CN106655781B - A kind of LCC controlled resonant converters PWM phase shifts mixing control and efficiency optimization method - Google Patents

Abstract

The invention discloses a method for PWM phase-shift hybrid control and efficiency optimization of an LCC resonant converter. The method includes the following steps: sampling the output voltage of the converter, making a difference with a reference value as the input of a voltage regulator, and obtaining the output c; Sampling the resonant current of the converter, and obtaining two coefficients k ₁ and k ₂ through an optimization algorithm; using k ₁ and k ₂ to calculate and correct the output command value c of the voltage regulator, and obtain a PWM phase-shift hybrid control method The two command values of : phase shift angle θ and duty cycle d; input the phase shift angle and duty cycle command value into the PWM phase-shift hybrid modulator to obtain the drive signals of the four switching tubes on the primary side of the resonant converter. The invention improves the degree of control freedom of the converter, and under the premise of maintaining the specified output power and ensuring the realization of ZVS, the resonant current is minimized by adjusting the coefficient to change the combination of control quantities, and the efficiency of the converter is improved.

Description

A PWM phase-shift hybrid control and efficiency optimization method for LCC resonant converter

technical field

The invention relates to the technical field of power electronics, in particular to a PWM phase-shift hybrid control and efficiency optimization method for an LCC resonant converter.

Background technique

High frequency is one of the development trends of modern power electronics technology. Realizing high frequency can increase the power density of the system and reduce the weight and volume of the device. Traditional PWM switching converters work in the hard switching state of forced on and off. Due to the non-ideal characteristics of power electronic switching devices, they are usually turned on when the voltage is not zero or turned off when the current is not zero. This results in a large switching loss and high heat generation of the switching device. Since the switching loss is proportional to the switching frequency, when the switching frequency increases, the switching loss and heat generation of the switching device will also increase, and even the switching device will be burned out. On the other hand, as the switching frequency increases, du/dt and di/dt of the system will also increase, causing serious electromagnetic interference. In order to solve the above problems, the soft switching technology first developed in the early 1980s has become a necessary means to reduce losses and improve efficiency.

Compared with the traditional PWM type DC/DC converter, the resonant converter is easy to realize soft switching, which can reduce the loss and contribute to the development of high frequency. In addition, the resonant converter has better load characteristics in extreme cases of load open circuit or short circuit, and is widely used in many fields. LCC series-parallel resonant converter has the advantages of both series resonant converter and parallel resonant converter, and has better output voltage regulation ability and load short-circuit protection ability. Since the LCC series-parallel resonant converter can take advantage of the parasitic parameters of the high-frequency transformer and use it as a part of the resonant circuit, it is suitable for high-voltage and high-frequency applications.

As a kind of soft switching (ZVS), the resonant switching converter has the advantages of high operating frequency, low loss, high efficiency, and small size. The LCC resonant switching converter has the advantages of being able to realize the ZVS turn-on of the primary switching tube in the full load range, the ZVS turn-off of the rectifier diode, and the advantages of easy magnetic integration and wide input voltage range. It has gained wide attention and application.

Resonant converters generally use frequency control or phase shift control. The frequency control is simple, reliable and easy to implement, and has wide applicability to low-order or high-order resonant converters. Its disadvantages are mainly as follows: in order to adjust the output switching frequency, it needs to be changed in a large range, which will cause significant electromagnetic compatibility problems and increase the difficulty of filter design. Phase-shift control solves the above problems, its switching frequency is constant, and the output voltage is controlled by adjusting the duty cycle. Usually the switching frequency is higher than the resonant frequency, and the resonant network is inductive at this time. However, the main problem with phase-shift control is that when the output power is small, it is necessary to increase the switching frequency to ensure that the switching tube realizes soft switching. Generally, in order to meet the soft switching condition, the switching frequency is set slightly higher than the resonant frequency. If the switching frequency continues to increase, the power factor of the resonant tank will decrease, which will lead to increased commutation and reduce the efficiency of the resonant converter. In other words, traditional phase-shift control cannot realize soft switching in a wide range.

The increase of converter resonant current will bring more conduction loss and greater device stress, resulting in lower converter efficiency. Under traditional phase-shift control, reducing the resonant current and ensuring the realization of ZVS are a pair of contradictions, that is, optimizing the conduction loss and switching loss cannot be realized at the same time, and optimizing one of them will inevitably destroy the characteristics of the other.

