Wide-voltage-range resonant inductor pre-energy-storage type LCL converter for elevator

Abstract

The invention relates to the technical field of elevator equipment, in particular to a wide-voltage-range resonant inductor pre-energy-storage type LCL converter for an elevator, which comprises a direct-current power supply U1, a first voltage stabilizing capacitor C1, a second voltage stabilizing capacitor C2, a resonant energy storage inductor L1, a resonant capacitor C3, a first bridge arm, a second bridge arm, a transformer T, an inverter circuit and a load R1, the inductance energy storage stage is added before the resonance stage, so that the gain range is effectively improved; by multiplexing the resonant energy storage inductor L1, the first bridge arm and the second bridge arm, high power density and high efficiency are achieved under the condition of not additionally arranging electrical components or additional circuits, the size of the converter is reduced, and the converter is suitable for an elevator energy feedback system; by arranging the transformer T, the input end and the output end are isolated, and the safety is improved; during working, a symmetrical working mode of an upper half cycle and a lower half cycle is adopted, the situation that the difference of currents flowing through the first switching tube S1, the second switching tube S2, the third switching tube S3 and the fourth switching tube is large is prevented, and the device is suitable for long-term operation.

Description

Technical Field

[0001] The present invention relates to the technical field of elevator equipment, and in particular to a wide voltage range resonant inductor pre-energy storage type LCL converter for elevators. Background Art

[0002] Resonant converters are widely used in various fields due to their good soft switching characteristics, but traditional resonant converters used in elevator energy feedback systems have the following problems: 1) When the energy storage battery is discharged more thoroughly in the energy feedback state, its terminal voltage variation range is extremely wide. In order to ensure that the voltage fluctuation of the inverter DC bus is within an acceptable range, the converter between the energy storage battery and the inverter DC bus is required to have a wide voltage operating range characteristic; 2) Due to the limitations of the elevator installation space, the converter is required to have a small size and high power density; 3) In order to maximize the storage and feedback of energy and reduce the need for equipment heat dissipation, the converter is required to have high efficiency within a wide voltage range.

[0003] At present, many studies have focused on how to broaden the gain range of resonant converters and achieve high efficiency in the full range. The main solutions adopted include: 1. Boost circuit and LLC cascade scheme (Source: X. Sun, J. Qiu, X. Li, B. Wang, L. Wangand X. Li, "An improved wide input voltage buck-boost + LLC cascaded converter," in Proc. 2015 IEEE Energy Convers. Congr. Expo., 2015, pp. 1473-1478.) The Boost+LLC combined resonant converter adopts the Boost and LLC cascade form in the case of wide DC gain. The Boost converter converts the wide input voltage into a constant or narrow range of intermediate bus voltage, which is connected to the LLC converter, so that the LLC circuit can operate near the resonant frequency point. The system voltage gain can be adjusted by controlling the duty cycle of the boost converter. The input voltage is first processed by the front-stage Buck-Boost circuit, and then further processed by the rear-stage LLC circuit. This two-stage gain mode effectively widens the voltage gain range of the resonant converter. The Boost cascade LLC converter has the advantages of simple control strategy and easy implementation.

[0004] Disadvantages: Only some switches are reused in the circuit, and the key inductor is not reused, which makes this solution larger in size and difficult to further improve its efficiency.

[0005] 2. Boost+Flyback combination circuit solution (Source: X. Lin, J. Xu, X. Zhou, and G.Zhou, "Zero-voltage zero-current switching DC-DC converter with high step-upand high efficiency," Electron. Lett., vol. 52, no. 14, pp. 1250-1252, 7.2016.) The combination mode of the Boost circuit and the Flyback circuit, the input voltage first passes through the Boost circuit and then passes through the Flyback circuit, which effectively widens the gain range. The Boost+Flyback combination circuit has a wide gain range by adding a flyback unit and a dual voltage unit to a soft switching CCM boost converter (a soft switching continuous conduction mode (CCM) boost converter, a boost unit and an equivalent boost unit connected in series).

[0006] Disadvantages: In the Boost+Flyback combination circuit, although the Boost inductor and the Flyback primary inductor are reused, there is no isolation between the input and output ends.

[0007] 3. Hybrid modulation scheme combining pulse frequency modulation and pulse width modulation (Source: H. Park and J.Jung, "PWM and PFM Hybrid Control Method for LLC Resonant Converters in High Switching Frequency Operation," IEEE Trans. Ind. Electron., vol. 64, no. 1, pp. 253-263, Jan. 2017.) When the LLC resonant converter is under high voltage gain, the circuit operates in pulse frequency modulation mode; when the LLC resonant converter is under low voltage gain, the maximum switching frequency is limited and the circuit enters pulse width modulation mode, thus achieving a wider gain range.

[0008] Disadvantages: In order to obtain high gain, the switching frequency is inevitably much smaller than the resonant frequency, resulting in decreased efficiency.

