A dc-dc converter automatically achieving equalization of energy storage cells

Abstract

The application discloses a DC-DC converter capable of automatically realizing energy storage cell balancing, realizes integration of an equalizer and the DC-DC converter, and comprises a front-stage circuit and a rear-stage circuit. i n switch devices K i a multi-winding transformer T, and the multi-winding transformer T contains n windings; in the rear-stage circuit, a positive electrode of the energy storage cell B i is connected to one end of an i winding w i of the multi-winding transformer T, the other end of the winding w i is connected to a positive electrode of the switch device K i , a negative electrode of the switch device K i is connected to a negative electrode of the energy storage cell B i ; all the windings w i and the positive electrodes of the energy storage cells B i are connected to the same end; the switch devices K i are connected in series, a positive electrode of the switch device K1 is an end point 3a of the rear-stage circuit, and a negative electrode of the switch device K n is an end point 3b of the rear-stage circuit. The DC-DC converter capable of automatically realizing energy storage cell balancing automatically completes voltage balancing while charging and / or discharging.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, and in particular to a DC-DC converter for automatically balancing energy storage cells. BACKGROUND

[0002] Series-connected energy storage cells are now widely used in portable electronic devices, household appliances, electric vehicles and other fields. There are inevitable tolerances between energy storage cells, plus uneven temperature distribution and aging differences, so the series-connected energy storage cells will gradually become unbalanced. When one energy storage cell reaches the boundary of the allowed operating range, the overall series-connected energy storage cell charging or discharging will be terminated, so that the capacity of the series-connected energy storage cells cannot be fully utilized. With repeated use, cell inconsistency will worsen, further deteriorating the group characteristics of the energy storage cells, and it is extremely easy for a small number of cells to overcharge or overdischarge, which will cause the performance of the series-connected energy storage cells to decline significantly, and in extreme cases may even cause a vicious accident such as burning or explosion, which greatly hinders the application and promotion of series-connected energy storage cells.

[0003] Therefore, in a series-connected energy storage system, an equalization system is usually needed to reduce the inconsistency between energy storage cells. The introduction of the equalization system can prolong the running time of the system, improve the utilization rate of the energy storage cells, prevent overcharging or overdischarging of the cells during operation, prolong the cycle life of the energy storage cells, and ensure the safe use of series-connected energy storage cells. In addition, in order to realize the energy flow in the energy storage system, a DC-DC converter is usually used to connect the series-connected energy storage cells.

[0004] For the above reasons, the energy storage system usually needs to be configured with an energy storage cell equalization circuit and a DC-DC converter. A typical energy storage system is shown in FIG. 1, in which series-connected energy storage cells B1-Bn are connected in series through a DC-DC converter. Figure 1A n The series-connected energy storage cells are charged or discharged through the DC-DC converter.

[0005] ​In the article "Battery Pack Active Balancing System Based on Bidirectional Flyback Converter", the authors Yinan, Liang Zhihua, Luoxin'er, etc. use a bidirectional flyback converter to balance the series energy storage cells. Each energy storage cell needs a magnetic element, and voltage detection closed-loop control is needed to balance. The balancing circuit proposed in the patent "Voltage Equalization Circuit for Series Energy Storage Device and Voltage Equalization System Containing the Circuit" (CN107800292B) needs to transfer energy greater than the difference between the energy storage cells, causing unnecessary loss. In the paper "A Low-Cost Multiwinding Transformer Balancing Topology for Retired Series-Connected Battery String," (IEEE Transactions on Power Electronics, vol. 36, no. 5, pp. 4931-4936), the charging balancer is proposed by using a multi-winding transformer, which reduces the cost of the system while improving the efficiency of the system compared to the balancer using a large number of diode structures. However, when it is used in applications with a large number of series energy storage cells, it is very difficult to make a large number of high-precision windings on the same magnetic core. SUMMARY

[0006] To overcome the shortcomings of the prior art, the present application aims to solve the technical problem of providing a DC-DC converter that automatically balances energy storage cells, integrates the balancer with the DC-DC converter, and realizes automatic balancing while completing the DC-DC conversion function. For the existing charging balancer based on a multi-winding transformer, it is difficult to make a large number of high-precision windings on the same magnetic core. A modular solution is proposed, which only needs one magnetic element per module, reducing the size of the system and having the advantage of strong scalability. The control method of the present application only needs at most two complementary PWM signals to realize constant current and constant voltage control, and the control method is simple.

[0007] The technical solution adopted by the present application to solve the technical problem is:

[0008] In the first aspect, the present application provides a DC-DC converter that automatically balances energy storage cells, which integrates the balancer with the DC-DC converter. The DC-DC converter that automatically balances energy storage cells contains a front-end circuit and a back-end circuit. The back-end circuit contains n energy storage cells B i , n switching devices K i , and a multi-winding transformer T. The multi-winding transformer T contains n windings, i = 1, 2, …, n. The back-end circuit contains energy storage cells B iThe positive terminal is connected to the i-th winding w of the multi-winding transformer T. i One end, winding w i The other end is connected to the switching device K. i The positive terminal, switching device K i The negative electrode and energy storage cell B i The negative terminals are connected; all windings w i With energy storage cell B i The positive terminals connected to each other are terminals with the same name; each switching device K i Interconnected, switching device K x The negative electrode and K x+1 The positive terminals of the switches are connected, x = 1, 2, ..., n-1. The positive terminal of the switching device K1 is the terminal 3a of the subsequent circuit. n The negative terminal is the terminal 3b of the subsequent circuit;

[0009] The front-end circuit includes at least one switching device K0 with four terminals, denoted as terminals 1a, 1b, 2a, and 2b. The functions of these four terminals are as follows: terminal 1a is connected to the positive terminal of an external load or power supply; terminal 1b is connected to the negative terminal of an external load or power supply; terminal 2a is connected to the positive terminal 3a of the switching device K1 in the subsequent circuit; and terminal 2b is connected to the positive terminal of the switching device K0 in the subsequent circuit. n The negative terminal 3b is connected.

