CN107069907B - Discharge circuit and discharge control method - Google Patents
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Abstract
The invention relates to a discharge circuit and a discharge control method, wherein the discharge control method comprises the following steps: judging whether the discharge condition is met, if so, executing the next step; acquiring a preset pulse signal, wherein the preset pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor; and a pulse signal is output to the switching tube to control the on-off of the switching tube so as to realize the discharging function. By implementing the technical scheme of the invention, the reliable work of the discharge circuit of the direct current charging module is ensured, and the discharge time can be effectively shortened.
Description
Technical Field
The invention relates to the field of direct current charging, in particular to a discharging circuit and a discharging control method.
Background
In the intelligent group charging system, a large number of direct current charging modules are arranged to realize the conversion from alternating current input to direct current and provide electric energy for charging the electric automobile. According to the national standard, the upper limit of the output voltage of some direct current charging modules is higher, and can reach 750V generally. In order to reduce output ripples, the dc charging module is generally configured with a filter capacitor with a certain capacity at its output port. However, when the filter capacitor is turned off in a no-load mode under the condition of outputting high voltage, the self-discharge speed of the port voltage is very slow, the application of a direct current charging module in an intelligent charging system is influenced, and a special discharge circuit needs to be designed to complete the rapid reduction of the output port voltage under a specified working condition.
The main functions of the discharge circuit of a general dc charging module are two points:
(1) when the direct current charging module is separated from the charging system (pulled out), the voltage of the output port is required to be rapidly reduced to be lower than the set voltage;
(2) the direct current charging module in the intelligent charging system realizes active discharging when the direct current charging module is positioned in the intelligent charging system according to the state of the system, and realizes related functions by matching with the intelligent charging system.
A conventional discharging circuit of a dc charging module is shown in fig. 1, and a discharging enable signal is used to control whether the discharging circuit operates. When the direct current charging module is in the system, the discharging enabling signal is at a low level, the switching tube S is disconnected, and the discharging circuit does not act; when the direct current charging module is separated from the system, the discharging enabling signal is at a high level, the switching tube S is conducted, and the discharging circuit starts to discharge.
Although the discharge circuit is simple to control, the discharge speed is high. However, since the output voltage is high, when the dc charging module outputs 750V, the energy stored in the capacitor C1 can reach 134 joule, and a large current is applied to the discharge resistor R1 during discharging, which causes a large amount of heat accumulation in the discharge resistor R1. This discharge control has two disadvantages:
(1) in order to enable the discharge resistor R1 to bear heat accumulation generated by transient large current, a high-power resistor device needs to be selected, which means that a high-cost and large-volume power resistor needs to be selected, and even the discharge resistor needs to be considered in the design of the air duct, so that the complexity of the module design is increased indirectly;
(2) the output discharge is controlled by a hardware discharge enable signal, and the discharge action is executed only when the module is separated from the system, so that the active discharge of the output end in the charging system cannot be realized, and the system function is influenced.
Disclosure of Invention
The present invention is directed to a discharge circuit and a discharge control method, which are provided to overcome the above-mentioned drawbacks of the prior art.
The technical scheme adopted by the invention for solving the technical problems is as follows: the discharge control method is used for controlling the discharge of the voltage on a filter capacitor through a discharge resistor and a switching tube, wherein the discharge resistor is connected with the switching tube in series and then connected with the filter capacitor in parallel, and the discharge control method comprises the following steps:
s10, judging whether a discharging condition is met, and if so, executing the next step;
s20, acquiring a preset pulse signal, wherein the preset pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor;
and S30, outputting the pulse signal to a switching tube to control the on-off of the switching tube so as to realize a discharging function.
Preferably, the first and second electrodes are formed of a metal,
the pulse signal is a pulse signal with fixed frequency and fixed pulse width; alternatively, the first and second electrodes may be,
the pulse signal is a pulse signal with constant frequency and variable pulse width, and the effective pulse discharge time is increased along with the increase of the number of discharge cycles; alternatively, the first and second electrodes may be,
the pulse signal is a pulse signal with a constant pulse width and a variable period.
Preferably, in step S30, the following steps are performed per discharge cycle:
s301, judging whether a fault flag bit is set, if so, executing S310; if not, executing step S302;
s302, starting timing by a timer;
step S303, judging whether the timing time reaches the effective pulse discharge time of the current discharge period, if not, executing step S304; if yes, go to step S305;
s304, outputting a high level to control the conduction of a switching tube, and then executing the step S303;
s305, outputting a low level to control the switch tube to be switched off;
s306, judging whether the timing time reaches the current discharge period time, if not, executing the step S305; if yes, go to step S307;
s307, resetting a timer;
step S308, acquiring a discharge starting voltage and a discharge cut-off voltage of the current discharge period, judging whether the ratio of the discharge cut-off voltage and the discharge starting voltage of the current discharge period is greater than a preset value, if so, generating a single fault that an external high voltage is continuously applied to an output port, and executing step S309; if not, starting to perform the next discharge period;
s309, setting the fault flag bit;
and S310, stopping discharging.
Preferably, when the pulse signal is a pulse signal with a fixed frequency and a fixed pulse width or a pulse signal with a fixed pulse width and a variable period, the effective pulse discharge time is set in advance according to formula 1:
wherein, tonFor a set effective pulse discharge time, R is the resistance of the discharge resistor, QRmaxMaximum discharge energy, k, sustainable by the discharge resistorcTo a derating factor, VmaxThe highest voltage required for discharge.
Preferably, when the pulse signal is a pulse signal with a constant frequency and a variable pulse width, the effective pulse discharge time is set in advance according to the following formula:
wherein, toniEffective pulse discharge time for the set i-th discharge period, R is the resistance of the discharge resistor, and QRmaxMaximum discharge energy, k, sustainable by the discharge resistorcTo a derating factor, ViIs the discharge voltage at the beginning of the ith discharge cycle and the discharge voltage V at the beginning of the first discharge cycle1To discharge as requiredMaximum voltage of Vi+1Is the discharge voltage at the end of the ith discharge cycle.
Preferably, the preset pulse signal enables both the discharge energy of the discharge resistor within the effective pulse discharge time and the average power of the discharge resistor within the discharge period to meet the derating requirement of the discharge resistor, specifically:
the effective pulse discharge time and the discharge cycle time satisfy the following conditions:
wherein Q isiDischarge energy of discharge resistor in discharge time of effective pulse of ith discharge periodoniEffective pulse discharge time, V, for the ith discharge periodiIs the discharge voltage at the beginning of the ith discharge cycle and the discharge voltage V at the beginning of the first discharge cycle1At the highest voltage of the desired discharge, Vi+1Is the discharge voltage at the end of the ith discharge cycle, τ is the charge-discharge time constant, and is the product of the discharge resistance and the capacitance of the filter capacitor, PiIs the average power of the i-th discharge period, TiIs the discharge period time of the ith discharge period, k is the maximum pulse power multiple which can be borne by the discharge resistor in the predetermined ith discharge period, P is the rated power of the discharge resistor, k is the rated power of the discharge resistorcFor derating factor, R is the resistance of the discharge resistor, QRmaxThe maximum discharge energy which can be borne by the discharge resistor.
