CN114679072A - A direct frequency tracking method for vehicle synchronous rectification speed detection - Google Patents

Abstract

The invention belongs to the technical field of power electronic applications, and relates to a direct frequency tracking algorithm used for rotational speed detection in vehicle synchronous rectification. The algorithm of the present invention includes 1) a self-detection module; (2) a grid control module; (3) a frequency analysis module. The basic work flow is briefly described as follows: V _DS is detected by the SD module. After the analog signal enters the GC module, a digital signal related to the phase voltage cycle is obtained through digital logic processing. information, and generate the corresponding SCT value, which is fed back to the GC module to generate the gate control signal. The beneficial effects of the present invention are that the algorithm has the advantages of simplicity, high efficiency, portability, safe on-time control function, and high commutation overlap immunity.

Description

A direct frequency tracking method for vehicle synchronous rectification speed detection

technical field

The invention belongs to the technical field of electronic circuits, and in particular relates to a direct frequency tracking method for vehicle synchronous rectification rotational speed detection.

Background technique

Synchronous rectification generally refers to the use of power metal-oxide-semiconductor field effect transistors (Metal-Oxide-Semiconductor Field-Effect Transistors) with low on-resistance and low on-voltage drop from traditional power diodes with large on-resistance and on-voltage drop in the circuit. Field-Effect Transistor, MOSFET) is replaced, so as to reduce the rectification loss and improve the rectification efficiency. For the synchronous rectification of automobile power generation, the phase voltage frequency changes with the speed, and it is not suitable to turn off the MOSFET through a constant Minimum On Time (MOT). However, the two methods of obtaining the phase voltage and frequency of the synchronous rectification for vehicles, the sampling of the additional circuit composed of passive components and the sampling of the rotational speed sensor will bring additional power loss and increase the difficulty and cost of chip design.

Therefore, a Directly Frequency Tracking (DFT) method is proposed to generate a safe on-time that varies with the rotational speed, so as to ensure that the synchronous rectification works normally when the vehicle AC powers. DFT directly obtains the phase voltage frequency by analyzing the drain-source voltage of the MOSFET, without additional passive circuits or sensors, and generates a safe on-time for the switch that varies with the rotational speed, so as to realize direct frequency-following synchronous rectification control, and then realize synchronous rectification. Accurate detection of rotational speed.

SUMMARY OF THE INVENTION

The invention mainly aims at the problem that the constant MOT is not suitable for turning off the MOSFET in the synchronous rectification for vehicles, and proposes a DFT method for detecting the rotational speed in the synchronous rectification for vehicles. The technical scheme of the present invention: the direct frequency tracking method mainly includes (1) a self-detection module (Self-Detector, SD); (2) a gate control module (Gate Controller, GC); (3) a frequency analysis module (Frequency Analyzer, FA). The basic workflow is briefly described as follows:

S1. When the engine starts to work and the external load is connected, the drain-source voltage v _DS of the MOSFET in the synchronous rectifier bridge is obtained through the SD module, and v _DS is compared with the turn-on voltage v _on to determine whether v _DS is less than v _on , and if so, enter the Step S2, otherwise, go to Step S6;

S2. In this phase voltage, determine whether the current generator speed n is between the allowable speeds. If so, the GC module outputs a high level, and triggers the turn-on signal controller for the first time to turn on the MOSFET through gate drive. In addition, the FA module outputs a high level. level, do not judge and turn off the MOSFET operation; if not, go to step S5;

S3. After the output of the FA module changes from a high level to a low level, compare v _DS with the turn-off voltage v _off to determine whether v _DS is greater than v _off , if so, turn off the MOSFET and go to step S5, otherwise go to step S5 Step S4,;

S4. Determine whether v _DS is greater than the turn-on voltage v _on , if so, go to step 5; if not, in this phase voltage cycle, v _DS is less than v _on for the second time, the GC module turns off the on-signal controller, and turns the MOSFET on Turn off, at this time, the safe conduction of the MOSFET following the rotation speed is realized.

S5 , compare v _DS with the reset voltage v _reset to determine whether v _DS is greater than v _reset , if yes, perform a logic reset, otherwise go back to step S4 .

S6. Compare v _DS with the reset voltage v _reset to determine whether v _DS is greater than v _reset , if yes, perform a logic reset, otherwise go back to step S1.

The implementation carriers of the direct frequency tracking method include: MCU, DSP, FPGA, ASIC, PLC, and the like.

The beneficial effects of the present invention are as follows: the direct frequency tracking method for vehicle synchronous rectification rotational speed detection according to the present invention, compared with the traditional synchronous rectification control technology in the frequency detection in the frequency detection control function of safety on-time lacks, replaces Due to the characteristics of low degree of commutation overlap immunity, this scheme has the advantages of simplicity, high efficiency, portability, safe on-time control function, and high degree of commutation overlap immunity.

