JPH0732636B2 - AC output voltage control device for PWM inverter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC output voltage control device for an inverter when an induction motor is driven by a variable voltage variable frequency inverter that is digitally controlled at high speed. In the instantaneous space vector controller, the AC output voltage of the verter was open loop control, but this is closed loop control.

(Prior Art) The basic operation of an induction motor drive by an instantaneous space vector control inverter according to the present invention is described in "Instantaneous", Vol. 106, No. 1, page 9 of the Institute of Electrical Engineers of Japan, published in January, 1986. High-speed torque control method for induction motors based on slip frequency control ", but the basic principle is that of induction motors represented by space vectors. And the momentary generated torque is calculated as a vector product of the primary magnetic flux ₁ vector, and according to the deviation between this and the torque command T ^* and the deviation between the primary magnetic flux vector length φ ₁ and the magnetic flux command value φ ₁ ^* , in advance. The switching pattern of the inverter which is made into a table is selected, and the output voltage of the inverter is updated every moment to instantaneously control the instantaneous torque and the primary magnetic flux.

FIG. 2 is a block diagram of an example in which the control method described in the above paper is applied. The inverter 3 is composed of six arms, each of which is formed by connecting a switching element such as a transistor and a diode in antiparallel, but is illustrated in a simplified manner by three changeover switches Su, Sv, Sw in the figure.

The three-phase voltage type inverter 3 has a positive bus from the DC voltage source 1.
Power is supplied via 1a and the negative bus bar 1b, and the control circuit 7 causes the change-over switches Su, Sv, Sw of the inverter 3 to be positive and negative bus lines 1a, 1
The alternating voltage converted by falling to the b side passes through the current detectors 5u, 5v, 5w and the phase terminals u, v,
Powered to w. The voltage of the DC voltage source 1 is detected by a voltage detector 2 inserted between the positive and negative buses.

In this control method, the electromagnetic force is treated as an instantaneous vector represented by orthogonal dq2 axes. That is, the voltage supplied to the electric motor by the inverter Similarly the current And the current induced on the rotor side of the motor When ₁ primary magnetic flux of the stator side, It is represented by ₁ = φ ₁ d + jφ ₁ q. Here, j represents a vector product.

From the three-phase voltage Vu, Vv, Vw and the three-phase primary current iu, iv, iw, Can be calculated by the following equations.

The primary magnetic flux ₁ of the electric motor can be derived from the following equation.

Where R _{1 is the} primary winding resistance L _{11 is the} primary inductance R _{2 is the} secondary winding resistance L _{22 is the} secondary inductance M is the mutual inductance, where m is the rotational angular velocity and p is the differential operator.

The primary magnetic flux ₁ is by its definition Organizing the first line of the formula and the formula Integrate both sides That is, the primary magnetic flux ₁ of the induction motor is obtained by the integral calculation of the equation.

On the other hand, the instantaneous torque T is the primary magnetic flux ₁ obtained by the equation It is calculated as a vector product of and.

If the changeover switches Su, Sv, Sw forming the inverter 3 are respectively inclined to the positive bus 1a side by 1, and the negative bus side is indicated by 0, the three changeover switches Su, Sv, Swv are shown. There are 8 possible switch states depending on the combination of Sw. When is calculated from the equation, it is as shown in the following voltage vector table. However, the actual value of V ₁ d V ₁ q is the value in the table. And the voltage E of the DC voltage source 1 detected by the voltage detector 2 are multiplied.

When the switch state number for each combination of switch states is k as in the above voltage vector table, the inverter 3 in each switch state is Is in the same direction as the d-axis, as in the voltage vector diagram shown in FIG. And then proceed 60 degrees clockwise And two kinds There will be 8 types.

Blocks 701 and 703b included in the control circuit 7 of FIG.
Is the changeover switch Su, Sv, Sw state and the voltage E of the DC voltage source 1 detected by the voltage detector 2, Is a block for calculating.

Block 702 detected by current detector 5u, 5v, 5w 3
From the phase currents iu, iv, iw Is a block for calculating.

This in block 703a Multiplied by the primary winding resistance R ₁ at block 704 From the primary winding resistance R ₁ Subtract the product of and.

