WO2019198312A1

WO2019198312A1 - Power conversion device

Info

Publication number: WO2019198312A1
Application number: PCT/JP2019/003736
Authority: WO
Inventors: 研吾後藤; 智道伊藤
Original assignee: 株式会社日立製作所
Priority date: 2018-04-11
Filing date: 2019-02-01
Publication date: 2019-10-17
Also published as: JP2019187105A

Abstract

The present invention addresses the problem of providing a power conversion device suppressing lowering of conversion efficiency due to the increase of the surrounding temperature of the power conversion device and capable of reducing temperature stress on semiconductor elements. The power conversion device is equipped with a cooler for cooling semiconductor elements within the power conversion device, wherein the semiconductor cooler can increase the power conversion efficiency of the power conversion device by increasing the cooling ability when outside temperature is high and lowering the temperatures of the elements.

Description

Power converter

The present invention relates to a power conversion device that converts AC power and DC power having a cooling function.

Power conversion devices using high-speed power semiconductor elements such as insulated gate bipolar transistors (IGBT) are used in various fields. In recent years, due to advances in semiconductor technology, large capacity semiconductor modules have been realized, and development of large capacity conversion devices is progressing.

In order to increase the capacity, multiple semiconductor modules may be connected in parallel. In this case, the element temperature rises due to the influence of the heat generated in other semiconductor modules in addition to the current flowing through the element. there's a possibility that. When the element temperature rises, the element life may be shortened or the electric characteristics of the element may be deteriorated.

For example, Patent Document 1 includes a heat exchange means capable of adjusting the cooling capacity for detecting the internal temperature and the external temperature of the power conversion device and exchanging heat between the inside and the outside, and from the detection of the electric power generated by the solar panel. A configuration is described in which the temperature rise inside the power conversion device is predicted and the cooling capacity of the heat exchange means is increased before the heat generation of the semiconductor element.

JP2016-146737

There are cooling methods such as natural air cooling, forced air cooling, and forced water cooling as element cooling methods. The forced air cooling method is a method in which, for example, the element temperature is lowered by forcing air to a heat sink that contacts the semiconductor element. The forced water cooling method is a method in which a water channel is formed in a heat sink that is in contact with a semiconductor element, and the element temperature is lowered by flowing water through the water channel.

The cooling of the semiconductor element is designed so that the maximum temperature of the junction is not more than the temperature specified by the semiconductor element under the condition of the maximum heat generation amount, and the cooling capacity is changed according to the heat generation amount of the semiconductor element. Not set. Under such conditions, when the ambient temperature of the semiconductor element rises significantly due to external factors, the temperature of the semiconductor element rises, which may cause a semiconductor element failure.

According to Patent Document 1, since the temperature change width of the semiconductor element can be suppressed, it is possible to reduce the temperature stress applied to the semiconductor element used in the power conversion device.

However, in the conventional example as described above, it is necessary to arrange a temperature sensor inside the power converter, and the cost increases due to the addition of the temperature sensor. In addition, there is a possibility that a temperature sensor malfunctions inside the power conversion device where the temperature is likely to rise.

Therefore, the present invention has been made to solve this drawback, and reduces the temperature stress of the semiconductor element without disposing a temperature sensor inside the power converter, and further reduces the efficiency without reducing the efficiency. Can be driven.

In order to solve the above-described problems, a power converter according to the present invention includes a power converter including a semiconductor element that converts power supplied from a DC power source into AC power, a cooler that cools the semiconductor element, and the cooler. In a power conversion device including a power source for driving, a controller for controlling driving of the cooler, and a detector for measuring outside air temperature, the controller for controlling driving of the cooler controls the outside air temperature. The cooling operation is determined according to the value of the detector to be measured.

According to the present invention, it is possible to reduce the temperature stress of the semiconductor element and improve the power conversion efficiency of the power converter.

