JP2016140122A - Control method for electric power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion system which includes a plurality of inverter circuits in one cooling system and is capable of achieving overheat protection control without posing problems such as degradation in control responsiveness, enlargement of a harmonic content of an inverter output current, noise due to vibration, and a change in load running state.SOLUTION: The electric power conversion system lowers switching frequencies of k units of inverter circuits (1≤k≤N-1) when a temperature of a cooling system has exceeded a predetermined threshold value A. When a temperature of the cooling system falls below a threshold value B which is set lower than the threshold value A, the electric power conversion system returns switching frequencies of the k units of inverter circuits for which the switching frequencies have been lowered to initial switching frequencies.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power conversion device in which a plurality of inverter circuits are provided in a set of cooling systems (heat radiators), and more particularly to overheat protection in switching elements of the inverter circuits.

  The following patent documents 1 to 3 are disclosed as techniques for continuously operating an inverter circuit while overheating protection is applied to a switching element of the inverter circuit.

(Patent Document 1: FIG. 6)
The detected temperature of the switching element and the first reference temperature are compared every predetermined time, and when the detected temperature exceeds the first reference temperature, a command for lowering the carrier frequency (that is, the switching frequency of the switching element) is output. To do. When the carrier frequency lowering command is input, the switching frequency is decreased by a predetermined value from the initial switching frequency.

  Also, when the detected temperature falls below the second reference value, a carrier frequency return command is output to return to the initial switching frequency.

(Patent Document 2: FIG. 7)
Means for detecting the switching element temperature is provided in the vicinity of the switching element, and the torque command value is limited so that the switching element is suppressed to the element upper limit temperature or less.

(Patent Document 3: FIG. 8)
The temperature estimation unit has a thermal circuit model for estimating a change in the junction temperature of the heat generating component for each of the plurality of heat generating components, and the power loss information of the heat generating component to be estimated selected from the plurality of heat generating components and other than the estimation target Obtain the power loss information of the heat-generating component and estimate the junction temperature to be estimated. The protection control unit selects reduction of the carrier frequency (that is, switching frequency of the switching element) or reduction of the inverter output current, and performs overheat protection control of the heat-generating component such as the switching element.

  Moreover, as shown in FIG. 1, in the power converter device which has a plurality of inverter circuits, what cools all inverter circuits 1a, 1b, 1c with one radiator is known.

Japanese Patent Laid-Open No. 3-178565 JP 2011-97672 A JP 2014-64435 A

  However, in a power conversion device in which a plurality of inverter circuits are provided in a set of cooling systems (heat radiators), the following problems occur when the techniques of Patent Documents 1 to 3 are applied to all inverter circuits. .

  In Patent Document 1, the switching frequency is lowered when the detected temperature exceeds the first reference temperature. This reduction in the switching frequency causes deterioration of the control response of the inverter. Further, the operation with the switching frequency lowered causes problems such as an increase in the harmonic component of the inverter output current, and noise due to vibration or the like when an electric motor is used for the inverter load.

  Further, in Patent Document 2, since the torque command value is limited when the switching element is in the vicinity of the element upper limit temperature, only light load operation can be performed, and the operation state of the load needs to be changed.

  In Patent Document 3, the switching frequency or output current of an inverter circuit having a high output current is reduced. However, when the switching frequency is lowered, the control response of the inverter circuit is deteriorated. Further, the operation with the switching frequency lowered causes problems such as an increase in the harmonic component of the inverter output current, and noise due to vibration or the like when an electric motor is used for the inverter load.

  Further, when the output current is reduced, only light load operation can be performed, and it is necessary to change the operation state of the load.

  Therefore, in the power conversion device in which a plurality of inverter circuits are provided in one cooling system (heat radiator), the problems described above occur in all the inverter circuits. In an inverter circuit, it is desirable to protect the switching element from overheating without reducing the output current or switching frequency.

  As described above, in a power conversion device in which a plurality of inverter circuits are provided in one cooling system, deterioration of control responsiveness, increase in harmonic components of inverter output current, noise due to vibration, load operating conditions It becomes a problem to perform overheat protection control without causing problems such as changes.

