Power converter and control method therefor, and energy storage system

Abstract

Provided in the present application are a power converter and a control method therefor, and an energy storage system. The power converter comprises a plurality of power conversion circuits which are connected in parallel. In response to the reduction of the total output power of output ends of the plurality of power conversion circuits, at least one of the plurality of power conversion circuits can be switched from an operation state to a stop state, so that the conversion efficiency of each power conversion circuit in the operation state is improved, thereby improving the operation efficiency of the power converter, and particularly improving the efficiency of the power converter in a light load.

Description

A power converter, a control method thereof, and an energy storage system

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of the People's Republic of China on October 18, 2023, with application number 202311353812.X and application name "A power converter, its control method and energy storage system", the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of energy technology, and in particular to a power converter, a control method thereof, and an energy storage system. Background Art

[0004] In energy storage systems, in order to achieve more charging and discharging and improve system cycle efficiency, multiple dimensions such as power conversion efficiency, battery state of charge (SOC) estimation accuracy, and energy consumption management are often comprehensively considered. As the power of power conversion equipment increases, based on requirements such as device power, cost, and output ripple, power conversion equipment in energy storage systems often adopts a topology structure with multiple power conversion circuits in parallel. Due to the conduction loss, switching loss, gate drive loss, etc. in the power conversion circuit during the conversion process, the actual conversion efficiency cannot reach 100%. There is a parabolic relationship between the total loss of the power conversion circuit and the switching frequency. Currently, factors such as output ripple, switching loss, temperature rise, minimum duty cycle limit, and electromagnetic compatibility (EMC) are often comprehensively considered to control the power conversion circuit to operate at the optimal switching frequency point to improve the conversion efficiency of the power conversion circuit. In a power conversion device composed of multiple power conversion circuits connected in parallel, when the load remains unchanged, preferentially controlling the switching frequency within the power conversion circuit to reduce conversion losses can indeed improve the conversion efficiency of the power conversion device. However, when the load falls into the light load range, the conversion efficiency of the power conversion circuit decreases significantly. This is especially true in a topology with multiple power converters connected in parallel, where each power converter operates at a low efficiency, which is not conducive to improving the cycle efficiency of the energy storage system.

[0005] Summary of the Invention

[0006] The present application provides a power converter, a control method thereof, and an energy storage system, for improving the operating efficiency of the power converter, especially improving the system efficiency under light load.

[0007] In a first aspect, an embodiment of the present application provides a power converter, which includes multiple power conversion circuits connected in parallel. The input end of each power conversion circuit is connected to the output end of the energy storage device, and the output end of each power conversion circuit is used to connect to a DC bus or an AC bus to connect to a load device or a power grid. The power conversion circuit is used to output a bus voltage or output AC power after power conversion of the battery voltage provided by the energy storage device. The power converter may also include a controller, each power conversion circuit includes multiple switching tubes, and the controller is used to control the on-off state of the switching tubes in each power conversion circuit to control the output voltage and output current of the power conversion circuit, thereby controlling the output efficiency and conversion efficiency of the power conversion circuit.

[0008] In the present application, when the load of the power converter changes and causes the total output power of the power converter to decrease, at least one power conversion circuit among the multiple power conversion circuits can be controlled to switch from a running state to a stopped state, so that after the total output power of the power converter is reduced to a set value, each power conversion circuit in the running state has a first conversion efficiency, and after at least one power conversion circuit is switched from the running state to the stopped state, each power conversion circuit in the running state has a second conversion efficiency, and the second conversion efficiency is greater than the first conversion efficiency, so as to improve the conversion efficiency of the power conversion circuit in the running state, thereby improving the operating efficiency of the power converter. The conversion efficiency can be obtained by calculating the input power and the output power.

[0009] In some embodiments of the present application, when the load of the power converter changes and causes the total output power of the power converter to increase, at least one power conversion circuit among the multiple power conversion circuits can be controlled to switch from a stop state to an operating state, so that after the total output power of the power converter increases to a set value, each power conversion circuit in the operating state has a third conversion efficiency, and after at least one power conversion circuit switches from a stop state to an operating state, each power conversion circuit in the operating state has a fourth conversion efficiency, and the fourth conversion efficiency is greater than the third conversion efficiency, so as to improve the conversion efficiency of the power conversion circuit in the operating state, thereby improving the operating efficiency of the power converter.

[0010] In some embodiments of the present application, the controller can obtain the current output voltage and output current of the output terminal of the power converter in real time, calculate the current total output power of the power converter in real time, determine the optimal operating number of multiple power conversion circuits based on the total rated power of the power converter and the preset load rate of the power converter, and control the number of power conversion circuits in operation among the multiple power conversion circuits to switch to the optimal operating number, so that the operating efficiency of each power converter is optimized. The preset load rate is determined by the relationship between the conversion efficiency and load rate of the multiple power conversion circuits and the preset conversion efficiency of the multiple power conversion circuits.

