Cell voltage measurement and equalization system, method and application for series battery packs

Abstract

The application is a single cell voltage measurement and equalization system, method and application for series battery pack, comprising: a control module; a measurement compensation module comprising a current limiting constant current circuit and a selection switch; n single cell voltage measurement and equalization units respectively corresponding to n battery cells connected in the series battery pack, comprising: a single-ended flyback-based DC / DC converter; a matching switch, one end of which is connected to the connection point of the primary winding of the transformer and the primary power switch, and the other end is used for connecting to the selection switch of the measurement compensation module; a hybrid clamping circuit, which is connected across the primary winding of the transformer. According to the working mode, the working mode of the clamping circuit is automatically switched: in the equalization mode, the active clamping mode is adopted to improve the efficiency, and in the measurement mode, the RCD clamping mode is switched to ensure the accuracy. At the same time, the system can automatically offset the on-voltage drop of the rectifier switch to reduce the measurement error, realizing the unification of high-efficiency equalization and high-precision voltage measurement.

Description

Technical Field

[0001] This invention relates to the field of battery management technology, and more specifically to a system and method for measuring and equalizing the voltage of individual cells in a series battery pack, and a battery management system including the system. Background Technology

[0002] In a battery pack composed of multiple cells connected in series, due to differences in manufacturing processes, usage environments, and aging levels, parameters such as voltage, capacity, and internal resistance of each cell will gradually become inconsistent, resulting in inconsistencies. These inconsistencies reduce the usable capacity of the battery pack, shorten its lifespan, and may even lead to safety issues. Therefore, a battery management system (BMS) must be able to accurately measure the voltage of each cell to assess its condition and perform energy balancing on cells with abnormal voltages to maintain the consistency of the battery pack.

[0003] In existing technologies, measurement techniques using the resistor voltage divider method have complex circuit configurations and poor scalability; while operational amplifier differential amplification methods require the use of expensive isolation operational amplifiers, leading to increased system costs. Regarding equalization, commonly used methods include passive equalization (energy-consuming) and active equalization (energy-transfer). Among these, active equalization topologies based on flyback converters have attracted widespread attention due to their simple structure and isolation characteristics.

[0004] Existing solutions typically design and implement voltage measurement and equalization circuits as independent subsystems, resulting in complex hardware structures, numerous components, and high costs. To address this issue, patent ZL202210515170.8 proposes an integrated solution for voltage measurement and equalization circuits, but it does not consider the impact of clamping circuits on equalization efficiency and measurement accuracy, nor does it consider the measurement error compensation problem introduced by the on-state voltage drop of the secondary rectifier switch.

[0005] Therefore, there is an urgent need for a solution that can deeply integrate high-precision voltage measurement with efficient active balancing to simplify system structure, reduce costs, and solve the measurement error problem caused by the on-state voltage drop of switching devices. Summary of the Invention

[0006] The purpose of this invention is to provide a system, method, and application for single-cell voltage measurement and equalization in series-connected battery packs, aiming to solve two main problems in the prior art: first, the voltage measurement circuit and the equalization circuit are independent, resulting in a complex system structure and high cost; second, in existing integrated solutions, the clamping circuit cannot achieve a balance between equalization efficiency and measurement accuracy, and the on-state voltage drop of the rectifier switch introduces measurement errors, affecting accuracy. This invention, through innovative circuit topology and timing control, achieves the multiplexing of the same single-ended flyback DC / DC converter and its clamping circuit for both measurement and equalization modes. The system can automatically switch the operating mode of the clamping circuit according to the operating mode: active clamping mode is used during equalization to improve efficiency, while switching to RCD clamping mode during measurement to ensure accuracy. Simultaneously, through a hardware compensation mechanism, the system can automatically offset the on-state voltage drop of the rectifier switch to reduce measurement errors. Thus, while simplifying the structure and reducing costs, it achieves a unified approach of high-efficiency equalization and high-precision voltage measurement.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A system for measuring and equalizing the voltage of individual cells in a series-connected battery pack, comprising: The control module is used to control the system to operate in equalization mode or measurement mode; The measurement compensation module includes a current-limiting constant current circuit and a selection switch; There are n individual cell voltage measurement and equalization units, each connected to one of the n individual cells in the series-connected battery pack; each unit includes: A DC / DC converter based on a single-ended flyback converter includes a primary-side power switch, a transformer, and a secondary-side rectifier switch. A matching switch, one end of which is connected to the connection point between the primary winding of the transformer and the primary power switch, and the other end of which is used to connect to the selection switch of the measurement compensation module; A hybrid clamping circuit is connected across the two ends of the primary winding of the transformer; The measurement compensation module is a common voltage measurement compensation resource in the system. Its selection switch is controlled by the control module to selectively connect the current limiting constant current circuit to the loop of any target single-unit voltage measurement and equalization unit. In the equalization mode, the control module controls the hybrid clamping circuit of the target unit to operate in active clamping mode and controls the primary-side power switch of the unit to operate, so as to perform equalization operation of charging or discharging the corresponding battery cells through the transformer. In the measurement mode, the control module is configured to perform the following operations: The hybrid clamping circuit of the control target unit operates in RCD clamping mode; Control the primary-side power switch of the target unit to enable the voltage information of the target battery cell to be transmitted to the primary-side circuit through the coupling of the primary and secondary sides of the transformer; Control the selection switch of the measurement compensation module to connect the current limiting constant current circuit to the target unit; At a predetermined voltage sampling time, the voltage at the common terminal of the selection switch is sampled to obtain a sampled value reflecting the voltage of the target battery cell.