Contents of the invention

Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a PWM phase-shift hybrid control and efficiency optimization method for an LCC resonant converter. Under the premise of realizing ZVS, the resonant current is minimized and the efficiency of the converter is improved.

Technical scheme: in order to achieve the above object, the technical scheme adopted in the present invention is:

A method for PWM phase-shift hybrid control and efficiency optimization of an LCC resonant converter, comprising the following steps executed sequentially:

Step 1. Sampling the output voltage of the LCC resonant converter to obtain the output voltage sampling value, making a difference between the output voltage sampling value and the reference value to obtain a voltage difference, and using the obtained voltage difference as the input of the voltage regulator to obtain the voltage regulator. Output instruction value c;

Step 2: Sampling the resonant current of the LCC resonant converter, and obtaining two correction coefficients k ₁ and k ₂ through an optimization algorithm;

Step 3, use the correction formula Calculate and obtain the two command values of phase shift angle θ and duty cycle d;

Step 4: Input the two command values of the phase shift angle θ and the duty cycle d into the PWM phase shift hybrid modulator to obtain the driving signals of the four switching tubes on the primary side of the LCC resonant converter;

In the above process, the calculation process of the optimization algorithm in the second step is:

Step (1) Set the initial value of k ₁ to 0, and obtain the initial value of k ₂ according to any steady-state point P ₀ (θ ₀ , d ₀ ) of the LCC resonant converter and the correction formula;

Step (2) Increase the values of k ₁ and k ₂ at the same time, and judge that the phase shift angle θ and duty cycle d after the increase of k ₁ and k ₂ meet the update conditions;

Step (3) If the update condition is met, then update the values of k ₁ and k ₂ , and obtain the new phase shift angle θ and duty ratio d, and repeat step (2), if the update condition is not met, go to step (4 );

Step (4) reduces the value of k ₂ , and judges whether the phase shift angle θ and the duty cycle d after the reduction of k ₂ meet the update condition;

Step (5) If the condition is not met, the algorithm ends and the values of k ₁ and k ₂ before the last update are output; if the condition is met, the value of k ₂ is updated and the values of k ₁ and k ₂ are output.

Further, in the present invention, the satisfaction of the updating conditions described in steps (2) and (4) is specifically to satisfy the following three conditions at the same time:

Condition (1), after the control variables θ and d are updated, the fluctuation of the unitized output power P _n of the LCC resonant converter does not exceed the set threshold;

Condition (2), the effective value of the resonant current of the LCC resonant converter decreases;

Condition (3), satisfying the realization condition of soft switching ZVS: φ _vi = φ-φ _AB1 ≥ 10°;

in:

φ _vi is the phase angle between the primary output voltage V _AB of the LCC resonant converter and the resonant current i _r ;

φ is the input impedance angle of the equivalent circuit of the LCC resonant converter;

φ _AB1 is the phase angle of the fundamental wave component V _AB1 of the primary side output voltage V _AB of the LCC resonant converter.

Further, in the present invention, the modulation of the LCC resonant converter by the PWM phase-shifting hybrid modulator in step 4 is performed according to the following four conditions:

Condition (1), the LCC resonant converter's primary-side lead-side upper switch tube S1 and primary-side lead-side lower switch tube S2 are complementary conduction, and the primary-side lagging-arm upper switch tube S3 and the primary-side lagging-arm lower switch Complementary conduction of tube S4;

Condition (2), the duty cycle of the switching tube S1 on the leading bridge arm of the primary side is constant, which is 50%;

Condition (3), the amplitude of the triangular carrier wave is 1, and the frequency is 2 times the switching frequency; the triangular carrier wave starts counting from 2θ[k]/π in the kth switching cycle, where θ[k] is the shift of the kth switching cycle Phase angle, k is any integer;

Condition (4), the driving signal of the switching tube S4 under the lagging bridge arm of the primary side is low level at the initial stage of the k cycle, and is turned to high level when the carrier is equal to d[k] on the rising edge of the first triangular carrier , in the subsequent falling edge of the triangular carrier, when the triangular carrier is equal to d[k], it turns to low level, and d[k] is the duty cycle command value.

