A power converter, control method, and related devices

Abstract

The application discloses a power converter, a control method and related devices, comprising: a controller and a three-phase power conversion circuit; each phase of the three-phase power conversion circuit comprises a four-switch Buck-Boost circuit, the direct current side of the three-phase power conversion circuit is used for connecting a direct current source, the alternating current side of the three-phase power conversion circuit is used for connecting a load or a power grid, and the load or the power grid is connected in a star type; the controller is used for adjusting the minimum value of the switching frequency of the four-switch Buck-Boost circuit working in a Buck mode according to the voltage of the direct current source, and determining the working switching frequency of the Buck mode according to the minimum value of the switching frequency of the Buck mode. The power converter can dynamically adjust the switching frequency of the power converter, reduce the switching loss as much as possible under the premise of meeting the ripple requirement, and improve the efficiency of the power converter.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, specifically to a power converter, control method, and related devices. Background Technology

[0002] Currently, in industrial and commercial sectors, voltage conversion generally employs a two-stage topology, consisting of a first-stage DC / DC circuit and a second-stage DC / AC circuit. The hardware structure of a two-stage topology is relatively complex, resulting in lower power density. Furthermore, control requires balancing the control objectives of both stages, leading to complex software control. Additionally, each stage of the two-stage topology incurs power conversion losses, thus resulting in lower efficiency. Summary of the Invention

[0003] In view of this, this application provides a power converter, control method and related device, which have high power density and conversion efficiency, and can dynamically adjust the switching frequency of the power converter to minimize switching losses and improve the efficiency of the power converter while meeting ripple requirements.

[0004] This application provides a power converter, including: a controller and a three-phase power conversion circuit; each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit, the DC side of the three-phase power conversion circuit is used to connect to a DC source, and the AC side of the three-phase power conversion circuit is used to connect to a load or a power grid, wherein the load or power grid is connected in a star configuration.

[0005] The controller is configured to adjust the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode according to the voltage of the DC source, and determine the operating switching frequency of Buck mode according to the minimum switching frequency of Buck mode.

[0006] In one possible implementation, the controller is specifically configured to adjust the minimum switching frequency of the Buck mode in a stepwise manner according to the voltage of the DC source, so that the minimum switching frequency of the Buck mode decreases as the voltage of the DC source increases and increases as the voltage of the DC source decreases; when the voltage of the DC source is within a preset voltage range, the maximum switching frequency of the Buck mode is less than the switching frequency of the four-switch Buck-Boost circuit operating in Boost mode.

[0007] In one possible implementation, the controller is further configured to select a reference switching frequency of the Buck mode based on the ripple setpoint of the Buck mode and the resonant frequency of the filter circuit, and determine the operating switching frequency of the Buck mode based on the reference switching frequency of the Buck mode, the minimum switching frequency of the Buck mode, and the maximum switching frequency of the Buck mode.

[0008] In one possible implementation, the controller is configured to: use the reference switching frequency as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit when the reference switching frequency is greater than or equal to the minimum switching frequency of the Buck mode and less than or equal to the maximum switching frequency of the Buck mode; use the minimum switching frequency of the Buck mode as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit when the reference switching frequency is less than the minimum switching frequency of the Buck mode; and use the maximum switching frequency of the Buck mode as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit when the reference switching frequency is greater than the maximum switching frequency of the Buck mode.

[0009] In one possible implementation, the controller is configured to adjust the minimum switching frequency of the Boost mode according to the phase of the DC source voltage and the AC side voltage; when the DC source voltage is within a preset voltage range, the maximum switching frequency of the Buck mode is less than the minimum switching frequency of the Boost mode.

[0010] One possible implementation is that the controller is specifically configured to adjust the minimum switching frequency of the Buck mode based on the voltage of the DC source and the phase of the AC side voltage.

[0011] One possible implementation is that the controller is configured to adjust the minimum switching frequency of the Boost mode based on the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

[0012] One possible implementation is that the controller is configured to adjust the minimum switching frequency of the Buck mode based on the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

[0013] One possible implementation of the four-switch Buck-Boost circuit includes: a first switch, a second switch, a third switch, a fourth switch, an inductor, and an AC-side capacitor;

[0014] The first and second switching transistors are connected in series to form a first bridge arm, and the two ends of the first bridge arm are respectively connected to the positive and negative terminals of the DC source; the third and fourth switching transistors are connected in series to form a second bridge arm, the first end of the first inductor is connected to the midpoint of the first bridge arm, and the second end of the first inductor is connected to the midpoint of the second bridge arm; the first end of the second bridge arm serves as the output terminal of the three-phase power conversion circuit, the second end of the second bridge arm is connected to the negative terminal of the DC source, and the two ends of the AC side capacitor are respectively connected to the first end of the second bridge arm and the negative terminal of the DC source.

[0015] This application also provides a control method for a power converter, the power converter including a three-phase power conversion circuit; each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit, the DC side of the three-phase power conversion circuit is used to connect to a DC source, and the AC side of the three-phase power conversion circuit is used to connect to a load or a power grid, wherein the load or power grid is connected in a star configuration.

[0016] The control method includes: obtaining the voltage of a DC source; adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode according to the voltage of the DC source; and determining the operating switching frequency of the Buck mode according to the minimum switching frequency of the Buck mode.

