Refrigerant abnormality determination device, power conversion device, and refrigerant abnormality determination method

Abstract

Provided is a refrigerant abnormality determination device (1) of a power conversion device that cools a switching element with a refrigerant and includes a temperature protection thermistor (6), wherein a pre-filter thermistor estimation temperature calculation unit (2) calculates a pre-filter thermistor estimation temperature on the basis of a thermistor temperature table (21) having a current command value or a current detection value of the power conversion device as a parameter. The pre-filter thermistor estimation temperature is input to the filter (3). An addition unit (5) calculates a thermistor estimation temperature by adding a refrigerant temperature value from the refrigerant temperature sensor (4) to the value output from the filter (3). An abnormality determination unit (8) determines that the refrigerant is abnormal when a determination time is equal to or smaller than a continuous time during which the difference between the inclination of a thermistor detection temperature from the thermistor (6) and the inclination of the thermistor estimation temperature from the addition unit (5) is equal to or greater than a threshold value.

Description

Refrigerant abnormality determination device, power conversion device, and refrigerant abnormality determination method

[0001] The present invention relates to a temperature protection technique for an IGBT (insulated gate bipolar transistor) in a power conversion device.

[0002] Some power conversion devices (such as motor drive inverters) equipped with switching elements include an IGBT module equipped with a thermistor, which detects the temperature of the switching element chip and provides temperature protection.

[0003] In addition, as a cooling technique for the switching elements, cooling water is circulated as a refrigerant through a water-cooled case in contact with the IGBT module, and the module is cooled by heat exchange. The cooling effect of the switching elements increases as the flow rate of the cooling water increases.

[0004] When using a thermistor to detect the temperature of an IGBT chip in a water-cooled inverter, the chip temperature can only be measured indirectly, so it is necessary to limit the output depending on the operating conditions or estimate the chip temperature to maintain the rated temperature and protect the chip from thermal damage. In other words, there is a temperature difference between the temperature of the thermistor measurement point and the chip temperature based on the thermal resistance value between them.

[0005] The water-cooled case of a water-cooled inverter is usually supplied with cooling water at a flow rate equal to or greater than the reference value, so the protection value for the thermistor temperature is set on the assumption that the cooling water flow rate is equal to or greater than the reference value.

[0006] As mentioned above, thermistor temperature-based protection does not directly measure the chip temperature like the temperature sensor diode method. Therefore, it cannot detect temperature increases due to cooling water abnormalities (e.g., detachment of a cooling hose), which may damage the switching elements. In particular, detecting operational abnormalities in the cooling water pump or other devices may not be fast enough, which may damage the IGBT. Furthermore, because thermistors have a time constant larger than the thermal time constant of the IGBT chip, they cannot protect the chip from temperature transients caused by factors such as a reduction in the cooling water flow rate.

[0007] Although a cooling water flow rate sensor can be installed to detect cooling abnormalities, this increases the cost and size of the equipment.

[0008] To solve these problems, a technique has been proposed for protecting the temperature of switching elements and detecting abnormalities in the cooling system based on the gradient of temperature change in the inverter (Patent Document 1).

[0009] Patent Application No. 2015-136217

[0010] The technology for detecting an abnormality based on the gradient of inverter temperature change, such as that described in Patent Document 1, is based on the premise that the loss generated by the switching elements (i.e., the inverter load) remains constant during temperature changes. Under conditions where the inverter load fluctuates, it becomes difficult to detect an abnormality in the cooling system.

[0011] In view of the above circumstances, an object of the present invention is to reliably detect an abnormality in the refrigerant and protect the switching elements from temperature fluctuations even under conditions where the inverter load fluctuates.

