JPH02197284A - Speed control method for induction motor - Google Patents

Abstract

PURPOSE:To eliminate necessity of a speed sensor by estimating current angular speed based on the vector ratio of current obtained from the voltage phase value and the current/voltage phase difference value in a three-phase inverter for driving an induction motor and a vector control circuit. CONSTITUTION:Average value Id of DC current to be fed from a DC power source 2 into a PWM three-phase inverter 3 is detected then it is divided by an inverter control rate mu and the phase difference theta against a command current i is operated 6. Then the phase difference theta and the voltage phase thetav are added together to operate 7 a vector ratio i1beta/i1alpha so as to estimate 8 a slip angular speed omegas. Primary angular speed omega0 is added to the estimated slip angular speed omegas thus determining an estimated rotary angular speed omegar. The primary angular speed omega0 is determined by adding a slip angular speed command omega obtained through a slip angular speed operating circuit 16 to a commanded rotary angular speed omega. By such arrangement, current angular speed can be estimated without requiring speed sensor resulting in facilitation of speed control.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for controlling the speed of an induction motor using vector control, and particularly to a method for controlling the speed of an induction motor without using a speed sensor.

B. Summary of the Invention The present invention provides a speed control method for an induction motor using vector control, in which a vector ratio of current is calculated from a voltage phase value and a current/voltage phase difference value, and the current angular velocity is estimated based on the vector ratio. As a result, it can be easily configured with hardware equivalent to a general-purpose inverter.
Furthermore, the present invention discloses a technique that eliminates the need for a speed sensor.

C1 Conventional technology Induction motor (hereinafter referred to as I)
V/F control is an example of a method for controlling the speed of the motor (abbreviated as M) without a speed sensor, but torque control is nonlinear and speed responsiveness is poor. Furthermore, the speed accuracy is poor, and an error equal to the slip frequency occurs.

Therefore, as a method for linearizing IM torque control and improving responsiveness, the following vector control method is used. The vector control method will be explained below.

The equation of the voltage of the IM is expressed in two-axis coordinates (α and β axes) rotating in synchronization with the -modal speed ω0. However, υ
, α and υ1β are α-β axis-order voltages, j, α, i, β are α-β axis-order currents, λ2α and λ, β are α-β
Shaft secondary magnetic flux, ω0 is primary angular velocity, ωr is rotor angular velocity,
R1 and R2 are primary and secondary resistances, Ll and L2 are primary and secondary inductances, and M is excitation inductance.

In addition, Lδ and P are Lσ−(Ll ・L 2−M2)
/L 2P=d/cat.

” In Equation (1), the slip angular velocity ωS is ωs−i+
o−ωr= (itβ/iu)×(1/+, )−(2)
However, τ2 is a quadratic time constant, τ2=L2/R2, and]
, α are constant, the secondary magnetic flux is λ, α−M i +
α, λ, β−〇 ・・・・・・・・・(3),
The torque T is T=M/L2(λ2α・i, β−λ2β・ilα−M2
/L2・11α・11β ...(4),
The torque is proportional to the primary current 11β.

The above is the principle of vector control, and the rotor angular velocity ωr is detected, and ω0 is determined and controlled by equation (2).

D0 Problems to be Solved by the Invention The vector control method described above generally requires a speed sensor, but a control method based on this method that does not require a speed sensor has also been proposed in Japanese Patent Application No. 63-39811, etc. ing.

However, in the above proposal, it is necessary to detect two phases of the IM line current in order to eliminate the need for a speed sensor, and the control calculations are also complicated. There was an issue that required the following.

The present invention was created in view of these problems, and
The object of the present invention is to provide an IM speed control method that can be easily configured with hardware such as a general-purpose inverter used in conventional V/F control methods and does not require a speed sensor.

