Power converter, power supply system and black start method

Abstract

Provided in the present application are a power converter, a power supply system and a black start method. The power converter comprises a controller and an inverter circuit; when the voltage of an alternating current bus is less than a first voltage threshold value, the controller is used for controlling the inverter circuit to output to the alternating current bus an alternating current having an amplitude of a first initial voltage, and then controlling the inverter circuit to output to the alternating current bus an alternating current having an amplitude of the rated voltage of the alternating current bus; when the voltage of the alternating current bus is greater than or equal to a second voltage threshold value but less than the rated voltage of the alternating current bus, the controller is further used for controlling the inverter circuit to output to the alternating current bus an alternating current having an amplitude of a second initial voltage, and then controlling the inverter circuit to output to the alternating current bus an alternating current having an amplitude of the rated voltage of the alternating current bus. In the present application, the power converter can implement on-load black start independently of information interaction with other power converters, and has high reliability, a simple structure, low cost and high applicability.

Description

Power converter, power supply system and black start method

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on February 4, 2024, with application number 202410161394.2, and priority to the Chinese patent application entitled “Power Converter, Power Supply System and Black Start Method”, all contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of power electronics technology, and in particular to a power converter, a power supply system, and a black start method. Background Art

[0003] In the field of power electronics technology, a power converter can supply power to a load (for example, a local electrical device). A power converter generally includes a plurality of power converters, which respectively convert the DC power transmitted by a DC power source (for example, a photovoltaic module, an energy storage battery, etc.) into AC power and transmit it to the AC bus, and provide the AC power to the load end through the AC bus. During the first startup or restart of the power supply system, each power converter is required to perform a loaded black start to transmit power to the load end. However, since the power consumption of the load end cannot be determined, when the power consumption of the load end is too large or the time when some power converters complete the black start is not synchronized (that is, serial startup), the output power of the system is less than the power consumption of the load end, which may cause the black start to fail. In the prior art, an information transmission module is usually installed between the power converters, or an upper-level controller is installed in the power supply system to enable each power converter to output AC power to the load synchronously. However, these black start methods are relatively cumbersome. The black start process completely relies on the information transmission module or controller in the system to couple the various power converters. It is not suitable for power supply systems where there is no information interaction between the power converters. In addition, the starting method is complex, the system deployment cost is high, the reliability is low, and the adaptability is poor. Summary of the Invention

[0004] The present application provides a power converter, a power supply system and a black start method, which can realize loaded black start based on the voltage of the AC bus without relying on information interaction with other power converters. It has high reliability, simple structure, low cost and strong applicability.

[0005] In a first aspect, the present application provides a power converter comprising a controller and an inverter circuit. Here, the DC end of the inverter circuit can be used to connect to a photovoltaic module or an energy storage battery, and the AC end of the inverter circuit can be used to connect to a load after being connected in parallel to an AC bus with other power converters. The controller can be connected to the inverter circuit. During a black start, when the voltage of the AC bus is less than a first voltage threshold, the controller can be used to control the inverter circuit to output AC power with an amplitude of a first initial voltage to the AC bus, and then control the inverter circuit to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus, thereby completing the black start. Here, the first initial voltage is greater than or equal to the first voltage threshold and less than the rated voltage of the AC bus. During a black start, when the voltage of the AC bus is greater than or equal to a second voltage threshold and less than the rated voltage of the AC bus, the controller can be used to control the inverter circuit to output AC power with an amplitude of a second initial voltage to the AC bus, and then control the inverter circuit to output AC power with an amplitude of the rated voltage of the AC bus voltage to the AC bus, thereby completing the black start. Here, the voltage of the alternating current with an amplitude of the second initial voltage is synchronized with the voltage of the AC bus, and the second voltage threshold is greater than or equal to the first voltage threshold.

[0006] In this application, during the initial startup or restart of each power converter in the power supply system, each power converter needs to perform a load black start to transmit electrical energy to the load end. Here, the power converter needs to be started together with other power converters in the system within a startup time, so that the power generated by multiple power converters is greater than the power consumed by the load to complete the black start of the system. Specifically, the controller in the power converter can obtain the voltage of the AC bus after initialization is completed, and then determine whether there are other power converters supplying power to the AC bus based on the voltage of the AC bus.

[0007] Using this application, the power converter can determine whether other power converters are supplying power to the AC bus based on the voltage of the AC bus, and then output different initial voltages to the AC bus based on the voltage of the AC bus, and then increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus. Here, the power converter can achieve on-load black start in scenarios that do not rely on communication or interaction with other power converters or upper-level controllers, with high reliability, simple structure, low cost, and strong applicability.

[0008] In a possible implementation, when the voltage of the AC bus is continuously less than a first voltage threshold within a set time, the controller may be configured to control the inverter circuit to output AC power with an amplitude of a first initial voltage to the AC bus.

[0009] Here, since the time it takes for multiple power converters to complete initialization may be different, that is, the power-on time of each power converter may be different, the power converter can continuously obtain the voltage of the AC bus within the set time, so as to more accurately determine whether there are other power converters supplying power to the AC bus. The set time here can be the duration between the power-on time of the power converter and the delayed start time, and the delayed start time can be the time when the power converter is delayed to start based on the application scenario. In other words, the controller here can continuously obtain the voltage of the AC bus within the set time. When the voltage of the AC bus is continuously less than the first voltage threshold within the set time, it can be considered that there are no other power converters in the system supplying power to the AC bus at this time. Here, the power converter with a relatively early power-on time can determine within the set time that there are no other power converters supplying power to the AC bus before supplying power to the AC bus, which can further improve the success rate of black start.

[0010] In one possible embodiment, the controller here can also be used to control the inverter circuit to increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus according to a set voltage step size or a set voltage change rate. Here, a method for increasing the output voltage can be preset in each power converter to ensure that each power converter remains synchronized during the process of increasing the output voltage. Specifically, a set voltage step size or a set voltage change rate can be preset for each power converter, and then the controller of each power converter can control the inverter circuit to synchronously increase the voltage of the AC power output to the AC bus according to the same set voltage step size or set voltage change rate and other parameters, so as to avoid the generation of large circulating currents between the power converters due to the asynchronous output voltage of the AC power during the voltage increase process, thereby causing a black start failure. The control method is simple, reliable, and applicable.

[0011] In one possible embodiment, after outputting AC power with an amplitude equal to the rated voltage of the AC bus to the AC bus, when the voltage of the AC bus is less than or equal to a third voltage threshold, the AC bus is powered off. The controller here can also be used to perform a black start again after the AC bus is powered off. Here, when the power consumption of the load in the system is too large, or the number of power converters started simultaneously in the system is too small, resulting in too little power output to the AC bus, etc., the AC bus may be powered off and the system black start fails. For example, the power-on time of each power converter in the system is different. When some power converters are powered on earlier and others are powered on later, it is possible that some power converters output AC power with an amplitude equal to the rated voltage of the AC bus to the AC bus, while other power converters have not yet started to output voltage. This may cause the output power of these power converters that output the rated voltage of the AC bus to be less than the power consumption of the load, thereby causing the AC bus to be powered off within the power-off detection time. Therefore, it can be understood that after outputting AC power with an amplitude equal to the rated voltage of the AC bus to the AC bus, when the voltage of the AC bus is less than or equal to the third voltage threshold, the AC bus loses power, it can be considered that the black start of the power converter has failed, and the controller can perform a black start again. The judgment method is simple and avoids continuing to output electrical energy to the AC bus after the AC bus loses power, thereby saving energy supply costs.

