller is connected to the isolation driver.

[0005] In the aforementioned aerospace half-bridge LLC circuit, the output voltage With reference voltage After calculation by the compensator, the EA signal is generated. The EA signal is then sent to the voltage-controlled oscillator after passing through the limiter. The VCO output signal of the voltage-controlled oscillator controls the frequency control pin of the PWM controller. The PWM control signal output by the PWM controller is sent to the drive end of the MOS bridge arm through the isolation driver.

[0006] In the aforementioned aerospace half-bridge LLC circuit, the overcurrent protection signal OCP generated by the comparator is sent to the PWM controller.

[0007] In the aforementioned aerospace half-bridge LLC circuit, the LC filter circuit includes an inductor. L in and capacitor C in ; wherein, the inductor L in One end of the inductor is connected to the positive terminal of the input voltage. L in The other end is respectively connected to the capacitor C in One end of the capacitor is connected to one end of the MOS bridge arm, one end of the capacitor bridge arm, and the cathode of diode D1; the capacitor... C in The other end of the capacitor is connected to the negative terminal of the input voltage. C in The other end is connected to the other end of the MOS bridge arm, the other end of the capacitor bridge arm, and the positive terminal of diode D2, respectively.

[0008] In the aforementioned aerospace half-bridge LLC circuit, the MOS bridge arm includes MOS transistors. Q 1 and MOSFET Q 2; wherein, the MOS transistor Q The drain of 1 is respectively connected to the inductor L in The other end of the transformer is connected to the other end of the capacitor bridge arm and the positive terminal of diode D2; the other end of the primary side of the transformer is connected to the MOS transistor. Q The source of 1 is connected; the MOS transistor Q The source of 1 and the MOS transistorQ The drains of 2 are connected together, and the MOS transistor is... Q The source of 2 is connected to the negative terminal of the input voltage.

[0009] The aforementioned aerospace half-bridge LLC circuit also includes diodes D5 and D6; wherein the cathode of diode D5 is connected to the MOSFET. Q The drain of diode D1 is connected to the MOSFET, and the anode of diode D5 is connected to the MOSFET. Q The source of diode D1 is connected to the source of diode D6; the cathode of diode D6 is connected to the MOS transistor. Q The drain of diode D2 is connected to the MOSFET, and the anode of diode D6 is connected to the MOSFET. Q The source poles of 2 are connected.

[0010] In the aforementioned aerospace half-bridge LLC circuit, the capacitor bridge arm includes a capacitor. C r1 and capacitor C r2 ; wherein, the capacitor C r1 One end is respectively connected to the inductor L in The other end, the MOS transistor Q The drain of diode D1 is connected to the anode of diode D2; the capacitor... C r1 The other end is respectively connected to the capacitor C r2 One end of the transformer is connected to one end of the primary side of the transformer.

[0011] In the aforementioned aerospace half-bridge LLC circuit, the output voltage... With reference voltage The input is compared with the PI controller to generate a control signal, which is then sent to the isolation driver to control the on / off state of the primary-side MOSFET.

[0012] In the aforementioned aerospace half-bridge LLC circuit, the compensator includes resistors R1, R2, R3, R4, and R5, capacitors C1, C2, and C3, and an operational amplifier; wherein one end of resistor R1 and one end of resistor R3 are both connected to a reference voltage. The other end of resistor R1 is connected to the inverting input of the operational amplifier; the other end of resistor R3 is connected to one end of capacitor C3, the other end of capacitor C3 is connected to one end of resistor R2, the other end of resistor R2 is connected to one end of capacitor C2, and the other end of capacitor C2 is connected to the output terminal of the operational amplifier; one end of capacitor C1 is connected to the inverting input of the operational amplifier; and one end of resistor R4 is connected to the output voltage. The other end of resistor R4 and one end of resistor R5 are both connected to the non-inverting input of the operational amplifier; the other end of resistor R5 is grounded.

[0013] In the aforementioned aerospace half-bridge LLC circuit, the transfer function of the compensator is: ; in, Let the transfer function of the compensator be... For DC gain, The first zero-point angular frequency, The second zero-point angular frequency, The first pole angular frequency, The second pole angular frequency, For the Laplace operator.

