KR100583974B1 - Method for PWM signal generation in inverter apparatus - Google Patents

Abstract

The present invention relates to a PWM signal generation method of the inverter device, and more particularly to a PWM signal generation method that can generate a PWM signal of the inverter device in a one-chip microcomputer using a triangular wave carrier. The PWM signal generating method of the present invention comprises the steps of creating a sin table from sin 0 ° to sin 90 ° in one cycle of sin divided into 12 sections, and calculating U phase, V phase, and W phase data for each section. And determining the detection of the current region according to the driving frequency, determining the values of the U phase, V phase, and W phase for each region, the sin table value according to the determined value of each phase, and the operation. Accessing a voltage value V / F table value according to frequency and providing a detected offset value to determine a PWM signal according to each phase.

Triangle wave modulation, PWM signal

Description

Method for generating pulse width modulation signal of inverter device {Method for PWM signal generation in inverter apparatus}             

1 is a connection diagram of a three-phase inverter device according to the present invention,

2 is a waveform diagram of a sawtooth wave modulation method;

3 is a waveform diagram of a triangular wave modulation method;

4 is a waveform diagram of a three-phase triangular wave modulation scheme;

5 is an operation process diagram for generating a PWM signal of the inverter device according to the present invention;

6 is a PWM cycle of the triangular wave modulation applied in this embodiment,

7 is a state diagram in which one period of a sine wave is divided into 12 sections;

8 is a table for determining the value of each phase in each region according to the present invention;

9 is an operation flowchart for determining a PWM signal according to the current operating frequency according to the present invention;

10 is a process diagram for determining the U phase, V phase, and W phase in one section.

Explanation of symbols on the main parts of the drawings

10: 3-phase AC induction motor 20: Microcomputer

Q1 ~ Q6: Inverter switching element

The present invention relates to a PWM signal generation method of the inverter device, and more particularly to a PWM signal generation method that can generate a PWM signal of the inverter device in a one-chip microcomputer using a triangular wave carrier.

The inverter device is a device having a plurality of switching elements on / off controlled to convert a DC voltage into a three-phase AC voltage. There is a need for a PWM signal for controlling the on / off operation of switching elements of such an inverter device.

In general, the PWM signal generator used in the conventional inverter device is implemented as a logic circuit mixed with the analog method and the digital method. However, in this case, there is a problem that it is impossible to generate a high voltage due to the nature of the hardware composed of specific elements. In addition, the conventional PWM signal generating device has a problem that the volume and manufacturing cost of the product is increased because it must be provided with a plurality of electrical elements for generating an appropriate PWM signal.

Accordingly, an object of the present invention is to provide a PWM signal generating method capable of generating a PWM signal of an inverter device in a one-chip microcomputer using a triangular wave carrier.                         

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PWM signal generation method of the inverter device according to the present invention for achieving the above object comprises the steps of setting a PWM period according to the sawtooth wave or triangular wave modulation; Preparing a sin table from sin 0 ° to sin 90 ° in one cycle of sin divided into 12 sections, calculating the U phase, V phase, and W phase data for each section, and present Determining a detection of a region, determining values of the U phase, V phase, and W phase for each region, a sin table value according to the determined value of each phase, and a voltage value V / F table according to the operating frequency Accessing the value and providing the detected offset value to determine the PWM signal according to each phase.

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According to the present invention, the carrier frequency applied at the time of generating the sin table is calculated by multiplying the PWM frequency value by 4 and dividing the external oscillation frequency by the multiplied value.

The division of 12 sections of one period of a sine wave of the present invention is characterized in that the maximum sampling number up to π / 2 is set to 1998, and is set in multiples of 666 at intervals of π / 6.

The sin table value of the present invention is characterized by being calculated by sin [(π / 2) * (N / 1998)] * 250.

The determination of the section of the driving frequency of the present invention is characterized by determining by dividing the current frequency by adding the previous frequency to 666.

According to the present invention, the PWM output signal of each phase according to the operation frequency for controlling the on / off operation of each switching element of the inverter is characterized in that the offset value is added or subtracted.

Hereinafter, a PWM signal generating method of an inverter device according to the present invention will be described with reference to the accompanying drawings.

1 shows a wiring diagram of a three-phase inverter device according to the present invention.