[0008] Preferably, each of the hybrid clamping circuits includes an active switch, a clamping capacitor, and a clamping resistor; the clamping capacitor and the clamping resistor are connected in parallel to form a parallel branch; the active switch and the parallel branch are connected in series to form a series branch; the series branch is connected across the two ends of the primary winding of the transformer; wherein, when operating in active clamping mode, the control module controls the active switch and the primary power switch to conduct complementaryly, and the conducting active switch provides a charging and discharging circuit for the clamping capacitor; when operating in RCD clamping mode, the control module controls the active switch to remain off, and the body diode of the active switch, the clamping capacitor, and the clamping resistor constitute an RCD clamping absorption circuit.

[0009] Preferably, the matching switch and the secondary rectifier switch are semiconductor switching devices of the same type, or are configured to have substantially the same on-state voltage drop under the same operating current, such that when the current-limiting constant current circuit provides compensation current, the on-state voltage drop of the matching switch can be used to compensate for the measurement error introduced by the on-state voltage drop of the secondary rectifier switch.

[0010] Preferably, the selection switch is a multiplexer or a single-pole multi-throw switch; its common terminal is connected to one end of the current-limiting constant current circuit, and its n selection terminals are respectively connected to the other end of the corresponding matching switches in the n individual cell voltage measurement and equalization units; wherein, when measuring any target battery cell, the control module controls the selection switch to turn on the corresponding selection terminal, thereby connecting the common current-limiting constant current circuit in series into the primary winding circuit of the target cell.

[0011] Preferably, the current-limiting constant current circuit is configured to provide a constant current, the value of which is much smaller than the peak current of the primary winding of the transformer during measurement operations, so as to avoid the influence of switching transient processes; the current-limiting constant current circuit includes a power supply management circuit and a constant current control circuit, the power supply management circuit is configured to automatically select the higher of the voltage of the common terminal of the selection switch and an internal reference power supply voltage as the main power supply, and the constant current control circuit is driven by the main power supply to generate and maintain the constant current.

[0012] Preferably, in the measurement mode, the control module is configured to: control the secondary current of the DC / DC converter to operate in discontinuous mode; control the selection switch to turn on when the secondary rectifier switch is turned on, and connect the current limiting constant current circuit to the primary winding circuit of the target cell; after a preset delay time, sample the voltage of the common terminal of the selection switch to calculate the voltage value of the target battery cell.

[0013] Preferably, the preset delay time is set from the moment the secondary rectifier switch is turned on until the moment when the theoretically calculated current flowing through the secondary rectifier switch drops to a value equal to the constant current provided by the current-limiting constant current circuit.

[0014] Preferably, in all the individual voltage measurement and equalization units, the same-name terminals of the primary winding of the transformer are connected to the power supply terminal, and the different-name terminals of the primary winding are respectively connected to one end of the corresponding primary power switch; the other end of all the primary power switches is connected to the reference ground terminal; the primary winding and secondary winding of the transformer have the same number of turns and are configured to have matching DC resistance characteristics.

