JP3057656B2 - Inverter control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control device, such as an induction motor for an air conditioner which performs cooling / heating by a refrigerating cycle, which can be rotated at a variable speed by changing its driving frequency. is there.

[0002]

2. Description of the Related Art Generally, compressors for air conditioners for home use, stores, offices, etc. are driven by an induction motor in terms of cost and robustness.
In the induction motor, the “slip” frequency, which is the difference between the drive frequency and the rotation frequency, varies depending on the load, and the efficiency also changes.

For this reason, instead of the so-called “V / F control” using an operation voltage proportional to a motion frequency command, a method of calculating a load state from a motor current and operating the motor with high efficiency is conventionally used. As a method, a method using vector control has been proposed.

FIG. 6 shows an example in which the vector control technique is applied to high-efficiency control.
This is quoted from "Inverter scroll package air conditioner noise reduction technology" on the page. For the induction motor 1 for driving the compressor, the AC power supply 6 is converted into DC by the diode bridge 5 and the smoothing capacitor 4, and then the voltage and frequency are varied by the three-phase PWM inverter circuit 2 to change the induction motor. 1 is changed. It is often difficult to attach a rotation detection sensor to a compressor for an air conditioner. To detect rotation and drive the motor with high efficiency, it is necessary to detect at least two currents to the motor 1. , It is necessary to calculate the number of revolutions using the constant of the motor 1. The basic contents of this technology are described in JP-B-63-34718 and the like, and a description thereof will be omitted.

In FIG. 6, motor currents Iu and Iv are detected by current sensors 3u and 3v, and excitation current and torque current calculation means 101 calculates excitation current I1d and torque current I1q of induction motor 1. Since the detected torque current I1q is substantially proportional to the slip frequency, the slip frequency fs can be calculated using the torque current I1q and the motor constant. This slip frequency fs
By varying the frequency command so as to compensate for, the control of a constant rotational speed can be realized.

That is, the slip frequency is calculated by the slip frequency control means 7, and the frequency is corrected so that the motor 1 can rotate at the same frequency as the rotation frequency command fref from the refrigeration cycle control means. In FIG. 6, a command fre from the refrigeration cycle control means is controlled by the addition means 8.
f and the value of the correction frequency are added to obtain an actual frequency command f1 for the three-phase PWM inverter circuit 2.

On the other hand, the excitation current command I1 * d determined by the current minimum addition control means 103 and the detected excitation current I1d
The primary resistance, which is one of the motor constants, is identified by the primary resistance identifying means 102 based on the difference from the above, and a more accurate primary resistance value is obtained. Based on the obtained primary resistance value, the exciting current command I1 * d, the torque current I1q and the actual frequency command, an actual primary voltage is determined by the primary voltage correcting means 104, and the three-phase PWM inverter circuit 2 Sent. In this way, based on the frequency command fref from the refrigeration cycle control means, control is performed such that the current is minimized while the rotation speed of the motor 1 is maintained as specified. According to the cited example, minimizing the current increases the efficiency by approximately 10% at a motor torque of 1.1 kgm,
In addition, an improvement effect has been recognized with other torques.

[0008]

However, minimizing the motor current does not always correspond to keeping the motor at maximum efficiency. That is, as shown in FIG. 2, when the applied voltage V1 of the motor is increased, a point V1 (Pmin) where the power consumption becomes minimum appears first, and then a point V1 (Imin) where the motor current becomes minimum appears. Because you do. Why
If the efficiency of the motor is almost unchanged,
It is considered to be almost proportional to the product of voltage and current,
If the voltage is higher than the current, the current is slightly lowered.

[0009]

Accordingly, the present invention provides a method for reducing the required output even under relatively exceptional use conditions.
An object of the present invention is to provide an inverter control device capable of realizing protection of a used semiconductor element. The slightly exceptional article mentioned above
As a specific example of the matter, for example, for air conditioning, heating may be performed despite the high environmental temperature. If the ambient temperature is high, the pressure of the refrigerant increases, and the load torque of the motor of the compressor increases.

[0011]

An inverter control device according to the present invention for solving the above problems is characterized by having the following configuration.

