Patent Application
20230208317
This application claims priority to foreign French patent application No. FR 2114585, filed on Dec. 28, 2021, the disclosure of which is incorporated by reference in its entirety.
In power electronics, many static converters have been developed, mainly inverters and rectifiers. More complex equipment is also found, such as switch-mode power supplies. These converters are equipped with electronic components which make it possible to switch an electrical signal. The switching components are often known as: “electronic switches”. Amongst these components, diodes, transistors, thyristors, and triacs etc. can be cited.
Power diodes started to be developed in the 1950s. In the 1960s, thyristors and power transistors appeared. Later, in the 1980s, insulated gate bipolar transistors known by the acronym IGBT appeared. This type of transistor combines the advantage of control by means of a field effect transistor, and the low losses by conduction of a bipolar transistor. Hitherto, IGBTs have made it possible to switch power levels of approximately 10 MW to speeds higher than 10 kHz. For lower power levels, transistors of the MOSFET type are also extensively used. In the 2000s, components, and in particular MOSFET transistors appeared, based on silicon carbide (SiC). They make it possible to achieve speeds greater than 1 MHz. More recently, gallium nitride GaN has also been introduced into MOSFET transistors in order to provide electronic switches. Gallium nitride makes it possible to increase the switching speed even more to frequencies greater than 10 MHz.
By switching electrical power signals, these components generate thermal losses which must be discharged. The electronic switches are mostly cooled by means of radiators making it possible to discharge the heat by convection of air circulating along walls of the radiator. The radiators can also be equipped with channels in which a cooling fluid circulates.
In order to ensure good thermal transfer of the component to its radiator, it is necessary to reduce as far as possible the thermal resistance of the path travelled by the heat from its area of emission in the core of the component as far as the radiator which permits dissipation of this heat. The electronic switch mostly has a metal sole plate which is positioned in the immediate vicinity of the core of the component, and via which the heat to be discharged passes. The sole plate can be insulated electrically against the component, or can form one of its connection points. During the fitting of the electronic switch, the sole plate is placed against the radiator. The contact of the sole plate on the radiator can be thermally improved by means of a thermally conductive paste. It is also possible to interpose an electrical insulator between the sole plate and the radiator in the form of a small plate based on aluminium oxide, mica or silicon.
The safety of users of equipment which uses electronic switches generally requires earthing of the radiators. For better dissipation of the heat, it is also possible to use the exterior housing of the equipment as a radiator. This makes it all the more necessary to connect the housing to the ground of the system comprising the equipment.
In
Common mode disturbances can circulate in the electrical architecture 10. These disturbances, which are represented in thick broken lines in
Hitherto, the common mode disturbances have been limited by means of inductive filters positioned for example on the direct network. As illustrated in
In addition, the electronic switches of the converters have a parasitic capacitor 24 formed between the channel for conduction of the switch, the sole plate and the radiator. This capacitor 24 is derived from the proximity between the conduction channel, the sole plate and the radiator, which proximity is necessary for the discharge of the heat released during switching operations.
Internal experimentations have shown that the common mode disturbances tend to be propagated via the parasitic capacitors 24 of the electronic switches in order to reach the ground 20. In
The invention proposes a solution to these problems by filtering at the source the currents which can pass into the parasitic capacitors of the electronic switches.
For this purpose, the subject of the invention is a component which is configured to switch an electrical signal, the component comprising:
Advantageously, the component is a resistor of at least 1 Ohm.
The subject of the invention is also a static converter comprising a plurality of components according to one of the preceding claims, wherein the conductive planes and the sole plates of each component are in common.
Advantageously, the converter comprises a first group and a second group of components, in each of the groups of components the conductive planes and the sole plates of each component are in common, the conductive plane of the first group is connected to a first reference voltage by means of a first inductor, and the conductive plane of the second group is connected to a second reference voltage by means of a second inductor, and the two inductors are coupled, and have an impedance of at least 1 µH.
The invention will be better understood and other advantages will become apparent from reading the detailed description of an embodiment provided by way of example, which description is illustrated by the appended drawing in which:
For the sake of clarity, the same elements will bear the same references in the different figures.
During its operation, the component 30 releases heat forming losses which must be discharged. This heat is mainly released during switching operations, and when the junction is active as a result of its internal resistance. The heat which is generated in the chip 32 is mainly drained towards a sole plate 46 which for example is made of metal alloy, for its good capacity to conduct heat. The sole plate 46 can for example be made of copper alloy or aluminium alloy. The sole plate 46 can be secured on a radiator, not represented in
As described above, a parasitic capacitor is formed between firstly the chip 32 and the parts 36 and 38 of the metallization, and secondly the sole plate 46, with the substrate 34 forming a dielectric of this parasitic capacitor. Another parasitic capacitor is formed in the chip 32 itself, between the electrodes thereof. A displacement current can form between the junction and the sole plate 46, through the parasitic capacitor. This current can be all the greater, the more the speed of switching increases. In practice, during switching, the current which circulates in the junction is established and is interrupted, forming a current step in a time chart. The applicant has noticed that the repetition of these current steps generates significant leakage currents circulating in the ground of the system through the parasitic capacitor of the component 30. The invention seeks to limit the current circulating in this parasitic capacitor by means of a filter placed as close as possible to the chip 32.
