Lcc resonant converter maximum power factor tracking method, device and capacitor charger

Abstract

The application is suitable for the field of power electronics, and provides a maximum power factor tracking method of LCC resonant converter, which comprises the following steps: constructing a relationship expression of power factor, voltage gain and switching frequency of the LCC resonant converter; obtaining a highest power factor charging curve of constant current charging or constant power charging according to the relationship expression of power factor, voltage gain and switching frequency; calculating corresponding bus reference voltage values at different times according to the highest power factor charging curve, and adjusting the LCC resonant converter according to the bus reference voltage values, so that the LCC resonant converter charges along the highest power factor charging curve to realize maximum power factor tracking. The application can track higher power factor, reduce circulating current and turn-off current, and significantly improve the working efficiency of the LCC resonant converter at light load by sampling the output capacitor voltage during the charging process and calculating the bus voltage value in real time according to the relationship of power factor, voltage gain and switching frequency.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and particularly relates to a method, apparatus and capacitor charger for maximum power factor tracking of LCC resonant converters. Background Technology

[0002] Pulsed power technology refers to an electrophysical technology that rapidly compresses, converts, or directly releases slowly stored, high-density energy to a load. It is widely used in many fields, including national defense research, high-tech research, and civilian industries.

[0003] Capacitor-charged power supplies (CCPS) are an important component of repetitive pulse power systems. Because they perform the boost function, their output voltage has a wide range, but their efficiency is very low under light loads. Therefore, the efficiency of CCPS under light loads needs to be optimized. A CCPS typically consists of two stages: the front stage is a power factor correction circuit that provides rectification and adjusts the bus voltage, while the rear stage is an LCC resonant converter that provides boost and regulates the output voltage and charging current. Since the losses in the rear LCC resonant circuit are greater than those in the front stage, optimizing the efficiency of the rear LCC resonant circuit during charging has become a key research focus for high-voltage CCPS.

[0004] As a crucial component in CCPS (High-Voltage CCPS), the LCC resonant converter boasts a wide load range and, under certain conditions, can achieve zero-voltage switching across the entire power range. In recent years, it has garnered significant attention from researchers and become a hot research topic in high-voltage CCPS. Currently, the most common charging methods are constant-current charging (CC) and constant-power charging (CP). However, existing LCC resonant converters exhibit low efficiency under light-load conditions in both charging methods. For instance, patent document CN111293889B employs a burst mode under extremely light load conditions, continuously switching between operating and standby states, but this does not improve efficiency under light load conditions.

[0005] Existing LCC resonant converters have low charging efficiency under light load conditions and need improvement. Summary of the Invention

[0006] The purpose of this invention is to provide a maximum power factor tracking method for an LCC resonant converter, which aims to solve the problem of low charging efficiency of existing LCC resonant converters under light load conditions.

[0007] This invention provides a method for maximum power factor tracking (MPF) of an LCC resonant converter. The method includes the following steps: constructing a relationship expression between the power factor, voltage gain, and switching frequency of the LCC resonant converter; obtaining a maximum power factor charging curve under constant current or constant power charging conditions based on the relationship expression; calculating the bus reference voltage value at different times based on the maximum power factor charging curve; and adjusting the LCC resonant converter according to the bus reference voltage value to charge along the maximum power factor charging curve, thereby achieving maximum power factor tracking.

[0008] Another objective of this invention is to provide a maximum power factor tracking (MPF) device for an LCC resonant converter. The device includes: a module for obtaining the relationship between power factor, voltage gain, and switching frequency, used to construct the relationship between the power factor, voltage gain, and switching frequency of the LCC resonant converter; a module for obtaining the maximum power factor charging curve, used to obtain the maximum power factor charging curve under constant current charging or constant power charging conditions based on the relationship between power factor, voltage gain, and switching frequency; and a maximum power factor tracking module, used to calculate the bus reference voltage value corresponding to different times based on the maximum power factor charging curve, and adjust the LCC resonant converter according to the bus reference voltage value so that it charges along the maximum power factor charging curve to achieve maximum power factor tracking.

