Eliminating Power Inductor Thermistor with Variable Air Gap

Abstract

A power system includes a converter including an inductor core defining a gap and a separator spanning the gap and contacting the core. The power system also includes a controller programmed to reduce power supplied by the converter in response to a current ripple amplitude output by the converter decreasing to less than a first threshold. The first threshold indicates a change in inductance through the core caused by a reduction in size of the separator due to temperature.

Description

Technical Field

[0001] The present disclosure relates to power converters, and in particular to inductor cores of power converters. Background Art

[0002] Electrified vehicles, including hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs), include a DC-DC converter with a boost inductor. The traction motor of an electrified vehicle includes an inverter that requires different voltages at different times. The DC-DC converter supplies the required voltage even when the battery input voltage remains within a narrow range. Because a large amount of current passes through the inductor and the amplitude of the voltage switches across the inductor, the temperature of the inductor may increase. Traditional inductor systems include a thermistor or other temperature measurement device to monitor the temperature of the inductor core. Summary of the invention

[0003] According to one embodiment, a power system is provided. The power system includes a converter, the converter including an inductor core defining a gap and a separator spanning the gap and contacting the core. The power system also includes a controller programmed to reduce the power supplied by the converter in response to a current ripple amplitude output by the converter decreasing to less than a first threshold. The first threshold indicates a change in inductance through the core caused by a reduction in size of the separator due to temperature.

[0004] According to one or more embodiments, the controller may be programmed to reduce the power supplied by the converter in response to the current ripple amplitude output by the converter increasing to greater than a second threshold. The second threshold may indicate a change in inductance through the core caused by an increase in the size of the separator due to temperature. In addition, the controller may be programmed to cut off the power supplied to the converter in response to the current ripple amplitude output by the converter increasing to greater than a third threshold, the third threshold being greater than the second threshold. In one or more embodiments, the separator may include a material that expands with increasing temperature. According to one or more embodiments, the temperature-induced size reduction may be based on a predetermined thermal expansion coefficient of the separator. In some embodiments, the controller may be programmed to cut off the power supplied to the converter in response to the current ripple amplitude output by the converter decreasing to less than a second threshold, the second threshold being less than the first threshold. According to one or more embodiments, the separator may include a material that softens with increasing temperature.

[0005] According to one embodiment, a method of controlling an electric power system is provided. The method includes varying, by a controller, power supplied by a converter in response to a change in a current ripple amplitude output by the converter. The converter includes an inductor core defining a gap and a separator spanning the gap and contacting the core. The change in the current ripple amplitude output by the converter indicates a change in inductance through the core caused by a change in the size of the separator due to temperature.

[0006] According to one or more embodiments, the current ripple amplitude change may be a decrease, the size change may be a decrease, and the change may include a decrease. According to another embodiment, the current ripple amplitude change may be an increase, the size change may be an increase, and the change may include a decrease. According to one or more embodiments, the current ripple amplitude change may be greater than a first threshold value to change the power supplied to the converter. In addition, the current ripple amplitude change may be greater than a second threshold value, the second threshold value is greater than the first threshold value, and the change may include cutting off the power supplied by the converter. In one or more embodiments, the change may include cutting off the power supplied by the converter.

[0007] According to one embodiment, a power system is provided. The power system includes a converter, the converter including an inductor core defining a gap and a separator spanning the gap and contacting the core. The power system also includes a controller programmed to reduce power supplied to the converter in response to an increase in the magnitude of a current ripple output by the converter to greater than a first threshold. The first threshold indicates a change in inductance through the core caused by an increase in the size of the separator due to temperature.

