A multi-battery-pack parallel charging system and a control method thereof

Abstract

This invention discloses a multi-winding transformer and multi-battery pack parallel charging system and its control method based on current feedback. The system includes an EMI filter unit, an AC-DC rectifier unit, a PFC unit, a switching power supply unit, a multi-winding transformer, N rectifier units, N differential-mode inductors, N filter capacitors, N current sampling units, N switching units, N battery pack interfaces, and a control unit. This invention utilizes the inductive reactance voltage drop of the differential-mode inductors to actively raise the secondary output voltage of the transformer, ensuring that all battery packs receive forward charging current simultaneously, even with different voltages. Combined with independent current sampling for each path and closed-loop power adjustment based on minimum current deviation, the system can automatically optimize charging current distribution, achieving a high-efficiency, low-ripple charging process. This invention features simultaneous charging across all paths, high power utilization, low output ripple, and moderate hardware cost.

Description

Technical Field

[0001] This invention relates to the field of battery charging technology, and more specifically to a multi-battery pack parallel charging system and its control method. Background Technology

[0002] Currently, mainstream fast charging solutions on the market adopt a "one charger, one battery pack" architecture, achieving maximum power charging through a communication protocol between the charger and the battery pack. This solution is technically mature, simple to control, and can fully utilize the charger's power capacity, shortening the charging time for a single battery pack. However, when users need to charge multiple battery packs, this solution has the following problems: First, multiple chargers need to work simultaneously, increasing equipment cost and space occupation; second, if there is only one charger, each battery pack can only be charged sequentially, resulting in a significant increase in total charging time and a poor user experience.

[0003] To address the aforementioned issues, the industry has proposed various technical solutions for parallel charging of multiple battery packs, mainly including the following categories: A company has proposed a modular battery system. Its core feature is the construction of at least two battery interfaces within the battery module, each equipped with an independent DC-DC converter. All DC-DC converters are electrically connected to a bus, allowing for independent adjustment of the current of each battery interface. The advantage of this approach is that the charging current of each channel can be independently controlled, theoretically enabling maximum power charging for each channel. Its technical limitations include high hardware costs (requiring multiple DC-DC converters) and the constraint that all DC-DC inputs must be connected to the same bus, resulting in a mandatory requirement for equal common bus voltage.

[0004] A company has proposed a multi-battery pack charging solution, with its representative patent CN111509804A featuring the following core technical characteristics: The charger has at least two charging ports, each forming a charging circuit with its connected battery module; each charging circuit has a corresponding priority level and a corresponding level state; a control component controls the corresponding charging circuits to operate sequentially according to the priority level; when the currently operating charging circuit charges its corresponding battery module to the level state corresponding to the next priority level, the control component controls the charging circuit corresponding to the next priority level to work together with the currently operating charging circuit, and so on, until all charging circuits are in operation. This solution employs a "priority-based sequential connection" control logic, actively scheduling the on / off state of each charging circuit through the control component, thus achieving sequential connection and parallel charging of multiple battery packs.

[0005] A company has proposed a method for controlling the charging power of multi-branch battery packs. This method dynamically sets the charging power control strategy by detecting overcurrent risks in each branch and circulating current risks between branches. This solution is primarily applied to vehicle battery systems, focusing on power control and risk monitoring.

[0006] The following technical issues still need to be addressed in the field of parallel charging of multiple battery packs: The contradiction between charging efficiency and cost: Independent DC-DC solutions can achieve maximum power charging for each channel, but the hardware cost is high; the control logic of the cascaded integration solution is relatively complex and there are patent barriers.

[0007] Insufficient control precision: Existing solutions generally lack independent and precise monitoring of the charging current of each circuit, and the power adjustment is relatively coarse, which cannot guarantee that each circuit is always in the optimal charging state.

[0008] High patent barriers: One company has filed a patent for a control method that "controls the charging circuit to work in sequence according to priority"; another company has filed a patent for a hardware architecture that "bus + multiple DC-DC output aggregation", which limits the design space for other technical routes.

[0009] Parallel circulating current risk: In existing parallel charging solutions, when the battery pack voltages are inconsistent, direct parallel connection will generate a large circulating current, which may damage the battery or charging equipment. Summary of the Invention

[0010] To address the shortcomings of the existing technologies, this invention provides a multi-battery pack parallel fast charging system and its control method that combines advantages in charging efficiency, control precision, and cost. It also circumvents existing patent barriers by providing a multi-winding transformer multi-battery pack parallel charging system and its control method.

