A PT-broken iron-coreless LED constant current drive system

Abstract

The present invention discloses an LED constant current driving system without an iron core in the PT broken state, which includes a non-linear saturation controlled voltage source, a transformer without an iron core, an uncontrolled rectification module, an output filter capacitor, m series-connected LED lights, a current sampling circuit, a brightness signal conversion module, an error calculation module, a PI compensator, and a PWM generator; the brightness signal conversion module converts the input brightness value B×100% into an output current set value i ref ; the error calculation module calculates the difference i LED between the current signal i ref and the output current set value i err , uses the PI compensator to perform compensation calculation on the difference i err to obtain an output phase shift angle θ, and the PWM generator outputs a PWM signal according to the phase shift angle θ to control the non-linear saturation controlled voltage source, thereby realizing the adjustment and control of the brightness of the LED lights. The present invention realizes the iron core removal of the isolation transformer in the LED constant current driving system and has a good application effect.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a PT-broken-state iron-core-free LED constant-current driving system. Background Art

[0002] The coreless transformer realizes the coreless transformer, which avoids the saturation of the magnetic core and the magnetic permeability will not be affected by temperature. Therefore, it has become a goal pursued by the power electronics industry.

[0003] In 1998, Professor Bender.CM proposed the use of parity-time (PT) symmetry theory to explain the existence of real characteristic roots of Hamiltonian H in non-Hermitian systems in the article "Real Spectra in Non-Hermitian Hamiltonians Having PT Symmetry". This theory has been successfully applied to many fields such as optics and materials science and has shown great advantages. In 2017, Professor Fan Shanhui of Stanford University proposed a wireless power transmission technology based on the parity-time (PT) symmetry principle in the paper "Robust wireless power transfer using a nonlinear parity-time-symmetric-circuit". The PT symmetry theory was applied to wireless power transmission, which to some extent solved the problems of anti-coil offset and anti-load change.

[0004] The application of PT symmetry theory in coreless transformers has the following characteristics: when the Hamiltonian H of the coreless transformer has real characteristic roots, the system is in a PT symmetric state, showing a constant voltage output characteristic; when there are no real characteristic roots, the system is in a PT symmetry breaking state, showing a constant current output characteristic. The operating frequency of the system in the PT symmetry breaking state corresponds to the natural frequency point of the coreless transformer. Under the premise of no control, the current under light load conditions has serious distortion problems, affecting the quality of power supply. Therefore, by utilizing its PT symmetry breaking state constant current characteristics and optimizing the waveform under light load conditions, the coreless transformer based on PT symmetry is applied to the LED constant current drive system, which will greatly simplify the system parameters and control design, and make the isolated power conversion device de-coreable. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and proposes a PT-broken coreless LED constant current drive system, which realizes the application of coreless transformers in LED constant current drive systems, that is, realizes the coreless isolation transformer in the LED constant current drive system, thereby greatly reducing the cost and weight of the transformer.

[0006] To achieve the above object, the technical solution provided by the present invention is: a PT-broken coreless LED constant current drive system, comprising a nonlinear saturated controlled voltage source, a coreless transformer, an uncontrolled rectifier module, an output filter capacitor, m series-connected LED lamps, a current sampling circuit, a brightness signal conversion module, an error calculation module, a PI compensator and a PWM generator;

[0007] The coreless transformer is composed of a primary series compensation capacitor, a primary leakage inductance, a primary winding stray resistance, an excitation inductance, a primary winding, a secondary winding, a secondary leakage inductance, a secondary series compensation capacitor and a secondary winding stray resistance. One end of the primary series compensation capacitor is connected to one end of a nonlinear saturation controlled voltage source, the other end of the primary series compensation capacitor is connected to one end of the primary leakage inductance, the other end of the primary leakage inductance is respectively connected to one end of the primary winding and one end of the excitation inductance, the other end of the excitation inductance is respectively connected to the other end of the primary winding and one end of the primary winding stray resistance. The other end of the primary winding stray resistance is connected to the other end of the nonlinear saturated controlled voltage source, one end of the secondary leakage inductance is connected to one end of the secondary series compensation capacitor, the other end of the secondary series compensation capacitor is connected to one end of the input of the uncontrolled rectifier module, the other end of the input of the uncontrolled rectifier module is connected to one end of the secondary winding stray resistance, the other end of the secondary winding stray resistance is connected to one end of the secondary winding, and the other end of the secondary winding is connected to the other end of the secondary leakage inductance; the output of the uncontrolled rectifier module is respectively connected to the output filter capacitor and m series LED lamps;

[0008] The current sampling circuit samples the current signal i flowing through the m series-connected LED lamps. LED , the current signal i LED The brightness signal conversion module converts the input brightness value B×100% into the output current given value i ref ; The error calculation module calculates the current signal i LED With the output current given value i ref The difference i err , the difference i err Input to the PI compensator; the PI compensator is used to calculate the difference i err The output phase shift angle θ is obtained by compensation calculation, and the phase shift angle θ is input to a PWM generator; the PWM generator outputs a PWM signal to control a nonlinear saturated controlled voltage source, thereby achieving regulation and control of the brightness of the LED lamp.

