CN118157467A - Totem-pole PFC circuit control method based on double feedforward average current - Google Patents
Totem-pole PFC circuit control method based on double feedforward average current Download PDFInfo
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Abstract
The invention belongs to the field of power factor correction of a switching power supply, and particularly relates to a totem-pole PFC circuit control method based on double feedforward average current, which comprises the following steps: s1, an alternating current power supply outputs a direct current voltage Uo after passing through totem pole PFC; s2, outputting direct-current voltage as a feedback value of a voltage outer ring to be compared with a reference value Uo_ref, and performing feedforward multiplication on the output direct-current voltage and the input voltage after being regulated by a PI controller, wherein the product is used as a given value of a current inner ring; s3, the given value and the input current iL are subjected to difference to obtain an error value, the error value is adjusted by the PI controller and then is fed forward with the duty ratio to be added and output, and the modulated signal wave of the bit circuit is output; s4, comparing the modulated signal wave with the carrier wave to obtain a control signal of the high-frequency switch. The method effectively reduces the harmonic distortion rate of the input inductance current, so that the inductance current is more similar to sinusoidal current, and the power factor of the circuit is improved. When the input voltage is unstable, the output voltage tracks the given value more rapidly, and the dynamic characteristic of the system is effectively improved.
Description
Technical Field
The invention belongs to the field of power factor correction of switching power supplies, and particularly relates to a totem-pole PFC circuit control method based on double feedforward average current.
Background
With the further improvement of social intelligence along with the social development, the development of power electronics technology is also very rapid. With the accompanying rapid rise in the number of various power electronics. With the application of a large number of power electronics, harmonic pollution problems are also accompanied. If there are a large number of harmonics in these power electronics, the pollution of the grid is extremely serious. In order to meet the EMI specification and the green energy requirement, it has become an essential link to reduce the harmonic pollution of the ac-dc conversion switching power supply. PFC (Power Factor Correction) is power factor correction, and the main working principle of the power factor correction is to enable the input inductance current to be sinusoidal as much as possible, reduce harmonic waves, and enable the input voltage to be in phase with the input current, so that pollution of electrical equipment to a power grid is reduced based on the input voltage and the input current, and the PFC circuit is widely applied at present. However, in the conventional active PFC circuit, when the grid voltage is input into the circuit, the ac is converted into dc by a rectifier bridge, and this process has a large power loss. In order to reduce power loss and improve efficiency, research heat of bridgeless PFC is gradually increased.
Among the numerous bridgeless PFC topologies, totem pole bridgeless PFC has very good performance. The number of components is the least in all PFC topologies at present, and the circuit topology is simple in structure and low in common mode noise. However, in the conventional totem pole PFC circuit based on Si MOS, the parasitic body diode of the MOS tube has long reverse recovery time and large reverse recovery loss, so that the totem pole PFC circuit cannot work in CCM (Continuous Conduction Mode) continuous conduction mode, and the application of the totem pole bridgeless PFC circuit is limited. However, with the application of the third generation semiconductors represented by silicon carbide (SiC), the problem of reverse recovery of the body diode and the problem of peak of zero crossing point of inductance current are improved, so totem-pole bridgeless PFC circuits adopting SiC devices are now adopted and become research hot spots.
At present, the totem pole PFC circuit adopts the most control mode to control the average current, but under the control scheme, the current sinusoidal degree is still not high enough, and if the input voltage is greatly changed, the response speed of the output voltage is also slower.
Disclosure of Invention
The invention aims to: aiming at the problems, the invention provides the double-feedforward average current control totem pole PFC circuit, which effectively reduces the harmonic distortion rate of input inductance current, enables the inductance current to be more similar to sinusoidal current, and improves the power factor of the circuit. Meanwhile, under the condition that the input voltage is unstable and has great variation, the output voltage tracks the given value more rapidly, and the dynamic characteristic of the system is effectively improved.
