Microgrid power supply system DC-DC converter and controlling method
A DC-DC voltage converter includes an input circuit, a parallel linked leg (PLL), an output circuit and a controller. The PLL includes an active leg switch, a leg inductor, a leg capacitor and a leg diode. The controller is configured to i) turn on the active input switch and the active leg switches while maintaining the active output switch at a turn off state for the first duty cycle period ii) turn off the active input switch and the active leg switches, and turn on the active output switch for a second duty cycle period following the first duty cycle period, and iii) turn off the active output switch while maintaining also turn off states of the active input switch and the active leg switches for a remaining period following the second duty cycle period. A method of controlling the DC-DC converter includes steps of i) to iii).
1. A DC-DC voltage converter comprising:
an input circuit;
at least one parallel linked leg (PLL), denoted by PLLj (j=1, . . . , n, n≥1);
an output circuit; and
a controller,
wherein
the input circuit further comprising: a pair of input terminals; an input inductor, a positive contact thereof connected to a higher voltage input terminal of the pair of input terminals; and an active input switch, wherein further
a positive port, a negative port and a gate port of the active input switch are connected to a negative contact of the input inductor, a lower voltage input terminal of the pair of input terminals and a first output port of the controller, respectively, and
the higher voltage input terminal and the lower voltage input terminal are configured to be connected to a higher voltage terminal and a lower voltage terminal of a DC voltage source, respectively,
the PLLj (j=1, . . . , n, n≥1), further comprising: an active leg switch S j ; a leg inductor L j connected with the active leg switch S j via a negative port of the active leg switch S j and a positive contact of the leg inductor L j and a leg capacitor C j ; and a leg diode D j connected with the leg capacitor C j , via a negative contact of the leg capacitor and a positive port of the leg diode D j , wherein further
a combination of the leg capacitor C j and the leg diode D j connected in parallel with the leg inductor L j , wherein the positive contact of the leg capacitor is connected to the positive contact of the leg inductor L j ,
a positive port and a gate port of the active leg switch S j are connected to the higher voltage input terminal and the first output port of the controller, respectively, and
the negative contact of the leg inductor L j constituting the PLL j is connected to
i) the lower voltage input port when j=1, or
ii) a negative contact of a leg capacitor C j-1 constituting a PLL j-1 when j≥2, and
the output circuit further comprising: an active output switch; an output diode; an output capacitor connected in series with the output diode; and a pair of output terminals, wherein
a positive port and a negative port of the output diode are connected to the negative contact of the input inductor and a positive contact of the output capacitor, respectively,
a negative contact of the output capacitor is connected to a negative contact of a leg capacitor C n constituting a PLL n ,
a positive port, a negative port, and a gate port of the active output switch are connected to the positive port of the output diode, a positive contact of the leg capacitor C n constituting the PLL n , and a second output port of the controller, respectively, and
a higher voltage output terminal and a lower voltage output terminal of the pair of the output terminals are connected to the positive contact and the negative contact of the output capacitor, respectively, and configured to be connected to a higher voltage input port and a lower voltage input port of an external load, respectively, and wherein
the controller further comprising: a circuitry; a programmed instruction; and the first output port and the second output port, wherein
the first output port is connected to the gate port of the active input switch and the gate port of the active leg switch S j , while the second output port is connected to the gate port of the active output switch, wherein further
the controller is configured to
turn on the active input switch and the active leg switch S j and maintain turn on states thereof while maintaining the active output switch at a turn off state for a first duty cycle period k 1 T, wherein k 1 and T denote a duty ratio of the first duty cycle, and a period for a complete switching cycle, respectively;
turn off the active input switch and the active leg switch S j , maintain turn off states thereof, and turn on the active output switch and maintain a turn on state thereof for a second duty cycle period k 2 T following the first duty cycle, wherein k 2 denotes a duty ratio for the second duty cycle and satisfies a relation (k 1 +k 2 )<1; and
turn off the active output switch and maintain the turn off state thereof while maintaining also turn off states of the active input switch and the active leg switch S j for a remaining period following the second duty cycle.
