The capacitance method balancing relay works in a continuous rotation mode, and the auxiliary battery method balancing relay works in a forward and reverse positioning mode.

　　The battery era is coming. Whether it is the new energy vehicle industry or the distributed energy storage industry, the use of batteries has exploded. Due to the low voltage of a single battery, batteries need to be cascaded in various applications to increase the total voltage. However, due to the performance differences of the battery cells, the battery pack will inevitably have deviations in the voltage of each cascade during use. Concepts come with applications.

　　Battery pack balancing is one of the management strategies of BMS (battery management system). Due to cost considerations, although there are many types of existing balancing schemes, the simplest lossy discharge method is often used in application cases, and the efficiency is not high. high. Most of the current balancing schemes are based on the premise that the consistency of the single cells in the battery pack is very high. Considering the cascade utilization of secondary batteries in the future, it is necessary to design better, simpler and more effective balancing schemes and strategies.

　　Looking at the current equalization solutions, the resistor discharge method is the simplest, but has the disadvantage of low efficiency and lossy equalization; solutions such as inductors, transformers, and voltage boosters have complex circuits and high costs; an electromagnetic relay group plus capacitor solution (see figure) 1), its advantages are low cost, simple circuit, and lossless equalization. Its disadvantages are low conversion frequency and the risk of short circuit when the electrical contacts are melted.

　　In Figure 1, assuming that the balancing command is executed, the relay corresponding to the battery with the highest voltage among the five single cells is first closed, and the capacitor is charged; the relay is disconnected, and then the relay corresponding to the battery with the lowest voltage is selected to be closed, the capacitor is discharged, and the relay is disconnected. Turn on to complete a balancing cycle. As we all know, electromagnetic relays are not suitable for frequent switching situations, so the theoretical equilibrium effect of Figure 1

　　The rate will be very low. If the electromagnetic relay is changed to an electronic switch, due to the small voltage difference between batteries, the electronic switch itself has a certain voltage drop, and there will be almost no equalization effect when using a simple electronic switch plus capacitor strategy. In view of the low switching frequency of electromagnetic relays, a feasible solution is to change the capacitor to a backup auxiliary battery and add a step-up and step-down circuit.

　　The larger capacity of the backup auxiliary battery is used to charge or discharge the relevant battery cells for a longer period of time. The birth of the concept of backup auxiliary batteries makes it possible to achieve deep equalization during the cascade utilization of secondary batteries. The relevant technical solutions are described in detail in the invention patent application (2018107804736) and will not be discussed here.

　　Returning to the observation in Figure 1, assuming that the relays J1 to J5 can operate at a higher switching frequency without short circuit failure due to contact bonding, the circuit in Figure 1 will achieve a good balancing effect. Transform the circuit in Figure 1 as shown in Figure 2:

　　Comparing Figure 1 and Figure 2, we can see that the relay group consisting of five relays in Figure 1 has become a component with only one set of moving contacts and five sets of static contacts in Figure 2. Assuming that five sets of static contacts are arranged on a certain disk, one set of movable contacts is driven by a rotating arm, and the power source is a motor, then the balancing circuit in Figure 1 has a high-efficiency balancing scheme with fast switching speed and no fear of inter-stage short circuits. .

　　This resulted in a completely new type of relay, which can be named the rotary relay, which is particularly suitable for battery pack balancing applications. One rotary relay can replace multiple separate electromagnetic relays, and the cost will also be greatly reduced. Moreover, the rotary relay has only one motor rotation command and is balanced independently. Compared with the electromagnetic relay group, it has the advantages of requiring fewer switch points and no need to frequently sample the battery voltage during the balancing period. It truly achieves the balancing strategy goals of the simplest circuit and the simplest calculation.

　　When the consistency of each single cell in the battery pack is good and the voltage difference is small, the relay plus capacitor solution can be used for balancing strategy; when the battery pack consistency is poor, the relay plus backup auxiliary battery solution should be used (it can also be configured Buck-boost circuit) for equalization. With the capacitive equalization method, the equalizing current is small, so a single rotary relay can integrate more than 20 groups of static contacts, and the single size is small. In the backup battery balancing method, if the balancing current is large, it is appropriate to have a smaller number of static contact groups within a single rotary relay. Taking the automotive power supply as an example, when the number of static contact groups is set to 4 groups, an effective configuration can be achieved.

