A power transmission method and device for a two-way wireless power transmission system

Abstract

The present invention discloses a power transmission method and device for a bidirectional wireless power transmission system, which belongs to the field of wireless power transmission, including: combining multiple adjacent switching cycles of the excitation voltage on both sides of the system into a modulation cycle, and modulating the excitation voltage on both sides of the system in units of one modulation cycle. In each modulation cycle, only the pulse width of a certain voltage half-wave is asymmetrically adjusted at the same time, and the pulse width of other voltage half-waves remains unchanged. The modulation order of each voltage half-wave needs to make the excitation voltage evenly distributed along the time axis. The total pulse width β of the excitation voltage in each modulation cycle at the load end of the system t The total pulse width α of the excitation voltage in each modulation cycle at the source end of the system is obtained by the PI link. t The external phase shift angle δ of the system is obtained by the load matching condition and the ZVS condition of all switching devices. The present invention makes it easier to achieve ZVS, so that the system can maintain a very high power factor in an extremely wide power range, reduce the reactive circulating current loss in the system, and improve the overall transmission efficiency of the system.

Description

Technical Field

[0001] The present invention belongs to the field of wireless power transmission, and more specifically, relates to a power transmission method of a bidirectional wireless power transmission system. Background Art

[0002] Electric vehicles can not only act as loads, but also as distributed energy storage units to interact with the power grid, provide power to the grid, and participate in the energy management and dispatch of the grid. The two-way flow of energy between the grid and electric vehicles requires the support of bidirectional inductive wireless power transmission technology. There are many benefits to using bidirectional wireless power transmission (BIPT) technology to charge and discharge electric vehicles. First, contactless charging and discharging can avoid safety hazards such as sparks, loose plugs, and leakage during rain; second, it does not occupy ground area and has low maintenance costs. Since the converter and inductive coil are buried underground, they are not as easily damaged as charging piles on the ground; third, in line with the development of smart grids and smart microgrids, once an electric vehicle is parked at a designated location, it can automatically participate in the interaction with the grid. The energy dispatch center of the grid will intelligently arrange the charging and discharging plan of the electric vehicle based on the owner's car usage habits and the real-time status of the grid operation, so that all parties can benefit in the end.

[0003] When adjusting the transmission power of the BIPT system, in order to maximize the transmission efficiency of the intermediate AC link, the internal phase shift angles α and β of the full-bridge converters on both sides must meet the load matching conditions. As the system transmission power becomes smaller and smaller, α and β also become smaller and smaller. In order to achieve ZVS soft switching of each switching device to reduce switching losses, the external phase shift angle δ also needs to be reduced accordingly. However, the reduction of δ will increase the reactive power in the system, thereby reducing the overall transmission efficiency of the system. Therefore, the smaller the system transmission power, the lower the transmission efficiency.

[0004] In order to improve the efficiency of the two-way wireless power transmission system under light load, a harmonic power transmission method has been proposed. This method adjusts the switching frequency of the full-bridge converters on both sides of the system to 1 / n of the original frequency, so that the system can achieve nth harmonic power transmission. However, this method can only improve the system efficiency in the range of 0 to 1 / n. 2 Efficiency within the rated power range, when the system's transmission power is greater than 1 / n 2 At rated power, the efficiency of the system cannot be optimized. 2 When the switching frequency is switched at the rated power point, the pulse width and distribution of the excitation voltage on both sides of the system will jump. The switching process is not continuous and smooth, which will affect the safe and stable operation of the system. Summary of the invention

[0005] In view of the defects of the prior art and the need for improvement, the present invention provides a power transmission method and device for a bidirectional wireless power transmission system, the purpose of which is to improve the transmission efficiency within the full power range of the system by means of harmonic power transmission, and the switching of harmonic orders and the modulation of the excitation voltage are continuous.

[0006] The bidirectional wireless power transmission system includes a source-end full-bridge inverter circuit, a source-end resonant compensation network, a coupling mechanism, a load-end resonant compensation network, a load-end rectifier circuit and a filter circuit, which are sequentially cascaded. The power transmission method includes:

[0007] Combine n adjacent switching cycles of the excitation voltage on both sides of the system into a modulation cycle, and use α t , β t Respectively represent the sum of the widths of all voltage pulses in each modulation cycle on both sides of the system, α t , β t The value range of is [0,2nπ]. When the BIPT system is fully loaded, the total pulse width α t , β t are all 2nπ, and the width of each voltage pulse half wave is π. As the system transmission power drops from the maximum value to 0, the width of each voltage pulse half wave is adjusted sequentially and asymmetrically within the modulation period, so that the total pulse width α t , β t It decreases monotonically from 2nπ to 0.