[0011] The technical solution adopted in this invention is: A parallel charging system for multiple battery packs with multiple winding transformers based on current feedback includes: An EMI filter unit is used to suppress electromagnetic interference on the power grid side; An AC-DC rectifier unit is used to convert AC input to DC power; A PFC (Power Factor Correction) unit is used to improve the power factor and reduce harmonics; A switching power supply unit, whose input terminal is connected to the output terminal of a PFC unit, is used to convert DC power into high-frequency AC power; the switching power supply unit adopts an isolated DC-DC topology, including but not limited to a two-transistor forward converter, LLC resonant converter, phase-shifted full-bridge converter, flyback converter, or push-pull topology. The control unit is connected to the signal output terminal of the current sampling unit to receive real-time current values ​​from each channel; it is also connected to the control terminal of each switching unit to dynamically adjust the output power of the switching power supply unit based on the current feedback from each channel. A multi-winding transformer, wherein the primary winding is connected to the output terminal of the switching power supply unit, and the secondary winding contains N independent windings (N≥2, preferably N=4). N rectifier units are connected one-to-one with the output terminals of N secondary windings to rectify the AC output of each secondary winding into DC. N differential-mode inductors are connected in series between the output terminals of N rectifier units and the corresponding filter capacitors. There is no magnetic coupling between the inductors, which are used to provide inductive reactance to high-frequency pulsating DC current. N filter capacitors are connected one-to-one with the output terminals of N differential mode inductors to smooth DC voltage. N current sampling units (precision sampling resistors + differential amplifier circuits) are connected in series in the output circuits of N rectifier units to collect the charging current of each circuit in real time. N switching units (MOSFETs or relays) are connected one-to-one with the output terminals of N current sampling units to independently control the on / off state of each charging circuit. N battery pack interfaces are connected one-to-one with the output terminals of N switch units to connect the battery packs to be charged; The AC power supply is connected in sequence to the EMI filter unit, the AC-DC rectifier unit, and the PFC (power factor correction) unit; The output of the PFC (Power Factor Correction) unit is connected to the input of the switching power supply unit; The output terminal of the switching power supply unit is connected to the input terminal of the multi-winding transformer; The output terminal of the multi-winding transformer is connected to the rectifier unit; The output of the rectifier unit is equipped with a differential mode inductor and a filter capacitor; The differential-mode inductor is connected in series between the output of the rectifier unit and the corresponding filter capacitor; A current sampling unit is connected in series in the output circuit of the rectifier unit; The output terminal of the current sampling unit is equipped with a switch unit for controlling the on / off state of the charging circuit; The output of the switching unit is equipped with a battery pack interface.

[0012] A control method for a multi-winding transformer and multi-battery pack parallel charging system based on current feedback includes the following steps: Step S0 (Access and Initialization): Detect the status of each battery pack, control the switching unit corresponding to the battery pack that meets the charging conditions to be turned on, and keep the switching unit that does not meet the conditions turned off.

[0013] Step S1 (Current Closed-Loop Pre-Adjustment): The control unit uses the initial target current as a reference and adjusts the input power of the switching power supply unit to ensure that the charging current in all currently conducting loops is not greater than the target current, and that at least one charging current is close to Imax.

[0014] Step S2 (Constant Current Charging Stage): The control unit continuously reads the values ​​of each current sampling unit at a frequency of 1-10kHz, calculates the current deviation of each circuit, and dynamically adjusts the total input power of the switching power supply unit according to the minimum current deviation in all conducted circuits.

[0015] Step S3 (Voltage Plateau Handling): Monitor the voltage of each battery pack in real time. If the battery pack voltage approaches the maximum charging voltage, reduce the set charging current value for that circuit. Step S4 (Full Charge Cut-off and Power Readjustment): When the voltage of any battery pack reaches the full charge voltage, turn off the switch of that circuit, remove it from the set of current closed-loop regulation, and recalculate the total target power based on the total demand of the remaining conducting circuits.

[0016] Step S5 Fault Removal: The chip is always communicating with the battery pack. If the battery pack overheats, a single cell voltage is too high, the battery pack fails, or communication is interrupted, the switch is immediately turned off, the chip is removed from the current closed-loop regulation set, and the total target power is recalculated based on the total demand of the remaining conducting loops.

[0017] Step S6 (Termination): Repeat S2-S5 until all battery pack switches are turned off, and the system terminates charging.

[0018] A control method for a parallel charging system of multiple battery packs with multiple winding transformers based on current feedback includes the following control steps: Step s101: The system powers on and starts up; Step s102, system initialization; Step s103: Detect the status of each battery pack; and read the Imax of each battery pack to see if there is a fault in the battery pack. If so, mark the fault and jump to s104. Step s104: Determine if the initial voltage is greater than 20.5V; if it is greater than 20.5V, proceed to step s105; otherwise, proceed to step s113. Step s105: Determine if the container is full; if yes, proceed to s132; otherwise, proceed to step s106. Step s106, current pre-adjustment; the Iset of each battery pack is pre-adjusted to 1 / 5 of the Imax of this battery pack; Step s107: Read the battery pack voltage value, read the battery pack fault data, and determine if there is a fault. If yes, proceed to step s111; otherwise, proceed to s108. In step s108, if the voltage is greater than 20.8V, proceed to step s109; otherwise, proceed to step s116. In step s109, Iset decreases by 0.1A; Step s110: Determine if Iset is less than 0.2A. If yes, proceed to step s111; otherwise, proceed to step s120. Step s111: Turn off the switch and mark the battery as faulty, then proceed to step s112; Step s112: Are all battery pack circuits closed? If yes, jump to s132; otherwise, jump to s122. Step s113: Determine if the condition is met; if the battery pack is not faulty, proceed to s114; otherwise, proceed to s115. Step s114: Turn on the switch and jump to step s106; Step s115: Turn off the switch and proceed to step s106; In step s116, if the voltage is less than 20.7V, proceed to step s117; otherwise, proceed to step s121. In step s117, Iset increases by 0.1A; Step s118: Determine if Iset is greater than Imax; if yes, proceed to step s119; otherwise, proceed to s110. Step s119, Iset=Imax, jump to step s120; Step s120, apply the new current; jump to step s122; Step s121, maintain the current Iset; Step s122, current closed loop; Step s123, set the PI target; Step s124: Read the sampled current; Step s125: Calculate the error; If the error is greater than 0.1A in step s126, proceed to step s127; otherwise, proceed to step s129. Step s127, increase power; Step s128, jump to step s106; If the error is less than -0.1A in step s129, proceed to step s130; otherwise, proceed to step s131. Step s130, reduce power; jump to step s128; Step s131, maintain power; jump to step s128; Step s132, charging terminated.

