JP5131725B2 - Control device for power converter - Google Patents

Description

  The present invention relates to a control device for a power converter for driving an AC motor at a variable speed, and more particularly to a control device for suppressing a motor current to a predetermined value or less.

In general, when an electric motor is driven at a variable speed using a power converter, it is desired by the user that the power converter continues to operate as much as possible regardless of the situation. However, when the motor is suddenly accelerated or decelerated or when the load changes suddenly, an excessive current flows through the power converter, so it is necessary to increase the current rating of the power converter in anticipation of this, and the high cost of the device There arises a problem of increasing the size and volume.
In order to solve this problem, conventionally, for example, a method described in Patent Document 1 is used to suppress an increase in motor current.

Below, the prior art described in patent document 1 is demonstrated.
FIG. 8 is a block diagram for performing current limitation of the voltage-type PWM inverter described in the above document. In the figure, 301 is a DC power source, 302 is a three-phase voltage type PWM inverter comprising transistors Tr _{1 to} Tr ₆ and freewheeling diodes D _{1 to} D ₆ , and IM is a three-phase induction motor as a load.

The inverter 302 performs well-known V / f (voltage / frequency) constant control. That is, based on the frequency set value set by the frequency setter 307, the output voltage command value of the inverter 302 is generated by the voltage command value calculation circuit 308. This voltage command value is input to the PWM pattern generation circuits 309 to 311 for each phase (U, V, W phase), and is compared with the carrier waveform 312 by the adder / subtractor 309b and the comparator 309c, and PWM for the transistors of the upper and lower arms of each phase. A signal is generated. Reference numeral 309d denotes a sign inverter.
Control is performed so that the output voltage of the inverter 302 matches the command value by driving the transistors Tr ₁ to Tr _{6 in} accordance with the PWM signal.

Here, the output current of the inverter 302 is limited as follows.
Each phase output current of the inverter 302 is detected by a current detector 303, and deviations exceeding the current limit value are detected together with their polarities by coefficient units 304 to 306 having dead zones corresponding to current limit values. This deviation is input to the adder / subtractor 309a in the PWM pattern generation circuits 309 to 311 of each phase, and acts as an offset with respect to the output voltage command value, thereby correcting the output voltage command value.

For example, when the current of each phase exceeds a positive limit value (the direction in which the current flows from the inverter 302 toward the motor IM), the output voltage command value is corrected by a negative offset via the coefficient units 304 to 306. Then, control is performed in the direction of decreasing the positive current, and the current is decreased by turning off the upper arm transistor of the phase. On the contrary, when the current of each phase exceeds the negative limit value, the output voltage command value is corrected by the positive offset via the coefficient units 304 to 306, and the control works in the direction of decreasing the negative current. Thus, the current is decreased by turning off the lower arm transistor of the phase.
Conventionally, a method of limiting the motor current in this way has been adopted.

JP-A-62-123965 (page 2, lower right column, line 19 to page 3, lower right column, line 10, FIG. 1 to FIG. 3)

  However, according to the method described above, the current may not be limited depending on the region to which the induced voltage vector of the electric motor IM belongs. Hereinafter, this will be described with reference to FIGS.

First, FIG. 9 shows an equivalent circuit of a three-phase voltage source inverter, where “1” indicates that the upper arm switching element of the U, V, and W phases on the output side is ON, and the lower arm switching element is ON. as "0" to state you are, these switching patterns _{S u,} S v, is represented by a switch to select the _{S w.}
For example, when the switching element of the upper arm of the U phase is on, and the switching element of the lower arm of the V phase and W phase is on, the switching pattern (S _u S _v S _w ) is (100). In FIG. 9, C ₁ and C ₂ are voltage dividing capacitors as the DC power supply 301 in FIG.

