CN116613976A

CN116613976A - Power conversion circuit, control method thereof, battery pack and energy storage system

Info

Publication number: CN116613976A
Application number: CN202310456121.6A
Authority: CN
Inventors: 杨思为; 郭海滨; 钟少辉; 孟元东
Original assignee: Huawei Digital Power Technologies Co Ltd
Current assignee: Huawei Digital Power Technologies Co Ltd
Priority date: 2023-01-16
Filing date: 2023-04-21
Publication date: 2023-08-18
Also published as: CN116054590A

Abstract

The application provides a power conversion circuit, an energy storage device and an energy storage system. The power conversion circuit comprises a controller, a first-stage DC/DC conversion circuit, a plurality of second-stage DC/DC conversion circuits, a switch module, a first capacitor, a plurality of second capacitors and a battery. When the voltage of the battery is smaller than a first voltage threshold and the voltages at two ends of the first capacitor and the second capacitor are smaller than a third voltage threshold, the controller controls the switch module to be opened or closed so that the plurality of second-stage DC/DC conversion circuits are connected in series, or when the voltage of the battery is larger than the second voltage threshold and the voltages at two ends of the first capacitor and the second capacitor are smaller than the third voltage threshold, the controller controls the switch module to be opened or closed so that the plurality of second-stage DC/DC conversion circuits are connected in parallel, so that the boosting ratio of two sides of the first-stage DC/DC conversion circuit is changed, voltage mutation is not generated in the capacitor when the series-parallel connection mode of the plurality of second-stage DC/DC conversion circuits is switched, safe switching is guaranteed, cost is reduced, and electric energy conversion efficiency of a system is improved.

Description

Power conversion circuit, control method thereof, battery pack and energy storage system

Technical Field

The present application relates to the field of electronic technologies, and in particular, to a power conversion circuit, a control method thereof, a battery pack, and an energy storage system.

Background

The energy storage system is a device for storing energy and can be applied to the field of photovoltaic power generation. For example, the energy storage system can receive an input voltage provided by a power generation device such as a photovoltaic panel through a power supply circuit, process the input voltage, provide an output voltage for an energy storage device such as a battery, and store electric energy provided by the output voltage by the battery. The energy storage system can also supply power for other electric equipment through the electric energy stored by the energy storage system.

In the prior art, when the power generation device is affected by external conditions, the voltage value of the input voltage supplied to the energy storage system is not stable. For the energy storage system, when different input voltages are received, the power supply circuit can adjust the voltage value of the output voltage provided by the power supply circuit to the battery in a mode of adjusting the on and off frequency of the switching tube, so that stable and reliable energy transfer is ensured.

For example, in the energy storage conversion system, a DC/DC conversion circuit that boosts a battery voltage to a normal operation voltage range and an inverter circuit that converts direct current output from the DC/DC conversion circuit into alternating current are included. In order to meet the requirement of the wide voltage operating range of the inverter, the boosting ratio range of the DC/DC conversion circuit is wide, and the system efficiency is relatively reduced when the boosting ratio is very high, and at this time, the series-parallel connection mode of a plurality of DC/DC conversion circuits needs to be switched. The output capacitors are generally connected in parallel at two ends of the DC/DC conversion circuit and used for stabilizing the voltages at two ends of the DC/DC conversion circuit, when the series-parallel working mode of the DC/DC conversion circuit is directly switched, voltage mutation occurs at the two ends of the output capacitors, so that large current is generated, contact adhesion of a switching switch is easy to cause, and components or loads connected with the DC/DC conversion circuit are easy to be damaged due to current impact caused by the voltage mutation.

Disclosure of Invention

The application provides a power conversion circuit and a control method, which solve the problem that the series-parallel connection of a direct current output circuit is easy to cause voltage mutation of a capacitor, ensure safe switching, improve the electric energy conversion efficiency of a system, and reduce the cost without adding additional circuit components.

In a first aspect, an embodiment of the present application provides a power conversion circuit, where the power conversion circuit includes a controller, a first stage DC/DC conversion circuit, a plurality of second stage DC/DC conversion circuits, and a switch module; the first end of the first-stage DC/DC conversion circuit is used for being connected with external equipment, and the second end of the first-stage DC/DC conversion circuit is connected with the first end of the switch module; the first end of the second-stage DC/DC conversion circuit is connected with the second end of the switch module, and the second end of the second-stage DC/DC conversion circuit is used for being connected with a battery; the two ends of the first-stage DC/DC conversion circuit are connected in parallel with a first capacitor, and the first capacitor is used for stabilizing the voltage of the first-stage DC/DC conversion circuit; each second-stage DC/DC conversion circuit is connected in parallel with a second capacitor, and the second capacitor is used for stabilizing the voltage of the correspondingly connected second-stage DC/DC conversion circuit; the controller is configured to control opening or closing of the switching module such that the plurality of second-stage DC/DC conversion circuits are connected in series when the voltage of the battery is less than the first voltage threshold and the voltage values of the first capacitor and the second capacitor are less than the third voltage threshold, or to control opening or closing of the switching module such that the plurality of second-stage DC/DC conversion circuits are connected in parallel when the voltage of the battery is greater than the second voltage threshold and the voltage values of the first capacitor and the second capacitor are less than the third voltage threshold. The power conversion circuit changes the voltage of the second port of the first-stage DC/DC conversion circuit by switching the serial-parallel connection mode of the plurality of second-stage DC/DC conversion circuits, thereby changing the boosting ratio of the first-stage DC/DC conversion circuit, improving the electric energy conversion efficiency of the system, avoiding the voltage mutation of the first capacitor and the second capacitor when the serial-parallel connection mode of the plurality of second-stage DC/DC conversion circuits is switched, thereby damaging a switch or a component connected with the switch and ensuring the safe switching.

In a possible implementation manner, the controller is configured to adjust the PWM signal of the first stage DC/DC conversion circuit to reduce the voltage values of the first capacitor and the second capacitor to be less than the third voltage threshold when the voltage of the battery is less than the first voltage threshold or when the voltage of the battery is greater than the second voltage threshold. The power conversion circuit provided by the application has simple control logic for adjusting the voltage values of the first capacitor and the second capacitor, does not need to additionally increase circuit components, reduces the cost and shortens the switching time.

In a possible implementation manner, the controller is configured to control the second stage DC/DC conversion circuit to stop operation before the controller adjusts the PWM signal of the first stage DC/DC conversion circuit.

In a possible implementation manner, the controller is further configured to control the first stage DC/DC conversion circuit to stop operating after adjusting the PWM signals of the first stage DC/DC conversion circuit to reduce the voltage values of the first capacitor and the second capacitor to be less than the third voltage threshold, so as to ensure that the whole circuit is in a state of stopping operating when the serial-parallel connection modes of the plurality of second stage DC/DC conversion circuits are switched, and ensure safe switching.

In a possible implementation manner, the controller is further configured to control the switch module to be turned on or off after the first-stage DC/DC conversion circuit stops working, so that the plurality of second-stage DC/DC conversion circuits are connected in series or in parallel, the whole switching time is short, and the whole loop is in a state of stopping working during switching, so that safe switching is ensured.

In a possible implementation manner, when the battery is in a charging state, the first stage DC/DC conversion circuit is used for reducing the voltage of the first port of the first stage DC/DC conversion circuit, and the second stage DC/DC conversion circuit is used for reducing the voltage of the first port of the second stage DC/DC conversion circuit to a charging voltage required by the battery to charge the battery; when the battery is in a discharging state, the second-stage DC/DC conversion circuit is used for boosting the voltage of the second port of the second-stage DC/DC conversion circuit, and the first-stage DC/DC conversion circuit is used for boosting the voltage of the second port of the first-stage DC/DC conversion circuit and outputting the voltage to external equipment through the first port of the first-stage DC/DC conversion circuit. The power conversion circuit can be applied to a battery charging scene and a battery discharging scene, realizes bidirectional conversion of electric energy, has wide application scene and improves the application flexibility of the power conversion circuit.

In a possible implementation manner, the power conversion circuit further comprises a detection circuit, the detection circuit is used for detecting the voltage value of the battery and the voltage values of the first capacitor and the second capacitor, so that accurate detection of charge and discharge voltages of the battery is realized, a serial-parallel connection mode among a plurality of second-stage DC/DC conversion circuits is changed according to the detection result, and therefore the purposes of changing the voltage of the second port of the first-stage DC/DC conversion circuit, changing the boosting ratio of two sides of the first-stage DC/DC conversion circuit and improving the electric energy conversion efficiency of the system are achieved. The power conversion circuit accurately detects the voltage of the first capacitor and the voltage of the second capacitor, so that the voltage of the first capacitor and the voltage of the second capacitor are smaller than a third voltage threshold value when the series-parallel connection is switched, the voltage is reduced below a safe working voltage, the damage to components caused by the large current generated by voltage mutation is avoided, and the safe switching is ensured.