Description of drawings

Fig. 1 is a generator synchronous rectification control system taking a three-phase generator as an example;

Fig. 2 is the control framework related to the direct frequency tracking method of the present invention;

Fig. 3 is the working flow chart of the direct frequency tracking method involved in the present invention;

Figure 4 is the co-simulation result waveform;

Detailed ways

Below in conjunction with accompanying drawing, the technical scheme of the present invention is described in detail:

As shown in Figure 1, the synchronous rectification structure of the automobile generator (taking a three-phase generator as an example), the rotor angle sensor transmits the angle of the engine AC motor unit to the rotational speed detection module, and calculates the rotational speed information by inputting the pulse signal, and the rotational speed detection module The rotational speed-related signal is provided and the voltage detection of the drain and the source is used for judgment to generate a gate control signal, and finally the gate is driven.

FIG. 2 shows the control architecture of the direct frequency tracking method of the present invention. According to the relationship between rotational speed and phase voltage period T _S :

The relationship function between the phase voltage period T _S and the drain-source voltage is defined as:

T _s =G(v _{DS_h1} ,v _{DS_l1} ,v _{DS_h2} ,v _{DS_l2} ,...,v _{DS_hi} ,v _{DS_li} ),i=1,2,3,... (2)

According to the mathematical analysis, the drain-source voltage of the MOSFET is first converted into the drain-source current, because the drain-source current is a function of ω (angular frequency) and time t. After Fourier expansion, equations (3) and (4) can be obtained. ):

Among them, t represents the turn-on time of the MOSFET. In formula (4), r _{on_D} (t) and t _D are the equivalent on-resistance and diode turn-on time of the diodes not mentioned in this patent. In addition, r _{on_M} (t) and t _M represent the equivalent on-resistance of the MOSFET and the on-time of the MOSFET. Therefore, it can be known that the drain-source voltage of the MOSFET contains rotational speed information, and by tracking the rotational speed in real time, a safe on-time that varies with the rotational speed can be generated for the synchronous rectifier switch.

The algorithm implementation circuit is mainly composed of three modules: 1) Self-detection module (composed of three high-precision high-speed comparators, namely: turn-on comparator, turn-off comparator, reset comparator, Self-Detector, SD); (2) Gate control module (mainly including three D flip-flops and several gate circuits, Gate Controller, GC); (3) Frequency analysis module (mainly including several counters, comparators and gate circuits, Frequency Analyzer, FA ) consists of three parts. The basic workflow is as follows: Detect v _DS through the SD module. After the analog signal enters the GC module, it is processed by digital logic to obtain a digital signal related to the phase voltage cycle. After the digital signal enters the FA module, it is processed by an algorithm, and the speed information is obtained through analysis. A corresponding Safe Conduction Time (SCT) value is generated and fed back to the GC module to generate a gate control signal.

Fig. 3 shows the working flow chart of the direct frequency tracking method involved in the present invention. The GC receives an initial signal from SD that characterizes the state of the switch. After logic processing, the GC outputs the control signal to the gate driver to further drive the switch. When the drain-source voltage of the MOSFET is less than the turn-on voltage, within the phase voltage cycle, if the rotational speed is within the allowable range, the GC module will output a high level to turn on the MOSFET through gate drive. At the same time, the output of FA jumps to a high level, and the comparison between the drain-source voltage and the turn-on voltage is no longer performed at this time. When SCT becomes low, the FA output jumps to a low level. At this time, the comparison between the drain-source voltage and the turn-on voltage is performed again. When the output of the comparison result is a high level, the GC module outputs a low level and then turns off the MOSFET. . When the drain-source voltage of the MOSFET drops to the turn-on voltage of the MOSFET for the second time, the GC module will no longer judge the turn-on MOSFET. Thus, the switch tube realizes the safe conduction of the speed following through the DFT.

Figure 4 shows the waveform of the co-simulation result. The curve results prove that the DFT algorithm follows the phase voltage frequency when the speed changes, thereby ensuring the normal conduction of the MOSFET under different phase voltage frequencies.

Claims (1)

1. a direct frequency tracking method for vehicle synchronous rectification rotational speed detection, is characterized in that, comprises the following steps: S1. When the engine starts to work and the external load is connected, the drain-source voltage v _DS of the MOSFET in the synchronous rectifier bridge is obtained through the self-test module, and the v _DS is compared with the turn-on voltage v _on to determine whether v _DS is less than v _on , and if so, enter the Step S2, otherwise, go to Step S6; S2. During the phase voltage period, determine whether the current generator speed n is between the allowable speeds. If so, the gate control module outputs a high level, and triggers the turn-on signal controller for the first time, turns on the MOSFET through gate drive, and passes the frequency The analysis module outputs a high level, and does not judge and turn off the MOSFET operation; if not, enter step S5; S3. After the output of the frequency analysis module changes from a high level to a low level, compare v _DS with the turn-off voltage v _off to determine whether v _DS is greater than v _off , if so, turn off the MOSFET and go to step S5, otherwise Enter step S4; S4. Determine whether v _DS is greater than the turn-on voltage v _on , if so, go to step 5; if not, in the phase voltage cycle, v _DS is less than v _on for the second time, turn off the turn-on signal controller through the gate control module, and set the The MOSFET is turned off, and at this time, the safe conduction of the MOSFET following the rotational speed is realized; S5. Compare v _DS with the reset voltage v _reset to determine whether v _DS is greater than v _reset , if so, perform a logical reset, otherwise go back to step S4; S6. Compare v _DS with the reset voltage v _reset to determine whether v _DS is greater than v _reset , if yes, perform a logic reset, otherwise go back to step S1.

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