High PF Brushless DC Motor Drive System Based on Bridgeless Buck PFC Converter

Abstract

The present invention discloses a high PF brushless DC motor drive system based on a bridgeless buck PFC converter, and relates to the technical field of brushless DC motor drive systems; the brushless DC motor drive system comprises a rear-stage inverter, a brushless DC motor and a front-stage bridgeless buck PFC converter; the topological structure of the front-stage bridgeless buck PFC converter comprises a buck conversion unit, a buck-boost conversion unit and an intermediate bus capacitor C o The buck conversion unit includes a switch tube S1 and a rectifier diode D R1 , diode D1, and inductor L1 are used for power conversion in the negative half cycle of AC input; the buck-boost conversion unit includes switch tube S2, rectifier diode D R2 , diode D2, and inductor L2 are used for power conversion in the positive half cycle of AC input; the front-stage bridgeless buck PFC converter realizes positive and negative bipolar AC input and unipolar DC output through buck conversion unit and buck-boost conversion unit; by controlling the output voltage V o , realizing closed-loop control of brushless DC motor speed.

Description

Technical Field

[0001] The invention belongs to the technical field of brushless DC motor drive systems, and in particular relates to a high PF brushless DC motor drive system based on a bridgeless buck PFC converter. Background Art

[0002] More than half of the world's electricity is consumed by motor-related industries, so research on efficient and high-performance motor drive systems has good low-carbon and environmental protection effects. Among them, brushless DC (BLDC) motors are currently widely used in various applications such as home appliances, industrial production lines, and consumer products due to their simple structure, high efficiency, high power density, low maintenance cost, and long life. They are considered to be the mainstream motors until 2023. However, the existing BLDC motor drive system has a low power factor (PF) and large input current harmonics, which makes it difficult to meet applications with high requirements for power factor and input current harmonics.

[0003] Traditional BLDC drive system such as Figure 1 As shown. AC input v in After being rectified by the diode bridge, the inverter is powered through the DC bus. The inverter supplies power to the BLDC motor through the switch tube, and realizes brushless commutation of the motor. The front-stage circuit of the traditional drive system has no input power factor correction (PFC) circuit, and the back-stage inverter mainly realizes closed-loop control of the BLDC motor by switching on and off power electronic devices. This system has problems such as low PF value, large input current harmonics, and high motor bus voltage (low-voltage BLDC motor cannot be used).

[0004] In this regard, by adding a buck PFC converter in the front stage, the system PF value can be improved, the input current harmonics and the motor bus voltage can be reduced. However, at present, the buck PFC converter has an input current dead time, resulting in poor PF value and input current harmonics, and the traditional buck PFC converter including a rectifier bridge has a high rectifier bridge conduction loss.

[0005] The present invention proposes a high PF brushless DC motor drive system based on a bridgeless buck PFC converter, which can realize closed-loop control of high PF value under a wide speed range of the BLDC motor, and the system control scheme is simple, so that the system can drive a low-voltage BLDC motor. Summary of the invention

[0006] The purpose of the present invention is to provide a high PF brushless DC motor drive system based on a bridgeless step-down PFC converter to solve the problems of low PF value, large input current harmonics, and high motor bus voltage in the traditional BLDC drive system in the prior art mentioned in the above background technology.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A high PF brushless DC motor drive system based on a bridgeless buck PFC converter includes a rear-stage inverter and a brushless DC motor, wherein the rear-stage inverter includes 6 switch tubes; and also includes a front-stage bridgeless buck PFC converter;

[0009] The topology structure of the front-stage bridgeless buck PFC converter includes a buck conversion unit, a buck-boost conversion unit and an intermediate bus capacitor C o ;

[0010] The buck conversion unit includes a switch tube S1, a rectifier diode D R1 , diode D1, and inductor L1 are used for power conversion in the negative half cycle of AC input;

[0011] The buck-boost conversion unit includes a switch tube S2, a rectifier diode D R2 , diode D2, and inductor L2 are used for power conversion in the positive half cycle of AC input;

[0012] The front-stage bridgeless buck PFC converter realizes positive and negative bipolar AC input and unipolar DC output through a buck conversion unit and a buck-boost conversion unit; by controlling the output voltage V o , realizing closed-loop control of brushless DC motor speed.

