Primary side feedback converter constant current control system and method

Abstract

This invention discloses a constant current control system and method for a primary-side feedback converter, comprising a main topology circuit and a control system. The control system includes an excitation current simulation module, an output current average value calculation module, a PID control module, and a PWM drive module. This control system is connected to the switching power supply in the main topology circuit to form a closed loop. The excitation current simulation module includes an integrator module, a proportional amplifier module, a first subtractor, a second subtractor, and a holding circuit module. The output current average value calculation module outputs the average current signal of the output diode to the PID control module based on the output signal and the primary-side current signal. The PID control module determines the switching cycle for the next cycle, and the PWM drive module outputs the drive signal for the switching transistors of the main topology circuit based on the switching cycle. This invention can achieve a high-precision constant output current through a primary-side feedback control method.

Description

Technical Field

[0001] This invention relates to the field of isolated converter technology, and in particular to a constant current control system and method for a primary-side feedback converter. Background Technology

[0002] For power supplies, high power density and high efficiency are long-term trends in the consumer electronics market. With technological advancements, switching power supplies are widely used in low-to-medium power applications. Isolated switching power supplies can achieve electrical isolation between input and output, offering features such as safety isolation and high reliability.

[0003] Traditionally, secondary-side feedback converters utilize optocouplers to feed output information back to the primary-side control circuit, a simple and effective method. However, the reliability of the system is affected by the nonlinearity and temperature drift of the optocouplers. To overcome this drawback, primary-side regulation (PSR) AC / DC converters are employed. In PSR flyback AC / DC converters, many constant output current control schemes have been proposed. In discontinuous conduction modulation (DCM) mode, the output current can be achieved through peak current control, as the output current is predicted based on the available primary peak current, demagnetization time, and switching cycle.

[0004] With the increasing demand for higher power, control algorithms for PSR control in CCM operation are receiving more and more attention, and effective multi-mode schemes applicable to both DCM and CCM modes are being applied. In existing technologies, a simulation control scheme based on detecting the primary current during the main switch's on-time has been proposed. This avoids the current sampling error caused by current spikes during power switch on-time. However, in high-frequency nonlinear flyback converters, due to the nonlinearity of the output diode current, it cannot estimate the output current. Referring to the PSR control scheme in LLC resonant converters, the output current can be estimated using the "magnetization current cancellation method." This method can recover the magnetization current using primary parameters, but it requires complex control circuitry. In existing improved schemes, the magnetization current can be completely canceled by a low-cost resistor and capacitor in the series RC branch; however, the voltage of the capacitor in the RC branch is neglected compared to the auxiliary winding voltage, which affects the simulation accuracy of the magnetization current. Summary of the Invention

[0005] The purpose of this invention is to provide a constant current control system and method for a primary-side feedback converter, which simplifies the control circuit and improves the accuracy of the output current.

[0006] The technical solution to achieve the purpose of this invention is as follows:

[0007] A constant current control system for a primary-side feedback converter comprises two parts: a main topology circuit and a closed-loop control system. The main topology circuit uses a transformer to achieve electrical isolation between the input and output, and its output signals are the primary winding voltage and the primary winding current.

[0008] The closed-loop control system includes an excitation current simulation module, an output diode current average value calculation module, a PID control module, and a PWM drive module. This control system is connected to the controlled switching power supply to form a closed loop. The present invention can achieve a high-precision constant output current through the primary-side feedback control method.

[0009] The excitation current simulation module receives the primary winding voltage signal v as its input. aux (t), at a known time t kn Excitation current I at time m The output signal is the excitation current i m (t), excitation current i m (t) Input to output current average value calculation module. The excitation current simulation module includes five sub-modules: an integration module, a proportional amplifier module, a first subtractor, a second subtractor, and a holding circuit module. Among them, the primary winding voltage v... aux (t) is the voltage of the primary winding or auxiliary winding, or its voltage division, v aux (t) is proportional to the voltage of the primary winding, v aux (t) The integral value v is obtained after passing through the integration module. aux_int (t), the scaling module for v aux_int (t) is proportionally amplified to obtain a variable signal i containing the excitation current. m_ac (t); The first subtractor will subtract i m_ac (t) and the known time t of the excitation current kn The specific value of time I m By performing the subtraction and holding the output DC voltage of the first subtractor at that known moment through the holding circuit module, i can be obtained. m_ac (t) and i m DC deviation i of (t) dc The second subtractor will subtract i m_ac DC deviation i in (t) dc Subtracting this will give you the excitation current i. m (t). The specific calculation formula is as follows.