2. The DC-DC voltage converter of claim 1 , further comprising an output switch diode inserted between the positive port of the output diode and the positive port of the active output switch, wherein a positive port and a negative port of the output switch diode are connected to the positive port of the output diode and the positive port of the active output switch, respectively.
3. The DC-DC voltage converter of claim 1 , wherein a protective diode is connected in parallel with at least one of the active input switch, the active leg switch S j , or the active output switch.
4. The DC-DC voltage converter of claim 1 , wherein the controller is further configured to operate the DC-DC converter in a continuous conduction mode (CCM) by adjusting at least a) the duty ratio k i for the active input switch and the active leg switch S j , b) the duty ratio k 2 for the active output switch, or c) a switching frequency f=1/T, and by satisfying following equations:
[
(
n
+
1
)
k
1
+
nk
2
]
(
1
-
k
1
-
k
2
)
2
2
(
(
n
+
1
)
-
k
2
)
(
n
+
1
)
<
L
RT
,
wherein, L denotes an inductance of the input inductor and the leg inductor, R denotes a resistance of load connected to the pair of output terminals.
5. The DC-DC voltage converter of claim 1 , wherein the controller is further configured to operate the DC-DC converter in a discontinuous conduction mode (DCM) by adjusting at least a) the duty ratio k 1 for the active input switch and the active leg switch S j , b) the duty ratio k 2 for the active output switch, or c) a switching frequency f and by satisfying following equations:
[
(
n
+
1
)
k
1
+
nk
2
]
(
1
-
k
1
-
k
2
)
2
2
(
(
n
+
1
)
-
k
2
)
(
n
+
1
)
>
L
RT
,
1
-
k
1
-
k
2
>
V
i
(
(
n
+
1
)
k
1
+
nk
2
)
V
o
-
(
n
+
1
)
V
i
wherein, L denotes an inductance of the input inductor and the leg inductor, R denotes a resistance of load connected to the pair of output terminals, V i and V o denote an input voltage and an output voltage, respectively.
6. The DC-DC voltage converter of claim 4 , wherein the controller is further configured to switch operation modes of the DC-DC converter between a continuous conduction mode (CCM) and a discontinuous conduction mode (DCM) by adjusting at least a) the duty ratio k 1 for the active input switch and the active leg switch S j , b) the duty ratio k 2 for the active output switch, or c) a switching frequency f, and by satisfying following equations:
a) for operating in the CCM mode;
[
(
n
+
1
)
k
1
+
nk
2
]
(
1
-
k
1
-
k
2
)
2
2
(
(
n
+
1
)
-
k
2
)
(
n
+
1
)
<
L
RT
,
b) for operating in the DCM mode;
[
(
n
+
1
)
k
1
+
nk
2
]
(
1
-
k
1
-
k
2
)
2
2
(
(
n
+
1
)
-
k
2
)
(
n
+
1
)
>
L
RT
,
and
1
-
k
1
-
k
2
>
V
i
(
(
n
+
1
)
k
1
+
nk
2
)
V
o
-
(
n
+
1
)
V
i
wherein V i is the input voltage and V o is the output voltage.
7. The DC-DC voltage converter of claim 1 , wherein the controller further comprises an input port monitoring an input voltage and an output voltage, the controller is further configured to:
store a specified target range of the output voltage;
monitor the input voltage and the output voltage; and
maintain the output voltage within the specified target range by adjusting at least one of a) the duty ratio k 1 , b) the duty ratio k 2 , or c) the switching frequency f.
8. The DC-DC voltage converter of claim 1 , the controller is further configured to:
estimate efficiencies η of the DC-DC converter for a plurality of candidate sets of the duty ratios k 1 and k 2 and a switching frequency f, in accordance with a model equation given below,
η
≅
1
1
+
nk
1
(
n
+
1
)
-
k
2
-
γ
v
d
+
V
i
(
∑
i
=
1
n
I
Ci
)
k
1
V
o
2
R
+
P
S
,
total
Loss
V
o
2
R
,
wherein V i and V o denote an input voltage and an output voltage, respectively, γ vd represents a non-ideality factor for all of the diodes and switches, the term (Σ i=1 n l Ci ) represents a total sum of charging current of the leg capacitors during the first duty cycle, P S,total Loss represents a total switching power loss at the switches, R denotes a resistance of load connected to the pair of output terminals, respectively;
select a plurality of candidate sets satisfying a requirement on a voltage gain of the DC-DC converter; and
implement a set of the duty ratios k 1 and k 2 and the switching frequency f giving a maximum value in the efficiency among the plurality of candidate sets.
