ISOP type two-stage converter for lithium battery formation and capacity grading and control method of ISOP type two-stage converter

Abstract

The invention discloses an ISOP type two-stage converter for formation and capacity grading of a lithium battery, and the converter comprises a pre-stage Buck circuit which is used for carrying out the preliminary step-down processing of an input voltage, and outputting a stable DC voltage through adjusting the duty ratio of a switching tube; the rear-stage LLC resonant converter is connected with the front-stage Buck circuit in series and comprises a plurality of resonant units which are connected in parallel in an interleaving manner, and each resonant unit comprises a half-bridge circuit, a resonant network, a high-frequency isolation transformer and a bidirectional full-bridge rectifying circuit; the control module outputs a control signal; the control signal adjusts the output voltage by changing the duty ratio of the preceding-stage Buck circuit, so that the LLC resonant converter works at the optimal resonance point. The device is suitable for being used in high-power battery formation and capacity grading occasions, has the characteristics of self-current-sharing and self-voltage-sharing, improves the power supply efficiency, and realizes wide-range voltage regulation.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial equipment monitoring and control systems, and in particular to an ISOP-type two-stage converter for lithium battery capacity conversion and a control method thereof. Background Art

[0002] With the rapid development of the new energy vehicle industry and battery technology, the demand for power lithium batteries continues to grow rapidly. Battery capacity division, as an important link in the production of lithium batteries, plays a key role in ensuring the performance of the battery. During the capacity division process, the battery needs to be repeatedly charged and discharged. However, the charging and discharging efficiency of traditional capacity division equipment is not high, resulting in a large amount of energy loss. Therefore, it is of great significance to study new high-efficiency battery capacity division DC-DC converters and their control methods.

[0003] The traditional Buck-Boost converter has low efficiency at high frequencies. It uses hard switching technology, which causes large losses in the switching process. In contrast, soft switching technology can achieve zero loss in the switching process, while suppressing the peak voltage during the switch-off process, thereby improving the efficiency and stability of the converter. However, existing soft switching technologies, such as phase-shifted full-bridge converters and variable-frequency LLC converters, have problems such as complex control, narrow voltage regulation range, and low efficiency.

[0004] Although the soft switching technology of the phase-shifted full-bridge converter can improve efficiency, its control is relatively complex and increases the large resonant inductance, which easily leads to the loss of duty cycle. Although the variable frequency LLC converter can achieve soft switching, its voltage regulation range is narrow, the efficiency is reduced when it deviates from the resonance point, and current equalization measures need to be taken when the output is staggered in parallel, which increases the complexity of control. Therefore, the existing technology has the contradiction of not being able to take into account efficiency, voltage regulation range and control simplicity in the application of high-power battery capacity. Summary of the invention

[0005] One of the purposes of the present invention is to provide an ISOP two-stage converter for battery capacity conversion, which is suitable for use in high-power battery capacity conversion occasions, has self-current and self-voltage characteristics, improves power supply efficiency, and realizes wide range voltage regulation.

[0006] Another object of the present invention is to provide a control method for an ISOP two-stage converter for battery capacity conversion, which is simpler than existing control schemes, realizes the bidirectional natural flow of energy, and improves the dynamic response speed and robustness of the system.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] Lithium battery capacity conversion using ISOP two-stage converter, including:

[0009] The front-stage Buck circuit is used to perform preliminary step-down processing on the input voltage and output a stable DC voltage by adjusting the duty cycle of the switch tube;

[0010] The rear-stage LLC resonant converter is connected in series with the front-stage Buck circuit and includes a plurality of resonant units connected in parallel. Each resonant unit includes a half-bridge circuit, a resonant network, a high-frequency isolation transformer and a bidirectional full-bridge rectifier circuit.

[0011] The control module outputs a control signal; the control signal adjusts the output voltage by changing the duty cycle of the front-stage Buck circuit, so that the LLC resonant converter operates at an optimal resonance point.

[0012] The above technical solution also includes a type III compensation network, which is used to compensate the feedback loop and adjust the frequency response characteristics through two zero-pole pairs and one origin pole.

[0013] In the above technical solution, the front-stage Buck circuit includes an input voltage Vin, a switch tube S 1 and S 2 、Inductance L b and output capacitor C b , switch tube S 1 The drain is connected to the positive terminal of the input voltage Vin, and the source is connected to the positive terminal of the input voltage Vin through the inductor L b Connect to the output capacitor C b The positive electrode of the switch tube S 2 The source is connected to the negative electrode of the input voltage Vin, and the drain is connected to the switch tube S 1 The source connection of the output capacitor C b The negative pole of the switch tube S 2 The source of and the negative electrode of the input voltage Vin.

[0014] In the above technical solution, the post-stage LLC resonant converter includes a bus capacitor C 1 , bus capacitance C 2 , switch tube S 3 , switch tube S 4 , switch tube S 5 , switch tube S 6 , resonant inductor L r1 , resonant inductor L r2 , resonant capacitor C r1 , resonant capacitor C r2 、Transformer T 1 、Transformer T 2 、Transformer T 3 , transformer T 4 , bidirectional full bridge circuit HS 1 , bidirectional full bridge circuit HS 2, bidirectional full bridge circuit HS 3 , bidirectional full bridge circuit HS 4 , output capacitor C out , battery V bat ; Among them, the bidirectional full-bridge circuit HS 1 , bidirectional full bridge circuit HS 2 , bidirectional full bridge circuit HS 3 and bidirectional full bridge circuit HS 4 Each of them consists of four switch tubes Q 1 , switch tube Q 2 , switch tube Q 3 And the switch tube Q 4 Composition, switch tube Q 1 Drain and switch tube Q 2 The drain is connected, and the intersection is the positive pole of the DC port; the switch tube Q 3 Source and switch tube Q 4 The source is connected, and the intersection is the negative pole of the DC port; the switch tube Q 1 Source and switch tube Q 3 The drain is connected, and the connection intersection is recorded as AC port A; the switch tube Q 2 Source and switch tube Q 4 Drain connection, the connection intersection is AC port B;