[0019] The advantages of this invention over the prior art are: 1. Simultaneous charging across the entire circuit, high efficiency: The output voltage of the transformer is actively raised by utilizing the inductive reactance voltage drop of the differential mode inductor, ensuring that all connected battery packs (regardless of voltage level) always receive positive charging current, resulting in high system power utilization and short total charging time.

[0020] 2. Low output ripple and high safety: The differential-mode inductor and filter capacitor form an LC filter circuit, resulting in a clean output current that helps extend battery life. The inductor also has the ability to limit current and suppress sudden current changes, improving system safety.

[0021] 3. Moderate hardware cost: It only requires a multi-winding transformer and a small number of differential mode inductors and sampling resistors, which significantly reduces the cost compared to independent DC-DC solutions.

[0022] 4. Simple and reliable control logic: The voltage boosting mechanism automatically enables simultaneous charging of the entire circuit, and the current closed loop only requires fine-tuning, resulting in a simple algorithm.

[0023] This invention discloses a multi-winding transformer and multi-battery pack parallel charging system and its control method based on current feedback. By adding a differential-mode inductor, the system transitions from passively adapting to the battery pack voltage to actively raising the transformer output voltage. The inductor voltage drop VL = I × ZL acts as an "automatic level shifter"—low-voltage battery packs receive a larger voltage rise due to higher current, while high-voltage battery packs receive a smaller voltage rise due to lower current, ultimately automatically adjusting the transformer output voltage to a level that allows all battery packs to receive forward charging current.

[0024] 1. LC filtering function: The differential mode inductor and the filter capacitor form an LC low-pass filter, which significantly reduces the output ripple voltage, provides a cleaner charging current, and helps to extend battery life.

[0025] 2. EMI suppression: Inductors suppress high-frequency switching noise, reducing conducted and radiated electromagnetic interference.

[0026] 3. Current surge suppression: Inductors have the characteristic of suppressing the rate of change of current (di / dt). During switching transients or battery pack connection / disconnection, they can limit current surges and protect switching devices and battery packs.

[0027] 4. Current limiting protection: Even under abnormal conditions such as output short circuit or extreme voltage difference in the battery pack, the inductor can limit the rate of current rise, improving system safety.

[0028] This invention incorporates a differential-mode inductor, which significantly increases the inductive reactance and thus the inductor voltage drop. This change directly affects the transformer output voltage: in a leakage inductance-only scheme, the transformer output voltage is only slightly higher than the lowest battery pack voltage; in this invention, the transformer output voltage is significantly higher than all battery pack voltages. This invention ensures that the high-voltage battery pack always has a positive charging current. From the perspective of system power utilization, the leakage inductance-only scheme has a lower utilization rate because some power is not utilized; this invention enables simultaneous charging of the entire circuit, resulting in high power utilization and significantly shortening the total charging time. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the circuit structure of a parallel charging system for multiple battery packs with multiple winding transformers based on current feedback. Figure 2 This is a control flowchart for a multi-winding transformer and multi-battery pack parallel charging system based on current feedback. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and embodiments: Appendix Figure 1 and 2 It is known that a multi-battery pack parallel charging system includes: An EMI filter unit is used to suppress electromagnetic interference on the power grid side; An AC-DC rectifier unit is used to convert AC input to DC power; A PFC (Power Factor Correction) unit is used to improve the power factor and reduce harmonics; A switching power supply unit, whose input terminal is connected to the output terminal of a PFC unit, is used to convert DC power into high-frequency AC power; the switching power supply unit adopts an isolated DC-DC topology, including but not limited to a two-transistor forward converter, LLC resonant converter, phase-shifted full-bridge converter, flyback converter, or push-pull topology. A multi-winding transformer, wherein the primary winding is connected to the output terminal of the rectifier unit, and the secondary winding contains N independent windings (N≥2, preferably N=4). N rectifier units are connected one-to-one with the output terminals of N secondary windings to rectify the AC output of each secondary winding into DC. N differential-mode inductors are connected in series between the output terminals of N rectifier units and the corresponding filter capacitors. There is no magnetic coupling between the inductors, which are used to provide inductive reactance to high-frequency pulsating DC current. N filter capacitors are connected one-to-one with the output terminals of N differential mode inductors to smooth DC voltage. N current sampling units (precision sampling resistors + differential amplifier circuits) are connected in series in the output circuits of N rectifier units to collect the charging current of each circuit in real time. N switching units (MOSFETs or relays) are connected one-to-one with the output terminals of N current sampling units to independently control the on / off state of each charging circuit. N battery pack interfaces are connected one-to-one with the output terminals of N switch units to connect the battery packs to be charged; A control unit is connected to the signal output terminal of each current sampling unit to receive real-time current values ​​from each channel; it is connected to the control terminal of each switching unit to independently control the on / off state of each channel; and it is connected to the control terminal of the switching power supply unit to dynamically adjust the output power of the switching power supply unit based on the current feedback from each channel.

