Efficient LLC converter structure inverter and control method thereof

Abstract

The invention discloses an efficient LLC converter structure inverter which comprises a power switch, a resonant network, a high-frequency transformer and a diode rectifier. The power switch is composed of four switching tubes which are divided into two groups and connected in series, and on-off is controlled to convert direct-current voltage into square-wave voltage. The resonant network is combined with an adjustable resonant inductor, a capacitor and an excitation inductor, dynamic working parameters are obtained through voltage sampling and PI feedback adjustment, the resonant inductor is connected with a bias winding, and bias current is applied to change magnetic resistance; harmonic waves of the square wave voltage are eliminated through a resonance network, and fundamental frequency sine waves are output; the high-frequency transformer integrates a magnetic core, a primary side / secondary side coil and an air gap in a single magnetic structure; the diode rectifier converts alternating voltage output by the secondary side of the high-frequency transformer into direct current, outputs smoothing voltage of a filter capacitor, and reduces ripple waves; by optimizing the resonant network and the high-frequency transformer, a circuit soft switching technology is realized, so that the loss in an energy transmission process is reduced, and the overall efficiency of the inverter is improved.

Description

Technical Field

[0001] The invention relates to a resonant converter, and in particular to a high-efficiency LLC converter structure inverter and a control method thereof. Background Art

[0002] In the field of power electronics, an inverter is a device that converts direct current into alternating current. With the continuous development of power electronics technology, inverters have been widely used in various fields, such as renewable energy generation, motor drive, uninterruptible power supply, etc. However, traditional inverters have certain deficiencies in efficiency, stability and flexibility. For example, traditional inverters will produce large energy losses during the voltage conversion process, resulting in low efficiency; at the same time, traditional inverters are prone to voltage fluctuations when the load changes, and have poor stability; in addition, traditional inverters also have certain limitations in boost or buck functions, making it difficult to meet different application requirements.

[0003] Therefore, there is an urgent need for an efficient LLC converter structure inverter and a control method thereof to solve the technical problems existing in the above-mentioned prior art. Summary of the invention

[0004] The present invention overcomes the deficiencies of the prior art and provides a high-efficiency LLC converter structure inverter and a control method thereof.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a high-efficiency LLC converter structure inverter, including: a power switch, a resonant network, a high-frequency transformer and a diode rectifier; characterized in that: the power switch includes four switch tubes, which are divided into two groups, and each group has two switch tubes connected in series, and the DC input voltage is converted into a square wave voltage by controlling the on and off of the switch tubes; the resonant network design considers the combination of adjustable resonant inductance, resonant capacitance and excitation inductance of the load fluctuation degree, obtains the simplest resonant scheme, and obtains the dynamic parameters of the most suitable working conditions through voltage sampling and PI feedback regulation control method; the resonant inductor is connected to the bias winding, and a bias current is applied to the bias winding. , so that a DC flux bias is generated in the magnetic core, thereby changing the magnetic resistance of the magnetic circuit and then changing the resonant inductance; the square wave voltage enters the resonant network, and the resonant network eliminates the harmonics of the square wave voltage and outputs a sine wave of the fundamental frequency; the high-frequency transformer includes a magnetic core, a primary coil, a secondary coil and an air gap, and the inductance elements are integrated into a single magnetic structure, which has strong electromagnetic compatibility; the sine wave is transmitted to the secondary coil of the high-frequency converter through the high-frequency transformer, and the voltage is stepped up or down according to application requirements; the diode rectifier converts the AC voltage output by the secondary coil of the high-frequency transformer into a DC voltage, outputs a filter capacitor, smoothes the output voltage, and reduces ripple.

[0006] In a preferred embodiment of the present invention, the power switch adopts a half-bridge topology to generate a square wave voltage with an offset, the amplitude of which is half of the input voltage.

[0007] In a preferred embodiment of the present invention, the resonant inductor is connected in series with the resonant capacitor and the high-frequency transformer, and the magnetizing inductor is connected in parallel with the resonant inductor; the magnetizing inductor is connected to a bias winding, and a bias current is applied to the bias winding to generate a DC magnetic flux bias in the magnetic core, thereby changing the magnetic resistance of the magnetic circuit and then changing the magnetizing inductor.

