Device and method for improving charging and discharging safety

Abstract

The invention provides a device and method for improving charging and discharging safety, and the device comprises a bidirectional DC / DC module and a bidirectional DC / AC module which are connected with each other, and the bidirectional DC / DC module comprises a bidirectional Boost / Buck module and a bidirectional LLC module which are connected with each other; the bidirectional DC / DC module is connected with charging and discharging equipment, and the bidirectional DC / AC module is connected with a power grid; the bidirectional DC / DC module comprises a bidirectional Boost / Buck module and a bidirectional LLC module which are cascaded to realize a bidirectional DC / DC function; wherein the bidirectional Boost / Buck module is used for bidirectional step-up / step-down of direct-current voltage, and the bidirectional LLC module adopts an open-loop design and is used for electrical isolation of a charging and discharging equipment side and a power grid side. Based on the control strategy of the awakening circuit and the dormancy circuit, the working stress of the charging and discharging device is reduced, the service life attenuation of the hardware circuit is delayed, and the charging and discharging function failure is reduced, so that the purpose of improving the safety of the charging and discharging equipment is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of electric vehicles, bidirectional charging and discharging devices, and uninterruptible power supplies, and in particular relates to a device for improving charging and discharging safety. Background Art

[0002] In recent years, electric vehicle fire accidents have occurred frequently. According to statistics, 34% of electric vehicle fires occurred in the silent stage and 24% occurred in the charging stage. These spontaneous combustion accidents that occurred under non-driving conditions have caused great concern from all walks of life and seriously affected the public's confidence in the electric vehicle industry. At present, the safety protection of electric vehicle charging and discharging mainly focuses on the safety research of the battery itself and the research of charging and discharging devices.

[0003] In the existing research on charging and discharging devices, a four-switch Buck-Boost and capacitor-clamped LLC cascade multiplexed converter is proposed as a charging circuit (Lu Yiwen, Li Ping, Liu Guozhong, Zhao Feng, Wang Jiuhe. A CC / CV smooth switching wide output voltage charging circuit [J]. Power System Protection and Control 2024, 52 (03): 25-37.). Its advantage is that it realizes efficient transmission of electric energy, but the control of the multiplexed bridge arm is complex and there is a possibility of common conduction of the bridge arm. The article does not provide a prototype verification, and the charging and discharging safety still has risks; a pre-charging circuit solution is also proposed. By optimizing the circuit design, improving the quality of components, and strengthening the circuit connection, the problems of component damage and poor circuit connection in the charging circuit are solved ([3] Zhang Ruibin, Cheng Hui. Electric vehicle pre-charging principle and failure case analysis [J]. Automobile Maintenance Technician, 2024 (16): 52-54.). This method improves the safety of charging and discharging, but the cost will be greatly increased due to the addition of a pre-charging circuit. Summary of the invention

[0004] In view of the defects and shortcomings of the prior art, the present invention aims to provide a device and method for improving the safety of charging and discharging, which adopts a bidirectional Boost / Buck+open-loop LLC+three-level topology structure, with simple topology and control algorithm and high reliability. Based on the above device design, a method of "waking up" and "sleeping" some hardware circuits is mainly adopted, which reduces the working stress of the charging and discharging device, delays the life attenuation of the hardware circuit, and reduces the failure of the charging and discharging function, thereby achieving the purpose of improving the safety of the charging and discharging equipment.

[0005] This solution can be used in application scenarios of electric vehicles or other similar charging and discharging equipment.

[0006] The specific technical solutions are as follows: A device for improving charging and discharging safety: comprising a bidirectional DC / DC module and a bidirectional DC / AC module connected to each other, wherein the bidirectional DC / DC module comprises a bidirectional Boost / Buck module and a bidirectional LLC module connected to each other; the bidirectional DC / DC module is connected to a charging and discharging device, and the bidirectional DC / AC module is connected to a power grid; The bidirectional DC / DC module includes a bidirectional Boost / Buck module and a bidirectional LLC module which are cascaded to realize the bidirectional DC / DC function; wherein the bidirectional Boost / Buck module is used for bidirectional boost / step-down of DC voltage, and the bidirectional LLC module adopts an open-loop design for electrical isolation between the charging and discharging device side and the grid side.

