Power converter, control method thereof and energy storage system

Abstract

The invention provides a power converter, a control method thereof and an energy storage system, when high voltage ride through occurs, the bus voltage rises from a first voltage value to a second voltage value, and a DC-DC conversion circuit adjusts the maximum output power to a first power according to a control signal, and the power is output within the range less than or equal to the maximum output power, and the bus voltage is stabilized by changing the external characteristics of the DC-to-DC conversion circuit, so that the occurrence of bus voltage oscillation is avoided. The first power is greater than the second power, and the second power is the maximum output power of the DC-to-DC conversion circuit under the condition of no control signal when the bus voltage is the second voltage value. The output capacity of the DC-DC conversion circuit is increased under the condition of higher bus voltage, and the hardware cost of the system can be reduced and the waste of hardware resources can be avoided by adopting the mode that the DC-DC conversion circuit temporarily bears higher output power.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a power converter, a control method thereof and an energy storage system. Background Art

[0002] In a traditional two-stage energy storage system, the power converter connected between the DC source and the grid usually uses a bidirectional boost circuit at the front stage of the DC bus to boost the DC voltage of the DC source to the bus voltage, and uses an inverter (DC / AC) at the back stage of the DC bus to convert the bus voltage to AC. When a high voltage ride through (HVRT) occurs in the grid, that is, when the grid voltage temporarily rises to a certain percentage of the rated voltage due to a fault or other factors, the power generation equipment needs to ensure that it does not disconnect from the grid within a certain time range.

[0003] When the grid is in the process of high voltage ride-through, the bus voltage of the DC bus is pulled up as the grid voltage increases due to the uncontrolled rectification function of the inverter. When the bus voltage exceeds the normal working range of the boost circuit components, in order to prevent the boost circuit components from bearing large power, the boost circuit will reduce the maximum output power. The reduction in the maximum output power causes the bus voltage to be pulled down. When the bus voltage drops to the normal working range of the boost circuit, the boost circuit will restore the maximum output power, causing the bus voltage to rise again. The above process is repeated, causing the bus voltage to oscillate, making the system unstable. Summary of the invention

[0004] The present application provides a power converter, a control method thereof and an energy storage system for stabilizing bus voltage during high voltage ride-through.

[0005] In the first aspect, the present application provides a power converter, including: a DC-to-DC conversion circuit, a DC bus, and a DC-to-AC conversion circuit. Among them, one end of the DC-to-DC conversion circuit is used to connect to a DC source, which can be a photovoltaic module or a storage battery. The other end of the DC-to-DC conversion circuit is connected to one end of the DC-to-AC conversion circuit through a DC bus, and the other end of the DC-to-AC conversion circuit is used to connect to a power grid or a load. The DC-to-DC conversion circuit is used to convert the voltage of the electric energy from the photovoltaic module or the energy storage battery to the DC bus; the DC-to-AC conversion circuit is used to convert the bus voltage of the DC bus into AC power and output it to the power grid.

[0006] When the power grid is normal, that is, when the voltage of the power grid is the rated voltage, the rated voltage can be a set voltage range. For example, within ±10% of 220V belongs to the normal situation of the power grid. Due to the uncontrolled rectification function of the DC-AC conversion circuit, the bus voltage of the DC bus is the first voltage value, and the first voltage value is, for example, 800V.

[0007] When the power grid experiences high-voltage ride-through, that is, when the voltage of the power grid rises to more than the first multiple of the rated voltage. For example, when the voltage of the power grid rises to more than 110% of 220V, due to the uncontrolled rectification function of the DC-AC conversion circuit, the bus voltage rises as the power grid voltage rises. Specifically, the bus voltage rises from the first voltage value when the power grid is normal to the second voltage value. For example, it rises from 800V to 900V. At this time, if the external characteristics of the DC-DC conversion circuit are not changed, then because the second voltage value exceeds the range within which the devices of the DC-DC conversion circuit can operate normally, in order to avoid the devices bearing a large power, the DC-DC conversion circuit will reduce the maximum output power. For example, the maximum output power is reduced from 100kW to 80kW. The DC-DC conversion circuit needs to output power within a range less than or equal to the maximum output power. The reduction of the maximum output power causes the bus voltage to decrease. For example, the bus voltage decreases from 900V to 800V. When the bus voltage drops to within the normal operating range of the DC-DC conversion circuit, the DC-DC conversion circuit will restore the maximum output power. For example, the maximum output power is restored from 80kW to 100kW, causing the bus voltage to rise again. For example, the bus voltage rises from 800V to 900V. The above process repeats, resulting in the oscillation of the bus voltage and making the system unstable.

[0008] In an embodiment of the present application, when the power grid experiences high-voltage ride-through, for example, when the voltage of the power grid is 1.1 times 220V, the DC-DC conversion circuit switches to the external characteristics of high-voltage ride-through according to the control signal, that is, the DC-DC conversion circuit does not reduce the maximum output power according to the control signal. For example, the maximum output power remains at 100 kW before high-voltage ride-through occurs to stabilize the bus voltage. For example, the bus voltage is stabilized at 900V to avoid oscillation of the bus voltage and stabilize the system. Specifically, when the voltage of the power grid rises to be greater than the first multiple of the rated voltage, that is, when the power grid experiences high-voltage ride-through, the DC-DC conversion circuit adjusts the maximum output power to the first power according to the received control signal, so that the DC-DC conversion circuit outputs power within a range less than or equal to the maximum output power. The first power needs to be greater than the second power. For example, the first power is 100 kW and the second power is 80 kW. The second power is: when the bus voltage is the second voltage value, the maximum output power reduced by the DC-DC conversion circuit when no control signal is received. The second power can also be understood as: when the power grid is normal, that is, when the voltage of the power grid is the rated voltage and the bus voltage is set to the second voltage value, the maximum output power of the DC-DC conversion circuit. Since the second voltage value exceeds the normal operating range of the components of the DC-DC conversion circuit, in order to avoid the components from bearing a large power, the DC-DC conversion circuit will reduce the maximum output power. For example, the maximum output power, that is, the second power, is reduced from 100 kW to 80 kW, so that the DC-DC conversion circuit outputs power within a range less than or equal to the second power, that is, 80 kW.

