CN105006805A - Over-current protection apparatus and method for power factor correction (PFC) circuit - Google Patents

Abstract

The invention discloses an over-current protection apparatus and method for a power factor correction (PFC) circuit. The apparatus includes a first voltage detection module for detecting an input voltage of the PFC circuit; a current module for detecting an input current of the PFC circuit; a second voltage detection module for detecting an output voltage of the PFC circuit; a current over-current protection module for generating a first protection signal when the input current is less than or equal to a preset maximum permissible current and the input voltage is less than or equal to the output voltage; and a PFC control module for calculating a duty ratio of the PFC circuit in the next switch period when the first protection signal is received, calculating a maximum permissible duty ratio in the next switch period, and controlling the PFC circuit according to the duty ratio and the maximum permissible duty ratio in the next switch period. The apparatus can predict the over-current fault in advance, and effectively improves the over-current response speed of the PFC circuit, thereby effectively raising the reliability of the PFC circuit.

Description

The overcurrent protective device of power factor correction pfc circuit and method

Technical field

The present invention relates to household electrical appliance technical field, particularly a kind of PFC (Power Factor Correction, power factor correction) overcurrent protective device of circuit and a kind of over-current protection method of pfc circuit.

Background technology

At present, white domestic appliances such as convertible frequency air-conditioner, the refrigerator etc. much with energy-saving effect all need direct current supply, therefore need the single-phase or three-phase alternating current provided by electrical network to be converted to direct current through rectification circuit.And in order to reduce the current harmonics and reactive power that power consumption equipment produces, improve the electrical network quality of power supply, pfc circuit becomes a requisite link.

In home appliance; pfc circuit is generally Boost type pfc circuit; this main circuit will comprise inductance, fast recovery diode and IGBT (Insulated Gate Bipolar Transistor; insulated gate bipolar transistor); wherein, IGBT is the important devices realizing boost function and power factor emendation function, and IGBT is expensive; easily damage when overcurrent or overvoltage, therefore very important to the protection of IGBT.

Usually, hardware protection and software protection are mainly divided into the protection of IGBT.Wherein, hardware protection mainly passes through comparison circuit; the current flow and current threshold (current value that maximum permission is passed through) that pass through IGBT are compared, if current flow exceedes current threshold, then comparison circuit output protection signal is to turn off pfc circuit.Software protection is compared by the input current of pfc circuit and the lowest high-current value of setting of sampling, when the present input current of sampling exceedes lowest high-current value, is zero turn off pfc circuit by arranging the conducting duty ratio of IGBT.

But there is two problems in said method, one is do not distinguish whether electric current flows through IGBT, as long as namely present input current exceedes current threshold (being generally the lowest high-current value that IGBT allows to flow through) and just protects, but in fact in pfc circuit, the rated current of other components and parts is above this current threshold, not necessarily needs to protect when IGBT is in off state; Secondly, when pfc circuit is opened, normally just protect when the electric current of pfc circuit has has met or exceeded current threshold, therefore exist certain delayed, likely IGBT has been damaged and has just protected.Therefore, need to improve the guard method of IGBT.

Summary of the invention

The present invention is intended to solve one of technical problem in correlation technique at least to a certain extent.For this reason, one object of the present invention is that proposing one can improve overcurrent protection response speed, and then the overcurrent protective device of the pfc circuit of raising pfc circuit reliability.

Another object of the present invention is the over-current protection method proposing a kind of pfc circuit.

For achieving the above object, one aspect of the present invention embodiment proposes a kind of overcurrent protective device of pfc circuit, comprising: the first voltage detection module, and described first voltage detection module is for detecting the input voltage of described pfc circuit; Current detection module, described current detection module is for detecting the input current of described pfc circuit; Second voltage detection module, described second voltage detection module is for detecting the output voltage of described pfc circuit; Overcurrent protection module, described overcurrent protection module is connected with described second voltage detection module with described first voltage detection module, described current detection module respectively, and described overcurrent protection module generates the first guard signal when described input current is less than or equal to default maximum permissible current and described input voltage is less than or equal to described output voltage; PFC control module; described PFC control module is connected with described overcurrent protection module; described PFC control module calculates the duty ratio of described pfc circuit in next switch periods when receiving described first guard signal that described overcurrent protection module sends; and calculate the maximum permission duty ratio of described pfc circuit in next switch periods described, and described pfc circuit is controlled in the duty ratio of next switch periods and described maximum permission duty ratio according to described pfc circuit.

According to the overcurrent protective device of the pfc circuit of the embodiment of the present invention, the input voltage of pfc circuit is detected by the first voltage detection module, and the input current of pfc circuit is detected by current detection module, and the output voltage of pfc circuit is detected by the second voltage detection module, overcurrent protection module generates the first guard signal when input current is less than or equal to default maximum permissible current and input voltage is less than or equal to output voltage, PFC control module calculates the duty ratio of pfc circuit in next switch periods when receiving the first guard signal that overcurrent protection module sends, and calculate the maximum permission duty ratio of pfc circuit in next switch periods, and pfc circuit is controlled in the duty ratio of next switch periods and maximum permission duty ratio according to pfc circuit.Therefore; the overcurrent protective device of the pfc circuit of the embodiment of the present invention to limit with the duty ratio of switch tube by predicting in the maximum permission duty ratio of next switch periods pfc circuit breaker in middle pipe; avoid switching tube overcurrent damage; thus improve the response speed of overcurrent protection, and then improve the reliability of pfc circuit.