[0009] Furthermore, under full load conditions When the system is in the PT symmetry breaking state, it shows the inherent characteristic of constant current, and the output current effective value I LED_h satisfy In the above formula, ω is the output voltage frequency of the nonlinear saturated controlled voltage source; ω p is the resonant frequency of the primary circuit of the coreless transformer, expressed as The turns ratio of the primary and secondary windings is n p :n s ;ω s is the resonant frequency of the secondary circuit of the coreless transformer, expressed as R L is the equivalent load resistance of m LED lamps in series, expressed as C p is the capacitance value of the primary series compensation capacitor, C s is the capacitance value of the secondary side series compensation capacitor, L kp is the inductance value of the primary leakage inductance, L ks is the inductance of the secondary leakage inductance, R s is the resistance value of the secondary winding stray resistance, R p is the resistance value of the primary winding stray resistance, R o is the equivalent resistance value of m LED lamps connected in series, L m is the inductance of the excitation inductance, and the coupling coefficient between the primary and secondary windings is k.

[0010] Furthermore, the brightness signal conversion module converts the input brightness value B×100% into an output current given value i ref , the conversion formula is i ref =I LED_h ×B×100%.

[0011] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0012] 1. Compared with the application of traditional iron core transformers, the isolation transformer of the present invention realizes the elimination of iron core, the device cost is lower and there is no iron core loss of the transformer.

[0013] 2. Compared with the traditional coreless transformer, the coreless transformer based on the PT principle has the characteristics of high-efficiency constant current output in the broken state, and the brightness of the LED lamp can be adjusted through simple control. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the structural block diagram of the PT broken state iron-coreless LED constant current drive system.

[0015] Figure 2 This is the circuit structure diagram of the nonlinear saturated controlled voltage source.

[0016] Figure 3 This is the input and output diagram of the nonlinear saturated controlled voltage source.

[0017] Figure 4The present invention is fully loaded (100% P o ) waveforms of primary winding current and secondary winding current under ) working conditions.

[0018] Figure 5 The light load (20%P o ) waveforms of primary winding current and secondary winding current under ) working conditions. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0020] like Figure 1 As shown, this embodiment discloses a PT-broken coreless LED constant current driving system, including a nonlinear saturated controlled voltage source, a coreless transformer, an uncontrolled rectifier module, an output filter capacitor C o ', m series-connected LED lamps, a current sampling circuit, a brightness signal conversion module, an error calculation module, a PI compensator and a PWM generator;

[0021] The coreless transformer is connected in series with a primary side compensation capacitor C p ', primary leakage inductance L kp ', primary winding stray resistance R p ', Excitation inductance L m ', primary winding, secondary winding, secondary leakage inductance L ks ', secondary side series compensation capacitor C s ' and the secondary winding stray resistance R s ', the primary side series compensation capacitor C p ' is connected to one end of the nonlinear saturation controlled voltage source, and the primary side series compensation capacitor C p The other end of the primary leakage inductance L kp ' is connected to one end, the primary leakage inductance L kp The other end of the primary winding is connected to one end of the primary winding and the excitation inductance L m ' is connected to one end, the excitation inductance L m The other end of the primary winding and the primary winding stray resistance R p ' is connected to one end, the primary winding stray resistance R p The other end of the nonlinear saturation controlled voltage source is connected to the other end of the secondary leakage inductance L ks One end of the ' is connected in series with the secondary side compensation capacitor C s ' is connected to one end, and the secondary side is connected in series with a compensation capacitor C s The other end of the 'is connected to one end of the input of the uncontrolled rectifier module, and the other end of the input of the uncontrolled rectifier module is connected to the secondary winding stray resistance R s' is connected to one end, the secondary winding stray resistance R s The other end of the secondary winding is connected to one end of the secondary winding, and the other end of the secondary winding is connected to the secondary leakage inductance L ks 'The other end is connected; the output of the uncontrolled rectifier module is respectively connected to the output filter capacitor C o 'Connected to m LED lights in series;

[0022] The current sampling circuit samples the current signal i flowing through the m series-connected LED lamps. LED , the current signal i LED The brightness signal conversion module converts the input brightness value B×100% into the output current given value i ref ; The error calculation module calculates the current signal i LED With the output current given value i ref The difference i err , the difference i err Input to the PI compensator; the PI compensator is used to calculate the difference i err The output phase shift angle θ is obtained by compensation calculation, and the phase shift angle θ is input to a PWM generator; the PWM generator outputs a PWM signal to control a nonlinear saturated controlled voltage source, thereby achieving regulation and control of the brightness of the LED lamp.