[0009] In the present application, during high-voltage ride-through of the power grid, the DC-DC conversion circuit increases the output capacity, that is, the maximum output power, according to the control signal under the condition of a higher bus voltage. By means of the DC-DC conversion circuit briefly bearing a higher maximum output power, the hardware cost of the system can be reduced and waste of hardware resources can be avoided.

[0010] In some embodiments of the present application, when the power grid experiences high-voltage ride-through, after the DC-DC conversion circuit switches to the external characteristics of high-voltage ride-through, it can control the DC-DC conversion circuit not to reduce the maximum output power. Specifically, it can keep the maximum output power of the DC-DC conversion circuit not less than the maximum output power when the power grid is normal. For example, before high-voltage ride-through occurs and the power grid is normal, that is, when the voltage of the power grid is the rated voltage and the bus voltage is the first voltage value, the maximum output power of the DC-DC conversion circuit is the third power. Then, when high-voltage ride-through occurs, that is, after the bus voltage rises, the DC-DC conversion circuit can control the maximum output power, that is, the first power, to be greater than or equal to the third power according to the control signal. For example, both are 100 kW, to ensure the stability of the system load during the normal switching of the power grid to high-voltage ride-through. In the present application, the DC-AC conversion circuit connected to the power grid can be used to collect the voltage of the power grid, judge the level of high-voltage ride-through of the power grid, and then send the corresponding high-voltage ride-through flag to the DC-AC conversion circuit as a control signal. After receiving the high-voltage ride-through flag, that is, the control signal, the DC-AC conversion circuit switches to the external characteristics of high-voltage ride-through, that is, adjusts the maximum output power to the first power to increase the output capacity and avoid bus voltage oscillation. Until the high-voltage ride-through flag disappears, it resumes to the normal external characteristics and adjusts the maximum output power to the third power to ensure the stability of the system load during the normal switching of the power grid to high-voltage ride-through.

[0011] In the present application, when the power grid experiences high-voltage ride-through, according to the different multiples of the voltage of the power grid rising above the rated voltage, the rising ratio of the bus voltage is also different. When the voltage of the power grid rises to different multiples of the rated voltage, the DC-DC conversion circuit can maintain a fixed maximum output power, that is, the first power. Specifically, when the voltage of the power grid rises to the first multiple greater than the rated voltage and when the voltage of the power grid rises to the second multiple greater than the rated voltage, the DC-DC conversion circuit controls the maximum output power to be the fixed first power. For example, when the first multiple of the voltage of the power grid is 1.2 times and the second multiple is 1.3 times the rated voltage, the maximum output power of the DC-DC conversion circuit, that is, the first power, can be controlled to be the same as the third power, which is 100 kW, to ensure the stability of the system load during the normal switching of the power grid to high-voltage ride-through.

[0012] In some embodiments of the present application, when a high-voltage ride-through occurs in the power grid, the DC-AC conversion circuit can increase the maximum output power within a short time to withstand a higher output power. That is, when the voltage of the power grid rises to a first multiple greater than the rated voltage, the DC-AC conversion circuit adjusts the maximum output power to a first power within a first time period. If the power grid does not return to normal after the first time period, in order to avoid damage to the devices in the DC-AC conversion circuit due to overloading, it is necessary to reduce the maximum output power of the DC-AC conversion circuit. The DC-AC conversion circuit adjusts the maximum output power to a fourth power, and the fourth power is less than the first power to ensure the safe use of the devices in the DC-AC conversion circuit.

[0013] In some embodiments of the present application, when different levels of high-voltage ride-through occur in the power grid, the DC-AC conversion circuit can be controlled to maintain the high-voltage ride-through external characteristics for different durations, that is, the durations of maintaining the maximum output power at the first power are different. Specifically, when the voltage of the power grid rises to a first multiple greater than the rated voltage, the DC-AC conversion circuit adjusts the maximum output power to the first power within a first time period, and adjusts the maximum output power to the fourth power after the first time period. When the voltage of the power grid rises to a second multiple greater than the rated voltage, the DC-AC conversion circuit adjusts the maximum output power to the first power within a second time period, and adjusts the maximum output power to the fourth power after the second time period. The first multiple is greater than the second multiple, and the first time period is less than the second time period. In other words, the higher the high-voltage ride-through level, the shorter the duration for which the DC-AC conversion circuit maintains the high-voltage ride-through external characteristics. For example, when the voltage of the power grid rises to more than 110% to 120% of the rated voltage, the DC-AC conversion circuit can maintain the adjusted maximum output power at the first power for no less than 10 s; when the voltage of the power grid rises to more than 120% to 125% of the rated voltage, the DC-AC conversion circuit can maintain the adjusted maximum output power at the first power for no less than 1 s; when the voltage of the power grid rises to more than 125% to 130% of the rated voltage, the DC-AC conversion circuit can maintain the adjusted maximum output power at the first power for no less than 500 ms.