E. Means for Solving the Problems The means for solving the above problems in the present invention is to interpose a three-phase inverter and its vector control circuit between the induction motor and the DC power supply, and to connect the vector control circuit to the rotor. In a speed control method for an induction motor that commands angular velocity, a current vector ratio is calculated from a voltage phase value and a current/voltage phase difference value, and the current angular velocity is estimated based on the vector ratio.

In the F action vector control method, the -order voltage is applied based on the following equation.

The value marked with an asterisk (*) indicates the command value, and since the current is controlled to flow according to the command value, the rapidity values ωr and ω
By controlling S as ω0-ωr+ωS*, the torque T can be controlled in proportion to the current command value 11β.

By the way, if we do not use a speed sensor, it is impossible to determine ωO because ωr is unknown, and control becomes impossible. However, if we can estimate the slip angular velocity ωS when an arbitrary modulus velocity ω0 is given, then (2) From the formula, Δl\ωr-ω0-ωS (7) can be obtained. Note that the values marked with a square mark indicate estimated values.

In the case of hector control using a control voltage source that applies a primary voltage according to equation (6), even if an error occurs in the estimated value of the rotor speed, the change in the secondary magnetic flux λ2 is small, and the change in i lα is also small. Therefore, the estimated value of the slip angular velocity ωS is obtained by the following equation.

Cω5-(Lβ/itα)X(1/τ2)...(8
) Therefore, if the current vector ratio i, β/++α can be determined, ωS can be estimated, the rotor angular velocity ωr can be obtained, and control according to equations (5) and (6) becomes possible.

Figure 2 shows the current vector ratio i3β/ which is the principle of the present invention.
11 is an explanatory diagram showing a calculation method of 11α. FIG. In the same figure *, each phase angle regarding the current 11 when the primary voltage υ1 of the α-β axis is applied is as follows, and from these formulas, hβ/1, α is 11
β/i, a-tan φ1 -tan (φυ-θ) ... (10).

Here, φυ is known because it is a command value, and if the phase difference value (power factor angle) θ between the -order voltage and current is known, i, β/i, α
, it becomes possible to estimate ωr.

G. Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and shows a speed control circuit applied to a three-phase PWM inverter of the IM control circuit shown in FIG. First, to explain the overall configuration of Fig. 3, 31 is an IM, 32 is a DC power supply, 33 is a 3-phase PWM inverter, 34 is a PWM control circuit, υa, υb
, υC is the phase voltage, i a, i b, i c are the line currents, E
d is a DC voltage, Id is a DC current (average value), and these are the equations. Here, if the phase difference (power factor angle) between voltage and current is θ, the DC current Id is Id・3μ/π・i, cos θ...
(12). Here, the PWM control rate μ is expressed as *μ−υ+/(Ed/2).

If the phase difference value θ is substituted by Equation (12), the phase difference value θ can be calculated by simply detecting the DC current Td, and the slip angular velocity ωS can be estimated using Equations (8) and (10). Δωr is obtained from equation (7), and vector control becomes possible using equations (5) and (6). Since i is the peak value of the IM line current,
The peak value may be detected and calculated from the I-phase current.

FIG. 1 shows an embodiment of the present invention applied to the three-phase PWM inverter of the IM control circuit shown in FIG. 3, and embodies the progression of each of the above equations. In the figure, 1 is IM, 2 is DC power supply,
3 is a three-phase PWM inverter, 4 is a DC current detection circuit, and 5 is a 3-phase PWM inverter.
6 is a PWM control control rate division circuit, 6 is a phase difference calculation circuit,
7 is a vector ratio calculation circuit, 8 is a slip angular velocity estimation circuit, 9
is a PI calculation circuit, 10 is a command current calculation circuit, 11 is a command voltage coordinate calculation circuit, 12 is a voltage phase calculation circuit, 13 is a command voltage calculation circuit, 14 is a command voltage coordinate conversion circuit, and 15 is a control rate calculation of PWM control. The circuit 16 is a slip angular velocity calculation circuit.

* * Here, the -next color speed ωO is set to the set value ωr and ωS△
The control is performed by estimating ωS and finding ωr.