[0008] Further, adjusting the width of each voltage pulse half wave includes:

[0009] In each modulation cycle, only one voltage pulse half-wave width is adjusted at the same time, while the width of other voltage pulse half-waves remains unchanged. The modulation order of each voltage pulse half-wave needs to make the voltage pulse as evenly distributed as possible along the time axis, thereby reducing the fluctuation of the resonant current on both sides of the system. When adjusting the width of each voltage pulse half-wave, the half-wave asymmetric modulation method is adopted to make it easy for all switching devices to achieve ZVS. For the system source end, it is only necessary to move the time-lag edge of each voltage pulse while keeping its leading edge unchanged; for the system load end, it is only necessary to move the time-leading edge of each voltage pulse while keeping its lagging edge unchanged.

[0010] Specifically, using P max Represents the maximum transmission power of the system. When the system transmission power P∈((2n-1) 2 / (2n) 2 ,1]P max When α t (β t)∈(2n-1,2n]π, only the pulse width of one voltage half-wave needs to be adjusted, and the pulse width of the remaining voltage half-wave remains unchanged at π. At this time, the power transmission of the system can be regarded as fundamental power transmission. When the system transmission power P∈((2n-1) 2 / (2n) 2 ,1]P max When α t (β t )∈(2n-1,2n]π, only the pulse width of one voltage half-wave needs to be adjusted, and the pulse width of the remaining voltage half-wave remains unchanged at π. At this time, the power transmission of the system can be regarded as fundamental power transmission. When the system transmission power P∈((2n-2) 2 / (2n) 2 ,(2n-1) 2 / (2n) 2 ]P max When α t (β t )∈(2n-2,2n-1]π, the pulse width of the previously adjusted voltage half-wave has been reduced to 0, and the pulse width of another voltage half-wave begins to be adjusted. The pulse width of other voltage half-waves remains unchanged at π. At this time, the power transmission of the system can be equivalent to 2n / (2n-1) harmonic power transmission. By analogy, finally, when the system transmits power P∈(0,1 / (2n) 2 ]P max When α t (β t )∈(0,1]π, only one voltage half-wave exists in each modulation period, and the other voltage half-waves have been completely eliminated. At this time, the power transmission of the system can be regarded as 2nth harmonic power transmission.

[0011] The DC current is sampled at the load end of the BIPT system, and the total pulse width β of the excitation voltage at the load end in each modulation cycle is obtained by the PI controller after subtracting it from the given value. t , according to β t Get the pulse width of each switching cycle voltage: β1, β2, β3...β n .

[0012] On the other hand, the DC voltage U 2dc With the total pulse width β t Sent to the system source through the wireless communication module, according to U 2dc , β t The total pulse width α of the excitation voltage in each modulation cycle at the source end of the system can be obtained from the load matching condition function. t , α t Can be converted to α1, α2, α3...α n , thereby generating driving signals for switching devices Q1~Q4 by the PWM modulation link.

[0013] Finally, according to the ZVS conditions of the switching devices on both sides of the system, the phase synchronization link at the load end is composed of α t , β t The external phase shift angle δ can be obtained. δ and β1, β2, β3...β n They enter the PWM modulation link together to generate drive signals for switching devices Q5 to Q8.

[0014] The system ZVS soft switching condition function and load matching condition function are:

[0015] G1:

[0016] G2:

[0017] Among them, G1 and G2 represent the ZVS soft switching condition function and load matching condition function respectively, U 1dc , U 2dc Respectively represent the DC voltage on both sides of the system, φ is the preset phase margin value, 5°≤φ≤10°, u p 、u s They are the square wave excitation voltages on both sides of the system at the resonant frequency f r The sinusoidal AC component under |u p |、|u s | respectively u p 、u s The effective value of They are respectively the sinusoidal quantities u p 、u s The phase difference between the square wave voltages on both sides of the system.