[0015] Bus capacitance C 2 Positive electrode and switch tube S 5 The drain connection, bus capacitor C 1 Negative electrode and switch tube S 6 The source connection of the switch tube S 5 The source and switch tube S 6 The LLC resonant network consists of a resonant inductor L r2 , resonant capacitor C r2 、Transformer T 3 The resonant inductor on the r2 One end of the switch tube S 5 The source and switch tube S 6 The drain junction is connected to the resonant inductor L r2 The other end of the transformer T 3 The primary positive electrode is connected to the resonant capacitor C r2 One end of the switch tube S 6 The source of the resonant capacitor C r2 The other end of the transformer T 4 The primary negative pole of the transformer is connected, and the excitation inductance on the transformer is connected in parallel to the transformer T 3 , T 4 On the transformer T 3 The primary negative pole of the transformer T 4The primary positive pole of the transformer T 3 Secondary positive pole and bidirectional full bridge circuit HS 3 The AC port A is connected to the transformer T 3 The secondary negative pole and the bidirectional full-bridge circuit HS 3 The AC port B is connected to the transformer T 4 Secondary positive pole and bidirectional full bridge circuit HS 4 The AC port A is connected to the transformer T 4 The secondary negative pole and the bidirectional full-bridge circuit HS 4 AC port B connection; bidirectional full bridge circuit HS 1 , bidirectional full bridge circuit HS 2 The DC port positive pole and output capacitor C out Positive connection, bidirectional full bridge circuit HS 1 , bidirectional full bridge circuit HS 2 The negative terminal of the DC port and the output capacitor C out Negative connection; output capacitor C out Positive electrode and battery V bat Positive connection, output capacitor C out Negative electrode and battery V bat Negative connection.

[0016] In the above technical solution, the type III compensation network includes an operational amplifier, capacitors C3, C4, C5 and resistors R1, R2 and R3. Resistor R1 is connected in parallel with capacitor C3 and resistor R2. One end of capacitor C3 and one end of resistor R1 are connected to the positive electrode of the output voltage. The other end of capacitor C3 is connected to resistor R2. The other end of resistor R1 and the other end of resistor R2 are connected to intersection 1. Intersection 1 is connected to the negative input terminal of the operational amplifier. Capacitor C4 is connected in parallel with capacitor C5 and resistor R3. One end of capacitor C4 and one end of resistor R3 are connected to the negative input terminal of the operational amplifier. The other end of capacitor C4 is connected to capacitor C5. The other end of resistor R3 and the other end of capacitor C5 are connected to intersection 2. Intersection 2 is connected to the output terminal of the operational amplifier.

[0017] In the above technical solution, the switch tube S 3 With bidirectional full bridge circuit HS 1 The switch tube Q 1 And the switch tube Q 4 , bidirectional full bridge circuit HS 2 The switch tube Q 1 And the switch tube Q 4 Share the same drive signal PWM1A; switch tube S 4 With bidirectional full bridge circuit HS 1 The switch tube Q 2 And the switch tube Q 3 , bidirectional full bridge circuit HS 2The switch tube Q 2 And the switch tube Q 3 Share the same drive signal PWM1B; switch tube S 5 With bidirectional full bridge circuit HS 3 The switch tube Q 1 And the switch tube Q 4 , bidirectional full bridge circuit HS 4 The switch tube Q 1 And the switch tube Q 4 Share the same drive signal PWM2A; switch tube S 5 With bidirectional full bridge circuit HS 3 The switch tube Q 2 And the switch tube Q 3 , bidirectional full bridge circuit HS 4 The switch tube Q 2 And the switch tube Q 3 Share the same driving signal PWM2B;

[0018] PWM1A and PWM1B are a set of complementary duty cycles of 50% and a frequency of f r The PWM signals, PWM2A and PWM2B, are a set of complementary PWM signals with a duty cycle of 50% and a frequency of f r The PWM signals of PWM1A and PWM2A, PWM1B and PWM2B are 90° out of phase with each other.

[0019] In the above technical solution, the secondary bidirectional full-bridge circuit and the primary half-bridge circuit in a single LLC resonant unit use the same set of driving signals.

[0020] The present application provides a control method for an ISOP-type two-stage converter for lithium battery capacity conversion, which is used to control an ISOP-type two-stage converter for lithium battery capacity conversion as described above, comprising:

[0021] The control module adopts double closed-loop control, in which the outer loop samples the output voltage V out and with the reference voltage V ref Comparison, generate voltage error signal V err , adjusting the duty cycle of the front-stage Buck circuit according to the voltage error signal to control the output voltage of the rear-stage LLC resonant converter;

[0022] The inner loop samples the inductor current I L And with the reference current I ref Compare and generate current error signal I err , according to the voltage error signal I err Generate a duty cycle to drive the front-stage Buck circuit, adjust the inductor current of the front-stage Buck circuit, and achieve efficient operation of the resonant converter at the optimal resonance point.