[0008] In a preferred embodiment of the present invention, the primary coil is connected between the power switch and the resonant network, the secondary coil and the primary coil transmit energy through magnetic coupling, and the turns ratio is adjusted according to the output voltage through sensor monitoring and PI feedback regulation control; the air gap is arranged in the magnetic core to adjust the resonant inductance and the excitation inductance.

[0009] In a preferred embodiment of the present invention, a control method of a high-efficiency LLC converter structure inverter is provided, which is applied to the above-mentioned high-efficiency LLC converter structure inverter, and includes the following steps:

[0010] S1. Determine the basic parameters of the LLC converter, including input voltage range, output voltage, output power and estimated efficiency;

[0011] S2. According to the basic parameters, design a hierarchical adaptive PI control adjustment strategy for different output voltages based on resonant inductance or capacitance; when the increase / decrease in output voltage V>10%, according to the formula The resonant inductance is adjusted based only on reducing / increasing the magnetic resistance in the bias winding, and the resonant inductance is increased / decreased to suppress / increase the primary current; when the increase / decrease change in the output voltage V is less than 10%, according to the formula Adjust the adjustable resonant inductor and adjustable resonant capacitor to ensure the circuit resonant frequency f o unchanged, maintaining the stability of the resonant circuit. r represents the resonant inductance; N represents the number of coil turns; R m represents magnetic resistance, f o represents the resonant frequency;

[0012] S3. Design a control loop structure based on a hierarchical adaptive PI control adjustment strategy for different output voltages based on resonant inductance or capacitance; wherein a variable inductor of an EE-type magnetic core structure is designed, the bias winding is wound on the outer magnetic column of the EE-type magnetic core, the variable resonant inductor is wound on the middle magnetic core, and the PI control loop is respectively connected to the output voltage sensor and the DC power supply I m connected, the DC power supply I mConnected to the bias winding and provides a DC current m ; Among them, the voltage-controlled variable capacitor structure is designed, and the PI control loop and the voltage source U m When the PI control loop sends a signal to increase the voltage, the voltage applied between the two plates increases, and the electric field makes the silver particles approach each other, thereby reducing the gaps in the dielectric and the distance between the particles, and increasing the capacitance; when the PI control loop sends a signal to decrease the voltage, the potential difference applied by the voltage source to the two plates decreases, and the silver particles are drawn into the axial structure, forming a large number of gaps in the dielectric, reducing the capacitance, and realizing variable capacitance adjustment;

[0013] S4. Calculate the resonant network parameters of the variable resonant inductor, resonant capacitor and magnetizing inductor based on the basic parameters; wherein the calculation formula of the variable resonant inductor is: The calculation formula for the resonant capacitor is: The calculation formula of magnetizing inductance is: Where Q represents the peak gain; f o Represents the resonant frequency; R ac represents the equivalent impedance; K represents the gain ratio of the resonant capacitor to the magnetizing inductor;

[0014] S5. Based on the basic parameters and considering the dynamic regulation of the load, the core parameters are calculated by optimizing the AP value method. The AP value is the product of the core window area and the effective cross-sectional area of ​​the core. The calculation formula is:

[0015]

[0016] In the formula, k u represents the window utilization; k up represents the utilization rate of the primary measuring coil window; λ represents the ratio of the iron loss to the copper loss of the high-frequency transformer; B max represents the maximum magnetic flux density; ΔT represents the temperature change; k t Indicates the size constant, the value is 46.6*10 3 ; C R Represents the resonant capacitance; L R Represents the resonant inductance; L m represents the magnetizing inductance;

[0017] S6. Calculate the number of coil turns on the primary and secondary sides of the high-frequency transformer according to the resonant network parameters and the magnetic core parameters; wherein the calculation expression of the number of coil turns is: In the formula, A e Indicates the cross-sectional area of ​​the core, in m 2 ; ΔB represents the maximum swing of magnetic flux density, unit is Te, the value is 0.25~0.3T; n represents the coil ratio of high frequency transformer; V o Indicates the output voltage; VF represents the voltage drop across the diode rectifier; Indicates the minimum switching frequency;

[0018] In a preferred embodiment of the present invention, in step S1, the calculation expression of the input voltage range is: V min <V<V max ;in, V max =V opfc ; Where V opfc is the input voltage, the rated output voltage provided by the power factor correction pre-regulator; P in is the maximum input power; T HU To keep time; C DL It is a large capacitor in the DC link.

