A DC direct-mounted battery cluster series balancing circuit and its use method

Abstract

The present invention discloses a DC direct-mount battery cluster series balancing circuit and its use method, belonging to the field of circuit topology control technology. The circuit comprises: multiple groups of battery modules connected in series, wherein: each group of battery modules includes a battery cluster formed by multiple battery cells connected in series and a half-bridge submodule, the battery cluster and the half-bridge submodule are connected in parallel; the half-bridge submodule includes a filter capacitor and a switch connected in parallel, the switch including a first switch and a second switch, the first switch and the second switch are complementary, and the driving signals of the first switches of two adjacent battery modules differ by a phase shift time; any two adjacent battery modules are connected to an LC series branch consisting of an inductor and a capacitor through the midpoint of the first switch and the second switch. The present invention can improve the overall performance and service life of the battery pack.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit topology control, and in particular to a DC direct-hung battery cluster series balancing circuit and a use method thereof. Background Art

[0002] As the energy crisis intensifies and environmental issues become more prominent, industries around the world are gradually shifting towards low-energy consumption, low-pollution, and low-carbon development. Energy storage battery technology, as a core driving force, is not only accelerating the development of electric vehicles but also promoting the intelligent upgrade of large-scale distributed power grids. Lithium-ion batteries, due to their high energy density, low self-discharge rate, long cycle life, flexible assembly, and environmentally friendly characteristics, have become an ideal choice for fields such as electric vehicles, mobile communications, and aerospace.

[0003] In related technologies, battery clusters are typically assembled in series or parallel to meet the high voltage and large capacity requirements of energy storage systems. However, due to the inevitable variations in battery manufacturing and operation, this often leads to a "barrel effect," whereby overcharging or over-discharging of certain battery cells gradually degrades the performance of the entire battery pack, shortening its service life and potentially even causing safety risks such as deformation and explosion.

[0004] Based on this, there is an urgent need for a DC direct-mounted battery cluster series balancing circuit and a method of using the same to solve the above technical problems. Summary of the Invention

[0005] The present invention provides a DC direct-mount battery cluster series equalization circuit that can improve the overall performance and service life of the battery pack. The technical solution is as follows:

[0006] In one aspect, a DC direct-mounted battery cluster series balancing circuit is provided, the circuit comprising a plurality of battery modules connected in series, wherein:

[0007] Each group of battery modules includes a battery cluster formed by connecting multiple battery cells in series and a half-bridge sub-module, and the battery cluster and the half-bridge sub-module are connected in parallel;

[0008] The half-bridge submodule includes a filter capacitor and a switch connected in parallel, wherein the switch includes a first switch and a second switch, the first switch and the second switch are complementary to each other, and the driving signals of the first switches of two adjacent battery modules differ by a phase shift time;

[0009] Any two adjacent battery modules are connected to an LC series branch consisting of an inductor and a capacitor via a midpoint between the first switch and the second switch.

[0010] In another aspect, a method for using a DC direct-mounted battery cluster series balancing circuit is provided, the method comprising:

[0011] Adjusting the conduction states of the first switch and the second switch in the battery module so that the circuit is in different operating modes; wherein the operating modes include a first mode, a second mode, a third mode, and a fourth mode;

[0012] Calculating an initial current value and an initial voltage value of each working mode according to the resonant current and capacitor voltage of the battery module in each working mode;

[0013] The balanced power transmitted by the battery module to the LC series branch is determined according to the initial current value and the initial voltage value, and the balanced power is adjusted by using phase shift control to keep the circuit in a stable state.