[0007] Furthermore, the bidirectional Boost / Buck module is composed of 6 bidirectional Boost / Buck circuits, and the bidirectional LLC module is composed of 6 bidirectional LLC circuits; among them, 3 bidirectional Boost / Buck circuits and 3 bidirectional LLC circuits are cascaded in series to realize energy transfer between the DC voltage of the charging and discharging equipment and the positive bus voltage; and another 3 bidirectional Boost / Buck circuits and 3 bidirectional LLC circuits are cascaded in series to realize energy transfer between the DC voltage and the negative bus voltage.

[0008] Furthermore, each bidirectional Boost / Buck circuit is connected to a DC switching device, including a switch RLY1 connected in parallel and a switch RLY2 connected in series with a buffer resistor R1: In the discharge direction, the DC voltage is converted into bus voltage: When RLY2 is closed, the bidirectional LLC circuit is opened, and the DC voltage on the charging and discharging device side charges the bus electrolytic capacitor C1 through the buffer resistor R1; After the busbar slow start is completed, RLY1 is closed and RLY2 is opened; at this time, the bidirectional Boost / Buck circuit constitutes a standard Boost circuit; the DC voltage on the charging and discharging device side is boosted by the Boost circuit.

[0009] The bidirectional LLC circuit acts as an electrically isolated DC converter to electrically isolate the output voltage of the Boost circuit to the positive bus voltage; In the charging direction, the bus voltage charges the charging and discharging equipment: After RLY1 is closed, the bus voltage is electrically isolated through the bidirectional LLC circuit and then transmitted to the bidirectional Boost / Buck1 for voltage reduction. The bidirectional Boost / Buck circuit now constitutes a standard Buck circuit to charge the charging and discharging device (such as the battery of the charging and discharging device).

[0010] Furthermore, the switching frequencies of the branches of the bidirectional Boost / Buck module are the same and the phases of the main switch tubes of the branches turning on are 60° apart.

[0011] Furthermore, the voltage gain of the bidirectional LLC circuit is set to 2:1.

[0012] Furthermore, the bidirectional DC / AC module includes a three-phase DC / AC circuit and an AC switching device; the AC switching device is used to switch on / off the grid; the three-phase DC / AC circuit is used for energy transfer between the positive and negative busbars and the grid, and each phase is composed of three T-type three-level circuits in parallel.

[0013] Furthermore, the switching frequencies of the branches of the bidirectional Boost / Buck module are the same and the phases of the main switch tubes of the branches are 60° apart when they are turned on, so that the six bidirectional Boost / Buck circuits are staggered and connected in parallel for closed-loop control.

[0014] Furthermore, the multiple inverter inductors in the bidirectional DC / DC module and / or the bidirectional DC / AC module are implemented in a manner of having the same magnetic core but different windings, and are respectively used for different groups of circuits.

[0015] And, based on the above device design, a method for improving charging and discharging safety is provided, wherein a bidirectional Boost / Buck circuit and a bidirectional LLC circuit, one of which is connected to the positive bus and the other to the negative bus, and one branch of the three-phase circuit of the DC / AC circuit constitute one circuit, so that the device has a total of three circuits; after the slow start is completed, one, two or three circuits are enabled according to the set load threshold. The purpose is to select the least circuit to work, that is, wake up, according to the different load amounts; the circuit that is not working, that is, sleep. The dormant circuit reduces the working stress and reduces the life loss, thereby improving the safety of the device hardware.

[0016] Furthermore, by enabling or disabling each group of circuits, the load changes during charging and discharging of the battery side and when the grid side is connected to or disconnected from the grid can be accommodated.

[0017] Furthermore, a time-sharing and orderly working strategy is adopted to balance the duration of activation of each group of circuits.

