CN-115378272-B - Constant-current control system and method for primary side feedback converter

CN115378272BCN 115378272 BCN115378272 BCN 115378272BCN-115378272-B

Abstract

The invention discloses a constant-current control system and method of a primary side feedback converter, comprising a main topology circuit and a control system, wherein the control system comprises an exciting current simulation module, an output current average value calculation module, a PID control module and a PWM driving module, the control system is connected with a switching power supply in the main topology circuit to form a closed loop, the exciting current simulation module comprises an integration module, a proportional amplification module, a first subtracter, a second subtracter and a holding circuit module, the output current average value calculation module outputs an output diode average current signal to the PID control module according to an output signal and a primary side current signal, the PID control module determines the switching period of the next period, and the PWM driving module outputs a driving signal of a switching tube of the main topology circuit based on the switching period. The invention can realize higher-precision constant output current through a primary side feedback control method.

Inventors

WANG CHONG
Cong Lihui
YAO YU
SUN DAYING
SHENG CHUANXIANG
GU WENHUA

Assignees

南京理工大学

Dates

Publication Date: 20260505
Application Date: 20220822

Claims (9)

1. The primary side feedback converter constant current control system comprises a main topology circuit and a control system, and is characterized in that the control system comprises an exciting current simulation module, an output current average value calculation module, a PID control module and a PWM driving module, wherein the control system is connected with a switching power supply in the main topology circuit to form a closed loop, and the control system comprises: The exciting current simulation module comprises an integration module, a proportional amplification module, a first subtracter, a second subtracter and a holding circuit module, wherein the primary winding voltage v aux (t) of the main topology circuit passes through the integration module to obtain an integrated value v aux_int (t), the proportional amplification module carries out proportional amplification on v aux_int (t) to obtain a variable signal I m_ac (t) containing exciting current, the first subtracter carries out subtraction on I m_ac (t) and a numerical value I m at a known moment t kn of exciting current, the output direct current voltage of the first subtracter is held by the holding circuit module at the known moment t kn to obtain a direct current deviation I dc of I m_ac (t) and I m (t), and the second subtracter carries out subtraction on the direct current deviation I dc in I m_ac (t) to obtain an exciting current I m (t) to the output current average value calculation module; The output current average value calculation module outputs a diode average current signal i o (t) to the PID control module according to the output signal i m (t) and the primary side current signal i p (t); The PID control module determines a switching period T s of the next period and inputs the switching period T s to the PWM driving module; the PWM driving module outputs a driving signal of a switching tube of the main topology circuit based on a switching period T s .
2. The primary-side feedback converter constant current control system according to claim 1, wherein the integration module obtains an integrated value v aux_int (t) as: Where v aux_int (0) is the initial bias of the integrator and the primary winding voltage v aux (t) is the voltage of the primary main winding or auxiliary winding or its partial voltage, expressed as: v m (t) is the voltage on the primary winding of the transformer, if v aux (t) is the primary winding voltage division, then N a is equal to the primary winding turns N p ,R 1 and R 2 are the voltage division resistances, and if v aux (t) is from the auxiliary winding voltage division, then N a ,N p is the primary winding and auxiliary winding turns, respectively.
3. The primary-side feedback converter constant current control system according to claim 2, wherein the variable signal i m_ac (t) output by the proportional amplifying module is: Wherein i m_ac (0) is equal to v aux_int (0), and k is a proportionality coefficient.
4. A primary-side feedback converter constant current control system according to claim 3, wherein the scaling factor k is: Wherein, L m is excitation inductance.
5. The constant current control system of the primary feedback converter according to claim 1, wherein the output current average value calculating module includes a third subtracter and a proportional integrator, the difference between the primary current and the magnetizing current is obtained through the third subtracter, and the output current i o (t) is obtained by proportional integration of the difference: wherein N s is the number of secondary winding turns.
6. The primary-side feedback converter constant current control system according to claim 1, wherein the proposed PID control module determines the switching period T s by error calculation, PID calculation compensation calculation.
7. The primary-side feedback converter constant current control system according to claim 1, wherein the PWM driving module turns on the switching tube by setting the switching tube control signal to 1 every T s length.
8. The primary-side feedback converter constant current control system of claim 1, wherein the primary topology circuit employs a primary-side feedback active clamp flyback converter architecture.
9. A control method based on the primary-side feedback converter constant-current control system of any one of claims 1 to 8, comprising the steps of: The primary winding voltage v aux (t) of the main topology circuit passes through an integration module to obtain an integrated value v aux_int (t), a proportional amplification module is used for carrying out proportional amplification on v aux_int (t) to obtain a variable signal I m_ac (t) containing exciting current, a first subtracter is used for subtracting a value I m at a known time t kn of the exciting current from I m_ac (t), the output direct current voltage of the first subtracter is maintained through a maintaining circuit module at the known time t kn to obtain a direct current deviation I dc of I m_ac (t) and I m (t), and a second subtracter is used for subtracting the direct current deviation I dc in I m_ac (t) to obtain exciting current I m (t) to an output current average value calculation module; the output current average value calculation module outputs a diode average current signal i o (t) to the PID control module according to the output signal i m (t) and the primary side current signal i p (t); The PID control module determines a switching period T s of the next period and inputs the switching period T s to the PWM driving module; The PWM driving module outputs a driving signal of a switching tube of the main topology circuit based on a switching period T s , and controls the output current of the primary side feedback converter to be constant current.

