阅读说明：本技术 一种基于变电感的频率优化控制的crm升压变换器 (CRM boost converter based on variable inductance frequency optimization control ) 是由 刘劲滔 姚凯 刘乐 王泽松 李家镇 高阳 杨坚 于 2020-04-30 设计创作，主要内容包括：本发明公开了一种基于变电感的频率优化控制的CRM升压变换器,包括主功率电路、CRM控制和驱动电路、输出电压反馈电路、乘法器、整流后输入电压分压电路和可变电感控制电路,其中整流后输入电压分压电路的输出端连接乘法器的输入端,输出电压反馈电路的输出端连接乘法器的另一个输入端,乘法器的输出端连接CRM控制和驱动电路的一个输入端；可变电感控制电路通过施加的不同偏置电流来改变主功率电路中的可变电感的电感值。本发明实现了CRM升压PFC变换器开关频率变化范围的减小,变换器效率的提高,同时还能实现单位功率因数。(The invention discloses a variable inductance based CRM boost converter with frequency optimization control, which comprises a main power circuit, a CRM control and drive circuit, an output voltage feedback circuit, a multiplier, a rectified input voltage divider circuit and a variable inductance control circuit, wherein the output end of the rectified input voltage divider circuit is connected with the input end of the multiplier, the output end of the output voltage feedback circuit is connected with the other input end of the multiplier, and the output end of the multiplier is connected with one input end of the CRM control and drive circuit; the variable inductance control circuit varies the inductance value of the variable inductance in the main power circuit by applying different bias currents. The invention realizes the reduction of the change range of the switching frequency of the CRM boost PFC converter, improves the efficiency of the converter and can realize the unit power factor.)

1. A CRM boost converter based on variable inductance frequency optimization control is characterized by comprising a main power circuit (1) and a control circuit;

the main power circuit (1) comprises an input voltage source v_inEMI filter, diode rectifying circuit RB and variable inductor L_bVIAnd a switching tube Q_bDiode D_bFilter capacitor C and load R_Ld(ii) a Said input voltage source v_inThe output cathode of the diode rectifying circuit RB is a reference potential zero point, and the output anode of the diode rectifying circuit RB is connected with the variable inductor L_bVIIs connected to one end of a variable inductor L_bVIThe other end is respectively connected with a switch tube Q_bAnd diode D_bAnode of (2), diode D_bRespectively connected with one end of the filter capacitor C and the load R_LdIs connected with the other end of the filter capacitor C and the load R_LdThe other ends of the two ends of the three-phase current transformer are connected with a reference potential zero point and a load R_LdThe voltage at both ends is output voltage V_oOutput voltage V_oThe anode of the voltage feedback circuit is connected with the input end of the output voltage feedback circuit (3);the boost inductor in the main power circuit (1) is a variable inductor L_bVIThe inductance value is adjusted to an optimal value by applying bias current under different input voltages, the fixed bias current is introduced to adjust the inductance value to 0.767mH within the range of 90VAC-110.3VAC of the effective value of the input voltage, the fixed bias current is not introduced to adjust the inductance value to 1.0304mH within the range of 110.3VAC-249VAC, and the fixed bias current is introduced to adjust the inductance value to 0.645mH within the range of 249VAC-264VAC, so that the switching frequency can be ensured to be always greater than 30 kHz;

the control circuit comprises a CRM control and drive circuit (2), an output voltage feedback circuit (3), a rectified input voltage divider circuit (4), a multiplier (5) and a variable inductance control circuit (6); the output end of the CRM control and drive circuit (2) and the switching tube Q_bA gate connection of (a); the input end of the output voltage feedback circuit (3) is connected with the output voltage V of the main power circuit (1)_oThe output end of the positive pole of the voltage regulator is connected with one input end of the multiplier (5); input end of rectified input voltage divider circuit (4) and rectified input voltage sampling point V_gNamely, the output anode of the diode rectifying circuit RB is connected, and the output end of the diode rectifying circuit RB is connected with the other input end of the multiplier (5); the output end of the multiplier (5) is connected with one input end of the CRM control and drive circuit (2); input end of variable inductance control circuit (6) and rectified input voltage sampling point V_gThat is, the output anode of the diode rectification circuit RB is connected, and the output end is connected to the variable inductance L of the main power circuit (1)_bVIThe above.

