High PF variable speed motor drive system based on bridgeless buck-boost PFC converter

Abstract

The present invention discloses a high PF variable speed motor drive system based on a bridgeless buck-boost PFC converter, and relates to the technical field of motor drive systems; the variable speed motor drive system includes a rear-stage inverter, a brushless DC motor and a front-stage bridgeless buck-boost PFC converter; the topological structure of the front-stage bridgeless buck-boost PFC converter includes a buck unit, a buck-boost unit, an output capacitor C1 and an output capacitor C2; the buck unit and the buck-boost unit work in parallel in the positive and negative half power frequency cycles to eliminate the input current dead zone of the buck unit; by controlling the working mode of the front-stage bridgeless buck-boost PFC converter to control the output voltage of the front-stage bridgeless buck-boost PFC converter, the speed closed-loop control of the brushless DC motor is realized. In the present invention, the drive system proposes a variable speed control method integrating the front-stage bridgeless PFC circuit and the rear-stage inverter, and realizes the motor speed closed-loop control and the front-stage power factor correction without adding a sampling circuit.

Description

Technical Field

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

[0002] At present, more than 50% of the world's electricity is used in motor-related industries. Among them, motor variable speed drive systems based on brushless DC (BLDC) motors are widely used in ventilation, transportation, industrial production lines, robots and other occasions. However, the existing brushless DC 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. By studying motor drive systems with high power factor, high efficiency and high controllable output speed, it can provide useful help for high-quality industrial automation and carbon neutrality goals.

[0003] Traditional BLDC drive system such as Figure 1 As shown. AC input v in After being rectified by the diode bridge, the intermediate DC bus capacitor provides a stable DC voltage for the subsequent inverter. The inverter mainly uses the six-step commutation method, also known as the trapezoidal drive method, to realize the on and off of the three bridge arm switches of the inverter to achieve the brushless commutation of the brushless DC motor. The front-stage circuit of the traditional drive system has no input power factor correction (PFC) circuit, so the system has the problem of low PF value and large input current harmonics.

[0004] In this regard, by adding a traditional buck PFC converter in the front stage, the system PF value can be improved and the input current harmonics can be reduced. However, when it is necessary to drive a BLDC motor with a rated voltage of 160V, because the 160V output voltage is already higher than the peak value of the 110Vac AC input, the drive cannot be achieved by using only the traditional buck PFC converter. Therefore, under the 110Vac AC input voltage, in order to drive a BLDC motor with a rated voltage of 160V, a buck-boost PFC converter is required.

[0005] The present invention proposes a high PF variable speed motor drive system based on a bridgeless buck-boost PFC converter. By adding a bridgeless buck-boost PFC converter in the front stage, the speed adjustment of the rear stage motor can be achieved by controlling the intermediate bus voltage. Summary of the invention

[0006] The purpose of the present invention is to provide a high PF variable speed motor drive system based on a bridgeless buck-boost PFC converter to solve the problems of low PF value, large input current harmonics, and unsuitability for driving a BLDC motor with a rated voltage of 160V 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 variable speed motor drive system based on a bridgeless buck-boost PFC converter comprises a rear-stage inverter and a brushless DC motor, wherein the rear-stage inverter comprises 6 switch tubes; and also comprises a front-stage bridgeless buck-boost PFC converter;

[0009] The topological structure of the front-stage bridgeless buck-boost PFC converter includes a buck unit, a buck-boost unit, an output capacitor C1 and an output capacitor C2;

[0010] The voltage reduction unit includes a switch tube S b1 , switch tube S b2 、Diode D b1 、Diode D b2 , rectifier diode D R1 , rectifier diode D R2 、Inductance L b1 、Inductance L b2 ;

[0011] The buck-boost unit includes a switch tube S bb1 , switch tube S bb2 、Diode D bb1 、Diode D bb2 , rectifier diode D R3 , rectifier diode D R4 、Inductance L bb1 、Inductance L bb2 ;

[0012] The step-down unit and the step-up / step-down unit work in parallel in both the positive and negative half power frequency cycles to eliminate the input current dead zone of the step-down unit;

[0013] By controlling the working mode of the preceding bridgeless buck-boost PFC converter, the output voltage V of the preceding bridgeless buck-boost PFC converter can be controlled. o , realizing closed-loop control of brushless DC motor speed.

