A method for inhibiting overcurrent during starting of a wireless power-supplied direct-drive brushless DC motor

Abstract

The application discloses a method for inhibiting overcurrent during starting of a wireless power supply direct-drive brushless DC motor, and the method is applied to a wireless power transmission system. The application aims at the problem of excessive starting impact current caused by zero back electromotive force of the motor during starting of the wireless power supply direct-drive motor, and based on impedance frequency characteristics of an LCC-S high-order resonance network, a safe detuning frequency interval and an optimal detuning frequency point under a starting condition are derived through analysis and deduction; the inverter is controlled to work in the safe detuning frequency interval in an initial starting stage, the system input impedance is raised by raising the working frequency, the starting impact current is effectively inhibited, and meanwhile, stable transmission of active power is ensured to drive the motor to establish a rotating speed and a back electromotive force; after the motor working state reaches a preset threshold, the system is smoothly switched to a rated resonance frequency of the system, and the soft starting without impact is completed. The application effectively solves the overcurrent problem in the starting process of the direct-drive motor, and realizes smooth soft starting under the condition without a sensor.

Description

Technical Field

[0001] This invention belongs to the field of brushless DC motor technology, specifically a method for suppressing overcurrent during startup of a wirelessly powered direct-drive brushless DC motor. Background Technology

[0002] Wireless power transfer technology is a power supply technology that uses spatial media such as electric and magnetic fields to transmit electrical energy from the power source to the electrical device without contact. Compared with traditional wired power supply, it has the core advantages of good electrical isolation, safety and reliability, and strong environmental adaptability. It can be adapted to harsh electrical environments such as underground coal mines, underwater, and flammable and explosive environments, and has been widely used in industrial automation, consumer electronics, medical equipment and other fields.

[0003] The wireless power supply technology involved in this application is fundamentally different from conventional wireless charging technology: wireless charging uses energy storage devices such as batteries as the core load, first completing the energy storage and then supplying power to the back-end load, resulting in stable load characteristics; while this application targets the scenario where the wireless link directly drives motor-type loads, without an intermediate energy storage buffer, and drastic changes in load conditions will directly affect the wireless transmission link, placing extremely high demands on the system's transient response capability and impact suppression capability.

[0004] Brushless DC motors have become the mainstream load in wireless power supply direct drive scenarios due to their advantages such as high efficiency, excellent speed regulation performance, and long service life. However, such systems have serious overvoltage and overcurrent problems during the startup phase: the initial speed of the motor is zero, the back electromotive force of the winding is almost zero, and the armature is equivalent to a low-resistance load with a near short circuit. This will directly cause a sudden drop in the input impedance of the primary resonant network, resulting in a startup inrush current several times the rated value and the risk of secondary overvoltage. At best, this will trigger protection and cause startup failure; at worst, it will burn out power devices and damage the motor windings, seriously restricting the system's operational reliability and engineering applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for suppressing overcurrent during the startup of a wirelessly powered direct-drive brushless DC motor. This method can effectively suppress overvoltage and overcurrent problems generated during the system startup phase.

[0006] To achieve the above objectives, the present invention provides a method for suppressing overcurrent during startup of a wirelessly powered direct-drive brushless DC motor, comprising the following steps:

[0007] Step S1: Based on the impedance-frequency characteristics of the LCC-S resonant network and combined with the starting stall condition of the brushless DC motor, calculate the series resonant peak frequency f corresponding to the minimum value of the system input impedance. peak And according to the resonant peak frequency f peak Determine the safe detuning frequency range under startup conditions;

[0008] Step S2: When the system starts up, control the high-frequency full-bridge inverter to operate at the starting frequency within the safe detuning frequency range;

[0009] Step S3: Within the safe detuning frequency range, control the operating frequency to perform linear frequency reduction at a preset slope until the frequency switching trigger condition is met; during this process, use frequency changes to adjust the system impedance to suppress the starting inrush current, and gradually increase the active power transmission capacity to drive the motor to establish speed and back electromotive force.