2. CRM boost converter based on variable inductance frequency optimization control according to claim 1, characterized in that, the CRM control and drive circuit (2) includes an inductance L_zA sixth resistor R_zA seventh resistor R_tAn eighth resistor R_dZero-crossing detection, RS trigger, drive and first operational amplifier A₁；

The inductance L_zOne end of the first resistor is connected with a reference point potential zero point, and the other end of the first resistor is connected with a sixth resistor R_zOne terminal of (1), wherein the inductance L_zOne end of the reference potential zero point is connected with the variable inductor L in the main power circuit (1)_bVIConnection ofOne end of the output positive electrode of the diode rectifying circuit RB is a homonymous end; a sixth resistor R_zThe other end of the zero-cross detection circuit is connected with the input end of the zero-cross detection circuit, and the output end of the zero-cross detection circuit is connected with the S end of the RS trigger; the output end of the multiplier (5) is connected with a first operational amplifier A in the CRM control and drive circuit (2)₁The non-inverting input terminal of (1); a seventh resistor R_tOne end of the switch tube is connected with a reference potential zero point, and the other end of the switch tube is connected with a switch tube Q_bSource and first operational amplifier a₁The first operational amplifier A₁The output end of the resistor is connected with the R end of the RS trigger, and the Q end of the RS trigger is driven by an eighth resistor R_dAfter being connected in series, the switch tube Q is connected_bA gate electrode of (2).

3. The CRM boost converter based on variable inductance frequency optimization control of claim 1, wherein the output voltage feedback circuit (3) comprises a second operational amplifier A₂A third resistor R₃A fourth resistor R₄A fifth resistor R₅And a capacitor C₁；

The third resistor R₃And the output voltage V of the main power circuit (1)_oIs connected to the positive pole of the third resistor R₃And the other end of the first resistor and a fourth resistor R₄And a second operational amplifier A₂Is connected to the reverse input terminal of the fourth resistor R₄Is connected to a reference potential zero point, a second operational amplifier A₂The positive input terminal of the multiplier (4) is connected with a reference voltage, and the output terminal of the multiplier is connected with one input terminal of the multiplier (4).

4. The CRM boost converter based on variable inductance frequency optimization control of claim 1, characterized in that the input voltage divider circuit (4) comprises a first resistor R₁And a second resistor R₂；

The first resistor R₁One end of and an input voltage sampling point V_gThat is, the output anode of the diode rectification circuit RB is connected, and the other end of the diode rectification circuit RB is connected with the second resistor R₂Is connected to a second resistor R₂In addition toOne end is connected with the reference point zero point.

5. A CRM boost converter for variable inductance based frequency optimized control according to claim 1, characterized in that said multiplier (5) comprises a multiplier;

one input end of the multiplier is connected with the output end of the output voltage feedback circuit (3), and the other input end of the multiplier is connected with the output end of the input voltage divider circuit (4).

6. The CRM boost converter based on variable inductance frequency optimization control of claim 1, characterized in that, the variable inductance control circuit (6) comprises a peak sampling, TMS320F28377D chip;

the input end of peak value sampling and the sampling point V of rectified input voltage_gNamely, the output anode of the diode rectification circuit RB is connected, the output end of the diode rectification circuit RB is connected with the ADC input end of the TMS320F28377D chip, and the DAC1 output port of the TMS320F28377D chip is connected with the variable inductor L_bVIAnd (4) connecting.

Technical Field

The invention relates to an alternating current-direct current converter technology of an electric energy conversion device, in particular to a CRM boost converter based on variable inductance frequency optimization control.

Background

A Power Factor Correction (PFC) converter can reduce input current harmonics and improve an input Power Factor, and has been widely used. The PFC converter is divided into an active mode and a passive mode, and compared with the passive mode, the active mode has the advantages of high input power factor, small size, low cost and the like.

The active PFC converter may employ various circuit topology and control methods, wherein the Boost PFC converter is one of the commonly used PFC converters. The CRM Boost PFC converter is generally applied to medium and small power occasions, and has the advantages that a switching tube is switched on at zero current, a booster diode does not have reverse recovery, PF is high and the like, but the switching frequency of the CRM Boost PFC converter changes along with the change of input voltage and load, and the design of an inductor and an EMI filter is complex.

Aiming at the defect that the variation range of the Switching frequency of the CRM Boost PFC Converter is large, the YaoKa proposes that the variation range of the Switching frequency in a wide voltage range is greatly reduced by injecting a proper amount of harmonic waves into input current in a Critical reduction Mode PFC Converter With Fixed Switching frequency control document. The harmonic waves of the input current of the method all meet the IEC 61000-3-2Class D standard, and the ratio of the maximum value and the minimum value of the switching frequency is reduced to about 2 times from about 15 times. However, the research method has a complex control circuit, and meanwhile, when the input voltage is higher, the power factor is reduced more obviously, and the harmonic pollution to the power grid is greatly increased.