[0012] In one possible embodiment, after the AC bus loses power, when the voltage of the AC bus continues to be less than the first voltage threshold within a set waiting time, the controller can also be used to perform a black start again after the set waiting time expires. Here, after the AC bus loses power, or after the black start fails, the power converter can re-black start, that is, perform a black start again. It is understandable that the controller can wait for a period of time after the AC bus loses power, that is, perform a black start again after the set waiting time. Here, setting the set waiting time can ensure that as many power converters in the system as possible complete initialization, that is, are in the power-on state, while avoiding the power converter from frequently attempting to perform a black start within the set waiting time.

[0013] With this application, a power converter can wait for other power converters to be powered on within a set waiting time, while detecting whether other power converters are supplying power to the AC bus within the set waiting time. If no other power converters are supplying power to the AC bus within the set waiting time, the power converter can perform a black start again after the set waiting time. Here, after the AC bus loses power, the power converter can perform a black start again with load without relying on communication or interaction with other power converters or upper-level controllers, further improving the success rate and reliability of black starts, with low cost and strong applicability.

[0014] In one possible embodiment, after the AC bus loses power, if the voltage of the AC bus is greater than or equal to a second voltage threshold within a set waiting time, the controller may be configured to control the inverter circuit to output AC power with an amplitude of the second initial voltage to the AC bus, thereby performing a black start again. Here, if the voltage of the AC bus is greater than the second voltage threshold within the set waiting time, this indicates that another power converter is supplying power to the AC bus. At this point, the power converter can immediately perform a black start again, that is, the power converter can output AC power with an amplitude of the second initial voltage to the AC bus, or in other words, output AC power with a voltage synchronized with the voltage of the AC bus. This control method is simple, highly reliable, and highly applicable.

[0015] In one possible implementation, in a sixth possible implementation, the controller may be further configured to extend a set waiting time after a second black start fails. It is understood that the power converter may extend the set waiting time to allow more power converters to be successfully powered on or for the load's power consumption to decrease within the set waiting time, thereby further improving the success rate and reliability of the second black start, with low cost and strong applicability.

[0016] In one possible embodiment, in a seventh possible embodiment, the controller here may also be used to stop black starting again when the set waiting time is greater than the waiting time threshold and the voltage of the AC bus is less than the first voltage threshold, or the number of times the black start is restarted is greater than or equal to the restart threshold and the voltage of the AC bus is less than the first voltage threshold. It can be understood that when the load power consumption is too large, greater than the output power of the system, or when other power converters in the system fail to power on and require maintenance, etc., it may cause the system to temporarily fail to black start successfully. At this time, the power converter can stop the black start based on the excessive number of times the black start is restarted or the set waiting time is too long. It can be further understood that if after stopping the black start, if the voltage of the AC bus is greater than or equal to the second voltage threshold, the power converter obtains that there are other power converters supplying power to the AC bus, and restarts the black start based on the voltage of the AC bus. The judgment method is simple, avoids too many black starts, and further saves energy supply costs.

[0017] In the second aspect, the present application provides a power supply system, which may include multiple power converters as in the first aspect or any possible embodiment of the first aspect, the DC end of the inverter circuit of each power converter in the multiple power converters can be used to connect to a DC power supply, and the AC end of the inverter circuit of each power converter can be used to connect to a load after being connected in parallel to the AC bus.

[0018] Using this application, each power converter in the system can determine whether other power converters are supplying power to the AC bus based on the voltage of the AC bus within a set time. Based on the voltage of the AC bus, the converter can then output different initial voltages to the AC bus, and then increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus. Here, each power converter can achieve an on-load black start without relying on communication or interaction with other power converters or upper-level controllers, resulting in high reliability, simple structure, low cost, and strong applicability.

[0019] In a third aspect, the present application provides a black start method, the method comprising: during a black start process, when a voltage of an AC bus is less than a first voltage threshold, controlling an inverter circuit to output AC power having an amplitude of a first initial voltage to the AC bus, and then controlling the inverter circuit to output AC power having an amplitude of a rated voltage of the AC bus to the AC bus to complete the black start, wherein the first initial voltage is greater than or equal to the first voltage threshold and less than the rated voltage of the AC bus;

[0020] During the black start process, when the voltage of the AC bus is greater than or equal to the second voltage threshold and less than the rated voltage of the AC bus, the inverter circuit is controlled to output AC power with an amplitude of the second initial voltage to the AC bus, and the voltage of the AC power with an amplitude of the second initial voltage is synchronized with the voltage of the AC bus. Then, the inverter circuit is controlled to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus to complete the black start. The second voltage threshold is greater than or equal to the first voltage threshold.

[0021] In the present application, the controller in the power converter can obtain the voltage of the AC bus after initialization is completed, and then determine whether other power converters are supplying power to the AC bus based on the voltage of the AC bus. Using the present application, the power converter can determine whether other power converters are supplying power to the AC bus based on the voltage of the AC bus within a set time, and then output initial voltages of different sizes to the AC bus based on the voltage of the AC bus, and then increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus. Here, the power converter can achieve on-load black start in a scenario that does not rely on communication or interaction with other power converters or upper-level controllers, with high reliability, simple structure, low cost, and strong applicability.

[0022] In one possible implementation, when the voltage of the AC bus is less than a first voltage threshold, controlling the inverter circuit to output AC power having an amplitude of a first initial voltage to the AC bus includes:

[0023] When the voltage of the AC bus is continuously less than the first voltage threshold within a set time, the inverter circuit is controlled to output AC power with an amplitude of the first initial voltage to the AC bus.

[0024] Here, since the time it takes for multiple power converters to complete initialization may be different, that is, the power-on time of each power converter may be different, the power converter can continuously obtain the voltage of the AC bus within the set time, so as to more accurately determine whether there are other power converters supplying power to the AC bus. The set time here can be the duration between the power-on time of the power converter and the delayed start time, and the delayed start time can be the time when the power converter is delayed to start based on the application scenario. In other words, the controller here can continuously obtain the voltage of the AC bus within the set time. When the voltage of the AC bus is continuously less than the first voltage threshold within the set time, it can be considered that there are no other power converters in the system supplying power to the AC bus at this time. Here, the power converter with a relatively early power-on time can determine within the set time that there are no other power converters supplying power to the AC bus before supplying power to the AC bus, which can further improve the success rate of black start.

[0025] In one possible implementation, controlling the inverter circuit to output AC power with an amplitude equal to the rated voltage of the AC bus to the AC bus may include: controlling the inverter circuit to increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus according to a set voltage step or a set voltage change rate.

[0026] Here, a method of increasing the output voltage can be preset in each power converter to ensure that each power converter remains synchronized during the process of increasing the output voltage. Specifically, a set voltage step or a set voltage change rate can be preset for each power converter, and then the controller of each power converter can control the inverter circuit to synchronously increase the voltage of the AC power output to the AC bus according to the same set voltage step or set voltage change rate and other parameters, so as to avoid black start failure caused by large circulating current between power converters due to output voltage asynchrony during the voltage increase process. The control method is simple, reliable and applicable.

[0027] In a possible implementation, after outputting AC power with an amplitude equal to the rated voltage of the AC bus to the AC bus, when the voltage of the AC bus is less than or equal to a third voltage threshold, the AC bus is powered off. The method further includes: performing a black start again after the AC bus is powered off.

