EP4205272A1

EP4205272A1 - Bulk capacitor heating circuits in electrical power converters

Info

Publication number: EP4205272A1
Application number: EP20950583.3A
Authority: EP
Inventors: Chunyu DING; Jun Liu; Kaitong Lu; Bo Liang
Original assignee: Astec International Ltd
Current assignee: Astec International Ltd
Priority date: 2020-08-25
Filing date: 2020-08-25
Publication date: 2023-07-05
Also published as: TW202209798A; EP4205272A4; TWI765774B; WO2022040908A1; JP2023539843A

Abstract

An electrical power converter includes a power circuit having a bulk capacitor, an auxiliary circuit coupled to the power circuit for heating the bulk capacitor, and a control circuit coupled to the auxiliary circuit. The auxiliary circuit includes a switching device. The control circuit is configured to generate a control signal for controlling the switching device to allow the bulk capacitor to discharge and charge causing a temperature associated with the bulk capacitor to increase and a value of an equivalent series resistance associated with the bulk capacitor to decrease. Other example auxiliary circuits and electrical power converters are also disclosed.

Description

BULK CAPACITOR HEATING CIRCUITS IN ELECTRICAL POWER CONVERTERS

FIELD

The present disclosure relates to bulk capacitor heating circuits in electrical power converters.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.
An electrical power converter converts an input voltage and current into an output voltage and current. The power converter commonly includes one or more bulk capacitors positioned near the converter’s input and/or output. The bulk capacitors are commonly used to prevent substantial voltage deviation caused by, for example, load transients, input power transients, etc.
SUMMARY
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
According to one aspect of the present disclosure, an electrical power converter includes a power circuit having a bulk capacitor, an auxiliary circuit coupled to the power circuit for heating the bulk capacitor, and a control circuit coupled to the auxiliary circuit. The auxiliary circuit includes a switching device. The control circuit is configured to generate a control signal for controlling the switching device to allow the bulk capacitor to discharge and charge causing a temperature associated with the bulk capacitor to increase and a value of an equivalent series resistance associated with the bulk capacitor to decrease.
Further aspects and areas of applicability will become apparent from the description provided herein. It should be understood that various aspects of this disclosure may be implemented individually or in combination with one or more other aspects. It should also be understood that the description and specific examples herein are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
DRAWINGS
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Fig. 1 is a block diagram of an electrical power converter including a power circuit having a bulk capacitor and an auxiliary circuit coupled to the power circuit for heating the bulk capacitor according to one example embodiment of the present disclosure.
Fig. 2 is an electrical schematic diagram of an equivalent circuit for the bulk capacitor of Fig. 1.
Fig. 3 is an electrical schematic diagram of an electrical power converter including a power circuit having a bulk capacitor and an auxiliary circuit having a transformer, a diode, and a switching device controllable to cause the bulk capacitor to charge and discharge, according to another example embodiment.
Fig. 4 is a graph of current associated with the bulk capacitor of Fig. 3 according to yet another example embodiment.
Fig. 5 is a graph of current flowing through the switching device of Fig. 3 according to another example embodiment.
Fig. 6 is a graph of current flowing through the diode of Fig. 3 according to yet another example embodiment.
Fig. 7 is an electrical schematic diagram of an electrical power converter including an auxiliary circuit having a coupled inductor, a diode, and a switching device controllable to cause the bulk capacitor to charge and discharge, according to another example embodiment.
Fig. 8 is an electrical schematic diagram of an auxiliary circuit for heating a bulk capacitor of a power circuit, and including a snubber circuit according to yet another example embodiment.
Fig. 9 is an electrical schematic diagram of an electrical power converter including a power circuit having an AC/DC boost power factor correction (PFC) topology and the auxiliary circuit of Fig. 3, according to another example embodiment.
Fig. 10 is an electrical schematic diagram of an electrical power converter including a power circuit having an AC/DC bridgeless boost PFC topology and the auxiliary circuit of Fig. 3, according to yet another example embodiment.
Fig. 11 is an electrical schematic diagram of an electrical power converter including a power circuit having a totem-pole bridgeless boost PFC topology and the auxiliary circuit of Fig. 3, according to another example embodiment.