Disclosure of Invention

The invention aims to provide a CRM boost converter based on variable inductance frequency optimization control, which solves the problem of large switching frequency variation range of a CRM boost PFC converter under the traditional control, improves the efficiency of the converter and can ensure the unit power factor.

The technical solution for realizing the purpose of the invention is as follows: a CRM boost converter based on variable inductance frequency optimization control comprises a main power circuit and a control circuit;

the main power circuit comprises an input voltage source v_inEMI filter, diode rectifying circuit RB and variable inductor L_bVIAnd a switching tube Q_bDiode D_bFilter capacitor C and load R_Ld(ii) a Said input voltage source v_inThe output cathode of the diode rectifying circuit RB is a reference potential zero point, and the output anode of the diode rectifying circuit RB is connected with the variable inductor L_bVIIs connected to one end of a variable inductor L_bVIThe other end is respectively connected with a switch tube Q_bAnd diode D_bAnode of (2), diode D_bRespectively connected with one end of the filter capacitor C and the load R_LdIs connected with the other end of the filter capacitor C and the load R_LdThe other ends of the two ends of the three-phase current transformer are connected with a reference potential zero point and a load R_LdThe voltage at both ends is output voltage V_o(ii) a The boost inductor in the main power circuit is a variable inductor L_bVIThe switch frequency can be ensured to be always more than 30kHz by applying a fixed bias current to adjust the inductance value to be 0.767mH within the range of 90VAC-110.3VAC of the effective value of the input voltage, applying a fixed bias current to adjust the inductance value to be 1.0304mH within the range of 110.3VAC-249VAC, and applying a fixed bias current to adjust the inductance value to be 0.645mH within the range of 249VAC-264 VAC. The new control not only keeps the advantage that the unit power factor can be realized by the traditional constant on-time control, but also reduces the variation range of the switching frequency by improving the critical inductance value and improves the overall performance of the converter.

The control circuit comprises a CRM control and drive circuit, an output voltage feedback circuit, a rectified input voltage divider circuit, a multiplier and a voltage divider circuitA variable inductance control circuit; the output end of the CRM control and drive circuit and the switching tube Q_bA gate connection of (a); the input end of the output voltage feedback circuit is connected with the output voltage V of the main power circuit_oThe output end of the positive pole of the voltage divider is connected with one input end of the multiplier; input end of rectified input voltage divider circuit and input voltage sampling point V_gNamely, the output anode of the diode rectifying circuit RB is connected, and the output end of the diode rectifying circuit RB is connected with the other input end of the multiplier; the output end of the multiplier is connected with one input end of the CRM control and drive circuit; input end of variable inductance control circuit and rectified input voltage sampling point V_gI.e. the output anode of the diode rectification circuit RB is connected, the output terminal is connected to the variable inductor L_bVIThe above.

Further, the CRM control and drive circuit comprises an inductor L_zA sixth resistor R_zA seventh resistor R_tAn eighth resistor R_dZero-crossing detection, RS trigger, drive and first operational amplifier A₁；

The inductance L_zOne end of the first resistor is connected with a reference point potential zero point, and the other end of the first resistor is connected with a sixth resistor R_zOne terminal of (1), wherein the inductance L_zOne end of the reference potential zero point is connected with the variable inductor L in the main power circuit_bVIOne end connected with the output anode of the diode rectifying circuit RB is a homonymous end; a sixth resistor R_zThe other end of the zero-cross detection circuit is connected with the input end of the zero-cross detection circuit, and the output end of the zero-cross detection circuit is connected with the S end of the RS trigger; the output end of the multiplier is connected with a first operational amplifier A in the CRM control and drive circuit₁The non-inverting input terminal of (1); a seventh resistor R_tOne end of the switch tube is connected with a reference potential zero point, and the other end of the switch tube is connected with a switch tube Q_bSource and first operational amplifier a₁The first operational amplifier A₁The output end of the resistor is connected with the R end of the RS trigger, and the Q end of the RS trigger is driven by an eighth resistor R_dAfter being connected in series, the switch tube Q is connected_bA gate electrode of (2).

Further, the output voltage feedback circuit comprises a second operational amplifier A₂A third resistor R₃A fourth resistor R₄Fifth, theResistance R₅And a capacitor C₁；

The third resistor R₃And the output voltage V of the main power circuit_oIs connected to the positive pole of the third resistor R₃And the other end of the first resistor and a fourth resistor R₄And a second operational amplifier A₂Is connected to the reverse input terminal of the fourth resistor R₄Is connected to a reference potential zero point, a second operational amplifier A₂The positive input terminal of the multiplier is connected with a reference voltage, and the output terminal of the multiplier is connected with one input terminal of the multiplier.