[0008] According to one or more embodiments, the controller may be programmed to reduce the power supplied to the converter in response to the current ripple amplitude output by the converter decreasing to less than a second threshold. The second threshold may indicate a change in inductance through the core caused by a temperature-induced reduction in the size of the separator. In addition, the controller may be programmed to cut off the power supplied to the converter in response to the current ripple amplitude of the converter decreasing to less than a third threshold, the third threshold being less than the second threshold. In one or more embodiments, the separator may include a material that softens as the temperature increases. In one or more embodiments, the temperature-induced size increase may be based on a predetermined thermal expansion coefficient of the separator. According to one or more embodiments, the controller may be programmed to cut off the power supplied to the converter in response to the current ripple amplitude of the converter increasing to greater than a second threshold, the second threshold being greater than the first threshold. In one or more embodiments, the separator may include a material that expands as the temperature increases. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a circuit diagram of an electrical system.

[0010] Figure 2 is a schematic diagram of a conventional inductor core for a power converter system.

[0011] Figure 3A is a schematic diagram of an inductor core according to one or more embodiments.

[0012] Figure 3B is a schematic diagram of an inductor core according to one embodiment.

[0013] Figure 3C is a schematic diagram of an inductor core according to one embodiment.

[0014] Figure 4 is a graph of current through an inductor winding at different temperatures according to one embodiment. DETAILED DESCRIPTION

[0015] As required, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the present invention, which may be embodied in various and alternative forms. The drawings are not necessarily drawn to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, the specific structural details and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to employ the present invention in different ways.

[0016] Inductors are used in DC-DC power converters to store energy in a magnetic field during one part of the operating cycle and return all or part of the energy during another part of the cycle. Boost inductors are commonly used in DC-DC converters to provide the required voltage to the traction motor of an electrified vehicle power system. Figure 1 1 shows a circuit diagram of an electric power system 100. The electric power system 100 includes one (or more) high voltage traction batteries 105 and a high voltage and high current DC-DC converter (or DC / DC converter) 110. The DC / DC converter 110 includes a diode 150 and an insulated gate bipolar transistor (IGBT) 160. Although Figure 1 An IGBT is shown in FIG, but the transistor 160 is not limited to the IGBT and may include other transistors, such as a MOSFET transistor. The DC / DC converter 110 also includes a power inductor 120, a capacitor 140, and a resistor 170. Even when the battery 105 input voltage is maintained within a narrow range, the DC / DC converter 110 supplies the voltage required by the power system 100. The system 100 includes an ammeter 130 for sampling the current through the inductor, and a voltmeter 180 for measuring the voltage of the system 100. The current passing through the inductor 120 and the amplitude of the voltage switching across the inductor 120 may cause the temperature of the inductor 120 to increase, and therefore cause the inductor 120 to be likely to operate in a state exceeding its temperature rating, thereby causing safety and durability issues.

[0017] Conventional inductors, such as power inductor 120, typically include windings on a readily magnetizable core or a "ferromagnetic" core. Figure 2 Schematic diagram of a conventional inductor core 200 is shown. The inductor core 200 includes one or more core sections 210, 220 with one or more corresponding air gaps 230 between the sections 210, 220. The air gaps 230 in the core 200 help maximize the energy that can be stored in the inductor. Figure 2 is shown as having a width W. Conventional inductors include a thermistor for monitoring temperature and signaling to reduce power when the inductor temperature rises above a rated value. Including a thermistor creates safety and durability issues due to failure of an additional part and increases the cost of manufacturing the inductor.

[0018] According to one or more embodiments, a power system and a method for controlling the power system are disclosed. Figure 1 , the power system 100 includes a power inductor 120 as a part of a DC-DC converter 110. The power system 100 according to the present disclosure is capable of monitoring the temperature of the inductor without a thermistor or other separate temperature measuring device.

[0019] Figure 3A A schematic diagram of an inductor core 300 according to one or more embodiments of the present disclosure is shown. The inductor core 300 includes core sections 310, 320. The inductor core 300 is made of an easily magnetized material or a "ferromagnetic" material, and windings (not shown) are wound around the sections 310, 320 to form an inductor for an electric power system. Gaps 330 are provided between the core sections 310, 320, respectively. Although two core sections 310, 320 with corresponding gaps 330 are shown for illustrative purposes, any number of core sections with corresponding numbers of gaps may be envisioned.