[0018] In order to improve the charging and discharging safety protection capability in view of the frequent occurrence of fire accidents in charging and discharging equipment such as electric vehicle batteries, the present invention and its preferred solution have designed a charging and discharging device with a cascade topology structure, and verified the correctness of the function of the device through experiments. The safety of charging and discharging of the device has been improved through the following points: 1) The charging and discharging equipment side adopts a multi-channel parallel staggered form, and the charging and discharging voltage and current ripple is small, which protects the safety of the charging and discharging equipment; 2) The basic BOOST / BUCK topology is adopted, which is simple in topology; LLC open-loop control is adopted, which is simple in control. Not only the charging and discharging equipment side and the power grid are electrically isolated, reducing the high-frequency interference of the device, but also the topology and control are simple, reducing the risk of damage to the charging device caused by complex topology and algorithm.

[0019] 3) The “wake-up” and “sleep” control strategies reduce the life attenuation of the device hardware and improve the safety of charging and discharging. Moreover, since the sleep circuit does not work when the device is lightly loaded, there is no loss and the operating efficiency is high, which improves the endurance of charging and discharging equipment (such as electric vehicle batteries). BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 This is a structural block diagram of an apparatus according to an embodiment of the present invention; Figure 2 A block diagram of a bidirectional DC / DC module design according to an embodiment of the present invention; Figure 3 A bidirectional DC / DC circuit according to an embodiment of the present invention Figure 1 ; Figure 4 A bidirectional DC / DC circuit according to an embodiment of the present invention Figure 2 ; Figure 5 A block diagram of a bidirectional DC / AC module design according to an embodiment of the present invention; Figure 6 This is a diagram of a phase A bidirectional DC / AC circuit according to an embodiment of the present invention; Figure 7 This is a control flow chart of "wake up" and "sleep" in an embodiment of the present invention; Figure 8 This is a flow chart of the time-sharing and orderly working strategy control of an embodiment of the present invention; Fig. 9 This is a diagram showing the operation of the switching circuit between control mode 1 and control mode 2 according to an embodiment of the present invention; Fig.10 This is a diagram showing the operation of the switching circuit between control mode 1 and control mode 3 according to an embodiment of the present invention; Fig.11 This is a diagram showing the operation of the switching circuit between control mode 2 and control mode 3 according to an embodiment of the present invention; Fig.12 This is a waveform diagram of the stable operation of the device when fully loaded according to the embodiment of the present invention; a) Resonant cavity current waveform at full load b) Voltage and current waveforms on both sides at full load Fig.13 This is a waveform diagram of the device in wake-up mode when the load suddenly increases from 30% to 90% according to an embodiment of the present invention; a) DC side wake-up mode b) Grid side wake-up mode Fig.14 This is a waveform diagram of the device in sleep mode when the load is suddenly unloaded from 90% to 30% according to an embodiment of the present invention; a) DC side sleep mode b) Grid side sleep mode. DETAILED DESCRIPTION

[0021] In order to make the features and advantages of this patent more obvious and easy to understand, the following embodiments are specifically described in detail as follows: The following is a detailed description of the embodiments of the present invention in conjunction with the accompanying drawings: 1. Device design principle The basic circuit structure design of the device provided by the embodiment of the present invention is as follows Figure 1 As shown, it includes a bidirectional DC / DC module and a bidirectional DC / AC module connected to each other, and the bidirectional DC / DC module includes a bidirectional Boost / Buck module and a bidirectional LLC module connected to each other. Figure 1 In the diagram, the arrow pointing right indicates the discharge direction, and the arrow pointing left indicates the charge direction) 2 Design Principle of Bidirectional DC / DC Module Bidirectional DC / DC module design Figure 2 As shown, the bidirectional DC / DC module includes a bidirectional Boost / Buck module and a bidirectional LLC module, and the two modules are cascaded to achieve a bidirectional DC / DC function.

[0022] Among them, the bidirectional Boost / Buck module is used for bidirectional step-up / step-down of DC voltage, and the bidirectional LLC module adopts an open-loop design for electrical isolation between the charging and discharging equipment side and the grid side, reducing electromagnetic interference on both sides. The topology is simple and reliable, which improves the charging and discharging safety of the device.

