FIELD

This disclosure relates to electrical power circuits, more specifically to capacitor pre-charging circuits.

BACKGROUND

As system power levels increase, capacitor pre-charge provisions become more cumbersome. Typically, an electrical mechanical relay with a series resistor is used to “trickle charge” a capacitor. This is done to avoid excessive in-rush. The resistor must be large to account for both large current and high voltage. It may be necessary to place several resistors in series, either for power or for voltage, or both. These problems get exponentially worse as voltages increase. Typical pre-charge includes a pre-charge mechanical relay that can be engaged to pre-charge the capacitor. When the capacitor has charged, the main relay or contactor is closed and the pre-charge relay is opened (or in reverse order). In aircraft systems, for example, these relays and series resistors are bulky.

As system voltages increase, voltage sensing becomes more complicated. For example, the circuit described above generally requires two voltage sense circuits, one on each side of the main contactor. A typical voltage sense circuit consists of a resistive voltage divider. At low voltages, such as 28 VDC, this approach is relatively problem free. With higher voltages, the impedance of the divider increases to avoid excessive losses. To tolerate the higher voltages, resistor strings are typically employed. As the impedance increases to limit losses, susceptibility to moisture-induced leakage also increases. At hundreds-of-volts, high value precision resistors also suffer reliability problems because the resistive element must be thinner. Thus, voltage sense in high voltage applications suffers either from high dissipation, or susceptibility to moisture, for example.

Another approach is the e-field sense. The e-field sense uses a very high input impedance amplifier that approximates a capacitive voltage divider, rather than resistive. An amplifier will still require biasing to prevent tiny leakages from building up destructive voltages, and to keep the divider signal within the range of the amplifier. The high impedance biasing and the input leakage of an amplifier will create a measurement drift. Consequently, the e-field sense circuit is only effective in measuring AC voltage or momentary DC voltage. It is not practical for continuous DC voltage measurements.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for both improved capacitor pre-charging circuits and improved high voltage DC voltage measurement circuits. The present disclosure provides a solution for these needs.

SUMMARY

A capacitor pre-charge circuit configured to avoid inrush to a capacitor can include a plurality of components configured to ramp a pre-charge voltage over time up to a voltage maximum such that the a pre-charge voltage-over-time curve is not an asymptote. The plurality of components can be configured to linearly ramp voltage, for example, to the voltage maximum. In certain embodiments, the circuit can include an integrated voltage sense circuit.

The circuit can include a main input line, a main power line connected to the main input line, a pre-charge input line, an output-to-capacitor voltage line connecting the capacitor to the main power line and the plurality of components in parallel, a voltage sense circuit configured to sense an input voltage and/or the pre-charge voltage, and a ground line configured to connect the capacitor to ground and the plurality of components in parallel. The pre-charge input line can be connected to the main input line in parallel with the main power line.

The plurality of components can include a controller, at least one switch, and a flyback circuit. The controller can be configured to control the at least one switch to cause the flyback circuit to ramp the pre-charge voltage. The flyback circuit can include a first inductor magnetically coupled to a second inductor and at least one diode connected to the first inductor to form a flyback pathway.

In certain embodiments, the at least one switch can include a first switch and a second switch. The first switch can be disposed on the pre-charge input line between the main input line and the first inductor to selectively allow current to pass from the main input line and the pre-charge input line to the first inductor. The circuit can include a return line connected to the ground line and a first line connected to the pre-charge input line in between of the first inductor and the first switch such that the first line is in parallel with the pre-charge line ahead of the first inductor. The first line can be connected to the return line. The circuit can include a second line connected in between of the first inductor and the second switch and to the output-to-capacitor line, and a third line connected to the second line and the return line. The first inductor can be disposed between the first line and the second line. The at least one diode can include a first diode disposed on the first line and configured to allow current flow toward the first inductor, a second diode disposed on the second line and configured to allow current flow toward the capacitor, and a third diode disposed on the third line and configured to allow current flow from the return line to the second line. The second switch can be disposed between the first inductor and/or second line and the return line. The second inductor can be connected in a voltage sense circuit.

