Hybrid five-level bidirectional DC/DC converter and voltage match modulation method thereof
The present disclosure discloses a hybrid five-level bidirectional DC/DC converter and a voltage match modulation method thereof. The converter includes a first input filter capacitor C inp and a second input filter capacitor C inn , an output filter capacitor C o , a DC voltage source, a primary-side hybrid five-level unit, a primary-side two-level half bridge, a secondary-side single-phase full bridge H 2 , a high-frequency isolation transformer M 1 , a high-frequency inductor L s , and a controller. A positive pole of a DC bus of the primary-side hybrid five-level unit is coupled to a positive pole of the corresponding DC voltage source and to a positive pole of the input filter capacitor C inp respectively. A negative pole of the DC bus of the primary-side hybrid five-level unit is coupled to a negative pole of the corresponding DC voltage source and to a negative pole of the input filter capacitor C inn respectively. A terminal of the primary-side hybrid five-level unit is coupled to a midpoint between the first input filter capacitor C inp and the second input filter capacitor C inn connected in series. The primary-side hybrid five-level unit is coupled to a primary side of the high-frequency isolation transformer M 1 through the high-frequency inductor L s , and a midpoint of the primary-side two-level half bridge is coupled to another terminal of the primary side of the high-frequency transformer.
1. A hybrid five-level bidirectional DC/DC converter, comprising a first input filter capacitor C inp , and a second input filter capacitor C inn , an output filter capacitor C o , a DC voltage source, a primary-side hybrid five-level unit, a primary-side two-level half bridge, a secondary-side single-phase full bridge H 2 , a high-frequency isolation transformer M 1 , a high-frequency inductor L s and a controller; wherein
a positive pole of a DC bus of the primary-side hybrid five-level unit is coupled to a positive pole of the DC voltage source and to a positive pole of the input filter capacitor C inp respectively, a negative pole of the DC bus of the primary-side hybrid five-level unit is coupled to a negative pole of the DC voltage source and to a negative pole of the input filter capacitor C inn respectively, a terminal of the primary-side hybrid five-level unit is coupled to a midpoint between the first input filter capacitor C inp and the second input filter capacitor C inn connected in series, the primary-side hybrid five-level unit is coupled to a primary side of the high-frequency isolation transformer M 1 through the high-frequency inductor L s and a midpoint of the primary-side two-level half bridge is coupled to another terminal of the primary side of the high-frequency isolation transformer, wherein a transformation ratio of the high-frequency isolation transformer M 1 is N:1;
a positive pole of a DC bus of the secondary-side single-phase full bridge H 2 is coupled to a positive pole of a corresponding DC load and to a positive pole of the output filter capacitor C o respectively, a negative pole of the DC bus of the secondary-side single-phase full bridge H 2 is coupled to a negative pole of the corresponding DC load and to a negative pole of the output filter capacitor C o respectively, and an AC side of the secondary-side single-phase full bridge H 2 is coupled to a secondary side of the high-frequency isolation transformer; and
an input terminal of a control signal of the primary-side hybrid five-level unit, an input terminal of a control signal of the primary-side two-level half bridge, and an input terminal of a control signal of the secondary-side single-phase full bridge are respectively coupled to an output terminal of a switch signal corresponding to the controller,
wherein nine levels are produced by an AC port voltage v p of the primary-side five-level unit:
±
v
in
,
±
3
v
in
4
,
±
v
in
2
,
±
v
in
4
and 0, wherein v in represents an input DC voltage of the hybrid five-level bidirectional DC/DC converter; and an AC port voltage v s of the secondary-side single-phase full bridge H 2 produces three levels as follows: ±V out and 0, wherein v out represents an output voltage of the hybrid five-level bidirectional DC/DC converter,
wherein the controller comprises a sampling unit, a PI controller, and a modulation unit, wherein
the sampling unit comprises two signal input terminals, and the two signal input terminals respectively measure the input voltage v in and the output voltage v out ;
the PI controller uses an error obtained by comparing the output voltage v out and a reference voltage v ref thereof as an input, and uses an output x obtained after being processed by the PI controller as a modulation signal; and
the modulation unit uses the input voltage v in , the output voltage v out , the reference voltage v ref and the output x as input signals, and obtains a voltage transmission ratio F and drive signals based on the input voltage v in , the output voltage v out , and the transformation ratio N of the high-frequency isolation transformer.