According to one embodiment of present invention, described PFC control module according to following formulae discovery pfc circuit in the duty ratio of next switch periods:

${\mathrm{\ΔI}}_{in}=\frac{V_{in}}{fL}d$

Wherein, Δ I _infor the difference of the target input current of described pfc circuit in the input current of pfc circuit described in current switch period and next switch periods, d is the duty ratio of described pfc circuit in next switch periods, and f is the switching frequency of described pfc circuit, and L is PFC inductance value, V _infor the input voltage of described pfc circuit.

According to one embodiment of present invention, described PFC control module maximum permission duty ratio according to following formulae discovery:

$d_{max}=min\left\{\frac{(I_{max}-I_{in})fL}{V_{in}},\frac{{\mathrm{\ΔI}}_{c}fL}{V_{in}}\right\}$

Wherein, d _maxfor described maximum permission duty ratio, I _maxfor described default maximum permissible current, min{} for getting the small value, Δ I _cfor the maximum current increment preset, f is the switching frequency of described pfc circuit, and L is PFC inductance value, V _infor the input voltage of described pfc circuit, I _infor the input current of pfc circuit described in current switch period.

According to one embodiment of present invention, described PFC control module according to described pfc circuit when the duty ratio of next switch periods and described maximum permission duty ratio control described pfc circuit, wherein, when described pfc circuit is more than or equal to described maximum permission duty ratio in the duty ratio of next switch periods, described PFC control module controls the switching tube in described pfc circuit according to described maximum permission duty ratio; When described pfc circuit is less than described maximum permission duty ratio in the duty ratio of next switch periods, described PFC control module controls the switching tube in described pfc circuit according to the duty ratio of described pfc circuit in next switch periods.

According to one embodiment of present invention; when described input current is greater than described default maximum permissible current or described input voltage is greater than described output voltage; described overcurrent protection module exports the second guard signal to described PFC control module, outputs to the duty ratio of described pfc circuit for 0 to make described PFC control module.

For achieving the above object, the present invention on the other hand embodiment proposes a kind of over-current protection method of pfc circuit, comprises the following steps: the input voltage and the input current that detect described pfc circuit, and detects the output voltage of described pfc circuit; When described input current is less than or equal to default maximum permissible current and described input voltage is less than or equal to described output voltage, overcurrent protection module exports the first guard signal to PFC control module; Described PFC control module calculates the duty ratio of described pfc circuit in next switch periods when receiving described first guard signal that described overcurrent protection module sends; and calculate the maximum permission duty ratio of described pfc circuit in next switch periods described, and described pfc circuit is controlled in the duty ratio of next switch periods and described maximum permission duty ratio according to described pfc circuit.

According to the over-current protection method of the pfc circuit of the embodiment of the present invention, the input voltage of real-time detection pfc circuit, input current and output voltage, when input current is less than or equal to default maximum permissible current and input voltage is less than or equal to output voltage, overcurrent protection module exports the first guard signal to PFC control module, PFC control module calculates the duty ratio of pfc circuit in next switch periods when receiving the first guard signal that overcurrent protection module sends, and calculate the maximum permission duty ratio of pfc circuit in next switch periods, and pfc circuit is controlled in the duty ratio of next switch periods and maximum permission duty ratio according to pfc circuit.Therefore; the over-current protection method of the pfc circuit of the embodiment of the present invention to limit with the duty ratio of switch tube by predicting in the maximum permission duty ratio of next switch periods pfc circuit breaker in middle pipe; avoid switching tube overcurrent damage; thus improve the response speed of overcurrent protection, and then improve the reliability of pfc circuit.

According to one embodiment of present invention, according to following formulae discovery pfc circuit in the duty ratio of next switch periods:

${\mathrm{\ΔI}}_{in}=\frac{V_{in}}{fL}d$

Wherein, Δ I _infor the difference of the target input current of described pfc circuit in the input current of pfc circuit described in current switch period and next switch periods, d is the duty ratio of described pfc circuit in next switch periods, and f is the switching frequency of described pfc circuit, and L is PFC inductance value, V _infor the input voltage of described pfc circuit.

According to one embodiment of present invention, maximum permission duty ratio according to following formulae discovery:

$d_{max}=min\left\{\frac{(I_{max}-I_{in})fL}{V_{in}},\frac{{\mathrm{\ΔI}}_{c}fL}{V_{in}}\right\}$

Wherein, d _maxfor described maximum permission duty ratio, I _maxfor described default maximum permissible current, min{} for getting the small value, Δ I _cfor the maximum current increment preset, f is the switching frequency of described pfc circuit, and L is PFC inductance value, V _infor the input voltage of described pfc circuit, I _infor the input current of pfc circuit described in current switch period.

According to one embodiment of present invention, described PFC control module controls described pfc circuit in the duty ratio of next switch periods and described maximum permission duty ratio according to described pfc circuit, specifically comprise: when described pfc circuit is more than or equal to described maximum permission duty ratio in the duty ratio of next switch periods, described PFC control module controls the switching tube in described pfc circuit according to described maximum permission duty ratio; When described pfc circuit is less than described maximum permission duty ratio in the duty ratio of next switch periods, described PFC control module controls the switching tube in described pfc circuit according to the duty ratio of described pfc circuit in next switch periods.

