1. Technical Field
The present invention relates to a power conversion apparatus having a function of protecting power semiconductor devices such as semiconductor switching devices that form the power conversion apparatus from an overheating accident.
2. Background Art
Patent Literature 1 (Japanese Patent No. 3075303, in, e.g., paragraph [0006], FIG. 2, and the like) and Patent Literature 2 (Japanese Patent Application Publication No. 2009-17707, in, e.g., paragraphs [0048] to [0052], FIG. 1, FIG. 11, and the like) disclose related arts of a power conversion apparatus for variable velocity driving of electric motors in which a power semiconductor device such as a semiconductor switching device is mounted. The power conversion apparatus limits current flowing into a semiconductor device before the temperature of the semiconductor device exceeds an allowable temperature to destroy the semiconductor device, to thereby protect the semiconductor device and the power conversion apparatus from an overheating accident.
In
In this related art, the junction temperature estimating unit 405 estimates the temperature (the junction temperature) of a switching device and limits or blocks an output current by such a current limiting rate as illustrated in
In
In this related art, in the processes of steps S11 to S16 in
Moreover, when the highest temperature exceeds the temperature threshold (step S17: NO), the torque of the motor 301 is corrected so as to decrease the torque (S22) to thereby decrease the generation loss of the switching devices to realize overheat protection.
In the torque correction step (S22), a torque limiting amount is determined in advance according to a difference between an estimated temperature value and a temperature threshold, for example, and a torque command value is decreased by a ratio proportional to the difference between the estimated temperature value and the temperature threshold.
However, in Patent Literature 1 described above, as obvious from
Hereinafter, Patent Literature 3 will be described briefly with reference to
First, the control block diagram of
Subsequently, the current command calculating unit 603 calculates d- and q-axis current commands id* and iq* obtained by rotationally transforming the coordinates of the current flowing in the electric motor 302. Here, as described above, in order to output a largest torque with a smallest current, the current command calculating unit 603 calculates optimal d- and q-axis current commands id* and iq* by taking the detected velocity value ω1 and the output (voltage limit value) valim of a voltage limit value calculator 612 based on a detected DC voltage value Edc output from a voltage detecting unit 611 into consideration.
Under d- and q-axis voltage commands id* and iq*, subtractors 604d and 604q and d- and q-axis current regulators 605d and 605q calculate d- and q-axis voltage commands vd* and vq* so that the values id and iq obtained by a current coordinate transformer 614 rotationally transforming the coordinates of detected current values iu and iw (and iv) detected by current detectors 613u and 613w become the d- and q-axis current command values id* and iq*.
A voltage coordinate transformer 606 transforms the d- and q-axis voltage commands vd* and vq* to U-, V-, and W-phase voltage commands vu*, vv*, and vw* and transmits the voltage commands to a PWM circuit 607. The PWM circuit 607 performs PWM control while taking the DC voltage Edc into consideration to generate gate signals of semiconductor switching devices that form a power converter 610 such as an inverter.
Reference numeral 608 designates a three-phase AC power supply, 609 designates a rectifying circuit, 615 designates a pole position detector, and 616 designates a velocity detector.
Moreover, as illustrated in
The torque calculator 603j calculates an output torque τcalc of the electric motor based on the d- and q-axis current commands id* and iq* calculated by the current command calculator 603h, and the calculated torque value τcalc is fed back so that the load angle δ* is adjusted so as to match a torque command τ*. In particular, when the voltage necessary for the power converter 610 in
By using such a control method, it is possible to utilize the reactance torque of a permanent magnet-type synchronous electric motor such as an embedded magnet-type synchronous electric motor and to control the velocity of the electric motor with a desired torque and a smallest current stably.
As described above, in Patent Literature 3, optimal d- and q-axis current commands id* and iq* are calculated based on the torque command τ* of the electric motor 302, the output of the power converter 610, and the like.
However, if a current limiting unit for protecting a semiconductor device from overheating is provided at the subsequent stage of the current command calculator 603h in
In order to obviate this problem, although the control method described in
Next, the problem of the related art disclosed in Patent Literature 2 will be described.