[0009] 4. A combination of asymmetric pulse width modulation, pulse frequency modulation and symmetric duty cycle pulse width modulation (Source: F. Xingtian, W. Manman, T. Yuanyuan and S. Kang, "Self-adaptation loadchange control strategy for three-phase staggered parallel LLC resonantconverter," IET Trans. Power Electron., vol. 11, no. 14, pp. 2338-2345, 27 112018.) Three different modulation schemes are used in the half-bridge LLC to provide different ranges of voltage gain. There are three states of voltage gain modes: high, medium, and low, achieving a wider voltage gain range.

[0010] Disadvantages: Due to the large DC bias in the excitation current, the transformer may become saturated or larger in size.

[0011] 5. Boost-PWM controlled half-bridge LLC scheme (Source: Cho, Y. Kim, G. Moon: A Half-Bridge LLC Resonant Converter Adopting Boost PWM Control Scheme for Hold-UpState Operation[J]. IEEE Transactions on Power Electronics, 2014, 29(2): 841-850.) In normal operation, the converter is exactly the same as the traditional half-bridge LLC resonant converter. In high-gain mode, the resonant capacitor pre-charges the resonant inductor, and the auxiliary switch is turned off to transfer energy to the secondary side, which can effectively improve the voltage gain.

[0012] Disadvantages: The resonant capacitor is charged with energy for the resonant inductor through the auxiliary switch, and the range of gain improvement is limited. And because the upper and lower switches of the converter work asymmetrically, energy is only transferred to the secondary side in half a cycle, the device utilization rate is low, and the peak current of the secondary rectifier diode is four times that of normal operation. In addition, the current flowing through the upper and lower switches is quite different, which is not suitable for long-term operation.

[0013] 6. Boost+TER (three-element resonance) + Flyback structure (Source: Yuan Y, Lai L, Wu Q, et al. An Integrated Boost- LC -Resonant-Flyback Multimode Converter for Battery Charger Applications[J]. IEEE Transactions on Industrial Electronics, 2021, 68(12): 12196–12205.) The inductor is charged through the inherent bridge arm switch to avoid adding additional switching tubes. This structure solves the contradiction between the gain range and efficiency improvement of the traditional resonant converter to a certain extent and provides a wider voltage gain.

[0014] Disadvantages: Due to the introduction of the flyback mode, the following problems still exist when it is applied to elevator energy feedback scenarios: 1) The addition of a secondary transformer increases the volume, which does not meet the requirements for high power density and small volume; 2) An RCD clamping circuit needs to be set, resulting in increased losses.

[0015] The above-mentioned existing solutions limit the improvement of the efficiency and power density of the above-mentioned resonant converter due to the increase of the front-stage topology or the introduction of additional circuits, and also increase the complexity of the topology and control. As a result, the existing resonant converter has problems such as large size, low power density, low efficiency, no isolation between the input and output ends, and cannot operate for a long time when achieving a wide voltage gain. It is difficult to apply it to the scenario of the energy feedback system of the elevator. Therefore, it is necessary to propose a new type of resonant converter to solve the above-mentioned technical problems. Summary of the invention

[0016] The object of the present invention is to provide a wide voltage range resonant inductor pre-storage type LCL converter for elevators, which has the advantages of small size, high power density, high efficiency, isolation between input and output ends, and long-term operation.

[0017] The technical solution adopted by the present invention to solve the technical problem is: a wide voltage range resonant inductor pre-energy storage type LCL converter for elevators, including a DC power supply U1, a first voltage stabilizing capacitor C1, a second voltage stabilizing capacitor C2, a resonant energy storage inductor L1, a resonant capacitor C3, a first bridge arm, a second bridge arm, a transformer T, an inverter circuit and a load R1; One end of the first voltage-stabilizing capacitor C1 is connected to one end of the second voltage-stabilizing capacitor C2, the other end of the first voltage-stabilizing capacitor C1 is connected to the positive electrode of the DC power supply U1, and the other end of the second voltage-stabilizing capacitor C2 is connected to the negative electrode of the DC power supply U1; The first bridge arm includes a first switch tube S1, a third switch tube S3, a first body diode D11 and a third body diode D31; the source of the first switch tube S1 is connected to the negative electrode of the DC power supply U1, the drain of the first switch tube S1 is connected to the source of the third switch tube S3, and the drain of the third switch tube S3 is connected to the positive electrode of the DC power supply U1; the anode of the first body diode D11 is connected to the source of the first switch tube S1, and the cathode of the first body diode D11 is connected to the drain of the first switch tube S1; the anode of the third body diode D31 is connected to the source of the third switch tube S3, and the cathode of the third body diode D31 is connected to the drain of the third switch tube S3; The second bridge arm includes a second switch tube S2, a fourth switch tube S4, a second body diode D21 and a fourth body diode D41; the source of the second switch tube S2 is connected to the negative electrode of the DC power supply U1, the drain of the second switch tube S2 is connected to the source of the fourth switch tube S4, and the drain of the fourth switch tube S4 is connected to the positive electrode of the DC power supply U1; the anode of the second body diode D21 is connected to the source of the second switch tube S2, and the cathode of the second body diode D21 is connected to the drain of the second switch tube S2; the anode of the fourth body diode D41 is connected to the source of the fourth switch tube S4, and the cathode of the fourth body diode D41 is connected to the drain of the fourth switch tube S4; The gates of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 are connected to an external control circuit to control the on and off of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4; The primary side of the transformer T is provided with a leakage inductor L2 and a primary coil L3, and the secondary side of the transformer T is provided with a secondary coil; one end of the resonant energy storage inductor L1 is connected to the connection line between the first voltage stabilizing capacitor C1 and the second voltage stabilizing capacitor C2, and the other end of the resonant energy storage inductor L1 is connected to the connection line between the first switch tube S1 and the third switch tube S3; one end of the leakage inductor L2 is connected to the connection line between the first switch tube S1 and the third switch tube S3, and the other end of the leakage inductor L2 is connected to one end of the primary coil L3; the other end of the primary coil L3 is connected to the connection line between the second switch tube S2 and the fourth switch tube S4; the resonant capacitor C3 is connected in parallel to the series circuit composed of the leakage inductor L2 and the primary coil L3; the secondary coil of the transformer T is connected to the load R1 through an inverter circuit, and the inverter circuit is used to convert the alternating current output by the secondary coil of the transformer T into direct current.

