Half-bridge resonant inductive coupling type wireless power transmission system

Abstract

The invention relates to a half-bridge resonant inductive coupling type wireless power transmission system, which is specifically characterized in that a bridge rectifier diode D is connected in series with a first capacitor C1, one end of the first capacitor C1 is connected with a collector electrode of a first switch tube S1, and an emitter electrode of the first switch tube S1 is connected with a collector electrode of a second switch tube S2; the other end of the first capacitor C1 is connected with an emitting electrode of the second switch tube S2, an emitting electrode of the first switch tube S1 is connected with one end of the second capacitor C, the first switch tube S1 is connected with the diode D1 in parallel, the second switch tube S2 is connected with the diode D2 in parallel, and the transmitting coil L1 is connected between the other end of the first capacitor C1 and the other end of the second capacitor C; the transmitting coil L1 and the receiving coil L2 interact through mutual inductance, and the receiving coil L2 is connected with the load RL. According to the wireless charging system, the wireless charging technology can be used for charging the electric forklift, the plugging risk is eliminated, and the charging safety and convenience are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless charging power supplies, and particularly relates to a half-bridge resonant inductive coupling wireless power transmission system. Background Art

[0002] With the gradual increase in the popularity of electric forklifts, exploring and developing an efficient and flexible charging method for forklifts has become a major focus. Currently, electric forklifts mainly use wired charging, and during this process, it is necessary to ensure the safe isolation of the power supply and the vehicle control circuit, and configure a directional protective plug to prevent misoperation. However, the existing manual or mechanical separation charging methods are not only cumbersome to operate, but also increase the wear of the interface due to frequent plugging and unplugging, easily leading to an increase in contact resistance, overheating, and even the risk of fire.

[0003] Therefore, exploring the wireless charging technology for forklifts has become an urgent need, aiming to eliminate the plugging and unplugging risks and significantly improve the charging safety and convenience. Summary of the Invention

[0004] Existing electric forklifts usually use wired charging, which easily leads to an increase in contact resistance, overheating, and even the risk of fire. To solve the above problems, the present invention provides a half-bridge resonant inductive coupling wireless power transmission system, which can use wireless charging technology to charge electric forklifts, eliminate the plugging and unplugging risks, and significantly improve the charging safety and convenience.

[0005] The technical solution of the present invention is as follows:

[0006] A half-bridge resonant inductive coupling wireless power transmission system, comprising a bridge rectifier diode D, a capacitor C1, a capacitor C, a first switching tube S1, a second switching tube S2, a diode D1, a diode D2, a transmitting coil L1, a receiving coil L2, and a load R L ;

[0007] The bridge rectifier diode D is connected in series with the first capacitor C1. One end of the first capacitor C1 is connected to the collector of the first switching tube S1. The emitter of the first switching tube S1 is connected to the collector of the second switching tube S2. The other end of the first capacitor C1 is connected to the emitter of the second switching tube S2. The emitter of the first switching tube S1 is connected to one end of the second capacitor C. The first switching tube S1 is connected in parallel with the diode D1. The second switching tube S2 is connected in parallel with the diode D2. The transmitting coil L1 is connected between the other end of the first capacitor C1 and the second capacitor C;

[0008] The transmitting coil L1 and the receiving coil L2 interact through mutual inductance. The receiving coil L2 and the load R L are connected.

