A method for monitoring the ESR of output capacitor of Buck converter

Abstract

The present invention belongs to the technical field of output filter capacitor health monitoring, and discloses a method for monitoring the ESR of a Buck converter output capacitor, comprising: sampling the instantaneous value of the output terminal voltage v o (t) and processed by high-pass filter to obtain the instantaneous value v of the AC component of the output voltage o‑ac (t); Sample the drive signal of the switch tube Q and calculate the duty cycle D and the switching frequency f s , and simulate rectangular pulse signals G1(t) and G2(t) with an amplitude of 1 and symmetric about y=1 / 2; the current waveform i(t) is simulated by the current fitting unit, and is processed by the Switch module and the high-pass filter unit in turn to obtain the instantaneous value i of the AC component of the filter inductor current Lf_ac (t); Calculate the output capacitor ESR value of the Buck converter; This method does not require a series current monitoring structure, does not require a high-precision trigger sampling device, and is applicable to both CCM and DCM modes.

Description

Technical Field

[0001] The present invention belongs to the technical field of output filter capacitor health monitoring, and relates to a method for monitoring the ESR of a Buck converter output capacitor, and in particular to a method for monitoring the ESR of a Buck converter output capacitor based on output voltage. Background Art

[0002] Due to the advantages of high efficiency, small size, and low noise, power electronic converters have been widely used in military, aerospace, and industrial fields. In power electronic converters, in order to obtain a higher quality output voltage, capacitors must be used to filter out high-frequency noise, among which electrolytic capacitors are the most commonly used. A survey pointed out that electrolytic capacitors are the power devices with the highest failure rate in power electronic converters. After the electrolytic capacitor has been used for a period of time, the equivalent series resistance ESR of the capacitor will increase, and the capacitance C of the capacitor will decrease. When both change to a certain extent, it can be considered that the capacitor has failed. The failure of the capacitor will cause the operation failure of the converter and the system. In industry, the equivalent series resistance value and capacitance value of the electrolytic capacitor are important indicators used to measure the health of the capacitor. Buck converters are widely used in the fields of new energy power generation, computer power supply, and communication power supply. Therefore, monitoring the equivalent series resistance value ESR of the Buck converter filter capacitor is crucial to its health. However, the existing ESR identification process usually connects a current monitoring device in series in the circuit, which interferes with the working state of the converter. Or a high-precision instantaneous voltage sampling device is required. Therefore, it is impossible to provide a relatively simple and interference-free capacitor health monitoring method. Summary of the invention

[0003] In view of this, the object of the present invention is to provide a method for monitoring the ESR of a Buck converter output capacitor, which can monitor the ESR online in real time and monitor the health status of the electrolytic capacitor, thereby providing a research basis for fault prediction of power electronic circuits.

[0004] The present invention adopts the following technical solutions to solve the above technical problems:

[0005] A method for monitoring the ESR of a Buck converter output capacitor comprises the following steps:

[0006] Step A), sampling to obtain the instantaneous value v of the output voltage of the Buck converter o (t) and calculate its mean value to get the output voltage average value V o , the instantaneous value of the output voltage v o (t) After being processed by a high-pass filter, the instantaneous value v of the AC component of the output voltage is obtained o-ac (t);

[0007] Step B), sampling the driving signal of the switch tube Q, and calculating the duty cycle D and the switching frequency f according to the sampled driving signal of the switch tube Q s , and simulate two rectangular pulse signals with an amplitude of 1 and symmetric about y=1 / 2; the two rectangular pulse signals are rectangular pulse signal G1(t) and rectangular pulse signal G2(t);

[0008] Step C), the duty cycle D and switching frequency f obtained in step B) are s , rectangular pulse signal G1(t) and rectangular pulse signal G2(t) as the first input variable, and the input voltage V in and the output voltage mean V o And the filter inductance value L f As the second input variable, the required current waveform i(t) is simulated by the current fitting unit;

[0009]

[0010] Wherein, D is the pulse width of the rectangular pulse signal G1(t) and the rectangular pulse signal G2(t).

[0011] Step D), the current waveform i(t) is processed by the switch module and the high-pass filter unit in sequence to obtain the required instantaneous value i of the AC component of the filter inductor current. Lf_ac (t); wherein the processing by the Switch module is specifically to set the negative value in the current waveform i(t) to zero and keep the positive value unchanged;

[0012] Step E), calculating the output capacitor ESR value of the Buck converter according to the formula shown below;

[0013]

[0014] Where T = 1 / f s .