The embodiment of the application is not particularly limited to the structure of the switch module, and for example, the switch module may include a relay, a MOS tube or an IGBT tube.

In one possible implementation, the switch module includes a relay. The relay comprises a plurality of contacts, the contacts are connected with ports corresponding to the second-stage DC/DC conversion circuits, the series-parallel connection mode of the second-stage DC/DC conversion circuits is switched by switching the connection of the relay with different ports, the control logic is simple, the circuit architecture is simple, no additional circuit components are required, and the cost is reduced.

In one possible implementation, the switch module includes a plurality of MOS transistors. The MOS tubes are connected with the ports corresponding to the second-stage DC/DC conversion circuits, the serial-parallel connection mode of the second-stage DC/DC conversion circuits is switched by switching the connection of the MOS tubes and different ports, the control logic is simple, the circuit architecture is simple, the additional circuit components are not required to be added, the cost is reduced, the MOS tubes have the characteristic of short switching time, the rapid switching of the serial-parallel connection mode of the second-stage DC/DC conversion circuits can be realized, and the working efficiency of the system is improved.

In one possible implementation, the switching module includes a plurality of IGBT tubes. The plurality of IGBT tubes are connected with the ports corresponding to the plurality of second-stage DC/DC conversion circuits, the series-parallel connection mode of the plurality of second-stage DC/DC conversion circuits is switched by switching the connection between the IGBT tubes and different ports, the control logic is simple, the circuit architecture is simple, no additional circuit components are needed, the cost is reduced, the IGBT tubes have the advantages of reduced saturation voltage, high current carrying density and low driving power, and the working efficiency of the system is improved.

In a possible implementation manner, the first stage DC/DC conversion circuit is a Buck-Boost circuit, and the second stage DC/DC conversion circuit is an LLC conversion circuit. When the battery is in a charging state, the Buck-Boost circuit is used for reducing the voltage of the first port of the Buck-Boost circuit, and the LLC conversion circuit is used for reducing the voltage of the first port of the LLC conversion circuit to the charging voltage required by the battery; when the battery is in a discharging state, the LLC conversion circuit is used for boosting the voltage of the battery, and the Buck-Boost circuit is used for boosting the voltage of the second port of the Buck-Boost circuit and outputting the boosted voltage to external equipment. The LLC conversion circuit has simple structure, generally comprises components such as a switch tube, a transformer, a capacitor, an inductor and the like, has small volume and high power density, and improves the electric energy conversion efficiency of the system.

In a possible implementation manner, the first stage DC/DC conversion circuit is a Buck-Boost circuit, and the second stage DC/DC conversion circuit is a dual-active bridge conversion circuit. When the battery is in a charging state, the Buck-Boost circuit is used for reducing the voltage of a first port of the Buck-Boost circuit, and the double-active-bridge conversion circuit is used for reducing the voltage of a second port of the double-active-bridge conversion circuit to the charging voltage required by the battery; when the battery is in a discharging state, the double-active-bridge conversion circuit is used for boosting the voltage of the battery, and the Buck-Boost circuit is used for boosting the voltage of the second port of the Buck-Boost circuit and outputting the boosted voltage to external equipment. The double-active-bridge conversion circuit has the advantages of high conversion efficiency, high power density, lower voltage and current stress born by the power device, easy realization of soft switch, simple structure, easy integration and the like, and improves the electric energy conversion efficiency of the system.

In one possible implementation, the power conversion circuit includes a first stage DC/DC conversion circuit, two second stage DC/DC conversion circuits, a switching module, and a controller. The first end of the first-stage DC/DC conversion circuit is used for being connected with external equipment, the second end of the first-stage DC/DC conversion circuit is connected with the first end of the switch module, the first connecting point of the first-stage DC/DC conversion circuit is connected with the first connecting point of the second-stage DC/DC conversion circuit A, the second connecting point of the first-stage DC/DC conversion circuit is connected with the second connecting point of the second-stage DC/DC conversion circuit B, the second connecting point of the second-stage DC/DC conversion circuit A is connected with the second end of the switch module, and the first connecting point of the second-stage DC/DC conversion circuit B is connected with the second end of the switch module. The second ends of the second-stage DC/DC conversion circuit A and the second-stage DC/DC conversion circuit B are connected with the first end of the battery.

In one possible implementation, the external device is a dc source that provides an output voltage to the battery through a power conversion circuit.

In one possible implementation, the external device is a load and the battery provides a charging voltage to the load through the power conversion circuit.

In one possible implementation manner, the external device is an energy storage converter, and the energy storage converter can provide output voltage for the battery through the power conversion circuit, and can also receive the output voltage of the battery through the power conversion circuit to realize bidirectional conversion of electric energy.

In a second aspect, the present application provides a control method of a power conversion circuit, the power conversion circuit including a controller, a first stage DC/DC conversion circuit, a plurality of second stage DC/DC conversion circuits, and a switch module; the first end of the first-stage DC/DC conversion circuit is used for being connected with external equipment, and the second end of the first-stage DC/DC conversion circuit is connected with the first end of the switch module; the first end of the second-stage DC/DC conversion circuit is connected with the second end of the switch module, and the second end of the second-stage DC/DC conversion circuit is used for being connected with a battery; the first stage DC/DC conversion circuit is connected in parallel with a first capacitor; each second stage DC/DC conversion circuit is connected in parallel with a second capacitor. The control method comprises the following steps: when the voltage of the battery is smaller than a first voltage threshold value and the voltage values of the first capacitor and the second capacitor are smaller than a third voltage threshold value, the switch module is controlled to be opened or closed so that a plurality of second-stage DC/DC conversion circuits are connected in series; alternatively, when the voltage of the battery is greater than the second voltage threshold and the voltage values of the first capacitor and the second capacitor are less than the third voltage threshold, the switch module is controlled to be opened or closed so that the plurality of second-stage DC/DC conversion circuits are connected in parallel. The control method ensures that the voltage of the first capacitor and the voltage of the second capacitor are reduced when the plurality of second-stage DC/DC conversion circuits are switched in series/parallel, so that the capacitor cannot generate voltage mutation to generate large current, a switch or a component connected with the capacitor cannot be damaged, the control logic is simple, the switching time is short, and the electric energy conversion efficiency of the system is improved.

In a possible implementation manner, the control method of the power conversion circuit further includes: when the voltage of the battery is smaller than a first voltage threshold or when the voltage of the battery is larger than a second voltage threshold, PWM signals of the first-stage DC/DC conversion circuit are regulated to reduce the voltage values of the first capacitor and the second capacitor to be smaller than a third voltage threshold, so that the voltages at two ends of the first capacitor and the second capacitor are ensured to be within a safe working voltage range before the plurality of second-stage DC/DC conversion circuits are switched, and voltage mutation of the first capacitor and the second capacitor is avoided.

In a possible implementation manner, the control method of the power conversion circuit further includes: the second stage DC/DC conversion circuit is controlled to stop working before the PWM signal of the first stage DC/DC conversion circuit is regulated.

In a possible implementation manner, the control method of the power conversion circuit further includes: after PWM signals of the first-stage DC/DC conversion circuit are regulated to enable the first capacitor and the second capacitor to be reduced to be smaller than a third voltage threshold value, the first-stage DC/DC conversion circuit is controlled to stop working, and when a series-parallel connection mode of a plurality of second-stage DC/DC conversion circuits is switched, the whole circuit is in a state of stopping working, and safe switching is guaranteed.

In a possible implementation manner, the method for controlling the power conversion circuit further includes: after the first-stage DC/DC conversion circuit is controlled to stop working, the switching module is controlled to be opened or closed so that a plurality of second-stage DC/DC conversion circuits are connected in series or in parallel, the whole switching time is short, and the whole loop is in a stop working state during switching, so that safe switching is ensured.