[0023] In the above technical solution, the control module determines the compensation network through the following steps:

[0024] Based on the extended describing function method, small signal modeling of the post-stage LLC resonant converter is performed, the transfer function is determined and a Bode diagram is drawn to determine the crossover frequency;

[0025] Set the crossover frequency to 1 / 5 or 1 / 10 of the switching frequency and determine the required gain and phase compensation;

[0026] The values ​​of the resistors R1 , R2 , R3 and the capacitors C3 , C4 , and C5 are calculated so that the gain and phase compensation requirements are met at the crossover frequency.

[0027] In the above technical solution, the K coefficient method is used to calculate the values ​​of the resistors R1, R2, R3 and the capacitors C3, C4, and C5, including:

[0028] Calculate the k factor, where PB is the required phase gain;

[0029] Calculate the two zero frequencies f z1 =f c / k,f z2 =f z1 , calculate the two pole frequencies f p1 =kf c , f p2 =f p1 ; where f c is the crossover frequency;

[0030] According to the zero frequency and pole frequency, calculate the capacitance C 3 , capacitor C 4 , capacitor C 5 , resistor R 1 , resistor R 2 , resistor R 3 , where:

[0031] resistance resistance capacitance ,capacitance capacitance

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This application achieves soft switching operation by fixing the LLC resonant converter at the resonant frequency point, maximizes power efficiency, and enhances the ability to resist load interference. At the same time, it adopts a structure in which the input is in series and the output is staggered in parallel to reduce output ripple. It has the characteristics of input self-voltage balancing and output self-current balancing, and does not require complex current balancing strategies, which simplifies control and is particularly suitable for high-power capacity-sharing applications. In addition, the dual-loop fixed-frequency control combined with the feedback compensation network greatly improves the dynamic response speed and system stability of the converter, and supports a wide range of voltage regulation. The Buck-LLC two-stage converter controls the half-bridge circuit and the bidirectional full-bridge circuit through the same drive signal to achieve the natural bidirectional flow of energy, simplify the switching of the charge and discharge modes, and is particularly suitable for small current charge and discharge operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FIG. 1 is a main circuit topology diagram of an ISOP-type two-stage converter for battery capacity conversion according to an embodiment of the present invention.

[0035] Figure 2 FIG. 1 is a schematic diagram of a bidirectional full-bridge circuit of an ISOP-type two-stage converter for battery capacity conversion according to an embodiment of the present invention.

[0036] Figure 3 FIG. 1 is a schematic diagram of an ISOP-type two-stage converter for battery capacity conversion according to an embodiment of the present invention.

[0037] Figure 4 1 is a simulation waveform diagram of the output current 0A-100A of the ISOP type two-stage converter for battery capacity conversion according to an embodiment of the present invention.

[0038] Figure 5 The simulated waveform of the output current 0.5A-0.5A of the ISOP two-stage converter for battery capacity conversion according to an embodiment of the present invention.

[0039] Figure 6 It is a waveform diagram of the driving signals PWM1A, PWM2A, PWM1B and PWM2B of the subsequent LLC resonant converter of the present invention.

[0040] Figure 7 When the parameters of the two-phase LLC resonant cavity in the present invention are inconsistent, in this case, the parameters of the resonant inductance are different, L r1 =64uH, L r2 =60uH, the first phase output current, the second phase output current and the total output current I out Simulation waveform. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Embodiment 1:

[0043] The present embodiment provides an ISOP two-stage converter for battery capacity conversion, which is suitable for use in high-power battery capacity conversion occasions, has self-current and self-voltage characteristics, improves power supply efficiency, and realizes wide range voltage regulation.

[0044] Specifically, the ISOP two-stage converter for battery capacity conversion includes a front-stage Buck circuit, which is used to perform preliminary voltage reduction processing on the input voltage and output a stable DC voltage by adjusting the duty cycle of the switch tube; a rear-stage LLC resonant converter, which is connected in series with the front-stage Buck circuit and includes a plurality of resonance units connected in parallel, each resonance unit includes a half-bridge circuit, a resonant network, a high-frequency isolation transformer and a bidirectional full-bridge rectifier circuit; a control module, which outputs a control signal; the control signal adjusts the output voltage by changing the duty cycle of the front-stage Buck circuit, so that the LLC resonant converter operates at the optimal resonance point.

[0045] The front-stage Buck circuit includes an input voltage Vin, a switch tube S 1 and S 2 、Inductance L b and output capacitor C b , switch tube S 1 The drain is connected to the positive terminal of the input voltage Vin, and the source is connected to the positive terminal of the input voltage Vin through the inductor L b Connect to the output capacitor C b The positive electrode of the switch tube S 2 The source is connected to the negative electrode of the input voltage Vin, and the drain is connected to the switch tube S 1 The source connection of the output capacitor C b The negative pole of the switch tube S 2 The source of and the negative electrode of the input voltage Vin.

[0046] In the on state, the switch tube S 1 The switch tube S is turned on. 2 Turn off, the input voltage Vin passes through the inductor L b Directly supply power to the load, the current in the inductor begins to increase and store energy. At this time, the output voltage passes through the inductor L b and capacitor C b After smoothing together, the output is sent to the load. In the off state, the switch tube S 1Turn off, switch S 2 On, inductance L b The current in the synchronous switch tube S cannot be stopped immediately. 2 Continue to flow to the load. At this time, the energy in the inductor begins to release, the inductor current gradually decreases, and the capacitor C b The power supply continues and the output voltage remains stable. The inductor current increases when the switch is turned on and decreases when the switch is turned off. By adjusting the duty cycle of the switch, the average current in the inductor can be controlled, and thus the output voltage can be controlled.

[0047] The front-stage Buck circuit is widely used in various power conversion occasions, especially in battery charging, regulated power supply and buck converter, which need to convert higher input voltage into lower stable output voltage. In battery capacity application, the front-stage Buck circuit provides a suitable input voltage for the rear-stage LLC resonant converter by adjusting the output voltage to achieve efficient power conversion and control.