[0017] One possible implementation involves adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode based on the voltage of the DC source. Specifically, this includes: adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode in a stepwise manner based on the voltage of the DC source, such that the minimum switching frequency in Buck mode decreases as the voltage of the DC source increases and increases as the voltage of the DC source decreases; and when the voltage of the DC source is within a preset voltage range, the maximum switching frequency in Buck mode is less than the switching frequency of the four-switch Buck-Boost circuit in Boost mode.

[0018] One possible implementation further includes: selecting a reference switching frequency for the Buck mode based on the ripple setpoint of the Buck mode and the resonant frequency of the filter circuit, and determining the operating switching frequency of the Buck mode based on the reference switching frequency of the Buck mode, the minimum switching frequency of the Buck mode, and the maximum switching frequency of the Buck mode.

[0019] One possible implementation, wherein determining the operating switching frequency of the Buck mode based on the reference switching frequency of the Buck mode, the minimum switching frequency of the Buck mode, and the maximum switching frequency of the Buck mode, specifically includes:

[0020] When the reference switching frequency is greater than or equal to the minimum switching frequency of the Buck mode and less than or equal to the maximum switching frequency of the Buck mode, the reference switching frequency is used as the working switching frequency to control the power switching of the four-switch Buck-Boost circuit.

[0021] When the reference switching frequency is less than the minimum switching frequency of the Buck mode, the minimum switching frequency of the Buck mode is used as the working switching frequency to control the power switching of the four-switch Buck-Boost circuit.

[0022] When the reference switching frequency is greater than the maximum value of the switching frequency of the Buck mode, the maximum value of the switching frequency of the Buck mode is used as the working switching frequency to control the power switching of the four-switch Buck-Boost circuit.

[0023] One possible implementation further includes: adjusting the minimum switching frequency of the Boost mode according to the phase of the DC source voltage and the AC side voltage; when the DC source voltage is within a preset voltage range, the maximum switching frequency of the Buck mode is less than the minimum switching frequency of the Boost mode.

[0024] One possible implementation is that adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode according to the voltage of the DC source specifically includes: adjusting the minimum switching frequency of the Buck mode according to the phase of the DC source voltage and the AC side voltage.

[0025] One possible implementation further includes adjusting the minimum switching frequency of the Boost mode based on the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

[0026] One possible implementation, wherein adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode according to the voltage of the DC source, specifically includes: adjusting the minimum switching frequency of the Buck mode according to the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

[0027] This application also provides a control device, including a processor and a memory, wherein the memory is used to store programs, instructions or code, and the processor is used to execute the programs, instructions or code in the memory to perform the control method described above.

[0028] This application also provides a computer-readable storage medium storing a computer program, which is loaded by a processor to execute the control method described above.

[0029] The power converter provided in this application embodiment can adjust the minimum switching frequency of Buck mode according to the voltage of the DC source. Since the maximum ripple of the power converter generally occurs in Boost mode, the switching frequency of Buck mode does not need to meet the maximum ripple of the power converter. Therefore, there is an adjustment margin in the switching frequency of Buck mode. Buck mode can use the lowest possible switching frequency, which can reduce switching losses and improve the efficiency of the power converter. Attached Figure Description

[0030] Figure 1 A schematic diagram of a power converter provided in an embodiment of this application;

[0031] Figure 2 A schematic diagram showing the adjustable minimum switching frequency of the power converter in Buck mode according to an embodiment of this application;

[0032] Figure 3 A flowchart illustrating a method for determining the switching frequency in Buck mode, as provided in an embodiment of this application;

[0033] Figure 4 A schematic diagram of the switching frequency of Buck mode and Boost mode provided for embodiments of this application;

[0034] Figure 5 A schematic diagram of the switching frequency for another Buck mode and Boost mode provided in the embodiments of this application;

[0035] Figure 6 The relationship diagram between Buck mode and Boost mode and phase is provided in the embodiments of this application;

[0036] Figure 7 A schematic diagram illustrating the adjustment of the switching frequency based on the duty cycle and the voltage of a DC source, provided as an embodiment of this application;

[0037] Figure 8 A flowchart illustrating a control method for a power converter provided in an embodiment of this application;

[0038] Figure 9 This is a schematic diagram of a control device provided in an embodiment of this application. Detailed Implementation

[0039] Currently, in industrial and commercial sectors, voltage conversion generally employs a two-stage topology, consisting of a first-stage DC / DC circuit and a second-stage DC / AC circuit. The hardware structure of a two-stage topology is relatively complex, resulting in lower power density. Furthermore, control requires balancing the control objectives of both stages, leading to complex software control. Additionally, each stage of the two-stage topology incurs power conversion losses, thus resulting in lower efficiency.

[0040] Based on this, in the embodiments of this application, the power converter includes a single-stage three-phase power conversion circuit based on a four-switch Buck-Boost circuit, that is, the power converter is a single-stage power converter, which can improve power density, reduce power consumption and improve power conversion efficiency compared to a two-stage power converter.

[0041] To enable those skilled in the art to understand and implement the technical solutions provided in the embodiments of this application, the architecture of the power converter will be described below in conjunction with the accompanying drawings.

[0042] See Figure 1 This figure is a schematic diagram of a power converter provided in an embodiment of this application.