[0009] Another objective of this invention is to provide a capacitor charger that is controlled using an LCC resonant converter maximum power factor tracking method.

[0010] The present invention provides a maximum power factor tracking method for an LCC resonant converter. By sampling the output capacitor voltage during the charging process and calculating the bus voltage value in real time, the device can track a higher power factor during operation, reduce circulating current and shutdown current, and significantly improve the working efficiency of the LCC resonant converter under light load. Attached Figure Description

[0011] Figure 1 The control loop of the maximum power factor tracking method for an LCC resonant converter provided in this application embodiment;

[0012] Figure 2 A CCPS operation platform based on an LCC resonant converter is provided for embodiments of this application;

[0013] Figure 3 A waveform diagram of charging under constant current conditions using the maximum power factor tracking method of an LCC resonant converter, provided as an embodiment of this application;

[0014] Figure 4 A waveform diagram of charging under constant power conditions using the maximum power factor tracking method of an LCC resonant converter, provided as an embodiment of this application;

[0015] Figure 5 A comparison diagram of conventional constant current charging and maximum power factor tracking (MPFT) constant current charging at an output voltage of 50V is provided for embodiments of this application.

[0016] Figure 6 A comparison diagram of conventional constant current charging and MPFT constant current charging at an output voltage of 150V is provided for an embodiment of this application.

[0017] Figure 7 A comparison diagram of conventional constant current charging and MPFT constant current charging at an output voltage of 250V is provided for embodiments of this application.

[0018] Figure 8 A comparison diagram of conventional constant power charging and MPFT constant power charging at an output voltage of 50V is provided for embodiments of this application.

[0019] Figure 9 A comparison diagram of conventional constant power charging and MPFT constant power charging at an output voltage of 150V is provided for embodiments of this application.

[0020] Figure 10 A comparison diagram of conventional constant power charging and MPFT constant power charging at an output voltage of 250V is provided for embodiments of this application.

[0021] Figure 11 A comparison chart of the charging efficiency of conventional constant current and constant power charging and MPFT constant current and MPFT constant power charging is provided for embodiments of this application.

[0022] Figure 12 This is a block diagram of a maximum power factor tracking device provided in an embodiment of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] In this embodiment, a maximum power factor tracking (MPF) method for an LCC resonant converter is proposed. The method includes the following steps: constructing a relationship expression between the power factor, voltage gain, and switching frequency of the LCC resonant converter; obtaining the highest power factor charging curve under constant current charging or constant power charging conditions based on the relationship expression; calculating the bus reference voltage value corresponding to different times based on the highest power factor charging curve; and adjusting the LCC resonant converter according to the bus reference voltage value so that it charges along the highest power factor charging curve to achieve maximum power factor tracking.

[0025] In one embodiment of this application, such as Figure 1 The diagram illustrates the control loop of a maximum power factor tracking method provided in an embodiment of this application. This loop is a typical control loop, and the modules in the diagram represent the following: LPF: low-pass filter, ADC: analog sampler, U... dclink DC bus voltage.

[0026] This application proposes a charging method using maximum power factor tracking (MPF). This method can be applied to charging scenarios with constant current or constant power requirements, reducing turn-off current and reactive power, lowering switching losses, and improving efficiency under light loads. The scheme first establishes the relationship between power factor and voltage gain under constant current and constant power charging, then analyzes the charging process and applies the MPF tracking method to the control loop. Since the output capacitor voltage changes continuously during charging, the output reference voltage of the power factor correction circuit is recalculated each time the output capacitor voltage is sampled. This allows the DC bus voltage to adjust with the output capacitor voltage to achieve charging along the maximum power factor curve and improve charging efficiency. The relationship between power factor, voltage gain, and switching frequency can be input into software such as MATLAB to obtain the highest power factor charging curve under constant current or constant power charging.