[0015] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0016] 1. The present invention is applicable to both CCM and DCM modes;

[0017] 2. The present invention does not require a current monitoring structure to be connected in series in the circuit, and does not require a high-precision trigger sampling device;

[0018] 3. The circuit is simple and can realize accurate monitoring of ESR, which has important practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1Schematic diagram of the method for monitoring the ESR value of an output capacitor in the present invention;

[0020] Figure 2 The working waveform diagram and simulation current diagram of the monitoring method provided by the present invention; DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings:

[0022] The present invention discloses a method for monitoring the ESR of a Buck converter output capacitor, comprising the following steps:

[0023] Step A), sampling to obtain the instantaneous value v of the output voltage of the Buck converter o (t) and calculate its mean value V o , the instantaneous value of the output voltage v o (t) After being processed by a high-pass filter, the instantaneous value v of the AC component of the output voltage is obtained o-ac (t);

[0024] Step B), sampling the driving signal of the switch tube Q, and calculating the duty cycle D and the switching frequency f according to the sampled driving signal of the switch tube Q s , and simulate two rectangular pulse signals with an amplitude of 1 and symmetric about y=1 / 2; the two rectangular pulse signals are rectangular pulse signal G1(t) and rectangular pulse signal G2(t); the pulse width of the rectangular pulse signal G1(t) and the rectangular pulse signal G2(t) is D.

[0025] Step C), the duty cycle D and switching frequency f obtained in step B) are s , rectangular pulse signal G1(t) and rectangular pulse signal G2(t) as the first input variable, and the input voltage V in and the output voltage V o And the filter inductance value L f As the second input variable, the required current waveform i(t) is simulated by the current fitting unit;

[0026]

[0027] Step D), the current waveform i(t) is processed by the switch module and the high-pass filter unit in sequence to obtain the required instantaneous value i of the AC component of the filter inductor current. Lf_ac (t); wherein the processing by the Switch module is specifically to set the negative value in the current waveform i(t) to zero and keep the positive value unchanged;

[0028] Step E), calculating the output capacitor ESR value of the Buck converter according to the formula shown below;

[0029]

[0030] Where T = 1 / f s .

[0031] Figure 2 The working waveform diagram and simulation current diagram of the Buck circuit in the present invention are shown in FIG. Figure 2 (a) is CCM mode, Figure 2 (b) is DCM mode. The present invention provides a simulation result of the equivalent series resistance of the Buck converter output capacitor, and the simulation conditions are: input voltage V in =24V, inductance L f =220μH, switching frequency f s =50kHz, sampling frequency f c =10MHz. First, the circuit operation simulation is performed, and the output voltage v o (t) and its AC component v o_ac (t) is imported into Matlab Workspace. Then, according to D, f s Simulate the rectangular pulse signals G1(t) and G2(t) with an amplitude of 1. Then simulate the required current i(t) through the formula. Export the simulated current through the Switch module to retain the positive value and set the negative value to zero, and then pass it through the high-pass filter module to obtain the AC component of the inductor current i Lf _ ac (t) value; the obtained current i Lf _ ac (t) is imported into the Workspace of Matlab for data processing, and the value of the equivalent series resistance ESR of the capacitor can be calculated. The simulation results under different conditions are shown in Table 1, which shows that the Buck circuit output filter capacitor ESR value monitoring method provided by the present invention has a high tracking accuracy.

[0032] Table 1

[0033] ESR actual value / Ω 0.2 0.4 0.2 0.4 Duty cycle D 0.5 0.5 0.5 0.5 <![CDATA[R L / Oh]]> 10(CCM) 10(CCM) 100(DCM) 100(DCM) ESR calculation value / Ω 0.2054 0.4038 0.2014 0.4032

[0034] The Buck converter output capacitor ESR value monitoring method provided by the present invention has the advantages of not requiring a current monitoring structure to be connected in series in the circuit and not requiring a high-precision instantaneous voltage sampling device, and is applicable to both CCM and DCM modes.

[0035] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0036] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for monitoring the ESR of a Buck converter output capacitor, characterized in that: The following steps are involved: Step A), sampling to obtain the instantaneous value v of the output voltage of the Buck converter o (t) and calculate its mean value to get the output voltage average value V o , the instantaneous value of the output voltage v o (t) After being processed by a high-pass filter, the instantaneous value v of the AC component of the output voltage is obtained o-ac (t); Step B), sampling the driving signal of the switch tube Q, and calculating the duty cycle D and the switching frequency f according to the sampled driving signal of the switch tube Q s , and simulate two rectangular pulse signals with an amplitude of 1 and symmetric about y=1 / 2; the two rectangular pulse signals are rectangular pulse signal G1(t) and rectangular pulse signal G2(t); Step C), the duty cycle D and switching frequency f obtained in step B) are s , rectangular pulse signal G1(t) and rectangular pulse signal G2(t) as the first input variable, and the input voltage V in , output voltage average value V o And the filter inductance value L f As the second input variable, the required current waveform i(t) is simulated by the current fitting unit, and the current waveform i(t) is simulated according to the following formula: Wherein, D is the pulse width of the rectangular pulse signal G1(t) and the rectangular pulse signal G2(t); Step D), the current waveform i(t) is processed by the switch module and the high-pass filter unit in sequence to obtain the required instantaneous value i of the AC component of the filter inductor current. Lf_ac (t); wherein the processing by the Switch module is specifically to set the negative value in the current waveform i(t) to zero and keep the positive value unchanged; Step E), calculating the output capacitor ESR value of the Buck converter according to the formula shown below; Where T = 1 / f s .

Images