A DC conversion module, a control method, and a power supply for series formation of lithium batteries

Abstract

The present invention discloses a DC conversion module, a control method and a power supply for series formation of lithium batteries, which includes a main control and at least one DC conversion module. The charging input end of the DC conversion module is connected to the DC bus, and the charging output end of the DC conversion module is connected to the two poles of the series-connected lithium battery pack according to the polarity. Under the control of the main control, each of the DC conversion modules can be turned on simultaneously, or turned off simultaneously, or any number of them can be alternately turned on. In the present invention, multiple DC conversion modules form a multi-phase interleaved parallel output structure, which is beneficial to improving the continuity of the output of this kind of DC conversion module, increasing the gain range of the output of this kind of DC conversion module, and effectively reducing the output ripple of this kind of DC conversion module.

Description

Technical Field

[0001] The present invention relates to the technical field of DC converters, and particularly to a DC conversion module, a control method, and a power supply for series formation of lithium batteries. Background Art

[0002] With the development of the electric vehicle and energy storage industries, lithium batteries, which have many advantages such as high voltage, light weight, small size, long life, good safety, no pollution, low self-discharge rate, and wide operating temperature range, are widely used.

[0003] In the manufacturing process of lithium batteries, a formation process needs to be completed, that is, after the lithium batteries are assembled, a certain voltage and current are required to charge the lithium batteries for a certain period of time, and through the steps of discharging and standing, a series of chemical reactions occur inside the lithium batteries, thereby activating the battery cells of the lithium batteries and making the performance of the lithium batteries reach the standard.

[0004] Traditional parallel formation equipment forms independent channels for each lithium battery for formation. It is impossible to ensure that the currents passing through each lithium battery are exactly the same. Coupled with the influence of the output accuracy of the formation equipment, it is difficult to ensure the consistency of each lithium battery during the formation process; in addition, when high-power lithium batteries are formed, a large current is required. During parallel formation, the internal resistance of the formation equipment will consume a large amount of electric energy.

[0005] If each lithium battery is connected in series for unified formation, the same current can be obtained for each lithium battery after series connection, which better ensures the consistency of each lithium battery during the formation process; in addition, the series formation method can increase the port voltage of the formation circuit and reduce the loss of electric energy on the internal resistance of the formation equipment.

[0006] During the formation process of lithium batteries, their voltage will change with the progress of formation. The voltage range of a single lithium battery is generally 2.0V - 4.2V. When multiple lithium batteries are connected in series, the voltage change range will increase exponentially with the increase in the number of series-connected lithium batteries. Therefore, how to provide a power supply for battery formation with a wide gain range has become an urgent problem to be solved. Summary of the Invention

[0007] In order to overcome the above-mentioned disadvantages and deficiencies of the prior art, the purpose of the present invention is to provide a DC conversion module and a control method, which can provide an output voltage with a wide gain range.

[0008] Another purpose of the present invention is to provide a power supply for series formation of lithium batteries, which can automatically implement each formation process flow composed of series-connected storage batteries.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A DC conversion module includes a main controller and at least one DC conversion module. The charging input end of the DC conversion module is connected to the DC bus, and the charging output end of the DC conversion module is connected to the two poles of the series-connected lithium battery pack according to the polarity. Under the control of the main controller, each DC conversion module is turned on simultaneously, turned off simultaneously, or any number of them are turned on alternately.

[0011] Furthermore, the DC conversion module includes a switching device Q1, a switching device Q2, a switching device Q3, a switching device Q4, an inductor L1, and an inductor L2. The first pole of the switching device Q1 is connected to the DC bus, the second pole of the switching device Q1 is connected to one end of the inductor L1, the other end of the inductor L1 is connected to the positive pole of the series-connected lithium battery pack, the negative pole of the series-connected lithium battery pack is connected to one end of the inductor L2, the other end of the inductor L2 is connected to the first pole of the switching device Q3, and the second pole of the switching device Q3 is connected to the GND terminal. The first pole of the switching device Q4 is connected to the DC bus, the second pole of the switching device Q4 is connected to the other end of the inductor L2, the other end of the inductor L1 is connected to the first pole of the switching device Q2, and the second pole of the switching device Q2 is connected to the GND terminal. The control poles of the switching device Q1, the switching device Q2, the switching device Q3, and the switching device Q4 are all connected to the PWM output end of the main controller.