[0031] Operating characteristics of multi-winding transformers: In the hardware architecture of this invention, the secondary windings of a multi-winding transformer ideally have the same output voltage. However, actual transformers inevitably have leakage inductance, and the differences in parameters such as the line impedance and rectifier voltage drop of each winding result in slight differences in the actual output voltage of each secondary winding.

[0032] Based on the above physical characteristics, when the voltages of the battery packs are different, even if all battery packs are connected to their respective secondary windings at the same time, the system will automatically exhibit the following current distribution characteristics: The battery pack with the largest voltage difference from the secondary winding (i.e., the battery pack with the lowest voltage) receives the largest charging current; A battery pack with a smaller voltage difference from the secondary winding receives a smaller charging current. Even if the battery pack voltage is higher than the average winding voltage, due to leakage inductance and line impedance, the actual output voltage of each winding is not exactly the same. Therefore, all battery packs will receive a certain charging current, but the current magnitude is proportional to the voltage difference.

[0033] The core function of differential-mode inductors is to boost the output voltage on the secondary side of transformers. One of the core innovations of this invention is to utilize the inductive reactance voltage drop of the differential mode inductor to actively raise the output voltage of the secondary winding of the transformer, thereby enabling all battery packs to simultaneously obtain positive charging current.

[0034] (I) Basic Principles (assuming that the battery packs allow the same charging current) In a multi-winding transformer system, each secondary winding is connected to the battery pack via a rectifier bridge, differential-mode inductor, and filter capacitor. According to Kirchhoff's voltage law, the output voltage Vtrans of the transformer secondary winding satisfies: Vtrans = Vbattery + VL + Vloss in: • Vbattery: Battery pack voltage • VL = I × ZL: Inductive reactance voltage drop across the differential mode inductor (ZL = 2πfL) • Vloss: Line resistance, rectifier bridge voltage drop, and other losses (ii) Voltage rise mechanism When multiple battery packs are charged simultaneously, the charging current I of each circuit is inversely proportional to the battery pack voltage Vbatteryi—the lower the voltage of the battery pack, the greater the charging current.

[0035] Due to the presence of differential-mode inductance, a large inductive reactance voltage drop VL is generated when a large current flows through the inductor. Therefore: • Low-voltage battery pack circuit: I_large → VL_large → Vtrans output of this circuit, which is the Vtrans output of the transformer. High-voltage battery pack circuit: The transformer output Vtrans is the same, I is small → VL is small. Vtrans = Vbattery + VL + Vloss; Since the output voltage Vtrans of each secondary winding of the transformer is determined by the same primary winding, the actual Vtrans must simultaneously meet the requirements of all circuits. According to the "barrel effect," the actual Vtrans is determined by the circuit with the highest demand (i.e., the Vtrans required by the low-voltage battery pack circuit).

[0036] Therefore, the actual transformer secondary output voltage Vtrans is "raised" to: Vtransactual = max(Vbatteryi + VLi + Vlossi) ≈ Vbatterymin + VLmax; Where Vbatterymin is the lowest battery pack voltage, and VLmax is the maximum inductor voltage drop (occurring in the branch where the lowest voltage battery pack is located).

[0037] (III) Realization of simultaneous charging across the entire circuit Since Vtransactual is raised to a voltage higher than that of all battery packs (i.e., Vtransactual > Vbatteryi holds for all i), therefore: Each battery pack receives a positive charging current, the magnitude of which is determined by the impedance of that circuit. Ii = (Vtransactual - Vbatteryi - Vlossi) / ZLi With the addition of a differential-mode inductor, the system shifts from passively adapting to the battery pack voltage to actively boosting the transformer output voltage. The inductor voltage drop VL = I × ZL acts as an "automatic level shifter"—the low-voltage battery pack receives a larger voltage boost due to its higher current, while the high-voltage battery pack receives a smaller voltage boost due to its lower current, ultimately allowing the transformer output voltage to automatically adjust to a level that allows all battery packs to receive forward charging current.

[0038] This mechanism enables the invention to automatically achieve simultaneous charging of the entire circuit without any active control, transforming "partial battery pack idle waiting" into "high-efficiency parallel charging of the entire circuit".

[0039] Other functions of differential mode inductors: 1. LC filtering function: The differential mode inductor and the filter capacitor form an LC low-pass filter, which significantly reduces the output ripple voltage, provides a cleaner charging current, and helps to extend battery life.

[0040] 2. EMI suppression: Inductors suppress high-frequency switching noise, reducing conducted and radiated electromagnetic interference.

[0041] 3. Current surge suppression: Inductors have the characteristic of suppressing the rate of change of current (di / dt). During switching transients or battery pack connection / disconnection, they can limit current surges and protect switching devices and battery packs.

[0042] 4. Current limiting protection: Even under abnormal conditions such as output short circuit or extreme voltage difference in the battery pack, the inductor can limit the rate of current rise, improving system safety.

[0043] A charging control method based on the above system includes the following steps: Step S0 (Access and Initialization): Detect the status of each battery pack, control the switching unit corresponding to the battery pack that meets the charging conditions to be turned on, and keep the switching unit that does not meet the conditions turned off.

