A low-cost backup power charging circuit and method for a power distribution automation terminal

Abstract

The application discloses a low-cost backup power supply charging circuit and method for a power distribution automation terminal. The low-cost backup power supply charging circuit for the power distribution automation terminal comprises a charging protection circuit, a three-terminal voltage stabilizing circuit, a self-adaptive charging circuit and a backup power supply protection circuit. The input end of the self-adaptive charging circuit is connected with a power supply end PWR, and the output end is connected with a backup power supply. The self-adaptive charging circuit comprises a comparator D1 and a comparator D2, and a MOSFET tube V5 controlled by the comparator D1 and the comparator D2. The application can select different resistance values for current-limiting charging according to different input voltages, realizes charging of backup power supplies with different voltages, and has the advantages of strong applicability, short-circuit protection, low cost and the like.

Description

Technical Field

[0001] This invention relates to the field of power distribution technology, specifically to a backup power charging circuit for a power distribution automation terminal, and also to a method for charging the backup power. Background Technology

[0002] Distribution automation terminals mainly include feeder terminals (FTUs) and substation terminals (DTUs). The backup power for distribution automation terminals uses maintenance-free valve-regulated lead-acid batteries or supercapacitors, or other new energy batteries such as supercapacitors and lithium titanate batteries. There are many types available, and different sites require different backup power supplies.

[0003] Existing charging solutions use circuits with different principles for different backup power sources. For example, batteries are usually self-charged, while supercapacitors need to start charging from 0V. The initial charging stage is equivalent to a short circuit in the backup power source. Therefore, batteries and supercapacitors require different charging schemes, resulting in high management costs and inconvenient on-site matching. On the other hand, most backup power sources directly charge the battery by passing the voltage through a diode. If the battery short-circuits, it can easily damage related circuits and cause unnecessary losses. Summary of the Invention

[0004] This invention proposes a low-cost backup power charging circuit and method for power distribution automation terminals. Its purpose is to: 1. solve the problems of high management costs and inconvenient matching caused by different backup power supplies; 2. solve the problem that existing charging circuits and methods cannot achieve short-circuit protection function.

[0005] The technical solution of this invention is as follows:

[0006] A low-cost backup power charging circuit for a power distribution automation terminal includes a three-terminal voltage regulator circuit and an adaptive charging circuit.

[0007] The input terminal of the adaptive charging circuit is connected to the power supply terminal PWR, and the output terminal is connected to the backup power supply.

[0008] The adaptive charging circuit includes comparator D1 and comparator D2, and MOSFET V5 controlled by comparator D1 and comparator D2.

[0009] When the voltage at the power supply terminal PWR matches the supply voltage of comparator D1 and comparator D2, the power supply terminal PWR directly supplies power to comparator D1 and comparator D2 as the VCC terminal.

[0010] When the voltage at the power supply terminal PWR does not match the supply voltage of comparator D1 and comparator D2, the power supply terminal PWR is connected to the input terminal of the three-terminal voltage regulator circuit, and the output terminal of the three-terminal voltage regulator circuit is used as the VCC terminal to supply power to comparator D1 and comparator D2.

[0011] As a further improvement to the low-cost backup power charging circuit of the power distribution automation terminal: the three-terminal voltage regulator circuit includes a diode V2, a resistor R1, a Zener diode V3, a transistor V4, and a capacitor C2;

[0012] The power supply terminal PWR is connected to the positive terminal of diode V2; the negative terminal of diode V2 is connected to the collector of transistor V4, and also to one end of resistor R1; the other end of resistor R1 is connected to the base of transistor V4, and also to the cathode of Zener diode V3; the anode of Zener diode V3 is connected to ground terminal GND; the emitter of transistor V4 is connected to one end of capacitor C2, and the other end of capacitor C2 is connected to ground terminal GND.

[0013] The emitter of transistor V4 is the output terminal of the three-terminal voltage regulator circuit.

