WO2021043240A1

WO2021043240A1 - Pwm control-based motor phase current measurement method and air conditioner

Info

Publication number: WO2021043240A1
Application number: PCT/CN2020/113397
Authority: WO
Inventors: 冯正阳; 邵海柱; 耿焱; 时斌; 丛安平; 张波
Original assignee: 青岛海尔空调电子有限公司; 海尔智家股份有限公司
Priority date: 2019-09-04
Filing date: 2020-09-04
Publication date: 2021-03-11
Also published as: CN112448619A

Abstract

Provided are a pulse-width modulation (PWM) control-based motor phase current measurement method and air conditioner; said phase current measurement method comprises: during the process of starting a motor, measuring a current signal of a DC bus of the motor (S100); while measuring the current signal of the DC bus, reducing the PWM carrier frequency of the motor (S200); calculating the phase current of the motor according to the current signal of the DC bus (S300). By means of measuring the current signal of the DC bus of the motor, the PWM carrier frequency of the motor is reduced, increasing the duration of the current waveform, such that it is easier to collect the current and the collected current is more accurate.

Description

Motor phase current detection method based on PWM control and air conditioner

Technical field

The invention relates to the technical field of current detection, in particular to a method for detecting phase current of a motor based on PWM control and an air conditioner.

Background technique

Traditional compressor drive algorithms often use three-resistance sampling to detect the U, V, and W phase currents as the feedback value. However, the cost of this method is relatively high, and the detection components are large in size and difficult to integrate in the circuit. In theory, oneshunt current detection is also feasible. The total current at different moments can be detected by connecting the sampling resistor in series to the DC bus, and then based on the three-phase current relationship, the U, V and W phase currents.

However, when the compressor is just started, its speed is not high, and the PWM pulse width difference is small, which causes the actual detected current waveform duration to be too short, making the three-phase current detected by the program inaccurate.

Correspondingly, the art needs a new method for detecting the phase current of the motor based on PWM control and an air conditioner to solve the above-mentioned problems.

Summary of the invention

In order to solve the above-mentioned problems in the prior art, that is, to solve the problem of inaccurate current detection in the existing single-resistance current sampling method, the present invention provides a phase current detection method of a motor based on PWM control. Current detection methods include:

In the process of starting the motor, detecting the current signal of the DC bus of the motor;

Calculate the phase current of the motor according to the current signal of the DC bus,

The phase current detection method further includes:

While detecting the current signal of the DC bus, the PWM carrier frequency of the motor is reduced.

In the above-mentioned preferred technical solution of the motor phase current detection method based on PWM control, the step of "reducing the PWM carrier frequency of the motor" specifically includes:

The PWM carrier frequency of the motor is reduced, so that the effective current signal of the DC bus can be continuously detected.

The PWM carrier frequency of the motor is reduced to at least half of the reference frequency.

In the above-mentioned preferred technical solution of the motor phase current detection method based on PWM control, the motor startup process includes a positioning phase, a forced start phase, and a closed-loop control phase. The step of "reducing the PWM carrier frequency of the motor" specifically includes :

In the forced start phase, the PWM carrier frequency of the motor is reduced.

In the preferred technical solution of the above-mentioned PWM control-based motor phase current detection method, the motor is a motor of an air conditioner compressor.

The application also provides an air conditioner, including a compressor and a controller. The compressor includes a motor based on PWM control. A sampling resistor is provided on the DC bus of the motor, and the sampling resistor is used to detect the direct current. Bus current signal,

The controller is configured to calculate the phase current of the motor according to the current signal of the DC bus detected by the sampling resistor during the motor starting process,

The controller is further configured to reduce the PWM carrier frequency of the motor while detecting the current signal of the DC bus through the sampling resistor.

In the above-mentioned preferred technical solution of the air conditioner, the controller reduces the PWM carrier frequency of the motor so that the effective current signal of the DC bus can be continuously detected.

In the above-mentioned preferred technical solution of the air conditioner, the controller reduces the PWM carrier frequency of the motor to at least half of the reference frequency.

In the above-mentioned preferred technical solution of the air conditioner, the motor starting process includes a positioning phase, a forced starting phase, and a closed-loop control phase, and the controller reduces the PWM carrier frequency of the motor during the forced starting phase.