[0014] Preferably, one end of the AC input side is connected to the rectifier diode D R3 The cathode of the rectifier diode D R4 Anode, rectifier diode D R1 Anode, rectifier diode D R2The other end of the AC input side is connected to the cathode of the diode D b1 The anode of diode D b2 The cathode, inductance L bb1 One end of the inductor L bb2 One end of the output capacitor C1, the negative electrode of the output capacitor C2 are connected;

[0015] Rectifier diode D R3 The anode and the switch tube S bb1 The source connection of the switch tube S bb1 The drain and inductance L bb1 The other end of the diode D bb1 Anode connection;

[0016] Rectifier diode D R4 The cathode and the switch tube S bb2 The drain connection of the switch tube S bb2 The source and inductor L bb2 The other end of the diode D bb2 The cathode connection of

[0017] Rectifier diode D R1 The cathode and the switch tube S b1 The drain connection of the switch tube S b1 The source of the diode D b1 The cathode, inductance L b1 One end of the inductor is connected; b1 The other end of the diode D bb1 The cathode of and the positive electrode of output capacitor C1 are connected;

[0018] Rectifier diode D R2 The anode and the switch tube S b2 The source connection of the switch tube S b2 The drain of the diode D b2 Anode, inductor L b2 One end of the inductor is connected; b2 The other end of the diode D bb2 The anode of the output capacitor C2 is connected.

[0019] 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;

[0020] The positive electrode of the output capacitor C1 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;

[0021] The negative electrode of the output capacitor C2 is connected to the source electrode of the U-phase lower bridge arm switch tube T1, the source electrode of the V-phase lower bridge arm switch tube T3, and the source electrode of the W-phase lower bridge arm switch tube T5;

[0022] 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.

[0023] 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.

[0024] Preferably, the brushless DC motor speed closed-loop control is as follows:

[0025] The front-stage bridgeless buck-boost 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, and then the output voltage V of the front-stage bridgeless buck-boost PFC converter is controlled. o , to control the speed of the brushless DC motor;

[0026] The output reference voltage V of the front-stage bridgeless buck-boost PFC converter o,fb,rev The conversion formula to the target speed is as follows:

[0027] V o，fb，rev =V o，fb / (a*ω set -b)

[0028] In the formula, ω set is the target speed, V o,fb is the bus voltage sampling value of the previous bridgeless buck-boost 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.

[0029] Preferably, the control is performed using a single voltage loop, specifically as follows:

[0030] The bus voltage sampling signal of the front-stage bridgeless buck-boost PFC converter is connected to the output reference voltage V o,fb,revThe 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. b1 , switch tube S b2 , switch tube S bb1 , switch tube S bb2 The switch tube S b1 , switch tube S b2 , switch tube S bb1 , switch tube S bb2 Can be controlled using exactly the same drive signal.

[0031] Preferably, the working mode of the front-stage bridgeless buck-boost PFC converter is as follows:

[0032] Working mode 1: switch tube S b1 And switch tube S bb2 In the on state, the input terminal passes through the rectifier diode D R1 , switch tube S b1 , output capacitor C1, to the inductor L b1 and output capacitor C1, the inductor current i Lb1 Linear rise, switch tube S b1 The current and the inductor current i L1 The amplitude and direction are the same; at the same time, the input end passes through the rectifier diode D R4 , switch tube S bb2 , to the inductor L bb2 Charging, inductor current i Lbb2 Linear rise, switch tube S bb2 The current and the inductor current i Lbb2 The amplitude and direction are the same; the output capacitor C2 supplies energy to the subsequent circuit;

[0033] Working mode 2: switch tube S b1 And switch tube S bb2 Turn off, diode D b1 is turned on and stored in the inductor L b1 The energy passes through the diode D b1 Supply energy to the subsequent circuit, the inductor current i Lb1 linearly decreases until it reaches zero; at the same time, the inductance L bb2 Through diode D bb2 Freewheeling, inductor current i Lbb2 It decreases linearly until it reaches zero. In this stage, the inductor energy is transferred to the output capacitors C1 and C2 and supplies energy to the subsequent circuits.