Fig. 12 is an electrical schematic diagram of a control circuit for generating a pulse width modulated (PWM) control signal according to yet another example embodiment.
Fig. 13 is an electrical schematic diagram of a control circuit for generating a variable-frequency modulation (VFM) control signal according to another example embodiment.
Corresponding reference numerals indicate corresponding (but not necessarily identical) parts and/or features throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a, ” "an, " and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises, " "comprising, " “including, ” and “having, ” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first, ” “second, ” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
Spatially relative terms, such as “inner, ” “outer, ” "beneath, " "below, " "lower, " "above, " "upper, " and the like, may be used herein for ease of description to describe one element or feature's relationship to another element (s) or feature (s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the example term "below" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
Example embodiments will now be described more fully with reference to the accompanying drawings.
An electrical power converter according to one example embodiment of the present disclosure is illustrated in Fig. 1 and indicated generally by reference number 100. As shown in Fig. 1, the electrical power converter 100 includes a power circuit 102, an auxiliary circuit 104, and a control circuit 106. The power circuit 102 includes a bulk capacitor 108. The auxiliary circuit 104 is coupled to the power circuit 102 for heating the bulk capacitor 108. As shown, the auxiliary circuit 104 includes a switching device 110. The control circuit 106 is coupled to the auxiliary circuit 104. The control circuit 106 is configured to generate a control signal 112 for controlling the switching device 110 to allow the bulk capacitor 108 to discharge and charge causing a temperature associated with the capacitor 108 to increase and a value of an equivalent series resistance (ESR) associated with the bulk capacitor 108 to decrease.
An electrolytic capacitor such as the bulk capacitor 108 typically includes several elements. For example, Fig. 2 illustrates an equivalent circuit of the bulk capacitor 108 of Fig. 1. As shown, the bulk capacitor 108 includes a capacitance C, a resistance R in parallel with the capacitance C, an ESR 220, and an equivalent series inductance (ESL) 222. The resistance R represents an insulative resistance of the bulk capacitor’s dielectric. The ESR 220 and ESL 222 are in series with the capacitance C and the resistance R, and represent the combined resistive and inductive elements in the bulk capacitor 108, respectively.
In some examples, the bulk capacitor 108 and/or any one of the other bulk capacitors disclosed herein may have a large capacitance (e.g., the capacitance C of Fig. 2) . The size of the capacitor 108 may help reduce the voltage deviation in the power converter 100. For example, the voltage deviation generally reduces as the capacitance increases. As such, the bulk capacitor 108 and/or any one of the other bulk capacitors disclosed herein may have a capacitance ranging between, for example, 100 μF to greater than 1 mF.
The ESR (e.g., the ESR 220 of Fig. 2) associated with the bulk capacitor 108 may be temperature-dependent. For example, when the ambient temperature around the bulk capacitor 108 decreases (or increases) , the value of its ESR may increase (or decrease) . For instance, in low temperature environments (e.g., temperatures below -25 degrees Celsius, between -25 degrees Celsius and 20 degrees Celsius, above 20 degrees Celsius, etc. ) , the capacitor’s ESR may significantly change over time when the power converter 100 is started and the ambient temperature around the bulk capacitor 108 increases. In such examples, the capacitor’s ESR may change by a factor of ten as the ambient temperature around the bulk capacitor 108 increases. In some examples, the impedance ratio of bulk capacitor 108 at -40 degrees Celsius may be more than ten times higher than at 20 degrees Celsius.
When the power converter 100 starts up in a low temperature environment, the increased ESR may adversely affect the operation of the power converter 100. For example, when the power converter 100 starts up in a low temperature environment, the converter 100 may experience a large ripple voltage at the bulk capacitor 108 due (at least in part) to the increased ESR. This may occur, for example, when the bulk capacitor 108 is coupled at the output (e.g., an output bulk capacitor) of the power converter 100. In some cases, the large ripple voltage may cause an output voltage regulating accuracy to deteriorate, overvoltage protection circuitry to trigger, instability in a control loop, etc. In other examples, the increased ESR may cause high frequency noise across the bulk capacitor 108 which may decrease filtering effectiveness when, for example, the bulk capacitor 108 is coupled at the input (e.g., an input bulk capacitor) of the power converter 10.
