Power battery balancing and heating composite circuit based on bidirectional LC resonance

Abstract

The power battery equalization and heating composite circuit based on bidirectional LC resonance realizes the equalization and heating of the power battery by bidirectional switching of the LC resonance unit. The active equalization and heating composite circuit is innovatively designed. Without adding external equipment, it solves the technical problems of equalization current attenuation and low heating efficiency in the prior art. The equalization circuit and the heating circuit are integrated, which can not only equalize the power but also use the same circuit to heat the power battery in a low temperature environment, improve the performance of the power battery, and ensure the normal operation of the power battery. The resonant frequency is halved during the equalization and heating process compared with the traditional method to reduce the stringent requirements for precise control of the switch components and effectively improve the reliability of the device. The system only needs to obtain the power of the battery cell and the temperature information of the power battery, and reasonably select the function of the circuit to achieve coordination between the equalization and heating functions. It is not only low-cost, but also simple and reliable to implement.

Description

Technical Field

[0001] The present invention belongs to the technical field of power battery charge balancing and heating, and in particular relates to a power battery balancing and heating integrated circuit based on bidirectional LC resonance. Background Art

[0002] In the existing charging system for power battery packs, balancing circuits are mainly used to ensure the consistency of the power of each cell in the battery pack. The principle is to transfer electrical energy from high-power cells to low-power cells. However, the LC resonance unit used in some cases will gradually reduce the voltage difference and current in the circuit, so there is a problem of unsatisfactory balancing speed and efficiency.

[0003] There are two types of balancing circuits: active balancing and passive balancing. Currently, in addition to considering the basic purpose of single-cell battery balancing, the designs of these two methods ignore the heat generated during the battery balancing process. In the active balancing circuit, the current generated is large, and the heat generated inside the battery is large, but this heat is not reasonably utilized. In the passive balancing circuit, high-capacity batteries are mainly discharged through energy-consuming resistors. The heat generated by the energy-consuming resistors is directly dissipated into the air, and there is also a problem of heat energy waste. Power batteries will experience performance degradation and explosion in low-temperature environments, so there is a need for heating in low-temperature environments. The existing solution is mainly to set up a heating circuit and use the internal short circuit of the battery or external heating components to heat the battery. However, there is still a lack of technical solutions in this field to effectively utilize the heat generated in the above-mentioned balancing process for low-temperature heating of power battery packs. Summary of the invention

[0004] In view of the technical problems existing in the above-mentioned field, the present invention provides a power battery equalization and heating composite circuit based on bidirectional LC resonance, comprising: a battery pack, an LC resonance unit, an LC direction switching unit, positive busbars A+ and B+, negative busbars A- and B-, and a temperature sensing unit;

[0005] Wherein, the battery pack is composed of a number of battery cells connected in series;

[0006] The LC direction switching unit includes 8 power electronic switches Q1 to Q8, and a single switch group set for each battery cell; the positive electrode of the LC resonance unit is connected to one end of Q1, Q2, Q5, and Q6 respectively, and the negative electrode is connected to one end of Q3, Q4, Q7, and Q8 respectively; the other ends of Q1 and Q3 are connected to the electrode bus A+, the other ends of Q2 and Q4 are connected to the electrode bus B+, the other ends of Q5 and Q7 are connected to the electrode bus A-, and the other ends of Q6 and Q8 are connected to the electrode bus B-; the single switch group includes 4 switch elements, and each battery cell is connected to the electrode bus A+, B+, A-, and B- through each switch element;

[0007] The temperature sensing unit is used to detect the temperature of each battery cell;

[0008] During balancing, the LC direction switching unit cooperates with the power electronic switch and the single-cell switch component to cyclically switch four loop connection states in sequence at each current zero-crossing point of the sinusoidal alternating current flowing through the LC resonance unit: ① The high-power battery cell is forwardly connected to the LC resonance unit; ② The low-power battery cell is forwardly connected to the LC resonance unit; ③ The high-power battery cell is reversely connected to the LC resonance unit; ④ The low-power battery cell is reversely connected to the LC resonance unit.

[0009] The principle of switching the above four circuit connection states to achieve balancing is specifically as follows: when there are cells with higher and lower voltages in the battery pack, that is, there is a need for balancing, first the high-power battery cell is forwardly connected to the LC resonance unit to enter state ①, at which time the high-power battery cell is discharged and charged to the LC resonance unit, and the LC resonance unit begins to attenuate and oscillate. When the sinusoidal alternating current flowing through reaches the first zero crossing point, the high-power battery cell is disconnected from the LC resonance unit and forwardly connected to the low-power battery cell to enter state ②. At this time, the LC resonance unit transfers energy to the low-power battery cell under the action of the voltage difference, and switches to state ③ at the second current zero crossing point, so that the high-power battery cell is reversely connected to the LC resonance unit, and the LC resonance unit is charged again, and switches to state ④ at the third current zero crossing point, so that the LC resonance unit is reversely connected to the low-power battery cell, thereby transferring energy to the low-power battery again.

