JP3046147B2 - AC motor servo controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for servo-controlling the operation of an AC motor by turning on / off a power semiconductor element, that is, a servo control apparatus for an AC motor.

[0002]

2. Description of the Related Art When controlling the speed of an AC motor using an inverter, a power semiconductor element such as a power transistor or an IGBT is used to control the magnitude and direction of current flow of the motor. These power semiconductor elements are elements that generate a loss in the current control operation. In particular, the loss generated by these power semiconductor elements increases during the maximum torque output of the motor or during frequent acceleration / deceleration operations. This loss accounts for most of the total loss of the servo controller. Further, since it is a semiconductor, it has a small overload capacity and is easily damaged by overheating. For this reason, it is necessary to measure or estimate the temperature rise of these power semiconductor elements to prevent abnormal overheating and to reliably use them within an appropriate allowable temperature range, while maintaining high reliability of the servo control device. This is important in downsizing the device.

FIG. 3 shows a general configuration of a servo control device. The servo control device 20 shown in FIG.
0 is a converter unit 1 that converts three-phase AC power supplied from an externally provided three-phase AC power supply 101 to DC power.
And an inverter unit 104 for converting the DC output of the converter unit 100 into an AC current and supplying the AC current to the motor 1. The converter section 100 includes a diode group 102 and a smoothing capacitor 103, and performs rectification and smoothing of three-phase alternating current by these. In addition, the inverter unit 1
04 is a power transistor Q _{1 to} Q ₆ and a diode D
It is equipped with a ₁ ~D _6. Each power transistor Q _{1 to} Q
₆ is turned on / off by a pulse width modulation signal 12 described later. As a result, a three-phase alternating current having an execution value determined by the pulse width modulation signal 12 is supplied to the synchronous motor 1. The motor 1 is a three-phase AC synchronous motor having a permanent magnet as a rotor, and is driven by a current supplied from the inverter unit 104.

[0004] The servo control device 200 shown in this figure controls the rotation speed of the motor 1, and the servo control device 200 performs control based on a rotation speed command _VCMD given from the outside. On the other hand, the rotation angle of the motor 1 is detected by a rotation position detector 2 mechanically connected to the motor 1, and the detection result is sent to the speed detection circuit 3 and the three-phase sine wave generator 6 as a position detection signal POS. Supplied. The speed detection circuit 3 generates a speed feedback signal V by differentiating the position detection signal POS with time. The subtractor 4 outputs the rotation speed command V
_After subtracting V from _CMD , the PID compensator 5 amplifies the output of the subtractor 4. Thus, the effective current command value に 対 す る for motor 1 is generated.

The three-phase sine wave generator 6 generates a sine wave having a phase that differs by １ ／ cycle, based on the rotation angle of the motor 1 indicated by the position detection signal POS. Multipliers 7U, 7V, 7W connected to the subsequent stage
Multiplies each sine wave by the current command value Ι to generate each phase current command value Iuc, Ivc, Iwc. In other words, the three-phase sine wave generator 6 and the multipliers 7U, 7V, 7W function as converters for converting the effective current command value into each phase current command value. Subsequent to the multipliers 7U, 7V, 7W, a subtractor 10U,
10V and 10W are connected, and these are used to convert the respective phase currents Iu, Iv, Iw of the motor 1 detected by the current detectors 9U, 9V, 9W into respective phase current command values Iuc, Ivc, Iwc.
Subtract from The amplifiers 8U, 8V and 8W are connected to the subtractor 10
U, 10V, 10W output, that is, each phase current command value I
The difference between uc, Ivc, Iwc and each phase current Iu, Iv, Iw is amplified and supplied to the pulse width modulation circuit 11. The pulse width modulation circuit 11 converts the outputs of the amplifiers 8U, 8V, 8W into a pulse width modulation signal 12. This signal 12 is used for ON / OFF control of each of the power transistors Q _{1 to} Q ₆ as described above. Thus, each phase current Iu, Iv, I
w is controlled so as to match each phase current command value Iuc, Ivc, Iwc.