[0015] The present invention also provides a method for measuring the voltage of a single cell, applied to the aforementioned system for measuring and equalizing the voltage of a single cell in a series battery pack, comprising the following steps: The hybrid clamping circuit of the target unit operates in RCD clamping mode and controls its primary-side power switch to perform measurement operations. The measurement compensation module is controlled to connect the current-limiting constant current circuit to the target unit to provide error compensation; at a preset time during the conduction of the secondary rectifier switch, the voltage signal of the common terminal of the selection switch or an equivalent node is sampled. Based on the voltage signal, and by using the on-state voltage drop of the matching switch to offset the error introduced by the on-state voltage drop of the secondary rectifier switch, the voltage value of the target battery cell is calculated.

[0016] The present invention also provides a battery management system, including the aforementioned single-cell voltage measurement and equalization system for series-connected battery packs.

[0017] Compared with the prior art, the single-cell voltage measurement and equalization system and method for series battery packs provided by the present invention have the following significant advantages: High integration and reduced costs: By reusing the transformer and main power devices of the single-ended flyback DC / DC converter and adding a common measurement and compensation module, a unified design for high-precision individual voltage measurement and efficient active balancing is achieved. Compared with discrete solutions, this significantly reduces system complexity and hardware costs.

[0018] Hardware compensation enhances accuracy: An innovative approach incorporates a matching switch and a shared current-limiting constant-current circuit. By pairing the matching switch with the secondary rectifier switch and utilizing the current-limiting constant-current circuit (constant current source) to generate a precise small current in the measurement circuit, the on-state voltage drop of the matching switch compensates for the measurement error introduced by the on-state voltage drop of the secondary rectifier switch. This method directly cancels out the error source at the hardware level, overcoming the shortcomings of inaccurate software compensation models and their inability to adapt to temperature and current variations. This allows for high-precision individual voltage measurements across a wide temperature range and under various operating conditions.

[0019] Flexible operation and optimized efficiency: The hybrid clamping circuit is one of the key innovations. Operating in active clamping mode during equalization, it recovers transformer leakage inductance energy, improving equalization efficiency and reducing voltage stress on the primary-side switch. In measurement mode, it switches to RCD clamping mode; its simple and reliable structure effectively absorbs leakage inductance energy in a single measurement pulse, ensuring stability and accuracy during the measurement process. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall architecture of a single-cell voltage measurement and equalization system for a series battery pack provided in an embodiment of the present invention.

[0021] Figure 2 This is a detailed circuit diagram of a single-cell voltage measurement and equalization unit in one embodiment of the present invention, and it shows its connection relationship with the measurement compensation module and the battery cell.

[0022] Figure 3 This is a schematic diagram illustrating the working principle of the hybrid clamping circuit in RCD clamping mode (a) and active clamping mode (b) in one embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram of the circuit structure of a current-limiting constant current circuit in one embodiment of the present invention.

[0024] Figure 5 This is a signal timing waveform diagram of a key node in measurement mode according to an embodiment of the present invention.

[0025] Figure 6 This is a flowchart of a single-unit voltage measurement method provided in an embodiment of the present invention.

[0026] Figure 7 This is a schematic diagram of the battery management system in one embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Please see Figure 1 The present invention provides a single-cell voltage measurement and equalization system 100 for a series battery pack, which mainly includes a control module 110, a measurement compensation module 120, and n single-cell voltage measurement and equalization units 130. -1 Up to 130 -n The battery pack consists of n battery cells connected in series, from BAT1 to BATn. Each cell has 130 cells. -i Each (i=1,2,...,n) is connected to a corresponding battery cell BATi. The control module 110 sends control signals to each cell and the measurement compensation module 120 via control lines (not shown in the figure) to coordinate the system's operation in measurement mode or equalization mode. The measurement compensation module 120 is a common resource of the system, and its core is a current-limiting constant current circuit 121 and a multiplexer switch 122.

[0029] Please see Figure 2 With a specific unit voltage measurement and equalization unit 130 -i Taking this as an example, its internal structure will be explained in detail. Unit 130 -i This includes a single-ended flyback-based DC / DC converter. The converter includes a primary-side power switch S. 1-i (including MOSFETs), transformer T -i and secondary rectifier switch S 2-i Transformer T -i primary winding L p-i One end (the same name end) is connected to the system's common power supply terminal V. bus (For example, the total voltage of the battery pack or a stable auxiliary power source), the other end (the non-identical end) is connected to the primary-side power switch S. 1-i The drain electrode. S 1-i The source terminal is connected to the reference ground. The secondary winding L... s-i Connected to the battery cell BATi, its non-identical terminals are connected via the secondary rectifier switch S. 2-i (Including diodes and MOSFETs) are connected to the positive terminal of the battery cell, and the corresponding terminal is connected to the negative terminal of the battery cell. When S 2-i When using MOSFETs, they should operate in synchronous rectification mode.