[0010] Secondly, the present invention provides a DC-DC converter that automatically achieves energy storage unit balancing, characterized in that it integrates an equalizer and a DC-DC converter. The DC-DC converter that automatically achieves energy storage unit balancing comprises a front-end circuit and a back-end circuit. The back-end circuit has m modules, and any module j contains n energy storage units B. j,i n switching devices K j,i A multi-winding transformer T j Multi-winding transformer T j It contains n+1 windings, j = 1, 2, ..., m, i = 1, 2, ..., n;

[0011] The energy storage unit B in module j j,i The positive terminal is connected to the multi-winding transformer T. j The i-th winding w j,i One end, winding w j,i The other end is connected to the switching device K. j,i The positive terminal, switching device K j,i The negative electrode and energy storage cell B j,i The negative terminal is connected; multi-winding transformer T j winding w j,i With each energy storage unit Bj,i the end points connected with the positive pole of the positive electrode of the energy storage cell B are homonymous; j the winding w j,n+1 of the multi-winding transformer T j is connected in parallel with the winding w j,n+1 of the multi-winding transformer T j ; j the end points e j and f j,n+1 of the winding w j of the multi-winding transformer T j,i are homonymous;

[0012] the switching devices K j,i are connected in series with each other: the negative pole of the device K j,x is connected with the positive pole of the device K j,x+1 , x = 1, 2, ……n-1; the positive pole of the device K j,1 is the end point b j , and the negative pole of the device K j,n is the end point d j ;

[0013] the connection mode between the m modules is that the end point b y of the module y is connected with the end point d y-1 of the module y-1, y = 2, 3, ……m; the end point b1 is the end point 3a of the subsequent circuit, and the end point d m is the end point 3b of the subsequent circuit;

[0014] the front-stage circuit comprises at least one switching device K0, which has four end points, namely end points 1a, 1b, 2a and 2b, and the functions of the corresponding four end points are as follows: the end point 1a is used for being connected with the positive pole of an external load or power supply, the end point 1b is used for being connected with the negative pole of the external load or power supply, the end point 2a is used for being connected with the end point 3a of the subsequent circuit, and the end point 2b is used for being connected with the end point 3b of the subsequent circuit;

[0015] the end point 3a of the subsequent circuit is connected with the end point 2a of the front-stage circuit, and the end point 3b of the subsequent circuit is connected with the end point 2b of the front-stage circuit.

[0016] the front-stage circuit comprises one switching device K0, the positive pole of the switching device K0 is connected with the end point 1a, the negative pole of the switching device K0 is connected with the end point 2a, and the end point 1b is directly connected with the end point 2b through a wire.

[0017] The front-stage circuit comprises a switching device K0, an inductor L and a capacitor C; the negative electrode of the switching device K0 is connected with the terminal 1b of the front-stage circuit, the terminal 1b of the front-stage circuit is directly connected with the terminal 2a of the front-stage circuit through a wire, one end of the inductor L is connected with the terminal 1a of the front-stage circuit, the other end of the inductor L is connected with the positive electrode of the switching device K0, one end of the capacitor C is connected with the terminal 2b of the front-stage circuit, and the other end of the capacitor C is connected with the positive electrode of the switching device K0;

[0018] Or the positive electrode of the switching device K0 is connected with the terminal 1a of the front-stage circuit, the terminal 1b of the front-stage circuit is connected with the terminal 2b of the front-stage circuit, one end of the inductor L is connected with the terminal 1b of the front-stage circuit, the other end of the inductor L is connected with the negative electrode of the switching device K0 and one end of the capacitor C, and the other end of the capacitor C is connected with the terminal 2a of the front-stage circuit.

[0019] The energy storage unit is a battery or a super capacitor, and is a single unit or a combination of series and parallel connection of multiple units; the switching device K0 in the front-stage circuit is at least one of a MOSFET, an IGBT or a diode, the switching device K i / K j,i in the rear-stage circuit is one of a MOSFET, an IGBT or a diode; if the switching device K0 in the front-stage circuit is a diode, all the switching devices in the rear-stage circuit cannot be diodes, and if the switching device K i / K j,i in the rear-stage circuit is a diode, all the switching devices in the front-stage circuit cannot be diodes.

[0020] When the switching device K0 in the front-stage circuit is a diode and the switching device in the rear-stage circuit is a MOSFET or an IGBT, the drain of the MOSFET is the positive electrode of the switching device in the rear-stage circuit, the source of the MOSFET is the negative electrode of the switching device in the rear-stage circuit; the collector of the IGBT is the positive electrode of the switching device in the rear-stage circuit, and the emitter of the IGBT is the negative electrode of the switching device in the rear-stage circuit; the negative electrode of the diode is the positive electrode of the switching device in the front-stage circuit, and the positive electrode of the diode is the negative electrode of the switching device in the front-stage circuit;

[0021] When the switching device in the front-stage circuit is a MOSFET or an IGBT and the switching device in the rear-stage circuit is a diode, the drain of the MOSFET is the positive electrode of the switching device in the front-stage circuit, the source of the MOSFET is the negative electrode of the switching device in the front-stage circuit; the collector of the IGBT is the positive electrode of the switching device in the front-stage circuit, and the emitter of the IGBT is the negative electrode of the switching device in the front-stage circuit; the negative electrode of the diode is the positive electrode of the switching device in the rear-stage circuit, and the positive electrode of the diode is the negative electrode of the switching device in the rear-stage circuit;

[0022] When the switching devices in the current stage circuit and the subsequent stage circuit are MOSFET or IGBT, the drain of the MOSFET is the positive electrode of the switching device, and the source of the MOSFET is the negative electrode of the switching device; the collector of the IGBT is the positive electrode of the switching device, and the emitter of the IGBT is the negative electrode of the switching device.

[0023] When the switching device in the current stage circuit is a diode and the switching device in the subsequent stage circuit is IGBT or MOSFET, only the energy storage unit can be discharged, and the specific process of discharging the energy storage unit is:

[0024] (1) the switching device in the subsequent stage circuit is turned on, and the output voltage / output current of the converter is controlled by controlling the on-duty ratio of the switching device in the subsequent stage circuit;

[0025] (2) the switching device in the subsequent stage circuit is turned off, and the switching device in the current stage circuit is turned on.

[0026] When the switching device in the current stage circuit is IGBT or MOSFET and the switching device in the subsequent stage circuit is a diode, only the energy storage unit can be charged, and the specific process of charging the energy storage unit is:

[0027] (1) the switching device in the current stage circuit is turned on, and the output voltage / output current of the converter is controlled by controlling the on-duty ratio of the switching device in the current stage circuit;

[0028] (2) the switching device in the current stage circuit is turned off, and the switching device in the subsequent stage circuit is turned on.