[0006] The control device 200 is further provided with an overheat detecting section 300. The overheat detecting unit 300, in order to prevent its overheating breakdown, power transistors Q ₁ to Q ₆
Estimate the temperature rise. The overheat detection unit 300 is, for example,
As shown in FIG. 4, the absolute value circuit 13, amplifier 14, C
An R series circuit 15 and a comparator 16 are provided. The overheat detecting section 300 converts the effective current command value Ι into an absolute value by the absolute value circuit 13 and amplifies it by the amplifier 14. The output of the amplifier 14 is input to the CR series circuit 15. CR series circuit 1
5 is an externally preset allowable temperature rise value ΔT for a group of power transistors Q _{1 to} Q _6.
sref is compared with the comparator 16. As a result of the comparison, if the former is higher than the latter, a binarized overheat detection signal 17 is output and supplied to the pulse width modulation circuit 11.
The pulse width modulation circuit 11 controls all the power transistors Q _{1 to} Q ₆ to be turned off according to the overheat detection signal 17 to stop the current output. At the same time, the overheat detection signal 17 is output outside the servo controller as an overheat detection alarm signal ALM _TH .

Here, the CR series circuit 15 is a circuit expressing a heat sink as a heat equivalent circuit. Generally, the power transistors Q _{1 to} Q ₆ are mounted on an aluminum heat sink to reduce the temperature rise. Therefore, the temperature rise ΔT of the power transistors Q _{1 to} Q ₆ is substantially determined by the total loss P and the thermal time constant of the heat sink. In terms of a heat equivalent circuit, the total loss P is as shown in FIG. Can be expressed by a CR series circuit composed of a capacitor (C), which is considered as an input voltage, and a resistor (R).
The total loss P can be expressed as being proportional to the absolute value | I | of the effective current command value Ι, and the amplification factor of the amplifier 14 is a proportional constant between the total loss P and the absolute value | I | of the effective current command value Ι. It has become. That is, if the time constant of the CR series circuit 15 is previously set equal to the thermal time constant of the heat sink,
The output ΔT _S is an estimated temperature rise value of the power transistors Q _{1 to} Q ₆ . Therefore, by comparing this with the allowable temperature rise value ΔT _sref in the comparator 16,
As described above, the overheat detection signal 17 can be generated.

[0008]

However, the conventional apparatus has the following problems in overheating protection. Here, the configuration of FIGS. 3 to 5 will be described as an example.

Here, a case where torque is generated while the motor 1 is stopped (locked) will be considered. Under such conditions, since the magnitude and direction of the current of the motor 1 are fixed, the power transistors Q _{1 to} Q ₆
Intensively in one of them. In this case, only the temperature of the power transistor (one chip portion of Q _{1 to} Q ₆₎ in which loss occurs intensively rises abnormally. The overheat detecting section 300 includes power transistors Q _{1 to} Q ₆
The overheat protection is performed by estimating the temperature rise based on the total loss of the motor, and such overheat protection in the motor locked state is impossible in principle. For this reason, in an actual apparatus, the maximum value of the temperature rise of the chip section △ T _jmax in a state where the motor 1 is locked is considered in advance, and △ T _sref ′ =
△ T _serf - △ T _jmax become △ technique for setting the T _sref 'acceptable temperature rise value is taken. However, in this method, in order to guarantee the rated output current as the servo control device, it is necessary to previously design the heat sink large in order to reduce the heat resistance of the heat sink.

FIG. 6 shows another configuration of the overheat detecting section 300. In this configuration, the configuration shown in FIG. 4 is provided for each phase. That is, the current command values Iuc, Ivc, Iwc of each phase are input as an absolute value circuit.
U, 13V, 13W are amplifiers, 14U, 14V,
14W is 15U, 15V, 15W as CR series circuit
However, 16U, 16V, and 16W are provided as comparators, respectively, and the overheat detection signal 17 is obtained by logically adding the binary signals output from the comparators 16U, 16V, and 16W by the OR circuit 18. . The configuration shown in this figure is a configuration in which overheating is detected for each phase. Even if the motor 1 is locked and the magnitude and direction of the current are fixed, overheating can be detected in principle.

However, in order to realize the configuration of FIG. 6 with an electronic circuit, a configuration for determining the overheat detection performance, that is, an absolute value circuit, an amplifier circuit, and a C circuit that require high-precision operation are required.
Since an R series circuit must be provided for each phase, and the number of these circuits increases, the circuit scale and cost increase. When this configuration is realized by software using a CPU, unless the sampling cycle and the calculation cycle of each phase current command value are accelerated, the motor that rotates at high speed, and eventually overheats in response to an increase in the frequency of each phase current command value. Inability to maintain detection performance. For this reason, the occupation ratio of the overheat detection processing in the processing of the CPU increases, and the efficient use of the CPU cannot be achieved. In addition, since the effect of mutual temperature rise due to the loss of each phase power transistor group cannot be considered,
It was not possible to follow changes in the motor operating state, and accurate overheat protection was not possible.

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and an object of the present invention is to reliably and easily realize overheating protection of a power semiconductor element in a servo control device.

