CN110190752A - A bidirectional CLLLC-DCX resonant converter and its control method - Google Patents

Abstract

The invention discloses a bidirectional CLLLC-DCX resonant converter and a control method thereof. The converter of the invention includes two ports, two resonant circuits, two switch circuits and a transformer. The bidirectional CLLLC-DCX resonant converter disclosed by the present invention has a symmetrical circuit structure and consistent forward and reverse working performance. Under the control method of the present invention, the ZVS or ZCS soft switching of the switching tubes on the input side and output side can be well realized , can achieve constant voltage gain under normal load, and due to the existence of auxiliary diodes, the converter has the function of bidirectional automatic power limitation, and at the same time realizes the natural bidirectional flow of energy in forward and reverse operation modes, improving the efficiency and reliability of the converter .

Description

A bidirectional CLLLC-DCX resonant converter and its control method

technical field

The invention belongs to the technical field of switching power supplies, and more specifically relates to a bidirectional CLLLC-DCX resonant converter and a control method thereof.

Background technique

In recent years, DC-DC converters have been widely used in various fields, especially in various power supply systems such as high-voltage direct current transmission including energy storage units, micro-grids, and electric vehicles. With the continuous improvement of energy conversion requirements in the field of power electronics technology, converters are gradually developing towards high frequency, high efficiency, and high power density, and the energy storage unit of the above system needs to control energy when charging and discharging. The power converter is required to have the characteristics of bidirectional controllable power flow, so the demand for bidirectional and high frequency isolation is also increasing.

Among the isolated DC-DC converters, the LLC resonant converter has high power density and conversion efficiency because it can realize soft switching characteristics under the full load range. However, when the switching frequency is far away from the resonant frequency, a high loop current will be formed and the efficiency will become low. In order to solve the problem of wide voltage gain, a two-stage structure is usually used, one of which is an LLC resonant converter working at the resonance point. Since it does not change its voltage gain, it is called LLC-DCX, and the other is a non-isolated DC - a DC converter for adjusting the voltage gain. The traditional LLC resonant converter has a constant gain characteristic only when the switch resonant frequency is equal to the resonant frequency, and the switching frequency cannot be completely equal to the resonant frequency because of the need to add dead time to prevent the switches of the same bridge arm from being turned on at the same time; in addition, Generally, in order to improve the efficiency of the LLC resonant converter, the secondary switching tube usually uses a synchronous rectification control strategy, but in the bidirectional operation mode, due to the asymmetry of the resonant cavity, the forward and reverse work performance is different, and the reverse The soft switching characteristics of LLC will be lost during operation, and to detect the zero crossing of the current, the control logic needs to switch between forward and reverse, and at the same time, it is necessary to judge the flow direction of energy, which is very difficult in practical applications.

Contents of the invention

In order to solve the problems of asymmetry and control logic switching and constant gain, the invention discloses a bidirectional CLLLC-DCX resonant converter and a synchronous equal pulse width control method for controlling the converter. The topology of the converter Symmetrical, the technical problem to be solved is that the ZVS or ZCS soft switching of the MOS transistors on the input side and the output side can be well realized, and the constant voltage gain under normal load and the function of bidirectional power limitation of the converter can be realized, while positive and negative The natural bi-directional flow of energy to the run mode increases the efficiency and reliability of the converter.

The invention discloses a bidirectional CLLLC-DCX resonant converter, which includes a main circuit and a control circuit. The main circuit includes a first port, a second port, two resonant circuits, two switch circuits and a transformer. The first One of the first port and the second port can be selectively used as the power supply terminal, and the other one is correspondingly used as the load terminal; the circuit topology connecting the two ends of the transformer is the same, and the primary side of the transformer includes the resonant inductance L _{r_p} , the resonant capacitor C _{r_p1} and The resonant circuit composed of C _{r_p2} and its anti-parallel auxiliary diodes D ₁ and D ₂ , the switching circuit composed of switching tubes Q ₁ and Q ₂ ; the same is true for the secondary side of the transformer, including the resonant inductance L _{r_s} and the resonant capacitor C _{r_s1} and A resonant circuit composed of _{Cr_s2} and its anti-parallel auxiliary diodes D ₃ and D ₄ , a switching circuit composed of switching tubes Q ₃ and Q ₄ ;