[0027] As those skilled in the art will know, the sampling frequency can be set according to actual needs. Preferably, the sampling frequency can be set to 50kHz. Since the change in capacitor output voltage is on the order of seconds, a sampling frequency of 50kHz can ensure relatively accurate sampling values.

[0028] In this embodiment of the application, by adjusting the bus voltage U dclink The control strategies for achieving maximum power factor tracking mainly consist of voltage loop and current loop. The voltage loop primarily samples the output capacitor voltage and first calculates the reference value U of the bus voltage online. dc_Linkref The door signal is generated by the PFC controller and the V signal is generated by the door operator driver. GSThe control circuit is a pre-amplifier power factor correction circuit. The current loop primarily samples the output current and averages it. If constant current charging is selected, the reference current value is a given value; if constant power charging is selected, the reference current value is calculated from the power and voltage. The average value of the output current samples is subtracted from the reference current value to generate an error, which is compensated for by a PID controller. A sawtooth carrier wave is generated by a limiter and carrier generator, and then controlled by an amplifier and driver to power the LCC converter. Finally, either constant current or constant power charging is selected and achieved by adjusting the switching frequency.

[0029] Those skilled in the art will know that the most common bus capacitor charging strategies are constant current charging and constant power charging. When using the constant current-maximum power factor tracking (CC-MPFT) method, the lower the DC bus voltage, the higher the power factor before the voltage gain reaches M1. Therefore, under light load conditions, the DC bus reference voltage U... dc_Linkref You can choose U dcmin And U dclink The regulator controls the value to be equal to U. dc_Linkref To maximize power factor and efficiency.

[0030] In this embodiment of the application, as the load increases, U dcmin Unable to meet the requirements of constant current charging, therefore U dc_Linkref Continue increasing until the voltage gain reaches M2, after which U dc_Linkref Maintain at U dcmax When using constant power-maximum power factor tracking (CP-MPFT) charging technology, U was also selected before the voltage gain reached M1. dc_Linkref In order to maximize power factor and efficiency under light load conditions. Similarly, U dc_Linkref The voltage gradually increases until the voltage gain reaches M2. Unlike constant current charging, U... dc_Linkref The voltage gain gradually decreases after reaching M2. This is because when the output voltage is higher in the later stages of constant power charging, the required output current gradually decreases, requiring only a lower U. dc_Linkerf This application samples the output capacitor voltage during charging and calculates the bus voltage in real time based on the relationship between power factor, voltage gain, and switching frequency. This enables the tracking of higher power factors, reduces circulating current and turn-off current, and significantly improves the operating efficiency of the LCC resonant converter under light load conditions.

[0031] As one embodiment of this application, such as Figure 2 The diagram illustrates a CCPS operating platform based on an LCC resonant converter, provided in an embodiment of this application. The maximum power factor tracking method for an LCC resonant converter described in this embodiment can be applied to the aforementioned operating platform.

[0032] Those skilled in the art will understand that Figure 2 The structure shown is merely a schematic diagram of a portion of the structure related to the present application and does not constitute a limitation on the device to which the present application is applied. A specific LCC resonant converter may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0033] In the embodiments of this application, such as Figure 2 As shown, the method for adjusting the bus voltage to achieve maximum power factor tracking proposed in this invention was verified on an LCC resonant converter operating platform. The experimental results are as follows. Figure 3 and 4 shown. Specifically, Figure 3 The resonant current and output voltage waveforms during constant current charging using the bus voltage adjustment method for maximum power factor tracking provided in this application embodiment are as follows. Figure 4 The resonant current and output voltage waveforms of the method for adjusting the bus voltage to achieve maximum power factor tracking provided in the application embodiment during constant power charging.

[0034] Meanwhile, for comparison, the effect of using this maximum power factor tracking method is shown. The traditional charging method refers to a typical LCC resonant controller with a fixed bus voltage, i.e., an LCC resonant controller that does not sample the current or voltage values ​​at the output terminal to adjust the gating signal and the bus voltage.

