Control method of constant-voltage-gain isolation type bidirectional full-bridge DC/DC converter
The disclosure relates to power electronics technology and aims to provide a control method of constant-voltage-gain isolation type bidirectional full-bridge DC/DC converter, which is based on a single-phase-shifting modulation method. By enabling the difference between the M times of the input voltage and primary-referred value of the output voltage to be constantly zero, to realize the control goal that the ratio value between the primary-referred value of the output voltage and the input voltage is constantly M; the ratio value between the primary-referred value of the output voltage and the input voltage is defined as the voltage gain M, wherein an adjusting range is 0.5˜2; through introducing a feedforward compensator involving the input and output voltages and the input and output currents, a linear controller of the system is implemented.
1. A control method of a constant-voltage-gain isolation type bidirectional full-bridge DC/DC converter, wherein the method is realized on a single-phase-shifting (SPS) modulated isolation type bidirectional full-bridge DC/DC converter with the structure that:
the converter has an isolation transformer T with a turn ratio of n:1, a primary side H bridge is formed by four switches, and the other four switches form a secondary side H bridge;
two sides of the isolation transformer T are respectively connected by a primary side resonant tank composed of a resonant inductor L r1 and a resonant capacitor C r1 , and a secondary side resonant tank composed of a resonant inductor L r2 and a resonant capacitor C r2 ; the converter is also provided with an input-port DC bus capacitor C 1 , and is provided with an output-port DC bus capacitor C 2 ;
a single-phase-shifting (SPS) modulation method of the DC/DC converter comprises: in a switching cycle of the DC/DC converter, though turning on/off the switches of the primary side H bridge, a square wave voltage u ad with the duty ratio of 0.5 is generated between the midpoints of two bridge legs of the primary-side H bridge; in the same way, a square wave voltage u cd with the duty ratio of 0.5 is generated in between the midpoints of two bridge legs of the secondary-side H bridge; through shifting the phase angle φ that the midpoint voltage u ab of the two bridge legs of the primary-side H bridge leads the midpoint voltage u cd of the two bridge legs of the secondary-side H bridge, so that the power transmission of the DC/DC converter is adjusted,
wherein a ratio M between a primary-referred value of the output voltage and the input voltage is maintained to be constant by enabling a difference between the M times of the input voltage and primary-referred value of the output voltage to be constantly zero; wherein the ratio M is in an adjusting range of 0.5˜2; through introducing a feedforward compensator involving the input and output voltages and the input and output currents, a linear controller of the system is implemented.
2. The method according to claim 1 , wherein the constant-voltage-gain control method further comprises:
(1) measuring an input voltage u 1 , an input current i 1 , an output voltage u 2 and an output current i 2 of the converter, and filtering the input voltage u 1 , the input current i 1 , the output voltage u 2 and the output current i 2 through a low-pass filter G f to obtain filtered values u 1f , i 1f , u 2f , i 2f , respectively;
(2) a difference is made between M times of u 1f and n times of u 2f (that is the primary-referred value of u 2f ), wherein n is the turn ratio of the isolation transformer T; and then inputting an inverse of the difference into a PI controller which has a frequency domain expression of K P +K I /s, and an intermediate control quantity θ is obtained through the calculation of the PI controller; a calculation formula of the intermediate control quantity θ is:
θ
=
(
K
P
+
K
I
s
)
[
0
-
(
Mu
1
f
-
nu
2
f
)
]
(
1
)
in the above formula, K P and K I respectively refer to the proportion coefficient and integral coefficient of the PI controller, and s refers to a Laplace operator;
(3) by performing feedforward compensation on θ through four filtered values u 1f , i 1f , u 2f , i 2f , the phase shifting angle φ between the square wave voltages u ab and u cd can be obtained; calculation manner of the phase shifting angle φ is as follows:
φ
=
K
-
C
1
C
2
θ
+
MC
2
i
1
f
+
nC
1
i
2
f
nC
1
u
1
f
+
MC
2
u
2
f
(
2
)
in the formula, C 1 , C 2 are respectively the input-port and output-port capacitances; and a constant coefficient K is obtained through calculation according to the following formula:
K
=
π
2
[
C
r
1
C
r
2
w
s
2
(
n
2
L
r
2
+
L
r
1
)
-
n
2
C
r
1
-
C
r
2
]
8
nC
r
1
C
r
2
w
s
,
(
3
)
wherein C r1 , C r2 are capacitances of a resonant capacitor of the primary side and a resonant capacitor of the secondary side respectively, L r1 , L r2 are respectively inductances of a resonant inductor of the primary side and a resonant inductor of the secondary side, w s is a switching angular frequency.