[0014] As a further improvement to the low-cost backup power charging circuit of the power distribution automation terminal, the adaptive charging circuit also includes resistors R2, R3, R4, R5, R6, R7, R8, and R9, Zener diode V6, diode V7, inductor L1, and capacitor C3.

[0015] The PWR terminal is connected to the ground terminal GND through resistors R2, R3 and R4 connected in series, and is also connected to one end of resistor R5; the other end of resistor R5 is connected to the ground terminal GND through resistors R6 and R7 connected in series.

[0016] The connection point between resistors R6 and R7 is connected to the positive input terminal of comparator D1; the connection point between resistors R3 and R4 is connected to the negative input terminal of comparator D1 and the positive input terminal of comparator D2, respectively; the output terminal of comparator D1 is connected to the negative input terminal of comparator D2; the VCC terminal is also connected to the negative input terminal of comparator D2 through resistor R8.

[0017] The other end of resistor R5 is connected to the source of MOSFET V5. The output of comparator D2 is connected to the anode of Zener diode V6. The cathode of Zener diode V6 is connected to the gate of MOSFET V5. The drain of MOSFET V5 is connected to the cathode of diode V7. The anode of diode V7 is connected to ground GND. Resistor R9 is connected between the source and gate of MOSFET V5.

[0018] The drain of MOSFET V5 is also connected to one end of inductor L1, and the other end of inductor L1 is connected to ground GND through capacitor C3.

[0019] The other end of inductor L1 is the output terminal of the adaptive charging circuit.

[0020] As a further improvement to the low-cost backup power charging circuit of the power distribution automation terminal, it also includes a charging protection circuit, which includes a transient voltage suppression diode V1 and a capacitor C1.

[0021] The power supply terminal PWR is connected to one end of the transient voltage suppression diode V1 and also to the positive terminal of the capacitor C1; the other end of the transient voltage suppression diode V1 is connected to the ground terminal GND and also to the negative terminal of the capacitor C1.

[0022] As a further improvement to the low-cost backup power charging circuit of the power distribution automation terminal, it also includes a backup power protection circuit, which includes a transient voltage suppression diode V8. One end of the transient voltage suppression diode V8 is connected to the output terminal of the adaptive charging circuit, and the other end is connected to the ground terminal GND.

[0023] This invention also proposes a charging method based on the aforementioned low-cost backup power charging circuit for distribution automation terminals:

[0024] Resistor R5 is a current-limiting resistor. Based on the resistance value of resistor R5 and the current-limiting value, the resistance values ​​of resistors R2, R3, R4, R6, and R7 are set accordingly.

[0025] When the charging current on resistor R5 is less than the set current limit, the voltage at the positive input terminal of comparator D1 is greater than the voltage at its negative input terminal; at this time, the output of comparator D1 is an open-circuit output, and the output voltage is equal to the VCC terminal voltage. The voltage at the negative input terminal of comparator D2 is the VCC terminal voltage, and the voltage at the negative input terminal of comparator D2 is greater than the voltage at its positive input terminal. The output voltage of comparator D2 is low, and the source and drain of MOSFET V5 are turned on, charging inductor L1, capacitor C3 and backup power supply.

[0026] When the charging current on resistor R5 exceeds the set current limit, the voltage at the positive input terminal of comparator D1 is less than the voltage at its negative input terminal. At this time, the output of comparator D1 is low, the voltage at the negative input terminal of comparator D2 is low, the voltage at the negative input terminal of comparator D2 is less than the voltage at its positive input terminal, the output of comparator D2 is an open-collector (OC) gate output, and the output voltage is equal to the voltage at the VCC terminal. The source and drain of MOSFET V5 are not conducting. At this time, inductor L1 charges capacitor C3 and the backup power supply.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] I. This invention can achieve constant current charging by adjusting the resistance value of relevant resistors according to the voltage of the backup power supply and the set current limit value, thereby meeting the charging requirements of different types and voltages of backup power supplies such as lead-acid batteries, lithium batteries, and supercapacitors. Multiple backup power supplies can share the same charging scheme, which has strong applicability and solves the problems of high management cost and inconvenient matching of traditional solutions. At the same time, it has the function of output short circuit protection, which greatly improves the reliability of the system.