[0010] First, v aux (t) can be obtained by the integration module, which yields its integral value v. aux_int (t), i m_ac (t) via v aux_int (t) is obtained by scaling up, and the expression is as follows:

[0011]

[0012]

[0013] Where v aux_int (0) is the initial deviation of the integrator, i m_ac (0) and v aux_int (0) Equal, k is the proportionality coefficient. Primary winding voltage v aux (t) is the voltage of the primary winding or auxiliary winding, or its voltage division, and its expression is:

[0014]

[0015] v m (t) is the voltage on the primary winding of the transformer. If v aux (t) comes from the main winding component voltage, then N a Equal to the number of turns N of the main winding p R1 and R2 are voltage divider resistors; if v aux (t) comes from the auxiliary winding voltage, then N a N p These represent the number of turns in the main winding and the auxiliary winding, respectively, and R1 and R2 are voltage divider resistors.

[0016] Therefore i m_ac The formula (t) can be expressed as follows:

[0017]

[0018] i m_ac (t) Relative excitation current i m The expression for the DC deviation is as follows:

[0019] i dc =i m_ac (0)-i m (0)≈i m_ac (0)

[0020] Typically, the excitation current is zero when the switch is first turned on, then i m (0) equals zero, and the DC component can be approximated by the initial value i of the integral. m_ac (0).

[0021] Remember, I m It is a known time t kn The value of the excitation current at that time can be obtained from the primary current, control signal, primary winding voltage, etc. (For example, in a flyback converter, when the switching transistor control signal duty is "1", the excitation current is equal to the primary winding current, that is, I has I at this stage.) mThe current is equal to the primary winding current; in an LLC resonant converter, when the output diode current drops to zero, i.e., when the primary winding voltage reaches an inflection point, the value of the magnetizing current is equal to the value of the primary winding current, i.e., at this moment, I... m (This is equal to the primary winding current.)

[0022] After the first subtractor, i m_ac (t) minus the known time t kn Excitation current I at time m By keeping the output of the circuit module constant, i can be obtained. m_ac( t) and i m DC deviation i of (t) dc .

[0023] i dc =i m_ac (t kn )-I m

[0024] After passing through the second subtractor, i m_ac (t) Subtract the DC deviation i from the output of the holding circuit module dc The excitation current i can then be obtained. m (t).

[0025] i m (t)=i m_ac (t)-i dc

[0026] Furthermore, the proposed output current average value calculation module takes as input the output signal i from the excitation current simulation module. m (t) and primary current signal i p (t), whose output signal is the output diode current signal i o (t). i o (t) is sent to the PID control module to generate the loop compensation control signal. The average value of the output current is calculated using two submodules: a third subtractor and a proportional-integral converter. The specific calculation formula is as follows.

[0027] Due to the magnetizing current i m and primary current i p The difference between them is proportional to the current of the output diode, therefore i can be obtained. d (t). N p and N s These are the number of turns in the primary winding and the secondary winding, respectively. The difference between the primary current and the magnetizing current can be obtained through the third subtractor. The output current i is obtained by proportional-integral calculation of this difference. o (t).

[0028]

[0029] Furthermore, the input signal of the PID control module is the predicted average current i of the output diode. o The switching period T is calculated using algorithms such as error calculation and PID operation compensation. s The goal is to make i o (t) is equal to the target reference current I to be achieved. REF .

[0030] Furthermore, the PWM drive module implements duty cycle control, and its input signal is the switching period T. s The output is the drive signal for the switching transistor, based on T. s Size, every T s When the length is set to "1", the switching transistor is turned on.

