An efficiency optimization control method for wireless power transmission system based on rectifier mode switching

Abstract

The application provides a wireless power transmission system efficiency optimization control method based on rectifier mode switching, which can realize optimal efficiency in a wide load range and constant current output. In the control strategy, by judging the load size, the rectifier bridge works in a diode bridge mode when the load is light, works in a half-active bridge mode when the load is larger, and works in an H bridge mode when the load is heavy, and works in the optimal load point corresponding to the maximum efficiency in the half-active bridge and H bridge modes, so as to realize efficiency optimization in a wide load range. Meanwhile, the output current is constant by adjusting the DC input side voltage of the inverter. Compared with the prior art, the application has the advantages of not needing to use an additional DC-DC converter, reducing the control complexity, and being capable of realizing efficiency optimization in a wide load range.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wireless power transmission, and particularly relates to a wireless power transmission system efficiency optimization control method based on rectifier mode switching. BACKGROUND

[0002] Compared with the traditional cable charging method, the wireless power transmission method has the characteristics of safety, durability and flexibility, and gradually becomes a way to replace wired charging. When designing a wireless power transmission system, two factors need to be considered, one is to have constant output capacity, and the other is to run at high efficiency in a wide load variation range, which is particularly important in high-power application occasions. There are four ways to improve the efficiency:

[0003] 1) High quality factor passive element method: The efficiency of the wireless power transmission system is proportional to the quality factor, so high quality factor coils and compensation circuit elements can be used to improve the system efficiency.

[0004] 2) Passive impedance matching method: An array of capacitors is used to maintain system resonance through switching capacitor connection to achieve high efficiency operation, but this method requires multiple capacitors and switches, increasing the cost, and it cannot achieve stepless tuning.

[0005] 3) Active impedance matching method: By controlling the duty cycle of the power electronic converter to work at the optimal load point corresponding to the maximum efficiency, the maximum efficiency tracking is realized. For example, a DC-DC converter is connected in front of the inverter or behind the diode rectifier bridge, and by controlling the duty cycle to work at the optimal load point that realizes the maximum efficiency, or tracking the minimum input current corresponding to the minimum input power to realize the maximum efficiency tracking, but this method increases the additional power electronic converter and cost, and the control is more complex. In order to reduce the use of power electronic converters, the uncontrollable diode rectifier bridge can be replaced with a semi-active rectifier or H-bridge rectifier, and the duty cycle is adjusted to adjust the equivalent impedance seen from the AC side of the rectifier, so that it works at the optimal equivalent load point corresponding to the maximum efficiency. However, when the optimal equivalent load point is greater than the equivalent resistance seen from the AC input side of the uncontrollable diode rectifier bridge, it cannot always maintain maximum efficiency operation by adjusting the duty cycle.

[0006] 4) Mode switching: In order to overcome the problem that the controllable rectifier bridge (half-active bridge rectifier, H-bridge rectifier) cannot work at the optimal load point by adjusting the duty cycle, the primary side inverter and the secondary side rectifier can be operated in different modes, and the modes can be combined and switched under different loads, for example, full-bridge inverter-full-bridge rectifier mode, half-active bridge inverter-half-active bridge rectifier mode, full-bridge inverter-half-active bridge rectifier mode and half-active bridge inverter-full-bridge rectifier mode. This mode does not require additional hardware circuits and complex control methods, and can achieve efficiency optimization in a wide range. However, this mode does not always work at the optimal load point corresponding to the maximum efficiency, and the primary side and the secondary side need to be switched at the same time to achieve the set output voltage. At the same time, the adjustable range of the ratio of the output voltage to the input voltage is limited due to the influence of the converter operating mode, and the switching loss of the system is increased due to the on and off signals of the switching tube in the full load range, which reduces the efficiency.

