KR102238759B1 - Method and aparatus for controlling sensorless bldc motor - Google Patents

Abstract

In the present specification, a sensorless control method for controlling the switching angle by the back EMF of the non-conductive section existing on both sides of the conducting section in a BLDC that has a sinusoidal back EMF and is driven in a 120 degree conduction type is proposed. By implementing sensorless based on the back EMF integration according to the above technique, sensorless robust against noise can be implemented. In addition, by controlling the ratio of the integral values of the back EMF, it is possible to adjust the switching section, thereby enabling various controls such as field weakening control.

Description

Sensorless BLDC motor control method and device {METHOD AND APARATUS FOR CONTROLLING SENSORLESS BLDC MOTOR}

The technical idea of the present invention relates to a method and apparatus for controlling a sensorless BLDC motor, and more particularly, to a control technique using back electromotive force in a large-capacity multi-pole sensorless BLDC motor.

BLDC motors generate rotational force by sequentially applying a voltage synchronized with the rotor position to the stator's armature windings using an inverter. At this time, it is classified into BLDC with sine wave back EMF and BLDC with trapezoidal back EMF according to the form of back EMF, and the former is commonly used as PMSM (Permanent Magnet Synchronous Motor). The PMSM type can reduce torque ripple through vector control while maintaining the input phase current in the form of a sine wave. The trapezoidal type BLDC generates a stable torque by applying a square wave current to the flattening region of the back EMF.

In order to drive the BLDC, the position information of the rotor is essential, and for this purpose, the position information is generally obtained using an encoder or a Hall sensor. However, there are frequent cases where a sensorless drive is required without a sensor that detects the position of the rotor due to field conditions or economical reasons. The simplest sensorless method is to drive in a 120° conduction type and find and drive ZCP (Zero Crossing Point) of back EMF in the 60° section where no voltage is applied. There are various sensorless driving techniques of PMSM, but their implementation is complicated. Recently, there have been many cases in which PMSMs with sinusoidal back EMF are driven in a 120° conduction type for sensorless purposes. In this case, since the back electromotive force is a sine wave, there is a disadvantage in that the torque ripple is greatly increased when a square wave current is applied, but the torque ripple is not a big problem when operating at high speed.

On the other hand, as the utilization of the multi-pole type motor increases, research on the large-capacity multi-pole type BLDC sensorless control method is drawing attention. Due to the recent development of the electric motor industry, the production of multi-pole BLDCs of various capacities has been actively made. Due to its characteristics, the multi-pole BLDC operates at high speed to reduce the weight of the motor and realize high energy density. Due to high-speed operation and high-density, encoders and Hall sensors for BLDC drive have a higher size and higher-density burden, and the burden of vibration countermeasures due to high-speed operation is greater than that of the existing BLDC. Therefore, in order to reduce this burden, the demand for sensorless control is increasing rapidly. In particular, a large-capacity multi-pole BLDC with a large number of poles due to multi-polarization has a high frequency of applied voltage due to high-speed operation, so research for a stable sensorless is attracting attention.

Tae-Won Chun, “Sensorless Control of BLDC Motor Drive for an Automotive Fuel Pump Using a Hysteresis Comparator”, IEEE Transactions on Power Electronics, Vol.29, Issue 3, pp.1382-1391, 2014. Chun, T.W. Tra, Q.V. Lee, H.H. Kim, H.G. “Sensorless Control of BLDC Motor Drive for an Automotive Fuel Pump Using a Hysteresis Comparator”, IEEE Power Electronics, Vol.29, Issue 3, pp.1382-1391, 2014

A large-capacity multi-pole BLDC with a large number of poles due to multi-polarization requires a control method for a stable sensorless because the frequency of the applied voltage is high due to high-speed operation. In this specification, a new sensorless control method for controlling the back EMF of the non-conducting section existing on both sides of the conducting section in a BLDC driven by 120 degree conduction type is proposed.

The proposed sensorless control method is a method of integrating the back electromotive force appearing in the non-conducting section and adjusting the switching angle so that the values can be controlled.

The sensorless BLDC motor according to an aspect according to the technical idea of the present invention may include an operation unit and a control unit. The sensorless BLDC motor can be driven in a 120 degree conduction type. The calculation unit may obtain a first integral value of a portion in which the back EMF increases and a second integral value of a portion in which the back EMF decreases in a period in which the back EMF is positive among the non-conduction excitation periods. The operation unit may adjust the switching interval by changing a ratio of the first integral value and the second integral value. The control unit may control the switching angle so that the first integral value and the second integral value are the same. Controlling the switching angle may include calculating a switching angle error according to the phase shift based on the first integral value and the second integral value.

