Resonant switched capacitor converter and photovoltaic system

Abstract

The application discloses a resonant switching capacitor converter (RSCC) and a photovoltaic system. The RSCC comprises an input capacitor, an output capacitor, a controller and N resonant switching capacitor (RSC) branches. Each RSC branch comprises a switching module and an inductor-capacitor (LC) resonant circuit. N is an integer greater than or equal to 2. Two ends of the N RSC branches are respectively connected to two ends of the input capacitor. An output end of the RSCC is connected to the output capacitor. When the absolute value of the current of the LC resonant circuit in any one of the N RSC branches is greater than a first current threshold, the controller controls the switching module through which the current of the inductor-capacitor (LC) resonant circuit in the N RSC branches flows to be turned off for current limiting protection. The charging and discharging electric quantity of the positive and negative direct current buses is balanced, and the voltage of the positive and negative direct current buses at the input end of the RSCC is kept balanced.

Description

Technical Field

[0001] This application relates to the technical field, specifically to a resonant switched capacitor converter and a photovoltaic system. Background Technology

[0002] Currently, in order to improve power density and reduce power consumption, resonant switched capacitor converters (RSCCs) are used in DC-DC converters. RSCCs consist of a switch, a capacitor, and an inductor. The switch and capacitor realize the conversion of electrical energy, while the capacitor and inductor form a resonance, which enables soft switching during the operation of the switch, thereby reducing switching losses.

[0003] In practical applications, DC-DC converters typically include multiple resonant switched capacitor (RSC) branches connected in parallel. During RSCC operation, overcurrent may occur, meaning the current in the inductor becomes too large, requiring current limiting control. Current limiting control in existing technologies generally involves blocking the RSC branch experiencing overcurrent, i.e., stopping the switch, thereby achieving the purpose of current limiting.

[0004] However, the above current limiting methods can easily cause voltage imbalance on the DC bus, especially in bipolar inverter systems, resulting in voltage bias between the positive and negative buses, which can trigger protection shutdown. Summary of the Invention

[0005] In view of this, this application provides a resonant switched capacitor converter and a photovoltaic system that can perform current limiting control in a timely manner when the current in the RSC branch is overcurrent, and maintain the voltage balance between the positive bus and the negative bus.

[0006] This application provides a resonant switched capacitor converter (RSCC), comprising: an input capacitor, an output capacitor, a controller, and N resonant switched capacitor RSC branches; each RSC branch includes a switching module and an inductor-capacitor LC resonant circuit; N is an integer greater than or equal to 2;

[0007] The two ends of the N resonant switched capacitor RSC branches are respectively connected to the two ends of the input capacitor; the output terminal of the resonant switched capacitor converter RSCC is connected to the output capacitor.

[0008] The controller is used to turn off all switching modules through which the current flows in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches, for current limiting protection, when the absolute value of the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches exceeds a first current threshold.

[0009] Preferably, the RSCC level of the resonant switched capacitor converter is greater than or equal to two levels.

[0010] Preferably, the resonant switched capacitor converter RSCC is a three-level resonant switched capacitor converter RSCC, and each resonant switched capacitor RSC branch includes: a first diode, a second diode, a first switching module, a second switching module, a third switching module, and a fourth switching module;

[0011] The input capacitor includes a first input capacitor and a second input capacitor. The first end of the first input capacitor is connected to the positive input terminal of the resonant switched capacitor converter RSCC, and the second end of the first input capacitor is connected to the negative input terminal of the resonant switched capacitor converter RSCC through the second input capacitor.

[0012] The first terminal of the first switch module is connected to the positive input terminal, the second terminal of the first switch module is connected to the first terminal of the second switch module, the second terminal of the second switch module is connected to the third terminal of the third switch module, and the third terminal of the third switch module is connected to the negative input terminal through the fourth switch module.

[0013] The first terminal of the inductor-capacitor LC resonant circuit is connected to the second terminal of the second switching module. The second terminal of the inductor-capacitor LC resonant circuit is connected to the cathode of the first diode and the anode of the second diode. The anode of the first diode is connected to the positive output terminal of the resonant switched capacitor converter RSCC, and the cathode of the second diode is connected to the negative output terminal of the resonant switched capacitor converter RSCC.

[0014] Preferably, the resonant switched capacitor converter RSCC is a three-level resonant switched capacitor converter RSCC, and each resonant switched capacitor RSC branch includes: a fifth switch module, a sixth switch module, a first switch module, a second switch module, a third switch module, and a fourth switch module;

[0015] The input capacitor includes a first input capacitor and a second input capacitor. The first end of the first input capacitor is connected to the positive input terminal of the resonant switched capacitor converter RSCC, and the second end of the first input capacitor is connected to the negative input terminal of the resonant switched capacitor converter RSCC through the second input capacitor.

[0016] The first terminal of the first switch module is connected to the positive input terminal, the second terminal of the first switch module is connected to the first terminal of the second switch module, the second terminal of the second switch module is connected to the third terminal of the third switch module, and the third terminal of the third switch module is connected to the negative input terminal through the fourth switch module.

[0017] The first terminal of the LC resonant circuit is connected to the second terminal of the second switching module. The second terminal of the LC resonant circuit is connected to the second terminal of the fifth switching module and the first terminal of the sixth switching module. The first terminal of the fifth switching module is connected to the positive output terminal of the resonant switched capacitor converter RSCC. The second terminal of the sixth switching module is connected to the negative output terminal of the resonant switched capacitor converter RSCC.