[0018] The working principle of the present invention is as follows: The converter has two working modes, low gain mode and high gain mode, when in use. The external control circuit switches the working mode of the converter by controlling whether the first switch tube S1 and the third switch tube S3 of the first bridge arm participate in the work. When the first bridge arm does not participate in the work, the converter switches to the low gain mode. When the converter is in low gain mode, the converter is a half-bridge LCL converter. The external control circuit uses a pulse width modulation method (PWM) to alternately turn on the second switch tube S2 and the fourth switch tube S4, so that the primary coil L3 of the transformer T generates alternating current. The control method and gain characteristics of the converter in low gain mode are the same as those of the existing half-bridge LCL converter.

[0019] When the converter is in high gain mode, the converter is a full-bridge LCL converter. The external control circuit uses a pulse width modulation method (PWM) to control the on and off time of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4. In the first half cycle, the first switch tube S1 and the second switch tube S2 are turned on and off in sequence, and in the second half cycle, the third switch tube S3 and the fourth switch tube S4 are turned on and off in sequence, so that when the converter is in high gain mode, each half cycle switches in sequence between the four working stages of the inductor energy storage stage, the LC resonance stage, the LCL resonance stage, and the dead zone stage; In the inductor energy storage stage, the first switch tube S1 is turned on in the first half cycle, and the third switch tube S3 is turned on in the second half cycle. At this time, the DC power supply U1 pre-charges the resonant energy storage inductor L1; In the LC resonance stage, the second switch tube S2 is turned on in the first half cycle, and the fourth switch tube S4 is turned on in the second half cycle. The resonant energy storage inductor L1 and the resonant capacitor C3 form a resonant cavity, and the resonant capacitor C3 is charged. In the LCL resonance stage, the second switch tube S2 remains on in the first half cycle, and the fourth switch tube S4 remains on in the second half cycle. The resonant energy storage inductor L1, the resonant capacitor C3, and the leakage inductor L2 form a resonant cavity. The resonant capacitor C3 discharges to transfer energy to the primary coil L3 of the transformer T. The transformer T transfers the energy to the secondary coil and outputs it to the load R1 through the inverter circuit. In the dead zone stage, the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 are all turned off, the resonant capacitor C3 and the leakage inductor L2 form a resonant cavity, the resonant energy storage inductor L1 feeds the remaining energy back to the power supply to achieve reset, and the resonant capacitor C3 continues to discharge until the energy returns to zero; In high gain mode, the converter pre-charges the resonant energy storage inductor L1 through the DC power supply U1 before the resonance stage. The pre-charged resonant energy storage inductor L1 injects more energy into the resonant circuit, effectively improving the voltage gain range of the converter.

[0020] This converter can achieve a wide range of voltage gain by combining low-gain mode and high-gain mode. By reusing electrical components such as the resonant energy storage inductor L1, the first bridge arm, and the second bridge arm, high power density and high efficiency can be achieved without adding electrical components or additional circuits, making the converter smaller in size and suitable for the energy feedback system of the elevator. In addition, this converter can achieve isolation between the input and output ends by providing a transformer T to improve safety; when working, the symmetrical working mode of the upper half cycle and the lower half cycle can be adopted to prevent the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube from having large differences in current, which is suitable for long-term operation.

[0021] Furthermore, as described above, in a wide voltage range resonant inductor pre-energy storage type LCL converter for an elevator, the first bridge arm also includes a first junction capacitor C11 and a third junction capacitor C31, and the two ends of the first junction capacitor C11 are respectively connected to the source and drain of the first switch tube S1, and the two ends of the third junction capacitor C31 are respectively connected to the source and drain of the third switch tube S3; the second bridge arm also includes a second junction capacitor C21 and a fourth junction capacitor C41, and the two ends of the second junction capacitor C21 are respectively connected to the source and drain of the second switch tube S2, and the two ends of the fourth junction capacitor C41 are respectively connected to the source and drain of the fourth switch tube S4.