According to Patent Literature 2, overheating of a switching device can be prevented by decreasing the torque command value. Thus, when this technique is applied to the related art of Patent Literature 3, the value τ* described in
However, the torque decrease amount calculating unit disclosed in Patent Literature 2 has the following problem.
The temperature of a semiconductor device will be described before describing the problem of Patent Literature 2 is described in detail.
However,
From the above description, it can be understood that, when a coolant temperature rises due to abnormality or the like in a cooling system and it is necessary to protect a semiconductor device from overheating in a power conversion apparatus formed of an IGBT (insulated-gate bipolar transistor) module of the direct liquid cooling system described above, for example, a torque decrease amount is different depending on an operation state of the power conversion apparatus.
In contrast, as described above, Patent Literature 2 describes that a torque limiting amount is determined in advance according to a difference between an estimated temperature value and a preset temperature threshold, for example, and a torque command value is decreased by a ratio proportional to the difference between the estimated temperature value and the temperature threshold.
However, as described above, under such an operation condition that the output frequencies are different and the temperature rise values in relation to the coolant are different even if the occurring torque is the same, such a torque decreasing unit as disclosed in Patent Literature 2 may be unable to realize overheat protection reliably. Moreover, the torque command value decrease amount may be set to be large in advance. In this case, however, the torque may be decreased more than necessary depending on an operation state of the power conversion apparatus, and as a result, the power conversion apparatus maybe overprotected.
Therefore, the present invention provides a power conversion apparatus capable of preventing interference with a control system and protecting a semiconductor device from overheating appropriately and reliably without limiting the torque of an electric motor more than necessary.
In order to solve the problems of conventional apparatuses, the present invention provides a power conversion apparatus such as an inverter for driving an electric motor, including: a power semiconductor device; a control unit that controls the semiconductor device, based on an torque command of the electric motor; and a semiconductor temperature detecting/estimating unit that detects or estimates a temperature of the semiconductor device.
The present invention is characterized in that the power conversion apparatus of the present invention further includes a torque command adjusting unit that adjusts the torque command so that the temperature of the semiconductor device matches a preset temperature when a detected temperature value or an estimated temperature value of the semiconductor device, obtained by the semiconductor temperature detecting/estimating unit is equal to or higher than the preset temperature for performing overheat protection of the semiconductor device.
Here, the torque command adjusting unit includes: a regulating unit that operates to eliminate a deviation between the preset temperature and the detected temperature value or the estimated temperature value and a proportional regulator and an integral regulator; and a torque correction amount limiting unit that limits a torque correction amount output from the regulating unit so that the torque correction amount does not increase an absolute value of the torque command, and the torque command is corrected using the torque correction amount limited by the torque correction amount limiting unit.
The regulating unit may further include a differential regulator.
As a torque command correction method in the torque command adjusting unit, the torque correction amount may be added to the torque command as a decrease amount, and the torque correction amount may be multiplied by the torque command as a decrease rate.
In the present invention, in order to perform desired overheat protection during driving or braking, the torque command adjusting unit may include a polarity reversing unit that reverses a polarity of the torque correction amount according to a polarity of the torque command.
Further, the torque command adjusting unit may include a lower limit setting unit that sets a lower limit of the torque correction amount limiting unit, using an absolute value of the torque command.
In this case, an upper limit of the torque correction amount limiting unit may be set to zero.
Alternatively, the torque command adjusting unit may further include an integral regulator limiting unit that limits an output of the integral regulator, and an upper limit of an output of the integral regulator limiting unit may be set to a difference between zero and an output of the proportional regulator, and a lower limit of the output of the integral regulator limiting unit maybe set to a difference between a lower limit of the torque correction amount limiting unit and the output of the proportional regulator.
