An auxiliary power supply, a control method, and a photovoltaic system

Abstract

This application discloses an auxiliary power supply, a control method, and a photovoltaic system. The auxiliary power supply includes: a first terminal of a first switching transistor connected to the positive terminal of a DC bus via the first primary winding of a transformer, and a second terminal of the first switching transistor connected to the midpoint of the DC bus; a second terminal of a second switching transistor connected to the second terminal of the first switching transistor via the second primary winding of a transformer, and a second terminal of the second switching transistor connected to the negative terminal of the DC bus; a current sensor whose primary winding is connected in series with either the first or second switching transistor, and whose secondary winding is connected to a full-wave rectifier circuit; a switching transistor without a series current sensor connected in series with a sampling resistor; and a controller controlling the first and second switching transistors based on the first sampling voltage output from the full-wave rectifier circuit and the second sampling voltage of the sampling resistor. The controller detects the positive and negative currents of the two switching transistors, sums the two sampled currents, and the summed value is not too large to cause protection to fail to activate.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, specifically to an auxiliary power supply, a control method, and a photovoltaic system. Background Technology

[0002] With the continuous development of new energy sources, photovoltaic power generation is now being applied. The photovoltaic array in the photovoltaic system outputs direct current, but the voltage is relatively high and cannot be directly used to power the auxiliary power supply in the photovoltaic system. This is because the auxiliary power supply is used to power the control circuit in the photovoltaic system, and the control circuit generally uses a lower voltage power supply.

[0003] As the DC-side voltage of photovoltaic (PV) systems increases, ordinary single-transistor diodes are no longer sufficient to meet the voltage withstand requirements of auxiliary power supplies; for example, some PV systems can have DC voltages as high as 1500V. The auxiliary power supply can be supplied by connecting two flyback circuits in series, thus solving the voltage withstand problem of a single diode. (See also...) Figure 1 The figure shows a schematic diagram of the auxiliary power supply for a photovoltaic system. After the high-voltage DC bus voltage is divided equally, the half-bus voltage is reduced. The half-bus voltage can be met by using conventional low-voltage MOSFETs. Specifically, the drive signals of MOSFET1 and MOSFET2 can be controlled to be synchronized, that is, MOSFET1 and MOSFET2 operate synchronously to realize power transfer to the Vo side.

[0004] In practical applications, it is necessary to sample the current flowing through the MOSFET and promptly disconnect the MOSFET when the current becomes too high, thereby protecting its safety. However, existing technologies often encounter problems during current detection due to half-bus voltage deviations. Summary of the Invention

[0005] In view of this, this application provides an auxiliary power supply, a control method, and a photovoltaic system that can effectively detect the current flowing through the switching transistor and avoid the problem of failure to start normally due to excessive half-bus deviation.

[0006] This application provides an auxiliary power supply, including: a transformer, a first switching transistor, a second switching transistor, a full-wave rectifier circuit, a controller, and at least one current sensor;

[0007] The first end of the first switching transistor is connected to the positive end of the DC bus through the first primary winding of the transformer, and the second end of the first switching transistor is connected to the midpoint of the DC bus.

[0008] The first end of the second switching transistor is connected to the second end of the first switching transistor through the second primary winding of the transformer, and the second end of the second switching transistor is connected to the negative end of the DC bus.

[0009] The primary side of the current sensor is connected in series with the first switching transistor or the second switching transistor, and the secondary side of the current sensor is connected to the full-wave rectifier circuit; the switching transistor of the current sensor not connected in series is connected in series with the sampling resistor.

[0010] The output of the full-wave rectifier circuit is connected to the controller;

[0011] The controller is used to control the first and second switching transistors based on the first sampling voltage output from the full-wave rectifier circuit and the second sampling voltage of the sampling resistor.

[0012] Preferably, the full-wave rectifier circuit includes: a first diode, a second diode, and an output resistor;

[0013] The anode of the first diode is connected to the same-name terminal of the first secondary side of the current sensor, and the cathode of the first diode is connected to the opposite-name terminal of the first secondary side of the current sensor through the output resistor.

[0014] The anode of the second diode is connected to the opposite terminal of the second secondary side of the current sensor, the cathode of the second diode is connected to the opposite terminal of the first secondary side, and the same terminal of the second secondary side of the current sensor is connected to the cathode of the first diode.

[0015] Preferably, the first switching transistor is connected in series with the current sensor, and the second switching transistor is connected in series with the sampling resistor; the midpoint of the DC bus is grounded with the controller.

[0016] Preferably, the second switch is connected in series with the current sensor, and the first switch is connected in series with the sampling resistor; the negative terminal of the DC bus is grounded with the controller.

[0017] Preferably, the controller controls both the first and second switching transistors to turn off when the sum of the first and second sampled voltages is greater than a preset voltage threshold.

[0018] This application provides an auxiliary power supply, including: a transformer, a first switching transistor, a second switching transistor, a controller, a first current sensor, a first full-wave rectifier circuit, a second current sensor, and a second full-wave rectifier circuit;

[0019] The first end of the first switching transistor is connected to the positive end of the DC bus through the first primary winding of the transformer, and the second end of the first switching transistor is connected to the midpoint of the DC bus.

[0020] The first end of the second switching transistor is connected to the second end of the first switching transistor through the second primary winding of the transformer, and the second end of the second switching transistor is connected to the negative end of the DC bus.

