A power battery pack balancing and grid-connected device and control method

Abstract

A power battery inter-pack balancing and grid-connection device and control method primarily includes an anti-backflow diode, an inductor, a transistor switch, a freewheeling diode, and a high-voltage DC control switch. The anti-backflow diode enables unidirectional power output, the control switch enables bidirectional power output, and the transistor switch, inductor, and freewheeling diode enable controlled power flow. The control method includes unidirectional power output from the power battery, power battery balancing control, and bidirectional power battery input and output. This solution can adjust power battery balancing and grid-connection control based on the power battery voltage in different environments and at different SOCs, avoid grid-connection shock, and extend the power battery's service life.

Description

Technical Field

[0001] The present invention relates to the field of power systems and battery technology, and in particular to a battery pack balancing device and a grid-connected control method. Background Art

[0002] Currently, in electric and hybrid vehicles, the demand for ever-increasing power battery capacity leads to the common practice of connecting two battery packs in parallel for reasons of size, installation, and safety. During use, due to variations in battery consistency and temperature, voltage differences can be significant after prolonged use or storage. Alternatively, replacing one battery pack can create a significant voltage difference between the two packs. Simply connecting two packs in parallel can result in a significant surge current, damaging electrical components or significantly impacting the batteries. Furthermore, inappropriate charging currents at low temperatures can also harm the batteries. Summary of the Invention

[0003] The present disclosure provides a battery pack balancing device and control strategy for achieving controlled grid connection / balancing of power batteries, which not only meets the power demand of the power grid, but also can realize battery charge and discharge management according to the power battery operating conditions, avoid grid connection impact or overcharging of the power battery, and extend the service life of the power battery.

[0004] The battery pack balancing and grid-connected device provided in the present disclosure is arranged between the positive electrode of each power battery pack and the DC grid, and specifically includes:

[0005] Anti-backflow diode, used to achieve unidirectional power output;

[0006] High-voltage DC control switch, used to achieve bidirectional power output;

[0007] Switching transistors, freewheeling diodes, and inductors are used to achieve controlled flow of power;

[0008] in:

[0009] The anti-backflow diodes include two groups. The anodes of the first group of anti-backflow diodes are connected to the positive electrodes of the power battery packs, and the cathodes are connected to the positive electrode of the DC bus. Both ends of the first group of anti-backflow diodes are connected in parallel with a high-voltage DC control switch.

[0010] The drain of the transistor is connected to the positive electrode of the DC bus;

[0011] The source of the transistor is connected to the inductor, the other end of the inductor is connected to the anode of the second group of anti-backflow diodes, and the cathode of the second group of anti-backflow diodes is connected to the positive electrode of each power battery pack;

[0012] In addition, the source of the transistor is connected to the cathode of the freewheeling diode, and the anode of the freewheeling diode is connected to the negative electrode of the power battery pack.

[0013] Furthermore, the high-voltage DC control switch adopts a high-voltage DC contactor or a high-voltage DC relay.

[0014] Furthermore, the switching transistor is an IGBT transistor or a silicon carbide MOS transistor.

[0015] Furthermore, the device includes: a first group of anti-backflow diodes D1 and D2, a second group of anti-backflow diodes D3 and D4, and high-voltage DC control switches K1 and K2, wherein:

[0016] The positive electrode of the first battery pack is connected to the positive electrode of the DC bus through the diode D1, and the positive electrode of the second battery pack is connected to the positive electrode of the DC bus through the diode D2;

[0017] Both ends of D1 are connected in parallel with K1, and both ends of D2 are connected in parallel with K2;

[0018] The source of the transistor is connected to the inductor L, and the other end of L is connected to the positive electrode of the first battery pack via the diode D3 and connected to the positive electrode of the second battery pack via the diode D4;

[0019] At the same time, the source of the transistor is connected to the cathode of the freewheeling diode D5, and the anode of D5 is grounded.

[0020] The method for controlling the balancing of power battery packs applied to the above device comprises the following steps:

[0021] S1, unidirectional power output of the power battery: in a low-temperature environment and before the battery is heated, the battery with a higher SOC or terminal voltage outputs power to the grid in a unidirectional manner through the anti-backflow diode;

[0022] S2, power battery balancing: After completing step S1, the power battery is connected to the grid through the anti-backfeed diode. The switching transistor, inductor L, freewheeling diode and the second set of anti-backfeed diodes form a Buck circuit, and the battery with a higher terminal voltage controls the charging of the battery with a lower terminal voltage.