[0035] Figures 5 to 7 The diagram shows a comparison of the turn-off current of the LCC resonant converter maximum power factor tracking method used in this application embodiment with that of the traditional constant current charging method when the output voltage is 50V, 150V, and 250V.

[0036] Specifically, Figure 5 The figure shows a comparison between the shutdown current of the method described in this application and the traditional constant current charging technology when the output voltage is 50V. As can be seen from the figure, the shutdown current of the method described in this application is lower.

[0037] Figure 6 The figure shows a comparison between the shutdown current of the method described in this application and the traditional constant current charging technology when the output voltage is 150V. As can be seen from the figure, the shutdown current of the method described in this application is lower.

[0038] Figure 7 The diagram shows a comparison between the shutdown current of the method described in this application and that of conventional constant current charging technology when the output voltage is 250V.

[0039] Figures 8 to 10The diagram shows a comparison of the shut-off current of the method described in the embodiments of this application in constant power charging applications with that of conventional constant power charging technology when the output voltage is 50V, 150V, and 250V. (a) represents conventional technology, and (b) represents the method described in the embodiments of this application.

[0040] Specifically, Figure 8 The figure shows a comparison between the shutdown current of the method described in this application and the traditional constant power technology when the output voltage is 50V in a constant power charging application. As can be seen from the figure, the shutdown current of the method described in this application is lower.

[0041] Figure 9 The figure shows a comparison between the shutdown current of the method described in this application and the traditional constant power technology when the output voltage is 150V in a constant power charging application. As can be seen from the figure, the shutdown current of the method described in this application is lower.

[0042] Figure 10 The figure shows a comparison between the shutdown current of the method described in this application and the traditional constant power technology when the output voltage is 250V in a constant power charging application. As can be seen from the figure, the shutdown current of the method described in this application is lower.

[0043] like Figure 11 As shown, experimental data verify the efficiency improvement when the method described in the embodiments of this application is applied to constant current and constant power applications. Figure 11 As shown in (a), when the method described in the embodiments of this application is applied to a constant current charging strategy, the efficiency is greatly improved, especially under light load conditions, where the efficiency can be improved by up to 26.84%. Meanwhile, when the method described in the embodiments of this application is applied to a constant power charging strategy, the efficiency can be improved across the entire power range, such as... Figure 11 As shown in (b), efficiency can be improved by 11.63% under light load and by 2.66% under heavy load.

[0044] In one embodiment of this application, the output voltage gain is less than U. o / nU dcmin When using a lower bus reference voltage U dcmin This can reduce the turn-off current I. off This reduces turn-off losses and improves work efficiency. The expression for turn-off losses is:

[0045]

[0046] Among them I m It is the peak value of the resonant current. It is the angle by which the voltage of the resonant cavity leads the current.

[0047] In one embodiment of this application, the turn-off loss P of the MOSFET switch on the primary side of the transformer is... S_off With bus voltage U dc_Link and the turn-off current I off The relevant expression is:

[0048]

[0049] The smaller the turn-off current, the lower the bus voltage, and the smaller the turn-off loss, which will also improve efficiency.

[0050] In this embodiment, the relationship between the power factor, voltage gain, and switching frequency of the LCC resonant converter is expressed as follows:

[0051]

[0052] Where k is the ratio of the parallel resonant capacitor to the series resonant capacitor in the LCC resonant converter, and F n It is the ratio of the switching frequency to the resonant frequency, θ is the conduction angle of the diode on the secondary side of the transformer, and M is the voltage gain of the LCC resonant circuit, M = U. o / nU dclink θ is the conduction angle of the diode on the secondary side of the transformer, and θ is related to F. n The relationship with M is:

[0053]

[0054] In this embodiment of the application, preferably, the value of k can be set to 0.288, and the relationship expression between the power factor, voltage gain and switching frequency can be constructed by referring to the fundamental equivalent model of the LCC resonant converter.