[0014] In a second aspect, embodiments of the present application provide a control method for a power converter, which may specifically include the following steps:

[0015] When the power grid is normal, that is, when the voltage of the power grid is the rated voltage, the rated voltage can be a set voltage range. For example, within ±10% of 220 V belongs to the case where the power grid is normal. Due to the uncontrolled rectification function of the DC-AC conversion circuit in the power converter, the bus voltage of the DC bus is a first voltage value, that is, the DC-AC conversion circuit in the power converter controls the bus voltage of the DC bus in the power converter to be the first voltage value. For example, the first voltage value is 800 V.

[0016] When a high voltage ride-through occurs in the power grid, that is, when the voltage of the power grid rises to a first multiple greater than the rated voltage, for example, when the voltage of the power grid rises to more than 110% of 220V, due to the uncontrolled rectification function of the DC-to-AC conversion circuit, the bus voltage increases with the increase of the power grid voltage. Specifically, the bus voltage increases from the first voltage value when the power grid is normal to the second voltage value, for example, from 800V to 900V. At this time, if the external characteristics of the DC-to-DC conversion circuit are not changed, since the second voltage value exceeds the range in which the components of the DC-to-DC conversion circuit can work normally, in order to avoid the components from bearing a large power, the DC-to-DC conversion circuit will reduce the maximum output power, for example, the maximum output power is reduced from 100kw to 80kw. The DC-to-DC conversion circuit needs to output power within a range less than or equal to the maximum output power. The reduction in the maximum output power leads to a reduction in the bus voltage, for example, the bus voltage is reduced from 900V to 800V. When the bus voltage drops to within the normal operating range of the DC-DC converter circuit, the DC-DC converter circuit will restore the maximum output power, for example, the maximum output power is restored from 80kw to 100kw, causing the bus voltage to increase again, for example, the bus voltage increases from 800V to 900V. The above process is repeated, resulting in bus voltage oscillation, making the system unstable.

[0017] In the embodiments of the present application, when the power grid experiences high-voltage ride-through, for example, when the voltage of the power grid is 1.1 times of 220V, the DC-DC conversion circuit switches to the external characteristics of high-voltage ride-through according to the control signal, that is, the DC-DC conversion circuit does not reduce the maximum output power according to the control signal. For example, the maximum output power remains at 100 kW before the high-voltage ride-through occurs to stabilize the bus voltage. For example, the bus voltage is stabilized at 900V to avoid oscillation of the bus voltage and stabilize the system. Specifically, when the voltage of the power grid rises to be greater than the first multiple of the rated voltage, that is, when the power grid experiences high-voltage ride-through, the DC-DC conversion circuit adjusts the maximum output power to the first power according to the received control signal, so that the DC-DC conversion circuit outputs power within the range less than or equal to the maximum output power. The first power needs to be greater than the second power. For example, the first power is 100 kW and the second power is 80 kW. The second power is: when the bus voltage is the second voltage value, the maximum output power reduced by the DC-DC conversion circuit when no control signal is received. The second power can also be understood as: when the power grid is normal, that is, when the voltage of the power grid is the rated voltage and the bus voltage is set to the second voltage value, the maximum output power of the DC-DC conversion circuit. Since the second voltage value exceeds the normal operating range of the components of the DC-DC conversion circuit, in order to avoid the components from bearing a large power, the DC-DC conversion circuit will reduce the maximum output power. For example, the maximum output power, that is, the second power, is reduced from 100 kW to 80 kW, so that the DC-DC conversion circuit outputs power within the range less than or equal to the second power, that is, 80 kW.

[0018] In the present application, during the high-voltage ride-through of the power grid, by controlling the DC-DC conversion circuit to increase the output capacity, that is, the maximum output power, according to the control signal under the condition of a higher bus voltage, and by means of the DC-DC conversion circuit briefly bearing a higher output power, the hardware cost of the system can be reduced and the waste of hardware resources can be avoided.

[0019] In some embodiments of the present application, when the power grid experiences high-voltage ride-through, after the DC-DC conversion circuit switches to the external characteristics of high-voltage ride-through, it can control the DC-DC conversion circuit not to reduce the maximum output power. Specifically, it can keep the maximum output power of the DC-DC conversion circuit not less than the maximum output power when the power grid is normal. For example, before the high-voltage ride-through occurs and the power grid is normal, that is, when the voltage of the power grid is the rated voltage and the bus voltage is the first voltage value, the maximum output power of the DC-DC conversion circuit is the third power. Then, when the high-voltage ride-through occurs, that is, after the bus voltage rises, the DC-DC conversion circuit can control the maximum output power, that is, the first power, to be greater than or equal to the third power according to the control signal. For example, both are 100 kW, to ensure the load-carrying stability of the system during the normal switching of the power grid to high-voltage ride-through.

[0020] In this application, a DC-AC conversion circuit connected to the power grid can be used to collect the voltage of the power grid, and determine the level of high-voltage ride-through of the power grid. Then, a corresponding high-voltage ride-through flag is sent to the DC-AC conversion circuit as a control signal. After receiving the high-voltage ride-through flag, i.e., the control signal, the DC-AC conversion circuit switches to the high-voltage ride-through external characteristic, that is, adjusts the maximum output power to the first power to increase the output capacity and avoid bus voltage oscillation. Until the high-voltage ride-through flag disappears, it resumes to the normal external characteristic and adjusts the maximum output power to the third power to ensure the stability of the system under load during the normal switching of the power grid to high-voltage ride-through.