[0029] Second, according to the voltage at the PWR terminal, the present invention can select to add a three-terminal voltage regulator circuit to provide a matching power supply voltage for the comparator in the charging circuit.

[0030] Third, the circuit of this invention is simple, the logic is clear, it uses fewer components, the cost is low, and the reliability is high. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the circuit of the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings:

[0033] like Figure 1 A low-cost backup power charging circuit for a power distribution automation terminal includes a charging protection circuit, a three-terminal voltage regulator circuit, an adaptive charging circuit, and a backup power protection circuit.

[0034] The charging protection circuit includes a transient voltage suppression diode V1 and a capacitor C1. The power supply terminal PWR is connected to one end of the transient voltage suppression diode V1 and also to the positive terminal of the capacitor C1; the other end of the transient voltage suppression diode V1 is connected to the ground terminal GND and also to the negative terminal of the capacitor C1.

[0035] The three-terminal voltage regulator circuit includes diode V2, resistor R1, Zener diode V3, transistor V4, and capacitor C2.

[0036] The power supply terminal PWR is connected to the positive terminal of diode V2; the negative terminal of diode V2 is connected to the collector of transistor V4, and also to one end of resistor R1; the other end of resistor R1 is connected to the base of transistor V4, and also to the cathode of Zener diode V3; the anode of Zener diode V3 is connected to ground terminal GND; the emitter of transistor V4 is connected to one end of capacitor C2, and the other end of capacitor C2 is connected to ground terminal GND.

[0037] The emitter of transistor V4 is the output terminal of the three-terminal voltage regulator circuit.

[0038] A basic voltage regulator circuit is formed by the resistor R1 and the Zener diode V3. A stable voltage is obtained across the Zener diode V3. The base of the NPN transistor V4 is connected to this point, thus forming an emitter follower. The emitter voltage of the transistor V4 follows the base voltage, and the base voltage is higher than the emitter voltage by one diode voltage drop. The load-carrying capacity of this circuit is much greater than that of a single Zener diode. Furthermore, due to the high input impedance of the emitter follower, the output voltage is more stable. For example, using a 22V Zener diode with a transistor voltage drop of 0.6V, the output voltage is 22V minus 0.6V, resulting in a stable 21.4V at the VCC terminal.

[0039] The rated backup power supply voltage for a Distribution Automation Terminal Unit (FTU) is DC 24V, and for a Distribution Automation Terminal Unit (DTU) it is 48V. Therefore, the input voltage PWR of this circuit is typically 24V or 48V. Diode V1 is used for protection of the power output system. After passing through a three-terminal regulator circuit, it forms voltage VCC, which powers the subsequent comparators D1 and D2. The supply voltage range for the comparator components is generally between 1.8V and 36V. If the input voltage PWR is DC 24V, the three-terminal regulator circuit can be omitted, and the power supply terminal PWR can be used directly as VCC to power comparators D1 and D2. If the input voltage PWR is DC 48V, a three-terminal regulator circuit is needed to step down the voltage, and the output terminal of the three-terminal regulator circuit can be used as VCC to power the subsequent comparators D1 and D2.

[0040] The input terminal of the adaptive charging circuit is connected to the power supply terminal PWR, and the output terminal is connected to the backup power supply. The adaptive charging circuit includes comparators D1 and D2, and a MOSFET V5 controlled by comparators D1 and D2.

[0041] Specifically, the adaptive charging circuit also includes resistors R2, R3, R4, R5, R6, R7, R8, and R9, Zener diode V6, diode V7, inductor L1, and capacitor C3.