[0012] Therefore, one aspect of the present invention is a refrigerant abnormality determination device for a power conversion device that cools a switching element with a refrigerant and is equipped with a thermistor for temperature protection of the switching element, and includes: a pre-filter thermistor estimated temperature calculation unit that calculates a pre-filter thermistor estimated temperature based on a thermistor temperature table that uses a current command value or current detection value of the power conversion device as a parameter; a filter to which the pre-filter thermistor estimated temperature is input; an adder unit that calculates the thermistor estimated temperature by adding the refrigerant temperature value from a refrigerant temperature sensor to the value output from the filter; and an abnormality determination unit that determines that the refrigerant is abnormal if the continuous time during which the difference between the slope of the thermistor detected temperature from the thermistor and the slope of the thermistor estimated temperature from the adder is greater than or equal to a threshold value is greater than a determination time.

[0013] In one aspect of the present invention, in the refrigerant abnormality determination device, the thermistor is provided in a module of the switching element.

[0014] In one aspect of the present invention, in the refrigerant abnormality determination device, the carrier frequency of the gate on / off command for the switching element and the motor rotation speed command value or the motor rotation speed detection value are set as parameters of the thermistor temperature table.

[0015] In one aspect of the present invention, in the refrigerant abnormality determination device, the thermistor temperature table shows the relationship between the thermistor temperature and the current command value or the current detection value, the carrier frequency, the motor rotation speed command value or the motor rotation speed detection value, and the reference flow rate, which are obtained based on actual measurements of the thermistor temperature when the power conversion device operates under a predetermined current command value or the current detection value, a carrier frequency for a gate on / off command for the switching element, a motor rotation speed command value or the motor rotation speed detection value, and a reference flow rate of the refrigerant.

[0016] One aspect of the present invention is a power conversion device including the above-described refrigerant abnormality determination device.

[0017] One aspect of the present invention is a refrigerant abnormality determination method executed by a refrigerant abnormality determination device for a power conversion device in which switching elements are cooled by a refrigerant and which is equipped with a thermistor for temperature protection, the method comprising the steps of: calculating a pre-filter thermistor estimated temperature based on a thermistor temperature table in which a current command value or a current detection value is a parameter; inputting the pre-filter thermistor estimated temperature into a filter; calculating the thermistor estimated temperature by adding the refrigerant temperature value from a refrigerant temperature sensor to the value output from the filter; and determining that the refrigerant is abnormal if the continuous time during which the difference between the slope of the thermistor detected temperature from the thermistor and the slope of the calculated thermistor estimated temperature is greater than or equal to a threshold value is greater than a determination time.

[0018] According to the present invention, it is possible to determine whether the refrigerant is abnormal and to protect the switching elements from overheating even under conditions where the inverter load fluctuates.

[0019] The present invention relates to a refrigerant abnormality determination device, a refrigerant abnormality determination device, and a refrigerant abnormality determination device.

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] A refrigerant abnormality determination device 1 according to one embodiment of the present invention shown in FIG. 1 determines an abnormality in a refrigerant that protects the temperature of a switching element (IGBT) of a power conversion device that uses a thermistor temperature monitoring system.

[0022] The coolant may be a well-known cooling water, cooling oil, or the like used in the power conversion device. Examples of coolant abnormalities include loss of the coolant due to damage or detachment of the coolant supply path. The switching element module is joined to a coolant case (not shown).

[0023] The refrigerant abnormality determination device 1 includes a pre-filter thermistor estimated temperature calculation unit 2, a filter 3, a refrigerant temperature sensor 4, an adder 5, a thermistor 6, a slope calculation unit 7, and an abnormality determination unit 8.

[0024] The pre-filter thermistor estimated temperature calculation unit 2 calculates the pre-filter thermistor estimated temperature based on a thermistor temperature table 21 that uses the current command value or the current detection value of the power conversion device as a parameter.

[0025] The thermistor temperature table 21 shows the relationship between the thermistor temperature and the current command value or the current detection value, the carrier frequency, the motor rotation speed command value or the motor rotation speed detection value, and the reference flow rate, which are obtained based on the actual measurement value of the thermistor temperature when the power conversion device is operating under a predetermined current command value or the current detection value, the carrier frequency, the motor rotation speed command value or the motor rotation speed detection value, and the reference flow rate of the refrigerant.