[0014] Compared with the prior art, the present invention has the following advantages: This invention solves the problems of power loss and electromagnetic interference caused by increasing the switching frequency of existing hard-switching circuits such as forward converters and half-bridge converters in aerospace secondary power supply systems. Attached Figure Description

[0015] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A block diagram of a half-bridge LLC circuit for aerospace applications provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the AC equivalent circuit of an LLC converter provided in an embodiment of the present invention; Figure 3 The voltage transfer ratio function curve provided for the embodiments of the present invention ( L n =5) Schematic diagram; Figure 4 Provided for embodiments of the present invention L n A schematic diagram of the gain curve under the conditions of Q=4.5 and Q=0.39; Figure 5 This is a schematic diagram of LLC voltage gain curve considering parasitic parameters provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of a dual-pole-dual-zero compensator provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of a voltage closed-loop control block diagram provided in an embodiment of the present invention; Figure 8This is a schematic diagram of the amplitude-frequency curve of the controlled object provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of the phase frequency curve of the controlled object provided in an embodiment of the present invention; Figure 10 Bode plot of an input of 80V and an output of 120W provided in an embodiment of the present invention; Figure 11 Bode plot of the input 100V and output 120W as provided in the embodiments of the present invention; Figure 12 Bode plot of the input 110V and output 120W as provided in the embodiments of the present invention; Figure 13 A schematic diagram of LLC waveform under the conditions of input voltage 80V and output 120W provided in an embodiment of the present invention; Figure 14 This is a schematic diagram of the LLC waveform under the conditions of 100V input voltage and 120W output provided in an embodiment of the present invention. Figure 15 This is a schematic diagram of the LLC waveform under the conditions of an input voltage of 104V and an output of 120W, provided in an embodiment of the present invention. Figure 16 A schematic diagram of LLC waveform under the conditions of input voltage 110V and output 120W provided in an embodiment of the present invention; Figure 17 This is a schematic diagram of the no-load output waveform of the LLC circuit provided in an embodiment of the present invention; Figure 18 A schematic diagram of the LLC circuit efficiency curve provided in an embodiment of the present invention. Detailed Implementation

[0016] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0017] High power density and miniaturization are the main trends in the development of aerospace secondary power supplies, typically achieved by increasing the frequency. However, increasing the frequency can lead to problems such as increased switching losses and electromagnetic interference. Therefore, high switching frequencies are usually combined with soft-switching circuits. Considering the implementation methods of control circuits and the availability of control chips, soft-switching circuits applicable in the aerospace field include asymmetrical half-bridges, LLC circuits, phase-shifted full-bridges, and phase-shifted full-bridge LLC circuits. Phase-shifted full-bridges and phase-shifted full-bridge LLC circuits are suitable for high-power applications above 300W in aerospace applications. For circuits below 300W, asymmetrical half-bridges and LLC circuits offer advantages in terms of cost and size.

[0018] LLC circuits are resonant circuits. Compared to asymmetrical half-bridge circuits, they offer advantages such as achieving ZVS (Zero Voltage Switching) for the primary-side switch and ZCS (Zero Voltage Strain Switching) for the secondary-side switch across the entire load range, lower voltage and current stress on the secondary switch, and no DC bias magnetization in the transformer. These advantages make them suitable for widespread use in the aerospace field. LLC circuits operate under frequency conversion control conditions with a constant duty cycle of 50%, and there are currently no dedicated resonant control chips available for this purpose in the aerospace industry.

[0019] To address this issue, this embodiment proposes a half-bridge LLC frequency conversion control strategy suitable for the aerospace field, based on a half-bridge LLC circuit with clamping diodes. Frequency conversion control is achieved through a combination of a traditional PWM control chip and a voltage-controlled oscillator. To address the issue of high output voltage drift under no-load conditions in the half-bridge LLC circuit, an no-load control method is proposed to suppress the output voltage. Considering the multi-zero and multi-pole characteristics of the LLC circuit, a double-zero-bipolar compensator is used for loop stability design. Finally, a 100V to 12V LLC circuit with a rated power of 120W is built to verify the feasibility of the proposed frequency conversion control strategy.

[0020] like Figure 1 As shown, this embodiment provides a half-bridge LLC circuit for aerospace applications, including: an LC filter circuit, a MOS bridge arm, a capacitor bridge arm, and a resonant inductor L. r Transformer, diode D1, diode D2, diode D3, diode D4, filter capacitor C o Resistance R L The circuit includes a compensator, a limiter, a voltage-controlled oscillator, a PWM controller, an isolation driver, a comparator, and a PI controller; wherein the LC filter circuit is connected to the MOS bridge arm, and the MOS bridge arm is connected in parallel with the capacitor bridge arm; the cathode of diode D1 is connected to one end of the capacitor bridge arm, the anode of diode D1 is connected to the cathode of diode D2, and the anode of diode D2 is connected to the other end of the capacitor bridge arm; the resonant inductor L... r One end is connected to the middle of the capacitor bridge arm, and the resonant inductor L rThe other end is connected to one end of the primary winding of the transformer, and the other end of the primary winding of the transformer is connected to the middle of the MOS bridge arm; the anode of diode D3 is connected to one end of the secondary winding of the transformer, and the cathode of diode D3 is connected to the filter capacitor C. o One end of the resistor R L One end of the capacitor is connected to the negative terminal of diode D4, and the positive terminal of diode D4 is connected to the other end of the secondary side of the transformer. The filter capacitor C... o The other end, the resistor R L The other end and the middle of the secondary side of the transformer are both grounded; the compensator is connected to the limiter, the limiter is connected to the voltage-controlled oscillator, the voltage-controlled oscillator is connected to the PWM controller, the PWM controller is connected to the isolation driver, and the isolation driver is connected to the MOS bridge arm; the comparator is connected to the PWM controller, and the PI controller is connected to the isolation driver.