[0048] The rear-stage LLC resonant converter is connected in series with the front-stage Buck circuit, and comprises a plurality of resonance units connected in parallel in an interlaced manner. Each resonance unit comprises a half-bridge circuit, a resonance network, a high-frequency isolation transformer and a bidirectional full-bridge rectifier circuit. The output voltage is adjusted by changing the duty cycle of the front-stage Buck circuit so that the rear-stage LLC resonant converter operates at the optimal resonance point.

[0049] The subsequent LLC resonant converter further adjusts and converts the input voltage provided by the previous Buck circuit to meet the requirements of the final load. Figure 1 , 2 As shown, including bus capacitance C 1 , bus capacitance C 2 , switch tube S 3 , switch tube S 4 , switch tube S 5 , switch tube S 6 , resonant inductor L r1 , resonant inductor L r2 , resonant capacitor C r1 , resonant capacitor C r2 、Transformer T 1 、Transformer T 2 、Transformer T 3 , transformer T 4 , bidirectional full bridge circuit HS 1 , bidirectional full bridge circuit HS 2 , bidirectional full bridge circuit HS 3 , bidirectional full bridge circuit HS 4 , output capacitor C out , battery V bat ; Four bidirectional full-bridge circuits HS1 , HS 2 , HS 3 and HS 4 Each of them consists of four switch tubes Q 1 , Q 2 , Q 3 and Q 4 Composition, switch tube Q 1 Drain and switch tube Q 2 The drain is connected, and the intersection is the positive pole of the DC port; the switch tube Q 3 Source and switch tube Q 4 The source is connected, and the intersection is the negative pole of the DC port; the switch tube Q 1 Source and switch tube Q 3 The drain is connected, and the connection intersection is recorded as AC port A; the switch tube Q 2 Source and switch tube Q 4 Drain connection, the connection intersection is AC port B;

[0050] Bus capacitance C 2 Positive electrode and switch tube S 5 The drain connection, bus capacitor C 1 Negative electrode and switch tube S 6 The source connection of the switch tube S 5 The source and switch tube S 6 The LLC resonant network consists of a resonant inductor L r2 , resonant capacitor C r2 、Transformer T 3 The resonant inductor on the r2 One end of the switch tube S 5 The source and switch tube S 6 The drain junction is connected to the resonant inductor L r2 The other end of the transformer T 3 The primary positive electrode is connected to the resonant capacitor C r2 One end of the switch tube S 6 The source of the resonant capacitor C r2 The other end of the transformer T 4 The primary negative pole of the transformer is connected, and the excitation inductance on the transformer is connected in parallel to the transformer T 3 , T 4 On the transformer T 3 The primary negative pole of the transformer T 4 The primary positive pole of the transformer T 3 Secondary positive pole and bidirectional full bridge circuit HS 3 The AC port A is connected to the transformer T 3 The secondary negative pole and the bidirectional full-bridge circuit HS 3 The AC port B is connected to the transformer T 4Secondary positive pole and bidirectional full bridge circuit HS 4 The AC port A is connected to the transformer T 4 The secondary negative pole and the bidirectional full-bridge circuit HS 4 AC port B connection; bidirectional full bridge circuit HS 1 , bidirectional full bridge circuit HS 2 The DC port positive pole and output capacitor C out Positive connection, bidirectional full bridge circuit HS 1 , bidirectional full bridge circuit HS 2 The negative terminal of the DC port and the output capacitor C out Negative connection; output capacitor C out Positive electrode and battery V bat Positive connection, output capacitor C out Negative electrode and battery V bat Negative connection.

[0051] The post-stage LLC resonant converter generates a high-frequency AC signal through a half-bridge circuit, driving the resonant network composed of a resonant inductor and a resonant capacitor to operate near the resonant frequency. The resonant network efficiently transfers the input energy to the high-frequency isolation transformer, which then couples the energy to the secondary and converts the high-frequency AC into DC through a bidirectional full-bridge rectifier circuit to provide a stable output voltage. By adjusting the switching frequency of the half-bridge circuit, the output voltage can be precisely controlled, and low-loss, high-efficiency energy conversion can be achieved using soft switching technology.

[0052] In addition, in battery capacity splitting applications, the rear LLC resonant converter can switch naturally between charging and discharging modes. By controlling the duty cycle of the front-stage Buck circuit and the operating frequency of the rear-stage LLC resonant converter, the natural flow of energy in both directions can be achieved, which can support the charging and discharging process of the battery at the same time, and can switch naturally between different modes to meet the needs of the battery capacity splitting system. The front-stage Buck circuit provides a stable input voltage, and the rear-stage LLC resonant converter further adjusts the voltage through the resonant network and transformer to achieve efficient output voltage control.

[0053] The front-stage Buck circuit works in conjunction with the rear-stage LLC resonant converter. The front-stage Buck circuit provides a voltage stabilization function to ensure that the rear-stage resonant converter can operate under a stable input voltage, thereby achieving efficient energy conversion and voltage regulation of the entire system.