In order to solve the technical problems, the invention adopts the following technical scheme: a totem pole PFC circuit control method based on double feedforward average current, the totem pole PFC circuit is composed of two groups of bridge arms, an alternating current power supply, a boost inductor, a filter capacitor and a load resistor;
The two groups of bridge arms are divided into a high-frequency bridge arm and a power frequency bridge arm, the high-frequency bridge arm comprises a first switch tube and a second switch tube, the source electrode of the first switch tube is connected with the drain electrode of the second switch tube, the power frequency bridge arm comprises a third switch tube and a fourth switch tube, the source electrode of the third switch tube is connected with the drain electrode of the fourth switch tube, the drain electrode of the first switch tube of the high-frequency bridge arm is connected with the drain electrode of the third switch tube of the power frequency bridge arm, and the source electrode of the second switch tube of the high-frequency bridge arm is connected with the source electrode of the fourth switch tube of the power frequency bridge arm;
The positive electrode of the alternating current power supply is connected with one end of the boost inductor in series, the other end of the boost inductor is connected with the source electrode of the first switching tube of the high-frequency bridge arm, and the negative electrode of the alternating current power supply is connected with the source electrode of the third switching tube;
The filter capacitor is connected with the load resistor in parallel, one end of the filter capacitor is connected with the drain electrode of the first switching tube, and the other end of the filter capacitor is connected with the source electrode of the third switching tube;
the totem pole PFC circuit control method based on the double feedforward average current comprises the following steps:
step S1, an alternating current power supply outputs a direct current voltage Uo after passing through totem pole PFC;
S2, outputting direct-current voltage as a feedback value of a voltage outer ring to be compared with a reference value Uo_ref, and performing feedforward multiplication on the output direct-current voltage and the input voltage after adjustment by a PI controller, wherein the product is used as a given value of a current inner ring;
S3, performing difference between the given value and the input current iL to obtain an error value, adjusting the error value by a PI controller, performing addition output with duty ratio feedforward, and outputting a modulation signal wave of a bit circuit;
and S4, comparing the modulated signal wave with the carrier wave to obtain a control signal of the high-frequency switch.
Further, the first switching tube, the second switching tube, the third switching tube and the fourth switching tube are all SiC MOS.
Further, in step S2, the PI controller adjustment steps are as follows:
S21, carrying out large-signal modeling on a totem pole PFC circuit;
The equation can be derived from KCL law:
the equation is derived from KVL law:
Let the input inductor current i L (t) and the output voltage v o (t) be state variables, i.e., x= [ i L(t)vo(t)]T ], let the input vector u= [ v in (t) ]. The following state equation is obtained by combining the formula (1) and the formula (2):
Wherein d is the duty cycle, and T s is the switching period;
The combination of formulas (1) (2) (3) can be obtained:
Averaging the switching period of the formula (3) to obtain a complete state equation in the whole switching period:
Wherein:
s22, carrying out small-signal modeling on the totem pole PFC circuit;
According to modeling of the large signal model in the step S21, a circuit average value equivalent model is obtained:
wherein r is the equivalent internal resistance of the inductor;
The method is obtained through Law transformation:
Adding small signal disturbance on the basis of original stable signals to obtain an expression:
Middle order Then large signal analysis, formula (7) can be:
The AC/DC items are respectively corresponding to the same, and the second-order AC item is omitted to obtain:
The linear state equation of the formula (11) is subjected to Laplace transformation to obtain the following expression:
the control block diagram of the totem pole bridgeless PFC after simplification can be obtained according to the formula (12), and the control block diagram is eliminated from the formula (12) Order theThe transfer function of the output voltage to the duty cycle is obtained after the transfer function is simplified:
In the formula (12) Eliminating, and simplifying to obtain a transfer function of inductance current to duty ratio:
G id(s) and G vd(s) are controlled objects when a control loop design is carried out;
S23, obtaining an inner loop open loop transfer function of the current according to modeling data;
Is provided with The original transfer function G id(s) can be simplified according to equation (12), resulting in a simplified transfer function:
the PI controller transfer function is:
Gc(s)＝Kpu+kius (16)
Combining equation (15) and equation (16) to obtain the current inner loop open loop transfer function:
S24, acquiring a proportional coefficient and an integral coefficient of the current inner loop PI controller;
Leading the formula (16) and the formula (17) into corresponding modules, inputting parameters into a PID regulating module, and obtaining the proportional coefficient and the integral coefficient of the current inner loop PI controller;
s25, obtaining a voltage outer ring transfer function according to modeling data;
s26, the proportional coefficient and the integral coefficient of the voltage outer loop PI controller are obtained.
