Three-phase vehicle-mounted charger control method and system based on fixed-frequency phase-shifting

Abstract

The application discloses a three-phase vehicle-mounted charger control method and system based on fixed-frequency phase-shifting, which comprises the following steps: obtaining an output voltage feedback value of an LLC converter; comparing the output voltage feedback value with a preset voltage threshold value, and determining whether to execute a fixed-frequency phase-shifting control mode according to a comparison result; when the fixed-frequency phase-shifting control mode is executed, controlling the LLC converter to work at a fixed switching frequency, and adjusting phase-shifting angles between different bridge arms in the LLC converter, so that the output voltage of the LLC converter follows a charging voltage of a vehicle-mounted power battery. The application executes the fixed-frequency phase-shifting control on the LLC converter of the vehicle-mounted charger, does not need to increase the frequency, can keep a low switching loss, improves overall charging efficiency, adjusts the charging voltage through the phase-shifting control, does not need to greatly reduce the voltage through frequency increase, has a low requirement on a bus voltage of the vehicle-mounted charger, can optimize a transformer turn ratio, and improves a whole machine structure.

Description

Technical Field

[0001] This invention relates to the field of on-board charging control technology, and in particular to a control method and system for a three-phase on-board charger based on fixed-frequency phase shifting. Background Technology

[0002] LLC converters are widely used in on-board chargers for electric vehicles due to their ability to achieve soft switching at the rated operating point and their advantages such as high efficiency and high power density. On-board chargers need to charge the power battery, and their output voltage needs to cover a wide voltage range of the battery from low state of charge to full state of charge.

[0003] In existing technologies, on-board chargers typically employ frequency conversion control strategies to control LLC converters. When the battery voltage is low and the state of charge is low, the output voltage is reduced by increasing the switching frequency. However, existing technologies have the following problems: First, increasing the switching frequency leads to a significant increase in the switching losses (especially drive losses) of the switching transistors, thereby reducing the overall efficiency of the converter under low output voltage conditions. Second, in order to adapt to a wide range of output voltages, the design of LLC resonant network parameters (such as transformer turns ratio) must take into account both high and low voltage extremes, causing the converter to fail to achieve optimal performance at the most commonly used rated power point. For example, it is necessary to increase the transformer turns ratio or increase the bus voltage, resulting in complex core component design, increased cost, and low efficiency under rated operating conditions. Summary of the Invention

[0004] This invention provides a control method and system for a three-phase on-board charger based on fixed-frequency phase shifting, in order to solve the problems of low efficiency and difficult design optimization of existing on-board charger LLC converters over a wide output voltage range, especially under low output voltage conditions.

[0005] According to one aspect of the present invention, a control method for a three-phase on-board charger based on fixed-frequency phase shifting is provided. The three-phase on-board charger includes an LLC converter connected to an on-board power battery. The method includes: acquiring an output voltage feedback value of the LLC converter; comparing the output voltage feedback value with a preset voltage threshold, and determining whether to execute a fixed-frequency phase shifting control mode based on the comparison result; when executing the fixed-frequency phase shifting control mode, controlling the LLC converter to operate at a fixed switching frequency, and adjusting the phase shift angle between different arms of the LLC converter so that the output voltage of the LLC converter follows the charging voltage of the on-board power battery.

[0006] Optionally, comparing the output voltage feedback value with a preset voltage threshold and determining whether to execute the fixed-frequency phase-shift control mode based on the comparison result includes: executing the fixed-frequency phase-shift control mode when the output voltage feedback value is lower than the preset voltage threshold; and executing the frequency conversion control mode when the output voltage feedback value is higher than or equal to the preset voltage threshold.

[0007] Optionally, before executing the frequency conversion control mode, the method further includes: obtaining the phase shift angle in the fixed-frequency phase shift control mode; when the phase shift angle is less than a preset angle threshold, adjusting the output voltage of the LLC converter based on the fixed switching frequency and the preset fine-tuning frequency; wherein the preset fine-tuning frequency is less than the frequency adjustment step size in the frequency conversion control mode.

[0008] Optionally, when executing the fixed-frequency phase-shift control mode, controlling the LLC converter to operate at a fixed switching frequency and adjusting the phase shift angle between different bridge arms in the LLC converter so that the output voltage of the LLC converter follows the charging voltage of the vehicle power battery includes: determining the charging voltage value based on the state of charge or state of voltage of the vehicle power battery; calculating the voltage deviation value between the output voltage feedback value and the charging voltage value; and generating a phase-shift control signal based on the voltage deviation value.

