A current detection type synchronous rectification control method based on Rogowski coil

Abstract

The present invention relates to a current detection type synchronous rectification control method based on Rogowski coil, which is implemented as follows: in a full-bridge LLC resonant circuit, the secondary current is is detected by a Rogowski coil (Rogowski Coil), and is compared with a bias voltage Vbias after passing through an analog signal conditioning circuit to generate a series of zero-crossing detection pulses ZCD. The ZCD signal is captured by a capture module of a DSP to obtain the phase shift angle and conduction time of the corresponding synchronous rectifier tube relative to the primary switch tube.

Description

Technical Field

[0001] The invention relates to a synchronous rectification control method of an LLC resonant converter of an LED driving power supply, and in particular to a synchronous rectification control method based on a Rogowski coil current detection type. Background Art

[0002] For high-power LED driver power supplies, their high-power LED loads are mostly connected in series first and then in parallel to form a lighting system, and their subsequent DC / DC usually operates under low voltage and high current conditions. When silicon-based (Si) diodes are used for uncontrolled rectification on the low-voltage side, the efficiency of the subsequent DC / DC will be significantly reduced due to the large conduction loss when the diode is forward-conducted and the influence of reverse recovery loss. To solve this problem, synchronous rectification technology is widely used in DC / DC with low voltage and high current output.

[0003] The LLC resonant converter can simultaneously realize ZVS turn-on of the primary side and ZCS turn-off of the secondary side as well as magnetic integration, and is widely used as a post-stage DC / DC in high-power LED driver power supplies. In order to further realize high-efficiency and high-power density DC / DC LLC resonant converters, gallium nitride power devices (GaNHEMTs) have gradually been applied to LLC resonant converters. However, the three traditional synchronous rectification methods used in LLC resonant converters - voltage detection type, current drive type and sensorless synchronous rectification method - cannot meet the application requirements of GaN HEMT for high switching frequency or high efficiency. There is an urgent need to study a new type of efficient synchronous rectification control method. Summary of the invention

[0004] The technology of the present invention solves the problem: in view of the current situation that the traditional voltage detection type synchronous rectification method is not suitable for the high-frequency and high-current LLC resonant converter based on GaN HEMTs, a new Rogowski coil current detection type synchronous rectification control method for detecting the secondary current is provided.

[0005] Technical solution of the present invention: A current detection type synchronous rectification control method based on Rogowski coil is implemented as follows: In the full-bridge LLC resonant circuit, the secondary current of the LLC resonant converter is It is detected by a Rogowski coil and then coupled with the bias voltage after passing through the analog signal conditioning circuit. Vbias By comparison, a series of zero-crossing detection pulses ZCD are generated. After the ZCD signal is captured by the digital controller, the phase shift angle and conduction time of the corresponding synchronous rectifier tube relative to the primary switch tube are obtained. Based on the complete symmetry of the secondary-side rectification H-bridge topology of the LLC resonant converter and the consistency of the hardware design, the driving waveforms of the eight synchronous rectifier tubes are determined through one ZCD signal, and the synchronous rectification work of the LLC resonant converter is realized by adjusting the on and off of the synchronous rectifier tube.

[0006] The circuit model of the Rogowski coil is a second-order equivalent circuit. The Rogowski coil is connected to the secondary current of the LLC resonant converter through the mutual inductance Mc. is Coupling, the self-inductance of the Rogowski coil is Lc, the resistance of the Rogowski coil is Rc, and the parasitic capacitance of the Rogowski coil is Cc; in order to adjust the frequency response characteristics, a resistor Rd is added at the terminal of the Rogowski coil, wherein the self-inductance Lc of the Rogowski coil is connected in series with the resistor Rc, and the parasitic capacitance Cc of the Rogowski coil is connected in parallel with the externally added resistor Rd. The above two parts are connected in series with the mutual inductance Mc of the Rogowski coil, and the coil terminals are led out from both ends of the parasitic capacitance Cc of the Rogowski coil.

[0007] After the LLC resonant converter is started, the LLC resonant converter first operates in an open-loop working state with a fixed phase shift angle and a conduction time. When the phase shift angle and the conduction time are within a preset effective range, it is determined whether the turn-on point of the synchronous rectifier tube is ahead of the primary side of the LLC resonant converter. When the turn-on point is ahead of the primary side, the turn-on point time is compensated, otherwise the turn-off point time of the synchronous rectifier tube is compensated, and then the digital controller generates a corresponding drive signal, and finally ends; when the phase shift angle and the conduction time are not within the effective range, the LLC resonant converter is shut down.