[0026] The filter 3 has a function of outputting a value with a delay corresponding to the thermistor thermal time constant with respect to the change in input value over time (a typical example is an RC filter), and receives the pre-filter thermistor estimated temperature from the pre-filter thermistor estimated temperature calculation unit 2. The thermistor thermal time constant is determined based on the thermal time constant of the refrigerant case and the thermal time constant of the switching element.

[0027] The refrigerant temperature sensor 4 is provided at the input portion of a refrigerant case (not shown) that stores the refrigerant, and detects the refrigerant temperature.

[0028] The adder 5 adds the value of the refrigerant temperature detected by the refrigerant temperature sensor 4 to the value output from the filter 3 to calculate the thermistor estimated temperature.

[0029] The thermistor 6 is provided in the module of the switching element for temperature protection of the switching element, and outputs the detected temperature as a thermistor detected temperature.

[0030] The gradient calculation unit 7 calculates the gradient of the thermistor estimated temperature received from the addition unit 5 and the thermistor detected temperature received from the thermistor 6 .

[0031] The abnormality determination unit 8 determines that the refrigerant is abnormal when the continuous time during which the difference between the gradient of the thermistor detected temperature and the gradient of the thermistor estimated temperature is equal to or greater than a threshold value is equal to or greater than a determination time.

[0032] An example of the operation of the refrigerant abnormality determination device 1 will be described with reference to FIGS.

[0033] First, in a preliminary test, for example, a predetermined inverter (motor) current command value related to the loss generated by the switching element, a carrier frequency of a gate on / off command for the switching element, a motor rotation speed, and a thermistor temperature (at saturation) when the power conversion device is operated with a cooling water (refrigerant) at a reference flow rate are measured. The reference flow rate of the cooling water is set to the minimum flow rate possible for actual load operation. Then, based on the measured thermistor temperature, a thermistor temperature table 21 is created that shows the relationship between the current command value, the carrier frequency, the detected motor rotation speed (or the motor rotation speed command value), the reference cooling water flow rate, and the thermistor temperature. This thermistor temperature table 21 is stored in the pre-filter thermistor estimated temperature calculation unit 2. Note that if the carrier frequency is always constant or if a load other than a motor is used as the inverter load, only the current command value may be used as the parameter. Alternatively, the detected current value may be used as the parameter instead of the current command value.

[0034] Next, during actual load operation, the pre-filter thermistor estimated temperature calculation unit 2 calculates the pre-filter thermistor estimated temperature from the current command value, the carrier frequency, the motor rotation speed detection value or the motor rotation command value, and the reference flow rate of the cooling water based on the thermistor temperature table 21. This pre-filter thermistor estimated temperature is input to the filter 3.

[0035] Addition unit 5 calculates the thermistor estimated temperature by adding the refrigerant temperature value from refrigerant temperature sensor 4 to the value output from filter 3. In this way, the pre-filter thermistor estimated temperature calculated by pre-filter thermistor estimated temperature calculation unit 2 is supplied to addition unit 5 via filter 3 which takes into account the thermal time constant of the refrigerant case, thereby improving the accuracy of the thermistor estimated temperature when the loss generated by the switching element suddenly changes.

[0036] Next, the gradient calculation unit 7 calculates the gradient of the thermistor estimated temperature provided by the addition unit 5 and the gradient of the thermistor detected temperature provided by the thermistor 6 .

[0037] Then, the abnormality determination unit 8 performs the refrigerant abnormality determination process shown in FIG. 2-4, for example.

[0038] During normal operation, the thermistor detected temperature and thermistor estimated temperature transition from 0 to 5 seconds as shown in Figure 2. The estimated temperature is higher than the detected temperature because it is estimated using the worst-case value, taking into account variations in detection. The slope of the detected temperature and the estimated temperature calculated by the slope calculation unit 7 is shown in Figure 3 (processing cycle: 500 ms). The temperature rise component due to normal inverter operation appears from 0.5 seconds to 4 seconds in the figure. To remove the temperature rise component due to normal inverter operation, the difference between the slope of the thermistor detected temperature and the slope of the thermistor estimated temperature (slope of the detected temperature - slope of the estimated temperature) is calculated to extract only the temperature rise component due to a refrigerant abnormality (e.g., cooling water leakage), as shown in Figure 4. If the continuous time during which the difference in slope is greater than or equal to a threshold value is greater than or equal to a judgment time, the refrigerant is determined to be abnormal. The threshold value and judgment time are set to values ​​that can protect the switching element chip temperature based on the pre-test.