[0014] The technical solution provided by the present invention can at least bring the following beneficial effects: by designing a topological circuit with the ability to balance adjacent battery clusters, including multiple groups of battery modules connected in series, each group of battery modules is provided with a battery cluster formed by multiple battery cells connected in series and a half-bridge submodule, the half-bridge submodule includes a filter capacitor and a switch connected in parallel, the switch includes a first switch and a second switch, the first switch and the second switch are complementary, the driving signals of the first switches of two adjacent battery modules differ by a phase shift time, and the final topological circuit is obtained by connecting the battery cluster and the half-bridge submodule in parallel, and then connecting any two adjacent battery modules to an LC series branch composed of an inductor and a capacitor through the midpoint of the first switch and the second switch. This circuit uses the battery energy state as the balancing target. In practical applications, the use of this circuit can solve the energy difference problem between series battery clusters, thereby avoiding the "barrel effect". BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 This is a schematic diagram of a DC direct-mounted battery cluster series balancing circuit provided by one embodiment of the present invention;

[0017] Figure 2 This is a flow chart of a method for using a DC direct-mounted battery cluster series balancing circuit according to an embodiment of the present invention;

[0018] Figure 3 Schematic diagram of a switching sequence and balanced branch current and voltage waveforms using phase shift control provided by an embodiment of the present invention;

[0019] Figure 4 1 is a schematic diagram of an operating mode of a balancing branch using phase shift control provided by an embodiment of the present invention;

[0020] Figure 5 This is a relationship diagram between the balanced power, phase shift time, and frequency coefficient provided by an embodiment of the present invention;

[0021] Figure 6 This is a MATLAB / Simulink simulation model diagram of four battery clusters in series balancing provided by one embodiment of the present invention;

[0022] Figure 7 is a schematic diagram of current waveforms of a four-battery cluster provided by one embodiment of the present invention;

[0023] Figure 8 1 is a schematic diagram of a load current waveform provided by an embodiment of the present invention;

[0024] Figure 9 1 is a schematic diagram of an inductor current waveform of a balancing branch provided by an embodiment of the present invention;

[0025] Figure 10 FIG. 4 is a schematic diagram of a capacitor voltage waveform of a balancing branch provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] As mentioned earlier, due to different operating conditions such as the battery's operating temperature, the battery performance may decay at different rates, leading to overall inconsistency in the battery pack and triggering the "barrel effect."

[0028] Based on this, the concept of the present invention is to design a topology circuit based on LC series branches, which uses phase shift control to independently balance each battery in the circuit, thereby improving the consistency and working stability of the battery pack.

[0029] The specific implementation of the above concept is described below.

[0030] Please refer to Figure 1 An embodiment of the present invention provides a DC direct-mounted battery cluster series balancing circuit, which includes multiple groups of battery modules connected in series, wherein:

[0031] Each group of battery modules includes a battery cluster formed by connecting multiple battery cells in series and a half-bridge sub-module, and the battery cluster and the half-bridge sub-module are connected in parallel;

[0032] The half-bridge submodule includes a filter capacitor and a switch connected in parallel, wherein the switch includes a first switch and a second switch, the first switch and the second switch are complementary to each other, and the driving signals of the first switches of two adjacent battery modules differ by a phase shift time;

[0033] Any two adjacent battery modules are connected to an LC series branch consisting of an inductor and a capacitor via a midpoint between the first switch and the second switch.

[0034] Described below Figure 2 The method of using the circuit shown includes the following steps:

[0035] Step 200: Adjusting the conduction states of the first switch and the second switch in the battery module so that the circuit is in different operating modes; wherein the operating modes include a first mode, a second mode, a third mode, and a fourth mode;

[0036] Step 202: Calculate the initial current value and initial voltage value of each operating mode based on the resonant current and capacitor voltage of the battery module in each operating mode;

[0037] Step 204 : determining the balanced power transmitted by the battery module to the LC series branch according to the initial current value and the initial voltage value, and adjusting the balanced power by using phase shift control to keep the circuit in a stable state.

[0038] First, with respect to step 200 , the conduction states of the first switch and the second switch in the battery module are adjusted so that the circuit is in different operating modes.