[0013]

In order to achieve the above object, the present invention provides a first estimating means for estimating a temperature rise at a contact portion between a heat sink and a power semiconductor element group, and a method for estimating a rotation of an AC motor. A second estimating means for estimating a temperature rise inside the power semiconductor element group in the state, a third estimating means for estimating a maximum temperature rise inside the power semiconductor element group in the stopped state of the AC motor, and A means for determining whether the motor is in a rotating state or a stopped state; a temperature increase estimated by the second estimating means when the motor is determined to be rotating; By adding the temperature rise estimated by the estimating means to the temperature rise estimated by the first estimating means, a method of obtaining an estimated value of the temperature rise including from the contact portion to the power semiconductor element group is obtained. Characterized in that it comprises a and.

[0014]

According to the present invention, first, a temperature rise at a contact portion between the heat sink and the power semiconductor element group is estimated. This temperature rise is a value determined by the total loss of the power semiconductor element group. On the other hand, in the present invention, the temperature rise inside the power semiconductor element group is estimated for each of the rotation state (run state) and the stop state (lock state). As described above, in the run state and the lock state, the mode of heat generation inside the power semiconductor element group is different, and the maximum temperature rise is different. In the present invention,
Determines whether the AC motor is in a rotating state or a stopped state, and, based on the determination result, calculates an estimated value of the temperature rise inside the power semiconductor element group in any one of the states. And the estimated value of. Thus, an estimated value of the temperature rise from the contact portion to the power semiconductor element group is obtained. Therefore, in the present invention, the power semiconductor element can be reliably protected from overheating destruction, regardless of whether the AC motor is rotating or stopped.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. The same or corresponding components as those of the conventional example shown in FIGS. 3 to 6 are denoted by the same reference numerals, and description thereof is omitted.

FIG. 1 shows the configuration of a servo control device 200 according to an embodiment of the present invention. In this figure, the present embodiment differs from the conventional example in that an external setting constant group 19 is set in the overheat detecting section 300 from outside the servo control device. FIG. 2 shows the configuration of the heating detection unit 300 in this embodiment. The heating detector 300 in this embodiment is different from the prior art in that the absolute value circuit 2
0, an amplifier 21 and a CR series circuit 22 for estimating and detecting a temperature rise ΔT _fa of a contact portion between the heat sink and the power transistors Q _{1 to} Q ₆ .
Amplifier 24, switching circuit 25, run / lock determination circuit 2
6, a system for estimating and detecting the temperature rise ΔT _jf in the chip portion of the power transistors Q _{1 to} Q ₆ , which is composed of the CR series circuit 27 and the adder 30.
Further, these comparators 28 and 29 at the subsequent stage further include O
The R circuit 31 is connected. A feature of the present invention lies in the improvement of the configuration of such a heating detection unit 300 and, consequently, a method of estimating a temperature rise.

(1) Total Loss of Power Transistor Before describing the difference in circuit operation, first, the total loss P of the power transistors Q _{1 to} Q ₆ is determined by the absolute value | I | of the effective current value example value I. , And is substantially constant irrespective of the operation state of the motor 1, will be described for each state of the motor 1. (1.1) Motor Rotation State When the motor 1 is rotating, the generated losses of the power transistors Q _{1 to} Q ₆ are equal to each other. Therefore, to represent the loss generated any power transistor Q _n and P _n. This loss P _n is the sum of the switching losses P _nsw and on losses P _nc, they are

(Equation 1) Thus, P _n = (A + B) I _mean . Further, since each phase current Iu, Iv, Iw is a sine wave, I _mean = 2 / π · | I |. Therefore, the loss P _n is P _n = 2 / π · (A + B) · | I | Since the total loss P is obtained by multiplying the loss P _n by the number of power transistors, P = 12 / π · (A + B) · | I |

(1.2) Motor Lock State Here, the state in which the current flows in the direction of the arrow in the figure for each phase current is represented as positive. Motor 1 is Iu
= I> 0, Iv = Iw = −I / 2 <0, and the power transistors Q ₁ , Q ₄ , and Q ₆ cause loss, and the power transistor Q _{1 has} a loss. growing. Loss of the power transistor Q ₁ P ₁
Is the switching loss P ₁ s of the power transistor Q ₁
w and the on-loss P ₁ c, which are respectively

(Equation 2) Therefore, P ₁ = 2 (A + B) I. Since the sum of the generated losses of the power transistors Q ₄ and Q ₆ is equal to the generated loss P ₁ of the power transistor Q ₁ , the total loss P is P = 2 · P ₁ = 4 (A + B) · I When the rotation angle position of the motor 1 changes from this state, the magnitude and direction of each phase current changes, and accordingly, the transistor that generates the maximum loss changes. But,
Since the total loss P is proportional to the sum of the absolute values of the respective phase currents, the total loss P changes with the maximum at the stop position under the above-described conditions.
But the change is small. Therefore, the total loss P can be represented by P = 4 (A + B) · | I | regardless of the stop rotation angle position.