[0029] When the switching devices in the current stage circuit and the subsequent stage circuit are IGBT or MOSFET, both the energy storage unit can be charged and discharged, and the specific process of charging the energy storage unit is:

[0030] (1) the switching device in the subsequent stage circuit is turned off, and the switching device in the current stage circuit is turned on after a dead time, and the output voltage / output current of the converter is controlled by controlling the on-duty ratio of the switching device in the current stage circuit;

[0031] (2) the switching device in the current stage circuit is turned off, and the switching device in the subsequent stage circuit is turned on after a dead time.

[0032] The specific process of discharging the energy storage unit is:

[0033] (1) the switching device in the current stage circuit is turned off, and the switching device in the subsequent stage circuit is turned on after a dead time, and the output voltage / output current of the converter is controlled by controlling the on-duty ratio of the switching device in the subsequent stage circuit;

[0034] (2) The switch device in the post-stage circuit is turned off, and after a dead time, the switch device in the pre-stage circuit is turned on.

[0035] When the voltage of each energy storage cell in the series energy storage string is different, the average current flowing through each energy storage cell is different in the charging or discharging state, and the energy storage cell with higher voltage will flow more current in discharging and less current in charging than the energy storage cell with lower voltage; when the voltage of each energy storage cell in the series energy storage string is the same, the current flowing through each energy storage cell will be the same; the DC-DC converter for automatically realizing energy storage cell balancing automatically completes voltage balancing at the same time of charging and / or discharging.

[0036] Compared with the prior art, the positive progress effect of the present application is that:

[0037] (1) The equalizer and the DC-DC converter are integrated in the present application, the complexity and cost of the energy storage system are reduced by multiplexing the magnetic element and the switch, the volume required by the system is reduced, and the efficiency of the system is improved; the integrated energy storage system is shown in the schematic diagram Figure 1B .

[0038] (2) Automatic balancing is realized, compared with the traditional equalizer which needs to be balanced through voltage detection closed-loop control, the energy storage system is simplified, the balancing current depends on the voltage difference between the energy storage cells, there is no additional energy transmission, and the loss of the balancing system is reduced.

[0039] (3) A modular solution is proposed to solve the problem that the existing charging equalizer based on a multi-winding transformer cannot make a large number of high-precision windings on the same magnetic core, and the scalability of the system is improved.

[0040] (4) The control mode of the present application can realize constant current and constant voltage control only by using two complementary PWM signals, and the control mode is simple. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1A It is a schematic diagram of the structure of a typical energy storage system.

[0042] Figure 1B It is a schematic diagram of the structure of the integrated energy storage system of the present application.

[0043] Figure 2 It is a schematic diagram of the circuit connection of one embodiment of the DC-DC converter for automatically realizing energy storage cell balancing of the present application.

[0044] Figure 3 It is a schematic diagram of the circuit connection of one modular embodiment of the DC-DC converter for automatically realizing energy storage cell balancing of the present application.

[0045] Figure 4Three types of circuit connection diagrams for the pre-stage circuit; (1) Type One; (2) Type Two; (3) Type Three.

[0046] Figure 5A Circuit connection diagram for Example 1.

[0047] Figure 5B Charging process schematic for Example 1.

[0048] Figure 5C Discharging process schematic for Example 1.

[0049] Figure 6A Circuit connection diagram for Example 2.

[0050] Figure 6B Charging process schematic for Example 2.

[0051] Figure 7A Circuit connection diagram for Example 3.

[0052] Figure 7B Discharging process schematic for Example 3.

[0053] Figure 8A Circuit connection diagram for Example 4.

[0054] Figure 8B Charging state schematic for Example 4.

[0055] Figure 8C Discharging state schematic for Example 4.

[0056] Figure 9A Circuit connection diagram for Example 5.

[0057] Figure 9B Charging process schematic for Example 5.

[0058] Figure 9C Discharging process schematic for Example 5.

[0059] Figure 10A Circuit connection diagram for Example 6.

[0060] Figure 10B Charging process schematic for Example 6.

[0061] Figure 10C Discharging process schematic for Example 6.

[0062] Figure 11 Possible combinations of the DC-DC converter embodiments for automatic energy storage cell equalization of the present invention. DETAILED DESCRIPTION

[0063] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0064] The circuit connection diagram of the DC-DC converter for automatically balancing individual energy storage cells in this invention is as follows: Figure 2 As shown, it includes a front-end circuit and a back-end circuit. The specific circuit connection method of the back-end circuit is as follows: Energy storage cell B i The positive terminal is connected to the i-th winding w of the multi-winding transformer T. i One end of (i = 1, 2, ..., n), winding w i The other end is connected to the switching device K. i The positive terminal, switching device K i The negative electrode and energy storage cell B i The negative terminals are connected; all windings w i With energy storage cell B i The positive terminals connected to each other are terminals with the same name; each switching device K i Interconnected, switching device K x The negative electrode and K x+1 The positive terminals of the switching devices K1 and K2 are connected (x = 1, 2, ..., n-1). The positive terminal of the switching device K1 is the terminal 3a of the subsequent circuit. The terminal 3a of the subsequent circuit is connected to the terminal 2a of the preceding circuit. n The negative terminal is terminal 3b of the subsequent stage circuit, and terminal 3b of the subsequent stage circuit is connected to terminal 2b of the preceding stage circuit. The aforementioned switching device K... i (i = 1, 2, ..., n) represents one of the following: MOSFET, IGBT, or diode. When K... i When it is a MOSFET, the drain of the MOSFET is the device K. i The positive terminal of the MOSFET is the source terminal of device K. i The negative electrode; when K i When it is an IGBT, the collector of the IGBT is device K. i The positive electrode of the IGBT, the emitter electrode of the device K i The negative electrode; when K i When it is a diode, the cathode of the diode is device K. i The positive terminal of the diode is device K. i The negative electrode.

[0065] The front-stage circuit includes at least one switching device K0, which can directly or indirectly transmit energy to the rear-stage circuit, and has four endpoints, which are respectively denoted as endpoints 1a, 1b, 2a and 2b, and the functions of the corresponding four endpoints are as follows: the endpoint 1a is used for being connected with the positive pole of an external load or power supply, the endpoint 1b is used for being connected with the negative pole of the external load or power supply, the endpoint 2a is used for being connected with the positive pole of a leading-out endpoint 3a of a switching device K1 in the rear-stage circuit, and the endpoint 2b is used for being connected with the negative pole of a leading-out endpoint 3b of the switching device K1 in the rear-stage circuit. n

[0066] When the external power supply charges the series energy storage cells, the endpoints 1a and 1b are the input side of the front-stage circuit, and the current flows in from the endpoint 1a and flows out from the endpoint 1b. The endpoints 2a and 2b are the output side of the front-stage circuit, and the current flows out from the endpoint 2a and flows in from the endpoint 2b. The endpoints 3a and 3b are the input side of the rear-stage circuit, and the current flows in from the endpoint 3a and flows out from the endpoint 3b.

