A receiving end staggered parallel three-level circuit topology switching control method based on different load modes

Abstract

This invention proposes a topology switching control method for interleaved parallel three-level circuits at the receiving end based on different load modes. Specifically, the control method involves: firstly, setting a load current switching threshold based on the system load state to distinguish between light and heavy load conditions. When the load current exceeds the switching threshold, it is a heavy load state. In this case, if the receiving end three-level circuit is in single-arm mode, it needs to be switched to double-arm mode to reduce the current stress on the switching transistors and further reduce the output current ripple under heavy load. Similarly, when the load current is less than the switching threshold, it is a light load state. In this case, if the receiving end three-level circuit is in double-arm mode, it needs to be switched to single-arm mode to reduce switching losses and input voltage fluctuations, achieving efficient and reliable load power supply.

Description

Technical Field

[0001] This invention is applied to the field of dynamic wireless power supply for electric vehicles, automated guided vehicles (AGVs), rail transit, and other similar applications. In particular, it relates to a method for switching control of receiver topology based on interleaved parallel three-level circuits with different load modes. Background Technology

[0002] Dynamic wireless power supply technology originates from magnetically coupled resonant wireless power transfer technology. It involves laying a transmitting device under the road surface and using the principle of electromagnetic conversion. Through a magnetic coupling mechanism coil, electrical energy is converted into a high-frequency magnetic field. An onboard receiving coil and power electronic conversion device then convert the high-frequency magnetic field back into electrical energy, thus powering a moving electric vehicle. The basic structure of a dynamic wireless power supply system is as follows: Figure 1 As shown, it is divided into three main parts: the transmitting end system (ground part), the magnetic coupling mechanism, and the receiving end system (vehicle-mounted part).

[0003] Dynamic wireless power supply systems often employ bipolar power supply rails as the magnetic coupling mechanism for energy exchange, as shown in the schematic diagram below. Figure 2 As shown. The bipolar power supply rail consists of two parts: a rail core and a transmitting coil. The rail core can be classified into I-type, S-type, and N-type structures according to its shape and structure. The transmitting coil is tightly wound on the rail core, generating N and S alternating equivalent magnetic poles along the direction of travel. The polarities of two adjacent transmitting coils are opposite in real time. The magnetic lines of force above the rail extend longitudinally along the direction of rail laying.

[0004] When an electric vehicle operates using dynamic wireless power supply, the receiver placed on the vehicle side is primarily responsible for picking up the wireless power and converting it into electrical energy to meet the battery load power requirements of the electric vehicle under different load conditions. The dynamic wireless power supply process for electric vehicles faces the following challenges:

[0005] 1. During vehicle operation, the high-frequency voltage coupled from the wireless power supply transmitter to the receiver has the characteristic of high output voltage level. Traditional receiver modulation circuits such as Buck and Boost two-level circuit topologies are difficult to adapt to the high voltage stress on the switching devices caused by the high voltage level. At the same time, when the battery load provides energy to a high-power motor, the output current requirement under full load conditions is large. Traditional single-output circuits cannot achieve high current output. The receiver conversion circuit needs to meet the application requirements of high voltage input and high current output at the same time.

[0006] Second, the battery load of an electric vehicle simultaneously experiences both heavy and light load conditions during charging. For example... Figure 3The figure shows the charging characteristic curve of the battery supplying an electric vehicle. The battery's SOC changes during the charging process, with the battery voltage gradually increasing and the charging current gradually decreasing. This indicates a change in battery load from heavy to light during charging. Similarly, taking an electric bus as an example, the required supply current varies depending on the vehicle's load. To adapt to load changes in electric vehicles during dynamic wireless power supply, and considering efficiency issues under different loads, it is necessary to design a circuit topology that can flexibly switch according to the load state to achieve more efficient and reliable power transmission. Summary of the Invention

[0007] The purpose of this invention is to solve the problems in the prior art and to provide a method for switching control of the topology of the receiver interleaved parallel three-level circuit based on different load modes.

