Quasi-resonance equalization circuit based on bus LC and control method

Abstract

The invention belongs to the field of battery equalization, and discloses a quasi-resonance equalization circuit based on bus LC and a control method, the quasi-resonance equalization circuit comprises n batteries, 2n MOSFET switch tubes, n-1 LC energy storage modules and a switch controller; the n batteries are connected in series; and the LC storage module comprises a balancing capacitor C and a resonant inductor L which are connected in series. According to the invention, the equalization of the series battery pack can be realized, the control is simple, the equalization of any battery to any battery is realized, the distribution condition of initial voltage does not need to be considered, and the time required from the beginning of equalization to the end of equalization is irrelevant to the position of each battery monomer; the equalization speed is irrelevant to the number of the series batteries, after equalization is finished, the voltage difference of the batteries is small, and the voltage tends to be consistent.

Description

Technical Field

[0001] The present invention relates to the field of battery balancing, and in particular to a quasi-resonant balancing circuit based on a bus LC and a control method. Background Art

[0002] With the widespread use of lithium batteries, the consistency of single cells in the battery pack has become a key factor affecting performance and life. Due to differences in production, use and storage, the battery cells show inconsistencies in internal resistance, voltage, capacity, etc., and after multiple charge and discharge cycles, this imbalance will be aggravated, resulting in reduced battery performance, shortened life, and even safety hazards. In applications such as electric vehicles, battery balancing technology can adjust the differences between single cells to ensure efficient operation of the battery pack, extend service life, and improve overall performance and safety.

[0003] Battery balancing circuits can be divided into energy dissipation type and non-energy dissipation type. Energy dissipation type circuits use components such as resistors to consume the energy of high-voltage batteries to achieve balancing. Non-energy dissipation type circuits convert energy through energy storage components, which are more efficient and are further divided into transformer type, inductor type and capacitor type. Although the capacitor type balancing circuit is simple to control and small in size, it has a slow balancing speed. Summary of the invention

[0004] The purpose of the present invention is to disclose a quasi-resonant equalization circuit and a control method based on bus LC, so as to solve the technical problems raised in the background technology.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a quasi-resonant balancing circuit based on a bus LC, comprising n batteries, 2n MOSFET switch tubes, n-1 LC energy storage modules and a switch controller;

[0007] The n batteries are connected in series;

[0008] The LC storage module includes a balancing capacitor C and a resonant inductor L connected in series;

[0009] The 2n MOSFET switch tubes are divided into two switch groups, namely the S switch group and the Q switch group;

[0010] The drain of the first MOSFET switch tube S1 in the S switch group is connected to the positive electrode of the battery B1. i The drain of battery B i-1 The negative electrode of battery B i The positive electrode of is connected; i∈[2,n];

[0011] The nth MOSFET switch tube Q in the Q switch groupn The source and battery B n The negative pole of the Q switch group is connected, and the jth switch tube Q j The source of battery B j The negative electrode of battery B j+1 The positive connection of; j∈[1,n-1];

[0012] For the resonant inductor L in the jth LC energy storage module j and balancing capacitor C j , L j One end of C j The other end is connected to the jth MOSFET switch tube S in the S switch group. j The source of the Q switch group, the jth MOSFET switch tube Q j Drain connection; C j One end of is connected to the same node as the other n-2 balancing capacitors;

[0013] The switch controller is connected to the gate of each MOSFET switch tube respectively.

[0014] Preferably, the switch controller is used to generate a PWM control signal.

[0015] Preferably, the generated PWM control signal is a pair of complementary unipolar square wave signals, and the duty cycle of the switch control signal is 50%.

[0016] The present invention also provides a control method for the above-mentioned bus LC-based quasi-resonant equalization circuit, comprising:

[0017] The switch controller generates a pair of complementary PWM control signals to control the S switch group and the Q switch group to conduct alternately. Each switching cycle is divided into mode A and mode B.