A block 705 is a block for integrating the magnetic flux according to an equation, and the d and q biaxial components of the primary magnetic flux ₁ are obtained.

A block 710 is a magnetic flux vector position detecting means, in which the clockwise rotation angle θ of the primary magnetic flux ₁ with respect to the d axis is 30 °, 90 °, 150 °, 210 °, 270 °, as boundaries. 330
The control flag fθ is generated in the following manner depending on which region is divided every 60 °.

−30 ° ≦ θ <30 °: fθ = 1 30 ° ≦ θ <90 °: fθ = 2 90 ° ≦ θ <150 °: fθ = 3 150 ° ≦ θ <210 °: fθ = 4 210 ° ≦ θ < 270 °: fθ = 5 270 ° ≦ θ <330 °: fθ = 6 The block 706 is a block for calculating the magnetic flux vector length φ _1, that is, the absolute value by the following equation.

Magnetic flux command value φ given from the outside in block 708
The deviation of the magnetic flux is calculated by subtracting the magnetic flux vector length φ ₁ from ₁ ^* .

A block 711 is a hysteresis comparator as a first comparing means, and when the deviation of the magnetic flux sent from the block 708 is positive and exceeds a predetermined value, that is, when it is necessary to increase the magnetic flux, fφ = + 1 is set, and the deviation of the magnetic flux is When the negative value exceeds a predetermined value, that is, when the magnetic flux needs to be reduced, fφ = -1.

A block 707 is a block that calculates a vector product of both outputs of the blocks 702 and 705 by an equation to calculate an instantaneous torque T. In block 709, the instantaneous torque T is subtracted from a torque command T ^* given from the outside to calculate the torque. Calculate the deviation.

A block 712 is a hysteresis comparator for the instantaneous torque T as the second comparing means, and has a structure of a multiple hysteresis comparator. When the torque deviation is within the predetermined error range, only the inner comparator operates, and when the torque deviation exceeds the predetermined error range such as when the external torque command T ^* suddenly changes, the outer comparator also operates. Then, when the deviation of the torque becomes small again, only the inner comparator operates. The inner hysteresis comparator generates a control flag f _T0 that selects between the zero vector and other voltage vectors, and the outer hysteresis comparator determines which torque, power or regeneration, should be generated. Generate a control flag f _T1 which selects which must be applied in the direction. Therefore, the voltage vector is selected by the combination of these two control flags f _T0 and f _T1 ,
The voltage vector as shown in the next torque control flag table is output.

A block 713 is a block for determining the most suitable inverter output voltage for each combination of the control flags fθ, fφ, f _T1 , f _T0 output from the blocks 710, 711, 712, and the control flag fθ, fφ, f _T1 , f _T0
According to the above, knowing the switch state number k shown in the above voltage vector table, and sending a switching signal to the inverter 3,
Instantaneous control of magnetic flux and torque is performed.

As described above in detail, according to such a magnetic flux calculation type control method, the primary magnetic flux _{1 at} each moment is calculated while the calculation is performed with almost no internal constant of the induction motor.
The magnetic flux vector length φ ₁ is kept substantially constant, and the Lissajous figure drawn by the magnetic flux vector components φ ₁ d and φ ₁ q draws a circle, and high-speed torque control can be performed.

(Problems to be Solved by the Invention) Generally, when an induction motor is driven at a variable speed by a variable voltage variable frequency inverter, it is usual to make the output AC voltage and the frequency have a proportional relationship. Even in the instantaneous space vector control inverter, by controlling the magnetic flux command value φ ^* to be constant, it is attempted to control the output AC voltage and the frequency in a comparative relationship. When the input power supply voltage is near, the output AC voltage is saturated, and the absolute value of the primary magnetic flux ₁ may not be the magnetic flux command value φ ^* .

For this reason, the required torque cannot be generated and the torque control of the electric motor cannot be performed.Therefore, when this type of PWM inverter is used with its AC output voltage near the input power supply voltage, some processing is required in advance. .

An object of the AC output voltage control device of a PWM inverter according to the present invention is to suitably control the output voltage by reducing the magnetic flux command value as necessary when necessary.

