Magnetic integration planar transformer based on CLLC circuit
Technical Field
The invention relates to the field of electronic direct current conversion, in particular to a magnetic integrated planar transformer for a bidirectional CLLC converter.
Background
In recent years, in the field of vehicle-mounted chargers for pure electric vehicles or plug-in electric vehicles, bidirectional DC/DC converters having high power density and high efficiency have attracted increasing attention. Among them, the bidirectional CLLC converter is widely used because its output voltage range is wide and soft switching of a power device can be realized in a full load range.
The CLLC circuit adopted in the vehicle-mounted charger is shown in fig. 1 and comprises two full bridges formed by MOS (metal oxide semiconductor) tubes and a resonant cavity formed by two resonant capacitors Cr1 and Cr2, two resonant inductors Lr1 and Lr2 and an excitation inductor Lm of a transformer. The CLLC circuit utilizes the characteristic of the resonant cavity to realize that the body diode is firstly conducted before the MOS tube is switched on, thereby realizing the zero-voltage switching-on of the MOS tube in the inverter bridge, realizing the zero-current switching-off of the diode in the rectifier bridge and effectively improving the efficiency of the converter.
As described above, the conventional CLLC converter has three magnetic elements, and if three separate magnetic elements are adopted, the overall volume and weight of the converter are high, and meanwhile, the loss of the magnetic elements is also high, so that the requirements of the vehicle-mounted charger on power density and efficiency cannot be well met. Therefore, the CLLC circuit is required to solve the problems of large volume and high loss of the magnetic element.
In order to increase the power density of the converter, it is an effective method to integrate two resonant inductors and a transformer in the CLLC into one magnetic element by using a magnetic integration technology. Patent "CN 211654529U" has proposed a magnetism integration scheme, and it adopts two EE type magnetic cores combination to form three center pillars, two side columns, and two resonance inductance and a transformer of CLLC are wound respectively on the three center pillar that has the same air gap, and the air gap is not opened to two side columns, provides low magnetic resistance route for inductance and transformer to realize the decoupling zero magnetism integration of inductance and transformer. However, this method requires two magnetic cores to be combined, and the size of the transformer cannot be optimized. In the document "b.li, q.li and f.c.lee, a novel PCB with a converter with a controllable gap integration for a 6.6kW 500kHz high efficiency bi-directional on-board charger,2017IEEE Applied Power Electronics reference and exposure (APEC), Tampa, FL, USA, 2017", another method is adopted in which the primary and secondary windings of the transformer are separated, one part is wound around one core leg and the other part is wound around the other core leg, and the core leg is used to reduce the coupling degree of the primary and secondary sides of the transformer, thereby increasing the leakage inductance of the transformer, and thus using the leakage inductance as the resonant inductance of the CLLC. However, this method has a low utilization rate of the magnetic core, and the magnetic flux density in the center pillar of the magnetic core is large, which makes it possible to further optimize the magnetic flux density.
Disclosure of Invention
The invention aims to provide a magnetic integrated planar transformer based on a CLLC converter, which solves the problems of large volume, high magnetic loss and the like of a magnetic element in a CLLC circuit.
The technical scheme of the invention is as follows: the magnetic integrated planar transformer based on the CLLC circuit comprises a magnetic core M1, a magnetic core M2, a primary winding T1 of the transformer, a secondary winding T2 of the transformer, a side column V1 of the magnetic core, a side column V2 of the magnetic core, a middle column V3 of the magnetic core, a primary inductance winding Lp1, a primary inductance winding Lp2, a secondary inductance winding Ls1 and a secondary inductance winding Ls 2; the primary winding T1 of the transformer is wound on the center pillar V3 of the magnetic core, and the inductance formed by the winding is used as the excitation inductance of the transformer; the transformer secondary winding T2 is also wound on the magnetic center post V3, and the winding is well coupled with the transformer primary winding T1, so that the transformer has extremely low leakage inductance.
The magnetic core side column V1, the magnetic core side column V2 and the magnetic core center column V3 form a channel of main magnetic flux of the transformer; the primary side inductance winding Lp1 is wound on the side column V1 of the magnetic core; the primary side inductance winding Lp2 is wound on the side column V2 of the magnetic core; the secondary side inductor winding Ls1 is wound on the side column V1 of the magnetic core; and the secondary side inductor winding Ls2 is wound on the side column V2 of the magnetic core.
The primary side inductance winding Lp1 and the primary side inductance winding Lp2 have opposite winding directions and the same number of turns; the primary side inductance winding Lp1 and the primary side inductance winding Lp2 are connected in series to form a primary side inductance.
