CN116131623A - A low-cost single-input adjustable multi-output WPT system and its control method - Google Patents

Abstract

The invention relates to the technical field of magnetic coupling wireless power transmission, and particularly discloses a low-cost single-input adjustable multi-output WPT system and a control method thereof. In addition, the system and control method utilize inherent half-wave rectification channels (positive half-wave rectification circuit, negative half-wave rectification circuit) to detect the synchronous signals, rather than using additional detection circuits, thereby realizing a compact and cost-effective system.

Description

A low-cost single-input adjustable multi-output WPT system and its control method

Technical Field

The present invention relates to the technical field of magnetically coupled wireless power transmission, and in particular to a low-cost single-input adjustable multi-output WPT system and a control method thereof.

Background Art

Wireless power transfer (WPT) is a practical technology that facilitates widespread applications such as smartphones and electric vehicles (EVs). Single-input single-output (SISO) WPT systems have been widely studied due to their simplicity. In this digital age, electrical appliances are becoming increasingly complex. Conventional SISO WPT has difficulty meeting the requirements of multi-output charging targets. Therefore, the industry is calling for emerging wireless chargers equipped with multiple outputs.

To achieve multiple outputs, one approach is to increase the number of transmission paths by using a multiple-input multiple-output (MIMO) system. This means implementing multiple charging paths, involving a large number of transmitting and receiving devices.

In order to save costs, simplify the structure, and reduce the cross-coupling phenomenon caused by the MIMO system, it is more popular to use a single-input multiple-output (SIMO) WPT system. One way to achieve this is through a single-t or double-t resonant circuit, which can achieve voltage or current conversion by configuring passive components such as inductors and capacitors. However, this passive topology makes it difficult to adjust the output voltage or current during the charging process. Therefore, some scholars use dc-dc converters. Although dc-dc converters meet different charging requirements and have different outputs, they are still bulky and require more additional installation space.

Summary of the invention

The present invention provides a low-cost single-input adjustable multi-output WPT system and a control method thereof, and solves the technical problem of how to adjust the multi-channel output voltage during the charging process by using a simple circuit.

In order to solve the above technical problems, the present invention provides a low-cost single-input adjustable multi-output WPT system, comprising:

The primary transmitting end is provided with a high-frequency inverter and a primary controller;

The secondary side receiving end is provided with a receiving coil circuit and a positive half-wave rectifier circuit, a negative half-wave rectifier circuit, and a full-wave rectifier circuit connected in parallel at both ends of the receiving coil circuit, and is also provided with a secondary side controller;

The secondary side controller is used to collect the output voltage _Vc of the positive half-wave rectifier circuit and generate a corresponding PWM C control signal according to the error between _Vc and its reference voltage _Vcref to act on the positive half-wave rectifier circuit to adjust _Vc ;

The secondary side controller is further used to collect the output voltage V _b of the negative half-wave rectifier circuit and generate a corresponding PWM B control signal according to the error between V _b and its reference voltage V _bref to act on the negative half-wave rectifier circuit to adjust V _b ;

The primary-side controller is used to collect the output voltage _Va of the full-wave rectifier circuit through the secondary-side controller and control the conduction angle δ of the high-frequency inverter according to the error between _Va and its reference voltage _Varef , so as to adjust _Va .

Preferably, the positive half-wave rectifier circuit is provided with a diode D _c , a PMOS tube Q _c , a load R _c and a filter capacitor C _c , wherein the positive terminal of the diode D _c is connected to the positive output terminal of the receiving coil circuit, the negative terminal of the diode D _c is connected to the D terminal of the PMOS tube Q _c , the S terminal of the PMOS tube Q _c is connected to the load R _c and then to the negative output terminal of the receiving coil circuit, the G terminal of the PMOS tube Q _c is connected to the secondary side controller, and the filter capacitor C _c is connected in parallel to both ends of the load R _c .

