Printed circuit board for a three-phase power device having embedded directional impedance control channels

A printed circuit board having a first switching device (S1 or S2), a second switching device (S3 or S4), a third switching device (S5 or S6), and a common source node (26 or 166) that are each mounted to a surface of the printed circuit board (50 or 150). The printed circuit board further includes at least a first set of conductive paths in a first layer, a second set of conductive paths in a second layer, and a plurality of vias that connects the first layer to the second layer. The first set of conductive paths provides electrical conductivity between the common source node, the first switching device, the second switching device, and third switching device. The second set of conductive paths in the second layer provides electrical conductivity between the common source node, the first switching device, and the third switching device. The physical distance between the first low side switching device and the common source node and the distance between the third low side switching device and the common source node is greater than a distance between the second low side switching device and the common source node.

FIELD OF THE INVENTION

This invention in general relates to three-phase power devices (such as three-phase motors) and, more particularly, to a switching circuit mounted on a printed circuit board having embedded directional impedance control channels.

BACKGROUND OF THE INVENTION

A three-phase motor (such as a permanent magnet synchronous motor and induction motor) is used in automotive applications such as power steering systems. It is known to control the phase windings in a three-phase motor using pulse width modulated signals. The pulse width modulated signals are applied to an inverter or a series of switching devices that connect the phase windings of the motor to either a positive or negative (ground) terminal of the vehicle battery.

In particular, a series of switching devices are usually part of a switching circuit that drive the three-phase motor. A current sensor is used to help determine and track the voltages being applied to each phase winding of the motor. In the past, the switching circuit and current sensor have been mounted on a ceramic substrate. A series of wire bonds are used to interconnect the switching devices and components. The use of wire bonds and a ceramic substrate, however, is expensive and there is a need for less expensive materials and designs.

It would be beneficial to use a printed circuit board to mount and interconnect the switching devices, such as a printed circuit board made of an epoxy glass known as FR4. This would allow a manufacturer to use a Field Effect Transistor (FET) in the form of a surface mounted power device. It would also be beneficial to eliminate the need of wire bonds. This would reduce the cost of implementing the system by eliminating cycle time, factory automation equipment, and maintenance cost associated with traditional wire bond methods.

It has been found, however, that applying a system to a printed circuit board generates problems. For instance, a system that applies sinusoidal drive signals to a three-phase motor is subject to a phenomenon known as torque ripple. Torque ripple can be characterized as harmonics (distortion) in the sinusoidal motor drive voltages that are created when the voltage loss from phase to phase is not balanced. These torque ripple harmonics generate undesirable problems. For instance, consider a three-phase motor used in a power steering application in an automobile. A driver of the automobile will feel any torque ripple harmonics in the form of small but repetitive oscillations while turning the steering wheel. This is an undesirable condition to automobile drivers and a need exists for eliminating, or at least substantially reducing, the effect of torque ripple harmonics.

Accordingly, a need exists to reduce the cost of implementing a three-phase control system yet solves other problems associated with torque ripple harmonics. The present invention addresses ways to solve this need. In particular, the present invention solves the problem of torque ripple harmonics when applying the three-phase motor control circuitry in a printed circuit board layout. This is accomplished by providing a mechanism to optimize, or otherwise balance, the resistive and reactive impedances that occur when applying the three-phase motor control circuitry in a printed circuit board layout.

DETAILED DESCRIPTION

What is described is a design for implementing a switching circuit for a three-phase power device on a printed circuit board. The present invention uses embedded directional impedance control channels to balance the resistive and reactive impedance that occur when applying the switching circuit in a printed circuit board application. For purposes of illustration and description, an example of an application for a three-phase motor for automotive uses will be used. Three-phase motors, such as permanent magnet synchronous motors, may be used as part of a power steering system in an automobile. The present invention, however, is not limited to three-phase motors for automobiles and may be applicable to other three-phase devices.