[0023] Working principle of bidirectional DC / DC module like Figure 2 As shown, in a more specific design, the bidirectional Boost / Buck module of this embodiment is composed of 6 bidirectional Boost / Buck circuits, and the bidirectional LLC module is composed of 6 bidirectional LLC circuits. Among them, 3 bidirectional Boost / Buck circuits and 3 bidirectional LLC circuits are serially cascaded to realize the energy transfer between the DC voltage and the positive bus voltage of the electric vehicle; similarly, another 3 bidirectional Boost / Buck circuits and 3 bidirectional LLC circuits are serially cascaded to realize the energy transfer between the DC voltage and the negative bus voltage.

[0024] Detailed analysis of bidirectional DC / DC module operation The working principle of the bidirectional Boost / Buck module can be found in Figure 3 and Figure 4 .

[0025] Figure 3 The bidirectional DC / DC circuit 1 realizes the energy transfer between the DC voltage and the positive bus voltage. The figure shows the schematic diagram of one of the three parallel circuits for analysis, and the working principles of the other two circuits are the same.

[0026] The circuit includes a DC switching device, a bidirectional Boost / Buck circuit and a bidirectional LLC circuit. The bidirectional Boost / Buck1 circuit consists of an inductor L1, a switch tube Q 1-1 , switch tube Q 1-2 The bidirectional LL1 circuit consists of Q 1-3 —Q 1-10 Switching tube, resonant capacitor C r1 , resonant inductor L r1 , transformer T1 and bus electrolytic capacitor C1.

[0027] In the discharge direction, the DC voltage is generated into a positive bus voltage.

[0028] 1) When RLY2 in the DC switching device is closed, the bidirectional LLC1 circuit is opened, and the DC voltage on the electric vehicle side charges the bus electrolytic capacitor C1 through the buffer resistor R1; 2) After the busbar slow start is completed, close RLY1 and disconnect RLY2. 1-2 In the off state, the internal diode and the inductor L1 and the switch tube Q 1-1 , forming a standard Boost circuit. The DC voltage on the electric vehicle side is boosted by the Boost circuit.

[0029] 3) The bidirectional LLC1 circuit is designed as an open loop, which acts as an electrically isolated DC converter to electrically isolate the output voltage of the Boost circuit to the positive bus voltage.

[0030] In the charging direction, the positive bus voltage charges the electric vehicle.

[0031] 1) Direct closure of RLY1; 2) After the positive bus voltage is electrically isolated by the bidirectional LLC1 circuit, the bus voltage is transmitted to the bidirectional Boost / Buck1 for voltage reduction; 3) Switch Q in Bidirectional Boost / Buck1 Circuit 1-1 It is always in the off state, and its internal diode inductance L1 and switch tube Q 1-1 , forming a standard Buck circuit to charge electric vehicles.

[0032] Figure 4 The bidirectional DC / DC circuit 2 realizes the energy transfer between the DC voltage and the negative bus voltage. The working principle is similar to Figure 3 same.

[0033] Advantages of bidirectional DC / DC circuit 1) It is possible to use 6 bidirectional Boost / Buck circuits in staggered parallel closed-loop control on the electric vehicle side. By controlling the switching frequency of each branch to be the same and the phase difference of the main switch tube of each branch at the time of conduction to be 60 degrees (there are 6 branches in parallel on the electric vehicle side, and the control opening time of each branch is 60 degrees different, that is, staggered parallel closed-loop control is formed), it can reduce the current ripple on the electric vehicle side and improve the safety of battery use. In addition, the staggered parallel Boost converter can also achieve current balancing between phases and reduce the current stress of the device.

[0034] 2) Since the maximum range of the mainstream voltage on the electric vehicle side is: 150V-800V, in order to meet the low-voltage discharge on the electric vehicle side, the voltage gain of the bidirectional LLC is set to 2:1. The LLC circuit of the charging and discharging device is designed to work in an open-loop fixed frequency near the resonance point. Due to the use of open-loop control, the resonant frequency point is not affected by changes in load size, with high efficiency, simple control and higher reliability. Compared with the closed-loop LLC circuit, its complex control strategy leads to the risk of co-conduction of the upper and lower tubes of the same bridge arm, and low reliability; the open-loop topology is reliable and avoids failures caused by complex control. Reduce the possibility of device failure from the topology aspect.