[0022] Furthermore, in a wide voltage range resonant inductor pre-energy storage type LCL converter for an elevator as described above, the secondary coil of the transformer T is divided into a first secondary coil portion L4 and a second secondary coil portion L5 in the middle; the inverter circuit includes a first rectifier diode D1 and a second rectifier diode D2; the end of the first secondary coil portion L4 not connected to the second secondary coil portion L5 is connected to the anode of the first rectifier diode D1, and the cathode of the first rectifier diode D1 is connected to the positive electrode of the load R1; the end of the second secondary coil portion L5 not connected to the first secondary coil portion L4 is connected to the anode of the second rectifier diode D2, and the cathode of the second rectifier diode D2 is connected to the positive electrode of the load R1; the end at which the first secondary coil portion L4 and the second secondary coil portion L5 are connected to each other is connected to the negative electrode of the load R1.

[0023] Furthermore, in the wide voltage range resonant inductor pre-energy storage type LCL converter for elevators as described above, the number of turns of the primary coil L3: the number of turns of the first secondary coil part L4: the number of turns of the second secondary coil part L5 is n:1:1, and n is a constant greater than or equal to 1.

[0024] Furthermore, the wide voltage range resonant inductor pre-energy storage type LCL converter for elevators as described above also includes a rectifier capacitor C4, and the rectifier capacitor C4 is connected in parallel with the load R1.

[0025] The technical solution of the present invention has the following beneficial effects: small size, high power density, high efficiency, isolation between the input end and the output end, long-term operation, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a circuit structure diagram of an embodiment; Figure 2 is a waveform diagram of key components when the embodiment is in high gain mode; Figure 3 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Figure 4 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Figure 5 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Figure 6 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Figure 7 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Figure 8 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Fig. 9 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Fig.10 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Fig.11 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Fig.12 When the embodiment is in high gain mode - Equivalent circuit diagram at time; Fig.13 FIG. 4 is a voltage gain characteristic curve diagram of the embodiment when the embodiment is in high gain mode. DETAILED DESCRIPTION

[0027] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0028] like Figure 1 A wide voltage range resonant inductor pre-energy storage type LCL converter for an elevator according to an embodiment of the present invention comprises a DC power supply U1, a first voltage stabilizing capacitor C1, a second voltage stabilizing capacitor C2, a resonant energy storage inductor L1, a resonant capacitor C3, a first bridge arm, a second bridge arm, a transformer T, an inverter circuit, a load R1 and a rectifier capacitor C4; One end of the first voltage-stabilizing capacitor C1 is connected to one end of the second voltage-stabilizing capacitor C2, the other end of the first voltage-stabilizing capacitor C1 is connected to the positive electrode of the DC power supply U1, and the other end of the second voltage-stabilizing capacitor C2 is connected to the negative electrode of the DC power supply U1; The first bridge arm includes a first switch tube S1, a third switch tube S3, a first body diode D11, a third body diode D31, a first junction capacitor C11 and a third junction capacitor C31; the source of the first switch tube S1 is connected to the negative electrode of the DC power supply U1, the drain of the first switch tube S1 is connected to the source of the third switch tube S3, and the drain of the third switch tube S3 is connected to the positive electrode of the DC power supply U1; the anode of the first body diode D11 is connected to the source of the first switch tube S1, and the cathode of the first body diode D11 is connected to the drain of the first switch tube S1; the anode of the third body diode D31 is connected to the source of the third switch tube S3, and the cathode of the third body diode D31 is connected to the drain of the third switch tube S3; the two ends of the first junction capacitor C11 are respectively connected to the source and drain of the first switch tube S1, and the two ends of the third junction capacitor C31 are respectively connected to the source and drain of the third switch tube S3; The second bridge arm includes a second switch tube S2, a fourth switch tube S4, a second body diode D21, a fourth body diode D41, a second junction capacitor C21 and a fourth junction capacitor C41; the source of the second switch tube S2 is connected to the negative electrode of the DC power supply U1, the drain of the second switch tube S2 is connected to the source of the fourth switch tube S4, and the drain of the fourth switch tube S4 is connected to the positive electrode of the DC power supply U1; the anode of the second body diode D21 is connected to the source of the second switch tube S2, and the cathode of the second body diode D21 is connected to the drain of the second switch tube S2; the anode of the fourth body diode D41 is connected to the source of the fourth switch tube S4, and the cathode of the fourth body diode D41 is connected to the drain of the fourth switch tube S4; the two ends of the second junction capacitor C21 are respectively connected to the source and drain of the second switch tube S2, and the two ends of the fourth junction capacitor C41 are respectively connected to the source and drain of the fourth switch tube S4; The gates of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 are connected to an external control circuit to control the on and off of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4; The primary side of the transformer T is provided with a leakage inductor L2 and a primary coil L3, and the secondary side of the transformer T is provided with a secondary coil, and the secondary coil of the transformer T is divided into a first secondary coil part L4 and a second secondary coil part L5 from the middle; the number of turns of the primary coil L3: the number of turns of the first secondary coil part L4: the number of turns of the second secondary coil part L5 is n:1:1, and n is a constant greater than or equal to 1; One end of the resonant energy storage inductor L1 is connected to the connection line between the first voltage stabilizing capacitor C1 and the second voltage stabilizing capacitor C2, and the other end of the resonant energy storage inductor L1 is connected to the connection line between the first switch tube S1 and the third switch tube S3; one end of the leakage inductor L2 is connected to the connection line between the first switch tube S1 and the third switch tube S3, and the other end of the leakage inductor L2 is connected to one end of the primary coil L3; the other end of the primary coil L3 is connected to the connection line between the second switch tube S2 and the fourth switch tube S4; the resonant capacitor C3 is connected in parallel to the series circuit composed of the leakage inductor L2 and the primary coil L3; The inverter circuit includes a first rectifier diode D1 and a second rectifier diode D2; the end of the first secondary coil portion L4 not connected to the second secondary coil portion L5 is connected to the anode of the first rectifier diode D1, and the cathode of the first rectifier diode D1 is connected to the positive electrode of the load R1; the end of the second secondary coil portion L5 not connected to the first secondary coil portion L4 is connected to the anode of the second rectifier diode D2, and the cathode of the second rectifier diode D2 is connected to the positive electrode of the load R1; the end of the first secondary coil portion L4 and the second secondary coil portion L5 connected to each other is connected to the negative electrode of the load R1; the rectifier capacitor C4 is connected in parallel with the load R1.