Preferably, the negative half-wave rectifier circuit is provided with a diode D _b , a PMOS tube Q _b , a load R _b and a filter capacitor C _b , wherein the cathode end of the diode D _b is connected to the positive output end of the receiving coil circuit, the anode end of the diode D _b is connected to the S pole of the PMOS tube Q _b , the D pole of the PMOS tube Q _b is connected to the load R _b and then to the negative output end of the receiving coil circuit, the G pole of the PMOS tube Q _b is connected to the secondary side controller, and the filter capacitor C _b is connected in parallel to both ends of the load R _b .

Preferably, the full-wave rectifier circuit is provided with PMOS tube _Q5 , PMOS tube _Q6 , PMOS tube _Q7 , PMOS tube _Q8 , a filter capacitor _Cd , and a load _Ra , wherein the PMOS tube _Q5 , PMOS tube _Q6 , PMOS tube _Q7 , and PMOS tube _Q8 are connected to form a full-bridge rectifier circuit, the filter capacitor _Cd is connected in parallel between the two output ends of the full-bridge rectifier circuit, and the load _Ra is connected in parallel across the two ends of the filter capacitor _Cd .

Preferably, the receiving coil circuit includes a receiving coil _LS and a compensation capacitor _CS thereof.

Preferably, the secondary side controller is also used to perform synchronous rectification, which specifically includes the steps of:

S1, setting the conduction angle δ to δ ₀ , the duty cycle D _Qc of the positive half-wave rectifier circuit to D _Qc0 , and the duty cycle D _Qb of the positive half-wave rectifier circuit to D _Qb0 ;

S2, determining the zero crossing point by moving the time base of the PWM C control signal and the PWM B control signal;

S3. According to the determined zero-crossing point, a synchronous driving signal is provided to act on the full-wave rectifier circuit, so that the primary-side controller is synchronized with the secondary-side controller.

Preferably, the step S2 specifically includes the steps of:

S21, initialization time T ₀ , detection sequence n=0;

S22, measuring V _c and V _b at time sequence 0 and recording them as V _c0 and V _b0 ;

S23, determine whether V _c0 =V _b0 =0 is established, if yes, measure V _c and V _b of the subsequent time series, determine the zero crossing point according to V _c and V _b of the subsequent time series and go to step S3, if no, execute steps S24 to S25;

S24, timing +1, measure V _c and V _b at timing 1 and record them as V _c1 and V _b1 ;

S25, determine whether V _c1 > V _c0 and V _b1 > V _b0 are established, if yes, measure V _c and V _b of the subsequent time series, determine the zero crossing point according to V _c and V _b of the subsequent time series and go to step S3, if no, go to step S26;

S26, determine whether V _c1 =V _c0 >0 and V _b1 =V _b0 >0 is established, if yes, measure V _c and V _b of the subsequent time series, determine the anti-zero point according to V _c and V _b of the subsequent time series, shift the phase by 180° to obtain the zero point, and then go to step S3, if no, go to step S27;

S27, measuring V _c and V _b of the subsequent time sequence, and determining the inverse zero-crossing point according to V _c and V _b of the subsequent time sequence, and shifting the phase by 180° to obtain the zero-crossing point, and then entering step S3.

Preferably, in step S23, the zero-crossing point is determined according to V _c and V _b of the subsequent time sequence, specifically:

Determine whether V _c(n+1) =V _cn , V _b(n+1) =V _bn and V _cn =V _bn >0. If so, find the zero-crossing point, where V _cn and V _bn represent V _c and V _b at time sequence n, respectively, and V _c(n+1) and V _b(n+1) represent V _c and V _b at time sequence n+1, respectively. If not, re-determine after time sequence +1.

In step S25, the zero-crossing point is determined according to V _c and V _b of the subsequent time sequence, specifically:

Determine whether V _c(n+1) = V _cn and V _b(n+1) = V _bn are true. If so, find the zero crossing point. If not, re-determine after adding 1 to the timing sequence.

In step S26, the inverse zero point is determined according to V _c and V _b of the subsequent time sequence, specifically:

Determine whether V _c(n+1) =V _cn =0 and V _b(n+1) =V _bn =0 is true. If so, find the anti-zero point. If not, re-determine after the timing is increased by 1.