9. The DC-DC voltage converter of claim 1 , wherein the controller is further configured to satisfy a sum (k 1 +k 2 ) not greater than 0.8.
10. The DC-DC voltage converter of claim 1 , comprising at least two parallel linked legs wherein PLLj (j=1, . . . , n, n≥2).
11. A method of controlling a DC-DC converter, the DC-DC converter comprising: an input circuit; at least one parallel linked leg (PLL), denoted by PLLj (j=1, . . . , n, n≥1); an output circuit; and a controller, wherein
the input circuit further comprising: a pair of input terminals; an input inductor, a positive contact thereof connected to a higher voltage input terminal of the pair of input terminals; and an active input switch, wherein further
a positive port, a negative port and a gate port of the active input switch are connected to a negative contact of the input inductor, a lower voltage input terminal of the pair of input terminals and a first output port of the controller, respectively, and
the higher voltage input terminal and the lower voltage input terminal are configured to be connected to a higher voltage terminal and a lower voltage terminal of a DC voltage source, respectively,
wherein
the PLLj (j=1, . . . , n, n≥1), further comprising: an active leg switch S j ; a leg inductor L j connected in series with the active leg switch S j via a negative port of the active leg switch S j and a positive contact of the leg inductor L j and a leg capacitor C j ; and a leg diode D j connected in series with the leg capacitor C j via a negative contact of the leg capacitor and a positive port of the leg diode D j , wherein further
a combination of the leg capacitor C j and the leg diode D j connected in series is connected in parallel with the leg inductor L j , wherein the positive contact of the leg capacitor is connected to the positive contact of the leg inductor,
a positive port and a gate port of the active leg switch S j are connected to the higher voltage input terminal and the first output port of the controller, respectively, and
the negative contact of the leg inductor L j constituting the PLL j is connected to
iii) the lower voltage input port when J=1, or
iv) a negative contact of a leg capacitor C j-1 constituting a PLL j-i when j≥2,
wherein
the output circuit further comprising: an active output switch; an output diode; an output capacitor connected in series with the output diode; and a pair of output terminals, wherein
a positive port and a negative port of the output diode are connected to the negative contact of the input inductor, and a positive contact of the output capacitor, respectively,
a negative contact of the output capacitor is connected to a negative contact of a leg capacitor C n constituting a PLL n , respectively,
a positive port of the active output switch is connected to either one of
a) the positive port of the output diode, or
b) a negative port of an output switch diode, wherein a positive port of the output switch diode is connected to the positive port of the output diode,
a negative port and a gate port of the active output switch are connected to a positive contact of the leg capacitor C n constituting the PLL n and a second output port of the controller, respectively, and
a higher voltage output terminal and a lower voltage output terminal of the pair of the output terminals are connected to a positive contact and a negative contact of the output capacitor, respectively, and configured to be connected to a higher voltage input port and a lower voltage input port of an external load, respectively, and
wherein further
the controller further comprising: a circuitry; a programmed instruction; and the first output port and the second output port of control signals, wherein
the first output port is connected to the gate port of the active input switch and the gate port of the active leg switch S j , while the second output port is connected to the gate port of the active output switch,
wherein, the method comprising:
turning on the active input switch and the active leg switch S j and maintaining turn on states thereof while maintaining the active output switch at a turn off state for a first duty cycle period k 1 T, wherein k 1 and T (where T=1/f) denote a first duty ratio, and a period for a complete switching cycle, respectively, f denotes a switching frequency;
turning off the active input switch and the active leg switch S j and maintaining turn off states thereof, and turning on the active output switch and maintain a turn on state thereof for a second duty cycle period k 2 T following the first duty cycle, wherein k 2 denotes a second duty ratio and satisfies a relation (k 1 +k 2 )<1; and
turning off the active output switch and maintaining the turn off state thereof while maintaining also turn off states of the active input switch and the active leg switch S j for time span (1−k 1 -k 2 )T following the second duty cycle.