[0030] Unit 130 -i It also includes a matching switch S3-i One end of it is connected to the primary winding L of the transformer. p-i Non-same-name end and S 1-i Drain connection point (node ​​A) -i One end leads out to the outside of the unit for connecting to the corresponding selection terminal of the selection switch 122 of the measurement compensation module 120. Specifically, the matching switch S... 3-i With secondary rectifier switch S 2-i MOSFETs or diodes of the same model should be selected, or they should be screened and matched to ensure that their on-state voltage drops are basically the same under the same current.

[0031] Unit 130 -i Another key component is the hybrid clamping circuit 140. -i It is connected across the primary winding L of the transformer. p-i The two ends. For example... Figure 3 As shown, in a preferred embodiment, the hybrid clamping circuit 140 -i By a clamping capacitor C c-i A clamping resistor R c-i And an active switch S 4-i Composition. C c-i With R c-i After parallel connection, then with S 4-i Series connection. One end of this series branch is connected to V. bus (or L) p-i (One end with the same name), the other end is connected to node A. -i (L) p-i (non-same-name end).

[0032] like Figure 3 As shown in (a), when the hybrid clamping circuit 140 -i When operating in RCD clamping mode, leakage inductance current flows through the active switch S. 4-i body diode D 4-i unidirectional injection clamping capacitor C c-i Then immediately through the clamping resistor R c-i A circuit is formed, and ultimately energy is transferred through the resistor R. c-i The current is converted into heat dissipation, and the direction of the current is shown by the dashed arrow in the figure.

[0033] like Figure 3 As shown in (b), when the hybrid clamping circuit 140 -i When operating in active clamping mode, the leakage inductance current mainly flows through the active switch S. 4-i and clamping capacitor C c-i Almost no flow passes through the clamping resistor R. c-iThe direction of the current is shown by the dashed arrow in the figure. The leakage inductance current flows bidirectionally in resonance, not only feeding energy back to the system, but also resonating the voltage across the main switch to zero, thus creating zero-voltage turn-on conditions for it.

[0034] By using the clamping capacitor C that participates in the resonance c-i Capacitive X C ci is set to be much smaller than the clamping resistor R. c-i The resistance value (e.g., R) c-i > 100·X C (ci) can be achieved so that the leakage inductance current mainly flows through the active switch S 4-i and clamping capacitor C c-i Almost no flow passes through the clamping resistor R. c-i .

[0035] Please see Figure 4 Taking a specific current-limiting constant current circuit 121 as an example, its internal structure will be explained in detail.

[0036] The current-limiting constant current circuit of the present invention includes two functional modules: a power supply management circuit and a constant current control circuit.

[0037] The power supply management circuit includes Zener diodes ZD1 and ZD2: the anode of Zener diode ZD1 is directly connected to the internal reference power supply VCC terminal, and its cathode is connected to the same node V as the cathode of Zener diode ZD2; the anode of Zener diode ZD2 is connected to the common terminal of the selection switch.

[0038] The constant current control circuit includes an operational amplifier, a transistor, and a resistor. The output node V of the power supply management circuit is connected to the collector of the transistor in the constant current control circuit; the emitter of the transistor is connected to the inverting input ("-") terminal of the operational amplifier, and both are connected to one end of the resistor R1, the other end of which is connected to ground. The non-inverting input ("+") terminal of the operational amplifier is connected to the reference voltage V. ref The output of the operational amplifier is connected to the base of the transistor.

[0039] Measurement mode working principle: When it is necessary to measure the voltage of the i-th battery cell BATi, the control module 110 performs the following operations: Control of the hybrid clamping circuit 140 -i active switch S 4-i Keep it off. At this time, S... 4-i body diode D 4-i C c-i and R c-i This constitutes a typical RCD passive clamp absorption circuit (such as...) Figure 3 (as shown in Figure (a)).

