TWI821069B - Power converter and method of operating the same - Google Patents

Abstract

A power converter receives an input voltage and provides an output voltage to supply power to a load. The power converter includes a PFC circuit and a controller, the controller obtains a switching frequency based on an instantaneous value of the input voltage, and obtains an upper limit frequency and a lower limit frequency based on an effective value of an input current of the PFC circuit. When the controller determines that the effective value is higher than a medium load threshold, the controller switches an operation mode of the PFC circuit from CRM or TCM to CCM based on the switching frequency being lower than the lower limit frequency, and limits the switching frequency to the lower limit frequency. Furthermore, the controller adjusts the lower limit frequency between a first lower limit frequency and a second lower limit frequency based on increase or decrease of the effective value.

Description

Power converters and methods of operation

The present invention relates to a power converter and an operating method thereof, in particular to a power converter that adjusts switching frequency based on load size and an operating method thereof.

The information industry has developed rapidly in recent years, and power supplies have played an important role. The power density and conversion efficiency of information power supply equipment in the Netcom and server industries are gradually required to increase while maintaining a fixed volume. In order to obtain higher efficiency and high power density, the AC/DC power converter in the front stage of the power supply uses a power factor corrector architecture that is gradually used, especially when using critical conduction mode ( The input current control technology of CRM (Critical-Conduction-Mode) or Triangular Current Mode (TCM; Triangular-Current-Mode) can increase the switching frequency and relatively reduce the size of the inductor core of the power factor corrector.

Common input current control methods are: TCM, CRM, discontinuous conduction mode (DCM; Discontinuous-Conduction-Mode) and continuous conduction mode (CCM; Continuous-Conduction-Mode). Among them, the power factor correction waveform diagram of the conventional power converter operating in the critical conduction mode is shown in FIG. 1A , and the power factor correction waveform diagram of the conventional power converter operating in the triangle current mode is shown in FIG. 1B . TCM and CRM input current control methods also operate at high-frequency switching frequencies. Compared with CCM input current control method, their turn on loss has a smaller advantage. However, in actual high-power applications, the inductor current peak (i.e., the maximum current) of the power factor corrector in these two control modes is approximately twice as large as that in the CCM input current control mode. The corresponding power switch must also withstand two twice the current stress. To this end, the conventional technology usually sets the hardware maximum fixed frequency and minimum fixed frequency of the power factor corrector. However, due to overload requirements of the power supply in special applications, it is easy to cause the inductor current of the power factor corrector to operate at a fixed minimum frequency for a long time, causing inductor saturation.

Therefore, how to design a power converter and its operation method to avoid the phenomenon that the inductor is prone to saturation due to overload requirements when the power factor corrector is operated in TCM and CRM is a major research topic that the creators of this project want to research. subject.

In order to solve the above problems, the present invention provides a power converter to overcome the problems of the conventional technology. Therefore, the power converter of the present invention receives an input voltage and provides an output voltage to power the load. The power converter includes a power factor correction circuit and a controller. The power factor correction circuit receives an input voltage and includes at least one power switch. The controller is coupled to the power switch and controls switching of the power switch to control the power factor correction circuit to convert the input voltage into an output voltage, and to control the input current of the power factor correction circuit to follow the input voltage. Among them, the controller obtains the switching frequency and frequency range based on the instantaneous value of the input voltage and the effective value of the input current. The frequency range includes the upper limit frequency and the lower limit frequency; when the controller determines that the effective value is higher than the medium load threshold, based on the switching frequency is lower than The operating mode of the power factor correction circuit is switched from the critical conduction mode to the continuous conduction mode and the switching frequency is limited to the lower limit frequency, or the operating mode is switched from the delta current mode to the continuous conduction mode and the switching frequency is limited to lower limit frequency. Wherein, when the controller determines that the effective value is higher than the medium load threshold, the controller adjusts the lower limit frequency between the first lower limit frequency and the second lower limit frequency based on the increase or decrease of the effective value.

In order to solve the above problems, the present invention provides an operating method of a power converter to overcome the problems of the conventional technology. Therefore, the power converter receives an input voltage and provides an output voltage to power the load; the power converter includes a power factor correction circuit, and the power factor correction circuit includes at least one power switch. The operating method of the power converter includes the following steps: obtaining the switching frequency and frequency range based on the instantaneous value of the input voltage and the effective value of the input current of the power factor correction circuit. The frequency range includes an upper limit frequency and a lower limit frequency. The switching frequency is determined based on the effective value being higher than the medium load threshold. (a) Based on the switching frequency being lower than the lower limit frequency, switching the operation mode of the power factor correction circuit from the critical conduction mode to the continuous conduction mode, and limiting the switching frequency to the lower limit frequency. Or (b) based on the switching frequency being lower than the lower limit frequency, changing the operation mode from the triangle current mode to the continuous conduction mode, and limiting the switching frequency to the lower limit frequency. Based on the increase of the effective value, the lower limit frequency is adjusted from the first lower limit frequency to the second lower limit frequency. The lower limit frequency is adjusted from the second lower limit frequency to the first lower limit frequency based on the reduction of the effective value.