According to one embodiment of present invention; the over-current protection method of above-mentioned pfc circuit; also comprise: when described input current is greater than described default maximum permissible current or described input voltage is greater than described output voltage; described overcurrent protection module exports the second guard signal to described PFC control module, outputs to the duty ratio of described pfc circuit for 0 to make described PFC control module.

Accompanying drawing explanation

Fig. 1 is the electrical block diagram of the overcurrent protective device of pfc circuit according to an embodiment of the invention.

Equivalent circuit diagram when Fig. 2 is switching tube IGBT conducting according to an embodiment of the invention.

Equivalent circuit diagram when Fig. 3 is switching tube IGBT according to an embodiment of the invention shutoff.

Fig. 4 is the oscillogram of the input current of input voltage according to an embodiment of the invention when being less than output voltage in a switch periods.

Fig. 5 is the current increment schematic diagram in the next switch periods of normal condition according to an embodiment of the invention.

Fig. 6 is that pfc circuit carries out the flow chart of overcurrent protection according to an embodiment of the invention.

Fig. 7 is the flow chart of the over-current protection method of pfc circuit according to the embodiment of the present invention.

Embodiment

Be described below in detail embodiments of the invention, the example of described embodiment is shown in the drawings, and wherein same or similar label represents same or similar element or has element that is identical or similar functions from start to finish.Be exemplary below by the embodiment be described with reference to the drawings, be intended to for explaining the present invention, and can not limitation of the present invention be interpreted as.

The overcurrent protective device of pfc circuit and the over-current protection method of pfc circuit that propose according to the embodiment of the present invention are described with reference to the accompanying drawings.

Fig. 1 is the electrical block diagram of the overcurrent protective device of pfc circuit according to an embodiment of the invention.As shown in Figure 1, the overcurrent protective device of this pfc circuit comprises: the first voltage detection module 10, current detection module 20, second voltage detection module 30, overcurrent protection module 40 and PFC control module 50.

Wherein, first voltage detection module 10 is for detecting the input voltage of pfc circuit, current detection module 20 is for detecting the input current of pfc circuit, second voltage detection module 30 is for detecting the output voltage of pfc circuit, overcurrent protection module 40 respectively with the first voltage detection module 10, current detection module 20 is connected with the second voltage detection module 30, overcurrent protection module 40 generates the first guard signal when input current is less than or equal to default maximum permissible current and input voltage is less than or equal to output voltage, PFC control module 50 is connected with overcurrent protection module 40, PFC control module 50 calculates the duty ratio of pfc circuit in next switch periods when receiving the first guard signal that overcurrent protection module 40 sends, and calculate the maximum permission duty ratio of pfc circuit in next switch periods, and pfc circuit is controlled in the duty ratio of next switch periods and maximum permission duty ratio according to pfc circuit.

In an embodiment of the present invention, the maximum permissible current preset can allow by switching tube the maximum current that passes through.

Particularly, the Boost type pfc circuit shown in Fig. 1 mainly comprises inductance L 1, fast recovery diode D, switching tube IGBT and electrochemical capacitor EC.When switching tube IGBT is in conducting state, as shown in Figure 2, the voltage in inductance L 1 is the voltage that AC power exports after diode rectifier bridge rectification to its equivalent electric circuit, i.e. the input voltage V of the pfc circuit of the first voltage detection module 10 detection _in.Due to input voltage V _inbe greater than zero, therefore, the electric current flowing through inductance L 1 rises gradually always, i.e. the input current I of the pfc circuit of current detection module 20 detection _inincrease gradually; When switching tube IGBT is in off state, as shown in Figure 3, the voltage in inductance L 1 is the input voltage V of pfc circuit to its equivalent electric circuit _inwith output voltage V _outdifference.Because Boost type pfc circuit only has boost function, therefore, under normal operating conditions, the input voltage V of pfc circuit _inbe less than output voltage V _out, the voltage reversal in inductance L 1, now, the electric current flowing through inductance L 1 will decline gradually, i.e. the input current I of current detection module 20 detection _inreduce gradually.Therefore, in a switch periods of switching tube IGBT, input current I _inwaveform as shown in Figure 4, when switching tube IGBT conducting, input current I _inthe rate of rise be tan α=V _in/ L; When switching tube IGBT turns off, input current I _indescending slope be tan β=(V _out-V _in)/L, wherein, L is the inductance value of PFC inductance value and inductance L 1.

And at some in particular cases, such as, when AC power rises suddenly as line voltage instability, due to the existence of electrochemical capacitor EC, make output voltage V _outstationary value cannot be risen to immediately, and may be just rise to stationary value after sluggish a period of time, therefore, during this period of time, input voltage V _inprobably exceed output voltage V _out, now, even if control switch pipe IGBT turns off, but due to the voltage (V in inductance L 1 _in-V _out) being greater than zero, the electric current flowing through inductance L 1 still can continue to rise, thus causes over-current phenomenon avoidance to occur.Therefore, in order to avoid over-current phenomenon avoidance occurs, need to ensure that switching tube IGBT turns off, to avoid input current I _inrising too fast, flowing through without big current in switching tube IBGT to ensure, in an embodiment of the present invention, as input voltage V simultaneously _inbe less than or equal to output voltage V _out, and input current I _inbe less than or equal to default maximum permissible current I _maxnamely switching tube IGBT when allowing the maximum current passed through; overcurrent protection module 40 sends the first guard signal to PFC control module 50; PFC control module 50 is after the first guard signal receiving overcurrent protection module 40 transmission; the duty ratio of pfc circuit in next switch periods is calculated according to control objectives; calculate pfc circuit in the maximum permission duty ratio of next switch periods simultaneously, and according to the duty ratio of next switch periods calculated and maximum permission duty ratio, the switching tube IGBT in pfc circuit is controlled.