[0020] A separator 340 is disposed in each respective gap 330, in contact with the core segments 310, 320. The separator 340 has a width A, filling the gap 330. Although two separators 340 are shown for illustrative purposes, any number of separators may be included in the gap. In some embodiments, not all gaps may include separators (i.e., only some gaps include separators). In other embodiments, all gaps include respective separators. The separator 340 is selected to control the width of the gap 330. The separator 340 is made of a material having a predetermined coefficient of thermal expansion. The predetermined coefficient of thermal expansion indicates to what extent the separator 340 will change the size of the gap 330. By selecting the material of the separator 340, the thermistor or other temperature measuring device can be removed from the power inductor. Given a predetermined coefficient of thermal expansion, the material selection of the separator 340 provides a known change in the gap width over a certain temperature range. This change in the gap width (indicating high temperature) causes a change in the magnetic resistance of the inductor core. Since the magnetic resistance of the core now varies with temperature, the inductance of the inductor now varies with changes in the temperature of the inductor.

[0021] In some embodiments, the material of the separator 340 can be selected so that the separator softens or shrinks at high temperature according to the thermal expansion coefficient, causing the width of the gap to shrink by α based on the thermal expansion coefficient and temperature change to become A-α, such as Figure 3B For example, as the core is magnetized and at high temperatures, the attractive forces between the core segments exert a compressive thrust on the softened separator 340, thereby shortening the width of the gap 330 and changing the inductance, as detected by a reduction in the current ripple amplitude.

[0022] In other embodiments, the material of the spacer 340 can be selected to control the width of the gap, so that the spacer expands at high temperature according to a predetermined thermal expansion coefficient, causing the width of the gap 330 to increase by α based on the thermal expansion coefficient and temperature change, becoming A+α, such as Figure 3CFor example, as the core is magnetized and at high temperatures, the separator 340 expands due to material properties and pushes the core segments 310, 320 apart, thereby changing the inductance, as detected by an increase in the current ripple amplitude.

[0023] Reference again Figure 1 , the power system 100 also includes a controller (not shown) electrically connected to the current sensor (e.g., ammeter 130) of the DC-DC converter and a microprocessor (not shown). The ammeter 130 and the microprocessor monitor the current ripple indicating the change in inductance without adding measurement components to the power system. The ammeter 130 and the microprocessor measure the current ripple on the inductor core over time and map the change in the current ripple magnitude (or amplitude), such as Figure 4 As shown. The microprocessor is configured to measure the current ripple through the DC-DC converter via the ammeter 130 when the average current may be the same, and is configured to determine the change in current over time (di / dt). The microprocessor obtains the input voltage level and the output voltage level from the voltmeter 180. The inductance can then be calculated using the following equation:

[0024] VL / (di / dt)=L

[0025] Where: VL is the voltage across the inductor,

[0026] L is the inductance of the inductor, and

[0027] di / dt is the rate of change of current through an inductor.

[0028] The microprocessor is configured to obtain the complete current waveform, not just the average current, by using a current sampling range that is greater than twice the fundamental frequency or Nyquist rate of the converter switching frequency. For example, if the converter switches at 10kHz, the microprocessor needs to sample at greater than 20kHz. For a given current through the inductor, a measured voltage across the inductor, and a measured di / dt, the microprocessor is configured to calculate the inductance of the inductor at this time, thereby correlating the inductance with the current ripple amplitude that varies with temperature. Although the average current remains unchanged, the current ripple changes at higher temperatures depending on the material selected for the separator, indicating a change in inductance. The change in inductance is associated with a known temperature change because it is based on a change in the size of the gap in the core, which is based on a predetermined thermal expansion coefficient that changes the width of the core gap by a known amount. By correlating the inductance and current of the inductor at different temperatures, the microprocessor can determine the temperature of the inductor based on a predetermined thermal expansion coefficient of the separator material that indicates certain inductance ranges.

