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. The power converter comprises a DC-to-DC conversion circuit, a DC bus, a DC-to-AC conversion circuit and a controller. The DC-to-DC conversion circuit is used for carrying out voltage conversion on the first DC from the photovoltaic module or the energy storage battery, and outputting a second DC to the DC-to-AC conversion circuit through the DC bus. The DC-AC conversion circuit is used for converting the second DC into AC and outputting the AC to a power grid. And when the power converter is in low voltage ride through, the controller controls the voltage value of the second direct current to a direct current bus voltage threshold value and controls the direct current-to-alternating current conversion circuit to output reactive current to the power grid. Wherein the voltage threshold value of the direct current bus is not lower than the amplitude value of the line voltage of the alternating current output by the direct current-to-alternating current conversion circuit. On the basis, voltage and current stress needing to be borne by devices of the DC-to-AC conversion circuit can be reduced, so that the loss of the devices is reduced, and the low-voltage ride-through overload capacity is improved.

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 power grid usually uses a bidirectional boost circuit in 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) in the rear stage of the DC bus to convert the bus voltage to AC. When low voltage ride through (LVRT) occurs, the power generation equipment needs to ensure that it does not disconnect from the power grid within a certain time range. At the same time, according to relevant standards, the power converter in the power generation equipment needs to provide a certain reactive current to support the power grid during low voltage ride through. In this case, the output current of the boost circuit is too high, which may cause excessive device losses in the inverter part and overheating. Therefore, how to reduce the device loss of the inverter during low voltage ride through and improve the low voltage ride through capability is a technical problem that needs to be solved in this field. Summary of the invention

[0003] The present application provides a power converter, a control method thereof, and an energy storage system, which are used to reduce the device loss of the inverter during low voltage ride-through and improve the low voltage ride-through capability.

[0004] In the first aspect, the present application provides a power converter, including: a DC-to-DC conversion circuit, a DC bus, a DC-to-AC conversion circuit and a controller. Among them, the DC-to-DC conversion circuit is used to convert the voltage of the first DC power from the photovoltaic component or the energy storage battery, and output the second DC power Vbus to the DC-to-AC conversion circuit through the DC bus, and the DC voltage of the DC bus is the voltage value of the second DC power; the DC-to-AC conversion circuit is used to convert the second DC power into AC power and output it to the power grid. When the power converter is in the process of low voltage crossing, the controller is used to control the voltage value of the second DC power to the DC bus voltage threshold, and the DC bus voltage threshold is not lower than the amplitude of the line voltage of the AC power output by the DC-to-AC conversion circuit. For example, the DC bus voltage threshold can be set to the minimum grid-connected DC bus voltage required for the DC-to-AC conversion circuit to be connected to the grid during the low voltage crossing period, that is: Among them, V g It is the effective value of the grid-connected line voltage when the DC-to-AC conversion circuit is actually running, ΔV is the preset bias voltage, and ΔV>0, and the preset bias voltage is usually between 10V and 50V. When the power converter is in the low voltage ride-through process, the controller is also used to control the DC-to-AC conversion circuit to output reactive current to the grid to support the grid.

[0005] In the present application, when low voltage ride-through occurs, the bus voltage at the input end of the subsequent DC-to-AC conversion circuit can be reduced by controlling the front-stage DC-to-DC conversion circuit in the power converter to operate to output a fixed DC bus voltage threshold, thereby reducing the voltage and current stress that the components of the DC-to-AC conversion circuit need to withstand during the low voltage ride-through, thereby reducing the component losses of the DC-to-AC conversion circuit and improving the low voltage ride-through overload capability.

[0006] In an embodiment of the present application, the DC-to-DC conversion circuit and the DC-to-AC conversion circuit can be arranged in the same device or in different devices. For example, the DC-to-DC conversion circuit is arranged in the optimizer of a photovoltaic device or the DC converter of an energy storage device, and the DC-to-AC conversion circuit is arranged in an inverter. The present application does not limit this.

[0007] In an embodiment of the present application, when low voltage ride-through occurs, that is, when the effective value of the grid voltage drops to a set value, the working mode of the DC / DC converter circuit can be controlled according to the relationship between the voltage value of the first DC power of the DC source and the DC bus voltage threshold. Specifically, when the voltage value of the first DC power is greater than the DC bus voltage threshold, the DC / DC converter circuit can be controlled to operate in a step-down mode, and specifically, the voltage value of the second DC power output by the DC / DC converter circuit can be controlled to be reduced to the DC bus voltage threshold. When the voltage value of the first DC power is less than the DC bus voltage threshold, the DC / DC converter circuit can be controlled to operate in a boost mode, and specifically, the voltage value of the second DC power output by the DC / DC converter circuit can be controlled to be increased to the DC bus voltage threshold. When the voltage value of the first DC power is equal to the DC bus voltage threshold, the DC / DC converter circuit can be controlled to operate in a pass-through mode, and specifically, the voltage value of the second DC power output by the DC / DC converter circuit can be controlled to be the voltage value of the first DC power.

[0008] In some embodiments of the present application, the DC-to-DC conversion circuit may specifically include: a first bridge arm, a second bridge arm, and an inductor. The first bridge arm and the second bridge arm each include an upper bridge arm and a lower bridge arm, the two ends of the first bridge arm are used to be respectively connected to the positive and negative poles of the photovoltaic component or the energy storage battery, the two ends of the second bridge arm are respectively connected to the positive and negative poles of the DC bus, and the lower bridge arm of the first bridge arm is connected to the lower bridge arm of the second bridge arm, so that the negative pole of the DC source is connected to the negative pole of the DC bus. The connection point of the upper bridge arm and the lower bridge arm in the first bridge arm is the midpoint of the first bridge arm, the connection point of the upper bridge arm and the lower bridge arm in the second bridge arm is the midpoint of the second bridge arm, the midpoint of the first bridge arm is connected to one end of the inductor, and the midpoint of the second bridge arm is connected to the other end of the inductor. When the voltage value of the first direct current is less than the DC bus voltage threshold, the following control method is specifically adopted to realize the DC-to-DC conversion circuit to work in the boost mode: the upper bridge arm of the first bridge arm is in the on state, the lower bridge arm of the first bridge arm is in the off state, and the upper bridge arm and the lower bridge arm in the second bridge arm are in the complementary on state, so as to realize the boost function. Among them, the two bridge arms are in the complementary on state means that when one bridge arm is in the on state, the other bridge arm is in the off state. When the voltage value of the first direct current is greater than the DC bus voltage threshold, the following control method is specifically adopted to realize the DC-to-DC conversion circuit to work in the step-down mode: the upper bridge arm of the second bridge arm is in the on state, the lower bridge arm of the second bridge arm is in the off state, and the upper bridge arm and the lower bridge arm in the first bridge arm are in the complementary on state, so as to realize the step-down function. When the voltage value of the first direct current is equal to the DC bus voltage threshold, the following control method is specifically adopted to realize that the DC-to-DC conversion circuit operates in the pass-through mode: the upper bridge arm of the first bridge arm and the upper bridge arm of the second bridge arm are both in the on state, the lower bridge arm of the first bridge arm and the lower bridge arm of the second bridge arm are both in the off state, and the DC source is directly connected to the DC bus.