[0031] A control method for a constant current control system based on the aforementioned primary-side feedback converter includes:

[0032] The primary winding voltage v of the main topology circuit aux (t) The integral value v is obtained after passing through the integration module. aux_int (t), the scaling module for v aux_int (t) is proportionally amplified to obtain a variable signal i containing the excitation current. m_ac (t); The first subtractor will subtract i m_ac (t) and the known time t of the excitation current kn The value of I at that time m Perform the subtraction, and at that known time t kn The output DC voltage of the first subtractor is held by a holding circuit module to obtain i. m_ac (t) and i m DC deviation i of (t) dc The second subtractor will subtract i m_ac DC deviation i in (t) dc Subtract to obtain the excitation current i m (t), to the output current average value calculation module;

[0033] The average output current calculation module calculates the average output current based on the output signal i m (t) and primary current signal i p (t), the average current signal of the output diode i o (t) is sent to the PID control module;

[0034] The PID control module determines the switching period T for the next cycle. s The input is sent to the PWM driver module;

[0035] The PWM drive module is based on the switching period T.s The drive signal for the switching transistor of the main topology circuit is output to control the output current of the primary-side feedback converter to be constant.

[0036] Compared with the prior art, the significant advantages of the present invention are:

[0037] (1) The excitation current simulation module proposed in this invention obtains the excitation current through the primary winding current and the primary winding voltage, realizes the accurate simulation of the output diode current in the nonlinear converter, overcomes the error in the existing excitation current restoration technology, improves the accuracy of the output current, and helps to develop the output control of the converter.

[0038] (2) The present invention adopts the primary-side feedback control method, which adjusts the circuit structure of the primary-side feedback converter without increasing the circuit complexity; it can eliminate optocouplers and simplify control, and avoid nonlinear and temperature drift optocouplers to realize the feedback of output signals, which has the advantages of low cost, simple control and high precision.

[0039] (3) The present invention can be applied to isolated or non-isolated switching power supply circuit structures, and has versatility, reusability and portability. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the circuit topology and loop control of the present invention.

[0041] Figure 2 This is a schematic diagram of the circuit topology and loop control implementation of a primary-side feedback active clamp flyback converter.

[0042] Figure 3 This is the waveform diagram of the primary-side feedback active clamp flyback converter.

[0043] Figure 4 This is a waveform diagram of the control loop of a primary-side feedback active clamp flyback converter. Detailed implementation method:

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] See Figure 1This invention discloses a constant current system for a primary-side feedback switching converter, comprising a main topology circuit and a closed-loop control system. The main topology circuit uses a transformer to achieve electrical isolation between the input and output, and its output signals are the primary winding voltage and the primary winding current. The proposed closed-loop control system includes an excitation current simulation module, an output current average value calculation module, a PID control module, and a PWM drive module. This control system is connected to the controlled switching power supply to form a closed loop. This invention can achieve a high-precision constant output current through the primary-side feedback control system.

[0046] This invention takes a primary-side feedback active clamp flyback converter as an example. Figure 2 This is a schematic diagram of the constant current system and control method of the primary-side feedback active clamp flyback converter, which mainly includes two parts: the main topology circuit and the closed-loop control system.

[0047] The main topology circuit adopts a primary-side feedback active clamp flyback converter structure, which is as follows: the negative terminal of the input DC voltage is connected to the input ground terminal, and the positive terminal of the input DC voltage is connected to the primary winding W of the transformer. p The opposite end, primary winding W p The terminal with the same name is connected to the drain of the switching transistor Q1, and the source of the switching transistor Q1 is connected to ground. The clamping circuit adopts an active clamping structure, including the switching transistor Q2 and the clamping capacitor C. r and sampling resistor R cs In this configuration, the source terminal of switch Q2 is connected to the same-name terminal of the primary winding, and the drain terminal of switch Q2 is connected to the clamping capacitor C. r Sampling resistor R cs When connected in series with the clamping capacitor using the above connection method, the current flowing into the clamping capacitor can be connected to C. r series resistor R cs Induction to generate an induced voltage V cs Output winding W s The same terminal is connected to the positive terminal of the output diode D1, and the output winding W... s The opposite terminal is connected to the output ground, and the negative terminal of the output diode is connected to the output capacitor C. l Positive terminal, output capacitor C l The negative terminal is connected to the output ground, and the load R L With capacitor C L Parallel connection; the transformer adds a primary auxiliary winding W. a The auxiliary winding's opposite-named terminal is connected to the input ground, and the same-named terminal is connected to a resistor voltage divider circuit to divide the voltage at the same-named terminal of the winding. The divided voltage value is the feedback voltage V. aux The input signal is given to the closed-loop control system. The input signal to the closed-loop control system is the feedback voltage v of the auxiliary winding. aux Primary winding current i pThe output signals are the control signal duty1 of switch Q1 and the control signal duty2 of switch Q2.