[0007] Therefore, how to design a control strategy to achieve maximum efficiency tracking and wide range output only by switching the mode of the secondary side rectifier, while minimizing the number of switching tube on and off, is of great significance to the stable operation of the inductive wireless power transmission system under load changes. SUMMARY

[0008] To achieve the above purpose, the application provides an inductive wireless power transmission system efficiency optimization control strategy based on rectifier mode switching:

[0009] The wireless power transmission system efficiency optimization control strategy based on rectifier mode switching provided by the application achieves maximum efficiency tracking in a wide range of load changes by switching the rectifier operating mode, and achieves constant output current by adjusting the inverter input voltage. The topology used in the application includes a high-frequency full-bridge inverter circuit composed of Q1, Q2, Q3 and Q4, a loosely coupled mechanism composed of primary side compensation capacitor C p , coil L p and coil L s , and their mutual inductance M, secondary side compensation capacitor C s , the internal resistance of the primary side coil and the secondary side coil are r p and r s , a rectifier bridge composed of Q5, Q6, Q7 and Q8, and a load R L . The rectifier bridge includes three operating modes, namely diode bridge operating mode, half-active bridge operating mode and full-bridge operating mode. A wireless power transmission system efficiency optimization control method based on rectifier mode switching includes the following steps:

[0010] Step 1: Give the driving signal of the rectifier in different modes:

[0011] In the diode bridge mode, the four switches do not need driving pulses;

[0012] In the half-active bridge mode, the switches Q5 and Q7 do not need driving pulses, the driving pulses of the switches Q6 and Q8 are complementary PWM signals, and the switch Q8 is turned on at point where the receiving side current crosses zero from negative to positive (1-D s_SA )π, where D s_SA is the duty ratio of the input side voltage in the half-active bridge mode.

[0013] In the full-bridge mode, the driving pulses of the switches Q5 and Q6 are complementary PWM signals, the driving pulses of the switches Q7 and Q8 are complementary PWM signals, the switch Q5 is turned on at point where the receiving side current crosses zero from negative to positive θ1, and the switch Q8 is turned on at point where the receiving side current crosses zero from negative to positive θ2, is the phase difference between the input side voltage and the current of the rectifier in the H-bridge mode, D s_H is the duty ratio of the input side voltage in the H-bridge mode, and their relationship is:

[0014]

[0015] Step two, calculate the AC side impedance of the rectifier in different modes:

[0016] The input voltage of the rectifier in the diode bridge mode, the half-active bridge mode and the H-bridge mode is V s_x (x=D, SA, H) is:

[0017]

[0018] where x=D represents the diode bridge mode, x=SA represents the half-active bridge mode, and x=H represents the H-bridge mode.

[0019] The input current I s_x (x=D, SA, H) of the rectifier in the diode bridge mode, the half-active bridge mode and the H-bridge mode is:

[0020]

[0021] where I s_D , I s_SA and I s_H are the effective values of the input current of the rectifier in the diode bridge mode, the half-active bridge mode and the H-bridge mode, respectively.

[0022] According to the voltage and current waveforms of the rectifier bridge in the three modes, the current I o_x (x=D, SA, H) filtered by the DC output capacitor in the diode bridge mode, the half-active bridge mode and the H-bridge mode is:

[0023]

[0024] Input impedance Z of rectifier in diode bridge, half-active bridge, H-bridge mode eq_x (x = D, SA, H) are:

[0025]

[0026] By combining (2), (3), (4) and (5), the equivalent impedance Z in diode bridge, half-active bridge and H-bridge mode is: eq_x_ (x = D, SA, H) are:

[0027]

[0028] where, R eq_D is the equivalent resistance on the AC side in diode bridge mode, R eq_SA and X eq_SA are the equivalent resistance and reactance on the AC side in half-active bridge mode, R eq_H and X eq_H are the equivalent resistance and reactance on the AC side in H-bridge mode.

[0029] Step three, calculate the efficiency from the inverter output side to the input side of the rectifier bridge:

[0030] I p_x and I s_x (x = D, SA, H) represent the current flowing through the primary side and the secondary side in x mode, R eq_x and X eq_x represent the resistance and reactance seen from the AC input side of the rectifier in x mode, and write KVL equations for the transmitting side and the receiving side:

[0031]

[0032] where, X p , X s and X m are the resonance reactance of the transmitting side, the resonance reactance of the receiving side and the mutual inductance, which are:

[0033]

[0034] Substitute (8) into (7) to get, the current I p_x flowing through the transmitting side and the current I s_x flowing through the receiving side are:

[0035]

[0036] The efficiency η from the inverter output side to the input side of the rectifier bridge is x (x = D, SA, H) are:

[0037]

[0038] ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively x (x=D,SA,H) are:

[0039]

[0040] From (11), it can be seen that the efficiency in diode bridge mode is related to the load, the efficiency in half-active bridge mode is related to the load and the duty cycle, and the efficiency in H-bridge mode is related to the load, the duty cycle and the phase-shift angle, therefore, the maximum efficiency tracking in half-active bridge mode and H-bridge mode can be realized by controlling the duty cycle.