[0010] Step S4: Real-time acquisition of primary voltage and current signals, calculation of load-side voltage and current signals based on the sampled primary voltage and current signals, thereby obtaining the motor's operating status; when the motor's operating status reaches the preset frequency cutting threshold, immediately stop linear frequency reduction, control the operating frequency to directly step switch to the system's rated resonant frequency f0, and complete the soft start.

[0011] As a further aspect of the present invention: the safe detuning frequency range is [f] peak +5%*f peak , f peak +15%*f peak The operating frequency of the entire linear frequency reduction process is strictly constrained within this range; the series resonant peak frequency f peak The calculation formula is:

[0012]

[0013] In the formula, k is the coupling coefficient of the magnetic coupling mechanism. M is the mutual inductance of the magnetically coupled transceiver coil mechanism, and L is... s For the self-inductance of the secondary receiving coil, L p L is the self-inductance of the primary-side transmitting coil. f1 This is the series compensation inductor in the primary-side LCC compensation network.

[0014] As a further aspect of the present invention: the primary-side LCC compensation network includes a series compensation inductor L f1 Parallel compensation capacitor C p1 Series compensation capacitor C p2 The secondary-side S-type compensation network includes the self-inductance L of the secondary-side receiving coil. s Series compensation capacitor C s The system's rated resonant angular frequency is The compensation network parameters satisfy the following rated resonance conditions:

[0015]

[0016]

[0017] .

[0018] As a further aspect of the present invention: the starting frequency of the linear frequency reduction control is selected from the upper limit of the safe detuning frequency range, which is 1.15*f. peak The termination frequency is selected from the lower limit of the safe detuning frequency range, which is 1.05*f. peak The slope of the linear frequency modulation is set according to the rated speed of the motor and the required start-up time to ensure that the motor can gradually build up speed and back electromotive force during the linear frequency modulation process.

[0019] As a further aspect of the present invention: the frequency switching triggering condition is a dual-threshold linkage condition, which must simultaneously satisfy the following two sub-conditions:

[0020] Sub-condition 1: The current operating frequency is within the safe detuning frequency range;

[0021] Sub-condition 2: The derived motor speed reaches 30% or more of the rated speed, or the derived motor back EMF reaches 30% or more of the rated back EMF.

[0022] When the above sub-conditions are met simultaneously, a frequency step switching operation is triggered without having to complete the full linear frequency reduction process.

[0023] A wireless power supply direct-drive brushless DC motor system for implementing the above method includes a DC power supply, a power supply-side filter capacitor, a high-frequency full-bridge inverter, a transmitting coil module, a receiving coil module, a single-phase uncontrolled rectifier module, a three-phase inverter, a motor-side filter capacitor, a brushless DC motor load module, a voltage and current sampling module, a digital signal processing module, and a pulse signal generation module, wherein:

[0024] The output terminal of the DC power supply is connected to the DC input terminal of the high-frequency full-bridge inverter. The AC output terminal of the high-frequency full-bridge inverter is connected to the input terminal of the primary-side LCC compensation network. The output terminal of the primary-side LCC compensation network is connected to the primary-side transmitting coil of the magnetically coupled transceiver coil mechanism. The secondary-side receiving coil of the magnetically coupled transceiver coil mechanism is connected to the input terminal of the secondary-side S-type compensation network. The output terminal of the secondary-side S-type compensation network is connected to the AC input terminal of the single-phase uncontrolled rectifier module. The DC output terminal of the single-phase uncontrolled rectifier module is connected to the DC input terminal of the three-phase inverter. The AC output terminal of the three-phase inverter is connected to the DC brushless motor load module. The sampling terminal of the voltage and current sampling module is connected to the output terminal of the high-frequency full-bridge inverter. The signal output terminal of the voltage and current sampling module is connected to the input terminal of the digital signal processing module and the pulse signal generation module. The control output terminal of the digital signal processing module and the pulse signal generation module is connected to the drive signal input terminal of the high-frequency full-bridge inverter.