[0043] The power converter provided in this application includes a three-phase power conversion circuit, and each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit, that is, the power converter includes a three-phase four-switch Buck-Boost circuit. The power converter provided in this application is a single-stage DC / AC converter, which can improve power density compared to a two-stage power converter. Furthermore, since the power converter is single-stage, it can reduce power consumption and improve energy conversion efficiency compared to a two-stage power converter. Moreover, the power converter provided in this application can be applied to DC sources with a wide voltage range, such as photovoltaic panels or energy storage batteries. For example, in one possible implementation, the output voltage is 311V, and the corresponding input voltage range can be 280V-380V.

[0044] The first terminals of the three-phase four-switch Buck-Boost circuit are connected in parallel to a DC source. The second terminals of each circuit are independent and connected to the three AC phases of the power converter, respectively. The input voltage of the DC source is denoted by Uin. The AC side of the power converter is connected to the power grid via the second switch K2. The power grid is a three-phase grid, consisting of phases A, B, and C, with phase voltages ua, ub, and uc, where ua, ub, and uc represent the phase voltages of the grid. Specifically, the first terminal of the second switch K2 is connected to the second terminal of the filter inductor Lg, and the first terminal of the filter inductor Lg is connected to the output terminals of the Buck-Boost circuit, with the three phases corresponding to output terminals a, b, and c, respectively.

[0045] The first Buck-Boost circuit includes a first switch S1, a second switch S2, a first inductor L1, a third switch S3, and a fourth switch S4. The first switch S1 and the second switch S2 are connected in series to form the first bridge arm, and the third switch S3 and the fourth switch S4 are connected in series to form the second bridge arm. The first end of the first inductor L1 is connected to the midpoint of the first bridge arm, and the second end of the first inductor L1 is connected to the midpoint of the second bridge arm. The first end of the second bridge arm serves as the output terminal a of the three-phase power conversion circuit, and the second end of the second bridge arm is connected to the negative terminal m of the DC source. The two ends of the AC-side capacitor Cfa are connected to the first end of the second bridge arm and the negative terminal m of the DC source, respectively.

[0046] The second Buck-Boost circuit includes a fifth switch S5, a sixth switch S6, a second inductor L2, a seventh switch S7, and an eighth switch S8. Switches S5 and S6 are connected in series to form the third bridge arm, and switches S7 and S8 are connected in series to form the fourth bridge arm. The first end of the second inductor L2 is connected to the midpoint of the third bridge arm, and the second end of the second inductor L2 is connected to the midpoint of the fourth bridge arm. The first end of the fourth bridge arm serves as the output terminal b of the three-phase power conversion circuit, and the second end of the fourth bridge arm is connected to the negative terminal m of the DC source. The two ends of the AC-side capacitor Cfb are connected to the first end of the fourth bridge arm and the negative terminal m of the DC source, respectively.

[0047] The third Buck-Boost circuit includes a ninth switch S9, a tenth switch S10, a third inductor L3, an eleventh switch S11, and a twelfth switch S12. Switches S9 and S10 are connected in series to form the fifth bridge arm, and switches S11 and S12 are connected in series to form the sixth bridge arm. The first terminal of the third inductor L3 is connected to the midpoint of the fifth bridge arm, and the second terminal of the third inductor L3 is connected to the midpoint of the sixth bridge arm. The first terminal of the sixth bridge arm serves as the output terminal c of the three-phase power conversion circuit, and the second terminal of the sixth bridge arm is connected to the negative terminal m of the DC source. The two ends of the AC-side capacitor Cfc are connected to the first terminal of the sixth bridge arm and the negative terminal m of the DC source, respectively.

[0048] The three-phase output terminals a, b, and c are connected to the negative terminal m of the DC source via corresponding AC-side capacitors Cfa, Cfb, and Cfc, respectively.

[0049] In off-grid mode, the AC side of the three-phase power converter circuit is suitable for connecting a load Rd, which is connected in a star configuration. Specifically, the three-phase output terminals a, b, and c are connected to the first terminal of the first switch K1 via corresponding filter inductors Lg, and the second terminal of the first switch K1 is connected to the neutral point N via the load Rd. The load Rd represents the load connected when the power converter is off-grid. In grid-connected mode, the three-phase output terminals a, b, and c are connected to the first terminal of the second switch K2 via corresponding filter inductors Lg, and the second terminal of the second switch K2 is connected to the three-phase power grid.

[0050] In a three-phase three-wire system, the voltage of the three-phase power grid relative to the negative terminal m of the DC source is the DC bias voltage Uoff.

[0051] When the power converter is off-grid, K2 is open and K1 is closed, operating in a three-phase four-wire system.

[0052] When the power converter is connected to the grid, K2 is closed and K1 is open, operating in a three-phase three-wire system.

[0053] Each phase in a three-phase power conversion circuit can operate independently and has both Boost and Buck modes. Taking phase A of the three-phase power conversion circuit as an example, when the output voltage is greater than the input voltage, the first switch S1 is normally closed, while the third switch S3 and the fourth switch S4 are alternately turned on, and the four-switch Buck-Boost circuit of phase A operates in Boost mode. Conversely, when the output voltage is less than the input voltage, the third switch S3 is normally closed, while the first switch S1 and the second switch S2 are alternately turned on, and the four-switch Buck-Boost circuit of phase A operates in Buck mode. Since the three-phase voltages on the AC side lag by 120 degrees, there is time decoupling between the Boost and Buck modes of each phase power conversion circuit in the three-phase power conversion circuit. That is, when one phase power conversion circuit operates in Buck mode, the other two phase power conversion circuits may operate in Boost mode. In related technologies, the switching frequency of Buck mode and the switching frequency of Boost mode are equal and fixed. While a higher switching frequency can reduce ripple, it also increases switching losses, thereby reducing the efficiency of the power converter. Therefore, a balance needs to be found between ripple and efficiency.

