JPH02206384A - Ac output voltage control system for pwm inverter - Google Patents

Abstract

PURPOSE:To enable smooth torque control by providing a first comparing means for carrying out flux operation and a second comparing means for carrying out torque operation then comparing an estimated AC voltage to be applied onto an induction motor with an inverter AC voltage command value thereby regulating a flux command. CONSTITUTION:First comparing means 711 for producing a flux increment/ decrement signal so that the absolute value of flux vector follows to a flux command provided within a predetermined allowable error, and second comparing means 712 for producing a torque increment/decrement signal so that instantaneous value of torque follows to a torque command provided within a predetermined allowable range are provided. AC voltage to be applied onto an induction motor 6 is estimated through utilization of an output signal from the second comparing means 712, then the estimated voltage is compared with AC voltage command value VREF, of an inverter 3, and if the estimated voltage is higher than VREF the flux command is reduced according to the difference. By such arrangement, smooth torque control can be carried out with reference to the first comparing means 711.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an inverter AC output voltage control method when an induction motor is driven by a high-speed digitally controlled variable voltage variable frequency inverter. In the instantaneous space vector control method, the AC output voltage of the inverter was controlled in an open loop, but this is now controlled in a closed loop. “ (Prior art) The basic operation of driving an induction motor by the instantaneous space vector control inverter according to the present invention is described in “IEEJ Transactions B, Volume 106, No. 1, Page 9 et seq. The basic principle is expressed as the vector product of the primary current iI of the induction motor and the primary magnetic flux φ1 vector expressed as a space vector. Calculate the instantaneous generated torque, select a pre-tabled inverter switching pattern according to the deviation between this and the torque command T'', and the deviation between the primary magnetic flux vector length φ1 and the magnetic flux command value φI9, and select the inverter switching pattern. The output voltage of the magnet is updated every moment to instantaneously control the instantaneous torque and primary magnetic flux.

FIG. 2 is a block diagram of an example to which the control method described in the paper is applied. The inverter 3 is composed of six arms each having a switching element such as a transistor and a diode connected in antiparallel, but is simplified in the figure by three changeover switches S1°Sv, Sw.

The three-phase voltage type inverter 3 is supplied with power from the DC voltage 'tA1 via the positive bus 1a and the negative bus 1-b, and the control circuit 7 controls the changeover switches 5urSv, S of the inverter 3.
, are turned to the positive and negative bus lines 1a, lb, and the converted AC voltage is supplied to each phase terminal u, v, w of the three-phase induction motor 6 via the current detectors 5u, 5v+5 collar. 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, electromagnetic force is handled as an instantaneous vector expressed by two orthogonal d-q axes. That is, the primary voltage Vl+
Similarly, if the current is the primary current i, and the current induced on the rotor side of the motor is the secondary current 12 + the primary magnetic flux on the stator side is φ, then Vl = V1d + J Vlq i, = ild + j It is expressed as i+Q iz=izd + j izQ φ1 =φId+j φ+Q. Here, j represents a vector product.

From iv and iw, the primary voltage V and primary current 11 can be calculated using the following equations.

Rearranging the first line of formula ■ and formula ■, Vl Rti+=Pφ1...
・■ That is, the primary magnetic flux φ1 of the induction motor is obtained by the integral calculation of equation (■).

Primary winding resistance Primary inductance Secondary winding resistance Secondary inductance Mutual inductance θ, is the rotational angular velocity, p is the differential operator. φ+ = Lz
L ten years old.

. . . ■ It is determined by equation (■) as a vector product of the bundle φ1 and the primary current 11.

T=φ1 X1l=φ, dXi, q-φ, qxi, cl
・＋・■Each changeover switch S that constitutes the inverter 3
u.

The case where Sv, S, respectively fall to the positive generatrix la side is 1
If the case of falling to the negative bus side is expressed as 0, eight switch states can be created from the combination of the three changeover switches Su, Sv, and S. The output voltage vector of the inverter 3 in these switch states is When v1 is calculated from equation (2), it is as shown in the following voltage vector table. However, the actual value of La Vl (l) is the value obtained by multiplying the numerical value in the table by f ten thousand and the voltage E of the DC voltage source 1 detected by the voltage detector 2.