A method for controlling a sensorless BLDC motor according to an aspect of the present invention includes a first integral value of a portion where the back EMF increases and a second integral value of a portion where the back EMF decreases in a section in which the back EMF is positive among the non-conducting excitation periods. And controlling the switching angle so that the first integral value and the second integral value are the same. Controlling the switching angle may include calculating a switching angle error according to the phase shift based on the first integral value and the second integral value.

The sensorless BLDC motor according to embodiments according to the technical idea of the present invention can implement a sensorless robust against noise even under severe load fluctuations. In addition, by controlling the ratio of the integral values of the back EMF, it is possible to adjust the switching section, thereby enabling various controls such as field weakening control.

In order to more fully understand the drawings cited in the present specification, a brief description of each drawing is provided.
1 shows a back electromotive force waveform of a BLDC motor.
2 shows a method of detecting back EMF according to whether or not the neutral point line is exposed.
3 shows back EMF and dark voltage waveforms in a non-conducting phase.
4 shows a three-phase current control inverter.
5 shows a dark voltage waveform in a non-conducting section when driving a PMSM having a sinusoidal back EMF.
6 shows the measured a-arm voltage and the integral value of the non-excitation section when a phase shift occurs at the switching angle during sensorless driving.
7 shows a block diagram of a sensorless BLDC motor.
8 is a block diagram of a method for controlling a sensorless BLDC motor.
9 shows the waveforms of the integral value of the three-phase back EMF and non-excitation phase back EMF.
10 shows an overall system block diagram of a rotor position estimation algorithm.
11 shows a power conversion device and a BLDC controller.
12 shows the measured dark voltage and non-excitation phase back EMF integral waveforms sampled in the reflux vector region and the intermediate part of the PWM.
13 shows the estimated position angle and phase current showing the starting characteristics.
14 shows a waveform for analyzing a current waveform characteristic according to a load in a BLDC having a sinusoidal back EMF.
Fig. 15 shows the excitation voltage and phase current waveforms when the load periodically suddenly appears.

The technical idea of the present invention is that various changes may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and will be described in detail through a detailed description. However, this is not intended to limit the technical idea of the present invention to a specific embodiment, it should be understood to include all changes, equivalents, and substitutes included in the scope of the technical idea of the present invention.

In describing the technical idea of the present invention, when it is determined that a detailed description of a related known technology may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted. In addition, a number (eg, first or second) used in the description of the present specification is only an identification symbol for distinguishing one component from another component.

In addition, in the present specification, when one component is referred to as "connected" or "connected" to another component, the one component may be directly connected or directly connected to the other component, but specially It should be understood that as long as there is no opposite substrate, it may be connected or may be connected via another component in the middle.

In addition, terms such as "~ unit", "~ group", "~ character", and "~ module" described in the present specification mean a unit that processes at least one function or operation, which is a processor or a microcomputer. Processor, Application Processor, Micro Controller, CPU (Central Processing Unit), GPU (Graphics Processing Unit), APU (Accelerate Processor Unit), DSP (Digital Signal Processor), ASIC ( Application Specific Integrated Circuit), FPGA (Field Programmable Gate Array), etc. may be implemented in hardware or software, or a combination of hardware and software.

In addition, it is intended to clarify that the division of the constituent parts in the present specification is merely divided by the main function that each constituent part is responsible for. That is, two or more constituent parts to be described below may be combined into one constituent part, or one constituent part may be divided into two or more for each more subdivided function. In addition, each of the constituent units to be described below may additionally perform some or all of the functions of other constituent units in addition to its own main function, and some of the main functions of each constituent unit are different. It goes without saying that it can also be performed exclusively by.

Hereinafter, embodiments according to the technical idea of the present invention will be sequentially described in detail.

1 shows a back electromotive force waveform of a BLDC motor.