Further, in step S2, the input voltage feedforward design step includes:
The instantaneous power absorbed in the grid P i is equal to the instantaneous output power P o, i.e.:
Pi＝Po (19)
since the waveform of the input voltage and current should be in-phase sine wave, the power grid voltage expression is set as:
The input current expression is:
Voltage feed forward signal K fb is introduced:
Pi＝Po＝2Kfbviiisin2ωt (22)
setting half sine wave input voltage |v in | as one input of multiplier, signal at output end of multiplier
I_ref＝Kfb|vin|Vc (23)
Wherein V c is the output error voltage of the voltage loop;
The current loop obtains an input current I in according to the error voltage V c and the current detection resistor R s:
The above formula is combined to obtain:
The voltage feedforward signal K fb available according to equation (25) is listed as follows:
combining expression (23) and expression (26) to obtain:
Further, in the step S3, the duty ratio feedforward design step is as follows:
the current response of the totem pole PFC circuit is as follows:
neglecting the effect of the input and output voltages on the current loop to get a small signal model:
The Laplace transform of formulas (28), (29) is obtained:
the duty cycle feedforward compensation amount can be obtained by making the actual duty cycle value and the ideal duty cycle value different from each other:
the combination of formulas (30), (31) can be obtained:
if it is desired to eliminate the influence of the current loop on the input and output voltages, the desired duty compensation expression is satisfied with equation (31), and the compensation amount is taken in this design:
the beneficial effects of the invention are as follows: according to the totem pole PFC circuit control method based on the double feedforward average current, the output response speed of the circuit can be effectively improved through voltage feedforward, the sine degree of input inductance current can be effectively improved through the design of duty ratio feedforward, and the harmonic distortion rate of the inductance current is reduced. The circuit control method is simple in control mode, easy to realize, free of additional hardware circuits and capable of effectively reducing cost.
Drawings
Fig. 1 is a flow chart of a totem pole PFC circuit control method based on double feed forward average current according to the present invention;
fig. 2 is a totem pole bridgeless PFC main circuit diagram;
fig. 3 is a diagram of six working states of totem pole bridgeless PFC;
fig. 4 is a simplified topology of a totem pole bridgeless PFC;
Fig. 5 is a diagram of two operating states of a totem pole bridgeless PFC after simplification;
FIG. 6 is a schematic diagram of a totem pole bridgeless PFC average equivalent model;
Fig. 7 is an equivalent block diagram of a totem pole bridgeless PFC simplified small signal model;
FIG. 8 is a Bode plot of transfer functions for totem pole bridgeless PFC at different input voltage values;
FIG. 9 is a graph of transfer function versus original transfer function for totem pole bridgeless PFC simplification;
fig. 10 is a totem pole bridgeless PFC current inner loop control block diagram;
FIG. 11 is a graph of totem pole bridgeless PFC output voltage versus;
fig. 12 is a graph comparing totem pole bridgeless PFC input current THD.
Description of the embodiments
The technical scheme of the invention is described in detail below with reference to the accompanying drawings and examples. The embodiment is implemented according to the technical scheme of the invention, and the specific implementation flow is clearly and completely expressed.