[0009] Preferably, it further includes 4 modes, including a first mode, a second mode, a third mode, and a fourth mode;

[0010] Mode 0: The first switching tube S1 is turned on, and the second switching tube S2 is turned off. At this time, the first switching tube S1 conducts with zero voltage. The grid voltage is rectified and filtered by a full-bridge rectifier and then injects energy into the transmitting coil L1 through the first switching tube S1. The DC voltage source, the first switching tube S1, the transmitting coil L1, and the second capacitor C form a loop, and the transmitting coil L1 and the second capacitor C generate a second-order oscillation;

[0011] Mode 1: The first switching tube S1 is turned off, and the second switching tube S2 is turned off. When the first switching tube S1 is turned off instantaneously, the diode D2 in parallel with the second switching tube S2 conducts for freewheeling. The transmitting coil L1 charges the second capacitor C through the diode D2. The conduction of the diode D2 provides the condition for the second switching tube S2 to conduct with zero voltage in the next mode;

[0012] Mode 2: The first switching tube S1 is turned off, and the second switching tube S2 is turned on. The second switching tube S2 conducts with zero voltage. At this time, no excitation source is working, and the transmitting coil L1 and the second capacitor C generate a second-order free oscillation;

[0013] Mode 3: The first switching tube S1 is turned off, and the second switching tube S2 is turned off. When the second switching tube S2 is turned off instantaneously, the diode D1 in parallel with the first switching tube S1 conducts for freewheeling. The transmitting coil L1 charges the second capacitor C reversely through the diode D1. The conduction of the diode D1 provides the condition for the first switching tube S1 to conduct with zero voltage in the next mode.

[0014] Preferably, the load R L is an electric forklift battery.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The power control strategy of wireless energy transmission based on a half-bridge resonant topology in the wireless charging of the electric forklift of the present invention controls the power by controlling the on-off frequency of the switching tubes in the half-bridge resonant inverter topology. Its essence is to control the input average current so as to achieve the magnitude of the output power. There is no need to add additional components at the transmitting and receiving ends to increase the volume of the device, and it has the advantages of simple and convenient energy regulation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the overall structure of the present invention;

[0018] Figure 2 is a simplified diagram of the system circuit topology;

[0019] Figure 3 is a waveform diagram of the system under full power mode;

[0020] Figure 4 is a waveform diagram of the system under low power mode. Detailed implementation mode

[0021] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] See Figure 1 , based on a half-bridge resonant inductive coupling wireless power transmission system, including a bridge rectifier diode D, a first capacitor C1, a second capacitor C, a first switch tube S1, a second switch tube S2, a diode D1, a diode D2, a transmitting coil L1, a receiving coil L2, and a load R L ;

[0023] The bridge rectifier diode D is connected in series with the first capacitor C1. One end of the first capacitor C1 is connected to the collector of the first switch tube S1. The emitter of the first switch tube S1 is connected to the collector of the second switch tube S2. The other end of the first capacitor C1 is connected to the emitter of the second switch tube S2. The emitter of the first switch tube S1 is connected to one end of the second capacitor C. The first switch tube S1 is connected in parallel with the diode D1. The second switch tube S2 is connected in parallel with the diode D2. The transmitting coil L1 is connected between the other end of the first capacitor C1 and the second capacitor C;

[0024] The transmitting coil L1 and the receiving coil L2 interact through mutual inductance. The receiving coil L2 and the load R L are connected.

[0025] It also includes 4 modes, including the first mode, the second mode, the third mode, and the fourth mode;

[0026] Mode 0: The first switch tube S1 is turned on, and the second switch tube S2 is turned off. At this time, the first switch tube S1 is turned on with zero voltage. The grid voltage is rectified and filtered by the full bridge and then injected into the transmitting coil L1 through the first switch tube S1. The DC voltage source, the first switch tube S1, the transmitting coil L1, and the second capacitor C form a loop, and the transmitting coil L1 and the second capacitor C generate a second-order oscillation;

[0027] Mode 1: The first switch tube S1 is turned off, and the second switch tube S2 is turned off. When the first switch tube S1 is turned off instantaneously, the diode D2 connected in parallel with the second switch tube S2 conducts for freewheeling. The transmitting coil L1 charges the second capacitor C through the diode D2. The conduction of the diode D2 provides a condition for the second switch tube S2 to be turned on with zero voltage in the next mode;