The invention also constructs a discharge circuit which is connected with the filter capacitor and comprises a discharge resistor, a switch tube and a controller, wherein the first end of the discharge resistor is connected with the first end of the filter capacitor, the second end of the discharge resistor is connected with the first end of the switch tube, and the second end of the switch tube is connected with the second end of the filter capacitor; furthermore, it is possible to provide a liquid crystal display device,
the controller is used for acquiring a preset pulse signal and outputting the pulse signal to the switching tube when the discharge condition is judged to be met, so as to control the on-off of the switching tube and realize the discharge function, wherein the preset pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor.
Preferably, the pulse signal is a pulse signal with fixed frequency and fixed pulse width; alternatively, the first and second electrodes may be,
the pulse signal is a pulse signal with constant frequency and variable pulse width, and the effective pulse discharge time is increased along with the increase of the number of discharge cycles; alternatively, the first and second electrodes may be,
the pulse signal is a pulse signal with a constant pulse width and a variable period.
Preferably, the controller is further configured to determine whether a ratio of a discharge cut-off voltage to a discharge start voltage in a current discharge cycle is greater than a preset value at the end of each discharge cycle, and if so, stop outputting the pulse signal when a single fault occurs in which an external high voltage is continuously applied to the output port.
Preferably, when the pulse signal is a pulse signal with a fixed frequency and a fixed pulse width or a pulse signal with a fixed pulse width and a variable period, the effective pulse discharge time is set in advance according to formula 1:
wherein, tonFor the effective pulse discharge time, R is the resistance of the discharge resistor, QRmaxMaximum discharge energy, k, sustainable by the discharge resistorcTo a derating factor, VmaxThe highest voltage required for discharge;
when the pulse signal is a pulse signal with constant frequency and variable pulse width, the effective pulse discharge time is preset according to the following formula:
wherein, toniEffective pulse discharge time for the set i-th discharge period, R is the resistance of the discharge resistor, and QRmaxMaximum discharge energy, k, sustainable by the discharge resistorcTo a derating factor, ViIs the discharge voltage at the beginning of the ith discharge cycle and the discharge voltage V at the beginning of the first discharge cycle1At the highest voltage of the desired discharge, Vi+1Is the discharge voltage at the end of the ith discharge cycle.
According to the technical scheme, the controller stores the preset pulse signal, and the pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor. When the controller judges that the discharging condition is met, the pulse signal is output to control the switching tube to be conducted discontinuously, so that heat accumulation on the discharging resistor caused by bearing instantaneous large current can be avoided, and the voltage of the output port of the direct current charging module is reduced rapidly while the discharging circuit of the direct current charging module is ensured to work reliably. Moreover, the discharging control mode is suitable for all output voltage levels of the direct current charging module, the output voltage does not need to be detected in the discharging control process, and the control method is simple. In addition, the discharging control mode is not only applied to the condition that the direct current charging module is separated from the charging system (is pulled out), but also can realize the active discharging of the direct current charging module according to the state of the charging system, thereby expanding the application range.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts. In the drawings:
fig. 1 is a circuit diagram of a filter capacitor and a discharging circuit at an output port of a dc charging module in the prior art;
FIG. 2 is a circuit diagram of a filter capacitor and a discharging circuit of an output port of a DC charging module according to a first embodiment of the present invention;
FIG. 3 is a flowchart of a first embodiment of a discharge control method according to the present invention;
FIG. 4 is a diagram of a first embodiment of voltages at an output port of a DC charging module when a pulse signal is a constant-frequency and constant-pulse-width pulse signal;
FIG. 5 is a graph of the pulse power characteristic of the discharge resistor;
FIG. 6 is a diagram illustrating a first embodiment of energy dissipated in the discharge resistor when the pulse signal is a constant-frequency and constant-pulse-width pulse signal;
FIG. 7 is a diagram of a first embodiment of the voltage at the output port of the DC charging module and the energy consumed by the discharging resistor when the 750V voltage is controlled to be discharged by using a pulse signal with a fixed frequency and a fixed pulse width;
FIG. 8 is a diagram of a second embodiment of the voltage at the output port of the DC charging module during the discharge control using the pulse signal with constant frequency and variable pulse width;
FIG. 9 is a diagram of a second embodiment of the voltage at the output port of the DC charging module and the energy consumed by the discharging resistor when the pulse signal is a pulse signal with a constant frequency and a variable pulse width;
FIG. 10 is a diagram of a second embodiment of voltages at an output port of a DC charging module when an initial discharge voltage is 750V and 600V respectively during discharge control using a pulse signal with a constant frequency and a variable pulse width;
fig. 11 is a flowchart of a first step S30 of the discharge control method according to the present invention.
Detailed Description
Fig. 2 is a circuit diagram of a filter capacitor and a discharge circuit of an output port of a dc charging module according to a first embodiment of the present invention, where the dc charging module includes a voltage conversion circuit (not shown), a filter capacitor C1 and a discharge circuit, where the voltage conversion circuit is configured to convert ac mains power into dc power and provide electric energy for an electric vehicle. A filter capacitor C1 is set at the output port of the dc charging module and is used to reduce the ripple of the output voltage. The discharge circuit comprises a discharge resistor R1, a switch tube S and a controller U1. The discharging resistor R1 preferably has a power resistor with a certain impact resistance, the first end of the discharging resistor R1 is connected to the first end of the filter capacitor C1, the second end of the discharging resistor R1 is connected to the first end of the switch tube S, the second end of the switch tube S is connected to the second end of the filter capacitor C1, the controller U1 is connected to the control end of the switch tube S, and the controller U1 is configured to obtain a preset pulse signal when a discharging condition is detected to be met, and output the pulse signal to the switch tube S to drive the switch tube S to be turned on and off, so as to implement a discharging function, specifically: when the pulse signal is at a high level, the switching tube S is conducted, and the discharge circuit starts to discharge; when the pulse signal is at a low level, the switching tube S is turned off, and the discharge circuit stops discharging. The pulse signal is set so that the discharge energy of the discharge resistor R1 in the effective pulse discharge time and the average power of the discharge resistor R1 in the discharge period both satisfy the derating requirement of the discharge resistor R1.