The magnetic flux generated by the primary side inductance winding Lp1 and the magnetic flux generated by the primary side inductance winding Lp2 are opposite in direction above the center pillar V3 of the magnetic core, are equal in magnitude and are completely offset; the primary inductance is decoupled from the transformer primary winding T1 and the secondary winding T2.
The secondary side inductance winding Ls1 and the secondary side inductance winding Ls2 are opposite in winding direction and have the same number of turns; and the secondary inductor winding Ls1 and the secondary inductor winding Ls2 are connected in series to form a secondary inductor.
The magnetic flux generated by the secondary side inductance winding Ls1 and the magnetic flux generated by the secondary side inductance winding Ls2 are opposite in direction above the center pillar of the magnetic core, are equal in magnitude and are completely offset; the secondary inductor is decoupled from the primary winding T1 and the secondary winding T2 of the transformer.
The primary side inductor and the secondary side inductor form a coupling inductor which is used as a resonant inductor of the CLLC converter; in the CLLC converter, the primary inductor and the secondary inductor generate magnetic fluxes in the magnetic core legs V1 and V2 in the same direction, and are superimposed on each other.
The primary winding of the transformer is connected in series with the primary winding of the coupling inductor, and the homonymous end of the primary winding of the transformer is connected with the synonym end of the primary winding of the coupling inductor; and the secondary winding of the transformer is connected with the secondary winding of the coupling inductor in series, and the homonymous end of the secondary winding of the transformer is connected with the homonymous end of the secondary winding of the coupling inductor.
The turn ratio of the coupling inductor and the turn ratio of the transformer can be equal or different; meanwhile, after the coupling inductor is used as the resonant inductor, in order to keep the resonant frequency and the inductance ratio of the CLLC resonant converter unchanged, the primary inductance value of the required coupling inductor and the excitation inductance value of the transformer can be calculated by the following derivation.
The CLLC converter adopts the structure shown in fig. 1, and the resonant capacitors of the primary side and the secondary side adopt a symmetrical form, so that the forward and reverse transfer functions are as follows:
wherein
a=k+h+kh,b=2k+h+1,c=1 (4)
Wherein N is the transformer turn ratio and P is the load power.
When the converter is operated at the resonant frequency wrWhen the secondary voltage and the primary voltage of the cavity have the same phase, i.e. at wrWhere the imaginary part of the denominator in the transfer function is equal to zero, then:
then, it can be solved:
the two-port network formed by the coupling inductor and the transformer is shown in FIG. 2, where N isrFor the turn ratio of the coupled inductor, the port characteristic equation of the two-port network is
The two-port network formed by the transformer and the discrete inductor is shown in fig. 3, and the port characteristic equation is
From the agreement of the two port property equations, one can find
Then
Definition of
In order to keep the resonant frequency before and after the inductive coupling unchanged, the equivalent inductance of the primary side after the coupling should be taken as
L1=m·Lr1 (17)
Further, the inductance value of the coupling inductor can be obtained
Meanwhile, in order to maintain the inductance ratio k to be constant, the exciting inductance of the transformer is taken as
The invention has the beneficial effects that: two resonant inductors and a transformer in the CLLC converter are integrated into a planar magnetic piece, so that the size of the converter is reduced, and the utilization rate of a magnetic core and the power density of the CLLC converter are improved. Meanwhile, the number of turns of the resonant inductor is reduced by utilizing the coupling of the inductor, the copper consumption is reduced, and the efficiency is improved.
Drawings
Fig. 1 is a schematic diagram of a conventional CLLC resonant converter;
FIG. 2 is a schematic diagram of an equivalent two-port network formed by coupling a resonant inductor and a transformer;
FIG. 3 is a schematic diagram of an equivalent two-port network formed by discrete resonant inductors and a transformer;
fig. 4 is a schematic diagram of the proposed magnetically integrated planar transformer after disassembly;
fig. 5 is a schematic view of a magnetic flux path of the proposed magnetically integrated planar transformer;
Detailed Description
The magnetic integrated planar transformer based on the CLLC circuit of the present invention is further described in detail with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will be more clearly described below, but it should be noted that the technical solutions of the present invention have many different forms of implementation and are not limited to the specific embodiments described. The drawings are only for the purpose of assisting in the description of the invention and for the purpose of aiding, and are therefore relatively simple and all not to scale.
Fig. 4 is an exploded view of a magnetic integrated planar transformer according to the present invention, which includes a magnetic core M1 and a magnetic core M2; a primary winding T1 and a secondary winding T2 of the transformer; a primary side inductance winding Lp1, a primary side inductance winding Lp 2; secondary side inductor winding Ls1 and secondary side inductor winding Ls 2; a core side leg V1, a core side leg V2, and a core center leg V3.