Further, in the present invention, in the condition (1) involved in the update condition, the calculation formula of the unitized output power P _n of the LCC resonant converter is:

Further, in the present invention, in the condition (3), the calculation formula of the equivalent input impedance angle φ of the LCC resonant converter and the phase angle φ _AB1 of V _AB1 is:

in:

A＝C _p /C _s is the ratio of resonant capacitance; C _s and C _p are series and parallel resonant capacitance respectively;

ω _s is the switching angular frequency;

ω _n is the per-unit switching frequency;

α is the turn-off angle of secondary rectification;

I _{r_rms} is the effective value of the resonant current;

V _o is the output voltage.

Beneficial effect:

(1) PWM phase-shift hybrid control is adopted, which has two control quantities, which improves the degree of freedom of control and enhances the degree of freedom of control of the converter.

(2) The adjustment coefficient is calculated by using the optimization algorithm. Under the premise of maintaining the specified output power and ensuring the realization of ZVS, the resonant current is minimized by changing the combination of control variables through the adjustment coefficient, and the efficiency of the converter is improved.

Description of drawings

Fig. 1 is the PWM phase-shift hybrid control principle diagram that the present invention is used for LCC resonant converter;

Fig. 2 is the schematic diagram of the hybrid control efficiency optimization method proposed by the present invention;

Fig. 3 is the control system block diagram of the inventive method;

Fig. 4 is a flowchart of an optimization algorithm for calculating adjustment coefficients k ₁ and k ₂ in the present invention;

Fig. 5 is a schematic diagram of a digital PWM phase-shifting hybrid modulator used in an LCC resonant converter according to the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

The present invention proposes a PWM phase-shift hybrid control and efficiency optimization method for an LCC resonant converter, and the block diagram of its control system is shown in FIG. 3 . The main steps include:

(1) Sample the output voltage of the LCC resonant converter, make a difference with the reference value and use it as the input of the voltage regulator to obtain the output c;

(2) Sampling the resonant current of the LCC resonant converter, and obtaining two correction coefficients k ₁ and k ₂ through an optimization algorithm;

(3) Use k ₁ and k ₂ to calculate and correct the output command value c of the voltage regulator, and obtain two command values of the PWM phase shift hybrid control method: phase shift angle θ and duty cycle d;

(4) Input the command value of the phase shift angle θ and the duty ratio d into the PWM phase shift hybrid modulator to obtain the driving signals of the four switching tubes on the primary side of the resonant converter, as shown in Figure 5.

An LCC resonant converter PWM phase-shifting hybrid control and efficiency optimization method of the present invention, the PWM phase-shifting hybrid modulator embodiment is shown in Figure 1, each switching period is T _s , the modulation method satisfies the following four principles conduct:

Condition (1), the LCC resonant converter's primary-side lead-side upper switch tube S1 and primary-side lead-side lower switch tube S2 are complementary conduction, and the primary-side lagging-arm upper switch tube S3 and the primary-side lagging-arm lower switch Complementary conduction of tube S4;

Condition (2), the duty cycle of the switching tube S1 on the leading bridge arm of the primary side is constant, which is 50%;

Condition (3), the amplitude of the triangular carrier wave is 1, and the frequency is 2 times the switching frequency; the triangular carrier wave starts counting from 2θ[k]/π in the kth switching cycle, where θ[k] is the shift of the kth switching cycle Phase angle, k is any integer;

Condition (4), the driving signal of the switching tube S4 under the lagging bridge arm of the primary side is low level at the initial stage of the k cycle, and is turned to high level when the carrier is equal to d[k] on the rising edge of the first triangular carrier , in the subsequent falling edge of the triangular carrier, when the triangular carrier is equal to d[k], it turns to low level, and d[k] is the duty cycle command value.

As can be seen from Fig. 1, when the PWM phase-shift hybrid control proposed by the present invention is adopted, the fundamental wave component V _AB1 of the primary side output voltage V _AB of the LCC resonant converter is:

in:

V _{AB1_m} and φ _AB1 are the amplitude and phase angle of V _AB1 respectively;

_Vin is the input DC voltage of the LCC resonant converter.

It can be seen from formula (1): when (θ, d) = (0, 0.5), that is, when the duty cycle of S4 is 50% and in phase with S1, V _{AB1_m} reaches the maximum value as follows:

The input power P _in of the LCC resonant converter can be obtained by the following formula:

in:

I _{r_m} is the resonance current amplitude;

Z _in is the equivalent circuit input impedance of the LCC resonant converter;

φ is the input impedance angle of the equivalent circuit of the LCC resonant converter.