[0018] Furthermore, the power factor angle θ and the transmission power P of the bidirectional wireless power transmission system can be expressed as:

[0019]

[0020]

[0021] Among them, ω r is the resonant angular frequency of the BIPT system, which can be expressed as

[0022] The present invention also provides a power transmission device of a bidirectional wireless power transmission system, comprising a computer-readable storage medium and a processor;

[0023] The computer-readable storage medium is used to store executable instructions;

[0024] The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the power transmission method of the above-mentioned two-way wireless power transmission system.

[0025] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0026] (1) The present invention realizes load matching of the BIPT system through the load matching condition function, thereby improving the transmission efficiency of the intermediate AC resonance link; and broadens the ZVS range of the BIPT system through the ZVS soft switching condition function G1, thereby reducing the switching loss and electromagnetic interference of the system.

[0027] (2) The present invention can continuously modulate the excitation voltage on both sides of the system and make the voltage pulses more evenly distributed along the time axis, thereby reducing the fluctuation of the resonant current on both sides.

[0028] (3) The present invention enables the BIPT system to maintain a very high system power factor within an extremely wide power range, and can achieve efficient harmonic power transmission. In addition, the change in harmonic order is smooth, which ultimately reduces the reactive circulating current loss in the BIPT system, improves the system power factor, and enhances the overall transmission efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the existing BIPT system.

[0030] Figure 2 Schematic diagram of the power transmission method of the BIPT system provided by the present invention.

[0031] Figure 3 The waveform diagram of the excitation voltage and resonant current on both sides provided by the embodiment of the present invention; wherein (a) is α t (β t )∈(5π,6π], (b) is the waveform of the voltage and current on both sides of the system, and (c) is the waveform of α t (β t )∈(4π,5π], (c) is the waveform of the voltage and current on both sides of the system, and (c) is α t (β t )∈(3π,4π], (d) is the waveform of the voltage and current on both sides of the system, t (β t )∈(2π,3π], (e) is the waveform of the voltage and current on both sides of the system, t (β t )∈(π,2π], (f) is the waveform of the voltage and current on both sides of the system, t (β t )∈(0,π], the waveform of the voltage and current on both sides of the system.

[0032] Figure 4 Schematic diagram of other modulation sequences of the excitation voltage pulse in each modulation period provided by the embodiment of the present invention; wherein (a), (b), (c), and (d) are different modulation sequence schemes of the excitation voltage pulse in each modulation period, respectively.

[0033] Figure 5 The embodiment of the present invention provides a curve showing the change of the system power factor angle with respect to the system transmission power.

[0034] Figure 6 The voltage and current experimental waveforms on both sides of the system provided in the embodiment of the present invention; wherein, (a) is the voltage and current experimental waveform at 85% full load, (b) is the voltage and current experimental waveform at 50% full load, and (c) is the voltage and current experimental waveform at 11% full load.

[0035] Figure 7 The embodiment of the present invention provides a curve showing the variation of system transmission efficiency with transmission power. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Before explaining the technical solution of the present invention in detail, the BIPT system is briefly introduced as follows:

[0038] The BIPT system includes a main circuit and a control circuit. Figure 1 As shown, it includes a source-end full-bridge inverter circuit, a source-end resonant compensation network, a coupling mechanism, a load-end resonant compensation network, a load-end rectifier circuit and a filter circuit that are cascaded in sequence; each full-bridge converter includes four switch tubes; Figure 1 In the main circuit shown, the source-end resonant compensation network and the load-end resonant compensation network are in double SS form. Depending on the actual situation, they can also be in double LCL or double LCC form. The control circuit includes AC and DC voltage and current sampling and conditioning circuits, a digital controller and its peripheral circuits, a drive circuit, and a protection circuit.

[0039] In order to solve the technical problem that the existing BIPT system cannot always maintain high transmission efficiency within a wide power range, the present invention provides a power transmission method for a BIPT system, the overall idea of ​​which is: by combining multiple switching cycles into a modulation cycle, sequentially and asymmetrically adjusting the width of each voltage pulse half-wave in each modulation cycle, it is easier for each switching device to achieve ZVS. At the same time, the reactive circulating current in the system is effectively suppressed, the system power factor is significantly improved, and the overall transmission efficiency is also improved.