[0021] In this application, when the power grid experiences high-voltage ride-through, the ratio of the increase in the bus voltage is different according to the multiple by which the voltage of the power grid rises above the rated voltage. When the voltage of the power grid rises to different multiples of the rated voltage, the DC-DC conversion circuit can maintain a fixed maximum output power, i.e., the first power. Specifically, when the voltage of the power grid rises above the first multiple of the rated voltage and when the voltage of the power grid rises above the second multiple of the rated voltage, the DC-DC conversion circuit controls the maximum output power to be the fixed first power. For example, when the first multiple of the rated voltage of the power grid is 1.2 times and the second multiple is 1.3 times, the maximum output power of the DC-DC conversion circuit, i.e., the first power, can be controlled to be the same as the third power, which is 100 kw, to ensure the stability of the system under load during the normal switching of the power grid to high-voltage ride-through.

[0022] In some embodiments of this application, when the power grid experiences high-voltage ride-through, the DC-AC conversion circuit can increase the maximum output power within a short time to withstand a higher output power. That is, when the voltage of the power grid rises above the first multiple of the rated voltage, the DC-AC conversion circuit adjusts the maximum output power to the first power within the first time period. If the power grid does not return to normal after the first time period, in order to avoid damage to the components in the DC-AC conversion circuit due to overloading, the maximum output power of the DC-AC conversion circuit needs to be reduced. The DC-AC conversion circuit adjusts the maximum output power to the fourth power, and the fourth power is less than the first power to ensure the safe use of the components in the DC-AC conversion circuit.

[0023] In some embodiments of the present application, when the power grid experiences high-voltage ride-through at different levels, the DC-AC conversion circuit can be controlled to maintain the high-voltage ride-through external characteristics for different durations, that is, the durations for maintaining the maximum output power at the first power are different. Specifically, when the voltage of the power grid rises to a first multiple greater than the rated voltage, the DC-AC conversion circuit adjusts the maximum output power to the first power within the first duration, and adjusts the maximum output power to the fourth power after the first duration. When the voltage of the power grid rises to a second multiple greater than the rated voltage, the DC-AC conversion circuit adjusts the maximum output power to the first power within the second duration, and adjusts the maximum output power to the fourth power after the second duration. The first multiple is greater than the second multiple, and the first duration is less than the second duration. In other words, the higher the high-voltage ride-through level, the shorter the duration for which the DC-AC conversion circuit maintains the high-voltage ride-through external characteristics. For example, when the voltage of the power grid rises to more than 110% to 120% of the rated voltage, the DC-AC conversion circuit can maintain the adjustment of the maximum output power to the first power for no less than 10 s; when the voltage of the power grid rises to more than 120% to 125% of the rated voltage, the DC-AC conversion circuit can maintain the adjustment of the maximum output power to the first power for no less than 1 s; when the voltage of the power grid rises to more than 125% to 130% of the rated voltage, the DC-AC conversion circuit can maintain the adjustment of the maximum output power to the first power for no less than 500 ms.

[0024] In a third aspect, an embodiment of the present application provides an energy storage system, including: an energy storage battery and the power converter provided in the first aspect. The power converter is connected to the energy storage battery, and the power converter is configured to convert the electric energy provided by the energy storage battery into alternating current and output it to the power grid or a load.

[0025] For the technical effects that can be achieved by any possible design in the second aspect and the third aspect, please refer to the technical effects that can be achieved by any possible design in the first aspect above, and will not be repeated here. These aspects or other aspects of the present application will be more clearly understood in the following description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the bus voltage of the prior art power converter when the power grid experiences high-voltage ride-through;

[0027] Figure 2 Schematic diagram of the structure of the power converter provided by the embodiment of the present application;

[0028] Figure 3 Schematic diagram of the bus voltage of the power converter provided by the embodiment of the present application when the power grid experiences high-voltage ride-through;

[0029] Figure 4Schematic diagram for comparing the maximum output power of the DC-DC conversion circuit in a power converter during high-voltage ride-through of the power grid. Detailed implementation manners

[0030] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings. However, the exemplary implementation manners can be implemented in various forms and should not be construed as being limited to the implementation manners described herein; on the contrary, these implementation manners are provided to make the present application more comprehensive and complete, and to fully convey the concept of the exemplary implementation manners to those skilled in the art.

[0031] Referring to Figure 1 , currently, during the high-voltage ride-through of the power grid, due to the uncontrolled rectification function of the inverter in the power converter, the bus voltage of the DC bus is pulled up as the grid voltage rises. When the bus voltage exceeds the range within which the devices of the boost circuit can operate normally, in order to avoid the devices of the boost circuit from bearing a large power, the boost circuit will reduce the maximum output power, and the reduction of the maximum output power causes the bus voltage to decrease. When the bus voltage drops to within the normal operating range of the boost circuit, the boost circuit will restore the maximum output power, causing the bus voltage to rise again. The above process repeats, resulting in bus voltage oscillation and making the system unstable.

[0032] In view of this, the embodiments of the present application provide a power converter, its control method, and an energy storage system. During high-voltage ride-through, by changing the external characteristics of the front-stage DC-DC conversion circuit (DC / DC) in the power converter, the DC / DC circuit does not reduce the maximum output power, and the occurrence of bus voltage oscillation can be avoided. By controlling the DC / DC circuit to increase the output capacity under a higher bus voltage condition and adopting the method of having the DC-DC conversion circuit (DC / DC) briefly bear a higher output power, the hardware cost of the system can be reduced, and the waste of hardware resources can be avoided.