[0013] Preferably, one end of the AC input side is connected to the rectifier diode D R2 Anode, rectifier diode D R1 The other end of the AC input side is connected to the cathode of the diode D1, one end of the inductor L2, and the intermediate bus capacitor C o The positive pole is connected;

[0014] Rectifier diode D R2 The cathode of is connected to the drain of the switch tube S2, and the source of the switch tube S2 is connected to the cathode of the diode D2 and the other end of the inductor L2;

[0015] Rectifier diode D R1The anode of the switch tube S1 is connected to the source of the switch tube S1, the drain of the switch tube S1 is connected to the anode of the diode D1 and one end of the inductor L1, and the other end of the inductor L1 is connected to the anode of the diode D2 and the intermediate bus capacitor C o The negative pole is connected.

[0016] Preferably, the six switch tubes are a U-phase lower bridge arm switch tube T1, a U-phase upper bridge arm switch tube T2, a V-phase lower bridge arm switch tube T3, a V-phase upper bridge arm switch tube T4, a W-phase lower bridge arm switch tube T5, and a W-phase upper bridge arm switch tube T6;

[0017] Intermediate bus capacitor C o The positive electrode is connected to the drain of the U-phase upper bridge arm switch tube T2, the drain of the V-phase upper bridge arm switch tube T4, and the drain of the W-phase upper bridge arm switch tube T6;

[0018] Intermediate bus capacitor C o The negative electrode is connected to the source of the U-phase lower bridge arm switch tube T1, the source of the V-phase lower bridge arm switch tube T3, and the source of the W-phase lower bridge arm switch tube T5;

[0019] The source of the U-phase upper bridge arm switch tube T2 and the drain of the U-phase lower bridge arm switch tube T1 are connected to the U-phase terminal of the brushless DC motor; the source of the V-phase upper bridge arm switch tube T4 and the drain of the V-phase lower bridge arm switch tube T3 are connected to the V-phase terminal of the brushless DC motor; the source of the W-phase upper bridge arm switch tube T6 and the drain of the W-phase lower bridge arm switch tube T5 are connected to the W-phase terminal of the brushless DC motor.

[0020] Preferably, the post-stage inverter realizes the commutation of the excitation coil current of the brushless DC motor through a six-step commutation method; the U-phase lower bridge arm switch tube T1, the V-phase lower bridge arm switch tube T3, and the W-phase lower bridge arm switch tube T5 adopt fixed chopping, and the U-phase upper bridge arm switch tube T2, the V-phase upper bridge arm switch tube T4, and the W-phase upper bridge arm switch tube T6 remain straight during the commutation period.

[0021] Preferably, the brushless DC motor speed closed-loop control is as follows:

[0022] The front-stage bridgeless buck PFC converter adopts a single voltage loop for control, and its output reference voltage is determined according to the target speed of the brushless DC motor. By controlling the output voltage V o , to control the speed of the brushless DC motor;

[0023] PFC converter output reference voltage V o,fb,rev The conversion formula to the target speed is as follows:

[0024] V o，fb，rev =V o，fb / (a*ω set -b)

[0025] In the formula, ω set is the target speed, V o,fb is the bus voltage sampling value of the previous bridgeless buck PFC converter, that is, the output voltage V o ; a and b are fixed values, which are related to the parameters of the brushless DC motor itself and can be obtained through testing.

[0026] Preferably, the control is performed using a single voltage loop, specifically as follows:

[0027] The bus voltage sampling signal of the front-stage bridgeless buck PFC converter is connected to the output reference voltage V o,ref The error feedback signal is compared with the triangular wave to generate the output signal of the comparator, and the output signal is used to directly drive the switch tube S1 and the switch tube S2.