12. The method of controlling the DC-DC converter of claim 11 , further comprising:
adjusting at least one of a) the duty ratio k 1 , b) the duty ratio k 2 , or c) the switching frequency f, and
operating the DC-DC converter in a continuous conduction mode (CCM) by satisfying a following condition:
[
(
n
+
1
)
k
1
+
nk
2
]
(
1
-
k
1
-
k
2
)
2
2
(
(
n
+
1
)
-
k
2
)
(
n
+
1
)
<
L
RT
,
wherein, L denotes an inductance of the input inductor and the leg inductor, R denotes a resistance of the load connected to the output terminals.
13. The method of controlling the DC-DC converter of claim 11 , further comprising
adjusting at least one of a) the duty ratio k 1 , b) the duty ratio k 2 , or c) the switching frequency f, and
operating the DC-DC converter in a discontinuous conduction mode (DCM) by satisfying following condition:
[
(
n
+
1
)
k
1
+
nk
2
]
(
1
-
k
1
-
k
2
)
2
2
(
(
n
+
1
)
-
k
2
)
(
n
+
1
)
≥
L
RT
,
and
1
-
k
1
-
k
2
>
V
i
(
(
n
+
1
)
k
1
+
nk
2
)
V
o
-
(
n
+
1
)
V
i
,
wherein, L denotes an inductance of the input inductor and the leg inductor, R denotes a resistance of the load connected to the output terminals, V 1 and V o denotes an input voltage and an output voltage, respectively.
14. The method of controlling the DC-DC converter of claim 11 , the method further comprising switching operation modes of the DC-DC converter between the continuous conduction mode (CCM) and a discontinuous conduction mode (DCM) by choosing a condition to be satisfied between below conditions a) and b):
a) for operating in the CCM mode;
[
(
n
+
1
)
k
1
+
nk
2
]
(
1
-
k
1
-
k
2
)
2
2
(
(
n
+
1
)
-
k
2
)
(
n
+
1
)
<
L
RT
,
b) for operating in the DCM mode;
[
(
n
+
1
)
k
1
+
nk
2
]
(
1
-
k
1
-
k
2
)
2
2
(
(
n
+
1
)
-
k
2
)
(
n
+
1
)
>
L
RT
,
and
1
-
k
1
-
k
2
>
V
i
(
(
n
+
1
)
k
1
+
nk
2
)
V
o
-
(
n
+
1
)
V
i
wherein V i is the input voltage and V o is the output voltage.
15. The method of controlling the DC-DC converter of claim 11 , wherein the controller further comprising an input port configured to monitor an input voltage and an output voltage, and the method further comprising:
storing a specified range of the output voltage;
monitoring the input voltage and the output voltage;
adjusting at least one of a) the duty ratio k 1 , b) the duty ratio k 2 , or c) a switching frequency f, and
maintaining the output voltage within the specified range.
16. The method of controlling the DC-DC converter of claim 11 , further comprising
estimating efficiencies η of the DC-DC converter for a plurality of candidate sets of the duty ratios k 1 and k 2 and a switching frequency f, in accordance with a model equation given below,
η
≅
1
1
+
nk
1
(
n
+
1
)
-
k
2
-
γ
v
d
+
V
i
(
∑
i
=
1
n
I
Ci
)
k
1
V
o
2
R
+
P
S
,
total
Loss
V
o
2
R
,
wherein V i and V o denote an input voltage and an output voltage, respectively, γ vd represents a non-ideality factor for the diodes and switches, the term (Σ i=1 n I Ci ) represents a total sum of charging current of the leg capacitors during the first duty cycle, P S,total Loss represents a total switching power loss at the switches, R denotes a resistance of load connected to the pair of output terminals, respectively;
selecting a plurality of candidate sets satisfying a requirement on a voltage gain of the DC-DC converter; and
choosing a set of the duty ratios k 1 and k 2 and the switching frequency f giving a maximum value in the efficiency among the plurality of candidate sets.