[0028] Here, when the power consumption of the load in the system is too large, or the number of power converters started simultaneously in the system is too small, resulting in too little power output to the AC bus, the AC bus may lose power and the system black start may fail. Therefore, it can be understood that after controlling the inverter circuit to output AC power with an amplitude equal to the rated voltage of the AC bus to the AC bus, the controller can continuously obtain the voltage of the AC bus during the power loss detection time. When the voltage of the AC bus is less than or equal to the third voltage threshold, the AC bus loses power, and a black start can be performed again. This simple judgment method avoids continuous power output to the AC bus after the AC bus loses power, thereby saving energy supply costs.

[0029] In a possible implementation, after the AC bus loses power, the method further includes: when the voltage of the AC bus is continuously less than the first voltage threshold within a set waiting time, performing a black start again after the set waiting time ends.

[0030] It is understood that after the AC bus loses power, or in other words, after the AC bus loses power, the power converter can restart the black start, that is, perform a black start again. It is understood that the controller can wait for a period of time after the AC bus loses power, that is, perform a black start again after a set waiting time. Here, setting a set waiting time can ensure that as many power converters in the system as possible complete initialization, that is, are in a powered-on state, while preventing the power converter from frequently attempting a black start within the set waiting time.

[0031] With this application, a power converter can wait for other power converters to be powered on within a set waiting time, while detecting whether other power converters are supplying power to the AC bus within the set waiting time. If no other power converters are supplying power to the AC bus within the set waiting time, the power converter can perform a black start again after the set waiting time. Here, after the AC bus loses power, the power converter can perform a black start again with load without relying on communication or interaction with other power converters or upper-level controllers, further improving the success rate and reliability of black starts, with low cost and strong applicability.

[0032] In a possible implementation, after the AC bus loses power, the method further includes: when the voltage of the AC bus is greater than or equal to a second voltage threshold within a set waiting time, controlling the inverter circuit to output AC power with an amplitude of a second initial voltage to the AC bus.

[0033] Here, if the voltage of the AC bus is greater than the second voltage threshold during the set waiting time, it indicates that another power converter is supplying power to the AC bus. At this point, a black start can be immediately performed again. That is, the power converter can output AC power with an amplitude of the second initial voltage to the AC bus, or in other words, output AC power with a voltage synchronized with the AC bus voltage. This control method is simple, reliable, and highly applicable. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a schematic diagram of an application scenario of a power converter provided in an embodiment of the present application;

[0035] FIG2 is a schematic structural diagram of a power converter provided in an embodiment of the present application;

[0036] FIG3 is a schematic diagram of a startup waveform of a power converter provided in an embodiment of the present application;

[0037] FIG4 is another schematic diagram of startup waveforms of a power converter provided in an embodiment of the present application;

[0038] FIG5 is a schematic diagram of another application scenario of the power converter provided in an embodiment of the present application;

[0039] FIG6 is a schematic structural diagram of a power supply system provided in an embodiment of the present application;

[0040] FIG7 is a flow chart of a black start method according to an embodiment of the present application;

[0041] FIG8 is another schematic flow chart of the black start method provided in an embodiment of the present application;

[0042] FIG9 is another schematic flow chart of a black start method according to an embodiment of the present application;

[0043] FIG10 is another flow chart of the black start method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0044] The power converter provided in this application can be applied to a variety of application fields such as the field of new energy power generation, the field of peak and frequency regulation of traditional power generation, and the field of power supply for important equipment. The specific application can be determined according to the actual application scenario and is not limited here. The power supply system provided in this application can be applied to different scenarios such as large-scale photovoltaic power stations, industrial and commercial power generation, and household power generation, and is not limited here. The following will take the photovoltaic power supply environment as an example of the application scenario of the power converter for explanation, and will not be repeated below.

[0045] Please refer to Figure 1, which is a schematic diagram of an application scenario of the power converter provided in an embodiment of the present application. The power converter provided in the present application is suitable for a power supply system, as shown in Figure 1, and the power supply system includes multiple power converters, namely power converters 1a to power converters 1n. One end of each power converter in power converters 1a to power converters 1n can be connected to a corresponding DC power supply, namely DC power supply 2a to DC power supply 2n. The other end of each power converter can be connected to a load 3 after being connected in parallel to the AC bus. For the sake of convenience, when introducing the working mode and connection relationship of the power converter in the power supply system by taking all the power converters in power converters 1a to power converters 1n as an example, the power converters are uniformly described as power converters 1, and the DC power supplies are uniformly described as DC power supply 2, and no further details are given below. In some feasible implementations, the power converter 1 can convert the DC power provided by the DC power supply 2 into AC power and transmit it to the load 3. For example, the power converter 1 may include a photovoltaic inverter and an energy storage converter, the DC power supply 2 may include an energy storage battery and a photovoltaic module, and the power converter 1 may convert the electrical energy stored in the energy storage battery or the DC power generated by the photovoltaic module into AC power and transmit it to the load 3. It can be understood that the DC power supply 2 provided in the present application is suitable for connecting the load 3 (for example, an AC power grid and an AC load) through the power converter 1 to power base station equipment in remote areas where there is no mains power or the mains power is poor, or to power household appliances (such as refrigerators, air conditioners, etc.) and other application scenarios for powering various types of electrical equipment. The specific application scenario can be determined according to the actual application scenario and is not limited here. It can be further understood that the load 3 may include electrical equipment or power transmission equipment such as transmission lines, power transfer stations, communication base stations or household appliances. It can be understood that the DC power supply 2 provided in the present application may include a DC energy storage device such as an energy storage battery, or include other power sources that can generate DC power, and may also include a pre-stage circuit with a DC power output function, such as a DC / DC transformer circuit or an AC / DC circuit.

[0046] This application only takes the example of a DC power supply 2 supplying power to a load 3 through a power converter 1 to introduce the power converter and power supply system provided by this application. It can be understood that the power converter provided by this application can also be applied to other power supply systems or power supply scenarios, which will not be described in detail below. Here, the power converter 1 can transmit electric energy between the DC power supply 2 and the load 3. During the first startup or restart of each power converter 1 in the power supply system, each power converter 1 needs to perform a loaded black start to transmit electric energy to the load 3 end. In the embodiment of the present application, any power converter 1 in the power supply system can be limited to a power converter 1a. It should be understood that when the power supply system has multiple power converters 1, the control method and circuit design of each power converter 1 are similar, so the following mainly uses one power converter 1a as an example for introduction. That is, the power converter 1a needs to be started together with other power converters in the system within a startup time, so that the power generation power of the multiple power converters is greater than the power consumption of the load 3 to complete the black start of the system. In other words, starting multiple power converters at the same time can avoid a black start failure caused by excessive power consumption at the load 3 end or the serial startup of multiple power converters, which results in the output power of the system being less than the power consumption at the load 3 end, or causing the AC bus to lose power. Taking the power converter 1a as an example, please refer to Figure 2 for details. Figure 2 is a structural schematic diagram of a power converter provided in an embodiment of the present application. As shown in Figure 2, the power converter 1a may include a controller 11a and an inverter circuit 12a. Here, the DC end of the inverter circuit 12a can be used to connect to a DC power supply 2a, and the AC end of the inverter circuit 12a can be used to connect to the load 3 after being connected in parallel with other power converters 1a to the AC bus. The controller 11a can be connected to the inverter circuit 12a.