[0023] S3, bidirectional input and output of power batteries: When a single or dual group of power batteries meet the conditions for high-power charging and discharging, by closing their corresponding high-voltage DC control switches, they can be directly connected to the grid to achieve uncontrolled charging and discharging.

[0024] Furthermore, the step S1 specifically includes:

[0025] When the power battery needs to be connected to the grid, the power battery first pre-charges the grid capacitor. After the pre-charging is completed, the battery with a higher SOC or terminal voltage outputs power to the grid through the first set of anti-backflow diodes, and the battery with a lower SOC or terminal voltage is cut off.

[0026] When the power required by the grid increases, the output terminal voltage of the power battery is lowered, and the battery with lower SOC or terminal voltage participates in discharge through the first set of anti-backflow diodes, thereby increasing the total output power of the battery.

[0027] Furthermore, the step S2 specifically includes:

[0028] After completing the unidirectional power output step of the power battery, the power battery is connected to the grid through the first set of anti-backflow diodes. At this time, the switching transistor, the inductor, the freewheeling diode and the second set of anti-backflow diodes connected to the two groups of power batteries form a Buck circuit. By adjusting the IGBT duty cycle, closed-loop control is performed to control the current flowing from the battery with higher terminal voltage to the battery with lower terminal voltage, and the battery with lower terminal voltage is controlled to be charged so that the two groups of batteries are close to balance.

[0029] Furthermore, the step S2 further includes:

[0030] When there is a generator or DC source on the bus, the total current flowing from the bus to the two groups of power batteries is controlled, and the batteries are charged in a controlled manner to make the two groups of batteries close to balance.

[0031] Furthermore, the step S3 specifically includes:

[0032] S31, bidirectional input and output of a single power battery group: When a single power battery group is heated or meets the conditions for high-power charging and discharging, the corresponding high-voltage DC control switch is closed to connect it directly to the grid, realizing uncontrolled charging and discharging;

[0033] At the same time, another group of power batteries is charged in a controlled manner through switching transistors and inductors to achieve balance between the two groups of batteries;

[0034] S32, two sets of power batteries bidirectional input and output:

[0035] When it is detected that the SOC or terminal voltage of the two power battery groups are within the allowable range, the corresponding high-voltage DC control switches are closed, so that the two power battery groups are directly connected to the grid to achieve uncontrolled charging and discharging.

[0036] Furthermore, the balancing device determines the battery temperature according to the temperature signal and then controls the corresponding high-voltage DC control switch to open or close.

[0037] Compared with the prior art, the beneficial effects of the present invention are: (1) according to the different SOC or terminal voltage conditions of the power battery, the power battery can be quickly connected to the grid while performing inter-group balancing, taking into account the peak shaving and valley filling function to stabilize the grid voltage; (2) the battery charge and discharge management is realized according to the power battery working condition, the charging / balancing current is effectively controlled, and the power battery grid connection impact or overcharging is avoided; (3) the power battery is effectively protected and the service life of the power battery is extended; (4) the cost is low and the control and measurement are simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present disclosure.

[0039] Figure 1 The circuit structure of an exemplary power battery pack balancing and grid-connected control device according to the present disclosure is as follows;

[0040] Figure 2 Schematic diagram of the overall relationship between an exemplary balancing and grid-connected control device, a power battery pack, and a DC grid;

[0041] Figure 3 4 is a flow chart of an exemplary power battery pack balancing and grid-connected control method according to the present disclosure. DETAILED DESCRIPTION

[0042] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0043] The present disclosure provides a power battery pack balancing and grid-connected device, which can achieve balancing between power battery packs and grid connection with the power grid, and effectively control the charge and discharge current during use, safely control the charge and discharge of the power battery, and thus improve the reliability of the power battery.

[0044] As attached Figure 1 and attached Figure 2 As shown, an exemplary embodiment according to the present disclosure includes:

[0045] Diodes: D1, D2, D3, D4, D5, among which D1-D4 are anti-backflow diodes and D5 is a freewheeling diode;

[0046] High-voltage DC control switches: K1, K2, K3, K4, K5, K6, of which K1 and K2 are built into the balancing device, K3, K4, K5, K6 are built into the power battery, K3 and K4 are the battery main switches, and K5 and K6 are pre-charge switches; high-voltage DC contactors or relays are used;

[0047] S is a switching transistor, preferably an IGBT transistor or a silicon carbide MOS tube;

[0048] L is the inductance,

[0049] Bus load: R L

[0050] Bus capacitor: C1.