[0008] This invention is achieved through the following technical solution: This invention proposes a topology switching control method for interleaved parallel three-level circuits at the receiving end based on different load modes. Specifically, the control method involves: First, setting a load current switching threshold based on the system load state to distinguish between light and heavy load conditions. When the load current exceeds the switching threshold, it is a heavy load state. In this case, if the receiving end three-level circuit is in single-arm mode, it needs to be switched to double-arm mode to reduce the current stress on the switching transistors and further reduce the output current ripple under heavy load. Similarly, when the load current is less than the switching threshold, it is a light load state. In this case, if the receiving end three-level circuit is in double-arm mode, it needs to be switched to single-arm mode to reduce switching losses and minimize fluctuations caused by the input voltage, achieving efficient and reliable load power supply.

[0009] Furthermore, taking a duty cycle D < 0.5 as an example, the two three-level circuits adopt an interleaved parallel control method, with a conduction time of DT. s The stagger angle is 90°, that is, the switching transistor S b1 Compared to S a1 Defining the switching transistor S with a 90° hysteresis turn-on. a1 S a2 S a3 S a4 For the advanced bridge arm, S b1 S b2 S b3 S b4 As a lagging bridge arm, when this circuit is used as a Buck converter, S a1 S a2 S b1 S b2 S acts as the main control switch for power control. a3 S a4 S b3 S b4 It acts as an auxiliary switch to provide freewheeling.

[0010] Furthermore, when the vehicle is in heavy-load mode and the battery input power demand is high, the large charging current is borne by the two sets of bridge arms of the interleaved parallel circuit. The interleaved parallel circuit structure can effectively reduce the ripple of the output current and effectively reduce the electrical stress of the switching devices when the large current is output on the resonant side. When the vehicle switches from heavy-load mode to light-load mode, the battery charging current begins to decrease, and the operating current of a single bridge arm is at a low amplitude. At this time, one of the two sets of bridge arms that were originally working simultaneously is used as the main output bridge arm, and the other set is switched to the filter bridge arm. The upper and lower switches in the filter bridge arm are closed, and the middle switch is open to reduce switching losses. This switches the flying capacitor in the bridge arm to the filter capacitor connected in parallel to the DC bus for voltage regulation and filtering, thereby reducing switching losses and improving the ability to suppress the input power fluctuations at the receiving end.

[0011] Furthermore, taking the lagging bridge arm as an example, when switching from a single bridge arm to a double bridge arm, the switching transistor S... b4 Turn off, switch S b1 Duty cycle D sb1 The value is gradually decreased from 1 to the control output value D, while the switching transistor S... b2 Duty cycle D sb2 The output value is gradually increased from 0 to the control output value D, thereby enabling pulse control of the corresponding switching transistor.

[0012] Furthermore, when switching from dual-arm mode to single-arm mode, the two main operating switches are gradually turned off. At this time, all switches in the bridge arm are in the off state, and the voltage across the flying capacitor is clamped. Then, the lower half of the switch S is turned on. b4 , to perform load voltage U o and flying capacitor voltage U cb Matching, when the load voltage is greater than the flying capacitor voltage, S b4 The switching on will cause the inductor current to rise, and through S b2 Charge the flying capacitor to boost the voltage, when S b4 When turned off, the inductor current flows through S b1 and S b2 Freewheeling, when the voltage across the flying capacitor is greater than or equal to the load voltage, S b4 The switch will no longer cause changes in inductor current, S b4 Normally open, charging is complete; at this time, the voltage across the flying capacitor is still not equal to the input voltage, and S gradually turns on. b3 The switching transistor, at this time S b3 With S turned off b2 Together, they form the Boost circuit. The power supply is the flying capacitor charged at the input port of the receiver. When S... b3 When the circuit is turned on, the inductor current rises, and the current flows through S... b3 Sb4 The flow returns to the receiver input, when S b3 When the circuit is turned off, the inductor current flows through S. b2 and S b4 The flying capacitor is charged until the voltage across it equals the input voltage, at which point charging ends. At this point, hold S... b4 The conduction is completed, and S is activated. b1 Turn off S b3 Then the switching process of a single bridge arm ends; the lagging bridge arm switches to a filter parallel bridge arm, and the flying capacitor switches to a filter capacitor, which effectively reduces switching losses and reduces input voltage fluctuations caused by dynamic power supply in light load mode.