In this embodiment, the discharge conditions include, for example: the direct current charging module is separated (pulled out) from the charging system, and the voltage of an output port of the direct current charging module is greater than the set voltage; alternatively, the dc charging module actively discharges according to the requirements of the charging system, for example, the system where the dc charging module is located requires a rapid reduction in module voltage to perform a specific function.
When a pulse signal is set, the design idea of effective pulse discharge time and discharge pulse interval time is as follows: the bleed energy of the discharge resistor R1 during the active pulse discharge time and the average power during the discharge period (active pulse discharge time plus discharge pulse interval time) need to meet de-rating requirements, i.e., the following two conditions are met: the discharge energy of the discharge resistor R1 in the effective pulse discharge time does not exceed the maximum withstand energy of the discharge resistor R1; the average power of the discharge resistor R1 in the discharge period does not exceed the pulse power de-rating of the discharge resistor R1.
In the above embodiment, the pulse signal is a pulse signal with a fixed frequency and a fixed pulse width; or, the pulse signal is a pulse signal with constant frequency and variable pulse width, and the effective pulse discharge time is increased along with the increase of the number of discharge cycles; alternatively, the pulse signal may be a pulse signal having a constant pulse width and a variable period, and the discharge period time may be increased as the number of discharge periods increases or may be decreased as the number of discharge periods increases.
In the technical scheme of the embodiment, the controller stores a preset pulse signal, and the pulse signal enables the discharge energy of the discharging resistor R1 in the effective pulse discharge time and the average power of the discharging resistor R1 in the discharge period to meet the derating requirement of the discharging resistor R1. When the controller U1 judges that the discharging condition is satisfied, the pulse signal is output to control the switch tube S to be conducted discontinuously, so that heat accumulation generated by bearing instantaneous large current on the discharging resistor R1 can be avoided, the voltage of the output port of the direct current charging module is quickly reduced while the reliable work of a discharging circuit of the direct current charging module is ensured, in addition, the discharging control mode is not only applied to the condition that the direct current charging module is separated from the charging system (is pulled out), but also can realize the active discharging of the direct current charging module according to the requirement of the charging system, and the application range is expanded.
Preferably, the controller U1 is further configured to determine, at the end of each discharge cycle, whether a ratio of a discharge cut-off voltage (a voltage at the output port of the dc charging module at the end of the current discharge cycle) to a discharge start voltage (a voltage at the output port of the dc charging module at the start of the current discharge cycle) in the current discharge cycle is greater than a preset value, and if so, stop outputting the pulse signal to stop the port discharge of the dc charging module.
It should be noted that, the above embodiments are described by taking the application of the discharging circuit to the dc charging module as an example, it should be understood that the discharging circuit of the present invention can also be applied to other devices with a filter capacitor, and when the voltage on the filter capacitor needs to be rapidly decreased, the discharging circuit can be used to perform discharging control on the voltage on the filter capacitor.
Fig. 3 is a flowchart of a first embodiment of a discharge control method according to the present invention, configured to perform discharge control on a voltage across a filter capacitor through a discharge resistor and a switching tube, where the discharge resistor is connected in series with the switching tube and then connected in parallel with the filter capacitor, and with reference to fig. 2, the discharge control method according to the embodiment includes:
s10, judging whether a discharging condition is met, and if so, executing the next step;
s20, acquiring a preset pulse signal, wherein the preset pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor;
and S30, outputting a pulse signal to the switching tube to control the on-off of the switching tube so as to realize a discharging function.
In step S20, the preset pulse signal is a pulse signal with a fixed frequency and a fixed pulse width; or the preset pulse signal is a pulse signal with constant frequency and variable pulse width, and the effective pulse discharge time is increased along with the increase of the number of discharge cycles; alternatively, the preset pulse signal is a pulse signal with a constant pulse width and a variable period, and in one embodiment, the discharge period time may decrease with the increase of the number of discharge periods, and in another embodiment, the discharge period time may also decrease with the increase of the number of discharge periods.
Moreover, the effective pulse discharge time and the discharge cycle time satisfy the following conditions:
wherein Q isiDischarge energy of discharge resistor in discharge time of effective pulse of ith discharge periodoniEffective pulse discharge time, V, for the ith discharge periodiIs the discharge voltage at the beginning of the ith discharge cycle and the discharge voltage V at the beginning of the first discharge cycle1At the highest voltage of the desired discharge, Vi+1Is the discharge voltage at the end of the ith discharge cycle, i.e. the discharge voltage at the beginning of the (i + 1) th discharge cycle, tau is the charge-discharge time constant and is the product of the discharge resistor resistance and the filter capacitor capacitance, PiIs the average power of the i-th discharge period, TiIs the discharge period time of the ith discharge period, k is the maximum pulse power multiple which can be borne by the discharge resistor in the predetermined ith discharge period, P is the rated power of the discharge resistor, k is the rated power of the discharge resistorcFor derating factor, R is the resistance of the discharge resistor, QRmaxThe maximum discharge energy which can be borne by the discharge resistor.
Regarding the value of k, it should be noted that when the pulse signal is a pulse signal with a constant frequency and a constant pulse width or a pulse signal with a constant frequency and a variable pulse width, the value of k may be determined according to a predetermined discharge cycle time. When the pulse signal is a pulse signal with a constant pulse width and a variable period, the value of k can be determined according to the pre-estimated discharge period time.
In an alternative embodiment, the predetermined pulse signal is a constant-frequency and constant-pulse-width pulse signal, and in conjunction with fig. 4, T is the discharge period time of the constant-frequency and constant-pulse-width pulse signal, TonEffective pulse discharge time, toffFor discharge pulse interval time, i.e. T ═ Ton+toffAnd, furthermore,
ton＝t2-t1＝t4-t3＝t6-t5＝…
toff＝t3-t2＝t5-t4＝t7-t6＝…
the controller is at t1Sending out high level signal at the moment, and discharging time t of effective pulseonInternal switchThe tube S is continuously conducted until t2The voltage of an output port of the time direct current charging module is V1Down to V2At the moment, the pulse signal with the fixed frequency and the fixed pulse width is changed from high level to low level, the switching tube S is turned off, and the voltage at the output port of the direct current charging module is in the discharge pulse interval time toffInternal holding V2And not changed until the next discharge period comes.
Referring to fig. 2, if the capacitance of the filter capacitor C1 at the output port of the dc charging module is C, the maximum voltage at the output port of the dc charging module is VmaxEnergy Q stored in a filter capacitor C1 of the output port of the direct current charging modulemaxThe highest can be reached:
during discharging, the energy can only be discharged in the form of heat energy through the discharge resistor R1, so a power resistor with a certain impact resistance is generally used as the discharge resistor R1 of the dc charging module.