According to one embodiment of present invention, PFC control module 50 calculates the duty ratio of pfc circuit in next switch periods according to following formula (1):

${\mathrm{\ΔI}}_{in}=\frac{V_{in}}{fL}d---\left(1\right)$

Wherein, Δ I _infor the difference of the target input current of pfc circuit in the input current of pfc circuit in current switch period and next switch periods, d is the duty ratio of pfc circuit in next switch periods, and f is the switching frequency of pfc circuit, and L is PFC inductance value, V _infor the input voltage of pfc circuit.

According to one embodiment of present invention, PFC control module 50 calculates maximum permission duty ratio according to following formula (2):

$d_{max}=min\left\{\frac{(I_{max}-I_{in})fL}{V_{in}},\frac{{\mathrm{\ΔI}}_{c}fL}{V_{in}}\right\}---\left(2\right)$

Wherein, d _maxfor maximum permission duty ratio, I _maxfor preset maximum permissible current, min{} for getting the small value, Δ I _cfor the maximum current increment preset, I _infor the input current of pfc circuit in current switch period.

Particularly, I is worked as _in≤ I _maxand V _in≤ V _outtime, can by current input current I _inand whether the current increment in the next switch periods of the Predicting Performance Characteristics of Boost type pfc circuit can make the input current of pfc circuit in next switch periods exceed maximum permissible current.

Suppose that the pfc circuit that PFC control module 50 calculates according to control objectives is d in the duty ratio of next switch periods, the switching frequency of pfc circuit is f, input current increment then in switching tube IGBT ON time, namely in current switch period in the input current of pfc circuit and next switch periods the difference of the target input current of pfc circuit as shown in above-mentioned formula (1).

In order to prevent the input current increment in a switch periods excessive, can set maximum current increment is Δ I _c, then corresponding pfc circuit is at the duty ratio d of next switch periods _cas shown in following formula (3):

$d_c=\frac{{\mathrm{\ΔI}}_{c}fL}{V_{in}}---\left(3\right)$

In addition, in order to ensure input current I _inbe no more than default maximum permissible current I _max, also need the difference (I according to maximum permissible current and input current _max-I _in) calculate the duty ratio d of pfc circuit in next switch periods _m, as shown in following formula (4):

$d_m=\frac{(I_{max}-I_{in})fL}{V_{in}}---\left(4\right)$

Therefore, in order to ensure that the current increment of pfc circuit in next switch periods had both been no more than maximum current increment Delta I _c, be also no more than the difference (I of maximum permissible current and input current _max-I _in), pfc circuit is at the maximum permission duty ratio d of next switch periods _maxneed meet above-mentioned formula (2), namely pfc circuit can not exceed maximum permission duty ratio d at the duty ratio d of next switch periods _max.Wherein, under normal operating conditions, the difference Δ I of the target input current of pfc circuit in the input current of pfc circuit and next switch periods in current switch period _in, maximum current increment Delta I _cand the difference (I of maximum permissible current and input current _max-I _in) relation between three as shown in Figure 5.

According to one embodiment of present invention, PFC control module 50 according to pfc circuit when the duty ratio of next switch periods and maximum permission duty ratio control pfc circuit, wherein, when pfc circuit is more than or equal to maximum permission duty ratio in the duty ratio of next switch periods, PFC control module 50 controls the switching tube in pfc circuit according to maximum permission duty ratio; When pfc circuit is less than maximum permission duty ratio in the duty ratio of next switch periods, PFC control module 50 controls the switching tube in pfc circuit according to the duty ratio of pfc circuit in next switch periods.

That is, as d>=d _maxtime, $d=d_{max}=min\left\{\frac{(I_{max}-I_{in})fL}{V_{in}},\frac{{\mathrm{\&Delta;I}}_{c}fL}{V_{in}}\right\},$ PFC control module 50 controls the switching tube IGBT in pfc circuit according to maximum permission duty ratio; As d < d _maxtime, what calculate according to control objectives remains unchanged at the duty ratio d of next switch periods, and PFC control module 50 controls the switching tube IGBT in pfc circuit according to the duty ratio of pfc circuit in next switch periods.

According to one embodiment of present invention; when input current is greater than default maximum permissible current or input voltage is greater than output voltage; overcurrent protection module 40 exports the second guard signal to PFC control module 50, outputs to the duty ratio of pfc circuit for 0 to make PFC control module 50.