However, the ESR value of the bulk capacitor 108 may be decreased by forcing the capacitor 108 to charge and discharge. For example, charging/discharging of the capacitor 108 may activate an electrolyte in the bulk capacitor 108 causing the temperature associated with the capacitor 108 to increase over time. This temperature change may be based on, for example, the frequency of the charging/discharging. As a result of the increasing temperature, the ESR value of the capacitor 108 may decrease to a suitable level. Due to the decreased ESR value, the ripple voltage, noise, etc. across the capacitor 108 may be minimized.
In the example of Fig. 1, the auxiliary circuit’s switching device 110 may be coupled to the bulk capacitor 108 to force it to charge and discharge. In such examples, the bulk capacitor 108 may be charged and discharged based on the state of the switching device 110. As such, when the switching device 110 to turned on and off (due to the generated control signal 112) , the bulk capacitor 108 may charge and discharge (e.g., as a voltage source) . For example, the bulk capacitor 108 may charge when the switching device 110 is off (e.g., in its open state) , and discharge its stored energy when the switching device 110 is on (e.g., in its closed state) . As such, the bulk capacitor 108 may receive a charging current when the switching device 110 is off, and the bulk capacitor 108 may provide a discharging current when the switching device 110 is on. In such examples, the capacitor 108 may charge and discharge once every switching cycle of the switching device 110.
In some examples, the auxiliary circuit 104 may be activated to start the charging/discharging process for heating (e.g. preheating) the capacitor 108 based on a parameter of the power converter 100. For example, when the power converter 100 is powered on in a low temperature environment, the control circuit 106 may generate the control signal 112 for controlling the switching device 110 in response to the power converter 100 receiving an input power. For instance, the control circuit 106 may sense a parameter (e.g., an input current, an input voltage, etc. ) of the power converter 100, and begin generating the control signal 112 in response to the sensed parameter. In such examples, the bulk capacitor 108 may be initially charged with the input power.
The control circuit 106 may stop generating the control signal 112 for controlling the switching device 110 in response to a parameter of the bulk capacitor 108 exceeding a defined threshold. In such examples, the switching device 110 may be turned off, and the auxiliary circuit 104 may be deactivated to stop the charging/discharging process for heating the capacitor 108. For example, a relationship between the ESR and temperature associated with the capacitor 108 may be known. In such examples, the control circuit 106 may sense a temperature associated with the capacitor 108, and stop generating the control signal 112 when the temperature increases above a defined value (e.g., 10 degrees Celsius, 20 degrees Celsius, 30 degrees Celsius, etc. ) . In such examples, the defined temperature may be determined based on a desired ESR associated with the capacitor 108. In other examples, the control circuit 106 may determine a value of the capacitor’s ESR (e.g., based on a sensed current) , and stop generating the control signal 112 when the ESR value falls below (e.g., exceeds) a defined value (e.g., 0.1 ohms, 0.09 ohms, etc. ) . In still other examples, the control circuit 106 may stop generating the control signal 112 when the number of charges and/or discharges of the bulk capacitor 108 exceeds a defined threshold.
The bulk capacitor 108 may be heated (e.g., preheated) before the power converter 100 enters a startup period. Thus, when the power converter 100 is powered on in a low temperature environment, the capacitor 108 may be heated to decrease the capacitor’s ESR to a desired value before the power converter 100 enters a startup period (e.g., a time period in which an effective capacitance of the converter is charged to allow the converter to provide a desired regulated output voltage) . In other examples, the heating process may be a portion of the startup process (e.g., an initial portion of the startup process) . Once the capacitor 108 is heated to a desired temperature (e.g., its ESR is decreased to a desired value) , the power converter 100 may enter, continue with, etc. its startup process.