Assuming that the rated power of the discharge resistor R1 is P, a pulse discharge strategy satisfying the derating of the discharge resistor R1 is designed in combination with the discharge resistor pulse power characteristic curve shown in fig. 5. In fig. 5, the horizontal axis t is the discharge pulse time (i.e., the discharge cycle time), and the vertical axis k is the pulse power multiple that can be tolerated by the discharge resistor R1 in the discharge pulse time t, so that the shorter the discharge pulse time is, the larger the pulse power multiple that can be tolerated by the discharge resistor R1 is, but the energy discharged from the discharge resistor R1 in the discharge pulse time is constant (i.e., k × P × t is a constant), and is the maximum discharge energy that can be tolerated by the discharge resistor R1.
According to the pulse power characteristic curve of the discharge resistor shown in fig. 5, the maximum discharge energy Q bearable by the discharge resistor in the discharge process can be calculatedRmaxComprises the following steps:
QRmax＝k×P×t
for the selected type of discharge resistor R1, the maximum allowable discharge energy is fixed, i.e. QRmaxIs a constant. Taking into account the maximum voltage VmaxContinuously applying the fault condition of the output port of the DC charging module, and ensuring the effective pulse discharge time t when the fault occurs in the discharge control processonThe internal discharge resistor R1 is not broken. If a fault condition that external high voltage is continuously applied to the output port of the direct current charging module occurs, the energy Q consumed on the discharge resistor R1 in a single discharge pulsemaxComprises the following steps:
wherein R is the resistance of the discharge resistor R1.
If the derating coefficient of the discharge resistor R1 is kcThen, the effective pulse discharge time can be set in advance according to equation 1:
wherein, tonFor a set effective pulse discharge time, R is the resistance of the discharge resistor, QRmaxMaximum discharge energy, k, sustainable by the discharge resistorcTo a derating factor, VmaxThe highest voltage required for discharge.
From the above, when the fault condition that the external high voltage is continuously applied to the output port occurs at the output end of the module, the discharge time t is even the effective pulse within a short timeonAnd pulse discharge is carried out, the discharge resistor still meets the energy and power derating, and the discharge resistor cannot be damaged.
In addition, the discharge period time T may be set according to hardware parameters of the dc charging module (e.g., the capacitance C of the filter capacitor C1, the resistance R of the discharge resistor R1, etc.).
When the discharge period time T and the effective pulse discharge time T corresponding to the pulse signal with the fixed frequency and the fixed pulse width are setonThen, the set discharge period time T and the effective pulse discharge time T are ensuredonThe derating requirement of the discharge resistor is met. The verification process is as follows:
discharge voltage V at the beginning of the first discharge cycle1The highest voltage V for the desired dischargemaxFor example, the highest voltage at the output port of the DC charging module in FIG. 2 is the effective pulse discharging time tonDischarge energy Q of internal discharge resistor R11Comprises the following steps:
wherein τ is a charge-discharge time constant, and τ is RC.
Average power P of discharge resistor R1 in discharge period T1Comprises the following steps:
and, Q1、P1The following conditions are to be satisfied:
where k is the maximum pulse power multiple that discharge resistor R1 can withstand in the first discharge period.
Referring to fig. 6, if there is no fault that the external high voltage is continuously applied to the output port of the dc charging module, the voltage at the output port decreases as the number of discharge cycles increases, and the energy consumed by the discharging resistor R1 is the largest in the first discharge cycle, and then decreases from cycle to cycle. Since the energy consumed by the discharging resistor R1 in the first discharging period is the largest and then is reduced from cycle to cycle, as long as the average power of the discharging resistor R1 in the first discharging period is ensured to meet the derating requirement, the average power of the discharging resistor R1 in other periods can also meet the derating requirement.
In an embodiment, assuming that a capacitance value of the filter capacitor C1 of the dc charging module is C475 uF, a discharge period T is 0.2s, a resistance value R of the discharge resistor R1 is 440ohm, a rated power P of the discharge resistor R1 is 12W, and a maximum pulse power multiple k that can be borne by the discharge resistor R1 in 200ms is 20, a maximum leakage energy that can be borne by the discharge resistor R1 in a discharge process is:
QRmax＝k·P·t＝20*12W*200ms＝48J
in this example, the derating factor k of the pick-and-place resistor R1c0.8, the highest voltage V of the output port of the DC charging modulemax750V, the effective pulse discharge time t is determined according to the following formulaon：
Therefore, the effective pulse discharge time t can be seton30ms, and a discharge cycle time of a pulse signal of a set fixed frequency and a set fixed pulse width is 200ms, so that a discharge pulse interval time toffIs 170 ms. Of course, in other embodiments, the effective pulse discharge time t may be setonLess than 30ms, e.g. 25ms, when the discharge pulse interval t is longeroff175ms, which is also within the scope of the present invention.
When the 750V voltage is controlled to discharge by using the pulse signal with fixed frequency and fixed pulse width, the voltage at the output port of the DC charging module and the energy consumed by the discharge resistor R1 are as shown in FIG. 7, wherein V iso0(t) is the voltage at the output port of the DC charging module during discharging, Qc0(t) is the energy discharged from the discharge resistor R1 during the discharge cycle. As can be seen from fig. 7, the discharge start voltage of the first discharge period is the highest, the energy consumed by the discharge resistor R1 is also the largest, and as the discharge period increases, the voltage at the output port of the dc charging module gradually decreases, and the energy consumed by the discharge resistor R1 also decreases accordingly.
And, during normal discharge, the discharge voltage V at the end of the first discharge cycle2I.e. the discharge voltage at the beginning of the second discharge cycle is:
due to the discharge voltage V at the beginning of the first discharge cycle1Is a VmaxTherefore, the energy Q discharged from the discharge resistor R11Comprises the following steps:
from this, the energy Q discharged at the discharge resistor R1 can be determined1(33.374J) is less than the maximum discharge energy Q that the discharge resistor R1 can bearRmaxIs less than 38.4J (48J × 0.8).
In addition, the average power P of the discharge resistor R1 in the discharge period T1Comprises the following steps:
i.e. the average power P of the discharge resistor R1 during the discharge period1(166.87W) is less than the 80% pulse power de-rating requirement of discharge resistor R1, i.e., less than 192W.
In the above embodiment, the discharge circuit can normally discharge the 750V voltage outputted by the dc charging module, and since the discharge voltage at the beginning of the discharge cycle is smaller and smaller as the number of the discharge cycles increases, if the energy and the average power consumed by the discharge resistor R1 in the first discharge cycle both satisfy the derating requirement of the discharge resistor R1, the discharge resistor R1 has no risk of overpower in the whole discharge cycle.