[0010] After going through a complete cycle, the LC resonant unit capacitor does not accumulate energy. Therefore, when entering the next cycle, the current will not decrease as the battery voltage difference decreases. The loop current in the four states is only related to the voltage of the high-capacity battery cell when the first attenuation oscillation occurs in states ① and ③. This can overcome the problem of the LC oscillation current gradually decreasing to a certain extent, thereby improving the balancing speed and efficiency.

[0011] Furthermore, when heating a battery pack with an odd number of battery cells, the LC direction switching unit cooperates with the power electronic switch and the single cell switch component to reverse the connection direction between the LC resonance unit and the battery pack at the last zero crossing point of each cycle of the sinusoidal current flowing through the LC resonance unit, thereby causing the internal resistance of the battery component to generate heat.

[0012] Furthermore, when heating a battery pack with an even number of battery cells, the battery cells are first divided into two groups, and the LC direction switching unit cooperates with the power electronic switch and the single-cell switch component to cyclically switch four loop connection states in sequence at each current zero crossing point of the sinusoidal alternating current flowing through the LC resonance unit: ① the first group of battery cells are forwardly connected to the LC resonance unit; ② the second battery cells are forwardly connected to the LC resonance unit; ④ the second group of battery cells are reversely connected to the LC resonance unit; ③ the first group of battery cells are reversely connected to the LC resonance unit.

[0013] The principle of switching the above four circuit connection states to achieve heating is as follows: when the battery pack is in a low temperature environment and has a heating demand, the first group of battery cells is first connected to the LC resonance unit in a forward direction to enter state ①. At this time, the first group of battery cells discharges and charges the LC resonance unit, and the LC resonance unit begins to decay and oscillate. When the sinusoidal alternating current flowing through reaches the first zero crossing point, the connection between the first group of battery cells and the LC resonance unit is disconnected and connected to the second group of battery cells in a forward direction to enter state ②. At this time, the LC resonance unit transfers energy to the second group of battery cells under the action of the voltage difference. At the second current zero crossing point, it switches to state ④, and the LC resonance unit is reversely connected to the second group of battery cells, thereby transferring energy to the low-power battery again. The second group of battery cells is reversely connected to the LC resonance unit, and the LC resonance unit is charged again. At the third current zero crossing point, it switches to state ③. Through this cycle, energy flows and transfers between the two batteries through the LC resonance unit, and the two groups of batteries generate heat due to the action of internal resistance.

[0014] After a complete cycle, the two groups of battery cells are charged alternately to generate heat. The LC resonant unit capacitor does not accumulate energy, and the current is always maintained at a high level, which increases the heating rate.

[0015] Furthermore, the power electronic switch adopts a pair of back-to-back connected bidirectional switch MOS tubes, a pair of back-to-back connected IGBTs or bidirectional thyristors.

[0016] Furthermore, the resonance frequency of the LC resonance unit is greater than 1000 Hz.

[0017] The power battery balancing and heating composite circuit based on bidirectional LC resonance provided by the present invention heats and balances the power battery by bidirectionally switching the LC resonance unit. The innovative design of the active balancing and heating composite circuit solves the technical problems of balancing current attenuation and low heating efficiency in the prior art without adding external equipment. The balancing circuit and the heating circuit are integrated, which can balance the power and use the same circuit to heat the power battery in a low temperature environment, thereby improving the performance of the power battery and ensuring the normal operation of the power battery. The resonant frequency during the balancing and heating process is halved compared to the traditional method. The switching states of the four groups of MOS tubes in operation require four synchronous control signals with a phase difference of 90 degrees, which still have certain precision requirements, but after the switching frequency of the MOS tube is reduced, the reliability of the device can be significantly improved. The system only needs to obtain the power of the battery cell and the temperature information of the power battery, and reasonably select the function of the circuit to achieve the coordination between the balancing and heating functions. It is not only low-cost, but also simple and reliable to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A circuit diagram of the present invention;

[0019] Figure 2 Four state cycles of connection between the battery and the bidirectional LC resonance unit in the present invention;

[0020] Figure 3 The cycle of the circuit state during the heating process of a battery pack with an odd number of battery cells;

[0021] Figures 4 to 7 Changes in the connection relationship of the LC resonant unit during the odd-numbered monomer heating cycle;

[0022] Figure 8 Cycle of circuit states during heating of a battery pack with an odd number of cells;

[0023] Fig. 9 It is an optional form of bidirectional power electronic switch.