[0021] The circuit front end is connected to LC The filter circuit is composed of L in and C in Combination; the primary-side power circuit consists of MOSFET bridge arms and capacitor bridge arms, the MOSFET bridge arms being composed of... Q 1 and Q 2 series, capacitor bridge arm consists of C r1 and C r2 Composed of series, D 1 and D The two diodes are connected in parallel respectively. C r1 and C r2 Both ends; L r The inductor is a resonant circuit, with one end connected to the middle of the capacitor bridge arm and the other end connected to the transformer. The other end of the transformer is connected to the middle of the MOSFET bridge arm. The secondary side of the transformer uses a full-wave rectifier circuit. D 3. D 4 and output filter capacitor C o The output voltage, after passing through a compensator and limiting, is input to a voltage-controlled oscillator (VCO). The VCO is connected to the frequency control pin RT of the PWM controller. The PWM control signal output by the PWM controller is sent to the drive terminal of the MOSFET via a driver. The overcurrent protection signal OCP generated by the comparator is sent to the PWM controller. The signal generated by the PI controller is sent to the driver.

[0022] The aerospace-grade half-bridge LLC circuit consists of a power circuit and a control circuit. The control circuit includes a frequency conversion control circuit, an overcurrent protection circuit, and a light-load mode control circuit. After output sampling, compensation network, and output voltage limiting, the output signal EA of the operational amplifier is sent to the VCO voltage-controlled oscillator. The VCO output controls the RT pin of the PWM controller, realizing the frequency conversion control of the LLC circuit. Finally, the output signal of the PWM controller is sent to an isolation driver to control the turn-on and turn-off of the primary-side MOSFET.

[0023] Output voltage With reference voltage After calculation by the compensator, the EA signal is generated. The EA signal is then sent to the voltage-controlled oscillator after passing through the limiter. The VCO output signal of the voltage-controlled oscillator controls the frequency control pin of the PWM controller. The PWM control signal output by the PWM controller is sent to the drive end of the MOS bridge arm through the isolation driver.

[0024] The overcurrent protection signal OCP generated by the comparator is sent to the PWM controller. The control loop is equipped with a current protection circuit, which generates the overcurrent protection signal OCP by comparing the sampled signal with the reference signal. The OCP signal is then sent to the PWM controller to shut down the output of the drive signal.

[0025] LC filter circuits include inductors L in and capacitor C in ; wherein, the inductor L in One end of the inductor is connected to the positive terminal of the input voltage. L in The other end is respectively connected to the capacitor C in One end of the capacitor is connected to one end of the MOS bridge arm, one end of the capacitor bridge arm, and the cathode of diode D1; the capacitor... C in The other end of the capacitor is connected to the negative terminal of the input voltage. C in The other end is connected to the other end of the MOS bridge arm, the other end of the capacitor bridge arm, and the positive terminal of diode D2, respectively.

[0026] MOSFET bridge arms include MOSFETs Q 1 and MOSFET Q 2; wherein, the MOS transistor Q The drain of 1 is respectively connected to the inductor L in The other end of the transformer is connected to the other end of the capacitor bridge arm and the positive terminal of diode D2; the other end of the primary side of the transformer is connected to the MOS transistor. Q The source of 1 is connected; the MOS transistorQ The source of 1 and the MOS transistor Q The drains of 2 are connected together, and the MOS transistor is... Q The source of 2 is connected to the negative terminal of the input voltage.

[0027] This aerospace half-bridge LLC circuit also includes diodes D5 and D6; wherein the cathode of diode D5 is connected to the MOSFET. Q The drain of diode D1 is connected to the MOSFET, and the anode of diode D5 is connected to the MOSFET. Q The source of diode D1 is connected to the source of diode D6; the cathode of diode D6 is connected to the MOS transistor. Q The drain of diode D2 is connected to the MOSFET, and the anode of diode D6 is connected to the MOSFET. Q The source poles of 2 are connected.

[0028] The capacitor bridge arm includes capacitors C r1 and capacitor C r2 ; wherein, the capacitor C r1 One end is respectively connected to the inductor L in The other end, the MOS transistor Q The drain of diode D1 is connected to the anode of diode D2; the capacitor... C r1 The other end is respectively connected to the capacitor C r2 One end of the transformer is connected to one end of the primary side of the transformer.