The fixed-frequency fixed-pulse-width pulse discharge control method can effectively improve the reliability of an output discharge circuit, when the circuit parameters of the direct-current charging module are fixed, the pulse discharge time obtained by calculation according to the highest voltage output by the module is suitable for all output voltage levels, the effective pulse discharge time is fixed in the whole discharge process, and the control method is simple.
In another alternative embodiment, the predetermined pulse signal is a pulse signal with a constant frequency and a variable pulse width, i.e. the discharge period T is fixed during the whole discharge processConstant, effective pulse discharge time T within discharge period TonAnd (4) the operation is variable.
Referring to fig. 8, the pulse discharging process with constant frequency and constant pulse width is similar to the pulse discharging process with constant frequency and constant pulse width, and as the number of discharging cycles increases, the voltage at the output port of the dc charging module also changes from V1Down to V2、V3Etc., with the difference that the effective pulse discharge time t is during the whole discharge processonThe number of discharge cycles increases continuously, and the discharge pulse interval time toffThen it is continuously decreased, i.e.:
ton:ton1＝t2-t1,ton2＝t4-t3,ton3＝t6-t5,…，ton1＜ton2＜ton3＜...
toff:toff1＝t3-t2,toff2＝t5-t4,toff3＝t7-t6,…，toff1＞toff2＞toff3＞...
{ton1，ton2，ton3,., which is the time array of effective discharge pulse, when the discharge condition is satisfied, no matter what the voltage at the output port of the DC charging module is, the time array is fixed by ton1Effective pulse discharge time as the first discharge period, and with ton2And the effective pulse discharge time is used as the second discharge period, and the like, until the voltage of the output port of the direct current charging module is reduced to be lower than the set voltage, the discharge circuit stops operating.
Referring to fig. 2, assume that the capacitance of the filter capacitor C1 at the output port of the dc charging module is C, and the maximum voltage at the output port of the dc charging module is VmaxThe resistance value of the discharge resistor R1 is R, the rated power of the discharge resistor R1 is P, and the maximum leakage energy which can be borne by the discharge resistor R1 is Q obtained according to the graph in FIG. 5Rmax(similar to the above embodiments, which are not described herein), the derating coefficient of the pick-and-place resistor R1 is kc. Considering that the highest external power may occur in the DC charging modulePressure VmaxThe discharge control process is required to ensure that the discharge resistor R1 is not damaged in each discharge period when the fault occurs.
Specifically, when the pulse signal is a pulse signal with a constant frequency and a variable pulse width, the effective pulse discharge time is set in advance according to the following formula:
wherein, toniEffective pulse discharge time V for set i-th discharge periodiIs the discharge voltage at the beginning of the ith discharge cycle and the discharge voltage V at the beginning of the first discharge cycle1The highest voltage required for discharge, i.e. V1＝Vmax，Vi+1Is the discharge voltage at the end of the ith discharge cycle, Vi+1Also the discharge voltage at the beginning of the (i + 1) th discharge cycle.
For example, in the first discharge period, the discharge voltage V at the beginning of the first discharge period1＝VmaxThus, the effective pulse discharge time of the first discharge cycle is:
discharge voltage V at the end of the first discharge cycle2I.e. the discharge voltage at the beginning of the second discharge cycle is:
the effective pulse discharge time of the second discharge cycle is:
discharge voltage V at the end of the second discharge cycle3I.e. the discharge voltage at the beginning of the third discharge cycle is:
similarly, the effective pulse discharge time in each subsequent discharge period can be calculated, and therefore an effective pulse discharge time array { t ] with constant frequency and variable pulse width can be formedon1，ton2，ton3，ton4，ton5，...}。
In addition, the discharge period time T may be set according to hardware parameters of the dc charging module (e.g., the capacitance C of the filter capacitor C1, the resistance R of the discharge resistor R1, etc.).
After obtaining the effective pulse discharge time array, the energy and average power discharged from the discharge resistor R1 in each discharge period need to be calculated, specifically:
discharge voltage V at the beginning of the first discharge cycle1Maximum voltage V of output port of DC charging modulemaxEnergy Q discharged from discharge resistor R11Comprises the following steps:
average power P of discharge resistor R1 in first discharge period1Comprises the following steps:
discharge voltage V at the beginning of the second discharge cycle2Energy Q discharged from discharge resistor R1 as discharge voltage at the end of the first discharge cycle2Comprises the following steps:
discharge resistor in the second discharge periodAverage power P of R12Comprises the following steps:
similarly, the energy and the average power discharged from the discharge resistor R1 in each discharge cycle can be calculated, and the energy and the average power discharged from the discharge resistor R1 in each discharge cycle both need to meet the maximum derating requirement of the discharge resistor R1, that is, the energy Q discharged from the discharge resistor R1 in each discharge cycle1、Q2… are all less than QRmax×kcAverage power P of discharge resistor R1 in each discharge cycle1、P2… are all less than k × P × kc。
When the discharge control is performed by using the pulse signal with the constant frequency and the variable pulse width, the higher the voltage is, the effective pulse discharge time t is shown in fig. 8onThe shorter; conversely, the lower the voltage, the effective pulse discharge time tonThe longer.
In a specific example, assuming that the capacitance C of the filter capacitor C1 is 475uF, the discharge period T is 0.2s, the discharge resistor R1 is 440ohm, the rated power P of the discharge resistor R1 is 12W, and the maximum pulse power multiple k that can be borne by the discharge resistor R1 in 200ms is 20, then the maximum leakage energy that can be borne by the resistor during the discharge process is:
QRmax＝k·P·t＝20*12W*200ms＝48J
if the derating coefficient k of the pick-and-place resistor R1cWhen the maximum voltage required for discharge is 750V at 0.8, the discharge control is performed,
effective pulse discharge time t in first discharge periodon1Comprises the following steps:
the voltage at the output port of the dc charging module at the end of the first discharge cycle, i.e. the discharge voltage V at the end of the first discharge cycle2Comprises the following steps:
effective pulse discharge time t in the second discharge periodon2Comprises the following steps:
the voltage at the output port of the DC charging module at the end of the second discharge cycle, i.e. the discharge voltage V at the end of the second discharge cycle3Comprises the following steps:
effective pulse discharge time t in the third discharge periodon3Comprises the following steps:
the voltage at the output port of the dc charging module at the end of the third discharge cycle, i.e. the discharge voltage V at the end of the third discharge cycle4Comprises the following steps:
effective pulse discharge time t in the fourth discharge periodon4Comprises the following steps:
the voltage at the output port of the dc charging module at the end of the fourth discharge cycle, i.e. the discharge voltage V at the end of the fourth discharge cycle5Comprises the following steps:
effective pulse discharge time t in fifth discharge periodon5Comprises the following steps:
since the calculated effective pulse discharge time (276ms) in the fifth discharge period exceeds the discharge pulse period time of the discharge period (200ms), it is shown that the discharge resistor R1 does not overpower even if the switch tube S is continuously turned on to continuously discharge the output port, and therefore the pulse width t in the fifth discharge period is taken ason5Is 200ms, i.e. full duty discharge, and the voltage V at the output port of the DC charging module at the end of the fifth discharge cycle6Comprises the following steps:
voltage V at output port of dc charging module at end of fifth discharging period694.993V, still higher than the set voltage (50V), so the sixth discharge cycle continues.