[0041] Step four, calculate the maximum efficiency that can be achieved at different loads:

[0042] ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively SA ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively s_SA ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively SA_opt ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively H ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively s_H ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively H_opt ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively

[0043]

[0044] ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively max_SA ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively max_H ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively max_D ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively

[0045]

[0046] Step five, calculate the switching conditions in three modes:

[0047] ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively max_D ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively max_SA ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively L_mc1 ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectively

[0048]

[0049] ηdiode,ηhalf,ηH are the efficiencies in diode bridge, half-active bridge and H-bridge mode respectivelymax_SA =η max_H The load resistance R is obtained when the maximum efficiency is equal in semi-active bridge mode and H-bridge mode. L_mc2 for:

[0050]

[0051] When R L <R L_mc1 At that time, η max_D >η max_SA The system operates in diode bridge mode; when R L_mc1 ≤R L <R L_mc2 At that time, η max_SA >η max_H The system operates in semi-active bridge mode; when R L ≤R L_mc2 At that time, η max_H ≥η max_SA The system operates in H-bridge mode, therefore, R L_mc1 It is a load switching from diode bridge mode to semi-active bridge mode, R L_mc2 It is a load switching from semi-active bridge mode to H-bridge mode.

[0052] As can be seen from (15), the switching load in the semi-active bridge mode and the H-bridge mode is related to the phase shift angle. Therefore, it is very necessary to determine the phase shift angle.

[0053] Step 5: Determine the phase shift angle in H-bridge mode:

[0054] When the minimum system efficiency is required to be η ref At that time, the system efficiency η in the semi-active bridge mode ref_SA Equal to η ref Load resistance R L _ ref for:

[0055]

[0056] Let R L_mc2 =R L _ ref The phase shift angle in H-bridge mode can be obtained as follows:

[0057]

[0058] From the above analysis, the rectifier works in different modes to achieve optimal efficiency in the full load range. When the rectifier works in diode bridge mode, the output current on the DC side does not change despite the change in load. However, when the rectifier works in half-active bridge mode and H-bridge mode, adjusting the duty cycle under different loads achieves optimal efficiency, but the output current of the rectifier bridge also changes. This cannot meet the constant current charging of the battery. Therefore, a method for achieving constant charging is needed.

[0059] Step six, constant current charging in diode bridge, half-active bridge and H-bridge modes:

[0060] When the inverter operates in complementary conduction mode with a conduction angle of 180°, the effective value of the inverter output voltage V p_x (x=D,SA,H) is:

[0061]

[0062] where V dc_x (x=D,SA,H) is the DC input voltage of the inverter in x mode.

[0063] The transconductance gain G of the resonant compensation network in diode bridge, half-active bridge and H-bridge modes ri_x (x=D,SA,H) is:

[0064]

[0065] The transconductance gain G of the output current to the input voltage in diode bridge, half-active bridge and H-bridge modes iv_x (x=D,SA,H) is:

[0066]

[0067] To achieve constant current charging, the input voltage of the inverter can be adjusted to achieve constant transconductance gain. If the system requires a constant output current of I ref , from equation (20), the input voltage V dc_D in diode bridge mode is:

[0068]

[0069] The input voltage V dc_SA in half-active bridge mode is:

[0070]

[0071] The input voltage V dc_H in H-bridge mode is:

[0072]

[0073] Through the above steps, the wireless power transmission system efficiency optimization control strategy based on rectifier mode switching of the application can realize the efficiency optimization of the wireless power transmission link in the full load range, while maintaining the constant output current.