The control signal 112 provided to the switching device 110 may have any suitable frequency. The frequency may be fixed or variable. For example, the control signal 112 may have a set frequency or a varying frequency. In examples where the control signal 112 has a varying frequency, the control circuit 106 may provide variable-frequency modulation (VFM) control. The frequency may have a value suitable (e.g., ranging from 10 kHz to 1 MHz) to ensure high-frequency charging/discharging of the bulk capacitor 108. As a result, the bulk capacitor 108 may be charged/discharged a desired number of times so that the temperature associated with the capacitor 108 reaches a desired value.
Additionally, the control signal 112 may have a fixed or variable duty cycle. For example, the on-time of the switching device 110 (e.g., the discharging time of the capacitor 108) and the off-time of the switching device 110 (e.g., the charging time of the capacitor 108) may be fixed. In such examples, the charging current provided to the capacitor 108 and the discharging current provided by the capacitor 108 based on the state of the switching device 110 may be substantially consistent for each charging/discharging cycle. In other examples, the duty cycle may vary. In such examples, the control signal may be a pulse width modulated (PWM) signal.
The on-time and off-time of the control signal 112 (and therefore the switching device 110) and the charging current and the discharging current may be determined based on various parameters to ensure the capacitor 108 is sufficiently heated before the output voltage is established. For example, the parameters may include the charge capacity of the capacitor 108, the power start-up time (e.g., a time from when an input voltage is received to when an output voltage is established) , etc.
In some examples, the auxiliary circuit 104 of Fig. 1 may include one or more components in addition to the switching device 110. For example, Fig. 3 illustrates a power converter 300 including a power circuit 302 having a bulk capacitor C1, and an auxiliary circuit 304 having a switching device, an inductive device, and a diode (e.g., a rectifier diode) D7. In some examples, the inductive device (e.g., a transformer, a coupled inductor, etc. ) may be a physically small device so long as it provides isolation.
In the particular example of Fig. 3, the switching device is shown as a MOSFET Q4, and the inductive device is shown as a transformer TX1. In other examples, other suitable switching devices and/or inductive devices may be employed. The auxiliary circuit 304 may be employable with the power circuit 102 of Fig. 1 and/or another other suitable power circuit having a bulk capacitor.
In the example of Fig. 3, the MOSFET Q4, the transformer TX1 and the diode D7 of the auxiliary circuit 304 are arranged in a flyback converter topology. More specifically, the auxiliary circuit 304 has an open-loop flyback converter topology. As such, in the example of Fig. 3, the MOSFET Q4 of the auxiliary circuit 304 is controlled without feedback.
As shown, a primary winding P1 of the transformer TX1 is coupled between the bulk capacitor C1 and the MOSFET Q4. Specifically, in the example of Fig. 3, the primary winding P1 is coupled to a drain terminal of the MOSFET Q4. A source terminal of the MOSFET Q4 is coupled to a reference voltage (e.g., ground) . As shown, the diode D7 is coupled between a secondary winding S1 of the transformer TX1 and the bulk capacitor C1. Specifically, the secondary winding S1 is coupled to an anode of the diode D7, and the bulk capacitor C1 is coupled to a cathode of the diode D7.
In the particular example of Fig. 3, the bulk capacitor C1 and the components of the auxiliary circuit 304 are coupled to ensure the capacitor C1 charges and discharges. For example, and as shown in Fig. 3, the bulk capacitor C1 is coupled to discharge as a voltage source to the transformer’s primary winding P1 when the MOSFET Q4 is turned on. During this time, current from the bulk capacitor C1 is discharged through the primary winding P1 and the MOSFET Q4 to the reference voltage. As a result, primary winding current increases and the transformer TX1 stores energy.
Additionally, and as shown in Fig. 3, the secondary winding S1 of the transformer TX1 is coupled to charge the bulk capacitor C1 when the MOSFET Q4 is turned off. For example, when the MOSFET Q4 is off, the energy stored in the transformer’s primary winding P1 is transferred to the secondary winding S1. During this time, energy in the secondary winding S1 is discharged causing current to flow from the secondary winding S1 through the diode D7 and to the capacitor C1 to charge the bulk capacitor C1.
The charging/discharging process of the bulk capacitor C1 is shown in Figs. 4-6. For example, Figs. 4-6 illustrate graphs 400, 500, 600 of the capacitor current I_C1, the current I_Q4 flowing through the MOSFET Q4, and the current I_D7 flowing through the diode D7, respectively. As shown, the graphs 400, 500, 600 include successive time periods T1, T2, T3 corresponding to charging and discharging cycles of the bulk capacitor C1. Specifically, the time period T1 corresponds to a discharging cycle of the capacitor C1, the time period T2 corresponds to a subsequent charging cycle of the capacitor C1, and the time period T3 corresponds to another discharging cycle of the capacitor C1.