[0009] Optionally, generating the phase-shift control signal based on the voltage deviation value includes: importing the voltage deviation value into a PID controller, and generating the phase-shift control signal based on the PID controller.

[0010] Optionally, the phase shift angle and the output voltage satisfy the gain-phase shift angle characteristic curve.

[0011] Optionally, the fixed switching frequency is the inherent resonant frequency of the resonant network of the LLC converter.

[0012] Optionally, the preset voltage threshold is set based on the rated voltage or maximum voltage of the on-board power battery.

[0013] Optionally, the LLC converter adopts an LLC topology or a CLLLC topology.

[0014] According to another aspect of the present invention, a three-phase on-board charger control system based on fixed-frequency phase shifting is provided for executing the above-described three-phase on-board charger control method based on fixed-frequency phase shifting. The three-phase on-board charger includes: an LLC converter connected to an on-board power battery; the system includes: a data acquisition module for acquiring the output voltage feedback value of the LLC converter; a decision module for comparing the output voltage feedback value with a preset voltage threshold and determining whether to execute a fixed-frequency phase shifting control mode based on the comparison result; and a voltage regulation drive module for controlling the LLC converter to operate at a fixed switching frequency and adjusting the phase shift angle between different arms of the LLC converter when executing the fixed-frequency phase shifting control mode, so that the output voltage of the LLC converter follows the charging voltage of the on-board power battery.

[0015] The technical solution of this invention, by performing fixed-frequency phase-shift control on the LLC converter of the on-board charger, can maintain low switching losses and improve overall charging efficiency without increasing the frequency. By adjusting the charging voltage through phase-shift control, there is no need to significantly reduce the voltage by increasing the frequency, which reduces the requirements on the bus voltage of the on-board charger, optimizes the transformer turns ratio, and improves the overall structure. This solves the problems of low efficiency and difficult design optimization of existing on-board charger LLC converters over a wide output voltage range, especially under low output voltage conditions.

[0016] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating a three-phase on-board charger control method based on fixed-frequency phase shifting, provided in an embodiment of the present invention;

[0019] Figure 2 A schematic diagram of the circuit topology of a three-phase on-board charger provided in an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of a three-phase on-board charger control system based on fixed-frequency phase shifting, provided as an embodiment of the present invention. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0022] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0023] Figure 1 This is a flowchart of a three-phase on-board charger control method based on fixed-frequency phase shifting provided by an embodiment of the present invention. This embodiment is applicable to application scenarios of low voltage or low power charging. The method can be executed by a three-phase on-board charger control system based on fixed-frequency phase shifting. The three-phase on-board charger control system based on fixed-frequency phase shifting can be implemented in hardware and / or software. The three-phase on-board charger control system based on fixed-frequency phase shifting can be configured in a three-phase on-board charger.

[0024] Figure 2 This is a schematic diagram of the circuit topology of a three-phase on-board charger provided in an embodiment of the present invention. See also... Figure 2 As shown, the three-phase on-board charger of the present invention includes: a filter circuit, a PFC converter, and an LLC converter. The primary side of the LLC converter is connected to the PFC converter, and the secondary side of the LLC converter is connected to the on-board power battery. The input side of the PFC converter is connected to the AC power grid via the filter circuit. In some optional embodiments, the LLC converter of the present invention may adopt an LLC topology or a CLLLC topology. See also Figure 2As shown, the LLC converter of this invention includes a resonant circuit and a dual active bridge (DAB) circuit. The resonant circuit includes a first inductor L1, a first capacitor C1, a transformer T1, a second inductor L2, and a second capacitor C2, forming a CLLLC resonant circuit structure. The dual active bridge circuit includes a primary-side H-bridge and a secondary-side H-bridge. The primary-side H-bridge includes a first power switch Q1, a second power switch Q2, a third power switch Q3, and a fourth power switch Q4. The secondary-side H-bridge includes a fifth power switch Q5, a sixth power switch Q6, a seventh power switch Q7, and an eighth power switch Q8. The first power switch Q1, the third power switch Q3, the fifth power switch Q5, and the seventh power switch Q7 are the upper bridge arm switches; the second power switch Q2, the fourth power switch Q4, the sixth power switch Q6, and the eighth power switch Q8 are the lower bridge arm switches.