[0074] The following will be described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0075] Figure 1 For the inductive wireless power transmission system topology based on rectifier mode switching;

[0076] Figure 2 For the diode bridge operation mode structure;

[0077] Figure 3 For the half-active bridge operation mode structure;

[0078] Figure 4 For the full-bridge operation mode structure;

[0079] Figure 5 For the system control strategy diagram;

[0080] Figure 6 For the rectifier bridge voltage and current waveform in the diode bridge operation mode;

[0081] Figure 7 The driving signal and rectifier bridge voltage and current waveform in the half-active bridge operation mode;

[0082] Figure 8 The driving signal and rectifier bridge voltage and current waveform in the H-bridge operation mode;

[0083] Figure 9 For the AC equivalent circuit of the inductive wireless power transmission system topology with rectifier mode switching;

[0084] Figure 10 For the output voltage and current waveform when the load changes from 5Ω to 10Ω in the diode bridge mode;

[0085] Figure 11 For the output voltage and current waveform when the load changes from 20Ω to 60Ω in the half-active bridge mode;

[0086] Figure 12 For the output voltage and current waveform when the load changes from 80Ω to 130Ω in the H-bridge mode;

[0087] Figure 13 Before adopting the proposed rectifier mode switching method, the system efficiency in the diode rectifier bridge mode, half-active bridge mode and H-bridge mode changes with the load;

[0088] Figure 14 To illustrate how the system efficiency varies with load across the entire load range after adopting the proposed rectifier mode switching method; Detailed Implementation

[0089] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0090] The technical solution adopted in this invention is as follows: Figure 1 As shown, a high-frequency full-bridge inverter circuit consisting of Q1, Q2, Q3, and Q4 is included, with primary-side compensation capacitor C. p coil L p and coil L s The loosely coupled mechanism consists of a mutual inductance of M and a secondary compensation capacitor C. s The internal resistances of the primary coil and the secondary coil are r and r, respectively. p and r s The rectifier bridge consisting of Q5, Q6, Q7, and Q8, and the load R L The rectifier bridge includes three operating modes: diode bridge mode, semi-active bridge mode, and full-bridge mode, such as... Figures 2-4 As shown. The control strategy block diagram is as follows. Figure 5 As shown, an efficiency optimization control method for a wireless power transmission system based on rectifier mode switching includes the following steps:

[0091] Step 1: Provide the drive signals for the rectifier in different modes:

[0092] The rectifier bridge voltage and current waveforms in diode bridge operation mode are as follows: Figure 6 As shown, the four switching transistors do not require drive pulses;

[0093] The drive signal and rectifier bridge voltage and current waveforms in the semi-active bridge operation mode are as follows: Figure 7 As shown, switches Q5 and Q7 do not require drive pulses, while the drive pulses for switches Q6 and Q8 are complementary PWM signals. Switch Q8 is driven by the zero-crossing point of the current on the receiving side from negative to positive (1-D). s_SA It is activated at π, where D s_SA This represents the duty cycle of the input voltage in semi-active bridge mode.

[0094] The drive signal and rectifier bridge voltage and current waveforms in full-bridge operation mode are as follows: Figure 8 As shown, the drive pulses for switches Q5 and Q6 are complementary PWM signals, and the drive pulses for switches Q7 and Q8 are complementary PWM signals. Switch Q5 turns on at θ1 after the zero-crossing point of the receiving-side current from negative to positive, and switch Q8 turns on at θ2 after the zero-crossing point of the receiving-side current from negative to positive. D represents the phase difference between the input voltage and current of the rectifier in H-bridge mode.s_H The duty ratio of the input side voltage in the H-bridge mode, and the relationship between them is:

[0095]

[0096] Step two, calculate the AC side impedance of the rectifier in different modes:

[0097] The input voltage of the rectifier in diode bridge, half-active bridge and H-bridge mode is V s_x (x=D, SA, H) is:

[0098]

[0099] Wherein, x=D represents the diode bridge mode, x=SA represents the half-active bridge mode, and x=H represents the H-bridge mode.

[0100] The input current of the rectifier in diode bridge, half-active bridge, H-bridge mode is I s_x (x=D, SA, H) is:

[0101]

[0102] Wherein, I s_D , I s_SA and I s_H are the effective values of the input current of the rectifier in diode bridge, half-active bridge and H-bridge mode respectively.