[0055] In one embodiment of this application, the bus reference voltage values ​​at different times are calculated under constant current charging conditions as follows:

[0056]

[0057] Among them: U dc_Linkref U is the bus reference voltage value. dcmin U is the minimum value of the bus voltage change. dcmax For the maximum bus voltage variation, the primary-to-secondary transformer turns ratio of the LCC resonant converter is 1:n, and the first output gain M1 = U o / nU dcmin The second output gain M2 = U o / nU dcmax U o This is the output voltage.

[0058] In this embodiment of the application, according to the above formula, when the output gain is less than M1, the bus voltage is the minimum output voltage U of the preceding stage. dcmin When the output voltage gain is greater than M1 and less than M2, the bus voltage increases linearly with the output capacitor voltage; when the output voltage gain is greater than M2, the bus voltage is the maximum output voltage U of the preceding stage. dcmax .

[0059] In one embodiment of this application, the bus reference voltage values ​​at different times are specifically calculated under constant power charging conditions as follows:

[0060]

[0061] Among them: U dc_Linkref U is the bus reference voltage value. dcmin U is the minimum value of the bus voltage change. dcmax For the maximum bus voltage variation, the primary-to-secondary transformer turns ratio of the LCC resonant converter is 1:n, and the first output gain M1 = U o / nU dcmin The second output gain M2 = U o / nU dcmax U o This is the output voltage.

[0062] In this embodiment of the application, according to the above formula, when the output gain is less than M1, the bus voltage is the minimum output voltage U of the preceding stage. dcmin When the output voltage gain is greater than M1 and less than M2, the bus voltage increases linearly with the output capacitor voltage. When the output voltage gain is greater than M2, based on the charging characteristics of constant power charging, the output current is small in the later stage of charging, and the lower the bus voltage, the higher the efficiency. Therefore, the bus voltage decreases linearly with the output capacitor voltage.

[0063] In one embodiment of this application, the maximum power factor tracking method for the LCC resonant converter further includes: the method further includes: obtaining the average value of the output current; comparing the reference current value with the average value of the output current to obtain the current error; compensating for the current error by a PID controller, and using the compensated output signal to control the LCC converter so that the LCC converter can obtain higher operating efficiency.

[0064] In this embodiment, the method for obtaining the average value of the output current is as follows: the output current is sampled to obtain the instantaneous value of the output current, and its average value is calculated. If constant current charging is selected, the reference current value is a given value; if constant power charging is selected, the reference current value is calculated from the power and voltage. The average value of the output current samples is subtracted from the reference current value to generate an error. This error is compensated by a PID controller, thereby enabling the LCC converter to achieve higher operating efficiency.

[0065] In one embodiment of this application, the method of controlling the LCC converter using the compensated output signal is as follows: the output signal is used to generate sawtooth waves through a limiting and carrier generator, and then the sawtooth waves are used to control the LCC converter through an amplifier and a driver.

[0066] In this embodiment of the application, by using a PID controller to compensate for errors, the LCC converter can achieve higher operating efficiency.

[0067] In one embodiment of this application, the method of adjusting the LCC resonant converter according to the bus reference voltage value to charge it along the highest power factor charging curve to achieve maximum power factor tracking is as follows: sampling the DC bus voltage to obtain the DC bus voltage value U. dclink The DC bus voltage U dclink The difference between the voltage and the reference bus voltage is controlled by a PI controller, and the output signal of the PI controller is used to control the upstream PFC rectifier to adjust the DC bus voltage U. dclink The reference voltage value is adjusted to the bus reference voltage value to achieve maximum power factor tracking.

[0068] In the embodiments of this application, such as Figure 1 As shown, U dc_Linkref The generation method can be as follows: the sampled voltage U0 is sequentially passed through LPF, ADC and MPFT to generate U dc_Linkref U can dclink with U dc_Linkref The input is to the PFC controller, which generates gate signals to control the gate driver. The gate driver then generates the gate drive signal V. GS Controlling the AC / DC PFC Vienna rectifier, i.e., realizing the DC bus voltage U dclink The difference between the voltage and the reference bus voltage is controlled by a PI controller, and the output signal of the PI controller is used to control the upstream PFC rectifier to adjust the DC bus voltage U. dclink The reference voltage value is adjusted to the bus reference voltage value to achieve maximum power factor tracking.