[0008] The advantages of the present invention over the prior art are that the present invention can accurately adjust the turn-on point and conduction time of the synchronous rectifier tube under different switching frequencies and frequency and load variations based on the Rogowski coil current detection type synchronous rectification method, and can realize a high-efficiency and high-power density GaN LLC resonant converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A control schematic diagram of a Rogowski coil current detection type synchronous rectification detection method according to the present invention;

[0010] Figure 2 is a second-order equivalent circuit diagram of the Rogowski coil in the present invention;

[0011] Figure 3 The present invention is a flowchart of the Rogowski coil current detection type synchronous rectification method. DETAILED DESCRIPTION

[0012] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0013] The full-bridge LLC resonant circuit topology using the Rogowski coil current sensing type synchronous rectification detection method is as follows Figure 1 As shown. This topology includes the primary H bridge, excitation inductor Lr , Excitation capacitor Cr , Secondary leakage inductance LS , two H bridges on the secondary side, input capacitor C, Rogowski coil, current sensor, comparator and digital controller. The primary H bridge consists of four switch tubes, namely the first primary switch tube Q1 , the second primary switch tube Q2、 The third primary switch Q3 And the fourth primary switch tube Q4 One of the two H-bridges on the secondary side consists of four switch tubes, namely the first secondary side switch tube QS1 , the second secondary switch tube QS2 , the third secondary switch tube Q3 , the fourth secondary switch tube Q4 and the first secondary diode Ds1 , the second secondary diode Ds2 , the third secondary diode Ds3 , the fourth secondary diode Ds4 The other consists of the fifth secondary switch tube Q5 , the sixth secondary switch tube Q6 , the seventh secondary switch tube Q7 、The eighth secondary switch tube Q8 and five secondary diodes Ds5 , the sixth secondary diode Ds6 , the seventh secondary diode Ds7 , the eighth secondary diode Ds8 Composition: In the primary H bridge, the first primary switch tube Q1 And the third primary switch tube Q3 Series, the second primary switch Q2 And the fourth primary switch tube Q4 Series, the first primary switch tube Q1 , and the third primary switch tube Q3 The series circuit formed by the second primary switch tube Q2 And the fourth primary switch tube Q4 The series circuit is connected in parallel, and the first primary switch tube Q1 And the third primary switch tube Q3 Switching tube connection point and excitation inductance Lr , Excitation capacitor Cr、 Secondary leakage inductance LS And the second switch Q2 And the fourth switch Q4 The connection points are connected; in an H bridge on the secondary side, the first secondary switch tube QS1 And the third secondary switch Q3 Series, second secondary switch QS2 and the fourth secondary switch Q4 Series, the first secondary switch QS1 And the third secondary switch Q3 The series circuit formed by the second secondary switch QS2 and the fourth secondary switch Q4 Series circuit in parallel; first secondary diode Ds1 Connected in parallel to the first secondary switch QS1 Both ends, the second secondary diode Ds2 Connected in parallel to the second secondary switch QS2 Two ends, the third secondary diode Ds3 Connected in parallel to the third secondary switch Q3 Both ends, the fourth secondary diode Ds4 Connected in parallel to the fourth secondary switch Q4 Two ends; in the other H bridge, the fifth secondary switch tube Q5 and the seventh secondary switch Q7 Series connection, the sixth secondary switch Q6 and the eighth secondary switch Q8 Series connection, the fifth secondary switch Q5 and the seventh secondary switch Q7 The series circuit formed by the sixth secondary switch tube Q6 and the eighth secondary switch Q8 Series circuit in parallel; fifth secondary diode Ds5 Connected in parallel to the fifth secondary switch Q5 Both ends, the sixth secondary diode Ds6 Connected in parallel to the sixth secondary switch Q6 Both ends, the seventh secondary diode Ds7 Connected in parallel to the seventh secondary switch Q7 Both ends, the eighth secondary diode Ds8 Connected in parallel to the eighth secondary switch Q8 Both ends; the first secondary switch tube QS1 And the second secondary switch QS2 The connection point of the fifth secondary switch tube Q5 and the sixth secondary switch Q6 The connection point of the third secondary switch tube is connected to Q3 And the fourth secondary switch Qs4 The connection point and the seventh secondary switch tube Q7 and the eighth secondary switch Q8 The first secondary switch is connected to the connection point of QS1 And the second secondary switch QS2 The connection point and the third secondary switch tube Q3 And the fourth secondary switch Qs4 The connection point is connected to both ends of the input capacitor C, and the positions of points A and B on the two H bridges on the secondary side H are the positions of the Rogowski coil. The output of the Rogowski coil is connected to the current sensor, comparator and digital controller. The program of the digital controller includes pulse condition determination, zero-crossing pulse capture and synchronous rectification opening point and conduction time calculation program.

[0014] The traditional voltage detection type synchronous rectification method realizes the modulation of the conduction time of the synchronous rectifier by detecting the drain-source voltage of the synchronous rectifier. The disadvantages of the voltage detection type synchronous rectification method are obvious when working at high frequency: the detection threshold voltage is very small, and the detection is easily interfered by noise; the package parasitic inductance is easy to cause the premature shutdown of the synchronous rectifier, increasing the additional rectification loss; the synchronous rectifier is turned on synchronously with the primary switch tube, which is easy to cause the synchronous rectifier to be hard turned on, increasing the additional switching loss. These disadvantages determine that the traditional voltage detection type synchronous rectification method is not suitable for high-frequency LLC resonant converters based on GaN HEMTs.