[0039] by Figure 1 Take the first and second battery modules of the circuit shown as an example. Figure 1 middle, U bj Battery cluster B j The equivalent voltage, r is the equivalent internal resistance of the battery cluster, U j For battery cluster B j Connected half-bridge submodule filter capacitors C j Voltage, switching device S j1 、S j2 For battery cluster B j The first and second switching devices of the connected half-bridge submodules, L rj andC rj For the j The inductance and capacitance of the LC series branch, U MVDC is the rated DC voltage of the medium voltage DC bus.

[0040] Due to the phase shift control strategy, the first switch S of the first battery module 11 and the second switch S 12 , and the first switch S of the second battery module 21 and the second switch S 22 The switching sequence and waveform are as follows Figure 3 As shown, the switching frequency f s It must be greater than the natural frequency of the LC series branch capacitance and inductance f r , that is, the frequency coefficient K= f s / f r Greater than 1. Assume that the phase shift time of the driving signal of the first switch of the first battery module and the first switch of the second battery module is T p , with the first capacitor C 1-way second capacitor C 2 transfer energy as an example, S 11 The turn-on signal precedes S 21 Phase shift time T p , then ideally, the phase shift control has four working modes, such as Figure 4 shown.

[0041] When the circuit is in the first mode, t At time 0, the first switch S of the first battery module is turned on. 11 and a second switch S of a second battery module adjacent to the first battery module 22 The first capacitor of the first battery module is connected by the LC series branch. C 1 and the second capacitor of the second battery module C 2 performs parallel charging and discharging; at this time, the inductor current of the LC branch i r From the initial value I r0 Starts to rise rapidly to achieve current commutation, and the LC branch capacitor voltage u cr From the initial value U r0 First go down and then go up.

[0042] Furthermore, at the preset first target moment t1. Switch the second switch S of the second battery module 22 Turn off, the current rises to I r1 , the capacitor voltage rises to U r1 , for the convenience of analysis, it is assumed that the DC capacitor C 1 and C 2 is large enough, the capacitor voltage is constant, then the resonant current and capacitor voltage are t 0 to t The first change curve of time period 1 i r1 and u cr1 for:

[0043]

[0044]

[0045] in, , C r is the LC branch capacitance, L r is the LC branch inductance; U r0 is the initial value of the LC branch capacitor voltage; I r0 is the initial value of the inductor current in the LC branch; U 1 is the voltage of the first capacitor; U 2 is the voltage of the second capacitor.

[0046] When the circuit is in the second mode, t At time 1, the first switch S of the first battery module is turned on. 11 and a first switch S of the second battery module 21 The first capacitor is turned on by the LC series branch. C 1 for parallel charging and discharging; at this time, the capacitor voltage changes from U r1 The current starts to rise and the voltage on the capacitor changes from I r1 Start by going up and then going down.

[0047] Furthermore, at the preset second target time t 2. Turn on the first switch S of the first battery module. 11 Shutdown, current drops to I r2 , the capacitor voltage rises to U r2 , then the resonant current and capacitor voltage change from t 1 tot The second change curve of time period 2 i r2 and u cr2 for:

[0048]

[0049] .

[0050] When the circuit is in the third mode, t At time 2, the second switch S of the first battery module is turned on. 12 and the first switch S of the second battery module 21 is turned on, so that the LC series branch is in an open circuit; at this time, there is no external energy transfer, the inductor current drops rapidly to zero and rises in the reverse direction, and the capacitor voltage first rises and then falls.

[0051] At the preset third target time t 3. Turn on the first switch S of the second battery module 21 Turn off, the inductor current reverses and rises to I r3 , the capacitor voltage drops to U r3 , then the resonant current and capacitor voltage change from t 2 to t The third change curve of 3 time periods i r3 and u cr3 for:

[0052]

[0053] .

[0054] When the circuit is in the fourth mode, the second switch S of the first battery module is turned on. 12 and a second switch S of the second battery module 22 The second capacitor is turned on by the LC series branch. C 2 for parallel charging and discharging; at this time, the capacitor voltage changes from U r3 Starts to decrease, the inductor current starts to decrease I r3 Start descending first and then ascending.