[0047] During a black start, when the voltage of the AC bus is less than a first voltage threshold, the controller 11a may be configured to control the inverter circuit 12a to output AC power with an amplitude of a first initial voltage U0 to the AC bus, and then control the inverter circuit 12a to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus, thereby completing the black start. Here, the first initial voltage U0 is greater than or equal to the first voltage threshold and less than the rated voltage of the AC bus. During a black start, when the voltage of the AC bus is greater than or equal to a second voltage threshold and less than the rated voltage of the AC bus, the controller 11a may be configured to control the inverter circuit 12a to output AC power with an amplitude of a second initial voltage to the AC bus, and then control the inverter circuit 12a to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus, thereby completing the black start. Here, the voltage of the AC power with an amplitude of the second initial voltage is synchronized with the voltage of the AC bus, and the second voltage threshold is greater than or equal to the first voltage threshold.

[0048] Using this application, the power converter 1a can determine whether other power converters 1a are supplying power to the AC bus based on the voltage of the AC bus, and then output different initial voltages to the AC bus based on the voltage of the AC bus, and then increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus. Here, the power converter 1a can achieve a load black start in a scenario that does not rely on communication or interaction with other power converters 1a or the upper-level controller 11a, with high reliability, simple structure, low cost, and strong applicability.

[0049] Please refer to FIG3 , which is a schematic diagram of a startup waveform of a power converter provided in an embodiment of the present application. As shown in part (a) of FIG3 , when the voltage of the AC bus is continuously less than the first voltage threshold within a set time, the controller 11a here can be used to control the inverter circuit 12a to output an AC power with an amplitude of the first initial voltage U0 to the AC bus. Here, the first initial voltage U0 is greater than or equal to the first voltage threshold and less than the rated voltage Un of the AC bus. Specifically, please refer to part (b) of FIG3 . After the controller 11a controls the inverter circuit 12a to output an AC power with an amplitude of the first initial voltage U0 to the AC bus, the inverter circuit 12a can also be controlled to increase the amplitude of the AC power output to the AC bus to the rated voltage Un of the AC bus to complete the black start. Here, the set time can be the duration between the power-on time of the power converter 1a and the delayed start time T0. It can be understood that in this application scenario, the power-on time of the power converter 1a coincides with the time 0 in FIG3 , and the delayed start time T0 of the power converter 1a coincides with the time Ta in FIG3 .

[0050] In some application scenarios, due to the different power-on times of each power converter, the delayed start time T0 corresponding to each power converter is also different. Please refer again to part (b) in Figure 3. The power-on time of the power converter 1a may be after time 0, that is, the delayed start time T0 corresponding to the power converter 1a may be after time Ta in Figure 3. Taking the case where time Tb is within the set time of the power converter 1a, within the set time, when the voltage of the AC bus is greater than or equal to the second voltage threshold and less than the rated voltage Un of the AC bus, the controller 11a can also be used to control the inverter circuit 12a to output AC power with an amplitude of the second initial voltage to the AC bus. Here, the second voltage threshold is greater than or equal to the first voltage threshold, and the voltage of the AC power with an amplitude of the second initial voltage is synchronized with the voltage of the AC bus, that is, the magnitude of the second initial voltage is equal to the voltage Ub of the AC bus corresponding to time Tb, and the phase of the second initial voltage is the same as the phase corresponding to the voltage Ub of the AC bus corresponding to time Tb. After the controller 11a controls the inverter circuit 12a to output AC power with an amplitude of the second initial voltage to the AC bus, it may further control the inverter circuit 12a to output AC power Un with an amplitude of the rated voltage of the AC bus to complete the black start.

[0051] Specifically, the controller 11a in the power converter 1a can obtain the voltage of the AC bus after initialization is completed, and then determine whether there are other power converters 1a supplying power to the AC bus by the voltage of the AC bus. Since the time when the initialization of multiple power converters 1a is completed may be different, that is, the power-on time of each power converter 1a may be different, the power converter 1a can continuously obtain the voltage of the AC bus within a set time to more accurately determine whether there are other power converters 1a supplying power to the AC bus. The set time here can be the time between the power-on time of the power converter 1a and the delayed start time T0, and the delayed start time T0 can be the time when the power converter 1a is delayed to start based on the application scenario. In other words, the controller 11a here can continuously obtain the voltage of the AC bus within a set time. When the voltage of the AC bus is continuously less than the first voltage threshold within the set time, it can be considered that there are no other power converters 1a supplying power to the AC bus in the system. At this time, the controller 11a can control the inverter circuit 12a to output a voltage greater than or equal to the first voltage threshold to the AC bus, that is, the first initial voltage U0. After controlling the inverter circuit 12a to output AC power with an amplitude of the first initial voltage U0 to the AC bus, the controller 11a may further control the inverter circuit 12a to increase the amplitude of the AC power output to the AC bus to the rated voltage Un of the AC bus, thereby completing the black start. Here, the power converter that powers on earlier can determine within a set time that no other power converter is supplying power to the AC bus before supplying power to the AC bus, further improving the success rate of the black start.

[0052] In some application scenarios, the controller 11a here can also continuously obtain the voltage of the AC bus within a set time. When the voltage of the AC bus is greater than or equal to the second voltage threshold and less than the rated voltage Un of the AC bus within the set time, it can be considered that other power converters 1a in the system are supplying power to the AC bus. At this time, the controller 11a can control the inverter circuit 12a to output a voltage synchronized with the voltage of the AC bus to the AC bus, that is, the second initial voltage. After controlling the inverter circuit 12a to output AC power with an amplitude of the second initial voltage to the AC bus, the controller 11a can also control the inverter circuit 12a to increase the amplitude of the AC power output to the AC bus to the rated voltage Un of the AC bus to complete the black start.

[0053] In some application scenarios, due to the different power-on times of each power converter, the delayed start time T0 corresponding to each power converter is also different. Please refer to part (b) of Figure 3 again. Taking the case where the time Tc is within the set time of the power converter 1a as an example, when the voltage of the AC bus is greater than or equal to the rated voltage Un of the AC bus, the controller 11a here can also be used to control the inverter circuit 12a to output AC power to the AC bus with a voltage synchronized with the voltage of the AC bus. Here, since the power-on times of each power converter 1a in the system may be different, the power converter 1a may complete the initial power-on after the amplitude of the AC power output to the AC bus is increased to the rated voltage Un of the AC bus by other power converters 1a. At this time, the voltage of the AC bus may be greater than or equal to the rated voltage Un of the AC bus. The controller 11a can also control the inverter circuit 12a to output AC power to the AC bus with a voltage synchronized with the voltage of the AC bus, so that the power converter 1a and the other power converters 1a synchronously supply power to the load 3, further improving the success rate of the system's loaded black start. The control method is simple, reliable, and highly applicable.

[0054] In some application scenarios, the controller 11a here can also be used to control the inverter circuit 12a to increase the amplitude of the AC power output to the AC bus to the rated voltage Un of the AC bus according to a set voltage step size or a set voltage change rate. For example, the set voltage change rate here can be the slope of the curve from time Ta to time Tn in part (b) of Figure 3. Here, a method for increasing the output voltage can be preset in each power converter 1a to ensure that each power converter 1a remains synchronized during the process of increasing the output voltage. Specifically, the set voltage step size or set voltage change rate of each power converter 1a can be preset, and then the controller 11a of each power converter 1a can control the inverter circuit 12a to synchronously increase the voltage of the AC power output to the AC bus according to the same set voltage step size or set voltage change rate and other parameters, so as to avoid the generation of large circulating currents between the power converters due to the asynchronous output voltage during the voltage increase process, thereby causing a black start failure. The control method is simple, reliable, and highly applicable.

