JP2020089027A - Power conversion device - Google Patents

Abstract

To provide a power conversion device capable of performing an overload protection appropriately even when a rotation number of a cooling fan is reduced.SOLUTION: A power conversion device has an inverter circuit 2 converting DC voltage into AC voltage, and energizing an electric motor 1 with the AC voltage, a current detector 5 detecting load current I1 flowing through the electric motor 1, a cooling fan 7 cooling the inverter circuit 2 or the electric motor 1, and an overload protection portion 8 protecting the inverter circuit 2 or the electric motor 1. The overload protection portion 8 preliminarily holds an energy time limit characteristic map determining a correspondence between the load current I1 and a continuous energization possible time, corrects the energy time limit characteristic map according to a rotation number of the cooling fan 7, and issues an energization stop command (Con) when a continuous energization time of the load current I1 reaches the continuous energization possible time based on the energy time limit characteristic map after the correction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a power converter, for example, an overload protection technique in a power converter that supplies power to a load.

Conventionally, in a power converter that supplies power to a load such as an electric motor, as a protection method against overcurrent or overload, a method of providing a current detection interrupt device (thermal relay) in a power supply line to the power converter is used. Was there. However, since this method simply compares the detected current value and the threshold value, it is not possible to consider the operating state such as the operating speed of the electric motor, and it is not possible to appropriately perform overload protection of the power converter and the electric motor. There were cases.

As a technique for solving such a problem, there is an inverter device as disclosed in Japanese Patent Publication No. 62-55379 (Patent Document 1). The inverter device stores in advance a thermal time period characteristic indicating a continuous operation possible time in consideration of a cooling effect peculiar to the electric motor, and a thermal history simulated value (integrated value) calculated according to the thermal time period characteristic and a current value supplied to the electric motor. ) And. This makes it possible to appropriately perform overload protection in consideration of the operating state of the electric motor. This method is generally called an electronic thermal relay.

Japanese Patent Publication No. 62-55379

Generally, electric motors and electric power conversion devices are required to have high output and small size. In order to eliminate the decrease in the heat dissipation effect caused by this, a cooling fan is often mounted in the electric motor and the power converter. In this case, the thermal time characteristic for the electronic thermal relay described above is determined on the assumption that the cooling fan is operating normally.

However, the rotation speed of the cooling fan may decrease due to, for example, failure, deterioration over time, or contamination. As described above, in a situation where the cooling effect is reduced as the rotation speed of the cooling fan is reduced, it may be difficult to appropriately perform overload protection by the electronic thermal relay. As a result, there is a possibility that the electric motor or the power conversion device will be burnt or damaged.

The present invention has been made in view of the above circumstances, and one of the objects thereof is to provide a power conversion device capable of appropriately performing overload protection even when the rotation speed of a cooling fan decreases. To do.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

The outline of a typical one of the embodiments disclosed in the present application will be briefly described as follows.

A power converter according to a representative embodiment of the present invention converts a DC voltage into an AC voltage, an inverter circuit that energizes a load with the AC voltage, a current detector that detects a load current flowing through the load, It has a cooling fan for cooling the inverter circuit or the load, and an overload protection unit for protecting the inverter circuit or the load. The overload protection unit holds a thermal time period characteristic map that defines the correspondence between the load current and the continuous energizable time, corrects the thermal time period characteristic map according to the rotation speed of the cooling fan, and continuously loads the load current. Issues an energization stop command when the continuous energization possible time based on the corrected thermal time period characteristic map is reached.

To briefly explain the effects obtained by the representative embodiment of the invention disclosed in the present application, it becomes possible to appropriately perform overload protection even when the rotation speed of the cooling fan is reduced.

It is a block diagram showing an example of composition around a power converter by one embodiment of the present invention. It is a schematic diagram showing an example of the outside of the electric power converter of Drawing 1. 2 is a block diagram showing a detailed configuration example of an overload protection unit in FIG. 1. FIG. It is a figure which represents notionally the content of the thermal time limit characteristic map for additions in FIG. It is a figure which represents notionally the content of the thermal time limit characteristic map for a subtraction in FIG. It is a conceptual diagram which shows the typical operation example of an integration system. It is a figure which shows an example of the actual holding content of the thermal time limit characteristic map for addition and subtraction in FIG. It is a schematic diagram which shows the operation example of the power converter device of FIG.