[0054] The power converter provided in this application embodiment can adjust the switching frequency according to the specific operating conditions of the power converter. The switching frequency of Buck mode and Boost mode can be different. Both the switching frequency of Buck mode and Boost mode can be adjusted, or the switching frequency of Boost mode can be fixed and only the switching frequency of Buck mode can be adjusted.

[0055] The power converter provided in this application embodiment has a switching frequency selection method that is applicable to both three-phase three-wire and three-phase four-wire power converters.

[0056] The following section, with reference to the attached diagram, will first introduce the adjustable minimum switching frequency of Buck mode and the fixed switching frequency of Boost mode.

[0057] See Figure 2 The figure is a schematic diagram showing that the minimum switching frequency of the power converter in Buck mode is adjustable according to the embodiment of this application.

[0058] The power converter provided in this application includes a controller and a three-phase power conversion circuit. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit. The DC side of the three-phase power conversion circuit is used to connect to a DC source, and the AC side of the three-phase power conversion circuit is used to connect to a load or power grid. The load or power grid is connected in a star configuration. The connection relationships of the power converter can be found in [reference needed]. Figure 1 The description will not be repeated here.

[0059] The power converter provided in this application embodiment first introduces that the minimum switching frequency of the Buck mode can be adjusted according to the voltage of the DC source, while the switching frequency of the Boost mode can remain fixed.

[0060] The controller adjusts the minimum switching frequency fbmin of the four-switch Buck-Boost circuit in Buck mode based on the DC source voltage Uin. The operating switching frequency in Buck mode is determined based on this minimum switching frequency. In other words, the operating switching frequency in Buck mode must be greater than or equal to the minimum switching frequency in Buck mode.

[0061] If the ripple meets the requirements, the operating switching frequency of Buck mode can be selected to be equal to the minimum switching frequency of Buck mode, thereby minimizing the power consumption of the power converter.

[0062] It should be understood that when the voltage of the DC source connected to the power converter is within a preset voltage range, the maximum switching frequency fbmax in Buck mode is less than the switching frequency fboost of the four-switch Buck-Boost circuit operating in Boost mode. Within this preset voltage range, the maximum ripple of the power converter depends on the Boost mode. The preset voltage range can be selected according to the specific application scenario and the actual parameters of the power converter. This application embodiment does not impose a specific limitation; for example, it can be within the range of 280V-380V.

[0063] This application does not specifically limit the method by which the controller adjusts the minimum switching frequency of Buck mode based on the DC source voltage. For example, the minimum switching frequency fbmin of Buck mode can be made to decrease as the DC source voltage Uin increases, and increase as the DC source voltage Uin decreases. Alternatively, it can be adjusted according to a pre-set relationship table between the DC source voltage and the minimum switching frequency of Buck mode.

[0064] It should be understood that the minimum switching frequency fbmin in Buck mode has an adjustable extreme value range. The maximum value of this range should be less than the switching frequency in Boost mode. For example, the maximum switching frequency in Buck mode should be lower than the switching frequency in Boost mode. For instance, the maximum switching frequency fbmax in Buck mode can be taken as 70% to 80% of the switching frequency fboost in Boost mode, ensuring reduced losses and improved power converter efficiency in Buck mode. Furthermore, the minimum value of the adjustable extreme value range should be greater than or equal to the minimum frequency determined by the parameters of the filter in the power converter, ensuring that the switching frequency is within the effective filtering frequency range of the filter. After adjusting the minimum switching frequency in Buck mode within the above extreme value range, the operating switching frequency of Buck mode is selected according to the specific parameters of the power converter. This application does not specifically limit the specific structure of the filter; the filter is a filter connected to the AC side of the power converter, for example... Figure 1 Lg in the filter refers to the internal components of the filter. In addition to Lg, the filter may also include other components, such as capacitors. Since the filter is a relatively mature component, it will not be discussed further here.

[0065] by Figure 2 The voltage Uin of the DC source shown is used as an example for illustration. Uin can also exhibit other trends. Figure 2 This is just an illustration. From Figure 2It can be seen that from the first sampling time t1, the second sampling time t2 to the third sampling time t3, the DC source voltage Uin gradually increases, and the minimum switching frequency fbmin of the Buck mode needs to gradually decrease. From the nth sampling time tn to the (n+1)th sampling time tn+1, the DC source voltage Uin gradually decreases, and the minimum switching frequency fbmin of the Buck mode needs to gradually increase.

[0066] For example, in industrial and commercial energy storage applications, within the DC source voltage range, the minimum switching frequency of the Buck mode should ensure that the ripple is less than the given maximum value. Furthermore, the higher the DC source voltage, the lower the minimum switching frequency of the Buck mode. The lower limit of the adjustable range for the minimum switching frequency of the Buck mode can be selected as 5 to 10 times the resonant frequency of the filter, thereby ensuring power quality. The closer the operating switching frequency of the Buck mode is to the maximum switching frequency fbmax of the Buck mode, the lower the ripple; the closer the operating switching frequency of the Buck mode is to the minimum switching frequency fbmin of the Buck mode, the lower the switching losses.

