KR100360243B1 - Apparatus for reducing noise of the compressor using random pulse width modulation and control method thereof - Google Patents

Abstract

The present invention relates to a noise reduction device for a compressor using a random PWM and a control method thereof. In the related art, when a compressor is driven at a fixed PWM frequency, switching noise occurs in a PWM switching frequency band, which affects the overall noise. There is a problem. Therefore, the present invention is to distribute the electromagnetic noise source of a fixed frequency to a wide frequency band by using a random PWM to reduce the electromagnetic noise, and also has an effect to significantly reduce the emotional noise. In addition, in order to reduce the power consumption of home appliances, the operation speed of the compressor will be extended to a lower speed range than now, so that a large effect can be obtained in improving the noise characteristics of the compressor in the low speed region.

Description

Noise reduction device of compressor using random PCM and its control method {APPARATUS FOR REDUCING NOISE OF THE COMPRESSOR USING RANDOM PULSE WIDTH MODULATION AND CONTROL METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device and a control method thereof for reducing the electromagnetic noise generated by pulse width modulation (PWM) and the emotional noise of noise quality. The present invention relates to a noise reduction device for a compressor using a random PWM and a control method thereof to reduce electromagnetic noise and emotional noise by dispersing the signal in a wide frequency band.

In recent years, the application of inverter systems has been increased to reduce power consumption, reduce noise due to low speed operation, and provide more comfortable functions to human beings such as air conditioners, refrigerators, and washing machines.

However, the inverter system is urgently required to reduce the electromagnetic noise generated by PWM and to improve the noise noise for the noise quality.

Therefore, the present invention reduces the electromagnetic noise and improves the emotional noise by applying a random PWM instead of a fixed PWM to the home appliance electrical appliance using the compressor, which will be described later.

FIG. 1 is a block diagram of a conventional noise reduction device of a compressor. As shown in FIG. 1, a power supply unit 11 and a power supply unit 11 provide a predetermined voltage to each of the necessary units when AC power is input. Inverter 12 for driving the BLDC motor according to the control signal input from the voltage input from the rotor and the rotor position of the BLDC motor is detected, and the resulting speed is calculated and output And a proportional integral controller 14 for adjusting the duty ratio of PWM by proportionally integrating the difference between the command value and the rotational speed detected by the detector 13, PWM pulse generation unit 15 for generating a PWM pulse for controlling the switching element of the inverter unit 12 using the duty ratio, and the switching element of the inverter unit 12 by the PWM pulse generated For turning on or off It consists of a gate signal generator 16 for generating a gate signal.

Looking at the prior art configured in this way in detail as follows.

When AC AC power is input, it is received by the power supply unit 11 and made into a constant DC voltage required by the inverter unit 12 and supplied to the inverter unit 12.

On the other hand, the six switching elements of the inverter unit 12 supplies a three-phase voltage generated by the conduction or interruption by the gate signal generated by the gate signal generator 16 to the BLDC motor.

Then, a magnetic field is generated in the stator of the BLDC motor by the three-phase voltage, and the rotor rotates.

As the rotor rotates, the home appliance electronics driven by the compressor is activated.

Accordingly, the rotor position and speed detector 13 detects the rotor position of the BLDC motor, detects the magnetic flux that changes according to the rotation of the rotor, and detects the motor speed ω.

At this time, the proportional integral controller 14 proportionally integrates the difference between the command speed (ω *) and the rotor position and the current speed (ω) of the motor detected by the speed detector 13 to obtain a duty ratio of PWM (Pulse Width Modulation). DUTY RATIO) is obtained and output to the PWM pulse generator 15.

Then, the PWM pulse generator 15 generates a constant PWM, that is, a fixed PWM pulse using the duty ratio, and supplies the same to the gate signal generator 16.

Therefore, the gate signal generator 16 receives the PWM pulses supplied from the PWM pulse generator 15 and conducts or cuts off the switching element of the inverter 12 to supply the three-phase voltage to the BLDC motor. Do it.

The PWM switching frequency used is fixed 7.8KHz.

However, in the prior art as described above, when driving the compressor at a fixed PWM frequency of 7.8KHz, it can be seen that the switching noise of 7.8KHz affects the overall noise as shown in FIG. The noise of the 7.8KHz band is generated by the peak current of the PWM frequency band in the current waveform shown in (b) (c) of FIG. 3. Thus, the noise generated by the compressor is mainly present in the 2 ~ 5KHz frequency band.

Therefore, an object of the present invention for solving the conventional problems as described above is the noise of the compressor using a random PWM to reduce the electromagnetic noise by distributing the electromagnetic noise source of a fixed operating frequency in a wide frequency band using a random PWM The present invention provides an abatement apparatus and a control method thereof.