  The present invention has been devised in view of the above-described conventional problems, and one aspect thereof includes an inverter circuit provided with N units (N ≧ 2) in one cooling system, and a switching element of the inverter circuit. A control unit that performs on / off control, wherein the control unit includes k units (1 ≦ k ≦ N) when a temperature of the cooling system exceeds a preset threshold A. -1) when the switching frequency of the inverter circuit is reduced, and when the temperature of the cooling system falls below a threshold value B set lower than the threshold value A, the switching frequency of the k inverter circuits reduced. The switching frequency is returned to the initial switching frequency.

  Further, as one aspect thereof, a current detector that detects an output current of each inverter circuit is provided, and when the temperature of the cooling system exceeds the threshold A, the control unit outputs an output current among N inverter circuits. K inverter circuits are counted from the larger one, and when the cooling system temperature exceeds the threshold A, the switching frequency of the identified k inverter circuits is reduced, and the cooling system temperature is reduced. When the value falls below the threshold value B, the switching frequency of the identified k inverter circuits is returned to the initial switching frequency.

  Further, as one aspect thereof, the control unit designates (Nk) units (1 ≦ k ≦ N−1) of high-response inverter circuits that do not change the switching frequency in advance, and the temperature of the cooling system is the threshold value. When A is exceeded, the switching frequency of k inverter circuits other than the designated high response inverter circuit is reduced, and when the temperature of the cooling system falls below the threshold B, other than the designated high response inverter circuit The switching frequency of the k inverter circuits is returned to the initial switching frequency.

  Further, as one aspect thereof, a current detector that detects an output current of each inverter circuit is provided, and when the temperature of the cooling system exceeds the threshold A, the control unit outputs an output current among N inverter circuits. (Nk) inverter circuits from the larger one are identified, and when the temperature of the cooling system exceeds the threshold A, k other than the (Nk) inverter circuits from the larger output current. When the switching frequency of the inverter circuit is reduced and the temperature of the cooling system falls below the threshold value B, the switch of k inverter circuits other than the (N−k) inverter circuits from the one with the larger output current The switching frequency is returned to the initial switching frequency.

  Further, as one aspect thereof, when the temperature of the cooling system exceeds the threshold value A, the control unit is configured from (N−k) units of N inverter circuits in which the frequency of the output voltage or output current is larger. When the temperature of the cooling system exceeds the threshold value A, the frequency of the output voltage or output current of the k inverter circuits other than the (N−k) inverter circuits is larger. When the switching frequency is reduced and the temperature of the cooling system falls below the threshold value B, the frequency of the output voltage or output current of k inverter circuits other than the (N−k) inverter circuits is larger. The switching frequency is returned to the initial switching frequency.

  According to the present invention, in a power converter provided with a plurality of inverter circuits in one cooling system, deterioration of control responsiveness, increase of harmonic components of inverter output current, noise due to vibration, change of load operating state, etc. It is possible to perform overheat protection control without causing this problem.

The figure which shows the main circuit of the power converter device in embodiment. 3 is a flowchart illustrating a control method according to the first embodiment. 10 is a flowchart illustrating a control method according to the second embodiment. 10 is a flowchart illustrating a control method according to the third embodiment. 10 is a flowchart illustrating a control method according to the fourth embodiment. Schematic which shows patent document 1. FIG. Schematic which shows patent document 2. FIG. Schematic which shows patent document 3. FIG.

  Hereinafter, Embodiments 1 to 4 of the power conversion device according to the present invention will be described in detail with reference to FIGS.

[Embodiment 1]
As shown in FIG. 1, the power conversion device according to the first embodiment includes a plurality of (N units) inverter circuits 1 a, provided in one cooling system (for example, a radiator: hereinafter referred to as a radiator). 1b, 1c (any number of two or more), a control unit 2 that drives and controls the inverter circuits 1a, 1b, 1c, a radiator temperature sensor 5 that measures the temperature of the radiator 3, a load 4a, 4b, 4c. Although not shown in FIG. 1, the power converter includes means for detecting the output current value of each inverter circuit 1a, 1b, 1c.

  Hereinafter, based on the flowchart shown in FIG. 2, the control method of the power converter device in this Embodiment 1 is demonstrated. The threshold value A, threshold value B, and threshold value C shown below are preset values, and their magnitudes are threshold value B <threshold value A <threshold value C.

  S1: First, the temperature of the radiator 3 is detected by the radiator temperature sensor 5.

  S2: Next, the control unit 2 compares the detection value (temperature information) of the radiator temperature sensor 5 with the threshold A. When the inverter circuits 1a, 1b, and 1c are operating and the temperature information of the radiator temperature sensor 5 exceeds the threshold value A, the process proceeds to S3. When the temperature information of the radiator temperature sensor 5 is equal to or less than the threshold value A, the process proceeds to S8 and the operation is continued.