From the voltage vector table voltage E of the DC voltage source 1 detected by the voltage detector 2,
This is a block that calculates the primary voltage vl using equation (2).

A block 702 is a block that calculates the primary current i1 from the three-phase currents iIl+IW+1M detected by the current detectors 5u, 5v, and 5- using the formula (2).

In block 703a, a primary winding is applied to this primary current i1.As shown in the voltage vector table above, when the switch state number for each combination of switch states is k, the output voltage v1(9) of the inverter 3 in each switch state is:
As shown in the voltage vector diagram shown in Figure 3, there are two types of zero vectors: v, Q) in the same direction as the d-axis, and v + (2) to v I (6) that proceed clockwise by 60''. There are eight types: L(0) and v + (7).

Blocks 701 and 70 included in the control circuit 7 in FIG.
3b subtracts the product of the primary winding resistance R1 and the primary current i from the changeover switch Su, Sv, Sw states and V.

Block 705 is a block that performs an integral calculation of the magnetic flux according to equation (2), and both d and q axis components of the first-order flux φ are obtained.

Block 710 is a magnetic flux vector position detecting means, and here, the rotation angle θ of the primary magnetic flux φ1 in the clockwise direction with respect to the d-axis is 30°, 906150°, and 21 as boundary lines.
The control flag fθ is generated as follows depending on which region partitioned by 60 degrees of 0', 270 degrees, and 330 degrees it belongs to.

-30"-e<30': f13=13
0°≦θ<90': fθ=290″≦θ<
150": f θ=3150"≦θ<
210" ・ fθ=421O@≦θ<270@
: fθ=5270@≦θ<330” ・fθ=6 The block 706 is a block that calculates the magnetic flux vector length φ, that is, the absolute value using the following equation.

φr=fr7−roLq” 06. ■Magnetic flux command value φ given from the outside in block 708,
The magnetic flux vector length φ1 is subtracted from ' to calculate the magnetic flux deviation.

Block 711 is a hysteresis comparator as a first comparison means, and when the deviation of the magnetic flux sent from block 708 is positive and exceeds a predetermined value, that is, when it is necessary to increase the magnetic flux, fφ=+1, and the deviation of the magnetic flux is When it is negative and exceeds a predetermined value, that is, when it is necessary to reduce the magnetic flux, rφ is set to −1.

Block 707 is a block that calculates the instantaneous torque T by calculating the vector product of both outputs of blocks 702 and 705 using equation (2), and in block 709, the instantaneous torque T is subtracted from the torque command T''1 given from the outside.
Calculate the torque deviation.

Block 712 is a hysteresis comparator for the instantaneous torque T as a second comparison means, and has a structure of a multiple hysteresis comparator. When the torque deviation is within a 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 T8 suddenly changes, the outer comparator also operates. , when the torque deviation becomes small again, only the inner comparator starts operating. This inner hysteresis comparator generates a control flag rye that selects between the zero vector and other voltage vectors,
The outer hysteresis comparator generates a control flag f□ which selects whether forward or regenerative torque should be generated, that is, in which direction the instantaneous slip frequency should be applied. Therefore, a voltage vector is selected by a combination of these two control flags f to and f 71, and a voltage vector as shown in the following torque control flag table is output.

The torque control flag table block 713 shows each control flag fθ, fφ, fr=, which is output from blocks 710, 711, and 712.
ft. This block determines the inverter output voltage that passes most through each combination of , and selects the control flags fθ, fφ+ 'a, + f from the voltage vector l-/selection table shown below.
T. Accordingly, the switching state number k shown in the voltage vector table is known, and a switching signal is sent to the inverter 3 to perform instantaneous control of magnetic flux and torque.

As explained above in detail, according to such a magnetic flux calculation type control method, the first-order flux φ1 at each instant is calculated while hardly using the internal constants of the induction motor.
By keeping the magnetic flux vector length φ substantially constant, the Lissajous figure drawn by the magnetic flux vector component φld+φ+Q is approximately circular, and high-speed torque control can be performed.