[0040] Example:

[0041] A BIPT system with a SS resonant network, such as Figure 1 As shown, the system includes a primary full-bridge conversion circuit, a primary resonant compensation network, a weakly coupled transformer, a secondary resonant compensation network, a secondary full-bridge conversion circuit and a filter circuit which are cascaded in sequence. 1dc and U 2dc is the DC bus voltage on both sides of the system, I 1dc and I 2dc is the DC current on both sides of the system, i p and i s is the resonant current on both sides of the system. The full-bridge converter on the source side consists of MOSFETs Q1~Q4, and the full-bridge converter on the secondary side consists of MOSFETs Q5~Q8. p and L s are the self-inductance of the coupling coils on both sides of the system, M is the mutual inductance between the coupling coils on both sides, C p and C s is the resonant compensation capacitor on both sides, r p and r s is the equivalent loss resistance of the resonant network on both sides.

[0042] like Figure 2 As shown, the power transmission method of the BIPT system provided in this embodiment includes:

[0043] Every three switching cycles of the excitation voltage on both sides of the system are combined into a modulation cycle, and the excitation voltage on both sides of the system is modulated in units of modulation cycles. At this time, the total pulse width α of the excitation voltage on both sides of the system in the modulation cycle is t , β t The value range of is [0,6π]. Figure 3 As shown in (a) in the figure, along the time axis, for the system source end, the width of each voltage pulse half wave is α1 to α6; for the system load end, the width of each voltage pulse half wave is β1 to β6. When the system is fully loaded, α t , β t All are 6π, α1~α6, β1~β6 are all π.

[0044] When the transmission power of the system decreases, the total pulse width α needs to be reduced t , β t , so, first reduce the pulse width α2(β2), when α2(β2) decreases from π to 0, then reduce α5(β5), when α5(β5) decreases from π to 0, then reduce α4(β4)... and so on, successively reduce the pulse width angles α2(β2), α5(β5), α4(β4), α1(β1), α3(β3), α6(β6), until finally α6(β6) decreases to 0, as shown in Figure 3 As shown in (a) to (f) in FIG. 1 , the modulation order can ensure that the distribution of the voltage pulse along the time axis is always relatively uniform, thereby suppressing the fluctuation of the resonant current on both sides of the system.

[0045] In addition to the above modulation sequence, there are some voltage pulse half-wave modulation sequences such as Figure 4 As shown, these modulation orders can also suppress the fluctuations of the resonant current on both sides of the system.

[0046] Using an asymmetric modulation method, when the pulse width of the source-end excitation voltage is reduced, the left edge of each pulse half-wave remains stationary and the right edge moves to the left; when the pulse width of the load-end excitation voltage is reduced, the right edge of each pulse half-wave remains stationary and the left edge moves to the right. Therefore, all switching devices in the system can easily achieve ZVS.

[0047] The DC current is sampled at the load end of the BIPT system, and the total pulse width β of the excitation voltage at the load end in each modulation cycle is obtained by the PI controller after subtracting it from the given value. t , β t It can be converted into the width of each voltage pulse half wave β1~β6.

[0048] At the same time, β t With the system DC output voltage U 2dc The total pulse width α of the excitation voltage in each modulation cycle of the system source end can be obtained by the load matching condition G2 through the wireless communication module. t , α t It can be converted into the width of each voltage pulse half wave α1~α6.

[0049] The value of δ can be derived from the system ZVS condition function G2. α1~α6 can generate driving signals for switching devices Q1~Q4 through the source-side PWM modulation link, and δ and β1~β6 can generate driving signals for switching devices Q5~Q8 through the load-side PWM modulation link.

[0050] In this embodiment, when α t (β t )∈(5π,6π], the BIPT system can be regarded as fundamental power transmission; when α t (β t)∈(4π,5π], the BIPT system can be regarded as 6 / 5th harmonic power transmission; when α t (β t )∈(3π,4π], the BIPT system can be regarded as 3 / 2nd harmonic power transmission; when α t (β t )∈(2π,3π], the BIPT system can be regarded as a second harmonic power transmission; when α t (β t )∈(π,2π], the BIPT system can be regarded as third harmonic power transmission; when α t (β t )∈(0,π], the BIPT system can be regarded as sixth harmonic power transmission.

