Modular high-performance battery equalizer

Abstract

The invention discloses a modularized high-performance battery equalizer which comprises a battery pack formed by connecting a plurality of lithium battery units in series, a transformer and an RCD absorption circuit, the equalizer adopts a layered parallel equalization mode, two switch tubes of a first layer are complementarily conducted, an energy transfer path is short, and a switch tube of a second layer starts to work after equalization of the first layer is completed. The primary winding and the secondary winding of the transformer are connected in parallel with an RCD absorption circuit used for absorbing peak voltage when the switching tube is switched on. The equalizer adopts a modular design and is connected in parallel through a multi-winding transformer, and the rated power of a used power device is low and is irrelevant to the number of series battery packs.

Description

Technical Field

[0001] The invention relates to a modular high-performance battery equalizer, belonging to the technical field of battery pack charging and discharging. Background Art

[0002] Due to the continuous exploitation of non-renewable energy such as coal, oil, and natural gas, the climate environment has been deteriorating, and the energy crisis has gradually emerged in recent years. Therefore, in order to alleviate the increasingly serious climate and environmental problems, many countries have invested more funds in the development of sustainable energy, and the large-scale development of electric vehicles is one of the most important measures. Most electric vehicle manufacturers choose lithium batteries as the power batteries of electric vehicles, and need to connect multiple battery cells in series and parallel to meet the voltage level required by electric vehicles. However, due to the differences in performance of each battery cell, the voltage of each battery cell will be inconsistent, which greatly affects the service life and safety of the battery pack. Therefore, studying an equalizer with fast balancing speed, high modularity, and low cost has positive practical significance for reducing the voltage inconsistency between battery cells.

[0003] Existing balancers are divided into passive balancers and active balancers, but passive balancers generate serious heat and have low energy utilization. Existing battery balancers are prone to problems such as long energy transfer paths, low balancing efficiency, and weak modularization when balancing multiple series lithium battery packs, and are easily affected by the voltage scale of the battery pack. Summary of the invention

[0004] Purpose of the invention: In view of the problems and shortcomings in the prior art, in order to improve the balancing efficiency of the battery pack, the present invention provides a modular high-performance battery balancer. The different modules of the battery balancer of the present invention are connected in parallel through a multi-winding transformer to achieve modularization, a short energy flow path, strong scalability, and good balancing efficiency. It can better complete the balancing work of multiple series lithium batteries, is not easily affected by the number of series batteries, and the power device used does not need to be changed after the selection is determined.

[0005] Technical solution: A modular high-performance battery balancer, including m balancing modules, each balancing module has n balancing circuits and a multi-winding transformer, and the n balancing circuits are connected to different windings of the transformer respectively; the transformers between different balancing modules are connected in parallel through a parallel bus; the transformer has n+1 windings. The jth (j=1,2,…,n) balancing circuit of the i-th (i=1,2,…,m) balancing module contains a double-layer structure, and the first layer structure contains two battery cells B connected in series. ij1 , B ij2 , 2 switch tubes S ij1 With S ij2 , and an inductor L ijThe second layer structure includes a switch tube S Mij And an RCD absorption circuit, in which an RCD absorption circuit is connected in parallel to each winding of the transformer to absorb the peak voltage generated when the switching tube is turned on.

[0006] The battery cell B in the equalizer ij2 The positive electrode and B ij1 The negative connection, B ij1 The positive electrode and the switch tube S ij1 The drain (D) connection, S ij1 The source (S) and S ij2 The drain (D) connection, S ij2 The source (S) and B ij2 The negative connection of the inductor L ij One end and B ij2 The positive electrode is connected to S ij2 The drain (D) of the second layer switch tube S Mij The drain (D) and S ij1 The drain (D) connection, S Mij The source (S) is connected to one end of the transformer winding, S ij2 The source (S) is connected to the other end of the transformer winding.

[0007] The inductor is used as an energy storage element to perform the balancing process of the first layer structure. The inductor cooperates with the switch tube to absorb and release the energy in the battery to complete the balancing work of the first layer. The current ripple of the inductor is:

[0008]

[0009] Where V o is the output voltage, V in is the input voltage, T is a switching cycle, and L is the inductance value.

[0010] Furthermore, the transformer primary voltage is:

[0011]

[0012] Furthermore, the balancing current is:

[0013]

[0014] where i = 1, 2, ..., m, j = 1, 2, ..., n, V Bij is the battery voltage of the jth balancing circuit of the i-th balancing module, i Bij For its balancing current, L eqij is the equivalent leakage inductance of the primary winding of the transformer, R eqij is the equivalent resistance of the primary winding of the transformer.