[0051] Among them, the anti-backflow diode is used to realize unidirectional power output, the contactor or relay is used to realize bidirectional power output, and the IGBT, inductor and freewheeling diode are used to realize the controlled flow of power flow.

[0052] The balancing control strategy between power battery groups using the above device mainly includes the following three parts: unidirectional power output of power batteries, power battery balancing control, and bidirectional input and output of power batteries.

[0053] The operation flow chart of the control strategy is as follows: Figure 3 The detailed steps are as follows:

[0054] 1. One-way output of power battery

[0055] When the power battery needs to be connected to the grid, power battery K5 and K6 are energized to pre-charge the grid capacitor. After pre-charging is completed, K3 and K4 are energized, and the battery with a higher SOC / terminal voltage outputs power to the grid through a diode (D1 or D2), while the battery with a lower SOC / terminal voltage is cut off. When the power required by the grid increases, the output power battery terminal voltage is lowered, and the battery with a lower SOC / terminal voltage participates in discharge through a diode (D1 or D2), thereby increasing the total output power of the battery.

[0056] During this process, the power battery can only discharge due to the presence of the diode and does not participate in charging. This allows the power battery to discharge in low-temperature environments without charging until it is fully heated, thus preventing damage to the battery from charging in low-temperature environments. The battery temperature is determined by the balancing device and controls the relay operation.

[0057] 2. Power battery balancing

[0058] After completing the unidirectional power output step of the power battery, the power battery is connected to the grid through diodes (referring to D1 and D2) (K1 and K2 are disconnected). At this time, the IGBT, inductor L, diodes D3 and D4, and freewheeling diode D5 form a Buck circuit. By adjusting the IGBT duty cycle, closed-loop control can be used to control the current flowing from the battery with higher terminal voltage to the battery with lower terminal voltage (pure electric mode), or when there is a generator or DC source on the bus, the total current flowing from the bus to the two power batteries (hybrid mode), effectively controlling the power battery charging current to avoid overcharging damage or affecting the battery life.

[0059] This allows controlled charging of the batteries, which balances the two battery groups; discharging is not affected at this time.

[0060] 3. Bidirectional input and output of power batteries

[0061] 1) Bidirectional input and output of a single power battery

[0062] When a single group of power batteries is heated or has high-power charging and discharging conditions, the corresponding contactor (K1 or K2) is closed, the diode (D1 or D2) is short-circuited, and the power battery is directly connected to the grid to achieve uncontrolled charging and discharging.

[0063] At the same time, another group of power batteries can be charged in a controlled manner through IGBT and inductance, thereby ultimately achieving balance between the two groups of batteries.

[0064] 2) Two sets of power batteries with bidirectional input and output

[0065] When it is detected that the SOC / terminal voltage of the two power battery groups is within the allowable range, the corresponding contactors (K1 and K2) are closed, the diodes (D1 and D2) are short-circuited, and the two power battery groups are directly connected to the grid to achieve uncontrolled charging and discharging.

[0066] According to this inter-group balancing and grid-connected control method, the SOC of the power battery can be adjusted according to the different charging and discharging capabilities of the power battery in a complex environment, taking into account the grid connection and balancing of the power battery, achieving balance during the grid connection process, and providing peak-shaving and valley-filling energy to the power grid as quickly as possible. At the same time, the battery can be effectively protected and its service life can be extended.

[0067] The above technical solutions are only exemplary embodiments of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the application methods and principles disclosed in the present invention, and are not limited to the methods described in the above specific embodiments of the present invention. Therefore, the methods described above are only preferred and do not have a restrictive meaning.