The torque command adjusting unit may further include: an integral regulator limiting unit that limits an output of the integral regulator; and an integral regulator operation adjusting unit that allows or stops an operation of the integral regulator, based on a deviation between the preset temperature and the detected temperature value or the estimated temperature value, and an output of the torque correction amount limiting unit. Moreover, a lower limit of an output of the integral regulator limiting unit may be set to a difference between a lower limit of the torque correction amount limiting unit and an output of the proportional regulator.
In this case, the integral regulator operation adjusting unit may allow the operation of the integral regulator when the detected temperature value or the estimated temperature value is equal to or higher than the preset temperature; may stop the operation of the integral regulator and clear the output of the integral regulator to zero when the detected temperature value or the estimated temperature value is lower than the preset temperature and the torque correction amount limited by the torque correction amount limiting unit is a value that does not decrease the absolute value of the torque command; and continue the operation of the integral regulator in other cases.
According to the present invention, a torque command of an electric motor is adjusted according to a deviation between a detected semiconductor temperature value or an estimated temperature value and a preset temperature. By doing so, it is possible to prevent interference with a control system of the electric motor and to protect a semiconductor device that forms a power converter from overheating appropriately and reliably without limiting the torque of an electric motor more than necessary.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First,
In
A control unit of the inverter 2 is configured similarly to that disclosed in Patent Literature 3 described above. The control unit of the inverter 2 includes a current command calculating unit 21 that calculates d- and q-axis current commands id* and iq* based on a torque command τ**, a detected DC voltage value, and a detected velocity value, subtractors 22d and 22q that calculate deviations between the d- and q-axis current commands id* and iq* and the d- and q-axis current id and iq, respectively, d- and q-axis current regulators 23d and 23q that output such d- and q-axis voltage commands vd* and vq* as to make these deviations zero, respectively, a voltage coordinate transformer 24 that transforms the d- and q-axis voltage commands vd* and vq* to three-phase voltage commands vu*, vv*, and vw* by coordinate transformation using a detected pole position value (phase angle) θ1, a PWM circuit 25 that generates a PWM signal based on the voltage commands vu*, vv*, and vw* and a detected DC voltage value, a gate driver 26 that generates a gate signal for a semiconductor switching device of the inverter 2 based on the PWM signal, and a current coordinate transformer 27 that generates d- and q-axis current id and iq by coordinate transformation using θ1 from the detected current values iu and iv (and iw) obtained by the current detector 3.
Since the operation of the control unit is obvious from Patent Literature 3, description thereof will not be provided. Moreover, the configuration of the control unit is not limited to the example illustrated in
Next, a configuration and an operation of a torque command adjusting unit 10A which is a main part of this embodiment will be described.
In the torque command adjusting unit 10A, a subtractor 12 calculates a deviation between a preset temperature of a semiconductor switching device (an allowable temperature before the semiconductor switching device is destroyed) and a detected semiconductor temperature value or an estimated semiconductor temperature value (hereinafter referred to simply as a semiconductor temperature) obtained by a semiconductor temperature detecting unit/semiconductor temperature estimating unit (hereinafter referred to simply as a semiconductor temperature detecting/estimating unit) 11. This deviation is input to a regulating unit that includes a proportional regulator 13, an integral regulator 14, and an adder 15. The output of the regulating unit, of which the upper limit is limited by a torque correction amount limiting unit 16, is used as a torque correction amount τcomp*, and the original torque command τ* is added thereto by the adder 17, whereby a final torque command τ** of the electric motor 4 is calculated. In the following description, it is assumed that a proportional gain Kp of the proportional regulator 13 is a positive value.
Moreover, in the following description, although an example in which the regulating unit includes the proportional regulator 13, the integral regulator 14, and the adder 15 has been described, a differential regulator or an equivalent regulator may be added thereto to form the regulating unit for the purpose of, for example, improving responsiveness to a steep change in temperature.
Here, with regard to how the semiconductor temperature detecting/estimating unit 11 detects the temperature of a semiconductor device (a semiconductor switching device or a recirculation diode), since a technique of mounting a temperature sensor on a semiconductor module that forms a power conversion apparatus such as an inverter, for example, is widely known, description thereof will not be provided. Moreover, since how the semiconductor temperature detecting/estimating unit 11 estimates the temperature of the semiconductor device is also known and disclosed in Patent Literature 1 and the like, description thereof will not be provided. Either one of a temperature detection method and a temperature estimation method may be used to obtain the temperature information of the semiconductor device.