[0011] In some embodiments of the present application, the controller may first determine the current total load rate of the multiple power conversion circuits based on the current total output power of the multiple power conversion circuits and the total rated power of the multiple power conversion circuits. The total load rate may specifically be equal to the ratio of the total output power to the total rated power. Afterwards, the controller determines the optimal operating number of the multiple power conversion circuits based on the total load rate and the known preset load rate. Finally, the controller controls the number of operating power conversion circuits in the multiple power conversion circuits to switch to the optimal operating number, so that the conversion power borne by the power conversion circuits in operation will increase to a high conversion efficiency range, completing the control of optimizing the conversion efficiency. Among them, the known preset load rate can be obtained through the efficiency curve of a known single power conversion circuit.

[0012] This application adopts the method of confirming the optimal operating number, which can control the power conversion circuit to operate in a high conversion efficiency range under the current load rate, thereby avoiding all power conversion circuits operating at light load and low efficiency points, reducing the total loss of the power converter, and significantly improving the system operating efficiency.

[0013] In some embodiments of the present application, the controller may specifically determine that the total load rate of the multiple power conversion circuits satisfies the preset load rate of the multiple power conversion circuits, then determine that the total load rate of the multiple power conversion circuits is in a set efficiency stage in the efficiency curve, that is, determine that the number of power conversion circuits currently in operation is the optimal operating number, and then maintain the currently operating number of power conversion circuits. The controller may also determine that the total load rate of the multiple power conversion circuits is outside the set efficiency stage in the efficiency curve if the total load rate of the multiple power conversion circuits does not satisfy the preset load rate of the multiple power conversion circuits, then determine that the total load rate of the multiple power conversion circuits is outside the set efficiency stage in the efficiency curve, and then determine the optimal operating number of the multiple power conversion circuits based on the preset load rate corresponding to the set efficiency stage, the rated power of the single power conversion circuit, and the current total output power of the multiple power conversion circuits.

[0014] In some embodiments of the present application, when the controller determines that there are multiple optimal operating numbers for multiple power conversion circuits, it can determine, among the multiple optimal operating numbers, the operating number with the highest conversion efficiency of the power conversion circuits in the operating state as the final optimal operating number. Specifically, when it is determined that the optimal operating number is not a unique value, the load rates corresponding to the multiple optimal operating numbers can be determined separately. Thereafter, based on the efficiency curve of a single power conversion circuit, the optimal efficiency point among the load rates corresponding to the multiple optimal operating numbers is determined, and the final optimal operating number is determined according to the optimal efficiency point to ensure that after switching to the optimal operating number, the power conversion circuits in the operating state all have the highest conversion efficiency.

[0015] In other embodiments of the present application, when the controller determines that there are multiple optimal operating numbers for the multiple power conversion circuits, the controller may determine, among the multiple optimal operating numbers, the operating number that is closest to the current operating number of the multiple power conversion circuits as the final optimal operating number. Specifically, when it is determined that the optimal operating number is not a unique value, the controller may control the number of operating power conversion circuits in the multiple power conversion circuits to switch to the optimal operating number that is closest to the current operating number of power conversion circuits, thereby reducing the number of operations of the power conversion circuits and facilitating stable operation of the system.

[0016] The above-mentioned power converter provided in the embodiment of the present application can be widely used in energy storage systems such as industrial and commercial energy storage, power station energy storage or charging stations.

[0017] In a second aspect, the present application provides an energy storage system, which may include a power converter of any possible design according to the first aspect and an energy storage device, wherein the input ends of the multiple power conversion circuits in the power converter are connected to the output ends of the energy storage device, and the output ends of the multiple power conversion circuits are connected to a load device or a power grid, and the power converter is used to output the electric energy provided by the energy storage device after power conversion. According to the total output power of the multiple power conversion circuits, different power conversion circuits in the multiple power conversion circuits can be controlled to be put into operation or stopped, so as to change the number of power conversion circuits in operation in the multiple power conversion circuits, so as to improve the output efficiency of each power conversion circuit in operation, thereby improving the operating efficiency of the power converter, especially improving the system efficiency under light load.

[0018] In a third aspect, the present application provides a control method for a power converter, wherein the power converter includes a plurality of power conversion circuits connected in parallel, and the control method includes: when the load of the power converter changes and causes the total output power of the power converter to decrease, at least one of the plurality of power conversion circuits can be controlled to switch from a running state to a stopped state, so that after the total output power of the power converter is reduced to a set value, each power conversion circuit in the running state has a first conversion efficiency, and after at least one power conversion circuit is switched from the running state to the stopped state, each power conversion circuit in the running state has a second conversion efficiency, and the second conversion efficiency is greater than the first conversion efficiency, so as to improve the conversion efficiency of the power conversion circuit in the running state, thereby improving the operating efficiency of the power converter. The conversion efficiency can be obtained by calculating the input power and the output power.

[0019] In some embodiments of the present application, when the load of the power converter changes and causes the total output power of the power converter to increase, at least one power conversion circuit among the multiple power conversion circuits can be controlled to switch from a stop state to an operating state, so that after the total output power of the power converter increases to a set value, each power conversion circuit in the operating state has a third conversion efficiency, and after at least one power conversion circuit switches from a stop state to an operating state, each power conversion circuit in the operating state has a fourth conversion efficiency, and the fourth conversion efficiency is greater than the third conversion efficiency, so as to improve the conversion efficiency of the power conversion circuit in the operating state, thereby improving the operating efficiency of the power converter.