[0015] Furthermore, the two switch tubes S in the first layer structure ij1 With S ij2 Driven by two complementary PWM signals with dead zones, the switch tubes of the second layer structure in the odd-numbered (i=1, 3, 5...) and even-numbered (i=2, 4, 6...) modules (referred to as odd-even modules) of the equalizer are driven by two complementary PWM signals. The overall steps are as follows:

[0016] S1, the two switch tubes in the first layer structure in all balancing modules begin to conduct complementary, and detect the voltages of the two battery cells associated with the first layer.

[0017] S2, when the voltages of the two batteries in the first layer are the same, the switches in the first layer are turned off at the same time, and the switches in the second layer of the odd-even module are driven by a pair of complementary PWM signals respectively.

[0018] Beneficial effects: The present invention modularizes the design of the traditional active half-bridge lithium battery equalizer. When the number of lithium batteries to be balanced is large, the modular design can achieve stable and rapid balancing without increasing the difficulty of balancing circuit design, which is more in line with actual needs. The specific advantages are as follows:

[0019] 1) By adopting hierarchical parallel balancing, the number of balancing targets is maximized, thus getting rid of the influence of the number of series-connected single cells and achieving fast balancing speed. The balancing experiment proves that in the first and second layer balancing, the number of parallel balancing targets has reached the maximum.

[0020] 2) Each balancing module has the same structure, is independent of each other, and has the shortest energy path. The balancing efficiency is independent of the number of batteries in series and is high and stable.

[0021] 3) A modular design is adopted, and the power devices used have low rated power. Once selected, they remain unchanged and have good expandability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A structural diagram of a single equalization circuit in a single module;

[0023] Figure 2 It is the equalization modal diagram of the first-layer structure of the equalizer;

[0024] Figure 3 It is the equalization modal diagram of the second-layer structure of the equalizer;

[0025] Figure 4 This is the working flow diagram of the equalizer;

[0026] Figure 5 It is the waveform of the equalizer's first-layer structure equalization operation;

[0027] Figure 6 Equalize the waveform for the second layer of the equalizer result;

[0028] Figure 7 It is the equalizer waveform diagram;

[0029] Figure 8 This is the topology diagram of the modular equalizer circuit. DETAILED DESCRIPTION

[0030] The present invention is further explained below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0031] The present invention provides a modular high-performance battery equalizer, which can transfer energy from higher battery cells to lower battery cells through energy storage elements such as inductors and transformers. The equalization circuit adopts a layered parallel structure to solve the impact of a small number of lithium batteries connected in series. There are only three switching tubes in an equalization circuit, which reduces switching losses, is simple to control, and has good reliability and scalability.

[0032] The balancer is used to balance multiple battery packs. The battery pack includes multiple lithium batteries connected in series. The balancer includes:

[0033] transformer;

[0034] bus;

[0035] A plurality of balancing modules are each coupled to the transformer, wherein

[0036] Each balancing module is associated with battery cells in multiple battery packs.

[0037] The n balancing circuits in each balancing module are double-layer structures, including switch tubes, inductors, capacitors and resistors.

[0038] Each balancing module is connected in parallel with the bus through a transformer.

[0039] Each balancing module can be used as a source of the balancer, so that the battery cell associated with the source releases energy and charges the battery cells in the multi-battery pack through the transformer and the bus, and

[0040] Each balancing module can be used as a receiving stage of the equalizer, and is used to charge a battery cell associated with the receiving stage in the multi-battery pack from a battery cell in the multi-battery pack via a transformer and a bus.

[0041] The single balancing circuit in each balancing module adopts a hierarchical parallel structure, which can balance the maximum number of batteries. When a large number of lithium batteries need to be balanced, the balancing can be achieved stably and quickly through modular design without increasing the difficulty of balancing circuit design.

[0042] The present invention is described in detail below in conjunction with the accompanying drawings:

[0043] like Figure 1 As shown, a single equalization circuit of a battery equalizer is shown. The circuit has a double-layer structure. The first layer contains two lithium battery cells B connected in series. 111 and B 112 , an inductor L 11 , and two switch tubes S 111 and S 112 , the first layer of two battery cells B is completed by inductance 111 and B 112 The second layer contains a switch tube S M11 And a peak voltage absorption circuit RCD circuit, the RCD circuit consists of a capacitor, a resistor and a diode, where the resistor is connected in parallel with the capacitor, the diode is connected in series with the capacitor, the different balancing circuits in the module are coupled through the transformer winding, and the modules are connected in parallel through the bus. And the polarity of the transformer secondary winding of the odd and even modules is opposite, which can avoid the problem of transformer bias.