(Problems to be Solved by the Invention) Generally, when an induction motor is driven at variable speed by a variable voltage variable frequency inverter, the output AC voltage and the frequency are usually in a proportional relationship. In the instantaneous space vector control inverter, the output AC voltage and frequency are controlled in a comparative relationship by controlling the magnetic flux command value φ0 as a constant, but as the frequency increases, the output AC voltage becomes lower than that of the inverter. When it comes to around the input power supply voltage, the output AC voltage becomes saturated, and the absolute value of the primary magnetic flux φ cannot become the magnetic flux command value φ1.

For this reason, the necessary torque cannot be generated and the torque of the motor cannot be controlled. Therefore, if this type of PWM inverter is used with its AC output voltage close to the input power supply voltage, some processing is required in advance. .

The AC output voltage control method of the PWM inverter according to the present invention aims to suitably control the output voltage by reducing the magnetic flux command value by the necessary amount when the need arises.

(Means for Solving the Problems) The AC output voltage control method of 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 calculates the absolute value of the magnetic flux vector. a first comparing means for generating a magnetic flux increase/decrease signal so as to follow a given magnetic flux command within a predetermined tolerance; and detecting in which region the magnetic flux vector exists among the regions equally dividing the circumference. a magnetic flux vector position detecting means for detecting the position of the magnetic flux vector, and a 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 tolerance; In the AC output voltage control method of a variable voltage variable frequency PWM inverter that determines an inverter output voltage vector having an optimal increase/demagnetization and acceleration/deceleration vector component from a combination of output signals of a comparison means and a magnetic flux vector position detection means, the second comparison The AC voltage applied to the induction motor is estimated using the output signal of the means, and this estimated voltage is compared with the AC voltage command value of the inverter, and if the estimated voltage is larger, the voltage is adjusted according to the deviation. The magnetic flux command is reduced by the magnetic flux command.

(Function) If the AC voltage applied to the induction motor is 2, and its frequency is f, then the absolute value φ1 of the first-order flux of the induction motor and the distance between them is V, /f=, φ1 ・...There is a relationship of ■. Here, is the proportionality constant. This AC voltage V
, becomes saturated with the input power supply voltage of the inverter, the absolute value φ1 of the first-order flux cannot match the magnetic flux command value φ0.

As shown in Fig. 3, the voltage vectors that the inverter outputs from time to time are of eight types: zero vectors v r (0) and v , (7) with equal absolute values and a direction of 60°.
Determined by

is a control flag f, generated in the second comparison means represented by block 712 in FIG. and rtt are selected as shown in the voltage vector selection table. Therefore, the AC voltage applied to the induction motor can be estimated using the output signal of the second comparison means.

That is, the AC voltage output by the inverter is the AC voltage V applied to the induction motor, and this AC voltage V increases as the amount of zero vector output by the inverter decreases. Therefore, the voltage vector v+
Create a formula that increases when any of (1) to v, (6) is output, and decreases when the zero vector v, (0) or v, (7) is output, and by this formula, the induction motor Estimate the AC voltage applied to

As can be seen from the voltage vector selection table, any of the voltage vectors v + (1) to v r (6) is output when both the control flag f7° and fTI are 1 or O. In this case, the control flag f7° and the zero vector v 1 (0) or v , (7) are output.

In other words, if the control flag tTo and f7I have a relationship of f7゜+fy+1=0, then the zero vector v, (0) or v
, (7) is output, and if there is a relationship of fto+f□-1≠0, the voltage vector v+(1)~v,
(6) means to output one of the following.

On the other hand, from equation (■), the AC voltage command value of the inverter V II
,, is VIIEF = kt f φ”
-@), but by comparing the AC voltage command value V When the estimated voltage is larger, the magnetic flux command value is decreased in accordance with the deviation and used as a reference for the first comparing means, thereby obtaining an AC output voltage control method for a PWM inverter that allows smooth torque control. be able to.

(Embodiment) Fig. 1 is a block diagram of an embodiment of a control device for an instantaneous space vector control inverter that incorporates the AC output voltage control method of a PWM inverter according to the present invention, and the differences from Fig. 2 are as follows. , AC voltage command value V as input to the control circuit 7
In addition to adding IIEF, 7'otsuku 714-71
8 is added, and the rest is the same as in FIG. 2, so only the different points will be described in detail below.