[0018] In mode A, during the conduction phase of PWM1, the S switch group is turned on, the Q switch group is turned off, and the energy bus composed of the battery, capacitor, and inductor is connected. The current flows out from any battery cell or cell group and flows to the LC storage module composed of capacitors and inductors for energy storage. After half a resonant cycle, the capacitor reaches the maximum value within a single cycle, and the capacitor current returns to zero. At this time, the switch tube realizes ZCS;

[0019] In mode B, during the conduction phase of PWM2, the S switch group is turned off, the Q switch group is turned on, and the LC storage module composed of capacitors and inductors releases energy. Any battery cell or cell group with a lower voltage begins to receive energy, realizing the charge transfer from high-energy to low-energy batteries. After half a resonant cycle, the capacitance is reduced to the minimum value within a single switching cycle, and the capacitor current returns to zero, and the switch tube achieves ZCS.

[0020] Beneficial effects:

[0021] (1) All MOSFET tubes are controlled by a pair of complementary PWM signals to achieve the balance of the series-connected battery pack, which is simple to control and highly reliable.

[0022] (2) Adding a resonant inductor to the switched capacitor loop achieves zero current switching, improves the efficiency and EMI characteristics of the balancing circuit, and makes the current waveform in the circuit smoother.

[0023] (3) Realize synchronous balancing of any battery to any battery.

[0024] (4) There is no need to consider the distribution of the initial voltage. The time required from the start to the end of balancing has nothing to do with the location of each battery cell; the balancing speed has nothing to do with the number of batteries connected in series.

[0025] (5) The proposed balancing topology is simple, easy to expand and modularize, and its size and cost are much smaller than other balancers.

[0026] (6) Excellent robustness performance. After balancing, the voltage difference between each battery is small, the voltage tends to be consistent, and the balancing speed is fast and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0028] Figure 1 It is a schematic diagram of a bus LC-based quasi-resonant equalization circuit of the present invention.

[0029] Figure 2 is a structural diagram of a six-battery equalization circuit of the present invention;

[0030] Figure 3(a)-Figure 3(c) is the circuit conduction diagram corresponding to mode A;

[0031] Figure 4(a)-Figure 4(c) is the circuit conduction diagram corresponding to mode B;

[0032] Figure 5 This is the equalization current path diagram of six batteries;

[0033] Figure 6 is the balancing current i of the present invention C1 , capacitor voltage V C1 and a driving signal waveform;

[0034] Figure 7It is a six-battery voltage equalization waveform diagram of the present invention;

[0035] Figure 8 is a structural diagram of a ten-battery equalization circuit of the present invention;

[0036] Fig. 9 It is a ten-battery voltage equalization waveform diagram of the present invention;

[0037] Fig.10 It is a modular structure diagram of the equalization circuit of the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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.

[0039] like Figure 1 , the present invention provides a quasi-resonant balancing circuit based on bus LC, including n batteries, 2n MOSFET switch tubes, n-1 LC energy storage modules and a switch controller;

[0040] The n batteries are connected in series;

[0041] The LC storage module includes a balancing capacitor C and a resonant inductor L connected in series;

[0042] The 2n MOSFET switch tubes are divided into two switch groups, namely the S switch group and the Q switch group;

[0043] The drain of the first MOSFET switch tube S1 in the S switch group is connected to the positive electrode of the battery B1. i The drain of battery B i-1 The negative electrode of battery B i The positive electrode of is connected; i∈[2,n];

[0044] The nth MOSFET switch tube Q in the Q switch group n The source and battery B n The negative pole of the Q switch group is connected, and the jth switch tube Q j The source of battery B j The negative electrode of battery B j+1 The positive connection of; j∈[1,n-1];

[0045] For the resonant inductor L in the jth LC energy storage module j and balancing capacitor C j , Lj One end of C j The other end is connected to the jth MOSFET switch tube S in the S switch group. j The source of the Q switch group, the jth MOSFET switch tube Q j Drain connection; C j One end of is connected to the same node as the other n-2 balancing capacitors;

[0046] The switch controller is connected to the gate of each MOSFET switch tube respectively.