[0051] In this embodiment, for the system ZVS condition function G1 and the load matching condition function G2, the phase margin φ is set to 8°, |u p |、|u s |、 Can be expressed as:

[0052]

[0053]

[0054] in

[0055]

[0056]

[0057] In this embodiment, the power factor angle θ and the transmission power P of the BIPT system can be expressed as:

[0058]

[0059]

[0060] Among them, ω r is the resonant angular frequency of the BIPT system, which can be expressed as The relationship curve between the system power angle θ and the transmission power P is as follows: Figure 5 As shown, the relationship curve between θ and P under the traditional three-phase shift power transmission method is also as follows Figure 5 As shown, here the system rated value is used as a reference, and P is normalized. When the traditional three-phase shift power transmission method is used, the system power angle θ increases continuously with the decrease of the transmission power P, which means that the reactive circulating current loss in the system will gradually increase, and the system transmission efficiency will continue to decrease; while the present invention can reduce the power factor angle of the system within the full power range, thereby improving the system power factor and improving the system transmission efficiency.

[0061] Based on the above ZVS condition function and load matching condition function, this embodiment can achieve ZVS of all switching devices and obtain maximum transmission efficiency.

[0062] The following is a further description of the beneficial effects that can be achieved by this embodiment in combination with actual experimental results. Figure 1 In the main circuit shown, the parameters of each component are: L p =183.25μH, L s =180.45μH, C p =19.11nF, C s =19.424nF, M=35.475μH, r p =0.32Ω,,r s =0.32Ω, system switching frequency f=85kHz, U 1dc =300V, U 2dc =300V, the controllers on both sides are TMS320F28377 DSP.

[0063] Based on the above conditions, the present invention is experimentally verified. Under different load conditions, the square wave excitation voltages u1, u2 and the resonant current i on both sides of the BIPT system are p 、i s Waveform Figure 6 As shown in the figure, the relationship between the transmission efficiency and transmission power of the BIPT system is as follows: Figure 7 shown.

[0064] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A power transmission method of a bidirectional wireless power transmission system, wherein the bidirectional wireless power transmission system comprises a source-end full-bridge inverter circuit, a source-end resonant compensation network, a coupling mechanism, a load-end resonant compensation network, a load-end rectifier circuit and a filter circuit which are cascaded in sequence, characterized in that: The power transmission method comprises: n adjacent switching cycles of the excitation voltages on both sides of the system are combined into one modulation cycle, and the excitation voltages on both sides of the system are modulated in units of one modulation cycle; in each modulation cycle, only the pulse width of one voltage half-wave is asymmetrically adjusted at the same time, and the pulse widths of other voltage half-waves remain unchanged; the modulation order of each voltage half-wave is selected so that the excitation voltage is evenly distributed along the time axis, where n is an integer greater than 1; At the load end of the system, the DC current sampled is subtracted from the given value and the total pulse width β of the excitation voltage in each modulation cycle at the load end is obtained by the PI controller. t , β t Converted into the pulse width of each voltage half-wave in each modulation cycle: β1, β2, β3…β 2n ; At the system source, according to β t The DC voltage U 2dc The total pulse width α of the excitation voltage in each modulation cycle at the system source end is obtained by the load matching condition function: t , and α t Converted into the pulse width of each voltage half-wave in each modulation cycle: α1, α2, α3…α 2n , generating a driving signal for a switching device of a source-side full-bridge inverter circuit through PWM modulation; Based on α t , β t , the phase δ of the square wave excitation voltage at the source end of the system lagging behind the square wave excitation voltage at the load end is obtained from the ZVS soft switching condition function of each switching device on both sides of the system. δ is related to β1, β2, β3…β n The driving signal of the switch device of the load-end rectifier circuit is generated through PWM modulation; the ZVS soft switching condition function G1 and the load matching condition function G2 are respectively: Among them, U 1dc , U 2dc Respectively represent the DC voltage on both sides of the system, φ is the preset phase margin value, 5°≤φ≤10°, u p 、u s They are the square wave excitation voltages u1 and u2 on both sides of the system at the resonant frequency f r The sinusoidal AC component under |u p |、|u s | respectively u p 、u s The effective value of u p 、u s The phase difference with u1 and u2.

2. The power transmission method according to claim 1, characterized in that: For the system source end, the time lag edge of each voltage half-wave is adjusted to keep its leading edge unchanged; for the system load end, the time lead edge of each voltage half-wave is adjusted to keep its lagging edge unchanged.

3. The power transmission method according to claim 1, characterized in that: The power factor angle θ and the transmission power P of the two-way wireless power transmission system can be expressed as: Among them, ω r is the resonant angular frequency of the BIPT system, which can be expressed as 4. A power transmission device for a two-way wireless power transmission system, characterized in that: comprising a computer readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the power transmission method of the bidirectional wireless power transmission system according to any one of claims 1 to 3.

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