[0040] Control primary-side power switch S 1-i Conducting for a short time T on At this time, the current flows from V bus Flowing through L p-i and S 1-i to ground, inductor L p-i Store energy.

[0041] S 1-i After being turned off, the energy stored in the transformer is transferred to the secondary side via magnetic coupling. The secondary side voltage causes S... 2-i When the primary winding is turned on (or synchronously turned on by the control module), energy is released to the battery cell BATi, and the secondary current Is decreases linearly from its peak value. At this time, the primary winding voltage is clamped at approximately (V). BAT-i + V f (Is))*N p / N s (When the secondary rectifier switch S) 2-i Select a diode, V f (Is) is the diode voltage drop; when the secondary rectifier switch S... 2-i MOSFET is selected, V f (Is) is the MOSFET on-state voltage drop), where N p / N s The turns ratio is preferably 1:1; V BAT-i This represents the voltage of the BATi cell.

[0042] In S 2-i When the circuit is turned on, the control module 110 controls the selection switch 122 of the measurement compensation module 120 to connect to the i-th channel. Therefore, the common current-limiting constant current circuit 121 is connected in series to V... bus -> L p-i -> S 3-i -> Selector switch 122 -> Current-limiting constant current circuit 121 -> In the loop formed by ground. The current-limiting constant current circuit 121 generates a current I with a constant magnitude (e.g., 25mA) and a fixed direction. -comp .

[0043] Please see Figure 5 The timing diagram. In S 2-i After conduction, the secondary current Is continuously decreases. Control module 110 waits for a preset delay time T. -delay T -delay Set from S 2-i From the start of conduction, until the theoretically calculated Is drops to exactly equal to the constant current I generated by the constant current source. -comp At this moment. Control module 110 at this moment ( Figure 5 Chinese-sample The voltage V at the common terminal (node ​​COM) of selector switch 122 -com Perform sampling.

[0044] Based on circuit analysis, at the sampling time: V -com = V A -i - V -on-S 3-i (I -comp ), where V A -i is node A -i The voltage.

[0045] Since the transformer turns ratio is 1:1 and the slight difference in DC resistance is negligible, under ampere-turn balance conditions, V A -i ≈ V BAT-i + V -on-S 2-i(I) -comp ).

[0046] Therefore, V -com ≈ V BAT-i + V -on-S 2-i(I) -comp ) - V -on-S 3-i (I -comp ).

[0047] Because S 2-i With S 3-i In constant current compensation current I -comp They have the same on-state voltage drop, so V -on-S 2-i(I) -comp ) ≈ V -on-S 3-i (I -comp ).

[0048] Finally, we obtain: the voltage V of a single battery cell. BAT-i Approximately equal to the voltage at the common terminal of selector switch 122 (i.e., the sampling voltage) V -com V BAT-i ≈ V -com .

[0049] Therefore, it can be seen that by matching switch S 3-i and constant current compensation current I -comp In coordination with the secondary rectifier switch S 2-i The on-state voltage drop is automatically canceled out, and the sampling voltage V -com Directly reflects the voltage V of a single battery cell BAT-i This achieves high-precision measurement. The current value I of the current-limiting constant current circuit 121 is... -comp Its power consumption is negligible, being much smaller than the equalization current. Its power management circuitry ensures a stable, constant current output under any individual cell voltage measurement.

[0050] How the equalization mode works: When it is necessary to balance (e.g., charge) the i-th battery cell, the control module 110 performs the following operations: Control of the hybrid clamping circuit 140 -i active switch S 4-i Work, so that it is connected to the primary-side power switch S 1-i Complementary conduction (with dead time). At this time, the circuit operates in active clamp flyback mode (e.g., Figure 3 (As shown in Figure (b)).

[0051] Control S 1-i High-frequency switching is performed with a certain duty cycle. When S 1-i When turned on, energy flows from V bus Stored in the transformer; when S 1-i When switched off, energy is transferred to the secondary side, through S 2-i Charging of individual battery cells (BATi). Active switch S 4-i In S 1-i During the turn-off period, it is turned on, acting as the clamping capacitor C. c-i It provides a low-impedance charging and discharging circuit, effectively recovering leakage inductance energy and clamping S. 1-i This reduces voltage stress, thereby improving balancing efficiency.

[0052] Please see Figure 6 The single-unit voltage measurement method 600 provided by the present invention, applied to the above-mentioned system, includes the following steps: S610: Controls the hybrid clamping circuit of the target unit to operate in RCD clamping mode and controls its primary-side power switch to perform measurement operations.

