A Monitoring Method for the Capacitance Value C of the Output Capacitor of a DCM Buck Converter

Abstract

The present invention belongs to the technical field of output filter capacitor health monitoring, and discloses a method for monitoring the capacitance value C of the output capacitor of a DCM buck converter based on the discharge law, including: sampling the instantaneous value v o (t) of the output voltage and the instantaneous value i L (t) of the inductor current. Then, process the instantaneous value i L (t) of the inductor current to obtain the period T of the circuit, and obtain the duty cycle D disc of the stage where the inductor current is zero in the period T through the Switch module. Then, use the instantaneous value i L (t) of the inductor current and the instantaneous value v o (t) of the output voltage to calculate the load resistance R o . Finally, sample the output voltages v o (t1) and v o (t2) at two moments at the trisection points of the stage where the inductor current is zero, and calculate the capacitance value C of the output capacitor of the buck converter through the formula. The method provided by the present invention does not need to monitor the switching tube drive signal and components such as inductors, and has wide applicability, providing a basis for the health monitoring of capacitors.

Description

Technical Field

[0001] The present invention belongs to the technical field of health monitoring of output filter capacitors of converters, and relates to a method for monitoring the capacitance value C of the output capacitor of a DCM buck converter, and particularly relates to a method for monitoring the capacitance value C of the output capacitor of a DCM buck converter based on the discharge law. Background Art

[0002] Due to advantages such as high efficiency, small volume, and low noise, power electronic converters have been widely used in military, aerospace, industrial and other fields. In power electronic converters, in order to obtain a higher quality output voltage, capacitors must be used to filter high-frequency noise, and electrolytic capacitors are the most commonly used. Some investigations have pointed out that electrolytic capacitors are the power devices with the highest failure rate in power electronic converters. After an electrolytic capacitor is used for a period of time, the equivalent series resistance ESR of the capacitor will increase, and the capacitance value C of the capacitor will decrease. When the two change to a certain extent, it can be considered that the capacitor has failed, and the failure of the capacitor will cause operation failures of the converter and the system. Industrially, the equivalent series resistance value and capacitance value of electrolytic capacitors are important indicators for measuring the health status of capacitors. Buck converters are widely used in new energy power generation, computer power supplies, communication power supplies and other fields. Therefore, monitoring the capacitance value C of the filter capacitor of the Buck converter is crucial for its health status. However, the existing identification process of the capacitance value C of the capacitor usually requires monitoring the driving signal of the switching tube and knowing the specific values of components such as inductors. Therefore, a relatively simple and non-interfering capacitor health monitoring method cannot be provided. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for monitoring the capacitance value C of the output capacitor of a DCM buck converter. This monitoring method is based on the discharge law to online and real-time monitor the capacitance value C, and can monitor the health status of the electrolytic capacitor without monitoring the driving signal of the switching tube.

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

[0005] A method for monitoring the capacitance value C of the output capacitor of a DCM buck converter based on the discharge law, comprising the following steps:

[0006] Step A), sampling the instantaneous value v o (t) of the output voltage at the load end of the buck converter and calculating its mean value to obtain the average output voltage V o ; sampling the instantaneous value i L (t) of the inductor current of the buck converter, and synchronously processing the instantaneous value i L (t) of the inductor current through a high-pass filter unit to obtain the instantaneous value i L-ac (t) of the AC component of the inductor current;

[0007] Step B), calculate the switching period T of the buck converter according to the instantaneous value i L (t) of the inductor current obtained by sampling, and process the instantaneous value i L (t) of the inductor current through the Switch module to calculate the duty cycle D of the stage where the inductor current of the buck converter is zero in the switching period T disc ; wherein, the processing through the Switch module specifically means assigning 1 to the part where the instantaneous value i L (t) of the inductor current is greater than 0.0009A and 0 to the rest;

[0008] Step C), subtract the instantaneous value i L (t) of the inductor current obtained by sampling from the instantaneous value i L-ac (t) of the AC component of the inductor current to obtain the instantaneous value i o (t) of the output current at the load end and calculate its average value to obtain the average output current I o ; calculate the load resistance value R o according to the average output voltage V o and the average output current I o ;

[0009] Step D), sample the instantaneous output voltage values v o (t1) and v o (t2) at two moments of one-third and two-thirds of the stage where the inductor current of the buck converter is zero;

[0010]

[0011]

[0012] where, t1 and t2 are the sampling moments.