Since the fifth discharge period is full duty discharge, the sixth discharge period is still full duty discharge, that is:
ton6＝200ms
the voltage at the output port of the dc charging module at the end of the sixth discharge cycle, i.e. the discharge voltage V at the end of the sixth discharge cycle7Comprises the following steps:
therefore, the discharge voltage can be lower than the set voltage of 50V after six discharge periods.
The effective pulse discharge time array corresponding to the above circuit parameters of the embodiment is thus obtained as: {30ms, 40ms, 59ms, 103ms, 200ms, 200ms }. The effective pulse discharge time and discharge period are accounted for by the energy and average power discharged across discharge resistor R1 during each discharge period. The energy discharged across discharge resistor R1 and the average power across the resistor during the six discharge pulse periods are shown in table 1.
TABLE 1
From the above table, when the constant-frequency variable-pulse-width pulse is used for the discharge control, the energy discharged from the discharge resistor R1 is less than 38.4J (48J × 0.8, i.e., the maximum discharge energy Q that can be borne by the discharge resistor R1 during the whole discharge processRmax80% derating), the average power of the discharge resistor R1 is smaller than 192W (20 × 12W × 0.8.8, namely 80% pulse power derating of the discharge resistor R1), and the obtained effective pulse discharge time array {30ms, 40ms, 59ms, 103ms, 200ms, 200ms } is suitable for the pulse discharge working condition of the full voltage level of the output port of the direct current charging module.
The voltage of the output port of the 750V direct current charging module is subjected to discharge control by adopting the pulse signal with the fixed frequency and the variable pulse width, the voltage waveform of the output port and the energy discharged from the discharging resistor R1 in a discharging period are shown in FIG. 9, and the pulse signal with the fixed frequency and the variable pulse width is adopted for discharge control, so that the pulse discharging time is obviously shortened under the same circuit parameters, and the energy and the average power discharged from the discharging resistor R1 in each discharging period meet the derating requirement, the reliability of the discharging circuit is ensured, the utilization rate of the discharging resistor R1 is improved, and the pulse discharging time is shortened.
When the discharge condition is met, the controller takes the value corresponding to the time array as the effective pulse discharge time of the current discharge period to perform discharge control, no matter what the voltage level of the output port of the direct current charging module is, when the output port voltages of 750V and 600V are subjected to pulse discharge control respectively by adopting the time array, the waveform of the port voltage is as shown in FIG. 10, so that the pulse discharge time is longest when the maximum voltage of the output port of the direct current charging module is 750V, the number of pulses is the largest, and the lower the discharge starting voltage is, the shorter the pulse discharge time is and the fewer the number of pulses are. The core point of this example is that the pulse discharge when the highest voltage 750V is output is taken as the worst working condition, and an effective discharge pulse sequence suitable for the full voltage range of the module output is obtained through calculation.
By adopting the fixed-frequency variable-pulse-width pulse discharge control method, the discharge pulse with fixed pulse width is replaced by the effective pulse discharge time array, the pulse discharge time can be reduced on the premise of ensuring the reliability of the discharge circuit, the output voltage does not need to be detected, and the control method is simple. In addition, the effective pulse discharge time t is obtained during the whole discharge processonThe time array is preset according to the highest voltage pulse discharge process (the worst working condition) output by the module, is suitable for the pulse discharge process of the module output full voltage grade, and can greatly reduce the total pulse discharge time under the condition of unchanged circuit parameters and processor overhead.
In an alternative embodiment, the preset pulse signal is a pulse signal with a constant pulse width and a variable period, that is, the discharge period time T is variable in the whole discharge process, but the effective pulse discharge time T in each discharge periodonAnd is not changed. The pulse signal with fixed pulse width and variable period is similar to the pulse discharge process with fixed frequency and fixed pulse width, the voltage of the output port of the DC charging module is gradually reduced along with the increase of the number of discharge periods, and the difference lies in that in the whole discharge process, the effective pulse discharge time tonWhile the discharge period time T is constant, it changes as the number of discharge periods increases, alternatively, the discharge period time T may decrease as the number of discharge periods increases.
Referring to fig. 2, if the capacitance of the filter capacitor C1 is C, the maximum voltage at the output port of the dc charging module is VmaxThe resistance value of the discharge resistor R1 is R, the rated power of the discharge resistor R1 is P, the maximum bearable discharge energy of the discharge resistor R1 is QRmax, and the derating system of the discharge resistor is obtained according to the graph of FIG. 5Number kc. Considering that the highest external voltage V may occur in the DC charging modulemaxThe fault condition continuously applied to the output port, in the discharge control method, the discharge resistor R1 is not damaged in each discharge period when the fault occurs.