For example, the MOSFET Q4 is on during the time period T1. During this period, the capacitor C1 discharges its stored energy causing current I_C1 to flow from the capacitor as shown in Fig. 4. The capacitor current flows through the MOSFET Q4 (and the primary winding P1 as explained above) , as shown by the increasing current I_Q4 during the time period T1 in Fig. 5. During the time period T1, no current flows through the diode D7, as shown in Fig. 6.
During the time period T2, the MOSFET Q4 is turned off. As such, no current flows through the MOSFET Q4, as shown in Fig. 5. During the time period T2, the diode current I_D7 and the capacitor current I_C1 spike and then decrease over time (see Figs. 6 and 7) as energy stored in the transformer TX1 is released back to the capacitor C1, as explained above. As such, the capacitor C1 is charged from the energy stored in the transformer TX1 during this time period.
During the time period T3, the MOSFET Q4 is turned on again and the bulk capacitor C1 is discharged again through the primary winding P1 and the MOSFET Q4 as explained above. This charging/discharging process of the bulk capacitor C1 may be repeated as necessary.
The MOSFET Q4 may be controlled with any suitable control circuit. In the particular example of Fig. 3, the power converter 300 includes a control circuit represented by a signal source V4 for controlling the MOSFET Q4. In such examples, the signal source V4 may provide a control signal to a gate terminal of the MOSFET Q4 via a resistor R3. In some examples, the control signal provided by the signal source V4 may have any suitable frequency and/or a fixed or variable duty cycle as explained above.
In some examples, the auxiliary circuit 304 may be activated and/or deactivated to start and/or stop the charging/discharging process of the bulk capacitor C1 based on one or more parameters of the power converter 300. For example, the signal source V4 may be controlled to generate its control signal in response to the power converter 300 receiving an input power as explained above. In such examples, the bulk capacitor 108 may be initially charged with the input power, and then discharged when the MOSFET Q4 is turned on. Additionally, the signal source V4 may be controlled to stop generating its control signal in response to a parameter of the bulk capacitor 108 exceeding (e.g., increases above and/or falls below) a defined threshold. The parameter associated with the bulk capacitor 108 may be, for example, a temperature, an ESR value, the number of charges and/or discharges, etc. When the signal source V4 stops generating its control signal, the MOSFET Q4 remains off (e.g., open) and the auxiliary circuit 304 is deactivated.
Additionally, the power converter 300 of Fig. 3 may include one or more components for converting an input voltage and current to an output voltage and current. For example, and as shown in Fig. 3, the power circuit 302 includes an optional rectifying circuit 314 with four diodes D6, D8, D9, D10. In the example of Fig. 3, the diodes D6, D8, D9, D10 are arranged in a full bridge configuration for converting AC power from an AC power source V3 into DC power. In other examples, another suitable rectifying circuit may be employed. Although not shown in Fig. 3, the power circuit 302 may additionally include one or more power switching devices, inductors, capacitors, etc.
In some examples, the auxiliary circuit 304 of Fig. 3 may include another suitable inductive device as explained above. For example, Fig. 7 illustrates a power converter 700 including the power circuit 302 and the control circuit (e.g., the signal source V4) of Fig. 3, and an auxiliary circuit 704 including the MOSFET Q4 and the diode D7 of Fig. 3, and a coupled inductor CI. The auxiliary circuit 704 functions in a similar manner as the auxiliary circuit 304 of Fig. 3 for heating the bulk capacitor C1 in the power circuit 302. For example, the bulk capacitor C1 may discharge as a voltage source to the coupled inductor’s winding W1 when the MOSFET Q4 is on, and charge from current flowing from the coupled inductor’s winding W2 (and through the diode D7) when the MOSFET Q4 is off.
In other examples, any one of the auxiliary circuits disclosed herein may include a snubber circuit for suppressing voltage spikes. For example, Fig. 8 illustrates an auxiliary circuit 804 that may be employed with any one of the power circuits disclosed herein, and/or another suitable power circuits. The auxiliary circuit 804 of Fig. 8 is substantially similar to the auxiliary circuit 304 of Fig. 3, but includes a snubber circuit 840 coupled across the primary winding P1 of the transformer TX1. As shown, the snubber circuit 840 includes a capacitor C2, a resistor R2, and a diode D2. The capacitor C2 and the resistor R2 are coupled in parallel, and the diode D2 is coupled between the parallel combination of the capacitor C2 and the resistor R2 and the primary winding P1. In the example of Fig. 8, the capacitor C2 may absorb energy generated from, for example, voltage spikes caused by the MOSFET Q4 changing state.
