Direct-current-to-direct-current converter with compensation for potential transformer saturation

A dual-active-bridge converter comprising:

• a primary converter having a plurality of primary switch pairs that operate at different phases or phase offsets with respect to each other;
• each primary switch pair comprising a first switched terminal of low-side semiconductor switch coupled to a corresponding second switched terminal of high-side semiconductor switch at a primary alternating current node, each primary switch pair comprising the low-side semiconductor switch having a second switched terminal coupled to one terminal of a primary direct current bus;
• the high-side semiconductor switch having a first switched terminal coupled to another terminal of the primary direct current bus;
• a secondary converter having a plurality of secondary switch pairs that operate at different phases or phase offsets with respect to each other;
• each secondary switch pair comprising a first switched terminal of low-side semiconductor switch coupled to a corresponding second switched terminal of high-side semiconductor switch at an secondary alternating current node, each secondary switch pair comprising the low-side semiconductor switch having a second switched terminal coupled to one terminal of a secondary direct current bus;
• the high-side semiconductor switch having a first switched terminal coupled to another terminal of the secondary direct current bus;
• a first DC offset detector to measure a first observed DC offset line-to-line voltage, associated with the primary alternating current nodes, between a respective first phase and a respective second phase, wherein the first DC offset detector comprises a first preconditioner having a first low-pass filter for averaging over time or smoothing the magnitudes of near DC, low frequency alternating current components in the first observed DC offset line-to-line voltage;
• a second DC offset detector to measure a second observed DC offset line-to-line voltage, associated with the primary alternating-current nodes, between the respective second phase and a respective third phase, wherein the second DC offset detector comprises a second preconditioner having a second low-pass filter for averaging over time or smoothing the magnitudes of near DC, low frequency alternating current components in the second observed DC offset line-to-line voltage;
• a transformer coupled between the primary alternating-current node and the secondary alternating current node;
• and
• an electronic controller configured to provide control signals to the control terminals of the semiconductor switches of the primary converter and the secondary converter based on a commanded current or target output current;
• the electronic controller configured to adjust the duty cycle through a duty cycle adjustment, between a respective pairs of semiconductor switches of the primary converter and second converter based on reducing or minimizing one or more of the time-averaged magnitudes of, near DC low frequency AC components in first estimated line-to-line DC offset voltage and the second estimated line-to-line DC offset voltage.