[0029] Output voltage With reference voltage The input is compared with the PI controller to generate a control signal, which is then sent to the isolation driver to control the on / off state of the primary-side MOSFET.

[0030] like Figure 6 As shown, the compensator includes resistors R1, R2, R3, R4, and R5, capacitors C1, C2, and C3, and an operational amplifier; wherein one end of resistor R1 and one end of resistor R3 are both connected to a reference voltage. The other end of resistor R1 is connected to the inverting input of the operational amplifier; the other end of resistor R3 is connected to one end of capacitor C3, the other end of capacitor C3 is connected to one end of resistor R2, the other end of resistor R2 is connected to one end of capacitor C2, and the other end of capacitor C2 is connected to the output terminal of the operational amplifier; one end of capacitor C1 is connected to the inverting input of the operational amplifier; and one end of resistor R4 is connected to the output voltage. The other end of resistor R4 and one end of resistor R5 are both connected to the non-inverting input of the operational amplifier; the other end of resistor R5 is grounded.

[0031] The transfer function of the compensator is: ; in, Let the transfer function of the compensator be... For DC gain, The first zero-point angular frequency, The second zero-point angular frequency, The first pole angular frequency, The second pole angular frequency, For the Laplace operator.

[0032] This embodiment uses an LLC circuit with clamping diodes to connect the resonant capacitor. C r Divided into two equal capacitors C r1 , C r2 Simultaneously, clamping diodes are connected in parallel across the two ends of the resonant capacitor. D 1. D 2. And determine that the LLC circuit has a first resonant point and a second resonant point.

[0033] In this embodiment, the duty cycle of the upper and lower switches in the LLC circuit is 50% each. Therefore, a square wave voltage is obtained on the left side of the resonant network, and the voltage calculated back to the primary side from the secondary side of the transformer is also a square wave voltage. Thus, this invention uses AC analysis methods to study the input-output characteristics of the LLC converter. The actual load can be obtained by calculating back to the primary side from the secondary side.

[0034] This embodiment uses fundamental frequency analysis to obtain the voltage transfer ratio of the LLC circuit and derive the voltage transfer ratio function curve. The two resonant points divide the LLC circuit into three regions. Switching frequency. f s < f p The circuit is capacitive and cannot achieve ZVS; f p ≤ f s <f o The circuit is inductive, which can achieve ZVS for the primary-side MOSFET and ZCS for the secondary-side switch. f s = f o This is called the critical mode; f o ≤ fs The circuit is inductive and can only achieve ZVS for the primary-side MOSFET.

[0035] Based on the principles of power circuit design, a compromise is made for the LLC power circuit to obtain the inductance ratio and quality factor, thus completing the design of the main power circuit.

[0036] The primary-side MOSFET in the LLC circuit always operates with a duty cycle of 50%. The circuit changes the voltage transfer ratio through frequency conversion control, thereby achieving closed-loop control.

[0037] The control process of the LLC frequency converter control strategy proposed in this embodiment is as follows: The output voltage and the reference voltage are processed by a compensator to generate an EA signal. The EA signal is then limited and sent to the VCO circuit. The VCO circuit converts the voltage signal into a frequency signal, controlling the operating frequency of the PWM control chip. Finally, the output signal of the PWM chip drives the primary-side MOSFET of the LLC circuit through an isolation driver, realizing closed-loop regulation. The lower limit operating frequency of the PWM control chip is... f min and upper limit working frequency f max All are determined by circuit parameters.

[0038] Due to the influence of parameters such as parasitic capacitance on the primary and secondary sides of the transformer, the half-bridge LLC circuit forms an additional resonant point in the high-frequency range, causing the output voltage of the LLC circuit to be too high under no-load conditions and unable to stabilize at the desired value. To address the issue of high output voltage drift in LLC circuits under no-load operation, this invention proposes an LLC no-load control method to solve the problem of high no-load voltage drift in LLC circuits.

[0039] This embodiment proposes an LLC no-load control method to control the output voltage. With reference voltage A comparison is performed to generate a control signal, which is then sent to the enable terminal of the drive circuit to control the on / off state of the primary-side MOSFET. The no-load control method proposed in this invention can effectively suppress the problem of high no-load voltage drift and adjust the voltage to near the desired value.

[0040] The worst-case operating condition of the LLC resonant converter is low input voltage and full output load. This invention designs a voltage compensator based on the small-signal characteristics of the worst-case operating condition. According to the worst-case operating condition, the transfer function of the LLC resonant converter... G vc ( sBased on the characteristics of double poles and single zeros, and the design principles of LLC resonant converter voltage compensators, a double pole-double zero voltage compensator is selected. The transfer functions of the compensator, voltage sampling network, voltage-controlled oscillator (VCO), and power circuit are determined, yielding the transfer function of the controlled object and the compensated open-loop transfer function. Based on this principle, the compensator is designed.