Additionally, any one of the auxiliary circuits disclosed herein may be employed in any suitable electrical power converter (e.g., switching power converter) having at least one bulk capacitor. For example, the auxiliary circuits may be employed with power circuits having different converter topologies such as buck, boost, buck-boost, etc. topologies for providing AC/DC, DC/AC and/or DC/DC power conversion. In some examples, boost topologies of the power circuits may include PFC circuitry. For example, Figs. 9-11 illustrate electrical power converters 900, 1000, 1100 including power circuits 902, 1002, 1102 having different boost PFC topologies, the auxiliary circuit 304 of Fig. 3, and the control circuit (e.g., the signal source V4) of Fig. 3 for controlling the MOSFET Q4 of the auxiliary circuit 304. Specifically, the power circuit 902 of Fig. 9 has an AC/DC boost power factor correction (PFC) topology, the power circuit 1002 of Fig. 10 has an AC/DC bridgeless boost PFC topology, and the power circuit 1102 of Fig. 11 has a totem-pole bridgeless boost PFC topology. In the power circuit 1002 of Fig. 10, some or all of the diodes D6, D7, D8, D9 may be replaced with MOSFETs (e.g., SiC MOSFETs) if desired. Additionally, in the power circuit 1102 of Fig. 11, some or all of the MOSFETs Q1, Q5 may be replaced with diodes if desired.
Additionally, the control circuits disclosed herein may include any suitable circuitry for generating control signals to control switching devices in the auxiliary circuits. For example, the control circuits may include an analog control circuit, a digital control circuit, or a hybrid control circuit (e.g., a digital control circuit and an analog circuit) . The digital control circuits may be implemented with one or more types of digital control circuitry. For example, the digital control circuits each may include a digital controller such as a digital signal controller (DSC) , a digital signal processing (DSP) , a microcontroller, a field-programmable gate array (FPGA) , an application-specific IC (ASIC) , etc.
In some examples, the control circuits may provide PWM control or VFM control as explained above. For example, Fig. 12 illustrates a control circuit 1206 employing PWM control, and Fig. 13 illustrates a control circuit 1306 employing VFM control. In some examples, the control circuit 1206 may include a logic component U3 providing a signal for driving transistors Q10, Q11, as shown in Fig. 12. Likewise, the control circuit 1306 may include a voltage-controlled oscillator (VCO) 1350 providing a clock signal CLK (e.g., having a 50%duty cycle) for driving transistors Q8, Q9, as shown in Fig. 13.
Any one of the control circuits 1206, 1306 may be employed to control the switching device in any one of the auxiliary circuits disclosed herein. For example, the transistors Q10, Q11 of Fig. 12 are controlled by the logic component U3 to generate a PWM control signal for controlling the MOSFET Q4 in the auxiliary circuit 304 of Fig. 3. Additionally, the transistors Q8, Q9 of Fig. 13 are controlled by the VCO 1350 to generate a VFM control signal for controlling the MOSFET Q4 in the auxiliary circuit 304 of Fig. 3.
Additionally, the control circuits 1206, 1306 may deactivate their associated auxiliary circuits. In such examples, the control circuits 1206, 1306 may receive, generate, etc. enable signals for deactivating the auxiliary circuits. For example, the logic component U3 of Fig. 12 and the VCO 1350 of Fig. 13 may be activated with enable signals. When the enable signals are not provided, the logic component U3 and the VCO 1350 may be deactivated. As a result, signals are not provided to drive the transistors Q8, Q9, Q10, Q11 of Figs. 12 and 13, and the transistors Q8, Q9, Q10, Q11 do not generate the control signals for controlling the MOSFET Q4. In such examples, the MOSFET Q4 remains off, and the auxiliary circuit 304 may be deactivated to stop the charging/discharging process.
By employing the auxiliary circuits disclosed herein, bulk capacitors in power converters may be effectively heated in a short period of time. Due at least in part to the heating, ESR values associated with the bulk capacitors (e.g., electrolytic capacitors) may be decreased. As a result, ripple voltage, noise, etc. in the power converters caused by high ESR values (e.g., in low temperature environments) may be minimized. As such, the auxiliary circuits may prevent triggering of overvoltage protection, reduce output ripple over-specification, increase control loop stability, etc.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

