Bidirectional insulated DC/DC converter and smart network
A bidirectional insulated DC/DC converter includes a first single-phase 3-level inverter, a second single-phase 3-level inverter, and an insulated transformer. The first single-phase 3-level inverter generates a first AC voltage between output terminals based on a first DC voltage received from a first DC circuit. The second single-phase 3-level inverter generates a second AC voltage between output terminals based on a second DC voltage received from a second DC circuit. The insulated transformer includes a primary winding that receives the first AC voltage from the output terminals and a secondary winding that receives the second AC voltage from the output terminals.
1. A bidirectional insulated DC/DC converter that exchanges DC power between first and second DC circuits, the bidirectional insulated DC/DC converter comprising:
a first single-phase 3-level inverter configured to generate a first AC voltage between a first output terminal and a second output terminal based on a first DC voltage received from the first DC circuit;
a second single-phase 3-level inverter configured to generate a second AC voltage between a third output terminal and a fourth output terminal based on a second DC voltage received from the second DC circuit;
an insulated transformer including a primary winding that receives the first AC voltage from the first and second output terminals and a secondary winding that receives the second AC voltage from the third and fourth output terminals; and
a control device configured to control the first and second single-phase 3-level inverters, wherein
the first single-phase 3-level inverter includes:
a first circuit connected between the first DC circuit and the first output terminal to generate a first-phase voltage; and
a second circuit connected between the first DC circuit and the second output terminal to generate a second-phase voltage,
the first single-phase 3-level inverter is configured to generate a difference between the first-phase voltage and the second-phase voltage as the first AC voltage,
the second single-phase 3-level inverter includes:
a third circuit connected between the second DC circuit and the third output terminal to generate the first-phase voltage; and
a fourth circuit connected between the second DC circuit and the fourth output terminal to generate the second-phase voltage,
the second single-phase 3-level inverter is configured to generate a difference between the first-phase voltage and the second-phase voltage as the second AC voltage,
the control device is configured to set any one of pulse widths of the first-phase voltage and the second-phase voltage and a phase difference between the first-phase voltage and the second-phase voltage such that an amplitude of an nth harmonic component (n is an odd number of 3 or more) included in each of the first and second AC voltages becomes zero.
2. The bidirectional insulated DC/DC converter according to claim 1 , wherein
the amplitude of the nth harmonic component is given by a following equation (1) when the pulse widths of the first-phase voltage and the second-phase voltage are equal to each other in each of the first and second single-phase 3-level inverters,
Vn= 4 E/n π·sin( nθ/ 2)·sin( nϕ/ 2) (1)
where Vn represents the amplitude of the nth harmonic component, E represents the first and second DC voltages, θ represents the pulse width, and ϕ represents the phase difference, and
the control device is configured to set the phase difference between the first-phase voltage and the second-phase voltage such that sin (nϕ/2)=0 is satisfied.
3. The bidirectional insulated DC/DC converter according to claim 2 , wherein
when the first DC voltage is higher than the second DC voltage, the control device is configured to narrow the pulse widths of the first-phase voltage and the second-phase voltage in the first single-phase 3-level inverter such that effective values of fundamental-wave components of the first and second AC voltages are matched with each other, and
when the second DC voltage is higher than the first DC voltage, the control device is configured to narrow the pulse widths of the first-phase voltage and the second-phase voltage in the second single-phase 3-level inverter such that the effective values of the fundamental-wave components of the first and second AC voltages are matched with each other.
4. The bidirectional insulated DC/DC converter according to claim 1 , wherein
the amplitude of the nth harmonic component is given by a following equation (1) when the pulse widths of the first-phase voltage and the second-phase voltage are equal to each other in each of the first and second single-phase 3-level inverters,
Vn= 4 E/n π·sin( nθ/ 2)·sin( nϕ/ 2) (1)
where Vn represents the amplitude of the nth harmonic component, E represents the first and second DC voltages, θ represents the pulse width, and ϕ represents the phase difference, and
the control device is configured to set the pulse widths of the first-phase voltage and the second-phase voltage such that sin (nθ/2)=0 is satisfied.
5. The bidirectional insulated DC/DC converter according to claim 4 , wherein
when the first DC voltage is higher than the second DC voltage, the control device is configured to narrow the phase difference between the first-phase voltage and the second-phase voltage in the first single-phase 3-level inverter such that effective values of fundamental-wave components of the first and second AC voltages are matched with each other, and
when the second DC voltage is higher than the first DC voltage, the control device is configured to narrow the phase difference between the first-phase voltage and the second-phase voltage in the second single-phase 3-level inverter such that the effective values of the fundamental-wave components of the first and second AC voltages are matched with each other.
6. The bidirectional insulated DC/DC converter according to claim 1 , wherein
the control device is further configured to set the phase difference between the first and second AC voltages such that a desired DC power is exchanged between the first and second DC circuits.
7. A smart network comprising:
the bidirectional insulated DC/DC converter according to claim 1 ; and
the first and second DC circuits, wherein
the first and second DC circuits are first and second DC power systems, respectively.
8. The smart network according to claim 7 , wherein each of the first and second DC power systems includes:
a DC bulbar connected to the first or second single-phase 3-level inverter;
a DC power supply configured to supply a DC power to the DC busbar;
a load driven by the DC power from the DC busbar; and
a power storage device configured to store the DC power from the DC busbar.
9. The bidirectional insulated DC/DC converter according to claim 2 , wherein
the control device is further configured to set the phase difference between the first and second AC voltages such that a desired DC power is exchanged between the first and second DC circuits.
10. The bidirectional insulated DC/DC converter according to claim 3 , wherein
the control device is further configured to set the phase difference between the first and second AC voltages such that a desired DC power is exchanged between the first and second DC circuits.
11. The bidirectional insulated DC/DC convener according to claim 4 , wherein
the control device is further configured to set the phase difference between the first and second AC voltages such that a desired DC power is exchanged between the first and second DC circuits.
12. The bidirectional insulated DC/DC converter according to claim 5 , wherein
the control device is further configured to set the phase difference between the first and second AC voltages such that a desired DC power is exchanged between the first and second DC circuits.