[0067] Figure 2 Specifically, the controller is used to adjust the minimum switching frequency of Buck mode in a stepped manner based on the voltage of the DC source. This application does not specifically limit the step size of the stepped adjustment; a smaller step size results in a smaller adjustment range for the minimum switching frequency and more precise adjustment. The step size can be set according to actual needs.

[0068] The controller includes a Buck modulator and a Boost modulator, which are separate from each other. The controller provides the Buck modulator with the minimum switching frequency of the Buck mode obtained from the voltage of the DC source.

[0069] The maximum ripple current of a typical power converter occurs when the inductor current is at its maximum in Boost mode. Therefore, as long as the ripple limit for Boost mode is met at that moment, the ripple limit does not need to be considered in Buck mode. To reduce power consumption, the minimum switching frequency of Buck mode can be adjusted. On the other hand, due to the overcurrent characteristics of Boost mode power converters, the power semiconductor devices used in the various switches, especially IGBTs, will generate significant losses, posing a challenge to heat dissipation design. When a higher switching frequency is selected, a larger number of IGBTs often need to be connected in parallel to meet the heat dissipation limit. When the switching frequency can be lowered, the heat dissipation problem can also be solved, reducing the number of switches connected in parallel and lowering hardware costs.

[0070] The power converter provided in this application embodiment can adjust the minimum switching frequency of Buck mode according to the voltage of the DC source. Since the maximum ripple of the power converter generally occurs in Boost mode, the switching frequency of Buck mode does not need to meet the maximum ripple of the power converter. Therefore, there is an adjustment margin in the switching frequency of Buck mode. Buck mode can use the lowest possible switching frequency, which can reduce switching losses and improve the efficiency of the power converter.

[0071] The power converter provided in this application embodiment, compared to the case of a fixed switching frequency in Buck mode, allows the minimum switching frequency of Buck mode in this application embodiment to be adjusted according to the voltage of the DC source. For example, when the voltage of the DC source increases, the minimum switching frequency of Buck mode decreases; when the voltage of the DC source decreases, the minimum switching frequency of Buck mode increases.

[0072] The above describes the adjustment method for the minimum switching frequency of Buck mode. It should be understood that after the controller obtains the minimum switching frequency of Buck mode, it needs to provide a reference switching frequency for Buck mode to the Buck modulator. The Buck modulator then generates a drive signal to control the operation of the switching transistors based on the reference switching frequency. Specifically, the controller is also used to select the reference switching frequency of Buck mode based on the ripple setpoint and the resonant frequency of the filter circuit, and to determine the operating switching frequency of Buck mode based on the reference switching frequency, the minimum switching frequency, and the maximum switching frequency.

[0073] It should be understood that once the hardware circuit is fixed, the ripple setpoint of the Buck mode and the resonant frequency of the filter circuit are both known quantities.

[0074] The following diagram illustrates how the switching frequency of the Buck mode is determined. When the controller determines that the reference switching frequency is greater than or equal to the minimum and less than or equal to the maximum switching frequency of the Buck mode, it uses the reference switching frequency as the operating switching frequency for the Buck mode, controlling the power switching of the four-switch Buck-Boost circuit. When the reference switching frequency is less than the minimum switching frequency of the Buck mode, the minimum switching frequency of the Buck mode is used as the operating switching frequency for the Buck mode, controlling the power switching of the four-switch Buck-Boost circuit. When the reference switching frequency is greater than the maximum switching frequency of the Buck mode, the maximum switching frequency of the Buck mode is used as the operating switching frequency for the Buck mode, controlling the power switching of the four-switch Buck-Boost circuit.

[0075] See Figure 3The figure is a flowchart illustrating a method for determining the switching frequency of a Buck mode according to an embodiment of this application.

[0076] The power converter provided in this application embodiment includes the following steps in determining the switching frequency in Buck mode:

[0077] S301: Select the reference switching frequency of Buck mode based on the ripple setpoint of Buck mode and the resonant frequency of the filter circuit.

[0078] S302: Obtain the minimum switching frequency of Buck mode based on the DC source voltage, and determine the maximum switching frequency of Buck mode based on the switching frequency of Boost mode.

[0079] S303: When the reference switching frequency is less than the minimum switching frequency of Buck mode, the minimum switching frequency of Buck mode is used as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit.

[0080] S304: When the reference switching frequency is greater than the maximum value of the Buck mode switching frequency, the maximum value of the Buck mode switching frequency is used as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit.

[0081] S305: When the reference switching frequency is greater than or equal to the minimum switching frequency of Buck mode and less than or equal to the maximum switching frequency of Buck mode, the reference switching frequency is used as the working switching frequency to control the power switching of the four-switch Buck-Boost circuit.

[0082] The power converter provided in this application embodiment has low requirements for the performance of the controller. The controller only needs to adjust the minimum switching frequency of the Buck mode according to the voltage of the DC source and give the minimum switching frequency of the Buck mode to the Buck modulator.

[0083] One specific adjustment method involves the controller adjusting the minimum switching frequency of the Buck mode based on the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

[0084] Since there is a conversion relationship between the phase of the AC side voltage and the duty cycle of the drive signal, another specific adjustment method is that the controller can also adjust the minimum switching frequency of the Buck mode according to the voltage of the DC source and the phase of the AC side voltage.

[0085] For ease of understanding, the following explanation will only take the implementation method of adjusting the minimum switching frequency of Buck mode based on the DC source voltage and the duty cycle of the drive signal as an example. Specifically, it can be adjusted using the following formula.