[0028] Preferably, the working mode of the front-stage bridgeless buck PFC converter is as follows:

[0029] Working mode 1: Switch tube S1 and switch tube S2 are in the on state, and the input end passes through the rectifier diode D R2 Charge the inductor L2, the inductor current i L2 Linearly rising, the current of switch tube S2 and the inductor current i L2 The amplitude and direction are the same; the intermediate bus capacitance C o Provide energy for the subsequent circuits;

[0030] Working mode 2: Switch tubes S1 and S2 are turned off, diode D2 is turned on, and the energy stored in inductor L2 supplies energy to the subsequent circuit. The inductor current i L2 Decreases linearly until it reaches zero;

[0031] Working mode 3: Switch tube S1 and switch tube S2 remain off. This working mode is when the inductor current i L2 The linear decrease starts when it reaches zero. At this time, the inductor current i L2 =0, and the intermediate bus capacitance C o Provide energy for the subsequent circuits;

[0032] Working mode 4: Switch tube S1 and switch tube S2 are in the on state, and the input end passes through the rectifier diode D R1 , switch tube S1, charges the inductor L1, and the inductor current i L1 Linear rise, switch tube S1, diode D R1 The current and the inductor current i L1 The amplitude and direction are the same; the intermediate bus capacitance C o Provide energy for the subsequent circuits;

[0033] Working mode 5: Switches S1 and S2 are turned off, diode D1 is turned on, and the energy stored in inductor L1 supplies energy to the subsequent circuit through diode D1. The inductor current i L1 Decreases linearly until it reaches zero;

[0034] Working mode 6: switch tube S1 and switch tube S2 remain off. This working mode is when the inductor current i L1 The linear decrease starts when it reaches zero. At this time, the inductor current i L1 =0, intermediate bus capacitance C o Provides energy for subsequent circuits.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The brushless DC motor drive system of the present invention adopts a front-stage PFC circuit and a rear-stage inverter integrated control method to achieve motor speed closed-loop control and front-stage power factor correction without adding a sampling circuit; and has a higher power factor and a lower intermediate system bus voltage, and can achieve PFC function and output voltage regulation (motor output speed regulation) through single voltage loop control.

[0037] (2) The brushless DC motor drive system of the present invention adopts a bridgeless step-down PFC converter, and the circuit topology does not include a diode rectifier bridge. The device conduction loss is low and the system efficiency is high. It can meet the voltage operation requirements of the low-voltage BLDC motor and achieve high PF value operation of the low-voltage BLDC motor drive system. At the same time, compared with the traditional BLDC motor drive system in the prior art, there is no increase in diode conduction loss.

[0038] (3) The control circuit of the brushless DC motor drive system in the present invention is simple, without adding a complex sampling circuit, and the PFC circuit can use the same drive signal to control two switch tubes, which is simple to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A circuit topology diagram of a conventional BLDC drive system in the background technology;

[0040] Figure 2 A circuit topology diagram of a high PF brushless DC motor drive system based on a bridgeless buck PFC converter in the present invention;

[0041] Figure 3 It is an equivalent simplified diagram of the circuit topology of the high PF brushless DC motor drive system based on the bridgeless buck PFC converter in the present invention;

[0042] Figure 4It is a positive half-cycle operation mode diagram of the front-stage bridgeless buck PFC converter in the high PF brushless DC motor drive system based on the bridgeless buck PFC converter in the present invention;

[0043] Figure 5 It is a negative half-cycle operation mode diagram of the front-stage bridgeless buck PFC converter in the high PF brushless DC motor drive system based on the bridgeless buck PFC converter in the present invention;

[0044] Figure 6 It is a simulation waveform diagram of key components of the front-stage bridgeless buck PFC converter in the high PF brushless DC motor drive system based on the bridgeless buck PFC converter in the present invention;

[0045] Figure 7 This is a simulation waveform diagram of key components of a high PF brushless DC motor drive system based on a bridgeless buck PFC converter in the present invention. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Embodiment 1:

[0048] The high PF brushless DC motor drive system based on bridgeless buck PFC converter is as follows:

[0049] See also Figure 2 The brushless DC motor driving system includes a front-stage bridgeless buck PFC converter, a rear-stage inverter and a brushless DC motor. Figure 2 The circuit topology and control method of the brushless DC motor drive system are given.