[0044] Step S1 (Current Closed-Loop Pre-Adjustment): The control unit uses the initial target current as a reference and adjusts the input power of the switching power supply unit to ensure that the charging current in all currently conducting loops is not greater than the target current. Step S2 (Constant Current Charging Stage): The control unit continuously reads the values ​​of each current sampling unit at a frequency of 1-10kHz, calculates the current deviation of each circuit, and dynamically adjusts the total input power of the switching power supply unit according to the minimum current deviation in all conducted circuits.

[0045] Step S3 (Voltage Plateau Handling): Monitor the voltage of each battery pack in real time. If the battery pack voltage approaches the maximum charging voltage, reduce the set charging current value for that circuit. Step S4 (Full Charge Cut-off and Power Readjustment): When the voltage of any battery pack reaches the full charge voltage, turn off the switch of that circuit, remove it from the set of current closed-loop regulation, and recalculate the total target power based on the total demand of the remaining conducting circuits.

[0046] Step S5 Fault Removal: The chip is always communicating with the battery pack. If the battery pack overheats, a single cell voltage is too high, the battery pack fails, or communication is interrupted, the switch is immediately turned off, the chip is removed from the current closed-loop regulation set, and the total target power is recalculated based on the total demand of the remaining conducting loops.

[0047] Step S6 (Termination): Repeat S2-S5 until all battery pack switches are turned off, and the system terminates charging.

[0048] A control method for a parallel charging system of multiple battery packs with multiple winding transformers based on current feedback includes the following control steps: Step s101: The system powers on and starts up; Step s102, system initialization; Step s103: Detect the status of each battery pack; and read the Imax of each battery pack to see if there is a fault in the battery pack. If so, mark the fault and jump to s104. Step s104: Determine if the initial voltage is greater than 20.5V; if it is greater than 20.5V, proceed to step s105; otherwise, proceed to step s113. Step s105: Determine if the container is full; if yes, proceed to s132; otherwise, proceed to step s106. Step s106, current pre-adjustment; the Iset of each battery pack is pre-adjusted to 1 / 5 of the Imax of this battery pack; Step s107: Read the voltage value of the battery pack, read the battery pack fault data, and determine whether there is a fault. If yes, proceed to step s111; otherwise, proceed to s108. In step s108, if the voltage is greater than 20.8V, proceed to step s109; otherwise, proceed to step s116. In step s109, Iset decreases by 0.1A; Step s110: Determine if Iset is less than 0.2A. If yes, proceed to step s111; otherwise, proceed to step s120. Step s111: Turn off the switch and mark the battery as faulty, then proceed to step s112; Step s112: Are all battery pack circuits closed? If yes, jump to s132; otherwise, jump to s122. Step s113: Determine if the condition is met; if the battery pack is not faulty, proceed to s114; otherwise, proceed to s115. Step s114: Turn on the switch and jump to step s106; Step s115: Turn off the switch and proceed to step s106; In step s116, if the voltage is less than 20.7V, proceed to step s117; otherwise, proceed to step s121. In step s117, Iset increases by 0.1A; Step s118: Determine if Iset is greater than Imax; if yes, proceed to step s119; otherwise, proceed to s110. Step s119, Iset=Imax, jump to step s120; Step s120, apply the new current; jump to step s122; Step s121, maintain the current Iset; Step s122, current closed loop; Step s123, set the PI target; Step s124: Read the sampled current; Step s125: Calculate the error; If the error is greater than 0.1A in step s126, proceed to step s127; otherwise, proceed to step s129. Step s127, increase power; Step s128, jump to step s106; If the error is less than -0.1A in step s129, proceed to step s130; otherwise, proceed to step s131. Step s130, reduce power; jump to step s128; Step s131, maintain power; jump to step s128; Step s132, charging terminated.

[0049] The output voltage of the transformer secondary side is actively raised by utilizing the inductive reactance voltage drop of the differential mode inductor, ensuring that all battery packs receive positive charging current simultaneously; The differential-mode inductor and the filter capacitor form an LC filter circuit, which significantly reduces output ripple. Each current path is sampled independently to achieve accurate sensing of the charging status of each battery pack; Dynamic power adjustment based on minimum current deviation automatically achieves "filling in the gaps"; All rechargeable battery packs are always on, with no step-by-step integration. Once fully charged, immediately disconnect and reduce power to avoid overcharging.

[0050] This invention enables simultaneous charging across the entire circuit, maximizing charging efficiency: by utilizing the inductive reactance voltage drop of the differential mode inductor to actively raise the transformer output voltage, it ensures that all battery packs (regardless of voltage level) always receive positive charging current, significantly improving system power utilization and significantly shortening the total charging time.

[0051] Low output ripple: The LC filter circuit significantly reduces the output ripple voltage, providing a clean charging current and helping to extend battery life.

[0052] Excellent EMI characteristics: The differential mode inductor's suppression of high-frequency switching noise, combined with the soft-switching characteristics of the LLC resonant topology, makes the system's EMI characteristics significantly better than traditional solutions.

[0053] Moderate hardware cost: Compared to independent DC-DC solutions (which require multiple DC-DC converters), this invention only requires one multi-winding transformer, N differential-mode inductors, and a small number of sampling resistors. The differential-mode inductors are standard magnetic components with low cost, resulting in a significant reduction in overall hardware cost.