[0018] Preferably, the controller is specifically configured to, when the current of the inductor-capacitor LC resonant circuit in any one of the N resonant switched capacitor RSC branches is positive and the current of the inductor-capacitor LC resonant circuit is greater than a first current threshold, control the first switching module with positive current in the inductor-capacitor LC resonant circuit of the N resonant switched capacitor RSC branches to turn off, and control the second switching module to turn off after a first preset time; control the fourth switching module with negative current in the inductor-capacitor LC resonant circuit of the N resonant switched capacitor RSC branches to turn off, and control the third switching module to turn off after a second preset time.

[0019] Preferably, the controller is specifically configured to, when the current of the inductor-capacitor LC resonant circuit in any one of the N resonant switched capacitor RSC branches is negative and the absolute value of the current of the inductor-capacitor LC resonant circuit is greater than a first current threshold, control the fourth switching module with negative current in the inductor-capacitor LC resonant circuit in the N resonant switched capacitor RSC branches to turn off, and control the third switching module to turn off after a second preset time; control the first switching module with positive current in the inductor-capacitor LC resonant circuit in the N resonant switched capacitor RSC branches to turn off, and control the second switching module to turn off after a first preset time.

[0020] Preferably, the controller is further configured to control all switching modules in the N resonant switching capacitor RSC branches to turn off when the absolute value of the current in the inductor-capacitor LC resonant circuit is greater than the second current threshold; the second current threshold is greater than the first current threshold.

[0021] This application also provides a photovoltaic system, including: a first DC-DC circuit and a second DC-DC circuit; the second DC-DC circuit includes the resonant switched capacitor converter RSCC described above;

[0022] The positive and negative input terminals of the first DC-DC circuit are used to connect to the positive and negative terminals of the photovoltaic string, respectively; the positive output terminal of the first DC-DC circuit is connected to the positive bus BUS+.

[0023] The positive and negative input terminals of the resonant switched capacitor converter RSCC are connected to the negative and positive output terminals of the first DC-DC circuit, respectively; the positive output terminal of the resonant switched capacitor converter RSCC is connected to the N line, and the positive output terminal of the resonant switched capacitor converter RSCC is connected to the negative bus BUS-.

[0024] Preferably, it further includes: a first DCAC circuit and a second DCAC circuit;

[0025] First DCAC circuit and second DCAC circuit.

[0026] The positive input terminal of the first DCAC circuit is connected to BUS+, and the negative input terminal of the first DCAC circuit is connected to the N line.

[0027] The positive input terminal of the second DCAC circuit is connected to the N line, and the negative input terminal of the second DCAC circuit is connected to BUS-.

[0028] This application also provides a control method for a resonant switched capacitor converter RSCC. The resonant switched capacitor converter RSCC includes: an input capacitor, an output capacitor, a controller, and N resonant switched capacitor RSC branches; each resonant switched capacitor RSC branch includes a switching module and an inductor-capacitor LC resonant circuit; N is an integer greater than or equal to 2.

[0029] Obtain the current of the LC resonant circuit of each resonant switched capacitor RSC branch;

[0030] When the absolute value of the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches exceeds the first current threshold, the switching modules through which the current flows in the LC resonant circuit of the N resonant switched capacitor RSC branches are turned off for current limiting protection.

[0031] Preferably, when the resonant switched capacitor converter RSCC is a three-level resonant switched capacitor converter RSCC, the switching module includes a first switching module, a second switching module, a third switching module and a fourth switching module, which are connected in series and then connected between the positive input terminal and the negative input terminal of the resonant switched capacitor converter RSCC.

[0032] When the absolute value of the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches exceeds the first current threshold, all switching modules controlling the current flow through the LC resonant circuit of the N resonant switched capacitor RSC branches are turned off. Specifically, this includes:

[0033] When the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches is positive and the current in the LC resonant circuit is greater than the first current threshold, the first switching module with the positive current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off, and the second switching module is turned off after a first preset time; the fourth switching module with the negative current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off, and the third switching module is turned off after a second preset time.

[0034] Preferably, when the absolute value of the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches is greater than the first current threshold, all switching modules through which the current flows in the LC resonant circuit of the N resonant switched capacitor RSC branches are turned off, specifically including:

[0035] When the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches is negative, and the absolute value of the current in the LC resonant circuit is greater than the first current threshold, the fourth switch module with the negative current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off, and the third switch module is turned off after a second preset time; the first switch module with the positive current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off, and the second switch module is turned off after a first preset time.

[0036] Preferably, it further includes: when the absolute value of the current in the inductor-capacitor LC resonant circuit is greater than the second current threshold, controlling all the switching modules in the N resonant switching capacitor RSC branches to turn off, and the second current threshold is greater than the first current threshold.

[0037] Therefore, this application has the following beneficial effects:

[0038] The RSCC provided in this application includes: an input capacitor, an output capacitor, a controller, and N switched capacitor RSC branches; each RSC branch includes a switching module and an inductor-capacitor LC resonant circuit; N is an integer greater than or equal to 2; the two ends of the N RSC branches are respectively connected to the two ends of the input capacitor; the output terminal of the RSCC is connected to the output capacitor; in order to ensure the voltage balance of the positive DC bus and negative DC bus at the RSCC input terminal (i.e., the voltage balance of C1 and C2), the technical solution provided in this application is that if the absolute value of the current of the LC resonant circuit of any one RSC branch exceeds the first current threshold, the current of all RSC branches is limited. Since all RSC branches are connected in parallel, limiting the current of all RSC branches ensures that the charging and discharging capacity of the multiple parallel RSC branches for the positive DC bus and negative DC bus at the RSCC input terminal is balanced, thereby ensuring that the voltage of the positive DC bus and negative DC bus at the RSCC input terminal remains balanced. Attached Figure Description

[0039] Figure 1 A schematic diagram of a photovoltaic system provided in this application;