The main purpose and effect of the present invention is to propose an operating mode of the power factor correction circuit. When the controller determines that the effective value is higher than the medium load threshold, the operating mode of the power factor correction circuit is changed based on the switching frequency being lower than the lower limit frequency. Adjust from CRM or TCM to CCM, and limit the switching frequency to the lower limit frequency. In addition, the controller also increases the lower limit frequency from the first lower limit frequency to the second lower limit frequency based on the increase in the effective value. In this way, the operating range (load range) can be changed widely, and the inductor current can be prevented from operating at a fixed minimum frequency for a long time, causing inductor saturation, and the ZVS load range can be changed widely.

In order to further understand the technology, means and effects adopted by the present invention to achieve the intended purpose, please refer to the following detailed description and drawings of the present invention. It is believed that the purpose, features and characteristics of the present invention can be understood in depth and For specific understanding, however, the attached drawings are only for reference and illustration, and are not intended to limit the present invention.

The technical content and detailed description of the present invention are as follows with reference to the drawings:

Please refer to FIG. 2A which is a circuit block diagram of the power converter with reduced power consumption according to the present invention. Please refer to FIG. 1 for details. The power converter 100 receives the input voltage Vin and provides the output voltage Vout to power the load 200 . The power converter 100 includes a power factor correction circuit 1, a driving circuit 2 and a controller 3. The power factor correction circuit 1 includes at least one inductor L, at least one power switch (SH, SL, S1, S2) and an output capacitor Cout. Taking the circuit structure of FIG. 2A as an example, the inductor L is configured at the input end of the power factor correction circuit 1 and receives the input voltage Vin. The output capacitor Cout is configured at the output end of the power factor correction circuit 1 and is coupled to the load 200 to provide the output voltage Vout to power the load 200 . The power switches (SH, SL, S1, S2) are coupled between the inductor L and the output capacitor Cout, and the driving circuit 2 is coupled between the controller 3 and the power switches (SH, SL, S1, S2).

The power converter 100 further includes an output detection circuit 4 and an input detection circuit 5. The output detection circuit 4 is coupled between the output capacitor Cout and the controller 3, and the input detection circuit 5 is coupled to the input of the power factor correction circuit 1. between terminal and controller 3. The output detection circuit detects the output voltage Vout to provide the feedback voltage V_fb corresponding to the output voltage Vout to the controller 3 . The input detection circuit 5 detects the input voltage Vin and the input current Iin at the input end of the power factor correction circuit 1 to provide an input signal S_in corresponding to the input voltage Vin and the input current Iin to the controller 3 . The controller 3 modulates the pulse width modulation signal PWM based on the feedback voltage V_fb and the input signal S_in to provide the pulse width modulation signal PWM to the driving circuit 2 .

The driving circuit 2 receives the pulse width modulation signal PWM, and drives the power switches (SH, SL, S1, S2) to switch on/off based on the pulse width modulation signal PWM. Therefore, the driving circuit 2 can operate the switching of the power switches (SH, SL, S1, S2) based on the pulse width modulation signal PWM to control the power factor correction circuit 1 to convert the input voltage Vin into the output voltage Vout, and control the power factor correction circuit The input current Iin of 1 follows the input voltage Vin. It is worth mentioning that in one embodiment of the present invention, the circuit structure of the power factor correction circuit 1 shown in FIG. 2A is only a schematic example. The power factor correction circuit 1 can use different circuit structures according to the requirements of the power converter 100 . Therefore, any AC/DC conversion circuit that can be used as the power factor correction circuit 1 should be included in the scope of this embodiment, and will not be described again here.

Please refer to FIG. 2B for a circuit block diagram of the controller of the present invention, and refer to FIG. 2A for details. The controller 3 includes an error amplifier 32 and a control module 30 , and the control module 30 includes a voltage controller 34 and a current controller 36 . The error amplifier 32 is coupled to the output capacitor Cout through the output detection circuit 4 to receive the feedback voltage V_fb corresponding to the output voltage Vout. The error amplifier 32 generates an error signal Ver based on the feedback voltage V_fb and the reference voltage Vref, and the control module 30 is coupled to the error amplifier 32 to receive the error signal Ver. The control module 30 generates the pulse width modulation signal PWM based on the error signal Ver and the input signal S_in, and mainly calculates the switching frequency of the power switches (SH1, SL1, SN, SP) through the voltage controller 34 and the current controller 36. And the switching frequency limitation/adjustment mechanism, and accordingly generates the pulse width modulation signal PWM accordingly.

