Single-phase voltage source AC/DC converter and interconnection system
A single-phase voltage source AC/DC converter according to the present invention generates a second axis voltage command from difference between a DC voltage detection value at a DC terminal and a DC voltage command value and controls a DC voltage by increasing and decreasing active power with the second axis voltage command. For example, the voltage at the DC terminal is increased by decreasing active power when the DC voltage detection value at the DC terminal is lower than the DC voltage command, while the DC voltage detection value at the DC terminal is decreased by increasing the active power when the DC voltage detection value at the DC terminal is higher than the DC voltage command.
1. A single-phase voltage source AC/DC converter, comprising:
a single-phase voltage source AC/DC converting circuit which has internal equivalent impedance as seen from an AC terminal, for converting power from a DC voltage source connected to a DC terminal to single-phase AC power to output from the AC terminal or for converting single-phase AC power from a single-phase AC source connected to the AC terminal to DC power to output from the DC terminal in accordance with a pulse width of a gate signal generated based on a PWM command;
a phase difference generating circuit, which has a phase delay single-phase AC generator for delaying a phase of a single-phase AC output voltage at the AC terminal and generating a delay single-phase alternating voltage, for generating a phase difference voltage corresponding to phase difference between the single-phase AC output voltage at the AC terminal and an internal electromotive voltage of the single-phase voltage source AC/DC converting circuit based on the delay single-phase alternating voltage;
a superior voltage control circuit to which a first axis voltage command for amplitude of the single-phase AC output voltage at the AC terminal and a second axis voltage command for a single-phase AC frequency at the AC terminal are input for outputting a voltage command signal generated so that the amplitude of the single-phase AC output voltage at the AC terminal approaches the first axis voltage command and a frequency command signal generated so that the single-phase AC frequency at the AC terminal approaches the second axis voltage command based on the first axis voltage command, the second axis voltage command, the phase difference voltage from the phase difference generating circuit and the single-phase AC output voltage at the AC terminal;
a frequency control circuit for determining an electrical angle of the internal electromotive voltage of the single-phase voltage source AC/DC converting circuit to generate a generated electrical angle based on a reference frequency of a single-phase AC output frequency at the AC terminal, the frequency command signal from the superior voltage control circuit, and an output signal from the phase difference generating circuit;
a subordinate voltage control circuit for outputting a signal generated so that the amplitude, the frequency, and the phase of the single-phase AC output voltage approach a synthesized value of a reference voltage of the single-phase AC output voltage at the AC terminal, the voltage command signal, and the generated electrical angle as the PWM command based on the single-phase AC output voltage at the AC terminal, the generated electrical angle of the frequency control circuit, and the voltage command signal from the superior voltage control circuit; and
a command value arithmetic circuit to which a DC voltage command value to specify a voltage at the DC terminal is set and which obtains the second axis voltage command by detecting a DC voltage detection value being the voltage at the DC terminal and calculating difference between the DC voltage command value and the DC voltage detection value.
2. The single-phase voltage source AC/DC converter according to claim 1 , wherein the command value arithmetic circuit calculates the difference between the DC voltage command value and the DC voltage detection value with a low pass characteristic circuit.
3. The single-phase voltage source AC/DC converter according to claim 2 ,
wherein the low pass characteristic circuit of the command value arithmetic circuit has characteristics of Equation 1
[
Equation
1
]
V
^
2
*
(
s
)
=
-
K
dc
1
+
T
Kdc
·
s
(
V
^
D
*
(
s
)
-
V
^
D
(
s
)
)
(
1
)
where,
V 2 * represents a second axis voltage command;
V D * represents a DC voltage command value;
V D represents a DC voltage detection value;
s represents a variable of laplace transform;
K dc represents a proportional gain;
T Kdc represents a first-order lag time constant; and
^ represents a laplace transform.
4. The single-phase voltage source AC/DC converter according to claim 1 ,
wherein the command value arithmetic circuit calculates the difference between the DC voltage command value and the DC voltage detection value with an integrating circuit.
5. The single-phase voltage source AC/DC converter according to claim 4 ,
wherein the integrating circuit of the command value arithmetic circuit has characteristics of Equation 2
[
Equation
2
]
V
^
2
*
(
s
)
=
-
1
T
dc
·
s
(
V
^
D
*
(
s
)
-
V
^
D
(
s
)
)
(
2
)
where,
V 2 * represents a second axis voltage command;
V D * represents a DC voltage command value;
V D represents a DC voltage detection value;
s represents a variable of laplace transform;
T dc represents a integral time constant; and
^ represents a laplace transform.
6. The single-phase voltage source AC/DC converter according to claim 1 , wherein the command value arithmetic circuit calculates the difference between the DC voltage command value and the DC voltage detection value with a parallel circuit in which a low pass characteristic circuit and an integrating circuit are parallely-arranged.
7. The single-phase voltage source AC/DC converter according to claim 6 ,
wherein the parallel circuit of the command value arithmetic circuit has characteristics of Equation 3
[
Equation
3
]
V
^
2
*
(
s
)
=
(
-
K
dc
1
+
T
Kdc
·
s
-
1
T
dc
·
s
)
(
V
^
D
*
(
s
)
-
V
^
D
(
s
)
)
(
3
)
where,
V 2 * represents a second axis voltage command;
V D * represents a DC voltage command value;
V D represents a DC voltage detection value;
s represents a variable of laplace transform;
K dc represents a proportional gain;
T Kdc represents a first-order lag time constant;
T dc represents a integral time constant; and
^ represents a laplace transform.
8. The single-phase voltage source AC/DC converter according to claim 1 , further comprising a DC current detecting circuit for detecting a DC current value at the DC terminal,
wherein the command value arithmetic circuit adds the DC current value detected by the DC current detecting circuit when calculating the difference between the DC voltage command value and the DC voltage detection value.
9. An interconnection system comprising:
the single-phase voltage source AC/DC converter according to claim 1 ; and
n (n is any positive integer) sets of DC devices which are connected to the DC terminal of the single-phase voltage source AC/DC converter via a DC/DC converters so that DC power is transmitted to and received from the DC terminal.