[0040] Figure 2 A schematic diagram of a three-level RSCC provided in this application;

[0041] Figure 3 A schematic diagram of a two-level RSCC provided in this application;

[0042] Figure 4 A schematic diagram of three three-level RSC branches connected in parallel, provided for this application;

[0043] Figure 5 A schematic diagram of an RSCC provided for an embodiment of this application;

[0044] Figure 6 The timing and current diagram of the RSCC when the current is normal are provided for the embodiments of this application;

[0045] Figure 7 The waveform diagram of the resonant circuit of the RSC branch provided in the embodiment of this application when the current is overcurrent;

[0046] Figure 8 The waveform and timing diagram of forward current overcurrent provided for embodiments of this application;

[0047] Figure 9 Waveforms and timing diagrams of negative current overcurrent provided for embodiments of this application;

[0048] Figure 10 Waveforms and timing diagrams showing overcurrent in both positive and negative directions provided in the embodiments of this application;

[0049] Figure 11 A schematic diagram of a photovoltaic system provided in an embodiment of this application;

[0050] Figure 12 A flowchart of an RSCC control method provided in an embodiment of this application. Detailed Implementation

[0051] To enable those skilled in the art to better understand the technical solutions provided in this application, specific application scenarios will be introduced below.

[0052] See Figure 1 The figure is a schematic diagram of a photovoltaic system provided in this application.

[0053] The photovoltaic system provided in this application includes a positive busbar BUS+, an N-line, and a negative busbar BUS-, wherein the voltage between BUS+ and the N-line is equal to the voltage between BUS- and the N-line under normal conditions. For example, the voltage of BUS+ is 1500V, the voltage of BUS- is -1500V, and the voltage of the N-line is 0V. This photovoltaic system includes both positive and negative voltages and can be called a bipolar photovoltaic system.

[0054] The photovoltaic system provided in this application includes: a first DC-DC circuit 10, a second DC-DC circuit 20, a first DC-AC circuit 30, and a second DC-AC circuit 40;

[0055] The positive and negative input terminals of the first DC-DC circuit 10 are used to connect to the positive and negative terminals of the photovoltaic string, respectively; the positive output terminal of the first DC-DC circuit 10 is connected to the positive bus BUS+.

[0056] The positive and negative input terminals of the second DC-DC circuit 20 are connected to the negative and positive output terminals of the first DC-DC circuit 10, respectively; the positive output terminal of the second DC-DC circuit 20 is connected to the N line, and the positive output terminal of the second DC-DC circuit 20 is connected to the negative bus BUS-.

[0057] The positive input terminal of the first DCAC circuit 30 is connected to BUS+, and the negative input terminal of the first DCAC circuit 30 is connected to the N line.

[0058] The positive input terminal of the second DCAC circuit 40 is connected to the N line, and the negative input terminal of the second DCAC circuit 40 is connected to BUS-.

[0059] In one scenario, both the first DC-DC circuit 10 and the second DC-DC circuit 20 employ boost circuits. Traditional boost circuits, such as Boost converters, consume significant power and are not conducive to increasing power density. Currently, the second DC-DC circuit 20 can use... Figure 2 The RSCC shown is used to implement this.

[0060] Figure 1 This is just a simplified illustration. In actual work, multiple DC-DC converters may be connected in parallel to the input of a DC-AC converter.

[0061] This application does not specifically limit the number of RSCC levels. For example, as long as it is greater than two levels, it is applicable, such as three levels, five levels, etc.

[0062] See Figure 2 The figure is a schematic diagram of a three-level RSCC provided in this application.

[0063] Figure 2 Only one resonant switched capacitor RSC branch is shown, where the switching module includes four switching transistors Q1-Q4, diodes D3 and D4 serve as freewheeling diodes at the input, and the resonant circuit includes an inductor L and a capacitor Cb connected in series. D1 and D2 are freewheeling diodes at the output.

[0064] C1 and C2 are output capacitors, and C3 and C4 are output capacitors.

[0065] Figure 2 A current sensor (CT) can be installed on an LC resonant circuit to detect the current in the resonant circuit.

[0066] Combination Figure 1 and Figure 2 Let's take a look. Figure 2 The input voltage Vin is Figure 1 The voltage between BUS+ and 0. Generally... Figure 1 The potential of the N-line in the reference is the ground, i.e., the 0 potential. Figure 2 The output voltage Vout is Figure 1The voltage between N and BUS- in the circuit.

[0067] The switching state of the switching transistor in the RSC branch can be controlled, so that the resonant circuit stores the energy at the input terminal (C1 and C2) when charging, and transfers the energy to the output terminal (C3 and C4) when discharging, thereby completing the power conversion.

[0068] It should be understood that Figure 2 The midpoint clamping is achieved using diodes (D3 and D4). Alternatively, D3 and D4 can be replaced with controllable switching transistors, which will not be elaborated here.

[0069] Additionally, RSCC can also be a two-level architecture, see [link / reference]. Figure 3 The figure is a schematic diagram of a two-level RSCC provided in this application.

[0070] Figure 3 The two-level RSCC shown illustrates the case where two two-level RSCC branches are connected in parallel.

[0071] Each RSC branch in a two-level RSCC circuit includes two switching transistors: Q1 and Q2 for the first RSC branch, and Q3 and Q4 for the second RSC branch. The resonant circuit of the first RSC branch includes an inductor L1 and a capacitor Cb1 connected in series. The resonant circuit of the second RSC branch includes an inductor L2 and a capacitor Cb2 connected in series. The output terminals of the first RSC branch include diodes D1 and D2, and the output terminals of the second RSC branch include diodes D3 and D4.

[0072] For DC-DC converters, the more RSC branches connected in parallel, the greater the power. Therefore, in practical applications, N RSC branches are generally connected in parallel.