In step S27, the inverse zero point is determined according to V _c and V _b of the subsequent time sequence, specifically:

Determine whether V _c(n+1) =V _cn =0 and V _b(n+1) =V _bn =0 is established. If so, find the anti-zero point. If not, re-determine after the timing is increased by 1.

The present invention also provides a low-cost control method for a single-input adjustable multi-output WPT system, comprising the steps of:

X1. Synchronizing the driving signals of the high-frequency inverter and the full-wave rectifier circuit;

X2. Start charging; during the charging process, collect the output voltage _Vc of the positive half-wave rectifier circuit and generate a corresponding PWM C control signal according to the error between _Vc and its reference voltage _Vcref to act on the positive half-wave rectifier circuit to adjust _Vc ; collect the output voltage _Vb of the negative half-wave rectifier circuit and generate a corresponding PWM B control signal according to the error between _Vb and its reference voltage _Vbref to act on the negative half-wave rectifier circuit to adjust _Vb ; collect the output voltage _Va of the full-wave rectifier circuit and control the conduction angle δ of the high-frequency inverter according to the error between _Va and its reference voltage _Varef to adjust _Va .

Furthermore, the step X1 specifically includes steps S1 to S3 as described in the system.

The present invention provides a low-cost single-input adjustable multi-output WPT system and a control method thereof. The system is provided with a positive half-wave rectifier circuit, a negative half-wave rectifier circuit, and a full-wave rectifier circuit at the secondary side receiving end, and a primary side controller and a secondary side controller are provided, so as to adopt positive and negative half-wave rectification and synchronous rectification to realize multi-channel output, and each output channel can be controlled to meet various charging requirements. In addition, the system and the control method use the inherent half-wave rectification channel (positive half-wave rectifier circuit, negative half-wave rectifier circuit) to detect the synchronization signal instead of using an additional detection circuit, thereby realizing a compact and cost-saving system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a topological structure diagram of a low-cost single-input adjustable multi-output WPT system provided in Embodiment 1 of the present invention;

FIG2 is an equivalent circuit diagram of (a) Ring #C and (b) Ring #B provided in Example 1 of the present invention;

FIG3 is a flow chart of synchronization signal detection and system charging provided by Embodiment 1 of the present invention;

4 is a diagram showing changes in the synchronization signal detection i _S , the drive signal (PWM C, PWM B), V _c , and V _b provided in Example 1 of the present invention: (a) state (a), (b) state (b), (c) state (c), (d) state (d), (e) synchronization signal detection end state, and (f) synchronization signal detection experiment end state;

FIG5 is a schematic diagram of zero phase angle verification provided by Embodiment 1 of the present invention;

6 is a dynamic response diagram provided by Example 1 of the present invention: (a) R _a from 10Ω to 30Ω and then back to 10Ω, (b) R _b from 20Ω to 30Ω and then back to 20Ω, (c) R _c from 20Ω to 30Ω and then back to 20Ω;

FIG. 7 is a waveform diagram of the dynamic response of the system provided in Example 1 of the present invention to an input disturbance.

DETAILED DESCRIPTION

The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and are not to be construed as limitations of the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute limitations on the scope of patent protection of the present invention, because many changes may be made to the present invention without departing from the spirit and scope of the present invention.

Example 1

In order to overcome the technical problems existing in the background technology and realize the adjustment of multiple output voltages during the charging process by using a simple circuit, an embodiment of the present invention provides a low-cost single-input adjustable multi-output WPT system, the circuit topology of which is shown in FIG1 and includes:

The primary transmitting end is provided with a DC power supply V _dc , a high-frequency inverter (composed of MOS tubes Q ₁ , Q ₂ , Q ₃ , Q ₄ ), a primary compensation network (composed of an inductor _LT , a capacitor _CT , _RT is the corresponding internal resistance) and a transmitting coil _LP ( _Rp is the corresponding internal resistance) connected in sequence, and a primary controller connected to the high-frequency inverter is also provided.

The secondary side receiving end is provided with a receiving coil circuit (including a receiving coil _LS and its compensation capacitor _CS , _RS is the corresponding resistor of the circuit), a positive half-wave rectifier circuit, a negative half-wave rectifier circuit, a full-wave rectifier circuit, and a secondary side controller.