[0020] In some embodiments of the present application, the current output voltage and output current of the output terminal of the power converter can be obtained in real time, the current total output power of the power converter can be calculated in real time, and the optimal operating number of multiple power conversion circuits can be determined based on the total rated power of the power converter and the preset load rate of the power converter. The number of power conversion circuits in operation among the multiple power conversion circuits is controlled to switch to the optimal operating number, so that the operating efficiency of each power converter is optimized. The preset load rate is determined by the relationship between the conversion efficiency and the load rate of the multiple power conversion circuits and the preset conversion efficiency of the multiple power conversion circuits.

[0021] In some embodiments of the present application, the current total load rate of the multiple power conversion circuits can be determined based on the current total output power of the multiple power conversion circuits and the total rated power of the multiple power conversion circuits. The total load rate can specifically be equal to the ratio of the total output power to the total rated power. Afterwards, the controller determines the optimal operating number of the multiple power conversion circuits based on the total load rate and the known preset load rate. Finally, the controller controls the number of operating power conversion circuits in the multiple power conversion circuits to switch to the optimal operating number, so that the conversion power borne by the power conversion circuits in operation will increase to a high conversion efficiency range, completing the control of optimizing the conversion efficiency. Among them, the known preset load rate can be obtained through the efficiency curve of a known single power conversion circuit.

[0022] In some embodiments of the present application, if it is determined that the total load rate of the multiple power conversion circuits meets the preset load rate of the multiple power conversion circuits, then it is determined that the total load rate of the multiple power conversion circuits is in a set efficiency stage in the efficiency curve, that is, the number of power conversion circuits currently in operation is determined to be the optimal operating number, and the currently operating number of power conversion circuits is maintained. Alternatively, if the total load rate of the multiple power conversion circuits does not meet the preset load rate of the multiple power conversion circuits, then it is determined that the total load rate of the multiple power conversion circuits is outside the set efficiency stage in the efficiency curve, and then the optimal operating number of the multiple power conversion circuits is determined based on the preset load rate corresponding to the set efficiency stage, the rated power of a single power conversion circuit, and the current total output power of the multiple power conversion circuits.

[0023] In some embodiments of the present application, when it is determined that there are multiple optimal operating numbers for multiple power conversion circuits, the operating number with the highest conversion efficiency among the multiple power conversion circuits in the operating state can be determined as the final optimal operating number. Specifically, when it is determined that the optimal operating number is not a unique value, the load rates corresponding to the multiple optimal operating numbers can be determined separately. Thereafter, based on the efficiency curve of a single power conversion circuit, the optimal efficiency point among the load rates corresponding to the multiple optimal operating numbers is determined, and the final optimal operating number is determined according to the optimal efficiency point to ensure that after switching to the optimal operating number, the power conversion circuits in the operating state all have the highest conversion efficiency.

[0024] In some embodiments of the present application, when it is determined that there are multiple optimal operating numbers for multiple power conversion circuits, the operating number closest to the current operating number of the multiple power conversion circuits can be determined as the final optimal operating number. Specifically, when it is determined that the optimal operating number is not a unique value, the number of operating power conversion circuits in the multiple power conversion circuits can be controlled to switch to the optimal operating number closest to the current operating number of power conversion circuits, which can reduce the number of operations of the power conversion circuits and facilitate stable operation of the system.

[0025] 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 and 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

[0026] Figure 1 is a schematic structural diagram of an energy storage system;

[0027] FIG2 is a schematic diagram showing the connection relationship of the power converter;

[0028] FIG3 is a schematic structural diagram of a power converter provided in an embodiment of the present application;

[0029] FIG4 is a schematic diagram of a circuit structure of a power conversion circuit provided in an embodiment of the present application;

[0030] FIG5 is a schematic diagram of another circuit structure of a power conversion circuit provided in an embodiment of the present application;

[0031] FIG6 is a schematic diagram of another circuit structure of a power conversion circuit provided in an embodiment of the present application;

[0032] FIG7 is a schematic diagram of another circuit structure of a power conversion circuit provided in an embodiment of the present application;

[0033] FIG8 is a schematic diagram of conversion efficiency of a power conversion circuit. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of this application clearer, this application will be further described in detail below with reference to the accompanying drawings.

[0035] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the specification and appended claims of this application, the singular expressions "a", "an", "said", "above", "the", and "this" are intended to also include expressions such as "one or more", unless the context clearly indicates otherwise.

[0036] References to "one embodiment" or "some embodiments" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in yet other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0037] In addition, the same reference numerals in the figures represent the same or similar structures, and their repeated description will be omitted. The words expressing positions and directions described in this application are all explained by using the drawings as examples, but they can be changed as needed, and the changes made are included in the scope of protection of this application. The drawings in this application are only used to illustrate the relative position relationship and do not represent the actual scale.

