Battery temperature adaptive passive equalization circuit

Abstract

The utility model discloses a battery temperature self-adaptive passive equalization circuit, and relates to the technical field of battery equalization, the positive and negative electrodes of a battery are connected with a BMS controller, the battery comprises a plurality of battery cells connected in sequence, and an equalization module is connected between each battery cell and the BMS controller. The equalization module comprises a resistor R1, a resistor R2, a nmos tube Q1, a nmos tube Q2, an operational amplifier OPAMP and a thermistor NTC. Wherein the resistor R1 and the nmos tube Q1 are connected to form a first circuit, and the resistor R2, the thermistor NTC and the nmos tube Q2 are sequentially connected to form a second circuit. The first circuit and the second circuit are connected with the positive electrode and the negative electrode of the battery cell, and the operational amplifier OPAMP is connected between the first circuit and the second circuit. According to the invention, the appropriate equalization current can be adaptively adjusted through the temperature feedback of the battery cell, so that the battery cell equalization can achieve a faster and safer equalization effect under the condition that the service life of the battery cell is not affected.

Description

Technical Field

[0001] The utility model relates to the technical field of battery balancing, and in particular to a battery temperature adaptive passive balancing circuit. Background Art

[0002] The significance of battery balancing is to use electronic technology to keep the voltage deviation of lithium-ion battery cells within the expected range, so as to ensure that each single cell is not damaged during normal use. If balancing control is not performed, as the charge and discharge cycles increase, the voltage of each single cell will gradually diverge, and the service life will be greatly reduced.

[0003] The main reason for battery balancing is that the charging and discharging stages are subject to large instantaneous currents. The charging stage is when braking energy is recovered, and the discharging stage is when the motor is started, etc., which requires high instantaneous energy. Large charging currents may cause some full batteries to directly exceed the damaged voltage range, while large discharging currents may cause some batteries to be in a deep discharge state, which affects the output current and damages the battery itself.

[0004] Battery balancing is generally divided into two types: active balancing and passive balancing. Active balancing is a method of balancing by transferring electricity, which is highly efficient and has low losses. Passive balancing generally discharges batteries with higher voltages through resistance discharge, releasing electrical energy in the form of heat, thus buying more charging time for other batteries.

[0005] At present, during the battery balancing process, the battery cells will heat up due to excessive balancing current, which will affect charging and discharging, causing certain safety hazards to the battery. Therefore, it is very important to invent a technology to adjust the balancing current through battery cell temperature feedback to implement battery balancing. Summary of the invention

[0006] Purpose of the utility model: The purpose of the utility model is to provide a battery temperature adaptive passive balancing circuit, which solves the potential safety hazards caused by excessive balancing current and heating of the battery cell during battery balancing. This application can adaptively adjust the appropriate balancing current through battery cell temperature feedback, so that the battery cell balancing can achieve a faster and safer balancing effect without affecting the battery cell life.

[0007] Technical solution: A battery temperature adaptive passive balancing circuit, wherein the positive and negative electrodes of the battery are connected to a BMS controller, the battery comprises a plurality of cells connected in sequence, and a balancing module is connected between each of the cells and the BMS controller;

[0008] The balancing module includes a resistor R1, a resistor R2, a nmos tube Q1, a nmos tube Q2, an operational amplifier OPAMP and a thermistor NTC;

[0009] The resistor R1 is connected to the nmos tube Q1 to form a first circuit, and the resistor R2, the thermistor NTC, and the nmos tube Q2 are connected in sequence to form a second circuit;

[0010] The first circuit and the second circuit are both connected to the positive and negative electrodes of the battery cell, and the operational amplifier OPAMP is connected between the first circuit and the second circuit.

[0011] Further: one end of the resistor R1 is connected to the positive electrode of the battery cell, and the other end is connected to the D electrode of the nmos tube Q1, and the S electrode of the nmos tube Q1 is connected to the negative electrode of the battery cell.

[0012] Further: one end of the resistor R2 is connected to the positive electrode of the battery cell, and the other end is connected to the thermistor NTC, the D pole of the nmos tube Q2 is connected to the thermistor NTC, and the S pole of the nmos tube Q2 is connected to the negative electrode of the battery cell.

