阅读说明：本技术 Llc谐振变换器及其控制方法 (LLC resonant converter and control method thereof ) 是由 漆宇 陈涛 苏亮亮 梅文庆 张志学 罗文广 李淼 丁红旗 于 2019-08-23 设计创作，主要内容包括：本发明提供一种能够双向运行的LLC谐振变换器,在任意时刻,原边PWM控制信号和副边PWM控制信号具有相同的恒定周期,使得原边桥式电路的各个开关器件与副边桥式电路的各个开关器件同步导通和/或同步关断。在正向运行模式中,根据LLC谐振变换器的实际传输功率的大小而改变副边脉冲宽度；在负向运行模式中,根据LLC谐振变换器的实际传输功率的大小而改变原边脉冲宽度,实现能量流方向的平滑切换,且有效控制输出电压稳定,可提升LLC型谐振变换器在能量双向流动下的输出电压稳态精度,并实现能量流方向变化临界点处的平滑切换。本发明还提供了该LLC谐振变换器的控制方法。(The invention provides an LLC resonant converter capable of bidirectional operation, wherein a primary side PWM control signal and a secondary side PWM control signal have the same constant period at any time, so that each switching element of a primary side bridge circuit and each switching element of a secondary side bridge circuit are synchronously switched on and/or synchronously switched off. In the forward operation mode, the pulse width of the secondary side is changed according to the actual transmission power of the LLC resonant converter; in a negative operation mode, the primary side pulse width is changed according to the actual transmission power of the LLC resonant converter, smooth switching of the energy flow direction is achieved, the output voltage is effectively controlled to be stable, the steady-state accuracy of the output voltage of the LLC resonant converter under the condition of energy bidirectional flow can be improved, and smooth switching of the energy flow direction change critical point is achieved. The invention also provides a control method of the LLC resonant converter.)

1. An LLC resonant converter comprises a transformer with a primary side and a secondary side, a primary side bridge circuit and an LLC resonant circuit connected to the primary side of the transformer, and a secondary side bridge circuit connected to the secondary side of the transformer; wherein

The LLC resonant converter can be selectively operated in a positive-going mode of operation or a negative-going mode of operation; in the forward operation mode, the primary side of the transformer transmits power to the secondary side of the transformer; in the negative-going operating mode, the secondary side of the transformer transmits power to the primary side of the transformer;

the LLC resonant circuit has a resonant period;

each switching element of the primary side bridge circuit is switched on and off under the control of a primary side PWM control signal with a primary side pulse width;

the secondary side bridge circuit is connected to the secondary side, and each switching device of the secondary side bridge circuit is switched on and off under the control of a secondary side PWM control signal with a secondary side pulse width;

at any moment, the primary side PWM control signal and the secondary side PWM control signal have the same constant period, and each switching device of the primary side bridge circuit and each switching device of the secondary side bridge circuit are synchronously switched on and/or synchronously switched off; and the number of the first and second electrodes,

in the forward operation mode, changing the secondary side pulse width according to the actual transmission power of the LLC resonant converter;

in the negative-going operation mode, the primary side pulse width is changed according to the actual transmission power of the LLC resonant converter.

2. The LLC resonant converter of claim 1, wherein:

in the forward mode of operation:

the actual transmission power of the LLC resonant converter can vary between zero and rated power and has a forward first decision point and a forward second decision point between zero and rated power;

if the actual transmission power is gradually increased from zero but not larger than a forward first judgment point, or the actual transmission power is gradually decreased from the rated power and smaller than a forward second judgment point, the pulse width of the secondary side and the pulse width of the primary side have the same pulse width set value;

and otherwise, adjusting the secondary side pulse width to a forward adjustment pulse width according to the resonance period of the LLC resonance circuit and the output voltage of the LLC resonance converter.

3. The LLC resonant converter of claim 2, wherein:

adding the pulse width set value to a resonance adjustment value and an output voltage adjustment value as the forward adjustment pulse width, wherein

The resonance adjustment value is (resonance period-constant period)/2;

the voltage regulation value is determined by regulating the voltage regulator according to the error between the measured output voltage value and the target output voltage value of the LLC resonant converter.

4. The LLC resonant converter of claim 1, wherein:

in the negative-going operating mode:

the actual transmission power of the LLC resonant converter can vary between zero and rated power and has a negative first decision point and a negative second decision point between zero and rated power;

if the actual transmission power is gradually increased from zero but is not larger than a negative first judgment point, or the actual transmission power is gradually decreased from the rated power and is smaller than a negative second judgment point, the pulse width of the secondary side and the pulse width of the primary side have the same pulse width set value;

otherwise, the primary side pulse width is adjusted to be the negative side adjustment pulse width according to the resonance period of the LLC resonance circuit and the output voltage of the LLC resonance converter.

5. The LLC resonant converter of claim 2, wherein:

adding the pulse width set value to a resonance adjustment value and an output voltage adjustment value as the negative adjustment pulse width, wherein

The resonance adjustment value is (resonance period-constant period)/2;

the voltage regulation value is determined by regulating the voltage regulator according to the error between the measured output voltage value and the target output voltage value of the LLC resonant converter.

