CN112003485A - Current continuous control method based on bridgeless SEPIC-PFC circuit - Google Patents

Abstract

The invention discloses a current continuous control method based on a bridgeless SEPIC-PFC circuit, which is used for realizing continuous alternating current side current and higher power factor and is suitable for high-power PFC application occasions; the method comprises the following implementation steps: the invention has the beneficial effects that the single period control technology is applied to a bridgeless SEPIC-PFC circuit with continuous current and isolation, so that the circuit achieves the effect of power factor correction and can control the output voltage to be stable.

Description

Current continuous control method based on bridgeless SEPIC-PFC circuit

Technical Field

The invention relates to the field of circuit control, in particular to a current continuous control method based on a bridgeless SEPIC-PFC circuit.

Background

The switching power supply has a series of advantages of small volume, high power density and high working efficiency, so that the switching power supply is more and more widely applied. However, as a high-frequency switching power supply for AC/DC conversion or some non-linear loads of AC mains, because the sinusoidal input current waveform of the AC input mains is distorted, a large amount of harmonic current components are generated, which directly affect the power supply quality of the power grid and the safety of users, especially the traditional single-phase diode rectifier bridge used in the front end of electronic equipment. In recent years, foreign and domestic scholars propose a plurality of bridge-free PFC circuits with isolation transformers based on SEPIC circuits, but the bridge-free PFC circuits basically work in an AC side current interrupted state, so that the current stress of a power switch device is increased, and the electromagnetic interference is serious.

One-cycle control (OCC) was proposed by Keyue M Smedley at the university of california in the 90 s of the 20 th century, which is a novel control method that does not require a multiplier. The single-period control idea is based on the duty ratio of a real-time control switch, so that the average value of a controlled quantity waveform in each period is exactly equal to or in direct proportion to a control reference quantity, the average input current tracks the reference current and is not limited by the load current, and the input current cannot be distorted even if the load current has large harmonic waves.

In recent years, the single-cycle control technology is widely applied to the BOOST-PFC circuit, for example, the 'single-cycle control method applied to the bridgeless SEPIC-PFC circuit' with the patent number CN104638900A is a discontinuous current control technology, but is not reported in the application of the bridgeless SEPIC-PFC with the current continuous belt isolation, so that the research on the application of the single-cycle control technology to the bridgeless SEPIC-PFC with the current continuous belt isolation is significant.

Disclosure of Invention

The invention provides a current continuous control method based on a bridgeless SEPIC-PFC circuit, which applies a single-period control technology to the bridgeless SEPIC-PFC circuit with continuous current and isolation to obtain continuous alternating-current side current and higher power factor and is suitable for high-power PFC application occasions.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a current continuous control method based on a bridgeless SEPIC-PFC circuit comprises the following steps:

s1 calculating static voltage gain of main circuit of bridgeless SEPIC-PFC circuit

S2: duty ratio expression

The power factor is corrected by the correction unit,

order to

Substituted into (4) to obtain

(i_L×R_s+n×U_m)×D＝n×U_m(6)

Wherein, U_iFor input voltage, U_oFor the output voltage, n is the ratio of the primary and secondary turns of the transformer, DIs the duty cycle in one switching cycle, i_LFor input of current, R_eIs an equivalent input resistance, R_sIs a sampling resistor; s3: building a circuit, constructing an expression of duty ratio D, and detecting input current i of the main circuit_LOutput voltage U_oConstructing the duty ratio D, using an integrator in the construction, according to the principle of single-period control in a CCM (continuous reduction mode) circuit, the output of the integrator should be

Where t is the integration time, R₁、C₁The product of the resistance and the capacitance used to construct the integrator is the integration time constant of the integrator, U_mThe error between the output voltage and the reference value is subjected to PI regulation to obtain an output value;

s4: using the input current i of the main circuit detected in step S3_LOutput voltage U_oThe expression of duty ratio D is realized through an adder and an integrator, and the output voltage error is obtained after passing through a PI regulator and a reset integrator (i)_L×R_s+n×U_m) X D, and n x U_mThe value of the Pulse Width Modulation (PWM) pulse sequence is output through a comparator and an RS trigger; the on-off control circuit is used for controlling on-off of a switch in the main circuit, when a PWM signal is at a high level, the switch in the main circuit is controlled to be on, when the PWM signal is at a low level, the switch in the main circuit is controlled to be off, and continuous alternating current and the same phase with alternating voltage are achieved through single-cycle control.

Due to the adoption of the technical scheme, the invention has the technical progress that:

the single-period control method is applied to a bridgeless SEPIC-PFC circuit with isolation, which has high practicability, realizes the continuous work of alternating current input current, and enables the input current to automatically track the input voltage and the phase position to achieve the effect of correcting the unit power factor; and the input current is continuous, so that the current stress of a power device is reduced, the PFC circuit is suitable for occasions with larger power, and the practicality is provided for the further development and the wide application of the single-cycle control theory.

Drawings

FIG. 1 is a main circuit diagram of a bridgeless SEPIC-PFC circuit with isolation for use in the present invention;

FIG. 2 is a bridgeless SEPIC-PFC circuit with isolation for current continuous mode single cycle control;

FIG. 3 shows the input voltage and input current waveforms at the AC side when the output voltage is 400V;

FIG. 4 is a waveform of 400V output voltage in the circuit;

FIG. 5 is an amplified waveform of the input current at the AC side when the output voltage is 400V in the circuit;

FIG. 6 shows the input voltage and input current waveforms at the AC side when the output voltage is 200V;

FIG. 7 is a 200V waveform of the output voltage in the circuit;

fig. 8 shows an ac-side input current amplification waveform when the circuit outputs a voltage of 200V.