[0055] Furthermore, at the preset fourth target time t 4. Turn on the second switch S of the first battery module. 12 Shutdown, current drops to I r4 , the capacitor voltage rises toU r4 , then the resonant current and capacitor voltage change from t 3 to t The fourth change curve of 4 time periods i r4 and u cr4 for:

[0056]

[0057] .

[0058] It is worth noting that by controlling the phase shift relationship (leading or lagging) of the upper and lower half-bridge switching devices in parallel with the battery balancing circuit and the capacitor, the direction of energy transfer can be controlled.

[0059] Then, for step 202, the initial current value and the initial voltage value of each working mode are calculated based on the resonant current and the capacitor voltage of the battery module in each working mode.

[0060] In the embodiment of the present invention, due to the periodicity of the resonant current, the initial value of each modal current can be obtained by combining the modal resonant current and capacitor voltage equations. I rm (m=0,1,2,3) and the initial value of the capacitor voltage U rm The expression:

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069] Where, T s is the switching cycle; T p is the phase shift time.

[0070] With respect to step 204 , the balanced power transmitted by the battery module to the LC series branch is determined according to the initial current value and the initial voltage value, and the balanced power is adjusted by using phase shift control to keep the circuit in a stable state.

[0071] In an embodiment of the present invention, the balanced power is determined by integrating the initial current value to calculate the average value of the DC capacitor input current when power is transferred from the first capacitor to the second capacitor; and calculating the balanced power of the first capacitor input to the LC series branch based on the average value.

[0072] Furthermore, the balanced power is adjusted in the following manner: initial power is calculated based on the monitoring data of the battery cluster in each group of the battery modules; and the shift ratio between adjacent battery modules is adjusted according to a preset target state so that the initial power reaches the balanced power that maintains the circuit in a stable state.

[0073] For example, when the power is supplied by the DC capacitor C 1-way DC capacitor C 2 When passing, the average value of the DC capacitor input current I C1 It can be obtained by integrating the current, which can be expressed as:

[0074]

[0075] in:

[0076]

[0077] Simplifying the above formula we can get:

[0078]

[0079] The DC capacitance can be further calculated C 1 Input LC branch power P C1 The expression:

[0080]

[0081] The relationship between balanced power, phase shift time and frequency coefficient is as follows: Figure 5 As shown, K = f s / f r is the frequency coefficient, D = T p / T sis the phase shift time ratio. As can be seen from the figure, as the phase shift time increases, the balanced power also increases. T p = T s When the switching frequency is 0.5 V, the balanced power reaches its maximum. Furthermore, as the switching frequency increases, the maximum balanced power decreases. This indicates that the ability of the balanced branches to balance power should be considered when selecting the switching frequency.

[0082] Furthermore, the existing battery balancing circuit composed of LC series is a resonant switched capacitor balancing circuit, which generally uses a fixed duty cycle of 50% to achieve resonant balancing. This method relies on the voltage difference between battery clusters. As can be seen from the above power expression, the phase shift control method can independently control the balancing power. Therefore, when the battery management system (BMS) monitors the battery status and obtains the energy state of the battery cluster, it only needs to adjust the balancing power provided by the BMS. P B To determine the shift ratio between adjacent battery clusters.

[0083] The practicability of the above method is demonstrated below with an embodiment.

[0084] based on Figure 1 The circuit topology with the ability to balance adjacent clusters is constructed using MATLAB / Simulink software. Figure 6 The simulation model shown in the figure is used to simulate and verify the topology. The simulation parameters are shown in Table 1 and the simulation conditions are shown in Table 2.