Particularly, as shown in Figure 1, current input voltage V is detected in real time by the first voltage detection module 10 _in, and detect current input current I in real time by current detection module 20 _in, and detect current output voltage V in real time by the second voltage detection module 30 _out.Overcurrent protection module 40 is to the current input current I detected _inwith the maximum permissible current I preset _maxcompare, simultaneously to the current input voltage V detected _inwith output voltage V _outcompare.Work as I _in> I _maxor V _in> V _outtime, overcurrent protection module 40 exports the second guard signal to PFC control module 50, and PFC control module 50 is after receiving the second guard signal, and the duty ratio controlling the switching tube IGBT in pfc circuit is 0; Work as I _in≤ I _maxand V _in≤ V _outtime; overcurrent protection module 40 exports the first guard signal to PFC control module 50; PFC control module 50 is after receiving the first guard signal; first according to the duty ratio d of control objectives compute switch pipe IGBT in next switch periods, and the maximum permission duty ratio d of next switch periods is calculated according to above-mentioned formula (2) _max, and to the duty ratio d of next switch periods and maximum permission duty ratio d _maxcompare.As d>=d _maxtime, d=d _max, PFC control module 50 is according to maximum permission duty ratio d _maxswitching tube IGBT in pfc circuit is controlled; As d < d _maxtime, the duty ratio d of next switch periods remains unchanged, and PFC control module 50 controls the switching tube IGBT in pfc circuit according to the duty ratio d of pfc circuit in next switch periods.Thus pass through the input voltage V of pfc circuit _in, input current I _inand output voltage V _outcarry out the duty ratio of limit switch pipe IGBT, to reach the object that prevention switching tube IGBT over-current phenomenon avoidance occurs.

Further, as shown in Figure 6, the overcurrent protection process of pfc circuit comprises the following steps:

S101, detects the input current I of pfc circuit _in, input voltage V _in, output voltage V _out.

S102, judges whether I _in> I _maxor V _in> V _out.If so, step S104 is performed; If not, step S103 is performed.

S103, the duty ratio d of compute switch pipe IGBT.

S104, the duty ratio d=0 of switching tube IGBT.

S105, calculates maximum permission duty ratio $d_{max}=min\left\{\frac{(I_{max}-I_{in})fL}{V_{in}},\frac{{\mathrm{\&Delta;I}}_{c}fL}{V_{in}}\right\}.$

S106, judges whether d>=d _max.If so, step S107 is performed; If not, step S108 is performed.

S107，d＝d _max。

S108, d are constant.

According to the overcurrent protective device of the pfc circuit of the embodiment of the present invention, the input voltage of pfc circuit is detected by the first voltage detection module, and the input current of pfc circuit is detected by current detection module, and the output voltage of pfc circuit is detected by the second voltage detection module, overcurrent protection module generates the first guard signal when input current is less than or equal to default maximum permissible current and input voltage is less than or equal to output voltage, PFC control module calculates the duty ratio of pfc circuit in next switch periods when receiving the first guard signal that overcurrent protection module sends, and calculate the maximum permission duty ratio of pfc circuit in next switch periods, and pfc circuit is controlled in the duty ratio of next switch periods and maximum permission duty ratio according to pfc circuit, thus by the input current of pfc circuit, input voltage and output voltage, and predict whether the input current of switching tube in next switch periods exceedes maximum permissible current in conjunction with the physical characteristic of pfc circuit, and when over-current phenomenon avoidance may occur, the duty ratio of limit switch pipe, thus the rising of limiting input current, effectively avoid switching tube overcurrent damage, thus improve the response speed of overcurrent protection, and then improve the reliability of pfc circuit.

Fig. 7 is the flow chart of the over-current protection method of pfc circuit according to the embodiment of the present invention.As shown in Figure 7, the over-current protection method of this pfc circuit comprises the following steps:

S1, detects input voltage and the input current of pfc circuit, and detects the output voltage of pfc circuit.

S2, when input current is less than or equal to default maximum permissible current and input voltage is less than or equal to output voltage, overcurrent protection module exports the first guard signal to PFC control module.Wherein, the maximum permissible current preset can allow by pfc circuit breaker in middle pipe the maximum current that passes through.

S3; PFC control module calculates the duty ratio of pfc circuit in next switch periods when receiving the first guard signal that overcurrent protection module sends; and calculate the maximum permission duty ratio of pfc circuit in next switch periods, and pfc circuit is controlled in the duty ratio of next switch periods and maximum permission duty ratio according to pfc circuit.

Particularly, the Boost type pfc circuit shown in Fig. 1 mainly comprises inductance, fast recovery diode, switching tube and electrochemical capacitor.When switching tube is in conducting state, as shown in Figure 2, the voltage on inductance is the voltage that AC power exports after diode rectifier bridge rectification to its equivalent electric circuit, i.e. the input voltage V of the pfc circuit of the first voltage detection module detection _in.Due to input voltage V _inbe greater than zero, therefore, the electric current flowing through inductance rises gradually always, i.e. the input current I of the pfc circuit of current detection module detection _inincrease gradually; When switching tube is in off state, as shown in Figure 3, the voltage on inductance is the input voltage V of pfc circuit to its equivalent electric circuit _inwith output voltage V _outdifference.Because Boost type pfc circuit only has boost function, therefore, under normal operating conditions, the input voltage V of pfc circuit _inbe less than output voltage V _out, the voltage reversal on inductance, now, the electric current flowing through inductance will decline gradually, i.e. the input current I of current detection module detection _inreduce gradually.Therefore, in a switch periods of switching tube, input current I _inwaveform as shown in Figure 4, when switching tube conducting, input current I _inthe rate of rise be tan α=V _in/ L; When switching tube turns off, input current I _indescending slope be tan β=(V _out-V _in)/L, wherein, L is the inductance value of PFC inductance value and inductance.