(1.3) Comparison of motor rotation state and motor lock state As described above, the total loss P is as follows: motor rotation state: P = 12 / π · (A + B) · | I | motor lock state: P = 4 . (A + B). | I |. As can be seen from these equations, the total loss P is proportional to the absolute value | I | of the effective current command value. Also, since 12 / π is approximately 4, the total loss P is
Can be regarded as not depending on the operation state of.

(2) Temperature rise at the contact portion between the heat sink and the power transistor ΔT _fa The temperature rise at the contact portion between the heat sink and the power transistor group caused by such total loss P ΔTf-a is the time expressed by the following equation. Has characteristics.

[0021]

(Equation 3) When the total loss P is transformed by substituting the expression represented by the absolute value | I | of the effective current command value into this expression,

(Equation 4) Becomes

(3) Temperature rise only at the chip portion of the power transistor {T _jf Next, temperature rise only at the chip portion of the power transistor}
Consider T _jf . In the motor run state, P _n = 2
/ Π · (A + B) · | I |

(Equation 5) It can be expressed as. In the motor lock state, in the maximum loss generating transistor, the temperature rise ΔT _jf of only the chip portion of the power transistor is P ₁ = 2 (A +
B) Because I is

(Equation 6) It can be expressed as.

(4) Operation of Overheat Detection Unit The overheat detection unit 300 operates based on the equations described in the above (1) to (3). First, the absolute value circuit 20 obtains the absolute value of the effective current command value I, and the amplifier 21 outputs the absolute value |
Amplify I |. C connected after the amplifier 21
The R series circuit 22 has time constants _Cfa and _Rfa .
By setting the amplification factor of the amplifier 21 in accordance with P · θ _fa , the output of the CR series circuit 22 becomes ΔT _fa . The comparator 28 calculates the allowable temperature rise ΔT _sref1 which is a constant included in the external setting constant group 19 and the estimated temperature rise ΔT _fa.
Are compared, and if the latter exceeds the former, binarized output is performed. Usually, as ΔT _sref1 , the servo controller 200
Output the rated output current when the power transistor Q ₁
Setting an allowable temperature rise value matched to the temperature rise value of the to Q ₆ and the heat sink contact portion.

On the other hand, the amplifiers 23 and 24 have an absolute value | I
| Is amplified. The amplification factor of the amplifier 23 is β, and the amplification factor of the amplifier 24 is πβ. The CR series circuit 27 has a time constant C _jf
-It has _Rjf . Therefore, when the amplifier 23 is switched to the CR series circuit 27 by the switching circuit 25, the estimated temperature rise ΔT _jf in the motor 1 run state is output from the CR series circuit 27, and when the amplifier 24 is connected, the motor 1 The estimated temperature rise value ΔT _jf in the locked state can be obtained. The run / lock determination circuit 26 determines whether the state of the motor 1 is run or locked based on the speed feedback signal V, and controls the switching circuit 25 to control the amplifier 2 during the run.
3 is connected to the CR series circuit 27 at the time of locking.

The adder 30 adds △ T _jf and △ T _fa and supplies the result to the comparator 29. The output of the adder 30 is a chip temperature rise estimated value ΔT with respect to the ambient temperature of the servo control device 200 of the transistor causing the maximum loss.
equivalent to _ja The comparator 29 includes a servo controller 200
Allowable temperature rise △ T _sr preset from outside
_ef2 is compared with the estimated temperature rise value ΔT _ja , and if the latter exceeds the former, it is binarized and output. Where △ T
_{In sref2} , an allowable temperature rise value suitably determined from the absolute maximum value of the junction temperature of the power transistor and the maximum value of the operating ambient temperature guaranteed by the servo control device is set. The OR circuit 31 performs a logical addition of the binarized outputs of the comparators 28 and 29 to obtain _{ T _fa > T _sref1 or △ T _fa >
When T _ja > △ T _sref2 , a heating detection signal 17 is output.