In one possible implementation manner, the control method of the power conversion circuit further includes: the voltage value of the battery and the voltage values of the first capacitor and the second capacitor are detected. The method realizes accurate detection of the charge and discharge voltage of the battery, and changes the serial-parallel connection mode among a plurality of second-stage DC/DC conversion circuits according to the detection, thereby changing the voltage of the second port of the first-stage DC/DC conversion circuit, changing the boosting ratio of the two sides of the first-stage DC/DC conversion circuit and improving the electric energy conversion efficiency of the system. The method also ensures that the voltages of the first capacitor and the second capacitor are reduced below the safe working voltage during serial-parallel switching by accurately detecting the terminal voltages of the first capacitor and the second capacitor, avoids damaging components caused by large current generated by voltage mutation, and ensures safe switching.

In a third aspect, the present application provides an energy storage device comprising a battery, a controller, a first stage DC/DC conversion circuit, a plurality of second stage DC/DC conversion circuits and a switch module; the first end of the first-stage DC/DC conversion circuit is used for being connected with external equipment, and the second end of the first-stage DC/DC conversion circuit is connected with the first end of the switch module; the first end of the second-stage DC/DC conversion circuit is connected with the second end of the switch module, and the second end of the second-stage DC/DC conversion circuit is connected with the battery; the first stage DC/DC conversion circuit is connected in parallel with a first capacitor; each second stage DC/DC conversion circuit is connected with a second capacitor in parallel; the controller is used for: when the voltage of the battery is smaller than a first voltage threshold value and the voltage values of the first capacitor and the second capacitor are smaller than a third voltage threshold value, the switch module is controlled to be opened or closed so that a plurality of second-stage DC/DC conversion circuits are connected in series; or when the voltage of the battery is greater than the second voltage threshold and the voltage values of the first capacitor and the second capacitor are smaller than the third voltage threshold, the switch module is controlled to be opened or closed so that a plurality of second-stage DC/DC conversion circuits are connected in parallel. The energy storage device comprises a two-stage DC/DC conversion circuit, and the voltage output by the power grid is output to the battery after two-stage voltage conversion, so that the voltage boosting of the two-stage DC/DC conversion circuit is lower, and the working efficiency of the energy storage device is improved. The voltage of the second port of the first-stage DC/DC conversion circuit is changed by switching the serial-parallel connection mode of the plurality of second-stage DC/DC conversion circuits, so that the boosting ratio of the first-stage DC/DC conversion circuit is changed, the electric energy conversion efficiency of the energy storage device is improved, the first capacitor and the second capacitor are prevented from being suddenly changed in voltage when the serial-parallel connection mode of the plurality of second-stage DC/DC conversion circuits is switched, the switch or components connected with the switch is prevented from being damaged, and the safe switching is ensured.

In an embodiment with reference to the third aspect, the controller is configured to adjust the PWM signal of the first stage DC/DC conversion circuit to reduce the voltage values of the first capacitor and the second capacitor to be less than the third voltage threshold when the voltage of the battery is less than the first voltage threshold or when the voltage of the battery is greater than the second voltage threshold. The power conversion circuit provided by the application has simple control logic for adjusting the voltage values of the first capacitor and the second capacitor, does not need to additionally increase circuit components, reduces the cost and shortens the switching time.

In an embodiment with reference to the third aspect, the controller is configured to control the second stage DC/DC conversion circuit to stop operating before the controller adjusts the PWM signal of the first stage DC/DC conversion circuit.

In combination with an embodiment of the third aspect, the controller is further configured to control the first stage DC/DC conversion circuit to stop operating after adjusting the PWM signals of the first stage DC/DC conversion circuit to reduce the voltage values of the first capacitor and the second capacitor to be less than the third voltage threshold, so as to ensure that the whole circuit is in a state of stopping operating when the serial-parallel mode of the plurality of second stage DC/DC conversion circuits is switched, and ensure safe switching.

In an implementation manner of the third aspect, the controller is further configured to control the switch module to be turned on or off after the first stage DC/DC conversion circuit stops working, so that the plurality of second stage DC/DC conversion circuits are connected in series or in parallel, the whole switching time is short, and the whole loop is in a state of stopping working during switching, so that safe switching is ensured.

In a fourth aspect, the present application provides an energy storage system, where the energy storage system includes an energy storage device and an energy storage converter provided in the third aspect, the energy storage device is connected to the energy storage converter, the energy storage converter is used to convert dc electric energy output by the energy storage device into ac electric energy and output the ac electric energy to a power grid or a load, and/or the energy storage converter is used to convert ac electric energy output by the power grid into dc electric energy and output the dc electric energy to the energy storage device.

The beneficial effects of the energy storage system refer to the specific description of the beneficial effects of the power conversion circuit and the battery pack, and are not repeated here. .

Drawings

Fig. 1 is a schematic diagram of a first topology of a power conversion circuit according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a second topology of a power conversion circuit according to an embodiment of the present application;

FIG. 3 is a third topology diagram of a power conversion circuit according to an embodiment of the present application;

FIG. 4 is a fourth schematic diagram of a power conversion circuit according to an embodiment of the present application;

FIG. 5 is a fifth schematic diagram of a power conversion circuit according to an embodiment of the present application;

FIG. 6 is a sixth topology diagram of a power conversion circuit according to an embodiment of the present application;

FIG. 7 is a schematic diagram of a first flow chart of a control method according to an embodiment of the present application;

fig. 8 is a schematic diagram of a first flow of a control method according to an embodiment of the present application.

Reference numerals illustrate:

a 100-power conversion circuit;

101-a first stage DC/DC conversion circuit; 102-a switch module; 103-a second stage DC/DC conversion circuit; 104-a controller; 105-a detection circuit; 106-a first capacitance; 107-a second capacitance;

1031-a second stage DC/DC conversion circuit a; 1032-a second stage DC/DC conversion circuit B;

200-an external device 200;

300-battery 300.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings. However, the example embodiments may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The same reference numerals in the drawings denote the same or similar structures, and thus a repetitive description thereof will be omitted. The words of the expression position and the direction described in the embodiment of the application are described by taking the attached drawings as an example, but can be changed according to the requirement and are all included in the protection scope of the application. The drawings of the embodiments of the present application are merely for illustrating relative positional relationships and are not to scale.

In embodiments of the present application, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature.

It is noted that in the following description, specific details are set forth in order to provide an understanding of the application. The present application may be embodied in many other forms than those herein described, and those skilled in the art may readily devise numerous other arrangements that do not depart from the spirit of the application. Therefore, the present application is not limited by the specific embodiments disclosed below.

For convenience of understanding, terms involved in the embodiments of the present application will be explained first.

And/or: merely one association relationship describing the associated object, the representation may have three relationships, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone.

A plurality of: refers to two or more.

And (3) connection: refers to an electrical connection, and two electrical component connections may be direct or indirect connections between two electrical components. For example, a may be directly connected to B, or indirectly connected to B through one or more other electrical components, for example, a may be directly connected to B, or directly connected to C, and C may be directly connected to B, where a and B are connected through C.

A battery: whether large-scale photovoltaic power generation or wind power generation, the grid voltage is typically high, such as 400V to 800V ac voltage, resulting in a dc side voltage of 550V to 1500V. However, the voltage of a single battery is typically small, such as the voltage of a single battery is typically less than 60V, and in order to meet the grid voltage requirement, multiple batteries are typically connected in series directly to obtain a high voltage. In the power conversion circuit provided by the application, one battery can be a battery pack, and one battery pack can be formed by connecting one or more battery units (the battery units can be single battery cores and the like, and the voltage of the battery units is usually between 2.5V and 4.2V) in series and parallel to form a minimum energy storage and management unit. For convenience of description, a battery will be described as an example. In other words, in the power conversion circuit provided by the application, the battery is the smallest energy storage and management unit consisting of one or more battery units connected in series and parallel.

Pulse width modulation (Pulse Width Modulation, PWM for short) is the digital encoding of analog signal levels by modulating the width of a series of pulses, equivalent to the desired waveform (including shape and amplitude), that is, by adjusting the change in duty cycle, which is the percentage of the time a signal is at a high level over the entire signal period, to adjust the change in signal, energy, etc.

Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET for short): the semiconductor device is a semiconductor device which works by applying the field effect principle, can also be called an MOS tube for short, and generally comprises three terminals of a grid electrode, a source electrode and a drain electrode.

Insulated gate bipolar transistor (Insulated Gate Bipolar Transistor, IGBT for short): the power semiconductor device is a compound full-control voltage-driven power semiconductor device which consists of a bipolar transistor (Bipolar Junction Transistor, BJT for short) and a MOSFET, and has the advantages of high input impedance of the MOSFET and low conduction voltage drop of the BJT.