[0047] Preferably, the switch controller is used to generate a PWM control signal.

[0048] Preferably, the generated PWM control signal is a pair of complementary unipolar square wave signals, and the duty cycle of the switch control signal is 50%.

[0049] The present invention also provides a control method for the above-mentioned bus LC-based quasi-resonant equalization circuit, comprising:

[0050] The switch controller generates a pair of complementary PWM control signals to control the S switch group and the Q switch group to conduct alternately. Each switching cycle is divided into mode A and mode B.

[0051] In mode A, during the conduction phase of PWM1, the S switch group is turned on, the Q switch group is turned off, and the energy bus composed of the battery, capacitor, and inductor is connected. The current flows out from any battery cell or cell group and flows to the LC storage module composed of capacitors and inductors for energy storage. After half a resonant cycle, the capacitor reaches the maximum value within a single cycle, and the capacitor current returns to zero. At this time, the switch tube realizes ZCS;

[0052] In mode B, during the conduction phase of PWM2, the S switch group is turned off, the Q switch group is turned on, and the LC storage module composed of capacitors and inductors releases energy. Any battery cell or cell group with a lower voltage begins to receive energy, realizing the charge transfer from high-energy to low-energy batteries. After half a resonant cycle, the capacitance is reduced to the minimum value within a single switching cycle, and the capacitor current returns to zero, and the switch tube achieves ZCS.

[0053] By alternately operating mode A and mode B, energy is directly transferred from any battery cell or cell group with a voltage higher than the average value to any battery cell or cell group with a voltage lower than the average value.

[0054] Furthermore, by classifying the system according to different equilibrium states, the system state can be subdivided into global equilibrium state, local equilibrium state, and static equilibrium state;

[0055] Global equilibrium state: All battery voltages have not reached equilibrium, and the LC energy storage modules are in the process of adjustment;

[0056] Local equilibrium state: the voltage of some batteries has reached equilibrium and the system is in the partial regulation stage;

[0057] Static equilibrium state: All LC energy storage modules in the system are in an energy equilibrium state, and the voltages of each battery tend to be consistent.

[0058] Example 1

[0059] Taking the six-battery balancing circuit as an example, its structure is as follows Figure 2 As shown. Without considering the dead time of the driving signal, the balancing process of the circuit includes two working states, corresponding to mode A and mode B respectively. Mode A is shown in Figure 3(a)-(c), S1, S2, S3, S4, S5, S6 are turned on, Q1, Q2, Q3, Q4, Q5, Q6 are turned off, and the current flows from the battery with higher battery voltage into the balancer to store energy. Mode B is shown in Figure 4(a)-(c), S1 to S6 are turned off, Q1 to Q6 are turned on, and the stored energy is released from the balancer to the battery with lower voltage to realize charge transfer. The current balancing path of the six batteries is shown in Figure 5 When the equilibrium state does not reach static equilibrium, the two modes work alternately, and the waveforms of the equilibrium current and capacitor voltage are as follows: Figure 6 shown.

[0060] Figure 7 The waveform of the six-battery voltage balance is shown in Figure 2. The simulation parameters of the circuit are as follows: the balance capacitor is 22μF, the resonant inductor is 10μH, and each resonant unit is set with a 50mΩ resistor as the circuit parasitic resistor; a 0.7F capacitor is used to replace the battery, and its initial voltage V B1 =3.8V, V B2 =3.7V, V B3 =3.6V, V B4 =3.5V, V B5 =3.4V, V B6 =3.3V, the maximum initial voltage difference is 0.5V. Figure 7 It can be seen that although the initial voltages of the batteries are different, as the balancing time increases, the voltages of the six batteries in the battery pack gradually approach and eventually reach a balanced state, and the balancing time is 1.75s. The experimental results show that the present invention can achieve synchronous balancing of any battery cell to any battery cell, and the balancing speed and efficiency are high.