[0073] See Figure 4 The figure is a schematic diagram of three three-level RSC branches connected in parallel according to this application.

[0074] The first RSC branch includes switching transistors Q1-Q4, clamping diodes D7 and D8, output diodes D1 and D2, and the resonant circuit includes an inductor L1 and a capacitor Cb1 connected in series.

[0075] The second RSC branch includes switching transistors Q5-Q8, clamping diodes D9 and D10, output diodes D1 and D2, and the resonant circuit includes an inductor L1 and a capacitor Cb1 connected in series.

[0076] The third RSC branch includes switching transistors Q9-Q12, clamping diodes D11 and D12, output diodes D1 and D2, and a resonant circuit consisting of an inductor L1 and a capacitor Cb1 connected in series.

[0077] RSCC Implementation

[0078] See Figure 5 The figure is a schematic diagram of an RSCC provided in an embodiment of this application.

[0079] The resonant switched capacitor converter RSCC provided in this embodiment includes: an input capacitor, an output capacitor (not shown in the figure), a controller 600, and N switched capacitor RSC branches; each RSC branch includes a switching module and an inductor-capacitor LC resonant circuit; N is an integer greater than or equal to 2; Figure 5 The two ends of the first RSC branch 501, the second RSC branch 502, and up to the nth RSC branch 50n are connected in parallel to the two ends of the input capacitor.

[0080] The embodiments of this application do not specifically limit the value of N. For example, it can be 2, 3 or a larger value. The larger the value of N, the greater the power of the converter. It can be selected according to the specific application scenario.

[0081] The embodiments in this application do not specifically limit the number of RSCC levels; for example, it can be a two-level topology or a three-level topology. For details, please refer to [link / reference needed]. Figure 2 The three-level or Figure 3 The two voltage levels are shown.

[0082] The two ends of each of the N RSC branches are connected to the two ends of the input capacitor; the output terminal of the RSCC is connected to the output capacitor.

[0083] The controller 600 is used to control all switching modules through which the current flows in the LC resonant circuit of any one of the N RSC branches to be turned off for current limiting protection when the absolute value of the current in the LC resonant circuit of any one of the N RSC branches is greater than a first current threshold.

[0084] Since the current in an LC resonant circuit is sometimes positive and sometimes negative (for example, taking the positive current flowing to the output terminal as an example), it is necessary to determine whether the absolute value of the current in the LC resonant circuit exceeds the first current threshold. There may be overcurrent in the positive current or overcurrent in the negative current.

[0085] During RSCC operation, the current in the LC resonant circuit may increase due to various reasons, exceeding the first current threshold. Specifically, this could be an increase in the current of the LC resonant circuit in one RSC branch or multiple RSC branches; this application does not specify a particular current threshold. However, to ensure voltage balance between the positive and negative DC buses at the RSCC input (i.e., voltage balance between C1 and C2), the technical solution provided in this application is to limit the current of all RSC branches if the absolute value of the current in the LC resonant circuit of any one RSC branch exceeds the first current threshold. Since all RSC branches are connected in parallel, limiting the current of all RSC branches ensures that the charging and discharging capacity of the multiple parallel RSC branches for the positive and negative DC buses at the RSCC input is balanced, thereby ensuring that the voltage of the positive and negative DC buses at the RSCC input remains balanced.

[0086] To enable those skilled in the art to better understand the technical solutions provided in the embodiments of this application, the following describes the situations where overcurrent occurs when the current in the resonant circuit is positive and when the current in the resonant circuit is negative.

[0087] For ease of description, the following will use... Figure 2 The following description uses a three-level RSCC circuit as an example. The specific value of N is not limited. Regardless of the value of N, during overcurrent, the switching modules through which the current flows are turned off. Of course, all switching modules can also be turned off. This application does not specifically limit the implementation method of the switching modules; they can include one controllable switching transistor or multiple controllable switching transistors. The number of controllable switching transistors can be set according to the voltage and current they withstand. Furthermore, the controllable switching transistors in the switching modules all include anti-parallel diodes. The following description uses an example where each switching module includes one controllable switching transistor. The type of controllable switching transistor can be any of the following: relay, insulated gate bipolar transistor (IGBT), metal-oxide-semiconductor field-effect transistor (MOSFET), SiC MOSFET (Silicon Carbide Metal Oxide Semiconductor Field-Effect Transistor), etc. When the switching transistor is a MOS transistor, it can be either a PMOS transistor or an NMOS transistor, but this application does not specifically limit this.

[0088] See also Figure 2The RSCC is a three-level RSCC, and each RSCC branch includes: first diode D1, second diode D2, first switch module Q1, second switch module Q2, third switch module Q3 and fourth switch module Q4;

[0089] The input capacitors include a first input capacitor C1 and a second input capacitor C2. The first end of the first input capacitor C1 is connected to the positive input terminal BUS+ of RSCC, and the second end of the first input capacitor C1 is connected to the negative input terminal 0 of RSCC through the second input capacitor C2.

[0090] The first terminal of the first switch module Q1 is connected to the positive input terminal BUS+, the second terminal of the first switch module Q1 is connected to the first terminal of the second switch module Q2, the second terminal of the second switch module Q2 is connected to the third terminal of the third switch module Q3, and the third terminal of the third switch module Q3 is connected to the negative input terminal 0 through the fourth switch module Q4.

[0091] The first terminal of the LC resonant circuit (L and Cb connected in series) is connected to the second terminal of the second switching module Q2. The second terminal of the LC resonant circuit is connected to the cathode of the first diode D1 and the anode of the second diode D2. The anode of the first diode D1 is connected to the positive output terminal BUS- of RSCC, and the cathode of the second diode D2 is connected to the negative output terminal 0 of RSCC.