[0055] In some feasible embodiments, during the process of the power converter 1 outputting AC power with an amplitude of the first initial voltage U0 to the AC bus, it takes a period of time to increase the output voltage of the power converter 1 to the corresponding first initial voltage U0. At this time, it is necessary to further specifically determine the magnitude of the first initial voltage U0. Specifically, if the magnitude of the first initial voltage U0 is too large, the time it takes for the power converter 1 to increase the output voltage to the first initial voltage U0 may be too long, or the charging current in the electronic components such as the capacitor in the power converter 1 may be too large. At the same time, if the magnitude of the first initial voltage U0 is too small, when the power converter 1 outputs AC power with an amplitude of the first initial voltage U0, other power converters may not be easily affected by the voltage change on the AC bus. In other words, the magnitude of the first initial voltage U0 should be greater than or equal to the target detection voltage and less than or equal to the target breakdown voltage. Here, the target detection voltage is used to identify the minimum value of the output voltage output by any power converter to the AC bus when the voltage of the other power converters can be detected by the voltage change on the AC bus. Here, the target breakdown voltage can be used to identify the maximum withstand voltage of the capacitor in the power converter, and can also be used to identify the maximum voltage value that can be reached when the power converter increases the voltage at the maximum rate within the initial voltage increase time.

[0056] For details, please refer to Figure 4, which is another schematic diagram of the startup waveform of the power converter provided in an embodiment of the present application. As shown in Figure 4, taking the case where the power converter 1a outputs AC power with an amplitude of the first initial voltage U0 to the AC bus as an example, the power-on time corresponding to the power converter 1a is time 0 in Figure 4, and the delayed startup time corresponding to the power converter 1a is time T0′ in Figure 4. When the voltage of the AC bus is continuously less than the first voltage threshold within a set time, the controller 11a here can be used to control the inverter circuit 12a to output AC power with an amplitude of the first initial voltage U0 to the AC bus. In other words, when the voltage of the AC bus is continuously less than the first voltage threshold from time 0 to time T0′, the controller 11a can control the inverter circuit 12a to output AC power with an amplitude of the first initial voltage U0 to the AC bus. From time T0′ to time T0, components such as capacitors in the inverter circuit 12a will begin to increase the voltage to increase the output voltage of the inverter circuit 12a to the first initial voltage U0. In some feasible embodiments, between time T0′ and time T0, other power converters may also reach the delayed start time. For example, the delayed start time corresponding to power converter 1n is time T1, and the voltage of the AC bus of controller 11n in power converter 1n is continuously less than the first voltage threshold within the set time. Then, controller 11n in power converter 1n may also control inverter circuit 12n to output AC power with an amplitude of the first initial voltage U0 to the AC bus from time T1 to time T2 (here, time T2 is after time T0 and is not shown in FIG4 ). Here, the voltage boost time of the power converter can be set to a relatively small value, that is, the time from time T0′ to time T0 and the time from time T1 to time T2 are both relatively short, that is, the output voltages of power converter 1a and power converter 1n can be considered to be synchronized. Here, the time it takes for each power converter to increase its voltage to the initial voltage can be set based on the specific application scenario. For example, it can be determined based on the voltage that the capacitor in the inverter circuit can withstand, or based on the time it takes for the controller to obtain the voltage of the AC bus, or based on factors such as the synchronization difference time of each power converter. Here, if any multiple power converters successively output voltages of the same magnitude and phase within the synchronization difference time, the output voltages of these power converters can be considered synchronized.

[0057] In some feasible embodiments, during the process of the power converter 1 outputting AC power having an amplitude of the first initial voltage to the AC bus, it is necessary to output AC power having an amplitude of the first initial voltage U0 according to a specific phase so that other power converters can quickly adjust the voltage change on the AC bus. For example, when the inverter circuit 12 in the power converter 1 is a single-phase inverter circuit, the initial phase of the first initial voltage U0 can be 90° or 270°.

[0058] In some feasible embodiments, after the AC bus loses power, when the voltage of the AC bus continues to be less than the first voltage threshold within a set waiting time, the controller 11a can also be used to continuously obtain the voltage of the AC bus from the end of the set waiting time to the set time, and control the inverter circuit 12a to output AC power with an amplitude of the first initial voltage U0 or an amplitude of the second initial voltage to the AC bus based on the voltage of the AC bus within the set time, so as to perform a black start again. Here, when the power consumption of the load 3 in the system is too large, or the number of power converters 1 started simultaneously in the system is too small, resulting in too little power output to the AC bus, etc., a black start failure, or AC bus power loss, may occur. After the AC bus loses power, the power converter 1 can restart the black start, that is, perform a black start again. Taking the power converter 1a as an example, the controller 11a can perform a black start again immediately after the AC bus loses power, and the set waiting time at this time can be considered to be 0. It can be further understood that the controller 11a can also wait for a period of time after the AC bus loses power before performing a black start again. In this case, the waiting time is set to be greater than 0, and the specific value of the waiting time can be determined based on the application scenario. Here, setting the waiting time can ensure that more power converters in the system, such as power converter 1n, complete initialization as much as possible, that is, are in the power-on state, while avoiding the power converter 1a from frequently attempting to perform a black start within the set waiting time. Accordingly, during the set waiting time, if the voltage of the AC bus is continuously less than the first voltage threshold, it means that no other power converter 1 is supplying power to the AC bus. At this time, similar to the process of the previous black start, the controller 11a can continuously obtain the voltage of the AC bus from the end of the set waiting time to the set time, and control the output voltage of the inverter circuit 12a to the AC bus based on the voltage of the AC bus within the set time. That is, when the voltage of the AC bus is continuously less than the first voltage threshold within the set time, it can be considered that no other power converter 1 in the system is supplying power to the AC bus. The controller 11a can control the inverter circuit 12a to output AC power with an amplitude of the first initial voltage U0 to the AC bus, and the controller 11a can also control the inverter circuit 12a to increase the amplitude of the AC power output to the AC bus to the rated voltage Un of the AC bus. It can be further understood that when the voltage of the AC bus is greater than or equal to the second voltage threshold and less than the rated voltage Un of the AC bus within a set time, it can be considered that other power converters 1 in the system are supplying power to the AC bus. The controller 11a can control the inverter circuit 12a to output AC power with an amplitude of the second initial voltage to the AC bus, and then control the inverter circuit 12a to increase the amplitude of the AC power output to the AC bus to the rated voltage Un of the AC bus.

[0059] By adopting the present application, the power converter 1a can wait for other power converters 1a to be in the power-on state within the set waiting time, and at the same time detect whether other power converters 1a supply power to the AC bus within the set waiting time. If no other power converter 1a supplies power to the AC bus within the set waiting time, the power converter 1a can output initial voltages of different sizes to the AC bus based on the voltage of the AC bus within the set time after the set waiting time, and then increase the amplitude of the AC power output to the AC bus to the rated voltage Un of the AC bus. Here, after the AC bus loses power, the power converter 1a can be loaded again for black start in a scenario without relying on communication or interaction with other power converters 1a or upper-level controllers, further improving the success rate and reliability of the black start, with low cost and strong applicability.