[0013] Further: the Vcc terminal of the operational amplifier OPAMP is connected to the positive electrode of the battery cell, and the Gnd terminal of the operational amplifier OPAMP is connected to the negative electrode of the battery cell.

[0014] Further: there is a first node P1 on the line connecting the resistor R2 and the thermistor NTC, and the non-inverting input terminal of the operational amplifier OPAMP is connected to the first node P1.

[0015] Further: the output end of the operational amplifier OPAMP is connected to the G pole of the nmos tube Q1.

[0016] Further: there is a second node P2 on the line connecting the output end of the operational amplifier OPAMP and the G pole of the nmos tube Q1, and the inverting input end of the operational amplifier OPAMP is connected to the second node P2.

[0017] Further: there is a third node P3 on the line connecting the in-phase input terminal of the operational amplifier OPAMP and the first node P1, and the balancing module also includes a filter capacitor C, one end of the filter capacitor C is connected to the third node P3, and the other end is connected to the negative electrode of the battery cell.

[0018] Further: the G pole of the nmos tube Q2 is connected to the BMS controller.

[0019] Further: the resistance value of the resistor R2 is greater than the resistance value of the resistor R1.

[0020] Beneficial effects of the utility model:

[0021] 1. When the battery cell group in the battery of the present application is unbalanced, the BMS controller starts the balancing module through a high level to achieve cell balancing;

[0022] 2. The balancing module of this application can adaptively adjust the appropriate balancing current according to the real-time temperature of the battery cell, so that the battery cell balancing can achieve a faster and safer balancing effect without affecting the life of the battery cell;

[0023] 3. This application realizes temperature feedback based on thermistor NTC, voltage following based on operational amplifier OPAMP, and balanced current regulation based on nmos tube;

[0024] 4. The balancing module of the present application also includes a filter capacitor C, which is used to reduce the AC pulse ripple coefficient and improve the efficient and smooth DC output. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The utility model is a schematic diagram of an overall battery temperature adaptive passive balancing circuit.

[0026] Figure 2 is a schematic diagram of the balancing module. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means a limitation on the utility model and its application or use. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the utility model.

[0028] Those skilled in the art will appreciate that, in the absence of conflict, the features in the following embodiments and implementations may be combined with each other.

[0029] The terms used in the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. For example, the words "upper", "lower", "front", "back", etc., which indicate the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device / element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0030] As used in this specification, the singular forms "a", "an", and "the" include plural objects, and the plural form "a plurality" includes more than two objects, unless the context clearly indicates otherwise. As used in this specification, the term "or" is generally used to include the meaning of "and / or", unless the context clearly indicates otherwise, and 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 directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements.

[0031] The utility model is further described below in conjunction with the accompanying drawings and embodiments:

[0032] like Figure 1 As shown, a battery temperature adaptive passive balancing circuit, the positive and negative electrodes of the battery are connected to the BMS controller, the battery includes multiple cells connected in sequence, and a balancing module is connected between each cell and the BMS controller, wherein the BMS controller is the battery management system. The battery management system is the link between the battery and the user, and its purpose is to improve the utilization rate of the battery, prevent the battery from overcharging and discharging, extend the battery life, and monitor the battery status.

[0033] BMS battery management system generally includes the following functions:

[0034] 1. Accurately estimate SOC: Accurately estimate the state of charge (SOC) of the power battery pack, that is, the remaining power of the battery, keep the SOC within a reasonable range, prevent damage to the battery due to excessive charging and discharging, and display the remaining energy of the battery at any time;

[0035] 2. Dynamic monitoring: During the battery charging and discharging process, the terminal voltage and temperature, charging and discharging current and total voltage of each battery in the battery pack are collected in real time to prevent the battery from overcharging and discharging;

[0036] 3. Balance between batteries: Make each battery in the battery pack reach a balanced and consistent state.

[0037] like Figure 2 As shown, the balancing module includes a resistor R1, a resistor R2, a nmos tube Q1, a nmos tube Q2, an operational amplifier OPAMP and a thermistor NTC.