[0038] Referring to Figure 1 , energy storage systems for industrial, commercial, or power plants typically include a battery rack (BR), a battery management system (BMS), a power converter, an energy management system, and core components such as cooling, heat dissipation, and fire protection. Referring to Figure 2 , the input of the power converter is coupled to the output of the battery rack, and the output of the power converter is coupled to the power grid or load equipment. The power converter is used to convert the electrical energy provided by the battery rack and output it to the power grid or load equipment. To increase system power, the power converter often includes multiple power conversion circuits connected in parallel, with the inputs of the multiple power conversion circuits coupled to the output of the battery rack, and the outputs of the multiple power conversion circuits coupled to the power grid or load equipment. When the load remains unchanged, the conversion efficiency of the power conversion device can be improved by preferentially controlling the switching frequency within the power conversion circuit to reduce conversion losses. However, when the load falls into the light load range, each power converter operates in a low-efficiency state, significantly reducing the conversion efficiency of the power converter, which is not conducive to improving the cycle efficiency of the energy storage system.

[0039] In order to overcome the above-mentioned problems, the present application provides a power converter, a control method thereof and an energy storage system, which controls the input or output of at least one power conversion circuit among the multiple power conversion circuits according to the change in the total output power of the multiple power conversion circuits, so as to change the number of power conversion circuits in operation among the multiple power conversion circuits, so that the conversion efficiency of each power conversion circuit in operation after the change is improved, thereby improving the operating efficiency of the power converter, especially improving the system efficiency under light load.

[0040] The power converter, its drive control method and energy storage system provided by the present application are described in detail below with reference to the accompanying drawings.

[0041] 3 , in an embodiment of the present application, the power converter includes multiple power conversion circuits connected in parallel. FIG3 schematically illustrates n power conversion circuits. The input end of each power conversion circuit is connected to the output end of the energy storage device, and the output end of each power conversion circuit is connected to the load device or the power grid. Each power conversion circuit is used to output the bus voltage Vbus or output AC power after power conversion of the battery voltage Vbat provided by the energy storage device. The power converter generally also includes a controller, and each power conversion circuit includes multiple switching tubes. The controller is used to control the on-off state of the switching tubes in each power conversion circuit to control the output voltage and output current of the power conversion circuit, thereby controlling the output efficiency and conversion efficiency of the power conversion circuit. The switching tube used in the power conversion circuit needs to be a switching tube that can switch the on-off state at a high frequency. For example, the switching tube can be selected from a variety of types of switching tubes such as a metal oxide semiconductor field effect transistor (MOSFET), a bipolar junction transistor (BJT), and an insulated gate bipolar transistor (IGBT). This embodiment of the present application will not list them one by one. Exemplarily, the controller can be any one of a microcontroller unit (MCU), a central processing unit (CPU), a general-purpose processor, a digital signal processing (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc., or a combination of any one or more of other programmable logic devices, transistor logic devices, and hardware components.

[0042] In the present application, at least one of the multiple power conversion circuits can be controlled to switch between a running state and a stopped state based on the total output power change of the output terminals of the multiple power conversion circuits, that is, at least one of the multiple power conversion circuits can be controlled to be put into operation or withdrawn from operation, so as to change the number of power conversion circuits in operation among the multiple power conversion circuits, so that the power conversion circuit in the running state after switching improves the conversion efficiency, thereby improving the operating efficiency of the power converter, especially improving the system efficiency under light load. Wherein, the power conversion circuit will output a waveform when it is in the running state, and will not output a waveform when it is in the stopped state.

[0043] Specifically, in the present application, when the load of the power converter changes and causes the total output power of the power converter to decrease, at least one power conversion circuit among the multiple power conversion circuits can be controlled to switch from a running state to a stopped state, so that after the total output power of the power converter is reduced to a set value, each power conversion circuit in the running state has a first conversion efficiency, and after at least one power conversion circuit is switched from the running state to the stopped state, each power conversion circuit in the running state has a second conversion efficiency, and the second conversion efficiency is greater than the first conversion efficiency, so as to improve the conversion efficiency of the power conversion circuit in the running state, thereby improving the operating efficiency of the power converter. The conversion efficiency can be obtained by calculating the input power and the output power.

[0044] Specifically, in the present application, when the load of the power converter changes and causes the total output power of the power converter to increase, at least one power conversion circuit among the multiple power conversion circuits can be controlled to switch from a stop state to an operating state, so that after the total output power of the power converter increases to a set value, each power conversion circuit in the operating state has a third conversion efficiency, and after at least one power conversion circuit switches from a stop state to an operating state, each power conversion circuit in the operating state has a fourth conversion efficiency, and the fourth conversion efficiency is greater than the third conversion efficiency, so as to improve the conversion efficiency of the power conversion circuit in the operating state, thereby improving the operating efficiency of the power converter.