[0021] The primary side of the first current sensor is connected in series with the first switching transistor, and the secondary side of the first current sensor is connected to the first full-wave rectifier circuit.

[0022] The primary side of the second current sensor is connected in series with the second switching transistor, and the secondary side of the second current sensor is connected to the second full-wave rectifier circuit; the output terminals of the first full-wave rectifier circuit and the second full-wave rectifier circuit are both connected to the controller.

[0023] The controller is used to control the first switching transistor and the second switching transistor based on the first sampling voltage output by the first full-wave rectifier circuit and the second sampling voltage output by the second full-wave rectifier circuit.

[0024] Preferably, the first full-wave rectifier circuit includes: a first diode, a second diode, and a first output resistor;

[0025] The anode of the first diode is connected to the same-name terminal of the first secondary side of the first current sensor, and the cathode of the first diode is connected to the opposite-name terminal of the first secondary side through the first output resistor.

[0026] The anode of the second diode is connected to the opposite terminal of the second secondary side of the first current sensor, the cathode of the second diode is connected to the opposite terminal of the first secondary side of the first current sensor, and the same terminal of the second secondary side of the first current sensor is connected to the cathode of the first diode.

[0027] The second full-wave rectifier circuit includes: a third diode, a fourth diode, and a second output resistor;

[0028] The anode of the third diode is connected to the same-name terminal of the first secondary side of the second current sensor, and the cathode of the third diode is connected to the opposite-name terminal of the first secondary side of the second current sensor through the second output resistor.

[0029] The anode of the fourth diode is connected to the opposite terminal of the second secondary side of the second current sensor, the cathode of the fourth diode is connected to the opposite terminal of the first secondary side of the second current sensor, and the same terminal of the second secondary side of the second current sensor is connected to the cathode of the third diode.

[0030] Preferably, the controller controls the first and second switching transistors to turn off when the sum of the first and second sampled voltages is greater than a preset voltage threshold.

[0031] This application also provides a control method for an auxiliary power supply, the auxiliary power supply including: a transformer, a first switching transistor, a second switching transistor, a full-wave rectifier circuit, a controller, and at least one current sensor; the first terminal of the first switching transistor is connected to the positive terminal of a DC bus through the first primary winding of the transformer, and the second terminal of the first switching transistor is connected to the midpoint of the DC bus; the first terminal of the second switching transistor is connected to the second terminal of the first switching transistor through the second primary winding of the transformer, and the second terminal of the second switching transistor is connected to the negative terminal of the DC bus; the primary side of the current sensor is connected in series with the first switching transistor or in series with the second switching transistor, and the secondary side of the current sensor is connected to the full-wave rectifier circuit; the switching transistor without a current sensor in series is connected in series with a sampling resistor;

[0032] The method includes:

[0033] Obtain the first sampled voltage of the full-wave rectifier circuit output and the second sampled voltage of the sampling resistor;

[0034] When the sum of the first sampling voltage and the second sampling voltage is greater than a preset voltage threshold, the first and second switching transistors are turned off.

[0035] This application also provides a control method for an auxiliary power supply, the auxiliary power supply including: a transformer, a first switching transistor, a second switching transistor, a first current sensor, a first full-wave rectifier circuit, a second current sensor, and a second full-wave rectifier circuit; the first terminal of the first switching transistor is connected to the positive terminal of a DC bus through the first primary winding of the transformer, and the second terminal of the first switching transistor is connected to the midpoint of the DC bus; the first terminal of the second switching transistor is connected to the second terminal of the first switching transistor through the second primary winding of the transformer, and the second terminal of the second switching transistor is connected to the negative terminal of the DC bus; the primary side of the first current sensor is connected in series with the first switching transistor, and the secondary side of the first current sensor is connected to the first full-wave rectifier circuit; the primary side of the second current sensor is connected in series with the second switching transistor, and the secondary side of the second current sensor is connected to the second full-wave rectifier circuit.

[0036] The method includes:

[0037] Obtain the first sampled voltage output by the first full-wave rectifier circuit and the second sampled voltage output by the second full-wave rectifier circuit;

[0038] When the sum of the first sampling voltage and the second sampling voltage is greater than a preset voltage threshold, the first and second switching transistors are turned off.

[0039] This application also provides a photovoltaic system, including any of the above auxiliary power sources; and further includes: an inverter;

[0040] The positive input terminal of the inverter is connected to the positive terminal of the DC bus, and the negative input terminal of the inverter is connected to the negative terminal of the DC bus.

[0041] The power supply for the positive and negative terminals of the DC bus comes from the photovoltaic array.

[0042] Preferably, it further includes: a DC-DC converter;

[0043] The DC-DC converter is connected between the photovoltaic array and the DC bus.

[0044] Therefore, this application has the following beneficial effects:

[0045] The auxiliary power supply includes at least one current sensor; it may include one or two current sensors. The secondary side of the current sensor is connected to a full-wave rectifier circuit; the output of the full-wave rectifier circuit is connected to a controller; the full-wave rectified current can output the positive and negative currents sampled by the current sensor.