Furthermore, the rectified input voltage divider circuit comprises a first resistor R₁And a second resistor R₂；

The first resistor R₁And a rectified input voltage sampling point V_gThat is, the output anode of the diode rectification circuit RB is connected, and the other end of the diode rectification circuit RB is connected with the second resistor R₂Is connected to a second resistor R₂The other end of the reference point is connected with a reference point zero point.

Further, the multiplier comprises a multiplier;

one input end of the multiplier is connected with the output end of the output voltage feedback circuit, and the other input end of the multiplier is connected with the output end of the input voltage divider circuit.

Further, the variable inductance control circuit comprises a peak sampling chip and a TMS320F28377D chip;

the input end of peak value sampling and the sampling point V of rectified input voltage_gNamely, the output anode of the diode rectification circuit RB is connected, the output end of the diode rectification circuit RB is connected with the ADC input end of the TMS320F28377D chip, and the DAC1 output port of the TMS320F28377D chip is connected with the variable inductor L_bVIAre connected.

Compared with the prior art, the invention has the remarkable advantages that: (1) under control, the power factor of the converter is still 1, and the control circuit is simple; (2) except that the critical inductance value is the same as that of the traditional control when the voltage is 264VAC, the change range of the switching frequency can be greatly reduced under other input voltages through the variable inductance technology; (3) the lowest frequency in the wide voltage range is constant at 30 kHz; (4) the design of the EMI filter and the inductor is simplified, the input filtering effect is improved, the switching loss and the magnetic core loss are reduced, and the efficiency of the converter is improved.

Drawings

Fig. 1 is a schematic circuit diagram of a CRM boost converter based on frequency optimization control of variable inductance in an embodiment of the present invention.

Fig. 2 is a schematic diagram of a main circuit of a Boost PFC converter in an embodiment of the present invention.

Fig. 3 is a graph of the inductor current waveform of the CRM Boost PFC converter in an embodiment of the present invention.

Fig. 4 is a waveform diagram of the inductor current of the CRM Boost PFC converter within half the power frequency cycle in an embodiment of the present invention.

Fig. 5 is a graph showing the inductance value variation over a wide input voltage range according to the embodiment of the present invention.

Fig. 6 is a graph showing the minimum value of the switching frequency over a wide input voltage range according to an embodiment of the present invention.

Fig. 7 is a graph of minimum switching frequency variation under conventional control combined with variable inductance control in an embodiment of the present invention.

Fig. 8 is a graph showing a variation of a minimum switching frequency under frequency optimization control based on a variable inductance according to an embodiment of the present invention.

FIG. 9 shows a variable inductor L in the main power circuit according to an embodiment of the present invention_bVIThe basic model diagram of (1).

Fig. 10 is a graph of the variation of the critical inductance at different input voltages according to an embodiment of the present invention.

FIG. 11 is a graph showing the minimum value of the switching frequency in a wide input voltage range under two kinds of control in the embodiment of the present invention.

Fig. 12 is a graph of the variation of the switching frequency in the second half of the power frequency cycle under the two controls in the embodiment of the present invention.

Detailed Description

The invention is described in further detail below with reference to the figures and the embodiments.

Working principle of 1 CRM Boost PFC converter

Fig. 2 is a Boost PFC converter main circuit.

Setting: 1. all devices are ideal elements; 2. the output voltage ripple is very small compared to its dc amount;

3. the switching frequency is much higher than the input voltage frequency.

Fig. 3 is a waveform of the inductor current in one switching cycle at CRM. When Q is_bWhen conducting, D_bCut-off and boost inductor L_bVoltage across v_gInductor current i_LbStarting from zero with v_g/L_bThe slope of (a) rises linearly; when Q is_bWhen turned off, i_LbBy D_bFollow current, at this time L_bVoltage across v_g－V_o，i_LbWith (V)_o－v_g)/L_bSince the Boost converter operates in CRM mode, at i_LbWhen the voltage drops to zero, the switch tube Q_bOn, a new switching cycle is started.

Without loss of generality, define the input AC voltage v_inThe expression of (a) is:

v_in＝V_msin ωt (1)

wherein V_mAnd ω is the amplitude and angular frequency of the input ac voltage, respectively;

then the rectified voltage v of the input voltage_gComprises the following steps:

v_g＝V_m·|sin ωt| (2)

peak value i of inductor current in one switching period_{Lb_pk}Comprises the following steps:

wherein t is_onIs Q_bOn-time of (d);

in each switching cycle, the boost inductor L_bVolt-second area balance at both ends, so Q_bOff time t of_offComprises the following steps:

as can be seen from fig. 3, the average value i of the inductor current in each switching cycle_{Lb_av}Half of its peak value, which can be obtained from equation (3):

as can be seen from equation (5), if within one power frequency period, the on-time t_onIs fixed, the average value of the inductor current is sinusoidal, i.e. the input power factor is 1. As can be seen from equation (4), the off time t_offThe switching frequency is changed along with the change of the input voltage instantaneous value, namely the switching frequency is changed continuously in a power frequency period.