[0045] In some embodiments of the present application, each power conversion circuit may specifically include a DC / DC converter (DCDC), which is used to convert the DC power provided by the energy storage device into different voltages by boosting or bucking the voltage for subsequent devices. Referring to Figure 4, the DCDC may specifically adopt an H-bridge topology to form a bidirectional BUCK / BOOST circuit, supporting bidirectional flow of charging and discharging energy and wide voltage range regulation. The H-bridge topology may specifically include an inductor, two bridge arms connected at both ends of the inductor, and two filter capacitors, each bridge arm including two bridge arm switches connected in series, and each bridge arm connected in parallel with a filter capacitor. The two ends of one of the bridge arms are respectively connected to the output end of the energy storage device and the midpoint of the bridge arm is connected to one end of the inductor, and the two ends of the other bridge arm are respectively connected to the DC bus and the midpoint of the bridge arm is connected to the other end of the inductor. Referring to Figure 5, the DCDC may also adopt a half-bridge LLC topology. Alternatively, referring to Figure 6, the DCDC may also adopt a full-bridge LLC topology.

[0046] In other embodiments of the present application, each power conversion circuit may include a power conversion system (PCS), which is used to convert DC power into AC power and is responsible for AC power grid construction. Referring to Figure 7, the PCS may specifically adopt a full-bridge inverter topology.

[0047] In other embodiments of the present application, each power conversion circuit may specifically include a DCDC and a PCS, the DCDC is connected between the energy storage device and the PCS, and the PCS is connected to the power grid as a subsequent device of the DCDC.

[0048] Figure 4 above illustrates two power conversion circuits as an example, and Figures 5 to 7 illustrate one power conversion circuit as an example. The power converter provided in the embodiments of the present application is applicable to various power conversion circuits and is not limited to a specific topology.

[0049] In some embodiments of the present application, the controller can obtain the current output voltage and output current of the output terminal of the power converter in real time, calculate the current total output power of the power converter in real time, determine the optimal operating number of multiple power conversion circuits based on the total rated power of the power converter and the preset load rate of the power converter, and control the number of power conversion circuits in operation among the multiple power conversion circuits to switch to the optimal operating number, so that the operating efficiency of each power converter is optimized. The preset load rate is determined by the relationship between the conversion efficiency and load rate of the multiple power conversion circuits and the preset conversion efficiency of the multiple power conversion circuits.

[0050] Specifically, the controller can first determine the current total load rate of the multiple power conversion circuits based on the current total output power of the multiple power conversion circuits and the total rated power of the multiple power conversion circuits. The total load rate can specifically be equal to the ratio of the total output power to the total rated power. Afterwards, the controller determines the optimal operating number of the multiple power conversion circuits based on the total load rate and the known preset load rate. Finally, the controller controls the number of operating power conversion circuits in the multiple power conversion circuits to switch to the optimal operating number, so that the conversion power borne by the power conversion circuits in operation will increase to a high conversion efficiency range, completing the control of optimizing the conversion efficiency. Among them, the known preset load rate can be obtained through the efficiency curve of a known single power conversion circuit.

[0051] This application adopts the method of confirming the optimal operating number, which can control the power conversion circuit to operate in a high conversion efficiency range under the current load rate, thereby avoiding all power conversion circuits operating at light load and low efficiency points, reducing the total loss of the power converter, and significantly improving the system operating efficiency.

[0052] In some embodiments of the present application, the controller may specifically determine that the total load rate of the multiple power conversion circuits satisfies the preset load rate of the multiple power conversion circuits, then determine that the total load rate of the multiple power conversion circuits is in a set efficiency stage in the efficiency curve, that is, determine that the number of power conversion circuits currently in operation is the optimal operating number, and then maintain the currently operating number of power conversion circuits. The controller may also determine that the total load rate of the multiple power conversion circuits is outside the set efficiency stage in the efficiency curve if the total load rate of the multiple power conversion circuits does not satisfy the preset load rate of the multiple power conversion circuits, then determine that the total load rate of the multiple power conversion circuits is outside the set efficiency stage in the efficiency curve, and then determine the optimal operating number of the multiple power conversion circuits based on the preset load rate corresponding to the set efficiency stage, the rated power of the single power conversion circuit, and the current total output power of the multiple power conversion circuits.

[0053] In an embodiment of the present application, different types of power conversion circuits have known efficiency curves corresponding to different preset load rates. Referring to FIG8 , the efficiency curve records the relationship between the load rate and conversion efficiency of the power conversion circuit, i.e., different load rates correspond to different conversion efficiencies. For example, using the efficiency curve shown in FIG8 as an example, a conversion efficiency of 96% or above can be set as a high-efficiency stage, corresponding to a load rate of greater than 20%. If it is determined that the total load rate of the multiple power conversion circuits is greater than 20%, the load rate is considered to be in the high-efficiency stage, and the number of power conversion circuits currently in operation is maintained. If it is determined that the total load rate of the multiple power conversion circuits is less than 20%, the load rate is considered to be outside the high-efficiency stage. Based on the preset load rate corresponding to the high-efficiency stage, the rated power of the single power conversion circuit, and the total output power of the multiple power conversion circuits, the optimal number of power conversion circuits in operation is determined. Alternatively, a conversion efficiency of 98% or above can be set as a high-efficiency stage, corresponding to a load rate of greater than 30%. If it is determined that the total load rate of the multiple power conversion circuits is greater than 30%, the load rate is considered to be in the high-efficiency stage, and the number of power conversion circuits currently in operation is maintained. If it is determined that the total load rate of multiple power conversion circuits is less than 30%, it is considered that the load rate is outside the high efficiency stage. Then, the optimal operating number of multiple power conversion circuits is determined based on the preset load rate corresponding to the high efficiency stage, the rated power of a single power conversion circuit, and the total output power of multiple power conversion circuits.