[0013] Step E), calculate the capacitance value C of the output capacitor of the buck converter according to the duty cycle D disc , the switching period T, the instantaneous output voltage value v o (t1), the instantaneous output voltage value v o (t2) and the load resistance value R o .

[0014]

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

[0016] The present invention utilizes the discharge characteristic of a capacitor to sample the voltages at two points on the curve of the capacitor discharging alone for parameter identification of the capacitance value C of the capacitor. Compared with other schemes that sample the load voltage at specific moments, this scheme does not require sampling the inductance value and the driving signal. The parameter sampling moments are two points in the middle of the curve, which can effectively avoid the interference generated when the circuit state changes and has good anti-interference ability. Moreover, it has a wide range of applicability and can be applied to other circuits with a stage of capacitor discharging alone, such as Boost circuits, etc. Brief Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of a monitoring system for the capacitance value C of the output capacitor of a DCM buck converter provided by an embodiment of the present invention. Detailed Embodiment

[0018] The technical solution of the present invention will be further described in detail below with reference to the drawings:

[0019] An embodiment of the present invention provides a monitoring system for the capacitance value C of the output capacitor of a DCM buck converter. The schematic structural diagram is as Figure 1 shown, and specifically includes: a buck converter (a loaded Buck converter), a high-pass filter unit, an analysis unit, a resistance calculation unit, a sampling unit, a Switch module, and a capacitance value calculation unit; wherein, the high-pass filter unit is used to perform high-pass filtering on the instantaneous value i L (t) of the inductor current obtained by sampling; the analysis unit is used to calculate the switching period T of the Buck circuit according to the instantaneous value i L (t) of the inductor current obtained by sampling; the Switch module is used to assign 1 to the part where the instantaneous value i L (t) of the inductor current is greater than 0.0009A and assign 0 to the rest; the sampling unit is used to sample the instantaneous output voltage values v o (t1) and v o (t2) at two moments, one-third and two-thirds of the stage when the inductor current is zero.

[0020] Based on the above monitoring system for the capacitance value C of the output capacitor of a DCM buck converter, the present invention provides a monitoring method for the capacitance value C of the output capacitor of a DCM buck converter, including the following steps:

[0021] Step A), sample the instantaneous output voltage value v o (t) at the load end of the buck converter and calculate its mean value to obtain the average output voltage V o ; sample the instantaneous value i L (t) of the inductor current of the buck converter, and synchronously process the instantaneous value i L (t) of the inductor current through the high-pass filter unit to obtain the instantaneous value i L-ac (t) of the AC component of the inductor current.

[0022] Step B), according to the instantaneous value of the inductor current \(i\) L (t) sampled, calculate the switching period \(T\) of the buck converter, and process the instantaneous value of the inductor current \(i\) L (t) through the Switch module to calculate the duty cycle \(D\) of the stage when the inductor current of the buck converter is zero in the switching period \(T\) disc ; where, the processing through the Switch module specifically means assigning 1 to the part of the instantaneous value of the inductor current \(i\) L (t) greater than 0.0009 A and 0 to the rest;

[0023] Step C), subtract the instantaneous value of the inductor current alternating current component \(i\) L (t) from the instantaneous value of the inductor current \(i\) L-ac (t) sampled to obtain the instantaneous value of the output current at the load end \(i\) o (t) and calculate its average value to obtain the average output current \(I\) o ; According to the average output voltage \(V\) o and the average output current \(I\) o calculate the load resistance value \(R\) o ;

[0024] Step D), sample the instantaneous output voltage values \(v\) o (t1) and \(v\) o (t2) at two moments of one-third and two-thirds of the stage when the inductor current of the buck converter is zero;

[0025]

[0026]

[0027] where, t1 and t2 are the sampling moments.

[0028] Step E), according to the duty cycle \(D\) disc , the switching period \(T\), the instantaneous output voltage value \(v\) o (t1), the instantaneous output voltage value \(v\) o (t2) and the load resistance value \(R\) o calculate the capacitance value \(C\) of the output capacitor of the buck converter.