It is a figure which shows the structure of the power converter device which converts from direct current | flow to alternating current which concerns on Example 1 of this invention. It is a figure which shows the structure of the power converter device which converts from alternating current to direct current which concerns on Example 1 of this invention. It is a figure which shows the static characteristic at the time of the low temperature of a semiconductor element (IGBT), and high temperature. It is a figure which shows the dynamic characteristic at the time of the low temperature and high temperature of a semiconductor element (diode). It is a figure which shows the dynamic characteristic at the time of the low temperature of a semiconductor element (IGBT), and high temperature. It is a figure which shows the transient thermal network of a semiconductor element (IGBT). It is a figure which shows the schematic diagram of the forced air cooling system of a semiconductor element. It is a figure which shows the schematic diagram of the forced water cooling system of a semiconductor element. It is a figure which shows the structure of the power converter device which converts from direct current | flow to alternating current which concerns on Example 2 of this invention. It is a figure which shows the structure of the power converter device which converts from alternating current to direct current which concerns on Example 2 of this invention. It is a figure which shows the structure of the power converter device which converts from direct current | flow to alternating current which concerns on Example 3 of this invention. It is a figure which shows the structure of the power converter device which converts from alternating current to direct current which concerns on Example 3 of this invention. It is a figure which shows the structure of the power converter device which converts from direct current | flow to alternating current which concerns on Example 4 of this invention. It is a figure which shows the relationship between the case temperature which concerns on Example 4 of this invention, and the lifetime of a semiconductor element. It is a figure which shows the structure of the power converter device which converts from alternating current to direct current which concerns on Example 4 of this invention. It is a figure which shows the structure of the power converter device which converts from direct current | flow to alternating current based on Example 5 of this invention. It is a figure which shows the seasonal characteristic of the load output which concerns on Example 5 of this invention. It is a figure which shows the structure of the power converter device which converts from alternating current to direct current which concerns on Example 5 of this invention. It is a figure which shows the seasonal characteristic of the load output which concerns on Example 6 of this invention. It is a figure which shows the structure of the power converter device which converts from alternating current to direct current which concerns on Example 6 of this invention.

Embodiments of the present invention will be described below with reference to the drawings. In each figure, the same part is given the same issue.

FIG. 1 is a diagram illustrating a configuration of a power conversion device 100 according to a first embodiment of the present invention. A power conversion apparatus 100 according to the first embodiment illustrated in FIG. 1 includes a semiconductor element 102 that converts DC power into an AC power source, and a cooler 103 that cools the semiconductor element. The power converter 100 is connected to a DC power source 101 and a load 104, and DC power output from the DC power source 101 is converted into AC power and supplied to the load 104.

FIG. 2 is a diagram showing a configuration when the AC power output from the AC power source 105 is converted into DC power and supplied to the load 104.

The cooling capacity of the cooler 103 is determined by the cooler drive system 110a. The cooling drive system 110 a has a configuration in which the cooling command value 112 determined by the cooler control unit 111 according to the outside air temperature detected by the outside air temperature detection unit 114 is input to the cooler power source 113. The cooler drive system 110a may be configured as a part of the power conversion apparatus 100. The cooler control unit 111 includes an interface for receiving measurement values from an external sensor such as the outside air temperature detection unit 114. The external sensor includes a sensor that is used to acquire information that is measured outside the power conversion device, such as outside air temperature and power generation amount information, or is collected outside.

The semiconductor element 2 converts the DC power supplied from the DC power supply 101 into AC power by switching such as PWM (Pulse Width Modulation) and outputs the AC power to the load 104. At this time, the semiconductor element generates a switching loss due to switching by PWM and a conduction loss caused by flowing the element.

Here, the loss of the semiconductor element will be described by taking the IGBT as an example. Formula (1), (2)
Indicates the conduction loss of the freewheeling diode arranged in parallel with the IGBT and IGBT. The conduction loss of a semiconductor element is a loss determined by the product of the current flowing during conduction and the voltage across the element. Equations (3) and (4) show the switching loss of the IGBT, and equation (5) shows the recovery loss of the diode. As shown in the equations (3) to (5), the switching loss is proportional to the PWM switching frequency f _sw and increases as the switching frequency increases. When this switching frequency is high, the switching loss is larger than the conduction loss, and occupies most of the element loss. Here, the IGBT is used for description, but the semiconductor device such as a MOSFET is not limited thereto.