[0012]

[0013]

The present invention is an inverter control device for an induction motor driven by an inverter capable of changing a command voltage and a command frequency, and detects a current flowing through the motor.
The detection signal by the current detection means for output and the inverter output
Excitation current of the induction motor based on the phase difference from the force voltage
Current conversion means for calculating torque and torque current;
Calculate slip frequency from flow value and motor time constant
Input the slip frequency calculation means and the calculated slip frequency.
A method of setting the drive frequency in addition to the inverter command frequency
Has a step, adjusting a current detection means for detecting a current flowing through the motor, means for calculating the power consumed by the motor by the product-sum of an inverter output waveform and the detection current, the output voltage of the inverter Power minimizing control means for minimizing the calculated power, and current minimizing control means for minimizing the detection current by adjusting the output voltage of the inverter, wherein the detection current is preset. When the detected current is equal to or less than the predetermined value, the output voltage of the inverter is adjusted based on the power minimizing control means. When the detected current is equal to or larger than the predetermined value, the output voltage of the inverter is adjusted by the current minimizing control means.

[0015]

[0016]

[0017]

According to the present invention, when the motor current is below a certain value,
High-efficiency operation control by power minimization control is realized,
When the current exceeds a certain value, the minimum current control operates and
It is controlled to lower the current first, and the power control element
Load conditions can be avoided.

[0018]

[0019]

[0020]

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a functional configuration of an embodiment of the present invention . In an air conditioner that performs cooling / heating, a drive power system of an induction motor 1 that drives a compressor for compressing a refrigerant converts an AC power supply 6 to DC once by a rectifier circuit including a diode bridge 5 and a smoothing capacitor 4. After the conversion, the three-phase PWM inverter circuit 2 converts the alternating current into three-phase alternating current, and drives the motor 1 at an arbitrary rotation speed. The three-phase PWM inverter circuit 2 is an IGBT
(Insulated Gate Bipolar Transistor) and the like, which can control the drive voltage and the drive frequency supplied to the motor 1 by varying the command voltage V1 and the command frequency f1.

The control system for controlling the inverter 2 receives the frequency fref as a target value and the current sensor 3, and outputs the above-described command voltage V1 and command frequency f1. Explaining this, the detection information of the current sensor 3 provided on one drive line of the three-phase induction motor 1 is input to the product-sum operation unit 16, the zero-cross timing detection unit 13, and the amplitude detection unit 12. The amplitude detecting means 12 detects the amplitude from input information which is a sine wave.

The zero-cross timing detecting means 13 detects the timing at which the current sensor information 4, which is AC, crosses zero. Zero-cross timing detection can be realized by a hardware system that inputs a detection circuit such as a comparison circuit to the timing circuit, but it can also be determined by computer software whether the read input signal is sign-inverted from the previous value. . The output result of the zero-cross timing detecting means 13 is sent to the phase comparing means 22. Similarly, the phase information of the primary frequency information f1 is input to the phase comparison unit 22 as a zero-cross timing as a comparison target, and the phase comparison is performed based on the time difference between the two pieces of timing information. The phase comparison result θ is calculated by the function generators 18 and 19
Sent to In the function generating means 18 and 19, “si
n (θ) ”and“ cos (θ) ”.
Send the result to 1. The multiplying means 20 and 21 respectively multiply with the output of the amplitude detecting means 12, and as a result I
τ and Im are sent to the slip frequency control means 7. The operation of this part will be described later.

The slip frequency control means 7 corrects the frequency value fs to be equal to the target frequency fref.
Is calculated, and the frequency command f1 is sent to the three-phase PWM inverter circuit 2 via the adding means 8.

On the other hand, one of the outputs of the amplitude detecting means 12 is sent to the voltage drop correcting means 15, and the voltage drop of the IGBT is calculated from the applied voltage information V1 to calculate the estimated value of the actual applied voltage. . The corrected applied voltage is sent to the sum-of-products calculating means 16 to calculate the sum of products with the output of the current sensor 3, that is, the power value.

The power value obtained by the sum-of-products calculating means 16 and the current value obtained by the amplitude detecting means 12 are input to the switching means 17, and one of them is supplied to the minimizing control means 11.
Is input to The switching control by the switching means 17 uses the amplitude value of the motor current. That is, when the current amplitude value is small, the power information is selected, and when the current amplitude is large, the current amplitude value is selected.

The minimizing control means 11 applies the voltage V1 to the motor 1 so that the power obtained by the amplitude of the current amount of the current sensor 3 or the product sum of the current and the voltage is minimized.
To adjust. The operation procedure of the minimization control means 11 will be described later.