[0009] In some embodiments of the present application, the upper bridge arm and the lower bridge arm of the first bridge arm and the second bridge arm may each include a switch tube. For example, the upper bridge arm of the first bridge arm includes the first switch tube, the lower bridge arm of the first bridge arm includes the second switch tube, the lower bridge arm of the second bridge arm includes the third switch tube, and the upper bridge arm of the second bridge arm includes the fourth switch tube. The connection point of the first switch tube and the second switch tube is connected to one end of the inductor, and the connection point of the third switch tube and the fourth switch tube is connected to the other end of the inductor. When the voltage value of the first direct current is less than the DC bus voltage threshold, the following control method is specifically adopted to realize that the DC-to-DC conversion circuit operates in a boost mode: the first switch tube is in a conducting state, the second switch tube is in an off state, and the third switch tube and the fourth switch tube are in a complementary conducting state to realize a boost function. Among them, two switch tubes are in a complementary conducting state, which means that when one switch tube is in a conducting state, the other switch tube is in an off state. When the voltage value of the first direct current is greater than the DC bus voltage threshold, the following control method is specifically adopted to realize the DC-to-DC conversion circuit to work in the step-down mode: the third switch tube is in the on state, the fourth switch tube is in the off state, and the first switch tube and the second switch tube are in the complementary on state to realize the step-down function. When the voltage value of the first direct current is equal to the DC bus voltage threshold, the following control method is specifically adopted to realize the DC-to-DC conversion circuit to work in the pass-through mode: the first switch tube and the third switch tube are both in the on state, the second switch tube and the fourth switch tube are both in the off state, and the DC source is directly connected to the DC bus.

[0010] In some other embodiments of the present application, both the upper bridge arm and the lower bridge arm may include two switch tubes connected in series. Specifically, the upper bridge arm of the first bridge arm may include a first switch tube and a second switch tube connected in series, the lower bridge arm of the first bridge arm includes a third switch tube and a fourth switch tube connected in series, the upper bridge arm of the second bridge arm includes a fifth switch tube and a sixth switch tube connected in series, and the lower bridge arm of the second bridge arm includes a seventh switch tube and an eighth switch tube connected in series. In the first bridge arm, there is a first capacitor between the connection point of the two switch tubes of the upper bridge arm, i.e., the first switch tube and the second switch tube, and the connection point of the two switch tubes of the lower bridge arm, i.e., the third switch tube and the fourth switch tube. In the second bridge arm, there is a second capacitor between the connection point of the two switch tubes of the upper bridge arm, i.e., the fifth switch tube and the sixth switch tube, and the connection point of the two switch tubes of the lower bridge arm, i.e., the seventh switch tube and the eighth switch tube. When the voltage value of the first direct current is greater than the DC bus voltage threshold value and the DC-to-DC conversion circuit operates in the step-down mode, the upper bridge arm and the lower bridge arm in the first bridge arm are in a complementary conduction state, specifically referring to: when the current flowing through the inductor points from the first bridge arm to the second bridge arm, that is, when the current points from the second switch tube to the fifth switch tube, the two switch tubes of the upper bridge arm in the first bridge arm, that is, the first switch tube and the second switch tube, are in a complementary conduction state, and the two switch tubes of the lower bridge arm in the first bridge arm, that is, the third switch tube and the fourth switch tube, are in an off state. When the current flowing through the inductor points from the second bridge arm to the first bridge arm, that is, when the current points from the fifth switch tube to the second switch tube, the two switch tubes of the lower bridge arm in the first bridge arm, that is, the third switch tube and the fourth switch tube, are in a complementary conduction state, and the two switch tubes of the upper bridge arm in the first bridge arm, that is, the first switch tube and the second switch tube, are in an off state. The upper bridge arm of the second bridge arm, that is, the fifth switch tube and the sixth switch tube, are in a conducting state, and the lower bridge arm of the second bridge arm, that is, the seventh switch tube and the eighth switch tube, are in an off state. When the voltage value of the first direct current is less than the DC bus voltage threshold and the DC-to-DC conversion circuit operates in the boost mode, the upper bridge arm and the lower bridge arm in the second bridge arm are in a complementary conduction state, specifically referring to: when the current flowing through the inductor points from the first bridge arm to the second bridge arm, that is, when the current points from the second switch tube to the fifth switch tube, the two switch tubes of the upper bridge arm in the second bridge arm, that is, the fifth switch tube and the sixth switch tube, are in a complementary conduction state, and the two switch tubes of the lower bridge arm in the second bridge arm, that is, the seventh switch tube and the eighth switch tube, are in an off state. When the current flowing through the inductor points from the second bridge arm to the first bridge arm, that is, when the current points from the fifth switch tube to the second switch tube, the two switch tubes of the lower bridge arm in the second bridge arm, that is, the seventh switch tube and the eighth switch tube, are in a complementary conduction state, and the two switch tubes of the upper bridge arm in the second bridge arm, that is, the fifth switch tube and the sixth switch tube, are in an off state. The upper bridge arm of the first bridge arm, that is, the first switch tube and the second switch tube, are in a conducting state, and the lower bridge arm of the first bridge arm, that is, the third switch tube and the fourth switch tube, are in an off state.When the voltage value of the first direct current is equal to the DC bus voltage threshold and the DC-to-DC conversion circuit operates in the pass-through mode, the upper bridge arm of the first bridge arm, i.e., the first switch tube and the second switch tube, and the upper bridge arm of the second bridge arm, i.e., the fifth switch tube and the sixth switch tube, are all in the on state, the lower bridge arm of the first bridge arm, i.e., the third switch tube and the fourth switch tube, and the lower bridge arm of the second bridge arm, i.e., the seventh switch tube and the eighth switch tube, are all in the off state, and the DC source is directly connected to the DC bus.