[0019] In a preferred embodiment of the present invention, the calculation formula of the maximum input power is: Among them, P o is the output voltage; I out is the maximum output current; E ff To estimate the efficiency, it is used to calculate the maximum input power at the maximum output power, and the value range is 0.88 to 0.96.

[0020] In a preferred embodiment of the present invention, the diode rectifier uses a fast recovery diode to reduce voltage drop and loss during the rectification process.

[0021] In a preferred embodiment of the present invention, the power switch also includes a driving circuit and a protection circuit, the driving circuit is used to provide a driving signal for the switch tube, and the protection circuit is used to cut off the driving signal when the switch tube has an abnormal situation of overcurrent, overvoltage or short circuit.

[0022] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0023] (1) The inverter provided by the present invention reduces the loss during energy transmission by optimizing the resonant network and the high-frequency transformer, thereby improving the overall efficiency of the inverter.

[0024] (2) The present invention can dynamically adjust the values ​​of the resonant inductor, the resonant capacitor and the magnetizing inductor to match the load changes and the changes in the working conditions, thereby enhancing the stability of the inverter.

[0025] (3) The inverter structure of the present invention is relatively simple and easy to manufacture and maintain, thereby reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 is a circuit schematic diagram of an LLC converter structure inverter according to a preferred embodiment of the present invention;

[0028] Figure 2 1. The waveform of the switch tube and the resonant current waveform of the preferred embodiment of the present invention when the tube is empty;

[0029] Figure 3 1 is a waveform diagram of the switching tube and the resonant current waveform diagram at half load of a preferred embodiment of the present invention;

[0030] Figure 4 1 is a waveform diagram of the switch tube and the resonant current waveform diagram when the switch tube is fully loaded according to a preferred embodiment of the present invention;

[0031] Figure 5 is a waveform diagram of a diode rectifier at half load according to a preferred embodiment of the present invention;

[0032] Figure 6 is a waveform diagram of a diode rectifier when fully loaded according to a preferred embodiment of the present invention;

[0033] Figure 7 1 is an efficiency curve diagram of an LLC converter structure inverter according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0036] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, "multiple" means two or more.

[0037] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0038] like Figure 1 As shown, a high-efficiency LLC converter structure inverter includes: a power switch, a resonant network, a high-frequency transformer and a diode rectifier; the characteristics are: the power switch includes four switch tubes, which are divided into two groups, and two switch tubes in each group are connected in series, and the DC input voltage is converted into a square wave voltage by controlling the on and off of the switch tubes; the resonant network is designed to consider the combination of adjustable resonant inductance, resonant capacitance and exciting inductance of the load fluctuation degree, to obtain the simplest resonant scheme, and the dynamic parameters of the most suitable working conditions are obtained by voltage sampling and PI feedback regulation control method; the resonant inductor is connected to the bias winding, and the bias current is applied to the bias winding to generate a magnetic core A DC magnetic flux bias is generated, thereby changing the magnetic resistance of the magnetic circuit and then changing the resonant inductance; the square wave voltage enters the resonant network, and the resonant network eliminates the harmonics of the square wave voltage and outputs a sine wave of the fundamental frequency; the high-frequency transformer includes a magnetic core, a primary coil, a secondary coil and an air gap, and the inductance elements are integrated into a single magnetic structure, which has strong electromagnetic compatibility; the sine wave is transmitted to the secondary coil of the high-frequency converter through the high-frequency transformer, and the voltage is stepped up or down according to application requirements; the diode rectifier converts the AC voltage output by the secondary coil of the high-frequency transformer into a DC voltage, outputs a filter capacitor, smoothes the output voltage, and reduces ripple.