As shown in FIG1 , the positive half-wave rectifier circuit is provided with a diode D _c , a PMOS tube Q _c , a load R _c and a filter capacitor C _c , wherein the positive terminal of the diode D _c is connected to the positive output terminal of the receiving coil circuit, the negative terminal of the diode D _c is connected to the D terminal of the PMOS tube Q _c , the S terminal of the PMOS tube Q _c is connected to the load R _c and then to the negative output terminal of the receiving coil circuit, the G terminal of the PMOS tube Q _c is connected to the secondary side controller, and the filter capacitor C _c is connected in parallel to both ends of the load R _c .

The negative half-wave rectifier circuit is provided with a diode D _b , a PMOS tube Q _b , a load R _b and a filter capacitor C _b , wherein the negative terminal of the diode D _b is connected to the positive output terminal of the receiving coil circuit, the positive terminal of the diode D _b is connected to the S pole of the PMOS tube Q _b , the D pole of the PMOS tube Q _b is connected to the load R _b and then to the negative output terminal of the receiving coil circuit, the G pole of the PMOS tube Q _b is connected to the secondary side controller, and the filter capacitor C _b is connected in parallel to both ends of the load R _b .

The full-wave rectifier circuit is provided with PMOS tube _Q5 , PMOS tube _Q6 , PMOS tube _Q7 , PMOS tube _Q8 , filter capacitor _Cd , and load _Ra , wherein PMOS tube _Q5 , PMOS tube _Q6 , PMOS tube _Q7 , and PMOS tube _Q8 are connected to form a full-bridge rectifier circuit, the filter capacitor _Cd is connected in parallel between two output ends of the full-bridge rectifier circuit, and the load _Ra is connected in parallel to both ends of the filter capacitor _Cd .

The secondary side controller collects the output voltage _Vc of the positive half-wave rectifier circuit and generates a corresponding PWM C control signal according to the error between _Vc and its reference voltage _Vcref to act on the positive half-wave rectifier circuit to adjust _Vc .

The secondary side controller collects the output voltage V _b of the negative half-wave rectifier circuit and generates a corresponding PWM B control signal according to the error between V _b and its reference voltage V _bref to act on the negative half-wave rectifier circuit to adjust V _b .

The primary side controller collects the output voltage _Va of the full-wave rectifier circuit through the secondary side controller and controls the conduction angle δ of the high-frequency inverter according to the error between _Va and its reference voltage _Varef to adjust _Va .

As shown in FIG1 , the primary side controller and the secondary side controller are provided with corresponding voltage divider circuits for voltage acquisition, and the PI controller generates corresponding PWM control signals, etc., and information is transmitted between the primary and secondary sides through a wireless communication transmitting and receiving end.

The control logic of the system can be obtained from Figure 1. There are two system controllers, namely the primary side controller and the secondary side controller. In addition, there are three closed control loops in the proposed system, including an outer loop (loop #A, corresponding to the full-wave rectifier circuit) and two inner loops (loop #B and loop #C, corresponding to the positive half-wave rectifier circuit and the negative half-wave rectifier circuit, respectively). Loop #A affects the output bus voltage (U _S ). Loop #B and loop #C are inner loops, and they are independent of each other. For the outer control loop #A, the secondary side controller samples the output voltage _Va through the A/D module after the voltage divider and then transmits it to the primary side. The primary side controller obtains _Va and sends the error between _Va and the reference _Varef to the proportional integral controller (PI controller), and then passes the processed result to the PSM controller to calculate the conduction angle δ to adjust the voltage _Va of loop #A.

For loops #B and #C, the secondary controller uses the A/D module after the voltage divider to sample the output voltages V _b and V _c , and then sends the error information (V _b and V _bref , V _c and V _cref ) to their PI controllers respectively, and then adjusts the voltages V _b and V _c by controlling D _Qb and D _Qc , where D _Qc is the duty cycle of the positive half cycle of PWM C (i.e., the driving signal of Q _c ), and D _Qb is the duty cycle of the negative half cycle of PWM B (i.e., the driving signal of Q _b ). Figures 2(a) and (b) are the equivalent circuits of loops #C and #B.