[0054] In some embodiments of the present application, when the controller determines that there are multiple optimal operating numbers for multiple power conversion circuits, it can determine, among the multiple optimal operating numbers, the operating number with the highest conversion efficiency of the power conversion circuits in the operating state as the final optimal operating number. Specifically, when it is determined that the optimal operating number is not a unique value, the load rates corresponding to the multiple optimal operating numbers can be determined separately. Thereafter, based on the efficiency curve of a single power conversion circuit, the optimal efficiency point among the load rates corresponding to the multiple optimal operating numbers is determined, and the final optimal operating number is determined according to the optimal efficiency point to ensure that after switching to the optimal operating number, the power conversion circuits in the operating state all have the highest conversion efficiency.

[0055] In other embodiments of the present application, when the controller determines that there are multiple optimal operating numbers for the multiple power conversion circuits, the controller may determine, among the multiple optimal operating numbers, the operating number that is closest to the current operating number of the multiple power conversion circuits as the final optimal operating number. Specifically, when it is determined that the optimal operating number is not a unique value, the controller may control the number of operating power conversion circuits in the multiple power conversion circuits to switch to the optimal operating number that is closest to the current operating number of power conversion circuits, thereby reducing the number of operations of the power conversion circuits and facilitating stable operation of the system.

[0056] The following is an example of how to optimize the conversion efficiency of the power converter described above in this application through specific embodiments.

[0057] When the power converter starts to power on, the controller can control all the power conversion circuits in parallel to be in operation. The controller can obtain the output voltage and output current of the power converter in real time and calculate the total output power P0 of the power converter in real time. The controller calculates the total output power P0 of the power converter according to the total output power P0 of the multiple power conversion circuits / the total rated power P0 of the multiple power conversion circuits. N The total load factor of the multiple power conversion circuits is determined. The total load factor is compared with the efficiency curve of a known single power conversion circuit, such as shown in FIG8 , to determine the optimal number of the multiple power conversion circuits to be operated.

[0058] If the total load rate is in the high efficiency stage, the number of power conversion circuits currently in operation is maintained. If the total load rate is outside the high efficiency stage, the optimal number of multiple power conversion circuits in operation is determined based on the preset load rate corresponding to the high efficiency stage, the rated power of a single power conversion circuit, and the total output power of the multiple power conversion circuits. Specifically, the two load rates γ1 and γ2 at the ends of the high efficiency range obtained from the efficiency curve, the rated power P of a single power conversion circuit, and the total output power of the multiple power conversion circuits are used. n The total output power P0 of the multiple power conversion circuits and the optimal operating number n satisfy Formula 1.

[0059] Formula 2 for calculating the optimal number of runs n can be derived from Formula 1.

[0060] An integer value that satisfies Formula 2 is calculated as the optimal operating number n. If the calculated optimal operating number n is not a unique value, the load factors corresponding to different n values ​​are calculated separately. The conversion efficiencies corresponding to these load factors are then obtained from the efficiency curve. The optimal conversion efficiency points are compared to determine the optimal operating number n. Alternatively, if the calculated optimal operating number n is not a unique value, the value closest to the currently operating number of power conversion circuits is used as the optimal operating number.

[0061] Finally, the controller controls all the switching tubes of the redundant power conversion circuits in the power converter to turn off, so that it exits the operating state. In this way, the conversion power borne by the power conversion circuits in the operating state increases to the high efficiency range, completing the control of optimizing the conversion efficiency.

[0062] The above-mentioned power converter provided in the embodiment of the present application can be widely used in energy storage systems such as industrial and commercial energy storage, power station energy storage or charging stations.

[0063] Based on this, the present application also provides an energy storage system, including the above-mentioned power converter and an energy storage device, wherein the input ends of the multiple power conversion circuits in the power converter are connected to the output ends of the energy storage device, and the output ends of the multiple power conversion circuits are connected to the load equipment or the power grid. The power converter is used to output the electric energy provided by the energy storage device after power conversion. According to the total output power of the multiple power conversion circuits, different power conversion circuits in the multiple power conversion circuits can be controlled to be put into or out of operation, so as to change the number of power conversion circuits in the multiple power conversion circuits that are in operation, so that the conversion efficiency of each power conversion circuit in operation is improved, thereby improving the operating efficiency of the power converter, especially improving the system efficiency under light load.

[0064] Based on the same inventive concept, an embodiment of the present application also provides a control method for a power converter, wherein the power converter includes multiple power conversion circuits connected in parallel, and the control method includes: according to the change of the total output power of the output ends of the multiple power conversion circuits, at least one power conversion circuit among the multiple power conversion circuits can be controlled to switch between the running state and the stopped state, that is, at least one power conversion circuit among the multiple power conversion circuits can be controlled to be put into or out of operation to change the number of power conversion circuits running among the multiple power conversion circuits, so that the power conversion circuit in the running state after switching improves the conversion efficiency, thereby improving the operating efficiency of the power converter, especially improving the system efficiency under light load.