[0038] Among them, the nmos tube includes a D pole, an S pole and a G pole. The nmos tube is divided into a fully conductive state and a non-fully conductive state. The non-fully conductive state is a linear amplification state. When the nmos tube is in a linear amplification state, if its Vgs continues to increase, its internal resistance will continue to decrease; conversely, if its Vgs continues to decrease, its internal resistance will continue to increase.

[0039] During the use of the nmos tube, the following situations may occur:

[0040] 1. The Vgs of the nmos tube continues to increase and is never greater than the turn-on voltage: At this time, the nmos tube is in a linear amplification state, and the internal resistance of the nmos tube continues to decrease as Vgs continues to increase;

[0041] 2. The Vgs of the nmos tube is always greater than the turn-on voltage: at this time, the nmos tube is in a fully turned-on state and the internal resistance is minimal;

[0042] 3. The Vgs of the nmos tube is less than the turn-on voltage and continues to decrease: At this time, the nmos tube is in a linear amplification state, and the internal resistance of the nmos tube continues to increase as Vgs continues to decrease.

[0043] The nmos tube Q1 and the nmos tube Q2 of the present application can both use the AO3401 nmos tube, which has the characteristics of high performance, low resistance, low loss, etc., and its on-resistance is only 0.07 ohms.

[0044] The NMOS tube of the present application may also be replaced by other linear voltage amplifiers or other linear voltage amplification circuits, such as voltage-controlled amplifier circuits, etc., to achieve that the greater the voltage, the smaller the internal resistance, and the smaller the voltage, the greater the internal resistance.

[0045] The operational amplifier OPAMP includes a non-inverting input terminal, an inverting input terminal, an output terminal, a Vcc terminal and a Gnd terminal, wherein the Vcc terminal is connected to the positive electrode of the battery cell, and the Gen terminal is connected to the negative electrode of the battery cell. The TLV9361 operational amplifier OPAMP can be selected for this application. This type of device has excellent DC and AC specifications, including rail-to-rail output, low offset voltage, low temperature drift, etc.

[0046] NTC thermistor refers to the thermistor phenomenon and material with a negative temperature coefficient, in which the resistance decreases exponentially as the temperature rises.

[0047] In the present application, the resistor R1 is connected to the nmos tube Q1 to form a first circuit, and the resistor R2, thermistor NTC, and nmos tube Q2 are connected in sequence to form a second circuit. The first circuit and the second circuit are both connected to the positive and negative poles of the battery cell, and an operational amplifier OPAMP is connected between the first circuit and the second circuit.

[0048] Among them, one end of the resistor R1 is connected to the positive electrode of the battery cell, and the other end is connected to the D electrode of the nmos tube Q1, the S electrode of the nmos tube Q1 is connected to the negative electrode of the battery cell, the G electrode of the nmos tube Q1 is connected to the output end of the operational amplifier OPAMP, and there is a second node P2 on the line connecting the output end of the operational amplifier OPAMP and the G electrode of the nmos tube Q1, and the inverting input end of the operational amplifier OPAMP is connected to the second node P2.

[0049] One end of the resistor R2 is connected to the positive electrode of the battery cell, and the other end is connected to the thermistor NTC. The D pole of the nmos tube Q2 is connected to the thermistor NTC. The S pole of the nmos tube Q2 is connected to the negative electrode of the battery cell. There is a first node P1 on the line connecting the resistor R2 and the thermistor NTC. The non-inverting input end of the operational amplifier OPAMP is connected to the first node P1.

[0050] There is a third node P3 on the line where the in-phase input terminal of the operational amplifier OPAMP is connected to the first node P1, and the equalization module also includes a filter capacitor C, one end of the filter capacitor C is connected to the third node P3, and the other end is connected to the negative electrode of the battery cell. The filter capacitor C is used to reduce the AC pulse ripple coefficient on the line where the in-phase input terminal of the operational amplifier OPAMP is connected to the first node P1, so as to improve the efficient and smooth DC output.