In the following embodiments, when referring to the number of elements, etc. (including the number, numerical value, amount, range, etc.), unless otherwise specified and in principle limited to a specific number, etc., The number is not limited to the specific number, and may be greater than or less than the specific number. Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily essential unless otherwise specified or in principle considered to be essential. Needless to say. Similarly, in the following embodiments, when referring to shapes, positional relationships, etc. of constituent elements, etc., the shapes are substantially the same, unless otherwise specified or in principle not apparently. And the like, etc. are included. This also applies to the above numerical values and ranges.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, the same members are denoted by the same reference symbols in principle and their repeated description is omitted.

<<Configuration around power converter>>
FIG. 1 is a block diagram showing a configuration example around a power conversion device according to an embodiment of the present invention. In addition to the power converter 10, FIG. 1 shows a three-phase power supply 3 that supplies power to the power converter 10 and a load to which power from the power converter 10 is supplied. The load is, for example, the electric motor (three-phase motor) 1 or the like. The power conversion device 10 includes an inverter circuit 2, a converter circuit 4, a current detector 5, a controller 6, an overload protection unit 8, and a current sensor 9.

The converter circuit 4 converts an AC voltage from the external three-phase power supply 3 into a DC voltage Vdc and supplies the DC voltage Vdc to the inverter circuit 2. The inverter circuit 2 converts the DC voltage Vdc into an AC voltage (three-phase AC voltage Vu, Vv, Vw), and energizes the electric motor 1 with the three-phase AC voltage Vu, Vv, Vw. The current sensor 9 is installed on the supply line of the three-phase AC voltage Vu, Vv, Vw. The current detector 5 detects the load current flowing through the electric motor 1 via the current sensor 9. In this example, the current detector 5 detects the u-phase current Iu and the w-phase current Iw via the current sensor 9, and coordinate-converts them into the d-axis current Id and the q-axis current Iq. Then, the current detector 5 detects the load current I1 by vector-synthesizing the d-axis current Id and the q-axis current Iq.

The controller 6 controls the inverter circuit 2 so that the operating state of the electric motor 1 approaches the target state. In this example, the controller 6 receives the speed command value Nref from the outside and outputs the three-phase voltage command values Vuref, Vvref, Vwref for rotating the electric motor 1 at a rotation speed based on the speed command value Nref, without using the position sensor. It is generated using vector control of.

Specifically, the controller 6 estimates the rotation speed of the electric motor 1 using, for example, an induced voltage observer, and based on the error between the rotation speed and the speed command value Nref, the d-axis and q-axis current command values. And three-phase voltage command values Vuref, Vvref, Vwref are calculated based on the error between the current command value and the d-axis current Id and the q-axis current Iq. The inverter circuit 2 performs a switching operation with a PWM (Pulse Width Modulation) signal based on the three-phase voltage command values Vuref, Vvref, and Vwref to generate the three-phase AC voltages Vu, Vv, and Vw. When the electric motor 1 is equipped with a position detector, the rotational speed of the electric motor 1 may be derived from the time difference result of the position detector output and input to the controller 6.

Here, the power converter 10 or the electric motor 1 is provided with a cooling fan 7 for cooling the power converter 10 (in particular, the inverter circuit 2) or the electric motor 1. The cooling fan 7 is equipped with a rotation angle sensor such as a rotary encoder, for example, and is installed for one or both of the power conversion device 10 and the electric motor 1. The cooling fan 7 always rotates regardless of whether the inverter circuit 2 or the electric motor 1 is operating. In particular, such a cooling fan 7 is often mounted in the electric power converter 10 or the electric motor 1 that handles electric power of kW level.