[0012] Furthermore,

[0013] The first-direction current from the DC bus sequentially passes through the switching device Q1, the inductor L1, the series-connected lithium battery pack, the inductor L2, and the switching device Q3, and then flows out from the GND terminal, or flows in from the GND terminal, sequentially passes through the switching device Q2, the inductor L1, the series-connected lithium battery pack, the inductor L2, and the switching device Q4, and then flows back to the DC bus, forming a positive-voltage charging circuit for the series-connected lithium battery pack;

[0014] The second-direction current from the DC bus and / or the series-connected lithium battery pack sequentially passes through the switching device Q4, the inductor L2, the series-connected lithium battery pack, the inductor L1, and the switching device Q2, and then flows out from the GND terminal, or flows in from the GND terminal, sequentially passes through the switching device Q3, the inductor L1, the series-connected lithium battery pack, the inductor L2, and the switching device Q1, and then flows back to the DC bus, thereby forming a positive-voltage discharging circuit, a zero-voltage discharging circuit, or a negative-voltage discharging circuit for the series-connected lithium battery pack.

[0015] Furthermore, the DC conversion module further includes a filter capacitor C1 and a filter capacitor C2. The filter capacitor C1 is connected between the GND terminal and the DC bus connected to the switching device Q1, and the filter capacitor C2 is connected between the GND terminal and the DC bus connected to the switching device Q4.

[0016] Further, the DC conversion module further includes an output capacitor C3, and the output capacitor C3 is connected in parallel across the positive and negative electrodes of the series-connected lithium battery pack.

[0017] Further, the main control integrates a current sampling feedback module and a voltage sampling feedback module. The current sampling feedback module is used to sample the output current passing through the inductor L1 or inductor L2 of each DC conversion module, and the voltage sampling feedback module is used to sample the output voltage across the two poles of the series-connected lithium battery pack.

[0018] Further, by giving a reference voltage v ref (s) to the main control, thereby controlling the duty cycles of the first PWM signal and the second PWM signal, the output voltage across the two poles of the series-connected lithium battery pack can be controlled, and any number of n DC conversion modules can be simultaneously turned on or simultaneously turned off or alternately turned on;

[0019] The first PWM signal is used to control the turning on and off of the switching devices Q1 and Q3 in n DC conversion modules;

[0020] The second PWM signal is used to control the turning on and off of the switching devices Q2 and Q4 in n DC conversion modules.

[0021] Further, among the n DC conversion modules, there is a phase difference between the first PWM signals received by adjacent DC conversion modules, and there is also a phase difference between the second PWM signals received by adjacent DC conversion modules; the first PWM signals and the second PWM signals with different phases drive each DC conversion module to form a multi-phase interleaved parallel output structure.

[0022] Further, in the frequency domain, after giving a reference voltage v ref (s) to the main control, the reference voltage v ref (s) and the output voltage v out (s) across the two poles of the series-connected lithium battery pack successively include:

[0023] A first PI controller, a second PI controller, and a control object, and there is a zero-output duty cycle compensation link between the second PI controller and the control object, and the reference voltage v ref (s) passes through a feedforward compensator and is compensated to between the second PI controller and the control object in a positive-phase comparison manner;

[0024] The transfer function of the first PI controller is

[0025] The transfer function of the second PI controller is

[0026] The transfer function of the controlled object is

[0027] The transfer function of the zero - output duty - cycle compensation link is D(s);

[0028] The transfer function of the feed - forward compensator is

[0029] In the formula, K P1 and K P2 are both proportional - link coefficients, K I1 and K I2 are both integral - link coefficients, K ff is the adjustment coefficient of the feed - forward compensator, and the value range of K ff is (0, 1);

[0030] V bus is the input voltage of the DC bus, R is the impedance when the load of the DC conversion module is a resistor, L is the sum of the inductances of the inductor L1 and the inductor L2, and C is the capacitance of the output capacitor C3;

[0031] When the DC conversion module is symmetrical, D(s) is always equal to 0.5.