[0103] According to the voltage and current waveforms of the rectifier bridge in three modes, the current I o_x (x=D, SA, H) filtered by the DC output capacitor in diode bridge, half-active bridge and H-bridge mode is obtained:

[0104]

[0105] The input impedance Z eq_x of the rectifier in diode bridge, half-active bridge and H-bridge mode is:

[0106]

[0107] By combining (2), (3), (4) and (5), the equivalent impedance Z eq_x_ of the rectifier in diode bridge, half-active bridge and H-bridge mode is obtained:

[0108]

[0109] Wherein, R eq_D is the equivalent resistance on the AC side in diode bridge mode, R eq_SA and X eq_SAR eq_H and X eq_H are the equivalent resistance and reactance at the AC side for H-bridge mode.

[0110] Step three, calculate the efficiency from the inverter output side to the rectifier bridge input side:

[0111] The AC equivalent circuit of the topology used in the present application is shown in Figure 9 where I p_x and I s_x (x=D,SA,H) represent the primary side current and the secondary side current for x mode, respectively, R eq_x and X eq_x represent the resistance and reactance seen from the AC input side of the rectifier for x mode, respectively, and write KVL equations for the transmitting side and the receiving side columns:

[0112]

[0113] where X p , X s and X m are the transmitting side resonant reactance, the receiving side resonant reactance and the mutual inductance, which are respectively:

[0114]

[0115] Substitute (8) into (7), the current I p_x flowing through the transmitting side and the current I s_x flowing through the receiving side are:

[0116]

[0117] The efficiency η x from the inverter output side to the rectifier bridge input side for x mode (x=D,SA,H) is:

[0118]

[0119] Solve (6), (8), (9) and (10) together, the efficiencies η x for diode bridge, half-active bridge and H-bridge mode (x=D,SA,H) are respectively:

[0120]

[0121] It can be seen from (11) that the efficiency for diode rectifier bridge mode is related to the load, the efficiency for half-active bridge mode is related to the load and the duty cycle, and the efficiency for H-bridge mode is related to the load, the duty cycle and the phase shift angle, so the maximum efficiency tracking for half-active bridge mode and H-bridge mode can be realized by controlling the duty cycle.

[0122] Step four, calculate the maximum efficiency that can be achieved at different loads:

[0123] ηdiode, ηhalf, ηH, efficiency from inverter output to rectifier bridge in diode bridge, half-active bridge and H-bridge mode respectively SA dD s_SA dD SA_opt ; ηH, efficiency from inverter output to rectifier bridge in H-bridge mode H dD s_H dD H_opt , are respectively:

[0124]

[0125] ηdiode, ηhalf, ηH, efficiency from inverter output to rectifier bridge in diode bridge, half-active bridge and H-bridge mode respectively max_SA and ηH max_H can be obtained by substituting (12) into (11), while the maximum efficiency ηdiode max_D of diode bridge mode under different loads is the same as (11). At this time, the maximum efficiency of diode bridge, half-active bridge and H-bridge mode under different loads is:

[0126]

[0127] Step five, calculate the switching conditions in three modes:

[0128] Let ηdiode max_D = ηhalf max_SA , the load resistance R L_mc1 when the maximum efficiency of diode bridge mode and half-active bridge mode is equal is:

[0129]

[0130] Let ηhalf max_SA = ηH max_H , the load resistance R L_mc2 when the maximum efficiency of half-active bridge mode and H-bridge mode is equal is:

[0131]

[0132] When R L < R L_mc1 , ηdiode max_D > ηhalf max_SA , the system runs in diode bridge mode; when R L_mc1 ≤ R L < R L_mc2 , ηhalf max_SA > ηH max_H , the system runs in half-active bridge mode; when R L ≤ RL_mc2 At that time, η max_H ≥η max_SA The system operates in H-bridge mode, therefore, R L_mc1 It is a load switching from diode bridge mode to semi-active bridge mode, R L_mc2 It is a load switching from semi-active bridge mode to H-bridge mode.

[0133] As can be seen from (15), the switching load in the semi-active bridge mode and the H-bridge mode is related to the phase shift angle. Therefore, it is very necessary to determine the phase shift angle.