6. LLC resonant converter according to claim 3 or 5, characterized in that:

the voltage regulator is a P regulator, a PI regulator or a PID regulator.

7. A control method of an LLC resonant converter, the LLC resonant converter comprises a transformer with a primary side and a secondary side, a primary side bridge circuit and an LLC resonant circuit which are connected to the primary side of the transformer, and a secondary side bridge circuit which is connected to the secondary side of the transformer; wherein

The LLC resonant converter can be selectively operated in a positive-going mode of operation or a negative-going mode of operation; in the forward operation mode, the primary side of the transformer transmits power to the secondary side of the transformer; in the negative-going operating mode, the secondary side of the transformer transmits power to the primary side of the transformer;

the LLC resonant circuit has a resonant period;

each switching device of the primary side bridge circuit is switched on and off under the control of a primary side PWM control signal with a primary side pulse width,

the secondary side bridge circuit is connected to the secondary side, each switching device of the secondary side bridge circuit is switched on and off under the control of a secondary side PWM control signal with a secondary side pulse width,

characterized in that the method comprises the following steps:

an initialization step: enabling the secondary side pulse width and the primary side pulse width to have the same pulse width set value;

a detection step: detecting the direction and the magnitude of the actual transmission power of the LLC resonant converter;

a judging step: judging whether the actual transmission power is gradually increased from zero but not larger than a first judgment point or whether the actual transmission power is gradually decreased from the rated power and is smaller than a second judgment point; if yes, circularly executing the detection step; otherwise, executing the adjusting step;

and (3) adjusting:

when the direction of actual transmission power is positive, changing the pulse width of the secondary side according to the resonance period of the LLC resonance circuit and the output voltage of the LLC resonance converter;

and when the actual transmission power direction is negative, changing the primary side pulse width according to the resonance period of the LLC resonance circuit and the output voltage of the LLC resonance converter.

8. The control method according to claim 7,

in the adjusting step, the pulse width setting value is added to a resonance adjusting value and a voltage adjusting value to change the secondary side pulse width or the primary side pulse width, wherein

The resonance adjustment value is (resonance period-constant period)/2;

the voltage regulation value is determined by regulating the voltage regulator according to the error between the measured output voltage value and the target output voltage value of the LLC resonant converter.

9. The control method according to claim 8, characterized in that:

the voltage regulator is a P regulator, a PI regulator or a PID regulator.

Technical Field

The invention relates to the field of power electronics, in particular to an LLC resonant converter and a control method thereof.

Background

In recent years, high-frequency power electronic technology has been developed, and research on novel power conversion technology in the fields of renewable energy, electric vehicles, electric power traction, and the like has attracted much attention. In the field of power grids, new concepts such as alternating-current and direct-current hybrid transmission and distribution networks, direct-current micro-grids, power electronic transformers, energy routers and the like are continuously proposed, and in the research hotspots and application occasions, DC/DC converters with energy flowing in two directions are needed to serve as interfaces between direct-current buses with different voltage levels. Meanwhile, in order to ensure high efficiency and high power density of the DC converter, the DC/DC converter is required to have a certain soft switching capability and an operating frequency as high as possible, and also have an electrical isolation capability. Based on the requirements, the LLC resonant converter serving as a high-efficiency isolated soft switching DC/DC converter has extremely high application potential and value in a DC conversion occasion.

The traditional two-way control strategy is: when energy flows in the forward direction, driving signals of the full-bridge devices T1-T4 on the primary side of the transformer are enabled, wherein the driving signals of T1 and T4 are set to be square waves with the duty ratio of about 50%, the driving signals of T2 and T3 are complementary with the driving signals of T1 and T4, and necessary dead time needs to be set between the driving signals of T2 and T3 and the driving signals of T1 and T4. At the moment, the secondary side full-bridge device V1-V4 can be blocked and is used for uncontrolled rectification; when the energy flows in the negative direction, the driving signals of the secondary side full-bridge devices V1-V4 are enabled, wherein the driving signals of V1 and V4 are set to be square waves with the duty ratio of about 50%, the driving signals of V2 and V3 are complementary with the driving signals of V1 and V4, and necessary dead time needs to be set between the driving signals of V2 and V3 and the driving signals of V1 and V4. At the moment, the primary side full-bridge device T1-T4 can be blocked and is used for uncontrolled rectification.

In addition, according to the deviation of the output voltage and the instruction value, the working frequency of the DC/DC converter is regulated through an analog or digital controller (such as a PI controller, a fuzzy controller and the like), so that the voltage conversion gain of the circuit is adjusted, and the output voltage is stabilized to realize power flow control.

The problems with the conventional control strategy are:

1) although energy can flow in two directions, the energy flow direction needs to be detected, namely, the detection precision of the energy flow direction is very dependent. The fluctuation is often large near the critical point of the energy bidirectional flow, the repeated switching of the operation condition of the resonant converter is easily caused at the critical point of the energy flow direction change, the detection of the energy flow direction is inaccurate or frequently changed, the oscillation of the output voltage is easily caused, and the smooth switching of the operation condition of the resonant converter cannot be realized; in addition, the power device of the primary and secondary full-bridge circuits of the transformer is repeatedly triggered and blocked, which affects the reliability and service life of the power device.