And at some in particular cases, such as, when AC power rises suddenly as line voltage instability, due to the existence of electrochemical capacitor, make output voltage V _outstationary value cannot be risen to immediately, and may be just rise to stationary value after sluggish a period of time, therefore, during this period of time, input voltage V _inprobably exceed output voltage V _out, now, even if control switch pipe turns off, but due to the voltage (V on inductance _in-V _out) being greater than zero, the electric current flowing through inductance still can continue to rise, thus causes over-current phenomenon avoidance to occur.Therefore, in order to avoid over-current phenomenon avoidance occurs, need to ensure that switching tube turns off, to avoid input current I _inrising too fast, flowing through without big current in switching tube to ensure, in an embodiment of the present invention, as input voltage V simultaneously _inbe less than or equal to output voltage V _out, and input current I _inbe less than or equal to default maximum permissible current I _maxnamely switching tube when allowing the maximum current passed through; overcurrent protection module sends the first guard signal to PFC control module; PFC control module is after the first guard signal receiving the transmission of overcurrent protection module; the duty ratio of pfc circuit in next switch periods is calculated according to control objectives; calculate pfc circuit in the maximum permission duty ratio of next switch periods simultaneously, and according to the duty ratio of next switch periods calculated and maximum permission duty ratio, the switching tube in pfc circuit is controlled.

According to one embodiment of present invention, the duty ratio of pfc circuit in next switch periods is calculated according to above-mentioned formula (1).

According to one embodiment of present invention, maximum permission duty ratio is calculated according to above-mentioned formula (2).

Particularly, I is worked as _in≤ I _maxand V _in≤ V _outtime, can by current input current I _inand whether the current increment in the next switch periods of the Predicting Performance Characteristics of Boost type pfc circuit can make the input current of pfc circuit in next switch periods exceed maximum permissible current.

Suppose that the pfc circuit that PFC control module calculates according to control objectives is d in the duty ratio of next switch periods, the switching frequency of pfc circuit is f, input current increment then in switching tube ON time, namely in current switch period in the input current of pfc circuit and next switch periods the difference of the target input current of pfc circuit as shown in above-mentioned formula (1).

In order to prevent the input current increment in a switch periods excessive, can set maximum current increment is Δ I _c, then corresponding pfc circuit is at the duty ratio d of next switch periods _cas shown in above-mentioned formula (3).In addition, in order to ensure input current I _inbe no more than default maximum permissible current I _max, also need the difference (I according to maximum permissible current and input current _max-I _in) calculate the duty ratio d of pfc circuit in next switch periods _m, as shown in above-mentioned formula (4).

Therefore, in order to ensure that the current increment of pfc circuit in next switch periods had both been no more than maximum current increment Delta I _c, be also no more than the difference (I of maximum permissible current and input current _max-I _in), pfc circuit is at the maximum permission duty ratio d of next switch periods _maxneed meet above-mentioned formula (2), namely pfc circuit can not exceed maximum permission duty ratio d at the duty ratio d of next switch periods _max.Wherein, under normal operating conditions, the difference Δ I of the target input current of pfc circuit in the input current of pfc circuit and next switch periods in current switch period _in, maximum current increment Delta I _cand the difference (I of maximum permissible current and input current _max-I _in) relation between three as shown in Figure 5.

According to one embodiment of present invention, PFC control module controls pfc circuit in the duty ratio of next switch periods and maximum permission duty ratio according to pfc circuit, specifically comprise: when pfc circuit is more than or equal to maximum permission duty ratio in the duty ratio of next switch periods, PFC control module controls the switching tube in pfc circuit according to maximum permission duty ratio; When pfc circuit is less than maximum permission duty ratio in the duty ratio of next switch periods, PFC control module controls the switching tube in pfc circuit according to the duty ratio of pfc circuit in next switch periods.

That is, as d>=d _maxtime, $d=d_{max}=min\left\{\frac{(I_{max}-I_{in})fL}{V_{in}},\frac{{\mathrm{\&Delta;I}}_{c}fL}{V_{in}}\right\},$ PFC control module controls the switching tube in pfc circuit according to maximum permission duty ratio; As d < d _maxtime, what calculate according to control objectives remains unchanged at the duty ratio d of next switch periods, and PFC control module controls the switching tube in pfc circuit according to the duty ratio of pfc circuit in next switch periods.

According to one embodiment of present invention; the over-current protection method of above-mentioned pfc circuit also comprises: when input current is greater than default maximum permissible current or input voltage is greater than output voltage; overcurrent protection module exports the second guard signal to PFC control module, outputs to the duty ratio of pfc circuit for 0 to make PFC control module.

Particularly, as shown in Figure 1, current input voltage V is detected in real time by the first voltage detection module _in, and detect current input current I in real time by current detection module _in, and detect current output voltage V in real time by the second voltage detection module _out.Overcurrent protection module is to the current input current I detected _inwith the maximum permissible current I preset _maxcompare, simultaneously to the current input voltage V detected _inwith output voltage V _outcompare.Work as I _in> I _maxor V _in> V _outtime, overcurrent protection module exports the second guard signal to PFC control module, and PFC control module is after receiving the second guard signal, and the duty ratio controlling the switching tube in pfc circuit is 0; Work as I _in≤ I _maxand V _in≤ V _outtime; overcurrent protection module exports the first guard signal to PFC control module; PFC control module is after receiving the first guard signal; first according to the duty ratio d of control objectives compute switch pipe in next switch periods, and the maximum permission duty ratio d of next switch periods is calculated according to above-mentioned formula (2) _max, and to the duty ratio d of next switch periods and maximum permission duty ratio d _maxcompare.As d>=d _maxtime, d=d _max, PFC control module is according to maximum permission duty ratio d _maxswitching tube in pfc circuit is controlled; As d < d _maxtime, the duty ratio d of next switch periods remains unchanged, and PFC control module controls the switching tube in pfc circuit according to the duty ratio d of pfc circuit in next switch periods.Thus pass through the input voltage V of pfc circuit _in, input current I _inand output voltage V _outcarry out the duty ratio of limit switch pipe, to reach the object that prevention switching tube over-current phenomenon avoidance occurs.