[0034] Working mode 3: switch tube S b1 And switch tube S bb2 Keep off, the working mode is in the inductor current iLbb2 and the inductor current i Lb1 The linear decrease starts when it reaches zero, at which time i Lb1 =i Lbb2 =0, and the output capacitors C1 and C2 provide energy for the subsequent circuits;

[0035] Working mode 4: switch tube S b2 And switch tube S bb1 In the on state, the input terminal passes through the rectifier diode D R3 , switch tube S bb1 , to the inductor L bb1 Charging, inductor current i Lbb1 Linear rise, switch tube S bb1 , rectifier diode D R3 The current and the inductor current i Lbb1 The amplitude and direction are the same; at the same time, the input end passes through the rectifier diode D R2 , switch tube S b2 , output capacitor C2, to the inductor L b2 The output capacitor C2 is charged; the output capacitor C1 supplies energy to the subsequent circuit;

[0036] Working mode 5: switch tube S b2 And switch tube S bb1 Turn off, diode D bb1 is turned on and stored in the inductor L bb1 The energy passes through the diode D bb1 Supply energy to the subsequent circuit, the inductor current i Lbb1 linearly decreases until it reaches zero; at the same time, the inductance L b2 Through the diode D b2 Freewheeling, inductor current i Lb2 It decreases linearly until it reaches zero. In this stage, the inductor energy is transferred to the output capacitors C1 and C2 and supplies energy to the subsequent circuits.

[0037] Working mode 6: switch tube S b2 And switch tube S bb1 Keep off, the working mode is in the inductor current i Lbb1 and the inductor current i Lb2 The linear decrease starts when it reaches zero, at which time i Lb2 =i Lbb1 =0, and the output capacitors C1 and C2 provide energy for the subsequent circuit.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The drive system of the present invention proposes a front-stage bridgeless PFC circuit and a back-stage inverter integrated variable speed control method, which realizes motor speed closed-loop control and front-stage power factor correction without adding a sampling circuit; and realizes input power factor correction through single voltage loop control, and realizes motor variable speed adjustment by adjusting the bus voltage, and has high power factor characteristics under wide output speed. Experiments have proved that the drive system of the present invention achieves a 160V regulated output when the AC input is 110Vac and the frequency is 50Hz.

[0040] (2) The drive system topology of the present invention adopts a bridgeless buck-boost PFC converter composed of a buck unit and a buck-boost unit in parallel. The circuit topology does not include a diode rectifier bridge, so the device has low conduction loss and high efficiency. At the same time, the two capacitors on the output side are in a series structure, which can achieve self-balancing of the voltages of the two capacitors without increasing the complexity of system control. In addition, due to the parallel architecture of the dual conversion units, there is no input current dead zone problem on the input side of the system, and it has a higher input PF, achieving high PF value operation under variable speed operation of the low-voltage BLDC motor.

[0041] (3) The control circuit of the driving system in the present invention is simple, and the four switching tubes of the PFC circuit can all use the same driving signal to achieve closed-loop control. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A circuit topology diagram of a conventional BLDC drive system in the background technology;

[0043] Figure 2 A circuit topology diagram of a high PF variable speed motor drive system based on a bridgeless buck-boost PFC converter in the present invention;

[0044] Figure 3 It is an equivalent simplified diagram of the circuit topology of the high PF variable speed motor drive system based on the bridgeless buck-boost PFC converter in the present invention;

[0045] Figure 4 It is a positive half-cycle operation modal diagram of the front-stage bridgeless buck-boost PFC converter in the high PF variable speed motor drive system based on the bridgeless buck-boost PFC converter in the present invention;