[0046] Because the full-wave rectifier circuit provided in this application can simultaneously detect the positive and negative currents of the first and second switching transistors, the positive and negative circulating currents in the circuit cancel each other out. The controller sums the two sampled currents, and the sum of the positive and negative currents will not be too large, effectively sampling the excitation current of the transformer at this moment. Since the sum of the two sampled currents will not be too large, the controller can start normally and slowly, avoiding a large duty cycle in the controller's output drive signal, and preventing abnormally large currents from triggering protection, which could lead to failure to start, such as the controller failing to start. Furthermore, when the auxiliary power supply detects that the sum of the two currents exceeds a preset current threshold, it indicates an overcurrent and will promptly control the two switching transistors to disconnect, protecting the safety of the switching transistors. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the power source for an auxiliary power supply of a photovoltaic system.

[0048] Figure 2 A schematic diagram of a sampling circuit for an auxiliary power supply;

[0049] Figure 3 A schematic diagram of an auxiliary power supply provided for an embodiment of this application;

[0050] Figure 4 A schematic diagram of another auxiliary power supply provided in an embodiment of this application;

[0051] Figure 5 A schematic diagram of yet another auxiliary power supply provided in an embodiment of this application;

[0052] Figure 6 A flowchart illustrating an auxiliary power supply control method provided in an embodiment of this application;

[0053] Figure 7 A flowchart illustrating another auxiliary power supply control method provided in this application embodiment;

[0054] Figure 8 This is a schematic diagram of a photovoltaic system provided in an embodiment of this application. Detailed Implementation

[0055] To enable those skilled in the art to better understand the technical solutions provided in this application, specific application scenarios will be introduced below.

[0056] The auxiliary power supply provided in this application embodiment mainly draws power from a relatively high DC voltage, and after step-down conversion, it supplies power to the control circuit, such as the controller in the control circuit, and can provide voltages such as 12V, 5V, and 3.3V.

[0057] This application does not specifically limit the application scenario of the auxiliary power supply. It is applicable to scenarios where multiple windings are connected in series for power supply, such as power supply from a two-transistor flyback circuit or a two-transistor forward circuit.

[0058] To facilitate understanding of the technical solutions provided in this application, the following embodiments use a photovoltaic system as an example. For details, please refer to... Figure 1 The topology shown is where Ubus is the DC bus voltage. Two DC bus capacitors are connected in series at the positive and negative terminals of the DC bus. The two DC bus capacitors are equal, so the DC bus voltage is evenly distributed, meaning that the voltage on each DC bus capacitor is half of the DC bus voltage, i.e., 1 / 2Ubus.

[0059] This application does not specifically limit the value of the DC bus voltage; for example, it can be 1500V or other values. The auxiliary power supply draws power from the DC bus, stepps down, and then supplies power to the control circuit of the photovoltaic system. It typically uses an isolated switching power supply, such as a forward or flyback circuit. However, the DC bus voltage is relatively high, and the voltage withstand capability of most switching transistors is limited. Therefore, to ensure that the voltage withstand range of the switching transistors is not exceeded, multiple windings are connected in series, with each winding corresponding to a single switching transistor. This is equivalent to multiple switching transistors connected in series, thereby reducing the voltage withstand capability of each individual transistor and protecting its safety. All of these switching transistors are controllable, meaning that the controller sends a drive signal to the gate of the switching transistor to control its switching state.

[0060] The controllable switching transistor can be any of the following: a relay, an insulated gate bipolar transistor (IGBT), a metal-oxide-semiconductor field-effect transistor (MOSFET, hereinafter referred to as MOS transistor), or a SiC MOSFET (Silicon Carbide Metal Oxide Semiconductor Field-Effect Transistor), etc. This embodiment uses a MOS transistor as an example, but this application does not specifically limit the application to this type.

[0061] In this embodiment, two switching transistors are connected in series, and each switching transistor is connected in series with one primary winding. It should be understood that the transformer may include more primary windings, corresponding to more switching transistors connected in series.

[0062] Figure 2 This is a schematic diagram of a method for sampling the current of a MOSFET using half-wave rectification.

[0063] for Figure 2 The half-wave rectifier shown has upper bus current i1 and lower bus current i2 rectified by CT1 and CT2 respectively. The sum of the two current sampling signals is then input to the controller. Figure 2 The circuit shown can only sample the forward currents of i1 and i2. When the voltages of the two half-buses are uneven, a large inrush current will be detected in the loop. By controlling the duty cycle of the drive signal of the MOSFET, the problems of transformer saturation and MOSFET overcurrent can be avoided.

[0064] This control method only samples unidirectional current, so current needs to be sampled on both the upper and lower buses. Assuming the voltage of the upper bus is relatively large, when the drive generates a wave, i2 is a large negative current and i1 is a large positive current. Due to the presence of the half-wave rectifier diode, the sampling voltage corresponding to the negative current is 0. The sum of i1 and i2 is a large value, which will trigger the protection shutdown, causing the auxiliary power supply to fail to start normally, or even causing the controller to fail.

[0065] based on Figure 2 To address the aforementioned technical problems, the auxiliary power supply provided in this application embodiment employs full-wave rectification, enabling the acquisition of both positive and negative currents. Furthermore, the negative current is directly acquired as a specific value, rather than zero. The controller can control the two switching transistors based on the sum of the positive and negative currents, thus preventing the protection shutdown and inability to start due to excessively high sampled voltage.