[0024] In the figure, S1-S4n are battery cell switch elements, and Q1-Q8 are power electronic switches. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0027] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] The present invention provides a power battery balancing and heating composite circuit based on bidirectional LC resonance, such as Figure 1 As shown, it includes: a battery pack, an LC resonance unit, an LC direction switching unit, positive bus bars A+ and B+, negative bus bars A- and B-, and a temperature sensing unit;

[0029] Wherein, the battery pack is composed of a number of battery cells connected in series;

[0030] The LC direction switching unit includes 8 power electronic switches Q1 to Q8, and a single switch group set for each battery cell; the positive electrode of the LC resonance unit is connected to one end of Q1, Q2, Q5, and Q6 respectively, and the negative electrode is connected to one end of Q3, Q4, Q7, and Q8 respectively; the other ends of Q1 and Q3 are connected to the electrode bus A+, the other ends of Q2 and Q4 are connected to the electrode bus B+, the other ends of Q5 and Q7 are connected to the electrode bus A-, and the other ends of Q6 and Q8 are connected to the electrode bus B-; the single switch group includes 4 switch elements, and each battery cell is connected to the electrode bus A+, B+, A-, and B- respectively through each switch element; the LC resonance unit includes an inductor that can pass a large current and a non-polar capacitor with high withstand voltage;

[0031] The temperature sensing unit is used to detect the temperature of each battery cell;

[0032] When balancing is required, such as when the SOC difference between two or more battery cells is greater than 3%, the system's active balancing mode is turned on. The LC direction switching unit cooperates through the power electronic switch and the single-cell switch component to define the position close to the inductor in the LC resonant unit as positive and the position close to the capacitor as negative. At each current zero-crossing point of the sinusoidal alternating current flowing through the LC resonant unit, the four loop connection states are switched in sequence: ① The high-power battery cell is forwardly connected to the LC resonant unit; ② The low-power battery cell is forwardly connected to the LC resonant unit; ③ The high-power battery cell is reversely connected to the LC resonant unit; ④ The low-power battery cell is reversely connected to the LC resonant unit. The complete cycle state changes are as follows: Figure 2 shown.

[0033] The principle of switching the above four circuit connection states to achieve balancing is as follows: when there are cells with higher and lower voltages in the battery pack, that is, when there is a need for balancing, first connect the high-power battery cell to the LC resonance unit in a forward direction and enter state ①. At this time, the high-power battery cell discharges and charges the LC resonance unit. The LC resonance unit begins to oscillate attenuated. When the sinusoidal AC current reaches the first zero crossing point, disconnect the high-power battery cell from the LC resonance unit and connect it in a forward direction to the low-power battery cell, entering state ②. At this time, the LC resonance unit transfers energy to the low-power battery cell under the action of the voltage difference. At the second current zero crossing point, switch to state ③, reversely connect the high-power battery cell to the LC resonance unit, and the LC resonance unit is charged again. At the third current zero crossing point, switch to state ④, reversely connect the LC resonance unit to the low-power battery cell, thereby transferring energy to the low-power battery again. The time spent in each state is Therefore, the switching frequency is Halved compared to existing technology.

[0034] After going through a complete cycle, the LC resonant unit capacitor does not accumulate energy. Therefore, when entering the next cycle, the current will not decrease as the battery voltage difference decreases. The loop current in the four states is only related to the voltage of the high-capacity battery cell when the first attenuation oscillation occurs in states ① and ③. This can overcome the problem of the LC oscillation current gradually decreasing to a certain extent, thereby improving the balancing speed and efficiency.

[0035] In a preferred embodiment of the present invention, when heating a battery pack having an odd number of battery cells, Figure 3 As shown, the LC direction switching unit works in coordination with the power electronic switch and the single switch component to reverse the connection direction between the LC resonance unit and the battery pack at the last zero-crossing point of each cycle of the sinusoidal current flowing through the LC resonance unit, thereby causing the internal resistance of the battery assembly to generate heat. Figure 4-Figure 7As shown, the arrow in the figure indicates the direction of current flow in the loop.

[0036] In a preferred embodiment of the present invention, when heating a battery pack having an even number of battery cells, Figure 8 First, the battery cells are divided into two groups, such as the series battery group is divided into two upper and lower parts, and the number of batteries connected in series in each part accounts for half of the overview. The LC direction switching unit cooperates with the power electronic switch and the monomer switch component to sequentially switch four circuit connection states at each current zero point of the sinusoidal alternating current flowing through the LC resonance unit: ① The first group of battery cells is forwardly connected to the LC resonance unit; ② The second battery cell is forwardly connected to the LC resonance unit; ④ The second group of battery cells is reversely connected to the LC resonance unit; ③ The first group of battery cells is reversely connected to the LC resonance unit.