[0092] See Figure 6 The figure shows the timing and current diagram of the RSCC when the current is normal, as provided in the embodiment of this application.

[0093] Combination Figure 4 , Figure 6 In the diagram, S1 corresponds to the drive signal for Q1, S2 corresponds to the drive signal for Q2, S3 corresponds to the drive signal for Q3, and S4 corresponds to the drive signal for Q4. Figure 4 The working principle of each RSC branch is the same, but in actual operation, the driving timing of the switching transistors at the same position may have a certain delay, that is, phase misalignment. For example, the first RSC branch and the second RSC branch are out of phase by 120 degrees, and the third RSC branch and the second RSC branch are out of phase by 120 degrees. Only the first RSC branch will be used as an example for introduction.

[0094] Figure 6 IL1, IL2, and IL3 represent the currents of the resonant circuit when there is no overcurrent in the three RSC branches.

[0095] See Figure 7 The figure shows the waveform of the resonant circuit of the RSC branch provided in the embodiment of this application when the current is overcurrent.

[0096] Where IL represents the current in the resonant circuit of a certain RSC branch. Where Iref is the first current threshold, and -Iref is the negative of the first current threshold.

[0097] from Figure 7 It can be seen that the forward current of the resonant circuit of the RSC circuit exceeds the first current threshold Iref. Therefore, current limiting control is required. The switching transistor through which the forward current flows is immediately turned off, and the forward current quickly drops to 0. After the fault is cleared, normal operation is restored and the current is normal.

[0098] For tolerance design, the absolute value of the peak value of the normal current is generally less than the first current threshold.

[0099] The following describes the process of current limiting control for the RSC branch during forward current overcurrent in the resonant circuit.

[0100] See Figure 8 The figure shows the waveform and timing diagram of forward current overcurrent provided in the embodiments of this application.

[0101] In the RSCC provided in this embodiment, when the current of the LC resonant circuit in any one of the N RSC branches is positive and the current of the LC resonant circuit is greater than the first current threshold, such as... Figure 8 As shown, an overcurrent occurs in the forward current of the RSC branch, and IL is greater than Iref. The controller, specifically, controls the first switch module in the N RSC branches to turn off. That is, when IL is greater than Iref, it immediately controls the drive signal S1 corresponding to the first switch module to switch from high to low. After a first preset time, it then controls the second switch module to turn off, that is, it controls the drive signal S2 corresponding to the second switch module to switch from high to low. The first preset time is a dead time set between Q1 and Q2 for safety operation.

[0102] When the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches is positive and the current in the LC resonant circuit is greater than the first current threshold, the first switching module with the positive current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off, and the second switching module is turned off after a first preset time; the fourth switching module with the negative current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off, and the third switching module is turned off after a second preset time.

[0103] It should be understood that, corresponding Figure 4The three three-level RSC branches are connected in parallel. If the current in one RSC branch is overcurrent, all three RSC branches will be current-limited. Specifically, Q1 will be turned off first, followed by Q2 after a first preset time. Due to the phase mismatch in the control timing between the different RSC branches, when the resonant current of the first RSC branch is positive, the resonant current of the second RSC branch may be negative. Therefore, the switching transistor flowing through it needs to be turned off. Similarly, the third RSC branch undergoes similar control. After the current is limited in all three RSC branches, the resonant current quickly drops to 0, thus preventing damage caused by overcurrent.

[0104] See Figure 9 The figure shows the waveform and timing diagram of negative current overcurrent provided in the embodiment of this application.

[0105] In the RSCC provided in this embodiment, when the current of the LC resonant circuit in any one of the N RSC branches is negative, and the absolute value of the current in the LC resonant circuit is greater than the first current threshold, such as... Figure 9 As shown, the overcurrent IL is negative at this time, and the absolute value of IL is greater than Iref. It should be understood that the absolute value can also be omitted; IL can be directly compared with the negative value of the first current threshold, -Iref. That is, IL is less than -Iref. Specifically, the controller is used to turn off the fourth switch module in the N RSC branches, that is, to control the drive signal S4 corresponding to the fourth switch module to change from high to low. After a second preset time, it controls the third switch module to turn off, that is, to control the drive signal S3 corresponding to the third switch module to change from high to low. The second preset time is a dead time set between Q3 and Q4 for safety operation.

[0106] When the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches is negative, and the absolute value of the current in the LC resonant circuit is greater than a first current threshold, the fourth switching module with negative current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off. After a second preset time, the third switching module is turned off. The first switching module with positive current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off. After a first preset time, the second switching module is turned off.

[0107] It should be understood that, corresponding Figure 4The three three-level RSC branches are connected in parallel. If the current in one RSC branch is overcurrent, all three RSC branches will be current-limited. Specifically, Q4 will be turned off first, followed by Q3 after a first preset time. Due to the phase mismatch in the control timing between the different RSC branches, when the resonant current of the first RSC branch is negative, the resonant current of the second RSC branch may be positive. Therefore, the switching transistor flowing through it needs to be turned off. Similarly, the third RSC branch is controlled in a similar way. After being turned off, the resonant current of the three RSC branches quickly drops to 0, thus preventing damage caused by overcurrent.

[0108] The above describes the overcurrent situation in the positive or negative circuit of the resonant circuit. In actual operation, it is possible for both the positive and negative circuits of the resonant circuit to experience overcurrent. The following is a detailed introduction with reference to the attached diagram.

[0109] See Figure 10 The figure shows the waveform and timing diagram of both positive and negative currents being overcurrent according to an embodiment of this application.