The primary side inductance winding Lp1 and the primary side inductance winding Lp2 are respectively wound on the magnetic core side column V1 and the magnetic core side column V2; the secondary side inductor winding Ls1 and the secondary side inductor winding Ls2 are wound on the magnetic core side column V1 and the magnetic core side column V2 respectively; and the primary winding T1 and the secondary winding T2 of the transformer are wound on the center pillar V3 of the magnetic core. The relative positions of the primary side inductance winding, the secondary side inductance winding and the transformer winding are selected in various ways. In the embodiment, the primary inductance windings Lp1 and Lp2 are located on the same horizontal line and are located at the top; secondary side inductance windings Ls1 and Ls2 are located on the same horizontal line and located at the lowest part; the transformer winding is located between the primary side inductance winding and the secondary side inductance winding.
The primary side inductance winding Lp1 and Lp2 have the same number of turns; and the secondary side inductor windings Ls1 and Ls2 have the same number of turns.
The air gaps of the core legs V1 and V2 are the same size, and the air gap of the core leg V3 may be the same size or different size from the air gaps of the legs V1 and V2.
As shown in fig. 4, Lp1 and Lp2 are connected in series to form a primary inductance winding (named as Lrp), that is, a terminal 2 of Lp1 is connected with a terminal 4 of Lp2, and the connection mode ensures that the winding directions of Lp1 and Lp2 are opposite; and then connecting the terminal 3 of the primary inductive winding Lrp with the terminal 5 of the primary winding T1 of the transformer, namely connecting the primary inductive winding Lrp with the primary winding T1 of the transformer in series.
As shown in fig. 4, Ls1 and Ls2 are connected in series to form a secondary inductance winding (named Lrs), that is, the terminal 10 of Ls1 is connected with the terminal 12 of Ls2, and this connection mode also ensures that the winding directions of Ls1 and Ls2 are opposite; then, the terminal 9 of the secondary inductor winding Lrs is connected with the terminal 7 of the transformer secondary winding T2, that is, the secondary inductor winding Lrs is connected in series with the transformer secondary winding T2.
After the wiring process is carried out, the whole magnetic integrated planar transformer is manufactured and is connected into the CLLC circuit to replace the original discrete magnetic component. The specific access mode is as follows: the terminal 1 is connected to point a in fig. 1, the terminal 6 is connected to point B in fig. 1, the terminal 11 is connected to point C in fig. 1, and the terminal 8 is connected to point D in fig. 1.
As shown in fig. 5, the Lp1 and the Lp2 have the same turns and opposite winding directions, and the currents passing through the Lp1 and the Lp2 have the same magnitude, so that the magnetic fluxes generated by the Lp1 and the Lp2 have the same magnitude and opposite directions on the center pillar V3, and the magnetic fluxes are cancelled, so that the primary side inductance winding Lrp is decoupled from the transformer. And similarly, the decoupling of the secondary side inductance winding and the transformer is realized.
As shown in fig. 5, magnetic fluxes generated by the primary inductance winding Lrp and the secondary inductance winding Lrs are superimposed on the side poles V1 and V2, so that the primary inductance Lrp and the secondary inductance Lrs are coupled, and the coupled inductance serves as a resonant inductance of the CLLC.
The shape of the core can be arbitrarily selected, and a flat E-shaped core is selected in the present embodiment. In addition, the core specification should meet the corresponding magnetic flux density requirements to prevent saturation of the core or excessive core loss.
The turn ratio Nr of the coupling inductor may take any value, but in practical applications, the turn ratio Nr is selected to be as small as possible, for example, 1:1, in order to reduce the number of winding turns and reduce copper loss.
After the coupling inductor is used as a resonant inductor, in order to keep the resonant frequency and the inductance ratio of the CLLC resonant converter unchanged, the primary side inductance L of the required coupling inductorrcAnd the exciting inductance L of the transformermcObtained by formula (1) and formula (2);
wherein
a=k+h+kh,b=2k+h+1,c=1,k=Lm/Lr1 (24)
In the above formula, N is the turn ratio of the transformer, Lr1、Lr2Primary and secondary side inductance values, L, of CLLC convertermIs the transformer magnetizing inductance value.
The invention has the beneficial effects that: two resonant inductors and a transformer in the CLLC converter are integrated into a planar magnetic piece, so that the size of the converter is reduced, and the utilization rate of a magnetic core and the power density of the CLLC converter are improved. Meanwhile, the number of turns of the resonant inductor is reduced by utilizing the coupling of the resonant inductor, the copper consumption is reduced, and the efficiency is improved.
The foregoing detailed description of the principles and embodiments of the present invention has been presented in terms of specific embodiments, but the invention is not limited to the specific embodiments described above, and variations can be made in the specific embodiments in light of the above teachings by those skilled in the art.