FIG. 10 equivalently shows a drive circuit of an electric motor using an inverter, where V is an output voltage vector of the inverter, e is an induced voltage vector of the electric motor, L is a leakage inductance of the electric motor, and i is an output current vector of the inverter. It is. From FIG. 10, the time change rate di / dt (which is a vector amount) of the current vector i can be expressed by Equation 1.
[Formula 1]
di / dt = (V−e) / L

Now, the inverter switching pattern _{(S u} S v S _w) is (000), (001), (010), (011), (100), (101), (110), and so on (111) There are eight patterns, and output voltage vectors V _{0 to} V ₇ corresponding to each pattern are as shown in FIG. FIG. 11 also shows an example of an induced voltage vector e, an output current vector i, and a time change rate vector di / dt of the current vector i.
In FIG. 11, I, II, III, and IV are regions on the coordinates to which the output voltage vector V belongs.

When the output voltage vector V is V ₁ (switching pattern (100)), consider the case where the induced voltage vector e is in the region III as shown in FIG. If the u-phase current i _u exceeds the current limit value in this state, the output voltage vector V is conventionally changed according to the switching pattern (000) in order to turn off the upper arm transistor and turn on the lower arm transistor. Since the zero voltage vector V ₀ is set, the time change rate vector di / dt of the current vector i is opposite to the induced voltage vector e according to the above-described Equation 1.
However, since the time change rate vector di / dt has a positive direction component of the u-phase current i _u as shown in FIG. 11, the output current vector i increases in the u-phase current direction. As a result, there is a problem that current limitation is not applied and the current rating of the inverter must be increased.

  Therefore, the problem to be solved by the present invention is that even in a situation where the motor current cannot theoretically be limited, it is unnecessary to increase the current rating of the power converter more than necessary by reliably limiting the current. It is an object of the present invention to provide a power converter control device that can be reduced in size and cost.

In order to solve the above-described problem, the invention according to claim 1 is a control device for a power converter for driving an AC motor at a variable speed, and the semiconductor switching of the power converter according to an output voltage command value of a rotating coordinate system. In a control device that generates a drive signal for an element,
Voltage adjustment means for calculating a voltage correction value for each axis component of the output voltage command value, using the detected current value of the motor, the current limit value of the motor, a motor constant, and the like;
The voltage adjusting means is
When the detected current value exceeds the current limit value, the voltage correction value for each axis component is calculated so that the direction of the output voltage vector of the power converter approaches the direction of the induced voltage vector of the motor,
By correcting each axis component of the original output voltage command value using these voltage correction values, the current of the electric motor is limited to the current limit value or less.

According to a second aspect of the present invention, in the control device for a power converter according to the first aspect, the voltage adjusting means determines a magnitude of a voltage vector to be corrected from a deviation between the current limit value and the current detection value. means for determining, by calculation using the respective axial components and the motor constants, such as the rotating coordinate system of the current detection value, the direction of the output voltage vector is closer to the direction of the induced voltage vector, the voltage vector correcting Means for determining an angle, and means for determining each axis component of the voltage correction value to be added to each axis component of the original output voltage command value using the magnitude and angle of the voltage vector to be corrected. Is.

  According to a third aspect of the invention, in the power converter control device according to the second aspect, as means for determining an angle of the voltage vector to be corrected, each axis component of the rotational coordinate system of the current detection value is further determined. An input differential calculation means or a high-pass filter is provided, and an output of the differential calculation means or the high-pass filter is used for adjusting the angle.

  According to a fourth aspect of the present invention, in the power converter control device according to the second aspect, as a means for determining an angle of the voltage vector to be corrected, a deviation between the current limit value and the current detection value is further determined. An input differential calculation means or a high-pass filter is provided, and an output of the differential calculation means or the high-pass filter is used for adjusting the angle.

  According to a fifth aspect of the present invention, in the power converter control device according to the second, third, or fourth aspect, a deviation between the current limit value and the current detection value, an output of the differential calculation means, or an output of a high-pass filter Means for limiting at least one upper limit value.

  According to a sixth aspect of the present invention, in the power converter control device according to any one of the first to fifth aspects, each axis component of the rotating coordinate system of the current detection value is specified by the magnitude of the current detection value. Means for obtaining the axis components of the voltage vector to be corrected using the output of the means.

