Disclosure of Invention
Therefore, the invention firstly provides the PT symmetrical MC-WPT system constructed based on the operational amplifier, so that the PT symmetrical MC-WPT system can flexibly adjust the output power level according to the requirement in a larger range by means of parameter design, and the power and the efficiency of the system are irrelevant to mutual inductance.
In order to achieve the above purpose, the specific technical scheme adopted by the invention is as follows:
The PT symmetrical MC-WPT system constructed based on the operational amplifier comprises a primary side circuit and a secondary side circuit, and is characterized in that the primary side circuit comprises a first negative resistance unit, a second negative resistance unit, a primary side coil and a primary side series resonance capacitor, the secondary side circuit comprises a secondary side coil, a secondary side series resonance capacitor, a parallel resonance inductor, a series resonance inductor and an electric load, the first negative resistance unit and the second negative resistance unit are constructed based on the operational amplifier, one end of the first negative resistance unit is grounded, the other end of the first negative resistance unit is used as a forward voltage output end, one end of the second negative resistance unit is grounded, the other end of the second negative resistance unit is used as a reverse voltage output end, the primary side coil and the primary side series resonance capacitor are connected in series between the forward voltage output end and the reverse voltage output end, the secondary side coil and the secondary side series resonance capacitor form a secondary side first series branch to be connected in parallel with the front side of the parallel resonance inductor, the series resonance inductor and the electric load form a secondary side second series branch to be connected in parallel with the back side of the parallel resonance inductor, and the secondary side and the series resonance coil and the secondary side series resonance inductor are connected in parallel to each other in series to realize wireless transmission.
Optionally, the first negative resistance unit and the second negative resistance unit have the same circuit structure and parameters and respectively comprise an operational amplifier, a first resistor, a second resistor and a third resistor, wherein the first resistor is connected between a normal phase input end and an output end of the operational amplifier, the second resistor is connected between an opposite phase input end and the output end of the operational amplifier, the third resistor is connected between the normal phase input end and a grounding end of the operational amplifier, and the opposite phase input end of the operational amplifier extends through a wire to form the normal voltage output end or the opposite voltage output end.
Optionally, the third resistor is formed by connecting two sub-resistors in series, and two anti-parallel diodes are arranged on one of the sub-resistors.
Based on the system, the invention also provides a parameter design method, which is used for the PT symmetrical MC-WPT system constructed based on the operational amplifier and comprises the following steps:
S1, determining a power consumption load resistance value RL, a power grade P, a negative resistance output voltage Uin, a primary coil inductance L1, a primary coil internal resistance Rp1, a secondary coil inductance L2, a secondary coil internal resistance Rp2, a natural frequency grade omega0 and an equivalent load resistance RLeq meeting a target power grade according to application scene requirements, wherein the negative resistance output voltage Uin is an effective voltage between the forward voltage output end and the reverse voltage output end;
s2, according toDetermining system parameters alpha and beta meeting a target power level, wherein Rs＝Rp2+RLeq represents the total secondary side resistance;
s3) determining the value of the secondary side total compensation inductance Leq according to L1＝α(L2+Leq);
S4, determining self-inductance values of the parallel resonance inductance La and the series resonance inductance Lb according to La＝Leq/(1-beta) and Lb＝Leq/beta;
s5, according toDetermining the capacitance values of a primary side series compensation capacitor C1 and a secondary side series compensation capacitor C2;
S6, keeping the primary coil and the secondary coil within a critical coupling range, and enabling the system to work at any bifurcation frequency to achieve constant power P and constant efficiency eta output.
Optionally, in step S6, the critical coupling range is k.gtoreq.k0, where k is the coupling coefficient between the primary coil and the secondary coil, and the coupling coefficient is critical valueIs the quality factor of the secondary coil.
Optionally, the bifurcation frequency of the system in step S6 is:
Optionally, the set parameters ensure the quality factor of the secondary coil
Optionally, the primary and secondary coils are set to have the same structure and parameters.