　　The capacitance method balancing relay works in a continuous rotation mode, and the auxiliary battery method balancing relay works in a forward and reverse positioning mode.

　　Taking a certain type of Tesla car battery as an example, the total number of single cells is 7104, and the single stage is 74 parallel, so the number of cascade strings is 96. According to the capacitive balancing scheme, each relay can balance 204/8 battery strings. , then at least 5 continuously rotating relays can complete the balancing work. The balance here refers to the battery string corresponding to each relay. Based on this calculation, 96 battery strings will have up to 5 different voltage values.

　　Theoretically, it is also possible to design an additional configuration of a continuous rotating relay with a smaller number of contacts and stronger overcurrent capability to eliminate the five different voltage values, but this design is not recommended. In particular, when some car battery strings have hidden dangers, they are extremely harmful to driving safety.

　　Therefore, adding a backup auxiliary battery balancing solution based on the capacitance balancing method is a reliable means for safe use of automotive batteries. Still taking the above-mentioned Tesla battery as an example, on the basis of 96 strings, the total battery pack is subdivided into 16 groups (series connection), each group contains 6 packages (series connection).

　　We use 16 groups as a standard. Each four groups corresponds to a four-channel forward and reverse positioning relay, which requires 4 positioning relays. These 4 positioning relays are then cascaded with a four-channel positioning relay with a stronger load capacity. Then lead a pair of balanced contacts to the outside of the battery box, for example, a two-core socket embodied on the surface of the battery box. In addition, when we insert the plug of a backup battery with a larger capacity (including a step-up or step-down circuit) into the balanced socket, which set of battery voltages among the 16 sets of batteries is low, and the 5 positioning relay combinations (4+1) are selected When the backup battery circuit is working, adjustable electrical energy is supplied to it.

　　It can be seen from this that a large-capacity backup battery not only plays a balancing role, but also plays a range-extending role. When the barrel effect is triggered, the backup battery can replace the short board to ensure safe driving of the car.

　　Therefore, the practical application of the above two types of rotary relays will play a positive and effective forward-looking role in the current balancing scheme. The common point in the structural design of the two types of rotary relays is that they both use a disc-type static contact group and a rotating arm-type movable contact group. The difference is that the contact area and number of groups are designed according to the contact capacity, and the contact area and group number are designed according to the contact capacity. Balance method to determine whether continuous rotation or forward and reverse positioning. Two examples are discussed below.

　　For example, there is currently a certain 17-cell lithium battery pack with a nominal voltage of 60V, which is mostly used in two-wheel electric vehicles. Adding a compact continuous rotation relay to the battery pack and reprogramming a relay motor start command on the BMS board perfectly achieves the balancing goal of this type of battery. Specifically, it is recommended that the battery is always balanced when charging, so that the charge reaches the maximum value;

　　During battery cycling and discharge, when the voltage difference between each battery string exceeds the design value, the equalization will stop for a certain period of time and the voltage difference will be re-monitored to determine whether to equalize again. The design of its relay disk and rotating arm is shown in Figure 3.

　　Four circles of conductive loops are laid out on the front of the relay disk. The inner two circles are continuous sliding contact wires. The sliding contact wires lead out wires on the back of the disc and are connected to a capacitor with high capacitance, high resistance and low leakage; the outer two circles are equal parts. 17 sets of sliding contacts. On the back of the disc, the negative end (blue block) of the first set of sliding contacts (shown as red and blue blocks) is short-circuited with the positive end of the second set. Operate in sequence until the negative end of the 17th set is terminal terminated. Each group of positive terminals leads to wires, plus the 17th group of negative terminals, for a total of 18 wires, which are connected to the 18 nodes of the battery pack in sequence. When the rotating arm on the right shown in Figure 3 continues to rotate, the capacitor will be cyclically connected in parallel with each single cell of the battery pack, and the capacitor will continue to charge and discharge, eventually making the voltages of each single cell in the battery pack consistent.