[0032] Further, after the output current i(t) is transformed into the frequency domain, it is fed back between the first PI controller and the second PI controller through an inner - loop feedback link; the transfer function of the inner - loop feedback link is G h (s)=RCs + 1;

[0033] In the formula, R is the impedance when the load of the DC conversion module is a resistor, and C is the capacitance of the output capacitor C3.

[0034] Further, after the output voltage v(t) is transformed into the frequency domain, it is fed back to the front of the first PI controller through an outer - loop feedback link;

[0035] The transfer function of the outer - loop feedback link is H(s), and H(s) is a unity - feedback transfer function.

[0036] Further, the working states of the series - connected lithium - battery pack include charging, positive - voltage discharging, zero - voltage discharging, negative - voltage discharging, and placement.

[0037] A power supply for series formation of lithium batteries, which is used to provide formation electric energy for a series - connected lithium - battery pack, includes an AC power grid, an AC / DC conversion module, a DC bus, and the DC conversion module according to any one of claims 1 - 6.

[0038] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0039] 1. For this type of DC conversion module, each DC conversion module can be turned on simultaneously, turned off simultaneously, or any number of them can be turned on alternately under the control of the main controller. Multiple DC conversion modules form a multi-phase interleaved parallel output structure, which is beneficial to improving the continuity of the output of this type of DC conversion module, increasing the gain range of the output of this type of DC conversion module, and effectively reducing the output ripple of this type of DC conversion module.

[0040] 2. For this type of power supply for series formation of lithium batteries, each DC conversion module can be turned on simultaneously, turned off simultaneously, or any number of them can be turned on alternately under the control of the main controller. Thus, each formation process of the series battery pack can be automatically realized. Multiple DC conversion modules form a multi-phase interleaved parallel output structure, which is beneficial to improving the continuity of the output of this type of DC conversion module and effectively reducing the output ripple of this type of DC conversion module. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the circuit schematic diagram of the DC conversion module of the present invention;

[0042] Figure 2 is the circuit schematic diagram of the DC conversion module of the present invention;

[0043] Figure 3 is the automatic control schematic diagram of the embodiment of the present invention;

[0044] Figure 4 is the schematic diagram of the power supply structure for series formation of lithium batteries of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The present invention will be further described in detail below in conjunction with embodiments, but the embodiments of the present invention are not limited thereto.

[0046] As Figure 1 shown, a DC conversion module is used to convert electrical energy from a DC bus into electrical energy suitable for forming a series lithium battery pack, and includes a main controller and at least one DC conversion module. The charging input end of the DC conversion module is connected to the DC bus, and the charging output end of the DC conversion module is connected to the two poles of the series lithium battery pack according to the polarity. Each of the DC conversion modules can be turned on simultaneously, turned off simultaneously, or any number of them can be turned on alternately under the control of the main controller.

[0047] As Figure 2 shown, the structures of multiple DC conversion modules are the same. It further includes: switching device Q1, switching device Q2, switching device Q3, switching device Q4, filter capacitor C1, filter capacitor C2, output capacitor C3, inductor L1, and inductor L2.

[0048] The specific connection method is as follows: the positive and negative electrodes of the series-connected lithium battery pack are respectively connected to two DC buses. In each of the DC conversion modules: the output capacitor is connected across the two ends of the series-connected lithium battery pack; one end of the inductor L1 is connected in series with the positive electrode of the lithium battery pack, and the other end is respectively connected to the first end of the switching device Q2. The second end of the switching device Q2 is connected to the GND terminal. The second pole of the switching device Q3 is connected to the GND terminal, and its first pole is respectively connected to one end of the inductor L2 and the second pole of the switching device Q4. The other end of the inductor L2 is connected to the negative electrode of the series-connected lithium battery pack, and the first pole of the switching device Q4 is connected to the DC bus. The control poles of the switching device Q1, the switching device Q2, the switching device Q3, and the switching device Q4 are all connected to the PWM output terminal of the main controller.