[0054] Theoretically resonant inductance L r1 =L r2 , resonant capacitor C r1 =C r2 , define the initial resonant frequency: Switching tube S 3 , switch tube S4 , switch tube S 5 , switch tube S 6 , bidirectional full bridge circuit HS 1 , bidirectional full bridge circuit HS 1 , bidirectional full bridge circuit HS 2 , bidirectional full bridge circuit HS 3 , bidirectional full bridge circuit HS 4 The initial resonant frequency is f r However, in actual situations, electronic devices cannot be completely consistent and are affected by parasitic parameters. In this application, through theoretical design, the approximate resonant frequency point fr is calculated, and the frequency is increased or decreased point by point near this point. It is checked whether it is in a resonant state based on the waveform of the resonant current, or judged based on the efficiency of the system. When the system is in a resonant state and the efficiency is at the highest point, it is the actual resonant frequency, that is, it is necessary to keep the Buck output voltage at the initial resonant frequency f r Adjust the resonant frequency so that the output voltage of the power supply is close to V out maximum.

[0055] The switch tube S 3 , bidirectional full bridge circuit HS 1 The switch tube Q 1 And the switch tube Q 4 , bidirectional full bridge circuit HS 2 The switch tube Q 1 And the switch tube Q 4 Share the same drive signal PWM1A. Switch tube S 4 , bidirectional full bridge circuit HS 1 The switch tube Q 2 And the switch tube Q 3 , bidirectional full bridge circuit HS 2 The switch tube Q 2 And the switch tube Q 3 The switch tube S shares the same driving signal PWM1B. 5 , bidirectional full bridge circuit HS 3 The switch tube Q 1 And the switch tube Q 4 , bidirectional full bridge circuit HS 4 The switch tube Q 1 And the switch tube Q 4 Share the same drive signal PWM2A. Switch tube S 5 , bidirectional full bridge circuit HS 3 The switch tube Q 2 And the switch tube Q 3 , bidirectional full bridge circuit HS 4 The switch tube Q 2 And the switch tube Q 3Share the same drive signal PWM2B. PWM1A and PWM1B are a set of complementary duty cycles of 50% and a frequency of f r The PWM signals, PWM2A and PWM2B, are a set of complementary PWM signals with a duty cycle of 50% and a frequency of f r The PWM signals of PWM1A and PWM2A, PWM1B and PWM2B are 90° out of phase. This driving mode realizes synchronous rectification, which can make it possible for the LLC resonant converter to charge and discharge without switching the working state of the switch tubes on the primary and secondary sides. By changing the duty cycle of the Buck converter, the natural switching of the charge and discharge mode can be realized, and the energy can flow in both directions.

[0056] In this embodiment, the switch tube S 1 With switch tube S 2 Adopt SIC MOSFET, model IMZ120R220M1H, switch tube S 3 , switch tube S 4 , switch tube S 5 , switch tube S 6 The super junction Simosfet is used, model IPL60R160CFD7, and the bidirectional full-bridge circuit uses an ordinary Simos tube, model HYG019N06LS1C2.

[0057] The control module outputs a control signal for regulation, and adopts a dual closed-loop voltage and current regulation system. The output voltage of the rear-stage LLC resonant converter is the outer loop, and the inductor current of the front-stage Buck circuit is the inner loop. The control signal adjusts the output voltage of the Buck converter by changing the duty cycle of the Buck converter, keeping the resonant frequency of the LLC resonant converter unchanged at the optimal resonance point. At this time, the gain of the LLC remains unchanged, and the output voltage of the LLC converter is equal to the output voltage of the Buck converter multiplied by the gain.

[0058] Furthermore, a type III compensation network is used to improve the performance of the feedback circuit. At the same time, the PWM frequencies in the two-phase LLC resonant units are the same but the phases differ by 90°. The secondary bidirectional full-bridge circuit and the primary half-bridge circuit in a single LLC resonant unit use the same set of driving signals, thereby realizing an alternative synchronous rectification technology.

[0059] In this application, a type III compensator is used. The type III compensation network is used to compensate for the feedback signal. It has three poles and two zeros in total. The frequency response characteristics are adjusted through two zero-pole pairs and one origin pole, including the phase margin and gain of the system at the crossover frequency and the gain of the low-frequency band. This case uses the K coefficient method for calculation, and the result is more accurate. The two zero-pole pairs consist of a pair of conjugate zeros and a pair of conjugate poles. The root mean square of the frequency of the conjugate poles and the conjugate zeros is the set crossover frequency, which can enable the system to obtain the maximum phase improvement at the crossover frequency, and the maximum phase improvement can be +180°.

[0060] The conjugate zero is in the mid-low frequency band, which is used to increase the gain of the system in the mid-frequency band and increase the phase margin of the system at the crossover frequency. The conjugate pole is in the mid-high frequency band and is used to adjust the gain and phase. When the frequency of the conjugate pole is far away from the crossover frequency, the phase decay of the system is slower and the phase boost is greater. The role of the origin pole is to correct the gain value of the system at the crossover frequency, and at the same time it can increase the low-frequency gain of the system and reduce the steady-state error. The reasonable setting of two zero-pole pairs and one origin pole can ensure that the phase margin of the system continues to increase while maintaining the stability of the system, which helps to enhance the anti-interference ability of the system, improve the dynamic response speed, reduce the overshoot, and adapt to the high performance requirements in the field of chemical composition.

[0061] The phase margin of the type III compensation network is increased to more than 90 degrees. It consists of an operational amplifier, capacitor C 3 , capacitor C 4 , capacitor C 5 , resistor R 1 , resistor R 2 , resistor R 3 Composition. Resistor R 1 and capacitor C 3 , resistor R 2 In parallel, capacitor C 3 One end and resistor R 1 One end is connected to the positive electrode of the output voltage, capacitor C 3 The other end of the resistor R 2 Connected, resistor R 1 The other end of the resistor R 2 The other end is connected to intersection 1, which is connected to the negative input terminal of the operational amplifier. 4 and capacitor C 5 , resistor R 3 In parallel, capacitor C 4 One end and resistor R 3 One end is connected to the negative input terminal of the operational amplifier, and the capacitor C 4 The other end of the capacitor C 5 Connected, resistor R 3 The other end of the capacitor C5 The other end is connected to intersection 2, and intersection 2 is connected to the output end of the operational amplifier.