[0066] The auxiliary power supply provided in this application embodiment may include two current sensors or one current sensor. When one current sensor is included, one switching transistor may use the current sensor to collect the current, and the other switching transistor may use a resistor to collect the current. When the auxiliary power supply includes two current sensors, each of the two switching transistors uses one current sensor to collect the current.

[0067] The following section will describe the two current sensors with reference to the attached diagram.

[0068] See Figure 3 This figure is a schematic diagram of an auxiliary power supply provided in an embodiment of this application.

[0069] The auxiliary power supply provided in this embodiment includes: a transformer T, a first switching transistor MOS1, a second switching transistor MOS2, a controller 100, a first current sensor CT1, a first full-wave rectifier circuit, a second current sensor CT2, and a second full-wave rectifier circuit;

[0070] The first terminal of the first switching transistor MOS1 is connected to the positive terminal BUS+ of the DC bus through the first primary winding of the transformer T. The second terminal of the first switching transistor MOS1 is connected to the midpoint of the DC bus, i.e. the N line. Under normal circumstances, two DC bus capacitors are connected in series between the positive terminal BUS+ and the negative terminal BUS- of the DC bus to share the DC bus voltage Ubus equally, i.e., each is half of the DC bus voltage Ubus, 1 / 2Ubus.

[0071] The first terminal of the second switching transistor MOS2 is connected to the second terminal of the first switching transistor MOS1 through the second primary winding of the transformer T, and the second terminal of the second switching transistor MOS2 is connected to the negative terminal BUS- of the DC bus.

[0072] The primary side of the first current sensor CT1 is connected in series with the first switching transistor MOS1, and the secondary side of the first current sensor CT1 is connected to the first full-wave rectifier circuit; the first current sensor CT1 is used to collect the first current i1 flowing through the MOS1 transistor.

[0073] The primary side of the second current sensor CT2 is connected in series with the second switching transistor MOS2, and the secondary side of the second current sensor CT2 is connected to the second full-wave rectifier circuit. The output terminals of the first full-wave rectifier circuit and the second full-wave rectifier circuit are both connected to the controller 100. The second current sensor CT2 is used to collect the first current i2 flowing through the MOS2 transistor.

[0074] The controller 100 is used to control the first switch MOS1 and the second switch MOS2 based on the first sampling voltage Vs1 output by the first full-wave rectifier circuit and the second sampling voltage Vs2 output by the second full-wave rectifier circuit.

[0075] One possible implementation is that the first full-wave rectifier circuit includes: a first diode D1, a second diode D2, and a first output resistor; it should be understood that other forms of full-wave rectifier circuits can also be used. Figure 3 The full-wave rectifier circuit shown is relatively simple, with few components, and full-wave rectification can be achieved using only two diodes.

[0076] The anode of the first diode D1 is connected to the same-name terminal of the first secondary side of the first current sensor CT1, and the cathode of the first diode D1 is connected to the opposite-name terminal of the first secondary side through the first output resistor; the voltage across the first output resistor is the first sampling voltage Vs1.

[0077] The anode of the second diode D2 is connected to the opposite terminal of the second secondary side of the first current sensor CT1, the cathode of the second diode D2 is connected to the opposite terminal of the first secondary side of the first current sensor CT1, and the same terminal of the second secondary side of the first current sensor CT1 is connected to the cathode of the first diode D1.

[0078] The second full-wave rectifier circuit includes: a third diode D3, a fourth diode D4, and a second output resistor;

[0079] The anode of the third diode D3 is connected to the same-name terminal of the first secondary side of the second current sensor CT2, and the cathode of the third diode D3 is connected to the opposite-name terminal of the first secondary side of the second current sensor CT2 through the second output resistor; the voltage on the second output voltage is the second sampling voltage Vs2.

[0080] The anode of the fourth diode D4 is connected to the opposite terminal of the second secondary side of the second current sensor CT2, the cathode of the fourth diode D4 is connected to the opposite terminal of the first secondary side of the second current sensor CT2, and the same terminal of the second secondary side of the second current sensor CT2 is connected to the cathode of the third diode D3.

[0081] Specifically, when the sum of the first sampling voltage and the second sampling voltage exceeds a preset voltage threshold, the controller 100 controls the first switch MOS1 and the second switch MOS2 to turn off. That is, the first drive signal GS1 output by the controller 100 is used to control the operation of the first switch MOS1, and the first drive signal GS2 output by the controller 100 is used to control the operation of the second switch MOS2. Specifically, the drive signals are output to the gates of the switches.

[0082] One possible implementation is to directly input the sum of the first sampling voltage Vs1 and the second sampling voltage Vs2 into the controller 100. For example, the first output resistor and the second output voltage can be directly connected in series to obtain the sum of the first sampling voltage Vs1 and the second sampling voltage Vs2. The sum of the two sampling voltages is then input into the controller 100, thus eliminating the need for the controller 100 to obtain the sum of the two voltages, thereby reducing the burden on the controller 100.

[0083] When a photovoltaic system is first started up or when the voltage of the upper and lower busbars deviates, it is easy for a negative current to flow through the MOSFET. Under normal circumstances, the MOSFET carries a positive current, and no current flows through the midpoint of the DC bus, i.e., no current flows through the N line.