Those skilled in the art can understand that, in the preferred technical solution of the present invention, the phase current detection method of the motor based on PWM control, the phase current detection method includes: detecting the current signal of the DC bus of the motor during the motor starting process; Calculate the phase current of the motor according to the current signal of the DC bus; while detecting the current signal of the DC bus, reduce the PWM carrier frequency of the motor.

By detecting the current signal of the DC bus of the motor and reducing the PWM carrier frequency of the motor, the duration of the current waveform is increased, the current is easier to collect, and the collected current is more accurate. At the same time, because this method does not require other hardware changes, it is simple and reliable to implement.

Further, by reducing the PWM carrier frequency of the motor to at least half of the reference frequency, the duration of the current waveform is extended by at least 2 times, there is sufficient sampling time when collecting the current, and the sampling result is more accurate. After repeated experimentation, observation, analysis and comparison by the inventor, when the PWM carrier frequency is the reference frequency, the detected effective current is very small, and the system cannot accurately collect the current; when the PWM carrier frequency is reduced to at least half of the reference frequency , The effective current can be collected in most cases when the motor is started, and the collected effective current has high accuracy.

Further, by reducing the PWM carrier frequency of the motor in the forced start phase, the method not only can effectively collect current, but also because the carrier frequency is modified only in the forced start phase, the operating performance of the system will not be affected.

Description of the drawings

The following describes the motor phase current detection method based on PWM control and the air conditioner of the present invention with reference to the accompanying drawings. In the attached picture:

Fig. 1 is a flowchart of a method for detecting phase current of a motor based on PWM control of the present invention;

Fig. 2 is a schematic diagram of sampling of the DC bus current of the present invention.

detailed description

The preferred embodiments of the present invention will be described below with reference to the drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention, and are not intended to limit the protection scope of the present invention. For example, although the following embodiments are described in conjunction with the motor of the air-conditioning compressor, this is not restrictive. Those skilled in the art can obviously also adjust the application scenarios of the present invention, and this adjustment does not deviate from the basics of the present invention. The principle, therefore, will also fall within the protection scope of the present invention. For example, the phase current detection method of the present application can also be applied to refrigerators, washing machines, etc.

First, referring to FIG. 1, the method for detecting the phase current of a motor based on PWM control of the present invention will be described. Among them, FIG. 1 is a flowchart of the method for detecting phase current of a motor based on PWM control of the present invention.

As shown in Fig. 1, in order to solve the problem of inaccurate current detection in the prior art using single-resistance current sampling, the detection method of the present invention mainly includes the following steps:

S100. Detect the current signal of the DC bus of the motor during the motor startup process; for example, set a sampling resistor on the DC bus, the sampling resistor is equipped with a current sensor, and detect the DC bus by obtaining the feedback value of the current sensor during the motor startup process的current signal.

S200. While detecting the current signal of the DC bus, reduce the PWM carrier frequency of the motor; for example, by modifying the program when the motor is started, the PWM carrier frequency is reduced to half of the reference frequency when detecting the current signal of the DC bus; After the current detection is over, the PWM carrier frequency is restored to the reference frequency to ensure the normal operation of the motor.

S300. Calculate the phase current of the motor according to the current signal of the DC bus; for example, after detecting the current of the DC bus at different moments, the current three-phase current can be indirectly converted based on the relationship between the power-on sequence and the three-phase current.

It can be seen from the above description that while detecting the current signal of the DC bus of the motor, the PWM carrier frequency of the motor is reduced, so that the duration of the current waveform is increased, the current is easier to collect, and the collected current is more accurate. At the same time, because this method does not require other hardware changes, it is simple and reliable to implement.

The phase current detection method of the present application will be described in detail below in conjunction with FIG. 1 and FIG. 2. Among them, FIG. 2 is a schematic diagram of sampling of the DC bus current of the present invention.

As shown in Figures 1 and 2, in a more preferred embodiment, the step of "reducing the PWM carrier frequency of the motor" is further as follows: reducing the PWM carrier frequency of the motor to a level that enables continuous detection of the DC bus The effective current signal, preferably, reduces the PWM carrier frequency of the motor to half of the reference frequency.