[0067] When the series energy storage cells discharge the external load, the endpoints 2a and 2b are the input side of the front-stage circuit, and the current flows in from the endpoint 2a and flows out from the endpoint 2b. The endpoints 1a and 1b are the output side of the front-stage circuit, and the current flows out from the endpoint 1a and flows in from the endpoint 1b. The endpoints 3a and 3b are the output side of the rear-stage circuit, and the current flows out from the endpoint 3a and flows in from the endpoint 3b.

[0068] Figure 2 In the formula, B i (i = 1, 2, ……, n) represents an energy storage cell, wherein n represents the number of series energy storage cells in the rear-stage circuit, the energy storage cell can be a battery or a super capacitor, and can be a single cell or a combination of multiple cells in series or parallel connection, which is hereinafter referred to as an energy storage cell; the front-stage circuit has three types; the multi-winding transformer T in the rear-stage circuit has n windings, and the transformation ratio between each winding is 1, K i (i = 1, 2, ……, n) represents a device with a switching function, which can be one of a MOSFET, an IGBT or a diode.

[0069] Further, when the number of series energy storage cells is large, it is very difficult to make a large number of high-precision windings on the same magnetic core, and the rear-stage circuit can be expanded to m modules, thereby improving the scalability of the system. At this time, the rear-stage circuit adopts a modular combination mode, is applied to a DC-DC converter which charges or discharges the energy storage cells and has an automatic balancing function, and a connection diagram of the rear-stage circuit expanded to m modules is as shown in Figure 3 The arbitrary module j (j = 1, 2, ……, m) includes n energy storage cells B j,i (i = 1, 2, ……, n), n switching devices K j,i ​, a multi-winding transformer T j , a multi-winding transformer T j containing n+1 windings; the positive pole of the energy storage cell B j,i in the module j is connected to the i winding w j of the multi-winding transformer T j,i , one end of the winding w j,i is connected to the positive pole of the switching device K j,i , the negative pole of the switching device K j,i is connected to the negative pole of the energy storage cell B j,i ; the winding w j (i=1, 2, ……n) of the multi-winding transformer T j,i is connected to the positive pole of the energy storage cell B j,i ; the two ends of the winding w j of each multi-winding transformer T j,n+1 are connected in parallel, the two ends of the winding w j of the multi-winding transformer T j,n+1 are e j and f j ; the end f j of the winding w j,n+1 of the multi-winding transformer T j is connected to the positive pole of the energy storage cell B j,i , the end e j of the winding w j,n+1 of the multi-winding transformer T j is connected to the positive pole of the energy storage cell B j,i ;

[0070] the end e y of the module y is connected to the end e y-1 of the module y-1, the end f y of the module y is connected to the end f y-1 of the module y-1 (where y=2, 3, ……m); each switching device K j,i is connected in series; the negative pole of the switching device K j,x is connected to the positive pole of K j,x+1 (where x=1, 2, ……n-1); the positive pole of the switching device K j,1 is the end b j , and the negative pole of the switching device K j,n is the end d j .

[0071] the end b y of the module y is connected to the end d y-1connected, wherein y = 2, 3,..., m, the end point bl is the end point 3a of the subsequent circuit, the end point 3a of the subsequent circuit is connected to the end point 2a of the previous circuit, the end point d m is the end point 3b of the subsequent circuit, the end point 3b of the subsequent circuit is connected to the end point 2b of the previous circuit; the end point la of the previous circuit is connected to the positive pole of the external load or power supply, and the end point lb of the previous circuit is connected to the negative pole of the external load or power supply.

[0072] The previous circuit has three types as shown in Figure 4 . Type one (see (1) in Figure 4 ) includes a switching device K0, the positive pole of the switching device K0 is connected to the end point la, the negative pole of the switching device K0 is connected to the end point 2a, and the end point lb is directly connected to the end point 2b through a wire.

[0073] Type two (see (2) in Figure 4 ) includes a switching device K0, an inductor L, and a capacitor C, the negative pole of the switching device K0 is connected to the end point lb and the end point 2a respectively, the end point lb is used to be connected to the negative pole of the external load or power supply, and the end point 2a is used to be connected to the positive pole of the switching device K 1,1 in the first module in the variable unit through the end point bl, one end of the inductor L is connected to the end point la, which is connected to the positive pole of the external load or power supply through the end point la, the other end of the inductor L is connected to the positive pole of the switching device K0 and one end of the capacitor C respectively, the other end of the capacitor C is connected to the end point 2b, which is used to be connected to the negative pole of the switching device K m,n in the mth module in the variable unit 2 through the end point d m .

[0074] Type three (see (3) in Figure 4 ) includes a switching device K0, an inductor L, and a capacitor C, the positive pole of the switching device K0 is connected to the end point la, the end point lb is directly connected to the end point 2b, at the same time, one end of the inductor L is connected to the end point lb, the other end of the inductor L is connected to the negative pole of the switching device K0, one end of the capacitor C is connected to the end point 2a, and the other end of the capacitor C is connected to the negative pole of the switching device K0. The above-mentioned switching device K0 can be one of MOSFET, IGBT or diode, when K0 is MOSFET, the drain of MOSFET is the positive pole of the switching device K0, and the source of MOSFET is the negative pole of the switching device K0; when K0 is IGBT, the collector of IGBT is the positive pole of the switching device K0, and the emitter of IGBT is the negative pole of the switching device K0; when K0 is diode, the negative pole of diode is the positive pole of the switching device K0, and the positive pole of diode is the negative pole of the switching device K0.

[0075] The current stage circuit uses the connection mode of type one, the converter can only be used for charging or discharging, that is, the voltage of the power supply / load side must be higher than the sum of the voltages of the battery, the current of the power supply / load side is intermittent, and the filtering difficulty is relatively large, and the current of the battery side is continuous, and the filtering difficulty is relatively small. The current stage circuit uses the connection mode of type two, the converter can be used for charging and discharging, and can also be used for charging and discharging; the current of the power supply / load side and the battery side is continuous, and the filtering difficulty is relatively small. The current stage circuit uses the connection mode of type three, the converter can be used for charging, discharging, charging and discharging; the current of the power supply / load side is intermittent, and the filtering difficulty is relatively large, and the current of the battery side is continuous, and the filtering difficulty is relatively small.