[0062] Embodiment 2:

[0063] See also Figure 3 The present application also provides a control method for an ISOP-type two-stage converter for lithium battery capacity conversion, which is used to control an ISOP-type two-stage converter for lithium battery capacity conversion as described above;

[0064] The method includes:

[0065] A dual closed-loop control is used, in which the outer loop samples the output voltage V out and with the reference voltage V ref Comparison, generate voltage error signal V err , adjusting the duty cycle of the front-stage Buck circuit according to the voltage error signal to control the output voltage of the rear-stage LLC resonant converter;

[0066] The inner loop samples the inductor current I L And with the reference current I ref Compare and generate current error signal I err , according to the voltage error signal I err Generate a duty cycle to drive the front-stage Buck circuit, adjust the inductor current of the front-stage Buck circuit, and achieve efficient operation of the resonant converter at the optimal resonance point.

[0067] Specifically, the outer loop has an output voltage V out Sampling, output voltage V out After the compensation network and the reference voltage V ref The error voltage V err , V err =V ref -V out . Error voltage V err Transmitted to the voltage PI controller, Among them I ref (t) represents the inductor reference current at time t, V err (t) represents the error voltage at time t, K pv is the proportional coefficient of the voltage PI controller, K iv is the integral coefficient of the voltage PI controller. In this implementation case, K pv The value of K is 2, iv The value of is 30.

[0068] The inner loop is the voltage to the inductor current I L To sample the inductor current I L With reference voltage I ref The error current I is obtained by subtractingerr , I err =I ref -I out . Error current I err Transmitted to the current PI controller, Where D(t) represents the inductor reference current at time t, I err (t) represents the error current at time t, K pi is the proportional coefficient of the voltage PI controller, K ii is the integral coefficient of the voltage PI controller. In this implementation case, K pi The value of K is 0.1, ii The value of is 50.

[0069] Furthermore, D(t) is fed into the PWM generator to generate a duty cycle of D(t) and a frequency of f r The complementary PWM1, PWM2, and PWM1 are used to drive the switch tube S 1 PWM2 is used to drive the switch tube S 2 .

[0070] Furthermore, the compensation network is often used to adjust the crossover frequency of the system to ensure that the system has appropriate gain and phase characteristics at this frequency, thereby improving the dynamic response and stability of the system. The control module determines the compensation network through the following steps:

[0071] Based on the extended description function method (EDA), the small signal modeling of the post-stage LLC resonant converter is performed, the transfer function H(s) is determined and the Bode diagram is drawn to determine the crossover frequency; the crossover frequency of the system is determined based on the Bode diagram, and the crossover frequency is generally taken as 1 / 5 or 1 / 10 of the switching frequency. In this application, the switching frequency is 100kHz, so the crossover frequency is taken as 10kHz. According to the phase gain G obtained from the switching frequency on the Bode diagram fc and phase PS, the design indicators of this system solution are: at the crossover frequency, the open-loop gain slope should be designed to be -1, the open-loop gain phase margin should be greater than 30°, and the gain margin GM should be no less than 10dB;

[0072] Set the crossover frequency to 1 / 5 or 1 / 10 of the switching frequency, and determine the required gain and phase compensation; determine the expected phase margin PM, and determine that the expected open-loop gain GM is not less than 10dB, then the required phase of the compensator is: PB = PM-PS + 90deg. Compensator gain:

[0073] Calculate the values ​​of resistors R1, R2, R3 and capacitors C3, C4, and C5 so that the gain and phase compensation requirements are met at the crossover frequency, including:

[0074] The K factor is calculated using the K coefficient method, where PB is the required phase gain;

[0075] Calculate the two zero frequencies f z1 =f c / k,f z2 =f z1 , calculate the two pole frequencies f p1 =kf c , f p2 =f p1 ; where f c is the crossover frequency;

[0076] Zero frequency f z1 、f z2 The frequency of the first and second zeros in the compensation network. The zero frequency refers to the frequency point where the gain of the transfer function begins to increase. Zeros are usually used to increase the phase margin of the system within a specific frequency range, thereby improving the stability of the system. p1 、f p2 The pole frequency is the frequency of the first and second poles in the compensation network. The pole frequency refers to the frequency point where the gain of the transfer function begins to decrease. The pole is used to limit the impact of high-frequency noise and control the gain to avoid system instability at high frequencies.

[0077] According to the zero frequency and pole frequency, calculate the capacitance C 3 , capacitor C 4 , capacitor C 5 , resistor R 1 , resistor R 2 , resistor R 3 , where:

[0078] resistance resistance capacitance ,capacitance capacitance

[0079] The setting of the Type III compensator takes into account the performance of the three frequency bands of low, medium and high. The gain at the low frequency is large enough to reduce the steady-state error. In the medium frequency band, choosing a suitable crossover frequency can keep the system away from the influence of switching noise. The slope at the crossover frequency is -1, that is, the amplitude of the open-loop gain decreases at a rate of -20dB / decade as the frequency increases. This ensures that the system has sufficient amplitude margin and phase margin, and can also optimize the dynamic performance of the system, including parameters such as adjustment time, peak time and overshoot. This slope characteristic reflects the responsiveness of the system in the frequency domain, and can better balance fast response and suppress oscillation, thereby improving the overall performance and robustness of the system. The gain is low enough in the high frequency band to reduce the impact of high-frequency noise on the system.