[0085] Table 1

[0086]

[0087] Table 2

[0088]

[0089] Under the operating conditions shown in the table above, when the simulation time t is in the range of [0, 0.5s], energy balancing is performed between battery clusters B1 and B2, the balancing power is the rated balancing power of 10kW, and energy is transferred from battery cluster B1 to battery cluster B2. When the simulation time t is in the range of [0.5s, 1s], energy balancing is performed between battery clusters B2 and B3, the balancing power is the rated balancing power of 10kW, and energy is transferred from battery cluster B2 to battery cluster B3. When the simulation time t is in the range of [1s, 1.5s], energy balancing is performed between battery clusters B3 and B4, the balancing power is the rated balancing power of 10kW, and energy is transferred from battery cluster B4 to battery cluster B3.

[0090] Figure 7is the output current curve of the battery cluster in the embodiment of the present invention, Figure 8 Figure 1 shows the load current curve for the embodiment of the present invention. Under operating condition 1, the battery cluster output currents are 60A, 40A, 50A, and 50A, respectively; under operating condition 2, the battery cluster output currents are 50A, 60A, 40A, and 50A, respectively; and under operating condition 3, the battery cluster output currents are 50A, 50A, 40A, and 60A, respectively. Under all three operating conditions, the load-side current is 50A. Therefore, under these operating conditions, energy balance is achieved between adjacent battery clusters without affecting the battery's external energy output.

[0091] Figure 9 is the inductor current of the LC series branch in the embodiment of the present invention I r1 、 I r2 、 I r3 , Figure 10 is the LC series branch capacitor voltage in the embodiment of the present invention U cr1 、 U cr2 、 U cr3 In this example, when the circuit is in steady state, under operating condition 1, only the first LC series balancing branch participates in energy relocation, achieving energy balance between battery clusters B1 and B2. Under operating condition 2, only the second LC series balancing branch participates in energy relocation, achieving energy balance between battery clusters B2 and B3. Under operating condition 3, only the third LC series balancing branch participates in energy relocation, achieving energy balance between battery clusters B3 and B4. Therefore, the circuit topology and control strategy of the present invention can achieve energy balance between adjacent battery clusters with energy state as the balancing target.

[0092] Finally, it should be noted that, in this document, relational terms such as first, second, third, and fourth are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0093] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A method for using a DC direct-mounted battery cluster series equalization circuit, characterized in that: The circuit comprises a plurality of battery modules connected in series, wherein: Each group of battery modules includes a battery cluster formed by connecting multiple battery cells in series and a half-bridge sub-module, and the battery cluster and the half-bridge sub-module are connected in parallel; The half-bridge submodule includes a filter capacitor and a switch connected in parallel, wherein the switch includes a first switch and a second switch, the first switch and the second switch are complementary to each other, and the driving signals of the first switches of two adjacent battery modules differ by a phase shift time; Any two adjacent battery modules are connected to an LC series branch consisting of an inductor and a capacitor through a midpoint between the first switch and the second switch; The method comprises: Adjusting the conduction states of the first switch and the second switch in the battery module so that the circuit is in different operating modes; wherein the operating modes include a first mode, a second mode, a third mode, and a fourth mode; When the circuit is in the first mode, at time t0, the first switch S of the first battery module is turned on. 11 and a second switch S of a second battery module adjacent to the first battery module 22 Turn on; use the LC series branch to charge and discharge the first capacitor C1 of the first battery module and the second capacitor C2 of the second battery module in parallel; at the preset first target time t1, the second switch S of the second battery module 22 Shutdown; When the circuit is in the second mode, at time t1, the first switch S of the first battery module is turned on. 11 and a first switch S of the second battery module 21 conduction; use the LC series branch to charge and discharge the first capacitor C1 in parallel; at the preset second target time t2, the first switch S of the first battery module 11 Turn off and turn on the second switch S of the first battery module 12 and the first switch S of the second battery module 21 conducting, so that the LC series branch is in an open circuit; Calculating an initial current value and an initial voltage value of each working mode according to the resonant current and capacitor voltage of the battery module in each working mode; determining the balanced power transmitted by the battery module to the LC series branch according to the initial current value and the initial voltage value, and adjusting the balanced power by using phase shift control to keep the circuit in a stable state; The determining, according to the initial current value and the initial voltage value, the balanced power transmitted by the battery module to the LC series branch includes: Integrate the initial current value to calculate the average current value input by the first capacitor C1 to the LC series branch when power is transferred from the first capacitor to the second capacitor. I C1 : in, ; C r is the LC branch capacitance, L r is the LC branch inductance; U 1 is the voltage of the first capacitor; U 2 is the voltage of the second capacitor; is the resonant current variation curve; Simplifying, we can get: The balanced power of the first capacitor input into the LC series branch is calculated based on the average value. P C1 : Where, T s is the switching cycle; T p is the phase shift time.