Fig. 4 is a graph of the waveforms of the inductor current, the peak envelope and the mean value over half the power frequency period.

As can be seen from equation (5) and FIG. 2, the input current i_inComprises the following steps:

setting the output power of the converter to P_oThe efficiency is 1, and the input and output power balance can be obtained:

the on-time t can be obtained from the equation (7)_onComprises the following steps:

by substituting the formula (8) for the formulae (5) and (6), the average value i of the inductor current can be obtained_{Lb_av}And an input current i_inComprises the following steps:

wherein 2P_o/V_mIs the fundamental current amplitude;

the turn-off time t is obtained from the equations (4) and (8)_offComprises the following steps:

the switching frequency f can be obtained by combining the formula (8) and the formula (11)_sComprises the following steps:

the above formula can be:

by observing the formula (13), it can be found that the switching frequency f in the power frequency period is changed along with the constant change of ω t when the converter parameter is determined_sAnd accordingly, constantly changing. The switching frequency is [0, pi/2 ]]Within the interval, the value decreases monotonically with t and is [ pi/2, pi]Within the interval, the interval monotonically increases with ω t, so that the minimum value f within the power frequency period is_{s_min}And maximum value f_{s_max}Occurring at the peak time and zero-crossing time of the input voltage, respectively, i.e. at a minimum value when ω t is pi/2 and at a maximum value when ω t is 0 or pi, i.e. at

According to formulae (14) and (15), with f_{s_max}Ratio f_{s_min}Can obtain the product

If the lowest switching frequency is limited to 30kHz, the maximum inductance value L can be obtained from the equation (12)_{b_max}Is expressed as

According to equation (18), a variation curve of the critical inductance value in a wide input voltage range can be obtained by combining specific parameters of the converter, as shown in fig. 5 below.

2 realizing frequency optimization control strategy based on variable inductance

The frequency optimization control provided by the invention utilizes a variable inductance technology to solve the problem of large switching frequency variation range under the control of the traditional fixed conduction time. Under the frequency optimization control based on the variable inductor, when a critical inductance value is designed, the critical inductance value is not limited by the minimum switching frequency any more, a larger inductance value can be selected, and when the switching frequency is lower than the audible frequency of 30kHz in a wide input voltage range, the value of the variable inductor is adjusted by applying bias current to the variable inductor control winding, so that the switching frequency is increased, and the requirement of the minimum switching frequency is met. Therefore, the critical inductance value is improved, the switching frequency variation range is reduced, the switching frequency in a wide input voltage range can be kept to be larger than 30kHz, and the design requirement of the converter is met.

According to the idea of frequency optimization control and analysis in conjunction with fig. 6, when the selected inductance value is greater than the minimum critical inductance value, the minimum value of the switching frequency is first lower than 30kHz at both sides of the low voltage and the high voltage, at this time, two voltage nodes whose inductance values need to be adjusted exist, which are called as adjustment points of the variable inductor, and the switching frequency can be increased to more than 30kHz only by adjusting the value of the inductor at the adjustment points of the variable inductor, as shown in fig. 7, the minimum switching frequency variation curve under the control of the conventional control in conjunction with the variable inductor is shown.

In combination with the above analysis, the frequency optimization control performs inductance value conversion only at two variable inductance adjustment points in order to simplify the control circuit as much as possible. In a certain range of low-voltage side, a fixed bias current i is applied to the variable inductance control winding_bias1Reducing the inductance value to V_{m_rms}The corresponding inductance critical value at 90V is 0.767 mH; within a certain range of the high-voltage side, a fixed bias current i is applied to the variable inductance control winding_bias2Reducing the inductance value to V_{m_rms}The corresponding inductance threshold at 264V is 0.645 mH. As can be seen from fig. 7, the new control method selects a larger inductance value, and the portions of the two sides with the switching frequency lower than 30kHz will be influenced by the inductance value adjustment and move upward as a whole, so that there must exist an optimal inductance value and two optimal adjustment points of the variable inductor, so that the variation range of the switching frequency within the wide input voltage range is minimized. The solution of the optimal inductance value and the two optimal adjustment points for the variable inductance is performed as follows:

writing equation (12) as relating to inductance L_bAnd an input voltage V_mIs shown in formula (19)

The observation (19) is a function of the input voltage V_mThe cubic function can be calculated to obtain the maximum value point of the minimum switching frequency curve in V within a wide input voltage range_mTaken at 267 VAC. Meanwhile, the change rate of the analysis formula (19) on the two sides of the maximum point can be obtained, and the change rate of the analysis formula (19) on the high-voltage side is higher, so that the change range of the switching frequency on the high-voltage side becomes a key factor for limiting the change range of the minimum value of the switching frequency.