[0028] Mode 2: The first switch tube S1 is turned off, and the second switch tube S2 is turned on. The second switch tube S2 is turned on with zero voltage. At this time, there is no excitation source working, and the transmitting coil L1 and the second capacitor C generate a second-order free oscillation;

[0029] Mode 3: The first switching transistor S1 is turned off, and the second switching transistor S2 is turned off. When the second switching transistor S2 is turned off instantaneously, the diode D1 in parallel with the first switching transistor S1 conducts for freewheeling. The transmitting coil L1 charges the second capacitor C reversely through the diode D1. The conduction of the diode D1 provides the condition for the zero-voltage conduction of the first switching transistor S1 in the next mode.

[0030] For the energy transmitting end and the energy receiving end, according to Kirchhoff's voltage law:

[0031]

[0032] where L1 and L2 are the primary and secondary resonant inductances respectively, R1 and R2 are the internal resistances of the primary and secondary resonant inductances respectively, ω is the angular frequency of the excitation voltage source U, M is the mutual inductance between the primary and secondary, I1 is the primary current, I2 is the secondary current, U is the excitation voltage, c is the primary capacitor, and R L is the load resistance.

[0033] Simplified from formula (1) and formula (2), we can get:

[0034]

[0035] Then the input power is:

[0036]

[0037] The first half cycle and the second half cycle of the half-bridge are symmetric processes. By using the symmetric control method, on the one hand, it can prevent the resonant coil from being magnetized asymmetrically, and on the other hand, it can ensure that the working states of the upper and lower switching transistors are the same, with the same device utilization rate and extended system service life.

[0038] From the process of modal analysis, it can be seen that the time from t0 to t1 is the first half cycle of energy injection, and the time from t2 to t3 is the second half cycle of energy injection. When the equivalent impedance of the system is purely resistive, and the equivalent impedance composed of the inductance mutual inductance and the capacitor is 0. At this time, the power is output at the maximum value, which is called the full-power mode. Only when the time from t0 to t1 is less than half of the resonant period, the corresponding diodes D1 and D2 can conduct for freewheeling, and the zero-voltage conduction of the two switching transistors can be realized. Therefore, this control strategy is also realized under this condition.

[0039] It can be seen from Equation (4) that the power is related to the conduction time of the upper and lower switching tubes and the working cycle. In this paper, based on a symmetric control method, the power control objective is achieved by controlling the working cycle T and the conduction time of the switching tubes t0~t1 = t2~t3. Since the dead time is much smaller than the energy injection time and can be ignored, it can be simplified to complementary PWM with a 50% conduction ratio of the upper and lower tubes. When t0~t1 decreases, i.e., ω increases, the power P also decreases. The power output can be reduced by decreasing the PWM period. The following further elaborates on this control strategy by comparing the full-power mode Figure 3 and the low-power mode Figure 4 :

[0040] Figure 3 In Figure 4 , the upper curve in the figure is the current waveform I of the resonant inductor L1 L , the middle curve in the figure is the drive voltage waveform PWM of the first switching tube S1, and the lower curve in the figure is the voltage waveform Uc of the second capacitor C;

[0041] When [t0~t1], this is Mode 0. The full-power mode time (t1 - t0) is half of the resonant period. The transmitting coil L1 and the second capacitor C undergo a second-order oscillation. In the previous time, the inductor current I L increases from 0 to the maximum value, and the capacitor voltage decreases from the maximum value to 0. The energy of the second capacitor C migrates to the inductor. In the subsequent time, the inductor current I L decreases from the maximum value to 0, and the capacitor voltage Uc increases from 0 to the maximum value. The inductor energy migrates to the second capacitor C. During the entire [t0~t1], the power supply injects energy into the resonance; in the low-power mode, before entering Mode 0, there is still a part of the energy I L in the inductor L1 that is not 0. This is due to the relatively fast switching frequency in the low-power mode. The inductor L1 first transfers the energy to the second capacitor C through a second-order oscillation, and then the second capacitor C charges the inductor L1, causing I L to start increasing positively from 0. Its characteristics are consistent with the second-order oscillation. Different from the full-power mode, the switching speed is relatively fast at this time. The inductor current does not complete half a cycle of the resonant state and enters the next mode. The inductor current is positive at this time. From the comparison between Figure 3 and Figure 4 , it can be known that the effective value of the current I L flowing through the inductor in the full-power mode is greater than that in the low-power mode, and in the low-power mode, as t1 - t0 increases, the effective value of I L becomes larger;