[0050] The circuit topology of the PFC converter mainly includes switch tube S1, switch tube S2, diode D1, diode D2, rectifier diode D R1 , rectifier diode D R2 , intermediate bus capacitance C o, inductor L1, inductor L2; the back-stage inverter part mainly includes 6 switch tubes, namely switch tube T1, switch tube T2, switch tube T3, switch tube T4, switch tube T5, switch tube T6; the BLDC motor mainly includes a built-in Hall position sensor and a motor body. Among them, the PFC converter circuit, since the buck conversion unit and the buck-boost conversion unit only process unipolar input, in order to realize the conversion of bipolar AC power into unipolar DC output, two conversion units are configured to realize positive and negative bipolar AC input and unipolar DC output.

[0051] Specifically, one end of the AC input side is connected to the rectifier diode D R2 Anode, rectifier diode D R1 The other end of the AC input side is connected to the cathode of the diode D1, one end of the inductor L2, and the intermediate bus capacitor C o The positive electrode of the rear inverter U phase upper bridge arm switch tube T2 drain, the rear inverter V phase upper bridge arm switch tube T4 drain, the rear inverter W phase upper bridge arm switch tube T6 drain and the intermediate bus capacitor C o The drain of the switch tube S2 is connected to the positive electrode of the rectifier diode D R2 The source of the switch tube S2 is connected to the cathode of the diode D2 and the other end of the inductor L2. The anode of the diode D2 is connected to one end of the inductor L1 and the intermediate bus capacitor C o The negative electrode of the rear inverter U phase lower bridge arm switch tube T1 source, the rear inverter V phase lower bridge arm switch tube T3 source, the rear inverter W phase lower bridge arm switch tube T5 source and the intermediate bus capacitor C o The source of the switch tube S1 is connected to the negative electrode of the rectifier diode D R1 The other end of the inductor L1 and the anode of the diode D1 are connected to the drain of the switch tube S1. The source of the upper bridge arm switch tube T2 of the U phase of the rear-stage inverter and the drain of the lower bridge arm switch tube T1 of the U phase are connected to the U phase terminal of the brushless DC motor. The source of the upper bridge arm switch tube T4 of the V phase of the rear-stage inverter and the drain of the lower bridge arm switch tube T3 of the V phase are connected to the V phase terminal of the brushless DC motor. The source of the upper bridge arm switch tube T6 of the W phase of the rear-stage inverter and the drain of the lower bridge arm switch tube T5 of the W phase are connected to the W phase terminal of the brushless DC motor.

[0052] See also Figure 3 , Figure 3 The simplified equivalent circuit of the brushless DC motor drive system and its control principle diagram are given. The working principle of the brushless DC motor drive system is as follows:

[0053] Figure 3 In the control of the PFC converter, a simple single voltage loop is still used, but its voltage reference is determined by the motor target speed. Figure 2In the reference voltage V o,ref Fixed to 1, by changing the feedback voltage V o,fb The coefficient (see Figure 2 Medium V o,fb,rev The bus voltage can be regulated by the relevant equations of Figure 3 Change V o,ref , but not the feedback voltage V o,fb The coefficient of the invention is modified. Figure 2 The bus voltage control method shown is because this method can avoid the situation where the PI parameter performance does not meet expectations when the reference voltage changes significantly, which is more conducive to stable operation of the system.