[0044] like Figure 2 As shown, path ① is the path for high-energy battery cells to release energy. Path ① starts from battery cell B 112 The positive terminal of the inductor L 11 The left end of 11 To switch tube S 112 The drain of the switch tube S 112 , from the switch tube S 112 The gate of the battery cell B 112 Path ② is the path for low-energy battery cells to absorb energy. Path ② is from battery cell B 111 To switch tube S 111 The drain of the switch tube S 111 , from the switch tube S 111 The gate to inductor inductance L 11 One end of the 11 Back to battery cell B 111 Taking the first balancing circuit unit of the first module as an example, assuming that battery unit B 112 Energy higher than battery cell B 111 At this time, it is necessary to control the energy from B 112 To B 111 Transfer, when the switch tube S 112When conducting, B 112 Discharge, inductor energy storage, when the switch tube S 111 When conducting, the inductor is 111 Release energy, and the process of other circuit units is similar.

[0045] The ripple current of the inductor is:

[0046]

[0047] Where V o is the output voltage V in is the input voltage, T is a switching cycle, and L is the inductance value.

[0048] When the first level of balancing is completed, such as Figure 3 As shown, the second-level balancing starts, wherein the second-level switch tubes of all units in the odd-numbered modules and the even-numbered modules are driven by a pair of complementary PWM signals. M11 and S M12 When turned on, the switch tube S M21 and S M22 When switched off, the two battery cells in the first layer transfer energy through the transformer.

[0049] The primary voltage of the transformer is:

[0050]

[0051] Where j = 1, 2…, 4, V B1j is the battery pack voltage of the jth balancing circuit in module 1, i B1j For its balancing current, L eq1j is the equivalent leakage inductance of the primary winding of the transformer, R eq1j is the equivalent resistance of the primary winding of the transformer.

[0052] The transformer primary side balancing current is:

[0053]

[0054] The turns ratio of the transformer is:

[0055]

[0056] The transformer secondary voltage is:

[0057]

[0058] Where V Bij is the battery voltage, V Twij is the transformer primary voltage, N w11 and N w11 is the number of turns of the primary and secondary sides of the transformer, L eqw11 and Leqw1 are the primary and secondary leakage inductances of the transformer, R eqw11 and R eqw1 are the equivalent resistances of the primary and secondary sides of the transformer, i Tw1 is the secondary current of the transformer.

[0059] The transformer secondary side balancing current is:

[0060]

[0061] Where V M1 and V M2 is the sum of the battery voltages of the first module and the second module, L eqw1 and L eqw2 is the leakage inductance of the secondary winding of transformer I and transformer II, t0 represents the start-up time of balancing, t represents the present moment, that is, what is required is the balanced current of the secondary side of the transformer at moment t.

[0062] The equalizer operation process is as follows Figure 4 As shown, the first switch tube S of the first level in the jth equalization circuit of the i-th module ij1 With the second switch tube S ij2 Using complementary PWM signal control with dead zone, the steps are as follows:

[0063] S1, the two switch tubes in the first layer structure in all modules begin to conduct complementary and detect the voltages of the two battery cells associated with the first layer.

[0064] S2, when the voltages of the two batteries in the first layer are the same, the switches in the first layer are turned off at the same time, and the switches in the second layer of the odd-even module are driven by a pair of complementary PWM signals respectively.

[0065] Figure 5 This is the operating waveform of the first-layer structure of the equalizer. The first-layer equalization can be generally divided into four processes:

[0066] At [t0~t1], the first switch tube S in the first layer ij1 On, S ij2 Shutdown, Battery B ij1 The inductor L is charged, and the inductor current i L for:

[0067]

[0068] [t1~t2] time, S ij1 , S ij2 are all turned off, and the inductor energy passes through S ij1 The anti-parallel diode on the battery B ij2 Charging, here with dead zone control can avoid the risk of circuit short circuit. At this time, the inductor current i L for:

[0069]

[0070] [t2~t3] time, S ij1 Shutdown, S ij2 The inductor L is turned on through S ij2 To battery B ij2 Charging, at this time the inductor current i L for:

[0071]