To this end, generally, there is a printed circuit board for a three-phase power device. The printed circuit board has a first switching device, a second switching device, a third switching device, and a common source node that are each mounted to a surface of the printed circuit board. The printed circuit board further includes at least a first set of conductive paths in a first layer, a second set of conductive paths in a second layer, and a plurality of vias that connects the first layer to the second layer. The first set of conductive paths provides electrical conductivity between the common source node, the first switching device, the second switching device, and third switching device. The second set of conductive paths in the second layer provide electrical conductivity between the common source node, the first switching device, and the third switching device. In this embodiment, the physical distance between the first low side switching device and the common source node and the distance between the third low side switching device and the common source node is greater than a distance between the second low side switching device and the common source node.

The present invention may be applied to a set of low side switching device and/or to a set of high side switching devices. Accordingly, in one embodiment, the switching devices are low side switching devices and the common source node may include a current sensor. In another embodiment, the switching devices are high side switching devices and the common source node may include a power source node.

In a further embodiment, there is a printed circuit board for a three-phase power device that has at least a first low side switching device, a second low side switching device, a third low side switching device, and a current sensor that are each mounted to a surface of the printed circuit board. The printed circuit, in one embodiment, has a first set of conductive paths in a first layer, a second set of conductive paths in a second layer, and a plurality of vias. The first set of conductive paths in the first layer of the printed circuit board provides electrical conductivity between the low side switching devices and the current sensor. The second set of conductive paths in the second layer of the printed circuit board provides electrical conductivity between the first low side switching device and the third low side switching device and the current sensor. The plurality of vias connect the first layer to the second layer of the printed circuit board. In this embodiment, the physical distance between the first low side switching device and the current sensor and the distance between the third low side switching device and the current sensor is greater than a distance between the second low side switching device and the current sensor. The printed circuit board may further have a third set of conductive paths in a third layer and a second plurality of vias. The third set of conductive paths in the third layer provides electrical conductivity between the first low side switching device and the third low side switching device.

In another embodiment, there is a printed circuit board for a three-phase power device having a switching circuit and a current sensor mounted on a surface of the printed circuit board. The switching circuit has three sets of switching devices where each set includes a high side switching device and a low side switching device. The printed circuit board comprises a first set of conductive paths in a first layer, a second set of conductive paths in a second layer, and a plurality of vias. The first set of conductive paths in the first layer of the printed circuit board provides electrical conductivity between each of the low side switching devices in the switching circuit and the current sensor. The second set of conductive paths in the second layer of the printed circuit board provides electrical conductivity between at least two of the low side switching devices of the switching circuit and the current sensor. The plurality of vias connects the first layer of the printed circuit board to the second layer of the printed circuit board. The second conductive paths assist in substantially balancing impedances between the low side switching devices of the switching circuit and the current sensor. The printed circuit board may further have a third set of conductive paths in a third layer and a second plurality of vias. The third set of conductive paths in the third layer provides electrical conductivity between at least two of the low side switching devices of the switching circuit.

There is also a printed circuit board for a three-phase power device that has at least a first low side switching device, a second low side switching device, a third low side switching device, and a current sensor, each mounted to a surface of the printed circuit board. Here, the printed circuit board comprises a first set of conductive paths in a first layer, a second set of conductive paths in a second layer, a third set of conductive paths in a third layer, and a first and second set of vias. The first set of conductive paths in the first layer of the printed circuit board provides electrical conductivity between the low side switching devices and the current sensor. The second set of conductive paths in the second layer of the printed circuit board provides electrical conductivity between the first low side switching device, the third low side switching device and the current sensor. The third set of conductive paths in the third layer of the printed circuit board provides electrical conductivity between the first low side switching device and the third low side switching device. The first set of vias connect the first layer of the printed circuit board to the second layer of the printed circuit board. The second set of vias connect the first layer of the printed circuit board to the third layer of the printed circuit board.