[0025] like Figure 1 and Figure 2 As shown, the three-phase on-board charger control method based on fixed-frequency phase shifting of the present invention includes the following steps:

[0026] S1: Obtain the output voltage feedback value of the LLC converter.

[0027] The output voltage feedback value can be understood as representing the DC output voltage from the LLC converter to the vehicle's power battery. This output voltage feedback value can be used as the feedback input for closed-loop control. In this embodiment, the output voltage feedback value can be obtained using a resistor divider network or a voltage transformer.

[0028] See Figure 2 As shown, the output voltage feedback value can be denoted as V-out.

[0029] S2: Compare the output voltage feedback value with the preset voltage threshold, and determine whether to execute the fixed frequency phase shift control mode based on the comparison result.

[0030] The preset voltage threshold can be understood as the lower limit of the voltage for measuring whether the vehicle's power battery is in a low voltage state or a low state of charge (SOC).

[0031] The fixed-frequency phase-shift control mode can be understood as the control strategy of LLC converter under low voltage or low charge conditions.

[0032] Optionally, the preset voltage threshold is set based on the rated voltage or maximum voltage of the vehicle's power battery. Specifically, the preset voltage threshold is set to 80% * V. bat V batTaking the rated voltage of the vehicle power battery as an example, the comparison between the output voltage feedback value and the preset voltage threshold is used to determine whether the vehicle power battery is in a low voltage state or a low charge state. When the vehicle power battery is in a low voltage state or a low charge state, the fixed frequency phase shift control mode is executed.

[0033] S3: When executing the fixed-frequency phase-shift control mode, the LLC converter is controlled to operate at a fixed switching frequency, and the phase shift angle between different bridge arms in the LLC converter is adjusted so that the output voltage of the LLC converter follows the charging voltage of the vehicle power battery.

[0034] Optionally, the fixed switching frequency is the inherent resonant frequency of the LLC converter's resonant circuit. The inherent resonant frequency of the resonant circuit is determined by the resonant parameters of the inductor and capacitor within its resonant cavity. See [link to relevant documentation] Figure 2 As shown, the resonant inductance value of the first inductor L1 is defined as L. r1 The resonant capacitance of the first capacitor C1 is C. r1 The resonant inductance value of the second inductor L2 is L r2 The resonant capacitance of the second capacitor C2 is C. r2 The magnetizing inductance of the primary winding of transformer T1 is L. m The turns ratio of transformer T1 is n. All resonant parameters are converted to the same side of the transformer (e.g., the primary side). The converted inductance and capacitance satisfy: L r2 '=L r2 *n 2 C r2 '=C r2 / n 2 Based on this, the total series resonant frequency f is calculated. r satisfy: ,in, Indicates the total series resonant inductance. ; This represents the total series resonant capacitance. Total parallel resonant frequency f m satisfy: ,in, This represents the total parallel resonant inductance. ; This represents the total series resonant capacitance. .

[0035] Specifically, when the battery voltage is low, the LLC converter is controlled to operate at its resonant frequency, maintaining this switching frequency constant. The output voltage is regulated by controlling the phase shift angle between different arms of the LLC converter. Thus, by performing fixed-frequency phase-shift control on the LLC converter of the on-board charger, there is no need to increase the frequency, maintaining low switching losses and improving overall charging efficiency. Regulating the charging voltage through phase shift control eliminates the need for significant voltage reduction through frequency increase, reducing the requirements on the on-board charger's bus voltage. This allows for optimization of the transformer turns ratio and improvement of the overall structure, solving the problems of low efficiency and design optimization difficulties in existing on-board charger LLC converters over a wide output voltage range, especially under low output voltage conditions.

[0036] In some optional embodiments, in step S2 above, the output voltage feedback value is compared with a preset voltage threshold, and it is determined whether to execute the fixed-frequency phase-shift control mode based on the comparison result, including: executing the fixed-frequency phase-shift control mode when the output voltage feedback value is lower than the preset voltage threshold; and executing the frequency conversion control mode when the output voltage feedback value is higher than or equal to the preset voltage threshold.