A relay: the electric control device is an electric appliance which causes a controlled quantity to generate a preset step change in an electric output circuit when the change of the input quantity reaches a prescribed requirement. It has an interactive relationship between a control system and a controlled system, and is generally applied to an automatic control circuit. The relay can be understood as an automatic switch which uses small current to control large current operation, so that the relay plays roles of automatic regulation, safety protection, a switching circuit and the like in a circuit, can be widely applied to remote control, remote measurement, communication, automatic control, electromechanical integration and power electronic equipment, and is one of the most important control elements.

Buck-Boost circuit: the Buck-Boost circuit is a common voltage/current conversion circuit, can realize Buck conversion and Boost conversion, and can be applied to voltage converters in various power systems.

LLC conversion circuit: the LLC conversion circuit is a resonant circuit which realizes constant output voltage by controlling the switching frequency (frequency adjustment), can realize zero voltage conduction (Zero Voltage Switching, ZVS for short) of two primary side main MOS switches and zero current turn-off (Zero Current Switching, ZCS for short) of a secondary side rectifier diode, can reduce the switching loss of a power supply and improve the efficiency and the power density of the power converter by a soft switching technology.

Double active bridge conversion circuit: the double-active-bridge conversion circuit generally comprises two full-bridge converters, the alternating current sides of the two full-bridge converters are connected with a transformer through an inductor, the full-bridge converters adopt square wave modulation to generate high-frequency square waves on the alternating current sides, and excitation reactance is ignored, so that the double-active-bridge conversion circuit is equivalent to two alternating current sources connected to two ends of the inductor, and the size and the direction of power flow can be adjusted by adjusting phase shift changes between the two alternating current sources. The double-active-bridge conversion circuit can realize electric isolation of the direct-current transformer and bidirectional flow of power, and the high-frequency isolation transformer greatly improves the power density and the modularization degree. In high voltage applications, due to device voltage and capacity levels, dual active bridge conversion circuits are commonly used in series to boost voltage levels and in parallel to boost power levels. The double-active-bridge conversion circuit has the advantages of high conversion efficiency, high power density, low voltage and current stress born by the power device, easy realization of soft switch, simple structure, easy integration and the like.

An embodiment of the present application provides a power conversion circuit, according to fig. 1, the power conversion circuit includes a controller 104, a first stage DC/DC conversion circuit 101, a plurality of second stage DC/DC conversion circuits 103, and a switch module 102; a first end of the first-stage DC/DC conversion circuit 101 is used for being connected with the external device 200, and a second end of the first-stage DC/DC conversion circuit 101 is connected with a first end of the switch module 102; a first terminal of the second stage DC/DC conversion circuit 103 is connected to a second terminal of the switch module 102, and a second terminal of the second stage DC/DC conversion circuit 103 is connected to a battery. The first stage DC/DC conversion circuit is connected in parallel with a first capacitor 106, and the first capacitor 106 is used for stabilizing the voltage of the second port of the first stage DC/DC conversion circuit; each second stage DC/DC conversion circuit is connected in parallel to a second capacitor 107, and the second capacitor 107 is used for stabilizing the voltage of the first port of the correspondingly connected second stage DC/DC conversion circuit. When the voltage of the battery 300 is smaller than the first voltage threshold, the step-up ratio of the two sides of the first-stage DC/DC conversion circuit is too high, so that the electric energy conversion efficiency of the system is reduced, when the voltage value of the first capacitor 106 and the second capacitor 107 is smaller than the third voltage threshold, the controller 104 controls the opening or closing of the switch module 102 so that the plurality of second-stage DC/DC conversion circuits are connected in series, and after the switching is completed, the voltage of the second port of the first-stage DC/DC conversion circuit 101 is equal to the sum of the voltages of the first ports of the plurality of second-stage DC/DC conversion circuits 103, so that the step-up ratio of the first-stage DC/DC conversion circuit 101 is reduced; when the voltage of the battery 300 is greater than the second voltage threshold, the step-up ratio of the two sides of the first stage DC/DC conversion circuit is too low, and when the voltage value of the first capacitor 106 and the second capacitor 107 is less than the third voltage threshold, the controller 104 controls the opening or closing of the switch module 102 so that the plurality of second stage DC/DC conversion circuits 103 are connected in parallel, and after the switching is completed, the second port voltage of the first stage DC/DC conversion circuit 101 is equal to the first port voltage of the plurality of second stage DC/DC conversion circuits 103, and the step-up ratio of the first stage DC/DC conversion circuit 101 is increased.

It should be noted that the controller 104 may be a general-purpose central processing unit (central processing unit, CPU), a general-purpose processor, a digital signal processing unit (digital signal processing, DSP), an application specific integrated circuit (application specific integrated circuits, ASIC), a field programmable gate array (field programmable gate array, FPGA) or other programmable logic device, a transistor logic device, a hardware component, or any combination thereof. The above-described processors may also be a combination of computing functions. For example, the controller 104 may include one or more microprocessor combinations, a combination of a DSP and a microprocessor, or the like.

In some examples, when the voltage of the battery is less than the first voltage threshold, the controller 104 controls the plurality of second-stage DC/DC conversion circuits 103 to stop working, the controller 104 adjusts the PWM signals of the first-stage DC/DC conversion circuits 101, after the first capacitor 106 and the second capacitor 107 are reduced to be less than the third voltage threshold, the controller controls the first-stage DC/DC conversion circuits 101 to stop working, the controller 104 controls the switch module 102 to open or close so that the plurality of second-stage DC/DC conversion circuits are connected in series, and after the switching is completed, the voltage of the second port of the first-stage DC/DC conversion circuits 101 is equal to the sum of the voltages of the first ports of the plurality of second-stage DC/DC conversion circuits 103, so that the step-up ratio of the first-stage DC/DC conversion circuits 101 is reduced. When the voltage of the battery 300 is greater than the second voltage threshold, the controller 104 controls the plurality of second-stage DC/DC conversion circuits 103 to stop working, the controller 104 controls the PWM signals of the first-stage DC/DC conversion circuits 101 to be adjusted, after the first capacitor 106 and the second capacitor 107 are reduced to be smaller than the third voltage threshold, the controller controls the first-stage DC/DC conversion circuits 101 to stop working, the controller 104 controls the switch module 102 to be opened or closed so that the plurality of second-stage DC/DC conversion circuits are connected in parallel, and after the switching is completed, the voltage of the second port of the first-stage DC/DC conversion circuits 101 is equal to the voltage of the first port of the plurality of second-stage DC/DC conversion circuits 103, so that the boost ratio of the first-stage DC/DC conversion circuits 101 is improved, and the battery is in a normal working voltage range. The electric energy conversion efficiency in a wide working voltage range is improved, voltage abrupt changes of the first capacitor 106 and the second capacitor 107 during switching of the serial-parallel connection mode of the plurality of second-stage DC/DC conversion circuits 103 are avoided, and therefore the switch or components connected with the switch are damaged, and safe switching is ensured. The control logic for adjusting the voltage values of the first capacitor 106 and the second capacitor 107 by the power conversion circuit provided by the embodiment of the application is simple, no additional circuit components are needed, the cost is reduced, and the switching time is shortened.

In some examples, the first stage DC/DC conversion circuit 101 is configured to step down the voltage of the first port of the first stage DC/DC conversion circuit 101, and the second stage DC/DC conversion circuit 103 is configured to step down the voltage of the first port of the second stage DC/DC conversion circuit 103 to a charging voltage required by the battery, so as to charge the battery; when the battery is in a discharge state, the second-stage DC/DC conversion circuit 103 is configured to boost the second port voltage of the second-stage DC/DC conversion circuit 103, and the first-stage DC/DC conversion circuit 101 is configured to boost the second port voltage of the first-stage DC/DC conversion circuit 101 and output the boosted second port voltage to the external device 200. The power conversion circuit can be applied to a battery charging scene and a battery discharging scene, realizes bidirectional conversion of electric energy, has wide application scene and improves the application flexibility of the power conversion circuit.