By reducing the PWM carrier frequency of the motor to half of the reference frequency, the current waveform duration is prolonged by 2 times, there is sufficient sampling time when collecting current, and the sampling result is more accurate. After repeated experimentation, observation, analysis and comparison by the inventor, when the PWM carrier frequency is the reference frequency, the detected effective current is very small, and the system cannot accurately collect the current; when the PWM carrier frequency is reduced to half of the reference frequency, The effective current can be collected in most cases when the motor is started, and the collected effective current has high accuracy.

In a more preferred embodiment, the motor starting process includes a positioning phase, a forced start phase, and a closed-loop control phase, and the step of reducing the PWM carrier frequency of the motor is performed in the forced start phase. For example, the reference frequency of the motor is 6kHz. When the motor starts, it starts and locates at the reference frequency of 6kHz; when it starts to the forced start phase, reduce the PWM carrier frequency to 3kHz and perform current sampling; when the motor continues to run to In the closed-loop control phase, the PWM carrier frequency is increased to the reference frequency of 6kHz to ensure the normal operation of the motor.

By reducing the PWM carrier frequency of the motor in the forced start phase, the method not only can effectively collect the current, but also because the carrier frequency is modified only in the forced start phase, the operating performance of the system will not be affected.

The specific implementation process of the phase current detection method of the present application will be introduced below with reference to FIG. 2 in conjunction with the motor of the air-conditioning compressor.

As shown in Figure 2, assuming that the waveform duration of the _{phase current W out} _{is 2000 us, V out} is 3000 us, and U _out is 4000 us, then the DC bus current is sampled at time a, and the current sample value I ₁ =I _u , Perform current sampling on the DC bus at time b, the current sampling value I ₂ =I _u +I _v =-I _w , and then according to the sum of the phase currents as zero I _u +I _v +I _w =0, the three-phase current value is obtained They are: I _u =I ₁ , I _w =-I ₂ , I _v =-(I _u +I _w )=-(I ₁ -I ₂ )=I ₂ -I ₁ . Under this condition, due to the _{large difference in duration between U out} , V _out and W _out , the actual sampling time a and b are relatively long, so there is no problem with sampling. However, in fact, when the air conditioner compressor motor is started, the _{difference in duration between U out} , V _out and W _out is generally not too large. For example, the waveform duration of _{W out} _{is 200 us, V out} is 300 us, and U _out is 400us, at this time, because the time difference between the two phases is too small, the actual output current waveform duration is too short, and it is impossible to sample the current with such a small duration.

At this time, if the carrier frequency is set to half of the previous one, and if the same current is output as before, the output duration of the three-phase PWM will become W _out ＝400us, V _out ＝600us, U _out ＝800us. The duration of the current is doubled before, so current sampling will be easier and more accurate.

It should be noted that since the current waveform has two changes in the same PWM carrier cycle, the DC bus current sampling can be performed either at the front end of the PWM carrier or at the back end of the PWM carrier. In Figure 2, the sampling of the DC bus current is performed at the front time of the PWM carrier, while the sampling of the DC bus current is performed at the rear time of the PWM carrier. The principle is the same as that performed at the front time of the PWM carrier. This is no longer exhausted.

It should also be noted that although the above embodiments are described in conjunction with the reduction of the PWM carrier frequency to half of the reference frequency, this is not restrictive. Obviously, those skilled in the art can also perform the reduction of the PWM carrier frequency. Adjustment, this adjustment does not deviate from the basic principle of the present invention, and therefore will also fall within the protection scope of the present invention. For example, those skilled in the art can also reduce the PWM carrier frequency to any value such as one-third, one-fourth of the original reference frequency.

The application also provides an air conditioner, including a compressor and a controller. The compressor includes a motor based on PWM control. The DC bus of the motor is provided with a sampling resistor, and the sampling resistor is used to detect the current signal of the DC bus.

Wherein, the controller is configured to reduce the PWM carrier frequency of the motor while detecting the current signal of the DC bus through the sampling resistor, and calculate the phase current of the motor based on the current signal of the DC bus detected through the sampling resistor during the motor starting process.