The system and the method provided by the invention can flexibly adjust the output power level according to the requirement in a larger range, the power and the efficiency of the system are irrelevant to mutual inductance, and meanwhile, the reasonable adjustment of the electrical parameters also has the characteristic of constant power and constant efficiency output when the load resistance changes. The invention can not only be used for wireless charging in occasions with high energy efficiency requirements such as wearable electronic equipment, human body implanted medical electronic equipment and the like, but also be used for wireless charging of high-space degree-of-freedom equipment such as small robots, unmanned aerial vehicles and the like.
Compared with the traditional PT symmetrical MC-WPT system constructed based on the operational amplifier, the invention has the following remarkable effects:
1) According to the invention, the primary and secondary side electrical parameters and the circuit structure of the system are designed to work in a PT symmetrical state, the output power and the efficiency of the system are not affected by mutual inductance change, and the output power level can be adjusted at will in a larger range, so that the system is suitable for various different power levels;
2) The working frequency of the system corresponds to the transmission distance, and the MC-WPT system can work in a PT symmetrical working mode without additional setting links and primary and secondary side communication, so that the MC-WPT system has strong position robustness and anti-offset capability;
3) The constant power and constant efficiency output can be realized when the load resistors with different sizes are driven by adjusting the electric parameters, so that the method is suitable for various electric equipment, and the application range of the technology is greatly expanded.
Detailed Description
The following examples are given for the purpose of illustration only and are not to be construed as limiting the invention, including the drawings for reference and description only, and are not to be construed as limiting the scope of the invention as many variations thereof are possible without departing from the spirit and scope of the invention.
The PT symmetrical MC-WPT system constructed based on the operational amplifier comprises a primary side circuit and a secondary side circuit, wherein the primary side circuit comprises a first negative resistance unit, a second negative resistance unit, a primary side coil and a primary side series resonance capacitor, the secondary side circuit comprises a secondary side coil, a secondary side series resonance capacitor, a parallel resonance inductor, a series resonance inductor and an electric load, the first negative resistance unit and the second negative resistance unit are constructed based on the operational amplifier, one end of the first negative resistance unit is grounded, the other end of the first negative resistance unit is used as a forward voltage output end, one end of the second negative resistance unit is grounded, the other end of the second negative resistance unit is used as a reverse voltage output end, the primary side coil and the primary side series resonance capacitor are connected in series between the forward voltage output end and the reverse voltage output end, the secondary side coil and the secondary side series resonance capacitor form a secondary side first series branch to be connected in parallel to the front side of the parallel resonance inductor, the secondary side resonance inductor and the electric load form a secondary side to be connected in parallel to the secondary side inductor, and the secondary side series resonance inductor and the secondary side load are connected in parallel to the secondary side to the series inductor to achieve wireless energy transmission.
In this embodiment, the first negative resistance unit and the second negative resistance unit have the same circuit structure and parameters and respectively include an operational amplifier, a first resistor, a second resistor and a third resistor, the first resistor is connected between the positive input end and the output end of the operational amplifier, the second resistor is connected between the negative input end and the output end of the operational amplifier, the third resistor is connected between the positive input end and the ground end of the operational amplifier, and the negative input end of the operational amplifier extends through a wire to form the positive voltage output end or the negative voltage output end. As can be seen from fig. 1, in the implementation, the third resistor is formed by connecting two sub-resistors in series, and two antiparallel diodes are disposed on one of the sub-resistors.
The "ground" terminals of the first negative resistance-Rg1 and the second negative resistance-Rg2 in FIG. 1 are connected together, substantially equivalent to an inverse series connection, V+ and V- represent the positive and negative DC power sources, respectively, that power the operational amplifier, I1 represents the primary current, I2 represents the secondary current, and M represents the mutual inductance between the primary coil L1 and the secondary coil L2.
Fig. 2 (a) is a schematic diagram of a negative resistance structure constructed based on a conventional operational amplifier, wherein Req represents a WPT system compensation topology, R1、R2、R3 represents an operational amplifier peripheral resistor forming a negative resistance, ui、uf、uo represents voltage signals of a non-inverting input terminal, an inverting input terminal and an operational amplifier output terminal,
For the negative resistance shown in fig. 2 (a), the resistance and the effective value U1 of the output voltage are shown in formula (1):
wherein UO represents the effective value of the voltage signal at the output of the operational amplifier.