Further, the overcurrent protection process of pfc circuit as shown in Figure 6, is just not described in detail here.

According to the over-current protection method of the pfc circuit of the embodiment of the present invention, the input voltage of real-time detection pfc circuit, input current and output voltage, when input current is less than or equal to default maximum permissible current and input voltage is less than or equal to output voltage, overcurrent protection module exports the first guard signal to PFC control module, PFC control module calculates the duty ratio of pfc circuit in next switch periods when receiving the first guard signal that overcurrent protection module sends, and calculate the maximum permission duty ratio of pfc circuit in next switch periods, and pfc circuit is controlled in the duty ratio of next switch periods and maximum permission duty ratio according to pfc circuit, thus by the input current of pfc circuit, input voltage and output voltage, and predict whether the input current of switching tube in next switch periods exceedes maximum permissible current in conjunction with the physical characteristic of pfc circuit, and when over-current phenomenon avoidance may occur, the duty ratio of limit switch pipe, thus the rising of limiting input current, effectively avoid switching tube overcurrent damage, thus improve the response speed of overcurrent protection, and then improve the reliability of pfc circuit.

In describing the invention, it will be appreciated that, term " " center ", " longitudinal direction ", " transverse direction ", " length ", " width ", " thickness ", " on ", D score, " front ", " afterwards ", " left side ", " right side ", " vertically ", " level ", " top ", " end " " interior ", " outward ", " clockwise ", " counterclockwise ", " axis ", " radial direction ", orientation or the position relationship of the instruction such as " circumference " are based on orientation shown in the drawings or position relationship, only the present invention for convenience of description and simplified characterization, instead of indicate or imply that the device of indication or element must have specific orientation, with specific azimuth configuration and operation, therefore limitation of the present invention can not be interpreted as.

In addition, term " first ", " second " only for describing object, and can not be interpreted as instruction or hint relative importance or imply the quantity indicating indicated technical characteristic.Thus, be limited with " first ", the feature of " second " can express or impliedly comprise at least one this feature.In describing the invention, the implication of " multiple " is at least two, such as two, three etc., unless otherwise expressly limited specifically.

In the present invention, unless otherwise clearly defined and limited, the term such as term " installation ", " being connected ", " connection ", " fixing " should be interpreted broadly, and such as, can be fixedly connected with, also can be removably connect, or integral; Can be mechanical connection, also can be electrical connection; Can be directly be connected, also indirectly can be connected by intermediary, can be the connection of two element internals or the interaction relationship of two elements, unless otherwise clear and definite restriction.For the ordinary skill in the art, above-mentioned term concrete meaning in the present invention can be understood as the case may be.

In the present invention, unless otherwise clearly defined and limited, fisrt feature second feature " on " or D score can be that the first and second features directly contact, or the first and second features are by intermediary indirect contact.And, fisrt feature second feature " on ", " top " and " above " but fisrt feature directly over second feature or oblique upper, or only represent that fisrt feature level height is higher than second feature.Fisrt feature second feature " under ", " below " and " below " can be fisrt feature immediately below second feature or tiltedly below, or only represent that fisrt feature level height is less than second feature.

In the description of this specification, specific features, structure, material or feature that the description of reference term " embodiment ", " some embodiments ", " example ", " concrete example " or " some examples " etc. means to describe in conjunction with this embodiment or example are contained at least one embodiment of the present invention or example.In this manual, to the schematic representation of above-mentioned term not must for be identical embodiment or example.And the specific features of description, structure, material or feature can combine in one or more embodiment in office or example in an appropriate manner.In addition, when not conflicting, the feature of the different embodiment described in this specification or example and different embodiment or example can carry out combining and combining by those skilled in the art.

Although illustrate and describe embodiments of the invention above, be understandable that, above-described embodiment is exemplary, can not be interpreted as limitation of the present invention, and those of ordinary skill in the art can change above-described embodiment within the scope of the invention, revises, replace and modification.

Claims (10)

1. an overcurrent protective device for power factor correction pfc circuit, is characterized in that, comprising:

First voltage detection module, described first voltage detection module is for detecting the input voltage of described pfc circuit;

Current detection module, described current detection module is for detecting the input current of described pfc circuit;

Second voltage detection module, described second voltage detection module is for detecting the output voltage of described pfc circuit;

Overcurrent protection module, described overcurrent protection module is connected with described second voltage detection module with described first voltage detection module, described current detection module respectively, and described overcurrent protection module generates the first guard signal when described input current is less than or equal to default maximum permissible current and described input voltage is less than or equal to described output voltage;

PFC control module; described PFC control module is connected with described overcurrent protection module; described PFC control module calculates the duty ratio of described pfc circuit in next switch periods when receiving described first guard signal that described overcurrent protection module sends; and calculate the maximum permission duty ratio of described pfc circuit in next switch periods described, and described pfc circuit is controlled in the duty ratio of next switch periods and described maximum permission duty ratio according to described pfc circuit.