　　The 17-channel continuous rotating relay is also suitable for battery packs with less than 17 series series. It is suitable for brand-new battery packs with good single-cell consistency. If applied to secondary batteries, uncontrollable balancing current may cause contact ablation and oxidation, losing the balancing effect. In particular, in order to prevent certain contacts from failing, the same set of batteries can be connected to two relays for time-sharing operation. The probability that the contacts of two relays on the same group number will fail at the same time is extremely low, so full autonomous balance can be achieved.

　　The example design goal of the forward and reverse positioning relay is large current balancing, usually with a range extension (capacity supplement) function, and the balancing component is a backup auxiliary battery. When applied to automobile battery packs, a feasible design solution is to configure four sets of switching contacts. When the backup auxiliary battery is always connected to the main battery pack and the balancing goal is the main purpose, the auxiliary battery does not need to be configured with a step-up and step-down circuit; when the backup battery is often replaced offline and charged separately for range extension purposes, the auxiliary battery needs Comes standard with boost or buck circuitry.

　　The contact design area of the 4-channel positioning relay is large, and the two moving contacts of the swing arm are designed on both sides of the rotation center to balance the joint force of the two pairs of moving and static contacts. In order to reduce contact resistance, the positioning relay cancels the concept of sliding contact line in the continuous rotation relay, and uses a flexible wire method to deal with the rotation angle difference of the arm. The design of its relay disk and rotating arm is shown in Figure 4.

　　In Figure 4, two conductive rings are arranged on the front of the disk. The conductive rings are divided into four equally spaced groups of sliding contacts. The inner ring is thick and short, and the outer ring is slender. The first set of contacts (red and blue) Color block) The outer circle is marked A1+, and the inner circle is marked A3-, in order. Then on the back of the disc, short-circuit A1- and A2+, A2- and A3+, A3- and A4+, and A4- to lead wire 5, plus wires 1, 2, 3, and 4 as shown in the figure, a total of 5 The cable can be connected to four battery packs with the same voltage level in the battery pack (single string or multi-string combination).

　　Each movable contact on the swing arm of the positioning relay is designed to be composed of multiple spring pieces to ensure over-current capability. The access terminal of the auxiliary battery is directly led out from the spiral arm. The risk of bending and breakage of the lead wire is eliminated by two measures. One is that the spiral arm only rotates back and forth within a range of 325 degrees. The other is that a flexible wire is used to circle one or two times on the spiral arm layer. to weaken the wire bending force.

　　Because positioning relays require precise positioning, they require more components and circuits such as angle detection or position detection than continuous rotation relays. Still taking the application of 4-channel positioning relays in automobile batteries as an example, a total of 5 four-channel positioning relays, large, 4 small, and 4 small, are configured in the main battery pack, and are cascaded in two levels in 1+4 mode. The maximum number of target battery strings is 16. Decompose the total number of strings in the target battery pack into integer parts less than or equal to 16, and each part has the same voltage level. Assuming 16 equal parts, when the voltage of each part is 24V, the total voltage of the battery pack can reach 384V, and when the voltage of each part is 48V, the total voltage of the battery pack can reach 768V. These two battery pack voltage levels basically cover the range from electric cars to electric vehicles. Bus application.

　　Therefore, according to this design, a two-core balancing (extended range) interface is set up on the battery pack box, and an external 24V or 48V backup auxiliary battery with optional capacity is connected, which not only achieves the partial balancing goal of the main battery pack (balance between battery packs) ), also has the effect of emergency response and range extension. The above two application examples are discussed based on the use of vehicle batteries. The requirements for vehicles are small and delicate components. When the application environment is transferred to an energy storage environment, the structural design of the above two types of rotary relays is allowed to be greatly changed. Adapt to the specific requirements of the energy storage environment.

　　The mixed application or separate application of the two types of rotary relays will play an efficient balancing role in the diversified use of new batteries or secondary batteries. Moreover, with the advancement of technology, the concept of balance will inevitably fade away, especially with the proposal of auxiliary battery solutions and the safe application of battery packs. The future goal is controllable regulation of energy flow.

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