In this embodiment, the amplifiers 23, 2
4 and the set values of ΔT _sref1 and ΔT _sref2 are set to 1
By multiplying by / 2, the amplifier 21 can be dispensed with. Further, in this embodiment, the three-phase AC synchronous motor 1 having a permanent magnet as a rotor is to be controlled, but may be a multi-phase induction motor. The present invention is sufficiently effective as long as each phase current command period at the time of locking is several times or more as compared with the thermal time constant of the chip portion of the power transistor.

As described above, according to the present embodiment, the temperature rise ΔT _jf of the power transistors Q _{1 to} Q ₆ is estimated, and the obtained estimated value ΔT _jf and the estimated value ΔT _j of the temperature rise at the contact portion are obtained. _{Since fa} is added to estimate the temperature rise ΔT _ja , regardless of whether the AC motor 1 is stopped (locked) or rotated (run), the power transistors Q _{1 to} Q ₆ Overheat protection can be provided. Therefore, even if the heat sink is designed to be small in size so that the rated output current can be guaranteed in most applications in which the locking phenomenon of the motor 1 does not occur in the normal control state, the output current may exceed the rated value. When it becomes
This can be detected. This is effective for the purpose of keeping the upper limit of the temperature of the power transistors Q _{1 to} Q ₆ low to some extent from the design stage of the servo control device, and ensuring long-term reliability of element operation. Even if the motor 1 is forcibly locked due to an accident such as a collision, the power transistors Q _{1 to} Q ₆ can be safely protected from overheating. Further, even in an application such as a servo press in which the lock phenomenon of the motor 1 occurs in the normal control state, an optimum press operation continuation time can be ensured by the heat sink temperature rise at the start of the press operation.

Further, since the required number of absolute value circuits, amplifier circuits and CR series circuits which require high precision operation is smaller than that of the conventional configuration, the circuit scale and cost are reduced when the present invention is realized by an electronic circuit. The advantage is that the more the number of phases of the motor 1 to be controlled increases, the more its effectiveness increases. Further, since the configuration is such that the execution current command value is input, the motor 1
The processing can be performed with an appropriate sampling and calculation cycle considering only the thermal time constant of the overheat protection target without being affected by the rotation speed of
It is possible to efficiently use the CPU.

Although the present invention has been described with reference to one embodiment, the present invention is not limited to the above-described embodiment.
The present invention can be variously modified.

[0030]

As described above, according to the present invention, the temperature rise ΔT _jf inside the power semiconductor element group is estimated, and the obtained estimated value ΔT _jf and the temperature rise at the contact portion are estimated. Since the temperature rise ΔT _ja of the power semiconductor element group is estimated by adding the value ΔT _fa , regardless of whether the AC motor is stopped (locked) or rotated (run), Overheat protection of the power semiconductor element group can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a servo control device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an overheat detection unit according to the embodiment.

FIG. 3 is a block diagram illustrating a configuration of a servo control device according to a conventional example.

FIG. 4 is a block diagram showing a configuration of an overheat detecting section in the conventional example.

FIG. 5 is a circuit diagram showing a heat equivalent circuit of a heat sink.

FIG. 6 is a block diagram showing another configuration example of the overheat detection unit in the conventional example.

[Explanation of symbols]

Reference Signs List 1 motor 11 pulse width modulation circuit 19 external setting constant group 20 absolute value circuit 21, 23, 24 amplifier 22, 27 CR serial circuit 25 switching circuit 26 run / lock determination circuit 28, 29 comparator 30 adder 31 OR circuit 100 converter part 104 inverter 200 servo controller 300 overheat detecting section Q ₁ to Q ₆ power transistors △ T _fa sink and the power transistor Q ₁ to Q
Estimated value of temperature rise at contact area of ₆ △ _Tjf Estimated value of temperature increase from contact area to chip

Claims (1)

(57) [Claims] 1. A means for servo-controlling a drive current of an AC motor by on / off control of a power semiconductor element group provided on a heat sink, and when a temperature rise of the power semiconductor element group is estimated and exceeds a set value. An overheat detection unit that outputs an overheat detection signal to the AC motor servo control device, wherein the overheat detection unit estimates a temperature rise at a contact portion between the heat sink and the power semiconductor element group; Second estimating means for estimating the temperature rise inside the power semiconductor element group when the AC motor is rotating; and third estimating means estimating the maximum temperature rise inside the power semiconductor element group when the AC motor is stopped. Means for determining whether the AC motor is in a rotating state or a stopped state; and, if it is determined that the AC motor is in a rotating state, the temperature rise estimated by the second estimating means. If it is determined that the vehicle is in the stop state, the temperature rise estimated by the third estimating means is added to the temperature rise estimated by the first estimating means. Means for calculating an estimated value of the temperature rise including: a servo control device for an AC motor.