The size of the back electromotive force changes in proportion to the speed, but the ZCP (Zero Crossing Point), which is the point where the back electromotive force becomes 0, always exists at a constant position angle regardless of the speed. Therefore, by detecting ZCP, 6 absolute rotor positions can be obtained. In the method of taking the ZCP of the phase voltage, as shown in FIG. 1, there is a 30° phase difference between the ZCP point and the switching point, so an algorithm capable of compensating for this is required. When the motor is Y-connected and the neutral point is exposed, the ZCP of the back EMF can be easily obtained. However, since most motors do not draw the neutral point to the outside, a virtual neutral point or a reference power source must be set to replace the neutral point.

2 shows a method of detecting back EMF according to whether or not the neutral point line is exposed.

When the neutral point line is exposed, a positive voltage can be obtained by taking an intermediate value of DC voltage as shown in FIG. 2(a), so that ZCP can be found. However, this method is difficult to use in the low-speed region where the back EMF is low, and since the phase delay filter is used to compensate for the 30° phase difference between the ZCP and the switching point, there is a disadvantage that the position resolution is deteriorated at high speed.

As shown in Fig. 2(b), a virtual neutral point can be set by Y-connecting the resistor. In this case, in the case of trapezoidal back EMF, the third harmonic component appears, but in the case of sinusoidal back EMF, this component does not appear, and sensorless control by the third harmonic is impossible.

Meanwhile, in the above two methods, if all three windings do not operate ideally, a phase shift occurs in the measured back EMF signal, which may lead to sensorless control failure.

3 shows back EMF and dark voltage waveforms in a non-conducting phase.

When the BLDC is normally driven in the method of finding the ZCP point by finding the voltage of the polarity based on the intermediate value of the DC voltage, the back EMF waveform in the non-conducting section appears symmetrically as shown in FIG. 3. At this time, the point at which ZCP becomes half of the DC voltage from the lower limit of the measured voltage corresponds to zero back EMF.

In this method, if all three windings of the motor do not operate ideally, such as starting or excessive load fluctuations, a phase shift occurs in the measured back EMF signal. Due to this, an abnormal current flows through the winding, and sensorless is not possible. In addition, this method has the disadvantage of having to generate an additional voltage to set the intermediate value of the DC voltage, which is the reference voltage.

4 shows a three-phase current control inverter.

According to various embodiments of the present disclosure, in FIG. 4, a method of detecting a dark voltage of an inverter, which is an electric motor terminal voltage based on a ground side of the inverter, is employed.

5 shows a dark voltage waveform in a non-conducting section when driving a PMSM having a sinusoidal back EMF.

When a BLDC motor having a sinusoidal back EMF as shown in FIG. 5(a) is normally driven, when the dark voltage of the inverter is measured, a voltage waveform as shown in FIG. 5(b) appears. A section occurs, and the start and end points of this section become the ZCP of the back EMF.

The dark voltage of the non-conducting section appears to be superimposed with the phase counter electromotive force as shown in Fig. 5(b) by the PWM (Pulse Width Modulation) of the other arms. Therefore, in order to remove the influence of the PWM of the other arm, it should be sampled in the middle of the PWM as shown in FIG. In this case, the measured dark voltage appears as shown in Fig. 5(d). As shown in FIG. 5(d), it can be seen that the measured phase back EMF appears symmetrically based on the maximum value of the actual back EMF in FIG. 5(a). If a phase shift occurs at the switching angle of the BLDC, the symmetry will disappear from the measured back EMF of FIG. 5(d). On the other hand, stable sensorless control is possible by switching in the inverter so that only the symmetry of the measured back EMF can be maintained. As a method for maintaining symmetry, the present specification proposes a method of taking integral information of the back electromotive force, which makes it robust against noise.

6 shows the measured a-arm voltage and the integral value of the non-excitation section when a phase shift occurs at the switching angle during sensorless driving.

In FIG. 6(a), it can be seen that during the non-conducting excitation period, back EMF information appears in the dark voltage only during the period in which the back EMF is positive. In this specification, the integral value of the portion of the non-conducting excitation section where the back EMF increases is defined as α, and the integral value of the portion where the back EMF decreases is defined as β.

As shown in Fig. 6(b), if the integral value of the non-excitation section can be calculated, the switching angle for symmetrical switching can be obtained. The integral value of the non-excitation section for sensorless is determined by the switching angle and phase back EMF. That is, if the phase back EMF information is known, the switching angle can be calculated using the phase back EMF integral value.

If BLDC has a sinusoidal back electromotive force waveform, each back electromotive force can be defined as follows.