[0039] Among them, the switch tube type can be selected according to the specific application scenario, such as MOSFET, IGBT, etc., to adapt to different power levels and switching frequencies. The resonant network consists of a resonant inductor, a resonant capacitor, and an exciting inductor. These components work together to eliminate the harmonic components of the square wave voltage and output a fundamental frequency sine wave.

[0040] The series connection of the resonant inductor and the resonant capacitor forms a basic LC resonant circuit, while the magnetizing inductor is connected in parallel with the resonant inductor to adjust the characteristics of the resonant network.

[0041] Furthermore, the power switch adopts a half-bridge topology to generate a square wave voltage with an offset whose amplitude is half of the input voltage.

[0042] Furthermore, the resonant inductor is connected in series with the resonant capacitor and the high-frequency transformer, and the magnetizing inductor is connected in parallel with the resonant inductor; the magnetizing inductor is connected to the bias winding, and a bias current is applied to the bias winding to generate a DC magnetic flux bias in the magnetic core, thereby changing the magnetic resistance of the magnetic circuit and then changing the magnetizing inductor.

[0043] Furthermore, the primary coil is connected between the power switch and the resonant network, the secondary coil and the primary coil transmit energy through magnetic coupling, and the turns ratio is adjusted according to the output voltage through sensor monitoring and PI feedback regulation control; the air gap is arranged in the magnetic core to adjust the resonant inductance and the excitation inductance.

[0044] The square wave voltage is generated by the DC voltage passing through the switching element (MOSFET or IGBT) through rapid switching. Since the switching element is not instantaneous, it will produce rich harmonic components, which are superimposed on the fundamental frequency sine wave, resulting in distortion of the output voltage waveform.

[0045] When a square wave voltage passes through a resonant network, the resonant network will produce a strong impedance change to the harmonic components at its resonant frequency. Specifically, the resonant network presents a low impedance to the fundamental frequency component, allowing the fundamental frequency component to pass smoothly; while it presents a high impedance to the harmonic component, thereby inhibiting the passage of the harmonic component.

[0046] Due to the high impedance of the resonant network to the harmonic components, the harmonic components will be greatly attenuated when passing through the resonant network. As the number of harmonics increases, the attenuation effect becomes more obvious. Therefore, when the square wave voltage passes through the resonant network, its harmonic components are effectively suppressed, and the output voltage waveform is closer to the ideal sine wave.

[0047] In practical applications, the resonant network also needs to consider the impact of load changes, temperature changes and other factors on its performance. In order to ensure the stable operation of the inverter, some additional measures need to be taken, such as dynamically adjusting the resonant network parameters and adding protection circuits.

[0048] Furthermore, a control method for a high-efficiency LLC converter structure inverter is provided, which is applied to the above-mentioned high-efficiency LLC converter structure inverter, and comprises the following steps:

[0049] S1. Determine the basic parameters of the LLC converter, including input voltage range, output voltage, output power and estimated efficiency;

[0050] Furthermore, in step S1, the calculation expression of the input voltage range is: V min <V<V max ;in, V max =V opfc ; Where V opfc is the input voltage, the rated output voltage provided by the power factor correction pre-regulator; P in is the maximum input power; T HU To keep time; C DL It is a large capacitor in the DC link.

[0051] S2. According to the basic parameters, design a hierarchical adaptive PI control adjustment strategy for different output voltages based on resonant inductance or capacitance; when the increase / decrease in output voltage V>10%, according to the formula The resonant inductance is adjusted based only on the reduction / increase of the magnetic resistance in the bias winding, and the resonant inductance is increased / decreased to suppress / increase the primary current; when the increase / decrease change in the output voltage V is less than 10%, according to the formula Adjust the adjustable resonant inductor and adjustable resonant capacitor to ensure the circuit resonant frequency f o unchanged, maintaining the stability of the resonant circuit. r represents the resonant inductance; N represents the number of coil turns; R m represents magnetic resistance, f o represents the resonant frequency;