[0069] As one embodiment of this application, such as Figure 12 As shown, a maximum power factor tracking (MPF) device for an LCC resonant converter is provided. The device includes: a bus reference voltage acquisition module, used to obtain a bus reference voltage value based on the sampling result obtained by sampling the output capacitor voltage; a maximum power factor charging curve acquisition module, used to obtain a maximum power factor charging curve based on the bus reference voltage value; and a maximum power factor tracking module, used to adjust the switching frequency based on the maximum power factor charging curve, thereby achieving maximum power factor tracking.

[0070] In the embodiments of this application, the description of the device can be found in the steps of a maximum power factor tracking method for an LCC resonant converter in various embodiments of this application. Further details will not be repeated here.

[0071] In one embodiment, the maximum power factor tracking device for an LCC resonant converter provided in this application is implemented using digital circuits. Preferably, a DSP28379 controller can be used. The various program modules of the maximum power factor tracking device for the LCC resonant converter are written into the controller. The controller plays a control role during the charging process, ensuring that the LCC resonant converter achieves the charging process along the maximum power factor charging curve, thereby optimizing the efficiency of the charging process.

[0072] In one embodiment, an LCC resonant converter charging device is proposed, which includes a sampling circuit, a control circuit, a drive circuit, and a power switch, and implements the following steps:

[0073] The sampling circuit samples the output capacitor voltage and obtains the bus reference voltage value based on the expression for power factor, voltage gain, and switching frequency. Based on the bus reference voltage value, the maximum power factor charging curve is obtained. Based on the maximum power factor charging curve, the switching frequency is adjusted to achieve maximum power factor tracking.

[0074] As an embodiment of this application, a maximum power factor tracking (MPF) device for an LCC resonant converter is provided. The device includes: a module for obtaining the relationship expression between power factor, voltage gain, and switching frequency, used to construct the relationship expression between the power factor, voltage gain, and switching frequency of the LCC resonant converter; a module for obtaining the maximum power factor charging curve, used to obtain the maximum power factor charging curve under constant current charging or constant power charging conditions based on the relationship expression between power factor, voltage gain, and switching frequency; and a maximum power factor tracking module, used to calculate the bus reference voltage value corresponding to different times based on the maximum power factor charging curve, and adjust the LCC resonant converter according to the bus reference voltage value so that it charges along the maximum power factor charging curve to achieve maximum power factor tracking.

[0075] In one embodiment, the maximum power factor tracking device for an LCC resonant converter provided in this application can be implemented as a computer program, which can run on a computer device, a microcontroller device, or a microcontroller. The computer device's memory can store the various program modules that make up the maximum power factor tracking device for the LCC resonant converter, for example... Figure 12The module shown includes a power factor-voltage gain and switching frequency relationship acquisition module, a maximum power factor charging curve acquisition module, and a maximum power factor tracking module. The computer program comprised of these modules causes the processor to execute the steps in the maximum power factor tracking method for an LCC resonant converter described in the various embodiments of this application. For a description of the operation mode of the LCC resonant converter maximum power factor tracking device, please refer to the steps in the maximum power factor tracking method for an LCC resonant converter in the various embodiments of this application. Further details are omitted here.

[0076] In this embodiment, the output capacitor voltage is sampled during the charging process, and the bus voltage value is calculated in real time based on the relationship between power factor, voltage gain and switching frequency. This enables the tracking of a higher power factor, reduces circulating current and turn-off current, and significantly improves the operating efficiency of the LCC resonant converter under light load.

[0077] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above methods.

[0078] As an embodiment of this application, a capacitor charging device is provided, which can be controlled using the aforementioned maximum power factor tracking method for an LCC resonant converter.