In some examples, the power conversion circuit further includes a detection circuit 105, where the detection circuit 105 is configured to detect a voltage value of the battery and voltage values of the first capacitor 106 and the second capacitor 107, to implement accurate detection of a charge-discharge voltage of the battery 300, and accordingly, to change a serial-parallel connection manner between the plurality of second stage DC/DC conversion circuits 103, so as to achieve the purpose of changing a voltage of the second port of the first stage DC/DC conversion circuit 101, changing a step-up ratio of two sides of the first stage DC/DC conversion circuit 101, and to improve an electrical energy conversion efficiency of the system. The power conversion circuit accurately detects the terminal voltages of the first capacitor 106 and the second capacitor 107, so that the voltages of the first capacitor 106 and the second capacitor 107 are smaller than a third voltage threshold value during series-parallel switching, the voltage is reduced below a safe working voltage, the damage to components caused by large current generated by voltage mutation is avoided, and the safe switching is ensured. The embodiment of the present application does not limit the specific position of the detection circuit 105, for example, the detection circuit 105 may be a part of the controller 104, or may be independent of the controller 104, and the controller 104 is configured to obtain the voltage value of the battery and the voltage values of the first capacitor 106 and the second capacitor 107 detected by the detection circuit 105.

The communication modes of the controller 104 and the detection circuit 105, and the first stage DC/DC conversion circuit 101 and the second stage DC/DC conversion circuit 103 are not particularly limited, and include wired and wireless communication modes, and the controller 104 and the detection circuit 105 may communicate based on an RS-485 bus or a CAN (Controller Area Network, controller 104 local area network) protocol. In other embodiments, communication may be based on other communication means as well.

In some examples, the switch module 102 includes a relay, a MOS transistor, or an IGBT transistor. The embodiment of the application does not particularly limit the specific number of relays, MOS tubes and IGBT tubes of the switch module 102. The specific number and manner of connection will be determined by one skilled in the art based on the specific application scenario, system architecture, and the specific number of second stage DC/DC conversion circuits 103.

In some examples, the first stage DC/DC conversion circuit 101 is a Buck-Boost circuit and the second stage DC/DC conversion circuit 103 is an LLC conversion circuit. Both Buck-Boost and LLC conversion circuits can implement bi-directional power conversion. The LLC conversion circuit has simple structure, generally comprises a switch tube, a transformer, a capacitor, an inductor and other components, has small volume and high power density, and improves the electric energy conversion efficiency. The LLC conversion circuit can output various different direct current voltages so as to meet the charging requirements of batteries in different scenes, the flexibility of the power conversion circuit is improved, and the LLC conversion circuits can realize the function of electric isolation. When the battery is in a charging state, the Buck-Boost circuit is used for reducing the voltage of the first port of the Buck-Boost circuit, and the LLC conversion circuit is used for reducing the voltage of the first port of the LLC conversion circuit to the charging voltage required by the battery; when the battery is in a discharging state, the LLC conversion circuit is used for boosting the voltage of the second port of the LLC conversion circuit, and the Buck-Boost circuit is used for boosting the voltage of the second port of the Buck-Boost circuit and outputting the boosted voltage to external equipment.

In some examples, the first stage DC/DC conversion circuit 101 is a Buck-Boost circuit and the second stage DC/DC conversion circuit is a dual active bridge conversion circuit. When the battery is in a charging state, the Buck-Boost circuit is used for reducing the voltage of the first port of the Buck-Boost circuit, and the double-active-bridge conversion circuit is used for reducing the voltage of the first port of the double-active-bridge conversion circuit to the charging voltage required by the battery; when the battery is in a discharging state, the double-active-bridge conversion circuit is used for boosting the voltage of the second port of the double-active-bridge, boosting the voltage of the second port of the Buck-Boost circuit and outputting the boosted voltage to external equipment.

It should be noted that, the specific topologies of the first stage DC/DC conversion circuit 101 and the second stage DC/DC conversion circuit 103 are not particularly limited in the embodiments of the present application. For example, when the power conversion circuit provided in the embodiment of the present application is only applied to a charging scenario or only applied to a discharging scenario, the first stage DC/DC conversion circuit 101 may be a Buck circuit or a Boost circuit, and the second stage DC/DC conversion circuit 103 may be another type of bridge topology.

The number of the second-stage DC/DC conversion circuits 103 is not particularly limited in the embodiment of the present application, and for example, the power conversion circuit may include 2 second-stage DC/DC conversion circuits, 3 second-stage DC/DC conversion circuits, 4 second-stage DC/DC conversion circuits, and the like, and the number of switches matches the number of the second-stage DC/DC conversion circuits. The number of the second stage DC/DC conversion circuits and the number of the switches can be selected and set by a person skilled in the art according to specific application situations and requirements.

Alternatively, the power conversion circuit includes two second-stage DC/DC conversion circuits 103, i.e., the power conversion circuit includes a second-stage DC/DC conversion circuit a1031 and a second-stage DC/DC conversion circuit B1032. As shown in fig. 2, a first end of the first stage DC/DC conversion circuit 101 is connected to an external device, a second end of the first stage DC/DC conversion circuit 101 is connected to a first end of the switch module 102, a first connection point a of the first stage DC/DC conversion circuit 101 is connected to a first connection point c of the second stage DC/DC conversion circuit a1031, a second connection point B of the first stage DC/DC conversion circuit 101 is connected to a second connection point f of the second stage DC/DC conversion circuit B1032, a second connection point d of the second stage DC/DC conversion circuit a1031 is connected to a first end of the switch module 102, and a first connection point e of the second stage DC/DC conversion circuit B1032 is connected to a second end of the switch module 102. The second terminals of the second-stage DC/DC conversion circuit a1031 and the second-stage DC/DC conversion circuit B1032 are connected to the first terminal of the battery.

Alternatively, according to fig. 2, the power conversion circuit includes a first stage DC/DC conversion circuit 101 and a second stage DC/DC conversion circuit a1031 and a second stage DC/DC conversion circuit B1032. The switching module 102 includes a relay including four contacts, namely, a first contact 1, a second contact 2, a third contact 3, and a fourth contact 4, the second stage DC/DC conversion circuit a1031 is connected in series with the second stage DC/DC conversion circuit B1032 when the second connection point d of the second stage DC/DC conversion circuit a1031 is connected to the second contact 2, the second stage DC/DC conversion circuit a1031 is connected in parallel with the second stage DC/DC conversion circuit B1032 when the first connection point e of the second stage DC/DC conversion circuit a1031 is connected to the first contact 1, and the first connection point e of the second stage DC/DC conversion circuit B1032 is connected to the third contact 3.

Alternatively, the power conversion circuit includes a first stage DC/DC conversion circuit 101 and a second stage DC/DC conversion circuit a1031 and a second stage DC/DC conversion circuit B1032. The switch module 102 includes four MOS transistors, namely, a MOS transistor Q1, a second MOS transistor Q2, a third MOS transistor Q3, and a fourth MOS transistor Q4, as shown in fig. 3. The first end of the first MOS tube Q1 is connected with the second connection point B of the first stage DC/DC conversion circuit 101, the second end of the first MOS tube Q1 is connected with the second connection point d of the second stage DC/DC conversion circuit A1031, the first end of the second MOS tube Q2 is connected with the first end of the fourth MOS tube Q4, the second end of the second MOS tube Q2 is connected with the second connection point d of the second stage DC/DC conversion circuit A1031, the first end of the third MOS tube Q3 is connected with the first connection point B of the first stage DC/DC conversion circuit 101B, the second end of the third MOS tube Q3 is connected with the first connection point e of the second stage DC/DC conversion circuit B1032, the first end of the fourth MOS tube Q4 is connected with the first end of the second MOS tube Q2, and the second end of the fourth MOS tube Q4 is connected with the first connection point e of the second stage DC/DC conversion circuit B1032. When the first MOS tube Q1 is conducted with the third MOS tube Q3 and the second MOS tube Q2 is disconnected with the fourth MOS tube Q4, the second-stage DC/DC conversion circuit A is connected with the second-stage DC/DC conversion circuit B in parallel; when the second MOS transistor Q2 is conducted with the fourth MOS transistor Q4 and the first MOS transistor Q1 is turned off with the third MOS transistor Q3, the second-stage DC/DC conversion circuit A is connected in series with the second-stage DC/DC conversion circuit B.