[0029]

[0030] The present invention simulates the monitoring method of the capacitance value \(C\) of the output capacitor of the above DCM buck converter, and the simulation conditions are: input voltage \(V\) in = 24 V, inductance \(L\) f = 220 μH, switching frequency \(f\) s = 50 kHz, sampling frequency \(f\)c = 10 MHz.

[0031] Specifically, first, circuit operation simulation is performed. After the operation stops, the output voltage v o (t) and the inductor current i L (t), and their AC components i L-ac (t) are imported into the Matlab Workspace and the mean value V of the output voltage is calculated. o Then, the time difference between adjacent peaks of the inductor current i L (t) is the switching period T of the Buck circuit. Then, the inductor current i L (t) passes through the Switch module, and the part greater than 0.0009 A is assigned 1 and the part less than 0.0009 A is assigned 0. Its mean value is the ratio D of the non-zero stage of the inductor current in the period T. on , and the ratio D of the zero stage of the inductor current disc = 1 - D on . Then, the instantaneous value i of the sampled inductor current L (t) is subtracted from the instantaneous value i of the AC component of the inductor current L-ac (t) to obtain the instantaneous value i of the output current at the load end o (t), and the average value I of the output current is calculated. o . The average value V of the output voltage o is divided by the average value I of the output current o to obtain the load resistance R. o . According to D disc and T, the sampling times t1 and t2 are calculated, and the instantaneous values u of the output voltage at two specific sampling times o (t1) and u o (t1) are sampled. Finally, the capacitance value C of the output capacitor is calculated using the formula. The simulation results under different conditions are shown in Table 1. It can be seen that the method for monitoring the capacitance value C of the output filter capacitor of the Buck circuit provided by the present invention has high tracking accuracy.

[0032] Table 1

[0033] <![CDATA[R o Actual value / Ω]]> 300 300 500 500 <![CDATA[R o Calculated value / Ω]]> 300.0033 300.0043 500.0072 500.0076 Actual value of C / μF 100 120 100 120 Calculated value of C / μF 99.2481 118.8848 101.0008 121.4221

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

[0035] Those skilled in the art can understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as the general understanding of those of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with their meaning in the context of the prior art, and will not be interpreted in an idealized or overly formal sense unless defined as such here.

[0036] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for monitoring the capacitance value C of the output capacitor of a DCM buck converter, where the buck converter is a loaded Buck converter, characterized in that, Including the following steps: Step A), sample the instantaneous value v of the output voltage at the load end of the buck converter o (t) and calculate its mean value to obtain the average output voltage V o ; sample the instantaneous value i of the inductor current of the buck converter L (t), synchronously process the instantaneous value i of the inductor current L (t) through a high-pass filter unit to obtain the instantaneous value i of the AC component of the inductor current L-ac (t); Step B), calculate the switching period T of the buck converter according to the instantaneous value i L (t) of the inductor current obtained by sampling, and subject the instantaneous value i L (t) of the inductor current to the processing of the Switch module to calculate the duty cycle D of the stage where the inductor current of the buck converter is zero in the switching period T disc ; wherein, the processing by the Switch module specifically means assigning 1 to the part where the instantaneous value i L (t) of the inductor current is greater than 0.0009 A and assigning 0 to the rest; Step C), subtract the instantaneous value i L (t) of the sampled inductor current from the instantaneous value i L-ac (t) of the AC component of the inductor current to obtain the instantaneous value i o (t) of the output current at the load end and calculate its mean value to obtain the average output current I o ; Calculate the load resistance R o based on the average output voltage V o and the average output current I o ; Step D), sampling the instantaneous output voltage values v o (t1) and v o (t2) at two moments which are one-third and two-thirds of the stage when the buck converter inductor current is zero; Wherein, t1 and t2 are sampling moments; Step E), according to the duty cycle Ddisc, the switching period T, the instantaneous output voltage value v o (t1), the instantaneous output voltage value v o (t2) and the load resistance value R o calculate the capacitance value C of the output capacitor of the buck converter; The calculation formula for the capacitance value C of the output capacitor is:

Images