For output channel #A, based on the relationship between input and output voltage, _Va can be expressed as:

Where U _S is the bus voltage. The output voltage of channel C can be expressed as:

Where ω represents the operating angular frequency of the system. Similarly, the output voltage of channel #B can be expressed as:

Since the main controller and the sub-controller are not synchronized, they need to be synchronized before formal charging. The flowchart of synchronization signal detection and system charging is shown in Figure 3. Before normal charging, the synchronization signal should be detected first. After finding the zero crossing point, the synchronization drive signal PWM 5, PWM 6, PWM 7, PWM 8 can be given. The system enters the normal charging stage. _{V a} , V _b , V _c can be adjusted by controlling δ, D _Qb and D _Qc .

More specifically, as shown in FIG3 , the synchronous rectification specifically includes the following steps:

S1. Set the conduction angle δ to δ ₀ , the duty cycle D _Qc of the positive half-wave rectifier circuit to D _Qc0 , and the duty cycle D _Qb of the positive half-wave rectifier circuit to D _Qb0 (initialize the system by transmitting a small amount of energy to the secondary receiving end for synchronization signal detection);

S2, determining the zero-crossing point by moving the time base of the PWM C control signal and the PWM B control signal; specifically comprising the steps of:

S21, initialization time T ₀ (since the main controller and the sub-controller are not synchronized, the initial reference time T ₀ of PWM C and PWM B is random), detection timing n=0;

S22, measuring V _c and V _b at time sequence 0 and recording them as V _c0 and V _b0 ;

S23, determine whether V _c0 =V _b0 =0 is established, if so (corresponding to state (a) in FIG4 ), measure V _c and V _b of the subsequent timing, and determine the zero crossing point (ZCP) according to V _c and V _b of the subsequent timing and go to step S3, if not, execute steps S24 to S25;

S24, timing +1, measure V _c and V _b at timing 1 and record them as V _c1 and V _b1 ;

S25, determine whether V _c1 > V _c0 and V _b1 > V _b0 are established. If so (corresponding to state (b) in FIG4 ), measure V _c and V _b of the subsequent time series, and determine the zero crossing point (ZCP) according to V _c and V _b of the subsequent time series and go to step S3. If not, go to step S26.

S26, determine whether V _c1 =V _c0 >0 and V _b1 =V _b0 >0 is established, if so (corresponding to state (c) in FIG. 4 ), measure V _c and V _b of the subsequent timing, and determine the anti-zero crossing point (Anti-ZCP) according to V _c and V _b of the subsequent timing, and shift the phase by 180° to obtain the zero crossing point and then go to step S3, if not (corresponding to state (d) in FIG. 4 ), execute step S27;

S27, measuring V _c and V _b of the subsequent time sequence, and determining the anti-zero crossing point (Anti-ZCP) according to V _c and V _b of the subsequent time sequence and shifting the phase by 180° to obtain the zero crossing point, and then entering step S3;

S3. According to the determined zero-crossing point, a synchronous driving signal is provided to act on the full-wave rectifier circuit, so that the primary side controller is synchronized with the secondary side controller.

In step S23, the zero-crossing point is determined according to V _c and V _b of the subsequent time sequence, specifically:

Determine whether V _c(n+1) =V _cn , V _b(n+1) =V _bn and V _cn =V _bn >0. If so, find the zero-crossing point, where V _cn and V _bn represent V _c and V _b at time sequence n, respectively, and V _c(n+1) and V _b(n+1) represent V _c and V _b at time sequence n+1, respectively. If not, re-determine after time sequence +1.

In step S25, the zero-crossing point is determined according to V _c and V _b of the subsequent time sequence, specifically:

Determine whether V _c(n+1) = V _cn and V _b(n+1) = V _bn are true. If so, find the zero crossing point. If not, re-determine after adding 1 to the timing sequence.