  S3: The control unit 2 identifies one inverter circuit having the maximum output current from the output current values of the inverter circuits 1a, 1b, and 1c. Among the inverter circuits 1a, 1b, and 1c, the switching frequency of one inverter circuit having the maximum specified output current is lowered, and the switching loss of the inverter circuit is reduced. Thereby, the increase in the total generated loss of the inverter circuits 1a, 1b, 1c is reduced, and the temperature rise of the entire radiator 3 is suppressed. As a result, all the inverter circuits 1a, 1b, 1c can be protected from overheating, and the operation of the load connected to the inverter circuit whose output current is not maximum can be continued without changing the output current or frequency.

  S4: The control unit 2 compares the temperature information of the radiator temperature sensor 5 with the threshold value B. When the temperature information of the radiator temperature sensor 5 becomes a value smaller than the threshold value B, the process proceeds to S5. When the temperature information of the radiator temperature sensor 5 is greater than or equal to the threshold value B, the process proceeds to S6.

  S5: In the control unit 2, the switching frequency is returned to the initial switching frequency, and the operation is continued (return to S1).

  S6: The control unit 2 compares the temperature information of the radiator temperature sensor 5 with the threshold value C. When the temperature information of the radiator temperature sensor 5 is larger than the threshold value C, the process proceeds to S7. When the temperature information of the radiator temperature sensor 5 is not more than the threshold value C, the process proceeds to S8.

  S7: The control unit 2 determines that the overheating is abnormal, and interrupts the operation of all the inverter circuits 1a, 1b, 1c.

  S8: In the control unit 2, the operation is continued as it is, and the process returns to S1.

  In the control method of the power conversion device according to the first embodiment, when the inverter circuits 1a, 1b, and 1c are operated, the heat generation from the semiconductor switching elements of the inverter circuits 1a, 1b, and 1c is predicted from the output current. Reduces only the switching frequency of the inverter circuit with high output, controls the overall loss to be below a certain value, and protects the inverter circuit from overheating while maintaining the response of the inverter circuit that does not change the switching frequency It is.

  Since the switching loss is substantially proportional to the inverter current, the first embodiment that lowers the switching frequency of the inverter circuit with the maximum output current has the effect of reducing the loss of the entire system (that is, the effect of reducing the temperature of the entire radiator 3). ) Is high.

  According to the first embodiment, in a power conversion device in which a plurality of inverter circuits 1a, 1b, and 1c are provided in one radiator 3, even if the temperature information of the radiator temperature sensor 5 exceeds the threshold value A, output is performed. The operation can be continued without changing the output current and output frequency of the inverter circuit whose current is not maximum. That is, the operation can be continued without changing the operation state of the loads 4a, 4b, and 4c connected to the inverter circuit whose output current is not maximum.

  In addition, the switching frequency is reduced only for the inverter circuit with the maximum output current, and the switching frequency does not change for other inverter circuits, so that the control responsiveness is deteriorated and the harmonics of the output current are increased. Further, it is possible to suppress an increase in noise of the motor load.

  In the first embodiment, the method of reducing the switching frequency of one inverter circuit having the maximum output current among the three inverter circuits has been described. However, among the N inverter circuits, the output current is large. The switching frequency of k inverter circuits (1 ≦ k ≦ N−1) counting from the side may be reduced.

[Embodiment 2]
The main circuit of the power conversion device according to the second embodiment is the same as that of the first embodiment.

  Hereinafter, based on the flowchart shown in FIG. 3, the control method of the power converter device in this Embodiment 2 is demonstrated.

  S9: In the control unit 2, one inverter circuit (hereinafter referred to as a high response inverter circuit) for which high control response is required is designated in advance among the inverter circuits 1a, 1b, and 1c.

  S1: The same as in the first embodiment.

  S2: In the control unit 2, the temperature information of the radiator temperature sensor 5 is compared with the threshold A, and when the radiator temperature sensor 5 exceeds the threshold A, the process proceeds to S10. Others are the same as in the first embodiment.

  S10: In the control unit 2, one high-response inverter circuit designated in S9 and two inverter circuits that are not high-response inverter circuits are allocated. The high response inverter circuit designated in S9 proceeds to S8 and continues operation as it is. Except for the high-response inverter circuit designated in S9, the process proceeds to S3.