The overload protection unit 8 protects the inverter circuit 2 or the electric motor 1 from overload. The overload protection unit 8 includes a rotation speed Nfan obtained from a rotation angle sensor of the cooling fan 7, a load current I1 from the current detector 5, a clear signal Con_clr, a preset electronic thermal level Ith, and an integrated threshold value. Sth is input. The overload protection unit 8 determines the overload state or the non-overload state while reflecting the rotation speed Nfan of the cooling fan 7 using these input information. The overload protection unit 8 issues an energization stop command to the inverter circuit 2 via the operation permission signal Con when it is determined that the overload state is present. In response to this, the inverter circuit 2 stops energizing the electric motor 1.

In FIG. 1, the current detector 5, the controller 6, and the overload protection unit 8 are typically configured by a microcontroller or the like. In this case, the current detector 5 performs the program processing on the u-phase current Iu and the w-phase current Iw detected by using the analog-digital converter, and thereby the load current I1, the d-axis current Id, and the q-axis current Iw. Calculate Id. The controller 6 and the overload protection unit 8 are also implemented by program processing. However, a part or all of these may of course be configured by a dedicated hardware circuit.

FIG. 2 is a schematic diagram showing an example of the outer shape around the power conversion device of FIG. 1. The power conversion device 10 is composed of, for example, one housing in which each block shown in FIG. 1 is mounted. The operation panel 11 and the like are also installed in the housing, for example. The cooling fan 7a is installed so as to cool the inside of the casing, and particularly cools the heat generated by the transistor of the inverter circuit 2. The overload protection unit 8 detects the number of times Nfan_a of the cooling fan 7a based on the rotation angle sensor of the cooling fan 7a. The cooling fan 7b is installed in the electric motor 1 and cools heat generated by, for example, the coil of the electric motor 1 (parasitic resistance thereof). The overload protection unit 8 detects the number of times Nfan_b of the cooling fan 7b based on the rotation angle sensor of the cooling fan 7b.

<<Outline of overload protection unit>>
FIG. 3 is a block diagram showing a detailed configuration example of the overload protection unit in FIG. The overload protection unit 8 shown in FIG. 3 includes a storage unit 81 that holds the thermal time period characteristic maps 801, 802 in advance, an absolute value calculation unit 803, map data read processing units 804, 807, a correction unit 82, and an overload protection unit 82. The load determining unit 83 and the latch processing unit 813 are provided. First, assuming that the cooling fan 7 is installed in either the power conversion device 10 or the electric motor 1, conceptual processing contents of the overload protection unit 8 will be described.

The thermal time period characteristic maps 801, 802 define the correspondence relationship between the load current I1 and the continuous energizable time. The correction unit 82 corrects the thermal time period characteristic maps 801, 802 according to the rotation speed Nfan of the cooling fan to generate a corrected thermal time period characteristic map. The overload determination unit 83 issues an energization stop command via the overload detection signal Con_res when the continuous energization time of the load current I1 reaches the continuous energization possible time based on the corrected thermal time limit characteristic map.

FIG. 4 is a diagram conceptually showing the contents of the thermal time limit characteristic map 801 for addition in FIG. FIG. 5 is a diagram conceptually showing the contents of the thermal time limit characteristic map 802 for subtraction in FIG. The addition operation time ΔTp shown in FIG. 4 represents a time to be sequentially added when the continuous energization time of the inverter circuit 2 is determined by using the integration method. The continuous energizable time becomes longer as the addition operation time ΔTp increases, and becomes shorter as the addition operation time ΔTp decreases. Similarly, the subtraction operation time ΔTm shown in FIG. 5 represents the time to be successively subtracted when the continuous energization time of the inverter circuit 2 is determined using the integration method. Contrary to the case of the addition operation time ΔTp, the continuous energizable time becomes shorter as the subtraction operation time ΔTm increases, and becomes longer as the subtraction operation time ΔTm decreases.