According to the present invention, the voltage correction value for each axis component is calculated so that the output voltage vector of the power converter approaches the induced voltage vector of the motor, using the detected current value, the current limit value, the motor constant, and the like of the motor. However, by correcting each axis component of the original output voltage command value using these voltage correction values, the motor current can be reliably kept below the current limit value even in a situation where the motor current cannot theoretically be limited. Can be limited.
For this reason, the current rating of the power converter is not increased more than necessary, and the power converter can be reduced in size and cost.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention, and corresponds to the invention according to claim 1. In addition, this figure has shown the structure of the whole system containing the power converters 10, such as an inverter, and AC motors 20, such as an induction motor. In addition, as a control method of the electric motor 20, a general V / f constant control in which the main magnetic flux of the electric motor 20 is made constant and the variable speed driving is performed by keeping the ratio between the output voltage and the frequency constant. Used.

In FIG. 1, in accordance with the primary frequency command value (speed command value of the motor 20) f ₁ ^* , the F / V conversion means 30 generates the q-axis voltage command value v _q ^{* of} the rotating coordinate system according to the primary frequency. Is done. Here, the q-axis is orthogonal to the d-axis parallel to the primary magnetic flux, and the d-axis and q-axis constitute dq rotation coordinates. The d-axis voltage command value v _d ^* is always 0.

The q-axis voltage command value v _q ^* obtained by the F / V conversion means 30 is converted into a coordinate conversion means using an angle command value θ ₁ ^* obtained by integrating the primary frequency command value f ₁ ^* by the integration means 40. The coordinates are converted into the three-phase AC voltage command values v _U ^* , v _V ^* , v _W ^* of the stationary coordinate system by 80.
The voltage command values v _U ^* , v _V ^* , and v _W ^* are converted by the PWM pulse generation means 90 into an on / off command for the power semiconductor switching element that constitutes the power converter 10. The power converter 10 turns on and off a predetermined switching element based on the on / off command, thereby converting the DC voltage of the DC input terminals P and N into a three-phase AC voltage and supplying the same to the electric motor 20.

At this time, the voltage equation on the rotation coordinates, if the induced voltage of each axis of the electric motor 20 e _d, and e _q, is represented by Equation 2.

In Equation 2, p is a differential operator, R ₁ is a stator winding resistance of the motor 20, and if the motor 20 is an induction motor, ω ₁ is a primary angular frequency, and L _σ = L ₁ − M ² / L ₂ , L ₁ = M + l ₁ , L ₂ = M + l ₂ , M is the mutual inductance of the stator and rotor (between the primary and secondary windings), and l ₁ and l ₂ are the stator and rotor ( The leakage inductance of the primary and secondary windings is shown.
Here, the voltage and current vector diagram on the rotation coordinates in the steady state is as shown in FIG.

Now, in a steady state in which the power converter 10 is operating the electric motor 20 by the V / f constant control as described above, for example, when the load of the electric motor 20 changes and an overload current tends to flow. Suppose.
At this time, in order to limit the magnitude of the motor current, if the magnitude and phase are adjusted so that the output voltage vector V of the power converter 10 approaches the induced voltage vector e of the motor 20, it is apparent from FIG. Thus, i _d and i _q can be reduced, and an increase in motor current can be suppressed.

Here, as can be seen from Equation 2 and the vector diagram of FIG. 2, the voltages v _d and v _q output from the power converter 10 and the current i _d flowing into the motor 20 can be obtained without knowing the rotation speed and magnetic flux of the motor. , I _q , the induced voltages _ed , e _q can be estimated.
The present invention has been made paying attention to this point, and the vector sum of the respective axis currents i _d and i _q detected by the voltage adjustment means 50 of FIG. 1 via the current detection means 60 and the coordinate conversion means 70. When the magnitude of the current i exceeds the preset current limit value I _lim ^* , the rotation coordinates are generated by the voltage correction value generated according to the currents i _d , i _q , the current limit value I _lim ^*, etc. By manipulating each axis voltage command value v _d ^* , v _q ^* of the system and adjusting the magnitude and phase of the output voltage vector V of the power converter 10, the motor current i is desired to be less than the limit value I _lim ^*. It adjusts so that it may become the value of.