[0110] Figure 10 As can be seen, both the positive and negative currents of the resonant circuit experienced overcurrent. Therefore, when the positive current IL was overcurrent, S1 was first controlled to go low, followed by S2. When the negative current IL was overcurrent, S4 was first controlled to go low, followed by S3.

[0111] It should be understood that when the current of the resonant circuit is normal in the next cycle, the drive signals of each switching module can be restored, that is, the current limiting stops and the normal wave generation resumes.

[0112] The following section discusses how overcurrent in resonant circuits can occur, but timely current limiting does not affect the normal operation of the RSCC. However, when the current in the resonant circuit becomes too large, it is necessary to immediately shut down and stop operation. A detailed explanation follows.

[0113] The controller is also used to control all switching modules in the N RSC branches to turn off when the absolute value of the current in the LC resonant circuit is greater than the second current threshold; the second current threshold is greater than the first current threshold.

[0114] It should be understood that the RSCC provided in this application embodiment can limit the current of all RSC branches in a timely manner when the current of the resonant circuit is overcurrent, which can ensure the voltage balance of the positive bus and the negative bus, and will not trigger the protection shutdown. Moreover, after the current is limited, the RSCC can usually return to normal in a very short time, so as not to affect the normal operation of the RSCC and there is no need to interrupt the shutdown.

[0115] It should be understood that the above embodiments are all based on the example of a diode as the clamping switch in the RSC branch. Figure 2 and Figure 3 D1 and D2 in the circuit can also be controllable switching transistors, i.e., they can be used as switching modules, which will not be elaborated here.

[0116] Photovoltaic System Examples

[0117] Based on the resonant switched capacitor converter provided in the above embodiments, this application also provides a photovoltaic system, which will be described in detail below with reference to the accompanying drawings.

[0118] See Figure 11 The figure is a schematic diagram of a photovoltaic system provided in an embodiment of this application.

[0119] The photovoltaic system provided in this embodiment includes: a first DC-DC circuit 10 and a second DC-DC circuit 20; wherein, the second DC-DC circuit 20 includes the RSCC20 described above; the number of RSC branches in RSCC20 is not specifically limited, nor is the number of second DC-DC circuits included in the photovoltaic system.

[0120] The positive and negative input terminals of the first DC-DC circuit 10 are used to connect to the positive and negative terminals of the photovoltaic string, respectively; the positive output terminal of the first DC-DC circuit 10 is connected to the positive bus BUS+.

[0121] The positive and negative input terminals of RSCC20 are connected to the negative and positive output terminals of the first DC-DC circuit 10, respectively; the positive output terminal of RSCC20 is connected to the N line, and the positive output terminal of RSCC20 is connected to the negative bus BUS-.

[0122] When an overcurrent occurs in the RSC branch of RSCC20, it will cause an imbalance in the voltage between the positive and negative DC bus at the RSCC input terminal, i.e. Figure 11 The voltage imbalance between the input capacitors C1 and C2 causes the RSCC20 to shut down for protection, which in turn causes the entire photovoltaic system to shut down for protection, resulting in wasted solar energy and affecting the power generation efficiency of the photovoltaic system.

[0123] In addition, the photovoltaic system provided in this application embodiment also includes: a first DCAC circuit 30 and a second DCAC circuit 40;

[0124] First DCAC circuit 30 and second DCAC circuit 40;

[0125] The positive input terminal of the first DCAC circuit 30 is connected to BUS+, and the negative input terminal of the first DCAC circuit 30 is connected to the N line.

[0126] The positive input terminal of the second DCAC circuit 40 is connected to the N line, and the negative input terminal of the second DCAC circuit 40 is connected to BUS-.

[0127] Generally, the first DC-DC circuit 10 can be a boost circuit, such as a boost converter. Furthermore, in the photovoltaic system provided in this application embodiment, the first DC-DC circuit 10 and RSCC 20 can have maximum power point tracking (MPPT) functionality. The first DC-DC circuit 10 and RSCC 20 can be integrated into an MPPT combiner box, and the outputs of multiple MPPT combiner boxes are connected to an inverter circuit. That is, the photovoltaic system can include multiple first DC-DC circuits 10 and multiple RSCC 20s.

[0128] Method Implementation Examples

[0129] Based on the RSCC and photovoltaic system provided in the above embodiments, this application also provides an RSCC control method, which will be described in detail below with reference to the accompanying drawings.

[0130] See Figure 12 The figure is a flowchart of an RSCC control method provided in an embodiment of this application.

[0131] The control method for resonant switched capacitor RSCC provided in this embodiment includes: an input capacitor, an output capacitor, a controller, and N switched capacitor RSC branches; each RSC branch includes a switching module and an inductor-capacitor LC resonant circuit; N is an integer greater than or equal to 2;

[0132] S1201: Obtain the current of the LC resonant circuit of each RSC branch;

[0133] For example, a current sensor can be set on each resonant circuit to obtain the current of the resonant circuit in each RSC branch.

[0134] S1201: When the absolute value of the current in the LC resonant circuit of any one of the N RSC branches is greater than the first current threshold, the switching modules through which the current flows in the LC resonant circuit of the N RSC branches are turned off for current limiting protection.

[0135] Since the current in an LC resonant circuit is sometimes positive and sometimes negative (for example, taking the positive current flowing to the output terminal as an example), it is necessary to determine whether the absolute value of the current in the LC resonant circuit exceeds the first current threshold. There may be overcurrent in the positive current or overcurrent in the negative current.

