阅读说明：本技术 一种高精度的限流电路 (High-precision current limiting circuit ) 是由 郭铁厂 顾焕涛 付兴利 吴庭宇 于 2019-10-25 设计创作，主要内容包括：本发明提供一种高精度的限流电路,包括电压环PI调节器、电流环PI调节器、钳位电压源和钳位电路；电压环PI调节器将给定电压参考信号与输出电压反馈信号作差,并进行比例积分运算；电流环PI调节器将电压环PI调节器的输出和电流环反馈信号作差,并进行比例积分运算；钳位电压源用来给钳位电路提供电压值；钳位电路通过限制电流环PI调节器信号的最大值,进而限制限流电路所在直流变换器的输出电流。本发明的电路,在不损失电路其它特性的情况下,可有效提升限流精度。(The invention provides a high-precision current limiting circuit, which comprises a voltage ring PI regulator, a current ring PI regulator, a clamping voltage source and a clamping circuit, wherein the voltage ring PI regulator is connected with the current ring PI regulator; the voltage loop PI regulator makes a difference between a given voltage reference signal and an output voltage feedback signal, and performs proportional integral operation; the current loop PI regulator makes a difference between the output of the voltage loop PI regulator and a current loop feedback signal, and performs proportional integral operation; the clamping voltage source is used for providing a voltage value for the clamping circuit; the clamp circuit limits the output current of the direct current converter where the current limiting circuit is located by limiting the maximum value of the current loop PI regulator signal. The circuit of the invention can effectively improve the current limiting precision under the condition of not losing other characteristics of the circuit.)

1. A high-precision current limiting circuit comprises a voltage loop PI regulator, a current loop PI regulator, a clamping voltage source and a clamping circuit;

the voltage loop PI regulator makes a difference between a given voltage reference signal and an output voltage feedback signal, performs proportional integral operation and then sends the difference to the current loop PI regulator; the current loop PI regulator makes a difference between the output of the voltage loop PI regulator and a current loop feedback signal, and performs proportional integral operation; the clamping voltage source is used for providing a voltage value for the clamping circuit; the clamping circuit limits the output current of the direct current converter where the current limiting circuit is located by limiting the maximum value of a current loop PI regulator signal V _ Clamp, and the current limiting effect is achieved.

2. The current-limiting circuit with high precision as claimed in claim 1, wherein the voltage loop PI regulator is composed of resistors R2, R4, R5, R7, R8, capacitors C2, C4 and an operational amplifier U2B, one end of a voltage loop Reference signal V _ Reference is connected to one end of R7, the other end of R7 is connected to both the positive input terminal of U2B and one end of R8, and the other end of R8 is connected to the ground signal AGND; the output voltage Feedback signal V _ Feedback is connected with one end of R4, the other end of R4 is simultaneously connected with the reverse input end of U2B, one end of R2 and one end of C2, the other end of R2 is connected with one end of C4, and the other end of C4 is simultaneously connected with the other end of C2, the output pin of U2B and one end of R5; the other end signal V _ Clamp of R5 is output as a voltage loop PI regulator.

3. The current-limiting circuit with high precision according to claim 2, wherein the current loop PI regulator is composed of resistors R1, R3, R6, capacitors C1, C3 and an operational amplifier U1B, one end of the signal V _ Clamp is connected to R6, and the other end of the signal R6 is connected to the positive input end of the U1B; an output current Feedback signal I _ Feedback is connected with one end of R3, the other end of R3 is simultaneously connected with the inverting input end of U1B, one end of R1 and one end of C1, the other end of R1 is connected with one end of C3, the other end of C3 is simultaneously connected with the other end of C1 and the output pin of U1B, and an output pin signal PI _ OUT2 of U1B is output as a current loop PI regulator.

4. The current-limiting circuit with high precision as claimed in claim 3, wherein the clamping voltage source is composed of resistors R9, R10, R11, a capacitor C7 and a precision programmable voltage regulator VT1, the +15V power supply is connected with one end of R9, and the other end of R9 is connected with one end of C7, the cathode of VT1 and one end of R10; the other end of the C7 is connected with the anode of VT1 and one end of R11, and then is connected with AGND signal; the other end of R10, the other end of R11 and 2 pins of VT1 are connected together, wherein the common end of R9, R10, VT1 and C7 is used as an output signal V _ Source.

5. The current-limiting circuit with high precision as claimed in claim 4, wherein the clamp circuit is composed of capacitors C5, C6, diode D1 and operational amplifier U1A, the +15V power supply is connected to one end of C5 and 8 pins of U1A, and the other end of C5 is grounded AGND; c6 one end ground AGND, another end connects 4 pins and-15V power of U1A at the same time; the forward input end of U1A is connected with V _ Source signal, the 1 pin of U1A is connected with the cathode of D1, the 2 pin is connected with the anode of D1, and then the output of the clamping circuit is used for limiting the voltage of the output signal V _ Clamp of the voltage ring PI regulator.

6. The high-precision current limiting circuit according to claim 5, wherein the output signal V of the clamp voltage source can be adjusted by adjusting the resistance values of R10 and R11_{_}And Source, finishing the setting of the output current limiting value.