[0011] In some embodiments of the present application, the DC-to-DC conversion circuit may further include: a first relay connected in parallel with the upper bridge arm of the first bridge arm. When the voltage value of the first DC power is less than or equal to the DC bus voltage threshold and the DC-to-DC conversion circuit operates in a boost mode or a pass-through mode, the first relay is controlled to close, and the current flows through the first relay with lower impedance instead of the upper bridge arm of the first bridge arm, which can reduce the loss of the DC-to-DC conversion circuit. When the voltage value of the first DC power is greater than the DC bus voltage threshold and the DC-to-DC conversion circuit operates in a step-down mode, the first relay is controlled to be disconnected to ensure that the upper bridge arm and the lower bridge arm in the first bridge arm are in a complementary conduction state, thereby realizing the step-down function.

[0012] In other embodiments of the present application, the DC-to-DC conversion circuit may further include: a second relay connected in parallel with the upper bridge arm of the second bridge arm. When the voltage value of the first DC power is greater than or equal to the DC bus voltage threshold and the DC-to-DC conversion circuit operates in a buck mode or a pass-through mode, the second relay is controlled to close, and the current flows through the second relay with lower impedance instead of the upper bridge arm of the second bridge arm, which can reduce the loss of the DC-to-DC conversion circuit. When the voltage value of the first DC power is less than the DC bus voltage threshold and the DC-to-DC conversion circuit operates in a boost mode, the second relay is controlled to be disconnected to ensure that the upper bridge arm and the lower bridge arm in the second bridge arm are in a complementary conduction state, thereby realizing the boost function.

[0013] In other embodiments of the present application, the DC-to-DC conversion circuit may also include: a first relay connected in parallel with the upper arm of the first bridge arm, and a second relay connected in parallel with the upper arm of the second bridge arm. When the voltage value of the first DC power is less than the DC bus voltage threshold and the DC-to-DC conversion circuit operates in the boost mode, the first relay is controlled to be closed and the second relay is disconnected, and the current flows through the first relay with lower impedance instead of the upper arm of the first bridge arm, which can reduce the loss of the DC-to-DC conversion circuit. When the voltage value of the first DC power is greater than the DC bus voltage threshold and the DC-to-DC conversion circuit operates in the step-down mode, the first relay is controlled to be disconnected and the second relay is closed, and the current flows through the second relay with lower impedance instead of the upper arm of the second bridge arm, which can reduce the loss of the DC-to-DC conversion circuit. When the voltage value of the first direct current is equal to the DC bus voltage threshold and the DC-to-DC conversion circuit operates in the pass-through mode, the first relay and the second relay are controlled to be closed, the current flows through the first relay with lower impedance and flows through the second relay with lower impedance after passing through the inductor, and the current does not flow through the upper bridge arm of the first bridge arm and the upper bridge arm of the second bridge arm, thereby reducing the loss of the DC-to-DC conversion circuit.

[0014] In some other embodiments of the present application, the DC-to-DC conversion circuit may also include: a third relay, the third relay being connected between the positive pole of the input terminal of the DC-to-DC conversion circuit and the positive pole of the output terminal of the DC-to-DC conversion circuit. When the voltage value of the first DC power is less than or greater than the DC bus voltage threshold, and the DC-to-DC conversion circuit operates in a boost mode or a buck mode, the third relay is controlled to be disconnected. When the voltage value of the first DC power is equal to the DC bus voltage threshold, and the DC-to-DC conversion circuit operates in a pass-through mode, the third relay is controlled to be closed, and the current flows through the third relay with lower impedance instead of the upper bridge arm of the first bridge arm and the upper bridge arm of the second bridge arm, which can reduce the loss of the DC-to-DC conversion circuit.

[0015] In a second aspect, the present application provides a control method for a power converter, comprising the following steps:

[0016] The DC-to-DC conversion circuit in the power converter is controlled to convert the voltage of the first DC power from the photovoltaic module or the energy storage battery, and output the second DC power to the DC-to-AC conversion circuit in the power converter through the DC bus; the DC-to-AC conversion circuit is controlled to convert the second DC power into AC power and output it to the power grid.

[0017] When the power converter is in the low voltage ride-through process, the voltage value of the second DC power is controlled to the DC bus voltage threshold, and the DC-to-AC conversion circuit is controlled to output reactive current to the power grid; the DC bus voltage threshold is not lower than the amplitude of the line voltage of the AC power output by the DC-to-AC conversion circuit.

[0018] In the present application, when low voltage ride-through occurs, the bus voltage at the input end of the subsequent DC-to-AC conversion circuit can be reduced by controlling the front-stage DC-to-DC conversion circuit in the power converter to operate to output a fixed DC bus voltage threshold, thereby reducing the voltage and current stress that the components of the DC-to-AC conversion circuit need to withstand during the low voltage ride-through, thereby reducing the component losses of the DC-to-AC conversion circuit and improving the low voltage ride-through overload capability.

[0019] In an embodiment of the present application, when low voltage ride-through occurs, that is, when the effective value of the grid voltage drops to a set value, the working mode of the DC-to-DC conversion circuit can be controlled according to the relationship between the voltage value of the first DC power of the DC source and the DC bus voltage threshold. Specifically, when the first DC power is greater than the DC bus voltage threshold, the DC-to-DC conversion circuit can be controlled to operate in a step-down mode, and specifically, the voltage value of the second DC power output by the DC-to-DC conversion circuit can be controlled to be reduced to the DC bus voltage threshold. When the voltage value of the first DC power is less than the DC bus voltage threshold, the DC-to-DC conversion circuit can be controlled to operate in a boost mode, and specifically, the voltage value of the second DC power output by the DC-to-DC conversion circuit can be controlled to be increased to the DC bus voltage threshold. When the voltage value of the first DC power is equal to the DC bus voltage threshold, the DC-to-DC conversion circuit can be controlled to operate in a pass-through mode, and specifically, the voltage value of the second DC power output by the DC-to-DC conversion circuit can be controlled to be the voltage value of the first DC power.

[0020] In some embodiments of the present application, the DC-to-DC conversion circuit may specifically include: a first bridge arm, a second bridge arm, and an inductor. In the control method, when the voltage value of the first DC power is less than the DC bus voltage threshold, the following control method is specifically used to control the DC-to-DC conversion circuit to operate in a boost mode: control the upper bridge arm of the first bridge arm to be in a conductive state, control the lower bridge arm of the first bridge arm to be in a closed state, and control the upper bridge arm and the lower bridge arm in the second bridge arm to be in a complementary conductive state to achieve a boost function. Among them, the two bridge arms are in a complementary conductive state means that when one bridge arm is in a conductive state, the other bridge arm is in an off state. When the voltage value of the first DC power is greater than the DC bus voltage threshold, the following control method is specifically used to control the DC-to-DC conversion circuit to operate in a buck mode: control the upper bridge arm of the second bridge arm to be in a conductive state, control the lower bridge arm of the second bridge arm to be in an off state, and control the upper bridge arm and the lower bridge arm in the first bridge arm to be in a complementary conductive state to achieve a buck function. When the voltage value of the first direct current is equal to the DC bus voltage threshold, the following control method is specifically adopted to control the DC-to-DC conversion circuit to operate in the pass-through mode: the upper bridge arm of the first bridge arm and the upper bridge arm of the second bridge arm are both controlled to be in the on state, and the lower bridge arm of the first bridge arm and the lower bridge arm are controlled to be in the off state, so that the DC source is directly connected to the DC bus.