  S3: The control unit 2 reduces the frequency of inverter circuits other than the high-response inverter circuit specified in S9.

  S4 to S8: The same as in the first embodiment.

  As described above, since the power conversion device according to the second embodiment does not lower the switching frequency of the designated inverter circuit, the responsiveness of the designated inverter circuit does not change.

  Further, by lowering the switching frequency of the inverter circuits other than the high-response inverter circuit designated in advance, the switching loss of the inverter circuit is reduced, and the total generated loss of the inverter circuits 1a, 1b, 1c is reduced. As a result, the temperature rise of the radiator 3 is suppressed, and all the inverter circuits 1a, 1b, 1c are protected from overheating.

  In addition, the power conversion device according to the second embodiment has the same effects as those of the first embodiment.

  In the second embodiment, the method of reducing the switching frequency of two inverter circuits other than the high-response inverter circuit among the three inverter circuits has been described. -K) The switching frequency of k inverter circuits other than the inverter circuits may be reduced.

[Embodiment 3]
In the third embodiment, the switching frequency of inverter circuits other than the inverter circuit having the maximum output current among the plurality of inverter circuits is reduced. The main circuit of the power conversion device according to the third embodiment is assumed to include detection means for detecting the output current value of each inverter circuit.

  Hereinafter, based on the flowchart shown in FIG. 4, the control method of the power converter device in this Embodiment 3 is demonstrated.

  S1: The same as in the first and second embodiments.

  S2: In the control unit 2, the temperature information of the radiator temperature sensor 5 is compared with the threshold A, and when the temperature information of the radiator temperature sensor 5 exceeds the threshold A, the process proceeds to S11. Others are the same as in the first and second embodiments.

  S11: When the inverter circuits 1a, 1b, 1c are operating and the temperature information of the radiator temperature sensor 5 exceeds the threshold A, the control unit 2 identifies one inverter circuit with the maximum output current. To do. One inverter circuit with the maximum output current moves to S8 and continues operation. The two inverter circuits with the maximum output current shift to S3.

  S3: The control unit 2 lowers the switching frequency of two inverter circuits other than the inverter circuit having the maximum specified output current among the inverter circuits 1a, 1b, and 1c. As a result, the switching loss of the inverter circuits other than the inverter circuit having the maximum output current is reduced, and the total generated loss of the inverter circuits 1a, 1b, and 1c is reduced. As a result, the temperature rise of the radiator 3 is suppressed, and all the inverter circuits 1a, 1b, 1c are protected from overheating.

  S4 to S8: The same as in the first and second embodiments.

  As described above, the power conversion device according to the third embodiment can be continuously operated without changing the output current and output frequency of the inverter circuit having the maximum output current. That is, the operation can be continued without changing the operation state of the load connected to the inverter circuit having the maximum output current.

  Moreover, this Embodiment 3 has the same effect as Embodiment 1,2.

  In the third embodiment, the method of reducing the switching frequency of two inverter circuits whose output current is not the maximum among the three inverter circuits has been described. The switching frequency of the k inverter circuits may be reduced.

[Embodiment 4]
In the fourth embodiment, the switching frequency of inverter circuits other than the inverter circuit that outputs the highest frequency among the plurality of inverter circuits is reduced.

  Hereinafter, based on the flowchart shown in FIG. 5, the control method of the power converter device in this Embodiment 4 is demonstrated.

  S1: The same as in the first and second embodiments.

  S2: In the control unit 2, the temperature information of the radiator temperature sensor 5 is compared with the threshold A, and when the temperature information of the radiator temperature sensor 5 exceeds the threshold A, the process proceeds to S12. Others are the same as in the first and second embodiments.

  S12: When the inverter circuits 1a, 1b, and 1c are operating, and the temperature information of the radiator temperature sensor 5 exceeds the threshold A, the frequency of the output voltage (or output current) is maximum in the control unit 2. One inverter circuit is specified. This specification can be made by comparing the output frequency command values of the inverter circuits 1a, 1b, and 1c. One inverter circuit having the maximum frequency of the output voltage (or output current) shifts to S8 and continues operation. The two inverter circuits whose output voltage (or output current) frequency is not maximum shift to S3.