7. The high accuracy current limiting circuit of claim 6 wherein the output voltage of the clamp voltage source is

Wherein, VT1 adopts precision programmable voltage regulator TL431, and Vref in the above formula is TL431 internal reference voltage.

8. The high-precision current-limiting circuit according to claim 7, wherein a cathode of a diode D1 is connected with an output end of an operational amplifier U1A, an anode of the diode D1 is connected with an inverted input end of U1A, an output signal V _ Clamp at an anode of D1 is used as a reference signal of a current loop PI regulator, and D1 and U1A form closed-loop feedback, so that the influence of D1 parameter change on V _ Clamp is eliminated.

Technical Field

The invention relates to aviation electrical system protection, and belongs to the field of electrical safety. In particular to a high-precision current limiting circuit.

Background

In order to improve the power supply reliability of an aviation power supply system, the aviation DC/DC converter is definitely provided with certain overload and short-circuit resistance in relevant standards, and the specific requirements are that 1) the overload capacity is as follows: the DC/DC converter can bear 150% and 200% rated load current for 5min and 5s respectively, and the output voltage meets the specification requirement; 2) short circuit resistance: the DC/DC converter should be able to output 300% of the rated load current for 5 s.

One of the current limiting function implementation strategies of the power converter in the aviation field is a control current inner loop.

A mode of controlling a current inner loop is to divide voltage through resistors, the circuit is simple in the mode, the current limiting precision is high, but a voltage dividing circuit needs to be connected into a loop in series, loop gain is affected, and certain difficulty is brought to later loop debugging. Loop stability may also be affected if the confidence is not good.

Another way to control the current inner loop is through diode clamping, which is connected in parallel to the circuit and has an or relationship with the main circuit. When the main circuit works normally, the current limiting circuit does not participate in the system work. When the system is over-current or short-circuit, the current limiting circuit is switched into the main circuit, and the output current is limited by controlling the current inner loop. However, this control method is easily affected by the diode parameters, resulting in low current limiting accuracy.

In a common aviation field power converter for realizing current limiting by controlling a current inner ring, one mode influences the loop characteristics and is not beneficial to loop debugging and system stability, and the other mode is greatly influenced by the difference of clamping diodes and influences the current limiting precision. With the development of the aviation industry, higher requirements are placed on an aviation power supply converter, and the influence on the stability of a loop is reduced and the current limiting precision is improved while the output current is effectively limited by the novel current limiting circuit.

Disclosure of Invention

The invention aims to provide a high-precision current limiting circuit for the current limiting protection of an aviation power supply converter product, and solves the problems that the traditional current limiting circuit influences the loop characteristic and the current limiting precision of output current is not high on the premise of meeting the basic function of effectively limiting the output current.

The invention has the technical scheme that the high-precision current limiting circuit comprises a voltage loop PI regulator, a current loop PI regulator, a clamping voltage source and a clamping circuit;

the voltage loop PI regulator makes a difference between a given voltage reference signal and an output voltage feedback signal, performs proportional integral operation and then sends the difference to the current loop PI regulator; the voltage ring PI regulator consists of resistors R2, R4, R5, R7, R8, capacitors C2 and C4 and an operational amplifier U2B, wherein one ends of voltage ring Reference signals V _ Reference and R7 are connected, the other end of R7 is simultaneously connected with the positive input end of the U2B and one end of the R8, and the other end of the R8 is connected with a ground signal AGND; the output voltage Feedback signal V _ Feedback is connected with one end of R4, the other end of R4 is simultaneously connected with the reverse input end of U2B, one end of R2 and one end of C2, the other end of R2 is connected with one end of C4, and the other end of C4 is simultaneously connected with the other end of C2, the output pin of U2B and one end of R5; a signal V _ Clamp at the other end of the R5 is output as a voltage loop PI regulator;

the current loop PI regulator makes a difference between the output of the voltage loop PI regulator and a current loop feedback signal, and performs proportional integral operation; the current loop PI regulator consists of resistors R1, R3, R6, capacitors C1, C3 and an operational amplifier U1B, wherein one ends of signals V _ Clamp and R6 are connected, and the other end of R6 is connected with the positive input end of U1B; an output current Feedback signal I _ Feedback is connected with one end of R3, the other end of R3 is simultaneously connected with the inverted input end of U1B, one end of R1 and one end of C1, the other end of R1 is connected with one end of C3, the other end of C3 is simultaneously connected with the other end of C1 and an output pin of U1B, and an output pin signal PI _ OUT2 of U1B is output as a current loop PI regulator;

the clamp voltage source is used for providing a voltage value for the clamp circuit and consists of resistors R9, R10, R11, a capacitor C7 and a precision programmable voltage stabilizer VT1, a +15V power supply is connected with one end of R9, and the other end of R9 is simultaneously connected with one end of C7, the cathode of VT1 and one end of R10; the other end of the C7 is connected with the anode of VT1 and one end of R11, and then is connected with AGND signal; the other end of R10, the other end of R11 and 2 pins of VT1 are connected together, wherein the common end of R9, R10, VT1 and C7 is used as an output signal V _ Source;