In step S26, the reverse zero crossing point is determined according to V _c and V _b of the subsequent time sequence, specifically:

Determine whether V _c(n+1) =V _cn =0 and V _b(n+1) =V _bn =0 is true. If so, find the anti-zero point. If not, re-determine after the timing is increased by 1.

In step S27, the reverse zero crossing point is determined according to V _c and V _b of the subsequent time sequence, specifically:

Determine whether V _c(n+1) =V _cn =0 and V _b(n+1) =V _bn =0 is established. If so, find the anti-zero point. If not, re-determine after the timing is increased by 1.

In this example, the zero crossing point is found by moving the time base of PWM C and PWM B. The final state after synchronization is shown in Figure 4(e). The final state of synchronization signal detection in the experiment is shown in Figure 4(f), which is highly consistent with Figure 4(e).

In order to verify the feasibility of the SIRMO WPT system proposed in this example, an experimental prototype was made according to Figure 1. The system parameters are shown in Table 1.

Table 1 System parameters

The output voltage and current (u _in and i _in ) of the inverter and the DC voltage output of the three channels (V _a , V _b , V _c ) are shown in Figure 5. It can be seen that u _in and i _in are in the same phase, which means that the inverter can achieve ZPA.

Figures 6(a), (b) and (c) are the dynamic response waveforms of the output voltage when the loads _Ra , _Rb and _Rc of the outer loop #A and the inner loops #B and #C are changed. It can be seen from Figure 6(a) that the change of the load _Ra of the outer loop #A not only affects itself, but also affects the two inner loops (#B and #C); it shows that _Ra changes from 10Ω to 30Ω and then returns to 10Ω; all voltages can be controlled to the reference values, i.e. 48V, 30V and 24V. It can be seen from Figure 6(b) that the change of the load _Rb of the inner loop #B only affects itself; it shows that _Rb changes from 20Ω to 30Ω and then returns to 20Ω; its own voltage _Vb can be maintained at 30V with a small overshoot/undershoot; _Va and _Vc have almost no change. Similarly, it can be seen from Figure 6(c) that the change of the load R _c of the inner loop #C only affects itself; it shows that R _c changes from 20Ω to 30Ω and then returns to 20Ω again; its own voltage V _c can be maintained at 24V with a small over/undershoot; V _a and V _b have almost no change.

Figure 7 depicts the input disturbance rejection response of the system. The input voltage varies from 80 V to 70 V and then back to 80 V. Due to the control strategy, the proposed system can maintain three voltages of 48 V, 30 V, and 24 V, respectively.

In summary, the system is equipped with a positive half-wave rectifier circuit, a negative half-wave rectifier circuit, and a full-wave rectifier circuit at the secondary side receiving end, and a primary side controller and a secondary side controller are set, so as to adopt positive and negative half-wave rectification and synchronous rectification to achieve multi-channel output, and each output channel can be controlled to meet various charging requirements. In addition, the system and control method use the inherent half-wave rectification channel (positive half-wave rectifier circuit, negative half-wave rectifier circuit) to detect the synchronization signal instead of using an additional detection circuit, thereby realizing a compact and cost-saving system. The laboratory prototype realizes the output of three voltage levels of 48V, 30V, and 24V, and the experimental results are highly consistent with the theoretical analysis. With the help of control logic, the system shows excellent robustness to different situations such as load changes and input disturbances.

Example 2

This embodiment provides a low-cost control method for a single-input adjustable multi-output WPT system, which is applied to the single-input adjustable multi-output WPT system of Embodiment 1 (including or excluding the primary side controller and the secondary side controller part). The control method specifically includes the following steps:

X1. Synchronize the drive signals of the high-frequency inverter and the full-wave rectifier circuit;

X2. Start charging; during the charging process, collect the output voltage _Vc of the positive half-wave rectifier circuit and generate a corresponding PWM C control signal based on the error between _Vc and its reference voltage _Vcref to act on the positive half-wave rectifier circuit to adjust _Vc ; collect the output voltage _Vb of the negative half-wave rectifier circuit and generate a corresponding PWM B control signal based on the error between _Vb and its reference voltage _Vbref to act on the negative half-wave rectifier circuit to adjust _Vb ; collect the output voltage _Va of the full-wave rectifier circuit and control the conduction angle δ of the high-frequency inverter based on the error between _Va and its reference voltage _Varef to adjust _Va .