[0046] Figure 5 It is a negative half-cycle operation modal diagram of the front-stage bridgeless buck-boost PFC converter in the high PF variable speed motor drive system based on the bridgeless buck-boost PFC converter in the present invention;

[0047] Figure 6 It is a waveform diagram of key components of the front-stage bridgeless buck-boost PFC converter in a half power frequency cycle in a high PF variable speed motor drive system based on a bridgeless buck-boost PFC converter in the present invention;

[0048] Figure 7 It is a simulation waveform diagram of key components of the front-stage bridgeless buck-boost PFC converter in the high PF variable speed motor drive system based on the bridgeless buck-boost PFC converter in the present invention;

[0049] Figure 8 It is a key simulation waveform diagram of the high PF variable speed motor drive system based on the bridgeless buck-boost PFC converter in the present invention. DETAILED DESCRIPTION

[0050] 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.

[0051] Embodiment 1:

[0052] The high PF variable speed motor drive system based on the bridgeless buck-boost PFC converter is as follows:

[0053] See also Figure 2 The high PF variable speed motor drive system based on the bridgeless buck-boost PFC converter mainly includes a front-stage bridgeless buck-boost PFC converter, a rear-stage inverter and a brushless DC motor. Figure 2 The circuit topology and control method of the variable speed motor drive system of the present invention are given.

[0054] The front-stage bridgeless buck-boost PFC converter circuit topology mainly includes the switch tube S of the buck unit b1 , switch tube S b2 , the switch tube S of the buck-boost unit bb1 , switch tube S bb2 , diode D b1 、Diode D b2 、Diode D bb1 、Diode D bb2 , rectifier diode D R1 , rectifier diode D R2 , rectifier diode D R3 , rectifier diode D R4 , output capacitor C1, output capacitor C2, inductor L b1 、Inductance L b2 、Inductance L bb1 、Inductance L bb2The back-end inverter part mainly includes 6 switch tubes, namely switch tube T1, switch tube T2, switch tube T3, switch tube T4, switch tube T5 and switch tube T6; the BLDC motor mainly includes a built-in Hall position sensor and a motor body. Among them, the PFC circuit always works in the positive and negative half-cycle of the power frequency at the same time because the buck unit and the buck-boost unit are in a parallel architecture. This method can eliminate the input current dead time of the buck unit, which is conducive to the system to achieve a high power factor.

[0055] In this embodiment, specifically, one end of the AC input side is connected to the rectifier diode D R1 Anode, rectifier diode D R2 The cathode of the rectifier diode D R3 The cathode connection of the rectifier diode D R4 The other end of the AC input side is connected to the anode of the diode D b2 The cathode of diode D b1 The anode of the buck-boost unit is L bb1 and inductor L bb2 One end of the output capacitor C1, the negative electrode of the output capacitor C2, and the positive electrode of the output capacitor C2 are connected.

[0056] Switching tube S bb1 The source and rectifier diode D R3 The anode of the switch tube S bb2 The drain and rectifier diode D R4 The cathode of the switch tube S b1 The drain and rectifier diode D R1 The cathode of the switch tube S b2 The source and rectifier diode D R2 connected to the anode.

[0057] Switching tube S bb1 The drain of the diode D bb1 The anode of the buck-boost unit is L bb1 The other end is connected.

[0058] Switching tube S bb2 The source of the diode D bb2 The cathode of the buck-boost unit is L bb2 The other end is connected.

[0059] Switching tube S b1 The source of the diode D b1 The cathode of the buck unit is L b1 The inductor L of the buck unit is connected to one end of b1 The other end of the diode D bb1The cathode of the output capacitor C1, the positive electrode of the output capacitor C1, the drain of the upper bridge arm switch tube T2 of the U phase of the subsequent inverter, the drain of the upper bridge arm switch tube T4 of the V phase of the subsequent inverter, and the drain of the upper bridge arm switch tube T6 of the W phase of the subsequent inverter are connected.