[0025] A startup execution process based on a method for suppressing overcurrent during startup of a wirelessly powered direct-drive brushless DC motor includes the following steps:

[0026] Step 1: In the parameter design phase, based on the system topology, motor rated parameters, and coupling characteristics, design the parameters of the primary-side LCC and secondary-side S-type compensation network, and determine the system's rated resonant frequency. ;

[0027] Step 2: Strategy Pre-setting Stage, derive the safe detuning frequency range based on the stall condition boundary [f] peak +5%*f peak , f peak +15%*f peak Set the linear down-frequency start frequency, slope, and frequency cut threshold;

[0028] Step 3: Start initialization. After receiving the start command, control the high-frequency full-bridge inverter to operate at the starting frequency, suppress the initial inrush current, and start primary-side signal acquisition.

[0029] Step 4: Linear frequency reduction control, reducing the operating frequency according to a preset slope, and comparing the derived motor status with the frequency cutting threshold in real time to ensure that the frequency is always constrained within the safe detuning frequency range;

[0030] Step 5: Step switching. Once the frequency switching trigger condition is detected, the linear frequency reduction is immediately interrupted, and the operating frequency is directly switched to the rated resonant frequency in a step. ;

[0031] Step 6: Steady-state operation, monitor system voltage, current and motor speed, and enter normal operation control mode after stabilization.

[0032] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention requires no modification to the main circuit hardware topology of the wireless power supply system. Based on the impedance frequency characteristics of the LCC-S high-order resonant network, it accurately locks the safe detuning frequency range and the optimal detuning frequency point under startup conditions through analytical derivation. In the initial startup stage, the inverter is controlled to operate within the safe detuning frequency range. By raising the operating frequency, the system input impedance is increased, effectively suppressing the startup inrush current while ensuring stable active power transmission to drive the motor to establish speed and back EMF. Once the motor's operating state reaches a preset threshold, it smoothly switches to the system's rated resonant frequency, completing a shockless soft start. Effective suppression of the startup large current can be achieved solely through optimization of the primary-side inverter switching frequency control strategy, avoiding the power loss, increased cost, and increased control complexity caused by additional hardware modules, and without affecting the system's rated transmission efficiency and operating characteristics. Attached Figure Description

[0033] Figure 1This is a schematic diagram of the system structure of the present invention.

[0034] Figure 2 This is a flowchart of the process of suppressing starting current and voltage in this invention.

[0035] Figure 3 This is a system efficiency diagram of the direct start method of the wireless direct drive brushless DC motor system in an embodiment of the present invention.

[0036] Figure 4 This is a system efficiency diagram of the frequency-switching startup method in an embodiment of the present invention.

[0037] Figure 5 This is a three-phase current diagram of the direct starting method of the wireless direct-drive brushless DC motor system in an embodiment of the present invention.

[0038] Figure 6 This is a three-phase current diagram of the frequency-switching start-up method in an embodiment of the present invention.

[0039] Figure 7 This is a system power diagram of the direct start method of the wireless direct drive brushless DC motor system in an embodiment of the present invention.

[0040] Figure 8 This is a system power diagram of the frequency-switching start-up method in an embodiment of the present invention. Detailed Implementation

[0041] The invention will now be further described with reference to the accompanying drawings.

[0042] like Figure 1 As shown, the wireless power supply direct-drive brushless DC motor system includes a DC power supply, a power supply-side filter capacitor, a high-frequency full-bridge inverter, a transmitting coil module, a receiving coil module, a single-phase uncontrolled rectifier module, a three-phase inverter, a motor-side filter capacitor, a DC brushless motor load module, a voltage and current sampling module, a digital signal processing module, and a pulse signal generation module (FPGA), wherein:

[0043] The output terminal of the DC power supply is connected to the DC input terminal of the high-frequency full-bridge inverter. The AC output terminal of the high-frequency full-bridge inverter is connected to the input terminal of the primary-side LCC compensation network. The output terminal of the primary-side LCC compensation network is connected to the primary-side transmitting coil of the magnetically coupled transceiver coil mechanism. The secondary-side receiving coil of the magnetically coupled transceiver coil mechanism is connected to the input terminal of the secondary-side S-type compensation network. The output terminal of the secondary-side S-type compensation network is connected to the AC input terminal of the single-phase uncontrolled rectifier module. The DC output terminal of the single-phase uncontrolled rectifier module is connected to the DC input terminal of the three-phase inverter. The AC output terminal of the three-phase inverter is connected to the DC brushless motor load module. The sampling terminal of the voltage and current sampling module is connected to the output terminal of the high-frequency full-bridge inverter. The signal output terminal of the voltage and current sampling module is connected to the input terminal of the FPGA. The control output terminal of the FPGA is connected to the drive signal input terminal of the high-frequency full-bridge inverter.

[0044] System workflow as follows Figure 2 As shown, firstly, based on the impedance frequency characteristics of the LCC-S resonant network and combined with the near-short-circuit condition of the DC brushless motor starting stall, the safe detuning frequency range under the starting condition is predetermined. In the initial stage of system startup, the frequency modulation control module controls the high-frequency full-bridge inverter to operate at the starting frequency within the safe detuning frequency range. Subsequently, within the safe detuning frequency range, linear frequency reduction control is performed with a preset slope to suppress the starting inrush current throughout the process, while gradually improving the system's active power transmission capability, driving the motor to smoothly establish speed and back EMF. When the voltage and current signals collected by the state detection module indicate that the motor operating state meets the preset frequency switching threshold, the frequency modulation control module controls the high-frequency full-bridge inverter to directly step switch the operating frequency to the system's rated resonant frequency, enabling the system to operate under the rated resonant condition and completing the motor's impact-free soft start.

[0045] The primary-side LCC compensation network includes a series compensation inductor L. f1 Parallel compensation capacitor C p1 Series compensation capacitor C p2 The self-inductance of the primary transmitting coil is L. p The system's rated resonant angular frequency is f0 is the system's rated resonant frequency, and the primary-side LCC compensation network satisfies the rated resonance condition: , The secondary-side S-type compensation network includes the self-inductance L of the secondary-side receiving coil. s Series compensation capacitor C s The rated resonance condition is met: The mutual inductance of the magnetically coupled transceiver coil mechanism is , where k is the coupling coefficient of the transmitting and receiving coils.

[0046] The method for determining the safe detuning frequency range is as follows: The series resonant peak frequency f corresponding to the minimum input impedance of the system under near-short-circuit conditions during the start-up of a DC brushless motor with a stalled rotor is used. peak The lower limit of the interval is used as the reference, and the highest detuning frequency f is used to meet the motor starting speed requirements. max The upper limit of the interval is given, and the final safe detuning frequency interval is [f]. peak +5%*f peak , f peak +15%*f peak The operating frequency of linear frequency modulation is constrained within this range throughout its entire range;

[0047] Among them, the series resonant peak frequency f peak The calculation formula is derived based on the system's core resonance parameters:

[0048]

[0049] The starting frequency of linear frequency reduction control is selected from the upper limit of the safe detuning frequency range or the upper part of the range. The ending frequency of linear frequency reduction is not lower than the lower limit reference value of the safe detuning frequency range. The slope of linear frequency regulation is matched and set according to the rated parameters of the motor and the starting time requirements to ensure that the motor can continuously build up speed and back electromotive force during the linear frequency regulation process.

[0050] The preset frequency cutting threshold is a dual-threshold linkage trigger condition, which must be met simultaneously: the system frequency is within the preset safe detuning frequency range threshold, and the motor speed reaches 30% or more of the rated speed, or the motor back EMF reaches 30% or more of the rated back EMF; during the linear frequency regulation process, the status detection module compares the operating status with the frequency cutting threshold in real time, and triggers the direct cutting operation when the condition is met, without having to complete the preset full linear frequency reduction stroke. Figure 2 The system workflow diagram details the steps involved in the system's operation.

[0051] The following is a specific example of the present invention.