2) Because the gain curves of the two modes of energy forward operation and energy reverse operation are inconsistent in the conventional bidirectional control strategy in a fixed frequency working mode, the steady-state output voltages in the forward and reverse operation modes are inconsistent. Under a certain working frequency, the circuit voltage conversion gain has a large difference in forward and reverse operation, the stable accuracy of the output voltage is often required to be improved through frequency conversion control, but the high-frequency transformer is easily saturated due to large fluctuation of the frequency, the current magnetic field curve changes, the normal stable operation working point of the transformer is changed, the magnetic circuit is saturated, the excitation inductance is rapidly reduced due to demagnetization, overcurrent spikes occur, overcurrent is caused, and the main circuit power device is damaged seriously.

Disclosure of Invention

Aiming at the problems, the invention provides a bidirectional LLC resonant converter with constant frequency and similar circuit voltage conversion gain curves in forward and reverse running and a control method thereof.

The invention provides an LLC resonant converter, comprising a transformer with a primary side and a secondary side, a primary side bridge circuit and an LLC resonant circuit which are connected to the primary side of the transformer, and a secondary side bridge circuit which is connected to the secondary side of the transformer; wherein the LLC resonant converter is selectively operable in a positive mode of operation or a negative mode of operation; in the forward operation mode, the primary side of the transformer transmits power to the secondary side of the transformer; in the negative-going operating mode, the secondary side of the transformer transmits power to the primary side of the transformer; the LLC resonant circuit has a resonant period; each switching element of the primary side bridge circuit is switched on and off under the control of a primary side PWM control signal with a primary side pulse width; the secondary side bridge circuit is connected to the secondary side, and each switching device of the secondary side bridge circuit is switched on and off under the control of a secondary side PWM control signal with a secondary side pulse width; at any moment, the primary side PWM control signal and the secondary side PWM control signal have the same constant period, and each switching device of the primary side bridge circuit and each switching device of the secondary side bridge circuit are synchronously switched on and/or synchronously switched off; and in the forward operation mode, the secondary side pulse width is changed according to the actual transmission power of the LLC resonant converter; in the negative-going operation mode, the primary side pulse width is changed according to the actual transmission power of the LLC resonant converter.

Preferably, in the forward operating mode: the actual transmission power of the LLC resonant converter can vary between zero and rated power and has a forward first decision point and a forward second decision point between zero and rated power; if the actual transmission power is gradually increased from zero but not larger than a forward first judgment point, or the actual transmission power is gradually decreased from the rated power and smaller than a forward second judgment point, the pulse width of the secondary side and the pulse width of the primary side have the same pulse width set value; and otherwise, adjusting the secondary side pulse width to a forward adjustment pulse width according to the resonance period of the LLC resonance circuit and the output voltage of the LLC resonance converter.

Preferably, the pulse width setting value is added to a resonance adjustment value and an output voltage adjustment value as the forward direction adjustment pulse width, wherein the resonance adjustment value is (resonance period-constant period)/2; the voltage regulation value is determined by regulating the voltage regulator according to the error between the measured output voltage value and the target output voltage value of the LLC resonant converter.

Preferably, in the negative-going operating mode: the actual transmission power of the LLC resonant converter can vary between zero and rated power and has a negative first decision point and a negative second decision point between zero and rated power; if the actual transmission power is gradually increased from zero but is not larger than a negative first judgment point, or the actual transmission power is gradually decreased from the rated power and is smaller than a negative second judgment point, the pulse width of the secondary side and the pulse width of the primary side have the same pulse width set value; otherwise, the primary side pulse width is adjusted to be the negative side adjustment pulse width according to the resonance period of the LLC resonance circuit and the output voltage of the LLC resonance converter.

Preferably, the pulse width setting value is added to a resonance adjustment value and an output voltage adjustment value as the negative adjustment pulse width, wherein the resonance adjustment value is (resonance period-constant period)/2; the voltage regulation value is determined by regulating the voltage regulator according to the error between the measured output voltage value and the target output voltage value of the LLC resonant converter.

Preferably, the voltage regulator is a P regulator, a PI regulator or a PID regulator.