[0049] The filtering capacitor C1 is incorporated between the GND terminal and the DC bus connected to the switching device Q1, and the filtering capacitor C2 is incorporated between the GND terminal and the DC bus connected to the switching device Q4; each of the DC conversion modules further includes an output capacitor C3; the output capacitor C3 is incorporated between the free end of the inductor L1 and the free end of the inductor L2. By setting the filtering capacitor C1 and the filtering capacitor C2, pulses, spikes and other clutter from the DC bus can be filtered out.

[0050] Specifically, during the formation process, the two ends of the output capacitor C3 are respectively connected to the positive and negative electrodes of the series-connected lithium battery pack; by setting the output capacitor C3, pulses, spikes and other clutter output from the DC conversion module to the series-connected lithium battery pack can be filtered out.

[0051] In each of the DC conversion modules, the first-direction current from the DC bus connected to the positive electrode of the series-connected lithium battery pack can flow out from the GND terminal after passing through the switching device Q1, the inductor L1, the series-connected lithium battery pack, the inductor L2, and the switching device Q3 in sequence; the first-direction current can also flow in from the GND terminal, pass through the switching device Q2, the inductor L1, the series-connected lithium battery pack, the inductor L2, and the switching device Q4 in sequence, and then flow out back to the DC bus.

[0052] Moreover, the second-direction current from the DC bus connected to the negative electrode of the series-connected lithium battery pack and / or the series-connected lithium battery pack can flow out from the GND terminal after passing through the switching device Q4, the inductor L2, the series-connected lithium battery pack, the inductor L1, and the switching device Q2 in sequence; the second-direction current can also flow in from the GND terminal, pass through the switching device Q3, the inductor L1, the series-connected lithium battery pack, the inductor L2, and the switching device Q1 in sequence, and then flow out back to the DC bus.

[0053] In each of the DC conversion modules, the main controller is provided with PWM output terminals, generating a first PWM signal and a second PWM signal. The switching device Q1 and the switching device Q3 are controlled by the first PWM signal issued by the main controller, and the switching device Q2 and the switching device Q4 are controlled by the second PWM signal issued by the main controller. The first PWM signal and the second PWM signal are complementary.

[0054] Specifically, the first PWM signal is used to control the turn-on and turn-off of the switching device Q1 and the switching device Q3, and the second PWM signal is used to control the turn-on and turn-off of the switching device Q2 and the switching device Q4; more specifically, the main controller controls the on-time and off-time of the switching device Q1 and the switching device Q3 by controlling the duty cycle D1 of the first PWM signal, and thus can control the output voltage across the two poles of the series-connected lithium battery pack. Similarly, the main controller controls the on-time and off-time of the switching device Q2 and the switching device Q4 by controlling the duty cycle D2 of the second PWM signal, and thus can control the output voltage across the two poles of the series-connected lithium battery pack.

[0055] Among them, the first PWM signal and the second PWM signal are complementary, that is, the first PWM signal and the second PWM signal are inverse-phase signals to each other, and the duty cycle D1 + D2 = 1; in addition, there is a turn-on dead zone between the first PWM signal and the second PWM signal to avoid the direct connection of the switching device Q1, Q3 and the switching device Q2, Q4, which may cause the bus short circuit or the battery short circuit.

[0056] When the number of the DC conversion modules is n, there is a phase difference between the first PWM signals received by adjacent DC conversion modules, and there is also a phase difference between the second PWM signals received by adjacent DC conversion modules. The first PWM signals and the second PWM signals with different phases drive each DC conversion module to form a multi-phase interleaved parallel output structure, which is beneficial to improving the continuity of the output of this type of DC conversion module group and effectively reducing the output ripple of this type of DC conversion module group.