[0023] Define the characteristic impedance Z of the primary winding p , the characteristic impedance Z of the secondary winding s , the quality factor Q of the primary winding p , the quality factor Q of the secondary winding s , respectively as follows:

[0024]

[0025] The primary and secondary resonant frequencies are equal, so ω0=ω p =ω s ; The circuit expression of the primary and secondary coupling coils is as follows:

[0026]

[0027] In the above formula, ω is the output voltage frequency of the nonlinear saturated controlled voltage source; ω p is the resonant frequency of the primary circuit, which can be expressed as The turns ratio of the primary and secondary windings is n p :n s ;ω s is the resonant frequency of the secondary loop, which can be expressed as R L is the equivalent load resistance of m LED lamps in series, which can be expressed as C pis the capacitance value of the primary series compensation capacitor, C s is the capacitance value of the secondary side series compensation capacitor, L kp is the inductance value of the primary leakage inductance, L ks is the inductance of the secondary leakage inductance, R s is the resistance value of the secondary winding stray resistance, R p is the resistance value of the primary winding stray resistance, R o is the equivalent resistance value of m LED lamps connected in series, L m is the inductance of the excitation inductance; the turns ratio of the coreless transformer is n=n p :n s , the coupling coefficient between the primary and secondary windings is k; U i is the input voltage of the nonlinear saturated controlled voltage source; are the primary and secondary winding current vectors respectively;

[0028] Substituting formula (1) into formula (2), we can get:

[0029]

[0030] There is a non-zero solution to the two-variable homogeneous linear equation system of formula (3), that is, the determinant of the matrix is ​​zero, and we have:

[0031]

[0032] When the original secondary loop parameters satisfy the parity-time symmetry breaking condition, they satisfy:

[0033]

[0034] The system outputs a constant current I in the PT symmetry breaking state. LED_h satisfy As shown in the formula, the output current has nothing to do with the load and exhibits a constant current characteristic.

[0035] When the load condition does not satisfy equation (5), the closed-loop system adjusts the phase shift angle θ to stabilize the output current, thereby achieving brightness control of the LED lamp. When the phase shift angle θ>0, set Then the output effective value of the nonlinear saturated controlled voltage source can be expressed as Among them U i is the input voltage of the nonlinear saturated controlled voltage source. The relationship between the system's current gain, phase shift angle and frequency can be expressed as:

[0036]

[0037] In formula (6), X p is the primary reactance, which can be expressed as X s is the secondary reactance, which can be expressed as The frequency ω and the phase shift angle θ satisfy the following equation, as shown below:

[0038]

[0039] The control method of the above-mentioned PT broken state iron-free LED constant current driving system is to convert the input brightness value B×100% into the output current given value i by the brightness signal conversion module. ref , the conversion formula is: ref =I LED_h ×B×100%; calculate the current signal i through the error calculation module LED With the output current given value i ref The difference i err , using PI compensator to compensate the difference i err The output phase shift angle θ is obtained by compensation calculation. The PWM generator outputs a PWM signal according to the phase shift angle θ to control the nonlinear saturated controlled voltage source, thereby realizing closed-loop control of the brightness of the LED lamp.

[0040] In order to further illustrate the usefulness and feasibility of the present invention, an embodiment is designed for illustration, and its parameters are:

[0041] Primary winding leakage inductance L kp =20uH, primary series capacitor C p =50nF, winding stray resistance R p =100mΩ; secondary winding leakage inductance L ks =20uH, secondary side series capacitor C s =50nF, winding stray resistance R s =100mΩ; the primary and secondary winding turns ratio is n p :n s =25:25, the primary excitation inductance is L m =20uH, the primary and secondary winding coupling coefficient is 0.5, and the negative impedance is Figure 2 The nonlinear saturated controlled voltage source shown is realized, U i =110V. The current value I calculated from the above parameters is LED =6.2A, due to the device's on-state voltage drop, loss, calculation deviation, etc., the given value is set to i ref =6A, due to the control of the closed-loop system, the output can be stable.

[0042] Optionally, the nonlinear saturation controlled voltage source of this embodiment is as follows: Figure 2 As shown, the structure is a full-bridge inverter circuit composed of switch tubes S1, S2, S3 and S4, and the structure is an inverter circuit composed of a first switch tube S1, a second switch tube S2, a third switch tube S3 and a fourth switch tube S4. The input voltage is a DC U iSpecifically, the DC voltage source U i The positive electrode is connected to the first switch tube S1 and the second switch tube S2, and the DC voltage source U i The negative electrode is connected to the third switch tube S3 and the fourth switch tube S4, the first switch tube S1 is connected to the third switch tube S3, the second switch tube S2 is connected to the fourth switch tube S4, and the nonlinear saturation controlled voltage source is not limited to the above structure.