[0054] like Figure 3 As shown, in essence, the control system of the present invention is to control the output voltage V of the front-stage PFC converter o , that is, the bus voltage V bus , realizing closed-loop control of motor speed. Among them, the inverter and DC motor can be equivalent to traditional brushed motors, but the BLDC motor in the system adopts switching devices and a mature six-step commutation method to realize brushless commutation to avoid the maintenance and loss of carbon brush heads of traditional brushed motors. In other words, in the system of the present invention, the brushless DC motor is similar to the brushed DC motor, and both control the input side voltage of the brushless DC motor in combination with a fixed linear conversion formula between the speed and the input bus voltage to achieve the purpose of controlling the motor speed.

[0055] The conversion formula is as follows:

[0056] V o,fb，rev =V o，fb / (0.065*ω set -1.826)

[0057] In the formula, ω se t is the target speed, V o,fb is the bus voltage sampling value of the PFC converter; the fixed value in the formula is related to the parameters of the brushless DC motor itself, and the correlation coefficient can be obtained through testing.

[0058] That is, for the system of the present invention, the output voltage V of the PFC converter is controlled o , in fact, it is also controlling the speed of the BLDC motor. It should be noted that this control method is determined by the linear relationship between the terminal voltage and the speed of the BLDC motor. For other motors, such as asynchronous motors, this voltage and speed conversion relationship does not necessarily exist.

[0059] From the above description, it can be seen that the wide output voltage V oClosed-loop control is very important for motor closed-loop control. Therefore, the working principle of the AC-DC bridgeless buck PFC converter of the present invention is explained below through modal diagrams.

[0060] See also Figure 4 , Figure 4 (a) is the equivalent circuit of the working mode 1 of the front-stage bridgeless buck PFC converter in the positive half cycle of the AC input; Figure 4 (b) is the equivalent circuit of the working mode 2 of the preceding bridgeless buck PFC converter in the positive half cycle of the AC input; Figure 4 (c) is the equivalent circuit of the operating mode 3 of the preceding bridgeless buck PFC converter in the positive half cycle of the AC input.

[0061] See also Figure 5 , Figure 5 (a) is the equivalent circuit of the working mode 4 of the front-stage bridgeless buck PFC converter in the negative half cycle of the AC input; Figure 5 (b) is the equivalent circuit of the working mode 5 of the preceding bridgeless buck PFC converter in the negative half cycle of the AC input; Figure 5 (c) is the equivalent circuit of the operating mode 6 of the preceding bridgeless buck PFC converter in the negative half cycle of the AC input.

[0062] Working mode 1: In this stage, the switch tube S1 and the switch tube S2 are in the on state, and the input end passes through the rectifier diode D R2 Charge the inductor L2, the inductor current i L2 Linearly rising, the current of switch tube S2 and the inductor current i L2 The amplitude and direction are the same. The intermediate bus capacitance C o Provides energy for subsequent circuits.

[0063] Working mode 2: Switch tubes S1 and S2 are turned off, diode D2 is turned on, and the energy stored in inductor L2 supplies energy to the subsequent circuit. The inductor current i L2 Decreases linearly until it reaches zero.

[0064] Working mode 3: Switch tube S1 and switch tube S2 remain off. This working mode is when the inductor current i L2 The linear decrease starts when it reaches zero. At this time, the inductor current i L2 =0, and the intermediate bus capacitance C o Provides energy for subsequent circuits.

[0065] Working mode 4: Switch tube S1 and switch tube S2 are in the on state, and the input end passes through the rectifier diode D R1 , switch tube S1, charges the inductor L1, and the inductor current i L1 Linear rise, switch tube S1, diode D R1 The current and the inductor current iL1 The amplitude and direction are the same. The intermediate bus capacitance C o Provides energy for subsequent circuits.