[0042] The PWR terminal is connected to the ground terminal GND via resistors R2, R3 and R4 connected in series, and is also connected to one end of resistor R5; the other end of resistor R5 is connected to the ground terminal GND via resistors R6 and R7 connected in series.

[0043] The connection point between resistors R6 and R7 is connected to the positive input terminal of comparator D1. The connection point between resistors R3 and R4 is connected to the negative input terminal of comparator D1 and the positive input terminal of comparator D2, respectively. The output terminal of comparator D1 is connected to the negative input terminal of comparator D2. The VCC terminal is also connected to the negative input terminal of comparator D2 through resistor R8.

[0044] The other end of resistor R5 is connected to the source of MOSFET V5. The output of comparator D2 is connected to the anode of Zener diode V6. The cathode of Zener diode V6 is connected to the gate of MOSFET V5. The drain of MOSFET V5 is connected to the cathode of diode V7. The anode of diode V7 is connected to ground GND. Resistor R9 is connected between the source and gate of MOSFET V5.

[0045] The drain of MOSFET V5 is also connected to one end of inductor L1, and the other end of inductor L1 is connected to ground GND through capacitor C3.

[0046] Resistor R5 is a current-limiting resistor; its value cannot be too large, as this can lead to excessive power consumption and heat generation. Generally, a surface-mount alloy sampling resistor is used, which offers advantages such as low resistance, high accuracy, low temperature coefficient, good stability, light weight, and easy soldering.

[0047] The other end of inductor L1 is the output terminal of the adaptive charging circuit and is also connected to network B+ / C+. Network B+ / C+ is connected to the positive terminal of the backup power supply, and network GND is connected to the negative terminal of the backup power supply.

[0048] The backup power protection circuit includes a transient voltage suppression diode V8, one end of which is connected to the output terminal of the adaptive charging circuit and the other end is connected to the ground terminal GND.

[0049] Implementation Method 1

[0050] The distribution automation terminal is an FTU, with a PWR output voltage of 24V and a current limit of 1A. At this time, a three-terminal regulator circuit is not used; comparators D1 and D2 can be directly powered by the PWR voltage. If the current-limiting resistor R5 is 0.05 ohms, the power consumption across this resistor is 0.05 watts. That is, the voltage at the negative input terminal of comparator D1 is PWR*R4 / (R2+R3+R4), and the voltage at the positive input terminal of comparator D1 is (PWR-I*R5)*R7 / (R6+R7). If the resistance values ​​of R2, R4, R6, and R7 are all 100K ohms, then the resistance value of R3 is 0.4175K ohms.

[0051] When the charging current is less than 1A, the voltage at the positive input terminal of comparator D1 is greater than the voltage at the negative input terminal. Comparator D1 operates as an open-collector (OC) gate, and the output voltage equals the voltage across resistor R8, which is 24V. The voltage at the negative input terminal of comparator D2 is greater than the voltage at the positive input terminal, and the output of comparator D2 is low. Since the source-drain voltage of the P-channel enhancement-mode MOSFET V5 generally needs to be less than 20V, a suitable Zener diode V6 is required to limit its voltage; a 10V Zener diode can be used. At this time, the source and drain of the P-channel enhancement-mode MOSFET V5 are conducting, and the PWR voltage charges inductor L1, capacitor C3, and the backup power supply.

[0052] When the charging current is greater than 1A, the voltage at the positive input terminal of comparator D1 is less than the voltage at the negative input terminal, so comparator D1 outputs a low level. The voltage at the negative input terminal of comparator D2 is less than the voltage at the positive input terminal, so comparator D2 is an open-circuit (OC) gate output. Therefore, at this time, the source and drain of the P-channel enhancement-mode MOSFET V5 are cut off, and inductor L1 charges capacitor C3 and the backup power supply. Diode V7 then functions as a freewheeling diode.