[0033] Referring to Figure 2, A power converter provided by an embodiment of the present application includes: a DC-DC conversion circuit, a DC bus, and a DC-AC conversion circuit. Among them, one end of the DC-DC conversion circuit is used to connect to a DC source, and the DC source can specifically be a photovoltaic module or an energy storage battery. The other end of the DC-DC conversion circuit is connected to one end of the DC-AC conversion circuit through the DC bus, and the other end of the DC-AC conversion circuit is used to connect to the power grid or a load. The DC-DC conversion circuit is used to perform voltage conversion on the electric energy from the photovoltaic module or the energy storage battery and output it to the DC bus; the DC-AC conversion circuit is used to convert the bus voltage Vbus of the DC bus into alternating current and output it to the power grid.

[0034] When the power grid is normal, that is, when the voltage of the power grid is the rated voltage, the rated voltage can be a set voltage range. For example, within ±10% of 220V belongs to the normal situation of the power grid. Due to the uncontrolled rectification function of the DC-AC conversion circuit, the bus voltage of the DC bus is the first voltage value, and the first voltage value is, for example, 800V.

[0035] When the power grid undergoes high-voltage ride-through, that is, when the voltage of the power grid rises to more than the first multiple of the rated voltage. For example, when the voltage of the power grid rises to more than 110% of 220V, due to the uncontrolled rectification function of the DC-AC conversion circuit, the bus voltage rises as the voltage of the power grid rises. Specifically, the bus voltage rises from the first voltage value when the power grid is normal to the second voltage value. For example, it rises from 800V to 900V. At this time, if the external characteristics of the DC-DC conversion circuit are not changed, then because the second voltage value exceeds the range within which the devices of the DC-DC conversion circuit can operate normally, in order to avoid the devices from bearing a large power, the DC-DC conversion circuit will reduce the maximum output power. For example, the maximum output power is reduced from 100kW to 80kW. The DC-DC conversion circuit needs to output power within a range less than or equal to the maximum output power. The reduction of the maximum output power causes the bus voltage to decrease. For example, the bus voltage decreases from 900V to 800V. When the bus voltage drops to within the normal operating range of the DC-DC conversion circuit, the DC-DC conversion circuit will restore the maximum output power. For example, the maximum output power is restored from 80kW to 100kW, causing the bus voltage to rise again. For example, the bus voltage rises from 800V to 900V. The above process repeats, resulting in the oscillation of the bus voltage and making the system unstable.

[0036] Refer to Figure 3, in the embodiment of the present application, when the power grid experiences high-voltage ride-through, for example, when the voltage of the power grid is 1.1 times of 220V, the DC / DC (direct current to direct current conversion circuit) switches to the external characteristics of high-voltage ride-through according to the control signal, that is, the DC / DC does not reduce the maximum output power according to the control signal. For example, the maximum output power remains at 100kW before the high-voltage ride-through occurs to stabilize the bus voltage. For example, the bus voltage is stabilized at 900V to avoid the oscillation of the bus voltage and stabilize the system. Specifically, when the voltage of the power grid rises to be greater than the first multiple of the rated voltage, that is, when the power grid experiences high-voltage ride-through, the DC / DC adjusts the maximum output power to the first power according to the received control signal, so that the DC / DC outputs power within the range less than or equal to the maximum output power. The first power needs to be greater than the second power. For example, the first power is 100kW and the second power is 80kW. The second power is: when the bus voltage is the second voltage value, the maximum output power reduced by the DC / DC when no control signal is received. The second power can also be understood as: when the power grid is normal, that is, when the voltage of the power grid is the rated voltage and the bus voltage is set to the second voltage value, the maximum output power of the DC / DC. Since the second voltage value exceeds the normal operating range of the components of the DC / DC, in order to avoid the components from bearing a large power, the DC / DC will reduce the maximum output power. For example, the maximum output power, that is, the second power, is reduced from 100kW to 80kW, so that the DC / DC outputs power within the range less than or equal to the second power, that is, 80kW.

[0037] In the present application, during the high-voltage ride-through of the power grid, the DC / DC increases the output capacity, that is, the maximum output power, according to the control signal under the condition of a higher bus voltage. By means of the DC / DC briefly bearing a higher maximum output power, the hardware cost of the system can be reduced and the waste of hardware resources can be avoided.

[0038] Refer to Figure 4, in some embodiments of the present application, when the power grid experiences high-voltage ride-through, after the DC / DC conversion circuit switches to the external characteristics of high-voltage ride-through, it can control the DC / DC conversion circuit not to reduce the maximum output power. Specifically, it can keep the maximum output power of the DC / DC conversion circuit not less than the maximum output power when the power grid is normal. For example, before high-voltage ride-through occurs and the power grid is normal, that is, when the voltage of the power grid is the rated voltage and the bus voltage is the first voltage value, the maximum output power of the DC / DC conversion circuit is the third power. Then, when high-voltage ride-through occurs, that is, after the bus voltage rises, the DC / DC conversion circuit can control the maximum output power, that is, the first power, to be greater than or equal to the third power according to the control signal. For example, both are 100 kw, to ensure the stability of the system load during the normal switching of the power grid to high-voltage ride-through.

[0039] In the present application, the DC / AC conversion circuit connected to the power grid can be used to collect the voltage of the power grid and determine the level of high-voltage ride-through of the power grid, and then send the corresponding high-voltage ride-through flag to the DC / DC conversion circuit as a control signal. After receiving the high-voltage ride-through flag, that is, the control signal, the DC / DC conversion circuit switches to the external characteristics of high-voltage ride-through, that is, adjusts the maximum output power to the first power to increase the output capacity and avoid bus voltage oscillation. Until the high-voltage ride-through flag disappears, it resumes to the normal external characteristics and adjusts the maximum output power to the third power to ensure the stability of the system load during the normal switching of the power grid to high-voltage ride-through.