[0052] S3. Design a control loop structure based on a hierarchical adaptive PI control adjustment strategy for different output voltages based on resonant inductance or capacitance; wherein a variable inductor of an EE-type magnetic core structure is designed, the bias winding is wound on the outer magnetic column of the EE-type magnetic core, the variable resonant inductor is wound on the middle magnetic core, and the PI control loop is respectively connected to the output voltage sensor and the DC power supply I m connected, the DC power supply I m Connected to the bias winding and provides a DC current m; Among them, the voltage-controlled variable capacitor structure is designed, and the PI control loop and the voltage source U m When the PI control loop sends a signal to increase the voltage, the voltage applied between the two plates increases, and the electric field makes the silver particles approach each other, thereby reducing the gaps in the dielectric and the distance between the particles, and increasing the capacitance; when the PI control loop sends a signal to decrease the voltage, the potential difference applied by the voltage source to the two plates decreases, and the silver particles are drawn into the axial structure, forming a large number of gaps in the dielectric, reducing the capacitance, and realizing variable capacitance adjustment;

[0053] S4. Calculate the resonant network parameters of the variable resonant inductor, resonant capacitor and magnetizing inductor based on the basic parameters; wherein the calculation formula of the variable resonant inductor is: The calculation formula for the resonant capacitor is: The calculation formula of magnetizing inductance is: Where Q represents the peak gain; f o Represents the resonant frequency; R ac represents the equivalent impedance; K represents the gain ratio of the resonant capacitor to the magnetizing inductor;

[0054] S5. Based on the basic parameters and considering the dynamic regulation of the load, the core parameters are calculated by optimizing the AP value method. The AP value is the product of the core window area and the effective cross-sectional area of ​​the core. The calculation formula is:

[0055]

[0056] In the formula, k u represents the window utilization; k up represents the utilization rate of the primary measuring coil window; λ represents the ratio of the iron loss to the copper loss of the high-frequency transformer; B max represents the maximum magnetic flux density; ΔT represents the temperature change; k t Indicates the size constant, the value is 46.6*10 3 ; C R Represents the resonant capacitance; L R Represents the resonant inductance; L m represents the magnetizing inductance;

[0057] S6. Calculate the number of coil turns on the primary and secondary sides of the high-frequency transformer according to the resonant network parameters and the magnetic core parameters; the calculation expression for the number of coil turns is: In the formula, A e Indicates the cross-sectional area of ​​the core, in m 2 ; ΔB represents the maximum swing of magnetic flux density, unit is Te, the value is 0.25~0.3T; n represents the coil ratio of high frequency transformer; V o Indicates the output voltage; V F represents the voltage drop across the diode rectifier; Indicates the minimum switching frequency;

[0058] S7. According to the working frequency and the number of turns of the high-frequency transformer, the high-frequency loss of the high-frequency transformer is calculated; wherein, the calculation formula of the high-frequency loss is: P f =k f *f o *B max *V c ; where k f Represents the loss factor; V c Indicates the volume of the magnetic core; f o Indicates the resonant frequency; B max Indicates the maximum magnetic flux density.

[0059] Furthermore, the calculation formula of the maximum input power is: Among them, P o is the output voltage; I out is the maximum output current; E ff E is the estimated efficiency, used to calculate the maximum input power at the maximum output power, and the value range is 0.88 to 0.96. For low-voltage output applications, E ff Generally, it is 0.88~0.92. For high voltage output applications, E ff It is generally taken as 0.92~0.96.

[0060] Furthermore, the diode rectifier adopts a fast recovery diode to reduce the voltage drop and loss during the rectification process.

[0061] The implementation method of dynamic adjustment is as follows: First, the key parameters such as load current and output voltage are monitored in real time through sensors to obtain real-time information on load changes and working conditions. The monitored data is then input into the control algorithm to calculate the values ​​of the resonant inductance, resonant capacitance and magnetizing inductance that need to be adjusted. After that, the parameters in the resonant network are dynamically adjusted according to the calculation results of the control algorithm through actuators (such as adjustable inductance, adjustable capacitance, etc.).

[0062] Advantages of dynamic adjustment: By dynamically adjusting the parameters in the resonant network, the inverter can always be ensured to work in the best state, thereby improving the overall efficiency. Dynamic adjustment can quickly respond to changes in load and working conditions, and enhance the stability of the inverter. Through dynamic adjustment, problems such as overheating and overcurrent caused by the inverter working in a non-optimal state for a long time can be avoided, thereby extending its service life.