In yet another embodiment, there is a printed circuit board that has a power source node, a first high side switching device, a second high side switching device, and a third high side switching device that are each mounted on the printed circuit board. The printed circuit board further includes at least a first set of conductive paths in a first layer, a second set of conductive paths in a second layer, and a plurality of vias that connect the first layer to the second layer. Here, the first set of conductive paths in the first layer provide electrical conductivity between the power source node, the first high side switching device, the second high side switching device, and the third high side switching device. The second set of conductive paths in the second layer provide electrical conductivity between the power source node, the first high side switching device, and the third high side switching device. The physical distance between the power source node and the first high side switching device and the distance between the power source node and the third high side switching device is greater than a distance between the power source node and the second high side switching device.

Now, turning to the drawings, an example use of a system for a three-phase motor in an automotive application will be explained. Referring toFIG. 1, there is a system20having generally a power source22, an inverter or switching circuit24, a current sensor26, and a motor28. For automotive use, the power source22may be an automobile DC battery having a positive terminal30and a negative terminal32. The negative terminal32may also be a ground connection. The motor28may be a motor having three phase windings A, B, C in a star connection, although other connection types may be used such as a delta connected motor. Such motors may include, for example, a permanent magnet synchronous motor or an induction motor.

The inverter or switching circuit24and the current sensor may be mounted on a surface of a printed circuit board, as will be explained in more detail below. The inverter or switching circuit24includes three sets of switching devices, one set for each phase winding of the motor28. A first set of switching devices S1, S2are capable of providing a first voltage Vato the first phase winding A. A second set of switching devices S3, S4are capable of providing a second voltage Vbto the second phase winding B. A third set of switching devices S5, S6are capable of providing a third voltage Vcto the third phase winding C.

In one embodiment, each set of switching devices has a high side switching device S1, S3, S5connected to the positive terminal30of the power source22and a low side switching device S2, S4, S6connected to the negative terminal32of the power source22(or a ground connection). Each switching device within a set is complimentary to the other switch within the same set. For example, when the high side switching device S1of the first set of switching devices S1, S2is closed, the corresponding low side switching device S2within the first set of switching devices S1, S2is open. Similarly, when the high side switching device S1of the first set of switching devices S1, S2is open, the corresponding low side switching device S2within the first set of switching devices S1, S2is closed.

By having complementary switching devices, the opening and closing of switching devices within each set allows each phase winding A, B, C of the motor28to be connected to a positive terminal30or a negative terminal32(or ground) of the power supply22. This permits a voltage Va, Vb, or Vcto be applied to a corresponding phase winding A, B, or C of the motor28, respectively. The current flowing through each phase winding A, B, or C is represented inFIG. 1by a corresponding variable i_a, i_b, or i_c, respectively.

As will be explained in more detail below, in one embodiment, the switching devices S1–S6may be field effect transistors (FETs), each having a source terminal, a drain terminal, and a gate terminal. The FET can be used as a switch by raising and lowering the voltage applied to the gate terminal above and below a threshold value. Applying a voltage above a threshold value will allow current to pass through a switching device S1–S6. Other suitable types of devices exist for the switching devices S1–S6such as power transistors like IGBT, power MOSFET, and bipolar.

Pulse width modulated (PWM) signals may be used to control the switching devices S1–S6. Referring toFIG. 2, a controller36is used to generate a PWM signal to each of the switching devices S1–S6. The controller36generates the PWM signal based on the current measurements provided by the current sensor26. The controller36may include a digital processor and memory to store software having control algorithms. The digital processor supplies the PWM signals based the control algorithms implemented in software. A suitable controller36may include a DSP processor and memory (not shown).

Referring back toFIG. 1, to adequately control the motor28, the currents for variables i_a, i_b, i_c need to be measured or otherwise known. In one embodiment, the current sensor26is positioned on the DC link between the power supply22and the switching circuit24. In particular, the current sensor26is located between the low side switching devices S2, S4, S6of the switching circuit24and the negative terminal30of the power supply22. The current sensor26may also be positioned between the low side switching devices S2, S4, S6of switching circuit24and a ground connection. In either event, the current sensor26is electrically connected to the low side switching devices S2, S4, S6of the switching circuit24. The present invention is directed to balancing the resistive and reactive impedances in this electrical connection when the switching circuit24and the current sensor26are implemented on, or mounted to, a surface of a printed circuit board.