A second aspect of the present invention provides a control method of an LLC resonant converter, said LLC resonant converter comprising a transformer having a primary side and a secondary side, a primary side bridge circuit and an LLC resonant circuit connected to the primary side of said transformer, and a secondary side bridge circuit connected to the secondary side of said transformer; wherein the LLC resonant converter is selectively operable in a positive mode of operation or a negative mode of operation; in the forward operation mode, the primary side of the transformer transmits power to the secondary side of the transformer; in the negative-going operating mode, the secondary side of the transformer transmits power to the primary side of the transformer; the LLC resonant circuit has a resonant period; each switching device of the primary side bridge circuit is switched on and off under the control of a primary side PWM control signal with a primary side pulse width, the secondary side bridge circuit is connected to the secondary side, and each switching device of the secondary side bridge circuit is switched on and off under the control of a secondary side PWM control signal with a secondary side pulse width, and the method is characterized by comprising the following steps: an initialization step: enabling the secondary side pulse width and the primary side pulse width to have the same pulse width set value; a detection step: detecting the direction and the magnitude of the actual transmission power of the LLC resonant converter; a judging step: judging whether the actual transmission power is gradually increased from zero but not larger than a first judgment point or whether the actual transmission power is gradually decreased from the rated power and is smaller than a second judgment point; if yes, circularly executing the detection step; otherwise, executing the adjusting step; and (3) adjusting: when the direction of actual transmission power is positive, changing the pulse width of the secondary side according to the resonance period of the LLC resonance circuit and the output voltage of the LLC resonance converter; and when the actual transmission power direction is negative, changing the primary side pulse width according to the resonance period of the LLC resonance circuit and the output voltage of the LLC resonance converter.

Preferably, in the adjusting step, the pulse width setting value is added to a resonance adjusting value and a voltage adjusting value to change the secondary side pulse width or the primary side pulse width, wherein the resonance adjusting value is (resonance period-constant period)/2; the voltage regulation value is determined by regulating the voltage regulator according to the error between the measured output voltage value and the target output voltage value of the LLC resonant converter.

Preferably, the voltage regulator is a P regulator, a PI regulator or a PID regulator.

The invention has the following advantages:

when the energy of the LLC resonant converter flows bidirectionally, the drive signals of the primary and secondary full-bridge devices of the LLC resonant converter are enabled to be effective and work under the fixed frequency, and the down-conversion operation is not needed. Therefore, higher working frequency can be designed, and the volume and weight of the high-frequency transformer can be reduced.

In addition, the smooth switching of the energy flow direction is realized by controlling the pulse width length of the driving signal of the primary and secondary full-bridge devices, the output voltage is effectively controlled to be stable, the stable precision of the output voltage of the LLC resonant converter under the condition of energy bidirectional flow can be improved, and the smooth switching of the energy flow direction change critical point is realized.

Drawings

The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. It is to be noted that the appended drawings are intended as examples of the claimed invention. In the drawings, like reference characters designate the same or similar elements.

Fig. 1 shows an LLC-type resonant converter circuit topology according to the invention;

FIG. 2 shows a power region decision diagram of the LLC resonant converter of the invention;

FIG. 3 shows a waveform diagram for a forward mode of operation of an LLC resonant converter as the invention;

fig. 4 shows a waveform diagram in a negative-going mode of operation of an LLC resonant converter as subject of the invention;

fig. 5 shows a schematic diagram of a voltage regulator for an LLC resonant converter of the invention.

Fig. 6 shows a schematic diagram of a control method of an LLC resonant converter as the invention.

Detailed Description

The detailed features and advantages of the present invention are described in detail in the detailed description which follows, and will be sufficient for anyone skilled in the art to understand the technical content of the present invention and to implement the present invention, and the related objects and advantages of the present invention will be easily understood by those skilled in the art from the description, claims and drawings disclosed in the present specification.

Referring to fig. 1, a first aspect of the invention provides an LLC resonant converter 100.

The LLC resonant converter 100 includes a transformer 110 having a primary side and a secondary side, a primary side bridge circuit 120 and an LLC resonant circuit 130 connected to the primary side of the transformer 110, and a secondary side bridge circuit 140 connected to the secondary side of the transformer 110.

The LLC resonant converter 100 can be selectively operated in a positive-going mode of operation or a negative-going mode of operation. In the forward mode of operation, the primary side of the transformer 110 transfers power to the secondary side of the transformer 110; in the negative-going mode of operation, the secondary side of the transformer 110 transfers power to the primary side of the transformer 110.

Resonant capacitor C_rHigh frequency transformer leakage inductance L_rAnd an excitation inductance L_mConstitute an LLC resonant circuit 130, i₁And i₂Representing the primary and secondary currents of the transformer, respectively. LLC resonant circuit 130 has a resonant period T_res。

Respective switching devices T of the primary side bridge circuit 120₁-T₄Switching on and off under the control of a primary side PWM control signal having a primary side pulse width WT; a secondary bridge circuit 140 is connected to the secondary side, each switching device V of the secondary bridge circuit 140₁-V₄On and off under the control of a secondary PWM control signal having a secondary pulse width WV. In order to realize the bidirectional flow of energy, each switching device T of the primary side bridge circuit 120 of the present embodiment₁-T₄And respective switching devices V of the secondary side bridge circuit 140₁-V₄All the fully-controlled power devices IGBT are used, however, the devices used in the LLC resonant converter 100 of the present invention are not limited, and may be selected from MOSFET, IGBT, IGCT, IPM, or other power semiconductor devices.

As in the prior art PWM control technique, by controlling the individual switching devices T of the primary bridge circuit 120₁-T₄And respective switching devices V of the secondary side bridge circuit 140₁-V₄The on/off of (b) enables the value of the actual transmission power P of the LLC resonant converter 100 to be varied between zero and the rated power RP. Accordingly, the secondary-side pulse width WV can be changed according to the magnitude of the actual transmission power P of the LLC resonant converter 100.