[0029] When a high core temperature is detected based on the current ripple amplitude, such as when the inductance signal indicates a temperature outside the temperature rating of the inductor, the microprocessor signals the controller to reduce the power supplied by the converter, thereby cooling the inductor. The power can be reduced by an amount based on a change in inductance (as measured by a decrease in current ripple below a first threshold or an increase above a second threshold), the change in inductance indicating a temperature close to the inductor rating. As previously discussed, whether the current ripple increases or decreases depends on the material selected for the air gap (increase or decrease in gap width, respectively).

[0030] In certain embodiments, if a change in inductance (as measured by current ripple) indicates a high temperature exceeding a rated value, wherein the current ripple decreases below a third threshold value that is lower than the second threshold value (for a decrease in the gap size), or the current ripple increases above a third threshold value that is higher than the second threshold value (for an increase in the gap width), the power supplied by the converter may be completely cut off. Thus, a conventional temperature measuring device may not be required, which improves safety and durability and reduces costs.

[0031] By using a spacer within the gap, the gap width can be controlled so that the inductance of the core changes by a known amount at high temperatures, indicating a need to reduce or cut off the power supplied by the converter. The material used for the spacer can soften or shrink, thereby reducing the width of the gap, or can expand, thereby increasing the gap, causing an inductance change that indicates high temperature, which is monitored by current switching through the inductor and the current ripple amplitude. By using a spacer with known characteristics, additional temperature monitoring components, such as thermistors, may not be required.

[0032] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms of the present invention. Rather, the words used in this specification are descriptive rather than restrictive, and it should be understood that various changes may be made without departing from the spirit and scope of the present invention. In addition, the features of various implementation embodiments may be combined to form other embodiments of the present invention.

[0033] According to the present invention, there is provided an electric power system having: a converter comprising an inductor core defining a gap and a partition spanning the gap and contacting the core; and a controller programmed to reduce the power supplied by the converter in response to a reduction in the amplitude of a current ripple output by the converter to less than a first threshold, the first threshold indicating a change in inductance through the core caused by a reduction in the size of the partition due to temperature.

[0034] According to one embodiment, the controller is programmed to reduce the power supplied by the converter in response to the current ripple amplitude output by the converter increasing to above a second threshold, the second threshold being indicative of a change in inductance through the core caused by a temperature-induced increase in the size of the separator.

[0035] According to one embodiment, the controller is programmed to cut off power supplied to the converter in response to the current ripple amplitude output by the converter increasing to be greater than a third threshold, the third threshold being greater than the second threshold.

[0036] According to one embodiment, the separator comprises a material that expands with increasing temperature.

[0037] According to one embodiment, the temperature induced size reduction is based on a predetermined coefficient of thermal expansion of the separator.

[0038] According to one embodiment, the controller is programmed to cut off power supplied to the converter in response to a current ripple amplitude output by the converter decreasing to less than a second threshold, the second threshold being less than the first threshold.

[0039] According to one embodiment, the separator comprises a material that softens with increasing temperature.

[0040] According to the present invention, a method for controlling an electric power system is provided, the method comprising: changing, by a controller, the power supplied by the converter in response to a change in the amplitude of a current ripple output by the converter, the converter comprising (i) an inductor core defining a gap and (ii) a partition spanning the gap and contacting the core, the change in the current ripple amplitude indicating a change in inductance through the core caused by a change in the size of the partition due to temperature.

[0041] According to one embodiment, the current ripple amplitude change is a decrease, the size change is a decrease, and the change includes a decrease.

[0042] According to one embodiment, the current ripple amplitude change is an increase, the size change is an increase, and the change includes a decrease.

[0043] According to one embodiment, the current ripple amplitude varies by more than a first threshold value to vary the power supplied to the converter.

[0044] According to one embodiment, the current ripple amplitude changes by more than a second threshold, the second threshold being greater than the first threshold, and the change comprises cutting off power supplied by the converter.

[0045] According to one embodiment, the changing comprises switching off power supplied by the converter.

[0046] According to the present invention, there is provided an electric power system having: a converter comprising an inductor core defining a gap and a partition spanning the gap and contacting the core; and a controller programmed to reduce the power supplied to the converter in response to an increase in the amplitude of a current ripple output by the converter to be greater than a first threshold, wherein the first threshold indicates a change in inductance through the core caused by an increase in the size of the partition due to temperature.