[0035] 3) Figure 3 and Figure 4 In the example, there are three bidirectional DC / DC circuits connected in parallel, which complete the energy transfer between the battery voltage and the positive bus and the negative bus. Therefore, the bidirectional DC / DC module is composed of three groups of DC / DC circuits connected in parallel, and each group of DC / DC circuits is composed of two bidirectional Boost / Buck circuits and a bidirectional LLC circuit. Each group of bidirectional DC / DC circuits is independently controlled and can enter the "wake-up" and "sleep" control modes when the load changes, reducing the life attenuation of the electronic system hardware, thereby improving the safety of charging and discharging. For specific control strategies, please refer to the subsequent Chapter 4.

[0036] Design Principle of Bidirectional DC / AC Module The bidirectional DC / AC module provided in the embodiment of the present invention is designed as follows Figure 5 As shown, the module includes a three-phase DC / AC circuit and an AC switching device. The AC switching device is used to switch between on-grid and off-grid; the three-phase DC / AC circuit is used for energy transfer between the positive and negative busbars and the grid, and the circuit adopts a T-type three-level topology.

[0037] Working principle of bidirectional DC / AC circuit The three-phase bidirectional DC / AC circuit has the same structure. Take the A-phase bidirectional DC / AC circuit as an example. Figure 6 .

[0038] The A-phase bidirectional DC / AC circuit is composed of three T-type three-level circuits connected in parallel, namely: bidirectional DC / AC circuit A-phase-1, bidirectional DC / AC circuit A-phase-2, and bidirectional DC / AC circuit A-phase-3.

[0039] That is to say, the DC / AC circuit has three phases, and each phase has three circuits in parallel. In the following "wake up" and "sleep" control modes, the first group of circuits of the DC / AC circuit is: A phase-1, B phase-1, C phase-1, to achieve the output A / B / C three-phase function. Similarly, the second group of circuits of the DC / AC circuit is: A phase-2; B phase-2; C phase-2. The three-phase circuits of the DC / AC circuit are: A phase-3; B phase-3; C phase-3.

[0040] The advantages of the T-type three-level topology are: fewer components, high efficiency, simple control and high reliability.

[0041] Advantages of bidirectional DC / AC circuit Depend on Figure 5 and Figure 6 It can be seen that the bidirectional DC / AC module of this embodiment is composed of three sets of bidirectional DC / AC circuits connected in parallel to realize energy transfer between the positive and negative busbars and the three-phase power grid. By independently controlling each set of bidirectional DC / AC circuits, similar to the bidirectional DC / DC circuit, it can enter the "wake-up" and "sleep" control modes. For specific control strategies, please refer to the subsequent Chapter 4.

[0042] "Wake up" and "Sleep" control strategies 4.1 Flowchart of control strategy The present invention is designed for the above circuit structure and provides a control strategy process as follows: Figure 7 As shown: After the device is turned on, it will start slowly. Figure 7 The control strategy is used to control each group of circuits in the device module. The hardware circuit status under the control strategy is shown in Table 1: Table 1 Control strategy and hardware circuit status table

[0043] Take light load (corresponding to load capacity 0-33%) as an example to illustrate the hardware operation of the device: When light load is applied, one group of the bidirectional DC / DC circuits of the device is in working state (wake-up mode), and the other two groups of circuits are in disconnected state (sleep mode): (1) Analysis of bidirectional DC / DC circuit operation When the load is light, a set of bidirectional DC / DC circuits includes: bidirectional Boost / Buck1 and bidirectional LLC1, bidirectional Boost / Buck4 and bidirectional LLC4, among which, bidirectional Boost / Buck1 and bidirectional LLC1 complete the energy transfer between the battery and the positive and negative bus bars; bidirectional Boost / Buck4 and bidirectional LLC4 complete the energy transfer between the battery and the positive and negative bus bars. The above set of bidirectional DC / DC circuits is in working state (wake-up mode). The other two sets of bidirectional DC / DC circuits are in stopped working state (sleep mode).