[0029] The converter has two working modes, low gain mode and high gain mode, when in use. The external control circuit switches the working mode of the converter by controlling whether the first switch tube S1 and the third switch tube S3 of the first bridge arm participate in the work. When the first bridge arm does not participate in the work, the converter switches to the low gain mode. When the converter is in low gain mode, the converter is a half-bridge LCL converter. The external control circuit uses a pulse width modulation method (PWM) to alternately turn on the second switch tube S2 and the fourth switch tube S4, so that the primary coil L3 of the transformer T generates alternating current. Since the circuit structure of the converter in low gain mode is the same as that of a traditional half-bridge LCL converter, the control method and gain characteristics are the same as those of a traditional half-bridge LCL converter, which will not be repeated in this article.

[0030] When the converter is in high gain mode, the converter is a full-bridge LCL converter. The external control circuit uses a pulse width modulation method (PWM) to control the on and off time of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4. In the first half cycle, the first switch tube S1 and the second switch tube S2 are turned on and off in sequence, and in the second half cycle, the third switch tube S3 and the fourth switch tube S4 are turned on and off in sequence, so that when the converter is in high gain mode, each half cycle switches in sequence in the four working stages of the inductor energy storage stage, the LC resonance stage, the LCL resonance stage, and the dead zone stage (as shown in Table 1); Table 1 Control method of this converter in high gain mode In the inductor energy storage stage, the first switch tube S1 is turned on in the first half cycle, and the third switch tube S3 is turned on in the second half cycle. At this time, the DC power supply U1 pre-charges the resonant energy storage inductor L1; In the LC resonance stage, the second switch tube S2 is turned on in the first half cycle, and the fourth switch tube S4 is turned on in the second half cycle. The resonant energy storage inductor L1 and the resonant capacitor C3 form a resonant cavity, and the resonant capacitor C3 is charged. In the LCL resonance stage, the second switch tube S2 remains on in the first half cycle, and the fourth switch tube S4 remains on in the second half cycle. The resonant energy storage inductor L1, the resonant capacitor C3, and the leakage inductor L2 form a resonant cavity. The resonant capacitor C3 discharges to transfer energy to the primary coil L3 of the transformer T. The transformer T transfers the energy to the secondary coil and outputs it to the load R1 through the inverter circuit. In the dead zone stage, the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 are all turned off, the resonant capacitor C3 and the leakage inductor L2 form a resonant cavity, the resonant energy storage inductor L1 feeds the remaining energy back to the power supply to achieve reset, and the resonant capacitor C3 continues to discharge until the energy returns to zero; In high gain mode, the converter pre-charges the resonant energy storage inductor L1 through the DC power supply U1 before the resonance stage. The pre-charged resonant energy storage inductor L1 injects more energy into the resonant circuit, effectively improving the voltage gain range of the converter.

[0031] like Figure 2 This is the waveform diagram of the key components when the converter is in high gain mode. - is a complete cycle of the converter, and the total duration of a complete cycle is ,in - For the first half cycle, - For the second half cycle, the inductance of the resonant energy storage inductor L1 is , the current is , after the inductor energy storage stage, the current value of the resonant energy storage inductor L1 is , the capacitance value of the resonant capacitor C3 is , voltage is , the inductance of leakage inductance L2 is , the current is , the current of the line between the resonant capacitor C3, the leakage inductance L2 and the connection node of the first bridge arm is , the output voltage of DC power supply U1 is , the voltage of load R1 is preset to a constant voltage , the driving voltages (gate voltages) of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 are respectively , , and The total duty cycle of the first switch tube S1 and the second switch tube S2 in their half cycle, and the total duty cycle of the third switch tube S3 and the fourth switch tube S4 in their half cycle are all fixed values. The duty cycle of the dead zone phase in its half cycle is a fixed value The duty cycle of the first switch tube S1 in its half cycle and the duty cycle of the third switch tube S3 in its half cycle are both ; When debugging the pulse width, due to is a fixed value, by adjusting the duty cycle By changing the duration of the inductor energy storage phase according to the size of the inductor, the voltage gain can be adjusted.