[0060] Switching tube S b2 The drain of the diode D b2 The anode of the buck unit, the inductor L b2 The inductor L of the buck unit is connected to one end of b2 The other end of the diode D bb2 The anode of the output capacitor C2, the source of the lower bridge arm switch tube T1 of the U phase of the subsequent inverter, the source of the lower bridge arm switch tube T3 of the V phase of the subsequent inverter, and the source of the lower bridge arm switch tube T5 of the W phase of the subsequent inverter are connected.

[0061] 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 of the rear inverter are connected to the U-phase terminal of the brushless DC motor.

[0062] 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 of the rear-stage inverter are connected to the V-phase terminal of the brushless DC motor.

[0063] 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 of the rear-stage inverter are connected to the W-phase terminal of the brushless DC motor.

[0064] See also Figure 3 , Figure 3 The simplified equivalent circuit of the system and the schematic diagram of its control principle are given. The working principle of the variable speed motor drive system in the present invention is as follows:

[0065] Depend on Figure 3 It can be seen that the control of the PFC converter still uses a simple single voltage loop for control, but its voltage reference is determined by the target speed of the motor. Figure 2 In the reference voltage V o,ref Fixed to 1, by changing the feedback voltage V o,fb The coefficient of can realize bus voltage regulation. In theory, this control principle is equivalent to 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.

[0066] like Figure 3 As shown, in essence, the control system of the present invention controls the output voltage V by controlling the buck-boost working mode 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 uses 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 and combine the fixed linear conversion formula between the speed and the input bus voltage (in this embodiment, see Figure 2 Medium feedback voltage V o,fb With V o,fb,rev The correction coefficient between ) is used to achieve the purpose of controlling the motor speed.

[0067] The conversion formula is as follows:

[0068] V o，fb，rev =V o，fb / (0.065*ω set -1.826)

[0069] In the formula, ω set 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.

[0070] It should be noted that the control method of the present invention is determined by the linear relationship between the terminal voltage and the rotational speed of the BLDC motor. For other motors, such a conversion relationship between voltage and rotational speed does not necessarily exist, such as an asynchronous motor.

[0071] Specifically, 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.

[0072] From the above description, it can be seen that the wide output voltage V o Closed-loop control is crucial for motor speed closed-loop control. Therefore, the working principle of the AC-DC bridgeless buck-boost converter of the present invention is described below through modal diagrams.

[0073] See also Figure 4 , Figure 4 (a) is the equivalent circuit of the working mode 1 of the front-stage bridgeless buck-boost PDF converter in the positive half cycle of the AC input; Figure 4 (b) is the equivalent circuit of the working mode 2 of the front-stage bridgeless buck-boost PDF converter in the positive half cycle of the AC input; Figure 4(c) is the equivalent circuit of the working mode 3 of the front-stage bridgeless buck-boost PDF converter in the positive half cycle of the AC input.

[0074] See also Figure 5 , Figure 5 (a) is the equivalent circuit of the working mode 4 of the front-stage bridgeless buck-boost PDF converter in the negative half cycle of the AC input; Figure 5 (b) is the equivalent circuit of the working mode 5 of the front-stage bridgeless buck-boost PDF converter in the negative half cycle of the AC input; Figure 5 (c) is the equivalent circuit of the working mode 6 of the front-stage bridgeless buck-boost PDF converter in the negative half cycle of the AC input.

[0075] Working mode 1: In this stage, the switch tube S b1 And switch tube S bb2 In the on state, the input terminal passes through the rectifier diode D R1 , switch tube S b1 , output capacitor C1, to the inductor L b1 and output capacitor C1, the inductor current i Lb1 Linear rise, switch tube S b1 The current and the inductor current i L1 The amplitude and direction are the same. At the same time, the input end passes through the rectifier diode D R4 , switch tube S bb2 , to the inductor L bb2 Charging, inductor current i Lbb2 Linear rise, switch tube S bb2 The current and the inductor current i Lbb2 The magnitude and direction of the output capacitor C2 are the same. The output capacitor C2 provides energy for the subsequent circuit.