[0047] According to one embodiment, the controller is programmed to reduce power supplied to the converter in response to a current ripple amplitude output by the converter decreasing to less than a second threshold value, the second threshold value being indicative of a change in inductance through the core caused by a temperature-induced reduction in size of the separator.

[0048] According to one embodiment, the controller is programmed to cut off power supplied to the converter in response to a current ripple amplitude of the converter decreasing to less than a third threshold, the third threshold being less than the second threshold.

[0049] According to one embodiment, the separator comprises a material that softens with increasing temperature.

[0050] According to one embodiment, the temperature-induced dimensional increase is based on a predetermined coefficient of thermal expansion of the separator.

[0051] According to one embodiment, the controller is programmed to cut off power supplied to the converter in response to a current ripple amplitude of the converter increasing to be greater than a second threshold, the second threshold being greater than the first threshold.

[0052] According to one embodiment, the separator comprises a material that expands with increasing temperature.

Claims

1. A power system, comprising: a converter comprising an inductor core defining a gap and a separator spanning the gap and contacting the inductor core, the separator having a known coefficient of thermal expansion; and A controller, the controller being configured to: responsive to a reduction in size of the separator due to a temperature change based on the coefficient of thermal expansion, detecting a reduction in current ripple amplitude output by the converter indicative of an inductance change, determining an inductance change based on the current ripple amplitude reduction, a measured voltage across the inductor, and a known current flowing through the inductor, and determining a temperature change based on the inductance change and the known coefficient of thermal expansion, and In response to the current ripple amplitude decreasing to less than a first threshold, power supplied by the converter is reduced.

2. The power system of claim 1 , wherein the controller is further configured to detect an increase in the current ripple amplitude output by the converter indicating an inductance change in response to an increase in size of the separator based on the thermal expansion coefficient due to temperature, determine an inductance change based on the increase in the current ripple amplitude, and determine a temperature change, and reduce the power supplied by the converter in response to the current ripple amplitude increasing to be greater than a second threshold.

3. The power system of claim 2, wherein the controller is further configured to cut off power supplied to the converter in response to the current ripple amplitude output by the converter increasing to be greater than a third threshold, the third threshold being greater than the second threshold.

4. The power system of claim 2, wherein the separator comprises a material that expands as temperature increases.

5. The power system of claim 1, wherein the controller is further configured to cut off power supplied to the converter in response to a current ripple amplitude output by the converter decreasing to less than a second threshold, the second threshold being less than the first threshold.

6. The power system of claim 1, wherein the separator comprises a material that softens as temperature increases.

7. A method for controlling an electric power system, the method comprising: measuring, by a controller, a change in a current ripple amplitude output by a converter, the converter comprising (i) an inductor core defining a gap and (ii) a separator spanning the gap and contacting the inductor core, determining a change in inductance based on a change in current ripple amplitude, a measured voltage across the inductor, and a known current flowing through the inductor; The power supplied by the converter is varied based on the change in inductance associated with a known temperature change causing a change in the dimensions of the spacer based on a known coefficient of thermal expansion causing a change in inductance through the inductor core.

8. The method of claim 7, wherein the current ripple amplitude change is a decrease, the size change is a decrease, and the changing includes a decrease.

9. The method of claim 7, wherein the current ripple amplitude change is an increase, the size change is an increase, and the alteration includes a decrease.

10. The method of claim 7, wherein the current ripple amplitude varies by more than a first threshold to vary the power supplied to the converter.

11. The method of claim 10, wherein the current ripple amplitude changes by more than a second threshold, the second threshold being greater than the first threshold, and the changing comprises cutting off power supplied by the converter.

12. The method of claim 7, wherein the changing comprises shutting off power supplied by the converter.

13. The method of claim 7, wherein the separator comprises a material that softens with increasing temperature.

14. The method of claim 7, wherein the separator comprises a material that expands with increasing temperature.

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