(1)

(One)

Therefore, the integral value in the region where the back EMF increases in the non-conducting excitation section is as follows.

(2)

(2)

에 대응되는 시간이다.Where t1 is

It is the time corresponding to.

로 설정하면 아래 식과 같다.Equation (2) is a function of the time axis and becomes a function in which the back EMF changes according to the electric speed of the motor. In order to simplify equation (2), the integral axis

If set to, it is as follows.

(3)

(3)

)의 함수로 표현된다. As can be seen from Equation (3), the integral function of the back electromotive force in the non-excitation phase becomes a function independent of the motor speed, and a simple changeover angle (

It is expressed as a function of ).

The integral value in the region where the back EMF decreases in the non-conductive excitation phase is as follows.

(4)

(4)

The condition in which the BLDC is normally driven and is symmetrically switched based on the maximum point of the back EMF is defined as Equation (5) when Equations (3) and (4) have the same value.

(5)

(5)

라 하면 식 (3), 식 (4), 식 (5)로부터 식 (6)이 주어진다.For the sensorless stable operation of BLDC, the angle of the condition that is switched symmetrically is

Equation (6) is given from Equation (3), Equation (4), and Equation (5).

(6)

(6)

를 구하기 위해 삼각함수 공식을 이용하면 아래 식과 같다.From equation (6)

If you use the trigonometric formula to find, it is as follows.

(7)

(7)

는 아래와 같다. From equation (7)

Is as follows.

(8)

(8)

가 아래 식과 같이 주어진다.If the integral value in the region where the back EMF increases in the non-conducting excitation section can be obtained, the switching angle is obtained from Equation (3).

Is given by the equation below.

(9)

(9)

가 아래 식과 같이 주어진다.In addition, if the integral value in the region where the back EMF decreases in the non-excitation phase can be obtained, the switching angle is obtained from Equation (4).

Is given by the equation below.

(10)

(10)

)는 아래와 같이 정의될 수 있다.From equations (9) and (10), information on the switching angle can be obtained through the integration of the back electromotive force before and after the switching operation of each arm. Based on this information, the switching angle error (

) Can be defined as follows.

(11)

(11)

Stable sensorless control can be implemented by floating the switching angle error defined in Equation (11) to the switching angle.

7 shows a block diagram of a sensorless BLDC motor.

The sensorless BLDC motor 700 may include an operation unit 710 and a control unit 720. The sensorless BLDC motor 700 may be driven in a 120 degree conduction type.

The operation unit 710 may obtain a first integral value of a portion in which the back EMF increases and a second integral value of a portion in which the back EMF decreases in a period in which the back EMF is positive among the non-conducting excitation periods. The operation unit 710 may adjust a switching section by changing a ratio of the first integral value and the second integral value.

The controller 720 may control the switching angle so that the first integral value and the second integral value are the same. Controlling the switching angle may include calculating a switching angle error according to the phase shift based on the first integral value and the second integral value.

In FIG. 7, the sensorless BLDC motor 700 is shown only for including the calculation unit 710 and the control unit 720, but this is for simplification of the invention, and the configuration of the sensorless BLDC motor of the present invention is limited thereto. It is not and may further include other component(s).

8 is a block diagram of a method for controlling a sensorless BLDC motor.

The sensorless BLDC motor obtains a first integral value of a portion in which the back EMF increases and a second integral value of a portion in which the back EMF decreases in a period in which the back EMF is positive in the non-conduction excitation period (S810). The sensorless BLDC motor may control a switching angle so that the first integral value and the second integral value are the same (S820). Controlling the switching angle may include calculating a switching angle error according to the phase shift based on the first integral value and the second integral value.

9 shows the waveforms of the integral value of the three-phase back EMF and non-excitation phase back EMF.

If the method of detecting the dark voltage of the inverter, which is the terminal voltage of the motor based on the ground side of the inverter, is adopted to detect the back EMF, negative back EMF information cannot be taken, and as shown in FIG. You can only take information. In FIG. 9, the non-excitation phase back EMF integration information appears in the order of _{α a} , α _c , α _b , β _a , β _c , and β _b. For sensorless control, a method of controlling the switching angle so that α, which is an integral value of a portion of the non-conduction section where the back EMF increases, and β, which is a decreasing integral value, are the same may be considered.

Hereinafter, the validity of the proposed method is verified for a 4kW class 28-pole BLDC. Table 1 shows the specifications of the motor under test.