[0086]

[0087] Where, ΔU max Δi represents the maximum value of the voltage ripple (one-sided). max This represents the maximum value of the current ripple (one-sided), where one-sided refers to the maximum value of the ripple rise or fall.

[0088] d buck This indicates the duty cycle of the drive signal in Buck mode. Uin represents the voltage of the DC source. L represents the inductance in the four-switch Buck-Boost circuit, i.e. Figure 1 In this context, L1, L2, or L3 are typically defined as L1 = L2 = L3. C represents... Figure 1 In general, the AC side capacitance is Cfa = Cfb = Cfc.

[0089] The above describes the adjustable minimum switching frequency in Buck mode. The following describes the situation where the switching frequency in Boost mode is also adjustable.

[0090] See Figure 4 The figure is a schematic diagram of the switching frequency of Buck mode and Boost mode provided in an embodiment of this application.

[0091] The power converter provided in this application embodiment has a controller that adjusts the minimum switching frequency of the Boost mode according to the phase of the DC source voltage and the AC side voltage; the maximum switching frequency of the Buck mode is less than the minimum switching frequency of the Boost mode.

[0092] like Figure 4 In the diagram, the horizontal axis represents the phase of the AC side voltage, and the vertical axis represents the switching frequency. Figure 4 The relationship between the minimum switching frequency fbmin1 in Buck mode and the phase of the AC side voltage is shown, as well as the relationship between the minimum switching frequency fsmin2 in Boost mode and the phase of the AC side voltage. In this embodiment, the maximum switching frequency fbmax1 in Buck mode and the maximum switching frequency fsmax2 in Boost mode are both fixed values.

[0093] Figure 5 and Figure 4 The difference is, Figure 5 The minimum switching frequency fbmin1 for Buck mode is adjusted in a stepped manner. Specifically, to avoid frequent adjustments to the minimum switching frequency, a threshold can be set for each change in the minimum switching frequency, such as 100Hz, or other switching frequency thresholds can be set.

[0094] The maximum switching frequency in Boost mode can be selected based on the passive components chosen in the power converter. In this embodiment, a minimum switching frequency for Boost mode is set to ensure ripple requirements are met.

[0095] Because there is a conversion relationship between the phase of the AC side voltage and the duty cycle of the drive signal, such as Figure 6 The diagram shows the relationship between Buck mode and Boost mode and phase. Therefore, another specific adjustment method involves the controller adjusting the minimum switching frequency of Boost mode based on the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source. This can be achieved using the following formula.

[0096]

[0097] Where, ΔU max Δi represents the maximum value of the voltage ripple (one-sided). max This represents the maximum value of the current ripple (one-sided), where one-sided refers to the maximum value of the ripple's rise or fall. d boost This indicates the duty cycle of the drive signal in Boost mode. g This is a reference value for the amplitude of the AC phase current. L represents the inductance in the four-switch Buck-Boost circuit, i.e. Figure 1 In this context, L1, L2, or L3 are typically defined as L1 = L2 = L3. C represents... Figure 1 In general, the AC side capacitance is Cfa = Cfb = Cfc.

[0098] See Figure 7 The figure is a schematic diagram of adjusting the switching frequency according to the duty cycle and the voltage of the DC source, provided in an embodiment of this application.

[0099] The power converter provided in this application embodiment allows the controller to operate based on the DC source voltage Uin and the duty cycle d of the Buck mode drive signal. buck To obtain the minimum switching frequency for Buck mode, the operating switching frequency for Buck mode is then generated. The operating switching frequency for Buck mode must be greater than or equal to the minimum switching frequency for Buck mode. Taking the A-phase power conversion circuit as an example, the operating switching frequency of Buck mode and the duty cycle d of the Buck mode drive signal are used. buck Generate the Buck mode drive signal, that is, drive the first switch S1 and the second switch S2.

[0100] Similarly, in the power converter provided in this application embodiment, the controller can determine the duty cycle d of the Boost mode drive signal based on the DC source voltage Uin and the Boost mode drive signal. buckTo obtain the minimum switching frequency for Boost mode, the operating switching frequency for Boost mode is then generated. The operating switching frequency for Boost mode must be greater than or equal to the minimum switching frequency for Boost mode. Taking the A-phase power conversion circuit as an example, the operating switching frequency for Boost mode and the duty cycle d of the Boost mode drive signal are used. boost The drive signal for Boost mode is generated, which drives the third switch S3 and the fourth switch S4. The operating switching frequency of Boost mode is between the minimum and maximum switching frequencies of Boost mode.

[0101] The power converter provided in this application embodiment can adjust not only the minimum switching frequency in Buck mode, but also the minimum switching frequency in Boost mode. Under the premise of meeting ripple requirements, it can use the lowest possible switching frequency, thereby further reducing switching losses and improving the overall efficiency of the power converter.

[0102] Based on the power converter provided in the above embodiments, this application also provides a control method for the power converter, which will be described in detail below with reference to the accompanying drawings.

[0103] See Figure 8 The figure is a flowchart of a control method for a power converter provided in an embodiment of this application.

[0104] This application provides a control method for a power converter, which includes a three-phase power conversion circuit. Each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit. The DC side of the three-phase power conversion circuit is used to connect to a DC source, and the AC side of the three-phase power conversion circuit is used to connect to a load or a power grid. The load or power grid is connected in a star configuration.

[0105] The control method includes:

[0106] S801: Obtain the voltage of the DC source.