[0021] In a third aspect, an embodiment of the present application provides an energy storage system, comprising: an energy storage battery and the power converter provided in the first aspect, wherein the power converter is connected to the energy storage battery, and the power converter is used to convert a first direct current provided by the energy storage battery into alternating current and output it to a power grid or a load.

[0022] The technical effects that can be achieved by any possible design in the second and third aspects can be referred to the technical effects that can be achieved by any possible design in the first aspect, and will not be repeated here. These or other aspects of the present application will be more concise and easy to understand in the description of the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1a A schematic diagram of the structure of a power converter provided in an embodiment of the present application;

[0024] Figure 1b A schematic diagram of a control strategy for a power converter during low voltage ride-through provided in an embodiment of the present application;

[0025] Figure 2 A schematic diagram of a specific circuit structure of a power converter provided in an embodiment of the present application;

[0026] Figure 3 Another specific circuit structure diagram of the power converter provided in the embodiment of the present application;

[0027] Figure 4a Another specific circuit structure diagram of the power converter provided in the embodiment of the present application;

[0028] Figure 4b Another specific circuit structure diagram of the power converter provided in the embodiment of the present application;

[0029] Figure 4c Another specific circuit structure diagram of the power converter provided in the embodiment of the present application;

[0030] Figure 4d Another specific circuit structure schematic diagram of the power converter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings. However, the exemplary embodiments can be implemented in various forms and should not be understood as being limited to the embodiments described herein; on the contrary, these embodiments are provided to make the present application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0032] At present, in order to reduce the device loss of the inverter in the power converter, i.e. the DC to AC conversion circuit, during low voltage ride-through, larger devices are generally used in the inverter to support low voltage ride-through or limit the output capacity. The use of larger devices will increase the cost, and limiting the output capacity may result in limited power generation capacity in the event of a fault, or inability to provide reactive power support during low voltage ride-through.

[0033] In view of this, an embodiment of the present application provides a power converter, a control method thereof and an energy storage system. During a low voltage ride-through period, the bus voltage at the input end of the subsequent DC-to-AC conversion circuit (DC / AC) is reduced by controlling the front-stage DC-to-DC conversion circuit (DC / DC) in the power converter to operate to output a fixed DC bus voltage threshold, thereby reducing the voltage and current stress that the components of the DC-to-AC conversion circuit (DC / AC) need to withstand during the low voltage ride-through period, thereby reducing the component losses of the DC-to-AC conversion circuit (DC / AC) and improving the low voltage ride-through capability.

[0034] Reference Figure 1a , a power converter provided in an embodiment of the present application includes: a direct current to direct current conversion circuit (DC / DC), a direct current bus, a direct current to alternating current conversion circuit (DC / AC) and a controller. Among them, one end of the direct current to direct current conversion circuit (DC / DC) is used to connect to a direct current source, which can be a photovoltaic module or a storage battery. The other end of the direct current to direct current conversion circuit (DC / DC) is connected to one end of the direct current to alternating current conversion circuit (DC / AC) through a direct current bus, and the other end of the direct current to alternating current conversion circuit (DC / AC) is used to connect to a power grid or a load. The direct current to direct current conversion circuit (DC / DC) is used to convert the voltage of the first direct current Vbat from the photovoltaic module or the energy storage battery, and output the second direct current Vbus to the direct current to alternating current conversion circuit (DC / AC) through the direct current bus. The direct current voltage of the direct current bus is the voltage value of the second direct current; the direct current to alternating current conversion circuit (DC / AC) is used to convert the second direct current Vbus into alternating current and output it to the power grid. When the power converter is in the low voltage ride-through process, the controller is used to control the voltage value of the second DC power Vbus to a DC bus voltage threshold value, and the DC bus voltage threshold value is not lower than the amplitude of the line voltage of the AC power output by the DC / AC conversion circuit. For example, the DC bus voltage threshold value can be set to the minimum grid-connected DC bus voltage required for the DC / AC conversion circuit to be grid-connected during the low voltage ride-through period, that is: Among them, V gIt is the effective value of the grid-connected line voltage when the DC-to-AC conversion circuit is actually running, ΔV is the preset bias voltage, and ΔV>0, and the preset bias voltage is usually between 10V and 50V. When the power converter is in the low voltage ride-through process, the controller is also used to control the DC-to-AC conversion circuit (DC / AC) to output reactive current to the grid to support the grid.

[0035] In the present application, when low voltage ride-through occurs, the bus voltage at the input end of the subsequent DC-to-AC conversion circuit (DC / AC) can be reduced by controlling the front-stage DC-to-DC conversion circuit (DC / DC) in the power converter to operate to output a fixed DC bus voltage threshold, thereby reducing the voltage and current stress that the components of the DC-to-AC conversion circuit (DC / AC) need to withstand during the low voltage ride-through, thereby reducing the component losses of the DC-to-AC conversion circuit (DC / AC) and improving the low voltage ride-through overload capability.

[0036] In an embodiment of the present application, a direct current to direct current conversion circuit (DC / DC) and a direct current to alternating current conversion circuit (DC / AC) can be arranged in the same device or in different devices. For example, a direct current to direct current conversion circuit (DC / DC) is arranged in an optimizer of a photovoltaic device or a DC converter of an energy storage device, and a direct current to alternating current conversion circuit (DC / AC) is arranged in an inverter. The present application does not limit this.

[0037] In the embodiment of the present application, when low voltage ride-through occurs, that is, when the effective value of the grid voltage drops to a set value, the working mode of the DC / DC converter circuit can be controlled according to the relationship between the voltage value of the first DC power of the DC source and the DC bus voltage threshold. Figure 1b Specifically, when the voltage value of the first DC power is greater than the DC bus voltage threshold, the DC-to-DC conversion circuit can be controlled to operate in a step-down mode, and specifically, the voltage value of the second DC power output by the DC-to-DC conversion circuit can be controlled to be reduced to the DC bus voltage threshold. When the voltage value of the first DC power is less than the DC bus voltage threshold, the DC-to-DC conversion circuit can be controlled to operate in a step-up mode, and specifically, the voltage value of the second DC power output by the DC-to-DC conversion circuit can be controlled to be increased to the DC bus voltage threshold. When the voltage value of the first DC power is equal to the DC bus voltage threshold, the DC-to-DC conversion circuit can be controlled to operate in a pass-through mode, and specifically, the voltage value of the second DC power output by the DC-to-DC conversion circuit can be controlled to be the voltage value of the first DC power.

