Voltage balancing in series-connected power switches

Patent metadata

Field	Value
Publication number	US-10230354-B2
Application number	US-201515315559-A
Country	US
Kind code	B2
Filing date	Jul 29, 2015
Priority date	Aug 8, 2014
Publication date	Mar 12, 2019
Grant date	Mar 12, 2019

Abstract

A method for voltage balancing series-connected power switching devices (IGBTs) each connected in parallel with a respective diverter having controllable impedance to controllably conduct current diverted from the associated power switching device, the method comprising the step of controlling each diverter to follow a series of at least two successively higher impedance states during an OFF period of the power switching devices. The series of impedance states for each diverter comprises a first impedance and then a second, higher impedance, the first impedance occurring in response to an indication of a start of the OFF period. The first impedance state preferably occurs during a tail current of the power switching device in parallel with the respective diverter and the second or later impedance state during a leakage current of that power switching device.

First claim

The invention claimed is:

1. A method of voltage balancing series-connected power-switching devices, wherein at least one power-switching device is connected in parallel with a respective diverter, each diverter having controllable impedance to controllably conduct current diverted from a respective power-switching device, the method comprising the steps of:
controlling each diverter to follow a series of successively higher impedance states during an off period of the power-switching devices, the series comprising at least two of the impedance states, wherein each the series comprises at least a first impedance of a diverter and then a second, higher impedance of the diverter, the first impedance occurring response to an indication of a start of the off period,
monitoring a signal of each diverter to thereby detect imbalance between the monitored signals, wherein each the signal indicates at least one of current through and voltage across the diverter,
wherein at least one of the successively higher impedance states of at least one diverter is responsive to detecting a reduction of a the imbalance.

2. The method defined in claim 1 , wherein
the first impedance occurs during a tail current of the power-switching device in parallel with the diverter and a later impedance state of the series occurs during a leakage current of the power-switching device,
the later impedance state occurs responsive to detecting an end of the tail current.

3. The method defined in claim 1 , wherein
at least one of the successively higher impedance states of a diverter occurs when a maximum detected difference between the monitored signals of the diverter and at least one other diverter is less than a predefined amount.

4. The method of claim 1 , wherein
at least one of the successively higher impedance states of at least one diverter occurs at a predefined time delay from the indication of the start of the off period.

5. The method of claim 1 , further comprising the step of:
turning at least one of the diverters off at a predefined time from the indication of the start of the off period.

6. The method of claim 1 , further comprising the step of:
controlling the diverter impedances synchronously.

7. A method of dynamic voltage balancing of series-connected power-switching devices, each the power-switching device coupled in parallel with a respective diverter having controllable impedance to controllably conduct current diverted from the power-switching device, the method comprising the steps of:
a) controlling each diverter to have a first impedance, wherein the power-switching devices are off; then
b) controlling each diverter to have a second, higher impedance to cause current to be commutated from the diverter to the power-switching device coupled in parallel with the diverter; and then
c) turning each power-switching device fully on;
d) each diverter when having the first impedance is controlled to have a predefined current for commutation in step b) to the power-switching device connected in parallel with the diverter;
e) feedback loops are used to control respective power-switching devices, each the feedback loop comprising a difference amplifier receiving from the diverter coupled in parallel with the power-switching device a feedback signal indicating at least one of current through and voltage across the diverter, wherein the difference amplifier controls the respective power-switching device based on a difference between a reference signal and the feedback signal, step b) comprises for each the feedback loop:
setting the reference signal to the difference amplifier to differ from the feedback signal;
the difference amplifier beginning to turn the power-switching device on responsive to the difference between the reference signal and the feedback signal;
detecting a degree of stabilization of the feedback loop; and then
increasing impedance of the diverter responsive to the change detection,

step c) comprises adjusting the reference signal to cause the feedback loop to fully turn on the power-switching device; and
f) the detecting a degree of stabilization of the feedback loop comprises detecting a predefined change of the feedback signal.

Assignees

• Reinhausen Maschf Scheubeck

Inventors

• Leedham Robert John
• Snook Mark

Classifications

• H03K17/567

  Circuits characterised by the use of more than one type of semiconductor device, e.g. BIMOS, composite devices such as IGBT · CPC title

• H03K17/0828 Primary

  in composite switches · CPC title

• H03K3/011 Primary

  Modifications of generator to compensate for variations in physical values, e.g. voltage, temperature {(to maintain energy constant H03K3/015)} · CPC title

• H03K17/107 Primary

  in composite switches · CPC title

• H03K17/168

  in composite switches · CPC title