[0032] When the converter is in high gain mode, the upper half cycle [ - ], the second half cycle [ - ] can be divided into 5 modes. The following is an example of the workflow of the 5 modes in the upper half of the cycle: 1) Mode 1[ - ]:The equivalent circuit is as follows Figure 3 As shown, Before the moment, the converter is in the dead zone phase after the fourth switch tube S4 is turned off in the second half of the previous cycle, and the residual current in the resonant energy storage inductor L1 is fed back to the power supply to 0; At this moment, due to the existence of the resonant energy storage inductor L1 and its initial current being 0, the first switch tube S1 is turned on in ZCS mode, so that the working phase of the converter is switched to the inductor energy storage phase; due to the first switch tube S1 being turned on, the DC power supply U1 charges the resonant energy storage inductor L1 for pre-energy storage, and the current of the resonant energy storage inductor L1 is With slope Linear increase.

[0033] 2) Mode 2[ - ]:The equivalent circuit is as follows Figure 4 As shown, At this moment, the voltage across the source and drain of the second switch tube S2 is is 0, achieving ZVS conduction. At this time, the first switch tube S1 has not been turned off, and both the first switch tube S1 and the second switch tube S2 are in the on state. The converter is still in the inductive energy storage stage. At this moment, the current of the resonant energy storage inductor L1 Rise to , mode 2 ends, at this moment the current of the resonant inductor is It can be expressed as: (1) in The external control circuit controls the switching frequencies of the first switch tube S1 , the second switch tube S2 , the third switch tube S3 , and the fourth switch tube S4 .

[0034] The total duration of the inductive energy storage phase is: (2) 3) Mode 3[ - ]:The equivalent circuit is as follows Figure 5 As shown, At this moment, the first switch tube S1 is turned off, and since the second switch tube S2 is turned on, the resonant capacitor C3 is connected in parallel with the first switch tube S1, and the voltage across the source and drain of the first switch tube S1 is is clamped, achieving ZVS shutdown, so that the working phase of the converter switches to the LC resonance phase; at this time, the current of the resonant energy storage inductor L1 and The difference between the first junction capacitor C11 and the third junction capacitor C31 is charged, and the energy pre-stored in the resonant energy storage inductor L1 begins to be injected into the resonant cavity. At this time, the voltage of the resonant capacitor C3 Less than , only the resonant energy storage inductor L1 and the resonant capacitor C3 participate in the resonance. At t3, the voltage of the resonant capacitor C3 is Rise to , mode 3 ends.

[0035] and The expression is: (3) The duration of the LC resonance phase can be expressed as: (4) in is the resonant characteristic impedance, is the binary resonant angular frequency.

[0036] 4) Mode 4[ - ]:The equivalent circuit is as follows Figure 6 As shown, At this moment, the voltage of the resonant capacitor C3 Rise to At this time, the working stage of the converter switches to the LCL resonance stage, the first rectifier diode D1 is turned on, and the current of the resonant energy storage inductor L1 It starts to rise from zero. At this time, the leakage inductance L2 of the transformer T begins to participate in the resonance, and the current through the resonant energy storage inductor L1 The resonant energy is transmitted to the first secondary coil L4. , , The expressions are: (5) In the formula is the angular frequency of the LCL resonance, , the expression is as follows: (6) In the formula is the self-inductance coefficient of leakage inductance L2 and the self-inductance coefficient of the resonant energy storage inductor L1 Ratio.

[0037] The duration of the LCL resonant phase can be expressed as: (7) 5) Mode 5[ - ]:The equivalent circuit is as follows Figure 7 As shown, At this moment, the second switch tube S2 is turned off, and the working phase of the converter switches to the dead zone phase (energy release phase), and the current The second junction capacitor C21 and the fourth junction capacitor C41 are charged and discharged, the resonant capacitor C3 and the leakage inductor L2 maintain resonance, and the energy is transferred to the secondary side of the transformer T to continue to supply energy to the load R1. The current of the resonant energy storage inductor L1 Feedback to DC power supply U1 is done through the third body diode D31. , , When both drop to 0, the energy is released, the second rectifier diode D2 achieves ZCS cutoff, and this mode ends.

[0038] Dead zone stage , , It can be expressed as: (8) (9) is the characteristic impedance of the resonance between the resonant capacitor C3 and the leakage inductance L2, is the resonant angular frequency of the resonant capacitor C3 and the leakage inductance L2, is the equivalent resistance of the circuit on the secondary side of transformer T, The value of When the ± sign is positive, The value of When the ± sign is negative, the value is expressed as: (10) The time it takes for the resonant capacitor C3 and the leakage inductor L2 to resonate and release energy to 0 is: (12) The time it takes for the feedback power to reach 0 can be expressed as: (13) The end of this stage means the end of the first half cycle of the converter. The second half cycle is symmetrical with the above working state. The equivalent circuits of the five modes in the second half cycle are: Figures 8 to 12 As shown, the conduction mechanism and voltage and current changes in the second half cycle are the same as those in the first half cycle, and will not be described in detail in this article.