[0039] When an abnormality is detected, the inverter is stopped by turning off all of the switching elements, and a fault signal indicating the occurrence of cooling water leakage is output to the outside, thereby preventing damage to the switching elements due to high temperatures.

[0040] Therefore, with the refrigerant abnormality detection device 1 of this embodiment, it is possible to detect refrigerant abnormalities and protect the temperature of the switching elements even when the inverter load fluctuates by using the thermistor temperature table 21 and filter 3. Furthermore, it is possible to detect abnormalities such as cooling water leakage and protect the switching elements without the need for a cooling water flow sensor, thereby reducing the cost and size of the inverter device.

[0041] The above embodiment utilizes the characteristic that the thermistor temperature rises rapidly when the coolant is drained, but the present invention can also be applied to configurations in which the thermistor is attached to a location other than the IGBT module (e.g., the surface of the coolant case), and can also be applied to coolants other than coolant (e.g., cooling oil).

[0042] REFRIGERATED REFRIGERATED TEMPERATURE DETECTION DEVICE 2 Pre-filter thermistor estimated temperature calculation unit 21 Thermistor temperature table 3 Filter 4 Refrigerant temperature sensor 5 Addition unit 6 Thermistor 7 Slope calculation unit 8 Abnormality determination unit

Claims

1. A refrigerant abnormality determination device for a power conversion device in which a switching element is cooled by a refrigerant and which is provided with a thermistor for temperature protection of the switching element, comprising: a pre-filter thermistor estimated temperature calculation unit that calculates a pre-filter thermistor estimated temperature based on a thermistor temperature table in which a current command value or a current detection value of the power conversion device is a parameter; a filter to which the pre-filter thermistor estimated temperature is input; an adder unit that calculates the thermistor estimated temperature by adding a refrigerant temperature value from a refrigerant temperature sensor to the value output from the filter; and an abnormality determination unit that determines that the refrigerant is abnormal if the continuous time during which the difference between the slope of the thermistor detected temperature from the thermistor and the slope of the thermistor estimated temperature from the adder is equal to or greater than a threshold value is equal to or greater than a determination time.

2. The refrigerant abnormality determination device according to claim 1, wherein the thermistor is provided in a module of the switching element.

3. The refrigerant abnormality determination device according to claim 1, wherein the carrier frequency of the gate on / off command for the switching element and the motor rotation speed command value or the motor rotation speed detection value are set as parameters of the thermistor temperature table.

4. The refrigerant abnormality determination device of claim 3, wherein the thermistor temperature table indicates the relationship between the thermistor temperature and the current command value or current detection value, the carrier frequency, the motor rotation speed command value or motor rotation speed detection value, and the reference flow rate, which are obtained based on the actual measured value of the thermistor temperature when the power conversion device is operating under a predetermined current command value or current detection value, a carrier frequency of a gate on / off command for the switching element, a motor rotation speed command value or motor rotation speed detection value, and a reference flow rate of the refrigerant.

5. A power conversion device comprising the refrigerant abnormality determination device according to claim 1.

6. A refrigerant abnormality determination method executed by a refrigerant abnormality determination device for a power conversion equipment in which switching elements are cooled by a refrigerant and which is equipped with a thermistor for temperature protection, comprising the steps of: calculating a pre-filter thermistor estimated temperature based on a thermistor temperature table having a current command value or a current detection value as a parameter; inputting the pre-filter thermistor estimated temperature to a filter; calculating a thermistor estimated temperature by adding a refrigerant temperature value from a refrigerant temperature sensor to the value output from the filter; and determining that the refrigerant is abnormal if the continuous time during which the difference between the slope of the thermistor detected temperature from the thermistor and the slope of the calculated thermistor estimated temperature is equal to or greater than a threshold value is equal to or greater than a determination time.

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