[0038] Reference Figure 1aIn the embodiment of the present application, the power converter generally further includes a collection unit. The output end of the collection unit is connected to the input end of the controller, and the output end of the controller is respectively connected to the control end of the DC-to-DC conversion circuit (DC / DC) and the control end of the DC-to-AC conversion circuit (DC / AC). The controller is used to receive and judge the parameters such as voltage, current and even temperature collected by the collection unit, and then use the control signal to control the action of the switch tube in the DC-to-DC conversion circuit (DC / DC), thereby controlling the DC-to-DC conversion circuit (DC / DC) to switch different working modes.

[0039] Reference Figure 2 In some embodiments of the present application, the DC-to-DC conversion circuit may specifically include: a first bridge arm M1, a second bridge arm M2, and an inductor L. The first bridge arm M1 and the second bridge arm M2 both include an upper bridge arm and a lower bridge arm, the two ends of the first bridge arm M1 are used to be connected to the positive and negative poles of the DC source respectively, the two ends of the second bridge arm M2 are connected to the positive and negative poles of the DC bus respectively, the lower bridge arm of the first bridge arm M1 and the lower bridge arm of the second bridge arm M2 are connected so that the negative pole of the DC source is connected to the negative pole of the DC bus. The connection point of the upper bridge arm and the lower bridge arm in the first bridge arm M1 is the midpoint of the first bridge arm M1, the connection point of the upper bridge arm and the lower bridge arm in the second bridge arm M2 is the midpoint of the second bridge arm M2, the midpoint of the first bridge arm M1 is connected to one end of the inductor L, and the midpoint of the second bridge arm M2 is connected to the other end of the inductor L. When the voltage value of the first direct current is less than the DC bus voltage threshold, the following control method is specifically adopted to realize the DC-to-DC conversion circuit (DC / DC) working in the boost mode: the upper bridge arm of the first bridge arm M1 is in the on state, the lower bridge arm of the first bridge arm M1 is in the off state, and the upper bridge arm and the lower bridge arm in the second bridge arm M2 are in the complementary on state, so as to realize the boost function. Among them, the two bridge arms are in the complementary on state means that when one bridge arm is in the on state, the other bridge arm is in the off state. When the voltage value of the first direct current is greater than the DC bus voltage threshold, the following control method is specifically adopted to realize the DC-to-DC conversion circuit (DC / DC) working in the buck mode: the upper bridge arm of the second bridge arm M2 is in the on state, the lower bridge arm of the second bridge arm M2 is in the off state, and the upper bridge arm and the lower bridge arm in the first bridge arm M1 are in the complementary on state, so as to realize the buck function. When the voltage value of the first direct current is equal to the DC bus voltage threshold, the following control method is specifically adopted to implement the DC-to-DC conversion circuit (DC / DC) operating in the pass-through mode: the upper bridge arm of the first bridge arm M1 and the upper bridge arm of the second bridge arm M2 are both in the on state, the lower bridge arm of the first bridge arm M1 and the lower bridge arm of the second bridge arm M2 are both in the off state, and the DC source is directly connected to the DC bus.

[0040] Reference Figure 2In some embodiments of the present application, the upper bridge arm and the lower bridge arm of the first bridge arm M1 and the second bridge arm M2 may each include a switch tube. For example, the upper bridge arm of the first bridge arm M1 includes the first switch tube T1, the lower bridge arm of the first bridge arm M1 includes the second switch tube T2, the lower bridge arm of the second bridge arm M2 includes the third switch tube T3, and the upper bridge arm of the second bridge arm M2 includes the fourth switch tube T4. The connection point of the first switch tube T1 and the second switch tube T2 is connected to one end of the inductor L, and the connection point of the third switch tube T3 and the fourth switch tube T4 is connected to the other end of the inductor L. When the voltage value of the first direct current is less than the DC bus voltage threshold, the following control method is specifically adopted to realize the DC / DC conversion circuit (DC / DC) working in the boost mode: the first switch tube T1 is in the on state, the second switch tube T2 is in the off state, and the third switch tube T3 and the fourth switch tube T4 are in the complementary on state to realize the boost function. Among them, the two switch tubes are in the complementary on state means that when one switch tube is in the on state, the other switch tube is in the off state. When the voltage value of the first direct current is greater than the DC bus voltage threshold, the following control method is specifically used to realize the DC / DC converter circuit (DC / DC) to work in the step-down mode: the third switch tube T3 is in the on state, the fourth switch tube T4 is in the off state, the first switch tube T1 and the second switch tube T2 are in the complementary on state, and the step-down function is realized. When the voltage value of the first direct current is equal to the DC bus voltage threshold, the following control method is specifically used to realize the DC / DC converter circuit (DC / DC) to work in the pass-through mode: the first switch tube T1 and the third switch tube T3 are both in the on state, the second switch tube T2 and the fourth switch tube T4 are both in the off state, and the DC source is directly connected to the DC bus.