Next, FIG. 3 shows a first embodiment of the voltage adjusting means 50, which corresponds to a broken line portion (control block for limiting current) in FIG. In FIG. 3, the voltage adjusting means is indicated by reference numeral 50A. This embodiment corresponds to the invention according to claim 2.
In this embodiment, when the motor current i exceeds the limit value I lim *, based on the output voltage command value v d *, v q * into voltage correction value (vector) Delta] v d, adding each Delta] v q Thus, the magnitude and phase of the output voltage of the power converter 10 are adjusted to control the current to be equal to or less than the limit value I lim * .

That is, first, the magnitude I of the current i is calculated by Equation 3. This calculation is performed by multiplication means 501, 502, addition / subtraction means 503, and square root calculation means 504 in FIG.
[Formula 3]
^{_{I = √ (i d 2 +}} i q 2)

On the other hand, ignoring the differential term of Equation 2 described above, only the steady state is considered, and for each of the detection currents i _d and i _q , a gain K ₂ corresponding to R ₁ and a gain K ₃ corresponding to ω ₁ L _σ Are added and subtracted by addition / subtraction means 506 and 508.
Also, calculated by subtraction unit 505 the difference ΔI between the magnitude I of the current determined by the current limit I _lim ^* and formulas 3, K ₁ multiplied by a gain K ₁ as the regulatory elements of the current control system to the difference ΔI The multiplication means 507 and 509 multiply the ΔI and the outputs of the addition / subtraction means 506 and 508 to obtain voltage correction values Δv _d and Δv _q of the respective axis components.
These voltage correction values Δv _d , Δv _q are added to the original output voltage command values v _d ^* , v _q ^* in the addition / subtraction means 51 _d , 51 _q to thereby output voltage command values v _d ^** for limiting the current. , V _q ^** .

The reason why the output voltage vector V of the power converter 10 can be brought close to the induced voltage vector e of the electric motor 20 by the operation as described above is as follows.
In FIG. 3, the output of the addition / subtraction means 506 is (R ₁ i _d −ω ₁ L _σ i _q ), which is equal to (v _d −e _d ) according to Equation 2. The output of the addition / subtraction means 508 is (R ₁ i _q + ω ₁ L _σ i _d ), which is equal to (v _q −e _q ) according to Equation 2. These _{(v d} -e _d), the _(v q -e _q) is d-axis component of the voltage correction value, since it is q-axis component, factors that determine the voltage correction value of the phase (direction). Further, the _{K 1} [Delta] I in the multiplication means 507,509 _{(v d} -e _d), by multiplying the _{(v q} -e q), the magnitude of the voltage correction value is determined.

The magnitude I of the current is greater than the limit value _{I lim} ^* _{K 1 ΔI} is a negative value, the voltage output from the multiplying means 507, 509 the correction value _{Δv d (= K 1 ΔI (} v d -e d )), _{v d} components in the same _{Δv q (= K 1 ΔI (} v q -e q)), v q component is negative, _{e d} component, _{e q} component becomes positive. These voltage correction value Delta] v _d, Delta] v _q is subtraction unit 51d, the voltage command value in 51 q _v ^d _{*, v} adds to the ^{q *,} the addition result, the more _{e d} component is larger difference ΔI of the current described above , E _q components become dominant, and the output voltage vector V following the final output voltage command values v _d ^** , v _q ^** approaches the direction of the induced voltage vector e.

In this way, by controlling the output voltage vector V of the power converter 10 in the direction of the induced voltage vector e by the voltage adjusting means 50A, the current magnitude I exceeds the limit value I _lim ^* as a result. It is possible to adjust so that there is no.

Next, FIG. 4 is a block diagram of the voltage adjusting means 50B according to the second embodiment, which corresponds to the invention according to claim 3.
This embodiment is different from the first embodiment (FIG. 3) in that the result of the calculation by the function G (s) for each axial current i _d , i _q is also corrected by the voltage via the addition / subtraction means 510, 511. This is the point used for calculating the values Δv _d and Δv _q , and the other basic configuration and operation are the same as in the first embodiment.