Another object of the present invention is to provide a noise reduction device for a compressor using a random PWM and a control method thereof by applying a random PWM to reduce the emotional noise that may be caused by a change in the resonance characteristics of the compressor due to variation of each component of the compressor. In providing.

1 is a block diagram of a drive of a conventional compressor.

2 is a noise characteristic diagram of a compressor for each PWM frequency.

FIG. 3 is a characteristic diagram showing a noise FFT (Fast Fourier Transform) and a current FFT when the compressor is driven by a fixed PWM in FIG. 1. FIG.

Figure 4 is a block diagram of the noise reduction device of the compressor using the present invention random PWM.

5 is a distribution chart showing the frequency of occurrence of random numbers.

FIG. 6 is a characteristic diagram showing a noise FFT and a current FFT when the compressor is driven by a random PWM in FIG. 4. FIG.

7 is a characteristic diagram showing the loudness, the sharpness and the fluctuation intensity of the sound for each frequency, which is an emotional noise evaluation factor according to the operation time of the conventional fixed PWM.

8 is a characteristic diagram showing the loudness, the sharpness of the sound and the fluctuation intensity of the sound, which is an emotional noise evaluation factor for each frequency according to the operation time of the random PWM of the present invention.

***** Explanation of symbols for the main parts of the drawing *****

20: inverter unit 30: rotor position and speed detection unit

40: proportional integral controller 50: PWM pulse generator

60: gate signal generator 70: random variable generator

80: PWM frequency determiner 90: PWM comparison signal generator

In order to achieve the above object, the present invention converts an input DC voltage into a three-phase voltage and supplies it to a BCD motor so as to operate at a low speed. The inverter generates random PWM to reduce electromagnetic noise and emotional noise. A PWM controller for generating a duty ratio of a current PWM using a PWM frequency generating means, a difference between a current speed and a command speed of the motor, and a random PWM frequency and a current PWM duty ratio generated by the random PWM frequency generating means. It generates a new PWM pulse, and characterized in that it comprises a PWM comparison signal generator for outputting the signal accordingly.

Hereinafter, with reference to the accompanying drawings in detail as follows.

4 is a block diagram of a noise reduction device of a compressor using the random PWM of the present invention. As shown in FIG. 4, the power supply unit 10 provides a predetermined voltage to each of the necessary parts when AC power is input. Inverter 20 for driving a BLDC motor according to a control signal input from the power supply unit 10 and a rotor position of the BLDC motor is detected, and Proportional integral controller 40 for adjusting the duty ratio of PWM by proportionally integrating the rotor position and speed detector 30 for calculating and outputting the speed according to the difference between the command value and the rotation speed detected by the detector 30. And a random variable generator 70 for generating a random number for random PWM, a PWM frequency determiner 80 for determining and outputting a PWM frequency based on the random number generated above, and the proportional integrator 40. And the PWM frequency determination unit 80 The PWM comparison signal generator 90 receives the duty ratio and the PWM frequency to determine and output the period and on time of the PWM frequency, and the PWM pulse using the period and the conduction time of the generated PWM frequency. PWM pulse generation unit 50 for generating and outputting the output signal, and the gate signal generator 60 for generating a gate signal for turning on or off the switching element of the inverter unit by the PWM pulse generated above Configure.

Referring to the operation and effect of the present invention configured as described in detail as follows.

The main noise source of general household electrical appliances consists of a cold air circulation fan and a compressor of the condenser and the evaporator, and the noise is most affected by the compressor.

The noise of the compressor can be classified into electromagnetic noise of the motor and mechanical noise generated by vibration and friction of the mechanism by suction and compression of the refrigerant during rotation of the motor.

Noise from the compressor is mainly in the 2-5 KHz frequency band. However, in the case of a compressor operated at a variable speed by an inverter, electromagnetic noise of PWM frequency caused by PWM is added during power conversion of the inverter.

For example, when the compressor is driven at high speed, mechanical noise caused by friction and valves increases, so that electromagnetic noise caused by PWM switching becomes relatively small.

When the compressor is operated at a low speed, mechanical noise is relatively reduced, but electromagnetic noise due to PWM is not reduced.

Therefore, except for the initial start of the compressor and the overload, which requires a large amount of cooling power, most of the operating time is operated in a low speed region where the system efficiency (EER, Energy Efficieny Ratio) is high to reduce power consumption and noise.

In low speed operation, electromagnetic noise reduction and sound quality improvement of compressor are important factors in determining noise.