2. The method according to claim 1, wherein When the circuit is in the first mode: exist t At time 0, the first switch S of the first battery module is turned on. 11 and a second switch S of a second battery module adjacent to the first battery module 22 conduction; The first capacitor of the first battery module is connected to the first capacitor of the first battery module by the LC series branch. C 1 and the second capacitor of the second battery module C 2. Perform parallel charging and discharging; At the preset first target moment t 1. Switch the second switch S of the second battery module 22 Turn off to get the resonant current and capacitor voltage from t 0 to t The first change curve of time period 1 i r1 and u cr1 : in, , C r is the LC branch capacitance, L r is the LC branch inductance; U r0 is the initial value of the LC branch capacitor voltage; I r0 is the initial value of the inductor current in the LC branch; U 1 is the voltage of the first capacitor; U 2 is the voltage of the second capacitor.

3. The method according to claim 2, wherein When the circuit is in the second mode: exist t At time 1, the first switch S of the first battery module is turned on. 11 and a first switch S of the second battery module 21 conduction; The first capacitor is connected by the LC series branch C 1. Perform parallel charging and discharging; At the preset second target time t 2. Turn on the first switch S of the first battery module. 11 Turn off to get the resonant current and capacitor voltage from t 1 to t The second change curve of time period 2 i r2 and u cr2 : in, I r1 for t LC branch inductor current value at time 1; U r1 for t LC branch capacitor voltage value at moment 1.

4. The method according to claim 3, wherein When the circuit is in the third mode: exist t At time 2, the second switch S of the first battery module is turned on. 12 and the first switch S of the second battery module 21 conducting, so that the LC series branch is in an open circuit; At the preset third target time t 3. Turn on the first switch S of the second battery module 21 Turn off to get the resonant current and capacitor voltage from t 2 to t The third change curve of 3 time periods i r3 and u cr3 : in, I r2 for t LC branch inductor current value at moment 2; U r2 for t LC branch capacitor voltage value at moment 2.

5. The method according to claim 4, wherein When the circuit is in the fourth mode: The second switch S of the first battery module 12 and a second switch S of the second battery module 22 conduction; The second capacitor is connected by the LC series branch C 2. Perform parallel charging and discharging; At the preset fourth target time t 4. Turn on the second switch S of the first battery module. 12 Turn off to get the resonant current and capacitor voltage from t 3 to t The fourth change curve of 4 time periods i r4 and u cr4 : in, I r3 for t LC branch inductor current value at moment 3; U r3 for t LC branch capacitor voltage value at moment 3.

6. The method according to claim 5, wherein The initial current value of each working mode is calculated by the following formula: Where, T s is the switching cycle; T p is the phase shift time.

7. The method according to claim 5, wherein The initial voltage value of each working mode is calculated by the following formula: Where, T s is the switching cycle; T p is the phase shift time.

8. The method according to claim 6, wherein The method of adjusting the balanced power by using phase shift control to keep the circuit in a stable state includes: Calculating initial power based on monitoring data of the battery clusters in each group of the battery modules; The shift ratio between adjacent battery modules is adjusted according to a preset target state so that the initial power reaches a balanced power for the circuit to maintain a stable state.

Images