The function G (s) corresponds to the differential term of Formula 2, and may be differentiated purely as in Formula 4, or may be substituted with a high-pass filter as in Formula 5. Incidentally, in Equation 4, 5, s is the gain corresponding to the Laplace operator, the _{K 4} Equation 2 L _sigma, T is an integration constant.
[Formula 4]
G (s) = sK ₄

In particular, the current limiting start point often has a large change with respect to the time of the current. In the first embodiment of FIG. 3, since the differential term of Formula 2 is ignored and only the steady state is considered, the current limiting starts. Sometimes the current magnitude I may exceed the limit value I _lim ^* .
To deal with such a problem, it is possible to cope with a transient state of current change by considering the differential term of Formula 2 using the function G (s) as in the second embodiment, and the current becomes steep. Even when the output voltage changes, as a result of the output voltage vector V approaching the induced voltage vector e at high speed, the current magnitude I can be suppressed to the limit value I _lim ^* .

FIG. 5 is a block diagram of the voltage adjusting means 50C according to the third embodiment, which corresponds to the invention according to claim 4.
In this third embodiment, the multiplication means 512 and 513 calculate the axial currents i _d and i using the function G (s) for the difference ΔI between the limit value I _lim ^* and the current magnitude I. The result of multiplication by _q is also used to calculate the voltage correction values Δv _d and Δv _q via the addition / subtraction means 510 and 511, and other basic configurations and operations are the same as those of the above-described embodiments. .

The function G (s) may be differentiated purely as in Equation 4 as described above, or may be substituted with a high-pass filter as in Equation 5.
As described above, the third embodiment makes it possible to limit the current as a result of the output voltage vector approaching the induced voltage vector at high speed even when the current difference ΔI changes sharply. is there.

Next, FIG. 6 is a block diagram of the voltage adjusting means 50D according to the fourth embodiment, which corresponds to the invention according to claim 5.
In this embodiment, limiters 514 and 515 are respectively provided in the subsequent stage of the function G (s) and the previous stage of the gain K ₁ in the third embodiment of FIG. 5, and the other configurations are the same as in the third embodiment. is there. The limiters 514 and 515 function as an upper limiter whose upper limit value is limited to zero.

In the above-described first to third embodiments, the current magnitude I is limited when the current magnitude I exceeds the limit value I _lim ^*. If exceeded a current limit limits I _lim ^* is performed, even then the magnitude I of the current falls below the limit value I _lim ^* to, the magnitude I of the current is permanently limit I _lim ^* Will be controlled.
That is, in order to avoid useless current limiting operation and return to the steady state, it is possible to determine whether or not the current magnitude I exceeds the limit value I _lim ^* and to perform current limiting control according to the determination result. We must always make judgments about necessity.

Therefore, the fourth embodiment shown in FIG. 6 is for solving the above problem. The limiter 514 limits the upper limit value of the output of the function G (s) to 0, and the limiter 515 limits the limit value I _lim. The upper limit value of the difference ΔI between ^* and the current magnitude I is limited to zero.
As a result, when the current magnitude I falls below the limit value I _lim ^* , the voltage correction values Δv _d and Δv _q become 0, so that the original voltage command values v _d ^* and v _q ^* are not corrected. , Automatically return to steady state. In other words, by limiting the upper limit value of the difference ΔI between the current limit value I _lim ^* and the current magnitude I and the upper limit value of the output of the function G (s) with 0, the current magnitude I is It is no longer necessary to determine whether the limit value I _lim ^* has been exceeded or to determine whether the current limit control is necessary. If the current magnitude I exceeds the limit value I _lim ^* , the current is automatically suppressed, and if it falls below, the current is automatically controlled. Therefore, current suppression can be stopped.
Note that only one of the limiters 514 and 515 may be provided. The same applies to the following fifth embodiment.

FIG. 7 is a block diagram of the voltage adjusting means 50E according to the fifth embodiment, which corresponds to the invention according to claim 6.
In this embodiment, dividing means 516 and 517 are provided in the input paths of the respective axis currents i _d and i _q in the fourth embodiment of FIG. 6, and values obtained by dividing i _d and i _q by the current magnitude I are used. Thus, the voltage correction values Δv _d and Δv _q are calculated, and the other configurations are the same as in the fourth embodiment.