[0041] Reference Figure 3In some other embodiments of the present application, both the upper bridge arm and the lower bridge arm may include two switch tubes connected in series. Specifically, the upper bridge arm of the first bridge arm M1 may include a first switch tube T1 and a second switch tube T2 connected in series, the lower bridge arm of the first bridge arm M1 includes a third switch tube T3 and a fourth switch tube T4 connected in series, the upper bridge arm of the second bridge arm M2 includes a fifth switch tube T5 and a sixth switch tube T6 connected in series, and the lower bridge arm of the second bridge arm M2 includes a seventh switch tube T7 and an eighth switch tube T8 connected in series. In the first bridge arm M1, a first capacitor C1 is provided between the connection point of the two switch tubes of the upper bridge arm, i.e., the first switch tube T1 and the second switch tube T2, and the connection point of the two switch tubes of the lower bridge arm, i.e., the third switch tube T3 and the fourth switch tube T4. In the second bridge arm M2, a second capacitor C2 is provided between the connection point of the two switch tubes of the upper bridge arm, i.e., the fifth switch tube T5 and the sixth switch tube T6, and the connection point of the two switch tubes of the lower bridge arm, i.e., the seventh switch tube T7 and the eighth switch tube T8. When the voltage value of the first direct current is greater than the DC bus voltage threshold and the DC / DC converter circuit (DC / DC) operates in the step-down mode, the upper bridge arm and the lower bridge arm in the first bridge arm M1 are in a complementary conduction state, which specifically means that when the current flowing through the inductor L points from the first bridge arm M1 to the second bridge arm M2, that is, when the current points from the second switch tube T2 to the fifth switch tube T5, the two switch tubes of the upper bridge arm in the first bridge arm M1, that is, the first switch tube T1 and the second switch tube T2, are in a complementary conduction state, and the two switch tubes of the lower bridge arm in the first bridge arm M1, that is, the third switch tube T3 and the fourth switch tube T4, are in an off state. When the current flowing through the inductor L points from the second bridge arm M2 to the first bridge arm M1, that is, when the current points from the fifth switch tube T5 to the second switch tube T2, the two switch tubes of the lower bridge arm in the first bridge arm M1, that is, the third switch tube T3 and the fourth switch tube T4, are in a complementary conduction state, and the two switch tubes of the upper bridge arm in the first bridge arm M1, that is, the first switch tube T1 and the second switch tube T2, are in an off state. The upper bridge arm of the second bridge arm M2, namely the fifth switch tube T5 and the sixth switch tube T6, is in the on state, and the lower bridge arm of the second bridge arm M2, namely the seventh switch tube T7 and the eighth switch tube T8, is in the off state. When the voltage value of the first direct current is less than the DC bus voltage threshold, and the DC / DC converter circuit works in the boost mode, the upper bridge arm and the lower bridge arm in the second bridge arm M2 are in a complementary conduction state, which specifically means that when the current flowing through the inductor L points from the first bridge arm M1 to the second bridge arm M2, that is, when the current points from the second switch tube T2 to the fifth switch tube T5, the two switch tubes of the upper bridge arm in the second bridge arm M2, namely the fifth switch tube T5 and the sixth switch tube T6, are in a complementary conduction state, and the two switch tubes of the lower bridge arm in the second bridge arm M2, namely the seventh switch tube T7 and the eighth switch tube T8, are in the off state.When the current flowing through the inductor L points from the second bridge arm M2 to the first bridge arm M1, that is, when the current points from the fifth switch tube T5 to the second switch tube T2, the two switch tubes of the lower bridge arm in the second bridge arm M2, namely the seventh switch tube T7 and the eighth switch tube T8, are in a complementary conduction state, and the two switch tubes of the upper bridge arm in the second bridge arm M2, namely the fifth switch tube T5 and the sixth switch tube T6, are in an off state. The upper bridge arm of the first bridge arm M1, namely the first switch tube T1 and the second switch tube T2, are in a conducting state, and the lower bridge arm of the first bridge arm M1, namely the third switch tube T3 and the fourth switch tube T4, are in an off state. When the voltage value of the first direct current is equal to the DC bus voltage threshold and the DC / DC conversion circuit works in the pass-through mode, the upper bridge arm of the first bridge arm M1, i.e., the first switch tube T1 and the second switch tube T2, and the upper bridge arm of the second bridge arm M2, i.e., the fifth switch tube T5 and the sixth switch tube T6, are all in the on state, the lower bridge arm of the first bridge arm M1, i.e., the third switch tube T3 and the fourth switch tube T4, and the lower bridge arm of the second bridge arm M2, i.e., the seventh switch tube T7 and the eighth switch tube T8, are all in the off state, and the DC source is directly connected to the DC bus.

[0042] Reference Figure 4a In some other embodiments of the present application, the DC / DC converter circuit may further include: a first relay K1 connected in parallel with the upper arm of the first bridge arm M1. When the voltage value of the first DC power is less than or equal to the DC bus voltage threshold and the DC / DC converter circuit (DC / DC) operates in a boost mode or a pass-through mode, the first relay K1 is controlled to be closed, and the current flows through the first relay K1 with a lower impedance instead of the upper arm of the first bridge arm M1, which can reduce the loss of the DC / DC converter circuit (DC / DC). When the voltage value of the first DC power is greater than the DC bus voltage threshold and the DC / DC converter circuit (DC / DC) operates in a step-down mode, the first relay K1 is controlled to be disconnected to ensure that the upper arm and the lower arm in the first bridge arm M1 are in a complementary conduction state, thereby realizing the step-down function.

[0043] Reference Figure 4b In some other embodiments of the present application, the DC / DC converter circuit may further include: a second relay K2 connected in parallel with the upper arm of the second bridge arm M2. When the voltage value of the first DC power is greater than or equal to the DC bus voltage threshold and the DC / DC converter circuit (DC / DC) operates in a buck mode or a pass-through mode, the second relay K2 is controlled to be closed, and the current flows through the second relay K2 with a lower impedance instead of the upper arm of the second bridge arm M2, which can reduce the loss of the DC / DC converter circuit (DC / DC). When the voltage value of the first DC power is less than the DC bus voltage threshold and the DC / DC converter circuit (DC / DC) operates in a boost mode, the second relay K2 is controlled to be disconnected to ensure that the upper arm and the lower arm in the second bridge arm M2 are in a complementary conduction state, thereby realizing the boost function.

[0044] Reference Figure 4c In some other embodiments of the present application, the DC / DC converter circuit may also include: a first relay K1 connected in parallel with the upper arm of the first bridge arm M1, and a second relay K2 connected in parallel with the upper arm of the second bridge arm M2. When the voltage value of the first DC power is less than the DC bus voltage threshold, and the DC / DC converter circuit (DC / DC) operates in the boost mode, the first relay K1 is controlled to be closed, and the second relay K2 is disconnected, and the current flows through the first relay K1 with lower impedance instead of the upper arm of the first bridge arm M1, which can reduce the loss of the DC / DC converter circuit (DC / DC). When the voltage value of the first DC power is greater than the DC bus voltage threshold, and the DC / DC converter circuit (DC / DC) operates in the buck mode, the first relay K1 is controlled to be disconnected, and the second relay K2 is controlled to be closed, and the current flows through the second relay K2 with lower impedance instead of the upper arm of the second bridge arm M2, which can reduce the loss of the DC / DC converter circuit (DC / DC). When the voltage value of the first direct current is equal to the DC bus voltage threshold and the DC / DC conversion circuit works in the pass-through mode, the first relay K1 and the second relay K2 are controlled to be closed, and the current flows through the first relay K1 with lower impedance and flows through the second relay K2 with lower impedance after passing through the inductor L. The current will not flow through the upper bridge arm of the first bridge arm M1 and the upper bridge arm of the second bridge arm M2, thereby reducing the loss of the DC / DC conversion circuit.