The output power P _o of the LCC resonant converter is

P _o ＝P _in ·η (4)

in:

η is the efficiency of the LCC resonant converter.

Substituting Equation (3) into Equation (4), the expression of the output power P _o of the LCC resonant converter can be obtained

In steady state, when V _AB1 reaches the maximum value, the LCC resonant converter can transmit the maximum power to the load, so the maximum output power is

Neglecting the difference in efficiency when the LCC resonant converter outputs different powers, the standard unit output power of the LCC resonant converter can be obtained from equations (1), (5) and (6)

For the LCC resonant converter, the switching frequency is generally set higher than the resonant frequency. In the case of high switching frequency, ensuring that all the switching tubes on the primary side achieve ZVS is the main way to improve the efficiency of the converter. The necessary conditions for all switch tubes to achieve ZVS are: before the switch tube is turned on, the series resonant inductor stores enough energy for the discharge of the parallel capacitor of the switch tube; The current reverses. Combined with Figure 1, the expression of ZVS realization conditions can be obtained:

in:

φ _vi is the phase angle between the primary output voltage V _AB of the LCC resonant converter and the resonant current i _r ;

φ is the input impedance angle of the equivalent circuit of the LCC resonant converter;

φ _AB1 is the phase angle of the fundamental component V _AB1 of the primary output voltage V _AB of the LCC resonant converter;

C _s and C _p are the series and parallel resonant capacitors respectively;

A＝C _p /C _s is the ratio of resonant capacitance;

ω _s is the switching angular frequency;

ω _n is the per-unit switching frequency;

α is the turn-off angle of secondary rectification;

I _{r_rms} is the effective value of the resonant current;

V _o is the output voltage.

The realization of switching tube ZVS can be guaranteed by increasing φ, which represents the degree of lagging voltage of the resonant tank current. When the circuit parameters are determined, φ can only be increased by increasing the switching frequency, and the increase in the switching frequency will greatly change the steady-state characteristics of the converter, increase the difficulty of device selection and parameter design in other links, and cause more loss.

In practice, in order to ensure ZVS, it can be realized by reducing φ _AB1 . The PWM phase-shift hybrid control proposed by the present invention has a higher degree of control freedom, and the phase-shift angle θ and the duty ratio d jointly determine the characteristics of φ _AB1 .

The expression of the effective value of the unitized resonant current under PWM phase-shift hybrid control is:

When the control quantity (θ, d) changes, the change law of I _n and φ _AB1 is opposite. Changing the control amount in order to reduce the resonant current will cause φ _AB1 to increase. From the first formula of Equation (8), it can be seen that this change will reduce the ZVS domain and destroy the ZVS characteristics of the LCC resonant converter. Therefore, reducing the resonant current and ensuring the realization of ZVS are a pair of contradictions, that is, optimizing the conduction loss and switching loss cannot be realized at the same time, and optimizing one aspect will inevitably destroy the characteristics of the other aspect. Therefore, in practice, a compromise between the two should be dealt with when designing the control method.

In order to solve the above problems, the present invention proposes an improved PWM phase-shifting hybrid control method, under the premise of maintaining the specified output power unchanged and ensuring the realization of ZVS, the resonance current is reduced by changing the combination of control quantities (θ, d) , so as to achieve the optimization purpose of improving the efficiency of the converter.

The principle of the improved PWM phase-shift hybrid control is further described in detail with reference to FIG. 2 . The curve in the figure is the contour line of the standard unit output power P _n . Assuming that the LCC resonant converter is in a certain stable state, the corresponding control variables (θ _A , d _A ) are represented by point A in the figure, and P _n =0.6 is taken as an example. The optimization process is: move the control quantity along the current contour line (that is, to ensure that the output power remains unchanged), and the direction of movement is the direction that can reduce the resonance current, as shown by the arrow in the figure. On the other hand, according to the change of the control quantity, the ZVS condition is judged in real time by formula (8). When φ _AB1 decreases to a certain extent, the control quantity stops moving and reaches point B. The control quantity (θ _B , d _B ) corresponding to this point is the optimal control point. When the load changes suddenly, the output power changes, and the control quantity moves from the current contour line to another contour line under the action of the voltage loop. Through the algorithm control (θ, d) only moves between different Pn contours on the line segment OA and its extension (the output power reduction is taken as an example in the figure), O is the maximum output power point (θ, d) = (0, 0.5). When the LCC resonant converter returns to the stable state, repeat the above steady-state optimization process to reach the optimal control point C: (θ _C , d _C ).