As described above, the rotation speed of the motor 1 is set to the target value f.
Control that minimizes the current or power of the motor 1 while maintaining the output at ref and maintaining the same output is realized.

The above-described slip frequency control means 7 and addition means 8 constitute command frequency control means. Further, the minimization control means 11 constitutes a command voltage control means. The transistor control circuit portion of the command frequency control means, the command voltage control means, and the inverter circuit 2 can be constituted by a microcomputer.

FIG. 5 shows a configuration of a microcomputer implemented in the present invention. A central processing unit (CPU) 301 for performing arithmetic and logical operations; a read-only memory (R) storing instructions and data for controlling the CPU;
OM) 302, a read / write memory (RAM) 303 for storing calculation results and the like, a timer unit 304 capable of measuring an external pulse cycle and requesting an interrupt process to the CPU at regular intervals, and an external analog signal input It comprises an A / D converter 305, a three-phase PWM inverter control unit 306, and a data bus 307 for connecting these in a time-division manner. The three-phase PWM inverter control unit is a timing pulse for performing switching control of a power transistor or an IGBT which is a power switching control element of the inverter (in FIG. 5,
U, V, W and their inverted outputs).

In the following, a partially detailed operation principle will be described. First, a description will be given of a slip frequency detection portion based on the phase difference between the motor current and the applied voltage. According to the above-mentioned JP-B-63-34718, the torque current component Iτ and the exciting current component Im are calculated as follows from the currents (Iu, Iv, Iw) of the three lines driving the three-phase induction motor.

[0033]

(Equation 1)

A and b are the applied voltage axes after the three-phase / two-phase conversion.
This is a coefficient for coordinate conversion.

K is a proportional constant. Therefore, if the frequency is constant, Iu, Iv, and Iw each have a phase of (2/3) π
Since the signals are shifted and the same, another current can be calculated from only one current information. As a result, the torque current Iτ and the exciting current Im have the following relationship with the amplitude I of the primary current.

[0036]

(Equation 2)

Im = I · sin (θ) Iτ = I · cos (θ) Here, θ is the phase difference between the voltage and the current when the two-phase conversion is performed. It is the same as the phase difference of the current. Therefore, the excitation current Im and the torque current Iτ can be obtained by obtaining the phase difference between the current and the voltage. The slip frequency can be determined using the exciting current Im and the torque current Iτ. Similarly, according to JP-B-63-34718, the slip frequency fs is calculated by the following equation.

[0038]

(Equation 3)

Here, P is a differential operator, and T2 is a secondary time constant of the motor. However, when the frequency is not changing, the influence of the differential operator can be neglected, so that the slip frequency fs is determined by the torque current Iτ and the exciting current Iτ.
It can be calculated by dividing m by the product of the secondary time constant T2 and 2π.

Next, the operation of the minimization control section will be described. FIG. 4 is a control flowchart showing the operation principle of the minimization control means 11. In FIG. 4, the command frequency fref
Is not changed, the minimization control starts. In the minimization control, first, in step 201, a voltage obtained by subtracting the minute voltage ΔV from the previous output voltage VOLD is output as the output voltage of the inverter. In step 202, a time until the slip frequency compensation control based on the output voltage is stabilized is waited. Whether the slip compensation control is stable or not depends on the inverter output frequency and the torque current Iτ.
Actual rotation frequency obtained from the difference from the slip frequency calculated
It can be determined whether the numbers almost match . Alternatively, it is also possible to experimentally obtain the time until the slip compensation control is stabilized, and wait for a time slightly longer than the obtained time. When the slip frequency compensation control is stabilized, the current i or the power value supplied to the motor 1 is read in step 203 and stored in the variable A. Next, in the judgment 204, the magnitude of the current value of the variable A and the previous value AOLD are compared, and if the current value is small,
Proceed directly to step 206, if larger, step 20
In step 5, the polarity of the minute voltage ΔV is inverted, and the process proceeds to step 206. In step 206, the current voltage V
And the variable A are transferred as the previous value to prepare for the next time. When step 206 is completed, the process proceeds to step 201 again. By performing such processing, it is possible to drive the motor 1 with the current corresponding to the minute voltage ΔV or the minimum current or power that leaves a power fluctuation. Also,
By storing the voltage corresponding to the minimum current or the minimum power reached by this method as the optimum value at that frequency, even after the command frequency fref passes through a different frequency, the optimum voltage at that frequency is immediately reached. can do. Since the current information used in the minimization control means 11 is an alternating current, an amplitude value or an effective value is used. The means for using such a value corresponds to the amplitude detecting means 12 in FIG.