Firstly, designing effective pulse discharge time t by the worst working condition of the maximum voltage output by the direct current charging moduleonThen, there are:
if a fault condition that an external high voltage is continuously applied to the output port of the direct current charging module occurs, the energy consumed on the discharge resistor R1 in a single discharge cycle is constant:
the discharge period time T at this time is required to ensure that the average power across the resistor meets the de-rating requirement. The maximum pulse power multiple that the electrical resistance can bear is k, then there are:
that is to say that the first and second electrodes,
the discharge period time T of the first discharge period can be obtained by the formula1。
Discharge voltage V at the end of the first discharge cycle2Comprises the following steps:
the discharge cycle time in the second discharge cycle is:
discharge voltage V at the end of the second discharge cycle3Comprises the following steps:
similarly, the discharge period time in each subsequent discharge period can be calculated, and a discharge period time array { T } with constant pulse width and variable period can be formed1，T2，T3，T4，T5，...}。
After obtaining the discharge period time array, the energy and the average power discharged from the discharge resistor R1 in each discharge period need to be calculated, specifically:
during the first discharge period, the discharge voltage V at the beginning of the discharge period1Maximum voltage V required for dischargemaxThat is, the highest voltage at the output port of the dc charging module in fig. 2, the energy Q discharged from the discharging resistor R11Comprises the following steps:
average power P of discharge resistor R1 in first discharge period1Comprises the following steps:
during the second discharge period, the discharge voltage V at the beginning of the discharge period2Is the discharge voltage at the end of the first discharge cycle, and therefore the energy Q discharged at the discharge resistor R12Comprises the following steps:
average power P of discharge resistor R1 in second discharge period2Comprises the following steps:
similarly, the energy and the average power discharged from the discharge resistor R1 in each discharge cycle can be calculated, and the energy and the average power discharged from the discharge resistor R1 in each discharge cycle both need to meet the maximum derating requirement of the discharge resistor R1, that is, the energy Q discharged from the discharge resistor R1 in each discharge cycle1、Q2… are all less than QRmax×kcAverage power P of discharge resistor R1 in each discharge cycle1、P2… are all less than k × P × kc。
FIG. 11 is a flowchart of a first embodiment of the discharging control method in step S30, wherein in step S30, the following steps are performed for each discharging cycle:
s301, judging whether a fault flag bit is set, if so, executing S310; if not, executing step S302;
s302, starting timing by a timer;
step S303, judging whether the timing time reaches the effective pulse discharge time of the current discharge period, if not, executing step S304; if yes, go to step S305;
s304, outputting a high level to control the conduction of a switching tube, and then executing the step S303;
s305, outputting a low level to control the switch tube to be switched off;
s306, judging whether the timing time reaches the current discharge period time, if not, executing the step S305; if yes, go to step S307;
s307, resetting a timer;
step S308, acquiring a discharge starting voltage and a discharge cut-off voltage of the current discharge period, judging whether the ratio of the discharge cut-off voltage and the discharge starting voltage of the current discharge period is greater than a preset value, if so, generating a single fault that an external high voltage is continuously applied to an output port, and executing step S309; if not, starting to perform the next discharge period;
s309, setting a fault flag bit;
and S310, stopping discharging.
Regarding the preset values in step S308, it should be noted that:
when the single fault that the external high voltage is continuously applied to the output port of the direct current charging module occurs, even if the discharging circuit of the output port passes through a discharging cycle, the voltage of the output port still keeps V0 unchanged, and the expected voltage drop of the output port does not occur, it can be judged that the single fault that the external high voltage is continuously applied to the output port occurs in the direct current charging module at the moment, and the action of the discharging circuit should be prohibited at the moment.
When the output port of the DC charging module is normally discharged, the discharge time t is in the effective pulseonThe voltage of the output port of the DC charging module is controlled by the discharge starting voltage V1Gradually decreases to V2And the three satisfy the following relation:
from the above formula, in the discharge period, the ratio of the discharge cut-off voltage to the discharge start voltage and the effective pulse discharge time tonRelated, tonThe longer the time, the smaller the ratio of the discharge cut-off voltage to the discharge start voltage.
Effective pulse discharge time t for discharge control using a pulse signal of constant frequency, constant pulse width or constant pulse width variable periodonIs constant, and therefore the ratio of the discharge cut-off voltage to the discharge start voltage is constant throughout the discharge, e.g. during the effective pulse discharge time tonWhen the discharge period is fixed to 30ms, the ratio of the discharge cut-off voltage to the discharge start voltage in each discharge period is 0.866. Therefore, in this case, the preset value may be set with direct reference to the ratio of the discharge cutoff voltage to the discharge start voltage, for example, to 0.866, or to a value greater than 0.866, for leaving a sufficient margin).
For the case of discharge control by using pulse signals with constant frequency and variable pulse width, the first dischargeEffective pulse discharge time t in a cycleonAt the shortest, the ratio of the discharge cutoff voltage to the discharge start voltage is also the largest, and the ratio is gradually decreased as the discharge period increases. For example, the ratio of the discharge cut-off voltage to the discharge start voltage in the first discharge period is 0.866, and the ratio of the discharge cut-off voltage to the discharge start voltage in the subsequent discharge period decreases as the discharge period increases. Therefore, in this case, the preset value may be set with reference to the maximum value of the ratio of the discharge cutoff voltage to the discharge start voltage, for example, the preset value is set to 0.9.
If k isfAt the end of each discharge period, comparing the discharge cut-off voltage with the discharge starting voltage, and if the discharge cut-off voltage is greater than k of the discharge starting voltagefAnd if the voltage is doubled, the direct current charging module is considered to have a discharge failure fault, at the moment, the relevant flag is set, and the pulse discharge of the next discharge period is forbidden. The fault detection logic is nested to execute in the pulse discharge control.
In one embodiment, referring to fig. 2, if the dc charging module has a single fault that an external high voltage is continuously applied to its output port, the first active pulse discharging time t passesonThe output port voltage still remains 750V, and in the first effective pulse discharge time, the energy discharged from the discharge resistor R1 is:
if the derating coefficient k of the taking and placing resistorcAt 0.8, the average power across discharge resistor R1 is:
even if the direct current charging module has a single fault that external high voltage is continuously applied, the direct current charging module still meets the derating requirement of the discharging resistor R1 in the first discharging period when discharging control is carried out, so that the discharging resistor R1 has no risk as long as the fault can be judged in time.
In summary, when the discharge period is over, the fault diagnosis is performed by judging whether the ratio of the discharge cut-off voltage to the discharge starting voltage in the discharge period exceeds the preset value, so that the reliability of the pulse discharge circuit can be effectively improved, and the overheating damage of the discharge resistor R1 can be avoided.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (9)
1. A discharge control method is used for controlling discharge of voltage on a filter capacitor through a discharge resistor and a switch tube, wherein the discharge resistor is connected with the switch tube in series and then connected with the filter capacitor in parallel, and the discharge control method is characterized by comprising the following steps:
s10, judging whether a discharging condition is met, and if so, executing the next step;
s20, acquiring a preset pulse signal, wherein the preset pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor;
s30, outputting the pulse signal to a switching tube to control the on-off of the switching tube so as to realize a discharging function;
the preset pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the de-rating requirement of the discharge resistor, and the preset pulse signal specifically comprises the following steps:
the effective pulse discharge time and the discharge cycle time satisfy the following conditions:
wherein Q isiDischarge energy of discharge resistor in discharge time of effective pulse of ith discharge periodoniEffective pulse discharge time, V, for the ith discharge periodiIs the discharge voltage at the beginning of the ith discharge cycle and the discharge voltage V at the beginning of the first discharge cycle1At the highest voltage of the desired discharge, Vi+1Is the discharge voltage at the end of the ith discharge cycle, τ is the charge-discharge time constant, and is the product of the discharge resistance and the capacitance of the filter capacitor, PiIs the average power of the i-th discharge period, TiIs the discharge period time of the ith discharge period, k is the maximum pulse power multiple which can be borne by the discharge resistor in the predetermined ith discharge period, P is the rated power of the discharge resistor, k is the rated power of the discharge resistorcFor derating factor, R is the resistance of the discharge resistor, QRmaxThe maximum discharge energy which can be borne by the discharge resistor.