(Means for Solving the Problem) An AC output voltage control device for a PWM inverter according to the present invention calculates instantaneous values of magnetic flux and torque from voltage and current signals of a three-phase induction motor, and the absolute value of the magnetic flux vector is First comparing means for generating an increase / decrease signal of the magnetic flux so as to follow a given magnetic flux command within a predetermined tolerance, and detecting in which region of the region where the magnetic flux vector is evenly divided Magnetic flux vector position detecting means, and second comparing means for generating a torque increase / decrease signal so that the instantaneous value of the torque follows a given torque command within a predetermined allowable error. A variable voltage variable frequency PWM in which determines an inverter output voltage vector having an optimum increase / decrease magnetization / acceleration / deceleration vector component from a combination of output signals of the comparison means and the magnetic flux vector position detection means. In the AC output voltage control device for a barter, the means for estimating the AC voltage applied to the induction motor using the output signal of the second comparing means is compared with the estimated voltage and the AC voltage command value of the inverter. And a means for decreasing the magnetic flux command in accordance with the deviation when the estimated voltage is larger.

(Operation) If the AC voltage applied to the induction motor is Vm and its frequency is f, the absolute value of the primary magnetic flux φ _{1 of} the induction motor and Vm / f = k ₁ φ ₁ ... I have a relationship. Where k ₁ is a proportional constant. When this AC voltage Vm is saturated with the input power supply voltage of the inverter, the absolute value φ _{1 of the} primary magnetic flux cannot match the magnetic flux command value φ ^* .

As shown in Fig. 3, the voltage vector output from the inverter momentarily has the same absolute value and the direction differs by 60 °. And two kinds The average AC voltage output by the inverter is 6 types other than the zero vector. Depends on the amount of.

These six types _Are selected as shown in the voltage vector selection table by the combination of the control flags f _T0 and f _T1 generated in the second comparison means represented by block 712 in FIG. Therefore, the AC voltage applied to the induction motor can be estimated using the output signal of the second comparing means.

That is, the AC voltage output from the inverter is the AC voltage Vm applied to the induction motor.
Becomes higher as the amount of the zero vector output from the inverter decreases, so that the combination of the control flags f _T0 and f _T1 generated by the second comparison means Increases when any of the Is produced, a formula is created that decreases, and the AC voltage applied to the induction motor is estimated by this formula.

As you can see from the voltage vector selection table, Is output when both of the control flags f _T0 and f _T1 are both 1 or 0, and the control flag f _T0
And f _T1 is 1 on the one hand and 0 on the other hand, Is output. In other words, this is the control flag f _T0
And f _T1 has a relationship of f _T0 + f _T1 −1 = 0, Is output and the relation of f _T0 + f _T1 −1 ≠ 0 is satisfied, Means to output either of

On the other hand, from the equation, the AC voltage command value V _REF of the inverter can be obtained as V _REF = k ₁ fφ ^* …, but the AC voltage command value V _REF given to the control circuit in this way and the above-mentioned estimation formula The estimated AC voltage applied to the induction motor calculated from the above is compared, and when the estimated voltage is larger, the magnetic flux command value is decreased according to the deviation and used as the reference of the first comparison means. Thus, it is possible to obtain an AC output voltage control device for a PWM inverter that can smoothly control torque.

(Embodiment) FIG. 1 is a block diagram of an embodiment of an instantaneous space vector control inverter controller incorporating an AC output voltage controller for a PWM inverter according to the present invention. AC voltage command value V _REF as input to circuit 7
Is added, and blocks 714 to 718 are added, and the other points are the same as those in FIG. 2 and only different points will be described in detail below.

A block 714 is a second comparison means, and a control flag f _T0 and f t which are calculated by the block 712 and are sent to the block 713 every moment.
_T1 is input in parallel to calculate f _T0 + f _T1 −1 = A ... And the calculation result A is sent to the block 715. As mentioned above, | A | is either 1 or 0. The nth operation result is represented by | A | n with a letter n. | A | n = 0
It can be determined that the inverter 3 generates a zero vector when, and the inverter 3 generates a non-zero voltage vector when | A | n = 1.