After the DC current detection circuit 4 detects the DC current 1d, and the control rate division circuit 5 divides Id/μ, the phase difference calculation circuit 6 calculates the phase difference θ using equation (13). If this phase difference θ is subtracted from the voltage phase Φυ, the current phase becomes Φi, and the vector ratio calculation circuit 7 calculates 11β/
X+α is obtained, and the slip angular velocity estimating circuit 8 calculates the estimated value ωS of the slip angular velocity using equation (2).

The PI calculation circuit 9 calculates i, from the error er between the set value and the estimated value.
, 8*, which outputs ・・・−・・＊−・2゜△
* - ωS - ωS. When the slip changes and ωr changes due to a change in the load on the IM, the set value ωS deviates from ωS of 1M, resulting in -order flow 1. As β changes and the DC current 1d changes, the estimated value ωS changes. This generates the error er, and the ΔPI calculation circuit 9 operates so as to eliminate this error er (enter the state of ωS*ωS), and controls the speed* of the IM to the set value 01.

The command current calculation circuit 10 calculates 1* using equation (14) and inputs it to the phase difference calculation circuit 6.

The command voltage coordinate calculation circuit 11 calculates * by equation (5).
* υ, α and υ1β are output and input to the voltage phase calculation circuit I2 and the command voltage calculation circuit 13. Voltage phase calculation circuit 1
2 calculates the voltage phase φυ using equation (9), and the command voltage calculation circuit 13 calculates v, (1” ” + IJ + l
Calculate υ1 as the square root of I'*, and convert it to command voltage coordinate conversion circuit 1.
4 calculates equation (11) using these and outputs the command voltages υE and υb1υC. The command voltage* output υ of the arithmetic circuit 13 is also input to the control rate calculation circuit I5, and the control rate μ-υ, /(Ed/2) is calculated. The slip angular velocity calculation circuit 16 is (6)*
* ωS is output according to the formula, and ω0 is given to the command voltage coordinate conversion circuit 14 by the sum with the set value ωr.

Thus, in embodiments of the present invention, the I
The torque of M can be controlled linearly with respect to the current command value, p *, and furthermore, by estimating the speed without a speed sensor, speed control with good responsiveness is realized. Furthermore, since the speed is estimated by obtaining the phase difference (power factor angle) θ by detecting only the DC current, no motor current detection means or the like is required, and the hardware becomes simple.

Even in conventional V/F control hardware that uses a general-purpose inverter, it is common to install a DC current detection circuit for fault current detection, so it is possible to use similar hardware to achieve accurate speed control without a speed sensor. becomes possible.

As explained in detail about the H9 invention, according to the present invention, an IM that can be easily configured with hardware equivalent to the general-purpose inverter used in the conventional ■/F control method and does not require a speed sensor.
speed control method can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a detailed explanatory diagram of the present invention, and FIG. 3 is a block diagram of an IM control circuit. ■, 31・Induction motor, 2, 32...DC power supply, 33
33-phase PWM inverter, 4. DC current detection circuit, 5.
... PWM control control rate multiplier circuit, 6... Phase difference calculation circuit, 7... Vector ratio calculation circuit, 8... Sliding angular velocity estimation circuit, 9... PI calculation circuit, 10 Command current calculation circuit,
II... Command voltage coordinate calculation circuit, 12... Voltage phase calculation circuit, 13... Command voltage calculation circuit, 14... Command voltage coordinate conversion circuit, 15... Control rate calculation circuit, 16...
・Sliding angular velocity calculation circuit. Outside 2 people q Mi U

Claims (1)

[Claims] (1) In an induction motor speed control method in which a three-phase inverter and its vector control circuit are interposed between the induction motor and a DC power source, and the vector control circuit is commanded to control the angular velocity of the rotor, the voltage phase value and current /A method for controlling the speed of an induction motor, characterized in that a vector ratio of current is calculated from a voltage phase difference value, and a current angular velocity is estimated based on the vector ratio.