Furthermore, since the switching frequencies of the input current control methods of Critical-Conduction-Mode (CRM) and Triangular-Current-Mode (TCM) are both frequency control, the input voltage Vin and input current Iin Both are a time function vac(ωt) of the instantaneous value of the input voltage Vin and a time function iac(ωt) of the instantaneous value of the input current Iin. That is to say, under a fixed load (corresponding to the effective value of the fixed input current Iin), the instantaneous value of the input voltage Vin at different mains voltage angles, the required switching frequencies of the power switches (SH, SL, S1, S2) are all Are not the same. The specific value of the switching frequency can be the instantaneous value of the input voltage Vin, the output voltage Vout, the inductance of the inductor L and the instantaneous value of the input current Iin and other related values (TCM). In addition, the power switch (SH, SL, S1, S2) needs to be considered. ) is obtained through the calculation of the voltage controller 34 and the current controller 36 . For example, under a fixed load condition, the angles of the input voltage Vin are 90 degrees and 45 degrees, and the switching frequencies are different. Among them, the switching frequency range of the CRM and TCM control methods can be from several kHz to several MHz (for example, but not limited to, 30KHz~3MHz).

3A is a schematic diagram of the switching frequency curve of the power converter of the present invention operating in the critical conduction mode. FIG. 3B is a schematic diagram of the switching frequency curve of the power converter of the present invention operating in the delta current mode. Refer to FIG. 2 in conjunction with the present invention. The controller 3 can mainly operate the power factor correction circuit 1 in CRM and TCM. The reason is that the input current control methods of CRM and TCM also operate at high-frequency switching frequencies, which is the same as the continuous conduction mode (Continuous-Conduction-Mode; CCM). ), it has the advantage of smaller turn on loss.

Because of the input current control method of CRM, when the input voltage is less than 1/2 of the output voltage, the power switch (SH, SL, S1, S2) can be switched by switching the power switch (SH, SL, S1, S2) of the fast arm. Operates in zero-voltage switching (Zero-Voltage Switching). When the input voltage is higher than 1/2 of the output voltage, the power switch (SH, SL, S1, S2) can be turned on when the drain-source voltage Vds is at the bottom. Therefore, conduction loss can be reduced. In addition, the input current control method of TCM can allow the power switches (SH, SL, S1, S2) of the fast arm to operate at ZVS at any phase angle of the input voltage.

Furthermore, in FIG. 3A , the switching frequency Fsw of the power converter 100 operating at CRM is a smile curve. In the half-wave of the input voltage Vin, when the load is lighter (that is, when the effective value corresponding to the input current Iin is lower, such as but not limited to 1A), the smile curve is higher, and vice versa. This means that when the effective value of the input current Iin is lower, the switching frequency Fsw will be higher, and vice versa. Among them, the switching frequency Fsw is higher when the angle of the input voltage Vin is close to the zero-crossing point, and is lower when the angle of the input voltage Vin is close to 90 degrees. Therefore, the switching frequency Fsw of the CRM operation is determined by the controller 3 according to the instantaneous value of the input voltage Vin and the instantaneous value of the input current Iin, and the switching frequency Fsw of each point is different.

On the other hand, in FIG. 3A , the controller 3 can also set a maximum frequency Fup_lim, and the maximum frequency Fup_lim usually refers to the upper limit of the hardware design of the power converter 100 . Specifically, each power converter 100 must set the maximum frequency Fup_lim according to the internal component design (such as but not limited to the inductance value of the inductor L, etc.) and the specifications of the controller 3 . When the maximum frequency Fup_lim is exceeded, it usually exceeds the upper limit that the controller 3 can control, causing the power converter 100 to be out of control and abnormal. Especially when the angle of the input voltage Vin is close to the zero-crossing point and the load is light (such as but not limited to 1A), the switching frequency Fsw has reached as high as 400KHz, which is bound to exceed the upper limit that the controller 3 can control, or may cause Obstacles in controller 3 specification selection.

In FIG. 3B , the switching frequency Fsw of the TCM when the power converter 100 operates is an M-shaped curve. Similarly, in the half-wave of the input voltage Vin, when the load is lighter (that is, when the corresponding effective value of the input current Iin is lower, such as but not limited to 1A), the M-shaped curve is higher, and vice versa. However, when the angle of the input voltage Vin is close to the zero-crossing point, the switching frequency Fsw is extremely low. As the angle of the input voltage Vin gradually leaves the zero-crossing point, the switching frequency Fsw will rise sharply. When the angle of the input voltage Vin approaches 90 degrees, the switching frequency Fsw will gradually decrease. Similarly, the switching frequency Fsw operating in the TCM is determined by the controller 3 according to the instantaneous value of the input voltage Vin and the instantaneous value of the input current Iin, and the switching frequency Fsw of each point is different.