[0076] Working mode 2: switch tube S b1 And switch tube S bb2 Turn off, diode D b1 is turned on and stored in the inductor L b1 The energy passes through the diode D b1 Supply energy to the subsequent circuit, the inductor current i Lb1 It decreases linearly until it reaches zero. At the same time, the inductance L bb2 Through diode D bb2 Freewheeling, inductor current i Lbb2 It decreases linearly until it reaches zero. In this stage, the inductor energy is transferred to the output capacitors C1 and C2 and supplies energy to the subsequent circuits.

[0077] Working mode 3: switch tube S b1 And switch tube S bb2 Keep off, the working mode is in the inductor current i Lbb2 and the inductor current i Lb1The linear decrease starts when it reaches zero, at which time i Lb1 =i Lbb2 =0, and the output capacitors C1 and C2 provide energy for the subsequent circuit.

[0078] Working mode 4: switch tube S b2 And switch tube S bb1 In the on state, the input terminal passes through the rectifier diode D R3 , switch tube S bb1 , to the inductor L bb1 Charging, inductor current i Lbb1 Linear rise, switch tube S bb1 、Diode D R3 The current and the inductor current i Lbb1 The amplitude and direction are the same. At the same time, the input end passes through the rectifier diode D R2 , switch tube S b2 , output capacitor C2, to the inductor L b2 The output capacitor C2 is charged. The output capacitor C1 supplies energy to the subsequent circuit.

[0079] Working mode 5: switch tube S b2 And switch tube S bb1 Turn off, diode D bb1 is turned on and stored in the inductor L bb1 The energy passes through the diode D bb1 Supply energy to the subsequent circuit, the inductor current i Lbb1 It decreases linearly until it reaches zero. At the same time, the inductance L b2 Through the diode D b2 Freewheeling, inductor current i Lb2 It decreases linearly until it reaches zero. In this stage, the inductor energy is transferred to the output capacitors C1 and C2 and supplies energy to the subsequent circuits.

[0080] Working mode 6: switch tube S b2 And switch tube S bb1 Keep off, the working mode is in the inductor current i Lbb1 and the inductor current i Lb2 The linear decrease starts when it reaches zero, at which time i Lb2 =i Lbb1 =0, and the output capacitors C1 and C2 provide energy for the subsequent circuit.

[0081] See also Figure 6 , Figure 6 This is a theoretical waveform diagram of the key components of the front-stage bridgeless buck-boost PFC converter in the present invention. Figure 6 It can be seen that the key components of the conversion unit mainly work within half of the power frequency cycle and do not interfere with each other.

[0082] In order to verify the feasibility of the motor drive system of the present invention under 110Vac input, the circuit is simulated and verified using PSIM simulation software. The simulation results of the drive system are as follows:

[0083] Specific parameters: AC input adopts sinusoidal signal fitting, AC voltage peak value is 156V, effective value is 110V, frequency is 50Hz, inductance L b1 =L b2 is 24uH, inductor L bb1 =L bb2 is 52uH, the intermediate bus capacitor C1=C2 is 2000uF, the motor output speed is 1000~2500rpm, the PFC converter switching frequency is 47kHz, the PI parameter P is 2, I is 0.005, and the converter maximum output voltage is 160V. The inverter switching frequency is 20kHz, 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 =2.2mH, C f =0.2uF.

[0084] See also Figure 7 , Figure 7 This is a waveform simulation diagram of the key components of the front-stage bridgeless buck-boost PFC converter. Figure 7 It can be seen that under the condition of AC input of 110Vac (i.e., AC input voltage peak of 156V) and frequency of 50Hz, the bridgeless PFC converter achieves a regulated output of 160V. b1 , S bb2 At input voltage v in The buck unit and the step-up / step-down unit are connected in parallel to realize the AC-DC conversion operation. b1 、Inductance L b2 The inductor L of the buck-boost unit bb1 , L bb2 The device simulation waveform is stable, and they only work in half of the power frequency cycle. The inductor current does not interfere with each other. Figure 6 The waveforms of the theoretical key devices are consistent with those shown in the figure, which verifies the working principle of the converter and also shows that the converter can be Figure 2 The system closed-loop control scheme shown achieves closed-loop stable operation.