In
In
That is, when the semiconductor temperature becomes higher than the preset temperature, the original torque command τ* is corrected and decreased by the negative torque correction amount τcomp* and is output as a final torque command τ**. Since a decrease in torque means a decrease in the current supplied from the inverter 2 to the electric motor 4, the generation loss of the semiconductor device decreases. That is, the operation of the regulating unit contributes only in the direction for decreasing the temperature of the semiconductor device. Moreover, when the regulating unit is formed of the proportional regulator 13, the integral regulator 14, and the like, the torque command can be adjusted automatically without decreasing the torque more than necessary regardless of an operating state of the apparatus, and the semiconductor device can be protected from overheating reliably.
A difference from
That is, the torque correction amount τcomp* in
By setting the lower limit of the torque correction amount limiting unit 16a to “−1,” it is possible to prevent the polarity of the final torque command τ** from being reversed from the original torque command τ*.
In a torque command adjusting unit 10C of this embodiment, the upper limit of the torque correction amount limiting unit 16a is set to “1” and the lower limit is set to “0”. When the semiconductor temperature is lower than the preset temperature, since the deviation output from the subtractor 12 is positive, the integral regulator 14 integrates the positive value having passed through the proportional regulator 13 and the output (that is, the torque correction amount τcomp*) of the regulating unit has a positive value. The torque correction amount τcomp* does not exceed “1” due to the operation of the torque correction amount limiting unit 16a. If the torque correction amount τcomp* is limited to “1,” the original torque command τ* becomes the final torque command τ** as it is without the magnitude being decreased by the multiplier 19.
On the other hand, when the semiconductor temperature is higher than the preset temperature, since the deviation output from the subtractor 12 is negative and a negative value having passed through the proportional regulator 13 is input to the integral regulator 14, the torque correction amount τcomp* having passed through the torque correction amount limiting unit 16a is limited to a value smaller than “1”. As a result, the magnitude of the original torque command τ* is decreased by the multiplier 19 and the decreased torque command τ* becomes the final torque command τ**.
Here, by setting the lower limit of the torque correction amount limiting unit 16a to “0,” it is possible to prevent the polarity of the final torque command τ** from being reversed from the original torque command τ* similarly to the above.
In the first embodiment of
Due to this, in the fourth embodiment, as illustrated in
That is, in
Due to this, during driving or braking of the electric motor 4, it is possible to realize the required overheat protection.
This embodiment is different from that of
Next, the operation of this embodiment will be described in detail.
For example, in the embodiment of
In this case, it is assumed that the regulating unit operates so that the semiconductor temperature does not exceed the preset temperature, the second torque correction amount τcomp** is decreased to −50%, and as a result, the final torque command τ** is increased to +150% (=τ*+τcomp**=200%-50%).
In such a state, it is assumed that the original torque command τ* is decreased in a step manner from +200% to +20%.
In this case, since the regulating unit has operated so that the difference between the preset temperature and the semiconductor temperature is “0,” the output of the integral regulator 14 is approximately −50% at the time point when the torque command τ* is decreased to +20%. Here, when the torque command τ* is decreased to +20%, since the output current of the inverter 2 decreases and the semiconductor temperature becomes lower than the preset temperature, the output of the subtractor 12 becomes positive. Due to this, a positive value is input to the integral regulator 14, and the output of the integral regulator 14 starts increasing toward a positive value from −50% due to the integration relaxation time of the integral regulator 14. That is, even when the original torque command τ* is decreased from +200% to +20% of the reference value, the semiconductor temperature becomes lower than the preset temperature, and it is not necessary to perform overheat protection, the output of the integral regulator 14 remains negative for a certain period. Thus, a period in which the first torque correction amount τcomp* which is the sum of the output of the proportional regulator 13 and the output of the integral regulator 14 is negative may be present.