On the other hand, in FIG. 3B , in addition to setting the maximum frequency Fup_lim, the controller 3 also sets a minimum frequency Flow_lim, and the minimum frequency Flow_lim usually refers to the lower limit of the frequency at which the power converter 100 can operate. Specifically, because in the operation of the TCM, when the angle of the input voltage Vin is close to the zero-crossing point, the calculated switching frequency Fsw is extremely low (for example, but not limited to, below 1 KHz). Too low switching frequency Fsw may cause the switching speed of the control power switch (SH, SL, S1, S2) to be too slow, causing the angle of the input voltage Vin to deviate from the zero-crossing point, but the switching speed cannot respond quickly enough, causing the power converter to 100 An out-of-control and abnormal situation.

Please refer to FIG. 4A , which is a diagram of the switching frequency operating range of the power converter of the present invention operating in the critical conduction mode, and refer to FIGS. 2A to 3A in conjunction. The controller 3 obtains the frequency range based on the effective value Iin_rms of the input current Iin. The frequency range Fr includes the upper limit frequency Fup and the lower limit frequency Flow. Among them, the upper limit frequency Fup and the lower limit frequency Flow are mainly composed of the smile curve in Figure 3A. The size of the input current Iin (expressed as an effective value) can correspond to each interval (interval I~V) in Figure 4A, and the input current Iin The size also corresponds to the size of the load 200. When the load 200 is no load or light load, the effective value Iin_rms of the input current Iin is low (for example, but not limited to interval I), and vice versa (heavy load) is high (for example, but not limited to interval V). The controller 3 also obtains the switching frequency Fsw based on the instantaneous value of the input voltage Vin, and confirms whether the switching frequency Fsw falls within the frequency range Fr. The instantaneous value of the input voltage Vin and the effective value Iin_rms of the input current Iin can be obtained by the controller 3 receiving the input signal S_in provided by the input detection circuit 5 .

When the load is no load or light load, the controller 3 operates the power converter 100 in interval I. Due to the characteristics of CRM, under a fixed load, the calculated switching frequency Fsw may exceed the maximum frequency Fup_lim limit of the hardware bandwidth, so the controller 3 can set the upper limit frequency Fup to the maximum frequency Fup_lim. When the calculated switching frequency Fsw exceeds the preset upper limit frequency Fup, it operates at a fixed frequency (that is, the upper limit frequency Fup equal to the highest frequency Fup_lim), and the operating mode of the power factor correction circuit 1 is switched from CRM to CCM. . Therefore, when operating in interval I and the switching frequency Fsw calculated by the controller 3 exceeds the preset upper limit frequency Fup, the controller 3 switches the operating mode of the power factor correction circuit 1 to CCM, and the switching frequency Fsw Set to a fixed frequency.

On the contrary, if the calculated switching frequency Fsw does not exceed the preset upper limit frequency Fup, the controller 3 switches the operating mode of the power factor correction circuit 1 to the CRM mode, and the switching frequency Fsw is calculated according to the controller 3 The result is a switching action (i.e. frequency conversion operation). It is worth mentioning that since the switching frequency Fsw of the power converter 100 operating in CRM is a smile curve, and the switching frequency Fsw in the interval I, no matter how low it is, it will not be lower than the lowest frequency Flow_lim of the hardware bandwidth, so the interval I The lower limit frequency Flow is not the lowest frequency Flow_lim.

When the load gradually increases and the effective value Iin_rms of the input current Iin leaves the interval I, it means that the load 200 increases and enters the interval II. The switching frequency Fsw calculated by the controller 3 will no longer be higher than the highest frequency Fup_lim, and the bottom of the smile curve (ie, the lower limit frequency Flow) will not touch the lowest frequency Flow_lim. Therefore, the controller 3 sets the operating mode of the power factor correction circuit 1 to CRM, and the switching frequency Fsw is modulated (ie, frequency-converted) according to the calculation of the controller 3 . Until the effective value Iin_rms of the input current Iin reaches the medium load threshold Tm, the controller 3 operates the power factor correction circuit 1 in the variable frequency CRM. Since in the interval I~II, the higher the effective value Iin_rms is, the lower the upper limit frequency Fup and the lower limit frequency Flow are. Therefore, the effective value Iin_rms is negatively correlated with the upper limit frequency Fup and the lower limit frequency Flow.