[0076] Embodiment 1

[0077] The circuit connection of the DC-DC converter for automatically realizing energy storage cell equalization in Embodiment 1 of the application is shown in Figure 5A

[0078] In Embodiment 1, the front stage circuit selects type one, and the rear stage circuit does not use the modular combination mode. i (i=1, 2, ……, n) represents an energy storage cell, n is the number of series energy storage cells, can be a battery or a super capacitor, can be a single cell or a combination of series and parallel connection of multiple cells, hereinafter referred to as an energy storage cell; each B i is connected in series, hereinafter referred to as a series energy storage string; the device K0 and the device K i are both MOSFETs; an external power supply can charge the energy storage string through the converter, and the energy storage string can discharge an external load through the converter; the turns ratio between the windings i of the multi-winding transformer T is 1.

[0079] The control method of the above circuit is that when the external power supply charges the energy storage cell string, the current schematic diagram of the charging process is shown in Figure 5B (1) and (2), Figure 5B The process of (1) is that the switching device K i (i=1, 2, ……, n) is turned off, after a dead time, the switching device K0 is closed, the output voltage / output current of the converter is controlled by controlling the conduction duty cycle of the switching device K0, and the series energy storage unit is charged. Figure 5B The process of (2) is that the switching device K0 is turned off, after a dead time, the switching device K i (i=1, 2, ……, n) is closed, due to the action of the transformer, in this process, the energy storage cell with a lower voltage will flow more current compared with the energy storage cell with a higher voltage.

[0080] When the energy storage cell string discharges an external load, the current schematic diagram of the discharging process is​Figure 5C The process of (1) is: switch device K0 is closed, after a dead time, switch device K Figure 5C The process of (1) is: switch device K0 is closed, after a dead time, switch device K i closed, the output voltage / output current of the converter is controlled by controlling the on-duty ratio of switch device K i , so that the energy storage cells string is directly discharged. Figure 5C The process of (2) is: switch device K i is closed, after a dead time, switch device K0 is closed, so that the energy storage cells string is discharged to the external load through switch device K0.

[0081] When the voltages of the energy storage cells in the series energy storage string are different, the average current flowing through each energy storage cell is different in the charging or discharging state. The energy storage cell with higher voltage will flow more current in discharging and less current in charging than the energy storage cell with lower voltage. When the voltages of the energy storage cells in the series energy storage string are the same, the current flowing through each energy storage cell will be the same. The voltage balancing control is automatically completed at the same time of charging and discharging in the embodiment.

[0082] Embodiment 2

[0083] The circuit connection of the embodiment 2 of the application is shown in Figure 6A .

[0084] In the embodiment 2, the front-stage circuit is selected as type one, and the rear-stage circuit does not use the modularized combination mode. i (i = 1, 2, ……n) represents an energy storage cell, n is the number of series energy storage cells, which can be a battery or a super capacitor, and can be a single cell or a combination of series and parallel connection of multiple cells, which is referred to as an energy storage cell hereinafter; each B i is connected in series, which is referred to as a series energy storage string hereinafter; switch device K0 is a MOSFET, and switch device K i is a diode; the external power supply can charge the energy storage string through the converter; the turns ratio between the windings i of the multi-winding transformer T is 1.

[0085] The control method of the above circuit is that, when the external power supply charges the energy storage cell string, the current schematic diagram of the charging process is shown in Figure 6B (1) and (2), Figure 6B The process of (1) is: switch device K0 is closed, device K i is reverse-biased, and the output voltage / output current of the converter is controlled by controlling the on-duty ratio of switch device K0 to charge the energy storage cell. Figure 6B The process of (2) is: switch device K0 is closed, diode K i is turned on, and the inductance of the transformer continues to flow to charge the energy storage cell.

[0086] When the voltage of each energy storage cell in the series energy storage string is different, the average value of the current flowing through each energy storage cell is different in the charging state. The energy storage cell with higher voltage will flow less current during charging compared with the energy storage cell with lower voltage. When the voltage of each energy storage cell in the series energy storage string is the same, the current flowing through each energy storage cell will be the same.

[0087] Embodiment 3

[0088] The circuit connection of the embodiment 3 of the application is shown as follows: Figure 7A

[0089] In the embodiment 3, the front-stage circuit is of type one, and the rear-stage circuit does not use the modularized combination mode. i (i = 1, 2, ……, n) represents an energy storage cell, and n is the number of series energy storage cells, which can be a battery or a super capacitor, and can be a single cell or a combination of series and parallel connection of multiple cells, which is referred to as an energy storage cell hereinafter; each B i is connected in series, which is referred to as a series energy storage string hereinafter; the switching device K0 is a diode, and the switching device K i is a MOSFET; the external power supply can charge the energy storage string through the converter, and the energy storage string can discharge the external load through the converter; the turns ratio between the turns i of the multi-turn transformer T is 1.

[0090] When the energy storage cell string discharges the external load, the current schematic diagram of the discharging process is shown as follows: Figure 7B Figure 5C The process of (1) is as follows: the switching device K i is closed, the diode K0 is reversely cut off, the output voltage / output current of the converter is controlled by controlling the on-off duty cycle of the switching device K i , so that the energy storage cell string directly discharges. Figure 7B The process of (2) is as follows: the switching device K i is turned off, and the diode K0 is turned on, so that the energy storage cell string discharges the external load through the switching device K0.

[0091] When the voltage of each energy storage cell in the series energy storage string is different, the average value of the current flowing through each energy storage cell is different in the discharging state. The energy storage cell with higher voltage will flow more current during discharging compared with the energy storage cell with lower voltage. When the voltage of each energy storage cell in the series energy storage string is the same, the current flowing through each energy storage cell will be the same.