[0061] Example 2

[0062] Figure 8 FIG. 1 is a circuit diagram of an embodiment of the present invention using a 10-battery equalization circuit as an example. Fig. 9 for Figure 8The simulation waveform of the embodiment, the simulation parameters are the same as those of embodiment 1, and the initial voltage is V B1 =3.8V, V B2 =3.7V, V B3 =3.6V, V B4 =3.5V, V B5 =3.4V, V B6 =3.3V, V B7 =3.2V, V B8 =3.1V, V B9 =3.0V, V B10 =2.9V, the maximum voltage difference is 0.9V. After 2.01s, the voltage of all battery cells converges to around 3.346V at the same time. Figure 7 and Fig. 9 It can be seen that the increase in the number of batteries has little effect on the balancing speed of the quasi-resonant balancing circuit based on the bus LC, and the circuit has excellent scalability and robustness. After the balancing is completed, the voltage difference between each battery is small and the voltage tends to be consistent.

[0063] Fig.10 The modular structure of the balancing circuit of the present invention is shown. It can be seen from the analysis that only one LC module needs to be added, without an additional external balancing circuit, to achieve automatic balancing between different battery groups, which reduces the complexity and cost of the system, makes the energy distribution between different battery groups more accurate, and helps to extend the overall service life of the series battery group.

[0064] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A quasi-resonant equalization circuit based on bus LC, characterized in that: It includes n batteries, 2n MOSFET switch tubes, n-1 LC energy storage modules and a switch controller; The n batteries are connected in series; The LC storage module includes a balancing capacitor C and a resonant inductor L connected in series; The 2n MOSFET switch tubes are divided into two switch groups, namely the S switch group and the Q switch group; The drain of the first MOSFET switch tube S1 in the S switch group is connected to the positive electrode of the battery B1. i The drain of battery B i-1 The negative electrode of battery B i The positive electrode of is connected; i∈[2,n]; The nth MOSFET switch tube Q in the Q switch group n The source and battery B n The negative pole of the Q switch group is connected, and the jth switch tube Q j The source of battery B j The negative electrode of battery B j+1 The positive connection of; j∈[1,n-1]; For the resonant inductor L in the jth LC energy storage module j and balancing capacitor C j , L j One end of C j The other end is connected to the jth MOSFET switch tube S in the S switch group. j The source of the Q switch group, the jth MOSFET switch tube Q j Drain connection; C j One end of is connected to the same node as the other n-2 balancing capacitors; The switch controller is connected to the gate of each MOSFET switch tube respectively.

2. The quasi-resonant equalization circuit based on bus LC according to claim 1, characterized in that: The switch controller is used to generate a PWM control signal.

3. The quasi-resonant equalization circuit and control method based on bus LC according to claim 2, characterized in that: The generated PWM control signal is a pair of complementary unipolar square wave signals, and the duty cycle of the switch control signal is 50%.

4. A control method for a bus LC-based quasi-resonant equalization circuit according to any one of claims 1 to 3, characterized in that: include: The switch controller generates a pair of complementary PWM control signals to control the S switch group and the Q switch group to conduct alternately. Each switching cycle is divided into mode A and mode B. In mode A, during the conduction phase of PWM1, the S switch group is turned on, the Q switch group is turned off, and the energy bus composed of the battery, capacitor, and inductor is connected. The current flows out from any battery cell or cell group and flows to the LC storage module composed of capacitors and inductors for energy storage. After half a resonant cycle, the capacitor reaches the maximum value within a single cycle, and the capacitor current returns to zero. At this time, the switch tube realizes ZCS; In mode B, during the conduction phase of PWM2, the S switch group is turned off, the Q switch group is turned on, and the LC storage module composed of capacitors and inductors releases energy. Any battery cell or cell group with a lower voltage begins to receive energy, realizing the charge transfer from high-energy to low-energy batteries. After half a resonant cycle, the capacitance is reduced to the minimum value within a single switching cycle, and the capacitor current returns to zero, and the switch tube achieves ZCS.

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