[0107] S802: Adjust the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode according to the voltage of the DC source, and determine the operating switching frequency of Buck mode based on the minimum switching frequency of Buck mode.

[0108] The power converter provided in this application embodiment can adjust the minimum switching frequency of Buck mode according to the voltage of the DC source. Since the maximum ripple of the power converter generally occurs in Boost mode, the switching frequency of Buck mode does not need to meet the maximum ripple of the power converter. Therefore, there is an adjustment margin in the switching frequency of Buck mode. Buck mode can use the lowest possible switching frequency, which can reduce switching losses and improve the efficiency of the power converter.

[0109] One possible implementation involves adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode based on the DC source voltage. Specifically, this includes: adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode in a stepwise manner based on the DC source voltage, so that the minimum switching frequency in Buck mode decreases as the DC source voltage increases and increases as the DC source voltage decreases; when the DC source voltage is within a preset voltage range, the maximum switching frequency in Buck mode is less than the switching frequency of the four-switch Buck-Boost circuit in Boost mode.

[0110] One possible implementation also includes: selecting the reference switching frequency of the Buck mode based on the ripple setpoint of the Buck mode and the resonant frequency of the filter circuit, and determining the operating switching frequency of the Buck mode based on the reference switching frequency of the Buck mode, the minimum switching frequency of the Buck mode, and the maximum switching frequency of the Buck mode.

[0111] One possible implementation involves determining the operating switching frequency of the Buck mode based on a reference switching frequency, a minimum switching frequency, and a maximum switching frequency. Specifically, this includes: when the reference switching frequency is greater than or equal to the minimum switching frequency and less than the maximum switching frequency, using the reference switching frequency as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit; when the reference switching frequency is less than the minimum switching frequency, using the minimum switching frequency as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit; and when the reference switching frequency is greater than the maximum switching frequency, using the maximum switching frequency as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit.

[0112] One possible implementation also includes: adjusting the minimum switching frequency of the Boost mode according to the phase of the DC source voltage and the AC side voltage; when the DC source voltage is within a preset voltage range, the maximum switching frequency of the Buck mode is less than the minimum switching frequency of the Boost mode.

[0113] One possible implementation involves adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode based on the DC source voltage. Specifically, this includes adjusting the minimum switching frequency in Buck mode according to the phase of the DC source voltage and the AC side voltage.

[0114] One possible implementation also includes adjusting the minimum switching frequency of the Boost mode based on the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

[0115] One possible implementation involves adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode based on the DC source voltage. Specifically, this includes adjusting the minimum switching frequency in Buck mode based on the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the DC source voltage.

[0116] In one possible implementation, see Figure 9 The figure is a schematic diagram of a control device provided in an embodiment of this application.

[0117] The control device may include a memory 1011 and a processor 1012. The processor 1012 may be connected to the power converter and can drive the switches in the various power conversion circuits of the power converter. For example... Figure 9 As shown, the memory can be random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (Electronic Programmable ROM), registers, hard disks, removable disks, etc.

[0118] The memory 1011 can store computer instructions. When the computer instructions stored in the memory 1011 are executed by the processor 1012, the processor 1012 can be used to execute the control method of the power converter. The memory 1011 can also store data, such as information like the ripple setpoint coefficient of the Buck mode and the resonant frequency of the filter circuit involved in the above embodiments.

[0119] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape) or a semiconductor medium (e.g., solid-state disk (SSD)).

[0120] This application also provides a readable storage medium for storing the methods provided in the above embodiments. Examples include random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (EPROM), registers, hard disks, removable disks, or any other form of storage medium in the art.

[0121] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the methods disclosed in the embodiments, since they correspond to the product embodiments disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the description of the product embodiments.

[0122] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A power converter, characterized in that, include: The controller and a three-phase power conversion circuit; each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit, the DC side of the three-phase power conversion circuit is used to connect to a DC source, and the AC side of the three-phase power conversion circuit is used to connect to a load or power grid, wherein the load or power grid is connected in a star configuration. The controller is configured to adjust the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode according to the voltage of the DC source, and determine the operating switching frequency of Buck mode according to the minimum switching frequency of Buck mode.

2. The power converter according to claim 1, characterized in that, The controller is specifically configured to adjust the minimum switching frequency of the Buck mode in a stepwise manner according to the voltage of the DC source, so that the minimum switching frequency of the Buck mode decreases as the voltage of the DC source increases and increases as the voltage of the DC source decreases; when the voltage of the DC source is within a preset voltage range, the maximum switching frequency of the Buck mode is less than the switching frequency of the four-switch Buck-Boost circuit operating in Boost mode.

3. The power converter according to claim 1 or 2, characterized in that, The controller is further configured to select a reference switching frequency for the Buck mode based on the ripple setpoint coefficient of the Buck mode and the resonant frequency of the filter circuit, and to determine the operating switching frequency of the Buck mode based on the reference switching frequency of the Buck mode, the minimum switching frequency of the Buck mode, and the maximum switching frequency of the Buck mode.

4. The power converter according to claim 3, characterized in that, The controller is configured to: use the reference switching frequency as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit when the reference switching frequency is greater than or equal to the minimum switching frequency of the Buck mode and less than or equal to the maximum switching frequency of the Buck mode; use the minimum switching frequency of the Buck mode as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit when the reference switching frequency is less than the minimum switching frequency of the Buck mode; and use the maximum switching frequency of the Buck mode as the operating switching frequency to control the power switching of the four-switch Buck-Boost circuit when the reference switching frequency is greater than the maximum switching frequency of the Buck mode.