[0057] Further, the DC conversion module further includes a current sampling feedback module and a voltage sampling feedback module. Among them, both the current sampling feedback module and the voltage sampling feedback module are analog quantity sampling modules and A / D signal conversion modules integrated on the main controller. The current sampling feedback module is used to sample the output current i(t) of the inductor L1 or the inductor L2 passing through each DC conversion module and feedback it to the main controller. The voltage sampling feedback module is used to sample the output voltage v(t) output between the two poles of the series lithium battery pack and feedback it to the main controller. In this embodiment, the current sampling feedback module samples from the free end of the inductor L1 of each DC conversion module by its analog quantity sampling module, calculates the average value through the A / D signal conversion module, and inputs it to the digital signal processor of the main controller. The voltage sampling feedback module samples from both ends of the series lithium battery pack or between the free end of the inductor L1 and the free end of the inductor L2 by its analog quantity sampling module and inputs it to the digital signal processor of the main controller.

[0058] As Figure 3 shown, the specific control process is as follows:

[0059] In the frequency domain, after a reference voltage v ref (s) is given to the main controller, the reference voltage v ref (s) and the output voltage v out (s) between the two poles of the series lithium battery pack successively include:

[0060] A first PI controller, a second PI controller, and a controlled object. And a zero output duty cycle compensation link is provided between the second PI controller and the controlled object, and the reference voltage v ref (s) passes through a feedforward compensator and is compensated to between the second PI controller and the controlled object in a positive-phase comparison manner;

[0061] The transfer function of the first PI controller is

[0062] The transfer function of the second PI controller is

[0063] The transfer function of the controlled object is

[0064] The transfer function of the zero output duty cycle compensation link is D(s);

[0065] The transfer function of the feedforward compensator is

[0066] In the formula, K P1 and K P2 are both proportional link coefficients, K I1 and K I2 are both integral link coefficients, K ffis the adjustment coefficient of the feed-forward compensator, K ff has a value range of (0, 1);

[0067] V bus is the input voltage of the DC bus, R is the impedance when the load of the DC conversion module is a resistor, L is the sum of the inductances of inductor L1 and inductor L2, and C is the capacitance of output capacitor C3;

[0068] When the DC conversion module is symmetric, D(s) is always equal to 0.5.

[0069] Actually, the main controller can control the magnitude of the output voltage v out (s) by controlling the duty cycles of the first PWM signal and the second PWM signal; the reference voltage v ref (s) is a quantity artificially given according to the formation process requirements of the series lithium battery pack, which is used to affect the duty cycles of the first PWM signal and the second PWM signal, thereby controlling the magnitude of the output voltage v out (s).

[0070] After the output current i(t) is transformed into the frequency domain, it is fed back between the first PI controller and the second PI controller through an inner-loop feedback link;

[0071] The transfer function of the inner-loop feedback link is G h (s) = RCs + 1;

[0072] In the formula, R is the impedance when the load of the DC conversion module is a resistor, and C is the capacitance of output capacitor C3.

[0073] After the output voltage v(t) is transformed into the frequency domain, it is fed back to the front of the first PI controller through an outer-loop feedback link; the transfer function of the outer-loop feedback link is H(s), and H(s) is a unity feedback transfer function.

[0074] In this embodiment, only one main controller is provided for the DC conversion module, but the current sampling and feedback module of the main controller samples from each DC conversion module, and the main controller can respectively control the turning on or off of the switching devices Q1, Q2, Q3, and Q4 of each DC conversion module. Therefore, for each DC conversion module, it has an independent closed-loop control loop.

[0075] Specifically, the main controller is an MCU with PWM output function, such as a control circuit board based on a switching power supply control chip or a Digital Signal Processor (DSP); in this embodiment, the main controller is a control circuit board based on a digital signal processor, which has multiple PWM output terminals and has a feedback control input terminal, and the model of its digital signal processor is TMS320F28379D.