When the controller 3 determines that the load is gradually increasing and the effective value Iin_rms is raised to the medium load threshold Tm, it enters interval III. In interval III, if the switching frequency Fsw calculated by the controller 3 based on the instantaneous value of the input voltage Vin is lower than the lower limit frequency Flow, the controller 3 switches the operating mode of the power factor correction circuit 1 from CRM to CCM, and The switching frequency Fsw is limited to a fixed frequency (ie, the lower limit frequency Flow). Among them, the lower limit frequency Flow can be the frequency calculated by the current effective value Iin_rms (that is, the lowest lower limit frequency Flow), or it can be the lowest frequency Flow_lim of the hardware bandwidth set by the controller 3, or it can be preset for the controller 3 a frequency value. Of course, the highest frequency Fup_lim of interval I can also be a frequency value preset by controller 3.

When the controller 3 determines that the load gradually increases from the medium load threshold Tm, the controller 3 will increase the lower limit frequency from the first lower limit frequency Flow_1 to the second lower limit frequency Flow_2 based on the increase in the effective value Iin_rms. On the contrary, the controller 3 lowers the lower limit frequency from the second lower limit frequency Flow_2 to the first lower limit frequency Flow_1 based on the decrease of the effective value Iin_rms. In this way, based on the increase of the effective value Iin_rms, the frequency at which the power factor correction circuit 1 enters CCM will gradually increase from the first lower limit frequency Flow_1 to the second lower limit frequency Flow_2. Therefore, as the load increases, the lower limit of the switching frequency Fsw will also increase as the load increases. When the switching frequency Fsw calculated by the controller 3 falls within the frequency range Fr, the controller 3 switches the operating mode of the power factor correction circuit 1 to CRM, and vice versa.

When the controller 3 determines that the load gradually increases from the medium load threshold Tm, and the decrease of the upper limit frequency Fup and the increase of the lower limit frequency Flow cause the upper limit frequency Fup to equal the lower limit frequency Flow (i.e., the second lower limit frequency Flow_2), the interval IV is entered. Since the upper limit frequency Fup decreases and the lower limit frequency Flow increases, the two curves will inevitably touch each other, so that the frequency range Fr in the interval IV no longer exists. Therefore, after interval IV, the switching frequency Fsw will completely leave the CRM and enter the CCM of a fixed frequency (fixed at the second lower limit frequency Flow_2) until the effective value Iin_rms rises to the overload threshold Th.

When the controller 3 determines that the effective value Iin_rms is higher than the overload threshold Th, it enters the interval V. The controller 3 still fixes the switching frequency Fsw at the second lower limit frequency Flow_2, but the controller 3 adjusts the second lower limit frequency Flow_2 based on the size of the effective value Iin_rms. Specifically, when entering the interval V, the controller increases the second lower limit frequency Flow_2 based on the increase in the effective value Iin_rms, and vice versa, decreases the second lower limit frequency Flow_2. Therefore, in the interval V, the size of the effective value Iin_rms is positively correlated with the second lower limit frequency Flow_2, and as the load increases, the second lower limit frequency Flow_2 will also increase as the load increases. It is worth mentioning that in one embodiment of the present invention, the medium load threshold Tm and the heavy load threshold Th can be determined according to the circuit parameters of the power factor correction circuit 1 (such as but not limited to the input voltage Vin, the inductance value of the inductor L, etc.) Design, and the threshold can be adjusted according to user needs.

On the other hand, due to this fixed frequency operation and the second lower limit frequency Flow_2 being adjusted with the size of the effective value Iin_rms, when operating under a fixed load, the adjustment of the input voltage Vin will cause the effective value Iin_rms and the switching frequency Fsw to change with the size of the effective value Iin_rms. The change is mainly because changes in the input voltage Vin will affect the input current Iin, causing the controller 3 to adjust the effective value Iin_rms based on the input voltage Vin, thereby changing the switching frequency Fsw. Specifically, when the input voltage Vin increases, the controller 3 will reduce the effective value Iin_rms, causing the switching frequency Fsw to also decrease. On the contrary, the effective value Iin_rms increases accordingly, causing the switching frequency Fsw to also increase. Therefore, the input voltage Vin has a negative correlation with the switching frequency Fsw and the effective value Iin_rms.

Please refer to FIG. 4B , which is a diagram of the switching frequency operating range of the power converter of the present invention operating in the triangle current mode, and refer to FIGS. 2A to 4A in conjunction. The difference between the TCM operation interval in Figure 4B and Figure 4A is that when the effective value Iin_rms is lower than the medium load threshold Tm, the controller 3 sets the lower limit frequency Flow to a fixed frequency. Referring again to Figure 3B, since the calculated switching frequency Fsw of the TCM is extremely low when the angle of the input voltage Vin is close to the zero-crossing point (for example, but not limited to, below 1KHz), a fixed lower limit frequency must be preset. Flow. Similar to Figure 4A, the lower limit frequency Flow can be the frequency calculated by the current effective value Iin_rms (that is, the lowest lower limit frequency Flow), or it can be the lowest frequency Flow_lim of the hardware bandwidth set by the controller 3, or it can be determined by the controller. 3A preset frequency value.