[0052] The system's DC input voltage is 170V, and the resonant operating frequency is set to 85kHz. Both the transmitting coil L1 and the receiving coil L2 are wound with Litz wire. The inductance of both the transmitting and receiving coils is 100µH, and the mutual inductance between them is M. 12 The primary resonant inductance is 30µH. f1 The primary-side parallel resonant capacitor C is 20µH. p1 The primary-side series resonant capacitor C is 175.3nF. p2 The secondary-side compensation capacitor C is 43.8nF. s The value is 35nF. The peak frequency f is obtained through the series resonant frequency. peakThe calculation formula shows that the safe detuning frequency range of this system is 116kHz-126kHz. The frequency modulation control module controls the primary side high-frequency inverter to linearly reduce its operating frequency from 126kHz to 116kHz within the 0-0.2S range. After 0.2S, the secondary side voltage and current signals are calculated from the primary side voltage and current signals to obtain the motor operating status. It is determined that the motor operating status has reached the frequency cutting threshold. When the motor operating status reaches the frequency cutting threshold, the primary side inverter operating frequency is stepped down from 116kHz to the resonant operating frequency of 85kHz. The motor operating status is stable, and the system successfully soft-starts.

[0053] Depend on Figure 3 and Figure 4 The comparison shows that, under stable operating conditions, the system efficiency using this startup method is the same as that using the direct startup method; Meanwhile, a comparison... Figure 5 and Figure 6 The primary and secondary peak values ​​of the starting current using this starting method are suppressed to 2 to 2.5 times the stable operating current, which is much smaller than 6 to 8 times that of direct starting.

[0054] The starting method of this invention has a strong suppressive effect on the voltage and current across the DC brushless motor during startup, and after stable operation, the overall transmission efficiency of the system is minimally affected. Furthermore, this method does not require additional complex topology circuitry, thus avoiding additional circuit costs and complex control. Figure 7 , Figure 8 It is known that when this startup method is used, there is no excessive power problem similar to that caused by direct startup at the moment of startup, and the impact on system power when it finally stabilizes is small.

Claims

1. A method for suppressing overcurrent during startup of a wirelessly powered direct-drive brushless DC motor, characterized in that, Includes the following steps: Step S1: Based on the impedance-frequency characteristics of the LCC-S resonant network and combined with the starting stall condition of the brushless DC motor, calculate the series resonant peak frequency f corresponding to the minimum value of the system input impedance. peak And according to the resonant peak frequency f peak Determine the safe detuning frequency range under startup conditions; Step S2: When the system starts, control the high-frequency full-bridge inverter to operate at the starting frequency within the safe detuning frequency range; Step S3: Within the safe detuning frequency range, control the operating frequency to perform linear frequency reduction at a preset slope until the frequency switching trigger condition is met; During this process, frequency changes are used to adjust the system impedance to suppress the starting inrush current, and the active power transmission capacity is gradually increased to drive the motor to establish speed and back electromotive force. Step S4: Real-time acquisition of primary side voltage and current signals, calculation of load side voltage and current signals based on the sampled primary side voltage and current signals, thereby obtaining the motor's operating status; when the motor's operating status reaches the preset frequency cutting threshold, immediately stop linear frequency reduction, control the operating frequency to directly step switch to the system's rated resonant frequency f0, and complete the soft start; The safe detuning frequency range is [f] peak +5%*f peak , f peak +15%*f peak The operating frequency of the entire linear frequency reduction process is strictly constrained within this range; the series resonant peak frequency f peak The calculation formula is: In the formula, k is the coupling coefficient of the magnetic coupling mechanism. M is the mutual inductance of the magnetically coupled transceiver coil mechanism, and L is... s For the self-inductance of the secondary receiving coil, L p L is the self-inductance of the primary-side transmitting coil. f1 This refers to the series compensation inductor in the primary-side LCC compensation network; The primary-side LCC compensation network includes a series compensation inductor L. f1 Parallel compensation capacitor C p1 Series compensation capacitor C p2 The secondary-side S-type compensation network includes the self-inductance L of the secondary-side receiving coil. s Series compensation capacitor C s The system's rated resonant angular frequency is The compensation network parameters satisfy the following rated resonance conditions: ； The frequency switching trigger condition is a dual-threshold linkage condition, which must simultaneously satisfy the following two sub-conditions: Sub-condition 1: The current operating frequency is within the safe detuning frequency range; Sub-condition 2: The derived motor speed reaches 30% or more of the rated speed, or the derived motor back EMF reaches 30% or more of the rated back EMF. When the above sub-conditions are met simultaneously, a frequency step switching operation is triggered without having to complete the full linear frequency reduction process.