[0045] Reference Figure 4d In some other embodiments of the present application, the DC / DC converter circuit may also include: a third relay K3, the third relay K3 is connected between the positive pole of the input terminal of the DC / DC converter circuit and the positive pole of the output terminal of the DC / DC converter circuit. When the voltage value of the first DC power is less than or greater than the DC bus voltage threshold, and the DC / DC converter circuit works in the boost mode or the buck mode, the third relay K3 is controlled to be disconnected. When the voltage value of the first DC power is equal to the DC bus voltage threshold, and the DC / DC converter circuit works in the pass-through mode, the third relay K3 is controlled to be closed, and the current flows through the third relay K3 with lower impedance instead of the upper bridge arm of the first bridge arm M1 and the upper bridge arm of the second bridge arm M2, which can reduce the loss of the DC / DC converter circuit.

[0046] Based on the same inventive concept, the embodiment of the present application further provides a control method for a power converter, which may specifically include the following steps:

[0047] The DC-to-DC conversion circuit in the power converter is controlled to convert the voltage of the first DC power from the photovoltaic module or the energy storage battery, and output the second DC power to the DC-to-AC conversion circuit in the power converter through the DC bus; the DC-to-AC conversion circuit is controlled to convert the second DC power into AC power and output it to the power grid.

[0048] When the power converter is in the low voltage ride-through process, the voltage value of the second DC power is controlled to the DC bus voltage threshold, and the DC-to-AC conversion circuit is controlled to output reactive current to the power grid; the DC bus voltage threshold is not lower than the amplitude of the line voltage of the AC power output by the DC-to-AC conversion circuit.

[0049] In the present application, when low voltage ride-through occurs, the bus voltage at the input end of the subsequent DC-to-AC conversion circuit can be reduced by controlling the front-stage DC-to-DC conversion circuit in the power converter to operate to output a fixed DC bus voltage threshold, thereby reducing the voltage and current stress that the components of the DC-to-AC conversion circuit need to withstand during the low voltage ride-through, thereby reducing the component losses of the DC-to-AC conversion circuit and improving the low voltage ride-through overload capability.

[0050] In an embodiment of the present application, when low voltage ride-through occurs, that is, when the effective value of the grid voltage drops to a set value, the working mode of the DC-to-DC conversion circuit can be controlled according to the relationship between the voltage value of the first DC power of the DC source and the DC bus voltage threshold. Specifically, when the first DC power is greater than the DC bus voltage threshold, the DC-to-DC conversion circuit can be controlled to operate in a step-down mode, and specifically, the voltage value of the second DC power output by the DC-to-DC conversion circuit can be controlled to be reduced to the DC bus voltage threshold. When the voltage value of the first DC power is less than the DC bus voltage threshold, the DC-to-DC conversion circuit can be controlled to operate in a boost mode, and specifically, the voltage value of the second DC power output by the DC-to-DC conversion circuit can be controlled to be increased to the DC bus voltage threshold. When the voltage value of the first DC power is equal to the DC bus voltage threshold, the DC-to-DC conversion circuit can be controlled to operate in a pass-through mode, and specifically, the voltage value of the second DC power output by the DC-to-DC conversion circuit can be controlled to be the voltage value of the first DC power.

[0051] In some embodiments of the present application, the DC-to-DC conversion circuit may specifically include: a first bridge arm, a second bridge arm, and an inductor. In the control method, when the voltage value of the first DC power is less than the DC bus voltage threshold, the following control method is specifically used to control the DC-to-DC conversion circuit to operate in a boost mode: control the upper bridge arm of the first bridge arm to be in a conductive state, control the lower bridge arm of the first bridge arm to be in a closed state, and control the upper bridge arm and the lower bridge arm in the second bridge arm to be in a complementary conductive state to achieve a boost function. Among them, the two bridge arms are in a complementary conductive state means that when one bridge arm is in a conductive state, the other bridge arm is in an off state. When the voltage value of the first DC power is greater than the DC bus voltage threshold, the following control method is specifically used to control the DC-to-DC conversion circuit to operate in a buck mode: control the upper bridge arm of the second bridge arm to be in a conductive state, control the lower bridge arm of the second bridge arm to be in an off state, and control the upper bridge arm and the lower bridge arm in the first bridge arm to be in a complementary conductive state to achieve a buck function. When the voltage value of the first direct current is equal to the DC bus voltage threshold, the following control method is specifically adopted to control the DC-to-DC conversion circuit to operate in the pass-through mode: the upper bridge arm of the first bridge arm and the upper bridge arm of the second bridge arm are both controlled to be in the on state, and the lower bridge arm of the first bridge arm and the lower bridge arm are controlled to be in the off state, so that the DC source is directly connected to the DC bus.

[0052] Based on the same inventive concept, an embodiment of the present application also 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 first direct current provided by the energy storage battery into alternating current and output it to a power grid or a load.

[0053] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A power converter, characterized in that: include: DC to DC conversion circuit, DC bus, DC to AC conversion circuit and controller; The DC-to-DC conversion circuit is used to convert the voltage of the first DC power from the photovoltaic module or the energy storage battery, and output the second DC power to the DC-to-AC conversion circuit through the DC bus; The DC to AC conversion circuit is used to convert the second DC power into AC power and output it to the power grid; When the power converter is in a low voltage ride-through process, the controller is used to: control the voltage value of the second DC power to a DC bus voltage threshold, wherein the DC bus voltage threshold is not lower than the amplitude of the line voltage of the AC power output by the DC-to-AC conversion circuit; When the power converter is in a low voltage ride-through process, the controller is further used to: control the DC-to-AC conversion circuit to output reactive current to the power grid.

2. The power converter according to claim 1, characterized in that When low voltage ride through occurs, the controller is used to: When the voltage value of the first direct current is greater than the DC bus voltage threshold, controlling the voltage value of the second direct current to decrease to the DC bus voltage threshold; When the voltage value of the first direct current is less than the DC bus voltage threshold, controlling the voltage value of the second direct current to increase to the DC bus voltage threshold; When the voltage value of the first direct current is equal to the direct current bus voltage threshold, the voltage value of the second direct current is controlled to be equal to the voltage value of the first direct current.