In short, when the switching frequency Fsw calculated by the controller 3 falls within the frequency range Fr, the controller 3 switches the operating mode of the power factor correction circuit 1 to TCM, and vice versa. Therefore, in interval I, when the switching frequency Fsw calculated by the controller 3 exceeds the preset maximum frequency Fup_lim or the lower limit frequency Flow, the controller 3 switches the operating mode of the power factor correction circuit 1 to CCM, and The switching frequency Fsw is set to a fixed frequency (ie, the highest frequency Fup_lim or the lower limit frequency Flow). In interval II, when the switching frequency Fsw calculated by the controller 3 exceeds the preset lower limit frequency Flow, the controller 3 switches the operating mode of the power factor correction circuit 1 to CCM, and sets the switching frequency Fsw to a fixed value. Frequency (i.e. lower limit frequency Flow).

In interval III, when the controller 3 determines that the load gradually increases and the effective value Iin_rms rises to the medium load threshold Tm, and the switching frequency Fsw calculated by the controller 3 based on the instantaneous value of the input voltage Vin is lower than the lower limit frequency Flow , the controller 3 switches the operating mode of the power factor correction circuit 1 from TCM to CCM, and limits the switching frequency Fsw to a fixed frequency (ie, the lower limit frequency Flow). Furthermore, the controller 3 will increase the lower limit frequency from the first lower limit frequency Flow_1 to the second lower limit frequency Flow_2 based on the increase of the effective value Iin_rms. In this way, based on the increase of the effective value Iin_rms, the frequency at which the power factor correction circuit 1 enters CCM will gradually increase from the first lower limit frequency Flow_1 to the second lower limit frequency Flow_2. It is worth mentioning that in one embodiment of the present invention, the operation mode of the controller 3 not mentioned in Figure 4B is the same as that in Figure 4A and will not be described again.

Furthermore, the present invention uses TCM or CRM input current control to solve the problem that power switches (SH, SL, S1, S2) in high-power applications need to withstand large current stress. Usually, when operating under light load conditions, the switching frequency is higher. Due to factors such as hardware bandwidth limitations, a maximum fixed operating frequency will be limited. On the contrary, when operating under heavy load conditions, the switching frequency is low. In order to prevent the inductor L of the power factor correction circuit 1 from saturating or reducing the current stress of the power switches (SH, SL, S1, S2), a minimum fixed operating frequency. Therefore, in practical applications, once the core (Ae value) of the inductor L is selected, the required inductance/number of turns of the inductor L can be determined. In order to obtain higher circuit efficiency, the minimum operating frequency is usually limited to a lower level. The reason is that 1. the above two control methods can achieve a wide change in the ZVS load range, 2. operating in CCM when the load is heavier can reduce the inductance L Core loss.

In addition, the rapid improvement in the performance of information industry equipment in recent years has led to some more extreme applications. For example, 1.2 times the rated power cannot be protected, or the instantaneous output must withstand nearly twice the power. In this way, the steady-state current and transient current of the input current Iin of the power factor correction circuit 1 will become larger in these special applications. These conditions will easily cause the inductor current Il to operate at a fixed minimum frequency for a long time, which will easily cause the saturation of the inductor L.

The main purpose and effect of the present invention is to retain the aforementioned advantages of increasing the power density per unit volume and high efficiency, and to apply it when the load is 1.2 times the rated power cannot be protected, or the instantaneous output can withstand twice as fast In the special environment of high power, and to avoid the saturation phenomenon of the inductor L, the present invention proposes a technology that can widen the operating range (load range) of the two control methods to achieve the effect of widening the ZVS load range.

Its main operation mode is as described in the interval III of Figure 4A~4B. When the controller determines that the effective value Iin_rms is higher than the medium load threshold Tm, the power factor correction circuit 1 is changed based on the switching frequency Fsw being lower than the lower limit frequency Flow. The operating mode is adjusted from CRM or TCM to CCM, and the switching frequency Fsw is limited to the lower limit frequency Flow. Furthermore, the controller 3 also increases the lower limit frequency Flow from the first lower limit frequency Flow_1 to the second lower limit frequency Flow_2 based on the increase of the effective value Iin_rms. In this way, the operating range (load range) can be changed widely, and the inductor current can be prevented from operating at a fixed minimum frequency for a long time, causing inductor saturation, and the ZVS load range can be changed widely.