Block 714 is a control flag f? which is calculated every moment by block 712 which is a second comparison means and sent to block 713. . and fTI are input in parallel, fyo ten fTI
1=A...
・Calculate ■ and send the calculation result A to block 715. As mentioned above, IAI is either 1 or O. The n-th calculation result is represented by A7 with a leg half n added. It can be determined that the inverter 3 generates a zero vector when A = O, and that the inverter 3 generates a non-zero voltage vector when IAI = 1.

Block 715 receives the output of block 714 and calculates AC voltage V to be applied to the induction motor according to an arithmetic expression represented by a function f(A'') of variable A.

Estimate.

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

For k=1−, 0<k<1, that is, 2〇 is a recurrence formula, and the nth solution f(
IAI), is the previous solution, that is, the n-1th solution f
(A)−+ and this time, that is, the nth information A
, , and.

The calculation result of 2〇 is information (decreases when A17 is O,
1, it gradually increases, but no matter how continuously ■ is given, it saturates at kr (A)n-1=K. That is, the saturated value f (
IAI)□8 is f(A)□, = to/to = (1-k)/,
Since we want to lower the magnetic flux command value φ9 when this value exceeds the AC voltage command value VIItF, k = 1.
/ (VIIEF + 1), the objective can be achieved. The initial value f(A) of the recurrence formula f(A). Of course, set it to O.

The calculation result of block 715 is sent to block 716 each time. In block 716, the AC voltage command value vtttr is subtracted from the information from block 715.
Send to 7.

In block 717, if the information obtained from block 716 is positive, that is, the estimated value of the AC voltage applied to the induction motor is the AC voltage command value Vllll! Only when it is larger than F, a value proportional to the deviation value is calculated and output, and block 718
send to However, the value sent to this block 718 is limited to a predetermined value.

In block 718, from magnetic flux command value φ9, block 717
The signal is subtracted and sent to block 708.

The signal sent from this block 718 becomes the magnetic flux command value that is referenced by block 711, which is the first comparing means.

As described above, in this embodiment, if switching is required for an AC output voltage that the inverter cannot output for some reason, it is possible to escape from this state by reducing the amount of magnetic flux as a reference. can.

(Effects of the Invention) As described above in detail with one embodiment, in the instantaneous space vector control method in which an instantaneous voltage vector is selected and output by the first comparison means based on magnetic flux calculation and the second comparison means based on torque calculation, The AC output voltage of the inverter can be controlled by making it possible to estimate the AC output voltage of the inverter without attaching an analog voltage detector to the main circuit output, and by controlling the magnetic flux command value based on the estimation result. can.

By incorporating the method of the present invention into a part of the system, it is possible to omit the conventional work of changing the magnetic flux command value by adjustment, and it is also possible to prevent torque pulsation due to output voltage saturation. became.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of a control device for an instantaneous space vector control inverter incorporating the AC output voltage control method of a PWM inverter according to the present invention, and Fig. 2 is a conventional induction motor instantaneous torque and magnetic flux control system. An example of a block diagram, FIG. 3 is an output voltage vector diagram of an inverter. 1...DC voltage Rla...Positive bus line

Claims (1)

[Claims] 1. Calculate the instantaneous values of magnetic flux and torque from the voltage and current signals of the three-phase induction motor, and generate a magnetic flux increase/decrease signal so that the absolute value of the magnetic flux vector follows the given magnetic flux command within a predetermined tolerance. a magnetic flux vector position detecting means for detecting in which area the magnetic flux vector exists among areas equally divided on the circumference; The second comparison means generates a torque increase/decrease signal so as to follow the given torque command, and the optimum increase/demagnetization and acceleration/deceleration are determined from the combination of the output signals of the first and second comparison means and the magnetic flux vector position detection means. In an AC output voltage control method of a variable voltage variable frequency PWM inverter that determines an inverter output voltage vector having a vector component, the AC voltage applied to the induction motor is estimated using the output signal of the second comparing means, An AC output voltage control method for a PWM inverter, characterized in that an estimated voltage and an inverter AC voltage command value are compared, and if the estimated voltage is larger, the magnetic flux command is decreased in accordance with the deviation.