[0085] See also Figure 8 Figure 8 This is the key waveform diagram of the operation of the drive system of the present invention. Figure 8The motor output speed can work stably at different target speeds, and the output voltage of the PFC converter is a constant value related to the speed, which verifies the feasibility of the closed-loop control method of controlling the motor speed by changing the bus voltage; and multiple inductors work alternately without mutual interference, indicating that the system can operate stably at such Figure 2 Shown is a single voltage loop under control.

[0086] 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 builds a traditional drive system architecture simulation circuit with the following parameters: the AC input voltage is 110Vac (peak value 156V), 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=0.01 and I=0.0001.

[0087] Table 1 shows the PF value and bus voltage value of the variable speed motor drive system of the present invention and the traditional system architecture at different speeds. As can be seen from Table 1, compared with the traditional system architecture, the PF value of the system architecture of the present invention is close to 0.99, which has a significantly higher PF value.

[0088] Table 1 Performance comparison of the converter of the present invention at 110Vac input

[0089]

[0090] According to the above theoretical analysis and simulation results, it can be seen that the high PF variable speed motor drive system based on the bridgeless buck-boost PFC converter proposed in the present invention can adjust the output voltage from 63.2V to 160.7V under the AC input voltage of 110Vac to achieve high PF value operation of the motor in a wide speed range of 1000rpm to 2500rpm. Compared with the traditional system bus that can only work at 152.8V and its PF value is only 0.2 to 0.3, the patent of the present invention achieves the performance of PF value higher than 0.97 under a wide speed range.

[0091] 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 variable speed motor drive system based on a bridgeless buck-boost 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-boost PFC converter; The topological structure of the front-stage bridgeless buck-boost PFC converter includes a buck unit, a buck-boost unit, an output capacitor C 1 and output capacitor C 2; The step-down unit includes a switch tube S b1 , switch tube S b2 ,diode D b1 ,diode D b2 , Rectifier diode D R1 , Rectifier diode D R2 ,inductance L b1 ,inductance L b2 ; The buck-boost unit includes a switch tube S bb1 , switch tube S bb2 ,diode D bb1 ,diode D bb2 , Rectifier diode D R3 , Rectifier diode D R4 ,inductance L bb1 ,inductance L bb2 ; The step-down unit and the step-up / step-down unit work in parallel in both the positive and negative half power frequency cycles to eliminate the input current dead zone of the step-down unit; By controlling the working mode of the preceding bridgeless buck-boost PFC converter, the output voltage of the preceding bridgeless buck-boost PFC converter is controlled. V o , realize the closed-loop control of brushless DC motor speed; One end of the AC input side and the rectifier diode D R3 The cathode of the rectifier diode D R4 Anode, rectifier diode D R1 Anode, rectifier diode D R2 The other end of the AC input side is connected to the cathode of the diode D b1 Anode, diode D b2 Cathode, inductor L bb1 One end of the inductor L bb2 One end of the output capacitor C 1 negative pole, output capacitor C 2's positive connection; Rectifier diode D R3 Anode and switch tube S bb1 The source connection of the switch tube S bb1 The drain and inductance L bb1 The other end of the diode D bb1 Anode connection; Rectifier diode D R4 The cathode and switch tube S bb2 The drain connection of the switch tube S bb2 The source and inductor L bb2 The other end of the diode D bb2 The cathode connection of Rectifier diode D R1 The cathode and switch tube S b1 The drain connection of the switch tube S b1 The source and diode D b1 Cathode, inductor L b1 One end of the inductor is connected; L b1 The other end of the diode D bb1 The cathode and output capacitor C 1's positive connection; Rectifier diode D R2 Anode and switch tube S b2 The source connection of the switch tube S b2 The drain and diode D b2 Anode, inductor L b2 One end of the inductor is connected; L b2 The other end of the diode D bb2 Anode, output capacitor C 2's negative connection; The brushless DC motor speed closed-loop control is as follows: The front-stage bridgeless buck-boost 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, thereby controlling the output voltage of the front-stage bridgeless buck-boost PFC converter. V o , to control the speed of the brushless DC motor; Output reference voltage of the front-stage bridgeless buck-boost 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-boost PFC converter, that is, the output voltage of the previous bridgeless buck-boost 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 single voltage loop is used for control, as follows: The bus voltage sampling signal of the front-stage bridgeless buck-boost PFC converter and the output reference voltage V o,fb,rev 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 b1 , switch tube S b2 , switch tube S bb1 , switch tube S bb2 The switch tube S b1 , switch tube S b2 , switch tube S bb1 , switch tube S bb2 Can be controlled using exactly the same drive signal.