[0037] The principle of switching the above four circuit connection states to achieve heating is as follows: when the battery pack is in a low temperature environment and has a heating demand, the first group of battery cells is first connected to the LC resonance unit in a forward direction to enter state ①. At this time, the first group of battery cells discharges and charges the LC resonance unit, and the LC resonance unit begins to decay and oscillate. When the sinusoidal alternating current flowing through reaches the first zero crossing point, the connection between the first group of battery cells and the LC resonance unit is disconnected and connected to the second group of battery cells in a forward direction to enter state ②. At this time, the LC resonance unit transfers energy to the second group of battery cells under the action of the voltage difference. At the second current zero crossing point, it switches to state ④, and the LC resonance unit is reversely connected to the second group of battery cells, thereby transferring energy to the low-power battery again. The second group of battery cells is reversely connected to the LC resonance unit, and the LC resonance unit is charged again. At the third current zero crossing point, it switches to state ③. Through this cycle, energy flows and transfers between the two batteries through the LC resonance unit, and the two groups of batteries generate heat due to the action of internal resistance. After a complete cycle, the two groups of battery cells are charged alternately to generate heat. The LC resonant unit capacitor does not accumulate energy, and the current is always maintained at a high level, which increases the heating rate.

[0038] In a preferred embodiment of the present invention, the power electronic switch is a pair of MOS tubes with sources connected to each other, a pair of IGBTs connected back to back, or a bidirectional thyristor. Fig. 9 The figure shows a bidirectional power electronic switch composed of two N-type MOS tube sources connected back to back, with the drains of the two MOS tubes serving as outputs. The diode in the figure is a diode inside the MOS tube.

[0039] Figure 1 At the same time, a composite equalization and heating system for a four-cell series-connected battery pack based on the present invention is shown.

[0040] It should be understood that the size of the serial numbers of the steps in the embodiment of the present invention does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0041] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A power battery equalization and heating composite circuit based on bidirectional LC resonance, characterized in that: The circuit includes: a battery pack, an LC resonance unit, an LC direction switching unit, positive busbars A+ and B+, negative busbars A- and B-, and a temperature sensing unit; Wherein, the battery pack is composed of a number of battery cells connected in series; The LC direction switching unit includes 8 power electronic switches Q1-Q8, and a single switch group set for each battery cell; the power electronic switch adopts a pair of bidirectional MOS tubes connected back to back, a pair of IGBTs or bidirectional thyristors connected back to back; the positive electrode of the LC resonance unit is respectively connected to one end of Q1, Q2, Q5, and Q6, and the negative electrode is respectively connected to one end of Q3, Q4, Q7, and Q8; the other ends of Q1 and Q3 are connected to the electrode bus A+, the other ends of Q2 and Q4 are connected to the electrode bus B+, the other ends of Q5 and Q7 are connected to the electrode bus A-, and the other ends of Q6 and Q8 are connected to the electrode bus B-; the single switch group includes 4 switch elements, and each battery cell is connected to the electrode bus A+, B+, A-, and B- through each switch element; The temperature sensing unit is used to detect the temperature of each battery cell; During balancing, the LC direction switching unit cooperates with the power electronic switch and the single switch component to sequentially switch four loop connection states at each current zero-crossing point of the sinusoidal alternating current flowing through the LC resonance unit: ① the high-power battery single cell is forwardly connected to the LC resonance unit; ② the low-power battery single cell is forwardly connected to the LC resonance unit; ③ the high-power battery single cell is reversely connected to the LC resonance unit; ④ the low-power battery single cell is reversely connected to the LC resonance unit; When heating a battery pack with an odd number of battery cells, the LC direction switching unit works in coordination with the power electronic switch and the single cell switch assembly to reverse the connection direction between the LC resonance unit and the battery pack at the last zero crossing point of each cycle of the sinusoidal current flowing through the LC resonance unit, thereby causing the internal resistance of the battery assembly to generate heat; When heating a battery pack with an even number of battery cells, the battery cells are first divided into two groups. The LC direction switching unit cooperates with the power electronic switch and the single-cell switch component to cyclically switch four loop connection states in sequence at each current zero-crossing point of the sinusoidal alternating current flowing through the LC resonance unit: ① the first group of battery cells are forwardly connected to the LC resonance unit; ② the second battery cell is forwardly connected to the LC resonance unit; ③ the second group of battery cells is reversely connected to the LC resonance unit; ④ the first group of battery cells is reversely connected to the LC resonance unit.

2. The circuit according to claim 1, characterized in that: The resonance frequency of the LC resonance unit is greater than 1000 Hz.

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