Specification RPM/V(KV) 120 [RPM/V] Weight w/o Wires 1000 [g] Diameter 89 [mm] Length 64.0 [mm] Slots, Poles 24, 28 Idle Current(Io) @10V 1.4 [A] Resistance 36 m[Ω] Inductance 30 [uH] Nominal Voltage 30-51 [V] Cruising power [30mins] 2730 [W] Bursts Current [30s] 112 [A] Peak power (30s) 5 k[W]

10 shows an overall system block diagram of a rotor position estimation algorithm.

In the open loop control for BLDC start, when the speed is generated by the speed pro, the position is calculated through the integrator and the applied switch is determined by the inverter by the vector generator. When the speed of the electric copper becomes the area where the back EMF can be stably detected, in order to remove the influence of the PWM of the other arm, the AD is sampled in the middle of the PWM low area _{, and V ag} , V _bg , and V _cg are detected according to the switching mode. Integrate the voltage value selectively. The integrated back EMF value is used as information for generating the switching vector by calculating the switching error by Equation (11) and correcting the error of the position estimation error. The speed information of the motor is obtained by counting the switching timing of the switching vector. When the switching algorithm is stabilized, the voltage of the vector can be controlled through the current and voltage controller based on the command speed and estimated speed information. On the other hand, for stabilization, it is possible to set a current limit value by a speed function.

11 shows a power conversion device and a BLDC controller.

In FIG. 11, the power conversion device may be composed of a 3-phase PWM inverter and a control board serving as a sensing and control unit, and may control the conduction angle of a BLDC motor by 120°. For example, a 200V, 140A class MOSFET can be used as the switching element used in the 3-phase PWM inverter, and the single power Allegro ACS758 can be used as a sensor for measuring the current. The main controller can be designed by TMS28335, a DSP from Texas Instruments, exclusively for controlling three-phase motors. In addition, 4 channels 16bit high-precision D/A can be used to verify internal and output variables.

12 shows the measured dark voltage and non-excitation phase back EMF integral waveforms sampled in the reflux vector region and the intermediate part of the PWM.

As shown in Fig. 12, it can be seen that the integrated value (α _a ) of the portion where the back EMF increases and the integral value (β _a ) that decreases remain the same, and the switching is symmetrical to the phase EMF, resulting in good sensorless control. have.

13 shows the estimated position angle and phase current showing the starting characteristics.

As shown in Fig. 13(a), it can be seen that the starting current increases to about 40 [A] at the maximum, and the phase switching is started satisfactorily after the end of the open loop control at about 50 [Hz]. It can be seen that it operates well at about 210 [rpm] in the normal state after starting.

14 shows waveforms for analyzing current waveform characteristics according to loads in BLDC with sinusoidal back EMF. It can be seen that the phase current ripple appears large in light loads, but its effect is reduced in medium loads. Fig. 15 shows the excitation voltage and phase current waveforms when a periodic load sudden change is performed at 4,000[W]/400[W]. In Fig. 15, good operation can be confirmed even when the load suddenly changes.

Claims (8)

In the control method of a sensorless BLDC motor,
Obtaining a first integral value of a portion in which the back EMF increases and a second integral value of a portion in which the back EMF decreases in a period in which the back EMF is positive among the non-conducting excitation periods; And
Including the step of controlling a switching angle so that the first integral value and the second integral value are the same,
Control method of sensorless BLDC motor. The method of claim 1,
The step of controlling the switching angle,
Comprising the step of calculating a switching angle error component according to a phase shift, based on the first integral value and the second integral value,
Control method of sensorless BLDC motor. The method of claim 1,
The sensorless BLDC motor is driven in a 120 degree conduction type,
Control method of sensorless BLDC motor. delete In a sensorless BLDC motor,
An operation unit that calculates a first integral value of a portion in which the back EMF increases and a second integral value of a portion in which the back EMF decreases in a period in which the back EMF is positive among the non-conduction excitation periods; And
Including a control unit for controlling a switching angle so that the first integral value and the second integral value are the same,
Sensorless BLDC motor. The method of claim 5,
The control unit,
Calculating a switching angle error according to a phase shift based on the first integral value and the second integral value,
Sensorless BLDC motor. The method of claim 5,
The sensorless BLDC motor is driven in a 120 degree conduction type,
Sensorless BLDC motor. delete

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