[0076] As Figure 1 shown, the DC conversion module in this embodiment is provided with four DC conversion modules, which are respectively called phase A, phase B, phase C, and phase D. At this time, there is a phase difference between the first PWM signals received by adjacent DC conversion modules, and there is also a phase difference between the second PWM signals received by adjacent DC conversion modules.

[0077] When this kind of DC conversion module is in use, there are the following situations:

[0078] 1. When charging the series lithium battery pack, the main control sends the first PWM signal to the switching device Q1 and the switching device Q3 to control the on and off of the switching device Q1 and the switching device Q3; at the same time, the main control sends the second PWM signal to the switching device Q2 and the switching device Q4 to control the on and off of the switching device Q2 and the switching device Q4. When the switching devices Q1 and Q3 are turned on, the first-direction current from the DC bus can flow through the switching device Q1, the inductor L1, the series lithium battery pack, the inductor L2, and the switching device Q3 in sequence, and then flow out from the GND terminal; when the switching devices Q1 and Q3 are turned off, the switching devices Q2 and Q4 are synchronously turned on and freewheel, and the current flows in from the GND terminal, passes through the switching device Q2, the inductor L1, the series lithium battery pack, the inductor L2, and the switching device Q4 in sequence, and then flows back to the DC bus. In both circuit states, the current flows into the series battery pack from the positive pole and flows out from the negative pole, so as to charge the series battery pack with positive voltage.

[0079] 2. When discharging the series lithium battery pack, the main control sends the first PWM signal to the switching device Q1 and the switching device Q3 to control the on and off of the switching device Q1 and the switching device Q3; at the same time, the main control sends the second PWM signal to the switching device Q2 and the switching device Q4 to control the on and off of the switching device Q2 and the switching device Q4. When the switching devices Q2 and Q3 are turned on, the second-direction current from the series lithium battery pack can flow through the switching device Q4, the inductor L2, the series lithium battery pack, the inductor L1, and the switching device Q2 in sequence, and then flow out from the GND terminal; when the switching devices Q2 and Q4 are turned off, the switching devices Q1 and Q3 are synchronously turned on and freewheel, and the current flows in from the GND terminal, passes through the switching device Q3, the inductor L2, the series lithium battery pack, the inductor L1, and the switching device Q1 in sequence, and then flows back to the DC bus. In both circuit states, the current flows into the series battery pack from the negative pole and flows out from the positive pole, so as to discharge the series battery pack with positive voltage, zero voltage or negative voltage.

[0080] 3. When placing the series-connected lithium battery pack, the main controller does not send any PWM signals to the switching devices Q1, Q2, Q3, and Q4. The circuit between the DC bus and the series-connected lithium battery pack is turned off, and the series-connected lithium battery pack is not charged or discharged.

[0081] In each of the above processes, by giving the reference voltage v ref (s) to the main controller, the duty cycles of the first PWM signal and the second PWM signal are controlled, and thus the output voltage applied between the two poles of the series-connected lithium battery pack can be controlled.

[0082] In this DC conversion module, each DC conversion module can be turned on simultaneously, or turned off simultaneously, or any number of them can be turned on alternately under the control of the main controller. Multiple DC conversion modules form a multi-phase interleaved parallel output structure, which is beneficial to improving the continuity of the output of this DC conversion module and increasing the gain range of the output of this DC conversion module, effectively reducing the output ripple of this DC conversion module.

[0083] In this embodiment, the switching devices Q1, Q2, Q3, and Q4 are power metal-oxide-semiconductor field-effect transistors (Power MOSFETs). Thus, the first poles of the switching devices Q1, Q2, Q3, and Q4 are drain electrodes, the second poles of the switching devices Q1, Q2, Q3, and Q4 are source electrodes, and the control poles of the switching devices Q1, Q2, Q3, and Q4 are gate electrodes.