[0136] During RSCC operation, the current in the LC resonant circuit may increase due to various reasons, exceeding the first current threshold. Specifically, this could be an increase in the current of the LC resonant circuit in one RSC branch or multiple RSC branches; this application does not specify a particular current threshold. However, to ensure voltage balance between the positive and negative DC buses at the RSCC input, the technical solution provided in this application is to limit the current of all RSC branches if the absolute value of the current in the LC resonant circuit of any one RSC branch exceeds the first current threshold. Since all RSC branches are connected in parallel, limiting the current of all RSC branches ensures that the charging and discharging capacity of the multiple parallel RSC branches on the positive and negative DC buses at the RSCC input is balanced, thereby ensuring that the voltage of the positive and negative DC buses at the RSCC input remains balanced.

[0137] When RSCC is a three-level RSCC, the switching module includes a first switching module, a second switching module, a third switching module, and a fourth switching module. The first switching module, the second switching module, the third switching module, and the fourth switching module are connected in series and then connected between the positive input terminal and the negative input terminal of RSCC.

[0138] When the absolute value of the current in the LC resonant circuit of any one of the N RSC branches exceeds the first current threshold, all switching modules controlling the current flow through the LC resonant circuits of the N RSC branches are turned off, specifically including:

[0139] When the current of the LC resonant circuit in any one of the N RSC branches is positive and the current of the LC resonant circuit is greater than the first current threshold, the first switching module in the N RSC branches is turned off, and the second switching module is turned off after a first preset time.

[0140] When the absolute value of the current in the LC resonant circuit of any one of the N RSC branches exceeds the first current threshold, all switching modules controlling the current flow through the LC resonant circuits of the N RSC branches are turned off, specifically including:

[0141] When the current of the LC resonant circuit in any of the N RSC branches is negative and the absolute value of the current in the LC resonant circuit is greater than the first current threshold, the fourth switch module in the N RSC branches is turned off, and the third switch module is turned off after a second preset time.

[0142] The method provided in this embodiment further includes: when the absolute value of the current in the LC resonant circuit is greater than the second current threshold, controlling all switching modules in the N RSC branches to turn off, where the second current threshold is greater than the first current threshold.

[0143] It should be understood that the RSCC control method provided in this application can limit the current of all RSC branches in a timely manner when the current of the resonant circuit is overcurrent. This can ensure the voltage balance of the positive bus and the negative bus, and will not trigger the protection shutdown. Moreover, after the current is limited, the RSCC can usually return to normal in a very short time, so as not to affect the normal operation of the RSCC and there is no need to interrupt the shutdown.

[0144] 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 resonant switched capacitor converter (RSCC), characterized in that, include: The system includes an input capacitor, an output capacitor, a controller, and N resonant switched capacitor RSC branches; each RSC branch includes a switching module and an inductor-capacitor LC resonant circuit; N is an integer greater than or equal to 2. The two ends of the N resonant switched capacitor RSC branches are respectively connected to the two ends of the input capacitor; The output terminal of the resonant switched capacitor converter RSCC is connected to the output capacitor; The controller is configured to, when the absolute value of the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches is greater than a first current threshold, control all switching modules through which the current flows in the inductor-capacitor LC resonant circuit of the N resonant switched capacitor RSC branches to turn off for current limiting protection. Specifically, if the direction of the current in the LC resonant circuit when the absolute value of the current is greater than the first current threshold is determined to be a first direction, then the switching modules with the current direction in the first direction are first controlled to turn off, and then the switching modules with the opposite direction are controlled to turn off.

2. The RSCC according to claim 1, characterized in that, The RSCC level of the resonant switched capacitor converter is greater than or equal to two levels.

3. The RSCC according to claim 2, characterized in that, The resonant switched capacitor converter RSCC is a three-level resonant switched capacitor converter RSCC, and each of the resonant switched capacitor RSC branches includes: a first diode, a second diode, a first switching module, a second switching module, a third switching module, and a fourth switching module; The input capacitor includes a first input capacitor and a second input capacitor. The first end of the first input capacitor is connected to the positive input terminal of the resonant switched capacitor converter RSCC, and the second end of the first input capacitor is connected to the negative input terminal of the resonant switched capacitor converter RSCC through the second input capacitor. The first end of the first switch module is connected to the positive input terminal, the second end of the first switch module is connected to the first end of the second switch module, the second end of the second switch module is connected to the third end of the third switch module, and the third end of the third switch module is connected to the negative input terminal through the fourth switch module. The first terminal of the inductor-capacitor LC resonant circuit is connected to the second terminal of the second switching module. The second terminal of the inductor-capacitor LC resonant circuit is connected to the cathode of the first diode and the anode of the second diode. The anode of the first diode is connected to the positive output terminal of the resonant switched capacitor converter RSCC, and the cathode of the second diode is connected to the negative output terminal of the resonant switched capacitor converter RSCC.

4. The resonant switched capacitor converter RSCC according to claim 2, characterized in that, The resonant switched capacitor converter RSCC is a three-level resonant switched capacitor converter RSCC, and each of the resonant switched capacitor RSC branches includes: a fifth switch module, a sixth switch module, a first switch module, a second switch module, a third switch module, and a fourth switch module; The input capacitor includes a first input capacitor and a second input capacitor. The first end of the first input capacitor is connected to the positive input terminal of the resonant switched capacitor converter RSCC, and the second end of the first input capacitor is connected to the negative input terminal of the resonant switched capacitor converter RSCC through the second input capacitor. The first end of the first switch module is connected to the positive input terminal, the second end of the first switch module is connected to the first end of the second switch module, the second end of the second switch module is connected to the third end of the third switch module, and the third end of the third switch module is connected to the negative input terminal through the fourth switch module. The first terminal of the inductor-capacitor LC resonant circuit is connected to the second terminal of the second switching module. The second terminal of the inductor-capacitor LC resonant circuit is connected to the second terminal of the fifth switching module and the first terminal of the sixth switching module. The first terminal of the fifth switching module is connected to the positive output terminal of the resonant switched capacitor converter RSCC. The second terminal of the sixth switching module is connected to the negative output terminal of the resonant switched capacitor converter RSCC.