[0092] Embodiment 4

[0093] The circuit connection of the embodiment 4 of the application is shown as follows: Figure 8A

[0094] ​​​In embodiment 4, the front-stage circuit selects type one, and the rear-stage circuit uses a modular combination mode. j,i (j = 1, 2, ……m, i = 1, 2, ……n) represents an energy storage unit, where n represents the number of energy storage units in series in each module, the energy storage unit can be a battery or a super capacitor, and can be a single unit or a combination of series and parallel connection of multiple units, hereinafter referred to as an energy storage unit, and m represents the number of modules. Each B j,i is connected in series, hereinafter referred to as a series energy storage string; an external power supply can charge the energy storage string through a transformer, and the energy storage string can discharge an external load through the transformer; a multi-winding transformer T j has n+1 windings, and the transformation ratio between each winding is 1, K0, K j,i (j = 1, 2, ……m, i = 1, 2, ……n) are MOSFETs.

[0095] The charging control method of the above circuit is that when an external power supply charges the energy storage unit string, the current diagram of the charging process is as shown in Figure 8B (1) and (2) of the application, Figure 8B The process of (1) is: the switching device K0 is opened, a dead time is passed, and the switching device K j,i (j = 1, 2, ……m, i = 1, 2, ……n) is closed, and the output voltage / output current of the transformer is controlled by controlling the on-duty of the switching device K0. Figure 8B The process of (2) is: the switching device K0 is opened, a dead time is passed, and the switching device K j,i (j = 1, 2, ……m, i = 1, 2, ……n) is closed.

[0096] When the external load discharges the series energy storage string, the current diagram of the discharging process is as shown in Figure 8C (1) and (2) of the application, Figure 8C The process of (1) is: the switching device K0 is opened, a dead time is passed, and the switching device K j,i (j = 1, 2, ……m, i = 1, 2, ……n) is closed, and the output voltage / output current of the transformer is controlled by controlling the on-duty of the switching device K0. j,i The energy storage unit discharges and charges the load. Figure 8C The process of (2) is: the switching device K j,i is opened, a dead time is passed, and the switching device K0 is closed, so that the energy storage unit string discharges the external load through the switching device K0.

[0097] When the voltage of each energy storage cell in the series energy storage string is the same, the current flowing through each energy storage cell is the same in the charging or discharging state. When the voltage of each energy storage cell in the series energy storage string is different, the current flowing through each energy storage cell is different in the charging or discharging state. The energy storage cell with a higher voltage will flow more current in discharging and less current in charging than the energy storage cell with a lower voltage. When the voltage of each energy storage cell in the series energy storage string is the same, the current flowing through each energy storage cell will be the same.

[0098] In Example 4, the device K j,i or K0 is replaced by a diode, and there are three combinations.

[0099] Example 5

[0100] The circuit connection of Example 5 of the present application is shown in Figure 9A :

[0101] In Example 5, the front-stage circuit is selected as type two, and the rear-stage circuit does not use the modular combination method. i (i = 1, 2, ……, n) represents an energy storage cell, and n is the number of series energy storage cells, which can be a battery or a super capacitor, and can be a single cell or a combination of series and parallel connection of multiple cells, hereinafter referred to as an energy storage cell; each B i is connected in series, hereinafter referred to as a series energy storage string; the device K0 and the device K i are both MOSFETs; the external power supply can charge the energy storage string through the converter, and the energy storage string can discharge the external load through the converter; the turns ratio between the turns i of the multi-turn transformer T is 1.

[0102] The control method of the above circuit is that when the external power supply charges the energy storage cell string, the current diagram of the charging process is shown in Figure 9B (1) and (2), Figure 9B The process of (1) is that the switching device K i (i = 1, 2, ……, n) is turned off, and after a dead time, the switching device K0 is closed. The output voltage / output current of the converter is controlled by controlling the on-duty of the switching device K0. Figure 9B The process of (2) is that the switching device K0 is turned off, and after a dead time, the switching device K i is closed.

[0103] When the energy storage cell string discharges the external load, the current diagram of the discharging process is shown in Figure 9C (1) and (2), Figure 9C The process of (1) is that the switching device K0 is turned off, and after a dead time, the switching device K i is closed. The output voltage / output current of the converter is controlled by controlling the on-duty of the switching device Ki The output voltage / output current of the on-duty control converter is controlled. Figure 9C The process in (2) is that the switch device K i is turned off, and after a dead time, the switch device K0 is closed.

[0104] When the voltages of the energy storage cells in the series energy storage string are different, the average current flowing through each energy storage cell is different in the charging or discharging state. The energy storage cell with a higher voltage will flow more current in discharging and less current in charging than the energy storage cell with a lower voltage. When the voltages of the energy storage cells in the series energy storage string are the same, the current flowing through each energy storage cell will be the same.

[0105] Like examples 1-4, example 5 can select a modular combination or a non-modular combination. In the modular combination, the switch device K0 and the switch device K j,i may be MOSFETs or IGBTs, or the switch device K0 or the switch device K j,i may be replaced by a diode; in the non-modular combination, the switch device K0 and the switch device K i may be MOSFETs or IGBTs, or the switch device K0 or the switch device K i may be replaced by a diode; therefore, there are six combinations in example 5.

[0106] Example 6

[0107] The circuit connection of the embodiment 1 of the application is shown in Figure 10A .

[0108] In example 6, the front-stage circuit is selected as type three, and the conversion voltage 2 does not use the modular combination. i (i = 1, 2, ……, n) represents an energy storage cell, and n is the number of series energy storage cells, which can be a battery or a super capacitor, and can be a single cell or a combination of series and parallel connection of multiple cells, which is referred to as an energy storage cell hereinafter; each B i is connected in series, which is referred to as a series energy storage string hereinafter; the switch device K0 and the switch device K i are MOSFETs; an external power supply can charge the energy storage string through the converter, and the energy storage string can discharge an external load through the converter; the turns ratio between the windings i of the multi-winding transformer T is 1.

[0109] The control method of the above circuit is that when the external power supply charges the energy storage cell string, the current schematic diagram of the charging process is shown in Figure 10B (1) and (2), Figure 10B The process in (1) is that the switch device K i(i = 1, 2, ……n) are turned off, the switching device K0 is closed, and the output voltage / output current of the converter is controlled by controlling the on-duty of the switching device K0. Figure 10B The process in the middle (2) is that the switching device K0 is turned off, and after a dead time, the switching device K0 is closed. i .

[0110] When the energy storage battery string discharges to the external load, the current schematic diagram of the charge-discharge process is as shown in Fig. 2. Figure 10C The process in the middle (1) and (2) is that the switching device K0 is turned off, and after a dead time, the switching device K0 is closed. Figure 10C The process in the middle (1) is that the switching device K0 is turned off, the switching device K i is closed, and the output voltage / output current of the converter is controlled by controlling the on-duty of the switching device K i . Figure 10C The process in the middle (2) is that the switching device K i is turned off, and after a dead time, the switching device K0 is closed.