[0065] In the present application, when the load of the power converter changes and causes the total output power of the power converter to decrease, at least one power conversion circuit among the multiple power conversion circuits can be controlled to switch from a running state to a stopped state, so that after the total output power of the power converter is reduced to a set value, each power conversion circuit in the running state has a first conversion efficiency, and after at least one power conversion circuit is switched from the running state to the stopped state, each power conversion circuit in the running state has a second conversion efficiency, and the second conversion efficiency is greater than the first conversion efficiency, so as to improve the conversion efficiency of the power conversion circuit in the running state, thereby improving the operating efficiency of the power converter. The conversion efficiency can be obtained by calculating the input power and the output power.

[0066] In the present application, when the load of the power converter changes and causes the total output power of the power converter to increase, at least one power conversion circuit among the multiple power conversion circuits can be controlled to switch from a stop state to an operating state, so that after the total output power of the power converter increases to a set value, each power conversion circuit in the operating state has a third conversion efficiency, and after at least one power conversion circuit switches from a stop state to an operating state, each power conversion circuit in the operating state has a fourth conversion efficiency, and the fourth conversion efficiency is greater than the third conversion efficiency, so as to improve the conversion efficiency of the power conversion circuit in the operating state, thereby improving the operating efficiency of the power converter.

[0067] In some embodiments of the present application, the current output voltage and output current of the output terminal of the power converter can be obtained in real time, the current total output power of the power converter can be calculated in real time, and the optimal operating number of multiple power conversion circuits can be determined based on the total rated power of the power converter and the preset load rate of the power converter. The number of power conversion circuits in operation among the multiple power conversion circuits is controlled to switch to the optimal operating number, so that the operating efficiency of each power converter is optimized. The preset load rate is determined by the relationship between the conversion efficiency and the load rate of the multiple power conversion circuits and the preset conversion efficiency of the multiple power conversion circuits.

[0068] In some embodiments of the present application, the current total load rate of the multiple power conversion circuits can be determined based on the current total output power of the multiple power conversion circuits and the total rated power of the multiple power conversion circuits. The total load rate can specifically be equal to the ratio of the total output power to the total rated power. Afterwards, the controller determines the optimal operating number of the multiple power conversion circuits based on the total load rate and the known preset load rate. Finally, the controller controls the number of operating power conversion circuits in the multiple power conversion circuits to switch to the optimal operating number, so that the conversion power borne by the power conversion circuits in operation will increase to a high conversion efficiency range, completing the control of optimizing the conversion efficiency. Among them, the known preset load rate can be obtained through the efficiency curve of a known single power conversion circuit.

[0069] In some embodiments of the present application, if it is determined that the total load rate of the multiple power conversion circuits meets the preset load rate of the multiple power conversion circuits, then it is determined that the total load rate of the multiple power conversion circuits is in a set efficiency stage in the efficiency curve, that is, the number of power conversion circuits currently in operation is determined to be the optimal operating number, and the currently operating number of power conversion circuits is maintained. Alternatively, if the total load rate of the multiple power conversion circuits does not meet the preset load rate of the multiple power conversion circuits, then it is determined that the total load rate of the multiple power conversion circuits is outside the set efficiency stage in the efficiency curve, and then the optimal operating number of the multiple power conversion circuits is determined based on the preset load rate corresponding to the set efficiency stage, the rated power of a single power conversion circuit, and the current total output power of the multiple power conversion circuits.

[0070] In some embodiments of the present application, when it is determined that there are multiple optimal operating numbers for multiple power conversion circuits, the operating number with the highest conversion efficiency among the multiple power conversion circuits in the operating state can be determined as the final optimal operating number. Specifically, when it is determined that the optimal operating number is not a unique value, the load rates corresponding to the multiple optimal operating numbers can be determined separately. Thereafter, based on the efficiency curve of a single power conversion circuit, the optimal efficiency point among the load rates corresponding to the multiple optimal operating numbers is determined, and the final optimal operating number is determined according to the optimal efficiency point to ensure that after switching to the optimal operating number, the power conversion circuits in the operating state all have the highest conversion efficiency.

[0071] In other embodiments of the present application, when it is determined that there are multiple optimal operating numbers for multiple power conversion circuits, the operating number closest to the current operating number of the multiple power conversion circuits can be determined as the final optimal operating number. Specifically, when it is determined that the optimal operating number is not a unique value, the number of operating power conversion circuits in the multiple power conversion circuits can be controlled to switch to the optimal operating number closest to the current operating number of power conversion circuits, which can reduce the number of operations of the power conversion circuits and facilitate stable operation of the system.

[0072] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A power converter, characterized in that: include: A plurality of power conversion circuits; the plurality of power conversion circuits are connected in parallel, the input ends of the plurality of power conversion circuits are used to connect to the output ends of the energy storage device, the output ends of the plurality of power conversion circuits are used to connect to a DC bus or an AC bus, and the power converter is used to output the electric energy provided by the energy storage system after power conversion; In response to a decrease in the total output power of the output ends of the plurality of power conversion circuits, at least one of the plurality of power conversion circuits is switched from a running state to a stopped state.