As shown in fig. 1, the totem pole PFC circuit control method based on double feedforward average current of the present invention is shown in fig. 2, where the totem pole PFC circuit is composed of two groups of bridge arms, an AC power supply AC, a boost inductor L, a filter capacitor C and a load resistor R;
The two groups of bridge arms are divided into a high-frequency bridge arm and a power frequency bridge arm, the high-frequency bridge arm comprises a first switch tube S1S1 and a second switch tube S2S2, the source electrode of the first switch tube S1 is connected with the drain electrode of the second switch tube S2, the power frequency bridge arm comprises a third switch tube S3 and a fourth switch tube S4, the source electrode of the third switch tube S3 is connected with the drain electrode of the fourth switch tube S4, the drain electrode of the first switch tube S1 of the high-frequency bridge arm is connected with the drain electrode of the third switch tube S3 of the power frequency bridge arm, and the source electrode of the second switch tube S2 of the high-frequency bridge arm is connected with the source electrode of the fourth switch tube S4 of the power frequency bridge arm;
the positive pole of the alternating current power supply is connected with one end of the boost inductor in series, the other end of the boost inductor is connected with the source electrode of the first switching tube S1 of the high-frequency bridge arm, and the negative pole of the alternating current power supply is connected with the source electrode of the third switching tube S3;
The filter capacitor is connected with the load resistor in parallel, one end of the filter capacitor is connected with the drain electrode of the first switching tube S1, and the other end of the filter capacitor is connected with the source electrode of the third switching tube S3;
the first switching tube S1, the second switching tube S2, the third switching tube S3 and the fourth switching tube S4 are all SiC MOS.
The totem pole PFC converter is evolved from Boost topology, as shown in fig. 3, and is in six working states of a totem pole PFC circuit, and the totem pole PFC converter can be equivalently two Boost circuits alternately working in the positive half cycle and the negative half cycle of the input voltage, so that the totem pole bridgeless PFC circuit can be simplified into Boost circuit topology, and further, the size signal model of the Boost circuit is analyzed, so that the working principle of the totem pole PFC circuit is obtained. Fig. 5 is a simplified circuit topology illustrating two operating states.
A totem-pole PFC circuit control method based on double feedforward average current comprises the following steps:
step S1, an alternating current power supply outputs a direct current voltage Uo after passing through totem pole PFC;
S2, outputting direct-current voltage as a feedback value of a voltage outer ring to be compared with a reference value Uo_ref, and performing feedforward multiplication on the output direct-current voltage and the input voltage after adjustment by a PI controller, wherein the product is used as a given value of a current inner ring;
First, large signal modeling is performed on a PI controller circuit, and an equation can be obtained according to KCL law:
the equation is derived from KVL law:
Let the input inductor current i L (t) and the output voltage v o (t) be state variables, i.e. x= [ i L(t)vo(t)]T). Let the input vector u= [ v in (t) ]. The following state equation is written in combination of the expression (1) and the expression (2).
Where d is the duty cycle and T s is the switching period.
The combination of formulas (1) (2) (3) can be obtained:
to obtain a complete state equation over the entire switching period, the switching period of equation (3) may be averaged to obtain:
Wherein:
secondly, modeling the small signal of the converter, and obtaining a circuit average value equivalent model according to the analysis of the large signal model and combining with fig. 6:
Wherein r is the equivalent internal resistance of the inductor.
The method is obtained through Law transformation:
Adding small signal disturbance based on original stable signal to obtain expression:
Middle order Then large signal analysis, formula (7) can be:
The AC/DC items are respectively corresponding to each other and the second-order AC item is removed to obtain:
The linear state equation of the formula (11) is subjected to Laplace transformation to obtain the following expression:
The control block diagram of the totem pole bridgeless PFC simplified can be obtained according to the equation (12), as shown in fig. 7. At the same time, cancel (12) Let/>The transfer function of the output voltage to the duty cycle can be obtained after the transfer function is simplified:
Similarly, in formula (12) Eliminating, and simplifying to obtain transfer function of inductance current to duty ratio:
In summary, modeling is completed on the size signal of the totem pole bridgeless PFC circuit, and G id(s) and G vd(s) can be understood as controlled objects when the control loop design is performed.
In equations (13) and (14), the output voltage V o and the duty cycle D' are variables, and in the totem pole PFC circuit, the output voltage is basically stable with only small fluctuation, so that the disturbance of the output voltage V o can be ignored in the subsequent controller design. But the totem-pole bridgeless PFC circuit discards the rectifier bridge at the input end of the traditional PFC circuit, namely, the input voltage of the converter is not direct current, but alternating current which changes with time, and the duty ratio calculation formula of the Boost PFC circuit is as followsAccording to the formula, the alternating voltage has a large influence on the duty ratio, so that the influence caused by the change of the duty ratio is not negligible when the controller is designed. Meanwhile, in order to obtain a higher power level of the control system, the sine degree of the inductance current is improved, and a continuous conduction double-feedforward average current control mode is adopted.