Here, P _ss is the IGBT conduction loss, I is the IGBT semiconductor element current, and V _CE is the IGBT voltage.

Here, P _sd is a diode conduction loss, I is a diode current, and V _ak is a diode ON voltage.

Here, P _on is the IGBT turn-on loss, f _sw is the switching frequency, and E _on is the turn-on loss per pulse.

Here, P _off is the IGBT turn-off loss, f _sw is the switching frequency, and E _off is the turn-off loss per pulse.

Here, P _err is the IGBT recovery loss, f _sw is the switching frequency, and E _err is the recovery loss per pulse.

FIG. 3 shows an example of the current dependency of the ON voltage of the semiconductor element 102. The ON voltage is a voltage applied to both ends of the semiconductor when the semiconductor element is conductive. When the current is the same, the high temperature characteristic 202 has a higher ON voltage than the low temperature characteristic 201. If the current is the same from equation (1), the conduction loss increases at high temperatures when the ON voltage is high. FIG. 4 shows an example of the current dependency of the recovery loss of the diode in the semiconductor element 102. Similar to FIG. 3, the recovery loss high temperature characteristic 204 has a characteristic that the recovery loss low temperature characteristic 203 is larger than the recovery loss low temperature characteristic 203, and the recovery loss increases according to the equation (5). Further, FIG. 5 shows an example of current dependency of the turn-on loss of the semiconductor element 102. As in FIG. 4, the turn-on loss high temperature characteristic 206 has a characteristic that the turn-on loss high temperature characteristic 205 is larger than the turn-on low temperature characteristic 205, and the switching loss increases according to the equation (4). The loss characteristics due to the temperature difference of the semiconductor element 102 described with reference to FIGS. 4 and 5 become more prominent when the switching frequency is high.

Semiconductor elements include power and insulating materials from the chip that is a heat generating element to the semiconductor element case and heat sink, and it acts as a thermal resistance against the heat generated in the chip. The IGBT is composed of a chip, a base, and the like, but each material has a heat capacity calculated in accordance with the mass and specific heat as well as the heat resistance, and the temperature changes with a time constant determined by the heat capacity and the heat resistance.

FIG. 6 shows a schematic diagram of the transient thermal resistance of the IGBT. The junction temperature 220 of the IGBT is calculated by the thermal circuit configured in FIG. The IGBT steady junction temperature 220 is calculated by the junction-case thermal resistance 210, the case-heat sink thermal resistance 211, the heat sink-ambient thermal resistance 212, and the ambient temperature 223 with the IGBT loss 209 as an input. The transient junction temperature of the IGBT is calculated by a thermal circuit obtained by adding the thermal capacity 213 of the chip, the thermal capacity 214 of the module, and the thermal capacity 215 of the heat sink to the above-described thermal resistance.

In the configuration of the thermal circuit network shown in FIG. 6, the transient junction temperature of the IGBT is expressed by Equation (6), and the steady junction temperature is expressed by Equation (7). As shown in equations (6) and (7), the junction temperature increases as the ambient temperature Ta increases.

Here, T _j is the IGBT junction temperature, _Ta is the ambient temperature, C _c is the chip heat capacity, C _m is the module temperature, _Ch is the heat sink heat capacity, R _th is the junction surface-case thermal resistance, and R _cf is the _case- The heat resistance between the heat sinks, R _ta is the heat resistance between the heat sink and the surroundings, and ω is the frequency.

FIG. 7 shows a cooling device according to the first embodiment. The semiconductor element 102 is installed on the air-cooling heat sink 103a and radiated through the heat sink heat radiating portion 103b. When there is no air cooling fan, the thermal resistance is determined by the shape of the heat radiating portion 103b of the heat sink, but it is possible to suppress the thermal resistance by forcing the cooling fan 103c to apply air to the 103b.

Natural convection will be explained using a vertical plate as an example. Natural convection heat transfer is expressed by equation (8).

Here, Nu is the Nusselt number, Gr is the Grashof number, and Pr is the Prandtl number.