[0084] CT1 and CT2 sample the upper bus current i1 and the lower bus current i2 through full-wave rectification. i1 can be either positive or negative; similarly, i2 can also be either positive or negative. The sum of the currents Vs1 and Vs2 is sent to the sampling pin of controller 100. Controller 100 outputs a drive signal to control MOS1 and MOS2 to operate synchronously. When controller 100 turns on the two MOS transistors, the current in the primary winding of transformer T rises, storing energy. When controller 100 detects that the current signal has reached the turn-on voltage threshold, it turns off the two MOS transistors, and diode D5 connected to the secondary winding of transformer T turns on, transferring energy to the secondary winding.

[0085] When bias occurs on the upper and lower busbars, for example, when the voltage on the upper busbar increases, the current i1 on the upper busbar becomes a positive current, and the current i2 on the lower busbar becomes a negative current. The amplitudes of the two currents are basically the same (difference is the excitation current of the transformer). At this time, due to the full-wave rectifier circuit provided in this application embodiment, the positive and negative currents i1 and i2 can be detected simultaneously. The positive and negative circulating currents in the loop cancel each other out. When i1 and i2 are summed, the sum of the positive and negative currents will not be too large, which is equivalent to sampling the excitation current of the transformer at this moment. Since the sum of i1 and i2 will not be too large, the controller 100 can start normally and slowly, avoiding a large duty cycle in the drive signal output by the controller 100, and preventing abnormally large currents from triggering protection, which would prevent the controller 100 from starting.

[0086] Similarly, when the voltage of the lower bus is relatively large, the current i2 of the lower bus is a positive current, and the current i1 of the upper bus is a negative current. The amplitudes of the two currents are basically the same (the difference is the excitation current of the transformer). Since the positive and negative currents of i1 and i2 can be detected simultaneously, the positive and negative circulating currents in the circuit cancel each other out, and the excitation current of the transformer at this moment is effectively sampled. Since the sum of i1 and i2 is not too large, the controller 100 can start normally and slowly, avoiding a large duty cycle in the drive signal output by the controller 100, and preventing abnormally large currents from triggering protection, which would prevent the controller 100 from starting.

[0087] The above describes the case where the auxiliary power supply includes two current sensors. The following describes the case where the auxiliary power supply includes one current sensor. Compared with the embodiment with two current sensors, one current sensor can be saved, reducing costs.

[0088] See Figure 4 This figure is a schematic diagram of another auxiliary power supply provided in an embodiment of this application.

[0089] The second switch MOS2 is connected in series with the current sensor, and the first switch MOS1 is connected in series with the sampling resistor Rs. The negative terminal BUS- of the DC bus is grounded with the controller 100, that is, the lower half of the bus is grounded with the control chip. Only one current sensor is needed, which saves costs. Furthermore, since the common ground is on the low voltage side, the controller 100 does not need too much signal isolation, thereby reducing the sampling difficulty.

[0090] The auxiliary power supply provided in this embodiment includes: a transformer T, a first switching transistor MOS1, a second switching transistor MOS2, a full-wave rectifier circuit, a controller 100, and a current sensor CT;

[0091] The first terminal of the first switching transistor MOS1 is connected to the positive terminal of the DC bus through the first primary winding of the transformer, and the second terminal of the first switching transistor MOS1 is connected to the midpoint of the DC bus, i.e. the N line.

[0092] The first terminal of the second switching transistor MOS2 is connected to the second terminal of the first switching transistor MOS1 through the second primary winding of the transformer, and the second terminal of the second switching transistor MOS2 is connected to the negative terminal BUS- of the DC bus.

[0093] The primary side of the current sensor CT is connected in series with the second switch MOS2, and the secondary side of the current sensor CT is connected to the full-wave rectifier circuit; the first switch MOS1 is connected in series with the sampling resistor Rs.

[0094] The output of the full-wave rectifier circuit is connected to controller 100;

[0095] The controller 100 is used to control the first switch MOS1 and the second switch MOS2 based on the first sampling voltage Vs1 output by the full-wave rectifier circuit and the second sampling voltage Vs2 of the sampling resistor.

[0096] The full-wave rectifier circuit includes: a first diode D1, a second diode D2, and an output resistor;

[0097] The anode of the first diode D1 is connected to the same-name terminal of the first secondary side of the current sensor CT, and the cathode of the first diode D1 is connected to the opposite-name terminal of the first secondary side of the current sensor CT through the output resistor.

[0098] The anode of the second diode D2 is connected to the opposite terminal of the second secondary side of the current sensor CT, the cathode of the second diode D2 is connected to the opposite terminal of the first secondary side, and the same terminal of the second secondary side of the current sensor CT is connected to the cathode of the first diode D1.

[0099] for Figure 3 and Figure 4 visible, Figure 4 One current sensor is missing and replaced with a resistance sensor; the rest of the connections remain unchanged and will not be described further here.

[0100] for Figure 4 In terms of, with Figure 3 The working principle is the same. CT can collect the positive and negative current of i2, and Rs can collect the positive and negative current of i1. That is, Vs1 is the voltage formed by the current i1 flowing through Rs.