Assume an optimal inductance value of L_optimalThe optimal adjustment point of the variable inductance on the high-voltage side is V_{h_optimal}The optimal adjustment point of the variable inductance on the low-voltage side is V_{l_optimal}Equation of availability

In combination with the specific parameters of the converter, L can be solved_optimal＝1030.4uH,V_{h_optimal}＝352.14VAC,V_{l_optimal}155.95VAC, and the minimum switching frequency variation range is 30 kHz-47.9 kHz.

According to the calculated optimal inductance value L_optimalOptimum adjustment point V of variable inductance on high-voltage side_{h_optimal_rms}249V, low-voltage side variable inductance optimal regulation point V_{l_optimal_rms}110.3V, in combination with equation (19), a variation curve of the minimum switching frequency under the frequency optimization control based on the variable inductance can be drawn, as shown in fig. 8. As can be seen from fig. 8, the switching frequency can be ensured to be always greater than 30kHz by adjusting the inductance value of the variable inductor twice in a wide input voltage range, i.e., by adjusting the inductance value to 0.767mH by applying a fixed bias current in the range of 90VAC to 110.3VAC, by adjusting the inductance value to 1.0304mH by applying a fixed bias current in the range of 110.3VAC to 249VAC, and by adjusting the inductance value to 0.645mH by applying a fixed bias current in the range of 249VAC to 264 VAC. The new control not only keeps the advantage that the unit power factor can be realized by the traditional constant on-time control, but also reduces the variation range of the switching frequency by improving the critical inductance value and improves the overall performance of the converter.

The basic model of variable inductance is shown in fig. 9, and is composed of two side auxiliary windings and a middle main winding, and the auxiliary windings N are controlled to flow through_CBias current I of_biasCan change the inductance L of the main magnetic core_bVIIn the present invention, a double E-type core is used, as shown in fig. 9. Main induction winding N_LWound on a central core with an air gap, auxiliary winding N_CWound on two side cores and two auxiliary windings connected in series to eliminate the current I from the main inductor_LbVIInduced voltage due to ripple. When no bias current exists, the main winding maintains the initial inductance value which is the same as the normal inductance; when there is a bias current I_biasFlows through N_CThen, a bias flux phi is generated along the external path of the double E-shaped magnetic core_biasWith phi_biasIncrease of phi_biasThe working point of the magnetic core on the B-H curve is pushed from the linear region to the nonlinear saturation region, the magnetic permeability mu of the magnetic core along the path is reduced, and when the main winding is electrified, main magnetic flux phi can be generated_mainDue to main magnetic flux phi_mainFlowing through the middle core and the outer path, the main core also being affected by the bias currentThe permeability is reduced. To sum up, I_biasThe effective permeability on the intermediate core is reduced, resulting in a main inductance L_bVIAnd decreases.

From the basic model of variable inductance of fig. 9, the calculation formula of variable inductance can be derived as:

in the formula I₁，l₃，l_gThe lengths of the auxiliary winding, the main winding and the air gap effective magnetic circuit are respectively; a. the₁、A₃Is the effective sectional area of the auxiliary magnetic core and the main magnetic core; n is₃Is the number of turns of the main winding; mu.s₀Is the air permeability; mu.s₃And mu_varThe effective permeability of the main and auxiliary windings respectively.

As can be seen from equation (21), the variable inductance is substantially a change in μ by the bias current₃And mu_varI.e. the effective permeability of the main and auxiliary windings.

A variable inductance model is built in simulation software LTSPICE, and variable inductance L is drawn_bVIWith the inductance value of the bias current I_biasThe variation is shown in fig. 9. The variable inductance parameter designed by the invention is combined, namely the inductance value is adjusted to 0.767mH by applying the fixed bias current within the range of 90VAC-110.3VAC of the effective value of the input voltage, the inductance value is not adjusted to 1.0304mH by applying the bias current within the range of 110.3VAC-249VAC, and the inductance value is adjusted to 0.645mH by applying the fixed bias current within the range of 249VAC-264 VAC.