Description

Constant-current control system and method for primary side feedback converter Technical Field The invention relates to the technical field of isolated converters, in particular to a constant-current control system and method for a primary side feedback converter. Background The requirement for power supplies, high power density and high efficiency, is a long-standing trend in the consumer electronics market. With the development of technology, the switch power supply is widely applied to occasions with medium and small power, and the isolation switch power supply can realize the electrical isolation of input and output and has the characteristics of safe isolation and high reliability. Traditionally, secondary side feedback converters utilize optocouplers to feed output information back to the primary side control circuit, which is a simple and efficient method. However, due to the nonlinearity of the optocoupler and temperature drift, the reliability of the system is affected. To overcome this disadvantage, a Primary Side Regulation (PSR) ac-dc converter is used. In PSR flyback ac-dc converters, a number of constant output current control schemes have been proposed. In Discontinuous Conduction Modulation (DCM) mode, the output current can be achieved by a peak current control method, since the output current is predicted from the primary peak current, demagnetization time and switching cycle available for primary side control. With the demand for higher power, the control algorithm of PSR control in CCM operation is getting more and more emphasized, and an effective multimode scheme suitable for DCM and CCM modes is applied. In the prior art, an analog control scheme based on detecting the primary current in the middle of the on-time of the main switch is proposed. And the power switch conduction instant current sampling error caused by current spikes is avoided. However, in a high frequency nonlinear flyback converter, it is not possible to estimate the output current due to the nonlinearity of the output diode current. With reference to the PSR control scheme in an LLC resonant converter, the output current can be estimated from the "magnetizing current cancellation method". This method allows the magnetizing current to be restored with a single parameter, but requires a complex control circuit. In the existing improvement, the magnetizing current can be completely cancelled by the low cost resistor and capacitor in the series RC branch, however, the voltage of the capacitor in the RC branch is ignored compared to the auxiliary winding voltage, which will affect the simulation accuracy of the magnetizing current. Disclosure of Invention The invention aims to provide a constant-current control system and method for a primary side feedback converter, which simplify a control circuit and improve the accuracy of output current. The technical solution for realizing the purpose of the invention is as follows: A constant-current control system of a primary side feedback converter comprises a main topology circuit and a closed-loop control system. The main topology circuit adopts a transformer to realize the electrical isolation of input and output, and the output signals are primary winding voltage and primary main winding current. The closed-loop control system comprises an excitation current simulation module, an output diode current average value calculation module, a PID control module and a PWM driving module, wherein the control system is connected with a controlled switching power supply to form a closed loop, and the high-precision constant output current can be realized through a primary side feedback control method. The exciting current simulation module is input with a primary winding voltage signal v aux (t), exciting current I m at a known time t kn, output signals are exciting current I m (t), and exciting current I m (t) is input to the output current average value calculation module. the exciting current simulation module comprises five sub-modules, namely an integrating module, a proportional amplifying module, a first subtracter, a second subtracter and a holding circuit module. The primary winding voltage v aux (t) is the voltage of the primary main winding or the auxiliary winding or the partial voltage thereof, v aux (t) is in a proportional relation with the voltage of the primary main winding, v aux (t) is subjected to an integration module to obtain an integrated value v aux_int (t), a proportional amplification module is used for carrying out proportional amplification on v aux_int (t) to obtain a variable signal I m_ac (t) containing exciting current, a first subtracter is used for subtracting a specific value I m when I m_ac (t) and a known time t kn of the exciting current are carried out, the output direct current voltage of the first subtracter is maintained through a maintaining circuit module at the known time to obtain a direct current deviation I dc of I m_ac (t) and I m (