[0101] and Figure 3 The auxiliary power supply shown is the same. Figure 4 The auxiliary power supply shown can simultaneously detect the positive and negative currents of i1 and i2. The positive and negative circulating currents in the circuit cancel each other out, effectively sampling the excitation current of the transformer at this moment. Since the sum of i1 and i2 is not too large, the controller 100 can start normally and slowly, avoiding a large duty cycle in the drive signal output by the controller 100, and preventing abnormally large current from triggering the protection, which would cause the controller 100 to fail to start.

[0102] Figure 4 This applies to the lower half of the busbar and the controller being powered. The following describes the case where the upper half of the busbar and the controller share a common ground.

[0103] See Figure 5 This figure is a schematic diagram of another auxiliary power supply provided in an embodiment of this application.

[0104] Figure 5 The auxiliary power supply shown has a first switching transistor MOS1 connected in series with the current sensor CT, and a second switching transistor MOS2 connected in series with the sampling resistor Rs; the midpoint of the DC bus, i.e., the N line, is grounded with the controller 100.

[0105] for Figure 5 In terms of, with Figure 3 The working principle is the same. The CT can collect the positive and negative currents of i1, and Rs can collect the positive and negative currents of i2. That is, Vs2 is the voltage formed by the current i2 flowing through Rs. Only one current sensor is needed, which saves costs. Furthermore, since the common ground is on the low voltage side, the controller 100 does not need too much signal isolation, thereby reducing the sampling difficulty.

[0106] and Figure 3 The auxiliary power supply shown is the same. Figure 5 The auxiliary power supply shown can simultaneously detect the positive and negative currents of i1 and i2. The positive and negative circulating currents in the circuit cancel each other out, effectively sampling the excitation current of the transformer at this moment. Since the sum of i1 and i2 is not too large, the controller 100 can start normally and slowly, avoiding a large duty cycle in the drive signal output by the controller 100, and preventing abnormally large current from triggering the protection, which would cause the controller 100 to fail to start.

[0107] Method Implementation Examples

[0108] Based on the auxiliary power supply provided in the above embodiments, this application also provides a control method for the auxiliary power supply, which will be described in detail below with reference to the accompanying drawings.

[0109] See Figure 6 The figure is a flowchart of an auxiliary power supply control method provided in an embodiment of this application.

[0110] First, the control method for the auxiliary power supply applied to a single current sensor is introduced. The auxiliary power supply includes: a transformer, a first switching transistor, a second switching transistor, a full-wave rectifier circuit, a controller, and at least one current sensor. The first terminal of the first switching transistor is connected to the positive terminal of the DC bus through the first primary winding of the transformer, and the second terminal of the first switching transistor is connected to the midpoint of the DC bus. The first terminal of the second switching transistor is connected to the second terminal of the first switching transistor through the second primary winding of the transformer, and the second terminal of the second switching transistor is connected to the negative terminal of the DC bus. The primary winding of the current sensor is connected in series with the first switching transistor or the second switching transistor, and the secondary winding of the current sensor is connected to the full-wave rectifier circuit. Switches of current sensors not connected in series are connected in series with a sampling resistor.

[0111] The method includes:

[0112] S601: Obtain the first sampling voltage output by the full-wave rectifier circuit and the second sampling voltage of the sampling resistor;

[0113] S602: When the sum of the first sampling voltage and the second sampling voltage is greater than a preset voltage threshold, control the first switch and the second switch to turn off.

[0114] Because the positive and negative currents of the first and second switching transistors can be detected simultaneously, the positive and negative circulating currents in the circuit cancel each other out, effectively sampling the transformer's excitation current at that moment. Since the sum of the currents of the first and second switching transistors is not too large, a normal, slow start-up is possible, avoiding a large duty cycle in the controller's output drive signal and preventing abnormally large currents from triggering protection, which could lead to startup failure, such as the controller failing to start. Furthermore, the use of only one sensor saves costs.

[0115] The following describes a method for controlling the auxiliary current applied to two current sensors.

[0116] See Figure 7 The figure is a flowchart of an auxiliary power supply control method provided in an embodiment of this application.

[0117] The auxiliary power supply control method provided in this embodiment includes: a transformer, a first switching transistor, a second switching transistor, a first current sensor, a first full-wave rectifier circuit, a second current sensor, and a second full-wave rectifier circuit; the first terminal of the first switching transistor is connected to the positive terminal of the DC bus through the first primary winding of the transformer, and the second terminal of the first switching transistor is connected to the midpoint of the DC bus; the first terminal of the second switching transistor is connected to the second terminal of the first switching transistor through the second primary winding of the transformer, and the second terminal of the second switching transistor is connected to the negative terminal of the DC bus; the primary side of the first current sensor is connected in series with the first switching transistor, and the secondary side of the first current sensor is connected to the first full-wave rectifier circuit; the primary side of the second current sensor is connected in series with the second switching transistor, and the secondary side of the second current sensor is connected to the second full-wave rectifier circuit.

[0118] The method includes:

[0119] S701: Obtain the first sampled voltage output by the first full-wave rectifier circuit and the second sampled voltage output by the second full-wave rectifier circuit;

[0120] S702: When the sum of the first sampling voltage and the second sampling voltage is greater than a preset voltage threshold, control the first switch and the second switch to turn off.

[0121] Since the positive and negative currents of the first and second switching transistors can be detected simultaneously, the positive and negative circulating currents in the circuit cancel each other out, effectively sampling the excitation current of the transformer at this moment. Since the sum of the currents of the first and second switching transistors is not too large, it can start normally and slowly, avoiding a large duty cycle in the drive signal output by the controller, and preventing abnormally large currents from triggering protection, which would prevent the controller from starting up.