[0079] This application provides a capacitor charging device that includes an LCC resonant converter. The LCC resonant converter can be controlled using a aforementioned maximum power factor tracking method. This application samples the output capacitor voltage during charging and calculates the bus voltage in real time based on the relationship between power factor, voltage gain, and switching frequency. This enables the converter to track a higher power factor, reduces circulating current and shutdown current, and significantly improves the efficiency of the LCC resonant converter under light load conditions.

[0080] It should be understood that although the steps in the flowcharts of the various embodiments of the present invention are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the various embodiments may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least a portion of the sub-steps or stages of other steps.

[0081] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0082] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for maximum power factor tracking in an LCC resonant converter, characterized in that, The method includes the following steps: Construct an expression relating the power factor, voltage gain, and switching frequency of an LCC resonant converter; Based on the relationship expression between the power factor, voltage gain, and switching frequency, the highest power factor charging curve under constant current charging or constant power charging conditions is obtained. Based on the highest power factor charging curve, calculate the bus reference voltage value corresponding to different times, and adjust the LCC resonant converter according to the bus reference voltage value so that it charges along the highest power factor charging curve to achieve maximum power factor tracking. The relationship between the power factor, voltage gain, and switching frequency of the LCC resonant converter is expressed as follows: ； Where PF is the power factor. It is the ratio of the parallel resonant capacitor to the series resonant capacitor in the LCC resonant converter. It is the ratio of the switching frequency to the resonant frequency, and M is the voltage gain of the LCC resonant circuit, M=U o / nU dclink , This is the DC bus voltage value. It is the conduction angle of the diode on the secondary side of the transformer. and and The relationship is: ； The calculation method for the bus reference voltage values ​​at different times under constant current charging conditions is as follows: ； in: This is the reference voltage value for the bus. This represents the minimum change in bus voltage. For the maximum bus voltage variation, the primary-to-secondary transformer turns ratio of the LCC resonant converter is 1:n, and the first output gain is... Second output gain , This refers to the output voltage. The specific calculation method for the bus reference voltage values ​​at different times under constant power charging conditions is as follows: ； The method further includes: Obtain the average value of the output current; The current error is obtained by comparing the reference current value with the average value of the output current. The current error is compensated by a PID controller, and the compensated output signal is used to control the LCC converter so that the LCC converter can achieve higher operating efficiency. The method for adjusting the LCC resonant converter according to the bus reference voltage value to charge it along the highest power factor charging curve, thereby achieving maximum power factor tracking, is as follows: The DC bus voltage is sampled to obtain the DC bus voltage value. , The DC bus voltage value The difference between the DC bus reference voltage and the DC bus voltage is controlled by a PI controller. The output signal of the PI controller is used to control the upstream PFC rectifier to adjust the DC bus voltage. The reference voltage value is adjusted to the bus reference voltage value to achieve maximum power factor tracking.

2. The method according to claim 1, characterized in that, The method for controlling the LCC converter using the compensated output signal is as follows: The output signal is used to generate sawtooth waves through a limiter and a carrier generator, and then the sawtooth waves are used to control the LCC converter through an amplifier and a driver.

3. A maximum power factor tracking device for an LCC resonant converter, characterized in that, The apparatus performs the method as described in claim 1 during operation, the apparatus comprising: The module for obtaining the relationship expression between power factor, voltage gain, and switching frequency is used to construct the relationship expression between power factor, voltage gain, and switching frequency of the LCC resonant converter. The highest power factor charging curve acquisition module is used to obtain the highest power factor charging curve under constant current charging or constant power charging conditions based on the relationship expression between the power factor, voltage gain, and switching frequency. The maximum power factor tracking module is used to calculate the bus reference voltage value corresponding to different times based on the highest power factor charging curve, and adjust the LCC resonant converter according to the bus reference voltage value so that it charges along the highest power factor charging curve to achieve maximum power factor tracking.

4. A capacitor charger, characterized in that, The capacitor charger is controlled using the method described in any one of claims 1-2.

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