[0084] Embodiment 2

[0085] A DC conversion module for converting electrical energy from a DC bus into electrical energy suitable for forming a series-connected lithium battery pack, including a main controller and at least one DC conversion module. The difference from Embodiment 1 is as follows:

[0086] The switching devices Q1, Q2, Q3, and Q4 are insulated gate bipolar transistors (Insulated Gate Bipolar Transistor, IGBT). Thus, the first poles of the switching devices Q1, Q2, Q3, and Q4 are collector electrodes, the second poles of the switching devices Q1, Q2, Q3, and Q4 are emitter electrodes, and the control poles of the switching devices Q1, Q2, Q3, and Q4 are gate electrodes.

[0087] Embodiment 3

[0088] Please refer to Figure 4, this embodiment provides a power supply for series formation of lithium batteries, which is used to provide formation electric energy for a series lithium battery pack. It includes an AC power grid, an AC / DC conversion module, and a DC bus. It also includes the DC conversion module group in Embodiment 1 or Embodiment 2.

[0089] Among them, the AC power grid can be taken from single-phase AC mains with a rated voltage of 220V or three-phase AC mains with a rated voltage of 380V; the AC / DC conversion module is a switching power supply based on switching devices, which is used to convert the AC mains provided by the AC power grid into direct current; the DC bus can be a copper bar with several connection terminals, or a busbar output port on the AC / DC conversion module.

[0090] The AC power grid, the AC / DC conversion module, the DC bus, the DC conversion module group, and the series lithium battery pack are connected in sequence.

[0091] Specifically, each phase wire of the AC power grid is correspondingly connected to the input end of the AC / DC conversion module. The DC bus is a copper bar with several connection terminals. The output end of the AC / DC conversion module is connected to the DC bus. The DC conversion module group leads out wires and connects them to the connection terminals of the DC bus.

[0092] For this power supply for series formation of lithium batteries, under the control of the main controller, each DC conversion module can be turned on simultaneously, or turned off simultaneously, or any number of them can be turned on alternately. Thus, each formation process flow of the series battery pack can be automatically realized. Multiple DC conversion modules form a multi-phase interleaved parallel output structure, which is beneficial to improving the continuity of the output of this DC conversion module group and effectively reducing the output ripple of this DC conversion module group.

[0093] The above embodiments are the preferred embodiments of the present invention. However, the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A control method for a DC conversion module, characterized in that, the DC conversion module includes a main control and at least one DC conversion module. The DC conversion module includes switching devices Q1, Q2, Q3, Q4, inductor L1, and inductor L2. The first pole of switching device Q1 is connected to the DC bus. The second pole of switching device Q1 is connected to one end of inductor L1. The other end of inductor L1 is connected to the positive pole of the series-connected lithium battery pack. The negative pole of the series-connected lithium battery pack is connected to one end of inductor L2. The other end of inductor L2 is connected to the first pole of switching device Q3. The second pole of switching device Q3 is connected to the GND terminal. The first pole of switching device Q4 is connected to the DC bus. The second pole of switching device Q4 is connected to the other end of inductor L2. The other end of inductor L1 is connected to the first pole of switching device Q2. The second pole of switching device Q2 is connected to the GND terminal. The control poles of switching devices Q1, Q2, Q3, and Q4 are all connected to the PWM output terminal of the main control. The specific method is as follows: By giving a reference voltage v ref (s) to the main controller, the duty cycles of the first PWM signal and the second PWM signal can be controlled, and thus the output voltage across the two poles of the series lithium battery pack can be controlled, achieving simultaneous on or off or alternating on of any number of n DC conversion modules; The first PWM signal is used to control the turning on and off of switching devices Q1 and Q3 in n DC conversion modules. The second PWM signal is used to control the turning on and off of switching devices Q2 and Q4 in n DC conversion modules. In the frequency domain, a reference voltage v is given to the main control ref (s). After that, the reference voltage v ref (s) and the output voltage v between the two poles of the series lithium battery pack out (s) successively include: A first PI controller, a second PI controller, and a controlled object, and a zero-output duty ratio compensation link is provided between the second PI controller and the controlled object, and the reference voltage v ref (s) passes through a feedforward compensator and is compensated to between the second PI controller and the controlled object in a positive-phase comparison manner; The transfer function of the first PI controller is The transfer function of the second PI controller is The transfer function of the controlled object is The transfer function of the zero-output duty cycle compensation link is D(s). The transfer function of the feedforward compensator is where K P1 and K P2 are both proportional link coefficients, K I1 and K I2 are both integral link coefficients, K ff is the adjustment coefficient of the feedforward compensator, and the value range of K ff is (0, 1); V bus is the input voltage of the DC bus, R is the impedance when the load of the DC conversion module is a resistor, L is the sum of the inductances of the inductor L1 and the inductor L2, and C is the capacitance of the output capacitor C3; When the DC conversion module is symmetric, D(s) is always equal to 0.