In the three-phase inverter device of the present invention, six switching elements Q1 to Q6 are connected between two power lines connecting the power source E. FIG. The switching elements Q1 to Q6 are formed in pairs of two up and down, and when one switching element is on, the other switching element is configured to be in an off state. And each arm (U, V, W) of the three-phase AC induction motor 10 is connected to the switching elements (Q1 ~ Q6).

The switching elements Q1 to Q6 have a duty ratio according to an on / off operation by a three-phase PWM signal output from the microcomputer 20. That is, the current flowing to the load of the three-phase AC induction motor 10 becomes the amount of time integration of the applied voltage. Therefore, it is possible to vary the equivalent voltage of the three-phase AC induction motor 10 by changing the duty ratio of the switching elements Q1 to Q6 occupied during a certain period.

Next, a look at the principle according to the PWM signal generation in the inverter device according to the present invention.

For single-phase inverters, the effective value of fundamental wave components is Edc / √2 for 100% modulation, and for three-phase inverters, the effective value of fundamental wave components (effective value of equivalent voltage for three-phase triangle wave modulation) is Edc / 2√2. At this time, the line voltage is √3 * Edc / 2√2, and about 0.612 * Edc (Vrms) can be obtained.

Fig. 2 shows a single phase sawtooth wave modulation method, and Fig. 3 shows a single phase triangle wave modulation method. Therefore, when the three-phase triangle wave is modulated, it is expressed as shown in FIG.

In the case of the saw-tooth wave modulation, the number of changes in the line voltage is 1/2 less than that of the triangular wave modulation, but the triangular wave modulation can obtain a better voltage waveform because the frequency of the main harmonic components is higher. When the sawtooth carrier is used, the switching loss is reduced to 1/2 of the triangular wave, but the distortion of the line current is large, and the motor efficiency is low.

In addition, the relationship between the carrier and the line current waveform shows that the lower the carrier frequency, the lower the amplitude of the line voltage, the larger the distortion of the current waveform, and the larger the smaller the distortion of the current waveform, the higher the amplitude. However, the switching speed of the power device is limited, the power loss is generated that much.

Next, a process of generating a PWM signal by triangular wave modulation in the inverter device according to the present invention will be described.

5 is an operation process diagram according to the PWM signal generation process in the inverter device of the present invention.

First, the microcomputer 20 performs a process of setting a carrier frequency (step 200).

In the present invention, the mode according to the carry frequency setting is divided into two types.

First is sawtooth modulation.

Carrier Frequency = External Oscillator Frequency / (PWM Frequency * 2)

= 16 * 10 ⁶ / (8KHz * 2)

= 1000 (where external oscillator frequency 16 * 10 ⁶ is assumed)

But for convenience of calculation,

Carrier frequency = 16 * 10 ⁶ / (511 * 2) = 15.65KHz or,

Carrier frequency = 16 * 10 ⁶ / (1023 * 2) = 7.82 KHz.

Second is triangular wave modulation.

Carrier Frequency = External Oscillator Frequency / (PWM Frequency * 4)

= 16 * 10 ⁶ / (8KHz * 4)

= 500

But for convenience of calculation,

Carrier frequency = 16 * 10 ⁶ / (500 * 4) = 8KHz or,

Carrier frequency = 16 * 10 ⁶ / (1023 * 4) = 3.9KHz.

By the carrier frequency setting method as described above, in the embodiment of the present invention, the triangular wave modulation shown in Fig. 6 is applied, and the set carrier frequency is 16 * 10 ⁶ / (500 * 4) = 8KHz.

When the carrier frequency for the triangular wave is set by the above process, the process of dividing sin 360 ° into 12 sections at intervals of 30 degrees is performed (step 210).

That is, sin 90 ° = A * sinθ

= sin 2Π * f * t

= sin 2Π * f * N / fc, where N is the number of samples, f is the initial operating frequency, fc is the carrier frequency, A is amplitude, and t is time.

And sin 90。 = 1, so

sin 2Π * f * N / fc = 1

2Π * f * N / fc = Π / 2 ......... (Equation 1)

If the operating frequency is 1Hz in the above formula (1), the maximum number of sampling is calculated,

2Π * 1 Hz * N / 7.992KHz = Π / 2

N = 1998 is obtained.