[0041] Specifically, this invention focuses on LLC circuits and provides a frequency conversion control strategy for aerospace half-bridge LLC circuits, which includes the following steps: Step 1: Design of the main power loop of the LLC circuit This invention provides a frequency conversion control strategy for aerospace half-bridge LLC circuits, the frequency conversion control block diagram of which is shown below. Figure 1 As shown. The control loop includes a frequency conversion control loop, an overcurrent protection loop, and a light-load mode control loop. After output sampling, compensation network, and output voltage limiting, the output signal EA of the operational amplifier is sent to the VCO voltage-controlled oscillator. The VCO output controls the RT pin of the PWM controller, realizing the frequency conversion control of the LLC circuit. Finally, the output signal of the PWM controller is sent to the isolation driver to control the turn-on and turn-off of the primary-side MOSFET. The control loop includes a current protection circuit. By comparing the sampled signal with the reference signal, an overcurrent protection signal OCP is generated. The OCP signal is sent to the PWM controller to turn off the output of the drive signal.

[0042] This invention employs an LLC circuit with a clamping diode to control the resonant capacitor. C r Divided into two equal capacitors C r1 , C r2 Simultaneously, clamping diodes are connected in parallel across the two ends of the resonant capacitor. D 1. D 2.

[0043] The operating principle of LLC circuit with clamping diode is the same as that of traditional LLC circuit. In addition to having all the advantages of traditional LLC circuit, it also has the following advantages: 1) The topology itself can realize the cycle-by-cycle current limiting function without any control intervention; 2) Reduce input current ripple; 3) Limit the voltage stress of resonant capacitor.

[0044] The LLC circuit has a first resonant point. f o Second resonant point f p Their expressions are respectively (1) (2) The AC equivalent circuit of the LLC converter is as Figure 2 shown. According to the duty cycles of the upper and lower switching transistors of the LLC circuit being 50% each, a square-wave voltage is obtained on the left side of the resonant network, and the voltage obtained by converting the secondary side of the transformer back to the primary side is also a square-wave voltage. Therefore, the input-output characteristics of the LLC converter are studied by the AC analysis method in this invention. R ac It is the AC equivalent load of the full-wave rectifier circuit for a voltage-type load, which is obtained by converting the actual load from the secondary side back to the primary side.

[0045] (3) This invention adopts the fundamental wave analysis method to obtain the voltage transfer ratio of the LLC circuit M The expression is (4) In the formula, the inductance coefficient L n = L m / L r , the normalized frequency f = f s / f o , f s is the switching frequency, Q is the quality factor.

[0046] According to formula (4), the voltage transfer ratio function curve can be obtained, as Figure 3 shown. It can be seen that the two resonant points divide the LLC circuit into three regions. When the switching frequency fs < fp, the circuit operates capacitively in region 3 and ZVS cannot be achieved; when fp ≤ fs < fo, the circuit operates inductively in region 2, and ZVS of the primary-side MOS transistor and ZCS of the secondary-side switching transistor can be achieved; when fs = fo, it is called the critical mode; when fo ≤ fs, the circuit operates inductively in region 1, and only ZVS of the primary-side MOS transistor can be achieved. Usually, the operating region is controlled in region 2 to maximize the efficiency.

[0047] The power circuit design of this invention mainly has two principles: 1) The minimum principle of the resonant capacitor C r The value of the resonant capacitor should be as small as possible to increase the characteristic impedance and ensure sufficient quality factor Q and small short-circuit current under heavy-load conditions; 2) The maximum principle of the excitation inductor L m The value of the excitation inductor should be as large as possible to reduce the loss and ensure reasonable voltage gain within the expected frequency modulation range.

[0048] Based on the above principles, a compromise is made for the LLC power circuit to obtain the inductance ratio. L n =5.5, quality factor Q=0.39.

[0049] Figure 4 The voltage gain curve of the LLC circuit selected for this invention is shown. Calculations show that the required gains at the minimum and maximum input voltages are 1.304 and 0.82, respectively. Setting the upper and lower limits of the circuit switching frequency to 300 kHz and 100 kHz respectively satisfies the gain requirements.

[0050] Step 2: LLC Variable Frequency Control Strategy The primary-side MOSFET in the LLC circuit always operates with a duty cycle of 50%. Figure 4 As can be seen, the circuit changes the voltage transfer ratio through frequency conversion control, thereby achieving closed-loop control. The control process is as follows: the output voltage and the reference voltage are processed by the compensator to generate the EA signal. The EA signal is then limited and sent to the VCO circuit. The VCO circuit can convert the voltage signal into a frequency signal to control the operating frequency of the PWM control chip. Finally, the output signal of the PWM chip drives the primary-side MOSFET of the LLC circuit through the isolation driver, realizing closed-loop regulation.