Fig. 2 (b) shows a novel negative resistance structure proposed by the present patent, which is composed of two traditional negative resistances with identical parameters in reverse series, and the two "grounds" are connected together, and the resistance-Rg and the effective value Uin of the output voltage are:
The negative resistance structure provided by the patent can be obtained by the formula (2), and the output voltage can be improved to be twice of the original output voltage.
In addition, for the secondary side compensation topology in fig. 1, equivalent analysis can be performed in the manner shown in fig. 3, and the equivalent resistance and the equivalent inductance thereof can be obtained through impedance equivalent transformation as shown in the formula (3):
Since the resonant frequency of PT symmetric MC-WPT systems can reach several hundred kHz, and in order to ensure a large effective power transmission distance, the quality factor of the WPT system loop is generally set large (i.e., the coil self-inductance is large). The simplification condition shown in the formula (4) is easily satisfied.
The equivalent resistance and the equivalent inductance of the secondary high-order compensation topology can be simplified into:
Defining β=la/(La+Lb), the electrical parameter relationship before and after the secondary high order compensation topology equivalent is:
as can be seen from the formulas (5) and (6), by selecting a suitable β, the compensation topology of the secondary side can be equivalent to a series connection of an inductance and a resistance, i.e., a conventional SS compensation topology.
In addition, the PT symmetric MC-WPT system constructed based on the operational amplifier shown in fig. 1 can be simplified into a circuit as shown in fig. 4, where-Rg represents the total negative resistance of the system, Leq represents the total compensation inductance of the secondary side, and RLeq is the equivalent load resistance.
When the system works in the PT symmetrical mode, the loop equation of the system can be obtained by the Kirchhoff Voltage Law (KVL) as shown in the formula (7):
where g=rg-Rp1 denotes the total negative resistance of the primary side, RS＝Rp2+RLeq denotes the total resistance of the secondary side, X1＝ωL1-1/ωC1 denotes the primary side reactance, and X2＝ω(L2+Leq)-1/ωC2 denotes the secondary side reactance.
The relationship between secondary and primary currents according to equation (7) is:
the relation between the primary side current and the secondary side current amplitude ratio is obtained as follows:
Order theThe relation that the primary and secondary electrical parameters should satisfy can be obtained by substituting formula (7) is:
From the following componentsAnd the working frequency of the system in the PT symmetrical mode is obtained as shown in a formula (11).
Wherein the method comprises the steps ofFor mutual inductance between the primary coil and the secondary coil of the system,Is the natural resonant frequency of the secondary coil,For the quality factor of the secondary coil of the system, omega1 and omega2 can only exist when the coupling coefficient is larger than k0, and k0 is the minimum coupling coefficient for ensuring the system works in the PT symmetrical modeTo ensure that the system operates in the minimum secondary figure of merit of the PT symmetric mode.
According to the law of conservation of energy, the primary side and secondary side current amplitude relationships shown in the combination formula (9) can obtain the output power and the transmission efficiency of the system as follows:
As can be seen from equation (12), the output power and transmission efficiency of the system are independent of the mutual inductance M, i.e., the power and efficiency are robust to variations in transmission distance, after the structural parameters of the system are determined.
Based on the above analysis, the present embodiment further provides a parameter design method, which is used for the aforementioned PT symmetric MC-WPT system constructed based on the operational amplifier, as shown in fig. 5, and includes the following steps:
S1, determining a power consumption load resistance value RL, a power grade P, a negative resistance output voltage Uin, a primary coil inductance L1, a primary coil internal resistance Rp1, a secondary coil inductance L2, a secondary coil internal resistance Rp2, a natural frequency grade omega0 and an equivalent load resistance RLeq meeting a target power grade according to application scene requirements, wherein the negative resistance output voltage Uin is an effective voltage between the forward voltage output end and the reverse voltage output end;
s2, according toDetermining system parameters alpha and beta meeting a target power level;
s3) determining the value of the secondary side total compensation inductance Leq according to L1＝α(L2+Leq);
S4, determining self-inductance values of the parallel resonance inductance La and the series resonance inductance Lb according to La＝Leq/(1-beta) and Lb＝Leq/beta;
s5, according toDetermining the capacitance values of a primary side series compensation capacitor C1 and a secondary side series compensation capacitor C2;
s6, keeping the primary coil and the secondary coil within a critical coupling range, namely meeting the condition that k is larger than or equal to k0, and enabling the system to work at any bifurcation frequency, so that constant power P and constant efficiency eta can be output.