The current sensor26may be a sensor that measures the voltage drop across a resistor. The current sensor26may be capable of converting the measured voltage drop to a current (represented by i_dc_link) through the DC link according to well-known methods. Alternatively, the measured voltage drop from sensor26may be provided to the controller36and the controller36may convert the sensed voltage drop to a current.

As explained above, each switching device within a set of switching devices is complementary to the other switching device. For a three-phase motor system, this results in eight possible switching states. The table illustrated inFIG. 3reflects the eight possible switching states as vectors V0–V7. The first column40in the table represents the states (open/closed) of the first set of switching devices S1, S2. The second column42in the table represents the states (open/closed) of the second set of switching devices S3, S4. The third column44in the table represents the states (open/closed) of the third set of switching devices S5, S6. The fourth column46reflects the relationship between the current through the DC link (i_dc_link) and the currents i_a, i—b, and i_c through the various phase windings A, B, and C. The fifth column48reflects the eight vector states. Out of the eight possible switching states, there are six active vector states (V1–V6) where current will flow through the DC link and two zero vector states (V0, V7) where no current will flow through the DC link.

As mentioned above, the application of sinusoidal drive voltages to a three-phase power device, such as a motor, is subject to torque ripple harmonics. The problem of torque ripple harmonics needs to be addressed when attempting to implement the switching circuit24and the current sensor26in a printed circuit board layout. It has been found that torque ripple harmonics will result when resistive and reactive impedances are not balanced. The present invention addresses ways to eliminate, or at least substantially reduce, the effect of the torque ripple harmonics.

Referring toFIG. 4, there is shown a printed circuit board50for a three-phase power device, such as the motor28described above. The printed circuit board50has a switching circuit24and a current sensor26mounted on a surface52of the printed circuit board50. The switching circuit24has three sets of switching devices. Each set of switching devices has a high side switching device S1, S3, S5and a low side switching device S2, S4, S6.

In this embodiment, the positive terminal30of the power source22is connected to the high side switching devices S1, S3, S5through a power supply conductive pad54. The power supply conductive pad54may actually supply power to the high side switching devices S1, S3, S5through multiple layers in the printed circuit board. This may be important if the current required to drive the three-phase power device is relatively high. The multiple layers may be electrically tied together through vias (not shown).

Each set of switching devices is connected to each other through a series of interconnecting pads56A,56B,56C. For instance, a first interconnecting pad56A provides electrical contact between a first high side switching device S1and a first low side switching device S2. A second interconnecting pad56B provides electrical contact between a second high side switching device S3and a second low side switching device S4. A third interconnecting pad56C provides electrical contact between a third high side switching device S5and a third low side switching device S6.

In one embodiment, where the high side switching devices S1, S3, S5are field effect transistors (FETs), each device has three terminals including a drain terminal58A,58B,58C, a source terminal60A,60B,60C, and a gate terminal62A,62B,62C. The drain terminals58A,58B,58C of the high side switching devices S1, S3, S5may be connected to the power supply conductive pad54. The source terminals60A,60B,60C may be connected to the interconnecting pads56A,56B,56C. And, the gate terminals62A,62B,62C may be electrically connected to a controller38(not shown) for control purposes.

The low side switching device S2, S4, S6may be connected to the current sensor26by a set of conductive paths76through a common conductive pad64. Here, the common conductive pad64may be part of a first conductive copper layer78of the printed circuit board50between the low side switching devices S2, S4, S6and the current sensor26. In an embodiment where the low side switching devices S2, S4, S6are field effect transistors (FETs), each device has three terminals including a drain terminal68A,68B,68C, a source terminal70A,70B,70C, and a gate terminal72A,72B,72C. The drain terminals68A,68B,68C of the high side switching devices S2, S4, S6may be connected to the interconnecting pads56A,56B,56C. The source terminals70A,70B,70C may be connected to the common conductive pad64. And, the gate terminals72A,72B,72C may be electrically connected to a controller38(not shown) for control purposes.