[0013] Furthermore, the specific structure of the interleaved parallel three-level circuit topology at the receiving end is as follows: the dynamic transmitting end performs AC-DC-AC power conversion on the power frequency AC, wherein uncontrolled rectification completes the low-frequency AC-DC conversion, and after capacitor filtering, the DC power is converted into high-frequency AC power by a full-bridge inverter circuit under synchronous phase-shift modulation. A single inverter supplies power to multiple rails, and L1 and C1 on the main resonant circuit resonate with each other. Each rail L p1 L p2 and L p3 Each capacitor is connected in series with a resonant capacitor and then output in parallel. Through magnetic field coupling, electrical energy is transferred to the receiving coil, completing dynamic wireless power supply. The DD coupling coil at the receiving end couples the high-frequency AC voltage coupled to the secondary side into the uncontrolled rectifier circuit module. After parallel DC output, it serves as the DC input voltage U of the interleaved parallel three-level circuit. m The receiver power modulation circuit adopts an interleaved parallel three-level circuit and performs topology switching control according to load requirements to provide efficient and reliable power supply for battery loads.

[0014] The beneficial effects of this invention are as follows:

[0015] As a power supply unit for high-power battery loads, the dynamic wireless power supply system for electric vehicles faces challenges in achieving high transmission power levels and wide electrical parameter ranges using traditional two-level DC / DC circuits. To meet the high-power requirements of dynamic wireless power supply for electric vehicles, this invention proposes a topology switching control strategy for the interleaved parallel three-level DC / DC circuit under different load conditions, based on the interleaved parallel three-level DC / DC circuit at the receiving end. This strategy better adapts to the different transmission requirements under light and heavy load modes during dynamic wireless power supply for high-power electric vehicles, and achieves efficiency improvement and fluctuation suppression under light load conditions, as well as reduction of output current stress and ripple under heavy load conditions. Attached Figure Description

[0016] Figure 1 This is a basic structural diagram of a dynamic wireless power supply system.

[0017] Figure 2This is a schematic diagram of a bipolar magnetic coupling mechanism.

[0018] Figure 3 This is a schematic diagram of the battery charging characteristics of an electric vehicle.

[0019] Figure 4 This is a schematic diagram of the overall circuit structure of a dynamic wireless power supply system.

[0020] Figure 5 This is a schematic diagram of the switching process and control signals of an interleaved parallel three-level circuit, where (a) is the modulation signal of the dual-bridge arm, (b) is the interleaved parallel mode of the dual-bridge arm aimed at reducing current ripple, and (c) is the filtering mode of the single-bridge arm aimed at reducing switching losses.

[0021] Figure 6 This is a schematic diagram of the process of switching from dual-arm mode to single-arm mode, where (a) the flying capacitor is charged or held, U cb ≥U o (b) Flying capacitor charging, U cb =U m .

[0022] Figure 7 This is a schematic diagram of the receiver topology switching control program. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Technical Terminology Explanation:

[0025] Wireless power transfer system (WPT)

[0026] Dynamic wireless power transfer system (DWPT)

[0027] Pulse Width Modulation (PWM)

[0028] like Figure 4The diagram shows the overall circuit structure of the dynamic wireless power supply system. The dynamic transmitter converts the mains frequency AC power into AC-DC-AC power. Uncontrolled rectification completes the low-frequency AC-DC conversion. After capacitor filtering, a full-bridge inverter circuit under synchronous phase-shift modulation converts the DC power into high-frequency AC power. A single inverter supplies power to multiple rail sections. L1 and C1 on the main resonant circuit resonate with each other. Each rail section L... p1 L p2 and L p3 After being connected in series with a resonant capacitor, they are connected in parallel for output. The electrical energy is then transmitted to the receiving coil via magnetic field coupling, thus completing dynamic wireless power supply.