[0051] Lower limit operating frequency of PWM control chip f min Depend on C T , R T2 Decision: Maximum operating frequency f max Depend on C T R T1 , R T2 The decision is made jointly, as shown in equations (5) and (6).

[0052] (5) (6) In the formula, the coefficient 1.46 is determined by the PWM control chip. The setting of the lower operating frequency needs to prevent the LLC circuit from operating in the capacitive region, therefore... And a certain margin is left.

[0053] Step 3: LLC No-load Control Mode Due to the influence of parasitic capacitances and other parameters on the primary and secondary sides of the transformer, the half-bridge LLC circuit forms an additional resonant point in the high-frequency range, causing the output voltage of the LLC circuit to be too high under no-load conditions and unable to stabilize at the desired value. This invention adds a light-load operating mode to the control loop.

[0054] LLC circuits may experience high output voltage drift during no-load operation, primarily due to the following reasons: 1) The voltage gain curve decays slowly at high frequencies, requiring an increase in switching frequency to reduce the gain and achieve no-load operation. However, the actual switching frequency cannot be increased indefinitely, causing the no-load output voltage to fail to stabilize at the desired value; 2) The influence of parasitic parameters on the primary and secondary sides of the transformer causes an additional resonant point to form on the LLC circuit's voltage gain curve at high frequencies, resulting in an increase in voltage gain instead of a decrease. Figure 5 The LLC voltage gain curve is taken into account for parasitic parameters.

[0055] Solutions to address the issue of high voltage drift under no-load conditions in LLC circuits include: 1) reducing the equivalent parallel capacitance of the transformer; 2) adding a parallel capacitor across the resonant inductor; 3) increasing the transformer turns ratio; 4) adding a parallel capacitor across the primary-side MOSFET; and 5) operating in Burst mode.

[0056] This invention proposes an LLC no-load control method to address this issue, which controls the output voltage. With reference voltage A comparison is performed to generate a control signal, which is then sent to the enable terminal of the drive circuit to control the on / off state of the primary-side MOSFET. The no-load control method proposed in this invention can effectively suppress the problem of high no-load voltage drift and adjust the voltage to near the desired value. The disadvantage is that the output ripple is relatively large under no-load conditions.

[0057] Step 4: Design of a Dual-Zero-Bipolar Compensator for LLC Circuits The worst-case operating condition of the LLC resonant converter is low input voltage and full output load; therefore, the voltage compensator is designed based on the small-signal characteristics under the worst-case condition. According to the worst-case condition, the transfer function of the LLC resonant converter is... G vc ( s The present invention, which features a double pole and a single zero, designs a voltage compensator for an LLC resonant converter based on the following principles: 1) Add an integral term to eliminate static error; 2) Increase ω z1 and ω z2 Two low-frequency zeros cancel out the two low-frequency poles of the controlled object, increasing the crossover frequency; 3) Add a mid-frequency pole ω p1 Offsetting ESR zero point ω esr ; 4) Add a high-frequency pole ω p2Increase the attenuation rate of the open-loop transfer function in the high-frequency range.

[0058] Choose a double-pole-double-zero voltage compensator, such as... Figure 6 As shown. According to Figure 6 The transfer function of the compensator is (7) In the formula, DC gain First zero-point angular frequency Second zero-point angular frequency ; First pole angular frequency Second pole angular frequency .

[0059] The voltage closed-loop control block diagram used in this invention is as follows: Figure 7 As shown. The transfer function of the compensator is... G v ( s The transfer function of the voltage sampling network is: H ( s The transfer function of the voltage-controlled oscillator (VCO) is: G vco ( s The transfer function of the power circuit is: G vf ( s ), Controlled object pass function G vc ( s )= G vco ( s ) G vf ( s ).

[0060] The transfer function of the voltage sampling network is H ( s )for (8) The transfer function of the voltage-controlled oscillator (VCO) is: G vco ( s ) (9) In the formula, The upper limit of the operating frequency set for the circuit. The lower limit of the operating frequency set for the circuit. This represents the range of VCO output voltage variation.

[0061] The transfer function of the power circuit is G vf ( s)for (10) In the formula, G DC The DC gain is the worst-case operating point.

[0062] Controlled object pass function G vc ( s Bird diagram Figure 8 and Figure 9 As shown.

[0063] The compensator design principles according to the present invention are as follows: (11) The compensated open-loop transfer function can be obtained. G ( s The expression is (12) The compensator was designed based on the above principles, and the actual circuit was tested. The Bode plot under the worst-case condition (i.e., minimum input voltage 80V, output full load 120W) is shown below. Figure 10 As shown. Crossover frequency 7.25 kHz, phase margin 49°, gain margin -15 dB.

[0064] Bode plots for verifying input 100V and 110V operating conditions are shown below. Figure 11 and Figure 12 As shown, both the phase margin and gain margin meet the requirements.