[0015] The present invention improves the traditional voltage detection type synchronous rectification method. Figure 1 As shown, the current detection type synchronous rectification control method based on the Rogowski coil of the present invention is composed of a Rogowski coil (RogowskiCoil) to detect the secondary current is The detected signal is then passed through the analog signal conditioning circuit and then compared with the bias voltage Vbias By comparison, a series of zero-crossing detection pulses (ZCD) are generated. The ZCD signal is captured by the digital controller to obtain the phase shift angle and conduction time of the corresponding synchronous rectifier tube relative to the primary switch tube. The driving waveform of the secondary rectifier tube is finally obtained based on the obtained phase shift angle and conduction time as well as the external pulse conditions.

[0016] Among them, the Rogowski coil is a circuit model such as Figure 2 The second-order equivalent circuit is shown in Figure 1. The coil is connected to the current through the mutual inductance Mc. i s Coupling. The self-inductance Lc and resistance Rc of the coil. The parasitic capacitance of the coil is Cc. To adjust the frequency response characteristics, a resistor Rd is added at the coil terminals.

[0017] Figure 1 During the startup of the full-bridge LLC resonant circuit, the secondary current is detected i s The analog signal detected by the Rogowski coil increases from zero. Due to the existence of the nonlinear region of the analog circuit, it may cause false triggering of the comparator and false triggering of the driver. To avoid this phenomenon, the full-bridge LLC resonant circuit should first work in an open-loop working state with a fixed phase shift angle and a fixed conduction time.

[0018] After several self-tests, the full-bridge LLC resonant circuit enters the closed-loop synchronous rectification state. The program flow chart is as follows: Figure 3As shown. After the start-up, the full-bridge LLC resonant circuit first operates in a fixed duty cycle. When the phase shift angle and the conduction time are not within the effective range, the fixed duty cycle continues to operate. When the phase shift angle and the conduction time are within the effective range, the closed-loop synchronous rectification link is entered. At this time, it is judged again whether the phase shift angle and the conduction time are within the effective range. When they are within the effective range, it is judged whether the turn-on point of the secondary switch tube is ahead of the primary side. When the turn-on point is ahead of the primary side, the turn-on point time is compensated, otherwise the turn-off point time is compensated. After that, the EPWM module in the digital controller generates a corresponding drive signal and ends at last; when the phase shift angle and the conduction time are not within the effective range, a shutdown signal is given.

[0019] Although the specific implementation methods of the present invention are described above, those skilled in the art should understand that these are only examples, and that various changes or modifications may be made to these implementation methods without departing from the principles and implementations of the present invention. Therefore, the scope of protection of the present invention is limited by the appended claims.

Claims

1. A current detection type synchronous rectification control method based on Rogowski coil, characterized in that: The implementation is as follows: In the full-bridge LLC resonant circuit, the secondary current of the LLC resonant converter is is It is detected by a Rogowski coil and then coupled with the bias voltage after passing through the analog signal conditioning circuit. Vbias By comparison, a series of zero-crossing detection pulses ZCD are generated. After the ZCD signal is captured by the digital controller, the phase shift angle and conduction time of the corresponding synchronous rectifier tube relative to the primary switch tube are obtained. Based on the complete symmetry of the secondary-side rectification H-bridge topology of the LLC resonant converter and the consistency of the hardware design, the driving waveforms of the eight synchronous rectifier tubes are determined through one ZCD signal, and the synchronous rectification work of the LLC resonant converter is realized by adjusting the on-off of the synchronous rectifier tube.

2. The current detection type synchronous rectification control method based on Rogowski coil according to claim 1 is characterized in that: The circuit model of the Rogowski coil is a second-order equivalent circuit. The Rogowski coil is connected to the secondary current of the LLC resonant converter through the mutual inductance Mc. is Coupling, the self-inductance of the Rogowski coil is Lc, the resistance of the Rogowski coil is Rc, and the parasitic capacitance of the Rogowski coil is Cc; in order to adjust the frequency response characteristics, a resistor Rd is added at the terminal of the Rogowski coil, wherein the self-inductance Lc of the Rogowski coil is connected in series with the resistor Rc, and the parasitic capacitance Cc of the Rogowski coil is connected in parallel with the externally added resistor Rd. The above two parts, namely the parasitic capacitance Cc of the Rogowski coil and the externally added resistor Rd, are connected in series with the mutual inductance Mc of the Rogowski coil, and the coil terminals are led out from both ends of the parasitic capacitance Cc of the Rogowski coil.

3. The current detection type synchronous rectification control method based on Rogowski coil according to claim 1 is characterized in that: After the LLC resonant converter is started, the LLC resonant converter first operates in an open-loop working state with a fixed phase shift angle and a conduction time. When the phase shift angle and the conduction time are within a preset effective range, it is determined whether the turn-on point of the synchronous rectifier tube is ahead of the primary side of the LLC resonant converter. When the turn-on point is ahead of the primary side, the turn-on point time is compensated, otherwise the turn-off point time of the synchronous rectifier tube is compensated, and then the digital controller generates a corresponding drive signal, and finally ends; when the phase shift angle and the conduction time are not within the effective range, the LLC resonant converter is shut down.

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