[0080] Figure 4 This is the simulated waveform of the system output current rising from 0A to 100A. It can be seen that the system responds quickly, has no overshoot, and the rise time is less than 2ms, which is much smaller than the industry standard of less than 20ms in the field of chemical composition. Figure 5 The output current waveform when switching from low current charging to low current discharging. It can be seen from the figure that the adjustment time is short, the natural switching of current charging and discharging mode can be realized, and the high-precision control of low current charging and discharging can be achieved; Figure 6 The waveform diagram of the four-way driving signals PWM1A, PWM1B, PWM2A, and PWM2B of the subsequent LLC resonant converter. The LLC fixed frequency used in this embodiment is 100kHz; Figure 7 When there is a large deviation between the parameters of the first-phase LLC resonant unit and the second-phase LLC resonant unit, from top to bottom are the simulation waveforms of the first-phase output current, the second-phase output current and the total output current. It can be seen that when there is a large difference in the system parameters, the average current difference of each phase is small, and it has a self-current balancing characteristic, but some output current ripple will be increased.

[0081] This application combines the front-stage Buck circuit with the rear-stage LLC resonant converter, adopts dual closed-loop control and type III compensation network, fixed at the resonant frequency point, the power supply efficiency is maximized, and the anti-load interference ability is strong. It realizes efficient and stable voltage conversion and precise output control, which is particularly suitable for battery capacity division system. Through the resonance mode and soft switching technology, the switching loss is significantly reduced, the system efficiency is improved, and the two-way natural flow of energy is supported at the same time, ensuring smooth switching between charging and discharging modes, and has a wide range of voltage regulation capabilities, which can adapt to different application requirements. The rear-stage LLC resonant converter adopts a structure of input series and output staggered parallel connection, which effectively reduces the output ripple, has the characteristics of input self-equalizing voltage and output self-equalizing current, and no current equalization strategy needs to be implemented. The control is simpler and more suitable for high-power occasions of capacity division.

[0082] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. ISOP type two-stage converter for lithium battery capacity conversion, characterized in that: include: The front-stage Buck circuit is used to perform preliminary step-down processing on the input voltage and output a stable DC voltage by adjusting the duty cycle of the switch tube; The rear-stage LLC resonant converter is connected in series with the front-stage Buck circuit and includes a plurality of resonant units connected in parallel. Each resonant unit includes a half-bridge circuit, a resonant network, a high-frequency isolation transformer and a bidirectional full-bridge rectifier circuit. The control module outputs a control signal; the control signal adjusts the output voltage by changing the duty cycle of the front-stage Buck circuit, so that the LLC resonant converter operates at an optimal resonance point.

2. The ISOP two-stage converter for lithium battery capacity conversion according to claim 1, characterized in that: The system also includes a type III compensation network, which is used to compensate the feedback loop and adjust the frequency response characteristics of the system through two zero-pole pairs and an origin pole.

3. The ISOP two-stage converter for lithium battery capacity conversion according to claim 1, characterized in that: The front-stage Buck circuit includes an input voltage Vin, switch tubes S1 and S2, and an inductor L b and output capacitor C b The drain of the switch tube S1 is connected to the positive electrode of the input voltage Vin, and the source is connected to the positive electrode of the input voltage Vin through the inductor L b Connect to the output capacitor C b The positive electrode of the switch tube S2 is connected to the negative electrode of the input voltage Vin, and the drain is connected to the source of the switch tube S1. The output capacitor C b The negative electrode of is connected to the source of the switch tube S2 and the negative electrode of the input voltage Vin.

4. The ISOP two-stage converter for lithium battery capacity conversion according to claim 1, characterized in that: The post-stage LLC resonant converter includes a bus capacitor C1, a bus capacitor C2, a switch tube S3, a switch tube S4, a switch tube S5, a switch tube S6, a resonant inductor L r1 , resonant inductor L r2 , resonant capacitor C r1 , resonant capacitor C r2 , transformer T1, transformer T2, transformer T3, transformer T4, bidirectional full-bridge circuit HS1, bidirectional full-bridge circuit HS2, bidirectional full-bridge circuit HS3, bidirectional full-bridge circuit HS4, output capacitor C out , battery V bat ; Wherein the bidirectional full-bridge circuit HS1, the bidirectional full-bridge circuit HS2, the bidirectional full-bridge circuit HS3 and the bidirectional full-bridge circuit HS4 are respectively composed of four switch tubes Q1, switch tube Q2, switch tube Q3 and switch tube Q4, the drain of switch tube Q1 is connected to the drain of switch tube Q2, and the connection intersection is the positive pole of the DC port; the source of switch tube Q3 is connected to the source of switch tube Q4, and the connection intersection is the negative pole of the DC port; the source of switch tube Q1 is connected to the drain of switch tube Q3, and the connection intersection is recorded as AC port A; the source of switch tube Q2 is connected to the drain of switch tube Q4, and the connection intersection is AC port B; The positive electrode of bus capacitor C2 is connected to the drain of switch tube S5, the negative electrode of bus capacitor C1 is connected to the source of switch tube S6, the source of switch tube S5 is connected to the drain of switch tube S6, and the LLC resonant network is composed of resonant inductor L r2 , resonant capacitor C r2 , the resonant inductor on the transformer T3 is connected in series, and the resonant inductor L r2 One end of is connected to the intersection of the source of the switch tube S5 and the drain of the switch tube S6, and the resonant inductor L r2 The other end is connected to the primary positive electrode of transformer T3, and the resonant capacitor C r2 One end of the resonant capacitor C is connected to the source of the switch tube S6. r2 The other end is connected to the primary negative pole of transformer T4, the excitation inductance on the transformer is connected in parallel to transformers T3 and T4, the primary negative pole of transformer T3 is connected to the primary positive pole of transformer T4; the secondary positive pole of transformer T3 is connected to the AC port A of the bidirectional full-bridge circuit HS3, and the secondary negative pole of transformer T3 is connected to the AC port B of the bidirectional full-bridge circuit HS3; the secondary positive pole of transformer T4 is connected to the AC port A of the bidirectional full-bridge circuit HS4, and the secondary negative pole of transformer T4 is connected to the AC port B of the bidirectional full-bridge circuit HS4; the DC port positive poles of the bidirectional full-bridge circuit HS1 and the bidirectional full-bridge circuit HS2 are connected to the output capacitor C out The positive electrode is connected to the negative electrode of the DC port of the bidirectional full-bridge circuit HS1 and the output capacitor C out Negative connection; output capacitor C out Positive electrode and battery V bat Positive connection, output capacitor C out Negative electrode and battery V bat Negative connection.