  S3: The control unit 2 lowers the switching frequency of two inverter circuits other than the inverter circuit having the maximum specified output frequency among the inverter circuits 1a, 1b, and 1c. Thereby, the switching loss of inverter circuits other than the inverter circuit that outputs the maximum frequency is reduced, and the total generated loss of the inverter circuits 1a, 1b, and 1c is reduced. As a result, the temperature rise of the radiator 3 is suppressed, and all the inverter circuits 1a, 1b, 1c are protected from overheating.

  S4 to S8: The same as in the first and second embodiments.

  As described above, the power conversion apparatus according to the fourth embodiment continues to operate without changing the output current and output frequency of the inverter circuits 1a, 1b, and 1c having the maximum output voltage (or output current) frequency. be able to. That is, the operation can be continued without changing the operation state of the load connected to the inverter circuit having the maximum frequency of the output voltage (or output current).

  The fourth embodiment can continue operation while protecting all inverter circuits from overheating without changing the control responsiveness of the inverter circuits connected to a load having a high output frequency and high responsiveness. Moreover, this Embodiment 4 has the same effect as Embodiment 1-3.

  In the fourth embodiment, the method of reducing the switching frequency of two inverter circuits in which the frequency of the output voltage (or output current) is not the maximum among the three inverter circuits has been described. However, the N inverter circuits Of these, the switching frequency of the k inverter circuits may be reduced, counting from the one having the smaller frequency of the output voltage (or output current).

  Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical idea of the present invention. Such variations and modifications are naturally within the scope of the claims.

DESCRIPTION OF SYMBOLS 1a, 1b, 1c ... Inverter circuit 2 ... Control part 3 ... Cooling system 4a, 4b, 4c ... Load 5 ... Radiator temperature sensor

Claims (6)

An inverter circuit provided with N units (N ≧ 2) in one cooling system;
A control unit for controlling on / off of the switching element of the inverter circuit;
A method for controlling a power conversion device comprising:
The controller is
When the temperature of the cooling system exceeds a preset threshold A, the switching frequency of the k inverter circuits (1 ≦ k ≦ N−1) is reduced,
When the temperature of the cooling system falls below a threshold value B set lower than the threshold value A, the switching frequency of the k inverter circuits having the reduced switching frequency is returned to the initial switching frequency. Control method for power converter. It has a current detector that detects the output current of each inverter circuit,
The controller is
When the temperature of the cooling system exceeds the threshold value A, the k inverter circuits are identified by counting from the one having the larger output current among the N inverter circuits,
When the temperature of the cooling system exceeds the threshold A, the switching frequency of the identified k inverter circuits is reduced,
2. The method of controlling a power converter according to claim 1, wherein when the temperature of the cooling system falls below the threshold B, the switching frequency of the identified k inverter circuits is returned to an initial switching frequency. . The controller is
(Nk) units of high-response inverter circuits that do not change the switching frequency are designated in advance,
When the temperature of the cooling system exceeds the threshold A, the switching frequency of the k inverter circuits other than the designated high response inverter circuit is reduced,
2. The power according to claim 1, wherein when the temperature of the cooling system falls below the threshold value B, the switching frequency of the k inverter circuits other than the designated high response inverter circuit is returned to the initial switching frequency. Control method of conversion device. It has a current detector that detects the output current of each inverter circuit,
The controller is
When the temperature of the cooling system exceeds the threshold A, (N−k) inverter circuits are identified from the N inverter circuits having the larger output current,
When the temperature of the cooling system exceeds the threshold A, the switching frequency of the k inverter circuits other than the (N−k) inverter circuits is reduced from the larger output current,
When the temperature of the cooling system falls below the threshold value B, the switching frequency of the k inverter circuits other than the (N−k) inverter circuits is returned to the initial switching frequency from the higher output current. The method for controlling a power conversion device according to claim 1, wherein: The controller is
When the temperature of the cooling system exceeds the threshold value A, (N−k) inverter circuits are identified from the N inverter circuits having the higher output voltage or output current frequency,
When the temperature of the cooling system exceeds the threshold A, the switching frequency of the k inverter circuits other than the (N−k) inverter circuits is reduced from the higher one of the frequency of the output voltage or output current,
When the temperature of the cooling system falls below the threshold value B, the switching frequency of the k inverter circuits other than the (N−k) inverter circuits from the higher frequency of the output voltage or output current is initially switched. The method for controlling a power converter according to claim 1, wherein the frequency is restored.   A power conversion device using the control method according to claim 1.

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