[0054] The control logic is simple: the voltage boosting mechanism automatically enables simultaneous charging of the entire circuit without the need for complex "step-by-step paralleling" control logic. The current closed loop only requires fine-tuning based on coarse adjustment, and the control algorithm is simple and reliable.

[0055] High safety: Differential mode inductors provide additional current limiting protection and suppress current surges; they can independently shut down any abnormal battery pack to prevent overcharging and overheating.

[0056] Example: A charging system for four-battery-pack power tools.

[0057] Hardware parameters: Four-battery pack fast charging system: Input section: EMI filter unit, AC-DC rectifier unit, PFC unit, used to convert AC input into stable DC power; Switching power supply unit: adopts isolated DC-DC topology (such as LLC resonant converter, two-transistor forward converter, etc.), with an operating frequency of 65kHz, and controls the output power by adjusting the switching frequency or PWM duty cycle; Multi-winding transformer: The primary winding is connected to the output terminal of the switching power supply unit, and the secondary winding contains 4 independent windings, which are electrically isolated from each other; Rectifier unit: 4 rectifier bridges, each connected to the output terminal of one of the 4 secondary windings; Differential mode inductors: Each channel is equipped with a 3μH power inductor, and there is no magnetic coupling between the inductors; Filter capacitor: Each channel is equipped with a filter capacitor, which together with the differential mode inductor forms an LC filter circuit; Current sampling unit: Each channel is equipped with a precision sampling resistor and a differential amplifier circuit, and the sampling frequency is adjustable; Switching unit: Each channel is equipped with a MOSFET or relay, and its on / off state is independently controlled by the control unit. Control unit: Microcontroller, responsible for current sampling, switching control, and output power regulation of the switching power supply unit. Battery packs: 4 battery packs with voltages of 17.0V, 18.0V, 19.0V, and 20.0V respectively. Initial state: The voltages of the four battery packs are: Battery Pack 1 (17.0V), Battery Pack 2 (18.0V), Battery Pack 3 (19.0V), and Battery Pack 4 (20.0V). The temperatures of all four packs are normal, all of them are allowed to charge, and all four switches are fully operational.

[0058] Analysis of the voltage rise mechanism of differential mode inductors: The system operating frequency is f = 65kHz, the differential mode inductance is Ldiff = 3μH, and the inductive reactance is calculated as follows: ZL = 2πfL = 2 × 3.14 × 65000 × 0.000003 ≈ 1.22Ω Step 1: Initial current distribution (set before closed-loop regulation) The control unit sets the target charging current for each battery pack. Due to the different battery pack voltages, the charging current is set as follows: Battery Pack 1 (17.0V): (e.g., 5A) Battery Pack 2 (18.0V): (e.g., 5A) Battery Pack 3 (19.0V): (e.g., 5A) Battery Pack 4 (20.0V): (e.g., 5A) Step 2: Inductor voltage drop calculation (ignoring line losses and rectifier bridge voltage drop in the circuit) VL1 = I1 × ZL = 5A × 1.22Ω ≈ 6.1V VL2 = I2 × ZL = 5A × 1.22Ω ≈6.1V VL3 = I3 × ZL = 5A × 1.22Ω ≈6.1V VL4 = I4 × ZL = 5A × 1.22Ω ≈6.1V Step 3: Output voltage of each transformer Ignore line loss Vloss (assuming it is small): Vtransrequired1 = 17.0V +6.1V = 23.1V Vtransrequired2 = 18.0V + 6.1V = 24.1V Vtransrequired3 = 19.0V + 6.1V = 25.1V Vtransrequired4 = 20.0V + 6.1V = 26.1V Step 4: Actual transformer output voltage Ensure that the charging current of each circuit does not exceed the allowable value, and that the actual Vtrans meets the minimum requirement: Vtransactual = min(23.1, 24.1, 25.1, 26.1) = 23.1V Step 5: Verify simultaneous charging across the entire circuit The actual voltage available for battery pack 1 is: 23.1V - 17.0V = 6.1V → actual current 6.1 ÷ 1.22 = 5A The actual voltage available for battery pack 2 is: 23.1V - 18.0V = 5.1V → The actual current is 5.1V ÷ 1.22V ≈ 4.18A. The actual voltage available for battery pack 3 is: 23.1V - 19.0V = 4.1V → The actual current is 4.1V ÷ 1.22V ≈ 3.36A. The actual voltage available for battery pack 4 is: 23.1V - 20.0V = 3.1V → The actual current is 3.1V ÷ 1.22V ≈ 2.54A. The transformer secondary output voltage Vtransactual = 23.1V, which is higher than the voltages of all battery packs (17.0V, 18.0V, 19.0V, 20.0V). Therefore, all battery packs receive positive charging current, and none of them are "idle".

[0059] Step 6: Voltage catch-up process: As charging proceeds: Among battery packs 1, 2, 3, and 4, battery pack 1 has the highest charging current, while the current decreases sequentially for battery packs 2, 3, and 4. This results in a higher charging current for lower battery pack voltages and a faster voltage increase, eventually leading to constant voltage charging once the battery pack voltage reaches 21V.

[0060] Step 7: Full filling excision When the voltage of any battery pack reaches the full charge voltage and the current is less than 100mA, the control unit shuts off the switch for that circuit. The target current for the remaining circuits is recalculated, and the input power of the switching power supply unit is adjusted accordingly to continue charging the remaining battery packs until they are fully charged.