Where L is the plate length, α is the heat transfer coefficient, λ is the thermal conductivity of the fluid, g is the gravitational acceleration, β is the volume expansion coefficient, v is the kinematic viscosity coefficient, Tw is the plate temperature, and Ta is the fluid temperature. It has become.

The heat transfer coefficient in the air at 20 ° C is expressed by equation (11) and is determined by the difference between the fluid temperature and the target heating element temperature.

On the other hand, forced convection heat transfer is expressed by equation (12).

Where Re is the Reynolds number and U is the flow velocity.

The forced convection heat transfer coefficient in air at 20 ° C. is expressed by equation (14), and the heat transfer coefficient increases as the flow velocity U increases. The thermal resistance decreases as the heat transfer coefficient increases as in equation (15).

Here, R is a thermal resistance, and S is a heat transfer area.
That is, the cooling capacity can be adjusted by changing the wind speed of the cooling air. Equations (11) and (15) are calculated by taking the characteristics of air at 20 ° C. as an example, but the coefficient also changes in the case of water cooling, and the forced convection heat transfer coefficient is Increase.

Further, FIG. 8 shows the cooling device according to the first embodiment, in which the semiconductor element 102 is disposed on the water cooling heat sink 103d, and in the water cooling heat sink 103d, there is a water channel from the water inlet 103e to the main portion of 103f. Cooled by flowing water. The thermal resistance of the water-cooled heat sink is determined by the flow rate determined by the flow rate of the water inlet and the cross-sectional area of the water channel, and the thermal resistance can be lowered by increasing the flow rate. In this way, when forcibly cooling with a fan or cooling with water, adjusting the cooling fan or water cooling pump can change the flow rate of cooling air or cooling water and make the cooling capacity variable. . By setting this variable cooling capacity high when the ambient temperature is high and further lowering the junction temperature of the semiconductor element, the power conversion device can be driven without deteriorating the power conversion efficiency. Further, when the ambient temperature is low, the loss generated in the power supply of the cooling system can be suppressed by setting the cooling capacity low.

In the first embodiment, the description is given with the power conversion device 100 that converts DC power into AC power, but the same effect can be obtained with the power conversion device that converts AC power into DC power shown in FIG. Moreover, the same effect is acquired also as an apparatus with which the output of the power supply of the cooler described in Example 1 increases according to a rise in outside air temperature, for example, a solar panel. Further, the same effect can be obtained even with a power source that can absorb the loss generated in the power converter as heat energy.

FIG. 9 shows the power conversion apparatus 100 according to the second embodiment. The difference from the first embodiment is configured by the power conversion device output detection unit 106 instead of the outside air temperature detection unit 114, and detects the power conversion device output value 115 between the power conversion device 100 and the load 104. The part 106 is configured. In addition, the same code | symbol is used about the same component as Example 1, and duplication description is abbreviate | omitted.

As described in Equation (1), the power loss of the semiconductor element 102 increases as the current increases. Therefore, when the power converter output value 115 is large, the junction temperature of the semiconductor element increases, and the efficiency of the semiconductor element increases. Decreases. Further, when the power converter output value 115 is small, the junction temperature of the semiconductor element becomes low, so the decrease in efficiency is small. Even if the cooler command value is a low design value under the condition that the junction temperature of the semiconductor element is low, the efficiency is not lowered. Although the output detection unit is used in the second embodiment, the same effect can be obtained even if the output detection unit is configured.

In the second embodiment, the power conversion device 100 that converts DC power to AC power is described. However, as shown in FIG. 10, the same effect can be obtained by a power conversion device that converts AC power to DC power. .

FIG. 11 shows the power conversion apparatus 100 according to the third embodiment. The difference from the first embodiment is that the outside air temperature detecting unit 114 is composed of the outside humidity detecting unit 116. In addition, the same code | symbol is used about the same component as Example 1, and duplication description is abbreviate | omitted.

Equation (16) is an equation indicating the relative humidity and the lifetime of the semiconductor element. As shown in Expression (16), the lifetime L of the semiconductor element is shortened as the relative humidity and temperature increase. Therefore, when the external humidity 117 is high, increasing the cooling capacity of the semiconductor element can reduce the element temperature, thereby prolonging the element life.