The connection relationship of each component in the main circuit is as follows: on the primary side of the transformer, the positive pole of the resonant capacitor C _{r_p1} and the drain of the switch tube Q1 are connected to the positive pole of the _first port at the same time, and the negative pole of the resonant capacitor C _{r_p1} is simultaneously connected to the positive pole of the resonant capacitor The positive pole of C _{r_p2} is connected to the negative pole of the primary side of the transformer, the source of the switching tube Q1 is connected to _one end of the resonant inductor L _{r_p} and the drain of the switching tube _Q2 , and the source of the switching tube _Q2 is connected to the negative pole of the resonant capacitor C _{r_p2} At the same time, it is connected to the negative pole of the first port, and the other end of the resonant inductance L _{r_p} is connected to the positive pole of the primary side of the transformer, and the auxiliary diodes D ₁ and D ₂ are connected in antiparallel to the resonant capacitors C _{r_p1} and C _{r_p2 respectively} ; similarly, in the transformer On the secondary side, the positive pole of the secondary side of the transformer is connected to one end of the resonant inductance L _{r_s} , and the other end of the resonant inductance L _{r_s} is connected to the source of the switching tube _Q3 and the drain of the switching tube _Q4 at the same time, and the drain of the switching tube _Q3 The pole is connected to the positive pole of the resonant capacitor C _{r_s1} and the second port at the same time, the negative pole of the resonant capacitor C _{r_s1} is connected to the positive pole of the resonant capacitor C _{r_s2} and the negative pole of the secondary side of the transformer at the same time, and the source of the switch tube _Q4 , the resonant capacitor C The cathode of _{r_s2} and the cathode of the second port are connected together at the same time, and the auxiliary diodes D ₃ and D ₄ are connected in antiparallel to the resonant capacitors C _{r_s1} and C _{r_s2 respectively} .

In another embodiment, the control circuit includes a controller and a drive circuit; the controller is a DSP controller for generating a set of complementary PWM drive signals, and the drive circuit isolates the received PWM drive signals from the controller After the sum voltage is enhanced, the driving voltage is provided for the switch tubes Q1-Q4 of the main circuit.

In another embodiment, the switch tubes Q1 - Q4 are switch tubes with anti-parallel body diodes and drain-source parasitic capacitances.

In addition, the present invention also discloses the control method of the bidirectional CLLLC-DCX resonant converter, the control method comprising:

In forward operation, when the current i _r1 flowing through the resonant inductor L _{r_p} is zero, the switch tubes Q ₁ and Q ₃ are turned on at the same time. After half a resonance period, i _r1 is zero again, and the switch tube Q is turned on at this time. ₁ and Q ₃ are turned off at the same time, after a dead time, i _r1 oscillates slightly near zero during the dead time, when Q ₂ and Q ₄ are turned on at the same time, i _r1 is also zero, after half a resonance cycle, Q ₂ and Q ₄ are turned off simultaneously when i _r1 is zero again;

In the reverse operation, when the current i _r2 flowing through the resonant inductance L _{r_s} is zero, the switch tubes Q ₁ and Q ₃ are turned on at the same time. After half a resonance cycle, i _r2 is zero again, and the switch tube Q is turned on at this time. ₁ and Q ₃ are turned off at the same time, after a dead time, i _r2 oscillates slightly near zero during the dead time, when Q ₂ and Q ₄ are turned on at the same time, i _r2 is also zero, after half a resonance cycle, _Q2 and _Q4 turn off simultaneously when i _r2 is zero again.