[0066] Working mode 5: Switches S1 and S2 are turned off, diode D1 is turned on, and the energy stored in inductor L1 is supplied to the load through diode D1. The inductor current i L1 Decreases linearly until it reaches zero.

[0067] Working mode 6: switch tube S1 and switch tube S2 remain off. This working mode is when the inductor current i L1 The linear decrease starts when it reaches zero. At this time, the inductor current i L1 =0, intermediate bus capacitance C o Provides energy for subsequent circuits.

[0068] The rear inverter mainly realizes the commutation of the excitation coil current of the BLDC motor through the mature six-step commutation method, which will not be described here. It should be noted that the lower switch tubes of the three bridge arms of the inverter adopt fixed chopping, and the upper switch tubes remain straight during the commutation period. This method can reduce the switching loss of the upper switch tubes of the bridge arm.

[0069] In order to verify the feasibility of the motor drive system of the present invention under AC input 220Vac, the circuit is simulated and verified using PSIM simulation software. The simulation results of the motor drive system are as follows:

[0070] Specific parameters: AC input adopts sinusoidal signal fitting, AC voltage peak is 311V, frequency is 50Hz, inductance L1 is 65uH, inductance L2 is 180uH, intermediate bus capacitance C o The resistor is 3000uF, the motor output speed is 1000~2500rpm, the PFC converter switching frequency is 47kHz, the P in the PI parameter is 4, I is 0.005, and the converter maximum output voltage is 160V. The inverter switching frequency is 20k, and the chopper duty cycle is 0.525. In addition, to ensure that the input current is continuous, an electromagnetic filter inductor L is added on the input side. f With input capacitor C f , respectively set to L f =3mH, C f =0.2uF.

[0071] Figure 6 This is a waveform simulation diagram of the key components of the front-stage bridgeless buck PFC converter. Figure 6 It can be seen that under the condition of AC input 220Vac and frequency 50Hz, the bridgeless buck converter achieves a 160V regulated output. And the inductor L1 and the inductor L2 are respectively inThe positive and negative half-cycles work alternately, realizing AC-DC conversion operation without a rectifier bridge. Moreover, the simulation waveforms of each device are stable, indicating that the converter can Figure 2 The system closed-loop control scheme shown achieves closed-loop stable operation. In addition, in the proposed system, the two inductors of the front-stage PFC converter work alternately in half of the input AC power frequency cycle, indicating that the PFC converter achieves stable bridgeless operation, that is, only one conversion unit is operating in half of the power frequency cycle, verifying the working principle of the converter.

[0072] Figure 7 This is the key waveform diagram of the brushless DC motor drive system. Figure 7 The motor output speed can work stably at different target speeds, the output voltage of its PFC converter can work stably at a fixed value, and the two inductors work alternately without mutual interference, indicating that the PFC converter can operate stably at Figure 2 Shown is a single voltage loop under control.

[0073] In addition, in order to compare the drive system architecture of the present invention with the traditional system architecture, according to Figure 1 The circuit shown in the figure constructs a traditional drive system architecture simulation circuit, and its parameters are as follows: the AC input effective value voltage is 220Vac (peak voltage 311V), the intermediate bus capacitor C o It is 3000uF, the inverter switching frequency is 20kHz, and the speed closed-loop control PI parameters are P=0.001 and I=0.0001.

[0074] Table 1 shows the PF value and bus voltage value of the BLDC motor drive system of the present invention and the traditional system architecture at different speeds. It can be seen from Table 1 that compared with the traditional system architecture, the system architecture of the present invention has a significantly higher PF value and a lower bus voltage. Moreover, when the target speed is set, the output voltage (i.e., the bus voltage) of the PFC converter will change accordingly, thereby changing the motor speed, verifying the speed closed-loop control method of this patent.