[0111] When the voltages of the energy storage batteries in the series energy storage string are different, the average current flowing through each energy storage battery is different in the charge or discharge state. The energy storage battery with a higher voltage will flow more current in the discharge state and flow less current in the charge state than the energy storage battery with a lower voltage. When the voltages of the energy storage batteries in the series energy storage string are the same, the current flowing through each energy storage battery will be the same.

[0112] Like examples 1-4, example 6 can select a modular combination mode or a non-modular combination mode. In the modular combination mode, the switching device K0 and the switching device K j,i may be MOSFETs or IGBTs, or the switching device K0 or the switching device K j,i may be replaced by a diode; in the non-modular combination mode, the switching device K0 and the switching device K i may be MOSFETs or IGBTs, or the switching device K0 or the switching device K i may be replaced by a diode; therefore, there are six combination modes in example 5.

[0113] The various combination modes of the front-stage circuit and the rear-stage circuit, the rear-stage circuit can be combined with the three front-stage circuits at will; the front-stage circuit can be combined with a single module of the rear-stage circuit or can be combined with multiple modules; the switching device K0 and the switching device Ki in the front-stage circuit and the rear-stage circuit cannot be diodes at the same time; because the use of IGBTs and MOSFETs does not affect the characteristics of the converter, the IGBTs and the MOSFETs are not distinguished in the combination modes; therefore, there are 18 combination modes (see Figure 11 ) in the present application.

[0114] When the switching devices in the front-stage circuit and the rear-stage circuit are all IGBTs or MOSFETs, the converter can realize balanced charging and balanced discharging; when the switching device in the front-stage circuit is a diode and the switching device in the rear-stage circuit is an IGBT or a MOSFET, the converter can only realize balanced discharging; when the switching device in the rear-stage circuit is a diode and the switching device in the front-stage circuit is an IGBT or a MOSFET, the converter can only realize balanced charging; whether the converter can charge or discharge the battery is only related to the types of the switching devices in the front-stage circuit and the rear-stage circuit, and has no relation with the selection of the three connection modes in the front-stage circuit and whether the rear-stage circuit adopts a modularized mode.

[0115] The unmentioned parts of the present application are applicable to the prior art.

Claims

1. A DC-DC converter that automatically implements energy storage cell equalization, characterized by, The integration of equalizer and DC-DC converter is realized, the DC-DC converter automatically realizing energy storage cell equalization comprises a front circuit and a rear circuit, the rear circuit comprises n energy storage cells B i , n switching devices K i , a multi-winding transformer T, the multi-winding transformer T contains n windings, i = 1, 2, …, n; the positive pole of the energy storage cell B i in the rear circuit is connected to one end of the i th winding w i of the multi-winding transformer T, the other end of the winding w i is connected to the positive pole of the switching device K i , the negative pole of the switching device K i is connected to the negative pole of the energy storage cell B i ; all the winding w i and the positive pole of the energy storage cell B i are connected to the same end; each switching device K i is connected in series, the negative pole of the switching device K x is connected to the positive pole of K x+1 , x = 1, 2, …, n-1, the positive pole of the switching device K1 is the end point 3a of the rear circuit, and the negative pole of the switching device K n is the end point 3b of the rear circuit. The front-stage circuit comprises at least one switching device K0, which has four terminals, namely terminals 1a, 1b, 2a and 2b. The functions of the corresponding four terminals are as follows: terminal 1a is used for connecting with the positive pole of an external load or power supply; terminal 1b is used for connecting with the negative pole of the external load or power supply; terminal 2a is used for connecting with the positive pole terminal 3a of a switching device K1 in a rear-stage circuit; and terminal 2b is used for connecting with the negative pole terminal 3b of the switching device K1 in the rear-stage circuit. n The front-stage circuit comprises at least one switching device K0, which has four terminals, namely terminals 1a, 1b, 2a and 2b. The functions of the corresponding four terminals are as follows: terminal 1a is used for connecting with the positive pole of an external load or power supply; terminal 1b is used for connecting with the negative pole of the external load or power supply; terminal 2a is used for connecting with the positive pole terminal 3a of a switching device K1 in a rear-stage circuit; and terminal 2b is used for connecting with the negative pole terminal 3b of the switching device K1 in the rear-stage circuit.

2. A DC-DC converter that automatically implements energy storage cell balancing, characterized by, The integration of equalizer and DC-DC converter is realized, the DC-DC converter automatically realizing energy storage cell equalization comprises a front circuit and a rear circuit, the rear circuit has m modules, any module j comprises n energy storage cells B j,i , n switching devices K j,i , a multi-winding transformer T j , the multi-winding transformer T j contains n+1 windings, j=1, 2, …, m, i=1, 2, …, n; The module j in the energy storage cell B j,i The positive pole of the multi-winding transformer T j The i winding w j,i One end of the winding w j,i The other end of the winding w j,i The positive pole of the switching device K j,i The negative pole of the switching device K j,i The negative pole of the energy storage cell B j The winding w j,i The winding w j,i The positive pole of each energy storage cell B j The winding w j,n+1 The winding w j The two ends of the winding w j,n+1 The two ends of the winding w j The two ends of the winding w j The two ends of the winding w j The two ends of the winding w j,n+1 The two ends of the winding w j The two ends of the winding w j,i The two ends of the winding w Each switching device K j,i is connected in series with each other j,x The negative terminal of device K j,x+1 x = 1, 2, …… n-1; the positive terminal of device K j,1 is the end point b j The negative terminal of device K j,n is the end point d j ; The connection between the m modules is: the end point b of module y is connected with the end point d of module y-1 y y=2, 3, …, m; the end point b1 is the end point 3a of the subsequent circuit, and the end point d y-1 of the subsequent circuit is the end point 3b of the subsequent circuit; y=2, 3, …, m. m ​ The front-stage circuit comprises at least one switching device K0, which has four terminals, namely terminals 1a, 1b, 2a and 2b, and the functions of the four terminals are as follows: the terminal 1a is used for being connected with the positive pole of an external load or power supply, the terminal 1b is used for being connected with the negative pole of the external load or power supply, the terminal 2a is used for being connected with the terminal 3a of the rear-stage circuit, and the terminal 2b is used for being connected with the terminal 3b of the rear-stage circuit. The terminal 3a of the rear-stage circuit is connected with the terminal 2a of the front-stage circuit, and the terminal 3b of the rear-stage circuit is connected with the terminal 2b of the front-stage circuit.