[0043] Figure 3 The output voltage and current diagram of the nonlinear saturated controlled voltage source is shown in Figure 1. The phase difference between the output voltage and current is θ / 2. Assume Then the output effective value of the nonlinear saturated controlled voltage source can be expressed as

[0044] Figure 4 The present invention is fully loaded (100% P o ) The waveform of the primary winding current and the secondary winding current under the working condition. The system is in the PT symmetry breaking state. The system has an inherent constant current characteristic. The constant current charging current value is 6A. At this time, the equivalent load value is 20Ω, and the brightness of the LED lamp is the brightest. Figure 5 The light load (20%P o ) The waveform of the primary winding current and the secondary winding current under the working condition, the current value of constant current charging is 6A, and the equivalent load value is 4Ω at this time.

[0045] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A PT-broken coreless LED constant current drive system, characterized in that: It includes a nonlinear saturated controlled voltage source, a coreless transformer, an uncontrolled rectifier module, and an output filter capacitor (C o '), m series-connected LED lamps, a current sampling circuit, a brightness signal conversion module, an error calculation module, a PI compensator and a PWM generator; The coreless transformer is connected with a primary side series compensation capacitor (C p '), primary leakage inductance (L kp '), primary winding stray resistance (R p '), excitation inductance (L m '), primary winding, secondary winding, secondary leakage inductance (L ks '), secondary side series compensation capacitor (C s ') and secondary winding stray resistance (R s '), the primary side series compensation capacitor (C p One end of the primary side series compensation capacitor (C p ') and the other end of the primary leakage inductance (L kp ') is connected to one end, the primary leakage inductance (L kp ') is connected to one end of the primary winding and the excitation inductance (L m ') is connected to one end, the excitation inductance (L m ') are connected to the other end of the primary winding and the primary winding stray resistance (R p ') is connected to one end of the primary winding, the stray resistance (R p The other end of the secondary leakage inductance (L ks ') is connected in series with the secondary side compensation capacitor (C s ') is connected to one end of the secondary side, and the secondary side is connected in series with a compensation capacitor (C s ') is connected to one end of the input of the uncontrolled rectifier module, and the other end of the input of the uncontrolled rectifier module is connected to the secondary winding stray resistance (R s ') is connected to one end of the secondary winding, the secondary winding stray resistance (R s The other end of the secondary winding is connected to one end of the secondary winding, and the other end of the secondary winding is connected to the secondary leakage inductance (L ks ') is connected to the other end; the output of the uncontrolled rectifier module is respectively connected to the output filter capacitor (C o ') and m LED lamps connected in series; The current sampling circuit samples the current signal i flowing through the m series-connected LED lamps. LED , the current signal i LED The brightness signal conversion module converts the input brightness value B×100% into the output current given value i ref ; The error calculation module calculates the current signal i LED With the output current given value i ref The difference i err , the difference i err Input to the PI compensator; the PI compensator is used to calculate the difference i err The output phase shift angle θ is obtained by compensation calculation, and the phase shift angle θ is input to a PWM generator; the PWM generator outputs a PWM signal to control a nonlinear saturated controlled voltage source, thereby achieving regulation and control of the brightness of the LED lamp.

2. A PT-broken coreless LED constant current drive system according to claim 1, characterized in that: At full load condition When the system is in the PT symmetry breaking state, it shows the inherent characteristic of constant current, and the output current effective value I LED_h satisfy ; above formula, U i is the input voltage of the nonlinear saturated controlled voltage source; is the output voltage frequency of the nonlinear saturated controlled voltage source; is the resonant frequency of the primary circuit of the coreless transformer, expressed as ; The turns ratio of the primary and secondary windings is n p :n s ; is the resonant frequency of the secondary circuit of the coreless transformer, expressed as ; R L is the equivalent load resistance of m LED lamps in series, expressed as ; C p is the capacitance value of the primary series compensation capacitor, C s is the capacitance value of the secondary side series compensation capacitor, L kp is the inductance value of the primary leakage inductance, L ks is the inductance of the secondary leakage inductance, R s is the resistance value of the secondary winding stray resistance, R p is the resistance value of the primary winding stray resistance, R o is the equivalent resistance value of m LED lamps connected in series, L m is the inductance of the excitation inductance, and the coupling coefficient between the primary and secondary windings is k.

3. A PT-broken coreless LED constant current drive system according to claim 2, characterized in that: The brightness signal conversion module converts the input brightness value B×100% into the output current given value i ref , the conversion formula is .

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