[0134] Step 5: Determine the phase shift angle in H-bridge mode:

[0135] When the minimum system efficiency is required to be η ref At that time, the system efficiency η in the semi-active bridge mode ref_SA Equal to η ref Load resistance R L _ ref for:

[0136]

[0137] Let R L_mc2 =R L _ ref The phase shift angle in H-bridge mode can be obtained as follows:

[0138]

[0139] The above analysis shows that the rectifier achieves optimal efficiency across the entire load range when operating in different modes under different loads. When the rectifier operates in diode rectifier bridge mode, although load changes will alter the efficiency, the DC output current remains unchanged. However, when the rectifier operates in semi-active bridge mode and H-bridge mode, adjusting the duty cycle under different loads achieves optimal efficiency, but the rectifier bridge output current also changes, which cannot meet the requirement of constant current charging for the battery. Therefore, a method to achieve constant charging needs to be provided.

[0140] Step 6: Implement constant current charging in diode rectifier bridge, semi-active bridge, and H-bridge modes:

[0141] When the inverter operates in complementary conduction mode and the conduction angle is 180°, the effective value of the inverter output voltage V p_x (x = D, SA, H) is:

[0142]

[0143] Among them, V dc_x (x=D,SA,H) represents the DC input voltage of the inverter in mode x.

[0144] Transconductance gain G of the resonant compensation network in diode bridge, half-active bridge and H-bridge mode ri_x (x=D,SA,H) is:

[0145]

[0146] Transconductance gain G of the output current to the input voltage in diode bridge, half-active bridge and H-bridge mode iv_x (x=D,SA,H) is:

[0147]

[0148] In order to realize constant current charging, the transconductance gain constant can be realized by adjusting the input voltage of the inverter. If the constant output current of the system is required to be I ref , by formula (20), the input voltage V dc_D in diode bridge mode is:

[0149]

[0150] The input voltage V dc_SA in half-active bridge mode is:

[0151]

[0152] The input voltage V dc_H in H-bridge mode is:

[0153]

[0154] Through the above steps, the wireless power transmission system efficiency optimization control strategy based on rectifier mode switching of the application can realize the efficiency optimization of the wireless power transmission link in the full load range, and can maintain the constant output current.

[0155] Embodiment: simulation result analysis.

[0156] The model is built in Matlab / Simulink, and the simulation parameters are as follows: the switching frequency f is 50 kHz, the self-inductance L p and L s of the coupling mechanism are 118 μH, the self-inductance M is 23.6 μH, the primary side resistance r p is 0.1235 Ω, and the secondary side resistance r s is 0.1235 Ω. Figure 10 is the output voltage and current waveform when the load changes from 5 Ω to 10 Ω in diode bridge mode, Figure 11 is the output voltage and current waveform when the load changes from 20 Ω to 60 Ω in half-active bridge mode, Figure 12For the output voltage and current waveforms of the load changing from 80Ω to 130Ω in the H-bridge mode, it can be seen that the constant current output is realized in the three modes when the load changes, and the load output current is about 2A. Figure 13 Before the proposed rectifier mode switching method is adopted, the system efficiency of the diode bridge mode, the half-active bridge mode and the H-bridge mode changes with the load, and it can be seen that when R L <20Ω, the efficiency of the diode bridge mode is the highest, when 20Ω L <74Ω, the efficiency of the half-active bridge mode is the highest, when 74Ω L >74Ω, the efficiency of the H-bridge mode is the highest. Figure 14 For the system efficiency changing with the load in the full load range after the proposed rectifier mode switching method is adopted, it can be seen that the efficiency of the proposed control method can be above 94% under the full range of load changes.

[0157] As can be seen from the above examples, the wireless power transmission system efficiency optimization control method based on rectifier mode switching proposed by the present application can realize efficiency optimization in the full load range, and also realize constant current output.

[0158] The above examples are only exemplary embodiments of the present application and are not used to limit the present application, and the protection scope of the present application is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present application within the spirit and protection scope of the present application, and such modifications or equivalent replacements shall also be considered to fall within the protection scope of the present application.