The block 715 receives the output of the block 714 and estimates the AC voltage Vm applied to the induction motor by the arithmetic expression represented by the variable f (| A |) of the variable | A |.

f (| A |) n = f (| A |) n- _1- kf (| A |) n- ₁ + K | A | n Here, k and K are constants having the following relationship.

k = 1-K, 0 <k << 1 That is, the formula is a recurrence formula and is the nth solution f
(| A |) n is the previous time, that is, the (n-1) th solution f (|
A |) n _-1 and this time, that is, the nth | A | n.

The calculation result of the formula decreases when information | A | n is 0, and gradually increases when it is 1, no matter how continuously 1 is given, it is saturated at kf (| A |) n _-1 = K To do. That is, the saturated value f (| A
|) _MAX is f (| A |) _MAX = K / k (1-k) / k, and when this value exceeds the AC voltage command value V _REF, we want to lower the specified magnetic flux value φ ^*. , If k = 1 / (V _REF +1) is given, the purpose can be achieved. The initial value f (| A |) ₀ of the recurrence formula f (| A |) n is of course set to 0.

The calculation result of the block 715 is sent to the block 716 every time.
In block 716, the AC voltage command value V _REF is subtracted from the information from block 715 and sent to block 717.

In block 717, if the information obtained from block 716 is positive,
That is, only when the estimated value of the AC voltage applied to the induction motor is larger than the AC voltage command value V _REF , the value proportional to the deviation value is arithmetically output and sent to the block 718. However, the value sent to this block 718 is limited to a predetermined value.

In block 718, the signal from block 717 is subtracted from the magnetic flux command value φ ^* and the result is sent to block 708.

The signal sent from this block 718 becomes the magnetic flux command value with which the block 711, which is the first comparison means, serves as a reference.

As described above, in the present embodiment, when the inverter needs switching for some reason due to the AC output voltage that cannot be output, the reference magnetic flux amount is reduced and it is possible to escape from this state. it can.

(Effects of the Invention) As described in detail with reference to the above-described embodiment, in the instantaneous space vector control device for selecting and outputting the instantaneous voltage vector by the first comparing means by the magnetic flux calculation and the second comparing means by the torque calculation, The AC output voltage of the inverter can be estimated without attaching an analog voltage detector to the main circuit output, and the AC output voltage of the inverter can be controlled by controlling the magnetic flux command value based on the estimation result. .

By incorporating the device of the present invention in a part of the system, the work of changing the magnetic flux command value by adjustment in the related art can be omitted, and further, the torque pulsation due to the output voltage saturation can be prevented in advance. became.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a controller for an instantaneous space vector control inverter incorporating an AC output voltage controller for a PWM inverter according to the present invention, and FIG. 2 is an instantaneous torque / flux control system for a conventional induction motor. FIG. 3 is a block diagram of an example, and FIG. 3 is an output voltage vector diagram of the inverter. 1 ... DC voltage source, 1a ... Positive bus 1b ... Negative bus, 2 ... Voltage detector 3 ... Inverter, 5u, 5v, 5w ... Current detector 6 ... 3-phase induction motor, 7 ... Control circuit

Claims (1)

[Claims] 1. An instantaneous value of a magnetic flux and a torm is calculated from a voltage and current signal of a three-phase induction motor, and an absolute value of the magnetic flux vector is controlled so as to follow a magnetic flux command given within a predetermined tolerance. First comparing means for generating an increase / decrease signal, magnetic flux vector position detecting means for detecting in which of the areas where the magnetic flux vector is divided into equal circles, and instantaneous value of the torque has a predetermined permissible error. Second, which generates a torque increase / decrease signal so as to follow the torque command given in
A variable voltage variable frequency PWM inverter having a comparison means and determining an inverter output voltage vector having an optimum increase / decrease magnetization and acceleration / deceleration vector component from a combination of output signals of the first and second comparison means and the magnetic flux vector position detection means. In the AC output voltage control device, means for estimating the AC voltage applied to the induction motor using the output signal of the second comparing means and the estimated voltage are compared with the inverter AC voltage command value to make the estimation. An AC output voltage control device for a PWM inverter, comprising means for reducing the magnetic flux command according to the deviation when the voltage is larger.