Please refer to FIG. 5 for a flow chart of the operation method of the power converter of the present invention, and refer to FIGS. 2A to 4B for details. The present invention mainly uses an operating method as shown in Figures 4A~4B to control the power factor correction circuit 1. Mainly, when the switching frequency Fsw calculated by the controller 3 falls within the frequency range Fr, the controller 3 will Switch the operating mode of the power factor correction circuit 1 to CRM or TCM, and vice versa to CCM. And according to the interval in which the effective value Iin_rms falls, the CCM is set to a fixed frequency or the switching frequency Fsw is adjusted as the effective value Iin_rms changes. Therefore, the operation method of the power converter 100 includes determining whether the effective value is higher than the overload threshold (S100). If so, the operation mode of the power factor correction circuit 1 is switched to CCM, the switching frequency is fixed at the second lower limit frequency, and the second lower limit frequency is adjusted based on the size of the effective value (S120). Otherwise, it is determined whether there is a frequency range (S200). If not, the operation mode of the power factor correction circuit 1 is switched to CCM, and the switching frequency is fixed at the second lower limit frequency (S220).

When the determination in step (S200) is yes, it is determined whether it is within the frequency range (S300). If so, the operation mode of the power factor correction circuit 1 is switched to CRM or TCM (S320), so that the switching frequency Fsw is adjusted through calculation by the controller 3. Otherwise, the operation mode of the power factor correction circuit 1 is switched to CCM (S400), and it is determined whether the effective value is higher than the medium load threshold (S420). If not, the switching frequency is limited to a fixed frequency (S440, that is, the upper limit frequency Fup or the lower limit frequency Flow). On the contrary, the switching frequency is fixed at the lower limit frequency, and the lower limit frequency is adjusted between the first lower limit frequency and the second lower limit frequency based on the increase or decrease of the effective value (S460). It is worth mentioning that in one embodiment of the present invention, process steps not described in Figure 5 can be referred to Figures 4A-4B and will not be described again.

However, the above are only detailed descriptions and drawings of preferred embodiments of the present invention. However, the characteristics of the present invention are not limited thereto and are not used to limit the present invention. The entire scope of the present invention should be applied in the following terms The patent scope shall prevail. All embodiments that are within the spirit of the patentable scope of the present invention and similar modified embodiments shall be included in the scope of the present invention. Anyone familiar with the art can easily think of it in the field of the present invention. Changes or modifications may be covered by the following patent scope of this case.

100:Power converter

1: Power factor correction circuit

L: inductance

SH, SL, S1, S2: power switch

Cout: output capacitor

2: Drive circuit

3:Controller

32: Error amplifier

30:Control module

34:Voltage controller

36:Current controller

4: Output detection circuit

5: Input detection circuit

200:Load

Vin: input voltage

Vout: output voltage

V_fb: feedback voltage

Vref: reference voltage

Iin: input current

Iin_rms:valid value

S_in: input signal

Ver: error signal

PWM: pulse width modulation signal

Fsw: switching frequency

Fup_lim: highest frequency

Flow_lim: lowest frequency

Fr: frequency range

Fup: upper limit frequency

Flow: lower limit frequency

Flow_1: first lower limit frequency

Flow_2: second lower limit frequency

I~V: interval

Tm: medium load threshold

Th: reload threshold

(S100)~(460): steps

Figure 1A is a power factor correction waveform diagram of a conventional power converter operating in critical conduction mode;

Figure 1B is a power factor correction waveform diagram of a conventional power converter operating in the triangle current mode;

Figure 2A is a circuit block diagram of a power converter with reduced power consumption according to the present invention;

Figure 2B is a circuit block diagram of the controller of the present invention;

Figure 3A is a schematic diagram of the switching frequency curve of the power converter of the present invention operating in critical conduction mode;

Figure 3B is a schematic diagram of the switching frequency curve of the power converter of the present invention operating in the triangle current mode;

Figure 4A is a switching frequency operating interval diagram of the power converter of the present invention operating in critical conduction mode;

Figure 4B is a switching frequency operating interval diagram of the power converter of the present invention operating in the triangle current mode; and

Figure 5 is a flow chart of the operating method of the power converter of the present invention.

(S100)~(S460): steps

Claims (18)