[0044] (2) Analysis of bidirectional DC / AC circuit operation When the load is light, one set of bidirectional DC / AC circuits includes: bidirectional DC / AC circuit A phase-1, bidirectional DC / AC circuit B phase-1, and bidirectional DC / AC circuit C phase-1, completing the energy transfer between the positive and negative busbars and the grid. The above set of bidirectional DC / AC circuits is in working state (wake-up mode), and the other two sets of DC / AC circuits are in stopped working state (sleep mode).

[0045] When the load changes, the control mode of the device changes accordingly, as shown in Table 1. For example, when the load changes suddenly from (0-33%) to (66-100%), the device switches from control mode 3 to control mode 1. The two sets of bidirectional DC / DC circuits and two sets of DC / AC circuits that were in "sleep" under control mode 3 are "woken up". At this time, the three sets of bidirectional DC / DC circuits and three sets of DC / AC circuits of the device are all in the "woken up" state.

[0046] When charging and discharging on the battery side and connecting to and disconnecting from the grid side, the device load can be light load or heavy load. The use of "wake-up" and "sleep" control strategies will greatly delay the hardware life decay of the device, thereby improving the reliability of the system hardware and enhancing the safety of charging and discharging of the device.

[0047] The above "wake up" and "sleep" actions are essentially to control the opening or closing of each branch circuit of the device of this solution. As a preference, it can be achieved by the switch tube of the circuit itself. Figure 3 and Figure 4 The Q1-1, Q1-2, Q4-1, Q4-1 and other switch tubes in the system are driven to turn on and off, thereby realizing the wake-up and sleep operations, and the control is easy to implement and the control logic is simple.

[0048] Control strategy refinement In the control strategy, when the machine is running in control mode 2 or control mode 3, once the load changes and reaches the corresponding load threshold, a time-sharing orderly working strategy is adopted to "sleep" the circuit that has been running again, and at the same time "wake up" the circuit that has been sleeping to work again, so that the "sleeping" and "waking up" circuits are alternated, further improving the life of each group of circuits and improving the safety of the charging and discharging device.

[0049] Figure 8 In the case of load changes, it is determined according to Table 1 whether control mode 2 is reached. If so, it is determined which combination was previously running in control mode 2. If it is combination 1, the combination 2 circuit will be run next time; if it is combination 2, the combination 3 circuit will be run next time; if it is combination 3, the combination 1 circuit will be run next time. If it is determined to be control mode 3, the time-sharing orderly working mode is the same. The purpose of control is: each group of circuits has "sleep" to reduce the circuit working stress and increase the circuit life. The circuit combinations in control mode 2 and control mode 3 are shown in the following tables respectively: Table 2 Circuit combination list

[0050] 4.3 Control strategy switching mode The specific control strategy switching modes are as follows: (1) When the device load switches between load threshold 1 and load threshold 2, according to the "wake-up and sleep" strategy of each group of circuits in a time-sharing and orderly manner, each group of circuits operates as follows: Fig. 9 As shown: (2) When the device load switches between load threshold 1 and load threshold 3, each group of circuits operates as follows according to the "wake-up and sleep" strategy for each group of circuits in a time-sharing and orderly manner. Fig.10 As shown: (3) When the device load switches between load threshold 2 and load threshold 3, each group of circuits operates as follows according to the "wake-up and sleep" strategy of each group of circuits in an orderly time-sharing manner. Fig.11 shown.

[0051] Experimental verification 5.1 Detailed parameters of prototype In order to verify the correctness of the device design, this embodiment uses a 40kW experimental prototype platform for verification.

[0052] The prototype main control chip uses two TMS320F28335s, which are used for the control of the bidirectional DC / DC module and the bidirectional DC / AC module respectively. Among them, the LLC power tube uses a Sic tube with a switching frequency of 150kHz; Boost / Buck and T-type three-level power tubes use IGBTs for cost considerations, with a switching frequency of 20kHz. In addition, there are three inverter inductors in the bidirectional DC / AC module, and each inverter inductor uses the same core and three windings, which are used in a three-phase parallel circuit, which is beneficial to reduce the volume of the inverter inductor and improve the power density of the device. Similarly, those skilled in the art can refer to this design and use the same implementation method for the bidirectional DC / DC circuit. See Table 2 for specific parameters.