[0122] System Implementation Examples

[0123] Based on the auxiliary power supply and its control method provided in the above embodiments, this application also provides a photovoltaic system. The application of the auxiliary power supply in the photovoltaic system is described below with reference to the accompanying drawings.

[0124] See Figure 8 The figure is a schematic diagram of a photovoltaic system provided in an embodiment of this application.

[0125] The photovoltaic system provided in this embodiment includes: an auxiliary power supply 300; and also includes: an inverter 200;

[0126] The positive input terminal of inverter 200 is connected to the positive terminal BUS+ of the DC bus, and the negative input terminal of inverter is connected to the negative terminal BUS- of the DC bus.

[0127] In addition, the photovoltaic system also includes: a photovoltaic array. A DC bus connects to the photovoltaic array.

[0128] The photovoltaic array is used to provide power to the positive terminal BUS+ and the negative terminal BUS- of the DC bus.

[0129] In addition, the photovoltaic system provided in this application embodiment may also include: a DC-DC converter (not shown in the figure); for example, the DC-DC converter may include a Boost circuit for boosting the output voltage of the photovoltaic array and providing it to the DC bus.

[0130] The DC-DC converter is connected between the photovoltaic array and the DC bus.

[0131] Since the photovoltaic system provided in this application includes the auxiliary power supply described in the above embodiments, the auxiliary power supply requires monitoring the current flowing through the switching transistor of the switching power supply. When the current is too large, the switching transistor needs to be disconnected in time to protect it. Furthermore, the technical solution provided in this application can detect both positive and negative currents. The sum of the currents of the upper and lower switching transistors will not result in an excessively large sum, which could trigger a protective shutdown and prevent the controller from starting. When the auxiliary power supply fails to function properly, the control circuit of the entire photovoltaic system will malfunction, causing the entire photovoltaic system to shut down.

[0132] 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. An auxiliary power supply, characterized by, Comprising: a transformer, a first switch tube, a second switch tube, a full-wave rectifier circuit, a controller and at least one current sensor; a first end of the first switch tube is connected to a positive end of a DC bus through a first primary winding of the transformer, and a second end of the first switch tube is connected to a midpoint of the DC bus; a first end of the second switch tube is connected to the second end of the first switch tube through a second primary winding of the transformer, and a second end of the second switch tube is connected to a negative end of the DC bus; a primary side of the current sensor is connected in series with the first switch tube or the second switch tube, and a secondary side of the current sensor is connected to the full-wave rectifier circuit; a switch tube not connected in series with the current sensor is connected in series with a sampling resistor; an output end of the full-wave rectifier circuit is connected to the controller; the full-wave rectifier circuit is used for detecting forward current and reverse current of the corresponding switch tube; and the sampling resistor is used for detecting the forward current and the reverse current of the corresponding switch tube; the controller is used for summing a first sampling voltage output by the full-wave rectifier circuit and a second sampling voltage of the sampling resistor, so that positive and negative circulating currents in a loop after the forward current and the reverse current are added are offset to each other; and the first switch tube and the second switch tube are controlled according to a result of the summation.

2. The auxiliary power supply of claim 1, wherein the full-wave rectifier circuit comprises a first diode, a second diode and an output resistor; an anode of the first diode is connected to a same-named end of a first secondary side of the current sensor, and a cathode of the first diode is connected to a different-named end of the first secondary side of the current sensor through the output resistor; an anode of the second diode is connected to a different-named end of a second secondary side of the current sensor, a cathode of the second diode is connected to the different-named end of the first secondary side, and a same-named end of the second secondary side of the current sensor is connected to the cathode of the first diode.

3. The auxiliary power supply of claim 1 or 2, wherein the first switch tube is connected in series with the current sensor, and the second switch tube is connected in series with the sampling resistor; and the midpoint of the DC bus is connected to the controller in common.

4. The auxiliary power supply of claim 1 or 2, wherein the second switch tube is connected in series with the current sensor, and the first switch tube is connected in series with the sampling resistor; and the negative end of the DC bus is connected to the controller in common.

5. The auxiliary power supply of any of claims 1-4, wherein, the controller, specifically when the result of the summation of the first sampling voltage and the second sampling voltage is greater than a preset voltage threshold, controls the first switch tube and the second switch tube to be both turned off.

6. An auxiliary power supply characterized by comprising: Comprising: a transformer, a first switch tube, a second switch tube, a controller, a first current sensor, a first full-wave rectifier circuit, a second current sensor and a second full-wave rectifier circuit; a first end of the first switch tube is connected to a positive end of a DC bus through a first primary winding of the transformer, and a second end of the first switch tube is connected to a midpoint of the DC bus; a first end of the second switch tube is connected to the second end of the first switch tube through a second primary winding of the transformer, and a second end of the second switch tube is connected to a negative end of the DC bus; The primary side of the first current sensor is connected in series with the first switch tube, and the secondary side of the first current sensor is connected to the first full-wave rectifier circuit; the first full-wave rectifier circuit is used to detect the forward current and the reverse current of the first switch tube; The primary side of the second current sensor is connected in series with the second switch tube, and the secondary side of the second current sensor is connected to the second full-wave rectifier circuit; the second full-wave rectifier circuit is used to detect the forward current and the reverse current of the second switch tube; the output end of the first full-wave rectifier circuit and the output end of the second full-wave rectifier circuit are both connected to the controller; The controller is used to sum the first sampling voltage output by the first full-wave rectifier circuit and the second sampling voltage output by the second full-wave rectifier circuit, so that the positive and negative circulating currents in the loop after the sum of the forward current and the reverse current cancel each other out; according to the sum result, the first switch tube and the second switch tube are controlled.