[0037] Optionally, before executing the frequency conversion control mode, the method further includes: obtaining the phase shift angle in the fixed frequency phase shift control mode; when the phase shift angle is less than a preset angle threshold, adjusting the output voltage of the LLC converter based on the fixed switching frequency and the preset fine-tuning frequency; wherein the preset fine-tuning frequency is less than the frequency adjustment step size in the frequency conversion control mode.

[0038] Specifically, in phase-shift control mode, when the phase shift angle decreases to near 0° (i.e., the output voltage is close to the maximum voltage value at the current switching frequency), the system records the corresponding switching frequency (e.g., the resonant frequency). ) and output power. Switch the operating mode to variable frequency control mode, and set the initial frequency in variable frequency control mode to . The output voltage V-out of the LLC converter is adjusted by fine-tuning the frequency.

[0039] Optionally, in step S3 above, when executing the fixed-frequency phase-shift control mode, the LLC converter is controlled to operate at a fixed switching frequency, and the phase shift angle between different bridge arms in the LLC converter is adjusted so that the output voltage of the LLC converter follows the charging voltage of the vehicle power battery. This includes: determining the charging voltage value based on the state of charge or voltage state of the vehicle power battery; calculating the voltage deviation between the output voltage feedback value and the charging voltage value; and generating a phase-shift control signal based on the voltage deviation value.

[0040] The charging voltage value can be understood as the theoretical charging voltage calculated based on the state of charge or state of voltage of the vehicle's power battery.

[0041] Optionally, generating a phase-shift control signal based on the voltage deviation value includes: importing the voltage deviation value into a PID controller and generating a phase-shift control signal based on the PID controller.

[0042] In this embodiment, the proportional coefficient, derivative coefficient, and integral coefficient of the PID controller can be established through experimental data calibration, or preset to fixed values ​​based on empirical data.

[0043] Specifically, in the fixed-frequency phase-shift control mode, the output voltage feedback value of the LLC converter and the state of charge (SOC) or voltage state of the on-board power battery are continuously monitored. The charging voltage value is calculated based on the SOC or voltage state of the on-board power battery. The voltage deviation between the output voltage feedback value and the charging voltage value is input to the PID controller, which processes it into a phase-shift control signal to adjust the phase of the LLC converter. Thus, through PID control technology, fixed-frequency phase-shift control of the LLC converter is achieved based on the output voltage deviation under low voltage or low charge conditions, enabling output voltage tracking under low voltage or low charge conditions and improving voltage regulation accuracy.

[0044] Optionally, the phase shift angle and output voltage satisfy the gain-phase shift angle characteristic curve.

[0045] The gain-phase angle characteristic curve can be understood as a curve characterizing the relationship between the output voltage gain and the phase angle of an LLC converter.

[0046] Specifically, when the phase shift angle is 0°, the circuit topology of the LLC converter is equivalent to that of a traditional full-bridge LLC operating at the resonant frequency. At this time, the voltage gain M of the LLC converter is approximately 1 / N (where N is the turns ratio of transformer T1), and the output voltage is at its highest. As the phase shift angle gradually increases from 0° to close to 180°, the voltage gain M monotonically decreases from its maximum value to close to 0, and the output voltage also decreases from its maximum value to close to 0. After processing the difference between the output voltage feedback value and the charging voltage value (i.e., the voltage deviation value) through PID control, the output control quantity is the phase shift angle. The system increases the phase shift angle to reduce the output voltage, or decreases the phase shift angle to increase the output voltage, in order to match the lower battery voltage.

[0047] Based on the above embodiments, the present invention also provides a three-phase on-board charger control system based on fixed-frequency phase shifting, for executing the three-phase on-board charger control method based on fixed-frequency phase shifting provided in any of the above embodiments.

[0048] See Figure 2 As shown, the three-phase on-board charger of the present invention includes: an LLC converter, which is connected to the on-board power battery.

[0049] Figure 3This is a schematic diagram of a three-phase on-board charger control system based on fixed-frequency phase shifting, provided as an embodiment of the present invention. Figure 3 As shown, the three-phase on-board charger control system includes: a data acquisition module 101, a decision module 102, and a voltage regulation drive module 103. The data acquisition module 101 acquires the output voltage feedback value of the LLC converter; the decision module 102 compares the output voltage feedback value with a preset voltage threshold and determines whether to execute a fixed-frequency phase-shift control mode based on the comparison result; the voltage regulation drive module 103, when executing the fixed-frequency phase-shift control mode, controls the LLC converter to operate at a fixed switching frequency and adjusts the phase shift angle between different arms of the LLC converter, so that the output voltage of the LLC converter follows the charging voltage of the on-board power battery.