To analyze what kind of influence the above mentioned input voltage changes may have on the circuit transfer function, MATLAB software is used to obtain a circuit transfer function bode diagram at different input voltages, as shown in fig. 8, which is a transfer function amplitude-frequency characteristic response diagram and a phase-frequency characteristic corresponding diagram when the input voltage is from 10v to 400 v. According to the graph, the input voltage is changed, and the Bode diagram of the transfer function G id(s) of the duty ratio to the inductance current is greatly different in the low frequency band, but the characteristics are almost consistent in the high frequency band.
Now based on the above analysis, it is assumed thatThat is, the output voltage is considered unchanged, and the original transfer function G id(s) can be simplified according to the equation (12), so as to obtain a simplified transfer function:
next, the availability of the simplified transfer function formula (15) is analyzed as shown in fig. 9. It can be seen that the amplitude-frequency characteristic and the phase-frequency characteristic of G id(s) 'and G id(s) are extremely similar in the high-frequency band, and the signal frequency generally processed by the current loop is relatively high, so that the simplified transfer function G id(s)' can be used for carrying out corresponding analysis and design on the current loop of the circuit in the design.
The circuit design index is as follows:
[1] input voltage:
[2] Input voltage frequency: 50Hz;
[3] output voltage: 750v;
[4] Rated load resistance: r=300Ω;
[5] Switching frequency: 72kHz;
[6] Efficiency is that: more than or equal to 90 percent;
[7] output rated power: p o = 5000w;
The design of the inner loop of the circuit control loop current is started according to the circuit design index.
The current control loop uses a PI controller whose control objective is to reduce the error value between the input inductor current (I L) and the input current reference value (I _ref) so that the error value is as close to zero as possible. While ensuring that the input inductor current can quickly and accurately follow the input current reference value (I _ref). In this loop, (I L、I_ref) is an input signal, and an output signal is a modulation signal of the entire circuit.
As shown in fig. 10, which is a control block diagram of the current inner loop, the PI controller transfer function is:
Gc(s)＝Kpu+kius (16)
the simplified current loop transfer function is combined, as shown in equation (15). The feedback coefficient is here set to 1. The overall current inner loop open loop transfer function can be obtained:
And opening sisotool a tool box in MATLAB software, and compensating the current loop by using the tool box to obtain the required PI parameters. Firstly, selecting a required architecture, leading the formulas (16) and (17) into corresponding modules, and then selecting PID regulation in automatic regulation. The cut-off frequency of the current loop is 1/10 of the selected switching frequency, which is 7.2kHz. The phase angle margin is set to 45deg. And inputting the set parameters into a PID regulating module to obtain a proportional coefficient k pi = 0.32 and an integral coefficient k ii = 1466.4 of the current inner loop PI controller.
The voltage outer loop also employs a PI controller, which acts to reduce the difference between the output voltage value (V o) and the output voltage reference value (V o_ref) so that the error between them tends to zero as much as possible, while ensuring that the output voltage (V o) follows the input voltage reference value (V o_ref) quickly and accurately. The control loop is located at the outermost ring of the control system.
Similar to the design thought and flow of the current inner loop, the transfer function of the voltage outer loop can be simplified into:
it should be noted that, because the input voltage frequency is 50Hz, there is a larger power frequency ripple in the 100Hz frequency band, and in order to suppress this ripple, the cutoff frequency of the voltage outer ring should be set lower and must not exceed 100Hz, which is 10Hz. The current inner loop design process is repeated to obtain a proportional coefficient k pu = 0.105 and an integral coefficient k iu = 6.6 of the voltage outer loop PI controller.