Due to this, in the embodiment of
In order to solve the problem, in a fifth embodiment of
In the lower limit setting unit 16b, the absolute value calculating unit 16c calculates the absolute value of the torque command τ*, and a value obtained by the multiplier 16d multiplying the absolute value by “−1” is set as the lower limit of the first torque correction amount τcomp*. With this configuration, in the above-described example, when the original torque command τ* is decreased to +20%, the first torque correction amount τcomp* is limited to −20% by the lower limit. In this case, the second torque correction amount τcomp** having passed through the polarity reversing unit 18 is also −20% and the final torque command value τ** obtained by adding the original torque command τ* and the torque correction amount τcomp** becomes 0. Thus, at least the driving torque may not be reverse to the braking torque.
The reason why the absolute value calculating unit 16c is provided in the lower limit setting unit 16b is to prevent the polarity of the torque command from being reversed when the original torque command τ* is negative (that is, the original torque command τ* is a braking torque) and the torque command τ* is corrected and to prevent the driving torque from being output.
This embodiment is different from that of
In the embodiments of
Another problem will be described based on the example used in description of
Since the first torque correction amount τcomp* is limited by the lower limit of the torque correction amount limiting unit 16a when the original torque command τ* is decreased to +20% of the reference value, the value of the first torque correction amount τcomp* may not be smaller than −20%, and as a result, the corrected final torque command τ** may not be smaller than “0”. However, since the initial value of the output of the integral regulator 14 is negative (−50%), the first torque correction amount τcomp* (that is, the second torque correction amount τcomp**) becomes a negative value and the original torque command τ* may be corrected although it is not necessary to perform overheat protection.
Naturally, it is desirable to change the torque correction amount τcomp* to “0” quickly when it is not necessary to perform overheat protection. However, when the time point when the torque command τ* is decreased to +20% is taken as a base point, the output of the integral regulator 14 gradually increases toward a positive value with the integration relaxation time from −50% as an initial value. Thus, it takes a considerable time for the torque correction amount τcomp* to become “0”. That is, although a state in which it is not necessary to perform overheat protection is created, the original torque command τ* is corrected for a long period of time, which is a second problem.
In order to solve the first and second problems, in a sixth embodiment, as illustrated in
Here, the sum of the output of the proportional regulator 13 and the output of the integral regulator 14 is the output of the regulating unit and the output of the regulating unit is limited by the torque correction amount limiting unit 16a. Thus, in a state in which the output of the regulating unit is limited by the torque correction amount limiting unit 16a, the following relation is satisfied.
Regulating unit output=Limit value of Torque correction amount limiting unit 16a=(Output of Proportional regulator 13)+(Output of Integral regulator 14).
This can be understood as follows.
Output of Integral regulator 14=(Limit value of Torque correction amount limiting unit 16a)−(Output of Proportional regulator 13)
Therefore, the upper and lower limits of the integral regulator limiting unit 16h can be understood as values obtained by subtracting the output of the proportional regulator 13 from the upper and lower limits of the torque correction amount limiting unit 16a, respectively, as illustrated in
According to the sixth embodiment, the first problem is solved as follows. The output of the integral regulator 14 does not become a positive value when it is not necessary to perform overheat protection. Moreover, the output of the regulating unit which is the sum of the output of the proportional regulator 13 and the output of the integral regulator 14 becomes “0,” and the output of the integral regulator 14 is maintained suitably. Thus, the responsiveness of the overheat protection function can be improved.
The second problem is solved as follows. In the above-described example, the initial value of the output of the integral regulator 14 is decreased to −50% when the torque command τ* is decreased from +200% to +20%. However, in the sixth embodiment, the output of the integral regulator 14 is limited to −20% if the output of the proportional regulator 13 is “0”. That is, when the time point when the torque command ξ* is decreased to +20% is taken as a base point, the output of the integral regulator 14 gradually increases toward a positive value with the integration relaxation time from −20% as an initial value. Thus, it is possible to shorten the period in which the torque command τ* is corrected when a state in which it is not necessary to perform overheat protection is created.