The low side switching device S2, S4, S6(through the current sensor26) may be connected to the negative terminal32of the power source22through a conductive pad66. Alternatively, the current sensor26may be connected to ground through the same conductive pad66. The connection to the negative terminal32, or ground connection, may be fed through multiple layers in the printed circuit board. This, again, may be important if the current required to drive the three-phase power device is relatively high. The multiple layers may be electrically tied together through vias (not shown).

Each switching device within a set is complimentary to the other switch within the same set. For example, as mentioned above, when the high side switching device S1of the first set of switching devices S1, S2is closed, the corresponding low side switching device S2within the first set of switching devices S1, S2is open. Similarly, when the high side switching device S1of the first set of switching devices S1, S2is open, the corresponding low side switching device S2within the first set of switching devices S1, S2is closed.

By having complementary switching devices, the opening and closing of switching devices within each set allows each phase winding A, B, C of the motor28to be connected to a positive terminal30or a negative terminal32(or ground) of the power supply22. This is accomplished by having a first terminal74A connected between the first high side switching device S1and the first low side switching device S2, a second terminal74B connected between the second high side switching device S3and the second low side switching device S4, and a third terminal74C connected between the third high side switching device S5and the third low side switching device S6. The terminals74A,74B,74C permit a voltage Va, Vb, or Vcto be applied to a corresponding phase winding A, B, or C of the motor28, respectively. The current flowing through each phase winding A, B, or C is represented inFIG. 1by a corresponding variable i_a, i_b, or i_c, respectively.

The layout of the connection between the positive terminal30of the power source22and the high side switching devices S1, S3, S5and the connection between the current sensor26and the negative terminal32of the power source22(or ground) should be highly symmetric and balanced, both physically and electrically. However, in a printed circuit board layout, it is not possible to make the connection between the low side switching devices S2, S4, S6and the current sensor26geometrically symmetric. Moreover, the connection between the low side switching devices S2, S4, S6themselves are not geometrically symmetric. One aspect of the present invention, as described further below, is directed to mechanisms in making these connections electrically symmetric and balanced to avoid problems associated with torque ripple harmonics.

In the design layout shown inFIG. 4, the physical distance between the source terminal70A of the first low side switching device S2and the current sensor26is greater than the physical distance between the source terminal70B of the second low side switching device S4and the current sensor26. Also, the physical distance between the source terminal70C of the third low side switching device S6and the current sensor26is greater than the physical distance between the source terminal70B of the second low side switching device S4and the current sensor26. Left with only the common conductive pad64as the electrically connecting member, it has been found that unacceptable torque ripple harmonics will occur during the operation of a three-phase power device.

To solve this problem, in one embodiment, a first set of vias80and a second set of conductive paths86in an embedded second conductive copper layer88of the printed circuit board50(as shown inFIG. 5) are added to the design. Moreover, the distance between the source terminal70A of the first low side switching device S2and the current sensor26is set to about twice the distance between the source terminal70B of the second low side switching device S4and the current sensor26. Moreover, the distance between the source terminal70A of the first low side switching device S2and the current sensor26is set to about twice the distance between the source terminal70B of the second low side switching device S4and the current sensor26.

The physical distances between the low side switching devices S2, S4, S6and the current sensor26are directly proportional to circuit resistance and impedance. In the printed circuit board layout inFIG. 4, with only the common conductive pad64, the voltage loss associated with the second low side switching device S4would be less than the losses associated with the first and third low side switching devices S2, S6. The addition of the first set of vias80and the second conductive paths86in the second layer88of the printed circuit board50(as shown inFIG. 5) provides a more balanced set of electrical paths between the low side switching devices S2, S4, S6and the current sensor26. The first set of vias80stitches, or otherwise connects, the first layer78to the second layer88. The first set of vias80should be placed at unique points or regions as shown inFIGS. 4–5. These points or regions are in proximity of the first low side switching device S2, the third low side switching device S6, and the current sensor26.

Referring toFIG. 5, in effect, the use of the first set of vias80adds a second parallel current path between first low side switching device S2and the current sensor26and between the third low side switching device S6and the current sensor26. This design helps eliminate, or at least substantially reduce, the effect of torque ripple harmonics.