3. The power converter according to claim 2, characterized in that: The DC-to-DC conversion circuit comprises: a first bridge arm, a second bridge arm and an inductor; The first bridge arm and the second bridge arm each include an upper bridge arm and a lower bridge arm, the two ends of the first bridge arm are respectively used to be connected to the positive and negative electrodes of the photovoltaic module or the energy storage battery, the two ends of the second bridge arm are respectively connected to the positive and negative electrodes of the DC bus, and the lower bridge arm of the first bridge arm is connected to the lower bridge arm of the second bridge arm; The connection point between the upper bridge arm and the lower bridge arm in the first bridge arm is the midpoint of the first bridge arm, the connection point between the upper bridge arm and the lower bridge arm in the second bridge arm is the midpoint of the second bridge arm, the midpoint of the first bridge arm is connected to one end of the inductor, and the midpoint of the second bridge arm is connected to the other end of the inductor; When the voltage value of the first direct current is less than the DC bus voltage threshold, the controller is used to control the upper bridge arm of the first bridge arm to be in an on state, the lower bridge arm of the first bridge arm to be in an off state, and the upper bridge arm and the lower bridge arm of the second bridge arm to be in a complementary on state; When the voltage value of the first direct current is greater than the DC bus voltage threshold, the controller is used to control the upper bridge arm of the second bridge arm to be in an on state, the lower bridge arm of the second bridge arm to be in an off state, and the upper bridge arm and the lower bridge arm of the first bridge arm to be in a complementary on state; When the voltage value of the first direct current is equal to the DC bus voltage threshold, the controller is used to control the upper bridge arm of the first bridge arm and the upper bridge arm of the second bridge arm to be in the on state, and the lower bridge arm of the first bridge arm and the lower bridge arm of the second bridge arm to be in the off state.

4. The power converter according to claim 3, characterized in that: The DC-to-DC conversion circuit also includes: a first relay connected in parallel with the upper bridge arm of the first bridge arm, and when the voltage value of the first DC power is less than or equal to the DC bus voltage threshold, the controller is used to control the first relay to close, and when the voltage value of the first DC power is greater than the DC bus voltage threshold, the controller is used to control the first relay to open.

5. The power converter according to claim 3 or 4, characterized in that: The DC-to-DC conversion circuit also includes: a second relay connected in parallel with the upper bridge arm of the second bridge arm, and when the voltage value of the first DC power is greater than or equal to the DC bus voltage threshold, the controller is used to control the second relay to close, and when the voltage value of the first DC power is less than the DC bus voltage threshold, the controller is used to control the second relay to open.

6. The power converter according to claim 3, characterized in that: The DC-to-DC conversion circuit also includes: a third relay, which is connected between the upper bridge arm of the first bridge arm and the upper bridge arm of the second bridge arm. When the voltage value of the first DC power is less than or less than the DC bus voltage threshold, the controller is used to control the third relay to be disconnected; when the voltage value of the first DC power is equal to the DC bus voltage threshold, the controller is used to control the third relay to be closed.

7. The power converter according to any one of claims 3 to 6, characterized in that: The upper bridge arm and the lower bridge arm each include a switch tube.

8. The power converter according to any one of claims 3 to 6, characterized in that: The upper bridge arm and the lower bridge arm each include two switch tubes connected in series; In the first bridge arm, a first capacitor is provided between a connection point of two switch tubes of the upper bridge arm and a connection point of two switch tubes of the lower bridge arm; in the second bridge arm, a second capacitor is provided between a connection point of two switch tubes of the upper bridge arm and a connection point of two switch tubes of the lower bridge arm; When the voltage value of the first direct current is greater than the DC bus voltage threshold, the controller is used to: When the current flowing through the inductor is directed from the first bridge arm to the second bridge arm, the two switch tubes in the upper bridge arm of the first bridge arm are controlled to be in a complementary conduction state, and the two switch tubes in the lower bridge arm of the first bridge arm are controlled to be in an off state; when the current flowing through the inductor is directed from the second bridge arm to the first bridge arm, the two switch tubes in the lower bridge arm of the first bridge arm are controlled to be in a complementary conduction state, and the two switch tubes in the upper bridge arm of the first bridge arm are controlled to be in an off state; When the voltage value of the first direct current is less than the DC bus voltage threshold, the controller is used to: When the current flowing through the inductor is directed from the first bridge arm to the second bridge arm, the two switch tubes in the upper bridge arm of the second bridge arm are controlled to be in a complementary conduction state, and the two switch tubes in the lower bridge arm of the second bridge arm are controlled to be in an off state; when the current flowing through the inductor is directed from the second bridge arm to the first bridge arm, the two switch tubes in the lower bridge arm of the second bridge arm are controlled to be in a complementary conduction state, and the two switch tubes in the upper bridge arm of the second bridge arm are controlled to be in an off state.

9. 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 8, wherein the power converter is connected to the energy storage battery, and the power converter is used to convert the first direct current provided by the energy storage battery into alternating current and output it to a power grid.

10. A method for controlling a power converter, characterized in that: include: Control the DC-to-DC conversion circuit in the power converter to convert the voltage of the first DC power from the photovoltaic module or the energy storage battery, and output the second DC power to the DC-to-AC conversion circuit in the power converter through the DC bus; control the DC-to-AC conversion circuit to convert the second DC power into AC power and output it to the power grid; When the power converter is in the low voltage ride-through process, the voltage value of the second DC power is controlled to a DC bus voltage threshold, and the DC-to-AC conversion circuit is controlled to output reactive current to the power grid, and the DC bus voltage threshold is not lower than the amplitude of the line voltage of the AC power output by the DC-to-AC conversion circuit.

11. The control method according to claim 10, characterized in that: Controlling the voltage value of the second direct current to a direct current bus voltage threshold includes: When the voltage value of the first direct current is greater than the DC bus voltage threshold, controlling the voltage value of the second direct current to decrease to the DC bus voltage threshold; When the voltage value of the first direct current is less than the DC bus voltage threshold, controlling the voltage value of the second direct current to increase to the DC bus voltage threshold; When the voltage value of the first direct current is equal to the direct current bus voltage threshold, the voltage value of the second direct current is controlled to be equal to the voltage value of the first direct current.

12. The control method according to claim 11, characterized in that: The DC-to-DC conversion circuit comprises: a first bridge arm, a second bridge arm and an inductor; The control method comprises: When the voltage value of the first direct current is less than the DC bus voltage threshold, the upper bridge arm of the first bridge arm is controlled to be in an on state, the lower bridge arm of the first bridge arm is controlled to be in an off state, and the upper bridge arm and the lower bridge arm of the second bridge arm are controlled to be in a complementary on state; When the voltage value of the first direct current is greater than the DC bus voltage threshold, the upper bridge arm of the second bridge arm is controlled to be in an on state, the lower bridge arm of the second bridge arm is controlled to be in an off state, and the upper bridge arm and the lower bridge arm of the first bridge arm are in a complementary on state; When the voltage value of the first direct current is equal to the DC bus voltage threshold, the upper bridge arm of the first bridge arm and the upper bridge arm of the second bridge arm are controlled to be in the on state, and the lower bridge arm of the first bridge arm and the lower bridge arm of the second bridge arm are controlled to be in the off state.

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