In the whole design process, the influence on the output voltage caused by load or input voltage fluctuation needs to be considered, and the influence caused by load or input voltage fluctuation should be eliminated or reduced as much as possible. Therefore, an input voltage feedforward control strategy is introduced, specifically as follows:
the totem pole bridgeless PFC circuit has very high efficiency, and the switching frequency (72 kHz) is far higher than the power grid voltage frequency (50 Hz), so that the energy stored or consumed by the PFC circuit in the power grid power frequency period is negligible, and the instantaneous power P i absorbed from the power grid can be approximately considered to be equal to the instantaneous output power P o, namely:
Pi＝Po (19)
According to the definition of the PFC circuit, the power factor is 1, so that the waveform of the input voltage and current can be considered as an in-phase sine wave, and the power grid voltage expression is as follows:
The input current expression is:
The input power expression is:
Pi＝viniin＝2viiisin2ωt (22)
obtained from (19)
Pi＝Po＝2viiisin2ωt (22)
As can be seen from equation (22), if the supply voltage is disturbed or fluctuates and the circuit requires a constant power output, the input current must be inversely proportional to the input voltage. However, for totem pole PFC circuits, which require a high power factor, the input current must closely track a given current reference, meaning that the instantaneous input current needs to exhibit a proportional change to the instantaneous input voltage. It can be seen that the two are contradictory.
To solve the above problem, a voltage feedforward signal K fb may be introduced, which is used to change the input voltage and the magnitude of the input current at the same time, for example, the input voltage suddenly drops from 400V to half of the original 200V, at this time, K fb immediately increases to twice the original, and the input current can be changed in proportion to the input voltage. When the voltage feedforward signal K fb is introduced, equation (22) can be modified as:
Pi＝Po＝2Kfbviiisin2ωt (22)
Now, the half sine wave input voltage |v in | is set as one input of the multiplier, and at this time, the signal I _ref at the output end of the multiplier is the half sine wave under the influence of |v in |, the amplitude of the signal I _ref is proportional to the output of the error amplifier, and the phase is the same as the input voltage, and can be expressed as:
I_ref＝Kfb|vin|Vc (23)
wherein V c is the output error voltage of the voltage loop;
The current loop obtains an input current I in according to the error voltage V c and the current detection resistor R s:
The above formula is combined to obtain:
From equation (25), it is known that the value of the output power P o varies with the square signal V in 2 of the input voltage V in, and that constant power output can be achieved if the influence of V in 2 is eliminated. Let the effective value of the input voltage V in be V in_rms V, and list the voltage feedforward signal K fb as the following expression:
Combining expressions (23), (26) yields:
Obviously, after the voltage feedforward signal K fb is introduced, if the error voltage V c remains unchanged, the effect of V in 2 is eliminated.
In summary, with the introduction of the input voltage feedforward, the control loop gain is not changed by the change of the input voltage, so that the normal operation of the circuit in the full input voltage range is easier to realize, and the stability of the system is obviously improved. Thus, the design of voltage feedforward is completed.
S3, performing difference between the given value and the input current iL to obtain an error value, adjusting the error value by a PI controller, performing addition output with duty ratio feedforward, and outputting a modulation signal wave of a bit circuit;
the zero crossing current spike problem is an inherent problem of totem pole PFC converters, and the cause of this spike is also quite numerous and complex. The duty ratio feedforward is added in the circuit control loop, so that the degree of interference of input current by input and output voltage can be effectively reduced, the distortion degree of the input current can be effectively reduced, and the method is relatively simple to realize and is very suitable for being applied to a digital control circuit.
The current response of the totem pole PFC circuit can be obtained by analyzing the influence of the input voltage and the output voltage on the current loop, and the current response is as follows:
If the effect of the input and output voltages on the current loop is ignored, the small signal model is available:
The Laplace transform of formulas (28), (29) is obtained:
the input-output voltage obtained by the formula (30) has no influence on the duty ratio and the inductive current, and the duty ratio and the inductive current are in a linear relation. The duty cycle feedforward compensation amount can be obtained by making the actual duty cycle value and the ideal duty cycle value different from each other:
the combination of formulas (30), (31) can be obtained:
to sum up, if it is necessary to eliminate the influence of the input and output voltages on the current loop, the required duty compensation expression needs to satisfy the formula (31), and the compensation amount is taken in this design:
The duty cycle feed forward design ends so far.