[0029] The DD coupling coil at the receiving end couples the high-frequency AC voltage coupled to the secondary side into the uncontrolled rectifier circuit module. After parallel DC output, it serves as the DC input voltage U of the interleaved parallel three-level circuit. m The receiving-end power modulation circuit employs an interleaved parallel three-level circuit and performs topology switching control according to load requirements, providing efficient and reliable power supply to the battery load. The implementation circuit proposed in this invention can implement both Buck modulation and Boost modulation; this invention only analyzes the Buck mode.

[0030] The circuit parameters that need to be collected in the circuit include the parallel output currents I of the two inductors. L1 I L2 and total output current I o The input voltage U of the interleaved parallel three-level circuit m Flying capacitor voltage U ca U cb and load output voltage U o After hardware filtering, each component participates in power control, overvoltage protection, and overcurrent protection. The control system uses the feedback voltage and current acquisition signals to achieve constant current control and outputs PWM control signals to realize the conduction control of the interleaved parallel three-level circuit switching transistors.

[0031] Figure 5 (a) is a schematic diagram of the pulse modulation control signal applicable to the dual-bridge arm mode. Taking a duty cycle D < 0.5 as an example, the two three-level circuits adopt an interleaved parallel control method, with an on-time of DT. s The stagger angle is 90°, that is, the switching transistor S b1 Compared to S a1 Turn-on is delayed by 90°. Define the switching transistor S. a1 S a2 S a3 S a4 For the advanced bridge arm, S b1 S b2 S b3 S b4It is a lagging bridge arm. When this circuit is used as a Buck converter, S a1 S a2 S b1 S b2 S acts as the main control switch for power control. a3 S a4 S b3 S b4 It acts as an auxiliary switch to provide freewheeling.

[0032] When the vehicle is in heavy-load mode and the battery input power demand is high, the larger charging current is borne separately by the two bridge arms of the interleaved parallel circuit, such as... Figure 5 As shown in (b), the interleaved parallel circuit structure can effectively reduce the ripple of the output current and effectively reduce the electrical stress of the switching devices when the large current is output on the resonant side. When the driving state switches from heavy load mode to light load mode, the battery charging current begins to decrease, and the operating current of the single bridge arm is at a low amplitude. At this time, the interleaved parallel operating mode increases the additional power loss, which is not conducive to improving the system transmission efficiency. This invention proposes a single bridge arm filter capacitor mode switching control in light load mode for the multiplexing mode of flying capacitors. One of the two sets of bridge arms that originally worked simultaneously is used as the main output bridge arm, and the other set is switched to the filter bridge arm, as shown in the figure. Figure 5 As shown in (c), the upper and lower switches in the filter bridge arm are closed, and the middle switch is open to reduce switching losses. This switches the flying capacitor in the bridge arm to a filter capacitor connected in parallel to the DC bus for voltage regulation and filtering, thereby reducing switching losses and improving the ability to suppress input power fluctuations at the receiving end.

[0033] Taking the lagging bridge arm as an example, when switching from a single bridge arm to a double bridge arm, the switching transistor S... b4 Turn off, switch S b1 Duty cycle D sb1 The value is gradually decreased from 1 to the control output value D, while the switching transistor S... b2 Duty cycle D sb2 The value is gradually increased from 0 to the control output value D, thereby affecting the corresponding switching transistor. Figure 5 (a) Pulse control is sufficient. However, switching from the dual-bridge-arm interleaved parallel mode to the single-bridge-arm filtering mode is difficult. At this time, the voltage across the flying capacitor is half of the input voltage. The switching process is essentially charging the voltage across the flying capacitor to the same value as the input voltage. If the bridge arm switching transistors are directly turned on and off, it will cause the instantaneous charging current spike to be too large, affecting circuit safety. The switching control strategy proposed in this invention can complete the switching of the single-bridge-arm filtering mode while ensuring that the charging current spike is small, and maintain output stability during the switching process.