Next, the operation of the voltage drop correction means 15 will be described. Fig. 3 shows the current and voltage characteristics when the power control element IGBT is turned on. Takanashi et al. "3rd Generation Intelligent Power Module" Mitsubishi Electric Technical Report Vol. 67, No. 9, 1993, pp71 This is quoted from No. 11. That is, it can be seen that when the collector current Ic becomes 10 A or more, the ON voltage Vce (sat) increases substantially linearly. Therefore, when the collector current Ic is determined, Vce (sat) is also determined. On the other hand, since the collector current Ic corresponds to the motor current I1, if the motor current I1 is known, V
You will know ce (sat). This correspondence does not change depending on the environment, and can be fixed once the IGBT and PWM modulation frequencies are determined. Therefore, it can be easily realized by storing the result of the check in advance in the microcomputer.

The present invention is not limited to an air conditioner,
The present invention can be widely applied to devices equipped with an inverter to which the command frequency f1 and the command voltage V1 are input, such as an air compressor for producing compressed air and other power machines.

As is apparent from the above description, according to the present invention, no two current detecting means are required unlike the related art, and only a single current detecting means is provided even in a three-phase motor. In accordance with the installation environment conditions, high-precision and high-efficiency inverter control that always keeps power consumption to a minimum ,
The maximum capacity of the power control element can be
Can be reduced, and the device can be downsized.

In the above embodiment, the slip frequency is detected.
The method using the motor parameters.
However, if the motor speed can be directly detected,
Ability to perform slip compensation control using numerical information
Needless to say.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a motor applied voltage, power consumption, and a motor current.

FIG. 3 is a current-voltage characteristic diagram when the power control element is ON.

FIG. 4 is a flowchart showing a computer program of the embodiment shown in FIG. 5;

FIG. 5 is a block diagram of an embodiment in which the control system of the present invention is implemented by a computer.

FIG. 6 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

 1 Induction motor 2 Inverter 3 Current sensor V1 Command voltage f1 Command frequency

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshiteru Ito 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Kazuharu Yoshioka 1006 Odaka Kazama Kadoma, Osaka Matsushita Electric Industrial Co., Ltd. Inside the company (72) Inventor Hideo Ogata 4-5-2-5 Takaidahondori, Higashiosaka-shi, Osaka Matsushita Refrigerating Machinery Co., Ltd. (72) Izumi Yoshida 4-5-2-5 Takaidahondori, Higashiosaka-shi, Osaka Matsushita Refrigerating Machinery Co., Ltd. (72) Inventor Shusaku Watanabe 4-5-2-5 Takaida Hondori, Higashiosaka City, Osaka Matsushita Refrigerating Machinery Co., Ltd. (56) References JP-A-57-170092 (JP, A) JP-A-62-31393 (JP, A) JP-A-64-69960 (JP, A) JP-A-1-231687 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02P 5 / 408-5/412 H02P 7/628-7/632 H02P 2 1/00

Claims (1)

(57) [Claims] 1. A inverter control device of an induction motor driven by an inverter capable of changing the command voltage and command frequency, according to the current detecting means for detecting a current flowing through the motor
Based on the phase difference between the detection signal and the inverter output voltage
Calculating the exciting current and the torque current of the induction motor.
The current conversion means and the slip frequency based on the converted current value and the time constant of the motor.
Frequency calculating means for calculating the slip frequency, and comparing the calculated slip frequency with the command frequency of the inverter.
Means for additionally setting a drive frequency; current detecting means for detecting a current flowing through the motor; means for calculating electric power consumed by the motor based on a product sum of an inverter output waveform and the detected current; Power minimizing control means for minimizing the calculated power by adjusting the output voltage of the inverter; and current minimizing control means for minimizing the detection current by adjusting the output voltage of the inverter; When the detected current is equal to or less than a predetermined value, the output voltage of the inverter is adjusted based on the power minimizing control means. When the detected current is equal to or more than the predetermined value, the output of the inverter is controlled by the current minimizing control means. An inverter control device for adjusting a voltage.