5.

2. The control method according to claim 1, characterized in that, Among the n DC conversion modules, there is a phase difference between the first PWM signals received by adjacent DC conversion modules, and there is also a phase difference between the second PWM signals received by adjacent DC conversion modules; the first PWM signals and the second PWM signals with different phases drive each DC conversion module to form a multi-phase interleaved parallel output structure.

3. The control method according to claim 1, characterized in that, After the output current i(t) is transformed into the frequency domain, it is fed back to between the first PI controller and the second PI controller through an inner-loop feedback link; the transfer function of the inner-loop feedback link is G h (s) = RCs + 1; wherein, R is the impedance when the load of the DC conversion module is a resistor, and C is the capacitance of the output capacitor C3.

4. The control method according to claim 1, characterized in that, After the output voltage v(t) is transformed to the frequency domain, it is fed back to before the first PI controller through an outer-loop feedback link. The transfer function of the outer-loop feedback link is H(s), and H(s) is a unit feedback transfer function.

5. The control method according to claim 1, characterized in that, The operating states of the series-connected lithium battery pack include charging, positive voltage discharging, zero voltage discharging, negative voltage discharging, and placement.

6. The control method according to claim 1, characterized in that, The charging input terminal of the DC conversion module is connected to the DC bus. The charging output terminal of the DC conversion module is connected to the two poles of the series-connected lithium battery pack according to the polarity. Under the control of the main control, each DC conversion module is turned on simultaneously, turned off simultaneously, or any number of them are turned on alternately.

7. The control method according to claim 1, characterized in that, The first-direction current from the DC bus passes through switching device Q1, inductor L1, the series-connected lithium battery pack, inductor L2, and switching device Q3 in sequence, and then flows out from the GND terminal, or flows in from the GND terminal, passes through switching device Q2, inductor L1, the series-connected lithium battery pack, inductor L2, and switching device Q4 in sequence, and then flows back to the DC bus, forming a positive voltage charging circuit for the series-connected lithium battery pack. The second-direction current from the DC bus and / or the series lithium battery pack sequentially passes through the switching device Q4, the inductor L2, the series lithium battery pack, the inductor L1, and the switching device Q2, and then flows out from the GND terminal, or flows in from the GND terminal, sequentially passes through the switching device Q3, the inductor L1, the series lithium battery pack, the inductor L2, and the switching device Q1, and then flows back to the DC bus, thereby forming a positive-voltage discharge loop, a zero-voltage discharge loop, or a negative-voltage discharge loop of the series lithium battery pack.

8. According to the control method described in claim 1, characterized in that the DC conversion module further includes a filter capacitor C1 and a filter capacitor C2. The filter capacitor C1 is connected between the GND terminal and the DC bus connected to the switching device Q1, and the filter capacitor C2 is connected between the GND terminal and the DC bus connected to the switching device Q4.

9. According to the control method described in claim 1, characterized in that the DC conversion module further includes an output capacitor C3, and the output capacitor C3 is connected in parallel across the positive and negative electrodes of the series lithium battery pack.

10. According to the control method described in claim 1, characterized in that the main control integrated current sampling feedback module and voltage sampling feedback module. The current sampling feedback module is used to sample the output current passing through the inductor L1 or inductor L2 of each DC conversion module, and the voltage sampling feedback module is used to sample the output voltage across the two poles of the series lithium battery pack.

Images