5. The ISOP two-stage converter for lithium battery capacity conversion according to claim 2, characterized in that: The III-type compensation network includes an operational amplifier, capacitors C3, C4, C5, and resistors R1, R2, and R3. Resistor R1 is connected in parallel with capacitor C3 and resistor R2. One end of capacitor C3 and one end of resistor R1 are connected to the positive electrode of the output voltage. The other end of capacitor C3 is connected to resistor R2. The other end of resistor R1 and the other end of resistor R2 are connected to intersection 1. Intersection 1 is connected to the negative input end of the operational amplifier. Capacitor C4 is connected in parallel with capacitor C5 and resistor R3. One end of capacitor C4 and one end of resistor R3 are connected to the negative input end of the operational amplifier. The other end of capacitor C4 is connected to capacitor C5. The other end of resistor R3 and the other end of capacitor C5 are connected to intersection 2. Intersection 2 is connected to the output end of the operational amplifier.

6. The ISOP two-stage converter for lithium battery capacity conversion according to claim 4, characterized in that: The switch tube S3 shares the same drive signal PWM1A with the switch tubes Q1 and Q4 in the bidirectional full-bridge circuit HS1, and the switch tubes Q1 and Q4 in the bidirectional full-bridge circuit HS2; the switch tube S4 shares the same drive signal PWM1B with the switch tubes Q2 and Q3 in the bidirectional full-bridge circuit HS1, and the switch tubes Q2 and Q3 in the bidirectional full-bridge circuit HS2; the switch tube S5 shares the same drive signal PWM2A with the switch tubes Q1 and Q4 in the bidirectional full-bridge circuit HS3, and the switch tubes Q1 and Q4 in the bidirectional full-bridge circuit HS4; the switch tube S5 shares the same drive signal PWM2B with the switch tubes Q2 and Q3 in the bidirectional full-bridge circuit HS3, and the switch tubes Q2 and Q3 in the bidirectional full-bridge circuit HS4; PWM1A and PWM1B are a set of complementary duty cycles of 50% and a frequency of f r The PWM signals, PWM2A and PWM2B, are a set of complementary PWM signals with a duty cycle of 50% and a frequency of f r The PWM signals of PWM1A and PWM2A, PWM1B and PWM2B are 90° out of phase with each other.

7. The ISOP two-stage converter for lithium battery capacity conversion according to claim 6, characterized in that: The secondary bidirectional full-bridge circuit and the primary half-bridge circuit in a single LLC resonant unit use the same set of driving signals.

8. A control method for an ISOP type two-stage converter for lithium battery capacity conversion, characterized in that: Used to control an ISOP type two-stage converter for lithium battery capacity conversion as described in any one of claims 1 to 7; comprising: The control module adopts double closed-loop control, in which the outer loop samples the output voltage V out and with the reference voltage V ref Comparison, generate voltage error signal V err , adjusting the duty cycle of the front-stage Buck circuit according to the voltage error signal to control the output voltage of the rear-stage LLC resonant converter; The inner loop samples the inductor current I L And with the reference current I ref Compare and generate current error signal I err , according to the voltage error signal I err Generate a duty cycle to drive the front-stage Buck circuit, adjust the inductor current of the front-stage Buck circuit, and achieve efficient operation of the resonant converter at the optimal resonance point.

9. A control method for an ISOP type two-stage converter for lithium battery capacity conversion as claimed in claim 8, characterized in that: The control module determines the compensation network by the following steps: Based on the extended describing function method, small signal modeling of the post-stage LLC resonant converter is performed, the transfer function is determined and a Bode diagram is drawn to determine the crossover frequency; Set the crossover frequency to 1 / 5 or 1 / 10 of the switching frequency and determine the required gain and phase compensation; The values ​​of the resistors R1 , R2 , R3 and the capacitors C3 , C4 , and C5 are calculated so that the gain and phase compensation requirements are met at the crossover frequency.

10. A control method for an ISOP type two-stage converter for lithium battery capacity conversion as claimed in claim 9, characterized in that: Calculate the values ​​of resistors R1, R2, R3 and capacitors C3, C4, and C5, including: The K factor is calculated using the K coefficient method, where PB is the required phase gain; Calculate the two zero frequencies f z1 =f c / k,f z2 =f z1 , calculate the two pole frequencies f p1 =kf c , f p2 =f p1 ; where f c is the crossover frequency; According to the zero frequency and the pole frequency, the values ​​of capacitor C3, capacitor C4, capacitor C5, resistor R1, resistor R2, and resistor R3 are calculated, where: resistance resistance capacitance ,capacitance capacitance

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