Therefore, in the present invention, the electromagnetic noise source having a fixed PWM frequency is distributed to a wide frequency band of random PWM to reduce electromagnetic noise. As shown in FIG. 2, the PWM switching of 7 KHz or less makes noise sensitive by the resonance characteristic of the compressor. If you want to apply random PWM, the minimum frequency should be set over 7 KHz.

In the case of fixed PWM, PWM switching above 15KHz can reduce audible noise, but power consumption is increased by increasing PWM switching loss, and oil supply of compressor is insufficient due to long initial start-up time. Can affect the reliability of the compressor.

Therefore, when determining the maximum frequency of the random PWM, the maximum frequency is selected to 11 KHz in consideration of the reliability of the compressor, the algorithm calculation time such as the hardware of the inverter system, position detection and speed control, EMI, and leakage current characteristics.

In addition, generation of random numbers for random PWM uses LCG (Linear Congruential Generator). The LCG can change the distribution and the period of the random number generated by the difference in coefficients, but because it generates a new number using the previous random number, it generates pseudo random number rather than exact random number. Way.

LCG is mainly expressed by m, a, b (coefficients), yo (random number), and the generation of random numbers is given by Equation (1) below.

In Equation 1, in order to obtain y (n + 1), which is the (n + 1) th random number, the value of a * y (n) + b using y (n), which is the (n) th random number After dividing, divide the obtained value by m and use the rest as a random number.

There are various methods such as Liederreiter's LCG, ANSIC's LCG, MAPLE's LCG and the like depending on the values of a, b and m.

In order to reduce the material cost of home inverter products, the 8-bit microcomputer is mainly used, so the maximum value is limited by the coefficients a, b, m and the like. Therefore, in the present invention, Liederreiter's LCG (2 ^ 16, 47485, 0,1), which can process the data most simply, is used.

The important characteristics of the generated random numbers are the distribution and the repetition period of the random numbers. To find out whether the applied LCG is appropriate, examine the random number period and the number of occurrences as follows.

5 shows the probability of occurrence in each frequency domain, that is, the frequency of occurrence of random numbers when the frequency of the random PWM is 8-11KHz. The period of generated random number is 16,385. If the average switching frequency of random PWM is 10KHz, the generation period is about 1.63 seconds. It can be said that the period is sufficiently long at low frequencies of less than 1 Hz.

In addition, when the generated random numbers are divided into 30 frequencies, the frequency of division of each frequency is equal to 546 times, indicating that the generated random numbers are evenly distributed.

Accordingly, AC AC power is received from the power supply unit 10 to supply a constant DC voltage required by the inverter unit 20 to supply three phase voltages generated by conducting / blocking six switching elements of the inverter unit 20. As it is supplied to a BLDC motor, a rotor field is generated in the stator to rotate the rotor.

As the rotor rotates, the home appliance electronics driven by the compressor is activated.

Accordingly, the rotor position and speed detector 30 detects the rotor position of the BLDC motor, detects the magnetic flux that changes according to the rotation of the rotor, and detects the motor speed ω.

Then, the proportional integral controller 40 proportionally integrates the difference between the command speed ω * and the current position ω of the motor detected by the rotor position and the speed detector 30 to proportionate the duty ratio of PWM (Pulse Width Modulation). DUTY RATIO) is obtained and provided to the PWM comparison signal generator 90.

At this time, the random variable generator 70 provides a random number set by the user to the PWM frequency determiner 80.

Accordingly, the PWM frequency determining unit 80 determines the period (T) of the PWM switching frequency between the minimum frequency and the maximum frequency previously selected according to the random number provided by the random variable generator 70, and generates a PWM comparison signal. Output to the unit 90.

Accordingly, the PWM comparison signal generator 90 compares the duty cycle of the PWM provided by the proportional integral controller 40 with the period of the PWM switching frequency provided by the PWM frequency determiner 80 to determine the period of the PWM switching frequency. The conduction time is determined and provided to the PWM pulse generator 50.

The PWM pulse generator 50 generates a PWM pulse to control the switching element of the inverter unit 20 using the PWM switching frequency, its period, and the conduction time, and supplies it to the gate signal generator 60.

Therefore, the gate signal generator 60 receives the PWM pulses supplied from the PWM pulse generator 50 and conducts or cuts off the switching element of the inverter 20 to supply the three-phase voltage to the BLDC motor. do.

As such, when driving the compressor by randomly generating a PWM pulse, it can be seen that noise is reduced as shown in FIG. That is, the noise of the compressor when driven with a fixed PWM is 39.3 dBA and 36.0 dBA, respectively, as shown in (a) of FIG. 3, and the noise of the compressor when driven with a random PWM is shown in FIG. ), The noise in the X-direction is reduced by about 2 dBA to 37.2 dBA and 35.1 dBA.