[0040] In the present application, when the power grid experiences high-voltage ride-through, according to the different multiples of the voltage of the power grid rising above the rated voltage, the rising ratio of the bus voltage is also different. When the voltage of the power grid rises to different multiples of the rated voltage, the DC / DC conversion circuit can maintain a fixed maximum output power, that is, the first power. Specifically, when the voltage of the power grid rises to the first multiple greater than the rated voltage and when the voltage of the power grid rises to the second multiple greater than the rated voltage, the DC / DC conversion circuit controls the maximum output power to be the fixed first power. For example, when the first multiple of the voltage of the power grid to the rated voltage is 1.2 times and the second multiple is 1.3 times, the maximum output power of the DC / DC conversion circuit, that is, the first power, can be controlled to be the same as the third power, which is 100 kw, to ensure the stability of the system load during the normal switching of the power grid to high-voltage ride-through.

[0041] In some embodiments of the present application, when the power grid experiences high-voltage ride-through, the DC / AC conversion circuit (DC / DC) can increase the maximum output power within a short period of time to withstand a higher output power. That is, when the voltage of the power grid rises to a first multiple greater than the rated voltage, the DC / AC conversion circuit (DC / DC) adjusts the maximum output power to a first power within a first duration. If the power grid does not return to normal after the first duration, in order to prevent the components in the DC / AC conversion circuit (DC / DC) from being damaged due to overloading, it is necessary to reduce the maximum output power of the DC / AC conversion circuit (DC / DC). The DC / AC conversion circuit (DC / DC) adjusts the maximum output power to a fourth power, and the fourth power is less than the first power, to ensure the safe use of the components in the DC / AC conversion circuit (DC / DC).

[0042] In some embodiments of the present application, when the power grid experiences high-voltage ride-through at different levels, the DC / AC conversion circuit (DC / DC) can be controlled to maintain the high-voltage ride-through external characteristics for different durations, that is, the durations of maintaining the maximum output power at the first power are different. Specifically, when the voltage of the power grid rises to a first multiple greater than the rated voltage, the DC / AC conversion circuit adjusts the maximum output power to the first power within a first duration, and adjusts the maximum output power to the fourth power after the first duration. When the voltage of the power grid rises to a second multiple greater than the rated voltage, the DC / AC conversion circuit adjusts the maximum output power to the first power within a second duration, and adjusts the maximum output power to the fourth power after the second duration. The first multiple is greater than the second multiple, and the first duration is less than the second duration. In other words, the higher the high-voltage ride-through level, the shorter the duration for which the DC / AC conversion circuit (DC / DC) maintains the high-voltage ride-through external characteristics. For example, when the voltage of the power grid rises to more than 110% to 120% of the rated voltage, the DC / AC conversion circuit (DC / DC) can maintain the adjustment of the maximum output power at the first power for no less than 10 s; when the voltage of the power grid rises to more than 120% to 125% of the rated voltage, the DC / AC conversion circuit (DC / DC) can maintain the adjustment of the maximum output power at the first power for no less than 1 s; when the voltage of the power grid rises to more than 125% to 130% of the rated voltage, the DC / AC conversion circuit (DC / DC) can maintain the adjustment of the maximum output power at the first power for no less than 500 ms.

[0043] Based on the same inventive concept, an embodiment of the present application also provides a control method for a power converter, which may specifically include the following steps:

[0044] When the power grid is normal, that is, when the voltage of the power grid is the rated voltage, the rated voltage can be a set voltage range. For example, within ±10% of 220V belongs to the normal situation of the power grid. Due to the uncontrolled rectification function of the DC-to-AC conversion circuit in the power converter, the bus voltage of the DC bus is the first voltage value, that is, the DC-to-AC conversion circuit in the power converter controls the bus voltage of the DC bus in the power converter to be the first voltage value. For example, the first voltage value is 800V.

[0045] When the power grid undergoes high-voltage ride-through, that is, when the voltage of the power grid rises to a first multiple greater than the rated voltage. For example, when the voltage of the power grid rises to more than 110% of 220V, due to the uncontrolled rectification function of the DC-to-AC conversion circuit, the bus voltage rises as the grid voltage rises. Specifically, the bus voltage rises from the first voltage value when the power grid is normal to the second voltage value. For example, it rises from 800V to 900V. At this time, if the external characteristics of the DC-to-DC conversion circuit are not changed, then because the second voltage value exceeds the range in which the devices of the DC-to-DC conversion circuit can work normally, in order to avoid the devices from bearing a large power, the DC-to-DC conversion circuit will reduce the maximum output power. For example, the maximum output power is reduced from 100kW to 80kW. The DC-to-DC conversion circuit needs to output power within a range less than or equal to the maximum output power. The reduction of the maximum output power causes the bus voltage to decrease. For example, the bus voltage decreases from 900V to 800V. When the bus voltage drops to within the normal working range of the DC-to-DC conversion circuit, the DC-to-DC conversion circuit will restore the maximum output power. For example, the maximum output power is restored from 80kW to 100kW, causing the bus voltage to rise again. For example, the bus voltage rises from 800V to 900V. The above process repeats, resulting in the oscillation of the bus voltage and making the system unstable.