And S4, comparing the modulated signal wave with the carrier wave to obtain a control signal of the high-frequency switch, and outputting a high-level control MOS tube to be turned on when the modulated signal wave is larger than the carrier wave.
Finally, the feasibility of theoretical analysis is verified in Matlab/Simulink through simulation.
As shown in fig. 11, the input voltage drops to half of the original voltage at any time, and the graph (a) shows the waveform of the output voltage obtained when the input voltage feedforward is added, compared with the waveform of the output voltage after the input voltage feedforward is not added in the graph (b), the response of the output voltage is obviously improved after the duty ratio feedforward is added, so that the tracking speed is faster and the fluctuation amplitude is obviously reduced.
As shown in fig. 12, fig. (a) shows a totem-pole bridgeless PFC input current THD graph when the duty-cycle feedforward is added, the input inductor current THD is found to be 7.37%, and fig. (b) shows a totem-pole bridgeless PFC input current THD graph when the duty-cycle feedforward is not added, the input inductor current THD is found to be 7.6%. From this, the current THD value is reduced by 0.23%, the current distortion is reduced, and the peak current at the zero crossing is reduced.
According to the totem pole PFC circuit control method based on the double feedforward average current, the output response speed of the circuit can be effectively improved through voltage feedforward, the sine degree of input inductance current can be effectively improved through the design of duty ratio feedforward, and the harmonic distortion rate of the inductance current is reduced. The circuit control method is simple in control mode, easy to realize, free of additional hardware circuits and capable of effectively reducing cost.
With the above-described preferred embodiments according to the present invention as an illustration, the above-described descriptions can be used by persons skilled in the relevant art to make various changes and modifications without departing from the scope of the technical idea of the present invention. The technical scope of the present invention is not limited to the description, but must be determined as the scope of the claims.
Claims (5)
1. A totem pole PFC circuit control method based on double feedforward average current is characterized in that the totem pole PFC circuit consists of two groups of bridge arms, an alternating current power supply, a boost inductor, a filter capacitor and a load resistor;
The two groups of bridge arms are divided into a high-frequency bridge arm and a power frequency bridge arm, the high-frequency bridge arm comprises a first switch tube and a second switch tube, the source electrode of the first switch tube is connected with the drain electrode of the second switch tube, the power frequency bridge arm comprises a third switch tube and a fourth switch tube, the source electrode of the third switch tube is connected with the drain electrode of the fourth switch tube, the drain electrode of the first switch tube of the high-frequency bridge arm is connected with the drain electrode of the third switch tube of the power frequency bridge arm, and the source electrode of the second switch tube of the high-frequency bridge arm is connected with the source electrode of the fourth switch tube of the power frequency bridge arm;
The positive electrode of the alternating current power supply is connected with one end of the boost inductor in series, the other end of the boost inductor is connected with the source electrode of the first switching tube of the high-frequency bridge arm, and the negative electrode of the alternating current power supply is connected with the source electrode of the third switching tube;
The filter capacitor is connected with the load resistor in parallel, one end of the filter capacitor is connected with the drain electrode of the first switching tube, and the other end of the filter capacitor is connected with the source electrode of the third switching tube;
the totem pole PFC circuit control method based on the double feedforward average current comprises the following steps:
step S1, an alternating current power supply outputs a direct current voltage Uo after passing through totem pole PFC;
S2, outputting direct-current voltage as a feedback value of a voltage outer ring to be compared with a reference value Uo_ref, and performing feedforward multiplication on the output direct-current voltage and the input voltage after adjustment by a PI controller, wherein the product is used as a given value of a current inner ring;
S3, performing difference between the given value and the input current iL to obtain an error value, adjusting the error value by a PI controller, performing addition output with duty ratio feedforward, and outputting a modulation signal wave of a bit circuit;
and S4, comparing the modulated signal wave with the carrier wave to obtain a control signal of the high-frequency switch.
2. The totem pole PFC circuit control method of claim 1 wherein the first, second, third, and fourth switching tubes are SiC MOS.