[0065] Example: This invention focuses on LLC circuits and provides a frequency conversion control strategy for aerospace half-bridge LLC circuits. An LLC circuit was built and experiments were conducted to verify the effectiveness and feasibility of the frequency conversion control strategy proposed in this invention.

[0066] Table 1 Parameters of the Half-Bridge LLC Circuit Experimental Platform

[0067] The LLC circuit consists of a main power circuit, a control circuit, a drive circuit, and an auxiliary power supply circuit. The circuit dimensions are 45mm x 75mm. It uses a 100V aerospace-grade bus for input, with an input voltage range of 80V-110V and a rated output of 12V / 10A. All circuit components meet aerospace-grade standards. The circuit resonant frequency... f o =190 kHz, transformer primary and secondary turns ratio n = 4:1:1, and the specific circuit parameters are shown in Table 1.

[0068] The experimental waveform under the conditions of input voltage 80V and output current 10A is as follows: Figure 13 As shown in the figure. It can be seen that the switching frequency of the LLC circuit... f s =125 kHz, operating in region 2, primary-side MOSFET V ds Voltage at V gs Before the arrival, it dropped to 0, achieving ZVS turn-on, from the rectifier diode. V d Voltage waveform and resonant inductor current i Lr Based on waveform inference, the rectifier diode achieves ZCS turn-off at this time.

[0069] The experimental waveform under the conditions of input voltage 100V and output current 10A is as follows: Figure 14 As shown in the figure. It can be seen that the switching frequency of the LLC circuit... f s =180 kHz, operating in region 2.

[0070] When the input voltage rises to 104V, the resonant inductor current curve exhibits a sine wave, indicating that the circuit is operating at its resonant frequency at this point. f o The experimental waveform is as follows Figure 15 As shown.

[0071] When the input voltage is increased to 110V, the experimental waveform is as follows: Figure 16 As shown. At this time, the LLC circuit is operating in region 1, the primary-side MOSFET achieves ZVS turn-on, and the secondary-side rectifier diode is hard-turn-off, so ZCS cannot be achieved.

[0072] The experimental waveform of the LLC circuit in this embodiment under no-load conditions with a 100V input is as follows: Figure 17 As shown, the output voltage exhibits a triangular wave shape and does not drift excessively. The voltage fluctuates within the range of -0.08V to +0.1V, indicating that the no-load control circuit proposed in this invention effectively suppresses voltage spikes.

[0073] The efficiency of the LLC circuit in this embodiment was tested, and the efficiency test curve is shown below. Figure 18 As shown, under the same load conditions, the higher the input voltage, the higher the efficiency. The efficiency under rated conditions reaches 92.6%, and the circuit has the highest efficiency of 93.04% when operating at the resonant point.

[0074] This embodiment provides a frequency conversion control strategy for aerospace half-bridge LLC circuits to address issues such as power loss and electromagnetic interference caused by increasing the switching frequency of existing hard-switching circuits like forward converters and half-bridge converters in aerospace secondary power systems. The strategy includes: a main power loop design for a half-bridge LLC circuit with clamping diodes, consisting of a power loop and a control loop. The control loop includes a frequency conversion control loop, an overcurrent protection loop, and a light-load mode control loop. The voltage gain curve is determined based on the circuit's voltage transfer ratio, inductance ratio, and quality factor. The LLC frequency conversion control strategy involves a dual-zero-bipolar compensator that, after calculation, sends the output signal to a voltage-controlled oscillator (VCO) for frequency conversion regulation. To address the issue of high voltage drift in LLC circuits under no-load conditions, this embodiment incorporates a no-load control mode into the control loop to suppress this phenomenon. Finally, the LLC circuit dual-zero-bipolar compensator design is based on the worst-case small-signal characteristics.

[0075] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A half-bridge LLC circuit for aerospace applications, characterized in that... include: LC filter circuit, MOS bridge arm, capacitor bridge arm, resonant inductor L r , transformer, diode D1, diode D2, diode D3, diode D4, filter capacitor C o , resistor R L , compensator, limiter, voltage-controlled oscillator, PWM controller, isolated driver, comparator and PI controller; wherein, The LC filter circuit is connected to the MOS bridge arm, and the MOS bridge arm is connected in parallel with the capacitor bridge arm; The negative terminal of diode D1 is connected to one end of the capacitor bridge arm, the positive terminal of diode D1 is connected to the negative terminal of diode D2, and the positive terminal of diode D2 is connected to the other end of the capacitor bridge arm. The resonant inductor L r One end is connected to the middle of the capacitor bridge arm, and the resonant inductor L r The other end is connected to one end of the primary side of the transformer, and the other end of the primary side of the transformer is connected to the middle of the MOS bridge arm; The positive terminal of diode D3 is connected to one end of the secondary side of the transformer, and the negative terminal of diode D3 is connected to the filter capacitor C. o One end of the resistor R L One end of the capacitor is connected to the negative terminal of diode D4, and the positive terminal of diode D4 is connected to the other end of the secondary side of the transformer. The filter capacitor C... o The other end, the resistor R L The other end and the middle of the secondary side of the transformer are both grounded; The compensator is connected to the limiter, the limiter is connected to the voltage-controlled oscillator, the voltage-controlled oscillator is connected to the PWM controller, the PWM controller is connected to the isolation driver, and the isolation driver is connected to the MOS bridge arm. The comparator is connected to the PWM controller, and the PI controller is connected to the isolation driver.