Specifically, referring to fig. 2, a positive first determination point PP1, a positive second determination point PP2, a negative first determination point NP1, and a negative second determination point NP2 are provided. The value of each of the above-mentioned decision points is ideally zero, but in actual operation, due to harmonic interference, it is necessary to take into account that the measured harmonic magnitude is slightly shifted from 0, for example, 25% to 35% of the rated power value. Here, the value of the forward first determination point PP1 may be about two-thirds of the value of the forward rated power, and the value of the forward second determination point PP2 may be about one-fourth of the value of the forward rated power. The negative first decision point NP1 may have a value of approximately two-thirds of the negative rated power value and the negative second decision point NP2 may have a value of approximately one-quarter of the negative rated power value. The forward first determination point PP1 and the forward second determination point PP2 may theoretically have the same value, or may be set to different values as needed; the negative first determination point NP1 and the negative second determination point NP2 may have the same value in theory or may be set to different values as needed.

In the LLC resonant converter of the invention, at any moment, the primary PWM control signal and the secondary PWM control signal have the same constant period Tsw, and each switching device T of the primary bridge circuit 120 is enabled₁-T₄With respective switching devices V of the secondary bridge circuit 140₁-V₄Synchronous on and/or synchronous off.

The LLC resonant converter of the present invention will be described below in a positive-going mode of operation and a negative-going mode of operation, respectively.

Forward mode of operation

In the forward operating mode, if the value of the actual transmission power P gradually increases from zero but is not greater than the forward first determination point PP1, the LLC resonant converter 100 operates at the location of region BP1 in FIG. 2.

If the value of the actual transmission power P gradually decreases from the rated power RP and is smaller than the forward second determination point PP2, i.e. the LLC resonant converter 100 is operated at the position of the region BP2 in fig. 2.

In the region BP1 and the region BP2, the respective switching devices T of the primary side bridge circuit 120₁-T₄And respective switching devices V of the secondary side bridge circuit 140₁-V₄All the driving signals are pulse width (T)_sw-2T_d) A fixed frequency square wave of/2, and a switching device T₁、T₂、T₃、T₄Respectively with the switching device V₁、V₂、V₃、V₄Keeps the switches synchronized. That is, the secondary side pulse width WV and the primary side pulse width WT have the same pulse width setting W0, and the pulse width setting:

W0＝(T_sw-2T_d)/2，

i.e. a duty cycle of D₁：

In the forward operation mode, if the value of the actual transmission power P gradually increases from zero and is greater than the forward first determination point PP1, or gradually decreases from the value of the actual transmission power P from the rated power RP and is not less than the forward second determination point PP2, the LLC resonant converter 100 operates at the position of region a in fig. 2.

At this time, each switching device T of the primary side bridge circuit 120₁-T₄The driving signal of (d) is still pulse width of (T)_sw-2T_d) /2 fixed frequency square wave, individual switching devices V of secondary bridge circuit 140₁-V₄The drive signal of (c) is set to a pulse width of (T)_res-2T_d) A fixed frequency square wave of/2 and the sum of the voltage regulation quantity Delta T, and a switching device T₁、T₂、T₃、T₄Can be connected to the switching device V₁、V₂、V₃、V₄Respectively kept synchronously on.

That is, the secondary side pulse width WV is adjusted to the forward adjustment pulse width WVMD according to the resonance period of the LLC resonance circuit 130 and the output voltage Vb of the LLC resonance converter 100.

Specifically, the pulse width set value W0 is added to a resonance adjustment value Wllc ═ T (T) and the output voltage adjustment value Δ T as the forward adjustment pulse width WVMD_res-T_sw) And/2, the forward regulation pulse width WVMD is W0+ Wllc + Δ T (T)_res-2T_d)/2+ΔT。

When the voltage adjustment amount Δ T is 0, the duty ratio D is obtained₂：

In other words, in the region a, the respective switching devices V of the secondary side bridge circuit 140 are caused to be switched by the voltage adjustment value Δ T₁-V₄Relative to the duty ratio D of the drive signal₂And (6) carrying out adjustment. The voltage regulation value delta T is based on the measured output voltage value V of the LLC resonant converter 100_bAnd a target output voltage value V_{b_ref}The error between the two is determined by the feedback regulation of the voltage regulator PI, and the regulation target is to make the measured output voltage value as stable as possible, as shown in fig. 5.

Thus, each switching device V according to the secondary bridge circuit 140₁-V₄The relationship between the duty ratio of the driving signal and the duty ratio D2 has the following two cases:

1) each switching device V₁-V₄The duty ratio of the drive signal is less than or equal to D₂Time of flight

2) Each switching device V₁-V₄Duty ratio of drive signal is greater than D₂And is less than D₁。

When each switching device V of the secondary side bridge circuit 140₁-V₄The duty ratio of the drive signal is less than or equal to D₂The LLC resonant converter waveforms are shown in fig. 3 (1).