[0039] Under the premise of ignoring losses, according to the power conservation of the primary and secondary sides of the transformer, we can get: (14) In the formula is the average current input to the primary side of transformer T, which is equal to The ratio of the sum of the integrals in each stage to the half-cycle time is Feedback to the power supply, not into the resonant cavity, so in the inductor energy storage stage, LC resonance stage, LCL resonance stage Integrate and get the integral values ​​respectively , , , the average input current can be expressed as: (15) Substituting the above expressions (2), (4), (8), and (15) into expression (14), we can obtain the relationship between the voltage gain G and the duty cycle of the inductor energy storage stage: , the total duty cycle of the switch tube working in half a cycle , normalized angular frequency ( , The external control circuit controls the switching angular frequency of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4), the inductance value and inductance value Ratio , Quality Factor ( ), and then plot it to get Fig.13 The voltage gain characteristic curve shown in this figure is =0.5, n=1, =0.68, =0.8 as an example), it can be seen from the figure that the voltage gain G changes with the quality factor Q and the duty cycle of the inductor energy storage mode. When debugging the pulse width, by adjusting the duty cycle of the inductor energy storage stage, The size of (that is, the duty cycle of the first switch tube S1 in its half cycle, the duty cycle of the third switch tube S3 in its half cycle) can be used to adjust the voltage gain. Therefore, the design of this converter has a strong control ability of the circuit.

[0040] This converter can achieve a wide range of voltage gain by combining low-gain mode and high-gain mode. By reusing electrical components such as the resonant energy storage inductor L1, the first bridge arm, and the second bridge arm, high power density and high efficiency can be achieved without adding electrical components or additional circuits, making the converter smaller in size and suitable for the energy feedback system of the elevator. In addition, this converter can achieve isolation between the input and output ends by providing a transformer T to improve safety; when working, the symmetrical working mode of the upper half cycle and the lower half cycle can be adopted to prevent the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube from having large differences in current, which is suitable for long-term operation.

[0041] The parameters of the resonant energy storage inductor L1 and the resonant capacitor C3 are designed as follows: Duty cycle of inductor energy storage stage =0, the converter starts to resonate directly without going through the inductor energy storage stage, and its gain characteristics are similar to those of the traditional LCL converter. This point is taken as the rated operating point, and the resonant energy storage inductor L1 and the resonant capacitor C3 are designed. According to the rated point output power , Quality Factor , normalized angular frequency , Gain get: (16) In this way, the inductance value of the resonant energy storage inductor L1 is obtained. , the capacitance value of the resonant capacitor C3 .

[0042] The leakage inductance L2 parameters are designed as follows: First, it is necessary to ensure that the resonant capacitor C3 and the leakage inductor L2 resonate to completely transfer energy to the secondary side of the transformer T during the dead zone when both switches are turned off. Therefore, the dead zone time must be greater than or equal to the time it takes for the resonance to release energy to 0: (17) Secondly, it is necessary to ensure that the resonant energy storage inductor L1 fully feeds back the energy to the DC power supply U1 during the dead zone phase, resets to the initial state, and creates conditions for the ZCS of the first switch tube S1 or the third switch tube S3 corresponding to the first bridge arm of the next half cycle. The dead zone phase time must meet the following conditions: (18) For the unknown quantity in expression (17), when When Simplified to The peak value, Simplified to The peak value of the wave is simplified to a standard sine wave, and the unknown quantity Can be considered as Substituting expressions (12) and (18) into (17) yields the inductance value of the leakage inductance L2: The implicit function of the leakage inductance L2 can be solved to obtain the inductance value .

[0043] To realize soft switching for the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4, the design is as follows: At the beginning of the inductive energy storage stage, in order to enable the first switch tube S1 or the third switch tube S3 of the first bridge arm connected in series with the resonant energy storage inductor L1 to achieve ZCS conduction, it is necessary to ensure that the current of the resonant energy storage inductor L1 drops to 0 after the dead zone stage, and the dead zone stage time must satisfy expression (18).

[0044] At the end of the inductive energy storage stage, in order to enable the first switch tube S1 or the third switch tube S3 of the first bridge arm connected in parallel with the resonant capacitor C3 to achieve ZVS shutdown, the first rectifier diode D1 or the second rectifier diode D2 to achieve ZCS shutdown, and the second switch tube S2 or the fourth switch tube S4 of the second bridge arm to achieve ZCS opening, it is necessary to ensure that the resonant capacitor C3 and the leakage inductance L2 resonate and release energy to 0 in the dead zone stage, and the dead zone stage time must satisfy expression (17).

[0045] like Figure 2 As shown, in order to clamp the voltage across the source and drain of the second switch tube S2 / fourth switch tube S4 of the second bridge arm to 0 when it is turned on to achieve ZVS conduction, it needs to have an overlapping conduction interval with the first switch tube S1 / third switch tube S3 of the first bridge arm.