2. The high PF variable speed motor drive system based on a bridgeless buck-boost PFC converter according to claim 1, characterized in that: 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; Output Capacitor C The positive pole of 1 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 connection; Output Capacitor C The negative pole of 2 and 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 connection; 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 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.

3. The high PF variable speed motor drive system based on a bridgeless buck-boost PFC converter according to claim 2, 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.

4. The high PF variable speed motor drive system based on a bridgeless buck-boost PFC converter according to any one of claims 1 to 3, characterized in that: The working mode of the front-stage bridgeless buck-boost PFC converter is as follows: Working mode 1: switch tube S b1 And switch tube S bb2 In the on state, the input terminal passes through the rectifier diode D R1 , switch tube S b1 , output capacitor C 1. To inductor L b1 and output capacitor C 1 Charging, inductor current i Lb1 Linear rise, switch tube S b1 The current and inductor current i L1 The amplitude and direction are the same; at the same time, the input end passes through the rectifier diode D R4 , switch tube S bb2 , to the inductor L bb2 Charging, inductor current i Lbb2 Linear rise, switch tube S bb2 The current and inductor current i Lbb2 The magnitude and direction of the output capacitor are the same. C 2 provides energy for the subsequent circuit; Working mode 2: switch tube S b1 And switch tube S bb2 Off, diode D b1 Conducting, stored in the inductor L b1 The energy passes through the diode D b1 Supply energy to the subsequent circuit, the inductor current i Lb1 linearly decreases until it reaches zero; at the same time, the inductance L bb2 Through the diode D bb2 Freewheeling, inductor current i Lbb2 The linear decreases until it reaches zero; in this stage, the inductor energy flows to the output capacitor C 1. Output capacitor C 2 transfer and supply energy to the subsequent circuit; Working mode 3: switch tube S b1 And switch tube S bb2 Keep off, the working mode is in the inductor current i Lbb2 and the inductor current i Lb1 The linear decrease to zero begins. i Lb1 = i Lbb2 =0, and the output capacitor C 1 and output capacitor C 2 provides energy for the subsequent circuit; Working mode 4: switch tube S b2 And switch tube S bb1 In the on state, the input terminal passes through the rectifier diode D R3 , switch tube S bb1 , to the inductor L bb1 Charging, inductor current i Lbb1 Linear rise, switch tube S bb1 , Rectifier diode D R3 The current and inductor current i Lbb1 The amplitude and direction are the same; at the same time, the input end passes through the rectifier diode D R2 , switch tube S b2 , output capacitor C 2. To inductor L b2 With output capacitor C 2Charge; output capacitor C 1 provides energy for the subsequent circuit; Working mode 5: switch tube S b2 And switch tube S bb1 Off, diode D bb1 Conducting, stored in the inductor L bb1 The energy passes through the diode D bb1 Supply energy to the subsequent circuit, the inductor current i Lbb1 linearly decreases until it reaches zero; at the same time, the inductance L b2 Through the diode D b2 Freewheeling, inductor current i Lb2 The linear decreases until it reaches zero; in this stage, the inductor energy flows to the output capacitor C 1. Output capacitor C 2 transfer and supply energy to the subsequent circuit; Working mode 6: switch tube S b2 And switch tube S bb1 Keep off, the working mode is in the inductor current i Lbb1 and the inductor current i Lb2 The linear decrease to zero begins. i Lb2 = i Lbb1 =0, and the output capacitor C 1 and output capacitor C 2 provides energy for the subsequent circuit.

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