3.A totem pole PFC circuit control method based on double feed forward average current as defined in claim 1, wherein in step S2, the PI controller adjusts the steps as follows:
S21, carrying out large-signal modeling on a totem pole PFC circuit;
The equation can be derived from KCL law:
the equation is derived from KVL law:
Let the input inductor current i L (t) and the output voltage v o (t) be state variables, i.e., x= [ i L(t)vo(t)]T ], let the input vector u= [ v in (t) ]. The following state equation is obtained by combining the formula (1) and the formula (2):
Wherein d is the duty cycle, and T s is the switching period;
The combination of formulas (1) (2) (3) can be obtained:
Averaging the switching period of the formula (3) to obtain a complete state equation in the whole switching period:
Wherein:
s22, carrying out small-signal modeling on the totem pole PFC circuit;
According to modeling of the large signal model in the step S21, a circuit average value equivalent model is obtained:
wherein r is the equivalent internal resistance of the inductor;
The method is obtained through Law transformation:
Adding small signal disturbance on the basis of original stable signals to obtain an expression:
Middle order Then large signal analysis, formula (7) can be:
The AC/DC items are respectively corresponding to the same, and the second-order AC item is omitted to obtain:
The linear state equation of the formula (11) is subjected to Laplace transformation to obtain the following expression:
the control block diagram of the totem pole bridgeless PFC after simplification can be obtained according to the formula (12), and the control block diagram is eliminated from the formula (12) Order theThe transfer function of the output voltage to the duty cycle is obtained after the transfer function is simplified:
In the formula (12) Eliminating, and simplifying to obtain a transfer function of inductance current to duty ratio:
G id(s) and G vd(s) are controlled objects when a control loop design is carried out;
S23, obtaining an inner loop open loop transfer function of the current according to modeling data;
Is provided with The original transfer function G id(s) can be simplified according to equation (12), resulting in a simplified transfer function:
the PI controller transfer function is:
Gc(s)＝Kpu+kius (16)
Combining equation (15) and equation (16) to obtain the current inner loop open loop transfer function:
S24, acquiring a proportional coefficient and an integral coefficient of the current inner loop PI controller;
Leading the formula (16) and the formula (17) into corresponding modules, inputting parameters into a PID regulating module, and obtaining the proportional coefficient and the integral coefficient of the current inner loop PI controller;
s25, obtaining a voltage outer ring transfer function according to modeling data;
s26, the proportional coefficient and the integral coefficient of the voltage outer loop PI controller are obtained.
4. A totem pole PFC circuit control method based on double feed forward average current as defined in claim 3, wherein in step S2, the input voltage feed forward design step comprises:
The instantaneous power absorbed in the grid P i is equal to the instantaneous output power P o, i.e.:
Pi＝Po (19)
since the waveform of the input voltage and current should be in-phase sine wave, the power grid voltage expression is set as:
The input current expression is:
Voltage feed forward signal K fb is introduced:
Pi＝Po＝2Kfbviiisin2ωt (22)
setting half sine wave input voltage |v in | as one input of multiplier, signal at output end of multiplier
I_ref＝Kfb|vin|Vc (23)
Wherein V c is the output error voltage of the voltage loop;
The current loop obtains an input current I in according to the error voltage V c and the current detection resistor R s:
The above formula is combined to obtain:
The voltage feedforward signal K fb available according to equation (25) is listed as follows:
combining expression (23) and expression (26) to obtain:
5. A totem pole PFC circuit control method based on double feed forward average current as defined in claim 4, wherein in step S3, the duty cycle feed forward design step is as follows:
the current response of the totem pole PFC circuit is as follows:
neglecting the effect of the input and output voltages on the current loop to get a small signal model:
The Laplace transform of formulas (28), (29) is obtained:
the duty cycle feedforward compensation amount can be obtained by making the actual duty cycle value and the ideal duty cycle value different from each other:
the combination of formulas (30), (31) can be obtained:
If it is desired to eliminate the influence of the current loop on the input and output voltages, the required duty compensation expression is satisfied with the expression (31), and the compensation amount is taken in this design:
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