[0046] In the embodiments of the present application, when the power grid undergoes high-voltage ride-through, for example, when the voltage of the power grid is 1.1 times of 220V, the DC-DC conversion circuit switches to the external characteristics of high-voltage ride-through according to the control signal, that is, the DC-DC conversion circuit does not reduce the maximum output power according to the control signal. For example, the maximum output power remains at 100kW before the high-voltage ride-through occurs to stabilize the bus voltage. For example, the bus voltage is stabilized at 900V to avoid the oscillation of the bus voltage and stabilize the system. Specifically, when the voltage of the power grid rises to be greater than the first multiple of the rated voltage, that is, when the power grid undergoes high-voltage ride-through, the DC-DC conversion circuit adjusts the maximum output power to the first power according to the received control signal, so that the DC-DC conversion circuit outputs power within the range less than or equal to the maximum output power. The first power needs to be greater than the second power. For example, the first power is 100kW and the second power is 80kW. The second power is: when the bus voltage is the second voltage value, the maximum output power reduced by the DC-DC conversion circuit without receiving the control signal. The second power can also be understood as: when the power grid is normal, that is, when the voltage of the power grid is the rated voltage and the bus voltage is set to the second voltage value, the maximum output power of the DC-DC conversion circuit. Since the second voltage value exceeds the normal working range of the devices of the DC-DC conversion circuit, in order to avoid the devices from bearing a large power, the DC-DC conversion circuit will reduce the maximum output power. For example, the maximum output power, that is, the second power, is reduced from 100kW to 80kW, so that the DC-DC conversion circuit outputs power within the range less than or equal to the second power, that is, 80kW.

[0047] In the present application, during the high-voltage ride-through of the power grid, by controlling the DC-DC conversion circuit to increase the output capacity, that is, the maximum output power, according to the control signal under the condition of a higher bus voltage, and by means of the DC-DC conversion circuit briefly bearing a higher output power, the hardware cost of the system can be reduced and the waste of hardware resources can be avoided.

[0048] In some embodiments of the present application, when the power grid undergoes high-voltage ride-through, after the DC-DC conversion circuit switches to the external characteristics of high-voltage ride-through, it can control the DC-DC conversion circuit not to reduce the maximum output power. Specifically, it can keep the maximum output power of the DC-DC conversion circuit not less than the maximum output power when the power grid is normal. For example, before the high-voltage ride-through occurs and the power grid is normal, that is, when the voltage of the power grid is the rated voltage and the bus voltage is the first voltage value, the maximum output power of the DC-DC conversion circuit is the third power. Then, when the high-voltage ride-through occurs, that is, after the bus voltage rises, the DC-DC conversion circuit can control the maximum output power, that is, the first power, to be greater than or equal to the third power according to the control signal. For example, both are 100kW, so as to ensure the load-carrying stability of the system during the normal switching of the power grid to high-voltage ride-through.

[0049] In this application, a DC-AC conversion circuit connected to the power grid can be used to collect the voltage of the power grid, and determine the level of high-voltage ride-through of the power grid. Then, a corresponding high-voltage ride-through flag is sent to the DC-AC conversion circuit as a control signal. After receiving the high-voltage ride-through flag, i.e., the control signal, the DC-AC conversion circuit switches to the high-voltage ride-through external characteristic, that is, adjusts the maximum output power to the first power to increase the output capacity and avoid bus voltage oscillation. Until the high-voltage ride-through flag disappears, it resumes to the normal external characteristic and adjusts the maximum output power to the third power to ensure the stability of the system under load during the normal switching of the power grid to high-voltage ride-through.

[0050] In this application, when the power grid undergoes high-voltage ride-through, according to the different multiples of the voltage of the power grid rising above the rated voltage, the ratio of the bus voltage rise is also different. When the voltage of the power grid rises to different multiples of the rated voltage, the DC-DC conversion circuit can maintain a fixed maximum output power, i.e., the first power. Specifically, when the voltage of the power grid rises above the first multiple of the rated voltage and when the voltage of the power grid rises above the second multiple of the rated voltage, the DC-DC conversion circuit controls the maximum output power to be the fixed first power. For example, when the first multiple of the voltage of the power grid to the rated voltage is 1.2 times and the second multiple is 1.3 times, the maximum output power of the DC-DC conversion circuit, i.e., the first power, can be controlled to be the same as the third power, which is 100 kw, to ensure the stability of the system under load during the normal switching of the power grid to high-voltage ride-through.

[0051] In some embodiments of this application, when the power grid undergoes high-voltage ride-through, the DC-AC conversion circuit can increase the maximum output power within a short time to withstand a higher output power. That is, when the voltage of the power grid rises above the first multiple of the rated voltage, the DC-AC conversion circuit adjusts the maximum output power to the first power within the first time period. If the power grid does not return to normal after the first time period, in order to avoid damage to the devices in the DC-AC conversion circuit due to overloading, the maximum output power of the DC-AC conversion circuit needs to be reduced. The DC-AC conversion circuit adjusts the maximum output power to the fourth power, and the fourth power is less than the first power to ensure the safe use of the devices in the DC-AC conversion circuit.

[0052] In some embodiments of the present application, when high-voltage ride-through of different levels occurs in the power grid, the DC-AC conversion circuit can be controlled to maintain the high-voltage ride-through external characteristics for different durations, that is, the durations for maintaining the maximum output power at the first power are different. Specifically, when the voltage of the power grid rises to more than the first multiple of the rated voltage, the DC-AC conversion circuit adjusts the maximum output power to the first power within the first duration, and adjusts the maximum output power to the fourth power after the first duration. When the voltage of the power grid rises to more than the second multiple of the rated voltage, the DC-AC conversion circuit adjusts the maximum output power to the first power within the second duration, and adjusts the maximum output power to the fourth power after the second duration. The first multiple is greater than the second multiple, and the first duration is less than the second duration. In other words, the higher the high-voltage ride-through level, the shorter the duration for which the DC-AC conversion circuit maintains the high-voltage ride-through external characteristics. For example, when the voltage of the power grid rises to more than 110% to 120% of the rated voltage, the DC-AC conversion circuit can maintain the adjustment of the maximum output power to the first power for no less than 10 s; when the voltage of the power grid rises to more than 120% to 125% of the rated voltage, the DC-AC conversion circuit can maintain the adjustment of the maximum output power to the first power for no less than 1 s; when the voltage of the power grid rises to more than 125% to 130% of the rated voltage, the DC-AC conversion circuit can maintain the adjustment of the maximum output power to the first power for no less than 500 ms.