the Clamp circuit limits the output current of the direct current converter where the current limiting circuit is located by limiting the maximum value of a current loop PI regulator signal V _ Clamp, so as to play a role in limiting current, the Clamp circuit consists of capacitors C5, C6, a diode D1 and an operational amplifier U1A, a +15V power supply is simultaneously connected with one end of C5 and the 8 pins of U1A, and the other end of C5 is grounded AGND; c6 one end ground AGND, another end connects 4 pins and-15V power of U1A at the same time; the forward input end of U1A is connected with V _ Source signal, the 1 pin of U1A is connected with the cathode of D1, the 2 pin is connected with the anode of D1, and then the output of the clamping circuit is used for limiting the voltage of the output signal V _ Clamp of the voltage ring PI regulator.

The invention has the beneficial effects that: the current limiting circuit is realized by controlling the reference voltage of the current inner loop. The expected voltage value can be accurately set through the clamping voltage source circuit, and after the voltage value is reprocessed through the clamping circuit, the voltage value is injected into the reference end of the current loop PI regulator in a parallel connection mode, and finally the output current limiting function is completed. The clamping voltage source provides an accurate clamping voltage value, the clamping circuit can improve the loading capacity of the clamping voltage source, and meanwhile, errors caused by diodes are eliminated through a feedback loop of the clamping circuit, and the current limiting precision is improved. By adopting the current limiting circuit, the current limiting precision can be effectively improved under the condition of not losing other characteristics of the circuit.

Drawings

FIG. 1 is a schematic diagram of a current limiting circuit

FIG. 2 is a voltage loop PI regulator

FIG. 3 is a current loop PI regulator

FIG. 4 is a clamp voltage source

FIG. 5 is a clamp circuit

Detailed Description

The connection structure of the present invention will be described in detail with reference to the accompanying drawings and examples.

The aviation power supply converter product mostly collects output current signals, compares the current feedback signals with current-limiting reference signals through a current loop PI regulator, and achieves the purpose of outputting and limiting current by influencing the duty ratio of PWM signals. The high-precision current limiting circuit provided by the invention is also the same in principle, but the current limiting circuit can eliminate the current limiting error caused by the diode parameters and improve the current limiting precision by matching the clamping voltage source with the clamping circuit.

A high-precision current limiting circuit comprises a voltage loop PI regulator, a current loop PI regulator, a clamping voltage source and a clamping circuit, and is shown in figure 1.

Fig. 2 shows a voltage loop PI regulator, which is composed of resistors R2, R4, R5, R7, R8, capacitors C2, C4, and an operational amplifier U2B. The voltage ring PI regulator mainly performs subtraction on a given voltage Reference signal V _ Reference and an output voltage Feedback signal V _ Feedback, performs correlation proportional integral operation, obtains an output signal V _ Clamp, and ensures that an output voltage value is consistent with an expected value.

Fig. 3 shows a current loop PI regulator, which is composed of resistors R1, R3, R6, capacitors C1, C3 and an operational amplifier U1B. The current loop PI regulator mainly performs subtraction between a V _ Clamp signal output by the voltage loop PI regulator or the clamping circuit and a current Feedback signal I _ Feedback, performs correlation proportional integral operation to obtain an output signal PI _ OUT2, and the maximum value of PI _ OUT2 is determined by V _ Clamp, so that the maximum value of the output current can be limited by adjusting the value of V _ Clamp.

Fig. 4 shows a clamp voltage source, which is composed of resistors R9, R10, R11, a capacitor C7, and a precision programmable regulator VT 1. Wherein TL431 is usually adopted as VT1, and the technical manual of TL431 can be easily calculated

Fig. 5 shows a clamp circuit, which is composed of capacitors C5, C6, diode D1 and operational amplifier U1A. During normal operation of the converter, the negative input signal V _ Clamp < the positive input signal V _ Source of U1A, and the output pin 1 of U1A is saturated in the positive direction, but the V _ Clamp signal remains unchanged due to the D1. When the output of the converter is over-current or short-circuited, the output voltage Feedback signal V _ Feedback is reduced, and U2B is saturated in the forward direction, so that V _ Clamp > V _ Source and U1A is saturated in the reverse direction. Reverse saturation of U1A will cause D1 to turn on in the forward direction, and V _ Clamp is diode clamped, so that V _ Clamp < V _ Source. Once V _ Clamp < V _ Source, U1A will saturate in forward direction again, D1 will cut off in reverse direction again, D1 loses its clamping effect on V _ Clamp, and if the converter is still in an overcurrent or short-circuit state, V _ Clamp will be greater than V _ Source again, and U1A will saturate in reverse direction again. And repeating the steps until the converter exits the overcurrent or short-circuit working state. Since the operational speed of the operational amplifier is in the order of microseconds or even nanoseconds, the above-mentioned reciprocating process is completed in the time of microseconds or even nanometers, and the outward expression is that V _ Clamp is equal to V _ Source, and the output current is limited. And when the converter exits from the overcurrent or short-circuit working state, V _ Clamp is less than V _ Source, and the converter restores to normal operation.