That is, since the maximum sampling number for sin π / 2 is 1998, if it is divided into three at 30 degree intervals, a value 666 for each interval can be obtained.

Thus, 666 * 12 = 7992, and each interval is divided as follows.

Section 1: 1 ~ 666 Section 2: 667 ~ 1332 Section 3: 1333 ~ 1998

4 sections: 1999 ~ 2664 5 sections: 2665 ~ 3330 6 sections: 3331 ~ 3996

7 sections: 3997 ~ 4662 8 sections: 4663 ~ 5328 9 sections: 5329 ~ 5994

10 sections: 5995 ~ 6660 11 sections: 6661 ~ 7326 12 sections: 7327 ~ 7992. This is shown in FIG.

That is, as shown in FIG. 7, the X-axis value is expressed from 0 to 360 degrees ⇒ 0 to 7992 (30 degrees is set to 666), and a sin 1 cycle is formed.

The Y-axis value is represented by −1 to 1 ⇒ 0 to 500.

At this time, since the carrier value for the Y axis is in the range of 0 to 511, an offset setting is required according to the phase.

Next, a process of creating a sin table is performed (step 220).

At this time, prepare a table according to sin0。 ~ sin90 。. The sin value created on the table is calculated as sin value * 250 and stored in the memory. 250 is a constant.

Therefore, the data for each phase value is obtained by the following formula.

Phase data for each interval = sin [(Π / 2) * (N / 1998)] * 250 (where N = 0 to 1998)

Thus, only the tables from sin 0 ° to sin90 ° are created because all values for the U phase, V phase, and W phase can be obtained if only the sin table for the portion is provided.

As an example, the values for the U phase, V phase and W phase in one section (0 to 666) shown in FIG. 7 are obtained as follows.

The U phase is obtained with reference to one section (0 to 666) in the sin table.

The V phase is obtained with reference to three sections (1332 to 1998) in the sin table.

The W phase is obtained with reference to two sections 666 to 1332 in the sin table. In this way, if only the values from sin 0 ° to sin90 ° are obtained, it is possible to obtain all values for each phase.

Next, a method of calculating data for each U phase, V phase, and W phase in each section is determined (step 230).

First, the area for each phase is determined. Each region is determined by dividing the sum of the current driving frequency and the previous data of the previous frequency with respect to the driving frequency by 666, and each region.

And the value of each phase for each area is determined.

The data value for each region is obtained by dividing by 256 again to reduce the computation time of the microcomputer after the sin table value is multiplied by the V / F value.

As an example, the determination of the values for the U phase, the V phase, and the W phase in one section (0 to 666) shown in FIG. 7 will be described.

The U phase value is positive and increases. The value reference range of the sin table is from 0 to 666.

Since the value of the U phase coincides with the value of the sin table, the data is obtained, multiplied by a V / F constant, divided by 256, and then an offset value is added. Therefore, the value of U phase in section 1 is determined by (pointer * v / f constant / 256) + offset. Here, the 'pointer' is a number for each section.

The V phase value is negative and increases. The value reference range of the sin table is 1332 to 1998.

Since the V phase value is shifted by the sin table reference range by 1332, the value is added to 1332 from the currently determined data value to obtain the value of the sin table, multiplied by the V / F constant, and divided by 256. ), So the calculated value is subtracted from the offset value. Therefore, the value of V on section 1 is determined by offset-[(pointer + 1332) * v / f constant / 256].

The W phase value is positive and decreases. The value reference range of the sin table is 666 to 1331.

The W phase value has a sin table reference range of 666 to 1332, but since the data has a decreasing characteristic, the reference value is obtained by subtracting the value of the sin table from the position subtracted by the currently determined data value at 1332 and multiplying the V / F constant. Divide by 256 And since the decision value is (+), add the offset value. Therefore, the value of W phase in section 1 is determined by [(1332-pointer) * v / f constant / 256]-offset.

Herein, the V / F value represents a voltage applied to an optimal operating frequency. That is, in the variable speed operation, the frequency of the current to be driven is varied. At this time, since the internal impedance of the motor changes with frequency, only changing the driving frequency exceeds the torque shortage and the magnetic saturation. For this reason, the voltage applied to the motor is also variable to perform the variable speed operation. Therefore, the V / F value is a table value according to the voltage applied to the optimum driving frequency during variable speed operation.

