Method and apparatus for reducing radiated emissions in switching power converters

Patent metadata

Field	Value
Publication number	US-9621094-B2
Application number	US-201514614080-A
Country	US
Kind code	B2
Filing date	Feb 4, 2015
Priority date	Jul 31, 2012
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

A filter for reducing radiated emissions in switching power converters such as a motor drive is disclosed. The switching power converter modulates a DC voltage input to generate a desired AC voltage output. Capacitors are connected in parallel between each output phase and a common connection, which may be a ground connection. The magnitude and layout of the capacitors are selected to minimize current conducted by the capacitors. The capacitors may be surface mount technology located proximate to the switching devices or the capacitors may be incorporated in the circuit board on which the switching devices are mounted. The filter may be applied to any of the switching elements in a motor drive, such as the inverter section, an active rectifier section, or a switched mode power supply.

First claim

We claim:

1. A motor drive operable to control operation of a motor connected to the motor drive, the motor drive comprising:
a direct current (DC) bus having a positive rail and a negative rail, wherein the DC bus is operable to have a DC voltage potential present between the positive rail and the negative rail;
an output having at least two terminals, wherein each terminal of the output is configured to be connected to the motor by a cable having a plurality of conductors, wherein
the cable includes an electrical shield connected to a first ground connection,
a cable capacitance located exterior to the motor drive is present between each of the conductors and the first ground connection;
a power module having a plurality of switching devices, the power module having an output terminal corresponding to each terminal of the output for the motor drive, wherein:
each switching device on the power module is connected between one of the positive rail and the negative rail and one of the terminals of the output, and
each switching device receives a control signal to alternately connect and disconnect one of the positive rail and the negative rail to the output responsive to the control signal;

a modulation module operable to generate the control signal for each of the plurality of switching devices;
at least one second ground connection, the at least one second ground connection located within the motor drive;
a circuit board on which the power module is mounted; and
a plurality of capacitors mounted on the circuit board, wherein each of the plurality of capacitors is electrically connected between one of the output terminals of the power module and the at least one second ground connection within the motor drive and each of the plurality of capacitors is mounted on the circuit board proximate to one of the output terminals of the power module.

2. The motor drive of claim 1 wherein the first ground connection and the at least one second ground connection within the motor drive are electrically connected.

3. The motor drive of claim 1
wherein the circuit board includes:
a first layer defining a conductive plane corresponding to each of the at least two terminals of the output, and
a second layer defining a ground plane, wherein each of the plurality of capacitors electrically connected between one of the output terminals of the power module and the at least one second ground connection is defined by a capacitance present between the corresponding conductive plane on the first layer and the ground plane on the second layer of the circuit board.

4. The motor drive of claim 1 further comprising:
a first additional capacitor electrically connected between the positive rail of the DC bus and a common connection; and
a second additional capacitor electrically connected between the negative rail of the DC bus and the common connection.

5. The motor drive of claim 1 wherein each of the plurality of capacitors is a surface mount capacitor between 1 and 10 nanofarads.

6. A power conversion section configured to convert a direct current (DC) voltage to an alternating current (AC) voltage, the power conversion section comprising:
a direct current (DC) bus having a positive rail and a negative rail, wherein the DC bus is operable to have the DC voltage present between the positive rail and the negative rail;
an output configured to provide the AC voltage to an electrical load via at least two first electrical conductors wherein each of the first electrical conductors includes a capacitance between the first electrical conductor and a first ground connection;
a plurality of switching devices, each switching device configured to selectively connect one of the positive rail and the negative rail to the output;
a plurality of second electrical conductors, wherein each of the second electrical conductors is connected within the power conversion section between at least one of the plurality of switching devices and the output;
a circuit board on which each of the plurality of switching devices is mounted, the circuit board including a plurality of second ground connections, wherein each of the plurality of second ground connections is located proximate to one of the second electrical conductors; and
a plurality of capacitors, wherein each capacitor is electrically connected between one of the plurality of second electrical conductors and a common electrical connection and wherein each of the plurality of capacitors is mounted on the circuit board proximate to one of the second electrical conductors.

7. The power conversion section of claim 6 wherein the common electrical connection is one of the plurality of second ground connections.

8. The power conversion section of claim 6 wherein each of the plurality of capacitors is a surface mount capacitor between 1 and 10 nanofarads.

9. The power conversion section of claim 6 wherein the circuit board comprises:
a first layer;
a second layer,
at least one conductive plane defined on the first layer of the circuit board, each of the at least one conductive planes corresponding to one phase of the AC voltage output from the power conversion section; and
a ground plane defined on the second layer of the circuit board, the ground plane adjacent to each of the at least one conductive planes, wherein each of the at least one conductive planes is electrically connected to one of the second electrical conductors.

10. The power conversion section of claim 6 further comprising:
a first additional capacitor electrically connected between the positive rail and the common electrical connection; and
a second additional capacitor electrically connected between the negative rail and the common electrical connection.

11. The power conversion section of claim 10 wherein the common electrical connection is one of the at least one second ground connections.

12. A power converter for a motor drive having a filter for reducing radiated emissions, the power converter comprising:
an input configured to receive a direct current (DC) voltage, the input having a positive terminal and a negative terminal;
a DC bus having a positive rail and a negative rail, wherein the positive rail is electrically connected to the positive terminal of the input, the negative rail is electrically connected to the negative terminal of the input, and the DC voltage from the input is present between the positive rail and the negative rail;
a converter output including a plurality of terminals, wherein:
each of the plurality of terminals is configured to be connected to one phase of a multi-phase alternating current (AC) voltage via a cable having a plurality of conductors,
the cable includes an electrical shield connected to a first ground connection, and
a cable capacitance located exterior to the motor drive is present between each of the conductors and the first ground connection;

a power module having a plurality of switching devices, wherein:
a pair of the plurality of switching devices corresponds to each of the plurality of terminals on the converter output,
each pair of the plurality of switching devices is connected in series between the positive rail and the negative rail,
the power module includes a plurality of module outputs, and
each module output is electrically connected between a first switching device and a second switching device in one of the pairs of switching devices;

a plurality of electrical conductors, wherein each of the plurality of electrical conductors is connected between one of the module outputs and one of the plurality of terminals on the converter output, wherein the first switching device of each pair of swi

Assignees

• Rockwell Automation Tech Inc

Inventors

• Vrankovic Zoran
• Winterhalter Craig
• Skibinski Gary

Classifications

• H02M1/126

  using passive filters · CPC title

• H02P27/06 Primary

  using DC to AC converters or inverters (H02P27/05 takes precedence) · CPC title

• H02P23/28 Primary

  Controlling the motor by varying the switching frequency of switches connected to a DC supply and the motor phases · CPC title

• H02P23/0095 Primary

  Electricity · mapped topic

• H02M5/458

  using semiconductor devices only · CPC title