The current limit value I _lim ^* of the power converter may be changed depending on the application. In this case, in the voltage adjusting units 50A to 50D of the first to fourth embodiments described above, the limit value I _lim ^{* is used.} There Once changed the gain K ₁ is also not have to change with it, it is necessary to reset the gain K _1.
In view of this point, in the fifth embodiment, the axial currents i _d and i _q are respectively divided by the current magnitude I and normalized, and the voltage correction values Δv _d and Δv _q are calculated using the values. I have to. As a result, the magnitudes of the respective axis currents i _d and i _q are normalized without depending on the magnitude of the limit value I _lim ^* , and there is an advantage that it is not necessary to reset the gain K ₁ .

It is a block diagram which shows embodiment of this invention. It is a voltage and current vector diagram on the rotation coordinate in the steady state of the embodiment. It is a block diagram which shows 1st Example of a voltage adjustment means. It is a block diagram which shows 2nd Example of a voltage adjustment means. It is a block diagram which shows 3rd Example of a voltage adjustment means. It is a block diagram which shows 4th Example of a voltage adjustment means. It is a block diagram which shows 5th Example of a voltage adjustment means. It is a block diagram which shows a prior art. It is an equivalent circuit diagram of a three-phase voltage source inverter. It is an equivalent circuit diagram of the electric motor drive circuit by an inverter. It is a vector diagram of the output voltage according to the switching pattern of the inverter.

Explanation of symbols

10: Power converter 20: AC motor 30: F / V conversion means 40: Integration means 50, 50A to 50E: Voltage adjustment means 51d, 51q: Addition / subtraction means 501, 502: Multiplication means 503, 505, 506, 508, 510 511: Addition / subtraction means 504: Square root calculation means 507, 509, 512, 513: Multiplication means 514, 515: Limiter 516, 517: Division means 60: Current detection means 70, 80: Coordinate conversion means 90: PWM pulse generation means

Claims (6)

A control device for a power converter for driving an AC motor at a variable speed, wherein the control device generates a drive signal for a semiconductor switching element of the power converter according to an output voltage command value of a rotating coordinate system.
Voltage adjustment means for calculating a voltage correction value for each axis component of the output voltage command value, using the detected current value of the motor, the current limit value of the motor, a motor constant, and the like;
The voltage adjusting means is
When the detected current value exceeds the current limit value, the voltage correction value for each axis component is calculated so that the direction of the output voltage vector of the power converter approaches the direction of the induced voltage vector of the motor,
A control apparatus for a power converter, wherein the current of the motor is limited to the current limit value or less by correcting each axis component of the original output voltage command value using these voltage correction values. In the control apparatus of the power converter according to claim 1,
The voltage adjusting means is
Means for determining a magnitude of a voltage vector to be corrected from a deviation between the current limit value and the current detection value;
By calculation using each axis component and motor parameters such as the rotating coordinate system of the current detection value, so that the direction of the output voltage vector approaches the direction of the induced voltage vector, means for determining the angle of the voltage vector correcting When,
Means for determining each axis component of the voltage correction value to be added to each axis component of the original output voltage command value using the magnitude and angle of the voltage vector to be corrected;
An apparatus for controlling a power converter, comprising: In the control apparatus of the power converter according to claim 2,
The means for determining the angle of the voltage vector to be corrected further comprises a differential operation means or a high-pass filter to which each axis component of the rotational coordinate system of the current detection value is input,
An apparatus for controlling a power converter, wherein the output of the differential calculation means or the high-pass filter is used for adjusting the angle. In the control apparatus of the power converter according to claim 2,
The means for determining the angle of the voltage vector to be corrected further comprises a differential calculation means or a high-pass filter to which a deviation between the current limit value and the current detection value is input,
An apparatus for controlling a power converter, wherein the output of the differential calculation means or the high-pass filter is used for adjusting the angle. In the control apparatus of the power converter according to claim 2, 3 or 4,
A control device for a power converter, comprising means for limiting at least one upper limit value among a deviation between the current limit value and the detected current value, an output of the differential calculation means, or an output of a high-pass filter. In the control apparatus of the power converter as described in any one of Claims 1-5,
Means for normalizing each axis component of the rotation coordinate system of the current detection value with the magnitude of the current detection value, and using the output of this means, obtaining each axis component of the voltage vector to be corrected Control device for power converter.

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