Claims

1. A wireless power transmission system efficiency optimization control method based on rectifier mode switching, by switching the rectifier operating mode to achieve maximum efficiency tracking within a wide range of load variation, and by adjusting the input voltage of the inverter to achieve constant output current, the wireless power transmission system topology includes a high-frequency H-bridge inverter circuit composed of Q1, Q2, Q3 and Q4, a loosely coupled mechanism composed of a primary side compensation capacitor C p , a coil L p and a coil L s , and their mutual inductance is M, a secondary side compensation capacitor C s , the internal resistance of the primary side coil and the secondary side coil is r p and r s , respectively, a rectifier bridge composed of Q5, Q6, Q7 and Q8, and a load R L , the rectifier bridge includes three operating modes, respectively, diode bridge operating mode, half-active bridge operating mode and H-bridge operating mode, characterized in that, The method comprises the following steps: 1) giving driving signals of the rectifier in different modes; 2) calculating AC side impedance of the rectifier in different modes; 3) calculating efficiency from the inverter output side to the input side of the rectifier bridge; 4) calculating maximum efficiency that can be achieved under different loads; 5) Calculate the switching condition in three modes: the mode switching strategy of the system is based on the size of the load resistance: by equating the maximum efficiency of the diode bridge and the semi-active bridge mode, derive the switching load R L_mc1 ; equate the maximum efficiency of the semi-active bridge and the H-bridge mode, derive R L_mc2 ; The system automatically switches according to the actual load: when R L < R L_mc1 , use the diode bridge mode, R L_mc1 < R L < R L_mc2 , use the semi-active bridge mode, R L > R L_mc2 , switch to the H-bridge mode, so as to always maintain the highest transmission efficiency; 6) realizing constant current charging in diode rectifier bridge, half-active bridge or H-bridge mode.

2. The efficiency optimization control method for a wireless power transfer system based on rectifier mode switching according to claim 1, characterized in that: In the step 1), the driving signals of the rectifier in different modes are given: In the diode bridge operation mode, the four switches do not need driving pulses; in the half-active bridge operation mode, the switches Q5 and Q7 do not need driving pulses, the driving pulses of the switches Q6 and Q8 are complementary PWM signals, and the switch Q8 is turned on at the point of π where the receiving side current crosses zero from negative to positive (1-D s_SA )π, where D s_SA is the duty ratio of the input side voltage in the half-active bridge mode; in the H-bridge operation mode, the driving pulses of the switches Q5 and Q6 are complementary PWM signals, the driving pulses of the switches Q7 and Q8 are complementary PWM signals, the switch Q5 is turned on at the point of θ1 where the receiving side current crosses zero from negative to positive, the switch Q8 is turned on at the point of θ2 where the receiving side current crosses zero from negative to positive, is the phase difference between the input side voltage and the current of the rectifier in the H-bridge mode, and D s_H is the duty ratio of the input side voltage in the H-bridge mode, and their relationship is:

3. The efficiency optimization control method for a wireless power transfer system based on rectifier mode switching according to claim 1, characterized in that: In the step 2), the AC side impedance of the rectifier in different modes is calculated: The rectifier input voltage is V s_x (x = D, SA, H) is: Wherein, x=D represents the diode bridge operation mode, x=SA represents the half-active bridge operation mode, and x=H represents the H-bridge operation mode; Diode bridge, half-active bridge, H-bridge mode rectifier input current I s_x (x = D, SA, H) is: where I s_D , I s_SA and I s_H are the effective values of the input current of the diode bridge, the half-active bridge and the H-bridge rectifier, respectively. According to the voltage and current waveforms of the rectifier bridge in the three modes, the current I filtered by the DC output capacitor in the diode bridge, half-active bridge and H-bridge modes is obtained o_x (x = D, SA, H) is: Input impedance Z of the rectifier in diode bridge, half-active bridge, H-bridge mode eq_x (x = D, SA, H) is: By combining (2), (3), (4) and (5), the equivalent impedance Z in diode bridge, half-active bridge and H-bridge modes is obtained eq_x_ (x = D, SA, H) are: wherein R eq_D is the equivalent resistance on the AC side in diode bridge mode, R eq_SA and X eq_SA are the equivalent resistance and reactance on the AC side in semi-active bridge mode, R eq_H and X eq_H are the equivalent resistance and reactance on the AC side in H-bridge mode.