2. The aerospace half-bridge LLC circuit according to claim 1, characterized in that: Output voltage With reference voltage After calculation by the compensator, the EA signal is generated. The EA signal is then sent to the voltage-controlled oscillator after passing through the limiter. The VCO output signal of the voltage-controlled oscillator controls the frequency control pin of the PWM controller. The PWM control signal output by the PWM controller is sent to the drive end of the MOS bridge arm through the isolation driver.

3. The aerospace half-bridge LLC circuit according to claim 1, characterized in that: The overcurrent protection signal OCP generated by the comparator is sent to the PWM controller.

4. The aerospace half-bridge LLC circuit according to claim 1, characterized in that: The LC filter circuit includes an inductor. L in and capacitor C in ;in, The inductor L in One end of the inductor is connected to the positive terminal of the input voltage. L in The other end is respectively connected to the capacitor C in One end of the transistor bridge arm, one end of the capacitor bridge arm, and the negative terminal of diode D1 are connected together. The capacitor C in The other end of the capacitor is connected to the negative terminal of the input voltage. C in The other end is connected to the other end of the MOS bridge arm, the other end of the capacitor bridge arm, and the positive terminal of diode D2, respectively.

5. The aerospace half-bridge LLC circuit according to claim 4, characterized in that: The MOS bridge arm includes a MOS transistor. Q 1 and MOSFET Q 2; among which, The MOS transistor Q The drain of 1 is respectively connected to the inductor L in The other end of the capacitor bridge arm is connected to the positive terminal of diode D2; The other end of the primary winding of the transformer is connected to the MOSFET. Q The source terminals of 1 are connected; The MOS transistor Q The source of 1 and the MOS transistor Q The drains of 2 are connected together, and the MOS transistor is... Q The source of 2 is connected to the negative terminal of the input voltage.

6. The aerospace half-bridge LLC circuit according to claim 5, characterized in that... It also includes: diode D5 and diode D6; among which, The cathode of diode D5 is connected to the MOSFET. Q The drain of diode D1 is connected to the MOSFET, and the anode of diode D5 is connected to the MOSFET. Q The source terminals of 1 are connected; The cathode of diode D6 is connected to the MOSFET. Q The drain of diode D2 is connected to the MOSFET, and the anode of diode D6 is connected to the MOSFET. Q The source poles of 2 are connected.

7. The aerospace half-bridge LLC circuit according to claim 5, characterized in that: The capacitor bridge arm includes capacitors. C r1 and capacitor C r2 ;in, The capacitor C r1 One end is respectively connected to the inductor L in The other end, the MOS transistor Q The drain of diode D1 is connected to the anode of diode D2; The capacitor C r1 The other end is respectively connected to the capacitor C r2 One end of the transformer is connected to one end of the primary side of the transformer.

8. The aerospace half-bridge LLC circuit according to claim 1, characterized in that: Output voltage With reference voltage The input is compared with the PI controller to generate a control signal, which is then sent to the isolation driver to control the on / off state of the primary-side MOSFET.

9. The aerospace half-bridge LLC circuit according to claim 1, characterized in that: The compensator includes resistors R1, R2, R3, R4, and R5, capacitors C1, C2, and C3, and an operational amplifier; wherein, One end of resistor R1 and one end of resistor R3 are both connected to a reference voltage. The other end of the resistor R1 is connected to the inverting input of the operational amplifier; The other end of resistor R3 is connected to one end of capacitor C3, the other end of capacitor C3 is connected to one end of resistor R2, the other end of resistor R2 is connected to one end of capacitor C2, and the other end of capacitor C2 is connected to the output terminal of the operational amplifier. One end of the capacitor C1 is connected to the inverting input of the operational amplifier; One end of the resistor R4 is connected to the output voltage. The other end of resistor R4 and one end of resistor R5 are both connected to the non-inverting input of the operational amplifier; the other end of resistor R5 is grounded.

10. The aerospace half-bridge LLC circuit according to claim 1, characterized in that: The transfer function of the compensator is: ； in, Let the transfer function of the compensator be... For DC gain, The first zero-point angular frequency, The second zero-point angular frequency, The first pole angular frequency, The second pole angular frequency, For the Laplace operator.

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