A power converter receives an input voltage and provides an output voltage to power a load. The power converter includes: a power factor correction circuit that receives the input voltage and includes at least one power switch; A controller coupled to the at least one power switch and controlling the switching of the at least one power switch to control the power factor correction circuit to convert the input voltage into an output voltage, and to control an input current tracking of the power factor correction circuit The input voltage; Among them, the controller obtains a switching frequency and a frequency range based on an instantaneous value of the input voltage and an effective value of the input current. The frequency range includes an upper limit frequency and a lower limit frequency; when the controller determines the effective value When it is higher than a medium load threshold, an operating mode of the power factor correction circuit is switched from a critical conduction mode to a continuous conduction mode based on the switching frequency being lower than the lower limit frequency, and the switching frequency is limited to the lower limit frequency. , or switch the operation mode from a triangle current mode to the continuous conduction mode, and limit the switching frequency to the lower limit frequency; and Wherein, when the controller determines that the effective value is higher than a medium load threshold, the controller adjusts the lower limit frequency between a first lower limit frequency and a second lower limit frequency based on the increase or decrease of the effective value. The power converter of claim 1, wherein when the controller determines that the switching frequency is higher than the upper limit frequency, the operation mode is switched to the continuous conduction mode and the switching frequency is limited to the upper limit frequency. The power converter of claim 1, wherein when the controller determines that the switching frequency is within the frequency range, the controller sets the operating mode to the critical conduction mode or the triangle current mode. For the power converter described in claim 1, when the controller determines that the effective value is lower than the medium load threshold and the operating mode is the critical conduction mode, the controller sets the lower limit frequency and the effective value to be negative. Related. In the power converter of claim 1, when the controller determines that the effective value is lower than the medium load threshold and the operation mode is the triangle current mode, the controller sets the lower limit frequency to a fixed frequency. The power converter as described in claim 1, wherein when the controller determines that the effective value is lower than a heavy load threshold and the upper limit frequency is equal to the second lower limit frequency, the operation mode is switched to the continuous conduction mode, And the switching frequency is limited to the second lower limit frequency. The power converter of claim 6, wherein when the controller determines that the effective value is higher than the overload threshold, the controller adjusts the second lower limit frequency based on the effective value, and the controller sets the effective value It is positively correlated with the second lower limit frequency. The power converter of claim 7, wherein the controller adjusts the switching frequency and the effective value based on the input voltage, and the controller sets the input voltage, the switching frequency, and the effective value to be negatively correlated. The power converter as described in claim 1, wherein the controller includes: an error amplifier coupled to an output end of the power factor correction circuit and generating an error signal based on the output voltage and a reference voltage; and a control module coupled to the error amplifier and generating a pulse width modulation signal based on the error signal and an input signal, and the pulse width modulation signal is used to control the switching of the at least one power switch; Wherein, the input signal includes the input voltage and the input current, and the control module obtains the instantaneous value and the effective value based on the input signal. A method of operating a power converter that receives an input voltage and provides an output voltage to power a load; the power converter includes a power factor correction circuit, and the power factor correction circuit includes at least one power switch ;The operation method includes the following steps: Obtaining a switching frequency and a frequency range based on an instantaneous value of the input voltage and an effective value of an input current of the power factor correction circuit, the frequency range includes an upper limit frequency and a lower limit frequency; Determine the switching frequency based on the effective value being higher than a medium load threshold; (a) Switch an operating mode of the power factor correction circuit from a critical conduction mode to a continuous conduction mode based on the switching frequency being lower than the lower limit frequency, and limit the switching frequency to the lower limit frequency; or (b) Switch the operating mode from a triangle current mode to the continuous conduction mode based on the switching frequency being lower than the lower limit frequency, and limit the switching frequency to the lower limit frequency; The lower limit frequency is raised from a first lower limit frequency to a second lower limit frequency based on the increase in the effective value; and Based on the reduction of the effective value, the lower limit frequency is adjusted from the second lower limit frequency to the first lower limit frequency. The operation method described in claim 10 further includes the following steps: It is determined that the switching frequency is higher than the upper limit frequency; and The operation mode is switched to the continuous conduction mode, and the switching frequency is limited to the upper limit frequency. The operation method described in claim 10 further includes the following steps: Determine that the switching frequency is within the frequency range; and The operating mode is set to the critical conduction mode or the delta current mode. The operation method described in claim 10 further includes the following steps: (a1) It is determined that the effective value is lower than the medium load threshold and the operation mode is the critical conduction mode; and (a2) Set the lower limit frequency to be negatively correlated with the effective value. The operation method described in claim 10 further includes the following steps: (b1) It is determined that the effective value is lower than the medium load threshold and the operation mode is the triangle current mode; and (b2) Set the lower limit frequency to a fixed frequency. The operation method described in claim 10 further includes the following steps: Determine that the effective value is lower than an overload threshold, and the upper limit frequency is equal to the second lower limit frequency; and The operation mode is switched to the continuous conduction mode, and the switching frequency is limited to the second lower limit frequency. The operation method described in request item 15 further includes the following steps: The effective value is determined to be higher than the reload threshold; and The second lower limit frequency is adjusted based on the effective value, and the effective value and the second lower limit frequency are set to be positively correlated. The operation method described in request item 16 further includes the following steps: The switching frequency and the effective value are adjusted based on the input voltage, and the input voltage, the switching frequency and the effective value are set to be negatively correlated. The operation method described in claim 10 further includes the following steps: Generate an error signal based on the output voltage and a reference voltage; Generating a pulse width modulation signal for controlling switching of the at least one power switch based on the error signal and an input signal; and The instantaneous value and the effective value are obtained based on the input signal to calculate the switching frequency, the upper limit frequency and the lower limit frequency.

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