According to the invention, a conductive plane 50 is positioned between the sole plate 46 and the insulating substrate 34. The conductive plane 50 is insulated electrically firstly by the chip 32 and the two parts 36 and 38 of the metallization, and secondly by the sole plate 46. On the chip and metallization side, the insulation of the conductive plane 50 is ensured by the substrate 34. On the sole plate 46 side, an insulating film 52 can be interposed between the conductive plane 50 and the sole plate 46. The conductive plane 50 can be a metal film which for example is made of copper alloy or aluminium alloy deposited on the face of the substrate 34 opposite the one which receives the metallization. The conductive plane 50 can be produced from any other type of conductive material, such as, for example, based on carbon. The conductive plane 50 can be continuous or produced in the form of a grid which has openings. The cross-section of the openings is defined according to the wavelength of the parasitic signals which it is wished to filter. It will be appreciated that the insulating film 52 is selected in order to ensure the electrical insulation of the conductive plane 50 relative to the sole plate 46. It is advantageous to select a material which has good thermal conduction properties, in order to avoid restricting the thermal transfer of the calorific energy dissipated by the chip 32 towards the sole plate 46. For this purpose it is possible to select an insulating film 52 based on silicon or mica. The electrical insulation of the conductive plane 50 against the sole plate 46 can also be ensured by means of a layer, for example of the varnish type, deposited on the conductive plane 50 facing the sole plate 46. The level of electrical insulation between the conductive plane 50 and the sole plate 46 is defined according to the difference of potential which can exist between the conductive plane 50 and the sole plate 46. This difference of potential will be specified hereinafter.
The component 30 also comprises an electrical contact 58, which is configured to connect the conductive plane 50 electrically. The connection makes it possible to provide a damping filter with an electronic component which can be on the exterior of the component 30. In the diagram of
In addition, by using a specific component in order to provide the resistor R, it is possible to position it at a selected location, in order for the dissipation of the energy of the parasitic current to be able to take place for example on a heat dissipater provided for this purpose. The resistance value of the specific resistive component R of at least one Ohm is added to the resistances of the parasitic capacitors and of the connection wires of the conductive plane 50 in its connection to the reference voltage. As previously stated, the resistance value of the specific resistive component R is approximately 1000 times greater than that of the resistances of the parasitic capacitors and of the connection wires. Consequently, almost all of the energy of the parasitic current is dissipated in the specific component. Other types of passive or even active components can be connected to the electrical contact 58. In particular, it is possible to connect passive components of the capacitor and/or inductor type between the electrical contact 58 and a reference voltage as a complement to, or in the place of, the resistor R. In the case of an inductor, during tests carried out internally, the applicant found that a value of at least 1 µH gave good results for participating in the damping of the parasitic current. In the case of a wound inductor, it is found that its value tends to decrease when the frequency of the current increases, mainly because of the skin effect. The inductance value of 1 µH starting from which the results are sensitive is measured at 10 kHz.
It is also possible to combine a specific resistive component R and a specific inductive component L with the capacitor 56, in order to obtain a damping circuit which makes it possible both to offset the resonance frequency and to damp the harmonics of the parasitic current.
These components can be positioned in the housing of the switching component 30. The electrical contact is then an extension of the conductive plane projecting from the substrate 34. The electrical contact 58 can also be a part of the conductive plane 50. The resistor R, or more generally the component connected to the electrical contact 58, can be fitted on the surface of the substrate 34. Alternatively, the electrical contact 58 can come out of the component, and allow a designer of equipment in which it is possible for example to locate the rectifier 12, the converter 14 and the load 18, to select a component to be connected to the electrical contact 58, which component is suitable for the equipment and the parasitic currents encountered.
The inverter 14, represented schematically in
The three transistors T+ of the first group have a common conductive plane 50+, and the transistors T- of the second group have a common conductive plane 50-. The converter 14 can comprise only a single sole plate common to all the transistors T+ and T-. The sole plate is for example connected to a ground of equipment in which the converter 14 is incorporated. Alternatively, it is possible to provide two distinct sole plates 46+ and 46-, one per group of transistors T+ on the one hand and T- on the other hand. The two sole plates 46+ and 46- can be connected to the same reference voltage or to two distinct reference voltages. For example the sole plate 46+ associated with the transistors T+ can be connected to the direct voltage 14+, and the sole plate 46- associated with the transistors T- can be connected to the direct voltage 14-, as illustrated in
The presence of two conductive planes 50+ and 50- gives rise to the presence of two capacitors, respectively 54+ and 54-, firstly between the transistors T+ and the conductive plane 50+, and secondly between the transistors T- and the conductive plane 50-. Associated with each conductive plane 50+ and 50-, there is an electrical contact 58, respectively 58+ and 58-.
It is easy to transpose the diagram shown in
It has been seen by means of
The two inductors L+ and L- can be coupled for example by winding them onto the same magnetic core. As a complement to the two inductors L+ and L-, it is possible to add other active or passive components. As described above, it is possible to connect between the common point of the two inductors, or between each inductor and the respective reference voltage, passive components of the resistor and/or capacitor and/or inductor type.
The use of two inductors coupled in common mode can be implemented for any other type of converter, and in particular for the rectifier 12.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2114585 | Dec 2021 | FR | national |