Fig. 3 shows the block diagram of the control system of the method of the present invention. First, the output voltage V _o of the converter is sampled, and the difference e from the reference value is used as the input of the voltage regulator to obtain the output c; the resonant current of the converter is sampled, and two coefficients k ₁ and k ₂ are obtained through an optimization algorithm ; Use k ₁ and k ₂ to calculate and modify the output command value c of the voltage regulator, and obtain two command values of the PWM phase-shift hybrid control method: phase shift angle θ and duty cycle d; the phase shift angle and duty cycle The ratio command value is input to the PWM phase-shift hybrid modulator to obtain the driving signals d ₁ , d ₂ , d ₃ , and d ₄ of the four switching tubes on the primary side of the resonant converter. In the figure, _Vin is the input voltage, i _r is the resonant current, i _R is the rectified output current, and i _o is the output current. S1-S4 is the primary switching tube, L _r is the resonant capacitor, C _s is the series resonant capacitor, C _p is the parallel resonant capacitor, Tr is the transformer, n is the primary and secondary turns ratio of the transformer, C _f is the output filter capacitor, R _L is the load.

In order to realize the above-mentioned improved PWM phase-shift hybrid control, the present invention proposes an optimization algorithm, through which two coefficients k ₁ and k ₂ are calculated, and the output command c of the voltage loop is corrected to obtain the two coefficients of the PWM phase-shift hybrid control. A control quantity (θ, d).

The main task of the command value correction link is first to calculate the command value of the phase shift angle according to the output of the voltage regulator, which plays a role in quickly adjusting the output voltage; secondly, to calculate the command value of the duty cycle, so that the control point is in a steady state or During the load mutation process, they are all on the straight line where the maximum power point (θ, d) = (0, 0.5) is located. From this, the correction formula of the command value can be obtained:

Among them, k1 and k2 are correction coefficients.

The flow chart of the optimization algorithm proposed by the present invention is shown in FIG. 4 .

First, assuming that the LCC resonant converter is at a certain steady-state point P ₀ (θ ₀ , d ₀ ), the initial value of k ₁ is 0, and the initial value of k ₂ can be calculated by inserting Equation (10) into Equation (7).

Increase k ₁ and k ₂ in turn, the increase of k ₁ will lead to a larger command value of the phase shift angle, and the increase of k ₂ is equivalent to increasing the slope of the line where the control point and the maximum power point are located, so that the calculated duty cycle command value becomes larger. The simultaneous increase of the two makes the control point move towards the direction of the decrease of the resonant current. The degree of increase determines the control accuracy of the system, which can be set according to specific needs in practice.

Then judge the following conditions in turn:

(1) According to formula (7), it is judged whether the fluctuation of P _n exceeds the threshold value (1%) after the control quantity is changed;

(2) Calculate its effective value from the resonant current sampling value, and judge whether it is reduced;

(3) calculate φ and φ _AB1 according to formula (1) and formula (8) and judge whether to satisfy the realization condition of ZVS, in order to reserve a certain margin, the present invention sets the realization condition of ZVS as: φ _vi ≥ 10 °

When the above three conditions are met at the same time, the values of k ₁ and k ₂ are updated and continue to increase until any one of the above three conditions is not satisfied.

Decrease the value of k ₂ and judge whether the above three conditions are met at the same time. If not, end the algorithm and output the values of k ₁ and k ₂ before the last update. If they are satisfied, update k ₁ and k ₂ and output them, and end Algorithm, the final optimal control point is obtained through formula (10).

From the above analysis, it can be seen that the PWM phase-shift hybrid control proposed by the present invention can make the system quickly stabilize, including the output power change process caused by the load mutation; and the command value optimization and correction link can maintain the specified output power unchanged and ensure ZVS On the premise of realization, the resonant current is minimized by changing the combination of control variables (θ, d), so as to achieve the optimal control goal of improving the efficiency of the converter.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also possible. It should be regarded as the protection scope of the present invention.

