Bidirectional insulated DC/DC converter and smart network using the same
A bidirectional insulated DC/DC converter narrows a pulse width of an AC fundamental wave voltage corresponding to a higher DC voltage of two DC voltages, to cause effective values of the AC fundamental wave voltages to coincide with each other, and then, sets a phase difference between the AC fundamental wave voltages in accordance with a value and a direction of a current that is desired to flow. Accordingly, even when the difference between the two DC voltages greatly varies, DC power can be stably transmitted and received.
1. A bidirectional insulated DC/DC converter for transmitting and receiving DC power between a first DC circuit and a second DC circuit, the bidirectional insulated DC/DC converter comprising:
a first inverter configured to generate a first AC fundamental wave voltage based on a first DC voltage received from the first DC circuit;
a second inverter configured to generate a second AC fundamental wave voltage that is equal in frequency to the first AC fundamental wave voltage based on a second DC voltage received from the second DC circuit;
an insulated transformer including a primary winding and a secondary winding insulated from each other and configured to receive the first AC fundamental wave voltage and the second AC fundamental wave voltage, respectively; and
circuitry configured to:
determine a pulse width of at least one of the first and second AC fundamental wave voltages based on sin −1 (A), ‘A’ being a term including a ratio of the first DC voltage to the second DC voltage;
determine a phase difference between the first and second AC fundamental wave voltages such that a desired DC power is transmitted and received between the first and second DC circuits; and
generate a control signal for each of the first and second inverters based on the determined pulse width and the determined phase difference.
2. The bidirectional insulated DC/DC converter according to claim 1 , wherein
when the first DC voltage is higher than the second DC voltage, the circuitry configured to narrow the pulse width of the first AC fundamental wave voltage, and
when the second DC voltage is higher than the first DC voltage, the circuitry configured to narrow the pulse width of the second AC fundamental wave voltage.
3. The bidirectional insulated DC/DC converter according to claim 2 , wherein,
on conditions that the first and second DC voltages are defined as Ea and Eb, respectively, and
that the pulse widths of the first and second AC fundamental wave voltages are defined as α and β, respectively,
the circuitry is configured to set
α=2 sin −1 ( Eb/Ea ) and β=π when Ea>Eb , and
α=π and β=2 sin −1 ( Ea/Eb ) when Eb>Ea.
4. The bidirectional insulated DC/DC converter according to claim 3 , wherein
on a condition that the phase difference between the first and second AC fundamental wave voltages is defined as θ,
the circuitry is configured to
generate a sawtooth waveform signal that changes from 0 to π at a frequency that is twice as high as a frequency of each of the first and second AC fundamental wave voltages,
S 1=π/2+(−θ/2+π/2−α/2) that is a first reference signal,
S 2=π/2+(−θ/2−π/2+α/2) that is a second reference signal,
S 3=π/2+(θ/2+π/2−β/2) that is a third reference signal, and
S 4=π/2+(θ/2−π/2+β/2) that is a fourth reference signal,
generate a first control signal and a second control signal for the first inverter based on cross points between the sawtooth waveform signal and the first and second reference signals, respectively, and
generate a third control signal and a fourth control signal for the second inverter based on cross points between the sawtooth waveform signal and the third and fourth reference signals, respectively.
5. The bidirectional insulated DC/DC converter according to claim 4 , wherein
the circuitry is configured to
change the first to fourth control signals from a first logic level to a second logic level at the cross points between the sawtooth waveform signal and the first to fourth reference signals, respectively, in an odd-numbered period of the sawtooth waveform signal, and
change the first to fourth control signals from the second logic level to the first logic level at the cross points between the sawtooth waveform signal and the first to fourth reference signals, respectively, in an even-numbered period of the sawtooth waveform signal.
6. The bidirectional insulated DC/DC converter according to claim 4 , wherein
the circuitry is configured to
change the first to fourth control signals from a first logic level to a second logic level at the cross points between the sawtooth waveform signal and the first to fourth reference signals, respectively, in an odd-numbered period of the sawtooth waveform signal, and stores information related to the cross points, and
based on the stored information, change the first to fourth control signals from the second logic level to the first logic level in an even-numbered period of the sawtooth waveform signal.
7. The bidirectional insulated DC/DC converter according to claim 1 , further comprising a first voltage detector and a second voltage detector configured to detect the first DC voltage and the second DC voltage, respectively, wherein
the circuitry is configured to set the pulse width of each of the first and second AC fundamental wave voltages based on detection results of the first and second voltage detectors.
8. The bidirectional insulated DC/DC converter according to claim 1 , further comprising at least one of:
a first reactor having one terminal for receiving the first AC fundamental wave voltage and the other terminal connected to one terminal of the primary winding; and
a second reactor having one terminal receiving the second AC fundamental wave voltage and the other terminal connected to one terminal of the secondary winding.
9. A smart network comprising:
the bidirectional insulated DC/DC converter according to claim 1 ; and
the first DC circuit and the second DC circuit,
the first DC circuit and the second DC circuit being a first DC power system and a second DC power system, respectively.
10. The smart network according to claim 9 , wherein
each of the first and second DC power systems includes
a DC bus connected to the first inverter or the second inverter,
a DC power supply configured to supply DC power to the DC bus,
a load driven by the DC power from the DC bus, and
a power storage device connected to the DC bus and storing the DC power.
11. The bidirectional insulated DC/DC converter according to claim 1 , wherein the term ‘A’ equals Eb/Ea or Ea/Eb, Ea representing the first DC voltage, and Eb representing the second DC voltage.