Referring to the design layout inFIG. 6, the common conductive pad64also provides a first set of conductive paths77in the first layer78of the printed circuit board50when current is fed between the low side switching devices S2, S4, S6themselves. It is noted that the physical distance between the source terminal70A of the first low side switching device S2and the source terminal70C of the third low side switching device S6is greater than the physical distance between the source terminal70A of the first low side switching device S2and the source terminal70B of the second low side switching device S4. Also, the physical distance between the source terminal70C of the third low side switching device S6and the source terminal70A of the first low side switching device S2is greater than the physical distance between the source terminal70C of the third low side switching device S6and source terminal70B of the second low side switching device S4. Again, left with only the common conductive pad64as the electrically connecting member, it has been found that unacceptable torque ripple harmonics will occur during the operation of a three-phase power device.

To solve this problem, in one embodiment, a second set of vias90and a third set of conductive paths97in an embedded third conductive copper layer98of the printed circuit board50(as shown inFIG. 7) are added to the design. Moreover, the distance between the source terminal70A of the first low side switching device S2and source terminal70C of the third low side switching device S6is set to about twice the distance between the source terminal70A of the first low side switching device S2and the source terminal70B of the second low side switching device S4. Moreover, the distance between the source terminal70C of the third low side switching device S6and the source terminal70A of the first low side switching device S2is set to about twice the distance between the source terminal70C of the third low side switching device S6and the source terminal70B of the second low side switching device S4.

The physical distances between the low side switching devices S2, S4, S6are directly proportional to circuit resistance and impedance. In the printed circuit board layout inFIG. 6, with only the common conductive pad64, the voltage loss associated with current between some switching devices would be less than the losses associated between other switching devices. The addition of the second set of vias90and the third conductive paths97in the third layer98of the printed circuit board50(as shown inFIG. 7) provides a more balanced set of electrical paths between the low side switching devices S2, S4, S6. The second set of vias90stitches, or otherwise connects, the first layer78to the third layer98. The second set of vias90must be placed at unique points or regions as shown inFIGS. 6–7. These points or regions are in proximity of the first low side switching device S2and the third low side switching device S6.

Referring toFIG. 7, in effect, the use of the second set of vias90adds a second parallel current path between first low side switching device S2and the third low side switching device S6. This design helps eliminate, or at least substantially reduce, the effect of torque ripple harmonics.

FIG. 8shows another embodiment where the present invention is applied to the high side switching devices S1, S3, S5. This embodiment addresses a potential need for current to funnel evenly out of one power source node, as well as evenly connect to each other when there are recirculating currents between any two of the switching devices. Accordingly,FIG. 8shows a layout of the connection between the positive terminal30of the power source22and the high side switching devices S1, S3, S5through a power source node166where the connection is not geometrically symmetric. An aspect of the present invention, as described further below, is directed to mechanisms in making these connections electrically symmetric and balanced to avoid problems associated with torque ripple harmonics.

In the design layout shown inFIG. 8, the physical distance between a power source node166and the first high side switching device S1is greater than the physical distance between the power source node166and the second high side switching device S3. Also, the physical distance between the power source node166and the third high side switching device S5is greater than the physical distance between the power source node166and the second high side switching device S3. Left with only a common conductive pad154as the electrically connecting member, unacceptable torque ripple harmonics may occur during the operation of a three-phase power device.

To solve this problem, in one embodiment, a first set of vias180and a second set of conductive paths186in an embedded second conductive copper layer188of the printed circuit board150(as shown inFIG. 9) are added to the design. Moreover, the distance between the source node166and the first high side switching device S1is set to about twice the distance between the source node166and the second high side switching device S3. Moreover, the distance between the source node166and the third high side switching device S5is set to about twice the distance between the source node166and the second high side switching device S3.