[0053] Implementation Method 2

[0054] The distribution automation terminal is a DTU, with a PWR output voltage of 48V and a current limit of 1A. A three-terminal voltage regulator circuit is required. Comparators D1 and D2 can be powered by the stepped-down VCC voltage. If the Zener diode V3 is a 27V Zener diode and the NPN transistor V4 has a voltage drop of 0.6V, then the output VCC will be 26.4V. If the current-limiting resistor R5 is still set to 0.05 ohms, then the power consumption across this resistor is 0.05 watts. That is, the voltage at the negative input terminal of comparator D1 is PWR*R4 / (R2+R3+R4), and the voltage at the positive input terminal of comparator D1 is (PWR-I*R5)*R7 / (R6+R7). If R2, R4, R6, and R7 are all 100K ohms, then the resistance of R3 will be 0.2086K ohms.

[0055] When the charging current is less than 1A, the voltage at the positive input terminal of comparator D1 is greater than the voltage at the negative input terminal. Comparator D1 operates as an open-collector (OC) gate, and the output voltage equals the voltage across resistor R8, which is 26.4V. The voltage at the negative input terminal of comparator D2 is greater than the voltage at the positive input terminal, so the output of comparator D2 is low. Since the source-drain voltage of the P-channel enhancement-mode MOSFET V5 generally needs to be less than 20V, a suitable Zener diode V6 is required to limit its voltage; a 36V Zener diode can be used. Therefore, the source and drain of the P-channel enhancement-mode MOSFET V5 are conducting, and the PWR voltage charges inductor L1, capacitor C3, and the backup power supply.

[0056] When the charging current is greater than 1A, the voltage at the positive input terminal of comparator D1 is less than the voltage at the negative input terminal, so comparator D1 outputs a low level. The voltage at the negative input terminal of comparator D2 is less than the voltage at the positive input terminal, so comparator D2 is an open-circuit (OC) gate output. Therefore, at this time, the source and drain of the P-channel enhancement-mode MOSFET V5 are cut off, and inductor L1 charges capacitor C3 and the backup power supply. Diode V7 then functions as a freewheeling diode.

[0057] When the backup power supply is almost fully charged, the charging current slowly decreases. At this time, the source and drain of the P-channel enhancement-mode MOSFET V5 are always conducting, charging the inductor L1 and capacitor C3 and the backup power supply. That is, it is in a floating charging state at this time.

[0058] When the backup power source is a supercapacitor, the supercapacitor is initially at 0V and is in a state of near short circuit during the initial charging.

[0059] If the backup power supply is continuously short-circuited, this circuit will continuously turn the P-channel enhancement-mode MOSFET V5 on and off, thereby achieving downstream protection and ensuring that the upstream PWR output circuit is not affected.

Claims

1. A low-cost backup power charging circuit for a power distribution automation terminal, characterized in that: Includes a three-terminal voltage regulator circuit and an adaptive charging circuit; The input terminal of the adaptive charging circuit is connected to the power supply terminal PWR, and the output terminal is connected to the backup power supply. The adaptive charging circuit includes comparator D1 and comparator D2, and MOSFET V5 controlled by comparator D1 and comparator D2. When the voltage at the power supply terminal PWR matches the supply voltage of comparator D1 and comparator D2, the power supply terminal PWR directly supplies power to comparator D1 and comparator D2 as the VCC terminal. When the voltage at the power supply terminal PWR does not match the supply voltage of comparator D1 and comparator D2, the power supply terminal PWR is connected to the input terminal of the three-terminal voltage regulator circuit, and the output terminal of the three-terminal voltage regulator circuit is used as the VCC terminal to supply power to comparator D1 and comparator D2. The adaptive charging circuit also includes resistors R2, R3, R4, R5, R6, R7, R8, and R9, a Zener diode V6, a diode V7, an inductor L1, and a capacitor C3. The PWR terminal is connected to the ground terminal GND through resistors R2, R3 and R4 connected in series, and is also connected to one end of resistor R5; the other end of resistor R5 is connected to the ground terminal GND through resistors R6 and R7 connected in series. The connection point between resistors R6 and R7 is connected to the positive input terminal of comparator D1; the connection point between resistors R3 and R4 is connected to the negative input terminal of comparator D1 and the positive input terminal of comparator D2, respectively; the output terminal of comparator D1 is connected to the negative input terminal of comparator D2; the VCC terminal is also connected to the negative input terminal of comparator D2 through resistor R8. The other end of resistor R5 is connected to the source of MOSFET V5. The output of comparator D2 is connected to the anode of Zener diode V6. The cathode of Zener diode V6 is connected to the gate of MOSFET V5. The drain of MOSFET V5 is connected to the cathode of diode V7. The anode of diode V7 is connected to ground GND. Resistor R9 is connected between the source and gate of MOSFET V5. The drain of MOSFET V5 is also connected to one end of inductor L1, and the other end of inductor L1 is connected to ground GND through capacitor C3. The other end of inductor L1 is the output terminal of the adaptive charging circuit.