Alternatively, the power conversion circuit includes a first stage DC/DC conversion circuit 101 and a second stage DC/DC conversion circuit a1031 and a second stage DC/DC conversion circuit B1032. The switch module 102 includes four IGBTs, namely a first IGBTQ1, a second IGBTQ2, a third IGBTQ3, and a fourth IGBTQ4, as shown in fig. 4. The power conversion circuit provided by the embodiment of the application comprises a first IGBTQ1, a second IGBTQ2, a third IGBTQ3 and a fourth IGBTQ4; the first end of the first IGBTQ1 is connected to the second connection point B of the first stage DC/DC conversion circuit 101, the second end of the first IGBTQ1 is connected to the second connection point d of the second stage DC/DC conversion circuit a1031, the first end of the second IGBTQ2 is connected to the first end of the fourth IGBTQ4, the second end of the second IGBTQ2 is connected to the second connection point d of the second stage DC/DC conversion circuit a1031, the first end of the third IGBTQ3 is connected to the first connection point B of the first stage DC/DC conversion circuit 101B, the second end of the third IGBTQ3 is connected to the first connection point e of the second stage DC/DC conversion circuit B1032, the first end of the fourth IGBTQ4 is connected to the first end of the second IGBTQ2, and the second end of the fourth IGBTQ4 is connected to the first connection point e of the second stage DC/DC conversion circuit B1032. When the first IGBTQ1 is turned on with the third IGBTQ3 and the second IGBTQ2 is turned off with the fourth IGBTQ4, the second stage DC/DC conversion circuit a is connected in parallel with the second stage DC/DC conversion circuit B; when the second IGBTQ2 is turned on with the fourth IGBTQ4 and the first IGBTQ1 is turned off with the third IGBTQ3, the second-stage DC/DC conversion circuit a1031 is connected in series with the second-stage DC/DC conversion circuit B1032.

Optionally, the power conversion circuit includes a first stage DC/DC conversion circuit 101 and two second stage DC/DC conversion circuits 103. According to fig. 5, the two second-stage DC/DC conversion circuits are two LLC conversion circuits, when the voltage of the battery is smaller than the first voltage threshold, the controller 104 controls the LLC conversion circuits to stop working, the controller 104 adjusts the PWM signals of the first-stage DC/DC conversion circuit 101, the voltages at the two ends of the first capacitor 106 and the second capacitor 107 are reduced to be smaller than the third voltage threshold, the controller 104 controls the first-stage DC/DC conversion circuit 101 to stop working, the controller 104 controls the switch module 102 to turn off K1 and K3 and close K2, the two LLC conversion circuits are in a series connection mode after the switching is completed, the voltage at the second port of the first-stage DC/DC conversion circuit 101 is the sum of the voltages at the first ports of the two LLC conversion circuits, and the step-up ratio at the two sides of the first-stage DC/DC conversion circuit 101 is reduced. When the voltage of the battery is greater than the second voltage threshold, the voltage of the second port of the first-stage DC/DC conversion circuit 101 is too high, the controller 104 controls the LLC conversion circuit to stop working, the controller 104 adjusts the PWM signals of the first-stage DC/DC conversion circuit 101, the voltages of the two ends of the first capacitor 106 and the second capacitor 107 are reduced to be smaller than the third voltage threshold, the controller 104 controls the first-stage DC/DC conversion circuit 101 to stop working, the controller 104 controls the switch modules 102 to close K1 and K3 and turn off K2, the two LLC conversion circuits are in a parallel connection mode after switching is completed, the voltage of the second port of the first-stage DC/DC conversion circuit 101 is equal to the voltage of the first ports of the two LLC conversion circuits, and the battery working voltage requirement is met.

According to fig. 6, the power conversion circuit comprises a first stage DC/DC conversion circuit 101 and two second stage DC/DC conversion circuits. The two second stage DC/DC conversion circuits are two double active bridge conversion circuits, when the voltage of a battery is smaller than a first voltage threshold value, the controller 104 controls the double active bridge conversion circuits to stop working, the controller 104 adjusts PWM signals of the first stage DC/DC circuits, the voltage of two ends of the first capacitor 106 and the second capacitor 107 is reduced to be smaller than a third voltage threshold value, the controller 104 controls the first stage DC/DC conversion circuit 101 to stop working, the controller 104 controls the switch module 102 to turn off K1 and K3 and close K2, the two double active bridge conversion circuits are in a series connection mode after switching is completed, the voltage of a second port of the first stage DC/DC conversion circuit 101 is the sum of the voltages of the first ports of the two double active bridge conversion circuits, and the step-up ratio of two sides of the first stage DC/DC conversion circuit 101 is reduced. When the voltage of the battery is greater than the second voltage threshold, the voltage of the second port of the first-stage DC/DC conversion circuit 101 is too high, the controller 104 controls the dual-active-bridge conversion circuit to stop working, the controller 104 adjusts the PWM signals of the first-stage DC/DC conversion circuit 101, the voltages of the two ends of the first capacitor 106 and the second capacitor 107 are reduced to be smaller than the third voltage threshold, the controller 104 controls the first-stage DC/DC conversion circuit 101 to stop working, the controller 104 controls the switch module 102 to close K1 and K3 and turn off K2, the two dual-active-bridge conversion circuits are in a parallel connection mode after the switching is completed, the voltage of the second port of the first-stage DC/DC conversion circuit 101 is equal to the voltage of the first port of the two dual-active-bridge conversion circuits, and the battery working voltage requirement is met.

It should be noted that, the embodiment of the present application is not particularly limited to the first voltage threshold, the second voltage threshold and the third voltage threshold, and those skilled in the art may preset relevant parameters according to specific application scenarios and system architectures.

For example, if the battery operating voltage interval is 20V-30V, the first voltage threshold is set to 24V, the second voltage threshold is set to 26V, and the third voltage threshold is set to 20V. The first port voltage of the first stage DC/DC conversion circuit 101 ranges from 600V to 900V. The detection circuit 105 detects the voltage value of the battery in real time while the system is in a charged state. When the battery voltage is less than 24V, the controller 104 controls the plurality of second-stage DC/DC conversion circuits 103 to stop working, the controller 104 controls the PWM signals of the first-stage DC/DC conversion circuits 101 to reduce the voltages at the two ends of the first capacitor 106 and the second capacitor 107 to below 20V, the controller 104 controls the first-stage DC/DC conversion circuits 101 to stop working, and after the whole circuit stops working, the controller 104 controls the switch modules 102 to be opened or closed so that the plurality of second-stage DC/DC conversion circuits 103 are in a series mode. The controller 104 confirms that the switching is completed, and the controller 104 instructs the first stage DC/DC conversion circuit 101 and the plurality of second stage DC/DC conversion circuits 103 to resume operation, and if the switching fails, the system alarms to shut down. When the battery voltage is greater than 26V and the second stage DC/DC conversion circuit 103 is controlled by the controller 104 to stop working, the PWM signals of the first stage DC/DC conversion circuit 101 are controlled by the controller 104, the voltages at the two ends of the first capacitor 106 and the second capacitor 107 are reduced to below 20V, the first stage DC/DC conversion circuit 101 is controlled by the controller 104 to stop working, and after the whole circuit stops working, the switch module 102 is controlled by the controller 104 to be opened or closed so that the plurality of second stage DC/DC conversion circuits 103 are in parallel connection. The controller 104 confirms that the switching is completed, and the controller 104 instructs the first stage DC/DC conversion circuit 101 and the plurality of second stage DC/DC conversion circuits 103 to resume operation, and if the switching fails, the system alarms to shut down.

In some examples, the external device 200 is a direct current source. The first stage DC/DC conversion circuit 101 receives the output voltage of the direct current source, performs voltage conversion, and supplies the output voltage to the plurality of second stage DC/DC conversion circuits 103; the second-stage DC/DC conversion circuit 103 performs voltage conversion on the output voltage supplied from the first-stage DC/DC conversion circuit 101, and supplies an input voltage required for charging to the battery.

In some examples, the external device 200 is a load. The battery supplies an output voltage to the second-stage DC/DC conversion circuit 103, the second-stage DC/DC conversion circuit 103 voltage-converts the output voltage supplied from the battery and transmits the voltage to the first-stage DC/DC conversion circuit 101, and the first-stage DC/DC conversion circuit 101 converts the input voltage supplied from the second-stage DC/DC conversion circuit 103 into a voltage required by an external load and supplies power to the external load.

In some examples, the external device 200 is an energy storage converter. When the battery 300 is in a charged state, the first-stage DC/DC conversion circuit 101 receives the output voltage of the energy storage converter, performs voltage conversion, and supplies the output voltage to the plurality of second-stage DC/DC conversion circuits 103; the second-stage DC/DC conversion circuit 103 performs voltage conversion on the output voltage supplied from the first-stage DC/DC conversion circuit 101, and supplies an input voltage required for charging to the battery. When the battery 200 is in a discharging state, the battery provides an output voltage to the second-stage DC/DC conversion circuit 103, the second-stage DC/DC conversion circuit 103 performs voltage conversion on the output voltage provided by the battery and then transmits the output voltage to the first-stage DC/DC conversion circuit 101, and the first-stage DC/DC conversion circuit 101 converts the input voltage provided by the second-stage DC/DC conversion circuit 103 and then provides the output voltage to the energy storage converter.