5. The power converter according to claim 1, characterized in that, The controller is used to adjust the minimum switching frequency of the Boost mode according to the voltage of the DC source and the phase of the AC side voltage. When the voltage of the DC source is within a preset voltage range, the maximum switching frequency of the Buck mode is less than the minimum switching frequency of the Boost mode.

6. The power converter according to claim 5, characterized in that, The controller is specifically used to adjust the minimum switching frequency of the Buck mode according to the voltage of the DC source and the phase of the AC side voltage.

7. The power converter according to claim 1, characterized in that, The controller is used to adjust the minimum switching frequency of the Boost mode according to the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

8. The power converter according to claim 7, characterized in that, The controller is used to adjust the minimum switching frequency of the Buck mode according to the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

9. The power converter according to any one of claims 1-8, characterized in that, The four-switch Buck-Boost circuit includes: a first switch, a second switch, a third switch, a fourth switch, an inductor, and an AC-side capacitor; The first and second switching transistors are connected in series to form a first bridge arm, and the two ends of the first bridge arm are respectively connected to the positive and negative terminals of the DC source; the third and fourth switching transistors are connected in series to form a second bridge arm, the first end of the first inductor is connected to the midpoint of the first bridge arm, and the second end of the first inductor is connected to the midpoint of the second bridge arm; the first end of the second bridge arm serves as the output terminal of the three-phase power conversion circuit, the second end of the second bridge arm is connected to the negative terminal of the DC source, and the two ends of the AC side capacitor are respectively connected to the first end of the second bridge arm and the negative terminal of the DC source.

10. A control method for a power converter, characterized in that, The power converter includes a three-phase power conversion circuit; each phase of the three-phase power conversion circuit includes a four-switch Buck-Boost circuit; the DC side of the three-phase power conversion circuit is used to connect to a DC source; the AC side of the three-phase power conversion circuit is used to connect to a load or power grid; the load or power grid is connected in a star configuration. The control method includes: Obtain the voltage of the DC source; Based on the voltage of the DC source, adjust the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode, and determine the operating switching frequency of Buck mode based on the minimum switching frequency of Buck mode.

11. The control method according to claim 10, characterized in that, Based on the voltage of the DC source, adjust the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode, specifically including: Based on the voltage of the DC source, the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode is adjusted in a stepwise manner, so that the minimum switching frequency in Buck mode decreases as the voltage of the DC source increases and increases as the voltage of the DC source decreases; when the voltage of the DC source is within a preset voltage range, the maximum switching frequency in Buck mode is less than the switching frequency of the four-switch Buck-Boost circuit in Boost mode.

12. The control method according to claim 10 or 11, characterized in that, Also includes: The reference switching frequency of the Buck mode is selected based on the ripple setpoint coefficient of the Buck mode and the resonant frequency of the filter circuit. The operating switching frequency of the Buck mode is determined based on the reference switching frequency of the Buck mode, the minimum switching frequency of the Buck mode, and the maximum switching frequency of the Buck mode.

13. The control method according to claim 12, characterized in that, The step of determining the operating switching frequency of the Buck mode based on the reference switching frequency of the Buck mode, the minimum switching frequency of the Buck mode, and the maximum switching frequency of the Buck mode specifically includes: When the reference switching frequency is greater than or equal to the minimum switching frequency of the Buck mode and less than or equal to the maximum switching frequency of the Buck mode, the reference switching frequency is used as the working switching frequency to control the power switching of the four-switch Buck-Boost circuit. When the reference switching frequency is less than the minimum switching frequency of the Buck mode, the minimum switching frequency of the Buck mode is used as the working switching frequency to control the power switching of the four-switch Buck-Boost circuit. When the reference switching frequency is greater than the maximum value of the switching frequency of the Buck mode, the maximum value of the switching frequency of the Buck mode is used as the working switching frequency to control the power switching of the four-switch Buck-Boost circuit.

14. The control method according to claim 10, characterized in that, Also includes: The minimum switching frequency of the Boost mode is adjusted according to the phase of the DC source voltage and the AC side voltage. When the voltage of the DC source is within a preset voltage range, the maximum switching frequency of the Buck mode is less than the minimum switching frequency of the Boost mode.

15. The control method according to claim 14, characterized in that, The step of adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode based on the voltage of the DC source specifically includes: The minimum switching frequency of the Buck mode is adjusted according to the phase of the DC source voltage and the AC side voltage.

16. The control method according to claim 10, characterized in that, Also includes: The minimum switching frequency of the Boost mode is adjusted based on the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

17. The control method according to claim 16, characterized in that, The step of adjusting the minimum switching frequency of the four-switch Buck-Boost circuit in Buck mode based on the voltage of the DC source specifically includes: The minimum switching frequency of the Buck mode is adjusted based on the duty cycle of the drive signal of the four-switch Buck-Boost circuit and the voltage of the DC source.

18. A control device, characterized in that, It includes a processor and a memory, the memory being used to store programs, instructions, or code, and the processor being used to execute the programs, instructions, or code in the memory to perform the control method as described in any one of claims 10-17.

19. A computer-readable storage medium, characterized in that, The system contains a computer program that is loaded by a processor to execute the control method as described in any one of claims 10-17.

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