Step X1 specifically includes steps S1 to S3 of Example 1.

The control method focuses on protecting the process of using positive and negative half-wave rectification and synchronous rectification to achieve multi-channel output and individually control each output channel.

The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims (10)

1. A low-cost single-input adjustable multiple-output WPT system, characterized by comprising: The primary transmitting end is provided with a high-frequency inverter and a primary controller; The secondary side receiving end is provided with a receiving coil circuit and a positive half-wave rectifier circuit, a negative half-wave rectifier circuit, and a full-wave rectifier circuit connected in parallel at both ends of the receiving coil circuit, and is also provided with a secondary side controller; The secondary side controller is used to collect the output voltage _Vc of the positive half-wave rectifier circuit and generate a corresponding PWM C control signal according to the error between _Vc and its reference voltage _Vcref to act on the positive half-wave rectifier circuit to adjust _Vc ; The secondary side controller is further used to collect the output voltage V _b of the negative half-wave rectifier circuit and generate a corresponding PWM B control signal according to the error between V _b and its reference voltage V _bref to act on the negative half-wave rectifier circuit to adjust V _b ; The primary-side controller is used to collect the output voltage _Va of the full-wave rectifier circuit through the secondary-side controller and control the conduction angle δ of the high-frequency inverter according to the error between _Va and its reference voltage _Varef , so as to adjust _Va . 2. A low-cost single-input adjustable multi-output WPT system according to claim 1, characterized in that: the positive half-wave rectifier circuit is provided with a diode D _c , a PMOS tube Q _c , a load R _c and a filter capacitor C _c , wherein the positive terminal of the diode D _c is connected to the positive output terminal of the receiving coil circuit, the negative terminal of the diode D _c is connected to the D pole of the PMOS tube Q _c , the S pole of the PMOS tube Q _c is connected to the load R _c and then connected to the negative output terminal of the receiving coil circuit, the G pole of the PMOS tube Q _c is connected to the secondary side controller, and the filter capacitor C _c is connected in parallel to both ends of the load R _c . 3. A low-cost single-input adjustable multiple-output WPT system according to claim 1, characterized in that: the negative half-wave rectifier circuit is provided with a diode D _b , a PMOS tube Q _b , a load R _b and a filter capacitor C _b , wherein the cathode end of the diode D _b is connected to the positive output end of the receiving coil circuit, the anode end of the diode D _b is connected to the S pole of the PMOS tube Q _b , the D pole of the PMOS tube Q _b is connected to the load R _b and then to the negative output end of the receiving coil circuit, the G pole of the PMOS tube Q _b is connected to the secondary side controller, and the filter capacitor C _b is connected in parallel to both ends of the load R _b . 4. A low-cost single-input adjustable multi-output WPT system according to claim 1, characterized in that: the full-wave rectifier circuit is provided with PMOS tube _Q5 , PMOS tube _Q6 , PMOS tube _Q7 , PMOS tube _Q8 , filter capacitor _Cd , and load _Ra , wherein PMOS tube _Q5 , PMOS tube _Q6 , PMOS tube _Q7 , and PMOS tube _Q8 are connected to form a full-bridge rectifier circuit, the filter capacitor _Cd is connected in parallel between the two output ends of the full-bridge rectifier circuit, and the load _Ra is connected in parallel to both ends of the filter capacitor _Cd . 5. A low-cost single-input adjustable multiple-output WPT system according to claim 1, characterized in that: the receiving coil circuit includes a receiving coil _LS and a compensation capacitor _CS thereof. 6. A low-cost single-input adjustable multiple-output WPT system according to claim 1, characterized in that the secondary side controller is also used for synchronous rectification, specifically comprising the steps of: S1, setting the conduction angle δ to δ ₀ , the duty cycle D _Qc of the positive half-wave rectifier circuit to D _Qc0 , and the duty cycle D _Qb of the positive half-wave rectifier circuit to D _Qb0 ; S2, determining the zero crossing point by moving the time base of the PWM C control signal and the PWM B control signal; S3. According to the determined zero-crossing point, a synchronous driving signal is provided to act on the full-wave rectifier circuit, so that the primary-side controller is synchronized with the secondary-side controller. 