[0060] In some feasible embodiments, the controller 11a here can also be used to control the inverter circuit 12a to output AC power with an amplitude of the second initial voltage to the AC bus within a set waiting time, so as to perform a black start again. Here, the controller 11a can also wait for a period of time after the AC bus loses power and then perform a black start again. In this case, the waiting time is set to be greater than 0, and the specific value of the waiting time can be determined based on the application scenario. Here, setting the set waiting time can ensure that as many power converters 1n in the system as possible complete initialization, that is, are in the power-on state, while avoiding the power converter 1a from frequently attempting a black start within the set waiting time. Accordingly, if the voltage of the AC bus is greater than the second voltage threshold during the set waiting time, it means that there are other power converters 1a supplying power to the AC bus. At this time, the power converter 1a can immediately perform a black start again, that is, the power converter 1a can output AC power with an amplitude of the second initial voltage to the AC bus. The control method is simple, reliable, and applicable.

[0061] In some feasible embodiments, the controller 11a can also be used to extend the set waiting time after a second black start fails. It is understood that the power converter 1a can extend the set waiting time to wait for more power converters 1a to be successfully powered on or wait for the power consumption of the load 3 to decrease during the set waiting time, further improving the success rate and reliability of the second black start, with low cost and strong applicability.

[0062] Please refer to FIG5 for details. FIG5 is a schematic diagram of another application scenario of the power converter provided in an embodiment of the present application. As shown in FIG5, when the power consumption of the load 3 is too large, greater than the output power of the system, or when other power converters in the system, such as the power converter 1k, fail to power on and need to be repaired, etc., the system may temporarily fail to successfully black start. Taking the power converter 1a as an example, the controller 11a here can also be used to stop the black start when the waiting time is set to be greater than the waiting time threshold and the voltage of the AC bus is less than the first voltage threshold, or the number of black starts is greater than or equal to the restart threshold and the voltage of the AC bus is less than the first voltage threshold. That is, the power converter 1a can stop the black start based on too many black starts or too long a waiting time. It can be further understood that if after stopping the black start, if the voltage of the AC bus is greater than or equal to the second voltage threshold, the power converter 1a obtains that there are other power converters 1a supplying power to the AC bus, and restarts the black start based on the voltage of the AC bus. The judgment method is simple, avoids too many black starts again, and further saves energy supply costs.

[0063] The present application also provides a power supply system, for details, please refer to Figure 6, which is a structural diagram of the power supply system provided in an embodiment of the present application. The power supply system may include a plurality of power converters or other power converters as in any possible embodiment of Figures 1 to 5, and this application only takes the power converter in Figure 1 as an example for introduction. As shown in Figure 6, the power supply system may include power converters 1a to 1n, and the DC ends of the inverter circuits (not shown in the figure) of each power converter in power converters 1a to 1n can be connected to their corresponding DC power supplies, that is, the DC power supplies in DC power supplies 2a to 2n. The AC end of the inverter circuit 12a of each power converter can be used to connect to the load 3 after being connected in parallel to the AC bus.

[0064] Using this application, each power converter 1a in the system can determine whether other power converters 1a are supplying power to the AC bus based on the voltage of the AC bus, and then output different initial voltages to the AC bus based on the voltage of the AC bus, and then increase the amplitude of the AC power output to the AC bus to the rated voltage Un of the AC bus. Here, each power converter 1a can achieve an on-load black start in a scenario that does not rely on communication or interaction with other power converters 1a or upper-level controllers, with high reliability, simple structure, low cost, and strong applicability.

[0065] Further referring to FIG6 , in some feasible embodiments, the power supply system may further include a grid-connected switch 5, and the AC end of the inverter circuit 12a of each power converter 1a may be connected in parallel to the AC bus and then connected to the grid 4 via the grid-connected switch 5. The controller 11a in each power converter 1a may be configured to start the converter via a black start when the grid 4 loses power or the grid-connected switch 5 is disconnected.

[0066] By adopting this application, each power converter 1a in the system can achieve load black start in a scenario where the power grid 4 loses power or the grid-connected switch 5 is disconnected, without relying on communication or interaction with other power converters 1a or upper-level controllers. It has high reliability, simple structure, low cost and strong applicability.

[0067] The present application also provides a black start method. For details, please refer to Figure 7, which is a flow chart of the black start method provided in an embodiment of the present application. The black start method can be applied to a power converter or a power converter in a power supply system as shown in any possible implementation of Figures 1 to 6. The power converter may include a controller and an inverter circuit. The DC end of the inverter circuit can be used to connect a DC power supply, and the AC end of the inverter circuit can be used to connect to a load after being connected in parallel with other power converters to the AC bus. The controller can be connected to the inverter circuit. As shown in Figure 7, the method includes:

[0068] S701: During a black start process, when the voltage of the AC bus is less than a first voltage threshold, the inverter circuit is controlled to output AC power with an amplitude of a first initial voltage to the AC bus, and then the inverter circuit is controlled to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus.

[0069] S702: During the black start process, when the voltage of the AC bus is greater than or equal to the second voltage threshold and less than the rated voltage of the AC bus, the inverter circuit is controlled to output AC power with an amplitude of the second initial voltage to the AC bus, and then the inverter circuit is controlled to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus.

[0070] In the present application, the controller in the power converter can obtain the voltage of the AC bus after initialization is completed, and then determine whether other power converters are supplying power to the AC bus based on the voltage of the AC bus. Using the present application, the power converter can determine whether other power converters are supplying power to the AC bus based on the voltage of the AC bus within a set time, and then output initial voltages of different sizes to the AC bus based on the voltage of the AC bus, and then increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus. Here, the power converter can achieve on-load black start in a scenario that does not rely on communication or interaction with other power converters or upper-level controllers, with high reliability, simple structure, low cost, and strong applicability.

[0071] In some feasible implementations, a method for increasing the output voltage can be preset in each power converter to ensure that each power converter remains synchronized during the process of increasing the output voltage. Specifically, a set voltage step or a set voltage change rate can be preset for each power converter, and then the controller of each power converter can control the inverter circuit to synchronously increase the voltage of the AC power output to the AC bus according to the same set voltage step or set voltage change rate and other parameters, so as to avoid black start failure caused by large circulating current between power converters due to output voltage asynchrony during the voltage increase process. The control method is simple, reliable and applicable.

[0072] In some feasible implementations, since the time for completing initialization of multiple power converters may be different, that is, the power-on time of each power converter may be different, the power converter can continuously obtain the voltage of the AC bus within a set time to more accurately determine whether other power converters are supplying power to the AC bus. For a specific control method, please refer to Figure 8, which is another flow chart of the black start method provided in an embodiment of the present application. As shown in Figure 8, the method may include:

[0073] S801: When the voltage of the AC bus is continuously less than a first voltage threshold within a set time, the inverter circuit is controlled to output AC power with an amplitude of a first initial voltage to the AC bus, and then the inverter circuit is controlled to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus.

[0074] S802: When the voltage of the AC bus is greater than or equal to the second voltage threshold and less than the rated voltage of the AC bus within a set time, control the inverter circuit to output AC power with an amplitude of the second initial voltage to the AC bus, and then control the inverter circuit to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus.

[0075] S803: When the voltage of the AC bus is greater than or equal to the rated voltage of the AC bus, control the inverter circuit to output AC power having a voltage synchronized with the voltage of the AC bus to the AC bus.