The controller can be configured to perform a method to operate the circuit. The method can include closing the first switch such that current builds in the first inductor while the capacitor is charged by current flowing through the second diode and the voltage sense circuit measures, from the second inductor, input voltage minus the voltage of the capacitor through the third diode, and then once charge current is reached, opening the first switch such that flyback current from the first inductor still charges capacitor forming a current loop from the capacitor through the first diode, through the first inductor, through the second diode, and back to the capacitor, during which time the voltage sense circuit senses, from the second inductor, pre-charge voltage across the capacitor. The method can include pulsing the first switch to change voltage readings until sensed pre-charge voltage about equals input voltage, then closing a main relay on the main power line while leaving the first switch closed, and pulsing the second switch thereafter to provide ongoing voltage measurement of capacitor voltage.

In certain embodiments, the flyback circuit can further include a third inductor magnetically coupled to the first and second inductor. The at least one switch can include a first switch. The first inductor can be disposed between the pre-charge input line and the first switch. The first switch can be configured to selectively allow current to pass from the main input line and the pre-charge input line to the first inductor. The circuit can further include a return line connected to the ground line, and a first line connected to between the third inductor and the output-to-capacitor line. The third inductor can be disposed between the return line and the first line. The circuit can include a second line connected between the first line and the pre-charge input line. The at least one diode can include a first diode disposed on the first line and configured to allow current flow toward the capacitor, and a second diode disposed on the second line and configured to allow current flow from the first line to the pre-charge input line, wherein the second inductor is connected in a voltage sense circuit.

The controller can be configured to perform a method to operate the circuit, the method comprising closing the first switch such that current builds the first inductor and the voltage sense circuit measures input voltage from the second inductor, and then opening the first switch such that the voltage sense circuit senses pre-charge voltage from the second inductor while flyback current through the third inductor charges the capacitor through the first diode. The method can include repeating until the input voltage and the pre-charge voltage are about the same, then closing a main relay on the main power line.

In certain embodiments, the flyback circuit can include a third inductor magnetically coupled to the first and second inductors, and the at least one switch can include a first switch. The first inductor can be disposed between the pre-charge input line and the first switch. The pre-charge input line can be connected to a low voltage control power and not to the main input line. The first switch can be configured to selectively allow current to pass from the pre-charge input line to the first inductor. The third inductor can be configured to convert the low voltage control power to a high voltage to charge the capacitor.

In certain embodiments, the circuit can include a return line connected to the ground line, and a first line connected to between the third inductor and the output-to-capacitor line. The third inductor can be disposed between the return line and the first line. The circuit can include a second line connected between the first line and the main input line. The at least one diode can include a first diode disposed on the first line and configured to allow current flow toward the capacitor, and a second diode disposed on the second line and configured to allow current flow from the first line to the main input line and/or the main power line. The second inductor can be connected in a voltage sense circuit.

In certain embodiments, the flyback circuit can include a fourth inductor magnetically coupled to the first, second, and third inductors. The circuit can include a return line connected to the ground line, a first line connected to between the third inductor and the output-to-capacitor line. The third inductor can be disposed between the return line and the first line. The circuit can include and a second line connected between the return line and the main input line. The fourth inductor can be disposed on the second line and the circuit can include a current sensor disposed on the second line to sense current on the second line through the fourth inductor. The at least one diode includes a first diode disposed on the first line and configured to allow current flow toward the capacitor, and a second diode disposed on the second line and configured to allow current flow toward the main input line and/or the main power line. The second inductor can be connected in a voltage sense circuit.

The circuit can include any other suitable circuit components and/or lines in any suitable connections. The controller can include any suitable hardware and/or software module(s) configured to perform any function disclosed herein, e.g., as described above. The controller can be configured to perform any other suitable method(s) and/or portion(s) thereof.

In accordance with at least one aspect of this disclosure, a capacitor pre-charge circuit configured to avoid inrush to a capacitor can include a flyback circuit configured to pre-charge the capacitor without high voltage resistive components. The circuit can include a voltage sense circuit that forms part of the flyback circuit. The circuit can include any embodiments of a circuit disclosed herein, e.g., as described above.

In accordance with at least one aspect of this disclosure, a method can include pre-charging a capacitor to an input power high voltage non-asymptotically. Pre-charging can include intermittent flyback. The method can include any other suitable method(s) and/or portion(s) thereof.

These and other features of the embodiments of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings.