At this time, the energy flow direction of the LLC resonant converter 100 is positive, and each switching device T of the primary bridge circuit 120 of the transformer₁-T₄Enable active. Switching device T₁、T₄The driving signal has a constant frequency and a duty ratio of D₁Square wave of (2), switching device T₂、T₃Drive signal and switching device T₁、T₄To have the necessary dead time T_d(e.g., 10 microseconds).

Respective switching devices V of the secondary side bridge circuit 140₁-V₄Is enabled in the forward mode of operation, and the secondary bridge circuit 140Each switching device V₁-V₄Respectively with the respective switching devices T of the primary bridge circuit 120₁-T₄The turn-on moments of time of are kept in sync.

As can be seen from fig. 1, since the primary bridge circuit 120 and the secondary bridge circuit 140 of the LLC resonant converter 100 are topologically symmetric, each switching period can be divided into two half switching periods before and after according to the driving signal timing sequence, and the main currents in the two half switching periods are opposite in direction, and have the same commutation manner and symmetry. Thus, only half of the switching period is described, and the other half of the switching period can be similarly derived.

According to the driving signal sequence, as shown in FIG. 3(1), a half switching period is divided into t₀To t₄Five moments, four time periods separated by the five moments, show the LLC resonant converter 100 current relationship and energy flow relationship as shown in table 1.

It is noted that when each switching device V of the secondary bridge circuit 140 is connected₁-V₄Duty ratio of the driving signal is less than or equal to D₂When the amount of (A) is changed within the range of (B), the results shown in Table 1 are not changed.

TABLE 1

When each switching device V of the secondary side bridge circuit 140_1-V₄Has a duty ratio larger than D₂And is less than D₁The waveforms of the LLC resonant converter 100 are shown in fig. 3 (2).

According to the driving signal sequence, as shown in FIG. 3(2), a half switching period is divided into t₀To t₄And t_{3_1}Six moments, five time periods separated by the six moments, have the LLC resonant converter 100 current relationship and energy flow relationship shown in table 2.

It is noted that when each switching device V of the secondary bridge circuit 140 is connected₁-V₄At a duty ratio greater than D₂And is less than D₁When the number of the terminal parts is changed within the interval of (1),the results shown in Table 2 are unchanged.

TABLE 2

As can be seen by comparing Table 2 with Table 1, the switching devices V of the secondary bridge circuit 140 are different₁-V₄Has a duty ratio larger than D₂And is less than D₁When, increase t₃Time to t_{3_1}A time period during which the primary side and the secondary side together release transfer energy to the high frequency transformer excitation flux.

It follows that it is preferable to have each switching device V of the secondary side bridge circuit 140₁-V₄Has a duty ratio larger than D₂And is less than D₁The energy transferred from the primary side to the secondary side over a half of the switching period is reduced by a certain amount, and this reduced energy can be used to regulate the output voltage. Therefore, by adjusting the individual switching devices V in the secondary bridge circuit 140₁-V₄The duty ratio of the driving signal (c) can stabilize the output voltage.

Negative running mode

In the negative-going mode of operation, the LLC resonant converter 100 operates at the location of region BN1 in fig. 2 if the value of the actual transmission power P increases gradually from zero but is not greater than the negative-going first decision point NP 1.

If the value of the actual transmission power P gradually decreases from the rated power RP and is smaller than the negative second determination point NP2, i.e. the LLC resonant converter 100 is operated at the position of the region BN2 in fig. 2.

In the region BN1 and the region BN2, the respective switching devices T of the primary side bridge circuit 120₁-T₄And respective switching devices V of the secondary side bridge circuit 140₁-V₄All the driving signals are pulse width (T)_sw-2T_d) A fixed frequency square wave of/2, and a switching device T₁、T₂、T₃、T₄Respectively with the switching device V₁、V₂、V₃、V₄Keeps the switches synchronized. That is, the secondary side pulse width WV and the primary side pulse width WT have the same pulse width setting W0, and

pulse width set value:

W0＝(T_sw-2T_d)/2，

i.e. a duty cycle of D₁：

In the negative operation mode, if the value of the actual transmission power P gradually increases from zero and is larger than the negative first determination point NP1, or gradually decreases from the nominal power RP and is not smaller than the negative second determination point NP2, the LLC resonant converter 1 operates at the position of the region C in fig. 2.

At this time, the actual transmission power P is transmitted from the secondary side of the transformer to the primary side of the transformer, thereby causing each switching device V of the secondary bridge circuit 140₁-V₄The driving signal of (d) is still pulse width of (T)_sw-2T_d) A fixed frequency square wave of/2, and the switching devices T of the primary bridge circuit 120₁-T₄The drive signal of (c) is set to a pulse width of (T)_res-2T_d) A fixed frequency square wave of/2 and the sum of the voltage regulation quantity Delta T, and a switching device T₁、T₂、T₃、T₄Respectively with the switching device V₁、V₂、V₃、V₄Keeps the switches synchronized. That is, the resonant period of the LLC resonant circuit 130 and the output voltage V of the LLC resonant converter 100_bThe primary side pulse width WT is adjusted to a negatively adjusted pulse width WTMD.