[0051] The G pole of the nmos tube Q2 is connected to the BMS controller to receive the high level given by the BMS controller. When an imbalance occurs in the battery cell group, the BMS controller gives a high level to the balancing module connected to the cell, and the balancing module starts to balance.

[0052] The resistance of the resistor R2 is greater than the resistance of the resistor R1 , and is much greater than the resistance of the resistor R1 , which makes the current in the second circuit always very small.

[0053] The operational amplifier OPAMP has a non-inverting input connected to the first node P1, an inverting input connected to the second node P2, and an output connected to the G pole of the nmos tube Q1, forming a typical negative feedback circuit. The input impedance of an ideal operational amplifier is infinite, so the current flowing into or out of the input pin of the operational amplifier will be infinitely small.

[0054] The operational amplifier OPAMP of this application forms a virtual disconnection: Since the differential input resistance of the operational amplifier is very large, and the input resistance of general-purpose operational amplifiers is generally above 1MΩ, the current flowing into the input terminal of the operational amplifier is often less than 1uA, which is much smaller than the current of the circuit outside the input terminal. Therefore, the two input terminals of the operational amplifier can usually be regarded as open circuits, and the greater the input resistance, the closer the two input terminals are to open circuits. "Virtual disconnection" means that when analyzing the linear state of the operational amplifier, the two input terminals can be regarded as equivalent to open circuits. This feature is called a false open circuit, or virtual disconnection for short.

[0055] The balancing current of the present application is the sum of the current in the first circuit, the current in the second circuit and the current passing through the operational amplifier OPAMP. Since the operational amplifier OPAMP is disconnected and the current in the second circuit is very small, when balancing the current of the present application, the current in the second circuit and the current passing through the operational amplifier OPAMP can be considered to be negligible, and only the current in the first circuit is used as a reference.

[0056] This application implements temperature feedback based on thermistor NTC, voltage following based on operational amplifier OPAMP, and balancing current regulation based on nmos tube. It adaptively adjusts the appropriate balancing current according to the real-time temperature of the battery cell, so that the battery cell balancing can achieve faster and safer balancing effect without affecting the battery cell life. The adaptive adjustment process is as follows:

[0057] 1. When an imbalance occurs in the battery cell group, the BMS controller gives a high level to the balancing module connected to the battery cell.

[0058] 2. The BMS controller gives a high level to the G pole of the nmos tube Q2, the Vgs of the nmos tube Q2 is greater than its turn-on voltage, and the nmos tube Q2 is turned on.

[0059] 3. The thermistor NTC is used as a temperature feedback unit to detect the temperature of the current balanced cell. Since the temperature is relatively low at the beginning of the balancing, the resistance of the thermistor NTC is relatively large at this time according to its own characteristics. According to the voltage division of the resistor R2 and the thermistor NTC, the thermistor NTC receives a high voltage due to its large resistance, so the first node P1 is a high voltage;

[0060] 4. The operational amplifier OPAMP has its non-inverting input connected to the first node P1, its inverting input connected to the second node P2, and its output connected to the G pole of the nmos tube Q1, forming a typical negative feedback circuit. This negative feedback circuit is also a voltage follower circuit, also called a unity gain buffer, which has the characteristic that the output is always equal to the input, so the G pole of the nmos tube Q1 is a high voltage at this time.

[0061] 5. The Vgs of the nmos tube Q1 is greater than its turn-on voltage, and the nmos tube Q1 is turned on. The current in the first circuit is determined by the cell voltage / (R1+Q1 internal resistance). Since the nmos tube Q1 is turned on at this time, the on-state internal resistance of the nmos tube Q1 is the smallest, so the current in the first circuit is the largest at this time.