[0076] Here, because the time it takes for multiple power converters to complete initialization may differ, that is, the power-on time of each power converter may be different, the power converter can continuously obtain the voltage of the AC bus within a set time to more accurately determine whether other power converters are supplying power to the AC bus. The set time here can be the duration between the power-on time of the power converter and the delayed start time, and the delayed start time can be the time when the power converter is delayed to start based on the application scenario. In other words, the controller here can continuously obtain the voltage of the AC bus within a set time. When the voltage of the AC bus is continuously less than the first voltage threshold within the set time, it can be considered that no other power converters in the system are supplying power to the AC bus. Here, the power converter with a relatively early power-on time can determine within the set time that no other power converters are supplying power to the AC bus before supplying power to the AC bus, which can further improve the success rate of the black start. It can be understood that when the voltage of the AC bus is greater than or equal to the second voltage threshold and less than the rated voltage of the AC bus within the set time, it can be considered that other power converters in the system are supplying power to the AC bus. At this point, the inverter circuit can be controlled to output AC power with an amplitude of the second initial voltage to the AC bus, and then controlled to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus. Here, the voltage of the AC bus may be greater than or equal to the rated voltage of the AC bus. The controller can also control the inverter circuit to output an output voltage synchronized with the voltage of the AC bus to the AC bus, so that the power converter and other power converters synchronize to supply power to the load, further improving the success rate of the system's loaded black start. The control method is simple, highly reliable, and highly applicable.

[0077] In some feasible embodiments, during the process of a power converter outputting AC power with a first initial voltage amplitude to an AC bus, it takes a period of time to increase the output voltage of the power converter to the corresponding first initial voltage. In this case, the magnitude of the first initial voltage needs to be further specifically determined. Specifically, if the magnitude of the first initial voltage is too large, the time it takes for the power converter to increase the output voltage to the first initial voltage may be too long, or the charging current in electronic components such as capacitors in the power converter may be too large. Furthermore, if the magnitude of the first initial voltage is too small, when the power converter outputs AC power with the first initial voltage amplitude, other power converters may not be easily affected by voltage changes on the AC bus. In other words, the magnitude of the first initial voltage should be greater than or equal to the target detection voltage and less than or equal to the target breakdown voltage. Here, the target detection voltage is used to identify the minimum value of the output voltage of any power converter output to the AC bus when the voltage of the power converter outputs to the AC bus and other power converters can detect voltage changes on the AC bus. Here, the target breakdown voltage can be used to identify the maximum withstand voltage of the capacitor in the power converter, or it can be used to identify the maximum voltage value that the power converter can reach when increasing the voltage at the maximum rate during the initial voltage increase time.

[0078] In some feasible implementations, when the power consumption of the load in the system is too large, or the number of power converters started simultaneously in the system is too small, resulting in too little power output to the AC bus, the AC bus may lose power, the system black start fails, and the controller may issue an alarm. For a specific control method, please refer to Figure 9, which is another flow chart of the black start method provided in an embodiment of the present application. As shown in Figure 9, the method may include:

[0079] S901: After outputting AC power having an amplitude equal to the rated voltage of the AC bus to the AC bus, continuously acquiring the voltage of the AC bus within a power failure detection time.

[0080] S902: When the voltage of the AC bus is lower than or equal to a third voltage threshold, the controller issues a black start failure alarm.

[0081] For example, the power-on time of each power converter in the system is different. When some power converters are powered on earlier and others are powered on later, it may happen that some power converters output AC power with an amplitude of the rated voltage of the AC bus to the AC bus, while other power converters have not started to output voltage. This may cause the output power of these power converters that output the rated voltage of the AC bus to be less than the power consumption of the load, thereby causing the AC bus to lose power within the power-off detection time. In specific applications, the specific duration of the power-off detection time can be determined based on the application scenario. Therefore, it can be understood that the controller can continuously obtain the voltage of the AC bus within the power-off detection time after controlling the inverter circuit to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus. When the voltage of the AC bus is less than or equal to the third voltage threshold, the controller can issue a black start failure alarm. The judgment method is simple and avoids continuously outputting electrical energy to the AC bus after the AC bus loses power, thereby saving energy supply costs.

[0082] In some feasible implementations, after the AC bus loses power, the power converter can re-start the black start, i.e., perform a black start again. Please refer to FIG10 , which is another flow chart of the black start method provided in an embodiment of the present application. As shown in FIG10 , the method may include:

[0083] S1001: After outputting AC power having an amplitude equal to the rated voltage of the AC bus to the AC bus, when the voltage of the AC bus is less than or equal to a third voltage threshold, the AC bus is powered off.

[0084] S1002: When the voltage of the AC bus is continuously lower than the first voltage threshold within the set waiting time, a black start is performed again after the set waiting time ends.

[0085] S1003: When the voltage of the AC bus is greater than or equal to the second voltage threshold within the set waiting time, control the inverter circuit to output AC power with an amplitude of the second initial voltage to the AC bus.

[0086] Here, when the load power consumption in the system is excessive, or the number of power converters activated simultaneously in the system is too small, resulting in insufficient power output to the AC bus, these situations may result in a black start failure, or in other words, a loss of power to the AC bus. After the AC bus loses power, the power converter can restart the black start, i.e., perform a black start again. It is understood that the controller can immediately perform a black start again after the AC bus loses power, and the set waiting time in this case can be considered to be zero. It is further understood that the controller can also perform a black start again after waiting for a period of time after the AC bus loses power, in which case the set waiting time is greater than zero. The specific value of the set waiting time can be determined based on the application scenario. Here, setting a set waiting time can ensure that as many power converters in the system as possible complete initialization, i.e., are in the powered-on state, while preventing the power converters from frequently attempting black starts within the set waiting time. Accordingly, if the voltage of the AC bus remains below the first voltage threshold during the set waiting time, it indicates that no other power converters are supplying power to the AC bus. At this point, similar to the previous black start process, the controller can continuously obtain the AC bus voltage from the end of the set waiting time to the set time, and control the output voltage of the inverter circuit to the AC bus based on the AC bus voltage during the set time. That is, when the AC bus voltage is continuously less than the first voltage threshold for the set time, it can be assumed that no other power converters in the system are supplying power to the AC bus. The controller can control the inverter circuit to output AC power with an amplitude of the first initial voltage to the AC bus, and the controller can also control the inverter circuit to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus. It will be understood that when the AC bus voltage is greater than or equal to the second voltage threshold and less than the rated voltage of the AC bus for the set time, it can be assumed that other power converters in the system are supplying power to the AC bus. The controller can control the inverter circuit to output AC power with an amplitude of the second initial voltage to the AC bus, and then control the inverter circuit to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus.

[0087] By adopting the present application, the power converter can wait for other power converters to be in the power-on state within the set waiting time, and at the same time detect whether other power converters are supplying power to the AC bus within the set waiting time. If no other power converters are supplying power to the AC bus within the set waiting time, the power converter can output initial voltages of different sizes to the AC bus based on the voltage of the AC bus within a set time after the set waiting time, and then increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus. Here, after the AC bus loses power, the power converter can be black-started again with load in a scenario that does not rely on communication or interaction with other power converters or upper-level controllers, further improving the success rate and reliability of the black start, with low cost and strong applicability.

[0088] In some feasible embodiments, after the AC bus loses power, the method may further include: when the voltage of the AC bus is greater than or equal to a second voltage threshold within a set waiting time, controlling the inverter circuit to output AC power with an amplitude of a second initial voltage to the AC bus to perform a black start again.