Claims

1. A method for controlling power battery pack balance between power battery packs and a grid-connected device, The device is arranged between the positive electrode of each power battery pack and the DC grid, and specifically includes: Anti-backflow diode, used to achieve unidirectional power output; High-voltage DC control switch, used to achieve bidirectional power output; Switching transistors, freewheeling diodes, and inductors are used to achieve controlled flow of power; in: The anti-backflow diodes include two groups. The anodes of the first group of anti-backflow diodes are connected to the positive electrodes of the power battery packs, and the cathodes are connected to the positive electrode of the DC bus. Both ends of the first group of anti-backflow diodes are connected in parallel with a high-voltage DC control switch. The drain of the transistor is connected to the positive electrode of the DC bus; The source of the transistor is connected to the inductor, the other end of the inductor is connected to the anode of the second group of anti-backflow diodes, and the cathode of the second group of anti-backflow diodes is connected to the positive electrode of each power battery pack; In addition, the source of the transistor is connected to the cathode of the freewheeling diode, and the anode of the freewheeling diode is connected to the negative electrode of the power battery pack; The high-voltage DC control switch adopts a high-voltage DC contactor or a high-voltage DC relay; The switching transistor is an IGBT transistor or a silicon carbide MOS transistor; The device includes: a first group of anti-backflow diodes D1 and D2, a second group of anti-backflow diodes D3 and D4, and high-voltage DC control switches K1 and K2, wherein: The positive electrode of the first battery pack is connected to the positive electrode of the DC bus through the diode D1, and the positive electrode of the second battery pack is connected to the positive electrode of the DC bus through the diode D2; Both ends of D1 are connected in parallel with K1, and both ends of D2 are connected in parallel with K2; The source of the transistor is connected to the inductor L, and the other end of L is connected to the positive electrode of the first battery pack via the diode D3 and connected to the positive electrode of the second battery pack via the diode D4; At the same time, the source of the transistor is connected to the cathode of the freewheeling diode D5, and the anode of D5 is grounded; Characterized in that the method comprises the following steps: S1, unidirectional power output of the power battery: in a low-temperature environment and before the battery is heated, the battery with a higher SOC or terminal voltage outputs power to the grid in a unidirectional manner through the anti-backflow diode; S2, power battery balancing: After completing step S1, the power battery is connected to the grid through the anti-backfeed diode. The switching transistor, inductor L, freewheeling diode and the second set of anti-backfeed diodes form a Buck circuit, and the battery with a higher terminal voltage controls the charging of the battery with a lower terminal voltage. S3, bidirectional input and output of power batteries: When a single or dual group of power batteries meet the conditions for high-power charging and discharging, by closing their corresponding high-voltage DC control switches, they can be directly connected to the grid to achieve uncontrolled charging and discharging.

2. The method according to claim 1, characterized in that The step S1 specifically includes: When the power battery needs to be connected to the grid, the power battery first pre-charges the grid capacitor. After the pre-charging is completed, the battery with a higher SOC or terminal voltage outputs power to the grid through the first set of anti-backflow diodes, and the battery with a lower SOC or terminal voltage is cut off. When the power required by the grid increases, the output terminal voltage of the power battery is lowered, and the battery with lower SOC or terminal voltage participates in discharge through the first set of anti-backflow diodes, thereby increasing the total output power of the battery.

3. The method according to claim 1, characterized in that The step S2 specifically includes: After completing the unidirectional power output step of the power battery, the power battery is connected to the grid through the first set of anti-backflow diodes. At this time, the switching transistor, the inductor, the freewheeling diode and the second set of anti-backflow diodes connected to the two groups of power batteries form a Buck circuit. By adjusting the IGBT duty cycle, closed-loop control is performed to control the current flowing from the battery with higher terminal voltage to the battery with lower terminal voltage, and the battery with lower terminal voltage is controlled to be charged so that the two groups of batteries are close to balance.

4. The method according to claim 3, characterized in that The step S2 further includes: When there is a generator or DC source on the bus, the total current flowing from the bus to the two groups of power batteries is controlled, and the batteries are charged in a controlled manner to make the two groups of batteries close to balance.

5. The method according to any one of claims 1 to 3, characterized in that: The step S3 specifically includes: S31, bidirectional input and output of a single power battery group: When a single power battery group is heated or meets the conditions for high-power charging and discharging, the corresponding high-voltage DC control switch is closed to connect it directly to the grid, realizing uncontrolled charging and discharging; At the same time, another group of power batteries is charged in a controlled manner through switching transistors and inductors to achieve balance between the two groups of batteries; S32, two sets of power batteries bidirectional input and output: When it is detected that the SOC or terminal voltage of the two power battery groups are within the allowable range, the corresponding high-voltage DC control switches are closed, so that the two power battery groups are directly connected to the grid to achieve uncontrolled charging and discharging.

6. The method according to claim 1, characterized in that The balancing device determines the battery temperature according to the temperature signal and then controls the corresponding high-voltage DC control switch to open or close.

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