[0063] An overvoltage protection circuit is configured in the inverter circuit. When the output voltage exceeds the set value, the circuit is automatically cut off to protect the load and the inverter.

[0064] An overcurrent protection circuit is configured in the inverter circuit. When the load current exceeds the set value, the circuit is automatically cut off to prevent the inverter from overloading.

[0065] Monitor the output waveform and efficiency of the inverter in real time. When any abnormality is found, take timely measures to make adjustments to ensure the stable operation of the inverter.

[0066] A fault diagnosis and early warning system is set up to monitor the working status of the inverter in real time. When a fault is found, a warning signal is issued in time and the fault location is indicated.

[0067] Furthermore, the power switch also includes a drive circuit and a protection circuit. The drive circuit is used to provide a drive signal for the switch tube, and the protection circuit is used to cut off the drive signal when the switch tube has an abnormal situation of overcurrent, overvoltage or short circuit. In addition, a complete protection mechanism is integrated into the control method, such as overcurrent protection, overvoltage protection, short circuit protection, etc., to ensure the safe and reliable operation of the inverter.

[0068] The LLC converter maintains high efficiency even at very high powers due to its resonant characteristic. This feature enables soft switching on both the primary and secondary sides, which reduces switching losses and thus improves efficiency.

[0069] The LLC topology also saves board space because it does not require an output inductor. This means that all inductors can be easily integrated into a single magnetic structure, saving area and cost. When all the inductive elements of a circuit are located in the same structure, its electromagnetic compatibility is greatly improved; because it is easier and cheaper to shield a single structure than three structures.

[0070] The present invention significantly reduces the loss in the energy transmission process by optimizing the resonant network and the high-frequency transformer, thereby improving the overall efficiency of the inverter, which is difficult to achieve with the existing technical solutions.

[0071] The present invention also has the ability to dynamically adjust the resonant inductance, resonant capacitance and magnetizing inductance to match changes in load and working conditions. This dynamic adjustment mechanism enhances the stability of the inverter, enabling it to maintain stable output voltage and current under various working conditions.

[0072] Compared with some complicated prior art solutions, the LLC converter structure inverter provided by the present invention has a relatively simple structure and is easy to manufacture and maintain, which reduces production costs and improves the market competitiveness of the product.

[0073] Due to the characteristics of high efficiency, stability and easy manufacturing of the present invention, it is suitable for a variety of application fields, such as new energy power generation, motor drive, uninterruptible power supply, etc., which makes the present invention have a wider application prospect and market demand.

[0074] Based on the above technical solution, the following embodiments are designed to verify the beneficial effects of this solution.

[0075] According to system requirements, the input voltage range is set to 200-400V; after being converted to DC by a diode rectifier and then smoothed by an output filter capacitor, the output voltage is 24V. According to load characteristics, the estimated output power is 100W, the corresponding output current range is about 0.5A to 2A, and the estimated efficiency is 0.92.

[0076] According to step S3 of the control method, the values ​​of the resonant inductance, the resonant capacitance and the magnetizing inductance are calculated, which are respectively: resonant inductance: L R Equal to 40μH; resonant capacitor: C R Equal to 0.1μF; magnetizing inductance: L m Equal to 150μH.

[0077] Select EE type magnetic core, and calculate the number of turns of the primary and secondary coils of the high-frequency transformer according to step S5. Assume that the cross-sectional area AP of the magnetic core is equal to 100mm 2 , maximum swing of magnetic flux density B max Equal to 0.27T.

[0078] In this embodiment, the experimental waveform during the experiment is as follows: Figures 2 to 6 As shown. Figure 2 It shows the waveform of the switch tube and the resonant current waveform when the tube is empty; Figure 3 What is shown is the waveform of the switch tube and the resonant current waveform at half load; Figure 4 The waveform of the switch tube and the resonant current waveform are shown in Figure 1. Figures 2 to 4 It can be seen that the LLC converter structure inverter provided by the present invention achieves zero voltage switching within the full load range. Figure 5 What is shown is the waveform of the diode rectifier at half load; Figure 6 The waveform shown is the diode rectifier waveform at full load; Figure 5 and Figure 6 It can be seen that the LLC converter structure inverter provided by the present invention achieves zero current switching within the full load range.