Specifically, the pulse width set value W0 is added to the resonance adjustment value Wllc and the output voltage adjustment value Δ T as the negative adjustment pulse width W_TMDWherein the resonance tuning value Wllc ═ T_res-T_sw) (vi)/2, then negative-going modulating pulse width WTMD ═ W0+ Wllc + Δ T ═ T_res-2T_d)/2+ΔT。

When the voltage adjustment amount Δ T is 0, the duty ratio D is obtained₂：

In other words, in the region C, the voltage adjustment value Δ T allows each switching device T of the primary bridge circuit 120 to be adjusted₁-T₄Relative to the duty ratio D of the drive signal₂And (6) carrying out adjustment. The voltage regulation value delta T is based on the measured output voltage value V of the LLC resonant converter 100_bAnd a target output voltage value V_{b_ref}The error between the two is determined by the feedback adjustment of the PI voltage regulator, and the adjustment target is to make the measured output voltage value as stable as possible, as shown in fig. 5.

Thus, the switching devices T are based on the primary bridge circuit 120₁-T₄Duty ratio and duty ratio D of driving signal₂Has the following two conditions:

1) each switching device T₁-T₄The duty ratio of the drive signal is less than or equal to D₂Time of flight

2) Each switching device T₁-T₄Duty ratio of drive signal is greater than D₂And is less than D₁。

When each switching device T of the primary bridge circuit 120₁-T₄Has a duty ratio less than or equal to D₂The LLC resonant converter waveforms are shown in fig. 4 (1).

At this time, the energy flow direction of the LLC resonant converter 100 is negative, and each switching device V of the transformer secondary bridge circuit 140₁-V₄Enable active. Switching device V₁、V₄The driving signal has a constant frequency and a duty ratio of D₁Square wave of (2), switching device V₂、V₃Drive signal and switching device V₁、V₄To have the necessary dead time T_d(e.g., 10 microseconds).

Primary side bridge circuit 120Each switching device T of₁-T₄Is enabled in the negative-going mode of operation, and each switching device T of the primary bridge circuit 120₁-T₄Respectively with the respective switching devices V of the secondary bridge circuit 140₁-V₄The turn-on moments of time of are kept in sync.

As can be seen from fig. 1, since the primary bridge circuit 120 and the secondary bridge circuit 140 of the LLC resonant converter 100 are topologically symmetric, each switching period can be divided into two half switching periods before and after according to the driving signal timing sequence, and the main currents in the two half switching periods are opposite in direction, and have the same commutation manner and symmetry. Thus, only half of the switching period is described, and the other half of the switching period can be similarly derived.

According to the driving signal sequence, as shown in FIG. 4(1), a half switching period is marked by t₀To t₄Five moments, four time periods separated by the five moments, show the LLC resonant converter 100 current relationship and energy flow relationship as shown in table 3.

It is noted that when each switching device T of the primary bridge circuit 120 is connected₁-T₄Duty ratio of the driving signal is less than or equal to D₂When the amount of (A) is changed within the range of (B), the results shown in Table 3 are not changed.

TABLE 3

When each switching device T of the primary bridge circuit 120₁-T₄Has a duty ratio larger than D₂And is less than D₁The waveforms of the LLC resonant converter 100 are shown in fig. 4 (2).

According to the driving signal sequence, as shown in FIG. 4(2), a half switching period is marked by t₀To t₄And t_{3_1}At six moments in timeThe five time periods separated by the six time instants show the current relationship and the energy flow relationship of the LLC resonant converter 100 in table 4.

It is noted that when each switching device T of the primary bridge circuit 120 is connected₁-T₄At a duty ratio greater than D₂And is less than D₁The results shown in Table 4 were not changed when the interval (2) was changed.

TABLE 4

From a comparison of table 4 with table 3, it can be seen that the switching devices T of the primary bridge circuit 120 are all the same₁-T₄Has a duty ratio larger than D₂And is less than D₁When, increase t₃From time t3_1, the primary and secondary together deliver energy to the high frequency transformer field flux discharge.

It follows that it is preferable to have each switching device V of the secondary side bridge circuit 140₁-V₄Has a duty ratio larger than D₂And is less than D₁The energy transmitted from the primary side to the secondary side is reduced by a certain amount during the whole half of the switching period, and the reduced energy can be used for regulating the output voltage V_b. Therefore, by adjusting the individual switching devices V in the secondary bridge circuit 140₁-V₄Can stabilize the output voltage V_b。

A second aspect of the invention provides a method of controlling an LLC resonant converter 100, the method comprising the steps of:

initialization step S0: so that the secondary side pulse width WV and the primary side pulse width WT have the same pulse width setting W0.

Referring to the above, the initial operation region of the LLC resonant converter 100 at the start-up defaults to the region B.