[0061] Basic working principle and explanation of this solution: The EMI unit (C10, C11, LF1) is an AC input mains filter unit. It mainly uses two capacitors and one common-mode inductor to achieve sinusoidal wave filtering. This unit is composed entirely of passive components. The rectifier unit (D5) rectifies the input AC power into DC power, but the DC power still has two saddle waves.

[0062] PFC Unit (L10, Q10, D10, C12): The function of the PFC unit is power factor correction, bringing the input power factor close to 1. The output stage of the PFC unit is followed by an electrolytic capacitor, C12, which is typically a large energy storage electrolytic capacitor. During operation, the PFC unit maintains a stable voltage of approximately 370V for capacitor C12 (input 220V). If the input power of the switching power supply unit is high, the voltage of C12 decreases, resulting in a higher output power for the PFC unit, ultimately stabilizing the voltage of capacitor C12 within a certain range.

[0063] Switching power supply unit: The switching power supply unit outputs the energy from the C12 electrolytic capacitor to the secondary side through a transformer. The power supply operates in a push-pull mode.

[0064] The switching power supply unit first receives the signal from the U1 current feedback unit. If the current signal is acceptable for output, Q5 and Q6 are turned on alternately. The switching power supply unit also features a soft start to ensure that there is no large inrush current at the start of charging; that is, the PWM duty cycle gradually increases from 0. As the duty cycles of Q5 and Q6 increase, the final input power also increases. If the U1 current feedback unit indicates that the current input power needs to be reduced, the switching power supply unit reduces the PWM output. Ultimately, the feedback input and PWM output reach a balance, and the switching power supply system stabilizes.

[0065] First, the control unit communicates with each battery pack and collects the battery pack voltage. If the battery pack voltage is greater than 20.5V, it marks the battery pack as fully charged and does not charge it. Battery packs not marked as fully charged have no communication faults and can be charged. If there is a fault, it marks the fault and removes the battery pack (removing a fully charged or faulty battery pack involves turning off the switch module). If there are no remaining battery packs, the system stops charging and enters standby mode.

[0066] If there is still a battery pack, read the maximum charging current Imax of the battery pack (generally, Iset is preset to one-fifth of Imax, only on the first startup, to prevent the surge current from being too large at the beginning of startup, Iset is increased to Imax within 1 second after the system starts working), and collect the actual current of this path corresponding to the current feedback module (initially it is 0), the control unit sends a signal to the switching power supply module to increase the input power through the current feedback module (the PWM of Q5 and Q6 of the switching power supply module is increased).

[0067] The control unit continuously monitors the charging current and battery pack voltage. If the voltage of each battery pack is less than 20.7V and the Iset of each channel is greater than the actual detected current of the corresponding channel by 0.1A, then the control unit sends a signal to the switching power supply module to increase the input power through the current feedback module. If the Iset of any channel is less than the actual detected current of the corresponding channel by 0.1A, then the control unit sends a signal to the switching power supply module to decrease the input power through the current feedback module.

[0068] Suppose there are 4 battery packs charging now, I1set=5A, actual current 1A, I2set=5A, actual current 2A, I3set=5A, actual current 3A, I4set=5A, actual current 5A. Since the actual charging current of battery pack 4 is consistent with the set current, the input power of the switching power supply cannot be increased. Therefore, the whole system is balanced at this time.

[0069] If the battery voltage of one circuit is greater than 20.8V, then the Iset of that circuit will be reduced by 0.1A (for example, if it was originally 5A, it will be changed to 4.9A). At this time, the feedback charging current may be 5.01A. The actual current is 0.1A greater than the set current. The control unit will send a signal to the switching power supply module to reduce the input power through the current feedback module. After the input power is reduced, the actual current of this circuit will also be reduced, possibly to 4.91A.

[0070] During this process, it is continuously determined that the actual current of each circuit has an error of less than 0.1A compared to its Iset. If this condition is not met, the input power of the switching power supply needs to be increased or decreased. Alternatively, if the Iset of a certain circuit is less than 0.2A, that circuit is disconnected (the switching unit of that circuit is turned off). After shutting down, the Iset and actual current of the remaining battery pack are reassessed, and the input power of the switching unit is adjusted or maintained based on their error.

[0071] Throughout the charging process, the system continuously communicates with the battery pack to detect faults, battery pack voltage, etc., until all battery pack switching modules are disconnected, at which point the entire system charging process terminates.