[0053] S620: Controls the multiplexer switch of the measurement compensation module to connect the current-limiting constant current circuit to the target unit to provide error compensation current.

[0054] S630: In the secondary rectifier switch S 2-i During the conduction period, at a preset time (preferably when the secondary current decays to equal the compensation current), the voltage signal of the common terminal of the selection switch or an equivalent node is sampled.

[0055] S640: Based on the voltage signal, and utilizing the matching switch S 3-i The on-state voltage drop offsets the error introduced by the on-state voltage drop of the secondary rectifier switch, and the voltage value of the target battery cell is calculated.

[0056] Please see Figure 7The present invention also provides a battery management system (BMS) 700, the core of which includes the aforementioned single-cell voltage measurement and equalization system 100 for series-connected battery packs. The BMS may also include a total voltage and current detection module 710, a temperature detection module 720, a state estimation and protection logic module 730, and a communication interface 740, etc. The single-cell voltage measurement and equalization system 100 for series-connected battery packs provides high-precision single-cell voltage measurement data to the state estimation and protection logic module 730 and executes the equalization commands it issues, jointly ensuring the safe, efficient, and long-life operation of the battery pack.

[0057] As one embodiment, a single-cell voltage measurement and equalization system for a series-connected battery pack includes: A control module; A measurement compensation module includes a current-limiting constant current circuit and a selection switch; n individual cell voltage measurement and equalization units are respectively connected to n individual cells in a series battery pack; each unit includes: A DC / DC converter based on a single-ended flyback converter, comprising a primary-side power switch, a transformer, and a secondary-side rectifier switch; A matching switch, one end of which is connected to the connection point between the primary winding of the transformer and the primary power switch, and the other end is used to connect to the selection switch of the measurement compensation module; A hybrid clamping circuit is connected across the two ends of the primary winding of the transformer; The control module is the centralized control module of the system, used to control the system to work in equalization mode or measurement mode; The measurement compensation module is a common single-unit voltage measurement compensation resource in the system. Its selection switch is controlled by the control module to selectively connect the current-limiting constant current circuit to the loop of any target single-unit voltage measurement and equalization unit. In the equalization mode, the control module controls the hybrid clamping circuit of the target unit to operate in active clamping mode and controls the primary-side power switch of the unit to operate, so as to perform equalization operation of charging or discharging the corresponding battery cells through the transformer. In the measurement mode, the control module is configured to perform the following operations: The hybrid clamping circuit of the control target unit operates in RCD clamping mode; Control the primary-side power switch of the target unit to enable the voltage information of the target battery cell to be transmitted to the primary-side circuit through the coupling of the primary and secondary sides of the transformer; Control the selection switch of the measurement compensation module to connect the current limiting constant current circuit to the target unit; At a predetermined voltage sampling time, the voltage at the common terminal of the selection switch is sampled to obtain a sampled value reflecting the voltage of the target battery cell.

[0058] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0059] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A system for measuring and equalizing the voltage of individual cells in a series-connected battery pack, characterized in that, include: The control module is used to control the system to operate in equalization mode or measurement mode; The measurement compensation module includes a current-limiting constant current circuit and a selection switch; There are n individual cell voltage measurement and equalization units, each connected to one of the n individual cells in the series-connected battery pack; each unit includes: A DC / DC converter based on a single-ended flyback converter includes a primary-side power switch, a transformer, and a secondary-side rectifier switch. A matching switch, one end of which is connected to the connection point between the primary winding of the transformer and the primary power switch, and the other end of which is used to connect to the selection switch of the measurement compensation module; A hybrid clamping circuit is connected across the two ends of the primary winding of the transformer; The measurement compensation module is a common voltage measurement compensation resource in the system. Its selection switch is controlled by the control module to selectively connect the current limiting constant current circuit to the loop of any target single-unit voltage measurement and equalization unit. In the equalization mode, the control module controls the hybrid clamping circuit of the target unit to operate in active clamping mode and controls the primary-side power switch of the unit to operate, so as to perform equalization operation of charging or discharging the corresponding battery cells through the transformer. In the measurement mode, the control module is configured to perform the following operations: The hybrid clamping circuit of the control target unit operates in RCD clamping mode; Control the primary-side power switch of the target unit to enable the voltage information of the target battery cell to be transmitted to the primary-side circuit through the coupling of the primary and secondary sides of the transformer; Control the selection switch of the measurement compensation module to connect the current limiting constant current circuit to the target unit; At a predetermined voltage sampling time, the voltage at the common terminal of the selection switch is sampled to obtain a sampled value reflecting the voltage of the target battery cell.