[0034] When switching from dual-arm mode to single-arm mode, the two main operating switches are gradually turned off. At this time, all switches in the bridge arm are off, and the voltage across the flying capacitor is clamped. Then, the lower half of the switch S is turned on. b4 , to perform load voltage U o and flying capacitor voltage U cb Matching, such as Figure 6 As shown in (a), when the load voltage is greater than the flying capacitor voltage, S b4 The switching on will cause the inductor current to rise, and through S b2 Charge the flying capacitor to boost the voltage, when S b4 When turned off, the inductor current flows through S b1 and S b2 Freewheeling, when the voltage across the flying capacitor is greater than or equal to the load voltage, S b4 The switch will no longer cause changes in inductor current, S b4 Normally open, charging is complete; at this time, the voltage across the flying capacitor is still not equal to the input voltage, and S gradually turns on. b3 The switching transistor, at this time S b3 With S turned off b2 Together, they form the Boost circuit, with the power supply being the charging of the flying capacitor at the input port of the receiver, such as... Figure 6 As shown in (b), when S b3 When the circuit is turned on, the inductor current rises, and the current flows through S... b3 S b4 The flow returns to the receiver input, when S b3 When the circuit is turned off, the inductor current flows through S. b2 and S b4 The flying capacitor is charged until the voltage across it equals the input voltage, at which point charging ends. At this point, hold S... b4 The conduction is completed, and S is activated. b1 Turn off S b3 Then the switching process of a single bridge arm ends. The lagging bridge arm switches to a filtered parallel bridge arm, and the flying capacitor switches to a filtered capacitor, effectively reducing switching losses and input voltage fluctuations caused by dynamic power supply in light-load mode.

[0035] The overall process of switching control for the interleaved parallel three-level circuit topology at the receiving end is as follows: Figure 7As shown, taking the lagging bridge arm as an example, the first step is to set a load current switching threshold based on the system load status to distinguish between light and heavy load conditions. When the load current is greater than the switching threshold, it is a heavy load condition. If the receiving end three-level circuit is in single-bridge arm mode, it needs to be switched to dual-bridge arm mode to reduce the current stress on the switching transistor and further reduce the output current ripple under heavy load. Similarly, when the load current is less than the switching threshold, it is a light load condition. If the receiving end three-level circuit is in dual-bridge arm mode, it needs to be switched to single-bridge arm mode to reduce switching losses and reduce the fluctuations caused by the input voltage, thereby achieving efficient and reliable load power supply.

Claims

1. A method for switching control of receiver interleaved parallel three-level circuit topology based on different load modes, characterized in that: The control method is as follows: First, a load current switching threshold needs to be set according to the system load status to distinguish between light and heavy load conditions. When the load current is greater than the switching threshold, it is a heavy load condition. At this time, if the receiving end three-level circuit is in single-bridge-arm mode, it needs to be switched to double-bridge-arm mode to reduce the current stress of the switching transistor and further reduce the output current ripple under heavy load. Similarly, when the load current is less than the switching threshold, it is a light load condition. At this time, if the receiving end three-level circuit is in double-bridge-arm mode, it needs to be switched to single-bridge-arm mode to reduce switching losses and reduce the fluctuation caused by the input voltage, thereby achieving efficient and reliable load power supply. When switching from dual-arm to single-arm mode, the two main operating switches are gradually turned off. At this point, all switches in the bridge arm are off, and the voltage across the flying capacitor is clamped. Then, the lower half of the switch, Sb4, is turned on to match the load voltage Uo and the flying capacitor voltage Ucb. When the load voltage is greater than the flying capacitor voltage, the turn-on of Sb4 will cause the inductor current to rise, charging the flying capacitor via Sb2. When Sb4 is turned off, the inductor current freewheels through Sb1 and Sb2. When the flying capacitor voltage is greater than or equal to the load voltage, the switch of Sb4 will no longer cause a change in the inductor current; Sb4 remains open, and charging ends. At this point, the flying capacitor voltage is still not equal to the input voltage. The switching transistor Sb3 is gradually turned on. At this time, Sb3 and the off Sb2 together form the Boost circuit. The power supply is used to charge the flying capacitor at the input port of the receiver. When Sb3 is turned on, the inductor current rises and flows back to the receiver input through Sb3 and Sb4. When Sb3 is turned off, the inductor current flows through Sb2 and Sb4 to charge the flying capacitor. When the voltage of the flying capacitor equals the input voltage, the charging ends. At this time, Sb4 is kept on and Sb1 is turned on, and Sb3 is turned off. The switching process of the single bridge arm ends. The lagging bridge arm switches to the filtered parallel bridge arm, and the flying capacitor switches to the filter capacitor. In light load mode, the switching loss is effectively reduced and the input voltage fluctuation caused by dynamic power supply is reduced.