Here, L is the semiconductor lifetime, A is the acceleration coefficient, n is the relative humidity coefficient, RH is the relative humidity, Ea is the activation energy, V is the voltage, K is the Boltzmann constant, and T is the absolute temperature.

In the third embodiment, the power conversion device 100 that converts DC power into AC power is described. However, as shown in FIG. 12, the same effect can be obtained with a power conversion device that converts AC power into DC power. .

FIG. 13 shows a power converter according to the fourth embodiment. The difference from the first embodiment is that the outside air temperature detection unit 114 includes a semiconductor power cycle number detection unit 118. In addition, the same code | symbol is used about the same component as Example 1, and duplication description is abbreviate | omitted.

FIG. 14 shows the relationship between the amount of change in the case temperature and the lifetime of the semiconductor element according to Example 4. Since semiconductor elements repeatedly increase and decrease in temperature according to the conditions under which they are used, fatigue and deterioration progress due to thermal stress. This deterioration corresponds to the deterioration of the aluminum wire bonding portion on the chip surface of the semiconductor element and the deterioration of the solder bonding portion used for bonding between the insulating substrate and the base. This fatigue and deterioration greatly depends on the temperature rise / fall range. This thermal stress is called power cycle life. A semiconductor device has a defined power cycle life, and as shown in FIG. 14, the power cycle life depends on the amount of change in junction temperature. As in the fourth embodiment, when the number of power cycles of the semiconductor becomes equal to or higher than a certain level, the temperature increase width can be reduced and the increase in the number of power cycles can be suppressed by increasing the cooling capacity.

In the fourth embodiment, the power conversion device 100 that converts DC power into AC power is described. However, as shown in FIG. 15, the same effect can be obtained with a power conversion device that converts AC power into DC power. .

FIG. 16 shows a power converter according to the fifth embodiment. The difference from the first embodiment is that the outside air temperature detection unit 114 includes a load output detection unit 120 and a load output accumulation unit 121. In addition, the same code | symbol is used about the same component as Example 1, and duplication description is abbreviate | omitted.

FIG. 17 shows an example of the seasonality of the power generation amount of the wind power generation system as an example of the load according to the fifth embodiment. The bar in FIG. 17 represents the power generation output for each month. Wind power generation systems vary greatly depending on the season, and this seasonal variation is particularly large in regions where power generation is high. Usually, since the power conversion efficiency of a power converter device is designed according to a rated output, when operating with the output lower than a rating, power conversion efficiency deteriorates. Therefore, it is possible to reduce the power conversion efficiency and increase the amount of power transmission by making the load output a database in the storage unit and making the system improve the cooling capacity more than usual during the period when the load output decreases. Become.

∙ Renewable energy is set as a frame of power transmission as a mechanism to ensure the stability of the power system, but there are cases where the amount of power generation is lower than the frame due to seasonality and weather conditions. Reducing this difference may be more important for system stability, etc. than using additional power for cooling. For example, in order to transmit more generated power, there is a control mode for improving the cooling capacity in order to improve the power conversion efficiency than usual, and the reduction in the amount of power generation can be suppressed.

In the fifth embodiment, the wind power generation system has been described as an example. However, load output data is accumulated even in a system with different output characteristics depending on the season, such as a solar power generation system and other natural energy power sources, and the load pattern is obtained. Accordingly, it is possible to suppress a decrease in power conversion efficiency by determining the cooling capacity accordingly.

In the fifth embodiment, the power conversion device 100 that converts DC power into AC power is described. However, as shown in FIG. 18, the same effect can be obtained with a power conversion device that converts AC power into DC power. . In FIG. 17, the control is performed for each month or season, but the control can be switched by another time span.

FIG. 19 shows the power conversion apparatus 100 according to the sixth embodiment. The difference from the first embodiment is that the outside air temperature detection unit 114 is configured by the load output prediction unit 122. In addition, the same code | symbol is used about the same component as Example 1, and duplication description is abbreviate | omitted.