[0048] The closed-loop control system includes an excitation current simulation module, an output current average value calculation module, a PID control module, and a PWM drive module. This control system is connected to the controlled switching power supply to form a closed loop. This invention can achieve a high-precision constant output current through the primary-side feedback control method.

[0049] The proposed excitation current simulation module takes the primary winding voltage signal v as its input. aux (t), at a known time t kn Excitation current I at time m The output signal is the excitation current i m (t), excitation current i m (t) Input to output current average value calculation module. The excitation current simulation module includes five sub-modules: an integration module, a proportional amplifier module, a first subtractor, a second subtractor, and a holding circuit module. Among them, the primary winding voltage v... aux (t) is the voltage of the primary winding or auxiliary winding, or its voltage division, v aux (t) is proportional to the voltage of the primary winding, v aux (t) The integral value v is obtained after passing through the integration module. aux_int (t), the scaling module for v aux_int (t) is proportionally amplified to obtain a variable signal i containing the excitation current. m_ac (t); The first subtractor will subtract i m_ac (t) and the known time t of the excitation current kn Specific value I m By performing the subtraction and holding the output DC voltage of the first subtractor at that known moment through the holding circuit module, i can be obtained. m_ac (t) and i m DC deviation i of (t) dc The second subtractor will subtract i m_ac DC deviation i in (t) dc Subtracting this will give you the excitation current i. m (t).

[0050] The current average value calculation module includes a third subtractor and a proportional-integral (PI) converter. The output of the third subtractor is connected to the input of the PI converter, and the PI converter outputs the diode current signal i. o (t) is fed into the PID control module;

[0051] Figure 4 These are the operating waveforms of the control loop of the primary-side feedback active clamp flyback converter, representing the duty cycles of the switching transistors: duty1, duty2, and v.aux_int (t), i m_ac (t), i p (t), i m (t), I m i d (t), i o (t) and the waveform of the on-time of switch S1 at a specific moment. v aux_int (t) by v aux (t) is obtained after passing through a reverse phase integrator, v aux_int (t1) is v aux_int The value of (t) at t1, where t1 is the moment when switch Q1 starts conducting. R int and C int It is a discrete element of an integrating circuit.

[0052]

[0053] Primary winding voltage v aux (t) is the voltage division of the primary auxiliary winding, from Figure 2 The voltage is obtained by dividing R1 and R2 in the circuit, v m (t) is the voltage on the primary winding of the transformer; N a N p These represent the number of turns in the main winding and the auxiliary winding, respectively. The voltage across the auxiliary winding has the opposite polarity to the voltage across the primary winding.

[0054]

[0055]

[0056] You can see v aux_int (t), the proportional relationship between the AC ripple of its current and the ripple of its excitation current, can also be seen from... Figure 4 It was observed in the middle.

[0057] i m_ac (t) via v aux_int (t) is obtained by scaling up, i m_ac (t1) and v aux_int (t1) are equal, and k is the proportionality coefficient, expressed as follows:

[0058]

[0059] When the proportionality constant k satisfies the following relationship

[0060]

[0061] i m_ac The formula (t) can be expressed as follows:

[0062]

[0063] i m_ac (t) Relative excitation current i m The expression for the DC deviation is as follows:

[0064] i dc =i m_ac (t1)-i m (t1)≈i m_ac (t1)

[0065] When the switching transistor Q1 starts conducting, the magnetizing current is zero, i.e. m (t1) equals zero, and the DC component can be approximated by the initial value i of the integral. m_ac (t1).