Detailed Description

The following further describes a specific embodiment of the present invention with reference to the drawings and technical solutions.

(1) Construction of integrators

A linear function of the duty ratio D is constructed, an integrator is used in the construction, and an LF412 chip and a corresponding resistor capacitor can be used in an actual circuit to form the integrator. According to the principle of single-period control in CCM (continuous reduction mode) circuit, the output of the integrator should be

Where t is the integration time, U_mTo output a voltage U_oAnd a reference value U_refThe output value of the error between the two is regulated by PI, and the output of the integrator can be an expression of D by adjusting the parameters.

The expression calculation process for duty ratio D is as follows:

calculating the static voltage gain of the bridge-free SEPIC-PFC circuit with continuous current and isolation:

the purpose of power factor correction is to make the AC input current follow the input voltage, i.e. to achieve U_i＝i_L×R_e

Order to

Substituted type (4)

i_L×R_s×D＝n×U_m-n×U_m×D (6)

(i_L×R_s+n×U_m)×D＝n×U_m (7)

Equation (7) is an expression of the duty ratio D.

In order to meet the condition, the integrator needs to be reset to be a single-period control 0 at the starting moment of each switching period, a reset switch needs to be added to the control circuit, the reset switch and the integrator form a reset integrator, and the DG308 can be selected as the reset switch in practice.

(2) Sampling output voltage and comparing with a voltage reference value to obtain an error, carrying out PI regulation on the error, and selecting proper parameters to obtain U_m(ii) a Building a circuit, constructing an expression of duty ratio D, and detecting input current i of the main circuit_LOutput voltage U_oConstructing the duty ratio D, using an integrator in the construction, according to the principle of single-period control in a CCM (continuous reduction mode) circuit, the output of the integrator should be

Where t is the integration time, R₁、C₁The product of the resistance and the capacitance used to construct the integrator is the integration time constant of the integrator, U_mIs the output value of the error between the output voltage and the reference value after PI regulation.

(3) Pulse Width Modulation (PWM) signal

Output (i) of the integrator_L×R_s+n×U_m) X D and n x U_mCompared with the difference value, the difference value is used as an input signal of the R end of the RS trigger, a multivibrator formed by the NE555 is used for obtaining a 50kHz signal of the S end signal, a signal output by the output end Q of the RS trigger is used for controlling the on-off of a switch in the main circuit,

the signal output by the end is used for controlling the on-off of a reset switch in the integrator.

(4) In order to verify the correctness of the single-cycle control method analyzed in the steps (1), (2) and (3), PSIM simulation is carried out on the circuit, and the parameters, U, of each element in the main circuit can be obtained according to the following conditions_i＝311sin(2π50t)，U_o＝400V，P＝3000W，f_s＝50kHz，Δi_L＝10％i_LN is 1; the simulation result is shown in fig. 3, fig. 4, fig. 5, fig. 6, fig. 7 and fig. 8, wherein fig. 3 is an alternating input voltage waveform and a current waveform, it can be seen from fig. 3 that the input current changes along with the input voltage, and the circuit can realize the purpose of unit power factor correction; FIG. 4 is a graph of the output voltage waveform, which shows that the output voltage can be maintained at a constant 400V DC voltage; FIG. 5 is an amplified waveform of the input current at the AC side, which can be seen to indicate that the converter is operating in a current continuous mode; FIGS. 6, 7 and 8 are simulations for the case where the output voltage is lower than the input voltage peak (311V), and FIG. 6 is a case where the AC input current i is lower than the input voltage peak_LAnd an output voltage U_iThe simulation waveform of (2) can also realize the correction of the unit power factor; FIG. 7 is an output voltage waveform with a stable output DC voltage of 200V; fig. 8 is an amplified waveform of the ac side input current, which can be derived from the converter operating in current continuous mode.

Claims (1)

1. A current continuous control method based on a bridgeless SEPIC-PFC circuit is characterized by comprising the following steps:

s1 calculating static voltage gain of main circuit of bridgeless SEPIC-PFC circuit

S2: duty ratio expression

The power factor is corrected by the correction unit,

order to

Substituted into (4) to obtain

(i_L×R_s+n×U_m)×D＝n×U_m (6)

Wherein, U_iFor input voltage, U_oIn order to output the voltage, the voltage is,n is the ratio of the primary and secondary turns of the transformer, D is the duty cycle in a switching cycle, i_LFor input of current, R_eIs an equivalent input resistance, R_sIs a sampling resistor;

s3: building a circuit, constructing an expression of duty ratio D, and detecting input current i of the main circuit_LOutput voltage U_oConstructing the duty ratio D, using an integrator in the construction, according to the principle of single-period control in a CCM (continuous reduction mode) circuit, the output of the integrator should be

Where t is the integration time, R₁、C₁The product of the resistance and the capacitance used to construct the integrator is the integration time constant of the integrator, U_mThe error between the output voltage and the reference value is subjected to PI regulation to obtain an output value;

s4: using the input current i of the main circuit detected in step S3_LOutput voltage U_oThe expression of duty ratio D is realized through an adder and an integrator, and the output voltage error is obtained after passing through a PI regulator and a reset integrator (i)_L×R_s+n×U_m) X D, and n x U_mThe value of the Pulse Width Modulation (PWM) pulse sequence is output through a comparator and an RS trigger; the on-off control circuit is used for controlling on-off of a switch in the main circuit, when a PWM signal is at a high level, the switch in the main circuit is controlled to be on, when the PWM signal is at a low level, the switch in the main circuit is controlled to be off, and continuous alternating current and the same phase with alternating voltage are achieved through single-cycle control.

Images