[0075] Table 1 Comparison of converter performance of the present invention at 220Vac input

[0076]

[0077] According to the above theoretical analysis and simulation results, it can be seen that the BLDC motor drive system based on the bridgeless buck PFC converter proposed in the present invention has a significantly higher PF value and a lower bus voltage than the traditional system architecture. Under 220Vac input, the bus voltage of the traditional system is around 309V, which cannot meet the working needs of the low-voltage BLDC motor. It is necessary to add a first-level buck DC-DC converter, and its existing PF value is less than 0.3. In contrast, the bus voltage of the drive system of the present invention maintains a fixed relationship with the motor speed, and the voltage is significantly lower than 309V, and the PF value is greater than 0.85.

[0078] The high PF brushless DC motor drive system based on the bridgeless buck PFC converter in the present invention can realize closed-loop control of high PF value under wide speed of BLDC motor. And the system control scheme is simple, which can enable the system to drive low-voltage BLDC motor. In this embodiment, the 160V voltage level BLDC motor is used as the back-stage motor. It should be noted that under 220Vac AC input voltage, for low-voltage BLDC motors such as 120V, 100V, 60V, etc., the buck drive system of the present invention is feasible, as long as the chopper duty cycle of the inverter is fixed according to the voltage and speed range of different BLDC motors, and then the conversion formula coefficient of bus voltage and motor speed is adjusted.

[0079] The above description is only used to help understand the method of the present invention and its core essence, but the protection scope of the present invention is not limited thereto. For those skilled in the art in the art, equivalent replacement or change according to the technical solution and inventive concept of the present invention within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A high PF brushless DC motor drive system based on a bridgeless buck PFC converter, comprising a rear-stage inverter and a brushless DC motor, wherein the rear-stage inverter comprises 6 switch tubes; characterized in that: It also includes a front-stage bridgeless buck PFC converter; The topology structure of the front-stage bridgeless buck PFC converter includes a buck conversion unit, a buck-boost conversion unit and an intermediate bus capacitor. C o ; The buck conversion unit includes a switch tube S 1. Rectifier diode D R1 ,diode D 1. Inductor L 1. Used for power conversion within the negative half cycle of AC input; The buck-boost conversion unit includes a switch tube S 2. Rectifier diode D R2 ,diode D 2. Inductor L 2. Used for power conversion within the positive half cycle of AC input; The front-stage bridgeless buck PFC converter realizes positive and negative bipolar AC input and unipolar DC output through buck conversion unit and buck-boost conversion unit; by controlling the output voltage of the front-stage bridgeless buck PFC converter V o , realize the closed-loop control of brushless DC motor speed; One end of the AC input side and the rectifier diode D R2 Anode, rectifier diode D R1 The other end of the AC input side is connected to the cathode of the diode D 1 cathode, inductor L One end of 2, the middle bus capacitor C o The positive pole is connected; Rectifier diode D R2 The cathode and switch tube S 2 is connected to the drain, the switch tube S 2 source and diode D 2 cathode, inductor L The other end of 2 is connected; Rectifier diode D R1 Anode and switch tube S 1 is connected to the source, the switch tube S 1 The drain and diode D 1 anode, inductor L 1 is connected to one end, the inductor L The other end of the diode D 2 anode and intermediate bus capacitor C o The negative pole is connected; 6 switch tubes are U-phase lower bridge arm switch tubes T 1. U-phase upper bridge arm switch tube T 2. V-phase lower bridge arm switch tube T 3. V-phase upper bridge arm switch tube T 4. W phase lower bridge arm switch tube T 5. W phase upper bridge arm switch tube T 6; Intermediate bus capacitor C o The positive electrode and the U-phase upper bridge arm switch tube T 2 drain, V phase upper bridge arm switch tube T 4 drain, W phase upper bridge arm switch tube T 6 drain connected; Intermediate bus capacitor C o The negative pole of the U-phase lower bridge arm switch tube T 1 Source, V phase lower bridge arm switch tube T 3 Source, W phase lower bridge arm switch tube T 5 source connected; U-phase upper bridge arm switch tube T 2 Source, U-phase lower bridge arm switch tube T 1 The drain is connected to the U-phase terminal of the brushless DC motor; the V-phase upper bridge arm switch tube T 4 source, V phase lower bridge arm switch tube T 3 The drain is connected to the V-phase terminal of the brushless DC motor; the W-phase upper bridge arm switch tube T 6 source, W phase lower bridge arm switch tube T 5. The drain is connected to the W phase terminal of the brushless DC motor; The brushless DC motor speed closed-loop control is as follows: The front-stage bridgeless buck PFC converter adopts a single voltage loop for control, and the output voltage of the front-stage bridgeless buck PFC converter is determined according to the target speed of the brushless DC motor. V o , to control the speed of the brushless DC motor; Output conversion voltage of the previous bridgeless buck PFC converter V o,fb,rev The conversion formula to the target speed is as follows: In the formula, ω se t is the target speed, V o,fb is the bus voltage sampling value of the previous bridgeless buck PFC converter, that is, the output voltage of the previous bridgeless buck PFC converter V o ; a and b are fixed values, which are related to the parameters of the brushless DC motor itself and can be obtained through testing; The bus voltage sampling signal of the front-stage bridgeless buck PFC converter V o,fb The output conversion voltage is obtained through the conversion formula V o,fb,rev , and then by V o,fb,rev With output reference voltage V o,ref The error feedback signal is compared with the triangular wave to generate the output signal of the comparator, which is used to directly drive the switch tube. S 1. Switching tube S 2.