[0046] The above description is only the preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications, combinations and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A wide voltage range resonant inductor pre-storage type LCL converter for elevators, characterized in that: It includes a DC power supply U1, a first voltage stabilizing capacitor C1, a second voltage stabilizing capacitor C2, a resonant energy storage inductor L1, a resonant capacitor C3, a first bridge arm, a second bridge arm, a transformer T, an inverter circuit and a load R1; One end of the first voltage-stabilizing capacitor C1 is connected to one end of the second voltage-stabilizing capacitor C2, the other end of the first voltage-stabilizing capacitor C1 is connected to the positive electrode of the DC power supply U1, and the other end of the second voltage-stabilizing capacitor C2 is connected to the negative electrode of the DC power supply U1; The first bridge arm includes a first switch tube S1, a third switch tube S3, a first body diode D11 and a third body diode D31; the source of the first switch tube S1 is connected to the negative electrode of the DC power supply U1, the drain of the first switch tube S1 is connected to the source of the third switch tube S3, and the drain of the third switch tube S3 is connected to the positive electrode of the DC power supply U1; the anode of the first body diode D11 is connected to the source of the first switch tube S1, and the cathode of the first body diode D11 is connected to the drain of the first switch tube S1; the anode of the third body diode D31 is connected to the source of the third switch tube S3, and the cathode of the third body diode D31 is connected to the drain of the third switch tube S3; The second bridge arm includes a second switch tube S2, a fourth switch tube S4, a second body diode D21 and a fourth body diode D41; the source of the second switch tube S2 is connected to the negative electrode of the DC power supply U1, the drain of the second switch tube S2 is connected to the source of the fourth switch tube S4, and the drain of the fourth switch tube S4 is connected to the positive electrode of the DC power supply U1; the anode of the second body diode D21 is connected to the source of the second switch tube S2, and the cathode of the second body diode D21 is connected to the drain of the second switch tube S2; the anode of the fourth body diode D41 is connected to the source of the fourth switch tube S4, and the cathode of the fourth body diode D41 is connected to the drain of the fourth switch tube S4; The gates of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 are connected to an external control circuit to control the on and off of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4; The primary side of the transformer T is provided with a leakage inductor L2 and a primary coil L3, and the secondary side of the transformer T is provided with a secondary coil; one end of the resonant energy storage inductor L1 is connected to the connection line between the first voltage stabilizing capacitor C1 and the second voltage stabilizing capacitor C2, and the other end of the resonant energy storage inductor L1 is connected to the connection line between the first switch tube S1 and the third switch tube S3; one end of the leakage inductor L2 is connected to the connection line between the first switch tube S1 and the third switch tube S3, and the other end of the leakage inductor L2 is connected to one end of the primary coil L3; the other end of the primary coil L3 is connected to the connection line between the second switch tube S2 and the fourth switch tube S4; the resonant capacitor C3 is connected in parallel to the series circuit composed of the leakage inductor L2 and the primary coil L3; the secondary coil of the transformer T is connected to the load R1 through an inverter circuit, and the inverter circuit is used to convert the alternating current output by the secondary coil of the transformer T into direct current.

2. A wide voltage range resonant inductor pre-storage type LCL converter for elevators as claimed in claim 1, characterized in that: The first bridge arm also includes a first junction capacitor C11 and a third junction capacitor C31, the two ends of the first junction capacitor C11 are respectively connected to the source and drain of the first switch tube S1, and the two ends of the third junction capacitor C31 are respectively connected to the source and drain of the third switch tube S3; the second bridge arm also includes a second junction capacitor C21 and a fourth junction capacitor C41, the two ends of the second junction capacitor C21 are respectively connected to the source and drain of the second switch tube S2, and the two ends of the fourth junction capacitor C41 are respectively connected to the source and drain of the fourth switch tube S4.

3. A wide voltage range resonant inductor pre-storage type LCL converter for elevators as claimed in claim 1 or 2, characterized in that: The secondary coil of the transformer T is divided into a first secondary coil portion L4 and a second secondary coil portion L5 in the middle; the inverter circuit includes a first rectifier diode D1 and a second rectifier diode D2; the end of the first secondary coil portion L4 not connected to the second secondary coil portion L5 is connected to the anode of the first rectifier diode D1, and the cathode of the first rectifier diode D1 is connected to the positive electrode of the load R1; the end of the second secondary coil portion L5 not connected to the first secondary coil portion L4 is connected to the anode of the second rectifier diode D2, and the cathode of the second rectifier diode D2 is connected to the positive electrode of the load R1; the end at which the first secondary coil portion L4 and the second secondary coil portion L5 are connected to each other is connected to the negative electrode of the load R1.

4. A wide voltage range resonant inductor pre-storage type LCL converter for elevators as claimed in claim 3, characterized in that: The number of turns of the primary coil L3: the number of turns of the first secondary coil portion L4: the number of turns of the second secondary coil portion L5 is n:1:1, where n is a constant greater than or equal to 1.

5. A wide voltage range resonant inductor pre-storage type LCL converter for elevators as claimed in claim 3, characterized in that: A rectifier capacitor C4 is also included, and the rectifier capacitor C4 is connected in parallel with the load R1.

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