Compared with the prior art, the present invention has the following beneficial effects:

1. The working performance is the same in forward and reverse operation, no need to replace the control logic, and the natural two-way flow of energy can be realized.

2. When running in the forward direction, it can realize zero current, zero voltage turn-on and zero current turn-off of Q1 and Q2, and zero-voltage turn-on of Q3 and Q4. When the excitation inductance is designed reasonably, the turn-off current of Q3 and Q4 is relatively Small; when running in reverse, it can realize zero current, zero voltage turn-on and zero current turn-off of Q3 and Q4, and zero-voltage turn-on of Q1 and Q2. Similarly, when the excitation inductance is designed reasonably, the turn-off current of Q1 and Q2 Also relatively small.

3. In the normal load range, the change of the load will not affect the voltage gain, and the voltage is a constant value; in the case of overload, due to the existence of the auxiliary diode, the output power will not exceed a maximum value, which plays the role of output protection.

Description of drawings

In order to more clearly illustrate the present invention or the technical solutions in the prior art, the accompanying drawings that need to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings in the following description are the present invention. For some embodiments of the invention, those skilled in the art can also obtain other drawings based on these drawings without creative effort.

Fig. 1 is a kind of bidirectional CLLLC-DCX resonant converter circuit structure schematic diagram provided by the present invention;

Fig. 2 (a) is the main waveform diagram of the transformer of the present invention working under the normal load situation;

Fig. 2 (b) is the main waveform diagram of transformer work of the present invention under the overload situation;

Fig. 3 is an equivalent circuit diagram of working conditions t ₀ to t ₃ when the converter of the embodiment of the present invention is working under normal load;

Fig. 4 is an equivalent circuit diagram of working conditions t ₀ - t ₄ when the converter is overloaded according to the embodiment of the present invention.

Detailed ways

The present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments, and the technical problems and beneficial effects solved by the technical solutions of the present invention are also described. It should be pointed out that the described embodiments are only intended to facilitate the implementation of the present invention understood without any limitation.

As shown in FIG. 1 , the main circuit of the bidirectional CLLLC-DCX resonant converter mainly includes two ports (first port and second port), two resonant circuits, two switch circuits and a transformer. One of the first port and the second port can be selectively used as the power supply terminal of the converter of the present invention, and the other is correspondingly used as the load terminal; the structures at both ends of the transformer are the same, and the primary side of the transformer includes a resonant inductance L _{r_p} A resonant circuit composed of resonant capacitors (C _{r_p1} , C _{r_p2} ) and their antiparallel auxiliary diodes (D ₁ , D ₂ ), and a switching circuit composed of switching tubes (Q ₁ , Q ₂ ). The same is true for the secondary side of the transformer, including a resonant circuit composed of resonant inductance L _{r_s} and resonant capacitors (C _{r_s1} , C _{r_s2} ) and their anti-parallel auxiliary diodes (D ₃ , D ₄ ). The switching tubes (Q ₃ , Q ₄ ) composed of switching circuits. The connection relationship is: the primary side of the transformer, the positive pole of the resonant capacitor C _{r_p1} and the drain of the switch tube Q1 are connected to the positive pole of the _first port at the same time, and the negative pole of the resonant capacitor C _{r_p1} is simultaneously connected to the positive pole of the resonant capacitor C _{r_p2} and the primary side of the transformer The negative pole is connected, the source of the switching tube Q1 is connected to _one end of the resonant inductor L _{r_p} and the drain of the switching tube _Q2 at the same time, the source of the switching tube _Q2 and the negative pole of the resonant capacitor C _{r_p2} are connected to the negative pole of the first port at the same time , while the other end of the resonant inductance L _{r_p} is connected to the anode of the primary side of the transformer, and the auxiliary diodes D ₁ and D ₂ are connected in antiparallel to the resonant capacitors C _{r_p1} and C _{r_p2 respectively} ; similarly, on the secondary side of the transformer, the secondary side of the transformer The positive pole is connected to one end of the resonant inductance L _{r_s} , and the other end of the resonant inductance L _{r_s} is connected to the source of the switching tube _Q3 and the drain of the switching tube _Q4 at the same time, and the drain of the switching tube _Q3 is connected to the resonant capacitor C _{r_s1} and The positive pole of the second port is connected, the negative pole of the resonant capacitor C _{r_s1} is connected with the positive pole of the resonant capacitor C _{r_s2} and the negative pole of the secondary side of the transformer at the same time, and the source of the switching tube _Q4 , the negative pole of the resonant capacitor C _{r_s2} are connected with the negative pole of the second port The negative poles are connected together at the same time, and the auxiliary diodes D ₃ and D ₄ are connected in antiparallel to the resonant capacitors C _{r_s1} and _{Cr_s2} respectively.