2. The method for suppressing overcurrent during startup of a wirelessly powered direct-drive brushless DC motor according to claim 1, characterized in that, The starting frequency for the linear frequency reduction control is selected from the upper limit of the safe detuning frequency range, which is 1.15*f. peak The termination frequency is selected from the lower limit of the safe detuning frequency range, which is 1.05*f. peak The slope of the linear frequency modulation is set according to the rated speed of the motor and the required start-up time to ensure that the motor can gradually build up speed and back electromotive force during the linear frequency modulation process.

3. A wireless power supply direct-drive brushless DC motor system, used to implement the method as described in any one of claims 1 or 2, characterized in that, The system includes a DC power supply, a power supply-side filter capacitor, a high-frequency full-bridge inverter, a transmitting coil module, a receiving coil module, a single-phase uncontrolled rectifier module, a three-phase inverter, a motor-side filter capacitor, a DC brushless motor load module, a voltage and current sampling module, a digital signal processing module, and a pulse signal generation module, wherein: The output terminal of the DC power supply is connected to the DC input terminal of the high-frequency full-bridge inverter. The AC output terminal of the high-frequency full-bridge inverter is connected to the input terminal of the primary-side LCC compensation network. The output terminal of the primary-side LCC compensation network is connected to the primary-side transmitting coil of the magnetically coupled transceiver coil mechanism. The secondary-side receiving coil of the magnetically coupled transceiver coil mechanism is connected to the input terminal of the secondary-side S-type compensation network. The output terminal of the secondary-side S-type compensation network is connected to the AC input terminal of the single-phase uncontrolled rectifier module. The DC output terminal of the single-phase uncontrolled rectifier module is connected to the DC input terminal of the three-phase inverter. The AC output terminal of the three-phase inverter is connected to the DC brushless motor load module. The sampling terminal of the voltage and current sampling module is connected to the output terminal of the high-frequency full-bridge inverter. The signal output terminal of the voltage and current sampling module is connected to the input terminal of the digital signal processing module and the pulse signal generation module. The control output terminal of the digital signal processing module and the pulse signal generation module is connected to the drive signal input terminal of the high-frequency full-bridge inverter.

4. A startup execution process based on the method of claim 1, characterized in that, Includes the following steps: Step 1: In the parameter design phase, based on the system topology, motor rated parameters, and coupling characteristics, design the parameters of the primary-side LCC and secondary-side S-type compensation network, and determine the system's rated resonant frequency. ; Step 2: Strategy Pre-setting Stage, derive the safe detuning frequency range based on the stall condition boundary [f] peak +5%*f peak , f peak +15%*f peak Set the linear down-frequency start frequency, slope, and frequency cut threshold; Step 3: Start initialization. After receiving the start command, control the high-frequency full-bridge inverter to operate at the starting frequency, suppress the initial inrush current, and start primary-side signal acquisition. Step 4: Linear frequency reduction control, reducing the operating frequency according to a preset slope, and comparing the derived motor status with the frequency cutting threshold in real time to ensure that the frequency is always constrained within the safe detuning frequency range; Step 5: Step switching. Once the frequency switching trigger condition is detected, the linear frequency reduction is immediately interrupted, and the operating frequency is directly switched to the rated resonant frequency in a step. ; Step 6: Steady-state operation, monitor system voltage, current and motor speed, and enter normal operation control mode after stabilization.

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