17. The method of controlling the DC-DC converter of claim 11 , wherein further the DC-DC converter comprising a plurality number Ti of the PLL with n not less than three, and the first duty cycle k 1 and the second duty cycle k 2 are configured to satisfy a condition (k 1 +k 2 ) is not greater than 0.8.
18. The method of controlling the DC-DC converter of claim 11 , wherein the the DC-DC converter comprises at least two parallel linked legs wherein PLLj (j=1, . . . , n, n≥2).
19. A microgrid power supply system comprising: a DC power source and a DC-DC converter, wherein the DC-DC converter further comprising;
an input circuit;
at least one parallel linked leg (PLL), denoted by PLLj (j=1, . . . , n, n≥1);
an output circuit; and
a controller,
wherein
the input circuit further comprising: a pair of input terminals; an input inductor, a positive contact thereof connected to a higher voltage input terminal of the pair of input terminals; and an active input switch, wherein further
a positive port, a negative port and a gate port of the active input switch are connected to a negative contact of the input inductor, a lower voltage input terminal of the pair of input terminals and a first output port of the controller, respectively, and
the higher voltage input terminal and the lower voltage input terminal are configured to be connected to a higher voltage terminal and a lower voltage terminal of a DC voltage source, respectively,
wherein
the PLLj (j=1, . . . , n, n≥1), further comprising: an active leg switch S j ; a leg inductor L j connected in series with the active leg switch S j via a negative port of the active leg switch S j and a positive contact of the leg inductor L j and a leg capacitor C j ; and a leg diode D j connected in series with the leg capacitor C j via a negative contact of the leg capacitor and a positive port of the leg diode D j , wherein further
a combination of the leg capacitor C j and the leg diode D j connected in series is connected in parallel with the leg inductor L j , wherein the positive contact of the leg capacitor is connected to the positive contact of the leg inductor,
a positive port and a gate port of the active leg switch S j are connected to the higher voltage input terminal and the first output port of the controller, respectively, and
the negative contact of the leg inductor L j constituting the PLL 1 is connected to
i) the lower voltage input port when j=1, or
ii) a negative contact of a leg capacitor C j-1 constituting a PLL j-1 when j≥2, wherein,
an output circuit further comprising: an active output switch; an output diode; an output capacitor connected in series with the output diode; a pair of output terminals, wherein
a positive port and a negative port of the output diode are connected to the negative contact of the input inductor and a positive contact of the output capacitor, respectively,
a negative contact of the output capacitor is connected to a negative contact of a leg capacitor C n constituting a PLL n ,
a positive port of the active output switch is connected to either one of
a) the positive port of the output diode, or
b) a negative port of an output switch diode, wherein a positive port of the output switch diode is connected to the positive port of the output diode,
a negative port and a gate port of the active output switch are connected to a positive contact of the leg capacitor C n constituting the PLL n and a second output port of the controller, respectively, and
a higher voltage output terminal and a lower voltage output terminal of the pair of the output terminals are connected to a positive contact and a negative contact of the output capacitor, respectively, and configured to be connected to a higher voltage input port and a lower voltage input port of an external load, respectively, and wherein
the controller further comprising: a circuitry; a programmed instruction; and the first output port and the second output port of control signals, wherein
the first output port is connected to the gate port of the active input switch and the gate port of the active leg switch S j , while the second output port is connected to the gate port of the active output switch, and
wherein further
the controller is configured to
turn on the active input switch and the active leg switch S j and maintain turn on states thereof while maintaining the active output switch at a turn off state for the first duty cycle period k 1 T, wherein k 1 and T denotes a first duty ratio, and a period for a complete switching cycle, respectively;
turn off the active input switch and the active leg switch S j , maintain turn off states thereof, and turn on the active output switch and maintain a state thereof for a second duty cycle period k 2 T following the first duty cycle period, wherein k 2 denotes a second duty ratio and satisfies a relation (k 1 +k 2 )<1; and
turn off the active output switch and maintain the turn off state thereof while maintaining also turn off states of the active input switch and the active leg switch S j for a remaining period following the second duty cycle period.