Preferably, the switch tubes (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) are switch tubes with anti-parallel body diodes and drain-source parasitic capacitances.

As shown in Figure 1, the voltage at the first port of the converter is V ₁ , and i ₁ is its current, while the voltage at the second port is V ₂ , and i ₂ is its current; i _r1 and i _r2 are the primary and secondary sides of the transformer respectively The resonant current flowing through the resonant inductors L _{r_p} and L _{r_s} ; i _m is the current flowing through the exciting inductance L _m ; u _cp1 , u _cp2 , u _cs1 , u _cs2 are the voltages at both ends of the primary and secondary side resonant capacitors; i _D1 , i _D2 , i _D3 , and i _D4 are the currents flowing through the primary and secondary auxiliary diodes respectively; Q ₁ , Q ₂ , Q ₃ , and Q ₄ represent the gate signals of the corresponding MOS transistors.

The specific control method is as follows:

When running in the forward direction, when the current i _r1 flowing through the resonant inductor L _{r_p} is zero, the switch tubes Q ₁ and Q ₃ are turned on at the same time. After half a resonance cycle, i _r1 is zero again, and the switch tube Q ₁ is turned on at this time. and _Q3 off at the same time. After a dead time, i _r1 oscillates slightly near zero during the dead time, when Q ₂ and Q ₄ are turned on at the same time, i _r1 is also zero, after half a resonance cycle, Q ₂ and Q ₄ are at i When _r1 is zero again it is turned off at the same time. The same is true for reverse operation. At this time, the zero-crossing point of the current i _r2 of the resonant inductance L _{r_s} is used as the node for turning on and off the switch tube. The working mode of the normal load and overload operation can be referred to in Figure 3-4. shown.

In addition to the main circuit, the bidirectional CLLLC-DCX resonant converter also includes a control circuit, the control circuit includes a controller and a driving circuit; the controller is a DSP controller, which is used to generate a set of complementary PWM driving signals, and the driving circuit will receive The PWM driving signal from the controller provides the driving voltage for the switch tubes Q ₁ -Q ₄ of the main circuit after isolation and voltage enhancement. The above switching tube control method can be implemented using a control circuit.

The present embodiment and its circuit topology work process are as follows:

Taking the forward operation as an example, as shown in Figure 2(a) and Figure 3, when the converter is operating under normal load, at time t ₀ , when the resonant current i _r1 starts to increase from zero, the switching tubes Q ₁ and Q ₃ At the same time, Q ₁ is turned on with zero current. If the parameters and dead time are designed reasonably, Q ₁ is just discharged at time t ₀ , and Q ₁ can be turned on at zero voltage at the same time. According to the volt-second balance characteristic of the inductor, the dead time Before the interval is turned on, the excitation current _im is a negative value, and the secondary current flows through the body diode of _Q3 , which clamps the voltage at both ends of _Q3 to zero, creating conditions for the zero-voltage turn-on of _Q3 ; by adjusting the dead time Let the switching frequency be equal to the resonant frequency, i _r1 is a sinusoidal signal, and when it reaches zero again after half a resonant period, the switching tubes Q ₁ and Q ₃ are turned off at the same time, at this time Q ₁ is turned off with zero current, and the secondary current is ni _m , n is the transformation ratio of the transformer, so Q ₃ has a cut-off current, if the value of L _m increases, the cut-off current will decrease accordingly; t ₁ to t ₃ is the dead time, at this time the primary side Q ₁ The junction capacitance of Q 2 is charged, the junction capacitance of Q ₂ is discharged, the junction capacitance of Q ₃ of the secondary side is charged, and the junction capacitance of Q ₄ is discharged. Since the value of i _r2 is greater than i _r1 , the junction capacitance of the secondary side is fully charged and discharged at t ₂ , t ₂ to t ₃ current flows from the body diode of Q ₄ to clamp the voltage across Q ₄ to zero. Under normal load conditions, if the parameters are selected reasonably, the input current is proportional to the output current. According to the principle of conservation of input and output power, the input and output voltages are also proportional, regardless of the load. Therefore, within the normal load range, the voltage gain is constant. constant. The waveform of the second half cycle is symmetrical, and the principle is the same.

As shown in Figure 2(b) and Figure 4, when the transformer is working under overload conditions, the corresponding MOS tubes are turned on or off when the resonant current i _r1 is zero; when the load is heavier, the theoretical output power will increase, the input current will increase, and the peak-to-peak voltage of the resonant capacitor will also increase within the same time period, but due to the existence of auxiliary diodes D ₁ and D ₂ , the voltage at both ends of the resonant capacitor will not exceed the input voltage, t ₁ At this time, the resonant capacitor C _{r_p2 is} charged to the same voltage as the power supply, and the corresponding resonant capacitor C _{r_p1 is} discharged to zero. At this time, the current turns to flow to _{D1 to clamp C r_p1 to} zero, the power supply is separated from the transformer, and there is no more power input , thus playing the role of two-way power limit. t ₂ to t ₄ is the dead time, which is similar to the normal load time. The junction capacitance of the original secondary side switching tube is charged and discharged, and for the same reason, the secondary side junction capacitance is charged and discharged at t ₃ due to the large secondary side current. The current flows through the body diode, clamping _Q4 to zero.

To sum up, the bidirectional CLLLC-DCX resonant converter disclosed in the present invention has the same forward and reverse working performance. Due to the addition of auxiliary inductances (L _p , L _s ), all power switch tubes (S ₁ , S ₂ , S ₃ , S ₄ ) Zero-voltage turn-on (ZVS) within the full load range, which reduces circulation loss and improves transmission efficiency. The working performance of the converter of the present invention is the same during forward and reverse operation, and when the direction of energy flow changes, the natural two-way flow of energy can be realized without replacing the control logic. In the range from rated load to no load, the voltage gain has nothing to do with the change of the load, and the voltage is a constant value; in the case of overload, the clamping effect of the auxiliary diodes (D ₁ , D ₂ , D ₃ , D ₄ ) makes the output The power will not exceed a maximum value, which can protect the output.

Through the synchronous and equal pulse width control method proposed by the present invention, the ZVS and ZCS soft switching of the MOS transistor on the input side and the ZVS soft switching on the output side can be well realized on the proposed bidirectional CLLLC-DCX resonant converter, and the normal load can be realized The function of constant voltage gain and bidirectional power limitation of the converter can be achieved, and the natural bidirectional flow of energy in the forward and reverse operation modes can be realized at the same time, and the efficiency and reliability of the converter can be improved.