As described in the fifth embodiment, when the load output is low, the loss of the semiconductor element increases. Therefore, by using the load output prediction value 123 that predicts the load output, the cooling capacity of the power conversion device is improved, thereby generating power. A decrease in efficiency can be suppressed. In addition, the same code | symbol is used about the same component as Example 1, and duplication description is abbreviate | omitted.

For example, in the case of a wind power generation system, the load output prediction unit according to the sixth embodiment is configured to perform output prediction via a wind speed prediction unit disposed at a position downstream of the wind turbine and adjust the cooling capacity. Even in the case of a solar power generation system, the weather prediction unit can predict the weather in advance, perform output prediction according to the weather prediction, and adjust the cooling capacity.

In the sixth embodiment, the description is given with the power conversion device that converts the DC power into the AC power. However, as shown in FIG. 20, the same effect can be obtained with the power conversion device that converts the AC power into the DC power.

100. Power converter, 101. DC power supply, 102. Semiconductor element, 103. Cooler, 103a. Air cooling heat sink, 103b. Heat sink heat sink for air cooling, 103c. Fan, 103d. Heat sink for water cooling, 103e. Water-cooled water inlet, 103f. Water-cooled water discharge section, 104. Load, 105. AC power supply, 106. An output detector of the power converter, 110a. A cooling system including an outside air temperature detector, 110b. A cooling system including an output detector, 110c. A cooling system including an external humidity detector, 110d. A cooling system including semiconductor element cycle number detection; 110e. A cooling system including a load output accumulator; 110f. A cooling system including a load output prediction unit; Cooler controller, 112. Cooler command value, 113. Cooler power supply, 114. Outside air temperature detector, 115. Output detection value, 116. Humidity detection unit, 117. External humidity detection value 118. Cycle number detection unit, 119. Number of cycles, 120. Load output detector 121. Load output storage section, 122. Load output prediction unit, 123. Load output predicted value 201. 202. ON voltage current dependency of semiconductor element at low temperature; 203. ON voltage current dependency of semiconductor element at high temperature, 204. Recovery loss current dependency of semiconductor element at low temperature Dependence on recovery loss current of semiconductor element at high temperature, 205. Dependence on switching loss current of semiconductor element at low temperature, 206. 209. Switching loss current dependency of semiconductor element at high temperature Total loss, 210. Bond-case thermal resistance, 211. Case-heat sink thermal resistance, 212. Heat sink-to-ambient thermal resistance, 213. Chip heat capacity, 214. Module heat capacity, 215. Heat sink heat capacity, 220. Bonding temperature, 221. Module case temperature, 222. Heat sink temperature, 223. Ambient temperature

Claims

A power converter that is electrically connected to a power source and a load and converts power received from the power source by switching of a semiconductor element,
A cooler for cooling the semiconductor element;
A cooler control unit for controlling the cooling capacity of the cooler,
The cooler control unit includes an interface with an external sensor.
The power conversion device according to claim 1,
A detector for detecting the external temperature of the power converter,
The cooler control unit controls the cooler based on temperature information outside the power converter.
The power conversion device according to claim 1,
A detector for detecting the external humidity of the power converter,
The cooler control unit controls the cooler based on humidity information outside the power converter.
The power conversion device according to claim 1,
A detector for detecting the output of the power converter,
The cooler control unit controls the cooler based on a detected value of an output of the power converter.
The power conversion device according to claim 1,
A temperature cycle storage unit for storing a temperature cycle of a semiconductor element of the power conversion device;
The cooler control unit controls the cooler based on temperature cycle information of a semiconductor element of the power converter.
The power conversion device according to claim 4,
A power converter output storage unit for storing the output of the power converter;
The cooler control unit controls the cooler based on information of the power converter output accumulation unit.
The power conversion device according to claim 1,
A predictor for predicting the output of the power converter,
The cooler control unit controls the cooler based on an output predicted value of the power converter.
The power conversion device according to claim 1,
A cooler power supply for adjusting the cooling capacity of the cooler;
The cooler control unit controls the cooler power supply.
A power conversion device for converting the power generated by a natural energy power source,
A cooler for cooling the elements of the power converter,
A power converter comprising a controller that controls the cooler according to the amount of power generated by the natural energy power source.