3. The DC-DC converter automatically achieving equalization of energy storage cells according to claim 1 or 2, characterized in that, The front-stage circuit comprises one switching device K0, the positive pole of the switching device K0 is connected with the terminal 1a, and the negative pole of the switching device K0 is connected with the terminal 2a; the terminal 1b is directly connected with the terminal 2b through a wire.

4. The DC-DC converter automatically achieving equalization of energy storage cells according to claim 1 or 2, characterized in that, The front-stage circuit comprises one switching device K0, one inductor L and one capacitor C; the negative pole of the switching device K0 is connected with the terminal 1b of the front-stage circuit, the terminal 1b of the front-stage circuit is directly connected with the terminal 2a of the front-stage circuit through a wire, one end of the inductor L is connected with the terminal 1a of the front-stage circuit, the other end of the inductor L is connected with the positive pole of the switching device K0, one end of the capacitor C is connected with the terminal 2b of the front-stage circuit, and the other end of the capacitor C is connected with the positive pole of the switching device K0. Or the positive pole of the switching device K0 is connected with the terminal 1a of the front-stage circuit, the terminal 1b of the front-stage circuit is connected with the terminal 2b of the front-stage circuit, one end of the inductor L is connected with the terminal 1b of the front-stage circuit, the other end of the inductor L is connected with the negative pole of the switching device K0 and one end of the capacitor C, and the other end of the capacitor C is connected with the terminal 2a of the front-stage circuit.

5. The DC-DC converter automatically achieving equalization of energy storage cells according to claim 1 or 2, characterized in that, The energy storage cell is a battery or a super capacitor, and is a single cell or a combination of series and parallel connection of multiple cells; the switching device K0 in the front-stage circuit is at least one of a MOSFET, an IGBT or a diode, and the switching device K i / K j,i is one of a MOSFET, an IGBT or a diode; if the switching device K0 in the front-stage circuit is selected as a diode, all the switching devices in the rear-stage circuit cannot be selected as diodes, and if the switching device K i / K j,i in the rear-stage circuit is selected as a diode, all the switching devices in the front-stage circuit cannot be selected as diodes.

6. The DC-DC converter automatically achieving equalization of energy storage cells according to claim 5, characterized in that, When the switching device K0 in the front-stage circuit is a diode, and the switching device in the rear-stage circuit is a MOSFET or an IGBT, the drain of the MOSFET is the positive pole of the switching device in the rear-stage circuit, the source of the MOSFET is the negative pole of the switching device in the rear-stage circuit; the collector of the IGBT is the positive pole of the switching device in the rear-stage circuit, and the emitter of the IGBT is the negative pole of the switching device in the rear-stage circuit; the negative pole of the diode is the positive pole of the switching device in the front-stage circuit, and the positive pole of the diode is the negative pole of the switching device in the front-stage circuit. When the switching device in the front-stage circuit is a MOSFET or an IGBT, and the switching device in the rear-stage circuit is a diode, the drain of the MOSFET is the positive pole of the switching device in the front-stage circuit, the source of the MOSFET is the negative pole of the switching device in the front-stage circuit; the collector of the IGBT is the positive pole of the switching device in the front-stage circuit, and the emitter of the IGBT is the negative pole of the switching device in the front-stage circuit; the negative pole of the diode is the positive pole of the switching device in the rear-stage circuit, and the positive pole of the diode is the negative pole of the switching device in the rear-stage circuit. When the switching devices in the front-stage circuit and the rear-stage circuit are both MOSFETs or IGBTs, the drain of the MOSFET is the positive pole of the switching device, and the source of the MOSFET is the negative pole of the switching device; the collector of the IGBT is the positive pole of the switching device, and the emitter of the IGBT is the negative pole of the switching device.

7. The DC-DC converter that automatically achieves equalization of energy storage cells according to claim 5, wherein, When the switching device in the current stage circuit is a diode and the switching device in the subsequent stage circuit is an IGBT or a MOSFET, only the energy storage unit can be discharged and cannot be charged, and the specific process of controlling the discharge of the energy storage unit is: (1) the switching device in the subsequent stage circuit is turned on, and the output voltage / output current of the converter is controlled by controlling the on-duty ratio of the switching device in the subsequent stage circuit; (2) the switching device in the subsequent stage circuit is turned off, and the switching device in the current stage circuit is turned on; When the switching device in the current stage circuit is an IGBT or a MOSFET and the switching device in the subsequent stage circuit is a diode, only the energy storage unit can be charged and cannot be discharged, and the specific process of controlling the charge of the energy storage unit is: (1) the switching device in the current stage circuit is turned on, and the output voltage / output current of the converter is controlled by controlling the on-duty ratio of the switching device in the current stage circuit; (2) the switching device in the current stage circuit is turned off, and the switching device in the subsequent stage circuit is turned on; When the switching device in the current stage circuit and the switching device in the subsequent stage circuit are both IGBTs or MOSFETs, the energy storage unit can be charged and discharged, and the specific process of controlling the charge of the energy storage unit is: (1) the switching device in the subsequent stage circuit is turned off, the switching device in the current stage circuit is turned on after a dead time, and the output voltage / output current of the converter is controlled by controlling the on-duty ratio of the switching device in the current stage circuit; (2) the switching device in the current stage circuit is turned off, the switching device in the subsequent stage circuit is turned on after a dead time; The specific process of controlling the discharge of the energy storage unit is: (1) the switching device in the current stage circuit is turned off, the switching device in the subsequent stage circuit is turned on after a dead time, and the output voltage / output current of the converter is controlled by controlling the on-duty ratio of the switching device in the subsequent stage circuit; (2) the switching device in the subsequent stage circuit is turned off, the switching device in the current stage circuit is turned on after a dead time.

8. The DC-DC converter automatically achieving equalization of energy storage cells according to claim 7, characterized in that, When the voltages of the energy storage units in the series energy storage string are different, the average current flowing through each energy storage unit is different in the charging or discharging state, and the energy storage unit with a higher voltage will flow more current in discharging and less current in charging than the energy storage unit with a lower voltage; when the voltages of the energy storage units in the series energy storage string are the same, the current flowing through each energy storage unit will be the same; the DC-DC converter for automatically achieving energy storage unit balancing automatically completes voltage balancing while charging and / or discharging.

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