Claims (4)

1. a kind of LCC controlled resonant converters PWM phase shifts mixing control and efficiency optimization method, it is characterised in that：It is executed including sequence Following steps：

Step 1: carrying out sampling to the output voltage of LCC controlled resonant converters obtains output voltage sampled value, output voltage is sampled Value makes the difference to obtain voltage difference with reference value, using obtained voltage difference as the input of voltage regulator, obtains voltage regulator Output order value c；

Step 2: being sampled to the resonance current of LCC controlled resonant converters, two correction factor k are obtained by optimization algorithm₁、 k₂；

Step 3: using correction formulaIt calculates and obtains this 2 command values of phase shifting angle θ and duty ratio d；

Step 4: this 2 command values input PWM phase shift hybrid modulation devices by phase shifting angle θ and duty ratio d, LCC resonant transformations are obtained The drive signal of four switching tubes of device primary side；

In the above process, the calculation process of optimization algorithm is in the step 2：

Step (1), setting k₁Initial value be 0, according to the arbitrary steady state point P of LCC controlled resonant converters₀(θ₀, d₀) and correct public Formula obtains k₂Initial value；

Step (2) while increasing k₁、k₂Value, judge k₁、k₂Whether phase shifting angle θ and duty ratio d after increase meet update item Part；

Step (3) updates k if meeting update condition₁、k₂Value, and obtain new phase shifting angle θ and duty ratio d, and repeat to walk Suddenly (2) are transferred to step (4) if being unsatisfactory for update condition；

Step (4) reduces k₂Value, judge k₂Whether phase shifting angle θ and duty ratio d after reduction meet update condition；

Step (5) terminates algorithm if being unsatisfactory for condition and exports the k before last time update₁、k₂Value, updated if meeting condition k₂Value, and export k₁、k₂Value；

The update condition that meets in the step (2), (4) is specially while meeting following 3 conditions：

After condition (1), control variable θ, d update, the standardization output power P of LCC controlled resonant converters_nFluctuation be no more than setting Threshold value；

Condition (2), LCC controlled resonant converters resonance current virtual value reduce；

Condition (3) meets Sofe Switch ZVS realization conditions：φ_vi=φ-φ_AB1≥10°；

Wherein：

φ_viFor LCC controlled resonant converter primary side output voltages V_ABWith resonance current i_rBetween phase angle；

φ is LCC controlled resonant converter equivalent circuit input impedance angle；

φ_AB1For LCC controlled resonant converter primary side output voltages V_ABFundametal compoment V_AB1Phase angle.

2. a kind of LCC controlled resonant converters PWM phase shifts mixing control and efficiency optimization method, feature exist as described in claim 1 In：PWM phase shifts hybrid modulation device carries out the modulation of LCC controlled resonant converters according to following 4 conditions in the step 4：

Condition (1), the primary side leading-bridge upper switch pipe S1 of LCC controlled resonant converters and primary side leading-bridge lower switch pipe S2 are complementary Conducting, primary side lagging leg upper switch pipe S3 and primary side lagging leg lower switch pipe S4 complementations conducting；

Condition (2), the duty ratio of primary side leading-bridge upper switch pipe S1 are constant, are 50%；

Condition (3), triangular carrier amplitude are 1, and frequency is 2 times of switching frequencies；Triangular carrier k-th of switch periods from 2 θ [k]/ π is started counting up, and wherein θ [k] is the phase shifting angle of k-th of switch periods, and k is arbitrary integer；

Condition (4), primary side lagging leg lower switch pipe S4 drive signals are low level k-th of switch periods starting stage, In first triangular carrier rising edge when carrier wave be equal to d [k] when be turned into high level, in subsequent triangular carrier failing edge when Overturning is low level when triangular carrier is equal to d [k], and d [k] is duty instruction value.

3. a kind of LCC controlled resonant converters PWM phase shifts mixing control and efficiency optimization method, feature exist as described in claim 1 In：In the condition (1), the standardization output power P of LCC controlled resonant converters_nCalculation formula be：

。

4. a kind of LCC controlled resonant converters PWM phase shifts mixing control as described in claim 1 and efficiency optimization method, feature It is：In the condition (3), LCC controlled resonant converter equivalent circuit input impedance angle φ and V_AB1Angle phi_AB1Calculating it is public Formula is：

Wherein：

A=C_p/C_sFor resonant capacitance ratio；C_s、C_pRespectively series and parallel resonant capacitance；

ω_sTo switch angular frequency；

ω_nFor standardization switching frequency；

α is that the rectification of secondary side turns off angle；

I_{r_rms}For resonance current virtual value；

V_oFor output voltage.