The embodiment of the present application further provides a control method of a power conversion circuit, as shown in fig. 7, in some examples, the power conversion circuit includes a controller 104, a first stage DC/DC conversion circuit 101, a plurality of second stage DC/DC conversion circuits 103, and a switch module 102; a first end of the first-stage DC/DC conversion circuit 101 is used for being connected with the external device 200, and a second end of the first-stage DC/DC conversion circuit 101 is connected with a first end of the switch module 102; a first terminal of the second stage DC/DC conversion circuit 103 is connected to a second terminal of the switch module 102, and a second terminal of the second stage DC/DC conversion circuit 103 is connected to a battery. The control method comprises the following steps: when the voltage of the battery 300 is smaller than a first voltage threshold, the step-up ratio at two sides of the first-stage DC/DC conversion circuit is too high, so that the electric energy conversion efficiency of the system is reduced, when the voltage value of the first capacitor 106 and the second capacitor 107 is smaller than a third voltage threshold, the switch module 102 is controlled to be opened or closed so that a plurality of second-stage DC/DC conversion circuits are connected in series, and after switching is completed, the voltage of the second port of the first-stage DC/DC conversion circuit 101 is equal to the sum of the voltages of the first ports of the plurality of second-stage DC/DC conversion circuits 103, so that the step-up ratio of the first-stage DC/DC conversion circuit 101 is reduced, and the electric energy conversion efficiency of the system is improved; when the voltage of the battery 300 is greater than the second voltage threshold, the step-up ratio of the two sides of the first stage DC/DC conversion circuit is too low, and when the voltage value of the first capacitor 106 and the second capacitor 107 is smaller than the third voltage threshold, the switch module 102 is controlled to be opened or closed so that the plurality of second stage DC/DC conversion circuits 103 are connected in parallel, and after the switching is completed, the voltage of the second port of the first stage DC/DC conversion circuit 101 is equal to the voltage of the first port of the plurality of second stage DC/DC conversion circuits 103, and the step-up ratio of the first stage DC/DC conversion circuit 101 is increased, so that the battery works within the normal working voltage range. The control method enables the voltages of the first capacitor 106 and the second capacitor 107 to be reduced below the safe working voltage value when the plurality of second-stage DC/DC conversion circuits 103 are switched in series/parallel, so that the phenomenon of large current generated by abrupt change of the voltages of the capacitors is avoided, a switch or a component connected with the capacitors is not damaged, the control logic is simple, the switching time is short, and the electric energy conversion efficiency of the system is improved.

In some examples, a method of controlling a power conversion circuit includes: when the voltage of the battery is smaller than the first voltage threshold or when the voltage of the battery is larger than the second voltage threshold, the PWM signals of the first-stage DC/DC conversion circuit 101 are adjusted to reduce the voltage values of the first capacitor 106 and the second capacitor 107 to be smaller than the third voltage threshold, so that the voltages at two ends of the first capacitor 106 and the second capacitor 107 are ensured to be within a safe working voltage range before the plurality of second-stage DC/DC conversion circuits 103 are switched, and voltage abrupt changes of the first capacitor 106 and the second capacitor 107 are avoided.

In some examples, a method of controlling a power conversion circuit includes: the second-stage DC/DC conversion circuit 103 is controlled to stop operation before the PWM signal of the first-stage DC/DC conversion circuit 101 is adjusted.

In some examples, a method of controlling a power conversion circuit includes: after the PWM signal of the first stage DC/DC conversion circuit 101 is adjusted to reduce the first capacitor 106 and the second capacitor 107 to be smaller than the third voltage threshold, the first stage DC/DC conversion circuit 101 is controlled to stop working, so that when the series-parallel connection mode of the plurality of second stage DC/DC conversion circuits 103 is switched, the whole circuit is in a state of stopping working, and safe switching is ensured.

In some examples, a method of controlling a power conversion circuit includes: after controlling the first-stage DC/DC conversion circuit 101 to stop operation, the switching module 102 is controlled to be opened or closed so that the plurality of second-stage DC/DC conversion circuits 103 are connected in series or in parallel.

In some examples, a method of controlling a power conversion circuit includes: the voltage value of the battery 300 and the voltage values of the first capacitor 106 and the second capacitor 107 are detected. The method realizes accurate detection of the charge and discharge voltage of the battery 300, and changes the serial-parallel connection mode among the plurality of second-stage DC/DC conversion circuits 103 according to the detection, thereby changing the voltage of the second port of the first-stage DC/DC conversion circuit 101, changing the boosting ratio of the two sides of the first-stage DC/DC conversion circuit 101 and improving the electric energy conversion efficiency of the system. The method also ensures that the voltage of the first capacitor 106 and the second capacitor 107 is smaller than a third voltage threshold value during series-parallel switching by accurately detecting the voltage of the first capacitor 106 and the second capacitor 107, and the voltage is reduced below a safe working voltage, so that the damage to components caused by large current generated by voltage mutation is avoided, and the safe switching is ensured.

The following describes the operation logic of the control method by taking specific method steps as an example, as shown in fig. 8, the control method includes the following steps:

Step S101: detecting a battery voltage;

step S102: judging whether the battery voltage is smaller than a first voltage threshold, if yes, executing step S103, otherwise, executing step S108;

step S103: the plurality of second stage DC/DC conversion circuits are controlled to stop working,

step S104: regulating a PWM signal of the second-stage DC/DC conversion circuit;

step S105: judging whether the first capacitor and the second capacitor are smaller than a third voltage threshold, if so, executing step S106; otherwise, executing step S104;

step S106: controlling the first stage DC/DC conversion circuit to stop working;

step S107: switching the control switch module to connect the plurality of second-stage DC/DC conversion circuits in series or in parallel;

step S108: judging whether the battery voltage is greater than a second voltage threshold, if so, executing step S103;

step S109: judging whether the serial-parallel connection states of the second-stage DC/DC conversion circuits are successfully switched, if so, executing the step S110, otherwise, executing the step S111;

step S110: controlling the first-stage DC/DC conversion circuit and the second-stage DC/DC conversion circuit to resume normal operation;

step S111: and (5) alarming and shutting down.

An embodiment of the present application provides an energy storage device, according to fig. 1, the energy storage device includes a battery 300, a controller 102, a first stage DC/DC conversion circuit, a plurality of second stage DC/DC conversion circuits and a switch module 102; wherein, a first end of the first stage DC/DC conversion circuit is used for connecting the external device 200, and a second end of the first stage DC/DC conversion circuit is connected with a first end of the switch module 102; a first end of the second-stage DC/DC conversion circuit 103 is connected to a second end of the switch module 102, and a second end of the second-stage DC/DC conversion circuit 103 is connected to the battery 300; the first stage DC/DC conversion circuit is connected in parallel with a first capacitor 106; each second stage DC/DC conversion circuit is connected in parallel with a second capacitor 107; the controller 102 is configured to: when the voltage of the battery 300 is less than the first voltage threshold and the voltage values of the first capacitor 106 and the second capacitor 107 are less than the third voltage threshold, the switch module 102 is controlled to be opened or closed so that the plurality of second-stage DC/DC conversion circuits are connected in series; or when the voltage of the battery 300 is greater than the second voltage threshold and the voltage values of the first capacitor 106 and the second capacitor 107 are less than the third voltage threshold, the switch module 102 is controlled to be opened or closed such that the plurality of second-stage DC/DC conversion circuits are connected in parallel. The energy storage device comprises a two-stage DC/DC conversion circuit, and the voltage output by the power grid is output to the battery 300 after two-stage voltage conversion, so that the voltage boosting of the two-stage DC/DC conversion circuit is lower, and the working efficiency of the energy storage device is improved. . The energy storage device provided by the embodiment of the application not only can realize bidirectional flow of electric energy, but also can ensure that the voltage of the first capacitor 106 and the second capacitor 107 is reduced to be smaller than the third voltage threshold value by adjusting the PWM signals of the first stage DC/DC conversion circuit 101 before the step-up ratio of the two sides of the first stage DC/DC conversion circuit 101 is required to be changed by switching the serial-parallel connection mode of the plurality of second stage DC/DC conversion circuits 103, namely, the voltage of the capacitors is ensured to be lower than the safe working voltage before the serial-parallel connection switching, so that the situation that the voltage of the first capacitor 106 and the second capacitor 107 is suddenly changed after the serial-parallel connection switching is completed is avoided, the electric energy conversion efficiency is improved, the safe switching is ensured, and the load and components connected with the capacitors are not damaged.