[0072] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the structure of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A parallel charging system for multiple battery packs with multi-winding transformers based on current feedback, characterized in that, include: An EMI filter unit is used to suppress electromagnetic interference on the power grid side; An AC-DC rectifier unit is used to convert AC input to DC power; A PFC unit is used to improve the power factor and reduce harmonics; A switching power supply unit, whose input terminal is connected to the output terminal of a PFC unit, is used to convert DC power into high-frequency AC power; the switching power supply unit adopts an isolated DC-DC topology, including but not limited to a two-transistor forward converter, LLC resonant converter, phase-shifted full-bridge converter, flyback converter, or push-pull topology. The control unit is connected to the signal output terminal of the current sampling unit to receive real-time current values ​​from each channel; it is also connected to the control terminal of each switching unit to dynamically adjust the output power of the switching power supply unit based on the current feedback from each channel. A multi-winding transformer, the primary winding of which is connected to the output of a switching power supply unit, and the secondary winding which contains N independent windings; N rectifier units are connected one-to-one with the output terminals of N secondary windings to rectify the AC output of each secondary winding into DC. N differential-mode inductors are connected in series between the output terminals of N rectifier units and the corresponding filter capacitors. There is no magnetic coupling between the inductors, which are used to provide inductive reactance to high-frequency pulsating DC current. N filter capacitors are connected one-to-one with the output terminals of N differential mode inductors to smooth DC voltage. N current sampling units are connected in series in the output circuits of N rectifier units to collect the charging current of each circuit in real time. N switching units are connected one-to-one with the output terminals of N current sampling units to independently control the on / off state of each charging circuit. N battery pack interfaces are connected one-to-one with the output terminals of N switch units to connect the battery packs to be charged; The AC power supply is connected in sequence to the EMI filter unit, the AC-DC rectifier unit, and the PFC unit; The output of the PFC unit is connected to the input of the switching power supply unit; The output terminal of the switching power supply unit is connected to the input terminal of the multi-winding transformer; The output terminal of the multi-winding transformer is connected to the rectifier unit; The output of the rectifier unit is equipped with a differential mode inductor and a filter capacitor; The differential-mode inductor is connected in series between the output of the rectifier unit and the corresponding filter capacitor; A current sampling unit is connected in series in the output circuit of the rectifier unit; The output terminal of the current sampling unit is equipped with a switch unit for controlling the on / off state of the charging circuit; The output of the switching unit is equipped with a battery pack interface.

2. The control method for a multi-winding transformer and multi-battery pack parallel charging system based on current feedback according to claim 1, characterized in that: Includes the following steps: Step S0: Detect the status of each battery pack, control the switch unit corresponding to the battery pack that meets the charging conditions to be turned on, and keep the switch unit that does not meet the conditions turned off; Step S1: The control unit uses the initial target current as a reference and adjusts the input power of the switching power supply unit to ensure that the charging current in all currently connected circuits is not greater than the target current. Step S2: The control unit continuously reads the values ​​of each current sampling unit at a frequency of 1-10kHz, calculates the current deviation of each circuit, and dynamically adjusts the total input power of the switching power supply unit according to the minimum current deviation in all conducting circuits. Step S3: Monitor the voltage of each battery pack in real time. If the battery pack voltage reaches the maximum charging voltage, reduce the current setting charging current value for that circuit. Step S4: When the voltage of any battery pack reaches the full charge voltage, turn off the switch of that circuit, remove it from the set of current closed-loop regulation, and recalculate the total target power based on the total demand of the remaining conducting circuits. Step S5 Fault Removal: The control unit is always communicating with the battery pack. If the battery pack overheats, a single cell voltage is too high, the battery pack fails, or communication is interrupted, the switch is immediately shut off and removed from the current closed-loop regulation set. The total target power is then recalculated based on the total demand of the remaining conducting loops. Step S6: Repeat S2-S5 until all battery pack switches are turned off and the system stops charging.

3. The control method for a multi-winding transformer and multi-battery pack parallel charging system based on current feedback according to claim 1, characterized in that: Step s101: The system powers on and starts up; Step s102, system initialization; Step s103: Detect the status of each battery pack; and read the Imax of each battery pack to see if there is a fault in the battery pack. If so, mark the fault and jump to s104. Step s104: Determine if the initial voltage is greater than 20.5V; If the voltage is greater than 20.5V, proceed to step s105; otherwise, proceed to step s113. Step s105: Determine if the container is full; if yes, proceed to s132; otherwise, proceed to step s106. Step s106, current pre-adjustment; the Iset of each battery pack is pre-adjusted to 1 / 5 of the Imax of this battery pack; Step s107: Read the battery pack voltage value, read the battery pack fault data, and determine if there is a fault. If yes, proceed to step s111; otherwise, proceed to s108. In step s108, if the voltage is greater than 20.8V, proceed to step s109; otherwise, proceed to step s116. In step s109, Iset decreases by 0.1A; Step s110: Determine if Iset is less than 0.2A; if so, proceed to step s111. Otherwise, proceed to step s120; Step s111: Turn off the switch and mark the battery as faulty, then proceed to step s112; Step s112: Are all battery pack circuits closed? If yes, jump to s132; otherwise, jump to s122. Step s113: Determine if the condition is met; if the battery pack is not faulty, proceed to s114; otherwise, proceed to s115. Step s114: Turn on the switch and jump to step s106; Step s115: Turn off the switch and proceed to step s106; In step s116, if the voltage is less than 20.7V, proceed to step s117; otherwise, proceed to step s121. In step s117, Iset increases by 0.1A; Step s118: Determine if Iset is greater than Imax; if yes, proceed to step s119; otherwise, proceed to s110. Step s119, Iset=Imax, jump to step s120; Step s120, apply the new current; jump to step s122; Step s121, maintain the current Iset; Step s122, current closed loop; Step s123, set the PI target; Step s124: Read the sampled current; Step s125: Calculate the error; If the error is greater than 0.1A in step s126, proceed to step s127; otherwise, proceed to step s129. Step s127, increase power; Step s128, jump to step s106; If the error is less than -0.1A in step s129, proceed to step s130; otherwise, proceed to step s131. Step s130, reduce power; jump to step s128; Step s131, maintain power; jump to step s128; Step s132, charging terminated.

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