The addition operation time ΔTp is infinite when the load current I1 is at the electronic thermal level Ith, as shown in the characteristic (referred to as the reference characteristic 20p) when the number Nfan of cooling fans in FIG. 4 is normal. It decreases as the electronic thermal level Ith increases. This reduction characteristic is an n-th power characteristic with respect to the load current I1 in consideration of heat generation associated with the load current I1. The electronic thermal level Ith represents a rated current, and represents a level at which no problem occurs even when the current continues to flow. Further, the addition operation time ΔTp decreases as the rotation speed Nfan decreases with reference to the reference characteristic 20p, as shown in the characteristic when the number Nfan of cooling fans in FIG. 4 decreases (referred to as the corrected characteristic 21p). Shift to decrease.

On the other hand, the subtraction operation time ΔTm is infinite when the load current I1 is at the electronic thermal level Ith, as shown by the reference characteristic 20m in FIG. Decrease in characteristics. Further, as shown by the corrected characteristic 21m in FIG. 5, the subtraction operation time ΔTm shifts in the increasing direction as the cooling fan rotation speed Nfan decreases with reference to the reference characteristic 20m. As described above, the correction unit 82 corrects the reference characteristics 20p and 20m of FIG. 4 and FIG. 5 (that is, the thermal time limit characteristic maps 801 and 802 of FIG. 3) according to the rotation speed Nfan of the cooling fan 7, and 4 and the corrected thermal time limit characteristic map as shown by the corrected characteristics 21p and 21m in FIG. 5 are generated.

FIG. 6 is a conceptual diagram showing a schematic operation example of the integration method. The overload protection unit 8 controls the continuous energizable time Tz by using, for example, an integration method as shown in FIG. The continuous energizable time Tz corresponds to the water in the tank 15. The water in the tank 15 is controlled by the supply valve 16 and the discharge valve 17. The overload determination unit 83 in FIG. 3 issues an operation stop command to the inverter circuit 2 when, for example, the water in the tank 15 is exhausted.

4 and 5, the state where the load current I1 is at the electronic thermal level Ith corresponds to the state where both the supply valve 16 and the discharge valve 17 are fully open in FIG. In this state, the continuous energizable time Tz does not increase or decrease, and the inverter circuit 2 can continue to flow the load current I1. Here, as shown in FIG. 4, when the load current I1 increases from the electronic thermal level Ith and the addition operation time ΔTp decreases, the supply valve 16 is controlled in the closing direction according to the decrease. As a result, the continuous energizable time Tz is controlled in the decreasing direction. Further, when the rotation speed Nfan of the cooling fan decreases and the addition operation time ΔTp shifts in the decreasing direction, the supply valve 16 moves in the closing direction, and the continuous energizable time Tz is controlled in the decreasing direction.

On the other hand, as shown in FIG. 5, when the load current I1 becomes smaller than the electronic thermal level Ith and the subtraction operation time ΔTm decreases, the discharge valve 17 is controlled in the closing direction according to the decrease. As a result, the continuous energizable time Tz is controlled in the increasing direction. As described above, on the assumption that the cooling fan 7 continues to rotate at all times, in the case of “I1<Ith”, the cooling effect is superior to the heating effect, and thus such a subtraction operation time ΔTm is provided. Thus, it becomes possible to increase the continuous energizable time Tz. When the rotation speed Nfan of the cooling fan decreases and the subtraction operation time ΔTm shifts in the increasing direction, the discharge valve 17 moves in the opening direction, and the continuous energizable time Tz is controlled in the decreasing direction.

<<Details of overload protection section>>
Next, detailed processing contents of the overload protection unit 8 of FIG. 3 will be described. FIG. 7 is a diagram showing an example of the actual held contents of the thermal time period characteristic maps 801 and 802 for addition and subtraction in FIG. The thermal time limit characteristic map 801 for addition actually corresponds to the load current I1 larger than the electronic thermal level Ith and the added value Dth_p corresponding to the continuous energizable time, as shown in the reference characteristic 22p of FIG. Establish a relationship. The thermal time limit characteristic map 802 for subtraction actually corresponds to the load current I1 smaller than the electronic thermal level Ith and the subtraction value Dth_m corresponding to the continuous energizable time, as shown in the reference characteristic 22m of FIG. Establish a relationship.