According to this embodiment, in a torque command adjusting unit 10G, an integral regulator operation adjusting unit 14a, to which the output of the subtractor 12 and the output (the first torque correction amount τcomp*) of the torque correction amount limiting unit 16a are input, is further provided, unlike the torque command adjusting unit in
In
On the other hand, the output of the integral regulator 14 is limited so that the output of the regulating unit, which is obtained by an addition of the output of the proportional regulator 13 and the output of the integral regulator 14 becomes “0”. Moreover, the output of the integral regulator 14 is limited by a value (that is, −Kp×(temperature deviation)) obtained by subtracting the output (Kp×(temperature deviation)) of the proportional regulator 13 from the upper limit “0” of the torque correction amount limiting unit 16a. That is, since the output of the proportional regulator 13 cancels the output of the integral regulator 14, the output (torque correction amount τcomp*) of the regulating unit becomes “0,” and torque correction is not performed.
Here, a case in which high-frequency noise components are superimposed on the semiconductor temperature will be considered.
In this case, the DC components of the deviation between the preset temperature and the semiconductor temperature (that is, the DC components of the outputs of the proportional regulator 13 and the integral regulator 14) cancel each other as described above. Thus, the output of the regulating unit becomes “0” and no problem occurs.
On the other hand, since the phase of the output of the integral regulator 14 is offset from the phase of the output of the proportional regulator 13 with the integration operation, it is not possible to cancel high-frequency noise components. Due to this, the torque command τ* may be modulated with high frequencies although the semiconductor temperature on which noise is superimposed is lower than the preset temperature. A high-frequency variation in the torque command τ* may obviously cause a high-frequency torque pulsation in the electric motor 4 driven by the inverter 2 and may have an adverse effect on mechanical loads connected to the electric motor 4.
In this case, although the noise may be reduced by passing the semiconductor temperature through a filter, the use of a filter may deteriorate the responsiveness of the overheat protection and may decrease the reliability of the overheat protection.
Thus, in the seventh embodiment illustrated in
The deviation between the preset temperature and the semiconductor temperature and the first torque correction amount τcomp* are input to the integral regulator operation adjusting unit 14a. The integral regulator operation adjusting unit 14a performs a process of allowing and stopping the operation of the integral regulator 14 and clearing the output of the integral regulator 14 to zero according to the flow illustrated in
That is, as illustrated in
With these operations, the problem, which may occur when high-frequency noise components are superimposed on the semiconductor temperature, can be solved as described above. When it is determined that the operation of the integral regulator 14 is to be stopped, the output of the integral regulator 14 is cleared to zero. Thus, it is not necessary to perform such an upper limiting process as performed by the integral regulator limiting unit 16h of
A second preset temperature higher than the preset temperature described in the first to seventh embodiments may be provided. A unit that stops the operation of the power conversion apparatus when the semiconductor temperature exceeds the second preset temperature may be provided. In this case, the second preset temperature is set to be equal to or lower than an absolute maximum rated temperature of a semiconductor device. By doing so, even if the power conversion apparatus falls into a state where it is unable to perform overheat protection in the first to seventh embodiments, the power conversion apparatus stops operating when the semiconductor temperature reaches the second preset temperature. Thus, overheat protection can be performed more reliably.
The present invention is directed to various power conversion apparatuses having a power semiconductor device such as a semiconductor switching device or a recirculation diode and can be used for overheat protection of the semiconductor devices and the power conversion apparatuses.
Number | Date | Country | Kind |
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2013-075596 | Apr 2013 | JP | national |
This application is a continuation application under 35 U.S.C. 120 of International Application PCT/JP2014/050392 having the International Filing Date of Jan. 14, 2014, and claims the priority of Japanese Patent Application No. JP PA 2013-075596, filed on Apr. 1, 2013. The identified applications are fully incorporated herein by reference.
Number | Date | Country | |
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Parent | PCT/JP2014/050392 | Jan 2014 | US |
Child | 14846571 | US |