4. The efficiency optimization control method for a wireless power transfer system based on rectifier mode switching according to claim 1, characterized in that: In step 3), the efficiency from the inverter output side to the rectifier bridge input side is calculated: I p_x and I s_x (x = D, SA, H) represent the primary side current and the secondary side current flowing in the x mode, respectively, R eq_x and X eq_x represent the resistance and the reactance seen from the AC input side of the rectifier in the x mode, respectively, and KVL equations are written for the transmitting side and the receiving side columns: where X p , X s , and X m are the transmit-side resonant reactance, the receive-side resonant reactance, and the mutual inductance reactance, respectively. Substituting (8) into (7) gives the current I flowing through the transmitting side p_x and the current I flowing through the receiving side s_x is: Efficiency η from inverter output side to rectifier bridge input side x (x = D, SA, H) is: Simultaneously (6), (8), (9) and (10), efficiency η in diode bridge, half-active bridge and H-bridge modes x (x = D, SA, H) are: It can be seen from (11) that the efficiency in the diode rectifier bridge mode is related to the load, the efficiency in the half-active bridge mode is related to the load and the duty cycle, and the efficiency in the H-bridge mode is related to the load, the duty cycle and the phase shift angle, so the maximum efficiency tracking in the half-active bridge mode and the H-bridge mode can be realized by controlling the duty cycle.

5. The efficiency optimization control method for a wireless power transfer system based on rectifier mode switching according to claim 1, characterized in that: In the step 4), the maximum efficiency that can be achieved under different loads is calculated: In half-active bridge mode, the efficiency η from the inverter output side to the rectifier bridge SA D s_SA Taking the partial derivative, the duty cycle corresponding to the optimal load point is D SA_opt In H-bridge mode, the efficiency η from the inverter output side to the rectifier bridge H D s_H Taking the partial derivative, the duty cycle corresponding to the optimal load point is D H_opt , respectively Efficiency η of half-active bridge and H-bridge mode at different loads at this time max_SA and η max_H (11) can be obtained by substituting (12) into (11), while the maximum efficiency η of the diode bridge, half-active bridge and H-bridge mode at different loads at this time is max_D (11), at this time, the maximum efficiency η of the diode bridge, half-active bridge and H-bridge mode at different loads is:

6. The efficiency optimization control method for a wireless power transfer system based on rectifier mode switching according to claim 1, characterized in that: In the step 5), the switching conditions in the three modes are calculated: Let η max_D = η max_SA , the load resistance R L_mc1 at which the maximum efficiencies of the diode bridge mode and the half-active bridge mode are equal is obtained as: Let η max_SA = η max_H , the load resistance R L_mc2 for the maximum efficiency of the half-active bridge mode and H-bridge mode is obtained: When R L <R L_mc1 At that time, η max_D >η max_SA The system operates in diode bridge mode; when R L_mc1 ≤R L <R L_mc2 At that time, η max_SA >η max_H The system operates in semi-active bridge mode; when R L ≥R L_mc2 At that time, η max_H ≥η max_SA The system operates in H-bridge mode, therefore, R L_mc1 It is a load switching from diode bridge mode to semi-active bridge mode, R L_mc2 It is the switching load from the semi-active bridge mode to the H-bridge mode; as can be seen from (15), the switching load in the semi-active bridge mode and the H-bridge mode is related to the phase shift angle.

7. The method of claim 1, wherein: In the step 5), the phase shift angle in the H-bridge mode is determined: When the system efficiency minimum is η ref , the system efficiency η ref_SA in the semi-active bridge mode equals η ref , the load resistance R L is: ref ​ Let R L_mc2 = R L _ ref The phase shift angle in H-bridge mode is:

8. The efficiency optimization control method of a wireless power transfer system based on rectifier mode switching according to claim 1, characterized in that: In the step 6), constant current charging in diode rectifier bridge, half-active bridge or H-bridge mode is realized: The effective value V of the inverter output voltage when the inverter operates in the complementary conduction mode and the conduction angle is 180° is p_x (x = D, SA, H) is: V dc_x (x = D, SA, H) is the DC input side voltage of the inverter in x mode; Transconductance gain G of the resonant compensation network in diode bridge, half-active bridge and H-bridge mode ri_x (x = D, SA, H) is: Transconductance gain G of output current to input voltage in diode bridge, half-active bridge and H-bridge mode iv_x (x = D, SA, H) is: To achieve constant current charging, the input voltage of the inverter can be adjusted to achieve constant transconductance gain, if the constant output current of the system is required to be I ref From equation (20), the input voltage V dc_D in the diode bridge mode is: V = V in - V drop dc_SA V = V in - V drop H-bridge mode input voltage V dc_H is:

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