The reference characteristics 22p and 22m shown in FIG. 7 are characteristics obtained by reversing the polarities of the reference characteristics 20p and 20m shown in FIGS. 4 and 5, respectively. The overload protection unit 8 of FIG. 3 actually issues an energization stop command to the inverter circuit 2 when the tank 15 is full, as shown in FIG. 6, instead of when the tank 15 is full. Take action. In this case, the continuous energizable time Tz corresponds to the remaining capacity in the tank 15. The overload protection unit 8 controls the continuous energizable time Tz in a decreasing direction by opening the supply valve 16 as the added value Dth_p increases, and opens the discharge valve 17 as the subtracted value Dth_m increases and thereby the continuous energizable time Tz. Is controlled in the increasing direction.

In FIG. 3, the absolute value calculation unit 803 converts the load current I1 into a load current (absolute value) |I1|. The map data read processing unit 804 for addition uses the load current (absolute value) |I1| as the pointer value Ath_p for each predetermined control cycle, and adds the added value corresponding to the load current I1 from the thermal time limit characteristic map 801 for addition. Read Dth_p. The correction unit 82 corrects the read added value Dth_p by weighting it with a coefficient proportional to the rotation speed Nfan of the cooling fan, and generates a corrected added value Dth_p_cal. In this example, the correction unit 82 generates the corrected addition value Dth_p_cal by multiplying the addition value Dth_p by the inverse number “1/(Nfan×Kfp)” of the value obtained by multiplying the rotation speed Nfan by the coefficient “Kfp”.

The subtraction map data read processing unit 807 uses the load current (absolute value) |I1| as the pointer value Ath_m for each predetermined control cycle, and subtracts the subtraction value corresponding to the load current I1 from the thermal time limit characteristic map 802 for subtraction. Read Dth_m. The correction unit 82 corrects the read subtraction value Dth_m by weighting it with a coefficient that is proportional to the rotation speed Nfan of the cooling fan, and generates a corrected subtraction value Dth_m_cal. In this example, the correction unit 82 generates the corrected subtraction value Dth_m_cal by multiplying the subtraction value Dth_m by the value “Nfan×Kfm” obtained by multiplying the rotation speed Nfan by the coefficient “Kfm”.

In this way, the correction unit 82 corrects the read added value Dth_p so as to increase as the cooling fan rotation speed Nfan decreases, thereby generating the corrected added value Dth_p_cal. Further, the correction unit 82 corrects the read subtraction value Dth_m so as to decrease as the rotation speed Nfan of the cooling fan decreases, thereby generating the corrected subtraction value Dth_m_cal. As a result, the post-correction addition value Dth_p_cal becomes a characteristic that the reference characteristic 22p is shifted in the increasing direction as shown by the post-correction characteristic 23p of FIG. 7, and the post-correction subtraction value Dth_m_cal is the post-correction characteristic of FIG. As indicated by 23 m, the reference characteristic 22 m is shifted in the decreasing direction.

The overload determination unit 83 sequentially integrates the corrected addition value Dth_p_cal or the correction subtraction value Dth_m_cal corrected by the correction unit 82, and issues an energization stop command when the integration value exceeds a predetermined integration threshold Sth. To do. Specifically, the overload determination unit 83 includes an addition/subtraction switching processing unit 810, an integration processing unit 811, and a comparison processing unit 812. The addition/subtraction switching processing unit 810 compares the load current (absolute value) |I1| with the electronic thermal level Ith. Then, the addition/subtraction switching processing unit 810 selects the post-correction addition value Dth_p_cal in the case of “|I1|≧Ith” as the addition/subtraction value Dth_cal to be output, and in the case of “|I1|<Ith”, the post-correction Select the subtraction value Dth_m_cal.

The integration processing unit 811 calculates the integration value Sint by integrating the addition/subtraction value Dth_cal that is sequentially input in each predetermined control cycle. The comparison processing unit 812 compares the integrated value Sint with the integrated threshold value Sth. Then, the comparison processing unit 812 determines the overload state when “Sint≧Sth” and asserts the overload detection signal Con_res, and when “Sint<Sth”, determines the non-overload state. Then, the overload detection signal Con_res is maintained at the negate level.