2. The discharge control method according to claim 1,
the pulse signal is a pulse signal with fixed frequency and fixed pulse width; alternatively, the first and second electrodes may be,
the pulse signal is a pulse signal with constant frequency and variable pulse width, and the effective pulse discharge time is increased along with the increase of the number of discharge cycles; alternatively, the first and second electrodes may be,
the pulse signal is a pulse signal with a constant pulse width and a variable period.
3. The discharge control method according to claim 1 or 2, wherein in step S30, the following steps are performed per discharge cycle:
s301, judging whether a fault flag bit is set, if so, executing S310; if not, executing step S302;
s302, starting timing by a timer;
step S303, judging whether the timing time reaches the effective pulse discharge time of the current discharge period, if not, executing step S304; if yes, go to step S305;
s304, outputting a high level to control the conduction of a switching tube, and then executing the step S303;
s305, outputting a low level to control the switch tube to be switched off;
s306, judging whether the timing time reaches the current discharge cycle time, and if not, executing the step S305; if yes, go to step S307;
s307, resetting a timer;
step S308, acquiring a discharge starting voltage and a discharge cut-off voltage of the current discharge period, judging whether the ratio of the discharge cut-off voltage and the discharge starting voltage of the current discharge period is greater than a preset value, if so, generating a single fault that an external high voltage is continuously applied to an output port, and executing step S309; if not, starting to perform the next discharge period;
s309, setting the fault flag bit;
and S310, stopping discharging.
4. The discharge control method according to claim 2, wherein when the pulse signal is a pulse signal having a constant frequency and a constant pulse width or a pulse signal having a constant pulse width and a variable period, an effective pulse discharge time is set in advance according to formula 1:
wherein, tonFor a set effective pulse discharge time, R is the resistance of the discharge resistor, QRmaxMaximum discharge energy, k, sustainable by the discharge resistorcTo a derating factor, VmaxThe highest voltage required for discharge.
5. The discharge control method according to claim 2, wherein when the pulse signal is a pulse signal having a constant frequency and a variable pulse width, an effective pulse discharge time is set in advance according to the following equation:
wherein, toniEffective pulse discharge time for the set i-th discharge period, R is the resistance of the discharge resistor, and QRmaxMaximum discharge energy, k, sustainable by the discharge resistorcTo a derating factor, ViIs the discharge voltage at the beginning of the ith discharge cycle and the discharge voltage V at the beginning of the first discharge cycle1At the highest voltage of the desired discharge, Vi+1τ is a charge/discharge time constant, and is a discharge voltage at the end of the ith discharge period.
6. A discharge circuit is connected with a filter capacitor and is characterized by comprising a discharge resistor, a switch tube and a controller, wherein a first end of the discharge resistor is connected with a first end of the filter capacitor, a second end of the discharge resistor is connected with a first end of the switch tube, and a second end of the switch tube is connected with a second end of the filter capacitor; furthermore, it is possible to provide a liquid crystal display device,
the controller is used for acquiring a preset pulse signal and outputting the pulse signal to the switching tube when the discharge condition is judged to be met, so as to control the on-off of the switching tube and realize a discharge function, wherein the preset pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the derating requirement of the discharge resistor;
the preset pulse signal enables the discharge energy of the discharge resistor in the effective pulse discharge time and the average power of the discharge resistor in the discharge period to meet the de-rating requirement of the discharge resistor, and the preset pulse signal specifically comprises the following steps:
the effective pulse discharge time and the discharge cycle time satisfy the following conditions:
wherein Q isiDischarge energy of discharge resistor in discharge time of effective pulse of ith discharge periodoniEffective pulse discharge time, V, for the ith discharge periodiIs the discharge voltage at the beginning of the ith discharge cycle and the discharge voltage V at the beginning of the first discharge cycle1At the highest voltage of the desired discharge, Vi+1Is the discharge voltage at the end of the ith discharge cycle, τ is the charge-discharge time constant, and is the product of the discharge resistance and the capacitance of the filter capacitor, PiIs the average power of the i-th discharge period, TiIs the discharge period time of the ith discharge period, k is the maximum pulse power multiple which can be borne by the discharge resistor in the predetermined ith discharge period, P is the rated power of the discharge resistor, k is the rated power of the discharge resistorcFor derating factor, R is the resistance of the discharge resistor, QRmaxThe maximum discharge energy which can be borne by the discharge resistor.
7. The discharge circuit of claim 6,
the pulse signal is a pulse signal with fixed frequency and fixed pulse width; alternatively, the first and second electrodes may be,
the pulse signal is a pulse signal with constant frequency and variable pulse width, and the effective pulse discharge time is increased along with the increase of the number of discharge cycles; alternatively, the first and second electrodes may be,
the pulse signal is a pulse signal with a constant pulse width and a variable period.
8. The discharge circuit of claim 6,
the controller is further configured to determine whether a ratio of a discharge cut-off voltage to a discharge start voltage in a current discharge cycle is greater than a preset value at the end of each discharge cycle, and if so, a single fault that an external high voltage is continuously applied to an output port occurs, and the output of the pulse signal is stopped.
9. The discharge circuit of claim 7,
when the pulse signal is a pulse signal with a fixed frequency and a fixed pulse width or a pulse signal with a fixed pulse width and a variable period, the effective pulse discharge time is preset according to a formula 1:
wherein, tonFor the effective pulse discharge time, R is the resistance of the discharge resistor, QRmaxMaximum discharge energy, k, sustainable by the discharge resistorcTo a derating factor, VmaxThe highest voltage required for discharge;
when the pulse signal is a pulse signal with constant frequency and variable pulse width, the effective pulse discharge time is preset according to the following formula:
wherein, toniEffective pulse discharge time for the set i-th discharge period, R is the resistance of the discharge resistor, and QRmaxMaximum discharge energy, k, sustainable by the discharge resistorcTo lowerCoefficient of quota, ViIs the discharge voltage at the beginning of the ith discharge cycle and the discharge voltage V at the beginning of the first discharge cycle1At the highest voltage of the desired discharge, Vi+1τ is a charge/discharge time constant, and is a discharge voltage at the end of the ith discharge period.
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