Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2001-09-20
2003-10-21
Martin, David (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S816000, C361S715000, C361S723000, C257S666000, C257S700000, C315S194000
Reexamination Certificate
active
06636429
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of electronics. More specifically, the invention relates to high frequency electromagnetic interference (“EMI”).
2. Background of the Invention
An inverter is commonly used to convert direct current (“DC”) to alternating current (“AC”) to power a three-phase load, such as a three-phase motor, or, alternatively, to convert AC from a three-phase source to DC. The inverter commonly contains six switches. Power modules often contain one or more pairs of complementary switches. The power module typically includes silicon dice on substrates that are secured to the module baseplate. Each switching pair has a positive or “high” side switch and a negative or “low” side switch for controlling the flow of electric current. Each switching pair is referred to herein as a “half bridge.” The “high side” of the bridge contains the positive switches, and the “low side” contains the negative switches. By the term “switch” is meant a switching device such as an insulated gate bipolar transistor (“IGBT”) or Bipolar Junction Transistor (“BJT”) or Metal Oxide Semiconductor Field Effect Transistor (“MOSFET”), either singly or in parallel.
Elements may be described herein as “positive” or “negative.” An element described as “positive” is shaped and positioned to be at a higher relative voltage than elements described as “negative” when the power module is connected to a power source. “Positive” elements are positioned to have an electrical connection that is connectable to the positive terminal of a power source, while “negative” elements are positioned to have an electrical connection that is connectable to a negative terminal, or ground, of the power source. Generally, “positive” elements are located or connected to the high side of the power module and “negative” elements are located or connected to the low side of the power module.
In a typical power module configuration, the high side switches are on one side of the module opposite the corresponding low side switches. A positive DC lead from a power source such as a battery is connected to a conducting layer in the high side of the substrate. Likewise, a negative DC lead from the power source is connected to a conducting layer in the low side of the substrate. The high side switches control the flow of current from the conducting layers of each high side substrate to output leads. Output leads, called “phase terminals” transfer alternating current from the three pairs of switches, or half bridges, to the motor.
Power modules typically have three half bridges combined into a single three-phase switching module, or single half-bridge modules that may be linked together to form a three-phase inverter. As would be understood by one of ordinary skill in the art, the same DC to AC conversion may be accomplished using any number of half bridges, which correspond to a phase, and each switching pair may contain any number of switching devices. For simplicity and clarity, all examples herein use a common three phase/three switching pair configuration. However, the invention disclosed herein may be applied to a power module having any number of switches.
Current flows from the power source through the positive DC lead to the conducting layer on the high side substrate. Current is then permitted to flow through one or more switching device on the high side to a conducting layer, commonly referred to as a phase output layer, on the low side. A phase terminal lead allows current to flow from this conducting layer on the low side to the motor. The current then flows from the motor to the corresponding conducting layer on the low side of a second switching pair through the low side switches and diodes to the negative DC lead to the power source.
Current flowing through various inductive paths within the module transiently stores energy which increases energy loss, reduces efficiency, and generates heat. When the flow of current changes, as in such a high frequency switching environment, large voltage overshoots often result, further decreasing efficiency. Additional materials regarding efficient configurations of power modules may be found in application Ser. No. 09/957,568, entitled “Substrate-Level DC Bus Design to Reduce Module Inductance,” application Ser. No. 09/957,047, entitled “Press (Non-soldered) Contacts for High Current Electrical Connections in Power Modules,” and application Ser. No. 09/882,708, entitled “Leadframe-Based Module DC Bus Design to Reduce Module Inductance,” which are hereby incorporated by reference in their entirety.
To minimize the negative effects of current gradients, noise and voltage overshoots associated with the switching process of the module, large capacitors are generally placed in a parallel arrangement between the positive and negative DC connections or from each DC connection to a ground or chassis. These large capacitors are commonly referred to as “X” or “Y” capacitors. Relatively large external capacitors of about around 100 micro Farads are needed. By “external” it is meant that the element referred to is located outside of a power module. High frequency noise, and voltage overshoots that are initiated in the module by the switching process travel away from the source of the noise and voltage overshoots. A low impedance network may be used to provide a return path for the high frequency energy associated with noise and voltage overshoots. The further the energy travels, the more difficult it is to provide a low impedance network to return the energy. Therefore, capacitors attached between the positive and negative DC connections or from the DC connections to ground must be relatively large to minimize the impact of noise, and voltage overshoots. In addition, these external capacitors typically cause stray inductance, which renders the capacitor ineffective at frequencies higher than about 10 kHz.
These and other problems are avoided and numerous advantages are provided by the method and device described herein.
BRIEF SUMMARY OF THE INVENTION
The present invention provides high frequency, low impedance network for use in a power module for reducing radiated and conducted electromagnetic interference and the resulting noise and voltage overshoots. By “a high frequency, low impedance network” it is meant any structure characterized by an equivalent impedance below about 10 nanoHenry (“nH”), and typically between about 100 picoHenry and about 10 nH, in a frequency range from between about 10 Mega Hertz (“MHz”) to about 1 Giga Hertz (“GHz”). Because the high frequency, low impedance is located relatively close to the source of noise and voltage overshoots inherent in the switching process, a much smaller capacitance may be used with more effective reduction of noise and voltage overshoots when compared to larger, external capacitors.
Elements may be described herein as “adjacent” to another element. By the term “adjacent” is meant that in a relationship so characterized, the components are located proximate to one another, but not necessarily in contact with each other. Normally there will be an absence of other components positioned in between adjacent components, but this is not a requirement. By the term “substantially” is meant that the orientation is as described, with allowances for variations that do not effect the cooperation and relationship of the so described component or components.
In accordance with the present invention, a method for reducing electromagnetic interference in a power module is provided. A high frequency, low impedance network is electrically connected to at least one of a positive conducting layer in a substrate or a negative conducting layer in a substrate. The high frequency, low impedance network is also electrically connected to ground.
In another aspect, a device is provided for reducing electromagnetic interference in a power module. The device includes a surface mount capacitor, a first electrical connection from the surface mount capacitor to at least one of a positive conducting layer in a high
Ahmed Sayeed
Flett Fred
Maly Douglas
Parkhill Scott
Ballard Power Systems Corporation
Bui Hung
Martin David
Seed IP Law Group PLLC
LandOfFree
EMI reduction in power modules through the use of integrated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with EMI reduction in power modules through the use of integrated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and EMI reduction in power modules through the use of integrated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3166575