The latch processing unit 813 negates the operation permission signal Con (that is, issues an energization stop command) when the overload detection signal Con_res is asserted (that is, in the overload state). The inverter circuit 2 performs the energizing operation while the operation permission signal Con is at the assert level, and stops the energizing operation while the operation permission signal Con is at the negate level. When the latch processing unit 813 receives the clear signal Con_clr, the latch processing unit 813 returns the operation permission signal Con to the assert level (that is, the energization permission state).

<<Operation of power converter>>
FIG. 8 is a schematic diagram illustrating an operation example of the power conversion device in FIG. 1. In FIG. 8, for example, the period T1 corresponds to the acceleration period of the electric motor 1, the period T2 corresponds to the steady rotation period of the electric motor 1, and the period T3 is the deceleration period of the electric motor 1 (the load current I1 in the reverse direction). Occurrence period). Usually, the load current (absolute value) |I1| generated during the steady rotation period (period T2) of the electric motor 1 is set to be equal to or lower than the electronic thermal level Ith.

On the other hand, in actual use, a load current (absolute value) |I1| larger than the electronic thermal level Ith may flow during the acceleration period (period T1) and deceleration period (period T3) of the electric motor 1. For example, even if the load current (absolute value) |I1| that exceeds the electronic thermal level Ith flows in this way, the integration method is used in order to continue the operation of the power conversion device 10 and the electric motor 1 without stopping. It would be beneficial to provide overload protection.

In FIG. 8, regarding the integral characteristic 25 when the rotation speed Nfan of the cooling fan is normal, the added value Dth_p is determined based on the reference characteristic 22p of FIG. 7 during the period T1, and the integrated value Sint depends on the added value Dth_p. It increases with a positive slope. In the period T2, the subtraction value Dth_m is determined based on the reference characteristic 22m of FIG. 7, and the integrated value Sint decreases with a negative slope according to the subtraction value Dth_m. In the period T3, the added value Dth_p larger than that in the period T1 is determined based on the reference characteristic 22p in FIG. 7, and the integrated value Sint increases with a positive slope according to the added value Dth_p. In this example, the integrated value Sint exceeds the integrated threshold Sth at the timing (tn) within the period T3. In response to this, the operation permission signal Con transits from the assert level to the negate level.

On the other hand, when the rotation speed Nfan of the cooling fan decreases, the positive slope in the periods T1 and T3 becomes larger than that in the case of the integral characteristic 25 based on the corrected characteristic 23p of FIG. 7, as indicated by the integral characteristic 26. Become. Further, the negative slope in the period T2 is smaller than that in the case of the integral characteristic 25 based on the corrected characteristic 23m of FIG. Accordingly, the integrated value Sint exceeds the integrated threshold Sth at a timing (tc) earlier than the timing (tn) within the period T3. As a result, the continuous energizable time Tz when the rotation speed Nfan of the cooling fan decreases becomes shorter than that when the rotation speed Nfan is normal.

<<Main effects of the embodiment>>
As described above, by using the power conversion device 10 according to the embodiment, the continuous energizable time Tz can be shortened according to the decrease in the rotation speed Nfan of the cooling fan 7, so that even when the rotation speed Nfan of the cooling fan 7 decreases. It becomes possible to properly perform overload protection. As a result, it is possible to prevent the power converter 10 and the electric motor 1 from being burnt out, damaged, etc., and to improve the reliability of the system.

Note that, here, the case where the cooling fan 7 is installed in either the power conversion device 10 or the electric motor 1 has been described as an example, but when the cooling fan 7 is installed in both of them, For example, two types of overload protection units 8 as shown in FIG. 3 (for the power conversion device 10 and for the electric motor 1) may be provided. Then, the operation of the inverter circuit 2 may be stopped when an energization stop command is issued from at least one of the two types of overload protection units 8.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Further, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. .. Further, it is possible to add/delete/replace other configurations with respect to a part of the configurations of the respective embodiments.