That is, the primary bridge is used whether the LLC resonant converter 100 is in the positive or negative operating modeRespective switching devices T of the mode circuit 120₁-T₄And respective switching devices V of the secondary side bridge circuit 140₁-V₄All the driving signals are pulse width (T)_sw-2T_d) A fixed frequency square wave of/2, and a switching device T₁、T₂、T₃、T₄Respectively with the switching device V₁、V₂、V₃、V₄Keeps the switches synchronized. That is, the secondary side pulse width WV and the primary side pulse width WT have the same pulse width setting value W0, and the pulse width setting value W0 ═ T (T)_sw-2T_d)/2。

Detection step S1: detecting the direction and the magnitude of the actual transmission power P of the LLC resonant converter 100; i.e. the actual operating region in which the LLC resonant converter operates is determined.

Determination step S2: judging whether the value of the actual transmission power P is gradually increased from zero but not larger than a first judgment point or whether the actual transmission power P is gradually decreased from the rated power RP and is smaller than a second judgment point;

the first and second decision points are the forward first decision point PP1 and the forward second decision point PP2 when the LLC resonant converter 100 is in the forward mode of operation. The first and second determination points are the negative first determination point NP1 and the negative second determination point NP2 when the LLC resonant converter 100 is in the negative operating mode.

In this determination step, it is actually determined whether the LLC resonant converter 100 still operates in the operating region B including the region BP1, the region BP2, the region BN1 and the region BN1, according to the direction and magnitude of the actual transmission power P.

If yes, the LLC resonant converter 100 operates in the region B, and the switching devices T of the primary bridge circuit 120₁-T₄And respective switching devices V of the secondary side bridge circuit 140₁-V₄All the driving signals are pulse width (T)_sw-2T_d) A fixed frequency square wave of/2 and the detection step S1 is performed cyclically.

Otherwise, the adjustment step S3 is executed.

Adjustment step S3: in the adjusting step, the drive signal pulse width of each switching device of the bridge circuit on the power receiving side is changed while keeping the drive signal frequency of all the switching devices constant.

That is, when the direction of the actual transmission power is positive, when the LLC resonant converter 100 operates in the region a, the secondary-side pulse width WV is changed in accordance with the resonance period of the LLC resonant circuit 130 and the output voltage Vb of the LLC resonant converter 100, that is, the pulse width set value W0 is added to the resonance adjustment value wlcc (the resonance period T) and the voltage adjustment value Δ T to change the secondary-side pulse width WV, and the resonance adjustment value wlcc (the resonance period T) is equal to_resConstant period T_sw) 2; the voltage regulation value delta T is based on the measured output voltage value V of the LLC resonant converter 100_bAnd a target output voltage value V_{b_ref}The error between these is determined by the voltage regulator feedback regulation, the target of which is to make the measured output voltage value Vb as stable as possible, as shown in fig. 5.

When the direction of the actual transmitted power is negative, when the LLC resonant converter 100 operates in the region C, the primary side pulse width WT is changed according to the resonance period of the LLC resonant circuit 130 and the output voltage of the LLC resonant converter 100. That is, the pulse width set value W0 is added to the resonance adjustment value Wllc (resonance period T) and the voltage adjustment value Δ T to change the primary side pulse width WT_resConstant period T_sw) 2; the voltage regulation value delta T is based on the measured output voltage value V of the LLC resonant converter 100_bAnd a target output voltage value V_{b_ref}The error between the two is determined by the feedback regulation of the voltage regulator PI, the regulation target is to make the measured output voltage value V_bAs stable as possible, as shown in fig. 5.

Preferably, the voltage regulator is a P regulator, a PI regulator or a PID regulator.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

For example, the novel bidirectional synchronous control strategy disclosed by the invention is suitable for all LLC resonant converters, is not limited to a specific application, and can only identify the working areas A and B if energy only needs to flow in a single direction, and the same control strategy implementation method is adopted to improve the accuracy of the output voltage.

The novel bidirectional synchronous control strategy set forth by the invention can be simply changed and popularized to be applied to circuit topologies of various forms such as three-level, multi-level, full-bridge circuit, half-bridge circuit and the like, and the novel bidirectional synchronous control strategy is included in the protection scope of the invention.

The circuit topology, the voltage grade and the power adopted by the LLC resonant converter are not limited, the topology of the converter can adopt various application topologies or occasions such as two-level, three-level, H-bridge cascade, chain, MMC, full bridge, half bridge, full wave, half wave rectification and the like, and the converter can be selectively provided with a filter.

The terms and expressions which have been employed herein are used as terms of description and not of limitation. The use of such terms and expressions is not intended to exclude any equivalents of the features shown and described (or portions thereof), and it is recognized that various modifications may be made within the scope of the claims. Other modifications, variations, and alternatives are also possible. Accordingly, the claims should be looked to in order to cover all such equivalents.

Certain terms are used throughout this specification to refer to particular system components. As one skilled in the art will appreciate, identical components may generally be referred to by different names, and thus this document does not intend to distinguish between components that differ in name but not function. In this document, the terms "including", "comprising" and "having" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to …".

Also, it should be noted that although the present invention has been described with reference to the current specific embodiments, it should be understood by those skilled in the art that the above embodiments are merely illustrative of the present invention, and various equivalent changes or substitutions may be made without departing from the spirit of the present invention, and therefore, it is intended that all changes and modifications to the above embodiments be included within the scope of the claims of the present application.