[0042] When [t1~t2], this is Mode 1. The time in this mode is extremely short. To prevent a short circuit of the power supply, a 0-voltage conduction condition is provided for the second switching tube S2. In the full-power mode, at the instant of t1, I LClose to but not zero, at this time the diode D2 can conduct for freewheeling, and it is the same as the full power mode in the low power mode;

[0043] The processes in the [t2~t3] and [t3~t4] stages, which are symmetric to the [t0~t1] and [t1~t2] stages, will not be elaborated here.

[0044] In an embodiment of the present invention, the load R L is an electric forklift battery.

[0045] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A half-bridge resonant inductively coupled wireless power transmission system, characterized in that: The invention comprises a bridge rectifier diode D, a capacitor C1, a capacitor C, a first switch tube S1, a second switch tube S2, a diode D1, a diode D2, a transmitting coil L1, a receiving coil L2 and a load R L ; The bridge rectifier diode D is connected in series with the first capacitor C1, one end of the first capacitor C1 is connected to the collector of the first switch tube S1, the emitter of the first switch tube S1 is connected to the collector of the second switch tube S2, the other end of the first capacitor C1 is connected to the emitter of the second switch tube S2, the emitter of the first switch tube S1 is connected to one end of the second capacitor C, the first switch tube S1 is connected in parallel with the diode D1, the second switch tube S2 is connected in parallel with the diode D2, and the transmitting coil L1 is connected between the other end of the first capacitor C1 and the second capacitor C; The transmitting coil L1 and the receiving coil L2 interact through mutual inductance, and the receiving coil L2 and the load R L connect.

2. The half-bridge resonant inductively coupled wireless power transmission system according to claim 1, characterized in that: It also includes 4 modes, including the first mode, the second mode, the third mode and the fourth mode; Mode 0: The first switch tube S1 is turned on, and the second switch tube S2 is turned off. At this time, the first switch tube S1 is turned on with zero voltage, and the grid voltage is rectified and filtered by the full-bridge and then injected into the transmitting coil L1 through the first switch tube S1. The DC voltage source, the first switch tube S1, the transmitting coil L1, and the second capacitor C form a loop, and the transmitting coil L1 and the second capacitor C generate second-order oscillations; Mode 1: The first switch tube S1 is turned off, and the second switch tube S2 is turned off. At the moment when the first switch tube S1 is turned off, the diode D2 connected in parallel with the second switch tube S2 is turned on for freewheeling. The transmitting coil L1 charges the second capacitor C through the diode D2. The conduction of the diode D2 provides a condition for the next mode switch tube S2 to be turned on with zero voltage. Mode 2: The first switch tube S1 is turned off, and the second switch tube S2 is turned on. The second switch tube S2 is turned on with zero voltage. At this time, there is no excitation source working, and the transmitting coil L1 and the second capacitor C have a second-order free oscillation; Mode 3: The first switch tube S1 is turned off, the second switch tube S2 is turned off, and the diode D1 connected in parallel with the first switch tube S1 is turned on for freewheeling at the moment the second switch tube S2 is turned off. The transmitting coil L1 reversely charges the second capacitor C through the diode D1, and the conduction of the diode D1 provides a condition for the zero-voltage conduction of the first switch tube S1 in the next mode.

3. The half-bridge resonant inductively coupled wireless power transmission system according to claim 1, characterized in that: The load R L For electric forklift batteries.

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