For example, here, the case where the overload protection unit 8 of the embodiment is applied to the motor system having the electric motor 1 as a load is taken as an example, but the overload protection unit 8 is not particularly limited to this, and the cooling fan is not limited thereto. It is equally applicable to various power systems that cool heat by.

1 motor 2 inverter circuit 3 three-phase power supply 4 converter circuit 5 current detector 6 controller 7 cooling fan 8 overload protection unit 9 current sensor 10 power converter 81 storage unit 82 correction unit 83 overload determination unit 801, 802 thermal time limit Characteristic map 804, 807 Map data reading processing unit Con Operation permission signal Dth_m Subtraction value Dth_p Addition value I1 Load current Ith Electronic thermal level Nfan Rotation speed Sint integrated value Sth Integrated threshold Tz Continuous energizable time

Claims (9)

An inverter circuit that converts a DC voltage into an AC voltage and energizes a load with the AC voltage,
A current detector for detecting a load current flowing through the load,
A cooling fan for cooling the inverter circuit or the load;
An overload protection unit for protecting the inverter circuit or the load,
Have
The overload protection unit,
A storage unit that holds a thermal time limit characteristic map that defines the correspondence relationship between the load current and the continuous energizable time,
A correction unit that generates a corrected thermal time limit characteristic map by correcting the thermal time limit characteristic map according to the rotation speed of the cooling fan;
An overload determination unit that issues a power supply stop command when the continuous energization time of the load current reaches the continuous energization possible time based on the corrected thermal time limit characteristic map,
Has,
Power converter. The power converter according to claim 1,
The correction unit generates the post-correction thermal time limit characteristic map by weighting the continuous energizable time based on the thermal time limit characteristic map with a coefficient proportional to the rotation speed of the cooling fan,
Power converter. The power converter according to claim 1,
The overload protection unit further includes a map data read processing unit,
The storage unit holds the thermal time limit characteristic map for addition, which defines a correspondence relationship between the load current larger than an electronic thermal level and an addition value corresponding to the continuous energizable time,
The map data read processing unit reads out the added value corresponding to the load current from the thermal time limit characteristic map for addition at predetermined control cycles,
The correction unit corrects the added value read from the map data read processing unit according to the rotation speed of the cooling fan,
The overload determination unit calculates an integrated value by integrating the added value corrected by the correction unit, and issues the energization stop command when the integrated value exceeds a predetermined integration threshold,
Power converter. The power converter according to claim 3,
The correction unit corrects the added value so as to increase as the rotation speed of the cooling fan decreases.
Power converter. The power converter according to claim 3,
The storage unit further holds the thermal time limit characteristic map for subtraction that defines a correspondence relationship between the load current smaller than the electronic thermal level and a subtraction value corresponding to the continuous energization possible time,
The map data read processing unit reads the subtraction value corresponding to the load current from the thermal time limit characteristic map for subtraction at each of the predetermined control cycles,
The correction unit corrects the subtraction value read from the map data read processing unit according to the rotation speed of the cooling fan,
The overload determination unit calculates the integrated value by integrating the subtraction value corrected by the correction unit,
Power converter. The power converter according to claim 5,
The correction unit corrects the subtraction value so as to decrease as the rotation speed of the cooling fan decreases.
Power converter. The power converter according to claim 1,
The power conversion device further includes
A converter circuit that converts an AC voltage from the outside into the DC voltage and supplies the DC voltage to the inverter circuit,
A controller that controls the inverter circuit so that the operating state of the load approaches the target state,
Have
The inverter circuit, the current detector, the overload protection unit, the converter circuit and the controller are mounted in one housing,
The cooling fan is installed to cool the inside of the housing,
Power converter. The power converter according to claim 1,
The load is an electric motor,
The cooling fan is installed in the electric motor,
Power converter. The power converter according to claim 1,
The cooling fan always performs a rotating operation regardless of whether the inverter circuit or the load is operating.
Power converter.

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