2. The high PF brushless DC motor drive system based on a bridgeless buck PFC converter according to claim 1 is characterized in that: The rear inverter realizes the current commutation of the excitation coil of the brushless DC motor through a six-step commutation method; the U-phase lower bridge arm switch tube T 1. V-phase lower bridge arm switch tube T 3. W phase lower bridge arm switch tube T 5Using fixed chopper, the U-phase upper bridge arm switch tube T 2. V-phase upper bridge arm switch tube T 4. W phase upper bridge arm switch tube T 6 Maintain direct flow during commutation period.

3. The high PF brushless DC motor drive system based on a bridgeless buck PFC converter according to claim 1 or 2, characterized in that: The working mode of the front-stage bridgeless buck PFC converter is as follows: Working mode 1: switch tube S 1 and switch tube S 2 is in the on state, the input end passes through the rectifier diode D R2 Directional Inductance L 2Charging, inductor current i L2 Linear rise, switch tube S 2 current and inductor current i L2 The amplitude and direction are the same; the intermediate bus capacitance C o Provide energy for the subsequent circuits; Working mode 2: switch tube S 1 and switch tube S 2 off, diode D 2 conduction, stored in the inductor L 2's energy supplies energy to the subsequent circuit, and the inductor current i L2 Decreases linearly until it reaches zero; Working mode 3: switch tube S 1 and switch tube S 2 remains off, the operating mode is in the inductor current i L2 The linear decrease starts when it reaches zero. At this time, the inductor current i L2 =0, and the intermediate bus capacitance C o Provide energy for the subsequent circuits; Working mode 4: switch tube S 1 and switch tube S 2 is in the on state, the input end passes through the rectifier diode D R1 , switch tube S 1. To inductor L 1 Charging, inductor current i L1 Linear rise, switch tube S 1. Diode D R1 The current and inductor current i L1 The amplitude and direction are the same; the intermediate bus capacitance C o Provide energy for the subsequent circuits; Working mode 5: switch tube S 1 and switch tube S 2 off, diode D 1 is on, stored in the inductor L 1 energy passes through the diode D 1 Supply energy to the subsequent circuit, inductor current i L1 Decreases linearly until it reaches zero; Working mode 6: switch tube S 1 and switch tube S 2 remains off, the operating mode is in the inductor current i L1 The linear decrease starts when it reaches zero. At this time, the inductor current i L1 =0, intermediate bus capacitance C o Provides energy for subsequent circuits.

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