[0089] Here, the controller can also wait for a period of time after the AC bus loses power and then perform a black start again. At this time, the waiting time is set to be greater than 0, and the specific value of the waiting time can be determined based on the application scenario. Here, setting the waiting time can ensure that as many power converters in the system as possible complete initialization, that is, are in the power-on state, while avoiding the power converter from frequently attempting to perform a black start within the set waiting time. Accordingly, during the set waiting time, if the voltage of the AC bus is greater than the second voltage threshold, it means that there are other power converters supplying power to the AC bus. At this time, the power converter can immediately perform a black start again, that is, the power converter can output AC power with an amplitude of the second initial voltage to the AC bus. The control method is simple, reliable, and applicable.

[0090] In some feasible embodiments, the method may further include: after a second black start fails, the controller extending a set waiting time. It is understood that the power converter may extend the set waiting time to allow more power converters to be successfully powered on or for the load power consumption to decrease within the set waiting time, thereby further improving the success rate and reliability of the second black start, with low cost and strong applicability.

[0091] In some feasible embodiments, the method may further include: when the set waiting time is greater than the waiting time threshold and the voltage of the AC bus is less than the first voltage threshold, or the number of times the black start is restarted is greater than or equal to the restart threshold and the voltage of the AC bus is less than the first voltage threshold, stopping the black start again. It is understandable that when the load power consumption is too large, greater than the output power of the system, or when other power converters in the system fail to power on and require maintenance, etc., it may cause the system to temporarily fail to black start successfully. At this time, the power converter may stop the black start based on the excessive number of times the black start is restarted or the set waiting time is too long. It is further understandable that if after stopping the black start, if the voltage of the AC bus is greater than or equal to the second voltage threshold, the power converter obtains that there are other power converters supplying power to the AC bus, and restarts the black start based on the voltage of the AC bus. The judgment method is simple, avoids too many black starts again, and further saves energy supply costs.

[0092] Using this application, the power converter can determine whether other power converters are supplying power to the AC bus based on the voltage of the AC bus within a set time, and then output different initial voltages to the AC bus based on the voltage of the AC bus, and then increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus. Here, the power converter can achieve on-load black start in scenarios that do not rely on communication or interaction with other power converters or upper-level controllers, with high reliability, simple structure, low cost, and strong applicability.

[0093] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A power converter, characterized in that: The power converter includes a controller and an inverter circuit, wherein the DC end of the inverter circuit is used to connect to a photovoltaic module or an energy storage battery, and the AC end of the inverter circuit is used to connect to a load through an AC bus. The controller is connected to the inverter circuit; During a black start, when the voltage of the AC bus is less than a first voltage threshold, the controller is configured to control the inverter circuit to output AC power having an amplitude of a first initial voltage to the AC bus, and then control the inverter circuit to output AC power having an amplitude of a rated voltage of the AC bus to the AC bus, so as to complete the black start, wherein the first initial voltage is greater than or equal to the first voltage threshold and less than the rated voltage of the AC bus; During the black start process, when the voltage of the AC bus is greater than or equal to a second voltage threshold and less than the rated voltage of the AC bus, the controller is used to control the inverter circuit to output AC power with an amplitude of a second initial voltage to the AC bus, where the voltage of the AC power with an amplitude of the second initial voltage is synchronized with the voltage of the AC bus, and then control the inverter circuit to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus to complete the black start, where the second voltage threshold is greater than or equal to the first voltage threshold.

2. The power converter according to claim 1, wherein: When the voltage of the AC bus is continuously less than the first voltage threshold within a set time, the controller is configured to control the inverter circuit to output AC power with an amplitude of the first initial voltage to the AC bus.

3. The power converter according to claim 1 or 2, characterized in that: The controller is used to control the inverter circuit to increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus according to a set voltage step size or a set voltage change rate.

4. The power converter according to any one of claims 1 to 3, characterized in that: After outputting AC power with an amplitude equal to the rated voltage of the AC bus to the AC bus, when the voltage of the AC bus is less than or equal to a third voltage threshold, the AC bus is powered off, and the controller is further configured to perform the black start again after the AC bus is powered off.

5. The power converter according to claim 4, characterized in that After the AC bus loses power, when the voltage of the AC bus continues to be less than the first voltage threshold within a set waiting time, the controller is further configured to perform the black start again after the set waiting time expires.

6. The power converter according to claim 4, characterized in that After the AC bus loses power, when the voltage of the AC bus is greater than or equal to the second voltage threshold within a set waiting time, the controller is further used to control the inverter circuit to output AC power with an amplitude of the second initial voltage to the AC bus to perform the black start again.

7. The power converter according to any one of claims 4 to 6, characterized in that: The controller is further configured to extend the set waiting time after the black start fails again.

8. The power converter according to any one of claims 4 to 7, characterized in that: The controller is further configured to stop performing the black start again when the set waiting time is greater than a waiting time threshold and the voltage of the AC bus is less than the first voltage threshold, or when the number of black starts is greater than or equal to a restart threshold and the voltage of the AC bus is less than the first voltage threshold.

9. A power supply system, characterized in that: The power supply system includes multiple power converters according to any one of claims 1 to 8, wherein the DC end of the inverter circuit of each power converter in the multiple power converters is used to connect to a photovoltaic component or an energy storage battery, and the AC end of the inverter circuit of each power converter is used to connect to a load through an AC bus.

10. A black start method, characterized in that: The method comprises: During a black start, when the voltage of the AC bus is less than a first voltage threshold, controlling the inverter circuit to output AC power with an amplitude of a first initial voltage to the AC bus, and then controlling the inverter circuit to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus, so as to complete the black start, wherein the first initial voltage is greater than or equal to the first voltage threshold and less than the rated voltage of the AC bus; During the black start process, when the voltage of the AC bus is greater than or equal to a second voltage threshold and less than the rated voltage of the AC bus, the inverter circuit is controlled to output AC power with an amplitude of a second initial voltage to the AC bus, and the voltage of the AC power with an amplitude of the second initial voltage is synchronized with the voltage of the AC bus. Then, the inverter circuit is controlled to output AC power with an amplitude of the rated voltage of the AC bus to the AC bus to complete the black start, and the second voltage threshold is greater than or equal to the first voltage threshold.

11. The black start method according to claim 10, wherein: When the voltage of the AC bus is less than a first voltage threshold, controlling the inverter circuit to output AC power with an amplitude of a first initial voltage to the AC bus includes: When the voltage of the AC bus is continuously less than the first voltage threshold within a set time, the inverter circuit is controlled to output AC power with an amplitude of the first initial voltage to the AC bus.

12. The black start method according to claim 10 or 11, characterized in that: The step of controlling the inverter circuit to output AC power having an amplitude equal to the rated voltage of the AC bus to the AC bus comprises: The inverter circuit is controlled to increase the amplitude of the AC power output to the AC bus to the rated voltage of the AC bus according to a set voltage step size or a set voltage change rate.

13. The black start method according to any one of claims 10 to 12, characterized in that: After outputting AC power having an amplitude equal to the rated voltage of the AC bus to the AC bus, when the voltage of the AC bus is less than or equal to a third voltage threshold, powering off the AC bus, the method further includes: After the AC bus loses power, the black start is performed again.

14. The black start method according to claim 13, characterized in that: After the AC bus loses power, the method further includes: When the voltage of the AC bus is continuously lower than the first voltage threshold within a set waiting time, the black start is performed again after the set waiting time ends.

15. The black start method according to claim 13, wherein: After the AC bus loses power, the method further includes: when the voltage of the AC bus is greater than or equal to the second voltage threshold within a set waiting time, controlling the inverter circuit to output AC power with an amplitude of the second initial voltage to the AC bus, so as to perform the black start again.

Images