An electrical power converter comprising:

a power circuit including a bulk capacitor;

an auxiliary circuit coupled to the power circuit for heating the bulk capacitor, the auxiliary circuit including a switching device; and

a control circuit coupled to the auxiliary circuit, the control circuit configured to generate a control signal for controlling the switching device to allow the bulk capacitor to discharge and charge causing a temperature associated with the bulk capacitor to increase and a value of an equivalent series resistance associated with the bulk capacitor to decrease.
The electrical power converter of any preceding claim, wherein the auxiliary circuit includes an inductive device having a first winding and a second winding, and wherein the first winding is coupled between the bulk capacitor of the power circuit and the switching device of the auxiliary circuit.
The electrical power converter of any preceding claim, wherein the bulk capacitor is coupled to discharge to the first winding when the switching device is turned on.
The electrical power converter of any preceding claim, wherein the auxiliary circuit includes a diode coupled between the second winding of the inductive device and the bulk capacitor of the power circuit.
The electrical power converter of any preceding claim, wherein the second winding is coupled to charge the bulk capacitor via the diode when the switching device is turned off.
The electrical power converter of any preceding claim, wherein the inductive device includes a transformer, and wherein the first winding is a primary winding of the transformer and the second winding is a secondary winding of the transformer.
The electrical power converter of any preceding claim, wherein the inductive device includes a coupled inductor.
The electrical power converter of any preceding claim, wherein the control circuit is configured to generate the control signal with a fixed duty cycle.
The electrical power converter of any preceding claim, wherein the auxiliary circuit includes an open-loop flyback converter topology.
The electrical power converter of any preceding claim, wherein the control circuit is configured to generate the control signal for controlling the switching device in response to the power converter receiving power.
The electrical power converter of any preceding claim, wherein the control circuit is configured to stop generating the control signal in response to a parameter of the bulk capacitor exceeding a defined threshold.
The electrical power converter of any preceding claim, wherein the control signal is a PWM control signal.
The electrical power converter of any preceding claim, wherein the control signal has a variable frequency.
The electrical power converter of any preceding claim, wherein the power circuit includes a bridge rectifying circuit.
The electrical power converter of any preceding claim, wherein the power circuit includes a power factor correction circuit.
The electrical power converter of any preceding claim, wherein the control circuit includes an analog circuit and/or a digital circuit.