[0053] Based on the same inventive concept, an embodiment of the present application further provides an energy storage system, including: an energy storage battery and the above-mentioned power converter provided in the embodiment of the present application. The power converter is connected to the energy storage battery, and the power converter is used to convert the electric energy provided by the energy storage battery into alternating current and output it to the power grid or load.

[0054] As described above, the above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, and all should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A power converter, characterized in that: include: DC to DC conversion circuit, DC bus and DC to AC conversion circuit; The DC-to-DC conversion circuit is used to convert the electric energy from the photovoltaic module or the energy storage battery into a voltage and output it to the DC bus; The DC to AC conversion circuit is used to convert the bus voltage of the DC bus into an AC voltage and output it to the power grid; The DC-to-AC conversion circuit is further used to control the bus voltage to be a first voltage value when the voltage of the power grid is the rated voltage; and to control the bus voltage to increase from the first voltage value to a second voltage value when the voltage of the power grid increases to a first multiple greater than the rated voltage; The DC-to-DC conversion circuit is further used to adjust the maximum output power to a first power according to a control signal when the voltage of the power grid increases to a first multiple greater than the rated voltage, and output power within a range less than or equal to the maximum output power; Among them, the first power is greater than the second power; the second power is: when the bus voltage is the second voltage value, the maximum output power of the DC-to-DC conversion circuit in the absence of the control signal.

2. The power converter according to claim 1, characterized in that The DC-to-DC conversion circuit is also used to control the maximum output power to be a third power when the voltage of the power grid is the rated voltage and the bus voltage is the first voltage value, and the first power is greater than or equal to the third power.

3. The power converter according to claim 1 or 2, characterized in that: The DC-to-AC conversion circuit is also used to send the control signal to the DC-to-DC conversion circuit when the voltage of the power grid increases to a first multiple greater than the rated voltage and when the bus voltage is controlled to increase from the first voltage value to a second voltage value.

4. The power converter according to any one of claims 1 to 3, characterized in that: The DC-to-DC conversion circuit is further configured to control the maximum output power to be the first power when the voltage of the power grid increases to a second multiple greater than the rated voltage.

5. The power converter according to any one of claims 1 to 4, characterized in that: The DC-to-DC conversion circuit is also used to, when the voltage of the power grid rises to a first multiple greater than the rated voltage, adjust the maximum output power to the first power within a first time period, and adjust the maximum output power to a fourth power after the first time period, the fourth power being less than the first power.

6. The power converter according to claim 5, characterized in that: The DC-to-DC conversion circuit is also used to, when the voltage of the power grid rises to a second multiple greater than the rated voltage, adjust the maximum output power to the first power within a second time period, and adjust the maximum output power to the fourth power after the second time period; the first multiple is greater than the second multiple, and the first time period is less than the second time period.

7. An energy storage system, characterized in that: include: An energy storage battery, and a power converter as described in any one of claims 1 to 6, wherein the power converter is connected to the energy storage battery, and the power converter is used to convert the electric energy provided by the energy storage battery into alternating current and output it to a power grid.

8. A control method for a power converter, characterized in that: include: When the voltage of the power grid is the rated voltage, the DC-to-AC conversion circuit in the power converter controls the bus voltage of the DC bus in the power converter to be a first voltage value; When the voltage of the power grid increases to a first multiple greater than the rated voltage, the DC-to-AC conversion circuit controls the bus voltage to increase from the first voltage value to a second voltage value, and the DC-to-DC conversion circuit in the power converter adjusts the maximum output power to the first power according to the control signal, and outputs power within a range less than or equal to the maximum output power; Among them, the first power is greater than the second power; the second power is: when the bus voltage is the second voltage value, the maximum output power of the DC-to-DC conversion circuit in the absence of the control signal.

9. The control method according to claim 8, characterized in that: Also includes: When the voltage of the power grid is the rated voltage and the bus voltage is the first voltage value, the DC-to-DC conversion circuit controls the maximum output power to be a third power, and the first power is greater than or equal to the third power.

10. The control method according to claim 8 or 9, characterized in that: Also includes: When the voltage of the power grid increases to a first multiple greater than the rated voltage, the DC-to-AC conversion circuit controls the bus voltage to increase from the first voltage value to a second voltage value, and sends the control signal to the DC-to-DC conversion circuit.

11. The control method according to any one of claims 8 to 10, characterized in that: Also includes: When the voltage of the power grid increases to a second multiple greater than the rated voltage, the DC-to-DC conversion circuit controls the maximum output power to be the first power.

12. The control method according to any one of claims 8 to 11, characterized in that: Also includes: When the voltage of the power grid increases to a first multiple greater than the rated voltage, the DC-to-DC conversion circuit adjusts the maximum output power to the first power within a first time period, and adjusts the maximum output power to a fourth power after the first time period, and the fourth power is less than the first power.

13. The control method according to claim 12, characterized in that: Also includes: When the voltage of the power grid increases to a second multiple greater than the rated voltage, the DC-to-DC conversion circuit adjusts the maximum output power to the first power within a second time period, and adjusts the maximum output power to the fourth power after the second time period; the first multiple is greater than the second multiple, and the first time period is less than the second time period.

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