2. The power converter according to claim 1, characterized in that In response to an increase in the total output power of the output ends of the plurality of power conversion circuits, at least one of the plurality of power conversion circuits is switched from a stopped state to an operating state.

3. The power converter according to claim 1 or 2, characterized in that: Also included is a controller, the controller being configured to: Determining the optimal operating number of the multiple power conversion circuits according to the current total output power of the output ends of the multiple power conversion circuits, the total rated power of the multiple power conversion circuits and the preset load rate of the multiple power conversion circuits; The number of the power conversion circuits in operation among the plurality of power conversion circuits is controlled to switch to the optimal operation number.

4. The power converter according to claim 3, characterized in that: The preset load rate is determined by the relationship between the conversion efficiency and the load rate of the plurality of power conversion circuits and the preset conversion efficiency of the plurality of power conversion circuits.

5. The power converter according to claim 3 or 4, characterized in that: The controller is specifically used for: Determining a current total load rate of the multiple power conversion circuits according to a current total output power of the output ends of the multiple power conversion circuits and a total rated power of the multiple power conversion circuits; If it is determined that the current total load rate of the plurality of power conversion circuits meets the preset load rate of the plurality of power conversion circuits, then the number of power conversion circuits currently in operation is determined to be the optimal operation number; or, If it is determined that the total load rate of the multiple power conversion circuits does not meet the preset load rate of the multiple power conversion circuits, the optimal operating number of the multiple power conversion circuits is determined based on the preset load rate of the multiple power conversion circuits, the rated power of a single power conversion circuit and the current total output power of the output ends of the multiple power conversion circuits.

6. The power converter according to any one of claims 3 to 5, characterized in that: The controller is specifically used for: When it is determined that there are multiple optimal operating numbers of the multiple power conversion circuits, the operating number with the highest conversion efficiency among the multiple power conversion circuits in operation is determined as the final optimal operating number.

7. The power converter according to any one of claims 3 to 5, characterized in that: The controller is specifically used for: When it is determined that there are multiple optimal operating numbers of the multiple power conversion circuits, an operating number among the multiple optimal operating numbers that is closest to the current operating number of the multiple power conversion circuits is determined as the final optimal operating number.

8. An energy storage system, characterized in that: include: An energy storage device and a power converter as described in any one of claims 1 to 7, wherein the input ends of the multiple power conversion circuits in the power converter are connected to the output ends of the energy storage device, the output ends of the multiple power conversion circuits are connected to a DC bus or an AC bus, and the power converter is used to output the electric energy provided by the energy storage system after power conversion.

9. A control method for a power converter, characterized in that: The power converter includes a plurality of power conversion circuits, and the control method includes: In response to a decrease in the total output power of the output ends of the plurality of power conversion circuits, at least one of the plurality of power conversion circuits is switched from a running state to a stopped state.

10. The control method according to claim 9, characterized in that: Also includes: In response to an increase in the total output power of the output ends of the plurality of power conversion circuits, at least one of the plurality of power conversion circuits is switched from a stopped state to an operating state.

11. The control method according to claim 9 or 10, characterized in that: Specifically include: Determining the optimal operating number of the multiple power conversion circuits according to the current total output power of the output ends of the multiple power conversion circuits, the total rated power of the multiple power conversion circuits and the preset load rate of the multiple power conversion circuits; The number of the power conversion circuits in operation among the plurality of power conversion circuits is controlled to switch to the optimal operation number.

12. The control method according to claim 11, characterized in that: The preset load rate is determined by the relationship between the conversion efficiency and the load rate of the plurality of power conversion circuits and the preset conversion efficiency of the plurality of power conversion circuits.

13. The control method according to claim 11 or 12, characterized in that: Determining the optimal operating number of the plurality of power conversion circuits according to the current total output power of the output ends of the plurality of power conversion circuits, the total rated power of the plurality of power conversion circuits, and the preset load rates of the plurality of power conversion circuits includes: Determining a current total load rate of the multiple power conversion circuits according to a current total output power of the output ends of the multiple power conversion circuits and a total rated power of the multiple power conversion circuits; If it is determined that the current total load rate of the plurality of power conversion circuits meets the preset load rate of the plurality of power conversion circuits, then the number of power conversion circuits currently in operation is determined to be the optimal operation number; or, If it is determined that the total load rate of the multiple power conversion circuits does not meet the preset load rate of the multiple power conversion circuits, the optimal operating number of the multiple power conversion circuits is determined based on the preset load rate of the multiple power conversion circuits, the rated power of a single power conversion circuit and the current total output power of the output ends of the multiple power conversion circuits.

14. The control method according to any one of claims 11 to 13, characterized in that: Also includes: When it is determined that there are multiple optimal operating numbers of the multiple power conversion circuits, the operating number with the highest conversion efficiency among the multiple power conversion circuits in operation is determined as the final optimal operating number.

15. The control method according to any one of claims 11 to 13, characterized in that: Also includes: When it is determined that there are multiple optimal operating numbers of the multiple power conversion circuits, an operating number among the multiple optimal operating numbers that is closest to the current operating number of the multiple power conversion circuits is determined as the final optimal operating number.

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