In order to further verify the effectiveness of the above system and method, the following MATLAB numerical simulation was used to verify the operating conditions and system characteristics, and the simulation parameters are shown in table 1.
Table 1 simulation parameter settings
By changing the coupling coefficient of the system, the change curves of the system working frequency, output power and transmission efficiency along with the coupling coefficient can be obtained as shown in fig. 6, 7 and 8 respectively.
As can be seen from the simulation results in FIG. 6, within the range of k.gtoreq.k0, any coupling coefficient corresponds to two operating frequencies satisfying the condition, namely frequency branch f1 and frequency branch f2, respectively.
From the simulation results in FIGS. 7 and 8, it can be seen that the output power and transmission efficiency of the system are constant and do not change with the change of the coupling coefficient in the range of k.gtoreq.k0, whether the frequency branch f1 or f2.
In addition, fig. 9 and fig. 10 show the variation curves of the output power and the transmission efficiency along with the inductance ratio of the primary side and the secondary side, and according to the simulation results in fig. 9 and fig. 10, it can be seen that by adjusting the inductance ratio α between the primary side and the secondary side, the system can flexibly adjust the output power in a larger range according to the actual requirements. When the smaller alpha is set, the system obtains higher output power by sacrificing part of transmission efficiency, and the application range of the PT symmetrical MC-WPT system constructed based on the operational amplifier is effectively improved.
Fig. 11 shows a comparison curve of output power under different system topologies, and it can be seen from fig. 11 that when the same primary-secondary side inductance ratio α is maintained, the output power improvement effect of the double negative resistance structure is remarkable compared with that of the single negative resistance structure, and the power improvement of the secondary side added with the higher-order compensation structure is also remarkable compared with that of the secondary side without compensation. Therefore, the system and the method provided by the patent have better lifting effect on the output power on the primary side and the secondary side.
Fig. 12 is a graph showing the variation of the system output power with the load resistance, and fig. 13 is a graph showing the variation of the system compensation inductance with the load resistance. As can be seen from fig. 12 and 13, constant power output can be achieved when different magnitudes of load resistors are driven by adjusting the parameter β, which is achieved by changing the values of the compensating inductances La and Lb. As shown in fig. 13, the different load resistances each correspond to a set of compensating inductances La and Lb that enable constant power output.
It can be seen that the simulation result is consistent with the theoretical deduction conclusion, the invention adjusts the primary-secondary side inductance ratio coefficient alpha and the secondary side compensation topological parameter beta according to the proposed parameter design criterion by adopting the double-negative resistance structure, the system based on the operational amplifier can realize the PT symmetrical working mode, and has the characteristics of randomly adjusting the output power in a large range, keeping constant power output, constant efficiency and the like when the coupling coefficient and the load resistance change.
In summary, the PT symmetrical MC-WPT system constructed based on the operational amplifier and the parameter design method provided by the invention have the following advantages:
(1) The system can automatically select proper working frequency to operate in the PT symmetrical mode without any additional links such as detection, control and adjustment, and has good position robustness on output power and transmission efficiency, and is not influenced by mutual inductance change.
(2) The two negative resistors are reversely connected in series to provide gain for the system, so that the output voltage of the primary negative resistor is doubled, and the output power is effectively improved from the power supply side.
(3) On the premise of smaller negative resistance output voltage, the equivalent resistance from the secondary side to the primary side can be reduced by adjusting the inductance ratio alpha of the primary side and the secondary side, and the output power of the system is effectively improved from the WPT compensation topology side.
(4) By adjusting the values of the La and the Lb inductors in the secondary side high-order compensation topology, beta can be adjusted in the range of 0 to 1, and further the same equivalent resistance RLeq of the secondary side high-order compensation topology can be ensured when different load resistors RL are used, so that constant power output can be achieved when different load resistors RL are driven, and the application scene of a PT symmetrical MC-WPT system constructed based on an operational amplifier is greatly expanded.
Finally, it should be noted that the foregoing examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the foregoing examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principles of the present invention should be made as equivalent substitutions, and are included in the scope of the present invention.