[0053] Table 3 Main circuit detailed parameters

[0054] 5.3 Verification of stable operation of the whole machine Experimental conditions: A 550V DC voltage was added to the DC side of the 40kW prototype electric vehicle, and three-phase AC power was added to the grid side for full load operation.

[0055] The experimental results are as follows Fig.12 shown.

[0056] Fig.12 a) It can be seen that when the single-channel bidirectional LLC circuit resonant cavity current i Lr1 Corresponding Sic tube drive waveform DR Q1-3 :Drive waveform low level -2V, high level +16V; single bidirectional LLC resonant cavity current i Lr =8.5A, LLC circuit achieves soft switching and stable operation; Fig.12 b) It can be seen that the DC side voltage of the prototype U BAT =550V, discharge current I BAT =72.5A, grid side A phase voltage u a =232.8V, grid side A phase current i a =19.2A. The prototype has a normal discharge waveform at full load, and the discharge function at a DC high voltage of 1000V is realized.

[0057] "Wake up" and "Sleep" function verification Taking charging as an example, two operating condition experiments, load sudden addition and load sudden unloading, were carried out on the electric vehicle side to verify the control strategy of the device.

[0058] Experimental conditions: DC side voltage 550V, grid side voltage 232.8V; load sudden increase is from 30% to 90% instantaneously, load sudden decrease is from 90% to 30% instantaneously.

[0059] The experimental results are as follows Fig.13 , Fig.14 shown.

[0060] Fig.13 In the example, the DC side waveform is the current waveform of the three parallel branches of bidirectional Boost / Buck1, bidirectional Boost / Buck2, and bidirectional Boost / Buck3 (corresponding to currents I1, I2, and I3). The "wake-up" and "sleep" states of the corresponding branches can be determined by the change in current. Similarly, the grid side waveform is the current waveform of the three parallel branches of the A-phase bidirectional DC / AC circuit (corresponding to current i a-1 、i a-2 、i a-3 ).

[0061] Fig.13 a) It can be seen that when the load is suddenly increased, the current waveform of I1 remains unchanged, I1=10.9A; the waveforms of I2 and I3 increase from 0A to 10.9A instantly. Fig.13 b) It can be seen that when the load is suddenly increased, i a-1 The current waveform remains unchanged, i a-1 =18.5A; the waveforms of I2 and I3 increase from 0A to 18.5A instantly. Fig.13 From the waveform results, it can be seen that when the load suddenly increases, the two branches on the DC side and the grid side are "woken up" and start working.

[0062] Fig.14 a) It can be seen that when the load is suddenly unloaded, the current waveform of I1 remains unchanged, I1=10.9A; the waveforms of I2 and I3 drop from 10.9A to 0A instantly. Fig.14 b) It can be seen that when the load is suddenly unloaded, i a-1 The current waveform remains unchanged, i a-1 =18.5A; the waveforms of I2 and I3 drop from 18.5A to 0A instantly. Fig.14 From the waveform results, it can be seen that when the load is suddenly unloaded, the two branches on the DC side and the grid side are "dormant" and shut down.

[0063] Through the experimental results, the "wake up" and "sleep" functions of the device were verified.

[0064] The "charging and discharging equipment" referred to in the present invention generally refers to electric vehicles, but the scheme is also applicable to scenarios such as electric vehicles and electric boats. This embodiment uses electric vehicles as an example to construct and test the scheme, but it does not mean that the scheme is only applicable to electric vehicles, nor does it mean that the protection scope only involves electric vehicles.

[0065] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

[0066] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of devices and methods for improving charging and discharging safety under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A device for improving charging and discharging safety, characterized in that: It includes a bidirectional DC / DC module and a bidirectional DC / AC module connected to each other, wherein the bidirectional DC / DC module includes a bidirectional Boost / Buck module and a bidirectional LLC module connected to each other; the bidirectional DC / DC module is connected to a charging and discharging device, and the bidirectional DC / AC module is connected to a power grid; The bidirectional DC / DC module includes a bidirectional Boost / Buck module and a bidirectional LLC module which are cascaded to realize the bidirectional DC / DC function; wherein the bidirectional Boost / Buck module is used for bidirectional boost / step-down of DC voltage, and the bidirectional LLC module adopts an open-loop design for electrical isolation between the charging and discharging device side and the grid side.