2. A voltage match modulation method for the hybrid five-level bidirectional DC/DC converter according to claim 1 , comprising:
setting a PI controller parameter of the controller, specifically, setting a proportionality coefficient k p and an integration coefficient k i , for the controller, and calculating the output x of the PI controller to serve as the modulation signal;
outputting the voltage transmission ratio F and the output x of the PI controller respectively to the modulation unit of the controller to calculate a control variable; and
driving, based on the control variable, a fully-controlled switch device of the primary-side hybrid five-level unit, a fully-controlled switch device of the primary-side two-level half bridge, and a fully-controlled switch device of the secondary-side single-phase full bridge to control actions of the fully-controlled switch devices to implement optimized operation.
3. The voltage match modulation method according to claim 2 , wherein the voltage transmission ratio F is:
F
=
Nv
out
v
in
wherein the transformation ratio N of the high-frequency isolation transformer serves as an initial value presetting.
4. The voltage match modulation method according to claim 2 , wherein the output x of the PI controller is:
x=k p ( v ref −v out )+ k i ∫( v ref −v out ) dt
wherein 0.1≤k p ≤10, 0.001≤k i ≤1, v ref represents a reference voltage; and the output x of the PI controller ranges from −0.5 to 1.
5. The voltage match modulation method according to claim 2 , wherein the number of the control variable is six: D p0 , D p2 , D p3 , D p4 , D s0 , and D ss ; wherein
D p0 controls a zero level of the primary-side hybrid five-level unit;
D p2 controls a ½ level of the primary-side hybrid five-level unit;
D p3 controls a ¾ level of the primary-side hybrid five-level unit;
D p4 controls a ±v in level of the primary-side hybrid five-level unit;
D s0 controls a zero level of the secondary-side single-phase full bridge H 2 ; and
D ss controls a phase shift between the primary-side hybrid five-level unit and the secondary-side single-phase full bridge H 2 .
6. The voltage match modulation method according to claim 5 , wherein the step of calculating the control variable comprises:
classifying, based on a value of the voltage transmission ratio F, the converter into five operation conditions to calculate six control variables:
in the first operation condition, 0<F< ¼ , specifically, 4×Nv out <v in , calculation of each control variable being as follows:
D ss =x
D s0 =0
D p4 =0
D p3 =0
D p2 =0
D p0 =1−4 F
in the second operation condition, ¼<F<½, specifically, v in <4×Nv out <2v in , calculation of each control variable is as follows:
D ss =x
D s0 =0
D p4 =0
D p3 =0
D p2 =4 F− 1
D p0 =0
in the third operation condition, ½<F<¾, specifically, 2v in <4×Nv out <3v in , calculation of each control variable is as follows:
D ss =x
D s0 =0
D p4 =0
D p3 =4 F− 2
D p2 =3−4 F
D p0 =0
in the fourth operation condition, ¾<F<1, specifically, 3v in <4×Nv out <4v in , calculation of each control variable is as follows: and
D ss =x
D s0 =0
D p4 =4 F− 3
D p3 =4(1 −F )
D p2 =0
D p0 =0
in the fifth operation condition, 1<F, specifically, v in <Nv out , calculation of each control variable is as follows:
D
ss
=
x
D
s
0
=
1
-
1
F
D
p
4
=
0
D
p
3
=
0
D
p
2
=
0
D
p
0
=
0
based on the aforementioned modulation method, following equation is satisfied:
∫ 0 t 5 v p ( t ) dt=∫ 0 t 5 Nv s ( t ) dt
wherein v p represents an AC port voltage of the primary-side five-level unit, and v s represents an AC port voltage of the secondary-side single-phase full bridge H 2 .
7. The voltage match modulation method according to claim 6 , wherein the modulation unit is set based on:
a duty ratio D p0 of the zero level of the primary-side five-level unit;
a duty ratio D p2 of the ½ level of the primary-side five-level unit;
a duty ratio D p3 of the ¾ level of the primary-side five-level unit;
a duty ratio D p4 of the ±v in level of the primary-side five-level unit;
a duty ratio D s0 of the zero level of the secondary-side single-phase full bridge H 2 ; and
the phase shift D ss between the primary-side five-level unit and the secondary-side single-phase full bridge H 2 ; wherein
a drive signal pulse is inputted in chronological order, and the fully-controlled switch device of the primary-side hybrid five-level unit and the fully-controlled switch device of the primary-side two-level half bridge H 2 are controlled to complete a modulation process.