[0050] The three-phase on-board charger control system based on fixed-frequency phase shifting provided in the embodiments of the present invention can execute the three-phase on-board charger control method based on fixed-frequency phase shifting provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method. The same parts will not be described again.

[0051] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0052] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A control method for a three-phase on-board charger based on fixed-frequency phase shifting, characterized in that, The three-phase on-board charger includes: an LLC converter, the LLC converter being connected to the on-board power battery; the method includes: Obtain the output voltage feedback value of the LLC converter; The output voltage feedback value is compared with a preset voltage threshold, and a determination is made based on the comparison result as to whether to execute the fixed-frequency phase-shift control mode, including: executing the fixed-frequency phase-shift control mode when the output voltage feedback value is lower than the preset voltage threshold; and executing the frequency conversion control mode when the output voltage feedback value is higher than or equal to the preset voltage threshold. When executing the fixed-frequency phase-shift control mode, the LLC converter is controlled to operate at a fixed switching frequency, and the phase shift angle between different bridge arms in the LLC converter is adjusted so that the output voltage of the LLC converter follows the charging voltage of the vehicle power battery. Before executing the frequency conversion control mode, the method further includes: Obtain the phase shift angle under the fixed-frequency phase shift control mode; When the phase shift angle is less than a preset angle threshold, the output voltage of the LLC converter is adjusted based on the fixed switching frequency and the preset fine-tuning frequency; wherein, the preset fine-tuning frequency is less than the frequency adjustment step size in the frequency conversion control mode; In the fixed-frequency phase-shift control mode, when the phase-shift angle decreases to close to 0°, the current switching frequency and output power are recorded, the working mode is switched to the variable frequency control mode, and the initial frequency of the variable frequency control mode is set to the recorded switching frequency.

2. The three-phase on-board charger control method based on fixed-frequency phase shifting according to claim 1, characterized in that, When executing the fixed-frequency phase-shift control mode, controlling the LLC converter to operate at a fixed switching frequency and adjusting the phase shift angle between different arms of the LLC converter so that the output voltage of the LLC converter follows the charging voltage of the vehicle power battery includes: The charging voltage value is determined based on the state of charge or state of voltage of the on-board power battery; Calculate the voltage deviation between the output voltage feedback value and the charging voltage value; A phase-shift control signal is generated based on the voltage deviation value.

3. The three-phase on-board charger control method based on fixed-frequency phase shifting according to claim 2, characterized in that, The step of generating a phase-shift control signal based on the voltage deviation value includes: The voltage deviation value is imported into the PID controller, and the phase shift control signal is generated based on the PID controller.

4. The three-phase on-board charger control method based on fixed-frequency phase shifting according to any one of claims 1-3, characterized in that, The phase shift angle and the output voltage satisfy the gain-phase shift angle characteristic curve.

5. The three-phase on-board charger control method based on fixed-frequency phase shifting according to any one of claims 1-3, characterized in that, The fixed switching frequency is the inherent resonant frequency of the resonant network of the LLC converter.

6. The three-phase on-board charger control method based on fixed-frequency phase shifting according to any one of claims 1-3, characterized in that, The preset voltage threshold is set based on the rated voltage or maximum voltage of the vehicle power battery.

7. The three-phase on-board charger control method based on fixed-frequency phase shifting according to any one of claims 1-3, characterized in that, The LLC converter adopts an LLC topology or a CLLLC topology.

8. A three-phase on-board charger control system based on fixed-frequency phase shifting, characterized in that, A three-phase on-board charger control method based on fixed-frequency phase shifting as described in any one of claims 1-7, wherein the three-phase on-board charger comprises: an LLC converter connected to an on-board power battery; the system comprises: The data acquisition module is used to acquire the output voltage feedback value of the LLC converter; The decision module is used to compare the output voltage feedback value with a preset voltage threshold and determine whether to execute the fixed-frequency phase-shift control mode based on the comparison result. The voltage regulation drive module is used to control the LLC converter to operate at a fixed switching frequency when executing the fixed frequency phase shift control mode, and to adjust the phase shift angle between different bridge arms in the LLC converter so that the output voltage of the LLC converter follows the charging voltage of the vehicle power battery.

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