The physical distances between the source node166and the high side switching devices S1, S3, S5are directly proportional to circuit resistance and impedance. In the printed circuit board layout inFIG. 8, with only the common conductive pad154, the voltage loss associated with the second high side switching device S3would be less than the losses associated with the first and third high side switching devices S1, S5. The addition of the first set of vias180and the second conductive paths186in the second layer188of the printed circuit board150(as shown inFIG. 9) provides a more balanced set of electrical paths between the source node166and the high side switching devices S1, S3, S5. The first set of vias180stitches, or otherwise connects, the first layer178to the second layer188. The first set of vias180should be placed at unique points or regions as shown inFIGS. 8–9. These points or regions are in proximity of the first high side switching device S1, the third high side switching device S5, and the source node166.

Referring toFIG. 9, in effect, the use of the first set of vias180adds a second parallel current path between the source node166and the first high side switching device S1and between the source node166and the third high side switching device S5. This design helps eliminate, or at least substantially reduce, the effect of torque ripple harmonics.

Referring to the design layout inFIG. 10, the common conductive pad154also provides a first set of conductive paths177in the first layer178of the printed circuit board150when current is fed between the high side switching devices S1, S3, S5themselves. It is noted that the physical distance between the drain terminal58A of the first high side switching device S1and the drain terminal58C of the third high side switching device S5is greater than the physical distance between the drain terminal58A of the first high side switching device S1and the drain terminal58B of the second high side switching device S3. Also, the physical distance between the drain terminal58C of the third high side switching device S5and the drain terminal58A of the first high side switching device S1is greater than the physical distance between the drain terminal58C of the third high side switching device S5and drain terminal58B of the second high side switching device S3. Again, left with only the common conductive pad154as the electrically connecting member, unacceptable torque ripple harmonics may occur during the operation of a three-phase power device.

To solve this problem, in one embodiment, a second set of vias190and a third set of conductive paths197in an embedded third conductive copper layer198of the printed circuit board150(as shown inFIG. 11) are added to the design. Moreover, the distance between the drain terminal58A of the first high side switching device S1and drain terminal58C of the third high side switching device S5is set to about twice the distance between the drain terminal58A of the first high side switching device S1and the drain terminal58B of the second high side switching device S3. Moreover, the distance between the drain terminal58C of the third high side switching device S5and the drain terminal58A of the first high side switching device S1is set to about twice the distance between the drain terminal58C of the third high side switching device S5and the drain terminal58B of the second high side switching device S3.

The physical distances between the high side switching devices S1, S3, S5are directly proportional to circuit resistance and impedance. In the printed circuit board layout inFIG. 10, with only the common conductive pad154, the voltage loss associated with current between some switching devices would be less than the losses associated between other switching devices. The addition of the second set of vias190and the third conductive paths197in the third layer198of the printed circuit board150(as shown inFIG. 11) provides a more balanced set of electrical paths between the high side switching devices S1, S3, S5. The second set of vias190stitches, or otherwise connects, the first layer178to the third layer198. The second set of vias190must be placed at unique points or regions as shown inFIGS. 10–11. These points or regions are in proximity of the first high side switching device S1and the third high side switching device S5.

Referring toFIG. 11, in effect, the use of the second set of vias190adds a second parallel current path between first high side switching device S1and the third high side switching device S5. This design helps eliminate, or at least substantially reduce, the effect of torque ripple harmonics.

What has been described is an improved procedure for implementing a switching circuit and current sensor on a printed circuit board for three-phase power devices. The above-described system provides a way to optimize, or otherwise balance, the resistive and reactive impedances in the system. In particular, the printed circuit board has multiple conductive paths in embedded layers that serve as directional impedance control channels. This balance helps eliminate, or substantially reduce, the effects of torque ripple harmonics. The design is particularly important in automotive applications where a balanced system is needed to provide power to a three-phase motor for power steering. The present invention solves undesirable oscillations that may occur when a driver is turning the steering wheel.

The above description of the present invention is intended to be exemplary only and is not intended to limit the scope of any patent issuing from this application. For example, the present discussion used a three-phase motor for automobile applications. The present invention is also applicable to other three-phase devices where pulse width modulation is used. The present invention is intended to be limited only by the scope and spirit of the following claims.