[0079] According to the embodiment, the efficiency curve is as follows Figure 7 As shown in the figure, within the output current range of this design (0.5A to 2A), the inverter exhibits high efficiency, especially in the range of 0.5A to 1.1A, where the efficiency is close to the optimal value. Compared with the traditional design method, the proposed design method has higher efficiency and a slower decline in a wider output current range.

[0080] from Figure 7It can be seen that when the output current is between 0.5A and 1.1A, the efficiency of the design method proposed by the present invention is higher than that of the traditional design method, and the efficiencies of the two methods are both high and close.

[0081] When the output current exceeds 1.1 A, the efficiency of both design methods begins to decrease, but the efficiency of the design method proposed by the present invention decreases relatively slowly. In the entire output current range, the overall efficiency of the design method proposed by the present invention is slightly higher than that of the traditional design method.

[0082] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A high-efficiency LLC converter structure inverter, comprising: A power switch, a resonant network, a high-frequency transformer and a diode rectifier; characterized in that: the power switch comprises four switch tubes, which are divided into two groups, and two switch tubes in each group are connected in series, and the DC input voltage is converted into a square wave voltage by controlling the on and off of the switch tubes; the resonant network considers the combination of an adjustable resonant inductor, a resonant capacitor and an exciting inductor of the load fluctuation degree to obtain a resonant scheme, and obtains the dynamic parameters of the working conditions through voltage sampling and PI feedback regulation control methods; the resonant inductor is connected to a bias winding, and a bias current is applied to the bias winding to generate a DC magnetic flux bias in the magnetic core to change The magnetic circuit magnetic resistance then changes the resonant inductance; the square wave voltage enters the resonant network, and the resonant network eliminates the harmonics of the square wave voltage and outputs a fundamental frequency sine wave; the high-frequency transformer includes a magnetic core, a primary coil, a secondary coil and an air gap, and the inductance elements are integrated into a single magnetic structure; the sine wave is transmitted to the secondary coil of the high-frequency converter through the high-frequency transformer, and the voltage is stepped up or down according to application requirements; the diode rectifier converts the AC voltage output by the secondary coil of the high-frequency transformer into a DC voltage, outputs a filter capacitor, smoothes the output voltage, and reduces ripple.

2. The high-efficiency LLC converter structure inverter according to claim 1, characterized in that: The power switch adopts a half-bridge topology, which generates a square wave voltage with an offset, and the amplitude is half of the input voltage.

3. The high-efficiency LLC converter structure inverter according to claim 1, characterized in that: The resonant inductor is connected in series with the resonant capacitor and the high-frequency transformer, and the magnetizing inductor is connected in parallel with the resonant inductor.

4. The high-efficiency LLC converter structure inverter according to claim 1, characterized in that: The primary coil is connected between the power switch and the resonant network, the secondary coil and the primary coil transmit energy through magnetic coupling, and the turns ratio is adjusted according to the output voltage through sensor monitoring and PI feedback regulation control; the air gap is set in the magnetic core to adjust the resonant inductance and the excitation inductance.