In case of the fixed PWM, the noise of 7.8KHz band is generated by the peak current as in (b) (c) of FIG. 3, but in the case of random PWM, the current of 7-11KHz is as in (b) (c) of FIG. 6. As the peak current does not occur because it is dispersed to, the noise in the 7.8KHz band is greatly reduced and the overall noise is reduced.

Table 1 below shows the evaluation results of the sound quality index of the fixed PWM and the random PWM when the refrigerator operates in normal operation state, that is, the motor operates at 2100 [rpm].

The sound quality index (SQ), ie, the degree of irritability, was evaluated for randomly selected evaluation subjects by recording noise during normal driving.

In general, the components for evaluating the sound quality index can be classified into loudness, sharpness, fluctuation, and roughness, but the roughness was negligibly small.

Therefore, the sound quality index (SQ) is expressed as a function of the loudness, sharpness, and fluctuation intensity as shown in Equation 2 below. The unit of the sound quality index (SQ) is expressed as UA (Unbiased Annoyance).

SQ = -10 + 17 * SL + 10 * SS + 10 * SF

Where SL is the loudness and is determined by the sound pressure level, the frequency of the sound, and the frequency bandwidth. 1 [sone] represents the magnitude of 40 [dBA] and 1 [kHz] pure sound.

SS represents the frequency distribution of the sound with its sharpness. It is determined by the loudness and frequency of the sound, and 1 [acum] indicates the roughness of 60 [dBA], 1 [kHz] pure sound.

SF is the fluctuation of sound, which represents the time distribution of sound pressure, and is determined by sound pressure level, sound frequency, modulation frequency, and so on. 1 [vail] represents the fluctuation of the sound when 60 [dBA], 1 [kHz] pure tone is 100% amplitude modulated to 4 [Hz].

As shown in Table 2, the sound quality index of the random PWM is 25.5 [UA], it can be seen that smaller than the 32.9 [UA] of the fixed PWM.

7 and 8 show the loudness, negative sharpness, and fluctuation of each frequency according to the operation time of the fixed PWM and the random PWM, and the fixed PWM is 7.8 KHz. When switching, it can be seen that the noise is reduced to a wider frequency band of the random 7-11KHz band, such as noise level, sharpness, and fluctuation intensity for each frequency.

As described in detail above, the present invention has the effect of reducing electromagnetic noise by reducing random noise by applying random PWM to an inverter system for driving a compressor and improving the sound quality index of emotional noise. In addition, in order to reduce the power consumption of home appliances, the operation speed of the compressor will be extended to a lower speed range than it is now, and thus, a great effect can be obtained in improving the noise characteristics of the compressor in the low speed region.

Claims (6)

An inverter system for converting an input DC voltage into a three-phase voltage and supplying it to a BCD motor for low speed operation, comprising: random PWM frequency generating means for generating a switching frequency of random PWM for reducing electromagnetic noise and emotional noise; A proportional integral controller for calculating the duty ratio of the current PWM by using a difference between the current speed and the command speed of the motor, and a switching frequency of the random PWM generated by the random PWM frequency generating means and the current output from the proportional integral controller. Compressor noise reduction device using a random PWM characterized in that it comprises a PWM comparison signal generator for generating a PWM pulse through the PWM pulse generator after determining the period and the conduction time of the switching frequency of the PWM using the PWM duty ratio. According to claim 1, The random PWM frequency generating means is a random variable generator for generating a random number adjusted by the user, and a PWM frequency determination unit for determining and outputting the switching frequency of the random PWM based on the random number generated above Compressor noise reduction device using a random PWM, characterized in that configured. The noise reduction apparatus of the compressor using the random PWM according to claim 2, wherein the PWM frequency determining unit selects the minimum frequency of the random PWM as 7 to 8 KHz in consideration of the resonance characteristics of the compressor. delete The noise reduction device of a compressor using a random PWM according to claim 2, wherein the PWM frequency determining unit selects the maximum frequency of the random PWM as 11 KHz in consideration of characteristics of the brushless motor, a position sensing algorithm, EMI, and leakage current. . Calculating a duty ratio of the PWM using a first step of generating a desired random number, a second step of determining a switching frequency of a random PWM according to the generated random number, and a difference between the command speed and the current motor speed And a fourth step of generating a new PWM pulse using the switching frequency of the random PWM determined in the second step and the duty ratio of the PWM calculated in the third step to control the switching element for driving the motor. Control method of the compressor noise reduction device using a random PWM, characterized in that consisting of.