2. The device for improving charge and discharge safety according to claim 1, characterized in that: The bidirectional Boost / Buck module is composed of 6 bidirectional Boost / Buck circuits, and the bidirectional LLC module is composed of 6 bidirectional LLC circuits; among them, 3 bidirectional Boost / Buck circuits and 3 bidirectional LLC circuits are serially cascaded to realize energy transfer between the DC voltage of the charging and discharging equipment and the positive bus voltage; and another 3 bidirectional Boost / Buck circuits and 3 bidirectional LLC circuits are serially cascaded to realize energy transfer between the DC voltage and the negative bus voltage.

3. The device for improving charge and discharge safety according to claim 2, characterized in that: Each bidirectional Boost / Buck circuit is connected to a DC switching device, including a switch RLY1 connected in parallel and a switch RLY2 connected in series with a buffer resistor R1: In the discharge direction, the DC voltage is converted into bus voltage: When RLY2 is closed, the bidirectional LLC circuit is opened, and the DC voltage on the charging and discharging device side charges the bus electrolytic capacitor C1 through the buffer resistor R1; After the busbar slow start is completed, RLY1 is closed and RLY2 is disconnected; at this time, the bidirectional Boost / Buck circuit constitutes a standard Boost circuit; the DC voltage on the charging and discharging device side is boosted by the Boost circuit; The bidirectional LLC circuit acts as an electrically isolated DC converter to electrically isolate the output voltage of the Boost circuit to the positive bus voltage; In the charging direction, the bus voltage charges the charging and discharging equipment: After RLY1 is closed, the bus voltage is electrically isolated through the bidirectional LLC circuit and then transmitted to the bidirectional Boost / Buck1 for voltage reduction. The bidirectional Boost / Buck circuit now constitutes a standard Buck circuit to charge the charging and discharging equipment.

4. The device for improving charge and discharge safety according to claim 2, characterized in that: The voltage gain of the bidirectional LLC circuit is set to 2:

1.

5. The device for improving charging and discharging safety according to claim 1, characterized in that: The bidirectional DC / AC module includes a three-phase DC / AC circuit and an AC switching device; the AC switching device is used to switch on / off the grid; the three-phase DC / AC circuit is used for energy transfer between the positive and negative busbars and the grid, and each phase is composed of three T-type three-level circuits in parallel.

6. The device for improving charge and discharge safety according to claim 2, characterized in that: The switching frequencies of the branches of the bidirectional Boost / Buck module are the same and the phases of the main switch tubes of each branch turn on at a time point different by 60°, so that the six bidirectional Boost / Buck circuits are staggered in parallel for closed-loop control.

7. The device for improving charge and discharge safety according to claim 1, characterized in that: The multiple inverter inductors in the bidirectional DC / DC module and / or the bidirectional DC / AC module are implemented in the manner of having the same magnetic core but different windings, and are respectively used for different groups of circuits.

8. A method for improving charge and discharge safety, characterized in that: A device for improving charging and discharging safety based on any one of claims 1-7: a bidirectional Boost / Buck circuit and a bidirectional LLC circuit, one of which is connected to a positive bus and the other to a negative bus, and one branch of a three-phase circuit of a DC / AC circuit form a circuit group, so that the device has a total of three circuit groups; after the soft start is completed, one, two or three circuit groups are enabled according to a set load threshold.

9. The method for improving charge and discharge safety according to claim 8, characterized in that: By enabling or disabling each group of circuits, it can adapt to changes in load during charging and discharging of the battery side and when the grid side is connected to or disconnected from the grid.

10. The method for improving charge and discharge safety according to claim 8, characterized in that: A time-sharing and orderly working strategy is adopted to balance the duration of activation of each group of circuits.

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