5. A control method for a high-efficiency LLC converter structure inverter, applied to a high-efficiency LLC converter structure inverter as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Determine the basic parameters of the LLC converter, including input voltage range, output voltage, output power and estimated efficiency; S2. According to the basic parameters, design a hierarchical adaptive PI control adjustment strategy for different output voltages based on resonant inductance or capacitance; when the increase / decrease in output voltage V>10%, according to the formula The resonant inductance is adjusted based only on the reduction / increase of the magnetic resistance in the bias winding, and the resonant inductance is increased / decreased to suppress / increase the primary current; when the increase / decrease change in the output voltage V is less than 10%, according to the formula Adjust the adjustable resonant inductor and adjustable resonant capacitor to ensure the circuit resonant frequency f o unchanged, maintaining the stability of the resonant circuit. R represents the resonant inductance; N represents the number of coil turns; R m represents magnetic resistance, f o represents the resonant frequency; S3. Design a control loop structure based on a hierarchical adaptive PI control adjustment strategy for different output voltages based on resonant inductance or capacitance; wherein a variable inductor of an EE-type magnetic core structure is designed, the bias winding is wound on the outer magnetic column of the EE-type magnetic core, the variable resonant inductor is wound on the middle magnetic core, and the PI control loop is respectively connected to the output voltage sensor and the DC power supply I m connected, the DC power supply I m Connected to the bias winding and provides a DC current m ; Among them, the voltage-controlled variable capacitor structure is designed, and the PI control loop and the voltage source U m When the PI control loop sends a signal to increase the voltage, the voltage applied between the two plates increases, and the electric field brings the silver particles closer to each other, thereby reducing the gaps in the dielectric and the distance between the particles, and increasing the capacitance; when the PI control loop sends a signal to decrease the voltage, the potential difference applied by the voltage source to the two plates decreases, and the silver particles are drawn into the axial structure, forming a large number of gaps in the dielectric, reducing the capacitance, and realizing variable capacitance adjustment; S4. Calculate the resonant network parameters of the variable resonant inductor, resonant capacitor and magnetizing inductor based on the basic parameters; wherein the calculation formula of the variable resonant inductor is: The calculation formula for the resonant capacitor is: The calculation formula of magnetizing inductance is: Where Q represents the peak gain; f o Represents the resonant frequency; R ac represents the equivalent impedance; K represents the gain ratio of the resonant capacitor to the magnetizing inductor; S5. Based on the basic parameters and considering the dynamic regulation of the load, the core parameters are calculated by optimizing the AP value method. The AP value is the product of the core window area and the effective cross-sectional area of ​​the core. The calculation formula is: In the formula, k u represents the window utilization; k up represents the utilization rate of the primary measuring coil window; λ represents the ratio of the iron loss to the copper loss of the high-frequency transformer; B max represents the maximum magnetic flux density; ΔT represents the temperature change; k t Indicates the size constant, the value is 46.6*10 3 ; C R Represents the resonant capacitance; L R Represents the resonant inductance; L m represents the magnetizing inductance; S6. Calculate the number of coil turns on the primary and secondary sides of the high-frequency transformer according to the resonant network parameters and the magnetic core parameters; wherein the calculation expression of the number of coil turns is: In the formula, A e Indicates the cross-sectional area of ​​the core, in m 2 ; ΔB represents the maximum swing of magnetic flux density, unit is Te, the value is 0.25~0.3T; n represents the coil ratio of high frequency transformer; V o Indicates the output voltage; V F represents the voltage drop of the diode rectifier; f s min Indicates the minimum switching frequency; S7. Calculate the high-frequency loss of the high-frequency transformer according to the operating frequency and the number of turns of the coil of the high-frequency transformer; wherein the calculation formula of the high-frequency loss is: f =k f *f o *B max *V c ; where k f Represents the loss factor; V c Indicates the volume of the magnetic core; f o Indicates the resonant frequency; B max Indicates the maximum magnetic flux density.

6. The control method of a high-efficiency LLC converter structure inverter according to claim 5, characterized in that: In step S1, the calculation expression of the input voltage range is: V min <V<V max ;in, V max =V opfc ; Where V opfc is the input voltage, the rated output voltage provided by the power factor correction pre-regulator; P in is the maximum input power; T HU To keep time; C DL It is a large capacitor in the DC link.

7. The control method of a high-efficiency LLC converter structure inverter according to claim 6, characterized in that: The calculation formula of the maximum input power is: Among them, P o is the output voltage; I out is the maximum output current; E ff To estimate the efficiency, it is used to calculate the maximum input power at the maximum output power, and the value range is 0.88 to 0.

96.

8. The control method of a high-efficiency LLC converter structure inverter according to claim 5, characterized in that: The diode rectifier adopts a fast recovery diode to reduce voltage drop and loss during the rectification process.

9. A high-efficiency LLC converter structure inverter or a control method for LLC converter structure inverter according to any one of claims 1 to 8, characterized in that: The power switch also includes a driving circuit and a protection circuit. The driving circuit is used to provide a driving signal for the switch tube, and the protection circuit is used to cut off the driving signal when the switch tube has an abnormal situation of overcurrent, overvoltage or short circuit.

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