In some examples, the controller 102 is configured to adjust the PWM signal of the first stage DC/DC conversion circuit 101 to reduce the voltage values of the first capacitor 106 and the second capacitor 107 to be less than the third voltage threshold when the voltage of the battery 300 is less than the first voltage threshold or when the voltage of the battery 300 is greater than the second voltage threshold. The power conversion circuit provided by the application has simple control logic for adjusting the voltage values of the first capacitor 106 and the second capacitor 107, does not need to additionally increase circuit components, reduces the cost and shortens the switching time.

In some examples, the controller 102 is configured to control the second stage DC/DC conversion circuit 103 to stop operating before the controller 102 adjusts the PWM signal of the first stage DC/DC conversion circuit 101.

In some examples, in one implementation manner, the controller 102 is further configured to control the first stage DC/DC conversion circuit 101 to stop operating after adjusting the PWM signal of the first stage DC/DC conversion circuit 101 to reduce the voltage values of the first capacitor 106 and the second capacitor 107 to be less than the third voltage threshold, so as to ensure that the whole circuit is in a stopped state when the series-parallel connection mode of the plurality of second stage DC/DC conversion circuits 103 is switched, and ensure safe switching.

In some examples, the controller 102 is further configured to control the switch module 102 to open or close after the first stage DC/DC conversion circuit 101 stops working, so that the plurality of second stage DC/DC conversion circuits 103 are connected in series or in parallel, the whole switching time is short, and the whole loop is in a state of stopping working during switching, so as to ensure safe switching.

The embodiment of the application provides an energy storage system. The energy storage system comprises the energy storage device and the energy storage converter, wherein the energy storage device is connected with the energy storage converter, the energy storage converter is used for converting direct-current electric energy output by the energy storage device into alternating-current electric energy and outputting the alternating-current electric energy to a power grid or a load, and/or the energy storage converter is used for converting alternating-current electric energy output by the power grid into direct-current electric energy and outputting the direct-current electric energy to the energy storage device. The energy storage system provided by the embodiment of the application not only can realize bidirectional flow of electric energy, but also can ensure safe switching while improving the electric energy conversion efficiency of the system by adjusting PWM signals of the first-stage DC/DC conversion circuit before the boosting ratio of the two sides of the first-stage DC/DC conversion circuit is required to be changed by switching the serial-parallel connection mode of the plurality of second-stage DC/DC conversion circuits, so that the voltages of the first capacitor and the second capacitor are reduced below a third voltage threshold value.

The foregoing is merely illustrative embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily think about variations or substitutions within the technical scope of the present application, and the application should be covered. Therefore, the protection scope of the application is subject to the protection scope of the claims.

Claims

1. A power conversion circuit, characterized in that the power conversion circuit comprises a controller, a first stage DC/DC conversion circuit, a plurality of second stage DC/DC conversion circuits and a switch module; the first end of the first-stage DC/DC conversion circuit is used for being connected with external equipment, and the second end of the first-stage DC/DC conversion circuit is connected with the first end of the switch module; the first end of the second-stage DC/DC conversion circuit is connected with the second end of the switch module, and the second end of the second-stage DC/DC conversion circuit is used for being connected with a battery;

the first stage DC/DC conversion circuit is connected in parallel with a first capacitor;

each second-stage DC/DC conversion circuit is connected with a second capacitor in parallel;

the controller is used for: when the voltage of the battery is smaller than a first voltage threshold value and the voltage values of the first capacitor and the second capacitor are smaller than a third voltage threshold value, controlling the opening or closing of the switch module so that the plurality of second-stage DC/DC conversion circuits are connected in series; or alternatively

When the voltage of the battery is larger than a second voltage threshold value and the voltage values of the first capacitor and the second capacitor are smaller than a third voltage threshold value, the switch module is controlled to be opened or closed so that the plurality of second-stage DC/DC conversion circuits are connected in parallel.

2. The power conversion circuit of claim 1, wherein the controller is further configured to adjust the PWM signal of the first stage DC/DC conversion circuit to reduce the voltage values of the first and second capacitors to less than the third voltage threshold when the voltage of the battery is less than the first voltage threshold or when the voltage of the battery is greater than the second voltage threshold.

3. The power conversion circuit of claim 2, wherein the controller is further configured to control the second stage DC/DC conversion circuit to cease operation prior to adjusting the PWM signal of the first stage DC/DC conversion circuit.

4. A power conversion circuit according to claim 2 or 3, wherein the controller is further configured to control the first stage DC/DC conversion circuit to stop operation after adjusting the PWM signals of the first stage DC/DC conversion circuit to reduce the voltage values of the first capacitor and the second capacitor to be less than the third voltage threshold.

5. The power conversion circuit according to claim 4, wherein the controller is configured to control opening or closing of the switching module such that the plurality of second-stage DC/DC conversion circuits are connected in series or in parallel after the first-stage DC/DC conversion circuit is stopped.

6. The power conversion circuit according to any one of claims 1 to 5, wherein,

the first stage DC/DC conversion circuit is used for reducing the voltage of a first port of the first stage DC/DC conversion circuit, and the second stage DC/DC conversion circuit is used for reducing the voltage of the first port of the second stage DC/DC conversion circuit to the charging voltage required by the battery; or alternatively

The second-stage DC/DC conversion circuit is used for boosting the voltage of a second port of the second-stage DC/DC conversion circuit, and the first-stage DC/DC conversion circuit is used for boosting the voltage of the second port of the first-stage DC/DC conversion circuit and outputting the voltage to the external equipment through a first end of the first-stage DC/DC conversion circuit.

7. The power conversion circuit according to any one of claims 1 to 6, further comprising a detection circuit for detecting a voltage value of the battery and a voltage value of the first capacitor and the second capacitor.

8. The power conversion circuit according to any one of claims 1 to 7, wherein the power conversion circuit comprises two second stage DC/DC conversion circuits.

9. The power conversion circuit according to any one of claims 1-8, wherein the external device is a direct current source, a load or an energy storage converter.

10. An energy storage device, characterized in that the energy storage device comprises a battery, a controller, a first stage DC/DC conversion circuit, a plurality of second stage DC/DC conversion circuits and a switch module; the first end of the first-stage DC/DC conversion circuit is used for being connected with external equipment, and the second end of the first-stage DC/DC conversion circuit is connected with the first end of the switch module; the first end of the second-stage DC/DC conversion circuit is connected with the second end of the switch module, and the second end of the second-stage DC/DC conversion circuit is used for being connected with the battery;

the first stage DC/DC conversion circuit is connected in parallel with a first capacitor; each second-stage DC/DC conversion circuit is connected with a second capacitor in parallel;

11. The energy storage device of claim 10, wherein the controller is further configured to adjust the PWM signal of the first stage DC/DC conversion circuit to reduce the voltage values of the first and second capacitors to less than the third voltage threshold when the voltage of the battery is less than the first voltage threshold or when the voltage of the battery is greater than the second voltage threshold.

12. The energy storage device of claim 11, wherein said controller is further configured to control said second stage DC/DC conversion circuit to cease operation prior to adjusting a PWM signal of said first stage DC/DC conversion circuit.

13. The energy storage device of claim 11 or 12, wherein the controller is further configured to control the first stage DC/DC conversion circuit to stop operating after adjusting the PWM signals of the first stage DC/DC conversion circuit to reduce the voltage values of the first capacitor and the second capacitor to be less than the third voltage threshold.

14. The energy storage device of claim 13, wherein the controller is configured to control opening or closing of the switch module such that the plurality of second stage DC/DC conversion circuits are connected in series or in parallel after the first stage DC/DC conversion circuit is deactivated.

15. An energy storage system, characterized in that the energy storage system comprises an energy storage device according to any one of claims 10-14 and an energy storage converter, the energy storage device being connected to the energy storage converter;

the energy storage converter is used for converting the direct current electric energy output by the energy storage device into alternating current electric energy and outputting the alternating current electric energy to a power grid or a load, and/or the energy storage converter is used for converting the alternating current electric energy output by the power grid into direct current electric energy and outputting the direct current electric energy to the energy storage device.