5. The resonant switched capacitor converter RSCC according to claim 3 or 4, characterized in that, Specifically, the controller is configured to, when the current of the LC resonant circuit in any one of the N resonant switched capacitor RSC branches is positive and the current of the LC resonant circuit is greater than the first current threshold, control the first switching module with positive current in the LC resonant circuit of the N resonant switched capacitor RSC branches to turn off, and control the second switching module to turn off after a first preset time; control the fourth switching module with negative current in the LC resonant circuit of the N resonant switched capacitor RSC branches to turn off, and control the third switching module to turn off after a second preset time.

6. The resonant switched capacitor converter RSCC according to claim 3 or 4, characterized in that, Specifically, the controller is configured to, when the current of the LC resonant circuit in any one of the N resonant switched capacitor RSC branches is negative and the absolute value of the current in the LC resonant circuit is greater than the first current threshold, control the fourth switch module whose current in the LC resonant circuit in the N resonant switched capacitor RSC branches is negative to turn off, and control the third switch module to turn off after a second preset time; control the first switch module whose current in the LC resonant circuit in the N resonant switched capacitor RSC branches is positive to turn off, and control the second switch module to turn off after a first preset time.

7. The resonant switched capacitor converter RSCC according to claim 3 or 4, characterized in that, The controller is further configured to control all the switching modules in the N resonant switching capacitor RSC branches to turn off when the absolute value of the current in the inductor-capacitor LC resonant circuit is greater than the second current threshold; the second current threshold is greater than the first current threshold.

8. A photovoltaic system, characterized in that, include: A first DC-DC circuit and a second DC-DC circuit; the second DC-DC circuit includes the resonant switched capacitor converter RSCC as described in any one of claims 1-7; The positive and negative input terminals of the first DC-DC circuit are used to connect to the positive and negative terminals of the photovoltaic string, respectively; the positive output terminal of the first DC-DC circuit is connected to the positive bus BUS+. The positive and negative input terminals of the resonant switched capacitor converter RSCC are connected to the negative and positive output terminals of the first DC-DC circuit, respectively; the positive output terminal of the resonant switched capacitor converter RSCC is connected to the N line, and the negative output terminal of the resonant switched capacitor converter RSCC is connected to the negative bus BUS-.

9. The photovoltaic system according to claim 8, characterized in that, Also includes: First DCAC circuit and second DCAC circuit. First DCAC circuit and second DCAC circuit. The positive input terminal of the first DCAC circuit is connected to the BUS+, and the negative input terminal of the first DCAC circuit is connected to the N line. The positive input terminal of the second DCAC circuit is connected to the N line, and the negative input terminal of the second DCAC circuit is connected to the BUS-.

10. A control method for a resonant switched capacitor converter (RSCC), characterized in that, The resonant switched capacitor converter (RSCC) includes: an input capacitor, an output capacitor, a controller, and N resonant switched capacitor RSC branches; each resonant switched capacitor RSC branch includes a switching module and an inductor-capacitor LC resonant circuit; N is an integer greater than or equal to 2. Obtain the current of the LC resonant circuit of each of the resonant switched capacitor RSC branches; When the absolute value of the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches is greater than a first current threshold, the switching modules through which the current flows in the LC resonant circuit of the N resonant switched capacitor RSC branches are all turned off for current limiting protection. Specifically, if the direction of the current in the LC resonant circuit when the absolute value of the current is greater than the first current threshold is determined to be a first direction, then the switching modules with the current direction in the first direction are turned off first, and then the switching modules with the opposite direction are turned off.

11. The control method according to claim 10, characterized in that, When the resonant switched capacitor converter RSCC is a three-level resonant switched capacitor converter RSCC, the switching module includes a first switching module, a second switching module, a third switching module and a fourth switching module. The first switching module, the second switching module, the third switching module and the fourth switching module are connected in series and then connected between the positive input terminal and the negative input terminal of the resonant switched capacitor converter RSCC. When the absolute value of the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches is greater than a first current threshold, all switching modules through which the current flows in the LC resonant circuit of the N resonant switched capacitor RSC branches are turned off, specifically including: When the current of the LC resonant circuit in any one of the N resonant switched capacitor RSC branches is positive and the current of the LC resonant circuit is greater than the first current threshold, the first switching module with the positive current of the LC resonant circuit in any of the N resonant switched capacitor RSC branches is turned off, and the second switching module is turned off after a first preset time; the fourth switching module with the negative current of the LC resonant circuit in any of the N resonant switched capacitor RSC branches is turned off, and the third switching module is turned off after a second preset time.

12. The control method according to claim 11, characterized in that, When the absolute value of the current in the LC resonant circuit of any one of the N resonant switched capacitor RSC branches is greater than a first current threshold, all switching modules through which the current flows in the LC resonant circuit of the N resonant switched capacitor RSC branches are turned off, specifically including: When the current of the LC resonant circuit in any one of the N resonant switched capacitor RSC branches is negative, and the absolute value of the current in the LC resonant circuit is greater than the first current threshold, the fourth switch module with the negative current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off, and the third switch module is turned off after a second preset time; the first switch module with the positive current in the LC resonant circuit of the N resonant switched capacitor RSC branches is turned off, and the second switch module is turned off after a first preset time.

13. The control method according to any one of claims 10-12, characterized in that, Also includes: When the absolute value of the current in the inductor-capacitor LC resonant circuit is greater than the second current threshold, all the switching modules in the N resonant switching capacitor RSC branches are turned off, and the second current threshold is greater than the first current threshold.

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