2. The system according to claim 1, characterized in that, Each of the hybrid clamping circuits includes an active switch, a clamping capacitor, and a clamping resistor; the clamping capacitor and the clamping resistor are connected in parallel to form a parallel branch; the active switch and the parallel branch are connected in series to form a series branch; the series branch is connected across the two ends of the primary winding of the transformer; wherein, when operating in active clamping mode, the control module controls the active switch and the primary power switch to conduct complementaryly, and the conducting active switch provides a charging and discharging circuit for the clamping capacitor; when operating in RCD clamping mode, the control module controls the active switch to remain off, and the body diode of the active switch, the clamping capacitor, and the clamping resistor constitute an RCD clamping absorption circuit.

3. The system according to claim 1, characterized in that, The matching switch and the secondary rectifier switch are semiconductor switching devices of the same type, or are configured to have the same on-state voltage drop under the same operating current, so that when the current-limiting constant current circuit provides compensation current, the on-state voltage drop of the matching switch can be used to compensate for the measurement error introduced by the on-state voltage drop of the secondary rectifier switch.

4. The system according to claim 1, characterized in that, The selection switch is a multiplexer or a single-pole multi-throw switch; its common terminal is connected to one end of the current limiting constant current circuit, and its n selection terminals are respectively connected to the other end of the corresponding matching switches in the n individual voltage measurement and equalization units; When measuring any target battery cell, the control module controls the selection switch to turn on the corresponding selection terminal, thereby connecting the common current-limiting constant current circuit in series into the primary winding circuit of the target cell.

5. The system according to claim 1, characterized in that, The current-limiting constant current circuit is configured to provide a constant current, the value of which is much smaller than the peak current of the primary winding of the transformer during measurement operations, in order to avoid the influence of switching transients. The current-limiting constant current circuit includes a power supply management circuit and a constant current control circuit. The power supply management circuit is configured to automatically select the higher of the voltage at the common terminal of the selector switch and an internal reference power supply voltage as the main power supply. The constant current control circuit is driven by the main power supply and is used to generate and maintain the constant current.

6. The system according to claim 1, characterized in that, In the measurement mode, the control module is configured to: control the secondary current of the DC / DC converter to operate in discontinuous mode; control the selection switch to turn on when the secondary rectifier switch is turned on, and connect the current limiting constant current circuit to the primary winding circuit of the target cell; after a preset delay time, sample the voltage of the common terminal of the selection switch to calculate the voltage value of the target battery cell.

7. The system according to claim 6, characterized in that, The preset delay time is set from the moment the secondary rectifier switch is turned on until the moment when the theoretically calculated current flowing through the secondary rectifier switch drops to a value equal to the constant current provided by the current-limiting constant current circuit.

8. The system according to claim 1, characterized in that, In all individual voltage measurement and equalization units, the same-name terminals of the primary windings of the transformers are connected to the power supply terminal, and the different-name terminals of the primary windings are respectively connected to one end of the corresponding primary power switch; the other end of all primary power switches is connected to the reference ground terminal. The primary and secondary windings of the transformer have the same number of turns and are configured to have matching DC resistance characteristics.

9. A method for measuring the voltage of a single cell, applied to the single cell voltage measurement and equalization system for a series battery pack as described in any one of claims 1-8, characterized in that, Includes the following steps: The hybrid clamping circuit of the target unit operates in RCD clamping mode and controls its primary-side power switch to perform measurement operations. The measurement compensation module is controlled to connect the current-limiting constant current circuit to the target unit to provide error compensation; At a preset moment during the conduction of the secondary rectifier switch, the voltage signal of the common terminal of the selection switch or an equivalent node is sampled; Based on the voltage signal, and by using the on-state voltage drop of the matching switch to offset the error introduced by the on-state voltage drop of the secondary rectifier switch, the voltage value of the target battery cell is calculated.

10. A battery management system, characterized in that, Including the single-cell voltage measurement and equalization system for series-connected battery packs as described in any one of claims 1-8.

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