7. A low-cost single-input adjustable multiple-output WPT system according to claim 6, characterized in that step S2 specifically comprises the steps of: S21, initialization time T ₀ , detection sequence n=0; S22, measuring V _c and V _b at time sequence 0 and recording them as V _c0 and V _b0 ; S23, determine whether V _c0 =V _b0 =0 is established, if yes, measure V _c and V _b of the subsequent time series, determine the zero crossing point according to V _c and V _b of the subsequent time series and go to step S3, if no, execute steps S24 to S25; S24, timing +1, measure V _c and V _b at timing 1 and record them as V _c1 and V _b1 ; S25, determine whether V _c1 > V _c0 and V _b1 > V _b0 are established, if yes, measure V _c and V _b of the subsequent time series, determine the zero crossing point according to V _c and V _b of the subsequent time series and go to step S3, if no, go to step S26; S26, determine whether V _c1 =V _c0 >0 and V _b1 =V _b0 >0 is established, if yes, measure V _c and V _b of the subsequent time series, determine the anti-zero point according to V _c and V _b of the subsequent time series, shift the phase by 180° to obtain the zero point, and then go to step S3, if no, go to step S27; S27, measuring V _c and V _b of the subsequent time sequence, and determining the inverse zero-crossing point according to V _c and V _b of the subsequent time sequence, and shifting the phase by 180° to obtain the zero-crossing point, and then entering step S3. 8. A low-cost single-input adjustable multiple-output WPT system according to claim 7, characterized in that: In step S23, the zero-crossing point is determined according to V _c and V _b of the subsequent time sequence, specifically: Determine whether V _c(n+1) =V _cn , V _b(n+1) =V _bn and V _cn =V _bn >0. If so, find the zero-crossing point, where V _cn and V _bn represent V _c and V _b at time sequence n, respectively, and V _c(n+1) and V _b(n+1) represent V _c and V _b at time sequence n+1, respectively. If not, re-determine after time sequence +1. In step S25, the zero-crossing point is determined according to V _c and V _b of the subsequent time sequence, specifically: Determine whether V _c(n+1) = V _cn and V _b(n+1) = V _bn are true. If so, find the zero crossing point. If not, re-determine after adding 1 to the timing sequence. In step S26, the inverse zero point is determined according to V _c and V _b of the subsequent time sequence, specifically: Determine whether V _c(n+1) =V _cn =0 and V _b(n+1) =V _bn =0 is true. If so, find the anti-zero point. If not, re-determine after the timing is increased by 1. In step S27, the inverse zero point is determined according to V _c and V _b of the subsequent time sequence, specifically: Determine whether V _c(n+1) =V _cn =0 and V _b(n+1) =V _bn =0 is established. If so, find the anti-zero point. If not, re-determine after the timing is increased by 1. 9. A control method for a low-cost single-input adjustable multi-output WPT system as claimed in any one of claims 1 to 5, characterized in that it comprises the steps of: X1. Synchronizing the driving signals of the high-frequency inverter and the full-wave rectifier circuit; X2. Start charging; during the charging process, collect the output voltage _Vc of the positive half-wave rectifier circuit and generate a corresponding PWM C control signal according to the error between _Vc and its reference voltage _Vcref to act on the positive half-wave rectifier circuit to adjust _Vc ; collect the output voltage _Vb of the negative half-wave rectifier circuit and generate a corresponding PWM B control signal according to the error between _Vb and its reference voltage _Vbref to act on the negative half-wave rectifier circuit to adjust _Vb ; collect the output voltage _Va of the full-wave rectifier circuit and control the conduction angle δ of the high-frequency inverter according to the error between _Va and its reference voltage _Varef to adjust _Va . 10. A low-cost single-input adjustable multi-output WPT system control method according to claim 9, characterized in that the step X1 specifically includes steps S1 to S3 according to any one of claims 6 to 8.

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