2. The low-cost backup power charging circuit for distribution automation terminals as described in claim 1, characterized in that: The three-terminal voltage regulator circuit includes diode V2, resistor R1, Zener diode V3, transistor V4, and capacitor C2; The power supply terminal PWR is connected to the positive terminal of diode V2; the negative terminal of diode V2 is connected to the collector of transistor V4, and also to one end of resistor R1; the other end of resistor R1 is connected to the base of transistor V4, and also to the cathode of Zener diode V3; the anode of Zener diode V3 is connected to ground terminal GND; the emitter of transistor V4 is connected to one end of capacitor C2, and the other end of capacitor C2 is connected to ground terminal GND. The emitter of transistor V4 is the output terminal of the three-terminal voltage regulator circuit.

3. The low-cost backup power charging circuit for distribution automation terminals as described in claim 1, characterized in that: It also includes a charging protection circuit, which includes a transient voltage suppression diode V1 and a capacitor C1; The power supply terminal PWR is connected to one end of the transient voltage suppression diode V1 and also to the positive terminal of the capacitor C1; the other end of the transient voltage suppression diode V1 is connected to the ground terminal GND and also to the negative terminal of the capacitor C1.

4. The low-cost backup power charging circuit for distribution automation terminals as described in claim 1, characterized in that: It also includes a backup power protection circuit, which includes a transient voltage suppression diode V8. One end of the transient voltage suppression diode V8 is connected to the output terminal of the adaptive charging circuit, and the other end is connected to the ground terminal GND.

5. A charging method based on the low-cost backup power charging circuit of the distribution automation terminal as described in claim 1, characterized in that: Resistor R5 is a current-limiting resistor. Based on the resistance value of resistor R5 and the current-limiting value, the resistance values ​​of resistors R2, R3, R4, R6, and R7 are set accordingly. When the charging current on resistor R5 is less than the set current limit, the voltage at the positive input terminal of comparator D1 is greater than the voltage at its negative input terminal; at this time, the output of comparator D1 is an open-circuit output, and the output voltage is equal to the VCC terminal voltage. The voltage at the negative input terminal of comparator D2 is the VCC terminal voltage, and the voltage at the negative input terminal of comparator D2 is greater than the voltage at its positive input terminal. The output voltage of comparator D2 is low, and the source and drain of MOSFET V5 are turned on, charging inductor L1, capacitor C3 and backup power supply. When the charging current on resistor R5 exceeds the set current limit, the voltage at the positive input terminal of comparator D1 is less than the voltage at its negative input terminal. At this time, the output of comparator D1 is low, the voltage at the negative input terminal of comparator D2 is low, the voltage at the negative input terminal of comparator D2 is less than the voltage at its positive input terminal, the output of comparator D2 is an open-collector (OC) gate output, and the output voltage is equal to the voltage at the VCC terminal. The source and drain of MOSFET V5 are not conducting. At this time, inductor L1 charges capacitor C3 and the backup power supply.

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