3 comparison of Performance

3.1 critical inductance value

As can be seen from the analysis of fig. 5 and 10, under the conventional constant on-time control, in order to ensure that the switching frequencies are all greater than the lowest frequency of 30kHz within the wide input voltage range, the critical inductance value is limited by the minimum value of 264VAC of the input voltage, which is only designed to be 0.645 mH. However, under the frequency optimization control based on the variable inductor, the inductance value is decreased when the bias current is increased according to the variable inductor characteristic described above, and the critical inductance value is not widened when selecting the critical inductance valueAnd limiting the minimum value of the inductance in the input voltage range. Therefore, the optimal inductance L calculated in the previous step can be selected when designing the critical inductance_optimal1030.4 uH. Compared with the traditional constant on-time control, the critical inductance value under the frequency optimization control based on the variable inductor is obviously improved.

3.2 variation of switching frequency

According to equation (19) and in combination with the foregoing analysis, the minimum variation curve of the switching frequency in a wide input voltage range under two controls can be plotted, as shown in fig. 11. It can be seen from fig. 11 that, after the new frequency optimization control based on variable inductance is adopted, the change range of the minimum value of the switching frequency is reduced from 30kHz to 78kHz under the traditional control to 30kHz to 47.9kHz, and the change range of the switching frequency is greatly reduced.

Further analyzing equation (12), and bringing the critical inductance values 0.645mH and 1.0304mH under the conventional constant on-time control and variable-inductor-based frequency optimization control into equation (12), respectively, a variation curve of the switching frequency in the half power frequency period under the two controls can be made, as shown in FIG. 12, where f_s1(V_m) The corresponding solid line is the frequency curve under conventional control, f_s2(V_m) The corresponding dotted line is the frequency curve under variable inductance frequency optimization control. As can be seen from the observation of FIG. 12, the variation range of the switching frequency is reduced in different degrees under different input voltages, and under the most common standard input voltages of 110VAC and 220VAC, the variation range of the switching frequency is respectively reduced from 47 kHz-79 kHz and 70 kHz-315 kHz under the traditional control to 30 kHz-49 kHz and 43 kHz-194 kHz under the variable inductance frequency optimization control, and the switching frequency is greatly reduced as a whole. The change range of the traditional control switch frequency at the low-voltage 90VAC is smaller, but the new control can further narrow the change range to 30 kHz-44 kHz; at the high voltage 264VAC, the switching frequency variation curves are completely overlapped in FIG. 12 because the new control method maintains the same critical inductance value as the conventional control. In summary, the new control can effectively reduce the maximum switching frequency f simultaneously_{s_max}With a minimum switching frequency f_{s_min}Is such that the absolute value | f of the switching frequency variation range_{s_max}-f_{s_min}The | is reduced, but the ratio of the two is always kept constant.

4 CRM boost converter based on variable inductance frequency optimization control

With reference to fig. 1, the rectified input voltage v_gThrough a first resistor R₁And a second resistor R₂Partial pressure to obtain v_A＝k_vgV_mL sin ω t l, where k_vgIs the coefficient of partial pressure, k_vg＝R₂/(R₁+R₂) (ii) a The output voltage passes through a third resistor R₃And a fourth resistor R₄To obtain a divided voltage v_B＝k_vgV_oWherein R is₃/R₄＝R₁/R₂。

Voltage division v in voltage ring control circuit_BAnd reference voltage V of error amplifier_refIn comparison, where V_ref2.5V via a fifth resistor R₅And a capacitor C₁The constituent regulator deriving an error signal v_EA，v_EAAnd v_AThe point voltage v is obtained after being connected into a multiplier_EComprises the following steps:

v_E＝v_EAk_vgV_m|sinωt| (22)

voltage v of equation (22)_EAnd a seventh resistor R_tControl switch tube Q after voltage comparison_bTurn off, sixth resistor R_zThe voltage on the switch tube Q is controlled after zero detection_bThe on-time of the change rule shown in the formula (8) is obtained.

With reference to fig. 1, the CRM boost converter for frequency optimization control based on variable inductance of the present invention includes a main power circuit and a control circuit;