7. The auxiliary power supply of claim 6, wherein, The first full-wave rectifier circuit comprises a first diode, a second diode and a first output resistor; The anode of the first diode is connected to the same end of the first secondary side of the first current sensor, and the cathode of the first diode is connected to the different end of the first secondary side through the first output resistor; The anode of the second diode is connected to the different end of the second secondary side of the first current sensor, the cathode of the second diode is connected to the different end of the first secondary side, and the same end of the second secondary side of the first current sensor is connected to the cathode of the first diode; The second full-wave rectifier circuit comprises a third diode, a fourth diode and a second output resistor; The anode of the third diode is connected to the same end of the first secondary side of the second current sensor, and the cathode of the third diode is connected to the different end of the first secondary side through the second output resistor; The anode of the fourth diode is connected to the different end of the second secondary side of the second current sensor, the cathode of the fourth diode is connected to the different end of the first secondary side, and the same end of the second secondary side of the second current sensor is connected to the cathode of the third diode.

8. The auxiliary power supply of claim 6 or 7, wherein, The controller specifically controls the first switch tube and the second switch tube to be turned off when the sum result of the first sampling voltage and the second sampling voltage is greater than a preset voltage threshold.

9. A control method of an auxiliary power supply, characterized by, The auxiliary power supply comprises a transformer, a first switch tube, a second switch tube, a full-wave rectifier circuit, a controller and at least one current sensor; the first end of the first switch tube is connected to the positive end of a DC bus through the first primary side winding of the transformer, and the second end of the first switch tube is connected to the midpoint of the DC bus; the first end of the second switch tube is connected to the second end of the first switch tube through the second primary side winding of the transformer, and the second end of the second switch tube is connected to the negative end of the DC bus; the primary side of the current sensor is connected in series with the first switch tube or the second switch tube, and the secondary side of the current sensor is connected to the full-wave rectifier circuit; the switch tube not connected in series with the current sensor is connected in series with a sampling resistor; The method comprises: obtaining a first sampling voltage of the full-wave rectifier circuit output and a second sampling voltage of the sampling resistor; the full-wave rectifier circuit is used for detecting the forward current and the reverse current of the corresponding switch tube; the sampling resistor is used for detecting the forward current and the reverse current of the corresponding switch tube; summing the first sampling voltage of the full-wave rectifier circuit output and the second sampling voltage of the sampling resistor, so that the positive and negative circulating currents in the loop cancel each other after the forward current and the reverse current are added; when the sum of the first sampling voltage and the second sampling voltage is greater than a preset voltage threshold, the first switch tube and the second switch tube are controlled to be turned off.

10. A control method of an auxiliary power supply, characterized by, The auxiliary power supply comprises a transformer, a first switch tube, a second switch tube, a first current sensor, a first full-wave rectifier circuit, a second current sensor and a second full-wave rectifier circuit; a first end of the first switch tube is connected to a positive end of a DC bus through a first primary winding of the transformer, and a second end of the first switch tube is connected to a midpoint of the DC bus; a first end of the second switch tube is connected to the second end of the first switch tube through a second primary winding of the transformer, and a second end of the second switch tube is connected to a negative end of the DC bus; a primary side of the first current sensor is connected in series with the first switch tube, and a secondary side of the first current sensor is connected to the first full-wave rectifier circuit; a primary side of the second current sensor is connected in series with the second switch tube, and a secondary side of the second current sensor is connected to the second full-wave rectifier circuit; The method comprises: obtaining a first sampling voltage of the first full-wave rectifier circuit output and a second sampling voltage of the second full-wave rectifier circuit output; the first full-wave rectifier circuit is used for detecting the forward current and the reverse current of the first switch tube; the second full-wave rectifier circuit is used for detecting the forward current and the reverse current of the second switch tube; summing the first sampling voltage of the first full-wave rectifier circuit output and the second sampling voltage of the second full-wave rectifier circuit output, so that the positive and negative circulating currents in the loop cancel each other after the forward current and the reverse current are added; when the sum of the first sampling voltage and the second sampling voltage is greater than a preset voltage threshold, the first switch tube and the second switch tube are controlled to be turned off.

11. A photovoltaic system characterized by, The auxiliary power supply comprises the auxiliary power supply of any one of claims 1-5 or the auxiliary power supply of any one of claims 6-8; further comprising: an inverter; a positive input end of the inverter is connected to a positive end of the DC bus, and a negative input end of the inverter is connected to a negative end of the DC bus; a power source of the positive end of the DC bus and the negative end of the DC bus is derived from a photovoltaic array.

12. The photovoltaic system of claim 11, wherein, Further comprising: a DCDC converter; the DCDC converter is connected between the photovoltaic array and the DC bus.

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