[0062] 6. The current in the first circuit is large, which will cause the current core temperature to rise. The resistance of the thermistor NTC will decrease according to its own characteristics. According to the voltage division of the resistor R2 and the thermistor NTC, the voltage divided by the thermistor NTC will also decrease due to the decrease in resistance, so the voltage at the first node P1 decreases;

[0063] 7. Based on the voltage following of the operational amplifier OPAMP, the G pole voltage of the nmos tube Q1 also decreases. When the Vgs of the nmos tube Q1 is less than its turn-on voltage, the nmos tube Q1 is in a linear amplification state. At this time, the smaller the Vgs, the greater its internal resistance. The current in the first circuit is determined by the cell voltage / (R1+Q1 internal resistance). Since the internal resistance of the nmos tube Q1 is constantly increasing at this time, the current in the first circuit is also constantly decreasing. As the current decreases, the temperature also decreases.

[0064] 8. When the temperature drops, the resistance of the thermistor NTC will increase according to its own characteristics, and the current in the first circuit will increase accordingly. The above process is repeated to achieve the temperature feedback of the battery cell to adaptively adjust the appropriate balancing current.

[0065] The above is only a specific implementation of the utility model, but the protection scope of the utility model is not limited thereto. Those skilled in the art should understand that the utility model includes but is not limited to the contents described in the above specific implementation. Any modification that does not deviate from the functional and structural principles of the utility model will be included in the scope of the claims.

Claims

1. A battery temperature adaptive passive balancing circuit, wherein the positive and negative electrodes of the battery are connected to a BMS controller, and the battery comprises a plurality of cells connected in sequence, characterized in that: A balancing module is connected between each of the battery cells and the BMS controller; The balancing module includes a resistor R1, a resistor R2, a nmos tube Q1, a nmos tube Q2, an operational amplifier OPAMP and a thermistor NTC; The resistor R1 is connected to the nmos tube Q1 to form a first circuit, and the resistor R2, the thermistor NTC, and the nmos tube Q2 are connected in sequence to form a second circuit; The first circuit and the second circuit are both connected to the positive and negative electrodes of the battery cell, and the operational amplifier OPAMP is connected between the first circuit and the second circuit.

2. A battery temperature adaptive passive balancing circuit according to claim 1, characterized in that: One end of the resistor R1 is connected to the positive electrode of the battery cell, and the other end is connected to the D electrode of the nmos tube Q1. The S electrode of the nmos tube Q1 is connected to the negative electrode of the battery cell.

3. The battery temperature adaptive passive balancing circuit according to claim 1, characterized in that: One end of the resistor R2 is connected to the positive electrode of the battery cell, and the other end is connected to the thermistor NTC. The D pole of the nmos tube Q2 is connected to the thermistor NTC, and the S pole of the nmos tube Q2 is connected to the negative electrode of the battery cell.

4. The battery temperature adaptive passive balancing circuit according to claim 1, characterized in that: The Vcc terminal of the operational amplifier OPAMP is connected to the positive electrode of the battery cell, and the Gnd terminal of the operational amplifier OPAMP is connected to the negative electrode of the battery cell.

5. The battery temperature adaptive passive balancing circuit according to claim 1, characterized in that: There is a first node P1 on the line connecting the resistor R2 and the thermistor NTC, and the non-inverting input terminal of the operational amplifier OPAMP is connected to the first node P1.

6. The battery temperature adaptive passive balancing circuit according to claim 1, characterized in that: The output end of the operational amplifier OPAMP is connected to the G pole of the nmos tube Q1.

7. The battery temperature adaptive passive balancing circuit according to claim 6, characterized in that: There is a second node P2 on the line connecting the output end of the operational amplifier OPAMP and the G pole of the nmos tube Q1, and the inverting input end of the operational amplifier OPAMP is connected to the second node P2.

8. The battery temperature adaptive passive balancing circuit according to claim 5, characterized in that: There is a third node P3 on the line connecting the in-phase input terminal of the operational amplifier OPAMP and the first node P1, and the balancing module also includes a filter capacitor C, one end of the filter capacitor C is connected to the third node P3, and the other end is connected to the negative electrode of the battery cell.

9. The battery temperature adaptive passive balancing circuit according to claim 1, characterized in that: The G pole of the nmos tube Q2 is connected to the BMS controller.

10. The battery temperature adaptive passive balancing circuit according to claim 1, characterized in that: The resistance value of the resistor R2 is greater than the resistance value of the resistor R1.

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