[0066] Figure 3 These are the operating waveforms of the primary-side feedback active clamp flyback converter, representing the duty cycles of the switching transistors: duty1, duty2, and i. p (t), i m (t), i d The waveform of (t) shows that when the control signal duty1 of the switching transistor Q1 is "1", the excitation current is equal to the primary winding current, that is, I has I during this stage. m Equal to the primary winding current i p .

[0067] After the first subtractor, i m_ac (t) minus the known time t n Excitation current I at time m ,Right now Figure 4 I in m The waveform is obtained by keeping the output constant through the holding circuit module, thus obtaining i. m_ac( t) and i m DC deviation i of (t) dc The circuit switch control signal is... Figure 4 The S1 waveform in the image.

[0068] i dc =i m_ac (t n )-I m

[0069] After passing through the second subtractor, i m_ac (t) Subtract the DC deviation i from the output of the holding circuit module dc The excitation current i is obtained. m (t), that is Figure 4 i in m The waveform of (t). This simulated excitation waveform is transmitted to the output current average value calculation module.

[0070] i m (t)=i m_ac (t)-i dc

[0071] The proposed output current average value calculation module takes the output signal i from the excitation current simulation module as its input signal. m (t) and primary current signal i p (t), i p (t) waveform as shown Figure 4 As shown.

[0072] Its output signal is the average current signal i of the output diode. o (t) is then sent to the PID control module to generate a loop compensation control signal. The output current average value calculation module includes two submodules: a third subtractor and a proportional-integral converter.

[0073] Due to the magnetizing current i m and primary current i p The difference between them is proportional to the current of the output diode, therefore the diode current i can be obtained. d (t), that is Figure 4 i in d (t) Waveform. N p and N s These are the number of turns in the primary winding and the secondary winding, respectively. The difference between the primary current and the magnetizing current can be obtained through the third subtractor. The output current i is obtained by proportional-integral calculation of this difference. o (t), that is Figure 4 i in o (t) Waveform.

[0074]

[0075] The proposed PID calculation module takes the average current i of the output diode as its input signal. o The switching period T is calculated using algorithms such as error calculation and PID operation compensation. s The goal is to make i o (t) is equal to the target reference current I to be achieved. REF The calculated result T s The data is transmitted to the PWM driver module, which implements duty cycle control based on T. s Size, every T s When the length is set to "1", the switching transistor is turned on.

[0076] A control method for a constant current control system based on the aforementioned primary-side feedback converter includes:

[0077] The primary winding voltage v of the main topology circuitaux (t) The integral value v is obtained after passing through the integration module. aux_int (t), the scaling module for v aux_int (t) is proportionally amplified to obtain a variable signal i containing the excitation current. m_ac (t); The first subtractor will subtract i m_ac (t) and the known time t of the excitation current kn The value of I at that time m Perform the subtraction, and at that known time t kn The output DC voltage of the first subtractor is held by a holding circuit module to obtain i. m_ac (t) and i m DC deviation i of (t) dc The second subtractor will subtract i m_ac DC deviation i in (t) dc Subtract to obtain the excitation current i m (t), to the output current average value calculation module;

[0078] The average output current calculation module calculates the average output current based on the output signal i m (t) and primary current signal i p (t), the average current signal of the output diode i o (t) is sent to the PID control module;

[0079] The PID control module determines the switching period T for the next cycle. s The input is sent to the PWM driver module;

[0080] The PWM drive module is based on the switching period T. s The drive signal for the switching transistor of the main topology circuit is output to control the output current of the primary-side feedback converter to be constant.

[0081] The method encompasses all the technical features of the corresponding system, which will not be elaborated upon here.

[0082] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the invention is limited to these descriptions. Many variations of the invention described herein are possible, and constant current algorithms can be used for control in other switching power supplies. Such variations should not deviate intentionally from the spirit and scope of the invention. Therefore, all modifications that are obvious to those skilled in the art should be included within the scope of these claims.