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it still can The technical solutions described in the foregoing embodiments are modified, or some of the technical features are replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (4)

1. a kind of two-way CLLLC-DCX controlled resonant converter, which is characterized in that including main circuit and control circuit, the main circuit Include first port, second port, two resonance circuits, two switching circuitries and a transformer, the first port and One of Two-port netwerk is optionally implemented as power end, another is then accordingly used as load end；Connect the electricity at transformer both ends Road topological structure is identical, and the primary side of transformer includes by resonant inductance L_{r_p}, resonant capacitance C_{r_p1}And C_{r_p2}And its inverse parallel auxiliary Diode D₁And D₂The resonance circuit of composition, by switching tube Q₁、Q₂The switching circuit of composition；The secondary side of transformer similarly, including by Resonant inductance L_{r_s}With resonant capacitance C_{r_s1}And C_{r_s2}And its inverse parallel booster diode D₃And D₄The resonance circuit of composition, by switching Pipe Q₃And Q₄The switching circuit of composition；

The connection relationship of all parts in the main circuit are as follows: in transformer primary side, resonant capacitance C_{r_p1}Anode and switching tube Q₁ Drain electrode simultaneously be connected with first port anode, resonant capacitance C_{r_p1}Cathode then simultaneously with resonant capacitance C_{r_p2}Anode and transformation The cathode of device primary side is connected, switching tube Q₁Source electrode simultaneously with resonant inductance L_{r_p}One end and switching tube Q₂Drain electrode be connected, Switching tube Q₂Source electrode and resonant capacitance C_{r_p2}Cathode be connected simultaneously with the cathode of first port, and resonant inductance L_{r_p}It is another End is then connected with the anode of transformer primary side, booster diode D₁、D₂Inverse parallel is in resonant capacitance C respectively_{r_p1}、C_{r_p2}；Equally , in transformer secondary, anode and the resonant inductance L of Circuit Fault on Secondary Transformer_{r_s}One end be connected, resonant inductance L_{r_s}The other end Simultaneously with switching tube Q₃Source electrode and switching tube Q₄Drain electrode be connected, switching tube Q₃Drain electrode simultaneously with resonant capacitance C_{r_s1}With The anode of Two-port netwerk is connected, resonant capacitance C_{r_s1}Cathode simultaneously with resonant capacitance C_{r_s2}Anode and Circuit Fault on Secondary Transformer it is negative Extremely it is connected, and switching tube Q₄Source electrode, resonant capacitance C_{r_s2}Cathode and the cathode of second port connect together simultaneously, auxiliary two Pole pipe D₃、D₄Inverse parallel is in resonant capacitance C respectively_{r_s1}、C_{r_s2}。

2. two-way CLLLC-DCX controlled resonant converter according to claim 1, which is characterized in that control circuit includes control Device and driving circuit；Controller is dsp controller, and for generating one group of complementary PWM drive signal, driving circuit will be received The PWM drive signal from controller, through isolation and voltage enhancing after be main circuit switching tube Q₁~Q₄Driving electricity is provided Pressure.

3. two-way CLLLC-DCX controlled resonant converter according to claim 1 or 2, which is characterized in that the switching tube Q₁~ Q₄For there are the switching tubes of antiparallel body diode and the parasitic capacitance of hourglass source electrode.

4. a kind of control method of two-way CLLLC-DCX controlled resonant converter as described in any one of claims 1-3, feature exist In the control method includes:

In forward direction operation, when flowing through resonant inductance L_{r_p}Electric current i_r1When being zero, while opening switching tube Q₁And Q₃, by half After harmonic period, i_r1It is again zero, at this time by switching tube Q₁And Q₃It simultaneously closes off, by a dead time, i_r1At dead zone It is interior to be vibrated a little near zero, Q₂And Q₄When simultaneously turning on, i_r1It also is zero, after half of harmonic period, Q₂And Q₄In i_r1 It is simultaneously closed off when being again zero.

In inverted running, when flowing through resonant inductance L_{r_s}Electric current i_r2When being zero, while opening switching tube Q₁And Q₃, by half After harmonic period, i_r2It is again zero, at this time by switching tube Q₁And Q₃It simultaneously closes off, by a dead time, i_r2At dead zone It is interior to be vibrated a little near zero, Q₂And Q₄When simultaneously turning on, i_r2It also is zero, after half of harmonic period, Q₂And Q₄In i_r2 It is simultaneously closed off when being again zero.