The calculation method of the U phase, V phase, and W phase obtained in each section by such a process is shown as a table in FIG.

When the calculation method of the U phase, V phase, and W phase for each section is determined by the above process, the detection of the current region is determined according to the current operating frequency detected thereafter, and then the value of each phase for each region is determined. The final PWM signal is determined (step 240).

Next, FIG. 9 is a flowchart illustrating an operation of determining a final PWM signal in step 240.

First, the current driving frequency is detected, and data of the previous frequency is added to the value of the driving frequency and set as current data (step 100).

It is determined whether the current data calculated in step 100 is less than 7992 (step 103).

In step 103, when the current data is larger than 7992, 7992 is subtracted from the current data and set as the current data (step 106).

In step 103, when the current data is smaller than 7992, or in step 106, the current data set by subtracting 7992 is set as the previous data in step 109.

In addition, it is determined in which section the current data is included in one cycle of sin. The process of determining whether the current data is included in the first section is step 112 and the process of determining whether the current data is included in the second section is step 118. The determination of each section is made by how many times the current data is included in 666. In this process, a process of determining which section of the current section is included in the current section is performed (steps 112 to 172).

When the current data is included in the sin 1 section, the jump to step 115 is performed to determine the value of each phase according to the 1 section.

A process of obtaining the value of each phase according to the one section is shown in FIG. 10.

To determine the U-phase PWM output, read the sin table value of the current data. And it reads the optimal voltage value V / F table value according to the current operation frequency. After detecting the offset value, the read sin value is multiplied by the V / F value, divided by 256, and then the offset value is added to determine the final PWM output signal according to the U phase.

To determine the V-phase PWM output, 1332 is added to the current data, set as the current data, and the sin table value for the current data is read. And it reads the V / F table value which is the optimum voltage value according to the current operation frequency. After detecting the offset value, the read sin value is multiplied by the V / F value, divided by 256, and then subtracted from the offset value to determine the final PWM output signal according to V phase.

In order to determine the PWM output on the W, the current data is subtracted at 1332, set as the current data, and the sin table value for the current data is read. And it reads the V / F table value which is the optimum voltage value according to the current operation frequency. After detecting the offset value, the read sin value is multiplied by the V / F value, divided by 256, and then the offset value is added to determine the final PWM output signal according to the W phase.

That is, the value of each phase of one section described in FIG. 10 summarizes one section of FIG. 8. Therefore, the value of each phase in each section is obtained based on FIG.

In this process, the PWM output signal determined in each section is output by the microcomputer 20, and the PWM output signal controls the on / off operation of each switching element.

That is, the PWM signal generation method of the inverter device according to the present invention is to modulate the PWM signal for driving the inverter device using a triangular wave carrier. In particular, the present invention can generate a desired PWM signal using only a one-chip microcomputer, and therefore, a high effect due to the reduction of the product and the cost of parts can be expected.

Claims (7)

Creating a sin table from sin 0 ° to sin 90 ° in a cycle of sin divided into 12 sections; Calculating data of U phase, V phase, and W phase for each section; Determining the detection of the current area according to the driving frequency; Determining values of the U phase, V phase, and W phase for each of the regions; Accessing the sin table value according to the determined value of each phase and the voltage value V / F table value according to the operating frequency, and providing a detected offset value to determine a PWM signal according to each phase. PWM signal generation method of the device. delete The method of claim 1, The carrier frequency applied at the time of generating the sin table is calculated by multiplying the PWM frequency value by 4 and dividing the external oscillation frequency by the multiplied value. The method of claim 1, The division of 12 sections of one period of the sine wave is the PWM signal generation method of the inverter device, characterized in that the maximum number of samples up to π / 2 is set to 1998, and set to a multiple of 666 at intervals of π / 6. The method of claim 1, And said sin table value is calculated by sin [(π / 2) * (N / 1998)] * 250. The method of claim 1, Determination of the interval of the operating frequency, PWM signal generation method of the inverter device, characterized in that determined by dividing the value by adding the previous frequency to the current operating frequency to 666. The method of claim 1, PWM output signal of each phase according to the operation frequency for controlling the on / off operation of each switching element of the inverter, PWM signal generation method of the inverter device, characterized in that the offset value is added or subtracted.

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