Claims

1. A constant current control system for a primary-side feedback converter, comprising a main topology circuit and a control system, characterized in that: The control system includes an excitation current simulation module, an output current average value calculation module, a PID control module, and a PWM drive module. This control system is connected to the switching power supply in the main topology circuit to form a closed loop; wherein: The excitation current simulation module includes an integrator module, a proportional amplifier module, a first subtractor, a second subtractor, and a holding circuit module; wherein, the primary winding voltage v of the main topology circuit... aux (t) The integral value v is obtained after passing through the integration module. aux_int (t), the scaling module for v aux_int (t) is proportionally amplified to obtain a variable signal i containing the excitation current. m_ac (t); The first subtractor will subtract i m_ac (t) and the known time t of the excitation current kn The value of I at that time m Perform the subtraction, and at that known time t kn The output DC voltage of the first subtractor is held by a holding circuit module to obtain i. m_ac (t) and i m DC deviation i of (t) dc The second subtractor will subtract i m_ac DC deviation i in (t) dc Subtract to obtain the excitation current i m (t), to the output current average value calculation module; The average output current calculation module calculates the average output current based on the output signal i m (t) and primary current signal i p (t), whose output signal is the average current signal i of the output diode. o (t) is sent to the PID control module; The PID control module determines the switching period T for the next cycle. s The input is sent to the PWM driver module; The PWM drive module is based on the switching period T. s Output the drive signal for the switching transistor of the main topology circuit.

2. The primary-side feedback converter constant current control system according to claim 1, characterized in that, The integration module obtains its integral value v. aux_int (t) is: Where v aux_int (0) is the initial deviation of the integrator, and the primary winding voltage v aux (t) is the voltage of the primary winding or auxiliary winding, or its voltage division, and its expression is: v m (t) is the voltage on the primary winding of the transformer, if v aux (t) is the main winding component voltage, then N a Equal to the number of turns N of the main winding p R1 and R2 are voltage divider resistors; if v aux (t) comes from the auxiliary winding voltage, then N a N p These are the number of turns in the main winding and the auxiliary winding, respectively.

3. The primary-side feedback converter constant current control system according to claim 2, characterized in that, The variable signal i output by the proportional amplification module m_ac (t) is: Among them, i m_ac (0) and v aux_int (0) are equal, and k is the proportionality coefficient.

4. The primary-side feedback converter constant current control system according to claim 3, characterized in that, The proportionality coefficient k is: Among them, L m It is the magnetizing inductor.

5. The primary-side feedback converter constant current control system according to claim 1, characterized in that, The output current average value calculation module includes a third subtractor and a proportional-integral (PI) converter. The difference between the primary current and the magnetizing current is obtained through the third subtractor, and the output current i is obtained by proportional-integrating the difference. o (t) is: Where, N s This represents the number of turns in the secondary winding.

6. The primary-side feedback converter constant current control system according to claim 1, characterized in that, The proposed PID control module determines the switching period T through error calculation and PID operation compensation calculation. s .

7. The primary-side feedback converter constant current control system according to claim 1, characterized in that, The PWM drive module is every T. s When the length is reached, the switch control signal is set to 1, and the switch is turned on.

8. The primary-side feedback converter constant current control system according to claim 1, characterized in that, The main topology circuit adopts a primary-side feedback active clamp flyback converter structure.

9. A control method for a constant current control system based on a primary-side feedback converter according to any one of claims 1 to 8, characterized in that, include: The primary winding voltage v of the main topology circuit aux (t) The integral value v is obtained after passing through the integration module. aux_int (t), the scaling module for v aux_int (t) is proportionally amplified to obtain a variable signal i containing the excitation current. m_ac (t); The first subtractor will subtract i m_ac (t) and the known time t of the excitation current kn The value of I at that time m Perform the subtraction, and at that known time t kn The output DC voltage of the first subtractor is held by a holding circuit module to obtain i. m_ac (t) and i m DC deviation i of (t) dc The second subtractor will subtract i m_ac DC deviation i in (t) dc Subtract to obtain the excitation current i m (t), to the output current average value calculation module; The average output current calculation module calculates the average output current based on the output signal i m (t) and primary current signal i p (t), the average current signal of the output diode i o (t) is sent to the PID control module; The PID control module determines the switching period T for the next cycle. s The input is sent to the PWM driver module; The PWM drive module is based on the switching period T. s The drive signal for the switching transistor of the main topology circuit is output to control the output current of the primary-side feedback converter to be constant.

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