2. The control method according to claim 1, characterized in that, With duty cycle D Taking <0.5 as an example, the two three-level circuits adopt an interleaved parallel control method, and the conduction time is DT s The stagger angle is 90°, that is, the switching transistor S b1 Compared to S a1 Defining the switching transistor S with a 90° hysteresis turn-on. a1 S a2 S a3 S a4 For the advanced bridge arm, S b1 S b2 S b3 S b4 As a lagging bridge arm, when this circuit is used as a Buck converter, S a1 S a2 S b1 S b2 S acts as the main control switch for power control. a3 S a4 S b3 S b4 It acts as an auxiliary switch to provide freewheeling.

3. The control method according to claim 2, characterized in that, When the vehicle is in heavy load mode and the battery input power demand is high, the large charging current is borne by the two sets of bridge arms of the interleaved parallel circuit. The interleaved parallel circuit structure can effectively reduce the ripple of the output current and effectively reduce the electrical stress of the switching devices when the large current is output on the resonant side. When the vehicle switches from heavy load mode to light load mode, the battery charging current begins to decrease and the operating current of a single bridge arm is at a low amplitude. At this time, one of the two sets of bridge arms that were originally working simultaneously is used as the main output bridge arm, and the other is switched to the filter bridge arm. The upper and lower switches in the filter bridge arm are closed, and the middle switch is open to reduce switching losses. This switches the flying capacitor in the bridge arm to the filter capacitor connected in parallel to the DC bus for voltage regulation and filtering, thereby reducing switching losses and improving the ability to suppress the input power fluctuations at the receiving end.

4. The control method according to claim 3, characterized in that, Taking the lagging bridge arm as an example, when switching from a single bridge arm to a double bridge arm, the switching transistor S... b4 Turn off, switch S b1 Duty cycle D sb1 Gradually decrease from 1 to the control output value D And the switching transistor S b2 Duty cycle D sb2 Gradually increase from 0 to the control output value D Then, pulse control can be applied to the corresponding switching transistors.

5. The control method according to claim 1, characterized in that, The specific structure of the interleaved parallel three-level circuit topology at the receiving end is as follows: the dynamic transmitting end performs AC-DC-AC power conversion on the power frequency AC, wherein the uncontrolled rectification completes the low-frequency AC-DC conversion, and after capacitor filtering, the DC power is converted into high-frequency AC power by a full-bridge inverter circuit under synchronous phase-shift modulation. A single inverter supplies power to multiple rail sections, and the main resonant circuit... L 1. C 1. Mutual resonance, each section of the guide rail L p1 , L p2 and L p3 Each capacitor is connected in series with a resonant capacitor and then connected in parallel to output power. Through magnetic field coupling, electrical energy is transferred to the receiving coil, completing dynamic wireless power supply. The DD coupling coil at the receiving end couples the high-frequency AC voltage coupled to the secondary side into the uncontrolled rectifier circuit module. After parallel DC output, this voltage serves as the DC input voltage for the interleaved parallel three-level circuit. U m The receiver power modulation circuit adopts an interleaved parallel three-level circuit and performs topology switching control according to load requirements to provide efficient and reliable power supply for battery loads.

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