Among them, in a possible implementation manner, the controller reduces the PWM carrier frequency of the motor so that the effective current signal of the DC bus can be continuously detected. More preferably, the controller reduces the PWM carrier frequency of the motor to at least half of the reference frequency.

Among them, in a possible implementation manner, the motor startup process includes a positioning phase, a forced startup phase, and a closed-loop control phase, and the controller reduces the PWM carrier frequency of the motor during the forced startup phase.

It should be noted that although there is no specific description in the above-mentioned embodiments, the above-mentioned controller may be the controller of the air conditioner itself, may be a controller specifically used to execute the method of the present invention, or may be a function of a general-purpose controller. The module or functional unit may also be a micro-control unit (MCU) configured by the motor itself, and this change does not constitute any limitation to the protection scope of the present invention.

By reducing the PWM carrier frequency of the motor when sampling the current of the compressor motor of the air conditioner, the duration of the current waveform is increased, the current is easier to collect, and the collected current is also more accurate. At the same time, because this method does not require other hardware changes, it is simple and reliable to implement.

Those skilled in the art should be able to realize that the method steps of the examples described in the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of both, in order to clearly illustrate the possibilities of electronic hardware and software. Interchangeability, in the above description, the composition and steps of each example have been generally described in accordance with the function. Whether these functions are executed by electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods for each specific application to implement the described functions, but such implementation should not be considered as going beyond the scope of the present invention.

Although the various steps are described in the above-mentioned order in the above-mentioned embodiment, those skilled in the art can understand that in order to achieve the effect of this embodiment, different steps need not be executed in this order, and they can be performed simultaneously ( Parallel) execution or in reverse order, these simple changes are all within the protection scope of the present invention. For example, although the above embodiments are described in conjunction with detecting the current signal of the DC bus while reducing the PWM carrier frequency of the motor, those skilled in the art can also adjust it, for example, it can be adjusted to first reduce the motor's PWM carrier frequency. PWM carrier frequency, and then detect the current signal of the DC bus.

So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

A method for detecting phase current of a motor based on PWM control. The method for detecting phase current includes:

In the process of starting the motor, detecting the current signal of the DC bus of the motor;

Calculate the phase current of the motor according to the current signal of the DC bus,

It is characterized in that the phase current detection method further includes:

While detecting the current signal of the DC bus, the PWM carrier frequency of the motor is reduced.
The method for detecting the phase current of a motor based on PWM control according to claim 1, wherein the step of "reducing the PWM carrier frequency of the motor" specifically includes:

The PWM carrier frequency of the motor is reduced, so that the effective current signal of the DC bus can be continuously detected.
The method for detecting the phase current of a motor based on PWM control according to claim 1, wherein the step of "reducing the PWM carrier frequency of the motor" specifically includes:

The PWM carrier frequency of the motor is reduced to at least half of the reference frequency.
The method for detecting the phase current of a motor based on PWM control according to claim 1, wherein the motor starting process includes a positioning phase, a forced start phase, and a closed-loop control phase, "reducing the PWM carrier frequency of the motor" The specific steps include:

In the forced start phase, the PWM carrier frequency of the motor is reduced.
The method for detecting the phase current of a motor based on PWM control according to any one of claims 1 to 4, wherein the motor is a motor of an air conditioner compressor.
An air conditioner includes a compressor and a controller, the compressor includes a motor based on PWM control, a sampling resistor is arranged on the DC bus of the motor, and the sampling resistor is used to detect the current signal of the DC bus,

The controller is configured to calculate the phase current of the motor according to the current signal of the DC bus detected by the sampling resistor during the motor starting process,

It is characterized in that the controller is further configured to reduce the PWM carrier frequency of the motor while detecting the current signal of the DC bus through the sampling resistor.
The air conditioner according to claim 6, wherein the controller reduces the PWM carrier frequency of the motor so that the effective current signal of the DC bus can be continuously detected.
The air conditioner according to claim 6, wherein the controller reduces the PWM carrier frequency of the motor to at least half of the reference frequency.
The air conditioner according to claim 6, wherein the motor start process includes a positioning phase, a forced start phase, and a closed-loop control phase, and the controller reduces the PWM carrier frequency of the motor during the forced start phase .