2. the overcurrent protective device of pfc circuit as claimed in claim 1, is characterized in that, described PFC control module according to following formulae discovery pfc circuit in the duty ratio of next switch periods:

${\mathrm{\&Delta;I}}_{in}=\frac{V_{in}}{fL}d$

Wherein, Δ I _infor the difference of the target input current of described pfc circuit in the input current of pfc circuit described in current switch period and next switch periods, d is the duty ratio of described pfc circuit in next switch periods, and f is the switching frequency of described pfc circuit, and L is PFC inductance value, V _infor the input voltage of described pfc circuit.

3. the overcurrent protective device of pfc circuit as claimed in claim 1 or 2, it is characterized in that, described PFC control module is maximum permission duty ratio according to following formulae discovery:

$d_{max}=min\left\{\frac{(I_{max}-I_{in})fL}{V_{in}},\frac{{\mathrm{\&Delta;I}}_{c}fL}{V_{in}}\right\}$

Wherein, d _maxfor described maximum permission duty ratio, I _maxfor described default maximum permissible current, min{} for getting the small value, Δ I _cfor the maximum current increment preset, f is the switching frequency of described pfc circuit, and L is PFC inductance value, V _infor the input voltage of described pfc circuit, I _infor the input current of pfc circuit described in current switch period.

4. the overcurrent protective device of pfc circuit as claimed in claim 1, is characterized in that, described PFC control module according to described pfc circuit when the duty ratio of next switch periods and described maximum permission duty ratio control described pfc circuit, wherein,

When described pfc circuit is more than or equal to described maximum permission duty ratio in the duty ratio of next switch periods, described PFC control module controls the switching tube in described pfc circuit according to described maximum permission duty ratio;

When described pfc circuit is less than described maximum permission duty ratio in the duty ratio of next switch periods, described PFC control module controls the switching tube in described pfc circuit according to the duty ratio of described pfc circuit in next switch periods.

5. the overcurrent protective device of pfc circuit as claimed in claim 1; it is characterized in that; when described input current is greater than described default maximum permissible current or described input voltage is greater than described output voltage; described overcurrent protection module exports the second guard signal to described PFC control module, outputs to the duty ratio of described pfc circuit for 0 to make described PFC control module.

6. an over-current protection method for power factor correction pfc circuit, is characterized in that, comprises the following steps:

Detect input voltage and the input current of described pfc circuit, and detect the output voltage of described pfc circuit;

When described input current is less than or equal to default maximum permissible current and described input voltage is less than or equal to described output voltage, overcurrent protection module exports the first guard signal to PFC control module;

Described PFC control module calculates the duty ratio of described pfc circuit in next switch periods when receiving described first guard signal that described overcurrent protection module sends; and calculate the maximum permission duty ratio of described pfc circuit in next switch periods described, and described pfc circuit is controlled in the duty ratio of next switch periods and described maximum permission duty ratio according to described pfc circuit.

7. the over-current protection method of pfc circuit as claimed in claim 6, it is characterized in that, according to following formulae discovery, pfc circuit is in the duty ratio of next switch periods:

${\mathrm{\&Delta;I}}_{in}=\frac{V_{in}}{fL}d$

Wherein, Δ I _infor the difference of the target input current of described pfc circuit in the input current of pfc circuit described in current switch period and next switch periods, d is the duty ratio of described pfc circuit in next switch periods, and f is the switching frequency of described pfc circuit, and L is PFC inductance value, V _infor the input voltage of described pfc circuit.

8. the over-current protection method of pfc circuit as claimed in claims 6 or 7, is characterized in that, maximum permission duty ratio according to following formulae discovery:

$d_{max}=min\left\{\frac{(I_{max}-I_{in})fL}{V_{in}},\frac{{\mathrm{\&Delta;I}}_{c}fL}{V_{in}}\right\}$

Wherein, d _maxfor described maximum permission duty ratio, I _maxfor described default maximum permissible current, min{} for getting the small value, Δ I _cfor the maximum current increment preset, f is the switching frequency of described pfc circuit, and L is PFC inductance value, V _infor the input voltage of described pfc circuit, I _infor the input current of pfc circuit described in current switch period.

9. the over-current protection method of pfc circuit as claimed in claim 6, is characterized in that, described PFC control module controls described pfc circuit in the duty ratio of next switch periods and described maximum permission duty ratio according to described pfc circuit, specifically comprises:

When described pfc circuit is more than or equal to described maximum permission duty ratio in the duty ratio of next switch periods, described PFC control module controls the switching tube in described pfc circuit according to described maximum permission duty ratio;

When described pfc circuit is less than described maximum permission duty ratio in the duty ratio of next switch periods, described PFC control module controls the switching tube in described pfc circuit according to the duty ratio of described pfc circuit in next switch periods.

10. the over-current protection method of pfc circuit as claimed in claim 6, is characterized in that, also comprise:

When described input current is greater than described default maximum permissible current or described input voltage is greater than described output voltage; described overcurrent protection module exports the second guard signal to described PFC control module, outputs to the duty ratio of described pfc circuit for 0 to make described PFC control module.