[0072] [t3~t4] time, S ij1 , S ij2 are all turned off, the inductor energy is fully released, and the dead time can prevent battery B ij2 Reverse discharge, at this time the inductor current i L for:

[0073] i L =0

[0074] In the formula, I t1 ,I t2 is the inductor current at time t1 and t2, V B11 、V B12 is the battery cell voltage, V D is the reverse diode conduction voltage drop on the switch tube, V mos is the on-state voltage drop of the switch tube, and the inductance value is L;

[0075] Figure 6 It is the operating waveform of the equalization between the modules of the second layer of the equalizer. The driving signal PWM+ of the second layer of the odd-numbered modules is complementary to the driving signal PWM- of the second layer of the even-numbered modules.

[0076] Figure 7 This is the change curve of the lithium battery voltage during the operation of the balancer when the voltages of the four battery cells are 3.9V, 3.8V, 3.6V, and 3.5V respectively. At (0~0.04s), the balancing of the two batteries in the first layer is completed, and the balancing between the modules in the second layer is carried out at (0.04s~0.275s).

[0077] In summary, the modular equalizer disclosed in the present invention adopts double-layer parallel balancing to solve the influence of the number of lithium batteries connected in series. The circuit structure of each layer and each module is independent and identical, the energy path is short, the efficiency is high, and energy transfer between any battery cells is realized.

Claims

1. A modular high-performance battery equalizer, It is characterized in that The invention comprises m balancing modules, each of which has n balancing circuits and a multi-winding transformer, wherein the n balancing circuits are respectively connected to different windings of the transformer; the transformers between different balancing modules are connected in parallel through a parallel bus; the transformer has n+1 windings; the j-th balancing circuit of the i-th balancing module comprises a double-layer structure, i=1,2,…,m, j=1,2,…,n, and the first layer structure comprises two battery units B connected in series ij1 , B ij2 , 2 switch tubes S ij1 With S ij2 , and 1 inductor L ij The second layer structure includes a switch tube S Mij And an RCD absorption circuit, in which an RCD absorption circuit is connected in parallel to each winding of the transformer to absorb the peak voltage generated when the switching tube is turned on.

2. The modular high-performance battery equalizer according to claim 1, It is characterized in that The battery cell B in the equalizer ij2 The positive electrode and B ij1 The negative connection, B ij1 The positive electrode and the switch tube S ij1 The drain connection, S ij1 The source and S ij2 The drain connection, S ij2 The source and B ij2 The negative connection of the inductor L ij One end and B ij2 The positive electrode is connected to S ij2 The drain connection of the second layer switch tube S Mij The drain and S ij1 The drain connection, S Mij The source of is connected to one end of the transformer winding, S ij2 The source is connected to the other end of the transformer winding.

3. The modular high performance battery equalizer according to claim 1, It is characterized in that The inductor acts as an energy storage element to perform the balancing process of the first layer structure. The inductor cooperates with the switch tube to absorb and release the energy in the battery to complete the balancing work of the first layer. ij1 With S ij2 Driven by two complementary PWM signals with dead zones, the switch tubes of the second layer structure in the odd-numbered and even-numbered modules of the equalizer are driven by two complementary PWM signals; the odd-numbered and even-numbered modules are referred to as odd-even modules.

4. The modular high performance battery equalizer according to claim 1, The characteristic is that Battery Cell B 112 Energy higher than battery cell B 111 At this time, it is necessary to control the energy from B 112 To B 111 Transfer, when the switch tube S 112 When conducting, B 112 Discharge, inductor energy storage, when the switch tube S 111 When conducting, the inductor is 111 Release energy; when the first layer of balancing is completed, the second layer of balancing begins, in which the second layer of switch tubes of all units in the odd-numbered modules and the even-numbered modules are driven by a pair of complementary PWM signals. M11 and S M12 When turned on, the switch tube S M21 and S M22 When switched off, the two battery cells in the first layer transfer energy through the transformer.

5. The modular high performance battery equalizer according to claim 1, It is characterized in that The switch tubes of the second layer structure in the odd-numbered and even-numbered modules of the equalizer are driven by two complementary PWM signals, and the steps are as follows: S1, the two switch tubes in the first layer structure of all balancing modules start to conduct complementary, and detect the voltages of the two battery cells associated with the first layer; S2, when the voltages of the two batteries in the first layer are the same, the switches in the first layer are turned off at the same time, and the switches in the second layer of the odd-even module are driven by a pair of complementary PWM signals respectively.

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