the main power circuit comprises an input voltage source v_inEMI filter, diode rectifying circuit RB and variable inductor L_bVIAnd a switching tube Q_bDiode D_bFilter capacitor C and load R_Ld(ii) a Said input voltage source v_inConnected with the input port of the EMI filter, the output port of the EMI filter is connected with the input port of the diode rectifying circuit RB, and two polesThe output cathode of the tube rectifying circuit RB is a reference potential zero point, and the output anode of the diode rectifying circuit RB and the variable inductor L_bVIIs connected to one end of a variable inductor L_bVIThe other end is respectively connected with a switch tube Q_bAnd diode D_bAnode of (2), diode D_bRespectively connected with one end of the filter capacitor C and the load R_LdIs connected with the other end of the filter capacitor C and the load R_LdThe other ends of the two ends of the three-phase current transformer are connected with a reference potential zero point and a load R_LdThe voltage at both ends is output voltage V_o(ii) a The boost inductor in the main power circuit is a variable inductor L_bVIThe switch frequency can be ensured to be always more than 30kHz by applying a fixed bias current to adjust the inductance value to be 0.767mH within the range of 90VAC-110.3VAC of the effective value of the input voltage, applying a fixed bias current to adjust the inductance value to be 1.0304mH within the range of 110.3VAC-249VAC, and applying a fixed bias current to adjust the inductance value to be 0.645mH within the range of 249VAC-264 VAC. The new control not only keeps the advantage that the unit power factor can be realized by the traditional constant on-time control, but also reduces the variation range of the switching frequency by improving the critical inductance value and improves the overall performance of the converter.

The control circuit comprises a CRM control and drive circuit, an output voltage feedback circuit, a rectified input voltage divider circuit, a multiplier and a variable inductance control circuit; the output end of the CRM control and drive circuit and the switching tube Q_bA gate connection of (a); the input end of the output voltage feedback circuit is connected with the output voltage V of the main power circuit_oThe output end of the positive pole of the voltage divider is connected with one input end of the multiplier; input end of rectified input voltage divider circuit and input voltage sampling point V_gNamely, the output anode of the diode rectifying circuit RB is connected, and the output end of the diode rectifying circuit RB is connected with the other input end of the multiplier; the output end of the multiplier is connected with one input end of the CRM control and drive circuit; input end of variable inductance control circuit and rectified input voltage sampling point V_gNamely, the output anode of the diode rectifying circuit RB is connected, and the output terminal is connected to the variable inductor.

Further, the CRM control and drive circuit 2 comprises an inductor L_zA sixth resistor R_zThe seventh power supplyResistance R_tAn eighth resistor R_dZero-crossing detection, RS trigger, drive and first operational amplifier A₁；

The inductance L_zOne end of the first resistor is connected with a reference point potential zero point, and the other end of the first resistor is connected with a sixth resistor R_zOne terminal of (1), wherein the inductance L_zOne end of the reference potential zero point is connected with the variable inductor L in the main power circuit_bVIOne end connected with the output anode of the diode rectifying circuit RB is a homonymous end; a sixth resistor R_zThe other end of the zero-cross detection circuit is connected with the input end of the zero-cross detection circuit, and the output end of the zero-cross detection circuit is connected with the S end of the RS trigger; the output end of the multiplier is connected with a first operational amplifier A in the CRM control and drive circuit₁The non-inverting input terminal of (1); a seventh resistor R_tOne end of the switch tube is connected with a reference potential zero point, and the other end of the switch tube is connected with a switch tube Q_bSource and first operational amplifier a₁The first operational amplifier A₁The output end of the resistor is connected with the R end of the RS trigger, and the Q end of the RS trigger is driven by an eighth resistor R_dAfter being connected in series, the switch tube Q is connected_bA gate electrode of (2).

Further, the output voltage feedback circuit 3 includes a second operational amplifier A₂A third resistor R₃A fourth resistor R₄A fifth resistor R₅And a capacitor C₁；

The third resistor R₃And the output voltage V of the main power circuit_oIs connected to the positive pole of the third resistor R₃And the other end of the first resistor and a fourth resistor R₄And a second operational amplifier A₂Is connected to the reverse input terminal of the fourth resistor R₄Is connected to a reference potential zero point, a second operational amplifier A₂The positive input terminal of the multiplier is connected with a reference voltage, and the output terminal of the multiplier is connected with one input terminal of the multiplier.

Further, the input voltage divider circuit 4 includes a first resistor R₁And a second resistor R₂；

The first resistor R₁One end of and an input voltage sampling point V_gI.e. the output anode of the diode rectifying circuit RB is connected, the other endAnd a second resistor R₂Is connected to a second resistor R₂The other end of the reference point is connected with a reference point zero point.

Further, the multiplier 5 includes a multiplier;

one input end of the multiplier is connected with the output end of the output voltage feedback circuit, and the other input end of the multiplier is connected with the output end of the rectified input voltage divider circuit.

Further, the variable inductance control circuit comprises a peak sampling chip and a TMS320F28377D chip;

the input end of peak value sampling and the sampling point V of rectified input voltage_gNamely, the output anode of the diode rectification circuit RB is connected, the output end of the diode rectification circuit RB is connected with the ADC input end of the TMS320F28377D chip, and the DAC1 output port of the TMS320F28377D chip is connected with the variable inductor L_bVIAre connected.